6,641 research outputs found
A basic lock-in amplifier experiment for the undergraduate laboratory
We describe a basic experiment for the undergraduate laboratory that demonstrates aspects of both, the science and the art of precision electronic measurements. The essence of the experiment is to measure the resistance of a small length of brass-wire to high accuracy using a simple voltage divider and a lock-in amplifier. By performing the measurement at different frequencies and different drive currents, one observes various random noise sources and systematic measurement effects
Superkamiokande and solar antineutrinos
We propose to exploit the angular distribution of the positrons emitted in
the inverse beta decay to extract a possible antineutrino signal from the
Superkamiokande background. From the statistics collected in just 101.9 days
one obtains a model independent upper bound on the antineutrino flux (for
energy greater than 8.3 MeV) Phi < 9*10^4 cm^-2 s^-1 at the 95% C.L. By
assuming the same energy spectrum as for the 8B neutrinos, the 95% C.L. bound
is Phi < 6*10^4 cm^-2 s^-1. Within three years of data taking, the sensitivity
to neutrino-antineutrino transition probability will reach the 1% level, thus
providing a stringent test of hybrid oscillation models.Comment: 7 pages, 1 figure, Late
Electron Correlations in the Quasi-Two-Dimensional Organic Conductor -(BEDT-TTF)I investigated by C NMR
We report a C-NMR study on the ambient-pressure metallic phase of the
layered organic conductor -(BEDT-TTF)I [BEDT-TTF:
bisethylenedithio-tetrathiafulvalene], which is expected to connect the physics
of correlated electrons and Dirac electrons under pressure. The orientation
dependence of the NMR spectra shows that all BEDT-TTF molecules in the unit
cell are to be seen equivalent from a microscopic point of view. This feature
is consistent with the orthorhombic symmetry of the BEDT-TTF sublattice and
also indicates that the monoclinic sublattice, which should make three
molecules in the unit cell nonequivalent, is not practically influential on the
electronic state in the conducting BEDT-TTF layers at ambient pressure. There
is no signature of charge disproportionation in opposition to most of the
-type BEDT-TTF salts.
The analyses of NMR Knight shift, , and the nuclear spin-lattice
relaxation rate, , revealed that the degree of electron correlation,
evaluated by the Korringa ratio [)], is in an
intermediate regime. However, NMR relaxation rate is enhanced above
200K, which possibly indicates that the system enters into a quantum
critical regime of charge-order fluctuations as suggested theoretically.Comment: 19pages, 6figure
On the Analysis of the Bifurcation Sets of Equilibrium Points in Parameter Space
WeB6 Regular Session: Nonlinear System Theory II, Paper WeB6.3Abstract: This paper addresses the problems of characterizing and estimating the bifurcation sets of equilibrium points in multi-parameter space of a class of nonlinear dynamical systems. Specifically, we investigate the sets of parameters that lead to saddle-node bifurcations and Hopf bifurcations at an equilibrium point of interest. First, a characterization of these sets is provided in terms of the zeros of some functions. Second, this characterization is exploited to estimate such sets through convex programming for the case of polynomial dynamical systems. In particular, two conditions are proposed for establishing whether a sublevel set of a given polynomial does not contain parameters that lead to bifurcations. By using these conditions, the largest of such sublevel sets can be estimated by solving an eigenvalue problem. Some numerical examples illustrate the proposed results.published_or_final_versio
Glutamate induces autophagy via the two-pore channels in neural cells
NAADP (nicotinic acid adenine dinucleotide phosphate) has been proposed as a second messenger for glutamate in neuronal and glial cells via the activation of the lysosomal Ca2+ channels TPC1 and TPC2. However, the activities of glutamate that are mediated by NAADP remain unclear. In this study, we evaluated the effect of glutamate on autophagy in astrocytes at physiological, non-toxic concentration. We found that glutamate induces autophagy at similar extent as NAADP. By contrast, the NAADP antagonist NED-19 or SiRNA-mediated inhibition of TPC1/2 decreases autophagy induced by glutamate, confirming a role for NAADP in this pathway. The involvement of TPC1/2 in glutamate-induced autophagy was also confirmed in SHSY5Y neuroblastoma cells. Finally, we show that glutamate leads to a NAADP-dependent activation of AMPK, which is required for autophagy induction, while mTOR activity is not affected by this treatment. Taken together, our results indicate that glutamate stimulates autophagy via NAADP/TPC/AMPK axis, providing new insights of how Ca2+ signalling glutamate-mediated can control the cell metabolism in the central nervous system
Site-site memory equation approach in study of density/pressure dependence of translational diffusion coefficient and rotational relaxation time of polar molecular solutions: acetonitrile in water, methanol in water, and methanol in acetonitrile
We present results of theoretical study and numerical calculation of the
dynamics of molecular liquids based on combination of the memory equation
formalism and the reference interaction site model - RISM. Memory equations for
the site-site intermediate scattering functions are studied in the
mode-coupling approximation for the first order memory kernels, while
equilibrium properties such as site-site static structure factors are deduced
from RISM. The results include the temperature-density(pressure) dependence of
translational diffusion coefficients D and orientational relaxation times t for
acetonitrile in water, methanol in water and methanol in acetonitrile, all in
the limit of infinite dilution. Calculations are performed over the range of
temperatures and densities employing the SPC/E model for water and optimized
site-site potentials for acetonitrile and methanol. The theory is able to
reproduce qualitatively all main features of temperature and density
dependences of D and t observed in real and computer experiments. In
particular, anomalous behavior, i.e. the increase in mobility with density, is
observed for D and t of methanol in water, while acetonitrile in water and
methanol in acetonitrile do not show deviations from the ordinary behavior. The
variety exhibited by the different solute-solvent systems in the density
dependence of the mobility is interpreted in terms of the two competing origins
of friction, which interplay with each other as density increases: the
collisional and dielectric frictions which, respectively, increase and decrease
with increasing density.Comment: 13 pages, 8 eps-figures, 3 tables, RevTeX4-forma
Phenomenological interaction between current quarks
We construct a phenomenological model which describes the dynamical chiral
symmetry breaking (DCSB) of QCD vacuum and reproduces meson spectra. Quark
condensates, the pion decay constant, and meson spectra are well reproduced by
phenomenological interaction which consists of a linear confining potential, a
Coulombic potential, and the 't Hooft determinant interaction. In this model,
the 't Hooft determinant interaction plays a important role not to only
\eta,\eta' mass difference, but other meson masses through DCSB.Comment: 18 pages, LaTe
Creation of 1-D Novel Structure inside Single-Walled Carbon Nanotubes Using Plasma Ion Irradiation Method
Proceedings of 2003 Third IEEE Conference on Nanotechnolog
- …