1,756 research outputs found
Dissipative quantum systems modeled by a two level reservoir coupling
The coupling between a quantum dynamical system and a two-level system
reservoir is analysed within the framework of the Feynman-Vernon theory. We
stress the differences between this new reservoir and the well-known bath of
oscillators and show that, in order to obtain the Langevin equation for the
system of interest in the high temperature regime, we have to choose a spectral
distribution function which is finite for .Comment: 6 pages, RevteX, preprint UNICAM
Ulcerative colitis: let's talk about extent
Ulcerative colitis (UC) is a chronic inflammatory disease in which clinical course varies substantially between patients.
The extent of the disease is usually pointed out as one of the factors
responsible for this variation. With this study, we pretended to evaluate the differences in natural history and pharmacological therapy
prescription between left-sided and extended UC
Non-Markovian Dynamics of Quantum Discord
We evaluate the quantum discord dynamics of two qubits in independent and
common non-Markovian environments. We compare the dynamics of entanglement with
that of quantum discord. For independent reservoirs the quantum discord
vanishes only at discrete instants whereas the entanglement can disappear
during a finite time interval. For a common reservoir, quantum discord and
entanglement can behave very differently with sudden birth of the former but
not of the latter. Furthermore, in this case the quantum discord dynamics
presents sudden changes in the derivative of its time evolution which is
evidenced by the presence of kinks in its behavior at discrete instants of
time.Comment: 6 pages, 4 figure
Microbial communities analysis assessed by pyrosequencing - a new approach applied to conservation state studies of mural paintings
The knowledge about the microbial communities
present in mural paintings is of utmost importance to develop
effective conservation and mitigation strategies. The present
paper describes a methodological approach for the detailed
characterisation of microorganisms thriving in mural paintings
by combining culture-dependent methods that allow the identification
of microorganisms capable of growing in the laboratory
conditions and to obtain high cell densities for further
studies, and culture independent methods, such as denaturing
gradient gel electrophoresis (DGGE) and pyrosequencing.
The coupled use of culture-dependent methods and DGGE
does not give enough information to investigate the diversity
and abundance of microorganisms present in wall paintings.
Pyrosequencing, a novel molecular technique, used here for
the first time in this area of research, allowed the identification
of a large number of microorganisms, confirming some already
identified by the cultivation-dependent methods such as
fungi of the genera Penicillium and Cladosporium, but also
providing a great contribution in the identification of several
genera and species, not previously identified in these artworks,
giving also a detailed overview of contaminants which was not possible with the other approaches. The results obtained
on several mural painting samples show a strong relationship
between the most deteriorated areas of the paintings
and higher microbial contamination
Circuit theory for decoherence in superconducting charge qubits
Based on a network graph analysis of the underlying circuit, a quantum theory
of arbitrary superconducting charge qubits is derived. Describing the
dissipative elements of the circuit with a Caldeira-Leggett model, we calculate
the decoherence and leakage rates of a charge qubit. The analysis includes
decoherence due to a dissipative circuit element such as a voltage source or
the quasiparticle resistances of the Josephson junctions in the circuit. The
theory presented here is dual to the quantum circuit theory for superconducting
flux qubits. In contrast to spin-boson models, the full Hilbert space structure
of the qubit and its coupling to the dissipative environment is taken into
account. Moreover, both self and mutual inductances of the circuit are fully
included.Comment: 8 pages, 3 figures; v2: published version; typo in Eq.(30) corrected,
minor changes, reference adde
Hidden gauge structure and derivation of microcanonical ensemble theory of bosons from quantum principles
Microcanonical ensemble theory of bosons is derived from quantum mechanics by
making use of a hidden gauge structure. The relative phase interaction
associated with this gauge structure, described by the Pegg-Barnett formalism,
is shown to lead to perfect decoherence in the thermodynamics limit and the
principle of equal a priori probability, simultaneously.Comment: 10 page
Obstrução Intestinal de Causa Rara e Ecografia Point-of-Care - Em que Ponto nos Encontramos?
Malignant neoplasms of the small bowel, especially from the jejunum, are among the rarest types of cancer. Given its location, a delayed diagnosis is frequent and sometimes only made in an emergency context. The authors present a case of intestinal obstruction, where ultrasonography was pivotal in establishing a diagnosis. Point-of-care ultrasonography seems to be particularly sensitive in assessing emergency patients with abdominal pain, allowing effective orientation and saving human and technical resources.info:eu-repo/semantics/publishedVersio
Non-Markoffian effects of a simple nonlinear bath
We analyze a model of a nonlinear bath consisting of a single two-level
system coupled to a linear bath (a classical noise force in the limit
considered here). This allows us to study the effects of a nonlinear,
non-Markoffian bath in a particularly simple situation. We analyze the effects
of this bath onto the dynamics of a spin by calculating the decay of the
equilibrium correlator of the spin's z-component. The exact results are
compared with those obtained using three commonly used approximations: a
Markoffian master equation for the spin dynamics, a weak-coupling
approximation, and the substitution of a linear bath for the original nonlinear
bath.Comment: 7 pages, 6 figure
Localization on short-range potentials in dissipative quantum mechanics
In this Letter the problem of the existence of a state localized on a weak
short-range attractive potential in the presence of dissipation is considered.
It is shown that, contrary to the pure quantum case, a localized state is
produced in any number of dimensions, while in low dimensions dissipation leads
to much stronger localization. The results have physical implications for the
dissipative dynamics of objects such as heavy particles in Fermi liquids and
for superconductivity in high- materials.Comment: RevTeX, 4 pages, 1 figure. Published versio
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