646 research outputs found
Radiative Transfer Limits of Two-Frequency Wigner Distribution for Random Parabolic Waves
The present note establishes the self-averaging, radiative transfer limit for
the two-frequency Wigner distribution for classical waves in random media.
Depending on the ratio of the wavelength to the correlation length the limiting
equation is either a Boltzmann-like integral equation or a Fokker-Planck-like
differential equation in the phase space. The limiting equation is used to
estimate three physical parameters: the spatial spread, the coherence length
and the coherence bandwidth. In the longitudinal case, the Fokker-Planck-like
equation can be solved exactly.Comment: typos correcte
Design and development of a low temperature, inductance based high frequency ac susceptometer
We report on the development of an induction based low temperature high
frequency ac susceptometer capable of measuring at frequencies up to 3.5 MHz
and at temperatures between 2 K and 300 K. Careful balancing of the detection
coils and calibration have allowed a sample magnetic moment resolution of
at 1 MHz. We will discuss the design and
characterization of the susceptometer, and explain the calibration process. We
also include some example measurements on the spin ice material CdErS
and iron oxide based nanoparticles to illustrate functionality
Light-ion production in the interaction of 96 MeV neutrons with oxygen
Double-differential cross sections for light-ion (p, d, t, He-3 and alpha)
production in oxygen, induced by 96 MeV neutrons are reported. Energy spectra
are measured at eight laboratory angles from 20 degrees to 160 degrees in steps
of 20 degrees. Procedures for data taking and data reduction are presented.
Deduced energy-differential and production cross sections are reported.
Experimental cross sections are compared to theoretical reaction model
calculations and experimental data at lower neutron energies in the literature.
The measured proton data agree reasonably well with the results of the model
calculations, whereas the agreement for the other particles is less convincing.
The measured production cross sections for protons, deuterons, tritons and
alpha particles support the trends suggested by data at lower energies.Comment: 21 pages, 13 figures, submitted to Phys. Rev.
Time Reversal Communication in Rayleigh-Fading Broadcast Channels with Pinholes
The paper presents an analysis of the time reversal in independent-multipath
Rayleigh-fading channels with inputs (transmitters) and outputs
(receivers).
The main issues addressed are the condition of statistical stability, the
rate of information transfer and the effect of pinholes. The stability
condition is proved to be
for broadband channels and
for narrowband channels where is the symbol rate,
is the bandwidth and is the {\em effective} number (maybe
less than 1) of transmitters. It is shown that when the number of screens,
, is relatively low compared to the logarithm of numbers of pinholes
is given by the {\em harmonic} (or {\em inverse}) {\em sum} of
the number of transmitters and the numbers of pinholes at all screens.
The novel idea of the effective number of time reversal array (TRA) elements
is introduced to derive the stability condition and estimate the channel
capacity in the presence of multi-screen pinholes. The information rate, under
the constraints of the noise power per unit frequency and the average
total power , attains the supremum in the regime . In particular, when the
optimal information rate can be achieved with statistically stable, sharply
focused signals.Comment: Corrected typos and minor change of conten
Proximal tubule morphology after single nephron obstruction in the rat kidney
Proximal tubule morphology after single nephron obstruction in the rat kidney. This study examined the effects on proximal tubule morphology of blocking single nephrons with paraffin wax for one day, one week, or one month in the rat. Proximal tubule lumens were blocked with a short column of wax using micropuncture. Chronically blocked and control (normal) tubules were fixed by either intravascular or intraluminal perfusion of glutaraldehyde solution. Proximal tubule segments down-stream to the wax block were examined by light and transmission electron microscopy. Intraluminal Alcian blue dye, serial sectioning, and nephron microdissection techniques were used to identify nephrons. One day after obstruction, all proximal tubule cells downstream to the block were injured. Some recovery was seen. S1 and S2 segments showed more severe damage than S3 segments. Alcian blue, which normally is excluded from cells, entered the cytoplasm of some damaged S1-S2 cells. After one week of obstruction, the tubule appeared to have reconstituted itself, but cells were less differentiated than normal. One month after obstruction, blocked tubules were atrophied. Tubule cells were simplified and were surrounded by a thickened basement membrane. The results suggest that prolonged proximal tubule blockade produces injury and atrophy of the proximal tubule probably due to ischemia and interruption of normal reabsorptive activity
Measurement of the Absolute Differential Cross Section for np Elastic Scattering at 194 MeV
A tagged medium-energy neutron beam has been used in a precise measurement of
the absolute differential cross section for np back-scattering. The results
resolve significant discrepancies within the np database concerning the angular
dependence in this regime. The experiment has determined the absolute
normalization with 1.5% uncertainty, suitable to verify constraints of
supposedly comparable precision that arise from the rest of the database in
partial wave analyses. The analysis procedures, especially those associated
with evaluation of systematic errors in the experiment, are described in detail
so that systematic uncertainties may be included in a reasonable way in
subsequent partial wave analysis fits incorporating the present results.Comment: 22 pages, 21 figures, submitted for publication in Physical Review
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