49,091 research outputs found
Pair creation and plasma oscillations
We describe aspects of particle creation in strong fields using a quantum
kinetic equation with a relaxation-time approximation to the collision term.
The strong electric background field is determined by solving Maxwell's
equation in tandem with the Vlasov equation. Plasma oscillations appear as a
result of feedback between the background field and the field generated by the
particles produced. The plasma frequency depends on the strength of the initial
background field and the collision frequency, and is sensitive to the necessary
momentum-dependence of dressed-parton masses.Comment: 11 pages, revteX, epsfig.sty, 5 figures; Proceedings of 'Quark Matter
in Astro- and Particlephysics', a workshop at the University of Rostock,
Germany, November 27 - 29, 2000. Eds. D. Blaschke, G. Burau, S.M. Schmid
Transport properties of a superconducting single-electron transistor coupled to a nanomechanical oscillator
We investigate a superconducting single-electron transistor capacitively
coupled to a nanomechanical oscillator and focus on the double Josephson
quasiparticle resonance. The existence of two coherent Cooper pair tunneling
events is shown to lead to pronounced backaction effects. Measuring the current
and the shot noise provides a direct way of gaining information on the state of
the oscillator. In addition to an analytical discussion of the linear-response
regime, we discuss and compare results of higher-order approximation schemes
and a fully numerical solution. We find that cooling of the mechanical
resonator is possible, and that there are driven and bistable oscillator states
at low couplings. Finally, we also discuss the frequency dependence of the
charge noise and the current noise of the superconducting single electron
transistor.Comment: 19 pages, 11 figures, published in PR
Measurement of spark probability of GEM detector for CBM muon chamber (MUCH)
The stability of triple GEM detector setups in an environment of high
energetic showers is studied. To this end the spark probability in a shower
environment is compared to the spark probability in a pion beam.Comment: 5 pages, 10 figure
Measuring the Cosmic Ray Muon-Induced Fast Neutron Spectrum by (n,p) Isotope Production Reactions in Underground Detectors
While cosmic ray muons themselves are relatively easy to veto in underground
detectors, their interactions with nuclei create more insidious backgrounds
via: (i) the decays of long-lived isotopes produced by muon-induced spallation
reactions inside the detector, (ii) spallation reactions initiated by fast
muon-induced neutrons entering from outside the detector, and (iii) nuclear
recoils initiated by fast muon-induced neutrons entering from outside the
detector. These backgrounds, which are difficult to veto or shield against, are
very important for solar, reactor, dark matter, and other underground
experiments, especially as increased sensitivity is pursued. We used fluka to
calculate the production rates and spectra of all prominent secondaries
produced by cosmic ray muons, in particular focusing on secondary neutrons, due
to their importance. Since the neutron spectrum is steeply falling, the total
neutron production rate is sensitive just to the relatively soft neutrons, and
not to the fast-neutron component. We show that the neutron spectrum in the
range between 10 and 100 MeV can instead be probed by the (n, p)-induced
isotope production rates 12C(n, p)12B and 16O(n, p)16N in oil- and water-based
detectors. The result for 12B is in good agreement with the recent KamLAND
measurement. Besides testing the calculation of muon secondaries, these results
are also of practical importance, since 12B (T1/2 = 20.2 ms, Q = 13.4 MeV) and
16N (T1/2 = 7.13 s, Q = 10.4 MeV) are among the dominant spallation backgrounds
in these detectors
Rashba quantum wire: exact solution and ballistic transport
The effect of Rashba spin-orbit interaction in quantum wires with hard-wall
boundaries is discussed. The exact wave function and eigenvalue equation are
worked out pointing out the mixing between the spin and spatial parts. The
spectral properties are also studied within the perturbation theory with
respect to the strength of the spin-orbit interaction and diagonalization
procedure. A comparison is done with the results of a simple model, the
two-band model, that takes account only of the first two sub-bands of the wire.
Finally, the transport properties within the ballistic regime are analytically
calculated for the two-band model and through a tight-binding Green function
for the entire system. Single and double interfaces separating regions with
different strengths of spin-orbit interaction are analyzed injecting carriers
into the first and the second sub-band. It is shown that in the case of a
single interface the spin polarization in the Rashba region is different from
zero, and in the case of two interfaces the spin polarization shows
oscillations due to spin selective bound states
Hanbury-Brown-Twiss correlations and noise in the charge transfer statistics through a multiterminal Kondo dot
We analyze the full counting statistics of charge transfer through a quantum
dot in the Kondo regime, when coupled to an arbitrary number of terminals N.
At the unitary Kondo fixed point and for N>2 we recover distinct
anticorrelations of currents in concurring transport channels, which are
related to the fermionic
Hanbury Brown and Twiss (HBT) antibunching.
This effect weakens as one moves away from the fixed point.
Furthermore, we identify a special class of current correlations that are due
entirely to the virtual polarization of the Kondo singlet.
These can be used for extracting information on the parameters of the
underlying Fermi-liquid model.Comment: 5 page
Genetic and serological heterogeneity of the supertypic HLA-B locus specificities Bw4 and Bw6
Gene cloning and sequencing of the HLA-B
locus split antigens B38 (B16.1) and B39 (B16.2) allowed
localization of their subtypic as well as their public
specificities HLA-Bw4 or -Bw6 to the c~-helical region of
the c~ 1 domain flanked by the amino acid positions 74-83.
Comparison of their amino acid sequences with those of
other HLA-B-locus alleles established HLA-Bw6 to be
distinguished by Ser at residue 77 and Asn at residue 80.
In contrast, HLA-Bw4 is characterized by at least seven
different patterns of amino acid exchanges at positions 77
and 80-83. Reactivity patterns of Bw4- or Bw6-specific
monoclonal antibodies reveal two alloantigenic epitopes
contributing to the HLA-Bw4 or -Bw6 specificity residing
next to the region of highest diversity of the cr domain
Thermal suppression of surface barrier in ultrasmall superconducting structures
In the recent experiment by Cren \textit{et al.} [Phys. Rev. Lett.
\textbf{102}, 127005 (2009)], no hysteresis for vortex penetration and
expulsion from the nano-island of Pb was observed. In the present paper, we
argue that this effect can be associated with the thermoactivated surmounting
of the surface barrier by a vortex. The typical entrance (exit) time is found
analytically from the Fokker-Planck equation, written in the form suitable for
the extreme vortex confinement. We show that this time is several orders of
magnitude smaller than 1 second under the conditions of the experiment
considered. Our results thus demonstrate a possibility for the thermal
suppression of the surface barrier in nanosized low- superconductors. We
also briefly discuss other recent experiments on vortices in related
structures.Comment: 12 pages, 2 figure
Conceptualizing throughput legitimacy: procedural mechanisms of accountability, transparency, inclusiveness and openness in EU governance
This symposium demonstrates the potential for throughput legitimacy as a concept for shedding empirical light on the strengths and weaknesses of multi-level governance, as well as challenging the concept theoretically. This article introduces the symposium by conceptualizing throughput legitimacy as an ‘umbrella concept’, encompassing a constellation
of normative criteria not necessarily empirically interrelated. It argues that in order to interrogate multi-level governance processes in all their complexity, it makes sense for us to develop normative standards that are not naïve about the empirical realities of how power is exercised within multilevel governance, or how it may interact with legitimacy. We argue that while throughput legitimacy has its normative limits, it can be substantively useful for these purposes. While being no replacement for input and output legitimacy, throughput legitimacy offers distinctive normative criteria— accountability, transparency, inclusiveness and openness— and points towards substantive institutional reforms.Published versio
The Two-Loop Euler-Heisenberg Lagrangian in Dimensional Renormalization
We clarify a discrepancy between two previous calculations of the two-loop
QED Euler-Heisenberg Lagrangian, both performed in proper-time regularization,
by calculating this quantity in dimensional regularization.Comment: 12 pages, standard Latex, no figures, uses a4wide.st
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