862 research outputs found
Dynamics of large anisotropic spin in a sub-ohmic dissipative environment close to a quantum-phase transition
We investigate the dynamics of a large anisotropic spin whose easy-axis
component is coupled to a bosonic bath with a spectral function J(\w)\propto
\omega^s. Such a spin complex might be realized in a single-molecular magnet.
Using the non-perturbative renormalization group, we calculate the line of
quantum-phase transitions in the sub-ohmic regime (). These quantum-phase
transitions only occur for integer spin . For half-integer , the low
temperature fixed-point is identical to the fixed-point of the spin-boson model
without quantum-tunneling between the two levels. Short-time coherent
oscillations in the spin decay prevail even into the localized phase in the
sub-ohmic regime. The influence of the reorganization energy and the recurrence
time on the decoherence in the absence of quantum-tunneling is discussed.Comment: 14 pages,7 figure
Quantum dynamics of a qubit coupled with structured bath
The dynamics of an unbiased spin-boson model with Lorentzian spectral density
is investigated theoretically in terms of the perturbation theory based on a
unitary transformation. The non-equilibrium correlation function and
susceptibility are calculated for both the
off-resonance case and the on-resonance case
. The approach is checked by the Shiba's relation and the
sum rule. Besides, the coherent-incoherent transition point can be
determined, which has not been demonstrated for the structured bath by previous
authors up to our knowledge.Comment: 25 pages, 11 figure
Deciding observational congruence of finite-state CCS expressions by rewriting
AbstractWe propose a term rewriting approach to verify observational congruence between guarded recursive (finite-state) CCS expressions. Starting from the complete axiomatization of observational congruence for this subset of CCS, a non-terminating rewriting relation has been defined. This rewriting relation is ω-canonical over a subclass of infinite derivations, structured fair derivations, which compute all the ω-normal forms. The rewriting relation is shown to be complete with respect to the axiomatization by proving that every structured fair derivation computes a term that denotes an rτ-normal process graph. The existence of a finite representation for ω-normal forms allows the definition of a rewriting strategy that, in a finite number of rewriting steps, decides observational congruence of guarded recursive (finite-state) CCS expressions
The antiquity of hydrocephalus: the first full palaeo-neuropathological description
The Pathology Museum of the University of Florence houses a rich collection of anatomical specimens and over a hundred waxworks portraying pathological conditions occurring in the nineteenth century, when the museum was established. Clinical and autopsy findings of these cases can still be retrieved from the original museum catalogue, offering a rare opportunity for retrospective palaeo-pathological diagnostics. We present a historical case of severe hydrocephalus backed by modern-day anthropological, radiological and molecular analyses conducted on the skeleton of an 18-month-old male infant deceased in 1831. Luigi Calamai (1796-1851), a wax craftsman of La Specola workshop in Florence, was commissioned to create a life-sized wax model of the child's head, neck and upper thorax. This artwork allows us to appreciate the cranial and facial alterations determined by 30 lb of cerebrospinal fluid (CSF) accumulated within the cerebral ventricular system. Based on the autopsy report, gross malformations of the neural tube, tumours and haemorrhage could be excluded. A molecular approach proved helpful in confirming sex. We present this case as the so-far most compelling case of hydrocephalus in palaeo-pathological research
“Heaven” of Data Deficient Species: The Conservation Status of the Endemic Amphibian Fauna of Vietnam
Predicting the true status of Data Deficient (DD) species is a prominent theme in recent conservation biology, but there still is much debate regarding the conservation approach that should be used for DD taxa and no definitive conclusions are yet available. We review and analyse the current data available on the conservation status of amphibians in Vietnam, with an emphasis on the DD species. We also compare Vietnamese DD frequency of occurrence with other regions of the world, examine the extent of the range of taxa divided by Red List status, and explore the protection attributes of the taxa based on their inclusion within protected areas of Vietnam. We documented that the analysis of amphibians in Southeast Asia, and especially in Vietnam, substantially agrees with patterns highlighted by previous global research, and confirms the risk that several DD species may silently go extinct without their actual risk ever being recognized. Importantly, our study showed that fine-scale analyses are essential to highlight the potential drivers of extinction risk for the DD species of amphibians. A crucial next step for conservation policies in Vietnam (and in surrounding countries) is developing and implementing species-specific studies targeted at addressing each species’ drivers of extinction and determining science-based strategies for minimizing their extinction risk
Propagation of sound in a Bose Einstein condensate in an optical lattice
We study the propagation of sound waves in a Bose-Einstein condensate trapped
in a one-dimensional optical lattice. We find that the velocity of propagation
of sound wavepackets decreases with increasing optical lattice depth, as
predicted by the Bogoliubov theory. The strong interplay between nonlinearities
and the periodicity of the external potential raise new phenomena which are not
present in the uniform case. Shock waves, for instance, can propagate slower
than sound waves, due to the negative curvature of the dispersion relation.
Moreover, nonlinear corrections to the Bogoliubov theory appear to be important
even with very small density perturbations, inducing a saturation on the
amplitude of the sound signal
Somatic embryogenesis from zygotic embryos and thin cell layers (TCLs) of Brazilian oil palm (Elaeis guineensis × Elaeis oleifera)
Oil palm hybrid BRS Manicoré is important for plantations in the north of Brazil, as it is resistant to fatal yellowing and is compact. Seed germination is slow and reduced, so somatic embryogenesis is a promising alternative for its propagation. Two kinds of starting explants were used: Zygotic embryos (ZE) and thin cell layers (TCL) from the base of seedling aerial parts. Two culture medium formulae were compared (Y3 and modified MS), and several growth regulators (2,4-D, Picloram, BA, 2iP), putrescine and activated charcoal (AC) were used during the different stages. Somatic embryos (SE) were obtained from ZE-derived embryogenic masses cultured on Y3 medium with or without 2,4-D (9 μM) + 1000 μM putrescine and 40% were converted into seedlings in the Y3 medium supplemented with 2 g.L-¹ AC and without growth regulators, under light. SE developed in 49 to 53% TCL-derived calli and 50% of them were converted into seedlings in the same conditions described for ZE calli. The yield of both processes was compared, showing the superiority of TCL explants for SE production.Key words: Y3 culture medium, clonal propagation, putrescine, thin cell layer
Phonon distributions of a single bath mode coupled to a quantum dot
The properties of an unconventional, single mode phonon bath coupled to a
quantum dot, are investigated within the rotating wave approximation. The
electron current through the dot induces an out of equilibrium bath, with a
phonon distribution qualitatively different from the thermal one. In selected
transport regimes, such a distribution is characterized by a peculiar selective
population of few phonon modes and can exhibit a sub-Poissonian behavior. It is
shown that such a sub-Poissonian behavior is favored by a double occupancy of
the dot. The crossover from a unequilibrated to a conventional thermal bath is
explored, and the limitations of the rotating wave approximation are discussed.Comment: 21 Pages, 7 figures, to appear in New Journal of Physics - Focus on
Quantum Dissipation in Unconventional Environment
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