1,750 research outputs found
Effects of simulated space radiation on selected optical materials
The effect of simulated Nimbus spacecraft orbital (1100 km, circular, and polar) radiation on wide bandpass glass filters, narrow bandpass thin film interference filters, and several fused silicas was determined by transmittance measurements over the 200 to 3400 nanom wavelength region. No changes were observed in the filters, which were shielded with fused silica during irradiation, after exposure to a 1-year equivalent orbital dose of electrons, nor in the fused silicas after the same electron exposure plus a 1-year equivalent dose of protons. Exposure to a 1/2-year equivalent dose of solar ultraviolet radiation caused a significant degradation in the transmittance of two ultraviolet-transmitting interference filters but had no effect on two colored glass filters that transmitted in the visible and near infrared regions. As a result of the ultraviolet exposure the fused silicas exhibited losses of several percent over the 200- to 300 nanom wavelength region
Strong pressure-energy correlations in liquids as a configuration space property: Simulations of temperature down jumps and crystallization
Computer simulations recently revealed that several liquids exhibit strong
correlations between virial and potential energy equilibrium fluctuations in
the NVT ensemble [U. R. Pedersen {\it et al.}, Phys. Rev. Lett. {\bf 100},
015701 (2008)]. In order to investigate whether these correlations are present
also far from equilibrium constant-volume aging following a temperature down
jump from equilibrium was simulated for two strongly correlating liquids, an
asymmetric dumbbell model and Lewis-Wahnstr{\"o}m OTP, as well as for SPC water
that is not strongly correlating. For the two strongly correlating liquids
virial and potential energy follow each other closely during the aging towards
equilibrium. For SPC water, on the other hand, virial and potential energy vary
with little correlation as the system ages towards equilibrium. Further proof
that strong pressure-energy correlations express a configuration space property
comes from monitoring pressure and energy during the crystallization (reported
here for the first time) of supercooled Lewis-Wahnstr{\"o}m OTP at constant
temperature
Kink Localization under Asymmetric Double-Well Potential
We study diffuse phase interfaces under asymmetric double-well potential
energies with degenerate minima and demonstrate that the limiting sharp
profile, for small interface energy cost, on a finite space interval is in
general not symmetric and its position depends exclusively on the second
derivatives of the potential energy at the two minima (phases). We discuss an
application of the general result to porous media in the regime of solid-fluid
segregation under an applied pressure and describe the interface between a
fluid-rich and a fluid-poor phase. Asymmetric double-well potential energies
are also relevant in a very different field of physics as that of Brownian
motors. An intriguing analogy between our result and the direction of the dc
soliton current in asymmetric substrate driven Brownian motors is pointed out
Ultraviolet and charged particle irradiation of proposed solar cell coverslide materials and conductive coatings for the Helios spacecraft
Coverslide materials consisting of Corning 7940 fused silica, multilayers of titanium and manganese oxides (blue reflector), and indium oxide (conductive-coating) were exposed to 16 UVSC up to 800 EUVSH in vacuum. Slight changes in optical transmittance and optical absorptance were found in the (200-360) millimicron regions of the fused silica and conductive coating respectively. Exposure to 4 KeV protons and 4.5 KeV electrons in vacuum, produced decreases of several percent in transmittance, (200-360) millimicron region in the fused silicas after total fluxes less or = 10 to the 14th power particles/sq cm. Sheet resistance of the conductive coating increased above 1.0 kilo-ohm/square after a total flux less or = 10 to the 14th power particles/sq cm. Solar cells with coverglasses utilizing the indium oxide conductive coating were exposed to 1 Mev electrons and 1 Mev protons in air and in vacuum. Total fluxes ranged from 10 to the 11th power particles/sq cm to 10 to the 15th power particle/sq cm. There was no appreciable degradation in the resistance of the conductive coating during or after these tests
Estimating the density scaling exponent of viscous liquids from specific heat and bulk modulus data
It was recently shown by computer simulations that a large class of liquids
exhibits strong correlations in their thermal fluctuations of virial and
potential energy [Pedersen et al., Phys. Rev. Lett. 100, 015701 (2008)]. Among
organic liquids the class of strongly correlating liquids includes van der
Waals liquids, but excludes ionic and hydrogen-bonding liquids. The present
note focuses on the density scaling of strongly correlating liquids, i.e., the
fact their relaxation time tau at different densities rho and temperatures T
collapses to a master curve according to the expression tau propto
F(rho^gamma/T) [Schroder et al., arXiv:0803.2199]. We here show how to
calculate the exponent gamma from bulk modulus and specific heat data, either
measured as functions of frequency in the metastable liquid or extrapolated
from the glass and liquid phases to a common temperature (close to the glass
transition temperature). Thus an exponent defined from the response to highly
nonlinear parameter changes may be determined from linear response
measurements
Aging effects manifested in the potential energy landscape of a model glass former
We present molecular dynamics simulations of a model glass-forming liquid
(the binary Kob-Anderson Lennard-Jones model) and consider the distributions of
inherent energies and metabasins during aging. In addition to the typical
protocol of performing a temperature jump from a high temperature to a low
destination temperature, we consider the temporal evolution of the
distributions after an 'up-jump', i.e. from a low to a high temperature. In
this case the distribution of megabasin energies exhibits a transient two-peak
structure. Our results can qualitatively be rationalized in terms of a trap
model with a Gaussian distribution of trap energies. The analysis is performed
for different system sizes. A detailed comparison with the trap model is
possible only for a small system because of major averging effects for larger
systems.Comment: 16 pages, 14 figure
Contribution of G inhibitory protein alpha subunits in paradoxical hyperalgesia elicited by exceedingly low doses of morphine in mice.
Aims: Although morphine, at higher doses, induces analgesia, it may also enhance sensitivity to pain at extremely low doses as shown in studies for testing an animal's sensitivity to pain. We used an antisense approach capable of selectively down-regulating in vivo G(i)(G inhibitory protein),G(o) and G(s) members of the G(alpha), sub-family protein subunits in order to establish if these proteins might be implicated in the effects induced by extremely low morphine doses on acute thermonociception. Main methods: Mice pretreated with a morphine hyperalgesic dose (1 mu g/kg) were submitted to hot plate test after pre-treatment with antisense oligodeoxynucleotides (aODNs) targeting G(i alpha), G(o alpha) and G(s alpha) regulatory proteins. The association of G-protein (guanine nucleotide-binding regulatory protein) coupled receptors with G protein was investigated using co-immunoprecipitation procedure. Key findings: The downregulation of the G(i alpha 1-3) and G(o alpha 1) proteins reversed the licking latency responses induced by 1 mu g/kg morphine administration toward the basal value whereas downregulation of the G(o alpha 2) and G(s alpha) proteins did not significantly modify the hyperalgesic response. Significance: These results suggest that G inhibitory proteins play a role in the production of low dose evoked morphine hyperalgesia in mouse. Immunoprecipitation studies revealed that both mu opioid receptor (mu OR) and alpha(2) adrenoreceptor (alpha(2) AR) are bound to G inhibitory proteins in hyperalgesic response to morphine extremely low dose. Both mu OR and alpha(2) AR appear to be necessary for low morphine dose induced hyperalgesic response through G inhibitory proteins. (C) 2011 Elsevier Inc. All rights reserved
Role of potassium channels in the antinociception induced by agonists of alpha2-adrenoceptors
1. The effect of the administration of pertussis toxin (PTX) as well as modulators of different subtypes of K(+) channels on the antinociception induced by clonidine and guanabenz was evaluated in the mouse hot plate test. 2. Pretreatment with pertussis toxin (0.25 μg per mouse i.c.v.) 7 days before the hot-plate test, prevented the antinociception induced by both clonidine (0.08–0.2 mg kg(−1), s.c.) and guanabenz (0.1–0.5 mg kg(−1), s.c.). 3. The administration of the K(ATP) channel openers minoxidil (10 μg per mouse, i.c.v.), pinacidil (25 μg per mouse, i.c.v.) and diazoxide (100 mg kg(−1), p.o.) potentiated the antinociception produced by clonidine and guanabenz whereas the K(ATP) channel blocker gliquidone (6 μg per mouse, i.c.v.) prevented the α(2) adrenoceptor agonist-induced analgesia. 4. Pretreatment with an antisense oligonucleotide (aODN) to mKv1.1, a voltage-gated K(+) channel, at the dose of 2.0 nmol per single i.c.v. injection, prevented the antinociception induced by both clonidine and guanabenz in comparison with degenerate oligonucleotide (dODN)-treated mice. 5. The administration of the Ca(2+)-gated K(+) channel blocker apamin (0.5–2.0 ng per mouse, i.c.v.) never modified clonidine and guanabenz analgesia. 6. At the highest effective doses, none of the drugs used modified animals' gross behaviour nor impaired motor coordination, as revealed by the rota-rod test. 7. The present data demonstrate that both K(ATP) and mKv1.1 K(+) channels represent an important step in the transduction mechanism underlying central antinociception induced by activation of α(2) adrenoceptors
Predicting the Effective Temperature of a Glass
We explain the findings by Di Leonardo et al. [Phys. Rev. Lett. 84, 6054
(2000)] that the effective temperature of a Lennard-Jones glass depends only on
the final value of the density in the volume and/or temperature jump that
produces the glass phase. This is not only a property of the Lennard-Jones
liquid, but a feature of all strongly correlating liquids. For such liquids
data from a single quench simulation provides enough information to predict the
effective temperature of any glass produced by jumping from an equilibrium
state. This prediction is validated by simulations of the Kob-Andersen binary
Lennard-Jones liquid and shown not to apply for the non-strongly correlating
monatomic Lennard-Jones Gaussian liquid.Comment: 5 pages, 6 figure
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