text:
namespace media {

class ChunkDemuxerStream;
class FrameProcessor;

// Contains state belonging to a source id.
class MEDIA_EXPORT SourceBufferState {
 public:
  // Callback signature used to create ChunkDemuxerStreams.
  using CreateDemuxerStreamCB =
      base::RepeatingCallback<ChunkDemuxerStream*(DemuxerStream::Type)>;

  using NewTextTrackCB = base::RepeatingCallback<void(ChunkDemuxerStream*,
                                                      const TextTrackConfig&)>;

  SourceBufferState(std::unique_ptr<StreamParser> stream_parser,
                    std::unique_ptr<FrameProcessor> frame_processor,
                    CreateDemuxerStreamCB create_demuxer_stream_cb,
                    MediaLog* media_log);

  SourceBufferState(const SourceBufferState&) = delete;
  SourceBufferState& operator=(const SourceBufferState&) = delete;

  ~SourceBufferState();

  void Init(StreamParser::InitCB init_cb,
            const std::string& expected_codecs,
            const StreamParser::EncryptedMediaInitDataCB&
                encrypted_media_init_data_cb,
            NewTextTrackCB new_text_track_cb);

  // Reconfigures this source buffer to use |new_stream_parser|. Caller must
  // first ensure that ResetParserState() was done to flush any pending frames
  // from the old stream parser.
  void ChangeType(std::unique_ptr<StreamParser> new_stream_parser,
                  const std::string& new_expected_codecs);

  // Appends new data to the StreamParser.
  // Returns true if the data was successfully appended. Returns false if an
  // error occurred. |*timestamp_offset| is used and possibly updated by the
  // append. |append_window_start| and |append_window_end| correspond to the MSE
  // spec's similarly named source buffer attributes that are used in coded
  // frame processing.
  // AppendChunks appends the provided BufferQueue.
  bool Append(const uint8_t* data,
              size_t length,
              base::TimeDelta append_window_start,
              base::TimeDelta append_window_end,
              base::TimeDelta* timestamp_offset);
  bool AppendChunks(std::unique_ptr<StreamParser::BufferQueue> buffer_queue,
                    base::TimeDelta append_window_start,
                    base::TimeDelta append_window_end,
                    base::TimeDelta* timestamp_offset);

  // Aborts the current append sequence and resets the parser.
  void ResetParserState(base::TimeDelta append_window_start,
                        base::TimeDelta append_window_end,
                        base::TimeDelta* timestamp_offset);

  // Calls Remove(|start|, |end|, |duration|) on all
  // ChunkDemuxerStreams managed by this object.
  void Remove(base::TimeDelta start,
              base::TimeDelta end,
              base::TimeDelta duration);

  // If the buffer is full, attempts to try to free up space, as specified in
  // the "Coded Frame Eviction Algorithm" in the Media Source Extensions Spec.
  // Returns false iff buffer is still full after running eviction.
  // https://w3c.github.io/media-source/#sourcebuffer-coded-frame-eviction
  bool EvictCodedFrames(base::TimeDelta media_time, size_t newDataSize);

  // Gets invoked when the system is experiencing memory pressure, i.e. there's
  // not enough free memory. The |media_time| is the media playback position at
  // the time of memory pressure notification (needed for accurate GC). The
  // |memory_pressure_level| indicates memory pressure severity. The
  // |force_instant_gc| is used to force the MSE garbage collection algorithm to
  // be run right away, without waiting for the next append.
  void OnMemoryPressure(
      base::TimeDelta media_time,
      base::MemoryPressureListener::MemoryPressureLevel memory_pressure_level,
      bool force_instant_gc);

  // Returns true if currently parsing a media segment, or false otherwise.
  bool parsing_media_segment() const { return parsing_media_segment_; }

  // Returns the 'Generate Timestamps Flag' for this SourceBuffer's byte stream
  // format parser as described in the MSE Byte Stream Format Registry.
  bool generate_timestamps_flag() const {
    return stream_parser_->GetGenerateTimestampsFlag();
  }

  // Sets |frame_processor_|'s sequence mode to |sequence_mode|.
  void SetSequenceMode(bool sequence_mode);

  // Signals the coded frame processor to update its group start timestamp to be
  // |timestamp_offset| if it is in sequence append mode.
  void SetGroupStartTimestampIfInSequenceMode(base::TimeDelta timestamp_offset);

  // Returns the range of buffered data in this source, capped at |duration|.
  // |ended| - Set to true if end of stream has been signaled and the special
  // end of stream range logic needs to be executed.
  Ranges<base::TimeDelta> GetBufferedRanges(base::TimeDelta duration,
                                            bool ended) const;

  // Returns the highest PTS of currently buffered frames in this source, or
  // base::TimeDelta() if none of the streams contain buffered data.
  base::TimeDelta GetHighestPresentationTimestamp() const;

  // Returns the highest buffered duration across all streams managed
  // by this object.
  // Returns base::TimeDelta() if none of the streams contain buffered data.
  base::TimeDelta GetMaxBufferedDuration() const;

  // Helper methods that call methods with similar names on all the
  // ChunkDemuxerStreams managed by this object.
  void StartReturningData();
  void AbortReads();
  void Seek(base::TimeDelta seek_time);
  void CompletePendingReadIfPossible();
  void OnSetDuration(base::TimeDelta duration);
  void MarkEndOfStream();
  void UnmarkEndOfStream();
  void Shutdown();
  // Sets the memory limit on each stream of a specific type.
  // |memory_limit| is the maximum number of bytes each stream of type |type|
  // is allowed to hold in its buffer.
  void SetMemoryLimits(DemuxerStream::Type type, size_t memory_limit);
  bool IsSeekWaitingForData() const;

  using RangesList = std::vector<Ranges<base::TimeDelta>>;
  static Ranges<base::TimeDelta> ComputeRangesIntersection(
      const RangesList& active_ranges,
      bool ended);

  void SetTracksWatcher(Demuxer::MediaTracksUpdatedCB tracks_updated_cb);

  void SetParseWarningCallback(SourceBufferParseWarningCB parse_warning_cb);

 private:
  // State advances through this list to PARSER_INITIALIZED.
  // The intent is to ensure at least one config is received prior to parser
  // calling initialization callback, and that such initialization callback
  // occurs at most once per parser.
  // PENDING_PARSER_RECONFIG occurs if State had reached PARSER_INITIALIZED
  // before changing to a new StreamParser in ChangeType(). In such case, State
  // would then advance to PENDING_PARSER_REINIT, then PARSER_INITIALIZED upon
  // the next initialization segment parsed, but would not run the
  // initialization callback in this case (since such would already have
  // occurred on the initial transition from PENDING_PARSER_INIT to
  // PARSER_INITIALIZED.)
  enum State {
    UNINITIALIZED = 0,
    PENDING_PARSER_CONFIG,
    PENDING_PARSER_INIT,
    PARSER_INITIALIZED,
    PENDING_PARSER_RECONFIG,
    PENDING_PARSER_REINIT
  };

  // Initializes |stream_parser_|. Also, updates |expected_audio_codecs| and
  // |expected_video_codecs|.
  void InitializeParser(const std::string& expected_codecs);

  // Called by the |stream_parser_| when a new initialization segment is
  // encountered.
  // Returns true on a successful call. Returns false if an error occurred while
  // processing decoder configurations.
  bool OnNewConfigs(std::string expected_codecs,
                    std::unique_ptr<MediaTracks> tracks,
                    const StreamParser::TextTrackConfigMap& text_configs);

  // Called by the |stream_parser_| at the beginning of a new media segment.
  void OnNewMediaSegment();

  // Called by the |stream_parser_| at the end of a media segment.
  void OnEndOfMediaSegment();

  // Called by the |stream_parser_| when new buffers have been parsed.
  // It processes the new buffers using |frame_processor_|, which includes
  // appending the processed frames to associated demuxer streams for each
  // frame's track.
  // Returns true on a successful call. Returns false if an error occurred while
  // processing the buffers.
  bool OnNewBuffers(const StreamParser::BufferQueueMap& buffer_queue_map);

  // Called when StreamParser encounters encrypted media init data.
  void OnEncryptedMediaInitData(EmeInitDataType type,
                                const std::vector<uint8_t>& init_data);

  void OnSourceInitDone(const StreamParser::InitParameters& params);

  // Sets memory limits for all demuxer streams.
  void SetStreamMemoryLimits();

  // Tracks the number of MEDIA_LOGs emitted for segments missing expected audio
  // or video blocks. Useful to prevent log spam.
  int num_missing_track_logs_ = 0;

  // During Append(), if OnNewBuffers() coded frame processing updates the
  // timestamp offset then |*timestamp_offset_during_append_| is also updated
  // so Append()'s caller can know the new offset. This pointer is only non-NULL
  // during the lifetime of an Append() call.
  raw_ptr<base::TimeDelta> timestamp_offset_during_append_;

  // During Append(), coded frame processing triggered by OnNewBuffers()
  // requires these two attributes. These are only valid during the lifetime of
  // an Append() call.
  base::TimeDelta append_window_start_during_append_;
  base::TimeDelta append_window_end_during_append_;

  // Keeps track of whether a media segment is being parsed.
  bool parsing_media_segment_;

  // Valid only while |parsing_media_segment_| is true. These flags enable
  // warning when the parsed media segment doesn't have frames for some track.
  std::map<StreamParser::TrackId, bool> media_segment_has_data_for_track_;

  // The object used to parse appended data.
  std::unique_ptr<StreamParser> stream_parser_;

  // Note that ChunkDemuxerStreams are created and owned by the parent
  // ChunkDemuxer. They are not owned by |this|.
  using DemuxerStreamMap = std::map<StreamParser::TrackId, ChunkDemuxerStream*>;
  DemuxerStreamMap audio_streams_;
  DemuxerStreamMap video_streams_;
  DemuxerStreamMap text_streams_;

  std::unique_ptr<FrameProcessor> frame_processor_;
  const CreateDemuxerStreamCB create_demuxer_stream_cb_;
  raw_ptr<MediaLog> media_log_;

  StreamParser::InitCB init_cb_;
  StreamParser::EncryptedMediaInitDataCB encrypted_media_init_data_cb_;
  NewTextTrackCB new_text_track_cb_;

  State state_;

  // During Append(), OnNewConfigs() will trigger the initialization segment
  // received algorithm. Note, the MSE spec explicitly disallows this algorithm
  // during an Abort(), since Abort() is allowed only to emit coded frames, and
  // only if the parser is PARSING_MEDIA_SEGMENT (not an INIT segment). So we
  // also have a flag here that indicates if Append is in progress and we can
  // invoke this callback.
  Demuxer::MediaTracksUpdatedCB init_segment_received_cb_;
  bool append_in_progress_ = false;
  bool first_init_segment_received_ = false;
  bool encrypted_media_init_data_reported_ = false;

  std::vector<AudioCodec> expected_audio_codecs_;
  std::vector<VideoCodec> expected_video_codecs_;
};

}  // namespace media

#endif  // MEDIA_FILTERS_SOURCE_BUFFER_STATE_H_

redpajama_set_name: RedPajamaGithub


text:
\section{Introduction}

The treatment of convection in stellar envelopes is one of the largest sources of uncertainty in stellar modeling.  Convection in stellar models is usually described by the B\"ohm-Vitense mixing length theory \citep[MLT;][]{1958ZA.....46..108B}, which was derived from Prandtl's mixing hypothesis \citep{prandtl1925}.    MLT represents convection with a single characteristic length, which is proportional to the local pressure scale height $l=\alpha H_P$, where $\alpha$ is a free parameter.  The mixing length parameter is arbitrary, and is usually held at a constant value, obtained from a calibrated solar model. \rev{This single parameter formulation of MLT is commonly used in 1D stellar model calculations, but there are other treatments that introduce additional free parameters to account for geometric properties of convection \citep[see e.g.,][]{2010ApJ...710.1619A}.} While MLT produces an accurate stratification in regions of efficient convection \citep{1989ApJ...336.1022C}, it does not account for the dynamical effects of convection, such as turbulent pressure and asymmetry in the velocity field, and the approximation breaks down near the surface where convection is inefficient.

By fixing the mixing length parameter, the MLT treatment of convection eliminates dependence on stellar properties that are expected to be relevant to convective dynamics.  These properties include the surface gravity and effective temperature of the star, and the chemical composition of the convection zone.  The recent work of \citet{2012ApJ...755L..12B} examined how the mixing length parameter would need to change to satisfy stellar mass and radius constraints from Kepler data. Their results indicate that the mixing length parameter changes with metallicity.  While useful for its application to stellar modeling, the results are limited by the unrealistic MLT representation of convection.  For the past few decades, radiation hydrodynamic simulations (RHD) have been used to provide a more accurate representation of near surface convection.

Pioneered by \citet{1985pssl.proc..215N}, 3D RHD simulations account for the realistic transition from convective to radiative energy transport.  Since then, simulations have been applied to dwarf stars  \citep[e.g.][]{2009A&A...501.1087R, 2009A&A...508.1429W, 2004IAUS..224..139F}, giants \citep[e.g.][]{2007A&A...469..687C, 2010A&A...524A..93C, 2012A&A...547A.118L}, and several more targeted studies of individual stars \citep[e.g.][]{2005MNRAS.362.1031R, 2006ApJ...636.1078S, 2007IAUS..239..388S,  2009A&A...506..167L, 2010A&A...513A..72B}

Efforts to systematically study the variation of stellar convection have been carried out by \citet{1995LIACo..32..213L, 1998IAUS..185..115L, 1999A&A...346..111L}, \citet{1999ASPC..173..225F}, and \citet{2011ApJ...731...78T}, and there are several ambitious efforts to examine metallicity and convection using grids of simulations by including a metallicity dimension in the grid parameter space.  These include the ongoing CIFIST \citep{2009MmSAI..80..711L} and STAGGERGRID \citep{2011JPhCS.328a2003C} projects.  Our work follows in a similar vein and employs a grid of 3D RHD simulations to isolate the effect of varying metallicity while fixing other dimensions of parameter space.

Determining how realistic stellar surface convection is sensitive to metallicity remains an area of active research.  Some of the simulations mentioned above were carried out at different metallicities and compositions, and there are a few studies comparing simulations at varied metallicity.  For example, \citet{2007ASPC..362..306J} examined 3D RHD simulations of convection in the sun and a population II star.  They find differences in the turbulent pressure and kinetic energy, but the stellar parameters corresponding to the simulations have different metallicity, effective temperature, and surface gravity. Similarly, \citet{2009IAUS..259..233S} compared 2D simulations of magneto-convection for the Sun and a metal poor solar-like analog, but with the same surface gravity and effective temperatures.  Their preliminary results show that the primary effect of the lower opacity in the metal-poor star is increased pressure and magnetic field strength.   We aim to perform a more systematic and rigorous study by using a grid of 3D  simulations to isolate the effect of metallicity over a range in effective temperature.

Other studies have focused on elemental abundances and spectral features.  For example,  \citet{1999A&A...346L..17A} used convection simulations corresponding to two halo stars in conjuction with spectral synthesis to estimate chemical abundances, which indicated that 1D models have led to overestimated primordial Li abundances.  Similarly \citet{2007A&A...469..687C} found differences in the predicted line strengths from 3D simulations of metal-poor red giant stars compared to corresponding 1D model atmospheres.   Their simulations cover a range in effective temperature and metallicity, and they found that spectral lines of neutral metals and molecules appear stronger in 3D simulations than in 1D models.  Results of such studies consistently show cooler atmospheres in lower metallicity simulations.  A recent study by \citet{2011A&A...528A..32C} examined 3D simulations of low-metallicity red giants, and confirmed that the cooler atmospheres in low-Z simulations was not the result of the approximations to the treatment of scattering.

Most previous studies of the effect of metallicity on convection have focused on atmospheric properties.  We aim to examine how metallicity determines the structure of the convection zone, particularly in the superadiabatic layer where energy transport transitions from convective to radiative, with the intent of improving stellar models.  In the present study, we endeavor to systematically explore the effect of varying heavy metal abundance and convection in the superadiabatic layer by computing several sets of simulations at various metallicities, spanning a range in effective temperature.  The effective temperature range for each metallicity set overlaps, enabling the comparison of simulations at varied $Z$ but fixed {\logg} and {\logteff}.   Section \ref{sec:code} outlines the numerical method and details of the simulation code, while Section \ref{sec:grid} describes the individual simulations that we present.  In Sections \ref{sec:salstructure} through \ref{sec:ttau} we present the effect of metallicity on the thermal structure and gas dynamics.

\section{The Radiation Hydrodynamics Code} \label{sec:code}

Our simulation code solves the compressible Navier-Stokes equations with radiative transfer.  Details are provided in \citet{2012ApJ...759..120T}.  It is an updated version of the code described in \citet{2003MNRAS.340..923R, 2004MNRAS.347.1208R}, and is based on the code of Kim, Chan \& Sofia \citep{1989ApJ...336.1022C, 1998ApJ...496L.121K}.

The simulation domain is a Cartesian box with periodic boundary conditions at vertical walls and closed surfaces at the top and bottom.  \rev{Our experiments with different boundary conditions consistently show that the effect of the boundary layer is less than one scale height from the edge of the computational domain, and this boundary layer has been removed from the figures.}  The computational domain spans the superadiabatic layer, which is the region of transition from convection to radiation.  The bottom of the domain is fully convective, while the top is fully radiative. Thus, the computational domain spans the transition region from convective to radiative energy transport, where convection is inefficient and MLT is insufficient.

The extent of the simulation domain is approximately 9 pressure scale heights (typically less than 0.1\% of the stellar radius for the simulations presented here), which is very small relative to the full extent of the convection zone (which is approximately 20 pressure scale heights in the sun), so curvature and radial variation of gravity are negligible and can be ignored.  Although the simulation domain is small relative to the full extent of the convection zone, it encompasses precisely the region where MLT fails to capture the effect realistic convection, such as the additional support of turbulent pressure.

Radiative transfer is treated with the diffusion approximation in the optically thick part of the domain.  In the optically thin layers where the diffusion approximation is invalid, the code can solve for the mean intensity using the 3D Eddington approximation \citep{1966PASJ...18...85U} or integration over long ray characteristics (similar to the method described by \citet{2003ASPC..288..519S}.  The simulations were computed using the 3D Eddington solver, which compares well with long characteristic ray integration, and offers some computational performance benefits.  A detailed comparison of the radiative transfer solvers has been presented in \citet{2012ApJ...759..120T}.  The code uses the OPAL equation of state and opacity tables \citep{2002ApJ...576.1064R} and the \citet{2005ApJ...623..585F} opacity tables at low temperatures.

\section{Grid of Simulations} \label{sec:grid}

Each simulation is characterized by its energy flux, surface gravity, and composition.  It is important to note that while we directly set the surface gravity and composition, the energy flux is a quantity that is calculated.  We define the effective temperature of the simulation as
\begin{equation}
T_{\rm eff}^4 = \frac{F_{\rm rad}}{\sigma}
\end{equation}
where $\sigma$ is Stefan-Boltzmann constant, and the radiative flux, $F_{\rm rad}$, is determined by the radiative transfer solver. Changing the metallicity in a simulation alters the thermal balance in the atmosphere, resulting in a different energy flux.  Without precise control over the radiative energy flux, it is difficult to compare simulations at constant effective temperature and varied metallicity.  To overcome this, we have computed a grid of simulations for several metallicities that span a small range in effective temperature.

The grid comprises four sets of simulations, each at a different metallicity. Each set spans a small range in effective temperature, which overlap with each other. All simulations in the grid have the same surface gravity set to $\log(g)=4.30$.  Properties of the grid are listed in Table \ref{tab:grid}. We can isolate the effect of metallicity by interpolating within the grid to achieve a desired effective temperature, or by comparing simulations that happen to have similar energy fluxes.  Simulations use opacity and equation of state tables with the heavy element abundance mixture of \citet{1998SSRv...85..161G}.

\rev{Since the computational domain spans a sufficiently small fraction of the stellar radius so that the gravitational field is homogeneous and curvature is neglected, the simulations do not contain information about the stellar radius.  As a result, the zero point of the radial coordinate is arbitrary, and the simulation domain cannot be expressed as a fractional stellar radius.}  Instead of using radius, we typically present properties of the simulations relative to the effective temperature surface.  This reference point (where $\langle{T}\rangle =T_{\rm eff}$) can be interpreted as the stellar `surface' because it is the point at which a black body yields the same energy flux as that of the simulation.  We define the height such that the zero point is fixed at the {\teff} surface, and it increases toward smaller optical depth.

In the following sections we compare space- and time- averaged quantities over the vertical (radial) coordinate.  The horizontal and temporal mean over a time $\Delta t$ and a box cross-sectional area of $L_x \times L_y$ is:
\begin{equation}
\label{eqn:mean}
\langle q \rangle = \frac{1}{\Delta t}\frac{1}{L_x L_y} \int_{t_o}^{t_o+\Delta t} \int_{0}^{L_x} \int_{0}^{L_y} q dx dy dt .
\end{equation}

Note that quantities are averaged over a sufficient interval to obtain statistical convergence, and the start of the time interval is after the simulation has thermally relaxed.  The rms of the same quantity is:
\begin{equation}
\label{eqn:rms}
q_{\rm rms} = \sqrt{\langle{q^2}\rangle - \langle{q}\rangle^2} .
\end{equation}

The correlation function between two turbulent quantities $q_1$ and $q_2$ is defined as:
\begin{equation}
\label{eqn:corr}
C[q_1,q_2] = \frac{\langle{q_1 q_2}\rangle - \langle{q_1}\rangle \langle{q_2}\rangle}{q_{\rm 1,rms}q_{\rm 2,rms}} .
\end{equation}

\begin{table}
  \caption{Properties of the simulations in the grid.  All simulations have the same surface gravity ($\log g = 4.30$).}
  \label{tab:grid}
  \begin{center}
    \leavevmode
    \begin{tabular}{lllll} \hline \hline
  $ID$          & Z              & X & $T_{\rm eff}$ & $\log T_{\rm eff}$      \\ \hline
s1 & 	0.040 & 	0.715 & 	4947	&	3.694  \\
s2 & 	0.040 & 	0.715 & 	5201	&	3.716  \\
s3 & 	0.040 & 	0.715 & 	5461	&	3.737  \\
s4 & 	0.040 & 	0.715 & 	5719	&	3.757  \\
s5 & 	0.020 & 	0.735 & 	5121	&	3.709  \\
s6 & 	0.020 & 	0.735 & 	5370	&	3.730  \\
s7 & 	0.020 & 	0.735 & 	5626	&	3.750  \\
s8 & 	0.020 & 	0.735 & 	5897	&	3.770  \\
s9 & 	0.010 & 	0.745 & 	5326	&	3.726  \\
s10 & 	0.010 & 	0.745 & 	5569	&	3.746  \\
s11 & 	0.010 & 	0.745 & 	5803	&	3.764  \\
s12 & 	0.010 & 	0.745 & 	6027	&	3.780  \\
s13 & 	0.001 & 	0.754 & 	5735	&	3.759  \\
s14 & 	0.001 & 	0.754 & 	5896	&	3.771  \\
s15 & 	0.001 & 	0.754 & 	6063	&	3.783  \\
s16 & 	0.001 & 	0.754 & 	6235	&	3.795  \\ \hline
    \end{tabular}
  \end{center}
\end{table}

\section{Results: SAL Structure} \label{sec:salstructure}

\subsection{Mean Stratification} \label{sec:meanstratifications}

The structure of the near surface layers is determined largely by the inefficient convection.  It is in precisely this region that convection models such as MLT fail to provide accurate stratifications. Figure \ref{fig:rhovsp}  shows the density as a function of total pressure (which includes both gas and turbulent pressure) for four simulations.

The simulations in Figure \ref{fig:rhovsp} were selected to show the effect of increasing the energy flux and changing the metallicity. The region of transition from convective to radiative energy transport, known as the superadiabatic layer (SAL), occurs just below the stellar surface. In Figure \ref{fig:rhovsp} the SAL is apparent as an abrupt change in the density-pressure relationship.  Over this pressure range, increasing the effective temperature primarily changes the density in these layers, while changing metallicity substantially changes both the density and the location of the SAL.  Higher metallicity simulations have SALs that occur at lower pressure and density.

The density in the SAL reflects the change in opacity as a result of changing metallicity. At these temperatures, the primary opacity source is from the $H^-$ ion.  \rev{Increasing the metallicity results in low ionization elements donating more electrons to hydrogen atoms, thereby increasing the opacity.}  The energy flux is determined by $\rho \kappa$ and the source function, so to maintain the same energy flux at higher opacity ($\kappa$), the density ($\rho$) must be correspondingly lower.

\begin{figure}[h]
\epsscale{1.2}
\plotone{./density_vs_pressure.eps}
\caption{Structures through the SAL for four select simulations.  Simulation pair (s13,s14) shows how the stratification changes with effective temperature, while simulations pairs (s4,s13) and (s8,s14) have essentially the same effective temperatures but different metallicities.  The density and pressure of the SAL are sensitive to changes in metallicity.}
\label{fig:rhovsp}
\end{figure}

\subsection{Superadiabatic Excess} \label{sec:sal}

\rev{Near the surface, where convection is inefficient, a useful quantity to examine is the radial variation of the superadiabatic excess ($\nabla - \nabla_{\rm ad}$), which is the difference between the temperature gradient, defined as:}
\begin{equation}\label{eqn:sae}
\nabla = \frac{d\ln(T)}{d\ln(P)} ,
\end{equation}
\rev{and the adiabatic temperature gradient.  Turbulent gas dynamics in the SAL contribute a significant fraction to the pressure term in Equation \ref{eqn:sae}.  The total pressure, $P = P_{\rm gas} + P_{\rm turb}$,  is the sum of the gas and turbulent pressures, where the turbulent pressure is calculated with the defintion in Section \ref{sec:pturb}.}  In the deep layers where the structure is nearly isentropic and convection is efficient, the temperature gradient is essentially adiabatic.  Nearer to the stellar surface, where the energy flux transitions from convective to radiative, we see a departure from adiabaticity characterized by a sharp peak in the superadiabatic gradient.  The difference between the two gradients (i.e.\ the superadiabatic excess), provides a measure of the inefficiency of convection, and reveals the depth at which there is a significant departure from efficient convection.

Figure \ref{fig:salpanel} shows the superadiabatic gradients as a function of pressure for our grid of simulations. Each panel in the figure corresponds to a different metallicity set. The temperature structures show a mild systematic change in the maximum suberadiabaticity (maximum of $\nabla - \nabla_{\rm ad}$) with the effective temperature of the simulations, \rev{although the variation is markedly less apparent than what is predicted by stellar models computed with MLT.  The more constrained range in superadiabaticity relative to MLT is generally consistent with the grid of simulations of \citet{2010Ap&SS.328..213T}, which show a smaller variation in the superadiabatic peak compared with MLT models at evolutionary stages from the main sequence to giants.} The simulations with larger effective temperatures have higher SALs, particularly for high-Z simulations, but the maximum suberadiabaticity becomes less sensitive to {\teff} at near-Solar and lower-Z.  We note, however, that while the temperature ranges overlap, they are not identical for each metallicity simulation set.

When the metallicity is changed and {\teff} is fixed, we find no significant change in the maximum superadiabaticity.  The top panel of Figure \ref{fig:saltrends} compares the superadiabatic gradients in two simulations that have almost the same effective temperatures (the effective temperatures differ by only $27K$) but a drastic change in metallicity (Z differs by a factor of 40).  In both simulations the maximum superadiabatic excess is approximately the same.  We do, however, see a marked shift in the depth of the SAL.  At lower metallicity, the conversion from efficient to inefficient convection happens at higher pressures and densities.

The degree of superadiabaticity corresponds to the rate at which energy transport transitions from convective to radiative.  A large value of the maximum SAL is the result of a steep entropy gradient.  The relatively constant SAL maximum as a function of metallicity suggests that the thermal structure changes (examined in section \ref{sec:meanstratifications}), rather than a large change in the convection-to-radiation transition.

We summarize the simulated SALs in the lower panels of Figure \ref{fig:saltrends}, which show the maximum superadiabaticity and its location for all the simulations in the grid.  In the top panel, each metallicity set shows a shallow trend with effective temperature, \rev{but there is no remarkable offset between them.} Although the maximum value of the SAL remains unchanged, the bottom panel of Figure \ref{fig:saltrends} shows that \rev{the change in} metallicity introduces a shift in the location of the SAL.  Lower-Z simulations have correspondingly higher densities to maintain the same energy flux.  Thus, radiative energy transport starts to become significant at higher density in the lower-Z simulations.

\begin{figure*
\epsscale{1.0}
\plotone{./SAL_4panel.eps}
\caption{Superadiabatic gradients ($\nabla - \nabla_{\rm ad}$) for the grid of simulations.  Each panel shows a set of simulations over a small range in effective temperature and at a given metallicity.  At a given metallicity, the maximum superadiabaticity changes with {\teff}, but at lower metallicity the maximum superadiabaticity becomes less sensitive to {\teff}.}
\label{fig:salpanel}
\end{figure*}

\begin{figure}[!h]
\epsscale{1.2}
\plotone{./SAL_trends.eps}
\caption{(\textit{a}): Superadiabatic gradients from simulations s4 and s13, which have different metallicities but the same effective temperature.  The maximum of the SAL remains essentially unchanged despite the considerable difference in metallicity.  The location of the SAL is sensitive to metallicity.  (\textit{b}): The maximum value of the superadiabaticity and (\textit{c}) location of the maximum superadiabaticity for all simulations in the grid.  Each line in panels (\textit{b}) and (\textit{c}) corresponds to a set of simulations with a fixed metallicity.  Simulations s4 and s13 are marked with diamond symbols.  Metallicity does not appear to directly affect the maximum of the SAL, but it does introduce a shift in the location of the SAL with respect to density.}
\label{fig:saltrends}
\end{figure}

\section{Results: Dynamics of Convection} \label{sec:dynamics}

\subsection{Mean Convective Velocities} \label{sec:vel}

One of the distinctions between mixing length theory and realistic convection is the asymmetry of the velocity field \rev{resulting from upflows being characterized by a larger filling factor at almost all depths in the simulation domain}.  The hot upflowing gas rises nearly adiabatically at approximately constant entropy \citep[e.g.][]{1999A&A...346..111L,1999AAS...194.2104S} until it radiates away energy near the surface before cycling back into the convection zone.  Stellar convection is characterized by large upflowing regions (granules) separated by cool fast downdrafts (intergranular lanes).  Figure \ref{fig:granulation} shows the vertical velocity at a horizontal slice where $\langle T \rangle =T_{\rm eff}$ for two simulations with different metallicities.  The flow pattern qualitatively resembles solar granulation with large expanding updrafts separated by cool fast downdrafts.  The difference in metallicity, however, causes the granulation pattern to be visibly different.  Granulation in the higher-Z simulation shows larger granules and sharper inter-granular lanes.

\begin{figure*
\begin{minipage}[b]{0.9\linewidth}
\epsscale{1.0}
\plotone{./granulation_velocity_horizontal.eps}
\caption{Vertical velocity at the effective temperature surface showing the characteristic granulation pattern from snapshots from two simulations in the grid. The two simulations have the same surface gravity and effective temperature, but metallicities of $Z=0.040$ (s4, left) and $Z=0.001$ (s13, right).}
\label{fig:granulation}
\end{minipage}
\end{figure*}

Asymmetry in the velocity field means that the average vertical velocity, $\langle w \rangle$, is dominated by the upflows through most of the simulation domain.  As shown in Figure \ref{fig:wvelpanel}, the average vertical velocities are small deep in the convection zone and rise to a maximum just below the surface near the peak of the SAL. The velocity profile is inverted above the convectively stable region (where $\nabla < \nabla_{\rm ad}$), and the average velocity becomes negative.

The maximum average vertical velocities of the different simulations are compared in Figure \ref{fig:wveltrends}. The trend with effective temperature (from velocity profiles in Figure \ref{fig:wvelpanel}) is apparent, but there is also a distinct metallicity dependence. At a given effective temperature, simulations with higher metallicity exhibit larger convective velocities.

The trend is a direct result of the changes in density stratification, which change in response to the different opacities caused by changing the metallicity (see Section \ref{sec:meanstratifications}).  In simulations with the same {\teff}, convection is responsible for transferring the same energy flux.  The different stratifications, however, require different velocities.  High-Z simulations have higher opacity, and consequently lower density through the SAL (see Figure \ref{fig:rhovsp}), so the convective velocities must be larger to sustain the same convective flux.

Larger convective velocities in the SAL mean that upflows will remain coherent over a larger spatial scale, even in the radiative domain where convection is no longer driven.  In Section \ref{sec:overshoot} we examine the strength of convection beyond the convectively stable boundary, and provide a measure of how it changes with metallicity.

\begin{figure*}
\begin{minipage}[b]{0.9\linewidth}
\epsscale{1.2}
\plotone{./wvel_4panel.eps}
\caption{Radial variation of average vertical velocities for all simulations in the grid.  Velocities are small in the deep region, and reach a maximum near the peak of the superadiabaticity.  Larger velocities are measured in simulations with higher metallicity or effective temperature.}
\label{fig:wvelpanel}
\end{minipage}
\end{figure*}

\begin{figure}
\epsscale{1.2}
\plotone{./wvel_trends.eps}
\caption{(\textit{top}): Radial variation of vertical velocity for simulations s4 and s13 (identified with diamond symbols in the bottom panel), which have approximately the same {\teff}.   (\textit{bottom}): The maximum average vertical velocity for all simulations in the grid.  The maximum velocity increases with effective temperature and metallicity.}
\label{fig:wveltrends}
\end{figure}

\subsection{Turbulent Pressure} \label{sec:pturb}

One of the physical phenomena absent in MLT-like prescriptions for convection is the additional pressure support from turbulence.  The so-called turbulent pressure is caused by turbulent fluctuations in the velocity field, and is a non-negligible contribution to hydrostatic balance through the SAL, and causes structural differences where turbulent pressure is significant.

We estimate turbulent pressure from the rms (Equation \ref{eqn:rms}) of the vertical velocity field as:
\begin{equation}
P_{\rm turb} = \rho w_{\rm rms} .
\end{equation}

Simulations of solar convection estimate turbulent pressure support at approximately 15\% to 18\% of the gas pressure near the peak of the SAL \citep{2009MmSAI..80..701K, 2012A&A...539A.121B}. We see similar results from our code. Turbulent pressure is negligible deep in the near-adiabatic part of the convection zone because of extremely large gas pressure, and is also quite small in the optically thin region where the gas density and rms velocities are small.

Figure \ref{fig:pturbpanel} compares the radial variation of turbulent pressure (relative to gas pressure) from all of the simulations. Turbulent pressure is a few percent in the deep convection zone, and increases at smaller depth, reaching a maximum near the peak of the SAL. Turbulent pressures in our grid can be as high as 10-16\% of the gas pressure.

As with the mean vertical velocities, we find that the turbulent pressure support scales with both the energy flux and metallicity. The high-Z simulations show more support from turbulence \rev{(as a fraction of gas pressure)} relative to the low-Z simulations. Comparing the turbulent pressure from each simulation (Figure \ref{fig:pturbtrends}) shows that the maximum turbulent pressure visibly increases with effective temperature, and there is a clear systematic offset that is correlated with changes in metallicity.  The increase in turbulent pressure is a result of larger rms velocities, which are also correlated with effective temperature and metallicity.

\begin{figure*
\begin{minipage}[b]{0.9\linewidth}
\epsscale{1.2}
\plotone{./pturb_4panel.eps}
\caption{Radial variation of average turbulent pressure for all simulations in the grid.  Turbulent pressure follows the same trend as the mean velocities (Figure \ref{fig:wvelpanel}), increasing with effective temperature and metallicity.}
\label{fig:pturbpanel}
\end{minipage}
\end{figure*}

\begin{figure}[!h]
\epsscale{1.2}
\plotone{./pturb_trends.eps}
\caption{(\textit{top}):  Radial variation of turbulent pressure for simulations s4 and s13 (identified with diamond symbols in the bottom panel), which have approximately the same {\teff}. (\textit{bottom}):  Maximum average turbulent pressure for all simulations in the grid.  Simulations with higher effective temperatures or metallicities show increased turbulent pressure.}
\label{fig:pturbtrends}
\end{figure}

\subsection{Overshoot} \label{sec:overshoot}

Convective regions in 1D stellar models are well defined and unambiguous.  The radial domain that is unstable to convection can be defined according to many equivalent criteria, such as $\nabla_{\rm ad} < \nabla$, $ds/dz<0$, or $F_{\rm conv}>0$.  Stratifications from 3D RHD simulations do not provide such clear boundaries, and there are several ways to estimate the edge of a driven convection zone, or the extent of a region influenced by convection.

It is well known that updrafts would not simply stop at the edge of the convectively unstable layer.  Instead, their momentum would carry them some distance beyond the convective boundary effectively extending the region of mixing.  The amount of additional mixing, or overshoot, will depend on the stratification of the atmosphere and the convective dynamics.

Simulations treat convection and the effect of overshoot self-consistently, and make no distinction between them. We can, however, quantify the amount of 'overshoot' by measuring correlations between turbulent fluctuations.  In convectively unstable regions, the upflows are coherent and turbulent fluctuations are highly correlated.  By measuring the vertical (radial) location where the fluctuations are no longer correlated, we can determine the height at which the convection no longer resembles the behavior of the unstable region.

We define the end of the convectively unstable region (and the start of the 'overshoot' region) to be the height at which $\nabla-\nabla_{\rm ad}$ is zero (see Figure \ref{fig:salpanel}).  We define the end of the 'overshoot' region to be where fluctuations in temperature and vertical velocity are no longer correlated, where the degree of correlation is defined by Equation \ref{eqn:corr}.  This definition has been used by \citet{1989ApJ...336.1022C} and \citet{2004MNRAS.347.1208R}. The size of the 'overshoot' region is the difference between these two heights.

The correlation through the deeper part of the convection zone is quite constant over this range in {\teff} and Z, ranging from  $C[T,V_z] = 0.77-0.85$, which is similar to the value measured by Chan \& Sofia (1989).  The rate at which the correlation drops, however, is sensitive to metallicity.  Figure \ref{fig:overshoot} compares the temperature-velocity correlations and superadiabatic gradients in two simulations with different metallicity and the same effective temperature.  The zero point of the radial height is defined to match the average effective temperature surface. The edge of the convectively unstable region, as defined by where the superadiabatic gradient is zero, is almost unchanged in the two simulations. The region affected by overshooting, as measured by the temperature-velocity correlation, is clearly larger in the higher metallicity simulation.

Figure \ref{fig:overshoottrends} shows the size of the overshoot region for the entire set of simulations.  There appears to be a small correlation of overshoot with effective temperature, particularly in the high-Z simulations, but the dominant effect is clearly by varying metallicity. The larger degree of 'overshoot' in high-Z simulations is attributed to the larger mean and turbulent velocities.  The faster moving high-Z upflows carry more momentum and are able to traverse more space before losing their identity.

\begin{figure*
\begin{minipage}[b]{0.9\linewidth}
\epsscale{1.2}
\plotone{./overshoot.eps}
\caption{Convective overshoot for simulations s4 (top) and s13 (bottom).  The left side shows the superadiabatic excess and correlation functions that are used to define the region of overshoot.  The right side shows the slices of the vertical velocity near the {\teff} surface.  Dashed lines show the measured boundaries of the overshoot region.  The high-Z simulation (s4) has larger velocities and more overshoot.}
\label{fig:overshoot}
\end{minipage}
\end{figure*}

\begin{figure
\epsscale{1.2}
\plotone{./overshoot_trends.eps}
\caption{The extent of convective overshoot for all simulations in the grid.  High-Z simulations have larger velocities which result in more convective overshoot.}
\label{fig:overshoottrends}
\end{figure}

\section{Results: {\ttau} Relations} \label{sec:ttau}

Convection also affects the structure above the region of driven convection because of convective overshoot.  By directly solving the hydrodynamics equations, simulations provide a self-consistent representation of the effect of convection, including overshoot, on the atmosphere.  The primary way in which the stratification in and above the convective envelope is altered is from the additional support provided by turbulent pressure (described in Section \ref{sec:pturb}).

1D Stellar structure models set the outer boundary condition by imposing a structure defined by a {\ttau} relation.  The Eddington {\ttau} is often used, but semi-empirical relations, such as those provided by \citet{1966ApJ...145..174K} and \citet{1981ApJS...45..635V} (VAL) can also be applied.  The semi-empirical relations implicitly include effects such as turbulent pressure, but are only valid for the Sun.  The location of the {\teff} surface with respect to optical depth is defined by the {\ttau} relation. The Eddington {\ttau} defines the {\teff} surface to be at $\tau=2/3$, while the semi-empirical relations show the {\teff} surface at smaller optical depths. Examining {\ttau} relations from simulations demonstrates how convective turbulence and overshoot affects the atmospheric structure, and to what degree it is sensitive to changes in metallicity.

The variation in {\ttau} relations with energy flux is rather small over the range of effective temperatures here.  In simulation sets of a given metallicity, the temperature variation at a given optical depth is typically less than a few percent.  The {\ttau} relation is more sensitive to changes in metallicity, however, as demonstrated in Figure \ref{fig:ttau}, which  shows {\ttau} relations for two simulations with the effective temperature but different metallicities.  The Eddington, Krisnha Swamy, and VAL {\ttau} relations are included for reference.  It is immediately apparent that the effect convective overshoot is sensitive to metallicity.  The comparison shows a discrepancy in the temperature at a given optical depth of up to 6\%.

There is a clear systematic effect in response to the changing metalicities. Low-Z stratifications are cooler than high-Z stratifications at a given optical depth.  The example presented in Figure \ref{fig:ttau} shows that the high-Z and low-Z atmospheres have temperatures of approximately $T/T_{\rm eff}= 0.846$ and $0.793$ at $\tau=0.01$, respectively.

Cooler atmospheric temperatures at low-Z in 3D simulations have been seen by \citet{1999A&A...346L..17A} and \citet{2011A&A...528A..32C}. They explain that the thermal structure of the atmosphere is determined by balancing the competing effects of radiative heating and adiabatic cooling from expanding upflows.  The decreased metallicity simulation has lower opacity and is less able to absorb radiation.  This leads to less radiative heating, so that balance is achieved at lower temperatures.

\begin{figure}[h]
\epsscale{1.2}
\plotone{./ttau_metallicity.eps}
\caption{Average {\ttau} relations for simulations s4 and s13 with varied metallicity, compared with analytic and semi-empirical {\ttau} relations for the Sun.  Low metallicity simulations have less radiative heating, resulting in a steeper {\ttau} relation in the optically thin layers.  Dotted lines mark the {\teff} surface and the $\tau=2/3$ optical surface, which by definition, occur at the same depth in the Eddington {\ttau} relation.}
\label{fig:ttau}
\end{figure}

\section{Discussion}

\rev{Simulations of near-surface convection provide a realistic description of convection, and self-consistently couple the atmosphere and superadiabatic layer to the adiabatic region below.  The resulting stratification differs from, and is superior to 1D stellar models computed with MLT treatment of convection.  Differences between simulations and 1D models arise because the MLT treatment of convection lacks a description for some physical processes that are present in the simulations.  In particular, MLT does not include the turbulent contribution to pressure support.  Additionally, the upflowing granulation near the surface modifies the {\ttau} relation as a result of enhanced adiabatic cooling that 1D models do not include.  Providing a representation of processes like these in 1D stellar models could potentially improve their accuracy.}

In Sections \ref{sec:salstructure} and \ref{sec:dynamics} we have shown how metallicity affects  near-surface convection in stars.   We are able to isolate the effect of metallicity by using a grid of simulations comprising sets of simulations at a fixed Z, but with overlapping {\teff} ranges.  Increasing metallicity increases the opacity, which alters the way in which energy transport transitions from convective to radiative.

When the effective temperature is held fixed, changing the metallicity alters the mean stratification through the superadiabaitc region, with low-Z simulations exhibiting higher densities and pressures through the SAL.  \rev{Additional changes in pressure come from the contribution to hydrostatic equilibrium from turbulent pressure.  Because of the larger gas pressure at low-Z, the turbulent pressure relative to the total pressure becomes smaller, although it is still significant.}  The increase in density is required to compensate for the drop in opacity, in order to maintain the radiative flux.  This effect is expected, and certainly not specific to 3D simulations, but it has ramifications for other properties of convection present in the simulations.

The simulations show an adjustment of the superadiabatic excess as a result of changes to the mean stratification.  In the deep part of the convection zone, energy is transported almost entirely by convection and the temperature gradient is essentially adiabatic.  Nearer to the surface, the temperature gradient becomes superadiabatic as energy is transferred outward more efficiently by radiation.  The degree of superadiabatic excess marks the transition from convective to radiative energy transport, and is sensitive to changes in metallicity.

Varying metallicity in the simulations induces remarkably little change in the maximum value of the superadiabaticity, even when the metallicity is reduced by a factor of 40.  \rev{The extent of the superadiabatic region also shows little remarkable variation between simulations.} This suggests that the rate of transition from convective to radiative energy transport is not drastically different in simulations of different metallicities.  The location of the transition, however, is quite different, as evidenced by a shift in the location of the superadiabatic peak. \rev{The SALs in the low-Z simulations occur at higher density.  The low-Z simulations have smaller opacity at a given density, and as a result the start of the transition to radiative energy transport occurs at higher density.}

The structure at small optical depth is set by the balance of radiative heating and adiabatic cooling from the convective updrafts.  3D simulations are able to account for accurate adiabatic cooling from the asymmetric flow that his characteristic of granulation.  Lower opacity in low-Z simulations results in less radiative cooling, and causes steeper {\ttau} gradients and cooler atmospheres.  This effect has been previously demonstrated using 3D simulations by \citet{1999A&A...346L..17A} and \citet{2007A&A...469..687C,2011A&A...528A..32C}. When metallicity is changed, our simulations show a substantial deviation (Figure \ref{fig:ttau} shows a change in temperature of up  to 8\%)  from the simple {\ttau} relations commonly used in stellar modeling.

Convective velocities are determined by the stratification, and the amount of energy flux that is transported.  Simulations with higher effective temperatures must transport more energy flux, and the convective velocities are expectedly larger.  The correlation of velocity and {\teff} exhibited in our simulation is consistent with the trend reported by \citet{2011ApJ...731...78T}. The energy fluxes are the same in simulations with the same {\teff} (but different Z), so differences in the convective velocities is a result of differences in the stratifications.  Because the high-Z simulations have lower density, the convective velocities must increase to maintain the energy flux.  Turbulent velocities are also strongly correlated with metallicity.  Our simulations show that the turbulent pressure \rev{as a fraction of gas pressure}, which is determined by the density and turbulent (rms) velocities, increases with effective temperature and metallicity.

Most of the simulation domain is convectively unstable, and, furthermore upflowing plumes do not simply stop in the radiative layers.  Instead, the momentum of the upflows carries them a certain `overshoot' distance before cycling back into the convection zone.  An expected consequence of larger mean and rms velocities is an increase in the overshoot distance.  We are able to measure boundaries on the overshoot region using correlations between turbulent fluctuations in temperature and velocity.  We find that high-Z simulations show significantly more overshoot.  Our simulations show a consistent and clear correlation between metallicity and overshoot, and in the most extreme case (between simulations with $Z=0.040$ and $Z=0.010$) we find a factor of $4.5$ change in overshoot distance.

The effect of convection, and its variation with stellar evolution, is typically not accurately represented in stellar modeling.  Most stellar models are calculated using MLT, or a similar prescription for convection, but there have been several attempts at including realistic convection in stellar models.  For example, \citet{1997ApJ...474..790D} introduced a variable mixing length parameter derived from the simulations of \citet{1996ApJ...461..499K}.  \citet{rosenthal1999} matched an envelope model to a solar simulation to include the effect of turbulent convection on oscillation frequencies, while \citet{li2002} included a two-parameter model for turbulent pressure and kinetic energy (calibrated with simulations) to 1D stellar models.

The goal of simulating stellar envelope convection remains a generalized improvement over the current MLT-like treatments.    Our simulations show that that imposing a solar-calibrated mixing length parameter on all stellar models is not accurate, and ultimately, any generalized improvement for the treatment of convection in stellar models will have to account for composition.   \rev{Simulations can help improve stellar models by providing a self-consistent and realistic description of convection across the relative parameter space, which includes composition.  While metallicity is an important contribution to the composition, other significant factors, such as helium abundance, warrant consideration as well.  To that end, we are currently using simulations to investigate the effect of helium on convection.}

\acknowledgments

JT is supported by NASA ATFP grant \#NNX09AJ53G to SB, and acknowledges a PGS-D scholarship from the Natural Sciences and Engineering Research Council of Canada. This work was supported in part by the facilities and staff of the Yale University Faculty of Arts and Sciences High Performance Computing Center.

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Are We as Doomed as That New York Magazine Article Says?
Why it's so hard to talk about the worst problem in the world
The nighttime Earth whizzes by the International Space Station in a photo taken in October 2016. NASA / Reuters
No one knows how to talk about climate change right now.
I don't have an idea about where to begin, and I write about it professionally. On the one hand, the natural consequences of climate change seem increasingly severe and devastating. Just in the past two years, I've written about how global warming will probably cause more mega-droughts in Arizona and New Mexico; how dangerously sweltering summer days are three times likelier to occur today than they were in 1900; and how even slightly warmer oceans will destroy the Great Barrier Reef.
On the other hand, a strategy for addressing climate change is coming together. The cost of solar and wind energy are plunging worldwide; carmakers are promising to take more of their fleet electric, and the amount of carbon released into the atmosphere from human activity has stabilized over the past three years. Decarbonizing will be an arduous and difficult global project—but technological development and government policy are finally bringing it into the realm of the possible.
But on the other, other hand, the Trump administration is methodically and successfully undermining the substance of American climate policy. It has spread untruths about climate science, abandoned the Paris Agreement, and stricken dozens of climate-focused EPA rules from the law books. Michael Oppenheimer, a Princeton professor who has observed climate diplomacy for 30 years, told me that this is one of the most dispiriting moments he can remember—and that he believes Earth is now doomed to warm by more than two degrees Celsius.
That's the state of the world right now. There are three ongoing shifts and no easy way to synthesize them. The facts don't lend themselves to an overwhelming vision. Instead, they suggest that the planet's economic system is in the middle of a difficult and supremely important political battle with itself. As Brad Plumer, a New York Times climate reporter, tweeted last week: There are "two radically opposed visions of the future; [it's] not yet clear which one will win out."
It's into that morass that this week's New York magazine walks. In a widely shared article, David Wallace-Wells sketches the bleakest possible scenario for global warming. He warns of a planet so awash in greenhouse gas that Brooklyn's heat waves will rival Bahrain's. The breadbaskets of China and the United States will enter a debilitating and everlasting drought, he says. And millions of brains will so lack oxygen that they'll slip into a carbon-induced confusion.
Unless we take aggressive action, "parts of the Earth will likely become close to uninhabitable, and other parts horrifically inhospitable, as soon as the end of this century," he writes. "No matter how well-informed you are, you are surely not alarmed enough."
It's a scary vision—which is okay, because climate change is scary. It is also an unusually specific and severe depiction of what global warming will do to the planet. And though Wallace-Wells makes it clear that he's not predicting the future, only trying to spin out the consequences of the best available science today, it's fair to ask: Is it realistic? Will this heat-wracked doomsday come to pass?
Many climate scientists and professional science communicators say no. Wallace-Wells's article, they say, often flies beyond the realm of what researchers think is likely. I have to agree with them.
At key points in his piece, Wallace-Wells posits facts that mainstream climate science cannot support. In the introduction, he suggests that the world's permafrost will belch all of its methane into the atmosphere as it melts, accelerating the planet's warming in the decades to come. We don't know everything about methane yet, but the picture does not seem this bleak. Melting permafrost will emit methane, and methane is an ultra-potent greenhouse gas, but scientists do not think so much it will escape in the coming century.
"The science on this is much more nuanced and doesn't support the notion of a game-changing, planet-melting methane bomb," writes Michael Mann, a climate scientist at Penn State, in a Facebook post. "It is unclear that much of this frozen methane can be readily mobilized by projected warming."
At other points, Wallace-Wells misstates what we know about the climate change that has already happened. Satellite data does not show that the world has warmed twice as fast as scientists thought, as he says; rather, the observed warming has tracked pretty close to what the models predicted. Carbon-dioxide levels only get high enough to seriously depress brain function in indoor spaces, though he implies it will become a global problem. Most importantly, we do not know nearly as much about climate change and war as he claims—an idea that I will return to in a moment.
This isn't to say that his piece is worth discarding in its entirety. Wallace-Wells paints a vivid and frightening version of a doomed world. Many scientists just don't think we live in that world—and they don't think it's helpful to tell people that we do.
Over the past decade, most researchers have trended away from climate doomsdayism. They cite research suggesting that people respond better to hopeful messages, not fatalistic ones; and they meticulously fact-check public descriptions of global warming, as watchful for unsupported exaggeration as they are for climate-change denial.
They do this not because they think that climate change will be peachy. They do it because they want to be exceptionally careful with facts for such a vital issue. And many of them, too, think that a climate-changed world will look less like a starved wasteland and more like our current home—just more unequal and more impoverished.
What does that world look like? We got a fairly good look late last month, actually, when a new consortium of economists and scientists called the Climate Impact Lab published their first study in the journal Science. Their research looks at how global warming will afflict Americans economically, on a county-by-county level. It tells a frightening but much more mundane story.
Climate change, they say, will not turn us into idiots before broiling us in our sleep. Instead, it will act as a kind of ecological reverse Robin Hood, stealing from the poor and giving to the rich. It will impoverish many of the poorest communities in the country—arrayed across the South and Southwest, and especially along the Gulf Coast—while increasing the fortunes of cities and suburbs on both of the coasts.
"This study—the climate equivalent of being informed that smoking carries serious risk of lung cancer—should be enough to motivate us," says Katharine Hayhoe, an atmospheric scientist and professor of political science at Texas Tech University. "The NYMag article is the climate equivalent of being told that everyone in the world's life will end in the most grisly, worst-case possible scenario if we keep on smoking."
The Climate Impact Labs' accounting is a much likelier view of what is "much more likely to occur than the doomsday scenario," she added.
Other communicators reject Wallace-Wells's approach for a third reason: He glosses over the many reasons that climate advocates now have hope. Many of these criticisms came not from researchers but from other climate communicators. "Through combo of exaggeration and hopelessness, [the NYMag piece] turns away those in the middle we need to persuade. It makes action harder," tweeted Ramez Naam, a technologist and novelist. "We've made huge climate strides. Business-as-usual used to mean six or seven degrees Celsius or warming. Now it looks like three to four, and [it's] trending down."
Chuck Wendig, another novelist, called the story irresponsible. "It leans very hard on the EXTINCTION PORN angle, and almost not at all on the BUT HERE'S WHAT WE DO angle," he said on Twitter.
I'm not so sure about this last angle. I have been writing about climate change nearly full-time for several years now. I don't think journalists should frame the truth to better inspire people—that's not our job.
But I vacillate considerably on the doom versus no-doom question. Consider what Wallace-Wells writes about climate change and war:
Researchers like Marshall Burke and Solomon Hsiang have managed to quantify some of the non-obvious relationships between temperature and violence: For every half-degree of warming, they say, societies will see between a 10 and 20 percent increase in the likelihood of armed conflict. In climate science, nothing is simple, but the arithmetic is harrowing: A planet five degrees warmer would have at least half again as many wars as we do today. Overall, social conflict could more than double this century.
That final sentence is simplistic; we cannot wield careful social science conclusions like an abacus. It is also too certain: While Burke and Hsiang have found links between conflict and climate change, another group of researchers from Oslo have found far weaker connections. They observe a link between natural disaster and war only when a country is divided by ethnicity.
Yet this is worrisome by itself. Consider the world that climate scientists say is more realistic: a place where sea levels cause mass migration within and without the developed world; where the economy is never great but isn't in shambles either; where voters fear for their livelihoods and superpowers poke at each others' weaknesses.
Does that world sound like a safe and secure place to live? Does it sound like a workable status quo? And how many small wars need to start in that world before they all fuse together? Who needs planet-killing methane burps when nine different countries have 15,000 nuclear weapons between them? In short, there are plenty of doomsday scenarios to worry about. They don't need to be catastrophic on their face to induce catastrophe.
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Home » Disorder » Schizophrenia » What is a Hallucination?
What is a Hallucination?
Posted by Derek Wood, RN, BC, MS | Feb 2, 2009
A hallucination is the brain's reception of a false sensory input. This essentially means that the person having a hallucination is experiencing an event through one of their senses that is not occurring in the real world. This can be through any of the senses, with tactile then auditory hallucinations being the most common. When auditory hallucinations are examined, the most common are hearing one's own thoughts as if they were being spoken aloud, followed by hearing one's name being called by a voice when alone.
People may experience hallucinations as part of their normal developmental stages, especially during the preschool years, in the 2-5 year old range. Common causes of hallucinations in people without a psychiatric diagnosis are exhaustion, sleep deprivation, social isolation and rejection, severe reactive depression, amputation of a limb (phantom limb syndrome), a reaction to medication, a reaction to hallucinogens such as LSD, a reaction to other drugs such as heroin and cocaine.
Physical (organic) causes of hallucinations include delirium, tumors leading to increased intercranial pressure, temporal lobe lesions, seizures, head injuries, and irritation of sensory pathways.
In persons with a psychiatric diagnosis, it is the psychotic disorders that are generally associated with hallucinations. These include all of the schizophrenic diagnoses, and affective disorders (such as Bipolar Disorder with psychotic features).
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NextWhat is Munchausen Syndrome by Proxy?
Derek Wood, RN, BC, MS
Derek Wood is a Nationally Board Certified Psychiatric/Mental Health Nurse, and holds a Master's degree in Psychology. His experience in the online arena of mental health can be traced back to 1997, when he was a host for Online Psych on AOL. He joined Get Mental Help, Inc. as Clinical Content Director for Mental Health Matters. Derek, with his wife Lisa, developed the original version of psychTracker (then called A Mood Journal), after his diagnosis with Schizo-Affective Bipolar, when they could not find a system available that was robust enough to help him effectively manage his symptoms and accurately interpret his charting. Derek has worked in the field of mental health since 2001, as a Unit Manager of an adult long-term treatment facility, a charge nurse in an adolescent short-term inpatient facility and long-term residential facility, and as a School Psychologist. He has also written several articles which are being used as CEU for nurses and educators.
Manic Depression: What Are The Symptoms?
Signs Of Depression
The Oxford Group and Alcoholics Anonymous: Part 4
The Facts about Alzheimers Disease
Copyright 1998 - 2022 Mental Health Matters. All Rights Reserved.


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Livestock in Sustainable Farming Systems
This excerpt is brought to you by Book of the Week – offering you a glimpse between the pages and an exclusive discount of a new book each week. Get the Book of the Week email newsletter delivered directly to your in box! This week's Book of the Week is Small Farms are Real Farms, by John Ikerd.
The challenges for livestock producers are fairly straightforward and similar in most respects to those of crop producers. Can livestock and poultry be produced by methods that conserve natural resources, protect the natural environment, provide adequate supplies of safe and healthful foods by socially acceptable means at reasonable costs, and still provide an acceptable level of economic return for livestock producers?
Large confinement beef, poultry, and dairy operations tend to be the focus of such concerns. Water and air pollution from livestock wastes, residues of antibiotics and growth additives in meats and milk, humane treatment of animals raised in confinement, and impacts of large, corporate operations on opportunities of smaller livestock producers are all questions raised by those concerned about the sustainability of conventional livestock systems.
Large commercial livestock feeding operations are the source of most questions regarding energy use in meat and milk production. Grain-fed beef, for example, yields only a small fraction of the energy embodied in the feedstuffs consumed by cattle in the production process. Poultry and pork production are more energy efficient than beef production, but all are far less efficient than direct human consumption of grains.
However, those in the livestock industry should insist that questions of energy efficiency in meat production be addressed in the same social context as the disproportionate use of energy in the more developed countries of the world in general. Affluent societies do consume more grain-fed meats, but affluent people use more energy of all types. The inequities in energy use reflect the reality of current world economic systems, not the ethics of cattle feeding or any other particular method of energy conversion.
Most environmental questions for livestock producers also relate to large-scale confinement animal feeding operations or CAFOs. Nutrient runoff from feedlots is an obvious potential source of water pollution. But mismanagement of manure removed from cattle feedlots or confinement hog and poultry facilities can be just as important. Farmers may apply manure at such times or by methods that result in most of the nutrients being volatilized, eroded, or leached rather than used by growing plants. Or they may apply manure effectively, but still apply the same amount of fertilizer they would have used without manure, resulting in pollution from excess nutrient application.
Confinement livestock and poultry operations are also the primary users of sub-therapeutic levels of antibiotics. Such practices may result in pathogenic resistance, thus reducing the effectiveness of these antibiotics for therapeutic uses in humans. Growth hormones have also been used extensively in livestock feeding operations. The association of DES with cancer has resulted in heightened public concern regarding the use of growth hormones in general. The concern for use of growth hormones is combined with public distrust of biotechnology in the current public controversy concerning the use of a genetically engineered bovine growth hormone, rGBH, in milk.
Social questions regarding animal welfare are also most frequently associated with confinement livestock operations. To date, producers of veal and caged layer chickens have received most of the animal welfare publicity. However, the basic issues are the same for all animals produced in confinement. To what extent can the activity of animals be restricted for purposes of production or economic efficiency without violating our social values concerning humane treatment of animals?
Forage-based beef production has some potentially strong positive ecological attributes of sustainability.
Confinement livestock operations can put more beef, pork, and chicken on the market at a lower dollar and cent cost than can freerange operations or farmer feeders. Thus, confinement operations have been considered more economically sustainable than alternative systems of livestock production. But questions are now being raised regarding ecologic and social costs of confinement production. The answers to these questions could shift the competitive balance in favor of less grain feeding, smaller farm-based operations, or even more grass- and forage-finished livestock.
One example of how small farmers could profit from this shift may be found in the Missouri beef industry. Many of Missouri's rolling farmlands are exceptionally well suited for forage-based beef production. Much of this land already supports herds of beef and dairy cattle. However, many of Missouri's marginal crop lands could be utilized more sustainably in forage production if cattle could compete with crops in terms of productivity and profitability.
Forage-based beef production has some potentially strong positive ecological attributes of sustainability. Many forage crops are close-growing perennials which protect the soil from erosion and facilitate water infiltration. Forages also require less nonrenewable energy to establish and harvest than do most row crops. And in many cases, forages are less reliant on the commercial fertilizers and pesticides that represent environmental risks.
Forages may also be the most efficient sustainable converters of solar energy on many soil types. In fact, the greatest inherent comparative advantage of cattle may be as intermediate energy converters. Some soils and climates will not grow crops that can be utilized directly by humans. Cattle, or other ruminants, may represent the most practical means of converting such energy to a form useful to humans.
Cattle on pastures are less likely to develop diseases than are cattle in feed lots and thus, are less likely to require use of antibiotics or other drugs than feedlot cattle. Parasites, however, may be a greater problem for range cattle. Growth hormones are sometimes used in cattle on pasture but less commonly than in feedlot cattle. Raising cattle on pastures is also commonly conceded as being more humane than is confinement cattle feeding.
In general, forage-based beef production tends to be more ecologically sound and socially responsible than is grain-based cattle feeding. However, forage-finished beef may well be more costly to produce and less acceptable to American consumers than is grain-fed beef. But intensively managed grazing systems offer promise of lower costs and greater production efficiency, resulting in both more pounds of beef per acre and higher quality meat products. Such systems require a much higher level of management and a somewhat higher labor input than do conventional grazing systems. However, the true cost of the human input depends on the nature of competition for management and labor within whole-farm systems. Time demands for managed grazing tend to be more evenly spread over time than do demands of most cropping systems.
Consumer acceptance of grass- and forage-finished beef remains a major challenge. Consumer surveys and test markets have indicated that consumers prefer the appearance, tenderness, and taste of marbled beef produced with grain. Grain-fed beef tends to be higher in saturated fats than is the leaner forage-finished beef, even though attempts to produce and mass-market beef leaner than the USDA Choice grade thus far have met with limited success. Forage-finished beef could be produced without growth hormones and without sub-therapeutic use of antibiotics, which could be positive attributes with health conscious consumers if production and marketing standards were developed to insure such practices. In addition, many processors are currently experimenting with merchandising livestock products through claims that they are produced by environmentally sound and socially responsible means.
Livestock have an important role to play in the development of a sustainable agriculture. Most of the questions of sustainability of livestock production are associated with large-scale, confinement animal feeding operations and most of the opportunities exist for grass- and forage-based livestock operations. Perhaps most important, the challenges of sustainability for grass and forage-based livestock production can be met through more careful and thoughtful management of the animals, grass and forage plants, and the land.
Dr. John Ikerd, Professor Emeritus of Agricultural Economics, retired from the University of Missouri in 2000. He was raised on a small dairy farm, worked in private industry, and held several other academic positions, prior to returning to the University of Missouri. In the 80's, John had a "conversion" of sorts after seeing the failures of the policies he had been advocating to farmers. He then reoriented his work toward agricultural and economic sustainability a means of supporting small family farms and rural communities. Since retiring, John has maintained an active speaking schedule and has authored numerous books and papers, many of which can be found at his university website. John is recognized as a longtime leading voice in the sustainable agriculture movement.
Learn from John in person this December!
Join John and other incredible speakers at our annual Acres U.S.A. Eco-Ag Conference and Tradeshow! Learn more about the upcoming conference and tradeshow and see our line-up of experts on eco-agriculture here.
Grassroots Rising, by Ronnie Cummins
Dirt to Soil, by Gabe Brown


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Q: What command should I use to display specific information about a directory, not its content? I need to know how to display info about a directory itself.
I have tried using ls -l on the directory where the directory I wanted to know about was in, but had no luck.

A: Use this command (The -d flag will make ls display only directories):
ls -ld directoryname

If you are looking for more detailed info, you can use the stat command (more info on stat):
stat directoryname

Here is an example of what stat will return:

redpajama_set_name: RedPajamaStackExchange


JA Titan (http://titan.ja.org) is a free Web-based business simulation program for high school-aged students. Set in the year 2030, students become CEOs of their own manufacturing company and must master key business decisions such as price, production levels, capital investment, marketing, and research and development. The goal of the game is to achieve the highest Performance Index possible. Games can be played against the computer, or against up to eight other players or teams of players. In addition, a school-based version of JA Titan is available with lesson plans and administrative features for teachers through local Junior Achievement Inc. offices. This version allows teachers and adult volunteers to create a series of economic scenarios such as a full business cycle; recession only; product introduction phase; or, most challenging of all, product obsolescence.


The Bloomberg Industry Leaderboard is the data visualization component of Bloomberg's new franchise The Year Ahead. This tool compares 55 global industries and the 600 market leaders within them along size, performance, profitability and forward-looking metrics. It looks at market performance the same way business leaders do—through an industry lens, and with an eye toward the future. The Leaderboard updates automatically on a daily basis.


1Dimmer + 2Relay Trail Click Module is both DIN-Rail and trail Click Mount, Bus Enabled, Cascadable. Good for Retrofit and for Installations where DB size is Limited. (Works for Both Wired S-BUS G4 and Wireless S-Wave enabled Networks). Consists of: 1 Leading Edge Dimmer Channels 2A per Channel, and 2 ch. Relay 5A.per ch.


Ashton. Sandy Spring is a city in Montgomery County, Maryland. As of the 2010 census, the population of the city was 5,628. The city lies near the junction of Route 108 (Ashton Road) and New Hampshire Avenue (Route 650).
Ashton – Sandy Spring, MD, is home to the Sandy Spring Museum and Sherwood High School. Sandy Spring Museum enriches lives, enhances community cohesion, and supports economic development with cultural and educational programming that showcases our rich history and connects visitors to a fuller future.
Ashton – Sandy Spring includes neighborhoods like Ashton Estates, Ashton Meadows, Ashton Oaks, Ashton Pond, Auburn Village, Bancroft, Bradfords Rest, Ednor Acres, Meadowsweet, Plainfield Orchard, and Springview.


Throw abroad your stirrers and say accost to the aboriginal acrylic alembic advancement in decades. Dutch Boy's artificial Twist & Cascade Acrylic Delivery System, contrarily accepted as a acrylic can, has a twist-off lid, centralized cloudburst spout, and mug handle. Need to remix? Just close, shake, and pour. Initially accessible for gallon cans of latex-based paints; quarts will soonfollow.


Discussion in 'Patriots Fan Tailgate Meet Ups' started by Noexcusesfornumber5, Jan 27, 2017.
Are there any good places in Jacksonville to watch the SB with a group of other Pats fans? I wonder if Boston's will be Pats heavy, but do you patsfans.com guys have a place that you go that is primarily a Pats place? I'm looking to go out rather than stay at home this year.
I know the Boston's in Tampa is 100% Patriot fans on game day, not sure about the one in Jacksonville. Perhaps @Ian or @KontradictioN might be able to help you out with that question, they live in that area.
Boston's in West Palm Beach (Delray) is a Pats hang out so I suspect its the same in Jacksonville.


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On Congress Blog
Congressional news and analysis
Global warming rally, bring shovel
By GLENN THRUSH
03/02/2009 09:38 AM EST
Opening statement: Just because it still snows from time to time doesn't mean global warming is a hoax.
But John Bresnahan correctly points out that it seems that a disproportionate number of GW events coincide with winter storms (and no, we're not going to provide other examples).
Bres passes along an Email from the organizers of PowerShift'09, who say they're going ahead with an outdoor Capitol rally -- despite the eight (?) inches of snow:
Just a reminder that PowerShift '09 events are STILL ON for today on the Hill -- we expect lawmakers, and thousands of climate advocates, at the 11:30 AM rally on the Capitol West Lawn; at 1:30 PM we have a Congressional briefing with Rep. Markey in 2172 Rayburn.
Glenn Thrush is senior staff writer at Politico Magazine.


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When it is estimated that only 60 of a species still exist in the wild, every single individual is important. Gemma Goodman and Anna Heath from our Research Team describe a recent rescue operation run by our White-bellied Heron network to save one bird. On November 11 in the Gengga [...]
By Gemma Goodman|2019-12-12T10:34:47+00:00December 11th, 2019|Asian Species, Biodiversity, Captive Breeding, Conservation, White-bellied Heron|Comments Off on Every heron counts: an international effort to save one bird
The Mabuwaya Foundation is a conservation organisation based in Isabela province, in Northern Luzon, the Philippines. The organisation was started to build local protection for the Critically Endangered Philippine crocodile, or "bukarot" as it is known locally. The Philippine crocodile has the unwanted label of being the world's rarest crocodile, and is only known [...]
By Anna Heath|2019-11-13T10:21:09+00:00November 13th, 2019|Asian Species, Community, People and Wildlife|Comments Off on Home is where the heart is: the true meaning of community conservation
A crocodile success story (in pictures)
The Philippine Crocodile is one of the rarest and most endangered crocodiles in the world. Once found throughout the Philippines, in 2001 there were only 12 known individuals left in the wild due to habitat loss, pollution and overfishing. However, local people have pulled together to support a strong comeback for their crocodiles, and [...]
By Anna Heath|2019-08-07T14:36:31+00:00July 31st, 2019|Asian Species, Captive Breeding, Community, Conservation, Conservation Optimism, People and Wildlife, Southeast Asia, Species|Comments Off on A crocodile success story (in pictures)
Lights, Camera, Heron!
Conservation Research Analyst Anna Heath on how a camera trap set up to capture images of one of the world's most iconic species, the tiger, may help in the battle to save one of the world's least well-known, the White-bellied Heron. Earlier this month, I arrived at work to a flurry of excited [...]
By Anna Heath|2019-04-24T09:04:34+00:00April 24th, 2019|Asian Species, Biodiversity, Captive Breeding, Conservation, White-bellied Heron|Comments Off on Lights, Camera, Heron!


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Бівер-Фоллс () — місто () в США, в окрузі Бівер штату Пенсільванія. Населення —  осіб (2010).

Географія
Бівер-Фоллс розташований за координатами  (40.759401, -80.323100). За даними Бюро перепису населення США в 2010 році місто мало площу 6,09 км², з яких 5,51 км² — суходіл та 0,58 км² — водойми.

Демографія

Згідно з переписом 2010 року, у місті мешкало  осіб у  домогосподарствах у складі  родин. Густота населення становила 1476 осіб/км². Було 4085 помешкань (671/км²).

Расовий склад населення:

До двох чи більше рас належало 4,4 %. Частка іспаномовних становила 1,2 % від усіх жителів.

За віковим діапазоном населення розподілялося таким чином: 20,3 % — особи молодші 18 років, 64,9 % — особи у віці 18—64 років, 14,8 % — особи у віці 65 років та старші. Медіана віку мешканця становила 34,1 року. На 100 осіб жіночої статі у місті припадало 89,1 чоловіків; на 100 жінок у віці від 18 років та старших — 85,2 чоловіків також старших 18 років.

Середній дохід на одне домашнє господарство становив  доларів США (медіана — ), а середній дохід на одну сім'ю —  доларів (медіана — ). Медіана доходів становила  долари для чоловіків та  доларів для жінок. За межею бідності перебувало 31,4 % осіб, у тому числі 56,1 % дітей у віці до 18 років та 11,6 % осіб у віці 65 років та старших.

Цивільне працевлаштоване населення становило  осіб. Основні галузі зайнятості: освіта, охорона здоров'я та соціальна допомога — 39,2 %, мистецтво, розваги та відпочинок — 13,5 %, роздрібна торгівля — 9,5 %, виробництво — 8,7 %.

Примітки

Джерела

Міста Пенсільванії
Населені пункти округу Бівер (Пенсільванія)
Університетські міста США

redpajama_set_name: RedPajamaWikipedia


text:
17/10/2013 by Editor
Nominee Services
Escrow Services in Malta
Trusts in Malta
Trust Companies in Malta
Chetcuti Cauchi advises extensively in the use of trusts in the international context. Chetcuti Cauchi's trust company, is today one of Maltas foremost fiduciary companies. Chetcuti Cauchi provides assistance in tax planning and in the setting up and management of trusts in Malta or elsewhere as well as the recognition in Malta of foreign trusts.
Although the identity of shareholders of Malta companies is publicly available at the public Register of Companies, shareholders may opt to have their shares held confidentially by a trust or fiduciary company which is authorised by the Malta Financial Services Authority to provide trust and fiduciary services. Chetcuti Cauchi Advocates' fiduciary company can also act as nominee shareholder to hold shares in a company incorporated by us if we are satisfied that the underlying reasons are legitimate.
Parties which are in the process of completing a transaction may benefit from escrow agency services whereby a third party such as Chetcuti Cauchi Advocates' licensed trust company can hold assets or financial instruments on behalf of the contracting parties while the transaction is still underway, in accordance with specific instructions and conditions as set out by them. Through the use Escrow services both contracting parties can eliminate risk by ensuring that all the conditions precedent are carried out prior to an exchange.
We offer our Escrow Services to parties involved in local or international private or commercial transactions. This service is ideal for independent parties seeking to transact commercial business together but who are unsure of their respective business practice or cultural background.
The setting up of trusts in Malta is regulated by the Trusts and Trustees Act. The Act provides for the creation of trusts and for the authorisation and supervision of trustees. In this regard, the MFSA is the competent authority for the purposes of the Act. The Act incorporates within its provisions the Hague Convention on the Law Applicable to Trusts and on their Recognition which Malta has ratified.
The concept of trust companies has also found its way into the Maltese legal system. Trust companies, often confused with trusts, are companies which are capable of holding participations in their own name but on behalf of third parties. In Malta, trust companies are now authorised and regulated by the Trusts and Trustees Act.
Act XI of 2014 introduced the notion of a Private Trust Company for family trusts with the addition of Article 43B to the Trusts and Trustees Act. The Private Trust company is a privately owned corporate trustee acting as the trustee of trusts holding the assets of a wealthy family. It is considered as an attractive option for family estate planning since the process by which it is registered is highly straightforward and simple and it allows the family members to influence the administration of a trust.
Trusts, particularly Unit Trusts, are highly efficient vehicles for businesses as well. Unit trusts allow several persons, both legal and natural, who are unable to accumulate large pools of moneys individually, to merge their resources and funds in order to access more substantive investment opportunities.
Escrow Agency & Security Services
Foundations & Charities Law
Malta Trusts & Professional Trustee Services
Property Trusts
Trustee Licences
Trusts in Civil Law Systems
Voluntary Organizations Law


For long-term storage of tissue biopsies, there are numerous factors that can influence sample integrity, including cross-contamination, temperature, evaporation, and vial sterility. Tissue samples are frequently stored and handled for years and sometimes decades; therefore, it is important for researchers to consider ways to reduce the risk of sample degradation.
Micronic has recently introduced a novel line of sealing devices, the CS100 series, which greatly improves the retrieval and handling of tissue tubes. With the CS100, you can cap and decap a single tube with ease. The CS100 is designed to eliminate any need to touch the cap with non-sterile methods and can eliminate virtually all risk of contamination when handling samples. Compatible with tubes in 96, 48 and 24- well formats, the CS100 can seal a tube in seconds according to its specified torque value. This prevents the risk of overturning the cap and distorting the threading closure, which could lead to evaporation of gas and eventually sample dehydration at ultra-low temperatures.
By storing biopsies in Micronic's 1ml or 3.5ml tissue tubes, which are certified DNase, RNase and pyrogen-free, the possibility of contamination from the storage tube itself is eliminated. Micronic's tissue tubes are specifically constructed with thick tube walls for tolerance to extremely low temperatures. Made from medical approved polypropylene, the tissue tube material has been tested and shown to have no measurable extractables, making them ideal for biological storage. Designed with a triple externally threaded closure, Micronic's tissue tubes greatly minimize any chance of the sample coming into contact with the cap. With Micronic products and careful attention to aseptic technique, tissue quality can be maintained over a long period of time.


The THS3491RGT evaluation module (EVM) is used to evaluate the THS3491 device, which is a high speed, high-voltage and low-distortion current-feedback amplifier in an 16-pin RGT package. The EVM is designed to quickly and easily demonstrate the functionality and performance of THS3491 in a gain of 5 V/V, driving an equivalent RLOAD = 100 Ω. The EVM is ready to connect to power supplies, signal source, and test instruments through the use of onboard connectors. The board is set up for single-ended input and output operation for interfacing with 50-Ω test equipment.


"He is a man inspired and a man who inspires. He is an icon of the struggle for good over evil who ennobles the human spirit of all humanity."-The Rev. Ivan Abrahams, top executive of the World Methodist Council, speaking of 95-year-old Nelson Mandela.
NEW YORK (UMNS) - Nelson Mandela, who celebrated his 95th birthday July 18, has embodied the struggle for social and spiritual transformation, said the Rev. Ivan Abrahams, a South African and top executive of the World Methodist Council. In 2000, Mandela received the World Methodist Peace Award.
NEW YORK (UMNS) - The religious folk who greeted Nelson Mandela at Riverside Church in 1990 were overwhelmed to be in the presence of a man who had become, as the Rev. Gardner C. Taylor described him that day, "the drum major in the music of freedom," writes UMNS reporter Linda Bloom in her Bloombytes blog. The South African leader marked his 95th birthday on July 18.
NASHVILLE, Tenn. (UMNS) - Bishop Gregory V. Palmer of the West Ohio Annual (regional) Conference finds a Gospel lesson and Bishop James Swanson of the Mississippi Conference gets personal in writing about the acquittal of George Zimmerman in the shooting death of Trayvon Martin. Retired Bishop Linda Lee, interim top executive of the United Methodist Commission on Religion and Race, invokes the biblical story of Esther in another piece on this subject. The United Methodist Commission on Religion and Race also has released a statement that speaks out on the issues of violence and incarceration.
INDIANAPOLIS (UMNS) - Ordaining a minister outside of an annual conference session is a rare event in the corporate life of The United Methodist Church. Such an ordination Tuesday night, July 16, was unique and so is Chaplain Anthony Hunley of the United States Army. Daniel R. Gangler of the Indiana Annual (regional) Conference shares the story.
NASHVILLE, Tenn. (UMNS) - New programs and loud worship services aren't the answer for churches wanting to reach young adults. It's authenticity in conversation, diversity, hospitality and more.
CHARLOTTE, N.C. (UMNS) - The spruced-up shacks called "tents" at historic Rock Creek Springs Camp Meeting Ground in North Carolina are worth a lot to some, and are priceless to others.