1,804 research outputs found
Thermopower of a superconducting single-electron transistor
We present a linear-response theory for the thermopower of a single-electron
transistor consisting of a superconducting island weakly coupled to two
normal-conducting leads (NSN SET). The thermopower shows oscillations with the
same periodicity as the conductance and is rather sensitive to the size of the
superconducting gap. In particular, the previously studied sawtooth-like shape
of the thermopower for a normal-conducting single-electron device is
qualitatively changed even for small gap energies.Comment: 9 pages, 3 figure
Metabolic Effects of Bariatric Surgery in Mouse Models of Circadian Disruption
Background/Objectives:
Mounting evidence supports a link between circadian disruption and metabolic disease. Humans with circadian disruption (for example, night-shift workers) have an increased risk of obesity and cardiometabolic diseases compared with the non-disrupted population. However, it is unclear whether the obesity and obesity-related disorders associated with circadian disruption respond to therapeutic treatments as well as individuals with other types of obesity. Subjects/Methods:
Here, we test the effectiveness of the commonly used bariatric surgical procedure, Vertical Sleeve Gastrectomy (VSG), in mouse models of genetic and environmental circadian disruption. Results:
VSG led to a reduction in body weight and fat mass in both ClockΔ19 mutant and constant-light mouse models (PP\u3e0.05). Within circadian-disrupted models, VSG also led to improved glucose tolerance and lipid handling (P\u3c0.05). Conclusions:
Together these data demonstrate that VSG is an effective treatment for the obesity associated with circadian disruption, and that the potent effects of bariatric surgery are orthogonal to circadian biology. However, as the effects of bariatric surgery are independent of circadian disruption, VSG cannot be considered a cure for circadian disruption. These data have important implications for circadian-disrupted obese patients. Moreover, these results reveal new information about the metabolic pathways governing the effects of bariatric surgery as well as of circadian disruption
Transport properties of single atoms
We present a systematic study of the ballistic electron conductance through
sp and 3d transition metal atoms attached to copper and palladium crystalline
electrodes. We employ the 'ab initio' screened Korringa-Kohn-Rostoker Green's
function method to calculate the electronic structure of nanocontacts while the
ballistic transmission and conductance eigenchannels were obtained by means of
the Kubo approach as formulated by Baranger and Stone. We demonstrate that the
conductance of the systems is mainly determined by the electronic properties of
the atom bridging the macroscopic leads. We classify the conducting
eigenchannels according to the atomic orbitals of the contact atom and the
irreducible representations of the symmetry point group of the system that
leads to the microscopic understanding of the conductance. We show that if
impurity resonances in the density of states of the contact atom appear at the
Fermi energy, additional channels of appropriate symmetry could open. On the
other hand the transmission of the existing channels could be blocked by
impurity scattering.Comment: RevTEX4, 9 pages, 9 figure
Detection of the spin character of Fe(001) surface states by scanning tunneling microscopy: A theoretical proposal
We consider the magnetic structure on the Fe(001) surface and theoretically
study the scanning tunneling spectroscopy using a spin-polarized tip (SP-STM).
We show that minority-spin surface states induce a strong bias dependence of
the tunneling differential conductance which largely depends on the orientation
of the magnetization in the SP-STM tip relative to the easy magnetization axis
in the Fe(001) surface. We propose to use this effect in order to determine the
spin character of the Fe(001) surface states. This technique can be applied
also to other magnetic surfaces in which surface states are observed.Comment: 5 pages, 4 figure
Fast solvers and efficient numerical cfd techniques for dynamic porous media problems
We present a fully implicit, monolithic finite element solution scheme to
efficiently solve the governing set of differential algebraic equations of incompressible poroelastodynamics.
Thereby, we proceed from a two-dimensional, biphasic, saturated porous
medium model with intrinsically coupled and incompressible solid and fluid constituents.
Our approach, motivated by well-accepted CFD techniques and originally developed for
the efficient simulation of incompressible flow problems, is characterized by the following
aspects: (1) a special treatment of the algebraically coupled volume balance equation
leading to a reduced form of the boundary conditions; (2) usage of a higher-order accurate
mixed LBB-stable finite element pair with piecewise discontinuous pressure for the spatial
discretization; (3) application of the fully implicit 2nd-order Crank-Nicolson scheme for
the time discretization; (4) use of a special fast multigrid solver for the resulting discrete
linear equation system. For the purpose of validation and to expose the merits and benefits
of our new solution strategy in comparison to other established approaches, canonical
one- and two-dimensional wave propagation problems are solved. Finally, a large-scale,
dynamic soil-structure interaction problem serves to reveal the efficiency of the special
multigrid solver in combination with the chosen finite element discretization
Computer simulation of the potential distribution inside the plasma chamber of negative ion source
In the paper the computational method and results of simulation of potential distribution inside the plasma region of the negative ion source are presented. The code uses the well known PIC method [1] for the local charge density determination and finite differences method for the Poisson equation [2]. For simplification, the plasma model does not take into account the interaction between the plasma particles. The results of calculations are compared with the experimental data obtained for the RF negative ion source [3]
Doping driven magnetic instabilities and quantum criticality of NbFe
Using density functional theory we investigate the evolution of the magnetic
ground state of NbFe due to doping by Nb-excess and Fe-excess. We find
that non-rigid-band effects, due to the contribution of Fe-\textit{d} states to
the density of states at the Fermi level are crucial to the evolution of the
magnetic phase diagram. Furthermore, the influence of disorder is important to
the development of ferromagnetism upon Nb doping. These findings give a
framework in which to understand the evolution of the magnetic ground state in
the temperature-doping phase diagram. We investigate the magnetic instabilities
in NbFe. We find that explicit calculation of the Lindhard function,
, indicates that the primary instability is to finite
antiferromagnetism driven by Fermi surface nesting. Total energy
calculations indicate that antiferromagnetism is the ground
state. We discuss the influence of competing and finite
instabilities on the presence of the non-Fermi liquid behavior in
this material.Comment: 8 pages, 7 figure
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