5,527 research outputs found
Synchronization of electrically coupled resonate-and-fire neurons
Electrical coupling between neurons is broadly present across brain areas and
is typically assumed to synchronize network activity. However, intrinsic
properties of the coupled cells can complicate this simple picture. Many cell
types with strong electrical coupling have been shown to exhibit resonant
properties, and the subthreshold fluctuations arising from resonance are
transmitted through electrical synapses in addition to action potentials. Using
the theory of weakly coupled oscillators, we explore the effect of both
subthreshold and spike-mediated coupling on synchrony in small networks of
electrically coupled resonate-and-fire neurons, a hybrid neuron model with
linear subthreshold dynamics and discrete post-spike reset. We calculate the
phase response curve using an extension of the adjoint method that accounts for
the discontinuity in the dynamics. We find that both spikes and resonant
subthreshold fluctuations can jointly promote synchronization. The subthreshold
contribution is strongest when the voltage exhibits a significant post-spike
elevation in voltage, or plateau. Additionally, we show that the geometry of
trajectories approaching the spiking threshold causes a "reset-induced shear"
effect that can oppose synchrony in the presence of network asymmetry, despite
having no effect on the phase-locking of symmetrically coupled pairs
'Unlicensed' natural killer cells dominate the response to cytomegalovirus infection.
Natural killer (NK) cells expressing inhibitory receptors that bind to self major histocompatibility complex (MHC) class I are 'licensed', or rendered functionally more responsive to stimulation, whereas 'unlicensed' NK cells lacking receptors for self MHC class I are hyporesponsive. Here we show that contrary to the licensing hypothesis, unlicensed NK cells were the main mediators of NK cell-mediated control of mouse cytomegalovirus infection in vivo. Depletion of unlicensed NK cells impaired control of viral titers, but depletion of licensed NK cells did not. The transfer of unlicensed NK cells was more protective than was the transfer of licensed NK cells. Signaling by the tyrosine phosphatase SHP-1 limited the proliferation of licensed NK cells but not that of unlicensed NK cells during infection. Thus, unlicensed NK cells are critical for protection against viral infection
A Simple Boltzmann Transport Equation for Ballistic to Diffusive Transient Heat Transport
Developing simplified, but accurate, theoretical approaches to treat heat
transport on all length and time scales is needed to further enable scientific
insight and technology innovation. Using a simplified form of the Boltzmann
transport equation (BTE), originally developed for electron transport, we
demonstrate how ballistic phonon effects and finite-velocity propagation are
easily and naturally captured. We show how this approach compares well to the
phonon BTE, and readily handles a full phonon dispersion and energy-dependent
mean-free-path. This study of transient heat transport shows i) how fundamental
temperature jumps at the contacts depend simply on the ballistic thermal
resistance, ii) that phonon transport at early times approach the ballistic
limit in samples of any length, and iii) perceived reductions in heat
conduction, when ballistic effects are present, originate from reductions in
temperature gradient. Importantly, this framework can be recast exactly as the
Cattaneo and hyperbolic heat equations, and we discuss how the key to capturing
ballistic heat effects is to use the correct physical boundary conditions.Comment: 9 pages, 5 figure
The association between church attendance and psychological health in Northern Ireland : a national representative survey among adults allowing for sex differences and denominational difference
This study extends previous research concerning the association between religion and psychological health in six ways: (1) by focusing clearly on religious attendance (church attendance); (2) by employing a robust measure of psychological distress (GHQ-12); (3) by studying a highly religious culture (Northern Ireland); (4) by taking sex differences into account (male or female); (5) by taking denominational differences into account (Catholic or Protestant); (6) and by obtaining a national representative sample (N = 4,281 adults aged 16 and above). Results from a 2 (sex) by 2 (denomination) ANCOVA demonstrated that Catholics recorded significantly lower levels of psychological health compared to Protestants, and that females showed significantly lower levels of psychological health compared to males. In addition, females reported higher frequency of religious service attendance than males, and Catholics reported higher attendance rates than Protestants. A significant positive association was found between frequency of religious attendance and GHQ-12 scores, and this association was moderated by sex and denomination. In conclusion, the results suggest that there may be sex and denominational differences in further understanding the relationship between frequency of religious attendance and psychological health
Key results of the mini-dome Fresnel lens concentrator array development program under recently completed NASA and SDIO SBIR projects
Since 1986, ENTECH and the NASA Lewis Research Center have been developing a new photovoltaic concentrator system for space power applications. The unique refractive system uses small, dome shaped Fresnel lenses to focus sunlight onto high efficiency photovoltaic concentrator cells which use prismatic cell covers to further increase their performance. Highlights of the five-year development include near Air Mass Zero (AM0) Lear Jet flight testing of mini-dome lenses (90 pct. net optical efficiency achieved); tests verifying sun-pointing error tolerance with negligible power loss; simulator testing of prism-covered GaAs concentrator cells (24 pct. AM0 efficiency); testing of prism-covered Boeing GaAs/GaSb tandem cells (31 pct. AM0 efficiency); and fabrication and outdoor testing of a 36-lens/cell element panel. These test results have confirmed previous analytical predictions which indicate substantial performance improvements for this technology over current array systems. Based on program results to date, it appears than an array power density of 300 watts/sq m and a specific power of 100 watts/kg can be achieved in the near term. All components of the array appear to be readily manufacturable from space-durable materials at reasonable cost. A concise review is presented of the key results leading to the current array, and further development plans for the future are briefly discussed
Effect of Multiple Higgs Fields on the Phase Structure of the SU(2)-Higgs Model
The SU(2)-Higgs model, with a single Higgs field in the fundamental
representation and a quartic self-interaction, has a Higgs region and a
confinement region which are analytically connected in the parameter space of
the theory; these regions thus represent a single phase. The effect of multiple
Higgs fields on this phase structure is examined via Monte Carlo lattice
simulations. For the case of N>=2 identical Higgs fields, there is no remaining
analytic connection between the Higgs and confinement regions, at least when
Lagrangian terms that directly couple different Higgs flavours are omitted. An
explanation of this result in terms of enhancement from overlapping phase
transitions is explored for N=2 by introducing an asymmetry in the hopping
parameters of the Higgs fields. It is found that an enhancement of the phase
transitions can still occur for a moderate (10%) asymmetry in the resulting
hopping parameters.Comment: 10 pages, 8 figures. References updated and minor typos correcte
Extension of a Kinetic-Theory Approach for Computing Chemical-Reaction Rates to Reactions with Charged Particles
Recently introduced molecular-level chemistry models that predict equilibrium and nonequilibrium reaction rates using only kinetic theory and fundamental molecular properties (i.e., no macroscopic reaction rate information) are extended to include reactions involving charged particles and electronic energy levels. The proposed extensions include ionization reactions, exothermic associative ionization reactions, endothermic and exothermic charge exchange reactions, and other exchange reactions involving ionized species. The extensions are shown to agree favorably with the measured Arrhenius rates for near-equilibrium conditions
- …