57 research outputs found
Moving Atom-Field Interactions: Quantum Motional Decoherence and Relaxation
The reduced dynamics of an atomic qubit coupled both to its own quantized
center of mass motion through the spatial mode functions of the electromagnetic
field, as well as the vacuum modes, is calculated in the influence functional
formalism. The formalism chosen can describe the entangled non-Markovian
evolution of the system with a full account of the coherent back-action of the
environment on the qubit. We find a slight increase in the decoherence due to
the quantized center of mass motion and give a condition on the mass and qubit
resonant frequency for which the effect is important. In optically resonant
alkali-metal atom systems, we find the effect to be negligibly small. The
framework presented here can nevertheless be used for general considerations of
the coherent evolution of qubits in moving atoms in an electromagnetic field.Comment: 9 pages, 1 figure, minor change
A generalized bag-like boundary condition for fields with arbitrary spin
Boundary conditions (BCs) for the Maxwell and Dirac fields at material surfaces are widely-used and physically well-motivated, but do not appear to have been generalized to deal with higher spin fields. As a result there is no clear prescription as to which BCs should be selected in order to obtain physically-relevant results pertaining to confined higher spin fields. This lack of understanding is significant given that boundary-dependent phenomena are ubiquitous across physics, a prominent example being the Casimir effect. Here, we use the two-spinor calculus formalism to present a unified treatment of BCs routinely employed in the treatment of spin-1/2 and spin-1 fields. We then use this unification to obtain a BC that can be applied to massless fields of any spin, including the spin-2 graviton, and its supersymmetric partner the spin-3/2 gravitino
Resumming the large-N approximation for time evolving quantum systems
In this paper we discuss two methods of resumming the leading and next to
leading order in 1/N diagrams for the quartic O(N) model. These two approaches
have the property that they preserve both boundedness and positivity for
expectation values of operators in our numerical simulations. These
approximations can be understood either in terms of a truncation to the
infinitely coupled Schwinger-Dyson hierarchy of equations, or by choosing a
particular two-particle irreducible vacuum energy graph in the effective action
of the Cornwall-Jackiw-Tomboulis formalism. We confine our discussion to the
case of quantum mechanics where the Lagrangian is . The
key to these approximations is to treat both the propagator and the
propagator on similar footing which leads to a theory whose graphs have the
same topology as QED with the propagator playing the role of the photon.
The bare vertex approximation is obtained by replacing the exact vertex
function by the bare one in the exact Schwinger-Dyson equations for the one and
two point functions. The second approximation, which we call the dynamic Debye
screening approximation, makes the further approximation of replacing the exact
propagator by its value at leading order in the 1/N expansion. These two
approximations are compared with exact numerical simulations for the quantum
roll problem. The bare vertex approximation captures the physics at large and
modest better than the dynamic Debye screening approximation.Comment: 30 pages, 12 figures. The color version of a few figures are
separately liste
The Taming of Closed Time-like Curves
We consider a orbifold, where acts by time and space
reversal, also known as the embedding space of the elliptic de Sitter space.
The background has two potentially dangerous problems: time-nonorientability
and the existence of closed time-like curves. We first show that closed causal
curves disappear after a proper definition of the time function. We then
consider the one-loop vacuum expectation value of the stress tensor. A naive
QFT analysis yields a divergent result. We then analyze the stress tensor in
bosonic string theory, and find the same result as if the target space would be
just the Minkowski space , suggesting a zero result for the
superstring. This leads us to propose a proper reformulation of QFT, and
recalculate the stress tensor. We find almost the same result as in Minkowski
space, except for a potential divergence at the initial time slice of the
orbifold, analogous to a spacelike Big Bang singularity. Finally, we argue that
it is possible to define local S-matrices, even if the spacetime is globally
time-nonorientable.Comment: 37 pages, LaTeX2e, uses amssymb, amsmath and epsf macros, 8 eps and 3
ps figures; (v2): Two additional comments + one reference added; (v3):
corrections in discussion of CTCs + some clarification
Анализ технологий по предупреждению формирования газовых гидратов на Заполярном нефтегазоконденсатном месторождении (ЯНАО)
Объектами исследования являются осложнения, возникающие при гидратоотложении в системах сбора и транспортировки газа. Предметом исследования являются комплексные методы предупреждения образования гидратов природного газа. Цель выпускной квалификационной работы – анализ методов и технологий защиты промыслового оборудования от осложнений, вызванных гидратообразованием.The objects of the following research are the problems appearing from the hydrate formation in gas gathering facilities and transportation systems. The subjects of the research are complex methods of preventing the formation of natural gas hydrates. The purpose of the graduation thesis is to analyze methods and technologies for protecting field equipment from problems caused by hydrate formation
Semiclassical Mechanics of the Wigner 6j-Symbol
The semiclassical mechanics of the Wigner 6j-symbol is examined from the
standpoint of WKB theory for multidimensional, integrable systems, to explore
the geometrical issues surrounding the Ponzano-Regge formula. The relations
among the methods of Roberts and others for deriving the Ponzano-Regge formula
are discussed, and a new approach, based on the recoupling of four angular
momenta, is presented. A generalization of the Yutsis-type of spin network is
developed for this purpose. Special attention is devoted to symplectic
reduction, the reduced phase space of the 6j-symbol (the 2-sphere of Kapovich
and Millson), and the reduction of Poisson bracket expressions for
semiclassical amplitudes. General principles for the semiclassical study of
arbitrary spin networks are laid down; some of these were used in our recent
derivation of the asymptotic formula for the Wigner 9j-symbol.Comment: 64 pages, 50 figure
Программное обеспечение для определения, построения и визуализации двухмерной и трехмерной графики
Работа направлена на создание библиотеки для работы с двухмерной и трехмернйой графикой и программного обеспечения, которое будет использовать данную библиотеку для трехмерной и двухмерной визуализации структуры проектов организации.The work is aimed at creating the software library for working with two-dimensional and three-dimensional graphics and software that will use this library for three-dimensional and two-dimensional visualization of the structure of the organization's projects
Численное моделирование влияния радиационного теплопереноса в микросферах тонкопленочных теплоизоляционных покрытий на тепловые потери теплопроводов
Объектом исследования является нанесенный на трубопровод слой сверхтонкой теплоизоляции толщиной 0,33 мм, предполагалось что слой состоит из связующего вещества заполненного микросферами с соотношением 38:62. Моделирование проводилось для микросфер с двумя значениями толщины стенки.
Цель работы – моделирование влияния радиационного теплопереноса в микросферах тонкопленочных теплоизоляционных покрытий на тепловые потери теплопроводов.
В ходе исследования с помощью функций и средств, имеющихся в пакете программ мультифизического моделирования COMSOL Multiphisics, было проведено моделирование тепловых режимов слоя изоляции.The object of the study is a layer of ultra-thin thermal insulation applied to the pipeline with a thickness of 0.33 mm. it was assumed that the layer consists of a binder filled with microspheres with a ratio of 38:62. The simulation was performed for microspheres with two values of wall thickness.
The aim of this work is to model the effect of radiation heat transfer in microspheres of thin-film thermal insulation coatings on heat losses of heat pipelines.
In the course of the study, the thermal modes of the insulation layer were simulated using the functions and tools available in the COMSOL Multiphisics multiphysics software package
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