3,201 research outputs found
Analytical approximation of spectrum for pulse X-ray tubes
Among the main characteristics of the pulsed X-ray apparatuses the spectral energy characteristics are the most important ones: the spectral distribution of the photon energy, effective and maximum energy of quanta. Knowing the spectral characteristics of the radiation of pulse sources is very important for the practical use of them in non-destructive testing. We have attempted on the analytical approximation of the pulsed X-ray apparatuses spectra obtained in the different experimental papers. The results of the analytical approximation of energy spectrum for pulse X-ray tube are presented. Obtained formulas are adequate to experimental data and can be used by designing pulsed X-ray apparatuses
Vacuum Cherenkov radiation
Within the classical Maxwell-Chern-Simons limit of the Standard-Model
Extension (SME), the emission of light by uniformly moving charges is studied
confirming the possibility of a Cherenkov-type effect. In this context, the
exact radiation rate for charged magnetic point dipoles is determined and found
in agreement with a phase-space estimate under certain assumptions.Comment: 4 pages, REVTeX
Random matrix models for phase diagrams
We describe a random matrix approach that can provide generic and readily
soluble mean-field descriptions of the phase diagram for a variety of systems
ranging from QCD to high-T_c materials. Instead of working from specific
models, phase diagrams are constructed by averaging over the ensemble of
theories that possesses the relevant symmetries of the problem. Although
approximate in nature, this approach has a number of advantages. First, it can
be useful in distinguishing generic features from model-dependent details.
Second, it can help in understanding the `minimal' number of symmetry
constraints required to reproduce specific phase structures. Third, the
robustness of predictions can be checked with respect to variations in the
detailed description of the interactions. Finally, near critical points, random
matrix models bear strong similarities to Ginsburg-Landau theories with the
advantage of additional constraints inherited from the symmetries of the
underlying interaction. These constraints can be helpful in ruling out certain
topologies in the phase diagram. In this Key Issue, we illustrate the basic
structure of random matrix models, discuss their strengths and weaknesses, and
consider the kinds of system to which they can be applied.Comment: 29 pages, 2 figures, uses iopart.sty. Author's postprint versio
Photocurrent, Rectification, and Magnetic Field Symmetry of Induced Current Through Quantum Dots
We report mesoscopic dc current generation in an open chaotic quantum dot
with ac excitation applied to one of the shape-defining gates. For excitation
frequencies large compared to the inverse dwell time of electrons in the dot
(i.e., GHz), we find mesoscopic fluctuations of induced current that are fully
asymmetric in the applied perpendicular magnetic field, as predicted by recent
theory. Conductance, measured simultaneously, is found to be symmetric in
field. In the adiabatic (i.e., MHz) regime, in contrast, the induced current is
always symmetric in field, suggesting its origin is mesoscopic rectification.Comment: related papers at http://marcuslab.harvard.ed
Quasiclassical fluctuations of the superconductor proximity gap in a chaotic system
We calculate the sample-to-sample fluctuations in the excitation gap of a
chaotic dynamical system coupled by a narrow lead to a superconductor. Quantum
fluctuations on the order of magnitude of the level spacing, predicted by
random-matrix theory, apply if (with the
Ehrenfest time and the Thouless energy). For \tau_E\agt\hbar/ E_T the
fluctuations are much greater than the level spacing. We demonstrate the
quasiclassical nature of the gap fluctuations in the large- regime by
correlating them to an integral over the classical dwell-time distribution.Comment: 4 pages, 3 figure
Cherenkov Radiation from Pairs and Its Effect on Induced Showers
We calculate the Cherenkov radiation from an pair at small
separations, as occurs shortly after a pair conversion. The radiation is
reduced (compared to that from two independent particles) when the pair
separation is smaller than the wavelength of the emitted light. We estimate the
reduction in light in large electromagnetic showers, and discuss the
implications for detectors that observe Cherenkov radiation from showers in the
Earth's atmosphere, as well as in oceans and Antarctic ice.Comment: Final version, with minor changes, to appear in PRD. 5 pages with 4
figure
Improved Search for Heavy Neutrinos in the Decay
A search for massive neutrinos has been made in the decay . No evidence was found for extra peaks in the positron energy spectrum
indicative of pion decays involving massive neutrinos (). Upper limits (90 \% C.L.) on the neutrino mixing matrix element
in the neutrino mass region 60--135 MeV/ were set, which are
%representing an order of magnitude improvement over previous results
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