1,713 research outputs found
GRB spectral parameter modeling
Fireball model of the gamma-ray bursts (GRBs) predicts generation of numerous
internal shocks, which efficiently accelerate charged particles and generate
relatively small-scale stochastic magnetic and electric fields. The accelerated
particles diffuse in space due to interaction with the random waves and so emit
so called Diffusive Synchrotron Radiation (DSR) in contrast to standard
synchrotron radiation they would produce in a large-scale regular magnetic
fields. In this contribution we present key results of detailed modeling of the
GRB spectral parameters, which demonstrate that the non-perturbative DSR
emission mechanism in a strong random magnetic field is consistent with
observed distributions of the Band parameters and also with cross-correlations
between them.Comment: 3 pages; IAU symposium # 274 "Advances in Plasma Astrophysics
Searching for dark matter sterile neutrino in laboratory
If the dark matter of the Universe is made of sterile neutrinos with the mass
in keV region they can be searched for with the help of X-ray satellites. We
discuss the prospects of laboratory experiments that can be competitive and
complimentary to Space missions. We argue that the detailed study of beta
decays of tritium and other nuclei with the help of Cold Target Recoil Ion
Momentum Spectroscopy (COLTRIMS) can potentially enter into interesting
parameter range and even supersede the current astronomical bounds on the
properties of dark matter sterile neutrino.Comment: RevTex, 6 pages, 1 figure. Journal version accepted in Phys.Rev.
Semiclassical Calculation of Multiparticle Scattering Cross Sections in Classicalizing Theories
It has been suggested in arXiv:1010.1415 that certain derivatively coupled
non-renormalizable scalar field theories might restore the perturbative
unitarity of high energy hard scatterings by classicalization, i.e. formation
of multiparticle states of soft quanta. Here we apply the semiclassical method
of calculating the multiparticle production rates to the scalar
Dirac-Born-Infeld (DBI) theory which is suggested to classicalize. We find that
the semiclassical method is applicable for the energies in the final state
above the cutoff scale of the theory L_*^{-1}. We encounter that the cross
section of the process two to N ceases to be exponentially suppressed for the
particle number in the final state N smaller than a critical particle number
N_{crit} ~ (E L_*)^{4/3}. It coincides with the typical particle number
produced in two-particle collisions at high energies predicted by
classicalization arguments.Comment: 17 pages, 4 figures, v2. Minor changes to match the published versio
Opioid Signal Transduction in Intact and Fragmented SH-SY5Y Neural Cells
Parameters of ligand binding, stimulation of low- K m GTPase, and inhibition of adenylate cyclase were determined in intact human neuroblastoma SH-SY5Y cells and in their isolated membranes, both suspended in identical physiological buffer medium. In cells, the Μ-selective opioid agonist [ 3 H]Tyr-D-Ala-Gly(Me)Phe-Gly-ol ([ 3 H]DAMGO) bound to two populations of sites with K D values of 3.9 and 160 n M , with <10% of the sites in the high-affinity state. Both sites were also detected at 4°C and were displaced by various opioids, including quaternary naltrexone. The opioid antagonist [ 3 H]naltrexone bound to a single population of sites, and in cells treated with pertussis toxin the biphasic displacement of [ 3 H]naltrexone by DAMGO became monophasic with only low-affinity binding present. The toxin specifically reduced high-affinity agonist binding but had no effect on the binding of [ 3 H]naltrexone. In isolated membranes, both agonist and antagonist bound to a single population of receptor sites with affinities similar to that of the high-affinity binding component in cells. Addition of GTP to membranes reduced the B max for [ 3 H]DAMGO by 87% and induced a linear ligand binding component; a low-affinity binding site, however, could not be saturated. Compared with results obtained with membranes suspended in Tris buffer, agonist binding, including both receptor density and affinity, in the physiological medium was attenuated. The results suggest that high-affinity opioid agonist binding represents the ligand-receptor-guanine nucleotide binding protein (G protein) complex present in cells at low density due to modulation by endogenous GTP. Opioid receptor coupling to adenylate cyclase in intact and fragmented cells occurred with similar efficiency: DAMGO inhibited adenylate cyclase with K i , values of 11 n M in cells and 26 n M in lysates, with 30% maximal inhibition in both preparations. Receptor coupling to G protein in membranes occurred with similar parameters: DAMGO stimulated low- K m GTPase with a K s of 31 n M and an S max of 48%. Both effector responses were blocked by naloxone and were strongly impaired by rigorous cell homogenization. These results indicate that opioid signal transduction in intact SH-SY5Y cells and their appropriately isolated membranes functions with similar efficiencies involving a large reserve of uncoupled receptors.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66450/1/j.1471-4159.1992.tb10032.x.pd
Advances in Engineering and Application of Optogenetic Indicators for Neuroscience
Our ability to investigate the brain is limited by available technologies that can record biological processes in vivo with suitable spatiotemporal resolution. Advances in optogenetics now enable optical recording and perturbation of central physiological processes within the intact brains of model organisms. By monitoring key signaling molecules noninvasively, we can better appreciate how information is processed and integrated within intact circuits. In this review, we describe recent efforts engineering genetically-encoded fluorescence indicators to monitor neuronal activity. We summarize recent advances of sensors for calcium, potassium, voltage, and select neurotransmitters, focusing on their molecular design, properties, and current limitations. We also highlight impressive applications of these sensors in neuroscience research. We adopt the view that advances in sensor engineering will yield enduring insights on systems neuroscience. Neuroscientists are eager to adopt suitable tools for imaging neural activity in vivo, making this a golden age for engineering optogenetic indicators. Keywords: optogenetic tools; neuroscience; calcium sensor; voltage sensor; neurotransmitter
Mechanisms and dynamics of the metastable decay in Ar-2(+)
A detailed experimental as well as theoretical investigation of the properties of the metastable dissociation Ar-2(+)--\u3eAr++Ar is presented. The mass-analyzed ion kinetic energy (MIKE) scan technique has been performed using a three sector field mass spectrometer. The possible mechanisms of the metastability of Ar-2(+) have been examined and the observed decay process is assigned to the II(1/2)(u)--\u3eI(1/2)(g) bound to continuum radiative transition, in agreement with earlier work. The calculation of the theoretical shape of the kinetic energy release distribution of fragment ions allowed us to construct the theoretical MIKE peak and compare it with the raw experimental data. The accuracy of various sets of potential energy curves for Ar-2(+) is discussed, as well as the way of production of the metastable Ar-2(+)[II(1/2)(u)] electronic state by electron impact. Excellent agreement between the experimental data and theoretical model has been observed. (C) 2004 American Institute of Physics
Field induced density wave in the heavy fermion compound CeRhIn5
Metals containing Ce often show strong electron correlations due to the
proximity of the 4f state to the Fermi energy, leading to strong coupling with
the conduction electrons. This coupling typically induces a variety of
competing ground states, including heavy-fermion metals, magnetism and
unconventional superconductivity. The d-wave superconductivity in CeTMIn5
(TM=Co, Rh, Ir) has attracted significant interest due to its qualitative
similarity to the cuprate high-Tc superconductors. Here, we show evidence for a
field induced phase-transition to a state akin to a density-wave (DW) in the
heavy fermion CeRhIn5, existing in proximity to its unconventional
superconductivity. The DW state is signaled by a hysteretic anomaly in the
in-plane resistivity accompanied by the appearance of non-linear electrical
transport at high magnetic fields (>27T), which are the distinctive
characteristics of density-wave states. The unusually large hysteresis enables
us to directly investigate the Fermi surface of a supercooled electronic system
and to clearly associate a Fermi surface reconstruction with the transition.
Key to our observation is the fabrication of single crystal microstructures,
which are found to be highly sensitive to "subtle" phase transitions involving
only small portions of the Fermi surface. Such subtle order might be a common
feature among correlated electron systems, and its clear observation adds a new
perspective on the similarly subtle CDW state in the cuprates.Comment: Accepted in Nature Communication
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