2,055 research outputs found
On subgroups in division rings of type
Let be a division ring with center . We say that is a {\em
division ring of type } if for every two elements the division
subring is a finite dimensional vector space over . In this paper
we investigate multiplicative subgroups in such a ring.Comment: 10 pages, 0 figure
Stabilizing Superconductivity in Nanowires by Coupling to Dissipative Environments
We present a theory for a finite-length superconducting nanowire coupled to
an environment. We show that in the absence of dissipation quantum phase slips
always destroy superconductivity, even at zero temperature. Dissipation
stabilizes the superconducting phase. We apply this theory to explain the
"anti-proximity effect" recently seen by Tian et. al. in Zinc nanowires.Comment: 4 pages, 3 figure
Fast label-free multilayered histology-like imaging of human breast cancer by photoacoustic microscopy
The goal of breast-conserving surgery is to completely remove all of the cancer. Currently, no intraoperative tools can microscopically analyze the entire lumpectomy specimen, which results in 20 to 60% of patients undergoing second surgeries to achieve clear margins. To address this critical need, we have laid the foundation for the development of a device that could allow accurate intraoperative margin assessment. We demonstrate that by taking advantage of the intrinsic optical contrast of breast tissue, photoacoustic microscopy (PAM) can achieve multilayered histology-like imaging of the tissue surface. The high correlation of the PAM images to the conventional histologic images allows rapid computations of diagnostic features such as nuclear size and packing density, potentially identifying small clusters of cancer cells. Because PAM does not require tissue processing or staining, it can be performed promptly and intraoperatively, enabling immediate directed re-excision and reducing the number of second surgeries
Analytical solutions to the spin-1 Bose-Einstein condensates
We analytically solve the one-dimensional coupled Gross-Pitaevskii equations
which govern the motion of F=1 spinor Bose-Einstein condensates. The nonlinear
density-density interactions are decoupled by making use of the unique
properties of the Jacobian elliptical functions. Several types of complex
stationary solutions are deduced. Furthermore, exact non-stationary solutions
to the time-dependent Gross-Pitaevskii equations are constructed by making use
of the spin-rotational symmetry of the Hamiltonian. The spin-polarizations
exhibit kinked configurations. Our method is applicable to other coupled
nonlinear systems.Comment: 12 figure
2*2 random matrix ensembles with reduced symmetry: From Hermitian to PT-symmetric matrices
A possibly fruitful extension of conventional random matrix ensembles is
proposed by imposing symmetry constraints on conventional Hermitian matrices or
parity-time- (PT-) symmetric matrices. To illustrate the main idea, we first
study 2*2 complex Hermitian matrix ensembles with O(2) invariant constraints,
yielding novel level-spacing statistics such as singular distributions,
half-Gaussian distribution, distributions interpolating between GOE (Gaussian
Orthogonal Ensemble) distribution and half Gaussian distributions, as well as
gapped-GOE distribution. Such a symmetry-reduction strategy is then used to
explore 2*2 PT-symmetric matrix ensembles with real eigenvalues. In particular,
PT-symmetric random matrix ensembles with U(2) invariance can be constructed,
with the conventional complex Hermitian random matrix ensemble being a special
case. In two examples of PT-symmetric random matrix ensembles, the
level-spacing distributions are found to be the standard GUE (Gaussian Unitary
Ensemble) statistics or "truncated-GUE" statistics
Tannaka-Krein duality for Hopf algebroids
We develop the Tannaka-Krein duality for monoidal functors with target in the
categories of bimodules over a ring. The \coend of such a functor turns out
to be a Hopf algebroid over this ring. Using the result of a previous paper we
characterize a small abelian, locally finite rigid monoidal category as the
category of rigid comodules over a transitive Hopf algebroid.Comment: 25 pages, final version, to appear in Israel Journal of Mathematic
The Josephson current in Fe-based superconducting junctions: theory and experiment
We present theory of dc Josephson effect in contacts between Fe-based and
spin-singlet -wave superconductors. The method is based on the calculation
of temperature Green's function in the junction within the tight-binding model.
We calculate the phase dependencies of the Josephson current for different
orientations of the junction relative to the crystallographic axes of Fe-based
superconductor. Further, we consider the dependence of the Josephson current on
the thickness of an insulating layer and on temperature. Experimental data for
PbIn/BaK(FeAs) point-contact Josephson junctions are
consistent with theoretical predictions for symmetry of an order
parameter in this material. The proposed method can be further applied to
calculations of the dc Josephson current in contacts with other new
unconventional multiorbital superconductors, such as and
superconducting topological insulator .Comment: 16 pages, 14 figure
Lower critical field and SNS-Andreev spectroscopy of 122-arsenides: Evidence of nodeless superconducting gap
Using two experimental techniques, we studied single crystals of the 122-FeAs
family with almost the same critical temperature, Tc. We investigated the
temperature dependence of the lower critical field of a single crystal under
static magnetic fields parallel to the axis. The temperature dependence of the
London penetration depth can be described equally well either by a single
anisotropic -wave-like gap or by a two-gap model, while a d-wave approach
cannot be used to fit the London penetration depth data. Intrinsic multiple
Andreev reflection effect spectroscopy was used to detect bulk gap values in
single crystals of the intimate compound, with the same Tc. We estimated the
range of the large gap value 6-8 meV (depending on small variation of and its a
space anisotropy of about 30%, and the small gap 1.7 meV. This clearly
indicates that the gap structure of our investigated systems more likely
corresponds to a nodeless s-wave two gaps.Comment: 9 pages, 6 figure
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