321 research outputs found
Ergodic Properties of the Spin - Boson System
We investigate the dynamics of a 2-level atom (or spin-1/2) coupled to a
mass-less bosonic field at positive temperature. We prove that, at small
coupling, the combined quantum system approaches thermal equilibrium. Moreover
we establish that this approach is exponentially fast in time. We first reduce
the question to a spectral problem for the Liouvillean, a self-adjoint operator
naturally associated with the system. To compute this operator, we invoke
Tomita-Takesaki theory. Once this is done we use complex deformation techniques
to study its spectrum. The corresponding zero temperature model is also
reviewed and compared.Comment: 31 pages, postscrip
Resonances for a Hydrogenic System or a Harmonic Oscillator Strongly Coupled to a Field
We calculate resonances which are formed by a particle in a potential which
is either Coulombian or quadratic when the particle is strongly coupled to a
massless boson, taking only two energy levels into consideration. From these
calculations we derive how the moving away of the particle from its attraction
center goes together with the energy lowering of hybrid states that this
particle forms with the field. We study the width of these states and we show
that stable states may also appear in the coupling.Comment: 17 pages, 6 figure
Entropic fluctuations in XY chains and reflectionless Jacobi matrices
We study the entropic fluctuations of a general XY spin chain where initially
the left(x0) part of the chain is in thermal equilibrium at inverse
temperature Tl/Tr. The temperature differential results in a non-trivial
energy/entropy flux across the chain. The Evans-Searles (ES) entropic
functional describes fluctuations of the flux observable with respect to the
initial state while the Gallavotti-Cohen (GC) functional describes these
fluctuations with respect to the steady state (NESS) the chain reaches in the
large time limit. We also consider the full counting statistics (FCS) of the
energy/entropy flux associated to a repeated measurement protocol, the
variational entropic functional (VAR) that arises as the quantization of the
variational characterization of the classical Evans-Searles functional and a
natural class of entropic functionals that interpolate between FCS and VAR. We
compute these functionals in closed form in terms of the scattering data of the
Jacobi matrix h canonically associated to the XY chain. We show that all these
functionals are identical if and only if h is reflectionless (we call this
phenomenon entropic identity). If h is not reflectionless, then the ES and GC
functionals remain equal but differ from the FCS, VAR and interpolating
functionals. Furthermore, in the non-reflectionless case, the ES/GC functional
does not vanish at 1 (i.e., the Kawasaki identity fails) and does not have the
celebrated ES/GC symmetry. The FCS, VAR and interpolating functionals always
have this symmetry. In the cases where h is a Schr\"odinger operator, the
entropic identity leads to some unexpected open problems in the spectral theory
of one-dimensional discrete Schr\"odinger operators
On the consequences of the fact that atomic levels have a certain width
This note presents two ideas. The first one is that quantum theory has a
fundamentally perturbative basis but leads to nonperturbative states which it
would seem natural to take into account in the foundation of a theory of
quantum phenomena. The second one consists in questioning the validity of the
present notion of time. Both matters are related to the fact that atomic levels
have a certain width. This note is presented qualitatively so as to evidence
its main points, independently of the models on which these have been tested.Comment: 8 page
What is absolutely continuous spectrum?
This note is an expanded version of the author's contribution to the
Proceedings of the ICMP Santiago, 2015, and is based on a talk given by the
second author at the same Congress. It concerns a research program devoted to
the characterization of the absolutely continuous spectrum of a self-adjoint
operator H in terms of the transport properties of a suitable class of open
quantum systems canonically associated to H
Level Crossing Rate of Macrodiversity System in the Presence of Multipath Fading and Shadowing
Macrodiversity system including macrodiversity SC receiver and two microdiversity SC receivers is considered in this paper. Received signal experiences, simultaneously, both, long term fading and short term fading. Microdiversity SC receivers reduces Rayleigh fading effects on system performance and macrodiversity SC receiver mitigate Gamma shadowing effects on system performance. Closed form expressions for level crossing rate of microdiversity SC receivers output signals envelopes are calculated. This expression is used for evaluation of level crossing rate of macrodiversity SC receiver output signal envelope. Numerical expressions are illustrated to show the influence of Gamma shadowing severity on level crossing rate
A comprehensive study of the delay vector variance method for quantification of nonlinearity in dynamical systems
Although vibration monitoring is a popular method to monitor and assess dynamic structures, quantification of linearity or nonlinearity of the dynamic responses remains a challenging problem. We investigate the delay vector variance (DVV) method in this regard in a comprehensive manner to establish the degree to which a change in signal nonlinearity can be related to system nonlinearity and how a change in system parameters affects the nonlinearity in the dynamic response of the system. A wide range of theoretical situations are considered in this regard using a single degree of freedom (SDOF) system to obtain numerical benchmarks. A number of experiments are then carried out using a physical SDOF model in the laboratory. Finally, a composite wind turbine blade is tested for different excitations and the dynamic responses are measured at a number of points to extend the investigation to continuum structures. The dynamic responses were measured using accelerometers, strain gauges and a Laser Doppler vibrometer. This comprehensive study creates a numerical and experimental benchmark for structurally dynamical systems where output-only information is typically available, especially in the context of DVV. The study also allows for comparative analysis between different systems driven by the similar input
Hamiltonian structure for dispersive and dissipative dynamical systems
We develop a Hamiltonian theory of a time dispersive and dissipative
inhomogeneous medium, as described by a linear response equation respecting
causality and power dissipation. The proposed Hamiltonian couples the given
system to auxiliary fields, in the universal form of a so-called canonical heat
bath. After integrating out the heat bath the original dissipative evolution is
exactly reproduced. Furthermore, we show that the dynamics associated to a
minimal Hamiltonian are essentially unique, up to a natural class of
isomorphisms. Using this formalism, we obtain closed form expressions for the
energy density, energy flux, momentum density, and stress tensor involving the
auxiliary fields, from which we derive an approximate, ``Brillouin-type,''
formula for the time averaged energy density and stress tensor associated to an
almost mono-chromatic wave.Comment: 68 pages, 1 figure; introduction revised, typos correcte
Use of Probiotics as Growth Promoters and Immunostimulators in Fingerlings of Cyprinid Fish Species
Intensive aquaculture production has required the development of an individual’s resistance to disease rather than depending upon antibiotics or chemotherapeutics. The role of gastrointestinal microflora in disease resistance has been established in many fish species, which has led to the concept of manipulating gastrointestinal microflora for better health management. A number of studies has been conducted in different fish species with various useful microorganisms called ‘probiotics’ to amplify gastrointestinal microflora to fight against various infectious diseases. Probiotics are beneficial microorganisms which protect the host from diseases. Probiotic protection can be achieved by various mechanisms. Most probiotics used in aquaculture belong to the lactic acid bacteria, the genus Bacillus, the photosynthetic bacteria, the yeast, notwithstanding other genera and species have also been used. The immunostimulatory effect of probiotics has been established in many fish species, but their direct involvement in the immune response is not well established. It has also been proven that the application of probiotics in aquaculture has beneficial effects on growth of fish as well as on the environment. At present, data about the efficacy of probiotics in commercial aquaculture of Serbia is still lacking. This review discusses mainly the studies and applications about effects, problems and perspectives of probiotics used in fingerlings of cyprinid fish species, and highlights immunostimulatory effects and growth promotion effects of commercial probiotic products. In the present paper the results that show positive influence of probiotics in cyprinides nutrition on production performance and immune system are summarized. Special accent is given to criteria for proper selection of probiotics in cyprinides production
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