2,427 research outputs found
Photon-assisted electron transport through a three-terminal quantum dot system with nonresonant tunneling channels
We have studied the electron transport through a quantum dot coupled to three
leads in the presence of external microwave fields supplied to different parts
of the considered mesoscopic system. Additionally, we introduced a possible
nonresonant tunneling channels between leads. The quantum dot charge and
currents were determined in terms of the appropriate evolution operator matrix
elements and under the wide band limit the analytical formulas for
time-averaged currents and differential conductance were obtained. We have also
examined the response of the considered system on the rectangular-pulse
modulation imposed on different quantum dot-leads barriers as well as the
time-dependence of currents flowing in response to suddenly removed (or
included) connection of a quantum dot with one of the leads.Comment: 34 pages, 12 figure
Structure of the exotic spin-flop states in BaCu2Si2O7
The unusual 2-stage spin flop transition in BaCu2Si2O7 is studied by
single-crystal neutron diffraction. The magnetic structures of the various
spin-flop phases are determined. The results appear to be inconsistent with the
previously proposed theoretical explanation of the 2-stage transition.Comment: 6 pages 5 figure
Positron emission tomography to quantify brain nicotine abstinence
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110042/1/cptclpt2005379.pd
Polar Actions on Berger Spheres
The object of this article is to study a torus action on a so-called Berger sphere. We also make some comments on polar actions on naturally reductive homogeneous spaces. Finally, we prove a rigidity-type theorem for Riemannian manifolds carrying a polar action with a fix point
Theory of double resonance magnetometers based on atomic alignment
We present a theoretical study of the spectra produced by
optical-radio-frequency double resonance devices, in which resonant linearly
polarized light is used in the optical pumping and detection processes. We
extend previous work by presenting algebraic results which are valid for atomic
states with arbitrary angular momenta, arbitrary rf intensities, and arbitrary
geometries. The only restriction made is the assumption of low light intensity.
The results are discussed in view of their use in optical magnetometers
Break-down of the density-of-states description of scanning tunneling spectroscopy in supported metal clusters
Low-temperature scanning tunneling spectroscopy allows to probe the
electronic properties of clusters at surfaces with unprecedented accuracy. By
means of quantum transport theory, using realistic tunneling tips, we obtain
conductance curves which considerably deviate from the cluster's density of
states. Our study explains the remarkably small number of peaks in the
conductance spectra observed in recent experiments. We demonstrate that the
unambiguous characterization of the states on the supported clusters can be
achieved with energy-resolved images, obtained from a theoretical analysis
which mimics the experimental imaging procedure.Comment: 5 pages, 3 figure
Transition amplitudes and sewing properties for bosons on the Riemann sphere
We consider scalar quantum fields on the sphere, both massive and massless.
In the massive case we show that the correlation functions define amplitudes
which are trace class operators between tensor products of a fixed Hilbert
space. We also establish certain sewing properties between these operators. In
the massless case we consider exponential fields and have a conformal field
theory. In this case the amplitudes are only bilinear forms but still we
establish sewing properties. Our results are obtained in a functional integral
framework.Comment: 33 page
Two-stage spin-flop transitions in S = 1/2 antiferromagnetic spin chain BaCu_2Si_2O_7
Two-stage spin-flop transitions are observed the in quasi-one-dimensional
antiferromagnet, BaCuSiO. A magnetic field applied along the
easy axis induces a spin-flop transition at 2.0 T followed by a second
transition at 4.9 T. The magnetic susceptibility indicates the presence of
Dzyaloshinskii-Moriya (DM) antisymmetric interactions between the intrachain
neighboring spins. We discuss a possible mechanism whereby the geometrical
competition between DM and interchain interactions, as discussed for the
two-dimensional antiferromagnet LaCuO, causes the two-stage
spin-flop transitions.Comment: 5 pages, 3 figures (included), accepted for publication in Phys. Rev.
Let
Ocean Planet or Thick Atmosphere: On the Mass-Radius Relationship for Solid Exoplanets with Massive Atmospheres
The bulk composition of an exoplanet is commonly inferred from its average
density. For small planets, however, the average density is not unique within
the range of compositions. Variations of a number of important planetary
parameters--which are difficult or impossible to constrain from measurements
alone--produce planets with the same average densities but widely varying bulk
compositions. We find that adding a gas envelope equivalent to 0.1%-10% of the
mass of a solid planet causes the radius to increase 5-60% above its gas-free
value. A planet with a given mass and radius might have substantial water ice
content (a so-called ocean planet) or alternatively a large rocky-iron core and
some H and/or He. For example, a wide variety of compositions can explain the
observed radius of GJ 436b, although all models require some H/He. We conclude
that the identification of water worlds based on the mass-radius relationship
alone is impossible unless a significant gas layer can be ruled out by other
means.Comment: 5 pages, 3 figures, accepted to Ap
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