1,512 research outputs found
Static and dynamic characterization of pull-in protected CMOS compatible poly-SiGe grating light valves
status: publishe
Antagonism of GABA-B but not GABA-A receptors in the VTA prevents stress- and intra-VTA CRF-induced reinstatement of extinguished cocaine seeking in rats
Stress-induced reinstatement of cocaine seeking requires corticotropin releasing factor (CRF) actions in the ventral tegmental area (VTA). However the mechanisms through which CRF regulates VTA function to promote cocaine use are not fully understood. Here we examined the role of GABAergic neurotransmission in the VTA mediated by GABA-A or GABA-B receptors in the reinstatement of extinguished cocaine seeking by a stressor, uncontrollable intermittent footshock, or bilateral intra-VTA administration of CRF. Rats underwent repeated daily cocaine self-administration (1.0 mg/kg/ing; 14 × 6 h/day) and extinction and were tested for reinstatement in response to footshock (0.5 mA, 0.5” duration, average every 40 s; range 10–70 s) or intra-VTA CRF delivery (500 ng/side) following intra-VTA pretreatment with the GABA-A antagonist, bicuculline, the GABA-B antagonist, 2-hydroxysaclofen or vehicle. Intra-VTA bicuculline (1, 10 or 20 ng/side) failed to block footshock- or CRF-induced cocaine seeking at either dose tested. By contrast, 2-hydroxysaclofen (0.2 or 2 μg/side) prevented reinstatement by both footshock and intra-VTA CRF at a concentration that failed to attenuate food-reinforced lever pressing (45 mg sucrose-sweetened pellets; FR4 schedule) in a separate group of rats. These data suggest that GABA-B receptor-dependent CRF actions in the VTA mediate stress-induced cocaine seeking and that GABA-B receptor antagonists may have utility for the management of stress-induced relapse in cocaine addicts
Accurate determination of the free-free Gaunt factor. II - relativistic Gaunt factors
When modelling an ionised plasma, all spectral synthesis codes need the
thermally averaged free-free Gaunt factor defined over a very wide range of
parameter space in order to produce an accurate prediction for the spectrum.
Until now no data set exists that would meet these needs completely. We have
therefore produced a table of relativistic Gaunt factors over a much wider
range of parameter space than has ever been produced before. We present tables
of the thermally averaged Gaunt factor covering the range log10(gamma^2) = -6
to 10 and log10(u) = -16 to 13 for all atomic numbers Z = 1 through 36. The
data were calculated using the relativistic Bethe-Heitler-Elwert (BHE)
approximation and were subsequently merged with accurate non-relativistic
results in those parts of the parameter space where the BHE approximation is
not valid. These data will be incorporated in the next major release of the
spectral synthesis code Cloudy. We also produced tables of the frequency
integrated Gaunt factor covering the parameter space log10(gamma^2) = -6 to 10
for all values of Z between 1 and 36. All the data presented in this paper are
available online.Comment: 8 pages, 8 figures, 2 table
Radiative cooling in collisionally and photo ionized plasmas
We discuss recent improvements in the calculation of the radiative cooling in
both collisionally and photo ionized plasmas. We are extending the spectral
simulation code Cloudy so that as much as possible of the underlying atomic
data is taken from external databases, some created by others, some developed
by the Cloudy team. This paper focuses on recent changes in the treatment of
many stages of ionization of iron, and discusses its extensions to other
elements. The H-like and He-like ions are treated in the iso-electronic
approach described previously. Fe II is a special case treated with a large
model atom. Here we focus on Fe III through Fe XXIV, ions which are important
contributors to the radiative cooling of hot, 1e5 to 1e7 K, plasmas and for
X-ray spectroscopy. We use the Chianti atomic database to greatly expand the
number of transitions in the cooling function. Chianti only includes lines that
have atomic data computed by sophisticated methods. This limits the line list
to lower excitation, longer wavelength, transitions. We had previously included
lines from the Opacity Project database, which tends to include higher energy,
shorter wavelength, transitions. These were combined with various forms of the
g-bar approximation, a highly approximate method of estimating collision rates.
For several iron ions the two databases are almost entirely complementary. We
adopt a hybrid approach in which we use Chianti where possible, supplemented by
lines from the Opacity Project for shorter wavelength transitions. The total
cooling including the lightest thirty elements differs significantly from some
previous calculations
Properties of Dust Grains in Planetary Nebulae -- I. The Ionized Region of NGC 6445
In this paper we study new infrared spectra of the evolved planetary nebula
NGC 6445 obtained with ISO. These data show that the thermal emission from the
grains is very cool and has a low flux compared to H beta. A model of the
ionized region is constructed, using the photo-ionization code CLOUDY 90.05.
Based on this model, we show from depletions in the gas phase elements that
little grain destruction can have occurred in the ionized region of NGC 6445.
We also argue that dust-gas separation in the nebula is not plausible. The most
likely conclusion is that grains are residing inside the ionized region of NGC
6445 and that the low temperature and flux of the grain emission are caused by
the low luminosity of the central star and the low optical depth of the grains.
This implies that the bulk of the silicon-bearing grains in this nebula were
able to survive exposure to hard UV photons for at least several thousands of
years, contradicting previously published results. A comparison between optical
and infrared diagnostic line ratios gives a marginal indication for the
presence of a t^2-effect in the nebula. However, the evidence is not convincing
and other explanations for the discrepancy are also plausible. The off-source
spectrum taken with ISO-LWS clearly shows the presence of a warm cirrus
component with a temperature of 24 K as well as a very cold component with a
temperature of 7 K. Since our observation encompasses only a small region of
the sky, it is not clear how extended the 7 K component is and whether it
contributed significantly to the FIRAS spectrum taken by COBE. Because our line
of sight is in the galactic plane, the very cold component could be a starless
core.Comment: 36 pages, 8 tables, 7 figures, accepted for publication in Ap
Reading Imagined Letter Shapes from the Mind's Eye Using Real-time 7 Tesla fMRI
We present a 7 Tesla fMRI proof-of-concept study of the first letter speller BCI that decodes imagined letter shapes from activity patterns in early visual cortical areas. New tools are developed to enable real-time population receptive field retinotopic mapping for encoding and decoding. Using two different letter shapes (H and T), classification performance of generated activity patterns during imagery reaches 80% accuracy in each individual. Using a denoising autoencoder, recognizable letter shapes could be reconstructed and displayed as feedback to participants in the scanner
Expanded Iron UTA spectra -- probing the thermal stability limits in AGN clouds
The Fe unresolved transition array (UTAs) produce prominent features in the
15-17?A wavelength range in the spectra of Active Galactic Nuclei (AGN). Here
we present new calculations of the energies and oscillator strengths of inner-
shell lines from Fe XIV, Fe XV, and Fe XVI. These are crucial ions since they
are dominant at inflection points in the gas thermal stability curve, and UTA
excitation followed by autoionization is an important ionization mechanism for
these species. We incorporate these, and data reported in previous papers, into
the plasma simulation code Cloudy. This updated physics is subsequently
employed to reconsider the thermally stable phases in absorbing media in Active
Galactic Nuclei. We show how the absorption profile of the Fe XIV UTA depends
on density, due to the changing populations of levels within the ground
configuration.Comment: ApJ in pres
Accurate determination of the free-free Gaunt factor; I - non-relativistic Gaunt factors
Modern spectral synthesis codes need the thermally averaged free-free Gaunt
factor defined over a very wide range of parameter space in order to produce an
accurate prediction for the spectrum emitted by an ionized plasma. Until now no
set of data exists that would meet this need in a fully satisfactory way. We
have therefore undertaken to produce a table of very accurate non-relativistic
Gaunt factors over a much wider range of parameters than has ever been produced
before. We first produced a table of non-averaged Gaunt factors, covering the
parameter space log10(epsilon_i) = -20 to +10 and log10(w) = -30 to +25. We
then continued to produce a table of thermally averaged Gaunt factors covering
the parameter space log10(gamma^2) = -6 to +10 and log10(u) = -16 to +13.
Finally we produced a table of the frequency integrated Gaunt factor covering
the parameter space log10(gamma^2) = -6 to +10. All the data presented in this
paper are available online.Comment: 10 pages, 5 tables, 3 figures. Fixed typo in Eq. 1
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