35,692 research outputs found
Probing Pauli Blocking Factors in Quantum Pumps with Broken Time-Reversal Symmetry
A recently demonstrated quantum electron pump is discussed within the
framework of photon-assisted tunneling. Due to lack of time-reversal symmetry,
different results are obtained for the pump current depending on whether or not
final-state Pauli blocking factors are used when describing the tunneling
process. Whilst in both cases the current depends quadratically on the driving
amplitude for moderate pumping, a marked difference is predicted for the
temperature dependence. With blocking factors the pump current decreases
roughly linearly with temperature until k_B T ~ \hbar\omega is reached, whereas
without them it is unaffected by temperature, indicating that the entire Fermi
sea participates in the electronic transport.Comment: 4 pages in RevTex4 (beta4), 6 figures; status: to appear in PR
Dynamics of a two-level system coupled with a quantum oscillator in the very strong coupling limit
The time-dependent behavior of a two-level system interacting with a quantum
oscillator system is analyzed in the case of a coupling larger than both the
energy separation between the two levels and the energy of quantum oscillator
(, where is the frequency of the
transition between the two levels, is the frequency of the
oscillator, and is the coupling between the two-level system and the
oscillator). Our calculations show that the amplitude of the expectation value
of the oscillator coordinate decreases as the two-level system undergoes the
transition from one level to the other, while the transfer probability between
the levels is staircase-like. This behavior is explained by the interplay
between the adiabatic and the non-adiabatic regimes encountered during the
dynamics with the system acting as a quantum counterpart of the Landau-Zener
model. The transition between the two levels occurs as long as the expectation
value of the oscillator coordinate is driven close to zero. On the contrary, if
the initial conditions are set such that the expectation values of the
oscillator coordinate are far from zero, the system will remain locked on one
level.Comment: 4 pages, 4 figures, to be published in Physical Review
Level Splitting in Association with the Multiphoton Bloch-Siegert Shift
We present a unitary equivalent spin-boson Hamiltonian in which terms can be
identified which contribute to the Bloch-Siegert shift, and to the level
splittings at the anticrossings associated with the Bloch-Siegert resonances.
First-order degenerate perturbation theory is used to develop approximate
results in the case of moderate coupling for the level splitting.Comment: 8 pages, 2 figure
Recommended from our members
Editorial.
Welcome to the third issue of our journal . We are delighted to feature in this issue two peer-reviewed papers looking in detail at some of the outcomes of the ring-fenced money used for researcher development in the UK under the guise of Roberts funding. In her paper looking at impact of the training provided by this funding on late stage doctoral student researchers, Walsh and colleagues draw our attention to detailed analysis of impact via a variety of evaluation approaches. She also alerts us to the question of whether such development programmes should run alongside the traditional apprenticeship style training of such students. The second paper by Heading and colleagues provides a detailed example of a development programme event in information management and provides further evidence for impact of such training.
Bai and Hudson move the focus to the research –teaching nexus and highlight the difficulty for TEFL staff in Chinese HEIs to develop a research strand in their careers. The importance in developing research capacity, providing support and mentoring to such staff is shown to be pivotal in their development.
Finally conceptions of research from a variety of viewpoints are analyzed by Pitcher. Pitcher considers how the PhD itself, alongwith how the knowledge and outcomes of PhD research are perceived. In a preliminary survey of students on these matters, Pitcher highlights the importance of alignment with these concepts between student and supervisor thus avoiding difficulties between apprentice and supervisor as the research progresses which might inhibit development
An evaluation of Skylab (EREP) remote sensing techniques applied to investigations of crustal structure
The author has identified the following significant results. Film positives (70mm) from all six S190A multispectral photographic camera stations for any one scene can be registered and analyzed in a color additive viewer. Using a multispectral viewer, S190A and B films can be projected directly onto published geologic and topographic maps at scales as large as 1:62,500 and 1:24,000 without significant loss of detail. S190A films and prints permit the detection of faults, fractures, and other linear features not visible in any other space imagery. S192 MSS imagery can be useful for rock-type discrimination studies and delineation of linear patterns and arcuate anomalies. Anomalous color reflectances and arcuate color patterns revealed mineralized zones, copper deposits, vegetation, and volcanic rocks in various locations such as Panamint Range (CA), Greenwater (Death Valley), Lava Mountains (CA), northwestern Arizona, and Coso Hot Springs (CA)
Far-from-equilibrium Ostwald ripening in electrostatically driven granular powders
We report the first experimental study of cluster size distributions in
electrostatically driven granular submonolayers. The cluster size distribution
in this far-from-equilibrium process exhibits dynamic scaling behavior
characteristic of the (nearly equilibrium) Ostwald ripening, controlled by the
attachment and detachment of the "gas" particles. The scaled size distribution,
however, is different from the classical Wagner distribution obtained in the
limit of a vanishingly small area fraction of the clusters. A much better
agreement is found with the theory of Conti et al. [Phys. Rev. E 65, 046117
(2002)] which accounts for the cluster merger.Comment: 5 pages, to appear in PR
Ionic profiles close to dielectric discontinuities: Specific ion-surface interactions
We study, by incorporating short-range ion-surface interactions, ionic
profiles of electrolyte solutions close to a non-charged interface between two
dielectric media. In order to account for important correlation effects close
to the interface, the ionic profiles are calculated beyond mean-field theory,
using the loop expansion of the free energy. We show how it is possible to
overcome the well-known deficiency of the regular loop expansion close to the
dielectric jump, and treat the non-linear boundary conditions within the
framework of field theory. The ionic profiles are obtained analytically to
one-loop order in the free energy, and their dependence on different
ion-surface interactions is investigated. The Gibbs adsorption isotherm, as
well as the ionic profiles are used to calculate the surface tension, in
agreement with the reverse Hofmeister series. Consequently, from the
experimentally-measured surface tension, one can extract a single adhesivity
parameter, which can be used within our model to quantitatively predict hard to
measure ionic profiles.Comment: 14 pages, 6 figure
Role of inertia in two-dimensional deformation and breakup of a droplet
We investigate by Lattice Boltzmann methods the effect of inertia on the
deformation and break-up of a two-dimensional fluid droplet surrounded by fluid
of equal viscosity (in a confined geometry) whose shear rate is increased very
slowly. We give evidence that in two dimensions inertia is {\em necessary} for
break-up, so that at zero Reynolds number the droplet deforms indefinitely
without breaking. We identify two different routes to breakup via two-lobed and
three-lobed structures respectively, and give evidence for a sharp transition
between these routes as parameters are varied.Comment: 4 pages, 4 figure
X-ray Emitting GHz-Peaked Spectrum Galaxies: Testing a Dynamical-Radiative Model with Broad-Band Spectra
In a dynamical-radiative model we recently developed to describe the physics
of compact, GHz-Peaked-Spectrum (GPS) sources, the relativistic jets propagate
across the inner, kpc-sized region of the host galaxy, while the electron
population of the expanding lobes evolves and emits synchrotron and
inverse-Compton (IC) radiation. Interstellar-medium gas clouds engulfed by the
expanding lobes, and photoionized by the active nucleus, are responsible for
the radio spectral turnover through free-free absorption (FFA) of the
synchrotron photons. The model provides a description of the evolution of the
spectral energy distribution (SED) of GPS sources with their expansion,
predicting significant and complex high-energy emission, from the X-ray to the
gamma-ray frequency domain. Here, we test this model with the broad-band SEDs
of a sample of eleven X-ray emitting GPS galaxies with Compact-Symmetric-Object
(CSO) morphology, and show that: (i) the shape of the radio continuum at
frequencies lower than the spectral turnover is indeed well accounted for by
the FFA mechanism; (ii) the observed X-ray spectra can be interpreted as
non-thermal radiation produced via IC scattering of the local radiation fields
off the lobe particles, providing a viable alternative to the thermal,
accretion-disk dominated scenario. We also show that the relation between the
hydrogen column densities derived from the X-ray (N_H) and radio (N_HI) data of
the sources is suggestive of a positive correlation, which, if confirmed by
future observations, would provide further support to our scenario of
high-energy emitting lobes.Comment: 29 pages, 3 figures, 6 tables; to appear in ApJ. A few clarifications
included, according to referee's suggestion
Review of Linac-Ring Type Collider Proposals
There are three possibly types of particle colliders schemes: familiar (well
known) ring-ring colliders, less familiar however sufficiently advanced linear
colliders and less familiar and less advanced linac-ring type colliders. The
aim of this paper is two-fold: to present possibly complete list of papers on
linac-ring type collider proposals and to emphasize the role of linac-ring type
machines for future HEP research.Comment: quality of figures is improved, some misprints are correcte
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