36,152 research outputs found
Biogeographical patterns of the neotropical genus Battus Scopoli 1777 (Lepidoptera Papilionidae)
A phylogenetic approach to the groups of species of the neotropical Troidines currently included in the genus Battus Scopoli 1777 has been conducted. In the light of historical and ecological processes of evolution in the neotropical biota, the cladogram of Battiti is discussed. General vicariance patterns, as well as dispersal events which contributed to the present distribution of the taxa, are suggested to have operated at different spatial and temporal points
New Theoretical Approach to Quantum Size Effects of Interactive Electron-hole in Spherical Semiconductor Quantum Dots
The issue of quantum size effects of interactive electron-hole systems in
spherical semiconductor quantum dots is put to question. A sharper theoretical
approach is suggested based on a new pseudo-potential method. In this new
setting, analytical computations can be performed in most intermediate steps
lending stronger support to the adopted physical assumptions. The resulting
numerical values for physical quantities are found to be much closer to the
experimental values than those existing so far in the literature
Recurrence for persistent random walks in two dimensions
We discuss the question of recurrence for persistent, or Newtonian, random
walks in Z^2, i.e., random walks whose transition probabilities depend both on
the walker's position and incoming direction. We use results by Toth and
Schmidt-Conze to prove recurrence for a large class of such processes,
including all "invertible" walks in elliptic random environments. Furthermore,
rewriting our Newtonian walks as ordinary random walks in a suitable graph, we
gain a better idea of the geometric features of the problem, and obtain further
examples of recurrence.Comment: 20 pages, 7 figure
Beyond the thermodynamic limit: finite-size corrections to state interconversion rates
Thermodynamics is traditionally constrained to the study of macroscopic
systems whose energy fluctuations are negligible compared to their average
energy. Here, we push beyond this thermodynamic limit by developing a
mathematical framework to rigorously address the problem of thermodynamic
transformations of finite-size systems. More formally, we analyse state
interconversion under thermal operations and between arbitrary
energy-incoherent states. We find precise relations between the optimal rate at
which interconversion can take place and the desired infidelity of the final
state when the system size is sufficiently large. These so-called second-order
asymptotics provide a bridge between the extreme cases of single-shot
thermodynamics and the asymptotic limit of infinitely large systems. We
illustrate the utility of our results with several examples. We first show how
thermodynamic cycles are affected by irreversibility due to finite-size
effects. We then provide a precise expression for the gap between the
distillable work and work of formation that opens away from the thermodynamic
limit. Finally, we explain how the performance of a heat engine gets affected
when one of the heat baths it operates between is finite. We find that while
perfect work cannot generally be extracted at Carnot efficiency, there are
conditions under which these finite-size effects vanish. In deriving our
results we also clarify relations between different notions of approximate
majorisation.Comment: 31 pages, 10 figures. Final version, to be published in Quantu
Quantization of the String Inspired Dilaton Gravity and the Birkhoff Theorem
We develop a simple scheme of quantization for the dilaton CGHS model without
scalar fields, that uses the Gupta-Bleuler approach for the string fields. This
is possible because the constraints can be linearized classically, due to
positivity conditions that are present in the model (and not in the general
string case). There is no ambiguity nor anomalies in the quantization. The
expectation values of the metric and dilaton fields obey the classical
requirements, thus exhibiting at the quantum level the Birkhoff theorem.Comment: 15 pages, Plain TeX, a shortened version will appear in Physics
Letters
Continuous-variable entanglement distillation and non-commutative central limit theorems
Entanglement distillation transforms weakly entangled noisy states into
highly entangled states, a primitive to be used in quantum repeater schemes and
other protocols designed for quantum communication and key distribution. In
this work, we present a comprehensive framework for continuous-variable
entanglement distillation schemes that convert noisy non-Gaussian states into
Gaussian ones in many iterations of the protocol. Instances of these protocols
include (a) the recursive-Gaussifier protocol, (b) the temporally-reordered
recursive-Gaussifier protocol, and (c) the pumping-Gaussifier protocol. The
flexibility of these protocols give rise to several beneficial trade-offs
related to success probabilities or memory requirements, which that can be
adjusted to reflect experimental demands. Despite these protocols involving
measurements, we relate the convergence in this protocols to new instances of
non-commutative central limit theorems, in a formalism that we lay out in great
detail. Implications of the findings for quantum repeater schemes are
discussed.Comment: published versio
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