55,729 research outputs found
Chern-Simons flows on Aloff-Wallach spaces and Spin(7)-instantons
Due to their explicit construction, Aloff-Wallach spaces are prominent in
flux compactifications. They carry G_2-structures and admit the G_2-instanton
equations, which are natural BPS equations for Yang-Mills instantons on
seven-manifolds and extremize a Chern-Simons-type functional. We consider the
Chern-Simons flow between different G_2-instantons on Aloff-Wallach spaces,
which is equivalent to Spin(7)-instantons on a cylinder over them. For a
general SU(3)-equivariant gauge connection, the generalized instanton equations
turn into gradient-flow equations on C^3 x R^2, with a particular cubic
superpotential. For the simplest member of the Aloff-Wallach family (with
3-Sasakian structure) we present an explicit instanton solution of tanh-like
shape.Comment: 1+17 pages, 1 figur
Investigation of the Heating Processes and Temperature Field of the Frequency-controlled Asynchronous Engine Based on Mathematical Models
The study of the temperature field of the engine for non-stationary modes is done. A numerical simulation of a non-stationary thermal process using dynamic EHD, the characteristic of the rate of rise of temperatures is done. An increase in the temperature of individual parts in the idle interval, when the power of heat release is significantly reduced, is established, and the reverse of the heat flow through the air gap is established. It is shown that the EHD method, in contrast to the FEM, is self-sufficient, which determines its practical value. In various parts of the speed control range in the implementation of various laws of regulation. At the same time, the main electrical, magnetic and additional losses associated with the fundamental voltage harmonics (FVH), and mechanical losses, as well as additional electrical and magnetic losses associated with the higher voltage harmonics, change. When using serial asynchronous engines as frequency-controlled. Permissible under the conditions of heating power is significantly reduced by the power of serial engines. Depending on the synchronous speed, the reduction is from 10 % to 20 %. Given the additional overheating due to higher voltage harmonics, as well as the deterioration of the cooling conditions when adjusting the rotational speed "down" from the nominal, it seems very relevant
Factorization of quantum charge transport for non-interacting fermions
We show that the statistics of the charge transfer of non-interacting
fermions through a two-lead contact is generalized binomial, at any temperature
and for any form of the scattering matrix: an arbitrary charge-transfer process
can be decomposed into independent single-particle events. This result
generalizes previous studies of adiabatic pumping at zero temperature and of
transport induced by bias voltage.Comment: 13 pages, 3 figures, typos corrected, references adde
Radiation Generated by Charge Migration Following Ionization
Electronic many-body effects alone can be the driving force for an ultrafast
migration of a positive charge created upon ionization of molecular systems.
Here we show that this purely electronic phenomenon generates a characteristic
IR radiation. The situation when the initial ionic wave packet is produced by a
sudden removal of an electron is also studied. It is shown that in this case a
much stronger UV emission is generated. This emission appears as an ultrafast
response of the remaining electrons to the perturbation caused by the sudden
ionization and as such is a universal phenomenon to be expected in every
multielectron system.Comment: 5 pages, 4 figure
Analysis and application of ERTS-1 data for regional geological mapping
Combined visual and digital techniques of analysing ERTS-1 data for geologic information have been tried on selected areas in Pennsylvania. The major physiolographic and structural provinces show up well. Supervised mapping, following the imaged expression of known geologic features on ERTS band 5 enlargements (1:250,000) of parts of eastern Pennsylvania, delimited the Diabase Sills and the Precambrian rocks of the Reading Prong with remarkable accuracy. From unsupervised mapping, transgressive linear features are apparent in unexpected density, and exhibit strong control over river valley and stream channel directions. They are unaffected by bedrock type, age, or primary structural boundaries, which suggests they are either rejuvenated basement joint directions on different scales, or they are a recently impressed structure possibly associated with a drifting North American plate. With ground mapping and underflight data, 6 scales of linear features have been recognized
Quantum transport on small-world networks: A continuous-time quantum walk approach
We consider the quantum mechanical transport of (coherent) excitons on
small-world networks (SWN). The SWN are build from a one-dimensional ring of N
nodes by randomly introducing B additional bonds between them. The exciton
dynamics is modeled by continuous-time quantum walks and we evaluate
numerically the ensemble averaged transition probability to reach any node of
the network from the initially excited one. For sufficiently large B we find
that the quantum mechanical transport through the SWN is, first, very fast,
given that the limiting value of the transition probability is reached very
quickly; second, that the transport does not lead to equipartition, given that
on average the exciton is most likely to be found at the initial node.Comment: 8 pages, 8 figures (high quality figures available upon request
The Immirzi Parameter as an Instanton Angle
The Barbero-Immirzi parameter is a one parameter quantization ambiguity
underpinning the loop approach to quantum gravity that bears tantalizing
similarities to the theta parameter of gauge theories such as Yang-Mills and
QCD. Despite the apparent semblance, the Barbero-Immirzi field has resisted a
direct topological interpretation along the same lines as the theta-parameter.
Here we offer such an interpretation. Our approach begins from the perspective
of Einstein-Cartan gravity as the symmetry broken phase of a de Sitter gauge
theory. From this angle, just as in ordinary gauge theories, a theta-term
emerges from the requirement that the vacuum is stable against quantum
mechanical tunneling. The Immirzi parameter is then identified as a combination
of Newton's constant, the cosmological constant, and the theta-parameter.Comment: 24 page
Double Well Potential: Perturbation Theory, Tunneling, WKB (beyond instantons)
A simple approximate solution for the quantum-mechanical quartic oscillator
in the double-well regime at arbitrary is
presented. It is based on a combining of perturbation theory near true minima
of the potential, semi-classical approximation at large distances and a
description of tunneling under the barrier. It provides 9-10 significant digits
in energies and gives for wavefunctions the relative deviation in real
-space less than .Comment: 13 pages, invited talk at "Crossing the boundaries: Gauge dynamics at
strong coupling (Shifmania)", Minneapolis, May 14-17, 200
Decoherence in Quantum Walks on the Hypercube
We study a natural notion of decoherence on quantum random walks over the
hypercube. We prove that in this model there is a decoherence threshold beneath
which the essential properties of the hypercubic quantum walk, such as linear
mixing times, are preserved. Beyond the threshold, we prove that the walks
behave like their classical counterparts.Comment: 7 pages, 3 figures; v2:corrected typos in references; v3:clarified
section 2.1; v4:added references, expanded introduction; v5: final journal
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