text:
\section{INTRODUCTION}
\label{introduction}

Protoplanetary disks are
crucial objects in low-mass star formation, possessing three vital functions: they
(i) aid the dissipation of angular momentum away from the  young stellar system,
(ii) allow the efficient accretion of matter onto the young star and
(iii) contain all material, dust and gas,
which may end up in a planetary system orbiting the main-sequence star.

In this work, we investigate the chemistry and molecular composition of a
protoplanetary disk surrounding a young star which
will evolve into a main-sequence star resembling our Sun.
At the low temperatures encountered in many astrophysical regions
($\sim$~10~K to $\sim$~100~K),
molecules are readily excited into higher rotational energy states and
subsequently emit radiation at (sub)millimeter wavelengths.
Early observations of T Tauri stars at these
wavelengths revealed the presence of molecular material in a flattened disk-like
structure (e.g.\ \citet{dutrey94}) and in Keplerian rotation about the parent star
(e.g.\ \citet{guilloteau94}).
Since then, molecular rotational line emission originating from a disk
has been observed in several
T Tauri systems including
TW Hydrae \citep{kastner97,vanzadelhoff01,vandishoeck03,ceccarelli04,thi04,qi04,qi06,qi08},
DM Tauri \citep{dutrey97,ceccarelli04,ceccarelli05,guilloteau06,dutrey07,pietu07} and
LkCa 15 \citep{vanzadelhoff01,aikawa03,qi03,thi04,dutrey07,pietu07}.
Most species detected are small simple molecules, molecular ions and radicals such as
CO, HCO$^+$, CN, HCN, CS, C$_2$H and N$_2$H$^+$, along with several associated
isotopologues (e.g.\ $^{13}$CO, C$^{18}$O, DCO$^+$, H$^{13}$CN, H$_2$D$^+$ and C$^{34}$S).
The most complex species observed to date is the small organic molecule,
formaldehyde, H$_2$CO \citep{dutrey97,aikawa03, dutrey07}
with methanol, CH$_3$OH, thus far eluding detection (e.g.\ \citet{thi04}).
\citet{ceccarelli05} report a detection of
deuterated water, HDO, in the disk of DM Tau, although this result
has since been disputed by \citet{guilloteau06}.

Infra-red emission has also been observed originating from disks
embedded in young stellar objects and arising from
vibrational transitions in gas-phase molecules capable of survival
in the warmest regions ($>$~350~K).
Thus, infra-red emission probes not only a different physical region of
the disk to that probed by (sub)mm emission, but also uses
different molecules as tracers, hence providing complimentary chemical
information.
The molecules detected thus far at infra-red wavelengths are CO, HCN, OH, H$_2$O,
CO$_2$ and C$_2$H$_2$ \citep{carr04,lahuis06,carr08,salyk08,pascucci09}
with an upper limit determined for CH$_4$ \citep{gibb07}.

Observations of molecular line emission from disks, to date, have been
hampered by the small angular size of these objects on the sky and
the limitations of existing facilities, explaining why the species
detected are those which are abundant and possess
relatively simple rotational energy spectra (e.g.\ CO).
Single-dish facilities which operate at (sub)mm wavelengths
such as the 15~m James Clerk Maxwell Telescope (JCMT) in Hawaii and
the IRAM~30~m telescope in Spain, have been predominantly
used in the detections of the molecular species in the T Tauri systems
listed.
With beam-sizes much larger than the typical source size,
usually a single molecular line profile is generated characterising
emission from the entire disk.
In order to spatially resolve the emission and hence trace the
radial and vertical physical and chemical structure, interferometry
must be employed and indeed, \citet{qi08} report spatially
resolved emission arising from molecular rotational transitions
in the disk of TW Hya using the Sub-Millimeter Array (SMA).

The discipline of (sub)mm astronomy is scheduled for a revolutionary transformation
with the first light of the Atacama Large Millimeter Array (ALMA) in Chile
expected in 2012 (see \url{http://www.almaobservatory.org}).
ALMA, with its 50 12~m telescopes and fully variable configuration, will have the
spatial resolution necessary to observe molecular line emission from protoplanetary
disks on sub-milli-arcsecond scales and enable the
tracing of the molecular content of disks to within $\approx$~0.1~AU of
the parent star at its highest operational frequencies.
It is anticipated that the sensitivity and high spectral resolution of ALMA
will lead to the potentially overwhelming detection of many further
molecular species, including complex organic molecules considered the
building blocks of life, in many astrophysical sources including protoplanetary disks.

Motivated by the impending completion of ALMA, we
have constructed a high resolution combined chemical and physical
model of a protoplanetary disk surrounding a typical T Tauri star using
as comprehensive a chemical network as computationally possible.
In the work presented here, our objectives were (i) to calculate
the chemical structure of protoplanetary disks on small
(sub-milli-arcsecond in the inner disk) scales,
(ii) to investigate the influence of various chemical
processes, such as non-thermal desorption and grain-surface chemistry,
thought to be important in disks, and
(iii) to subsequently determine potential molecular tracers of each process.
We also used our model to (i) compute molecular line emission profiles
for rotational transitions which have been observed in disks using
existing facilities, (ii) compare our modelled line profiles and intensities with existing
observations and (iii) produce molecular line emission maps at the expected
spatial resolution of ALMA for disks at various distances and inclinations.
This second study and corresponding set of results will be covered in a
subsequent paper (Walsh et al. in preparation).
Our study also aims to help answer some
fundamental questions concerning the evolution of stars, planets and ultimately, life.
Is it possible for primordial (possibly organic) material created
in a young star's protoplanetary
disk to survive the assimilation into planets and other planetary system objects?
Is our solar system's chemical and thus, planetary composition unique?
How intrinsically linked
are star formation, planet formation and the origin of life in the universe?
These questions are evermore important as we move into the era of exoplanet research
and the hunt for planets and the signatures of life in external stellar systems.

In Section~\ref{diskmodel} we
describe the theoretical foundation and generation
of the physical model used to characterise our protoplanetary disk (Section~\ref{physicalmodel}) and
the chemical network we have
collated and used in our calculation of the disk chemical evolution (Section~\ref{chemical model})
including gas-phase chemistry (Section~\ref{gasphasechemistry}),
 photochemistry (Section~\ref{photochemistry}), gas-grain interactions
(Section~\ref{gasgraininteractions}) and
grain-surface chemistry (Section~\ref{grainsurfacechemistry}).
The results of our chemical evolution calculations are
covered in Section~\ref{results} where we discuss the
chemical structure and stratification in the disk
(Section~\ref{chemicalstructure}),
the effects of our included chemical processes
(Sections~\ref{nonthermaldesorptioneffects} and \ref{grainsurfacechemistryeffects}),
the disk ionisation fraction (Section~\ref{diskionisationfraction}) and the radial
molecular column densities (Section~\ref{columndensities}).
We briefly discuss our work in relation to similar projects by other research groups
in Section~\ref{comparison} and finally,
in Section~\ref{summary}, we summarise our work and outline our main conclusions
and further work we intend to undertake.

\section{PROTOPLANETARY DISK MODEL}
\label{diskmodel}

\subsection{Physical Model}
\label{physicalmodel}

The physical model of a protoplanetary disk we use in this work is from
\citet{nomura05} with the addition of X-ray heating as described in
\citet{nomura07}.
They self-consistently modelled the density and temperature
profiles of gas and dust in a protoplanetary disk accounting for
UV and X-ray irradiation by the central star and
subsequently computed molecular hydrogen line
emission at ultraviolet and infrared wavelengths.
Here, we have used this model to compute
the chemical structure of a protoplanetary disk with the
ultimate aim to expand on their work by
calculating molecular line emission from disks at  (sub)mm wavelengths.
In the remainder of this section, we give a brief overview of our physical model and
we refer readers to the original papers for the mathematical and
computational details.

We consider an axisymmetric disk surrounding
a typical T Tauri star with mass, $M_\ast$~=~0.5~$M_\odot$, radius, $R_\ast$~=~2~$R_\odot$
and temperature, $T_\ast$~=~4000~K \citep{kenyon95}.
The density and temperature distributions are determined through iteratively solving
the equations for hydrostatic equilibrium in the vertical direction and the
local thermal balance between the heating and cooling of the gas.
The theoretical foundation of this model comes from the
\emph{standard accretion disk model} of \citet{lynden74} and \citet{pringle81} which
defines a surface density distribution for the disk given the parent star's
mass and radius and a disk mass accretion rate, $\dot{M}$.
The kinematic viscosity in the disk is parameterised according to the
work of \citet{shakura73}, the so-called \emph{$\alpha$-prescription}.
We adopt a viscous parameter,
$\alpha$~=~0.01 and a mass accretion rate, $\dot{M}$~=~10$^{-8}$~$M_\odot$~yr$^{-1}$.

The heating mechanisms included are grain photo-electric heating by
far-ultraviolet photons and X-ray heating due to hydrogen ionisation by
X-ray photons with cooling via gas-grain collisions and line transitions.
We use a model
spectrum created by fitting the observed XMM-Newton X-ray spectrum of the classical
T Tauri star, TW Hya (e.g.\ \citet{kastner02}) with a two-temperature thin thermal plasma model
(MEKAL model see e.g.\ \citet{liedahl95}).
The X-ray luminosity is $L_{X}$~$\sim$~$10^{30}$~erg~s$^{-1}$
 and the resulting X-ray spectrum is given in Figure~1 of \citet{nomura07}.

The UV radiation field in disks has two sources, the star and the interstellar medium.
In this disk model, the radiation field due
to the T Tauri star has three components: black-body emission at the star's effective temperature,
optically thin hydrogenic bremsstrahlung emission and strong Lyman-$\alpha$ line emission.
All components are necessary to accurately model the excess UV emission observed towards
classical T Tauri stars thought to arise from an accretion shock as
disk material impinges upon the stellar surface
(e.g.\ \citet{valenti00, johnskrull00}).
The total FUV luminosity  in our model is $L_{UV}$~$\sim$~$10^{31}$~erg~s$^{-1}$
 with the calculation of the radiation field in the disk described in detail in
Appendix~C of \citet{nomura05} and the resulting spectrum shown in Figure~C.1 in that paper.

We assume the dust and gas in the disk is well-mixed and adopt
the dust-size distribution model which reproduces the observational extinction
curve of dense clouds \citep{weingartner01}.
 The calculation of the dust opacity in the disk is as described in
Appendix~D of \citet{nomura05} with the
resulting monochromatic absorption coefficient shown in Figure~D.1.
We note here that this is an over-simplification of the treatment of the dust-size distribution in
protoplanetary disks and we are currently working on improving our model by adding in the effects
of dust-grain settling and coagulation.

In Figure~\ref{figure1} we display the resulting number density (cm$^{-3}$),  gas temperature (K)
and dust temperature (K)
as a function of disk radius and height (top, middle and bottom rows, respectively).
To illustrate the extreme vertical gradients in the physical conditions
at small radii, we display the density and temperature both within 10~AU (left panels) and
305~AU (right panels).
We describe the physical structure of our disk in the Appendix.

\begin{figure*}
\subfigure{\includegraphics[width=0.5\textwidth]{./density_map_10AU.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./density_map.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./gas_temp_map_10AU.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./gas_temp_map.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./dust_temp_map_10AU.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./dust_temp_map.eps}}
\caption{Number density (top),  gas temperature (middle) and  dust temperature (bottom)
as a function of disk radius and height up to maximum radii of $r$~=~10~AU (left) and 305~AU (right).}
\label{figure1}
\end{figure*}

\subsection{Chemical Model}
\label{chemical model}

The structure of the disk described in the preceding section leads to
a multitude of different physical regimes and as such, we need
to account for every chemical process which may occur.
The axisymmetric structure results in a cold, dense midplane where even the
most volatile molecules are expected to freeze out onto dust grains creating
an icy mantle and depleting the gas of molecules.
Moving in the vertical direction, the density decreases and the temperature
increases driving the evaporation of molecules from grain surfaces
and stimulating a rich gas-phase chemistry resulting in further molecular
synthesis.
Further towards the surface, the radiation fields increase in strength
dissociating and ionising molecules into constituent radicals, atoms and ions.
A similar stratification is expected in the radial direction as the temperature
and density in the disk midplane both increase with decreasing distance from the
star.
When the midplane dust temperature reaches a value higher than the desorption temperature
of a particular molecule, it is returned to the  gas phase.
This point is known as the \emph{snow line} and can occur at a unique radius
for each molecule.
At small radii, due to the high densities found in the midplane,
there is a significant column density of material shielding this region from
the intense UV and X-ray fields of the star such that molecules are expected to
survive in the midplane at radii within $\sim$~0.1~AU.

In order to investigate the chemical structure thoroughly, we used
a large gas-phase network supplemented with
gas-grain interactions, including freeze out and thermal desorption.
We considered various non-thermal desorption mechanisms, namely, cosmic-ray induced desorption,
 photodesorption and X-ray desorption.
To probe the efficacy of molecular synthesis on grain-surfaces
we also added a large grain-surface reaction network.

\subsubsection{Gas-Phase Chemistry}
\label{gasphasechemistry}

Our gas-phase chemistry is extracted from the latest release of the `dipole-enhanced' version
of the UMIST Database for Astrochemistry (\url{http://www.udfa.net}), henceforth referred to as `Rate06'
\citep{woodall07}.
We include almost the entire Rate06 gas-phase network removing only those species
(and thus reactions) which contain
fluorine, F, and phosphorus, P, in order to reduce computation time.
We deemed the loss of F- and P-containing species to have a minimal impact on the remaining chemistry.
Our gas-phase network thus consists of 4336 reactions involving 378 species composed of the
elements H, He, C, N, O, Na, Mg, Si, S, Cl and Fe.
The initial elemental fractional abundances (relative to total H nuclei density)
we use are the set of oxygen-rich low-metallicity abundances from
\citet{graedel82}, listed in Table~8 of \citet{woodall07}.
 We find by $10^{6}$ years, the typical age of protoplanetary disks, the chemistry has
forgotten its origins, justifying our use of initial elemental abundances.
We intend in future models to calculate the chemical evolution of a parcel of gas as it
follows a streamline in the accretion flow in which case the input abundances should reflect
the molecular make-up of the ambient cloud material.
Our model grid has over 12,000 grid points in 129
logarithmically spaced radial steps from 0.04~AU to 305~AU.

\subsubsection{Photochemistry}
\label{photochemistry}

 In the models presented here, we have approximated our photoreaction rates at each point in the
disk, $k^{ph}(r,z)$, by scaling the rates from Rate06 (which assume the interstellar UV field) using
the wavelength integrated UV flux calculated at each point, $G_{FUV}(r,z) = \int_{912\AA}^{2000\AA} G_{FUV}(\lambda,r,z) \;
\mathrm{d}\lambda$.
Hence, the rate for a particular photoreaction at each $(r,z)$ is given by
\begin{equation}
k^{ph} = \frac{G_{FUV}}{G_0}k_0 \quad \mathrm{s}^{-1},
\end{equation}
where $G_0$ is the interstellar UV flux and $k_0$ is the rate expected in the interstellar medium.

\subsubsection{Gas-Grain Interactions}
\label{gasgraininteractions}

Gas-grain interactions are important in large areas of protoplanetary disks
as the dust temperature can reach values lower than the freeze-out temperatures
of molecules.
If the  freeze out of gas-phase species is allowed, then the evaporation of molecules from
dust grains must also be included.
In this work, we consider both the thermal and non-thermal desorption of molecules from dust grains.
For the thermal desorption of a particular molecule to occur, the dust-grain temperature must exceed the
freeze-out temperature of that molecule.
Non-thermal desorption requires an input of energy from an external source and is thus independent
of dust-grain temperature.
As protoplanetary disks are irradiated by UV and X-ray photons from the central star
as well as UV photons and cosmic-rays originating from the interstellar medium,
the non-thermal desorption mechanisms we investigate are cosmic-ray induced desorption,
 photodesorption, and X-ray desorption.
Our gas-phase chemical network has thus been supplemented with an additional
1154 gas-grain interactions involving 149 surface species.

 The accretion rate (or freeze-out rate), $k_i^a$, of species $i$ onto dust-grain surfaces is treated
using the standard prescription \citep{hasegawa92},
\begin{equation}
k_i^a = S_i \sigma_d \left< v_i \right> n_d \quad \mathrm{s}^{-1},
\label{accretionrate}
\end{equation}
where $S_i$ is the sticking coefficient, here assumed to equal unity for all species,
$\sigma_d = \pi a^2$ is the geometrical cross section of a dust grain with radius, $a$,
$<v_i> = (k_BT/m_i)^{1/2}$ is the thermal velocity of species $i$ at a temperature,
$T$ and with mass, $m_i$, $k_B$ is Boltzmann's constant,
and $n_d$ is the number density of dust grains.

The thermal desorption rate, $k_i^d$, of species $i$ is dependent on dust-grain temperature,
$T_d$ \citep{hasegawa92}, and is given by
\begin{equation}
k_i^d = \nu_0(i) \exp \left( \frac{-E_d (i)}{T_d}\right) \quad \mathrm{s}^{-1},
\label{thermaldesorption}
\end{equation}
where $E_d(i)$ is the binding energy of species $i$ to the dust grain in units of K.
The characteristic vibrational frequency of each adsorbed species in its potential well,
$\nu_0 (i)$, is represented by a harmonic oscillator relation \citep{hasegawa92},
\begin{equation}
\nu_0(i) = \sqrt{\frac{2n_s E_d(i)}{\pi^2 m_i}} \quad \mathrm{s}^{-1},
\label{vibrationalfrequency}
\end{equation}
where, here, $E_d(i)$ is in units of erg and $n_s = 1.5 \times 10^{15}$~cm$^{-2}$ is the number
density of surface sites on each dust grain.
The binding energies, $E_d$, for several important molecules (mainly following those collated by
\citet{hasegawa92} and \citet{willacy98}) are listed in Table~\ref{table1}.
We intend to conduct a review of our set of desorption energies in light of
more recent experimental results  e.g.\ a recent investigation into the desorption of
methanol by \citet{brown07} determined a binding energy of $\approx$~5000~K, as opposed to
the theoretical value of 2140 K used here (see Table~\ref{table1}).
This binding energy was determined for pure methanol ice as opposed to methanol adsorbed
onto, or mixed with, water ice.
We find throughout our model that the ratio of methanol to water ice is less than 1\%.
Similar experiments for methanol adsorbed onto water ice (Brown, private communication)
suggest that the binding energy of methanol in this complex is comparable with that determined for
pure methanol but due to overlapping desorption features the results are difficult to analyse.
Recent work by \citet{bottinelli10} comparing laboratory data with observations of methanol in young stellar
objects (YSOs)
suggests that methanol ice in these environments likely exists as pure ice or mixed with CO and/or CO$_2$ ice
which is consistent with its formation via hydrogenation of CO on dust grains.
Considering the latter molecules are non-polar, it is possible that the binding energy of methanol in
astrophysical ices is lower than that determined in the laboratory experiments.
Increasing the binding energy of methanol to a value of $\approx$~5000~K
will increase the desorption temperature from $\approx$~30~K to 40~K to $\sim$~100~K.
This will push the `snow line' for methanol closer to the star but should have little effect on the
outer disk methanol abundances where the dust temperature is $<$~30~K.
We expect non-thermal desorption to dominate over thermal desorption in the upper layers of the disk.

\begin{deluxetable}{lcc}
\tablecaption{Molecular Binding Energies \label{table1}}
\tablewidth{0pt}
\tablehead{\colhead{Molecule} & \colhead{Binding Energy (K)} & \colhead{Reference}}
\startdata
CO         & 960  & 1\\
N$_2$      & 710  & 2\\
HCN        & 4170 & 2\\
CO$_2$     & 2690 & 3\\
H$_2$O     & 4820 & 4\\
NH$_3$     & 3080 & 4\\
CH$_4$     & 1080 & 2\\
C$_2$H$_2$ & 2400 & 2\\
H$_2$CO    & 1760 & 5\\
CH$_3$OH   & 2140 & 5
\enddata
\tablerefs{(1) \citet{sandford88}, (2) \citet{yamamoto83}, (3) \citet{sandford90},
(4) \citet{sandford93}, (5) \citet{hasegawa93}}
\end{deluxetable}

To calculate the cosmic-ray induced desorption rate for each species, $k_i^{crd}$,
we use the method of \citet{leger85} and \citet{hasegawa93}.
 They assume that dust grains with a radius of 0.1~$\mu$m are impulsively heated by the impact of
relativistic Fe nuclei with energies of 20 to 70 MeV nucleon$^{-1}$ which deposit, on average,
an energy of 0.4~MeV into each dust grain.
Assuming that the majority of molecules desorb around 70~K, the cosmic-ray induced desorption
rate can be approximated by
\begin{equation}
k_i^{crd} \approx f(70\;\mathrm{K})k_i^d(70\;\mathrm{K}) \quad \mathrm{s}^{-1},
\label{cosmicraydesorption}
\end{equation}
where $k_i^d(70\;\mathrm{K})$ is the the thermal desorption energy of species $i$ at a temperature
of 70~K, calculated using Equation~(\ref{thermaldesorption}).
The parameter, $f(70\;\mathrm{K})$, is the fraction of time spent by grains in the vicinity of 70~K
and can loosely defined as the ratio of the desorption cooling time ($\approx 10^{-5}$~s$^{-1}$) to
the time interval between successive heatings to 70~K (3.16~$\times 10^{13}$~s) so that
$f(70\;\mathrm{K})\approx 3.16 \times 10^{-19}$ (for further details see \citet{hasegawa93}).

Note that the method of calculating the cosmic-ray induced desorption rates is species
dependent and a function of surface binding energy.
In contrast, the  photodesorption rates are indiscriminate, based on the
experimental results of \citet{westley95} and \citet{oberg07}.
Their results suggest each photon absorbed by the grain mantle returns a particular
number of molecules, independent of binding energy, to the  gas phase
so that the desorption rate of each species varies according to its fractional abundance on
dust-grain surfaces.
The overall  photodesorption rate is calculated, similar to the work of \citet{willacy00} and
\citet{willacy07}, using
\begin{equation}
k^{pd} = F_{UV}Y_{UV}\sigma_{d}x_{d} \quad \mathrm{s}^{-1},
\label{photodesorption1}
\end{equation}
where, $F_{UV}$ is the UV radiative flux in units of photons~cm$^{-2}$~s$^{-1}$, $Y_{UV}$
is the experimentally determined  photodesorption yield in units of molecules photon$^{-1}$,
$\sigma_{d}$ is the geometrical dust-grain cross section in cm$^2$ and $x_{d}$ is the
fractional abundance of dust grains.
 Note that the attenuation of UV radiation is accounted for in our calculation of $F_{UV}$.
Hence, the  photodesorption rate for a specific species, $k_i^{pd}$, is calculated using
\begin{equation}
k_i^{pd} = k^{pd} \frac{n_i^s}{n_{tot}^s} \quad \mathrm{s}^{-1},
\label{photodesorption2}
\end{equation}
where, $k^{pd}$ is given by Equation~(\ref{photodesorption1}), $n_i^s$ is the number density
of species $i$ frozen out onto grain surfaces and $n_{tot}^s$ is the total
number density of grain-surface species.
More recent experiments by \citet{oberg09a,oberg09b} suggest that
 photodesorption rates are also dependent on the depth of the ice layer on grain
surfaces with the molecular yield also dependent on ice composition.
We intend to explore these experimental results in future models.

For the X-ray desorption rates, we follow the same formulation as for  photodesorption,
covered in the theory of \citet{leger85} and \citet{najita01}.
At this point, it is worth noting that X-ray desorption is the least
theoretically or experimentally
constrained of all the non-thermal desorption mechanisms considered here.
The overall X-ray desorption rate, $k^{xr}$, is given by
\begin{equation}
k^{xr} = F_{XR}Y_{XR}P_{abs}\sigma_d x_d \quad \mathrm{s}^{-1},
\label{xraydesorption}
\end{equation}
where, $F_{XR}$ is the X-ray photon flux in units of photons~cm$^{-2}$~s$^{-1}$,
$Y_{XR}$ is the desorption yield in units of molecules~photon$^{-1}$ and the
product, $P_{abs}\sigma_{d}$, is the effective  cross section with
$P_{abs}$, the probability of X-ray absorption by the dust grain.
The X-ray desorption rate for each
individual species, $k_i^{xr}$, is calculated according to
the fractional abundance of species $i$ on the dust grains
following Equation~(\ref{photodesorption2}).
Here, we adopt a value $Y_{XR} = 200$ from the investigations of
\citet{najita01} and for the effective grain  cross section we
use values from the work of \citet{dwek96} regarding energy deposition into grains
by energetic photons in the energy range 10~eV to 1~MeV.
\citet{najita01} consider X-ray desorption from grains of
various compositions and morphologies and conclude that both have a significant influence
on the X-ray desorption yields calculating values for
$Y_{XR}$ ranging between 10 and $\approx$~4000 molecules photon$^{-1}$.
In this work, we adopt a conservative estimate of the yield
of 200 molecules photon$^{-1}$ as this is the value for the dust morphology
which most closely matches our simple dust-grain model.
Given the large X-ray luminosities of T Tauri stars (see e.g.\ \citet{kastner97,kastner02}), we plan
a more thorough study on
the effects of X-ray desorption in protoplanetary disks taking into consideration the
X-ray energy spectrum as a function of disk radius and height and
investigating the full parameter space considered in the work of \citet{najita01}.

\subsubsection{Grain-Surface Chemistry}
\label{grainsurfacechemistry}

We use the grain-surface network from \citet{hasegawa92} and \citet{hasegawa93}
which has 221 reactions involving an additional 9 surface species which do not have
a gas-phase equivalent (e.g.\ CH$_3$O).
To calculate the reaction rate coefficients, we use the theory outlined
in detail in \citet{hasegawa92}.
The rate coefficient for a grain-surface reaction between species $i$ and $j$ can be defined as
\begin{equation}
k_{ij} = \kappa_{ij}\left( R_{diff}(i) + R_{diff}(j)\right) \left( 1/n_d \right) \quad \mathrm{cm}^{3}\;\mathrm{s}^{-1}.
\label{grainsurface1}
\end{equation}
Here, $\kappa_{ij}$ is the probability that the reaction happens upon encounter and is equal to unity
for an exothermic reaction without an energy barrier.
For reactions with an activation energy, $E_A$, and at least one light reactant
i.e.\ H or H$_2$, $\kappa_{ij} = \exp(-2b/\hbar\sqrt{2\mu E_A})$ where
$b$ is the barrier thickness and $\mu = m_im_j/(m_i+m_j)$ is the reduced mass
of the reaction system.
This expression is the exponential part of the quantum mechanical probability for
tunneling through a rectangular barrier of thickness, $b$.
The term, $R_{diff}$, is the diffusion rate of an adsorbed species and
is the inverse of the diffusion time, $t_{diff}$, defined as $t_{diff} = N_s t_{hop}$ s,
where $N_s$ is the total number of surface sites per dust grain and $t_{hop}$ is the timescale
for an adsorbed species to `hop' from one surface site to another.
The expression for $t_{hop}$ depends on the mass of the species and is given by
\begin{equation}
t_{hop} =
	\begin{cases}
        {\nu_0(i)}^{-1} \exp\left( \frac{2b}{\hbar}\sqrt{2m_iE_b(i)}\right) \; \mathrm{s} \;
        & \; \mbox{H/H$_2$} \\
        {\nu_0(i)}^{-1} \exp\left( \frac{E_{b}(i)}{kT_d} \right) \; \mathrm{s}
        & \; \mbox{other species}
        \end{cases}
\label{grainsurface2}
\end{equation}
where $E_b(i)\approx 0.3 E_d(i)$ is the energy barrier between surface sites.
All other parameters have been defined previously.

\section{RESULTS}
\label{results}

We calculate the chemical abundances in the disk as a function of disk radius,
height and time.
The results displayed here are extracted at a time of 10$^6$~yr, the
typical age of visible T Tauri stars with accompanying protoplanetary disks.
Throughout this section, fractional abundance refers to the abundance of each species
with respect to total particle number density.
In Section~\ref{chemicalstructure}, we display and discuss results from
model PH+CRH only, to illustrate the global chemical structure and
stratification in the disk.
 Table~\ref{table2} lists the names and ingredients of each model for which we present results.
Our `fiducial' model is model PH+CRH since most current chemical models
of protoplanetary disks include photodesorption and cosmic-ray induced desorption by default.
In model CRH we remove photodesorption to investigate the influence of cosmic-ray induced desorption,
in model XD we look at the effects of X-ray desorption only, and in model GR, we investigate the
addition of grain-surface chemistry to our fiducial model.
Of course, there are many more permutations of the ingredients
which are worthwhile considering in the future e.g. X-ray desorption plus grain-surface
chemistry.

\begin{deluxetable*}{lccccc}
\tablecaption{Chemical Models \label{table2}}
\tablewidth{0pt}
\tablehead{&\colhead{0}&\colhead{CRH}&\colhead{PH+CRH}&\colhead{XD}&\colhead{GR}}
\startdata
Thermal desorption & \checkmark  & \checkmark & \checkmark & \checkmark & \checkmark  \\
Cosmic-ray induced desorption  & & \checkmark & \checkmark &            & \checkmark  \\
 Photodesorption         & &            & \checkmark &            & \checkmark  \\
X-ray desorption               & &            &            & \checkmark &             \\
Grain-surface chemistry        & &            &            &            &  \checkmark
\enddata
\end{deluxetable*}

\subsection{Chemical Structure}
\label{chemicalstructure}

Figure~\ref{figure2} displays the fractional abundances of those molecules observed in disks
(CO, HCO$^+$, HCN, CN, CS, C$_2$H, H$_2$CO and N$_2$H$^+$)
as a function of disk radius and height, up to maximum radii of 10~AU (left column) and 305~AU
(right column).

The global abundance distribution of molecules is governed by the binding energy of each
molecule to dust grains and the UV radiation field strength.
We see most molecules existing predominantly in a molecular layer of varying thicknesses
at a height, $z/r$~$\approx$ 0.3 to 0.5 in the outer disk and $\approx$~0.2 to 0.3 in the inner disk
with  freeze out causing depletion
in the  midplane and photolysis causing destruction in the upper layers.
CO is an exception to this and is abundant
(x(CO)~$\approx$~$10^{-4}$) throughout the majority of the
depth of the outer disk ($>$~50~AU) with depletion due to  freeze out
in the disk  midplane only occurring beyond a radius of $\approx$~250~AU.
In the inner disk ($r$~$<$~50~AU), gas-phase CO is abundant in the disk  midplane due to its
low binding energy to the dust grains.
In this region, however, we see most molecules confined to the `molecular layer'.
In the outer disk HCO$^+$ has a peak fractional abundance of
$\sim$~10$^{-10}$ to $\sim$~$10^{-9}$ throughout most of the disk, mirroring the
distribution of CO.
Within $\approx$~50~AU, it is confined to a thin layer at a
height $z/r$~$\approx$~0.3 with x(HCO$^{+}$)~$\sim$~10$^{-6}$ which coincides
with the transition zone where the gas composition changes from molecular
to atomic hydrogen.

Gas-phase HCN has a peak fractional abundance of x(HCN)~$\sim$~$10^{-7}$
existing in the molecular layer throughout the disk.
HCN can remain frozen out onto dust grains within radii $\approx$~1~AU
of the parent star demonstrating the effects of the vastly different desorption energies
of CO and HCN (960~K and 4170~K, respectively).
The distribution of CN is complementary to that of HCN as it is
predominantly formed via the  photodissociation of the latter molecule.
Hence, throughout the disk, CN exists in a layer above that of
HCN with a fractional abundance $\sim$~10$^{-6}$.
In the outer disk, CN can survive in the surface region, however, the
increasing UV field strength in the inner disk means that
CN is also destroyed by  photodissociation in the disk surface.

The distribution of the radicals, CS and C$_2$H are similar to that of CN
since both are formed predominantly via the UV photolysis of larger precursor
molecules (e.g.\ H$_2$CS and C$_2$H$_2$).
H$_2$CO reaches its maximum fractional abundance (x(H$_2$CO)~$\sim$~$10^{-8}$) in the outer disk,
although, within 10~AU, this value is reduced to $\sim$~$10^{-10}$
and H$_2$CO is confined to the molecular layer.
H$_2$CO is returned to the  gas phase in the disk  midplane within $\approx$~1~AU.

The fractional abundance distribution for N$_2$H$^+$ is different to
any of the molecules considered thus far.
N$_2$H$^+$ reaches its maximum fractional abundance of $\approx$~$10^{-10}$ in the outer
disk only and is present where gas-phase CO is depleted e.g.\
in the disk  midplane beyond a radius of 250~AU.
In dense regions, the main destruction mechanism of N$_2$H$^+$ is via reaction
with CO.
In the upper layers, N$_2$H$^+$ increases in abundance due to the increased
abundance of both N$_2$ and cations, such as, H$_3$$^+$.
Within 10~AU, x(N$_2$H$^+$) remains less than $\approx$~10$^{-13}$.

\begin{figure*}
\subfigure{\includegraphics[width=0.5\textwidth]{./CO_map_10AU.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./CO_map.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./HCO+_map_10AU.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./HCO+_map.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./HCN_map_10AU.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./HCN_map.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./CN_map_10AU.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./CN_map.eps}}
\captcont{Fractional abundances of  several molecules observed in disks as a function of
disk radius and height up to maximum radii of 10~AU (left) and 305~AU (right).  }
\label{figure2}
\end{figure*}
\begin{figure*}
\subfigure{\includegraphics[width=0.5\textwidth]{./CS_map_10AU.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./CS_map.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./C2H_map_10AU.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./C2H_map.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./H2CO_map_10AU.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./H2CO_map.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./N2H+_map_10AU.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./N2H+_map.eps}}
\caption{(Continued.)}
\end{figure*}

Figure~\ref{figure3} displays the fractional abundances of those  additional molecules observed
at infrared wavelengths,  H$_2$O (top), OH (second),
CO$_2$ (third) and C$_2$H$_2$ (bottom), as a function of disk radius and height up to a maximum
radius of 10~AU.
We display results from within 10~AU only as infrared emission
originates from the inner hot, dense disk material.

Gas-phase H$_2$O is confined to the molecular layer with a fractional
abundance x(H$_2$O)~$\sim$~$10^{-4}$.  As above,  freeze out is responsible for
depletion in the  midplane and photolysis for depletion in the upper layers.
H$_2$O is returned to the  gas phase in the  midplane at a radius $\approx$~1 to 2~AU.
The distribution of OH  is complimentary to that of H$_2$O residing throughout the disk in a
layer above that of
gas-phase H$_2$O, reaching a peak fractional abundance of $\sim$~$10^{-4}$.
The distribution of CO$_2$ is similar to that of CO in the inner disk, existing only
in the midplane with a maximum value of $10^{-4}$ within a few AU of the star.
The snow-line for CO$_2$, however, is at the much smaller radius of $\sim$~10~AU
(as opposed to $\approx$~250~AU).
Acetylene, C$_2$H$_2$, reaches a peak fractional abundance of $\sim$~$10^{-8}$,
in the molecular layer.
C$_2$H$_2$ and similar molecules are formed in hotter regions where oxygen is
depleted from the gas phase
via freeze out of oxygen containing molecules onto dust grains driving a
carbon chemistry and hydrocarbon synthesis.

\begin{figure*}
\subfigure{\includegraphics[width=0.5\textwidth]{./H2O_map_10AU.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./OH_map_10AU.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./CO2_map_10AU.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./C2H2_map_10AU.eps}}
\caption{Fractional abundances of H$_2$O (top left), OH (top right),
CO$_2$ (bottom left) and C$_2$H$_2$ (bottom right)
as a function of disk radius and height up to a radius of 10~AU.}
\label{figure3}
\end{figure*}

In Figure~\ref{figure10} (online only) we display the fractional abundances of  the gas-phase
molecules discussed  above, along with constituent atoms and
grain-surface analogues where applicable, as a
function of disk height at radii $r$~=~0.1~AU, 1~AU, 10~AU
and 100~AU.

\subsection{Effects of Non-thermal Desorption}
\label{nonthermaldesorptioneffects}

In this section, we discuss the effects of each of our non-thermal desorption mechanisms,
cosmic-ray induced desorption,  photodesorption and X-ray desorption, on the disk chemical
structure (models CRH, PH+CRH and XD in Table~\ref{table2}, respectively).
We call our control model, which includes thermal desorption only, model 0.
First, we show in Figure~\ref{figure4} those regions of the disk in which molecules
are depleted if we take into account thermal desorption only
presenting, as an example, the gas-phase CO fractional abundance as a function of disk radius and
height from model 0.
We discuss how efficiently each non-thermal desorption mechanism works against
depletion throughout the disk in Sections~\ref{cosmicraydesorptioneffects}
to \ref{xraydesorptioneffects}.
We display the fractional abundances of several gas-phase species as a function of disk radius and
height comparing results from each of our non-thermal desorption models in
Figure~\ref{figure11} (online only).

In Figure~\ref{figure4} there are three notable areas where CO is depleted from the  gas phase,
(i) in the  midplane beyond a radius of $\approx$~250~AU, (ii) in a layer at a
height of $z/r$~$\approx$~0.3 and (iii) in the disk surface between a radius
of a few AU to $\approx$~50~AU.
In region (i), the depletion is due to freeze out of CO onto dust grains as the dust temperature
here is below the desorption temperature of CO.  The absence
of any non-thermal desorption means that CO is completely removed from the  gas phase.
For region (ii), the depletion is due to the destruction of CO by UV radiation.
At this point, the
UV field is strong enough to dissociate CO into its constituent atoms (atomic carbon and oxygen),
however, the dust temperature is also low enough for the  freeze out of molecules which have
binding energies larger than that of CO e.g.\ H$_2$O.
By a time of $10^6$~years, the time at which we extract our abundances, atomic carbon and oxygen
are trapped in molecules contained in the icy mantle.
Above this height, the dust temperature becomes high enough for many molecules to desorb thermally
thus replenishing the stock of C and O to reform CO.
In region (iii), a similar effect to that in region (ii) occurs
due to the decoupling of the dust and gas temperatures in
the disk surface with the dust temperature up to two orders of magnitude lower than the
gas temperature.
The thermal desorption rate is dependent only on the dust temperature ($\propto$~$\exp(-E_d/T_d)$)
whereas the accretion rate depends both on the gas temperature and the number density of dust grains
(see Equations~\ref{accretionrate} and \ref{thermaldesorption}).
Since the gas temperature can be much higher than the dust temperature in this region,
the accretion rate can supersede that of thermal desorption so that by $10^6$ years,
molecules which can survive the intense UV radiation field are able to  freeze out onto dust grains.
Specifically, H$_2$O molecules are able to survive as ice on dust grains thereby depleting
the  gas phase of oxygen-bearing molecules such as CO.

\begin{figure}
\centering
\includegraphics[width=0.5\textwidth]{./CO_0.eps}
\caption{Fractional abundance of gas-phase CO as a function of disk radius and height using
results from model 0.  }
\label{figure4}
\end{figure}

\subsubsection{Cosmic-ray Induced Desorption}
\label{cosmicraydesorptioneffects}

The left columns of Figures~\ref{figure5} and \ref{figure6} display the fractional abundances
of several molecules and molecular
ions as a function of disk height at radii $r$~=~10~AU and 305~AU, respectively,
comparing the results from model 0 (solid lines) with model CRH (dotted lines).
Cosmic-ray induced desorption has the smallest effect on the gas-phase abundances and
only in the outer disk  midplane.
The fractional abundances of gas-phase CO and H$_2$O are enhanced in the disk  midplane
at 305~AU in the results for model CRH, compared with those for model 0, although
the values reached remain orders of magnitude smaller than those in the upper disk layers.
The fractional abundance of N$_2$H$^+$ is also enhanced, due in part to the release of
N$_2$ from dust grains in this region by cosmic-rays and, in fact, reaches
its maximum fractional abundance in the disk  midplane.
As our model disk is truncated at 305~AU, we would expect the effects of cosmic-ray induced
desorption to continue beyond this radius.

\subsubsection{Photodesorption}
\label{photodesorptioneffects}

 Photodesorption is the most experimentally constrained non-thermal desorption mechanism
we have included in our model.
 Photodesorption has an effect in the upper disk layers where the UV radiation
field has reached an appreciable strength yet the temperature remains low
enough for  freeze out to occur.
We compare the results from model 0 (solid lines) with those from model
PH+CRH (dotted lines) in the middle plots of Figures~\ref{figure5} and \ref{figure6}.
 Photodesorption enhances the abundance of molecules in the molecular region
of the disk, counteracting the depletion effects discussed at
the beginning of Section~\ref{nonthermaldesorptioneffects}.
Clearly seen at a radius of 10~AU is the smoothing of molecular
abundances throughout the middle region of the disk with both model results
converging higher in the surface.
At a radius of 305~AU, there is a smoothing out of abundances counteracting depletion
but also a slight difference in the distribution of molecules
in the surface regions.
The fractional abundances of CO and CS are enhanced in model PH+CRH
relative to model 0, whereas those of HCO$^+$, H$_2$O, HCN and N$_2$H$^+$ are reduced.
This is due to the alteration of gas-phase chemistry when  photodesorption is included as
a significant amount of all molecules can remain in the  gas phase in the mid and upper
layers of the disk.  Thus, those molecules which ordinarily would be frozen out in the absence
of photodesorption are available to take part in gas-phase reactions e.g.\ N$_2$H$^+$ is
destroyed via reaction with gas-phase CO so that an enhancement in the abundance of the latter leads to a
corresponding drop in that of the former.

\subsubsection{X-ray Desorption}
\label{xraydesorptioneffects}

X-ray desorption is the least theoretically or  experimentally constrained non-thermal
desorption mechanism we considered, hence, we have used
conservative estimates of molecular yields and thus X-ray desorption
rates.
The right-hand plots in Figures~\ref{figure5} and \ref{figure6} suggest that, even using conservative
estimates, X-ray desorption has the largest effect on gas-phase molecular abundances.
X-rays, with their higher energy, can penetrate deeper into the disk material
than UV photons, hence, X-rays have an effect in the disk  midplane as well as
in the molecular region.
At $r$~=~10~AU (top plot), the abundances of both H$_2$O and CS are enhanced in model XD
relative to the results from models 0, CRH and PH+CRH.
X-ray desorption also acts to smooth out abundances in the upper disk, similar
to the effects of  photodesorption.
At 305~AU, the effects of the inclusion of X-ray desorption are most apparent.
The fractional abundances of all molecules considered here, with the exception
of CS, are enhanced in the  midplane of the disk, to values comparable with
those found in the upper disk regions.
In fact, it appears that the inclusion of X-ray desorption acts to smooth
or homogenise the fractional abundances of gas-phase
CO, H$_2$O and HCO$^+$ throughout the depth of the disk.
Again, as seen in the results for  photodesorption, the gas-phase distributions
are altered in model XD compared with model 0 due to the alteration of
the gas-phase chemistry.
In the upper disk, the results for models PH+CRH and XD are similar with the
exception of the fractional abundance of CS which is enhanced in abundance between
height of $\approx$~70~AU and $\approx$~150~AU in model XD relative to
model PH+CRH.

\begin{figure*}
\centering
\subfigure{\includegraphics[width=0.32\textwidth]{./0_vs_CRH_10AU.eps}}
\subfigure{\includegraphics[width=0.32\textwidth]{./0_vs_PH+CRH_10AU.eps}}
\subfigure{\includegraphics[width=0.32\textwidth]{./0_vs_XD_10AU.eps}}
\subfigure{\includegraphics[width=0.32\textwidth]{./0_vs_CRH_10AU_1.eps}}
\subfigure{\includegraphics[width=0.32\textwidth]{./0_vs_PH+CRH_10AU_1.eps}}
\subfigure{\includegraphics[width=0.32\textwidth]{./0_vs_XD_10AU_1.eps}}
\caption{Fractional abundances of several gas-phase molecules and molecular ions
as a function of disk height at a radius, $r$~=~10~AU comparing
results from model 0 (solid lines) with each non-thermal desorption model (dotted lines),
CRH (left), PH+CRH (middle) and XD (right).
 Note that the results for N$_2$H$^+$ from model 0 are too small to appear on our plot.}
\label{figure5}
\end{figure*}

\begin{figure*}
\centering
\subfigure{\includegraphics[width=0.32\textwidth]{./0_vs_CRH.eps}}
\subfigure{\includegraphics[width=0.32\textwidth]{./0_vs_PH+CRH.eps}}
\subfigure{\includegraphics[width=0.32\textwidth]{./0_vs_XD.eps}}
\subfigure{\includegraphics[width=0.32\textwidth]{./0_vs_CRH_1.eps}}
\subfigure{\includegraphics[width=0.32\textwidth]{./0_vs_PH+CRH_1.eps}}
\subfigure{\includegraphics[width=0.32\textwidth]{./0_vs_XD_1.eps}}
\caption{Fractional abundances of several gas-phase molecules and molecular ions
as a function of disk height at a radius, $r$~=~305~AU comparing
results from model 0 (solid lines) with each non-thermal desorption model (dotted lines),
CRH (left), PH+CRH (middle) and XD (right).}
\label{figure6}
\end{figure*}

\subsection{Effects of Grain-surface Chemistry}
\label{grainsurfacechemistryeffects}

The addition of grain surface chemistry is expected to aid the synthesis
of complex organic molecules in regions of the disk where significant  freeze out has occurred.
In this discussion, we look at the abundances of small organic (saturated)
molecules in the outer disk in particular.
In model GR (see Table~\ref{table2}), in addition to grain-surface chemistry, we also
add cosmic-ray induced desorption and  photodesorption.
Figure~\ref{figure7} shows the fractional abundances of several small organic molecules
as a function of disk height at radii, $r$~=~100~AU (left) and 305~AU (right), for model
PH+CRH (solid lines) compared with model GR (dotted lines).
At 100~AU, the fractional abundance of HCOOH (formic acid) and H$_2$CO (formaldehyde)
are enhanced in the disk  midplane in model GR, relative to model PH+CRH, with the abundance
of HCOOH also enhanced in the upper disk layer.
Most of the organic molecules considered reach their peak fractional abundance between
25 and 40~AU.
Here, the fractional abundances of CH$_3$OH (methanol),
HCOOCH$_3$ (methyl formate) and CH$_3$OCH$_3$ (dimethyl ether) are all enhanced
to a value $\sim$~$10^{-13}$ in model GR, orders of magnitude larger than the respective values
from model PH+CRH.
At the very outer edge of our disk model, $r$~=~305~AU, the fractional abundances of
all molecules are enhanced in model GR relative to model PH+CRH.
Of note is the extreme enhancement seen in the abundances of
CH$_3$OH, HCOOCH$_3$ and CH$_3$OCH$_3$, again by several orders of magnitude, to fractional
abundances which are potentially observable ($\sim$~$10^{-11}$ to $\sim$~$10^{-10}$).
 By fitting observed line intensities of rotational transitions in a selection of molecules
with a simple disk model,
\citet{thi04} estimate the column density of the relatively complex molecule, H$_2$CO, in several protoplanetary
disks as lying between $\sim$~10$^{12}$ and 10$^{13}$~cm$^{-2}$ which in the outer disk translates roughly
to a fractional abundance of $\sim$~10$^{-10}$ as the H$_2$ column density here is
$\sim$~10$^{22}$~cm$^{-2}$.
Complex organic molecules in hot cores and dark clouds are routinely observed with fractional abundances
$\gtrsim$~10$^{-11}$ (see e.g. \citet{herbst09}).
We display the fractional abundances of the molecules discussed in this section as a function
of disk radius and height comparing results from model PH+CRH and model GR in Figure~\ref{figure12}
(online only).

\begin{figure*}
\subfigure{\includegraphics[width=0.5\textwidth]{./organics_100AU.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./organics_305AU.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./organics_100AU_1.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./organics_305AU_1.eps}}
\caption{Fractional abundances of several small organic molecules as a function of disk
height at radii, $r$~=~100~AU (left) and 305~AU (right) for model PH+CRH (solid lines) and
model GR (dotted lines).}
\label{figure7}
\end{figure*}

\subsection{Disk Ionisation Fraction}
\label{diskionisationfraction}

The ionisation fraction in protoplanetary disks is an important parameter as it is thought that
this drives the accretion flow in the disk through the coupling of the gas with
the strong magnetic fields generated by the system.
The required turbulence is generated via magneto-rotational instabilities or MRI
\citep{balbus91,hawley91}.
For effective accretion, the ionisation fraction is required to exceed a critical
level which is dependent on the nature of the star-disk system (see e.g. \citet{ilgner06}).
Regions in which the ionisation fraction falls below this critical value and where
effectively magneto-hydrodynamic accretion is switched off, are termed `dead zones'.

Figure~\ref{figure8} shows the electron fractional abundance as a function of disk radius and
height within a radius of 10~AU (left) and 305~AU (right) using the results from model PH+CRH.
The ionisation fraction varies between a minimum value of $\sim$~$10^{-12}$ in the densest region of
the disk up to a value of $\sim$~0.1 in the hottest, most irradiated surface region closest to
the star.
 We find that we attain similar electron abundances throughout the disk regardless of
chemical model.  The ionisation threshold required for effective accretion is related to the magnetic
Reynold's number \citep{gammie96} which must be determined in advance of addressing the location of
any `dead zones' in our particular star-disk system.
The question of whether accretion is suppressed in our disk model will be considered in detail
in a subsequent publication in which we also investigate the effects of the recalculation
of photo-rates and direct X-ray ionisation on the disk chemical structure and ionisation
fraction.

\begin{figure*}
\subfigure{\includegraphics[width=0.5\textwidth]{./electrons_map_10AU.eps}}
\subfigure{\includegraphics[width=0.5\textwidth]{./electrons_map.eps}}
\caption{Fractional  abundance of electrons as a function of disk radius and
height up to maximum radii of 10~AU (left) and 305~AU (right).}
\label{figure8}
\end{figure*}

\subsection{Radial Column Densities}
\label{columndensities}

The column density, $N_i$, at each radius, $r$, for each species, $i$,
is calculated by integrating the number density over the depth of the disk i.e.\
\begin{equation}
N_i(r) = \int^{z_{+\infty}}_{z_{-\infty}} n_i(r,z)\; \mathrm{d}z \qquad \mathrm{cm^{-2}}.
\label{columdensity}
\end{equation}
The radial column densities provide an excellent means to trace the radial mass
distribution in the disk and also to compare directly results from each of our chemical models to
determine the species sensitive to each chemical process.
In Table~\ref{table3} we list the column densities of various important molecules
at radii of 1~AU, 10~AU, 100~AU and 305~AU for each chemical model and we display
the column densities of many of the molecules discussed thus far,
as a function of radius, up to maximum
radii of 10~AU (left) and 305~AU (right) in Figure~\ref{figure13} (online only).

At a radius of 1~AU, the column densities are relatively insensitive to the choice
of chemical model, unsurprising given that most molecules are in the  gas phase
at this radius and the chemistry is dominated in the  midplane by neutral-neutral
reactions and in the surface by photo-chemistry.

At 10~AU, the effects of the inclusion of non-thermal desorption become apparent.
The column densities for those models which include  photodesorption
are consistently higher for all molecules with the column densities of
HCN, CN and CS particularly
sensitive.
X-ray desorption has a similar effect although we also see a dramatic increase in the
column densities of H$_2$O and CO$_2$ due to the penetrative power of X-rays in this
region.
This is due to the relatively strong X-ray field at this radius coupled with
the low column density of intervening absorbing material (from the disk surface
to the  midplane).
Grain-surface chemistry has only a mild effect at 10~AU on the column densities of
the listed molecules.
For the molecular ions, HCO$^+$ and N$_2$H$^+$, the addition of  photodesorption
causes a rise in  the column densities of both molecules while the addition
of X-ray desorption produces a fall in the column density of the former
and a rise in that of the latter.

At 100~AU, we see some of the same behaviour as at 10~AU with  photodesorption
increasing the column densities of CO, HCN, CN, CS, C$_2$H, H$_2$CO, H$_2$O, CO$_2$ and
C$_2$H$_2$ with HCN, CS and CO$_2$ particularly affected.
X-ray desorption further enhances the column densities of these species.
Here, we begin to see the effects of grain-surface chemistry with
HCN, H$_2$O and CO$_2$ casualties of the increased synthesis of more complex species.

Finally, in the outer disk, the effects of cosmic-ray induced desorption
on the column density of N$_2$H$^{+}$ become apparent, so that this molecule is
a potential observable tracer of this desorption mechanism.
We can also see how both  photodesorption and X-ray desorption act to counteract
the depletion of CO onto dust grains in the outer cold disk  midplane thus
enhancing its overall column density.
In the outer disk,  observable in the column densities is the detrimental effect
that the addition of grain-surface chemistry
has on the column densities of HCN and CS in particular, as N and S atoms are incorporated
into larger, more complex species, via grain-surface reactions.
We can also see the dramatic effect on methanol due to the inclusion of
grain-surface chemistry with its column density enhanced by around three orders of
magnitude.

\begin{deluxetable}{lccccc}
\tablecaption{Column Densities\label{table3}}
\tablewidth{0pt}
\tablehead{\colhead{Species} & \colhead{0} & \colhead{CRH} & \colhead{PH+CRH} & \colhead{XD} &
\colhead{GR}}
\startdata
\cutinhead{1 AU}
H$_2$       & 1.9(25) & 1.9(25) & 1.9(25) & 1.9(25) & 1.9(25)\\
CO          & 2.3(21) & 2.3(21) & 2.3(21) & 2.3(21) & 2.3(21) \\
HCO$^+$     & 1.7(14) & 1.7(14) & 1.7(14) & 1.7(14) & 1.7(14) \\
HCN         & 2.0(17) & 2.0(17) & 2.0(17) & 2.0(17) & 2.0(17) \\
CN          & 2.7(14) & 2.7(14) & 2.7(14) & 2.7(14) & 2.7(14) \\
CS          & 4.5(12) & 4.5(12) & 4.5(12) & 4.5(12) & 4.5(12) \\
C$_2$H      & 4.1(14) & 4.1(14) & 4.1(14) & 4.1(14) & 4.1(14) \\
H$_2$CO     & 1.3(12) & 1.3(12) & 1.3(12) & 1.3(12) & 1.3(12) \\
N$_2$H$^+$  & 5.5(10) & 5.5(10) & 5.3(10) & 5.2(10) & 5.3(10) \\
OH          & 1.7(16) & 1.7(16) & 1.7(16) & 1.7(16) & 1.7(16) \\
H$_2$O      & 1.7(21) & 1.7(21) & 1.7(21) & 1.6(21) & 1.7(21) \\
CO$_2$      & 4.6(20) & 4.6(20) & 4.6(20) & 4.6(20) & 4.6(20) \\
C$_2$H$_2$  & 1.8(15) & 1.8(15) & 1.8(15) & 1.8(15) & 1.7(15) \\
CH$_3$OH    & 2.6(14) & 2.6(14) & 2.6(14) & 2.6(14) & 2.6(14) \\
\cutinhead{10 AU}
H$_2$       & 2.6(24) & 2.6(24) & 2.6(24) & 2.6(24) & 2.6(24) \\
CO          & 3.6(20) & 3.6(20) & 3.6(20) & 3.8(20) & 3.2(20) \\
HCO$^+$     & 4.9(13) & 4.9(13) & 5.4(13) & 3.5(13) & 4.4(13) \\
HCN         & 2.7(11) & 2.7(11) & 7.1(14) & 8.0(14) & 7.0(14) \\
CN          & 1.6(13) & 1.6(13) & 3.9(14) & 3.9(14) & 2.1(14) \\
CS          & 2.0(12) & 1.5(12) & 1.0(14) & 2.5(14) & 3.4(13) \\
C$_2$H      & 3.6(13) & 3.6(13) & 2.1(14) & 2.1(14) & 1.4(14) \\
H$_2$CO     & 3.1(11) & 3.0(11) & 1.4(12) & 1.4(12) & 1.4(12) \\
N$_2$H$^+$  & 1.4(09) & 1.4(09) & 1.4(10) & 1.4(10) & 1.6(10) \\
OH          & 8.7(15) & 8.7(15) & 8.8(15) & 8.8(15) & 8.8(15) \\
H$_2$O      & 2.6(15) & 2.6(15) & 4.3(15) & 2.0(16) & 4.3(15) \\
CO$_2$      & 4.4(16) & 4.4(16) & 4.9(16) & 1.3(18) & 4.0(16) \\
C$_2$H$_2$  & 1.1(14) & 1.1(14) & 8.7(13) & 2.8(13) & 1.5(14) \\
CH$_3$OH    & 2.1(07) & 2.1(07) & 7.7(07) & 1.6(08) & 8.5(07) \\
\cutinhead{100 AU}
H$_2$       & 2.0(23) & 2.0(23) & 2.0(23) & 2.0(23) & 2.0(23) \\
CO          & 2.2(19) & 2.2(19) & 2.3(19) & 2.8(19) & 2.2(19) \\
HCO$^+$     & 2.2(14) & 2.2(14) & 2.2(14) & 8.3(13) & 4.9(13) \\
HCN         & 1.6(12) & 1.6(12) & 2.1(14) & 3.7(14) & 2.3(13) \\
CN          & 1.2(13) & 1.2(13) & 2.6(14) & 2.6(14) & 2.4(14) \\
CS          & 7.0(09) & 7.0(09) & 3.2(13) & 9.7(13) & 1.7(13) \\
C$_2$H      & 1.1(13) & 1.1(13) & 1.2(14) & 1.2(14) & 1.1(14) \\
H$_2$CO     & 7.3(11) & 7.2(11) & 1.9(12) & 1.9(12) & 1.7(12) \\
N$_2$H$^+$  & 5.0(10) & 5.2(10) & 3.7(10) & 3.1(10) & 7.0(10) \\
OH          & 4.4(14) & 4.4(14) & 2.2(14) & 2.2(14) & 2.8(14) \\
H$_2$O      & 1.2(14) & 1.2(14) & 1.1(15) & 2.6(15) & 7.3(14) \\
CO$_2$      & 3.8(12) & 3.8(12) & 3.4(15) & 1.2(16) & 7.7(14) \\
C$_2$H$_2$  & 2.8(12) & 2.8(12) & 1.9(13) & 2.0(13) & 1.6(13) \\
CH$_3$OH    & 5.6(06) & 5.6(06) & 7.5(07) & 1.5(08) & 4.8(08) \\
\cutinhead{305 AU}
H$_2$       & 5.7(22) & 5.7(22) & 5.7(22) & 5.7(22) & 5.7(22) \\
CO          & 5.2(17) & 5.2(17) & 1.2(18) & 1.8(18) & 1.1(18) \\
HCO$^+$     & 3.2(13) & 3.2(13) & 1.2(13) & 2.6(13) & 3.6(13) \\
HCN         & 2.8(13) & 2.8(13) & 9.1(13) & 1.8(14) & 7.4(12) \\
CN          & 9.9(13) & 9.9(13) & 1.6(14) & 1.7(14) & 1.6(14) \\
CS          & 2.0(10) & 2.0(10) & 3.1(12) & 4.3(13) & 8.3(11) \\
C$_2$H      & 3.1(13) & 3.1(13) & 8.0(13) & 8.0(13) & 7.2(13) \\
H$_2$CO     & 6.3(12) & 6.3(12) & 2.1(12) & 2.5(12) & 2.4(12) \\
N$_2$H$^+$  & 2.5(12) & 5.1(12) & 5.0(12) & 3.7(12) & 1.2(13) \\
OH          & 7.9(14) & 8.0(14) & 8.0(13) & 1.7(14) & 2.0(14) \\
H$_2$O      & 1.4(15) & 1.4(15) & 7.8(14) & 1.4(15) & 1.2(15) \\
CO$_2$      & 9.4(13) & 9.5(13) & 1.9(15) & 3.4(15) & 7.9(14) \\
C$_2$H$_2$  & 1.3(13) & 1.3(13) & 1.3(13) & 3.1(13) & 2.3(13) \\
CH$_3$OH    & 1.6(08) & 1.6(08) & 5.6(07) & 7.7(08) & 1.6(11)
\enddata
\tablecomments{$a(b)$ means $a \times 10^{b}$}
\end{deluxetable}

\subsection{Comparison with Other Models}
\label{comparison}

A direct comparison with other chemical models of protoplanetary disks is difficult as no
two models are identical in either their physical basis or their chemical networks.
Given the plethora of preceding work in this field, we limit this short discussion
to more recent models which are comparable to ours in chemical complexity.

The work presented here builds upon previous investigations into the importance of
cosmic-ray induced desorption and  photodesorption in disks by \citet{willacy00} and \citet{willacy07},
the latter of which uses the model of \citet{dalessio01} for their physical framework.
We obtain encouragingly similar results to \citet{willacy07} in particular, although,
her primary objective was the investigation into deuterated species in disks.
As such, the reaction network of the non-deuterated species was truncated to accommodate
the additional reactions involving deuterium and deuterium-containing molecules.
Our work also differs in that our physical model includes X-ray heating and also explicitly
determines the gas temperature which can decouple from the dust-grain temperature
in regions where cooling via gas-grain collisions is inefficient.
\citet{willacy09} also use their deuterated reaction network and adapt their model
to investigate the chemical structure of a disk within 30~AU of the central star.
Again, we achieve similar results although differences in the set of
molecular desorption energies used manifests as differences in the positions of `snow lines' for
molecules such as HCN.
Also differing prescriptions for
the UV radiation field in the disk leads to different distributions of radicals such as C$_2$H and CN.

 Photodesorption and cosmic-ray induced desorption are now routinely included in modern chemical
models of protoplanetary disks (e.g.\ \citet{woitke09, henning10}).
X-ray desorption and grain-surface chemistry have both been included in work by
by other groups (e.g.\ \citet{semenov08,henning10}) although not explicitly investigated given
the theoretical uncertainty behind the exact mechanism of X-ray desorption for the
former process and the usual truncation of chemical networks for the latter.
Our work presented here and subsequent follow-up publications  on
X-ray desorption and grain-surface chemistry, we hope, will go some way to
addressing this.

\section{SUMMARY}
\label{summary}

In this work, we have presented a selection of results from our high-resolution combined
chemical and physical model of a protoplanetary disk surrounding a typical T Tauri star, constructed
in order to trace the physical and thus chemical structure on small scales.
We use a protoplanetary disk model in which the gas density and temperature distributions
are obtained self-consistently and UV and X-ray irradiation by the central star is calculated
by solving the radiative transfer equation.
To this we applied a large comprehensive
chemical network including gas-phase chemistry, gas-grain interactions and grain-surface
chemistry.
We investigated the effects of each non-thermal desorption mechanism thought to
be important in disks: cosmic-ray induced desorption,  photodesorption and X-ray desorption.
We also added a large grain-surface network to investigate the effectiveness of grain-surface
reactions on the synthesis of relatively complex organic molecules.

Using the results from model PH+CRH (see Table~\ref{table2}) extracted at a time
of $10^{6}$~years, we find that the disk chemical structure closely mirrors the disk physical structure
with the  freeze out of molecules onto dust grains creating an icy mantle
in the cold, dense  midplane and an abundance of molecules
in a layer above the  midplane created through sublimation and the resulting
rich gas-phase chemistry.
In the disk surface, the molecular abundances drop as the UV and X-ray radiation fields peak in strength
dissociating molecules and ionising both molecules and atoms.
The resulting disk ionisation fraction increases with increasing disk height.
There is similar stratification in the radial direction as the increasing temperature drives the
evaporation of molecules.
The temperature dependence of the desorption energies results in a unique `snow-line' for each molecules
with more volatile molecules returned to the gas in the  midplane at larger radii than
less volatile ones.
In particular, both HCN and H$_2$O remain frozen onto dust grains to within $\approx$~1 to 2 AU
of the central star.

The addition of cosmic-ray induced desorption has only a small effect on
the gas-phase abundances in the outer disk  midplane although since our model is truncated at
305~AU we would expect that this effect will continue at radii beyond this value.
 Photodesorption, the most experimentally constrained of the mechanisms considered here,
has a larger effect although only in the molecular and surface regions of the disk where there is
an appreciable UV flux.
It is especially effective at enhancing the gas-phase abundances of non-volatile molecules such as
H$_2$O.
X-ray desorption, has the largest effect, smoothing the abundances of gas-phase species throughout the
height of the disk and acting to homogenise the fractional abundances.
However, X-ray desorption is the least theoretically or experimentally constrained and thus our
results must be treated with caution, pending further investigation.

The addition of grain-surface chemistry also yields some encouraging results worthy
of revisiting and further study.
In the outer disk, where the  freeze out of molecules is most prevalent, the abundances
of relatively complex organic molecules e.g.\ CH$_3$OH, HCOOCH$_3$ and CH$_3$OCH$_3$ are enhanced
to potentially observable values when grain-surface chemistry and  photodesorption are included
in our model.
Thus, the observation of rotational transitions of these, and related, species in protoplanetary
disks should provide an excellent means of testing grain-surface chemistry theory.
Due to limitations in existing facilities, the most complex molecule observed, as yet, in disks is H$_2$CO.
ALMA, however, will have the sensitivity and spectral resolution necessary to
observe rotational transitions in these minor species.
 Indeed, preliminary synthetic spectra we have calculated suggest that the rotational
transition lines of methanol are enhanced above the detection threshold of ALMA when grain-surface
chemistry is included in our model (Walsh et al., in preparation).

We have shown that running models
of this nature, in which we test experimental data and theory,
varying the different chemical ingredients, are necessary for disentangling the different physical influences
on the chemical content of protoplanetary disks.
The influence of the physical conditions and processes on the molecular content is also a strong function
of radius and so high-resolution models, which trace the chemical structure on small scales, are also preferred.
In this brief overview of our model, we have shown that X-ray desorption and grain-surface chemistry can have
a powerful effect on the molecular content of disks and we intend to expand upon the work presented here with
follow-up papers on both chemical processes.
Although in this paper we have shown that the distribution and radial column densities of particular
molecules are sensitive to the inclusion or omission of certain chemical processes, in order to test the
viability of using these molecules as tracers we must compute the radiative transfer in the disk and directly
compare our results with observations.  This work will be reported in a subsequent paper (Walsh et al., in
preparation).

\acknowledgments

 We wish to thank an anonymous referee for his or her constructive comments
which helped improve our paper.
C.\ Walsh acknowledges DEL for a studentship and JSPS for the award of a short-term
fellowship to conduct research in Japan.  H.\ Nomura acknowledges the JGC-S Scholarship
Foundation, the Grant-in-Aid for Scientific Research 21740137 and the
Global COE Program ``The Next Generation of Physics, Spun from Universality and
Emergence'' from MEXT, Japan.
Astrophysics at QUB is supported by a grant from the STFC.

redpajama_set_name: RedPajamaArXiv


text:
Rasheed O. Reid
Photo: Spalding County Sheriff's Office
Student faces child porn charge after allegedly recording boy with special needs
Chelsea Prince, The Atlanta Journal-Constitution
Authorities in Spalding County are asking parents to check their children's phones after they learned high school students were sharing pornographic video of a classmate.
A 17-year-old student is facing charges in connection with the distribution of the video, which was recorded during school hours, according to Spalding County Sheriff Darrell Dix. A spokesman for Dix said the incident happened at a school in the Griffin-Spalding County School System but did not confirm which one.
"This video was of a 15-year-old student that we are considering the victim due to circumstances uncovered during the investigation," a sheriff's spokesman said on Facebook.
The student has special needs, according to the sheriff's office.
The sheriff's office was first made aware of the video on Friday. The parents of the 15-year-old boy have been notified, the spokesman said, but the video continues to be shared among students.
"At this point our priority is protecting the victim and stopping the spread of this video," the spokesman said. "What happened is a crime. It is unlawful to record, posses, or distribute child pornography, and the student who made the video has been charged accordingly. Students who shared or possessed the video can also be charged. These incidents can destroy young people's lives and often drive some to harm themselves or commit suicide."
The 17-year-old student, identified as Rasheed O. Reid, has been arrested on a felony charge of distribution of child pornography. Authorities said he will likely be charged as an adult, Channel 2 Action News reported.
Deputies are now urging parents to inspect their children's phones and delete the video or any other pornographic content.
They are also encouraging parents to protect their children and others by keeping a close eye on kids' activity on phones and social media.
"If they don't like it," the spokesman said, "be a parent, not a friend."
Additional charges are possible as the investigation continues.
—Please return to AJC.com for updates.
A mobile home was completely destroyed in the blaze.

redpajama_set_name: RedPajamaCommonCrawl


Well the the check gauges light came on and temp gauge was all the way up into the orange. So I pulled into the nearest parking lot which happened to be a Home Depot. HD had pre-mix on the shelf so I restarted the car and topped it off. No little bubbles - just big burps. Didn't get 2 blocks and it was back in the orange again. Did the leap frog every 2 blocks until back home. I thought it was a head gasket but forgot to look for white smoke out the tailpipe. I guess I only imagined the worst case. But before I dropped it off for testing I realized it could be a water pump though the last I had one fail it was slow and intermittent.
Good news the block and system tested good and it's just the water pump. When I asked about replacing the head gaskets the shop said nearly $1900 just in labor. I think that would have sent my Z28 with 270,000mi to the boneyard as I don't have the garage space to R&R the heads.
So now I'm thinking I should buy an new Opti so I don't have to pay shop prices for one when this one quits. I have the impression a good dowse of water from the pump usually kills the Opti.
Any suggestions? I like the Summit Opti for less than 200 bucks.
Re: Water pump failed. How long before Opti does too?
Good job on catching the overheating before blowing the head gaskets! I recently failed to do just that and got the privilege of doing a valve job on my 1995 that was a bunch of work and about $1,300 in parts and machine work. I do not have any experience that would recommend an opti change after a dousing. I do have experience with two of the Summit optis and can share that for what its worth.
I have installed two of the summit units, the first back in 2010 and then a second one in late 2013. The first ran 23,000 miles and the second ran 24,000 miles. The good new is that both ran perfectly right out of the box which apparently is not always the case. I had heard reports of OEM optis lasting much longer than the 24K mile mark so I switched away from the Summit brand. I currently am running a Delphi unit but only have 22,000 miles on it so i can't say if it will last any longer than the Summits.
I did test the sealing on the last summit unit I had installed and discovered it did not have any sealing on the input shaft bearing so the vacuum signal coming from the engine basically drew in air through the bearing as well as through the air feed line from the air cleaner/MAF.
Thx man that's good info. Who sells Delphi Opti's? I didn't see Delphi's at Summit or Rock Auto last I checked.
I only replaced the Opti late last year so I don't have a ton of miles on it yet.
I don't think the Delphi unit is available right now. I think pontiacstogo is on the scent with the eBay seller. Check out berrington1 feedback score on eBay and it is 99.2% and they are all happy optispark customers. From what Injuneer and others say here at camaroz28.com most of the other vendors would love to get that high of customer satisfaction!
What I have now is an AC Delco Opti that I bought through Summit when they were at a bargain price around $200. But rumor on line was those AC Delco units were not Mitsubishi sensor equipped.
Yes I've read only good about the Opti Doctors Opti distributors but $400 is a lot to have sitting on the shelf. I think for $400 I will try to locate an original Opti to use for donor parts.
If I had the garage space now I think I should take my current Opti off for disassembly and inspection. But the long range plan would be to have a reliable spare Opti ready for installation. $400 is a lot of overtime for me.
If you are doing a water pump you might as well do the Opti. Mine was the other way,....Opti went out so I did the water pump too.
i got lucky I guess and got a new old stock GM Opti. A local dealer had it on the shelf and didn't even know it. From investigating all but a very select few remanufactured ones are no good. They should go 100k if you don't regularly soak them. There is a TSB which I have not personally seen that goes over sealing the Opti. with silicone sealer. This also must be safe for EFI and Cats. Be sure to look on the tube.
Might as well do belts too and get the good ones. Might as well do all the filters too. Again get the best available. I forgot spark plugs, might as well do them too. Again doing research it's hard to beat the OEM. be sure to check the plug wires too. Another $75-100. But a pain if you have to do them later.
I'm going for the Spectra unit from Rock Auto at $90. Unless someone has a better choice for that money I will say I've always had good luck with Spectra products. And like mentioned I will seal it up well but after a good inspection.
FWIW I have a positive pressure system in the works but that will only happen as I find time for it. Much more fun that way.
Cardo0, Good luck with the Spectra and post an update once you are back on the road.
Couldn't you just do the MSD cap / rotor kit for the opti you have? Worst case if you get into your current opti and it looks really bad, return the kit then go the Spectra route.
Cost wise, I bought a pre-owned Dynaspark from a member here years ago for $250, then sent it in for a rebuild for another $100. Most of the quality opti's even back in the day were $400+. I totally get the cost barrier, but since you are worried about cost, I think it makes more sense to spend an extra $200 now, versus what you would pay to have the unit replaced in an unknown (an possibly very short) time period.
I would do an MSD cap and rotor on the current AC Delco unit once its out and I can inspect it but no shop will let the car take up space while I tinker. I need a unit to swap in or pay their price for one. The shop I'm using quoted me something north of $500 for a reman AC Delco Opti and they're on back order, Just don't have the garage space right now with a frame off in progress on another car.
And I will inspect that Spectra unit now while I have time and if it's to junky then I can look for something else while my current Opti is working. Well that's the plan for now. Spectra products are Canadian made and deserve a look though the price is to good to be true.
We live in Vegas, so we know too well about the gamble. Even if it looks okay, it might turn up to flat out not function when it goes into the car. A question I would ask before going that route to the shop is, what is the cost for just replacing the Opti? I would be willing to bet that they would be charging 400+ labor to get that far. I hear you, but to me the risk is not worth the reward.
I got a $440 quote from Imperial Auto to R&R an Opti but that don't include parts. So it's more that I read the $300 to $400 Opti's fail like junk that has me think why spend more for junk? I mean if I'm gonna get disappointed why not for less $$$$? I can always spring for the Opti Docs reman if needed. I tried a Cardone rebuild once and it lasted maybe a year (too bad I traded in my original for the core charge). But you can find a Cardone video that claims they have sealed up their reman Opti's as it was a major cause in failure. Well I can seal a Spectra to my satisfaction so why not?
I guess what I'm saying is I prefer to prove things to myself as I don't really trust the internet hearsay much. I read on the forums that the current AC Delco Opti's didn't have the Mitsubishi sensor at the time I bought my latest but w/o checking my maintenance records I'll say I have at least 50K mi on this one. And how many have just plain goofed up their Opti install then blaming it on the manufacturer??
What I need to do is get my O-scope out and take some data now while the car is running well enough. Then I will something for comparison whatever I use. And that's what I like about my high mileage daily driver it becomes a test machine for whatever I want to do with it. No warranty conflicts or aesthetic worries with this old car.
Cardo...if I understand your posts you don't have garage space to do this yourself??
If you are intent on the $90 Spectra, try it. "Maybe" you will be one of the lucky ones who gets good life out of a ….cheap part. If going that route, put blue loc-tite on rotor screws and dialectic grease on O rings before install.
Quick Reply: Water pump failed. How long before Opti does too?


When I got saved it was by this verse John 8:32 – "and you will know the truth and the truth will set you free" My understanding was that, know the truth about myself and that would set me free, which is what happened. The more I studied the Bible the real truth I discovered was knowing the Word and that will set you free. Just there I realized that the Bible is living and alive,the further you dig,more is revealed. I can't wait to get stuck into the word daily.
Just as the writer says it cuts to the bone, everyday more is revealed. It will expose all the evil. Just when you think you have this thing called faith waxed there is a new revelation. That's what I find so humbling.
I must just warn we humans get lethargic about things. We must not forget to follow God' s word, enthusiastically and diligently. We must make God the centre of our life's.
Previous postWhy am I discouraged?


Embrace popular retro Scandi style with this on-trend 3 seater couch. Featuring a generously wide back with button-in back cushions and a plump seat, this beautiful couch will cocoon you while you relax in style. Elegant tapered pale timber legs and gently contoured arms add to the eye-catching designer look.


text:
Kerns Announces Coaching Staff
Written by Andrew Korba
BOONE, N.C. – Appalachian State head men's basketball head coach Dustin Kerns has finalized his first Mountaineer coaching staff for the upcoming 2019-20 season
Patrick Moynihan, Bob Szorc and Frank Young have been tabbed as assistant coaches, while Bradley Fey has been named director of basketball operations. In addition, Jason Allison has been retained as special assistant to the head coach.
"Staff chemistry and alignment are critical, and we are very fortunate to have that here at Appalachian State with our coaching staff," Kerns said. "These guys were impactful in our time at Presbyterian together, and I am thankful they will be joining the App State family alongside Jason Allison, who I've known for a long time and respect the job he does. This group has had great experiences in basketball as players and coaches, while also being a part of March Madness."
Moynihan owns five years of coaching experience:
Served as an assistant with Kerns at Presbyterian for two seasons, seeing the Blue Hose win total increase from five to 11 in 2017-18 and from 11 to 20 in 2018-19
No stranger to the Sun Belt, Moynihan was a graduate assistant at Troy for the 2016-17 season
At Troy, he helped spark a 13-win improvement, culminating in the Sun Belt Tournament title for the Trojans and a berth in the NCAA Tournament
Spent two seasons as a graduate assistant at North Alabama, helping the Lions go 16-13 in 2015-16
Held an assistant position at Buford High School in Buford, Ga. and with the Atlanta All-Stars AAU from 2013-14
Four-year letter winner at North Georgia, where he graduated with a degree in finance and management in 2013
Kerns on Moynihan: "Patrick is a rising star in coaching. He has a true passion and great coaching pedigree. He has a very good understanding and reputation in the recruiting world. He is great at building relationships and will develop our players both on and off the court. Coach Moynihan will be an outstanding fit here at App State."
Szorc boasts a background of coaching that began in the high school ranks, before moving into roles in Division II and Division I:
Worked as an assistant under Kerns in 2018-19 at Presbyterian, seeing the Blue Hose win two games in the CIT
Spent four seasons at Division II Delta State from 2013-17, including one year as associate head coach
In four seasons at Delta State, helped the Statesmen post 72 total wins, including a 23-9 record in 2016-17 and an appearance in the NCAA Division II South Region Semifinals
Served as head coach on the high school level at Wheaton Warrenville South High School in Wheaton, Ill. and Alleman Catholic High School in Rock Island, Ill.
Graduated from St. John's University in Collegeville, Minn.
Kerns on Szorc: "Bob is a coach's coach. He has been a head coach and has such a drive to grow and develop and be the best he can be. He is an incredible teacher of the game and a relentless recruiter who brings valuable experience to our staff. Coach Szorc will be a huge asset to our staff and players here at App State."
Young owns six years of experience across various staffs, while also playing overseas for five seasons after a decorated career at West Virginia:
Served as an assistant with Kerns at Presbyterian for the previous two seasons, assisting in all aspects with the program
Spent three seasons at North Florida as the director of operations, helping the Ospreys qualify for the NCAA Tournament in 2015 and the NIT in 2016
Assistant coach at West Virginia Wesleyan in 2013-14
Played for EnBW Ludwigsburg (2007), Rotterdame Challengers (2008), Landstede Club (2008-09) and the Crailsheim Merlins (2010-11) over the course of five years
In four seasons at West Virginia, averaged 7.4 points in 125 career games. During his senior season, set a school record for 3-pointers made (117) and led the Mountaineers to the NIT championship while earning tournament MVP honors
Graduated from West Virginia in 2007 with a degree in marketing and earned his MBA from Florida Institute of Technology in 2013
Kerns on Young: "Frank is a star. He had a stellar playing career but has now transitioned into a very good coach who understands what it takes to play at the highest level. He has a great rapport with players and in recruiting. More importantly, Coach Young is a high-character person and will be a tremendous addition for our program."
Fey brings experience on the operational front to the High Country:
Served as the director of operations at Presbyterian in 2018-19 under Kerns
Worked as a graduate assistant at Jacksonville University for two seasons, assisting with all aspects of basketball operations
Appeared in 89 games over four seasons at DePauw in Greencastle, Ind.
As a junior in 2014-15, helped the Tigers capture the North Coast Athletic Conference Tournament title and earn a spot in the NCAA Division III Tournament
Graduated from DePauw in 2016 with a degree in sociology and earned his master's in educational leadership from Jacksonville in 2018
Kerns on Fey: "Bradley was an integral part of our success at PC and we expect him to do the same here at App State. He handles a lot of behind the scenes things that may not be seen by the public, but is valuable and important to our program. We are thrilled about having Bradley Fey on the mountain with us."
Allison begins his sixth season on the App State staff:
Promoted to associate head coach for the 2018-19 season, after serving as an assistant for the previous four seasons at Appalachian State
Responsible for the recruitment of three-time All-Sun Belt honoree Ronshad Shabazz
Spent nine seasons as an assistant at Virginia Military Institute, helping the Keydets make three appearances in the Big South Tournament championship game
Also has coached at the college level at King College and Lees-McRae and on the high school level at Gaston Day School and Lynchburg Christian Academy
Graduated from Liberty in 1999 with a degree in physical education and played three seasons for the Flames
Kerns on Allison: "I've known Jason for a long time through the coaching circles and always had a lot of respect for the job he does and the man he is. Jason will be a huge asset in the transition and I am very excited about him, Hope and his family remaining in Boone with the App State family."
Kerns and the Mountaineers will open the 2019-20 season in November. Season tickets for the 2019-20 season are on sale and can be purchased by clicking here or contacting the ticket office at 828-262-2079.


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Swiss Butzi by Othmar Klauser
October 13, 2016 / No Comments
Chris sent this in. His description is better than I could do, so here it is. The YouTube link at the end is in German. I which I could understand the old carver.
I would like to contribute with a mask which I found some time ago on a local internet platform. I knew instantly that it would be a mask from the area around Sargans, eastern Switzerland, as of its style and the characteristic hood attached to the mask. The previous owner had the (unused) mask in her family for a long time, but she did not know much more about it. I managed to find a carver in Flums who could finally identify the initials on the rear: the mask was carved by a now very old carver named Othmar Klauser (KO), in the village of Flums. It was carved in 1966, and this was his mask number 18. The old man was truly happy to see his mask again, after such a long time… It is a typical so-called "Butzi"-mask from this area, combining human features with monster-like ones. "Butzi" means more or less "mask", and therefore it was a mask "zum go butzne" (meaning to put a mask on one's face and wear old cloths and then wildly mess around, day and night – a teenagers' as well as male adults' joy during carnival, or Fasnet). As far as I know, these activities plus the carving of masks were banned in the first half of the 20th century, and afterwards saw a revival. See this video for another great (but recently deceased) carver of the area: https://www.youtube.com/watch?v=kWErVaKwbVI
Chris, 1037
By Bob Ibold
Masterpiece from Europe
Unusual African fish mask
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Mask of the future
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A - high value*
B - collectible*
C - decorative art
D - low value
* A and B do not always imply higher dollar value. Most masks get a C or D, however we usually don't post them.
Jan 17, 2022 How to Get Started Collecting Masks – A Beginner's Guide
Jan 07, 2022 Indonesian Tiger Mask
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Masks of the World - 2022 ©


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Dr. Wiley is an internal medicine doctor in the Miami area.
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Dr. Wiley sees patients and can be reached at the following location.


Purpose: To learn how to advance a runner to third base when softball hitting.
Procedure: First, second, and third baseman are in place and a runner is on second. The outfielders are behind the cage at home, with one hitter hitting while the others wait in line. Hitters and runners should wear helmets. A coach is on the mound behind an L-shaped screen, either throwing or feeding the pitching machine. The hitter hits the ball to the right side of the diamond to move the runner to third base. Mix in a few drag or push bunts to advance the runner.