text:
\section{Introduction}

Radio emission from pulsars experiences several propagation effects from the ionised interstellar medium (ISM), as the index of refraction varies with electron density and frequency.  The signal acquires a group delay $\Delta t$, known as dispersion, scaling as $\Delta t \propto \mathrm{DM}\,\nu^{-2}$, where DM is the integrated column density of free electrons, and $\nu$ is the observing frequency.
Spatial variations in the electron density result in multi-path propagation, with deflected paths acquiring a geometric time delay from the path-length difference compared to the direct line-of-sight. When these delays are large (compared to the pulse duration), it is observed as scattering, a one-sided broadening of pulses often resembling an exponential tail.  When these delays are small, we observe it as scintillation, the constructive and destructive interference of different deflected images at the observer, resulting in a time and frequency dependence of the observed flux.  These delays are steeper in frequency than dispersion, and are expected to scale roughly as $\tau \sim \nu^{-4}$.

One of the central goals of pulsar timing is to directly detect gravitational waves, in a so-called pulsar timing array (\citealt{Hobbs2013}, \citealt{desvignes+16}, \citealt{verbiest+16}, \citealt{arzoumanian+18}).  The most stable pulsars are observed on weekly to monthly cadence over many years, and $\sim$nHz gravitational waves could be observed in timing residuals correlated in time and position on the sky \citep{hellings+83}.  This effect is expected to be tiny, with a fractional change of the arrival time compared to the gravitational wavelength of order $10^{-15}$, so it requires careful understanding of all other effects which would change the arrival times of pulses.  While PTA pulsars are selected for their stability, they all experience variable dispersion and scattering to some degree due to the relative motion of the pulsar and observer with respect to the ISM.  Variable dispersion measures have been measured and corrected using multifrequency data (eg. \citealt{keith+13}), while changes in scattering time are often estimated using the statistical relation between the scintillation bandwidth (the frequency width of scintillation) and scattering time (eg. \citealt{levin+16, shapiro+20}, see \citealt{verbiest+18} for a review of how these effects limit precision pulsar timing). Dispersion and scattering both scale strongly with frequency, and are often covariant. One can look for variable delays following a $\nu^{-2}$ and $\nu^{-4}$ scaling \citep{lam+19}; the technique of wide-band template matching has recently been developed as a way to jointly fit for these effects \citep{liu+14, pennucci+14, pennuci19, nanograv20b}.

In this paper, we begin to apply the methods of \citet{hemberger+08} to PTA pulsars, in which scintillation arcs are used to estimate time delays from multi-path propagation.
We analyse PSR J0613$-$0200  over 7 years, in roughly monthly cadence, using data from the Large European Array for Pulsars (LEAP) \citep{stappers+11, bassa+16}, and a 3-month bi-weekly observing campaign using the 100--m Effelsberg radio telescope.  This pulsar is of particular interest; it shows the strongest evidence of a 15\,nHz strain, but since the signal appears most strongly in this pulsar, it is believed to arise from an unmodelled non-GW signal \citep{aggarwal+19}. In Section \ref{sec:theory}, we give an overview of some necessary background of scintillation, and summarise the methods of \citet{hemberger+08}.  In Section \ref{sec:data}, we describe our observations with the LEAP telescope, our short-term observing campaign with the Effelsberg telescope.  In Section \ref{sec:methods} we outline our methods, in Section \ref{sec:results} we present our results, and we discuss the ramifications and future prospects in Section \ref{sec:conclusions}.

\section{Background on Theory of Scintillation}
\label{sec:theory}

\subsection{Thin screen theory and stationary phase approximation}
\label{sec:scint}
The theory of scattering in thin screens is outlined in detail in \citet{walker+04} and \citet{cordes+06}, and we summarise some of the pertinent relations here.

The ``stationary phase approximation'' assumes that the observed signal can be described as a coherent summation over all images of the pulsar (stationary phase points, regions where light can be deflected to the observer).  Each image has a geometric time delay $\tau_{i}$ and a fringe rate (or Doppler rate) $f_{D,i}$, with a magnification $\mu_i$ and intrinsic phase $\phi_i$.  In this approximation, the contribution of all of the images is
\begin{equation}
g_{E}(\tau, f_{D}) = \sum_{i} \sqrt{\mu_{i}} e^{-i \phi_{i}}\, \delta(f_{D} - f_{D,i}) \delta(\tau - \tau_{i}).
\label{eq:field}
\end{equation}
What we observe is the intensity as a function of time and frequency $I(\nu, t) = |E(\nu, t)|^{2}$, called the dynamic spectrum, formed using sufficiently fine channels to fully resolve the scintillation in frequency\footnote{equivalently, one must Fourier transform over a long enough timespan of E(t) fully encompassing g(t) (by a factor of 2, due to the Nyquist Theorem) -- the longest timescales correspond to the finest frequencies} and each time bin averaged over many pulse rotations.
The 2D power spectrum of $I(\nu, t)$ is referred to as the secondary spectrum, which expresses the intensity in terms of its conjugate variables $f_{D}$ and $\tau$, and contains the contribution of interference between all \textit{pairs} of images
\begin{equation}
|\tilde{I}(\tau, f_{D})|^{2} \approx \sum_{i,j} \mu_{i} \mu_{j}\, \delta(f_{D} - f_{D,ij}) \delta(f_{D} + f_{D,ij}) \delta(\tau - \tau_{ij}) \delta(\tau + \tau_{ij}),
\label{eq:secspec}
\end{equation}
where $f_{D, ij}$ and $\tau_{ij}$ are the differences between two interfering images,
\begin{align}
f_{D, ij} &= \frac{ (\bm{\theta_{i}} - \bm{\theta_{j}} ) \cdot \bm{v}_{\rm eff} }{\lambda}, \\
\tau_{ij} &= \frac{d_{\rm eff} (\theta_{i}^{2} - \theta_{j}^{2})}{2 c}.
\end{align}
We note that, since the dynamic spectrum is a real function, the secondary spectrum is point-symmetric.

The effective distance $d_\mathrm{eff}$ and effective velocity
$\bm{v}_\mathrm{eff}$ depend on the fractional distance of the screen from the pulsar $s$ as
\begin{align}
d_{\rm eff} &= (1/s - 1) d_{\rm psr},  \\
\bm{v}_{\rm eff} &= (1/s - 1) \bm{v}_{\rm psr} + \bm{v}_{\oplus} - \bm{v}_{\rm scr} / s, \\
s &= 1 - d_{\rm scr} / d_{\rm psr}.
\end{align}
Where, $d_\mathrm{psr}$ and $\bm{v}_\mathrm{psr}$,
are the pulsar's distance and velocity,
$\bm{v}_{\oplus}$ and $\bm{v}_{\rm scr}$ are the velocities of the Earth and scattering screen, respectively (and where we are only considering the 2D velocity on the plane of the sky).

Considering one image as the direct line-of-sight, then $\theta_i$ or $\theta_j=0$, and  $\tau$ and $f_{D}$ are related through their common dependence on $\theta$:
\begin{equation}
\tau = \eta f_{D}^{2}, \quad\mbox{with}\quad \eta = d_{\rm eff} \lambda^{2} / 2c v_{\rm eff, ||}^{2},
\end{equation}
where $\lambda$ is the observing wavelength, and where $v_{\rm eff, ||}$ is the effective velocity along the position vector $\hat{\theta}$ to the image.   For a 1D distribution of images, we denote the angle of the screen's axis with $\psi$.
Many images along a line interfering with the direct line of sight
then results in a parabolic distribution of power in the secondary spectrum, while the commonly seen ``inverted arclets'' (eg. \citealt{stinebring+01}) arise from the interference between subimages.

The curvature $\eta$ depends on the distance to the screen, the effective velocity, and the angle between the velocity and the screen. Structures in the secondary spectrum move along the main parabola from left to right (negative to positive $f_{D}$) due to the effective velocity as
\begin{equation}
    \frac{d f_{D}}{dt} = \frac{1}{2 \eta \nu} \left(1 - \nu f_{D} \frac{d \eta}{dt} \right).
\end{equation}
The motion of points in the secondary spectrum is uniquely defined by the curvature of the parabolic arc and its time-derivative -- in other words, clumps of power in the secondary spectrum must move, and the resulting bulk scattering time is necessarily variable.  Variable motion from the Earth's or the pulsar's orbit will contribute to $\nu f_{D} \frac{d \eta}{dt}$.

\subsection{The interstellar response}

In this section we summarise and expand upon the method of \citet{hemberger+08}, to use the secondary spectrum to estimate the total time delays from multipath propagation.

The electric field that we observe is the intrinsic signal of the pulsar convolved with the impulse response function of the ISM,
\begin{equation}
    E(t) = (E_{\rm int} * g_E)(t),
\end{equation}
where $E_{\rm int}$ is the intrinsic signal of the pulsar, and $g_E(t)$ is the interstellar impulse response function of the field.

We measure the time-averaged intensity, not the direct electric field.  The quantity of interest is then the time shift of the intensity $\langle \tau \rangle_{I(t)}$, where
\begin{equation}
    I(t) = \mean{|E(t)|^{2}} = \mean{|(E_{\rm int} * g_E)(t)|^{2}},
\end{equation}
where $\mean{}$ denotes the average over many pulses.
First we must find a suitable way to describe the effect of response function of the field $g_E(t)$ on the intensity.  Under the assumption that the intrinsic field is temporally incoherent, then
\begin{align}
  \mean{E\sub{int}(t_1) E^{*}\sub{int}(t_2)} &= I\sub{int} (t_1) \delta (t_1-t_2),
  \label{eq:incoh}
\end{align}
and it can be shown that the observed intensity can be written as
\begin{equation}
    I(t) = (I\sub{int} * g_{I})(t)
\end{equation}
where $g_I(t) = |g_E(t)|^2$ can be thought of as the intensity response function.  Equation \ref{eq:incoh} is written unrigorously for infinite bandwidth -- in the real case of a finite bandwidth, the delta function would be replaced by a sinc function with width $\sim 1/BW$.

With the above assumptions, we now have the intensity written in a form resembling \citet{hemberger+08}, and can follow their steps.
The goal of this method is to estimate the time shift from the intensity response function, $\langle \tau \rangle_{g_I(t)} \equiv \tau_s$.  Two properties of convolutions are important for this method, that the centroid and the variance of two convolved functions are additive
\begin{equation}
 \langle \tau \rangle_{f * g} = \langle \tau \rangle_{f} + \langle \tau \rangle_{g}, \quad \textrm{and} \quad \sigma^{2}_{f * g} = \sigma^{2}_{f} + \sigma^{2}_{g}
\end{equation}
For simplicity, we define the center of the pulse to be at $t=0$, and define the pulse width to be $w$.
When $w \gg \tau_{s}$ (as is the case for this paper, as the $\sim \mu$s delays are much smaller than the $\sim$\,ms pulse width), then using the two convolution properties above, we have
\begin{equation}
    \langle \tau \rangle_{I} = \langle \tau \rangle_{I_{\rm int}} + \langle \tau \rangle_{g_I} = \tau_s,
\end{equation}
and
\begin{equation}
    \sigma^{2}_{I} = \sigma^{2}_{I_{\rm int}} + \sigma^{2}_{g_I} \sim w^{2} + \tau_{s}^{2} \approx w^{2},
\end{equation}
since $\langle \tau \rangle_{I_{\rm int}} = 0$ by definition.  This means that the shape of the pulse is effectively unchanged, yet it still has a bulk time delay from the response.

\subsection{ Estimating time delays from the Secondary Spectrum }

Now we address how to estimate the time delays of the intensity response function in practice.
As we are only concerned with measuring time delays, in this section we drop the time dependence for simplicity, focusing on the imprint of the impulse response function on the spectrum.

The Fourier transform of the intensity spectrum is
\begin{equation}
    \tilde{I}(\nu) = \tilde{I}_{\rm int}(\nu) \tilde{g_I}(\nu),
\end{equation}
where the convolution between the pulsar's signal and impulse response becomes a direct multiplication.  The intrinsic profile $I_{\rm int}$ is assumed to be stable, and only slowly varying across frequency after averaging over many pulse rotations, so we treat it as a constant.  The secondary spectrum is obtained by Fourier transforming and squaring the spectrum $I(\nu)$, resulting in
\begin{equation}
    |I(\tau)|^{2} = I_\text{int}^{2} (g_I(\tau) * g^{*}_I(-\tau)).
\label{eq:Itau}
\end{equation}
This is the autocorrelation of the intensity impulse response function,
and we see that this form cannot necessarily recover the total time delay as it only measures differences in $\tau$, not an absolute time.

To simplify, we return to the stationary phase approximation, as discussed in Section \ref{sec:scint}.  The intensity response function is the square modulus of the field as given in equation \ref{eq:field}, where if we assume that the images lose coherence when integrating over the full observation we have
\begin{equation}
    g_I(\tau) = \sum_{i} \mu_{i} \delta(\tau_{i}).
\end{equation}
We wish to estimate this from the secondary spectrum.  To examine a limiting case, let us assume most of the power is near the undeflected line of sight (defined as $j=0$), then $\tau_{0} = 0$, $\mu_0 \approx 1$, and $\mu_0 \gg \mu_i$. Then, taking only positive $\tau$, and averaging over $f_{D}$, equation \eqref{eq:secspec} becomes
\begin{equation}
|I(\tau)|^{2} \approx \sum_{i} \mu_{0} \mu_{i} \delta(\tau_{i}),
\label{eq:Itau_centralimage}
\end{equation}
In this limit, there will be a visibly strong parabolic arc without inverted arclets.
The total time delay would then be determined from the expectation value in $\tau$, where the contribution of the bright central image divides out
\begin{align}
    \langle \tau \rangle_{I} &= \frac{\sum_{i} \mu_{0} \mu_{i} \tau_{i}}{\sum_{i} \mu_{0} \mu_{i}} \\ &= \frac{\sum_{i} \mu_{i} \tau_{i}}{\sum_{i} \mu_{i} } \\ &= \langle \tau \rangle_{g_I}
    \label{eq:Igequiv}
\end{align}
The contribution of the phases can be neglected if every pixel in the secondary spectrum contains only one pair of interfering images -- while not necessarily the case, this is aided by the time axis of the dynamic spectrum and many channels, which separates the power in the secondary spectrum in $f_{D}$ as well as $\tau$.

We see that in the limit of a strong central image, we can recover the total time delays from the secondary spectrum.
More generically, how well the time delays can be computed from the secondary spectrum is dependent on the unknown distribution of images (or the functional form of $g_I(\tau)$).  In the case of strong scattering, there is no reason to expect a single undeflected line of sight image, but rather there may be many bright, scattered images at small angular separation.  In this case, the time delay computed from the above formula will be overestimated, due to the cross-terms of bright central images interfering.  This will bias the result high by a factor of $\sim 2m / (m+1)$, where $m$ is the number of bright images, leading to a difference as large as a factor of 2.  In the case of a discretised secondary spectrum, this will only begin to matter if the image separations are larger than one pixel in $\tau$, otherwise it will approximate the case of one bright central image.
Additionally, we are still limited by the fact that the secondary spectrum measures differences in time delays, rather than absolute time delays; if there is a time-shift applied to all images, it would not be captured by our estimate.

With the above caveats mentioned, we use equations \ref{eq:Itau_centralimage} and \ref{eq:Igequiv} as our basis to measure time delays throughout the paper.  These include the assumption of a strong central image, which we believe gives a reasonable estimate for our purposes.  We describe how to compute time delays in practice from our data in Section \ref{sec:delays}, after detailing our data reduction and secondary spectra creation.

\section{Observations}
\label{sec:data}

\subsection{LEAP}

The Large European Array for Pulsars (LEAP) is a phased array of
five large radio telescopes in Europe; the Effelsberg telescope,
the Lovell telscope at Jodrell Bank Observatory, the Westerbork
Synthesis Radio Telescope, the Nan\c cay Radio Telescope and the
Sardinia Radio Telescope \citep{stappers+11}. The coherent addition of radio signals
from all these telescopes results in an effective 195\,m diameter
dish. The overview of LEAP is given in \citet{bassa+16}.
Observations have been made  monthly since 2012, with whichever subset of these telescopes was available.

The voltage data from each site are shipped or transferred to Jodrell Bank Observatory to be correlated and coherently added on a designated CPU cluster, using a specifically designed software correlator (details in \citealt{smits+17}).  Correlation involves a polarisation calibration based on an observation of PSR~J1022+1001 or PSR~B1933+16 from the same epoch, correlation on a calibrator to find an initial phasing solution, then self-calibration on the pulsar to determine the time delays and fringe drift rates for each telescope
throughout the observation, using Effelsberg as a time and position reference.  The coherently added voltages are stored on tape, allowing us to re-reduce the data with arbitrary time or frequency resolution.
The high sensitivity, and the flexibility offered by storing the baseband data has enabled LEAP to do single pulse studies of MSPs \citep{liu+16, mckee+19}; for these same reasons, it is an ideal telescope for the scintillation work presented in this paper.  Typical observing lengths are $30-60$\,minutes, with bandwidths of $80-128$\,MHz (comprised of 16\,MHz subbands), depending on the subset of telescopes used for a given observation.
As we will show in Section \ref{sec:screen}, the angular extent of the scattering screen is unresolved by LEAP, so we can safely treat it as a single-dish instrument for our purposes.

\subsection{Effelsberg 100--m Telescope}
\label{sec:effelsberg}

From March to June 2020, we had a roughly bi-weekly monitoring campaign using the Effelsberg telescope.  Baseband data were recorded as 8-bit ``dada''\footnote{\url{http://psrdada.sourceforge.net/}} files using the PSRIX backend (described in \citealt{lazarus+16}), using the central feed of the 7-beam receiver (``P217mm'').  The data were recorded in 25\,MHz subbands, with a usable bandwidth of 1250-1450\,MHz, and typical observation lengths of $90\,$minutes.  While Effelsberg alone is less sensitive than LEAP, this is compensated through the larger exposure times and bandwidth.

\section{Methods}
\label{sec:methods}

\subsection{Creating dynamic and secondary spectra}

We created folded archives from the baseband data using \texttt{dspsr} \citep{vanStraten+11}, coherently de-dispersing and folding with 10\,s bins, 128 phase bins, and sufficient channels to fully resolve scintillation - 62.5\,kHz, and 50.0\,kHz channels for LEAP and Effelsberg respectively. The subbands were combined in frequency using the \texttt{psrchive} tool \texttt{psradd} \citep{hotan+04} to form one combined archive per observation. The following processing steps for data from either telescope are identical unless expressly stated otherwise.

After summing polarisations, each folded archive contains a data cube $I(t, \nu, \textrm{phase})$.
We use a fixed off-pulse region relative to the pulse, a contiguous $50\%$ section with no apparent pulsed emission (in Figure \ref{fig:template}, phase 0.5--1.0)
We divide by the time average of the off-pulse region across the full observation to approximately remove the bandpass, and in each time and frequency bin, we subtract the mean of the off-pulse region to remove variable background flux. Sub-integrations with an off-pulse standard deviation $>5\times$ the mean rms value were masked, as were any time bins or frequency channels with $>30\%$ of flagged sub-integrations.

The LEAP dada files are saved separately in each sub-band, in individual 10\,s files; a small number of these files were missing, and were filled with zeros, and included in our mask.  To reduce artefacts caused by Fourier transforming over a window function, masked pixels were iteratively in-painted using the mean of the nearest pixels.  While more sophisticated methods of inpainting exist, this is sufficient for our analysis, as typically no more than $5\%$ of data are flagged.

A time and frequency averaged profile was created, and zeroed everywhere the S/N was below 5$\,\sigma$.  This profile was used to weight each phase bin, before summing over pulse phase to create the dynamic spectrum I(t, $\nu$).
Over a narrow band, it is sufficient to simply use a 2D FFT, which we used for this analysis (over a wider band, the $\nu^{-2}$ scaling of $\eta$ causes arcs to smear in the secondary spectrum, summarised in \citealt{gwinn+19}).
Before taking a FFT, we padded the edges by a factor of two with the mean value of the dynamic spectra, to mitigate artefacts caused by edge effects.
A few representative LEAP dynamic and secondary spectra, at the same time of several years, are shown in Figure \ref{fig:dynspec}.

\begin{figure*}
\center{}
\includegraphics[width=1.0\textwidth,trim=0cm 0.0cm 0cm 0cm, clip=true]{J0613-0200-dynpanomara.pdf}\\
\includegraphics[width=0.992\textwidth,trim=-0.55cm 0cm 0cm 0.0cm, clip=true]{J0613-0200-SSpanomara.pdf}
\vspace{-3mm}
\caption[Dynamic Spectra of LEAP pulsars]{{\it Top:} Dynamic Spectra of 5 observations around the same time of year, to have comparable contributions from the Earth's velocity. The colourbar extends from $2\sigma$ below the mean to $5\sigma$ above. {\it Bottom:} Corresponding secondary spectra, with a logarithmic colourbar extending three orders of magnitude.  Clear arcs with noticeable localised clumps of power are seen, these correspond to prominent diagonal features in the above dynamic spectra.  The observation from 2013 is anomalous, showing extremely fine stripes in the dynamic spectrum, corresponding to power at large time delays.
\label{fig:dynspec}}
\end{figure*}

\subsection{Measuring arc curvatures}
\label{sec:curvature}

The main power in the secondary spectrum of PSR J0613$-$0200  follows a parabolic arc, suggesting scattering dominated by a highly anisotropic, thin-screen.  As described in Section \ref{sec:screen}, the arc curvature encodes $v_{\rm eff}$ and $d_{\rm eff}$; we wish to measure the arc curvature for each observation, to probe the changing velocities of the system, and to localise power for measuring time delays.
One method often used to measure parabolic curvatures is the Hough transform, finding the peak of the power summed over different possible parabolic curvatures \citep{bhat+16}.  While this technique works very well for thin parabolic arcs, it leads to a broad maximum (and correspondingly large uncertainties) for broad parabolae, as seen in our data. We determine the curvature in a different way;  in $\tau$ steps of $0.125\,\mu$s in the secondary spectrum (where $\tau > 0.5\,\mu$\,s, to avoid confusion in the bright centre), we find the peak value of $I(f_{D})$ for both positive and negative $f_{D}$. We keep only points where the peak is $>4\times$ the rms of the background, estimated from the region of $I(|f_{D}| > 10\,\mu\text{s})$. This set of points in $f_{D}$ and $\tau$ is fit with a parabola, using an orthogonal minimisation routine, to find the best-fit curvature and error.

\subsection{Integrating the secondary spectrum}
\label{sec:delays}

For purposes of measuring time delays, the $x$-axis $f_{D}$ is not important, except to localise the scattered power in this parameter space.  We isolate the power in a $1\,$mHz region surrounding the main arc, as defined by our measured arc curvatures.
We subtract the averaged background far from the main arc, assuming the noise is well described as a function of time-delay.  We measure the total time delay through the expectation value of $\tau$, computed as
\begin{equation}
\langle \tau \rangle = \frac{ \int_{0}^{T} \tau |I(\tau)|^{2} d\tau}{\int_{0}^{T} |I(\tau)|^{2} d\tau},
\label{eq:tauint}
\end{equation}
where $T = 8 \mu$s, defined by our choice of channelisation.

Artefacts in the dynamic spectrum, such as RFI, phasing imperfections, and the window function lead to correlated features in the secondary spectrum.  As such, the noise properties are not always well behaved, and direct error propagation underestimates the error on $\langle \tau \rangle$.  We estimate our errors directly from the cumulative function in equation \eqref{eq:tauint}; at high enough $T$ the integral plateaus, with residual variations caused by the effect of integrating noise in the secondary spectrum. We take the mean and standard deviation of equation \eqref{eq:tauint} between $T=4-8\,\mu$s as our measurement and error of $\langle \tau \rangle$ respectively.

\subsection{"Timing" a convolved template}
To illustrate the effects of scattering on a profile,
we can directly convolve our measure of the amplitude of $g_I(\tau)$ into a template profile and measure the time offset using the standard Fourier template-matching algorithm outlined in the appendix of \citet{taylor92}.  We create an analytic template using the standard \texttt{psrchive} tool \texttt{paas} \citep{hotan+04}, fitting the profile with a series of von Mises functions, and interpolate the solution to have the equivalent 31.25\,ns bins of our measured $|I(\tau)|^{2}$.  We convolve the two, and measure the relative time delay between the convolved template against the original one.  Figure \ref{fig:template} shows this convolution applied to one of our observations.  The measured time delay in this way agrees perfectly with the method in the previous section; timing recovers the shift correctly, even when the effects are not visibly noticeable.

We note again that this is not precisely the intensity impulse response, but rather its autocorrelation, but it is close enough in amplitude to demonstrate that the convolved template is visually identical (with residuals at the $0.1\%$ level after aligning the template), yet is measurably delayed. In addition, $|I(\tau)|^{2}$ is noticeably clumpy and poorly described by an exponential, even after being effectively smoothed by the autocorrelation.

\begin{figure}
\includegraphics[width=1.0\columnwidth,trim=0cm 1.0cm 0.0cm 1.0cm, clip=true]{J0613-TemplateShift.pdf}
\caption[Template convolved with scattering tail]{The effects of scattering on a pulse profile. {\it Top:} Analytic profile, before and after convolving with the scattering tail measured from scintillation.  The inset panel shows $\tilde{I}(\tau)$ measured on 2017-02-17 in the way described in Section \ref{sec:delays}.  The resulting convolved profile looks identical by eye to the original, as the time delays are largely sub-bin.  {\it Middle:} The residual of the original and convolved profile, {\it Bottom:}
the residual between the template and shifted profile, after shifting them into closest alignment.
The middle, uncorrected residuals are only as large as $1\%$, while after aligning the residuals are below the $0.1\%$ level.  This reinforces the fact that the main contribution of scattering is a bulk time shift, rather than a noticeable change in profile shape.
\label{fig:template}}
\end{figure}

\begin{figure}
\center{}
\includegraphics[width=1.0\columnwidth,trim=0cm 0cm 0cm 1.5cm, clip=true]{J0613-0200-ccorrexample.pdf} \\
\includegraphics[width=1.0\columnwidth,trim=0cm 0cm 0cm 1.5cm, clip=true]{J0613-0200-3correxample.pdf}
\vspace{-5mm}
\caption[Cross correlation]{Two examples of 2D ACFs.  The cut through dt=0 is fit with a Gaussian to measure the scintillation bandwidth, to infer the bulk scattering time. {\it Top:} the same data as in Figure \ref{fig:template}, well fit by a 1D Gaussian.  {\it Bottom:} ACF of the leftmost panel of Figure \ref{fig:dynspec}, showing 3 distinct frequency scales.
\label{fig:acf}}
\end{figure}

\subsection{Inferred time delay from the frequency ACF}
\label{sec:acf}
A standard way to infer the time delays from scattering is to construct the auto-correlation functions $R(\Delta \nu) = (I * I) (\Delta \nu)$.  Fitting the width (specifically, the HWHM) of the ACF in frequency gives the scintillation bandwidth $\nu_{\rm scint}$, which is inversely proportional to the bulk scattering delay as $\langle\tau \rangle = C / 2\pi\nu_{\rm scint}$ (C is commonly assumed to be 1, and depends on the assumptions of the scattering distribution).  This method is often used when arcs cannot be resolved nicely, as $\Delta \nu$ can typically be measured simply and robustly.  However, if $g_E(t)$ is not smooth, then the ACF will be poorly described as a single Gaussian.  Two such examples of an ACF, one well described, and one poorly described by a 1D Gaussian fit are shown in Figure \ref{fig:acf}, along with their derived $\nu_{\rm scint}$ and $\langle \tau \rangle$.  In the second case, a single Gaussian would preferentially fit the broad component, and result in an inferred time delay which is low, while power at large time delays results in the narrow peak smaller than 1\,MHz.

Our error includes both the measurement error of the fit, in addition to the ``finite scintle error'', which is a counting error of $\sqrt{N_{\rm scintles}}$, estimated in the same manner as \citet{levin+16} as
\begin{equation}
    \delta \langle \tau \rangle / \langle \tau \rangle \approx [( 1 + \eta_{t} T_{\rm obs} / t_{\rm scint}) (1 + \eta_{\nu} BW / \nu_{\rm scint})]^{-1/2}.
\end{equation}
The values of $\eta$ are the filling fraction of scintles, assumed here to be $0.2$.

\section{Results}
\label{sec:results}

\begin{figure*}
\center{}
\includegraphics[width=1.0\textwidth,trim=0cm 0cm 0cm 0cm, clip=true]{J0613-0200-scattering.pdf}
\vspace{-7mm}
\caption[Cross correlation]{{\it Top:} Variations in the bulk scattering time from every LEAP observation.  Black points are estimated through integrating $\tilde{I}(\tau)$, as described in Section \ref{sec:delays}. The red points are delays inferred from the measurements of $\nu_{\rm scint}$ from the ACF, described in Section \ref{sec:acf}.
{\it Middle:} The measured arc curvatures for each observation, with a best-fit model of a 1D scattering screen from 2014 onwards overplotted.  {\it Bottom:}  Measured DM values from NANOGrav 12.5 year data release \protect{\citep{nanograv20a}}.
\label{fig:scattering}}
\end{figure*}

\subsection{Evolution of scattering time from LEAP: month to year timescales}

We present our measurements of the bulk time delay in the top panel of Figure \ref{fig:scattering}.  We find significant persistent scattering at the $\sim80\,$ns level, and a few cases of strong scattering variability on several month to year timescales.  The timescales are set by the time it takes power to move through the secondary spectrum, as described in Section \ref{sec:theory}.  The most striking feature is the strong excess scattering in 2013, where the bulk scattering is variable and extends above $200\,$ns.  This is not captured very well by the ACF method, as the Gaussian fit latches onto the broad-scale scintillation rather than the narrow peak caused by the large time delays, as described in Section \ref{sec:acf}.  As hinted at in Figure \ref{fig:acf}, this could potentially be remedied by using a multi-component model to the ACF, as in principle the ACF contains the equivalent information as the secondary spectrum, only differing by a Fourier transform.

In the bottom panel of Figure \ref{fig:scattering}, we plot the DM values of PSR J0613$-$0200  from NANOGrav's 12.5 year release \citep{nanograv20a}. The DM is steeply decreasing prior to 2013, and there is clear annual variation; this was studied in detail in \citet{jones+17}, with data spanning from 2006 until near the end of 2013.  The authors fit the time variations of DM with a 1-year period sinusoid and a linear trend, to capture the contribution of the pulsar's observed trajectory through the ISM from the pulsar's and Earth's velocity, respectively.  The residuals of the DM show a borderline significant dip of $2-3 \times 10^{-3}$\,pc\,cm$^{-3}$  at MJDs 56300--56400, the beginning of 2013.

Although the ecliptic latitude of the pulsar is quite large ($-25.4^{\circ}$), part of the annual variation that appears in the DM time series might be explained with the contribution of the Solar wind. The time of closest approach for PSR J0613$-$0200  is in mid-June each year, and by modelling the distribution of electrons in the Solar wind as spherical \citep{edwards+06} with an electron density of 7.9 cm$^{-3}$ at the Earth orbit \citep{madison+19}, we expect a DM displacement in the order of $2\times10^{-4}$\,pc\,cm$^{-3}$  at the closest approach. By allowing the amplitude of the Solar wind approximation to vary year by year, we find a model that accounts for both the ISM and the Solar wind is preferred in 7 years across the dataset, while an ISM-only model favoured elsewhere. The years in which the complete model is preferred show a general compatibility with an amplitude of 7.9 cm$^{-3}$, and after the subtraction of the time-dependent approximation of the Solar wind the most significant remaining feature is the steep gradient of the DM leading into 2013.

Similar events of increased scattering have been seen in PSR J1017-7156 and PSR J1603-7202 by the Parkes Pulsar Timing Array (PPTA), in which the scintillation bandwidth and timescale decrease suddenly associated with a jump in DM of several $10^{-3}$\,pc\,cm$^{-3}$ , interpreted as an extreme scattering event \citep{coles+15}.  While we do not see an increase in DM of this order, the increased scattering we observe in PSR J0613$-$0200  may be of similar origin.

\subsection{Location and nature of the scattering screen}
\label{sec:screen}

As mentioned in \ref{sec:delays}, we fit the parabolic curvature of each observation to determine the masks for estimating the time delays. The arc curvatures contain the effective velocity, and vary throughout the year from the Earth's motion. The existence of parabolic arcs suggests highly anisotropic scattering; for a one-dimensional screen, the arc curvature then depends only on the effective velocity parallel to the screen.  By measuring the change in arc curvature over the year, one can measure the distance and orientation of the scattering screen.

We perform only a simple analysis here, currently ignoring the contribution from the pulsar's orbital motion.  We fit the observed curvature values beyond 2013 with a 1-dimensional screen, using measured values of the pulsar's distance of 780$\pm80$\,pc and proper motion of $\mu_{ra}=1.822 \pm 0.008$\,mas/yr, $\mu_{dec}=-10.355 \pm 0.017$\,mas/yr from \citet{desvignes+16}.  The three free parameters are the fractional screen distance $s$, the orientation of the screen $\psi$, and $v_{\rm ism,||}$, the velocity of the scattering screen parallel to its axis of anisotropy.  A 1D screen fits the data well, shown in the middle panel of Figure \ref{fig:scattering}, while the best fit values are in Table \ref{table:fitresults}.
Using the screen distance, and the largest detectable time delays of $\tau \approx 5\,\mu$s, the largest angular extent of the screen is $\theta \approx \sqrt{2c \tau / d_{\rm eff}} \approx 3$\,mas, smaller than the resolution of the longest baselines of LEAP.

During the increased scattering of 2013, the best-fit model poorly matches the data.  Here, we investigate this year separately.  The secondary spectra spanning 2013 are shown sequentially in Figure \ref{fig:CS2013}.  Persistent clumps of power can be tracked throughout the year, and features can be seen to cross the line of $f_{D} = 0$, indicating a changing sign of $\bm{v}_{\rm eff}$.  From this, we can fit directly the signed value of $1/\sqrt{\eta} \propto v_{\rm eff}$ (with the same free parameters $s$, $\psi$, and $v_{\rm ism,||}$), where the locations of velocity zero-crossings are quite constraining.  The measures of $\bm{v}_{\rm eff}$, and best fit model are shown in Figure \ref{fig:veff2013}.

The best fit screen parameters for 2013, and for all data beyond 2013 are tabulated in Table \ref{table:fitresults}.  The distance of the screen is consistent between both fits, with the orientation and parallel screen velocity differing between the two.  This implies that the strong scattering plausibly arises from the same physical region. In addition, the absolute velocity of the screen need not be changing, as the orientation differs and we are only sensitive to the component of the screen velocity parallel to $\psi$; the results of both fits are consistent with a screen velocity of $|v_{\rm scr}| = 15\pm2$\,km/s at an angle of $\phi_{\rm vel} = 15^{\circ} \pm 10^{\circ}$ (East of North).

We note however that the models above are incomplete, as a proper treatment needs to include the binary motion of the pulsar, which we have neglected. The orbit is 1.2 days, and $v_{orb} \sin(i) = 19.9\,$km\,s$^{-1}$.  Each observation is much smaller in duration than the orbit, but is at an effectively random orbital phase. This will add scatter in the velocities, and thus the curvatures. To properly account for the orbital velocity, one would need to jointly fit for $i$ and $\Omega$ - such a fit has been performed successfully on 16 years of arc curvature values of J0437-4715 in \citet{reardon+20}, measuring the inclination with $0.3^{\circ}$ precision and the longitude of ascending node with $0.4^{\circ}$ precision.
Regardless, a 1D screen is a good fit to the data beyond 2013 (where each year the curvature peaks around November and is minimal around May), where the annual variation is the strongest effect.

\begin{figure*}
\center{}
\includegraphics[width=1.0\textwidth,trim=0cm 0.cm 0cm 0cm, clip=true]{J0613_2013panorama.pdf}\\
\vspace{-3mm}
\caption[Secondary Spectra of 2013 anomalous scattering]{ Secondary spectra of all observations covering the anomalous scattering in 2013, with a logarithmic colourbar extending four orders of magnitude. The power can be seen to cross the $f_{D}=0$ line, indicating the sign of $\bm{v}_{\rm eff}$ is changing throughout the year, and power can be seen to travel from left to right along the parabola.
\label{fig:CS2013}}
\end{figure*}

\begin{figure}
\center{}
\includegraphics[width=1.0\columnwidth,trim=0cm 0.0cm 0cm 0cm, clip=true]{J0613_2013veff.pdf}
\caption{ Effective velocity of 2013 scattering event, and best fit 1D model. The sign of $v_{\rm eff}$ was assigned to switch when the dominant power in the secondary spectra was clearly seen to cross the $f_{D} = 0$ axis.
\label{fig:veff2013}}
\end{figure}

\begin{table}
    \caption{Fit parameters of 1D screen to the arc curvatures, as defined in Section \ref{sec:screen} }
    \centering
    \begin{tabular}{|c|c|c|c|}
    \hline
     & $s$ & $\psi_{\rm scr}$\ (degrees) & $v_{\rm ism,||}$\ (km/s) \\
    \hline
     2014 onwards & $0.62 \pm 0.06$ & $16 \pm 2$ & $-1.2 \pm 2.5$ \\
    \hline
     2013 event & $0.58 \pm 0.10$ & $-36 \pm 9$ & $12.8 \pm 2.8$ \\
    \hline
    \end{tabular}
    \label{table:fitresults}
\end{table}

\subsection{Arclet evolution with Effelsberg: Scattering time on week to month timescales}

We investigate the variability of scattering on week to month timescales with the Effelsberg observing campaign described in Section \ref{sec:effelsberg}.
The secondary spectra of all of our observations are shown in Figure \ref{fig:CS2020}.  A clear parabolic arc, with a hint of inverted arclets is seen, and can be seen to clearly move through the secondary spectrum from left to right.
We show three examples of larger, zoomed in secondary spectra in Figure \ref{fig:SecSpecZoom} to emphasise these features.
We estimate the total time delay from the secondary spectrum using the methods of Section \ref{sec:delays}, shown in the bottom panel of Figure \ref{fig:arclet}.  The total time delays are consistent with what was found with LEAP's monitoring, showing steady scattering at around 60--100\,ns, decreasing slightly over two months.

We also attempt to measure the effect of a single arclet, which is akin to contribution of a pulsar passing a single, compact point of scattering in the ISM, not unlike an echo.  We track the position, and total fractional flux of the arclet seen travelling to the upper-right in the final 7 panels of Figure \ref{fig:CS2020}.  This same feature first appears to be moving towards the origin in panels of MJD 58951-58958, although it is less prominent.  We fit a flux centroid in an ellipse around the arc, to track its motion in $f_{D}$ and $\tau$.  We measure the fraction of the flux in the arc, compared to that integrated over the full parabola, which are plotted in the top panel of Figure \ref{fig:arclet}.  The motion of the arc unsurprisingly traces out a parabola over time,as seen in PSR B0834+06 \citep{hill+05}, and is similar to echoes seen in the Crab pulsar (eg. \citealt{backer+00, lyne+01}).  The strength of the arclet is quite asymmetric about the origin, and at its peak contains $\approx 4\%$ of the total pulsar flux.  The total time shift arising from this arclet can be estimated as $\langle \tau \rangle_{\rm arclet} \approx \tau_{\rm arclet} (I_{\rm arclet} / I)$, and is shown in the middle panel of Figure \ref{fig:arclet}.  The contribution from a single arclet as it passes in front of the pulsar contributes a variable scattering of $\sim 20\,$ns over a 2 month period.

\begin{figure*}
\center{}
\includegraphics[width=1.0\textwidth,trim=0cm 0.0cm 0cm 0cm, clip=true]{J0613_2020panorama.pdf}\\
\vspace{-3mm}
\caption[Secondary Spectra of 2020 weekly monitoring]{ Secondary spectra of our roughly bi-weekly monitoring campaign with Effelsberg, with a logarithmic colourbar extending three orders of magnitude.  Power can be seen to travel from left to right along the parabola, most evident by following the power in the last six panels.  The arc curvature does not abruptly change between observations, despite being at random orbital phases, suggesting that the scattering screen resulting in these arcs is not very sensitive to the pulsar's orbit.
\label{fig:CS2020}}
\end{figure*}

\begin{figure}
\center{}
\includegraphics[width=0.9\columnwidth,trim=0cm 0.3cm 0cm 1cm, clip=true]{Ef-SecSpec1.pdf}\\
\vspace{-5mm}
\includegraphics[width=0.9\columnwidth,trim=0cm 0.3cm 0cm 1cm, clip=true]{Ef-SecSpec2.pdf}\\
\vspace{-5mm}
\includegraphics[width=0.9\columnwidth,trim=0cm 0.3cm 0cm 1cm, clip=true]{Ef-SecSpec3.pdf}
\vspace{-2mm}
\caption[Secondary Spectra zooms]{ Zoomed in Effelsberg secondary spectra from Figure \ref{fig:CS2020} for three different epochs, panels 1, 2 and 4.  The red dotted line shows our best fit parabolic curvature, while blue dotted inverted parabolae are plotted with the same curvature, with their apex on the main parabola -- these are to guide the eye towards faint structures in the secondary spectra which may be inverted arclets, and to help visualise the general trend of power moving from left to right along the parabola. More sensitive, or longer observations will be required to reveal the possible structure of inverted arclets more clearly.
\label{fig:SecSpecZoom}}
\end{figure}

\begin{figure}
\center{}
\includegraphics[width=1.0\columnwidth,trim=0cm 1.5cm 0cm 1.5cm, clip=true]{J0613-arcletevolution.pdf}
\caption[Cross correlation]{ Arclet evolution, and time delays from bi-weekly observations with Effelsberg. {\it Top:} Magnification (fraction of total intensity) and time delay of one arclet seen moving through the secondary spectrum. Red crosses are expected positions of the undetected arclet.  {\it Middle:} contribution of the single arclet to the total time delay to the pulsar's signal.  {\it Bottom:}  Estimate of the bulk scattering time inferred from the secondary spectra.
\label{fig:arclet}}
\end{figure}

\subsection{Comparison to earlier results}

Previous analysis using the ACF in \citet{levin+16} measures the time delay from scintillation to be $\langle \tau \rangle = 11.7\pm4.9$\,ns, monitoring this pulsar up until October 2013.  Additionally, \citet{shapiro+20} estimate a time delay of $\langle \tau \rangle = 43.6\pm2.3$\,ns in a similar manner.  The frequency channels used in these papers were 1.5625\,MHz wide, a common standard in timing archives, and would have averaged over the fine scintillation structures due to power at high delays.  \citet{keith+13} estimate a scintillation bandwidth of 1.64\,MHz, for which one would infer a time delay of 97\,ns.  This measurement is from before we have data, so we cannot directly compare, but this value is much closer to the order of the time delays we measure.

\subsection{Effects of uncorrected scattering}

In this section, we aim to make from our measurements a simple estimate of the single-pulsar gravitational wave signal arising from unaccounted scattering.  We stress that this is a conservative upper-limit, as we do not know the extent to which variable scattering is absorbed in red-noise modelling, or in measurements of DM.  The GW strain $h$ at a given periodicity $P$ is related to the amplitude TOA variations $\delta t$ as roughly $h \sim 2\pi \delta t / P$. Since \citet{aggarwal+19} find excess signal at $15\,$nHz, which is $\sim 2.1$\,years, we estimate this using the long-term variable time delays from LEAP shown in Figure \ref{fig:scattering}.  We perform a Lomb-Scargle periodogram on the measured values of $\langle \tau \rangle$, and convert to a measure of $h$ while taking into account the proper normalizations, shown in Figure \ref{fig:ls}.  The measured value at $15\,$nHz is $\sim 10^{-15}$, still an order of magnitude lower than the single pulsar limit of $h = 9.7\times 10^{-15}$ from the EPTA (95\% upper limit, from Table 1 in \citealt{lentati+15}).  As PTA upper limits are improved, scattering variations, if unaccounted for, may begin to limit the timing precision.

\begin{figure}
\center{}
\includegraphics[width=1.0\columnwidth,trim=0cm 1cm 0cm 0cm, clip=true]{J0613-LombScargleStrain.pdf}
\caption{ Estimated strain signal which would arise from uncorrected scattering, obtained from a Lomb-scargle periodogram of the bulk time delays $\langle \tau \rangle$ from Figure \ref{fig:scattering}.
\label{fig:ls}}
\end{figure}

\section{Conclusions}
\label{sec:conclusions}

We have measured variable time delays on a PTA millisecond pulsar, using similar methods to those laid out in \citet{hemberger+08}.
The next logical step will be to perform timing with scattering timescales subtracted from TOAs, to see if this improves the timing residuals.  One can apply this approach to study the variable scattering in many PTA pulsars.  With LEAP we can re-reduce the data to whatever time and frequency resolution we like, but regular timing observations would benefit with a second reduction with fine frequency channels at the expense of phase bins.  Going further, methods to obtain the interstellar response directly may be important, including holography \citep{walker+08}, cyclic spectroscopy \citep{demorest11, walker+13, palliyaguru+15, dolch+20}, or directly by using bright giant pulses in special cases \citep{main+17}. Only these methods, in which the interstellar delays are measured directly (as opposed to measuring delay differences, as we do in the secondary spectrum) can retrieve overall delays that are not related to the characteristic timescale of the scattering tail.  New analysis techniques such as the $\theta$-$\theta$ diagram \citep{sprenger+20}, which expresses the secondary spectrum in terms of the angular coordinates on the scattering screen, may be useful as well. This technique can be used to precisely measure arc curvatures, and could be used to efficiently perform holography of 1D screens (Baker et al. in prep.).

Scattering is statistically expected to follow $\sim\lambda^{4}$, yet scattering arising from discrete structures (observed as arclets, or localised clumps of power in secondary spectra) will be localised at a fixed $\tau$ as a function of wavelength.  Observations over a wide frequency range will help to inform the amplitude scaling of arclets, and thus the contribution of discrete arclets to the total scattering time at different frequencies.  In addition, scattering occurs from density gradients in the ISM, so the link between variable DM and scattering should be explored in more detail.  In the case where the DM and scattering variations occur in the same scattering screen, they could potentially be inferred from the other quantity; a predictive model of scattering from DM (or vice versa) would be a great step towards removing these effects from timing observations.

Knowing the screen distance and orientation, the location of power in the secondary spectrum is predetermined, but the amplitudes are dependent on the physics of scattering and lens models.  In recent years, some predictive models of scintillation properties have been developed  (eg. \citealt{simard+18, gwinn+19}), which can be tested using measurements tracking arclets in time and frequency.

We used annual variations in the arc curvature to determine properties of the scattering screen, while orbital variations were ignored.  Orbital variations can give an additional orbital constraint, such as the inclination (including the ``sense'', \citealt{rickett+14, reardon+19, reardon+20}), and could possibly lead to precise pulsar distances \citep{boyle+12}. Such analysis would be greatly improved with precise, quantitative measurements of the arc curvature.
Additionally, one could instantaneously measure the scattering screen's properties using the multiple telescopes of LEAP, either using the visibilities \citep{brisken+10} or more simply using the inter-station time delays of the dynamic spectra (\citealt{simard+19}, while the method of combining of visibilities and intensites is outlined in \citealt{simard+19b}).  This is being investigated, and will be the subject of future work.

As scattering screens are likely much smaller than the angular separation between pulsars, scattering variations are very unlikely to directly correlate between
pulsars in a way that mimics a Hellings \& Downs curve \citep{hellings+83}.
But while no direct correlation is expected between pulsars, it is possible that scattering is variable on similar timescales if pulsar proper motions and distances are comparable, and if the screen distance is not at an extreme (ie. not too close to the pulsar or to the Earth).  Several of the EPTA pulsars show variable scintillation arcs, similar to those shown in this paper, and will be subject of future work.  As PTAs become more sensitive, any PTA result relying on a small number of pulsars may need to consider the effects of variable scattering when interpreting the significance of a potential gravitational wave signal.

\section*{Acknowledgements}
RAM thanks Daniel Reardon for useful advice on modelling variable arc curvature, and Tim Sprenger for useful comments on the manuscript.

This work is supported by the ERC Advanced Grant ``LEAP", Grant Agreement Number 227947 (PI M.\,Kramer).
The European Pulsar Timing Array (EPTA) is a collaboration between European Institutes, namely ASTRON (NL), INAF/Osservatorio Astronomico di Cagliari (IT), the Max-Planck-Institut f{\"u}r Radioastronomie (GER), Nan{\c c}ay/Paris Observatory (FRA), The University of Manchester (UK), The University of Birmingham (UK), The University of Cambridge (UK), and The University of Bielefeld (GER), with an aim to provide high-precision pulsar timing to work towards the direct detection of low-frequency gravitational waves.
 The Effelsberg 100-m telescope is operated by the Max-Planck-Institut f{\"u}r Radioastronomie.
 Pulsar research at the Jodrell Bank Centre for Astrophysics and the observations using the Lovell Telescope are supported by a consolidated grant from the STFC in the UK.
The Westerbork Synthesis Radio Telescope is operated by the Netherlands Foundation for Radio Astronomy, ASTRON, with support from NWO.
The Nan{\c c}ay Radio Observatory is operated by the Paris Observatory, associated with the French Centre National de la Recherche Scientifique.

The Sardinia Radio Telescope (SRT) is funded by the Department of Universities and Research (MIUR), the Italian Space Agency (ASI), and the Autonomous Region of Sardinia (RAS), and is operated as a National Facility by the National Institute for Astrophysics (INAF). From Mar 2014 - Jan 2016, the SRT data were acquired as part of the Astronomical Validation of the SRT. We thus thank the SRT Astronomical Validation Team, and in particular: M. Burgay, S. Casu, R. Concu, A. Corongiu, E. Egron, N. Iacolina, A. Melis, A. Pellizzoni, and A. Trois. We also thank M. Pilia and A. Possenti for helping with observations.

 SC acknowledges the support by the ANR Programme d'Investissement d'Avenir (PIA) under the FIRST-TF network (ANR-10-LABX-48-01) project. SC and IC acknowledge financial support from Programme National de Cosmologie and Galaxies (PNCG) and Programme National Hautes Energies (PNHE) funded by CNRS, CEA and CNES, France.

 KL is supported by the European Research Council for the ERC Synergy Grant BlackHoleCam under contract no.\ 610058.  K.J.Lee gratefully acknowledges support from National Basic Research Program of China, 973 Program, 2015CB857101 and NSFC 11373011. DP gratefully acknowledges financial support from the research grant "iPeska" (P.I. Andrea Possenti) funded under the INAF national call PRIN-SKA/CTA with Presidential Decree 70/2016. WWZ was supported by the National Natural Science Foundation of China Grant No. 11873067 the CAS-MPG LEGACY project and the Strategic Priority Research Program of the Chinese Academy of Sciences Grant No. XDB23000000.

\section*{Data Availability}
The timing data used this article shall be shared on reasonable request to the corresponding author.

redpajama_set_name: RedPajamaArXiv


The countryside is a wonderful place to work, and the men and women who toil away at forestry, farming and gamekeeping play a vital role in its upkeep and the diversity of wildlife that lives in it. Countryside-based jobs are thought to give you greater satisfaction and feelings of well-being than many urban-based occupations, even if you are not so greatly financially rewarded.
Gamekeeping is a practical career, with most of your time being spent on your own or occasionally with another keeper from the estate. The hours are long and the work can be physically demanding.
It is also incredibly specialised. There is so much to learn that often a keeper who has been working in the profession for 40 years will still discover something from a friend or neighbour, or see a fox do something that, until that moment, they thought was impossible.
Starting out in gamekeeping used to be much more straightforward than it is today. You would begin on the rearing field or in the beating line and then work your way up with no formal training required, just a willingness to work hard and put in the hours. Now employers want to see qualifications from young people, but a practical job such as gamekeeping can't be learned in the classroom alone. It is an industry where there is no substitute for experience. There is a way, however, that allows you to gain this experience and learn while studying the profession at the same time.
There is an apprentice scheme, which gives young people a chance to get into keepering where they otherwise would not be able to do so, and the scheme suits exactly the sort of person who would like to become a keeper — apprenticeships are job-based, meaning that you will be employed and learn the role from your peers, with some assistance from your local college. There is a requirement that you pass certain skills elements, which include English and maths. To some would-be gamekeepers these subjects sound pointless for people who would like to embark on a job in the great outdoors managing habitat and wildlife.
But remember, without the basic skills of maths and English, you could be hampered in progressing to headkeeper one day. Estate employers need heads of departments to write reports and attend meetings. This is the reality in a world of high technology and European Union grants, and a keeper must be able to work out how many posts are needed to create that new pen or how many tons of wheat are needed to feed your birds, alongside your fundamental knowledge of fieldcraft.
Most agricultural colleges offer a diploma apprenticeship scheme, which often would be in wildlife and game management. These are day-release programmes which, from an employer's point of view, can be a bit tiresome at busy times of year, as you have one of your staff unavailable for a day. However, because of the nature of the work some colleges offer a block release system where the apprentice can attend the college to pass the academic side of things in one- or two- week blocks.
You do have to pay your apprentice — at the moment it is currently £2.73 per hour and you should follow the Government's working time directive. Again, this is not always practical when your job works with the rhythm of nature and it's not the usual nine-to-five routine.
The apprentice will usually leave the college with certificates in first aid, all-terrain vehicles, chainsaw safety and maintenance, herbicide use as well as other important health and safety qualifications. This means the employer does not have to spend thousands of pounds on additional training.
Apprenticeships are a good way to bring practical young people into our profession; it gives them the chance to learn from an experienced gamekeeper in real-life situations. They will gain skills that can't be taught elsewhere and the experience will leave them in good stead for moving on to another job in keepering further down the line.
The flip side is that the experienced keeper might also learn a thing or two from the apprentice, most of whom bring a wealth of knowledge with them from their courses. You can find more information on apprenticeships at www.gamekeeperstrust.org.uk.
The first step is probably the hardest. You need to find an estate or shoot that is willing to take you on and give you the support and guidance that you need to finish the course. Finding an estate is much easier if you are already beating and generally helping out on a shoot in your spare time. I would only recommend somebody seriously look at going into keepering if they have had some prior experience of it, otherwise the work can be a bit of a shock to the system. If you are helping out during the holidays and at weekends, even if the keeper or owner of that estate can't employ you as an apprentice, they might be able to help you find somebody that can.
Once you have found an employer the next step is to find a local college that offers apprenticeships in gamekeeping or wildlife management. If you have been unable to find an employer, the college can often help you in this regard. It is worth speaking to the lead tutor before you embark on any type of course to make sure you know exactly what is required.
Then it is up to you to knuckle down and get on with learning on the job through real life situations that can only be understood first-hand.
Aged 16 to 18 years: Employers will receive 100 per cent of the training costs.
19 to 23 years old: Employers will receive up to 50 per cent.
24 years old or over: Sometimes employers or the apprentice may have to pay for all training.
This is paid directly to the organisation that supports the apprenticeship. Usually this will be a learning provider, meaning that as an employer you don't pay any fees. There are also grants for employers for training apprentices — colleges will know if you are eligible for them.
You don't have to employ your apprentice at the course's end.
Keep an eye on the Shooting UK marketplace where gamekeeping jobs and trainee gamekeeping positions are advertised reguarly.


text:
Orchestre de Paris er et fransk symfoniorkester med base i Paris. Orkestret spiller de fleste af deres koncerter i Salle Pleyel.

Historie
I 1967, efter opløsningen af Orchestre de la Société des Concerts du Conservatoire, blev dirigent Charles Münch indkaldt af kulturministeren, André Malraux, og hans chefdirigent, Marcel Landowski, for at danne et nyt orkester i Paris. Kort efter oprettelsen af orkestret døde Münch (1968), og Herbert von Karajan blev ansat som konstitueret chefdirigent fra 1969 til 1971. Efterfølgende chefdirigenter inkluderer Sir Georg Solti, Daniel Barenboim og Semyon Bychkov. Christoph von Dohnányi tjente som artistisk rådgiver fra 1998-2000.

Under hans ansættelsesperiode så Barenboim et behov for et permanent kor til orkestret, og han ansatte den engelske kormester Arthur Oldham til at danne Chœur de l'Orchestre de Paris (Orchestre de Paris' kor) i 1976. Oldham forblev med koret til hans pensionering i 2002. Siden 2002 deler Didier Bouture og Geoffroy Jourdain direktionen af koret.

Christoph Eschenbach var chefdirigent fra 2000 til 2010. Han dirigerede optagelser af musik af Luciano Berio, Marc-André Dalbavie, og Albert Roussel med orkestret. I maj 2007 blev Paavo Järvi orkestrets sjette chefdirigent og indtrådte fra sæsonen 2010-2011.

I 1998 solgte Crédit Lyonnais, som havde kontrol over Salle Pleyel, salen til en fransk forretningsmand, Hubert Martigny. Salle Pleyel blev lukket i 2002, hvilket efterlod orkestret uden et fast spillested. Théâtre des Champs-Élysées og Théâtre du Châtelet blev begge benyttet i sæsonen 2001-2002. Fra efteråret 2002 havde orkestret sikret Théâtre Mogador, hvor det spillede de næste fire sæsoner. I 2003 sikrede den franske regering en ny ordning, hvormed Martigny skulle betale for renovering af Salle Pleyel, og udleje salen til Cité de la Musique, som derefter skulle købe salen i 2056. Efter renoveringer genåbnede Salle Pleyel i september 2006 og blev endnu engang Orchestre de Paris' base. Det er planlagt, at orkestret skal flytte til det nye Philharmonie de Paris, nær Cité de la Musique i Parc de la Villette i 2012, hvor det er meningen at salen er færdigbygget.

Chefdirigenter
 Charles Münch (1967–1968)
 Herbert von Karajan (musisk rådgiver, 1969–1971)
 Sir Georg Solti (1972–1975)
 Daniel Barenboim (1975–1989)
 Semyon Bychkov (1989–1998)
 Christoph von Dohnányi (artistisk rådgiver, 1998–2000)
 Christoph Eschenbach (2000–2010)
 Paavo Järvi (2010–nu)

Hitlister
Orchestre de Paris kom i 1989 i en usædvanlig situation, idet dets indspilning af Ravels Boléro blev et hit på den nederlandske hitliste. Indspilningen, der blev lavet i 1982 under Daniel Barenboims direktion, blev udgivet som en Cd-single til at koincidere med succesen fra sangen "No more boleros" af den nederlandske popsanger Gerard Joling, som inkluderer dele af Ravels værk. Med nummerets spilletid på 17 minutter forbliver Orchestre de Paris' single den længste indspilning nogensinde på den nederlandske Top 40.

Referencer

Eksterne henvisninger
 Officiel hjemmeside

Symfoniorkestre
Etableret i 1967
Musik i Paris

redpajama_set_name: RedPajamaWikipedia


Since Hurricane Maria devastated Puerto Rico more than a month ago, New Yorkers have done their part to help those suffering from the devastating aftermath of this historic storm. Help has come in many different forms and while more than 50 Red Cross employees and volunteers from the Greater NY region have put their lives on hold to travel to the US territory, other staff members have supported families arriving here in NYC from hurricane-affected regions.
Since October 11, 2017, as part of an effort led by the New York City, the American Red Cross in Greater NY has provided a host of services to thousands of individuals from Puerto Rico and other hurricane-ravaged regions.
"The stories are heartbreaking. People have lost everything," said Chris Losavio, Regional Director of Client Services and Recovery, American Red Cross in Greater New York. "We are so glad to bring some comfort to them during what will most likely be a long recovery," he said.
Initially, Red Cross teams were stationed at JFK JetBlue Terminal to provide information as well as health and mental-health support. Volunteers also distributed "comfort kits" containing basic hygiene items. In their first week at JFK the Red Cross met with 1200+ Puerto Ricans who had left the island.
On October 19, 2017 Red Cross support transitioned from JFK to a Service Center (Julia De Burgos Latino Cultural Center; 1680 Lexington Avenue in Manhattan) set up by New York City for recent arrivals affected by Hurricanes Harvey, Irma and Maria. Since then Red Cross teams have been staffing the Center seven days a week and meeting with about 75 families per day.
And considering how the individual situation of each family varies, all Red Cross casework occurs one-on-one so volunteers can best tailor services to each household.
Along with numerous NYC agencies, other organizations offering support at the Center include: Catholic Charities, Salvation Army, NY Disaster Interfaith Services (NYDIS) and CUNY.
Families can schedule appointments at the Service Center by calling 311.


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Tension headaches are the most common type of headache, and make up about 75% of chronic headaches. Tension headaches are typically the result of misaligned vertebrae in the back or neck. This misalignment causes strain and spasms in the muscles at the back of the neck and base of the head, which triggers pain sensations in the brain. Those who spend long hours on phones or computers are prone to this type of tension headache. Tension headaches may also be caused by injuries to muscles and tissue, such as one experiences from whiplash injury. The chiropractic team at CORE Health Centers is ready to help naturally realign the vertebrae associated with tension headaches, and start your path to pain relief.
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text:
Schools/College Work Experience
University Summer Placements
2022 Summer Placements
Applications for 2022 are now closed
Applications for 2023 and the list of projects available with open in December 2022.
Below are the 12-week summer placements projects available starting in June 2022. Follow the links below to find out more about each project and to apply. All applications must be made via our online application portal, for further information on how to apply follow the link below.
How to Apply Register to Apply Login to your Application
Please note that all applications for the placements below need to be completed electronically within our e-recruitment platform. If you have a disability which means that you cannot complete the application within the e-recruitment platform or require reasonable adjustments at any stage of the recruitment process, please email diamond.students@diamond.ac.uk and include 'Reasonable Adjustments' in the title of your email.
If you are disabled and would like to be considered under the Guaranteed Interview Scheme, please let us know via the online application process.
Life Science Placements
Click on each project to learn more
Time-resolved protein crystallography (22001SP)
Antibiotic resistance has become a considerable human health issue over the past decades.(Bush et al., Nat Rev Microbiol, 2011, DOI: doi:10.1038/nrmicro2693) Vancomycin, a glycopeptide antibiotic targeting bacterial cell wall biosynthesis, is considered an antibiotic of last resort due to its efficiency... Applications are now closed
Purification of Promiscuous Enzymes (22003SP)
A recent study on NAD/FAD-dependent ketoreductases found that shining light of a specific wavelength on these enzymes bestowed upon them the ability to break one of the strongest chemical bonds in nature... Applications are now closed
Working with big data: Investigation on the effective use of Diamond MX beamlines (22004SP)
Protein crystallography as a discipline has enabled one of the biggest breakthroughs of the 20th century with over 27 Nobel Prizes having been awarded... Applications are now closed
Combinatorial fragment soaking with Xchem (22005SP)
Fragment-based methods are a staple of modern drug discovery, using collections of small molecules to sample a larger proportion of chemical space than is achieved by... Applications are now closed
EM insights into channel dynamics (22006SP)
In this project you will you use cutting edge cryo-EM techniques and technologies to investigate systems essential to Haemophillus influenzae, a pathogen responsible for thousands of deaths each year... Applications are now closed
Small Angle-Scattering to study Antimicrobial Peptides  (22007SP)
The increased prevalence of multi antibiotic-resistant pathogens has been listed by the World Health Organisation (WHO) as one of the biggest threats to modern day healthcare... Applications are now closed
Technical Placements
Optical testing a von Hámos Spectrometer (22002SP)
X-ray emission spectroscopy (XES) is a powerful tool for probing the occupied and spin states of metals. In biology this has great relevance for the transition metal ions in metalloproteins (Fe, Cu, Mn, etc), these elements are unique... Applications are now closed
Design of sample environment support gear (22011SP)
Beamline I12-JEEP is designed for unique experiments which use complex sample environments and bespoke configurations of the beamline equipment. The beamline can accept a wide variety of... Applications are now closed
Physical Science Placements
Click each project to learn more
Materials for nuclear waste clean-up (22008SP)
This project presents an opportunity for a student to research the synthesis and structural characterisation of inorganic materials for potential application in the selective removal of radioactive cations from environments contaminated with nuclear waste... Applications are now closed
Modelling interactions between photo-emitted electrons (22009SP)
Angle-resolved photoemission spectroscopy (ARPES) is the most direct probe of electronic structure in solids. By analysing the energy and momentum of the photoelectrons that are ejected when the sample is illuminated by an ultraviolet... Applications are now closed
Angle-dependent electrical resistance in magnetic materials (22010SP)
Electrical resistance is a fundamental property of a material. It indicates how well an electric current can be conducted and can be dependent on the strength and direction of the magnetisation in some materials. This phenomenon is known as the anisotropic magnetoresistance (AMR)... Applications are now closed

redpajama_set_name: RedPajamaCommonCrawl


text:
Q: Heading name format not picked up in Match/Index Function with VBA I have a heading in a table that starts with "Enter"/loads of spaces, (Enter, "Act", Enter, "Sales) this is what it looks like:

Act

Sales

I'm trying to do an Index/Match with multiple criteria, but it's not picking up that heading. It's raw data that all runs through a macro, so I don't want to manually change it every time.
I've tried recording the formula with a separate macro and just copy that into my code, but it's not working. It works with other headings though.
This is the code that gives an error:
With wsReturns.ListObjects("Table_Waste_Returns")
    .ListColumns("Sales Value").DataBodyRange.Cells(1, 1).FormulaArray = _
     "=INDEX(Table_SAPBW [[ " & Chr(10) & "Act" & Chr(10) & _
      "Sales]] ,MATCH([@[Site Main descr]]&[@Article],Table_SAPBW[Site]&Table_SAPBW[Sales Set Article],0),1)"
End With

And this part seems to be the problem, the heading:
"Table_SAPBW [[ " & Chr(10) & "Act" & Chr(10) & "Sales]]"

It should match 2 criteria and then get a third column's data. As mentioned before it works with other headings, just not this one. I think it's all the spaces in the beginning.
Any workaround will be a great help!

A: Finally found an answer! Just add VBA. in front of Chr(10). This is my edited and working version:
     "=INDEX(Table_SAPBW [[ " & VBA.Chr(10) & "Act" & VBA.Chr(10) & "Sales]] ,MATCH([@[Site Main descr]]&[@Article],Table_SAPBW[Site]&Table_SAPBW[Sales Set Article],0),1)"

redpajama_set_name: RedPajamaStackExchange


For details of how to participate, please visit the Stars Rewards FAQ.
Rebates and rewards (together with any reward points that may be accumulated as part of this program) may not be transferred, bartered, sold or traded in any way. Rebates and Rewards can only be won, and reward points can only be accumulated, via real money play – when a reward point target is reached, players will win randomized Stars Rewards in exchange for those points, as detailed in the Stars Rewards FAQ. Stars Rewards may include cash, game credit or StarsCoin (our virtual loyalty token that can only be exchanged for certain goods via the Rewards Store).
Last amended February 27, 2018.


text:
Gibbs Cancer Center Greer, SC 240590 5
Tindall Delivers with Surgical Precision
In 2018, Spartanburg Regional Health Services began formulating plans for a 191,000-square-foot expansion for the Gibbs Cancer Center and Research Institute at Pelham. This new facility would greatly expand the existing hospital's oncology and cancer rehabilitation services, bringing state-of-the-art technologies and capabilities to the Upstate. The trouble was, after reviewing the original project scope and design, it seemed that cast-in-place would not be the most ideal solution for the bridge connecting the two structures. That's when Tindall was given the opportunity to show their team the possibilities of precast concrete.
Proving What's Possible with Precast
One of the challenges with the original project scope was the need to cast Y-shaped columns on site for the structure's pedestrian bridge. Creating these columns would have created significant site congestion at the hospital complex and had significant impacts on the project's overall schedule. The Tindall team developed an alternative design that not only solved the immediate challenge of the cast-in-place columns but went above and beyond what the center's team thought precast could do. This new design included precast versions of the Y-shaped columns, a total precast bridge, and architectural wall panels. This plan utilized 76,000 square feet of precast concrete to completely eliminate the need for cast-in-place elements.
By converting the pedestrian bridge into total precast and expanding the project scope to include architectural wall panels, Tindall provided a holistic solution that reduced costs, minimized site congestion, and provided a significantly faster erection schedule. The new design's sandblasted precast wall panels also eliminated the need for the original field-laid brick building, further reducing the project's schedule and budget. In the end, Tindall leveraged years of engineering expertise and research and development to deliver an alternative precast design that saved the customer time, reduced the overall budget, and helped bring the Gibbs Cancer Center to life
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Vannoy Construction
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191,000 sq.-ft. structure
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Converted from cast-in-place design


After regulating digital currency exchanges in the country last year, the Japanese Diet has signed a landmark bill that will allow the use of digital currencies like Bitcoin as a legal method of payment. The long-awaited bill, which goes into effect today (April 1), still does not recognize Bitcoin as a currency, but it has accepted that Bitcoin and other cryptocurrencies have "asset-like values" that can be used "as payment to indefinite parties for the cost of purchase or rent of items or receipt of services and which can be transferred by means of electronic data processing systems," explained Bitflyer exchange. "Bitcoin will continue to be treated as an asset unless there are future revisions or directives to Japanese tax law," the exchange noted.
The Securities and Exchange Commission (SEC) has denied a bid to list a Bitcoin exchange-traded fund on the New York Stock Exchange. The decision presents the second Bitcoin-tied ETF turned down by the SEC. On 10th March, the agency rejected an effort from investors Cameron and Tyler Winklevoss to list a Bitcoin ETF on the Bats BZX Exchange – though last week Bats moved to fight that rebuffing, seeking an effective rehearing of the SEC's decision. In its notice, the SEC cited justifications similar to those used in the Winklevoss ETF decision, namely a lack of market surveillance and a dearth of regulation in some jurisdictions.
Digital currency exchange Coinbase has received approval to offer trading of Litecoin and ether in New York state. As a result, the startup has become the first business to provide Litecoin trading to customers in New York and just the second to offer ether trading. Almost a year ago, Gemini Trust Company, a digital asset exchange run by Cameron and Tyler Winklevoss, became the first company to provide trading of the Ethereum token in the state.
A group of international banks is reportedly planning the launch of cross-border payment services backed by blockchain. According to Nikkei, the group – which includes Bank of Tokyo-Mitsubishi UFJ, Standard Chartered, Bank of America Merrill Lynch, Banco Santander, the Royal Bank of Scotland and the Canadian Imperial Bank of Commerce – is eyeing a 2018 launch, with a focus on both retail and commercial customers. Distributed ledger startup Ripple will provide the underlying technology, the paper said.
Compared to two weeks ago, the price of Bitcoin has increased by around eleven percent, with the exchange rate currently at about $1,083 per BTC. The price of Ethereum increased by more than 37 percent at the same time, taking Ether up to a rate of $49.22 per ETH. Ethereum Classic even gained about 58 percent, with the price increasing to $2.80 per ETC. Zcash didn't move as much but did lose roughly three percent. One ZEC is now trading at roughly $68 per coin.


text:
Live Music Recommendations for The Austin Chronicle
DJ Kofa for KVRX
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Mediakix Influencer Marketing Blog Posts
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Jeremy Steinberger Journalist
Nov 20 Press Fest ATX Showcases the Power of Zines
Jeremy Steinberger
How zines bring diversity to the media industry.
Camille Simonelema believes a zine can be really anything, as long as it's self-published. Camille is a co-founder of Free Rent ATX, the local Austin art collective behind Press Fest Austin at The Vortex on November 11th.
The event was an exhibition for independent publishers, zine makers, comics and more. With no single definition of what a zine can be, Camille said while drinking a Kombucha at the 2nd rendition of Press Fest Austin, the medium attracts a mixed bag of publishers.
"That's the cool part of this community. There are literally all different kinds of people with different backgrounds and interests," Simonelema said. "We all have one thing in common, though, and that's loving to share our expression with others through self-publishing."
Simonelema had the idea to start Press Fest Austin after the city lost its only other zine festival, Austin Zine Fest, in 2015. Her goal was to create an outlet for independent publishers in Austin so they could come together to meet other independent creators and celebrate their art.
On a gloomy Saturday afternoon, exhibitors traded Instagram handles, art, and love as they displayed their work over a soundtrack of Velvet Underground and Radiohead gently playing in the background.
Beth Comics was stationed across the Vortex's brown rubble courtyard from POMEgranate Magazine, two exhibitors who were a microcosm of the wide range of minority communities represented at the event.
On Press Fest Austin's website, Beth Comics is self-described as "super queer, super witchy, super horny comics" and POMEgranate Magazine as a feminist publication for "thoughtful and sensitive weirdos."
Simonelema said she realized this kind of diversity is central to zine culture after attending Denver Zine Fest last year.
"The Denver Zine Fest was mostly queer comics and zines," she said. "Going to that zine fest showed me that zine culture is for everyone, any person, from people of color to queer, to transgender, to straight."
Tolerance and inclusion are not so prominent in the larger print and news industry, however. Minorities make up just over 12 percent of the newspaper workforce, according to a 2015 study by The American Society of News Editors. The census also showed that Women made up just 35 percent of newspaper staff in 2015, a percentage that hasn't increased past 35 since the turn of the century.
This issue originates from the difficulties minority journalists face after graduating college. Minorities are 17 percentage points less likely than non-minorities to find a full-time journalism position within their year of graduation, according to a 2013 study by the University of Georgia.
Associate journalism Professor George Sylvie studies media diversity at the University of Texas at Austin. He diagnosed this discrepancy as a multifaceted issue but stressed embedded media racism, a lack of opportunities, and the meager entry-level salary of journalists as its main symptoms.
"People of color often don't want to be journalists because journalist's don't get paid nearly as much as public school teachers or doctors," he said. "Also, in this country, we still have substantial amounts of racism in various walks of life and that extends to media hiring."
After being turned away by the industry, minorities have historically responded by building their own publications autonomously, Sylvie said.
"Minority press has gone back as far as the late 1800's," he said. "Freedom's Journal and publications of that kind sprang up to give people of color a voice so they could cover issues that they were actually interested in."
This history reflects the power and importance of independent publications such as zines in any media landscape. They play an important role in developing young writers' voices so they can inform their community about important issues otherwise lost in the homogenous shuffle of mainstream media.
But how wide an audience can these independent publications really reach? Professor Sylvie questioned how much space if any, zines take up within a regular person's daily news consumption routine.
"That's part of the problem of zines and independent publications," he said when asked about the reach of zines. "News is still dominated by mainstream publications because there's still that notion for what news is that hasn't changed," he said.
While this highlights the small informing power of independent publications, Sylvie went on to discuss the important role zines still play in diversifying the news cycle.
"They are the ones mainly involved in civil rights areas of news," he said. "They're going to be the one that covers police brutality or they're going to cover whether the poor neighborhood has good streets."
This optimism for the importance of independent publications was shared by many on hand at Press Fest Austin who felt they play an important role in the media landscape.
"I like to think of zines as a platform for un-capitalized voices to reach wider audiences," Jess Hogan, owner of Neither Nor Zine Distro, said behind her table at the event. "Instead of just staying in your journal, by self-publishing these people get noticed who would otherwise be left behind by history."
With the potential demise of net neutrality looming, internet regulation is imminent. Although it's tough to call this a win for media, it is possible that it could spark an even greater resurgence of zines and magazines. They could become one of the only platforms for independent publishers to write and share, and if that's the case, those like the creators on hand at Press Fest Austin will transition from media outcast to media pioneers.
Dec 12 Siblings and Austin Natives, The Bishops are Here to Stay
Nov 1 Interview: David Wexler Talks VR, Making 3D Visuals for Flying Lotus, The Weeknd & More
Sep 26 The Destructive Legacy of Pablo Escobar
Feb 26 Review: George Brainard's Library Photo Exhibit Excavates the Roots of Austin Culture
Jul 27 The San Marcos Music Scene Runs Deep
What I can't stop listening to right now:
Verge Campus Texas


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text:
Gannett Co., Inc. Announces Pricing of $675 Million of Senior Notes
McLEAN, VA – Gannett Co., Inc. (NYSE: GCI) today announced that it has priced its offering of senior notes due 2021 (the "2021 Notes") and senior notes due 2024 (the "2024 Notes" and together with the 2021 Notes, the "Notes") previously announced.
The face value of the 2021 Notes is $350 million, with an interest rate of 4.875%. The 2021 Notes were priced at 98.531% of face value. Subject to certain exceptions, the 2021 Notes may not be redeemed by the Company prior to September 15, 2017.
The Notes are being made available in a private offering that is exempt from the registration requirements of the Securities Act of 1933, as amended (the "Securities Act"), with closing expected to occur on September 8, 2014, subject to customary closing conditions.
The Company intends to use the net proceeds from the offering plus available cash and borrowings under its revolving credit facility to finance the acquisition of all of the outstanding membership interests of Classified Ventures, LLC ("Cars.com") that it does not already own. Any remaining proceeds may be used for general corporate purposes.
The Notes will be guaranteed by certain of the Company's subsidiaries. The Company will deposit the net proceeds from the offering of the Notes into an escrow account until the satisfaction of certain conditions, including the consummation of the acquisition of Cars.com. If the Company determines in its sole discretion that the acquisition will not be completed without any amendment, modification or waiver that is materially adverse to the holders of the Notes or if the acquisition has not been consummated on or prior to December 31, 2014 (subject to extension to May 18, 2015 in certain circumstances), the Notes will be subject to a special mandatory redemption. Escrowed funds would be released and applied to pay for any such redemption.
The Notes are being offered only to "qualified institutional buyers" as defined in Rule 144A under the Securities Act and outside the United States in reliance on Regulation S under the Securities Act. The Notes have not been and will not be registered under the Securities Act or any state securities laws and may not be offered or sold in the United States absent registration except pursuant to an applicable exemption from the registration requirements of the Securities Act and applicable state securities laws.
There can be no assurance that the Notes offering will close on the terms described herein or at all.
This press release does not constitute an offer to sell or the solicitation of an offer to buy the Notes or any other securities.
About Gannett
Gannett Co., Inc. (NYSE: GCI) is an international media and marketing solutions company that informs and engages more than 110 million people every month through its powerful network of broadcast, digital, mobile and publishing properties. Our portfolio of trusted brands offers marketers unmatched local-to-national reach and customizable, innovative marketing solutions across any platform. Gannett is committed to connecting people – and the companies who want to reach them – with their interests and communities. For more information, visit www.gannett.com.
Jeremy Gaines
Vice President, Corporate Communications
jmgaines@gannett.com
For investor inquiries, contact:
Jeffrey Heinz
jheinz@gannett.com


The chapters do not contain excessively long, boring discussions; rather, they are presented with adequate discussions. Worked-out problems are especially beneficial to understand the concepts. If one solves and understands these examples, they can attack the end-of-chapter problems more easily. The end-of-chapter problems are classified into 3 categories; standard difficulty, medium difficulty and challenging problems. Therefore, a student can make use of his time according to the level of difficulty of his course, background etc. If you little time to practice and a fair knowledge of the subject matter, you could easily start with medium level problems and try the harder ones as well.
Some chapters contain some interesting articles about everyday physical phenomena which are related to the concepts presented. Hence, the student has a chance to relate theory and life and get a more profound comprehension of physics.


Thomas is on a path of exploration of sound and music that has taken six decades, with an emphasis on ancient and folkloric instruments of natural materials. Didjeridu, flutes of bamboo, bone and wood, nose flutes, conch shells, kamale n'goni, hulusi and khomus are among his many wind, string and percussion instruments.
Certified through the Sound & Music Institute as a sound healing facilitator, Thomas leads sessions with individuals and groups large and small. He also brings this capacity to the many yoga classes for which he plays. For this work, Thomas follows an intention and improvisational approach he calls "Guided Intuition".
Thomas holds a Bachelor's degree in English from Harvard and a Master's in Art Education from Massachusetts College of Art. As artist in residence in schools all over the country, he has worked with many students, introducing them to and/or helping them construct unusual musical instruments from all around the world.
Thomas currently performs with the quintet, Levanta and Sonark Trio. He has performed and/or recorded with Steve Gorn, Roswell Rudd, John Medeski, Club D'elf, Peter Blum and Arm-of-the-Sea Theater, among others.