5,520 research outputs found
Consistent thermodynamics for spin echoes
Spin-echo experiments are often said to constitute an instant of
anti-thermodynamic behavior in a concrete physical system that violates the
second law of thermodynamics. We argue that a proper thermodynamic treatment of
the effect should take into account the correlations between the spin and
translational degrees of freedom of the molecules. To this end, we construct an
entropy functional using Boltzmann macrostates that incorporates both spin and
translational degrees of freedom. With this definition there is nothing special
in the thermodynamics of spin echoes: dephasing corresponds to Hamiltonian
evolution and leaves the entropy unchanged; dissipation increases the entropy.
In particular, there is no phase of entropy decrease in the echo. We also
discuss the definition of macrostates from the underlying quantum theory and we
show that the decay of net magnetization provides a faithful measure of entropy
change.Comment: 15 pages, 2 figs. Changed figures, version to appear in PR
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Accessing and assessing lunar resources with PROSPECT
PROSPECT is a package in development by ESA to assess the in-situ resource potential of lunar regolith. PROSPECT will: obtain sub-surface regolith samples, extract volatiles, identify chemical species, quantify abundances, and characterize isotopes
Membrane shape as a reporter for applied forces
Recent advances have enabled 3-dimensional reconstructions of biological structures in vivo, ranging in size and complexity from single proteins to multicellular structures. In particular, tomography and confocal microscopy have been exploited to capture detailed 3-dimensional conformations of membranes in cellular processes ranging from viral budding and organelle maintenance to phagocytosis. Despite the wealth of membrane structures available, there is as yet no generic, quantitative method for their interpretation. We propose that by modeling these observed biomembrane shapes as fluid lipid bilayers in mechanical equilibrium, the externally applied forces as well as the pressure, tension, and spontaneous curvature can be computed directly from the shape alone. To illustrate the potential power of this technique, we apply an axial force with optical tweezers to vesicles and explicitly demonstrate that the applied force is equal to the force computed from the membrane conformation
Quantum Computation with Quantum Dots
We propose a new implementation of a universal set of one- and two-qubit
gates for quantum computation using the spin states of coupled single-electron
quantum dots. Desired operations are effected by the gating of the tunneling
barrier between neighboring dots. Several measures of the gate quality are
computed within a newly derived spin master equation incorporating decoherence
caused by a prototypical magnetic environment. Dot-array experiments which
would provide an initial demonstration of the desired non-equilibrium spin
dynamics are proposed.Comment: 12 pages, Latex, 2 ps figures. v2: 20 pages (very minor corrections,
substantial expansion), submitted to Phys. Rev.
Three Dimensional Secondary Ion Mass Spectrometry Imaging and Retrospective Depth Profiling
Secondary Ion Mass Spectrometry (SIMS) for three dimensional analysis of materials is an exciting and rapidly developing technique. We describe a framestore datasystem for ion microprobe instruments and present images and three dimensional SIMS data acquired and processed with this system. The concept of retrospective depth profiling is introduced, particularly as a means to optimise concentration detection limits. We examine the dependence of concentration detection limits on spatial resolution
Gravitational collapse of an isentropic perfect fluid with a linear equation of state
We investigate here the gravitational collapse end states for a spherically
symmetric perfect fluid with an equation of state . It is shown that
given a regular initial data in terms of the density and pressure profiles at
the initial epoch from which the collapse develops, the black hole or naked
singularity outcomes depend on the choice of rest of the free functions
available, such as the velocities of the collapsing shells, and the dynamical
evolutions as allowed by Einstein equations. This clarifies the role that
equation of state and initial data play towards determining the final fate of
gravitational collapse.Comment: 7 Pages, Revtex4, To appear in Classical and Quantum Gravit
Physical nature of the central singularity in spherical collapse
We examine here the nature of the central singularity forming in the
spherically symmetric collapse of a dust cloud and it is shown that this is
always a strong curvature singularity where gravitational tidal forces diverge
powerfully. An important consequence is that the nature of the naked
singularity forming in the dust collapse turns out to be stable against the
perturbations in the initial data from which the collapse commences.Comment: Latex file, 11 pages, 2 figures, Updated version to match the
published version in PR
Physical mapping of chromosomes 3HS and 3DS
Relatório de estágio do mestrado em Ensino da Educação Física nos Ensinos Básico e Secundário, apresentado à Faculdade de Ciências do Desporto e Educação Física da Universidade de CoimbraO presente documento divide-se em duas partes: a reflexão dos aspetos relacionados com o estágio pedagógico e o desenvolvimento do tema-problema.
Numa primeira fase será dado enfoque à prática da docência, desenvolvida na escola E.B.2,3 Dr. Daniel de Matos. Serão apresentadas as expectativas iniciais em relação à prática, serão apresentadas e justificadas as opções metodológicas tomadas ao longo do estágio, serão relatadas as atividades desenvolvidas durante o estágio e será realçada a componente ética e profissional da profissão. De seguida será realizada uma justificação das opções tomadas. Para finalizar a primeira parte do presente trabalho será feita uma análise reflexiva sobre a prática pedagógica.
Na segunda parte temos o tema-problema e seu desenvolvimento, num documento que se pretende orientador da prática docente e auxiliar de como resolver comportamentos de desvio da tarefa por parte dos alunos. Servirá também para analisar e mostrar conclusões sobre o problema que a escola atual, enquanto organização enfrenta, a indisciplina.
Será efetuada uma pequena investigação, em que o objetivo é analisar a perceção dos docentes de uma escola pública sobre a gravidade dos comportamentos de indisciplina praticados.
O objetivo é chegar a alguma conclusão que possa ajudar/beneficiar os professores da escola na procura de estratégias e metodologias que possam minimizar o impacto deste tipo de comportamentos no normal funcionamento da aula.
This document is divided into two parts: a reflection of aspects related to teaching practice and development of the “theme-issue”.
Initially focus will be given to the practice of teaching, developed in E.B.2, 3 Dr. Daniel de Matos school. Initial expectations will be presented, as well as the methodological choices made along the stage and its reasons. The activities made during the internship will be reported and I will emphasize ethics and professional component of the teacher’s profession. Then I will do a justification of the choices made. To finish the first part of this work I will make a reflective analysis of teaching practice.
In the second part we have the “theme-issue” and its development, a document intended to be the guiding teaching practice and assist in solving the task behaviors of misuse by students. Will also serve to analyze and display conclusions about the problem that the current school, as an organization, faces, the indiscipline.
Will be performed a little investigation, in which the objective is to analyze the perceptions of teachers in a public school on the severity of disruptive behaviors committed.
The goal is to achieve some conclusion that can help / benefit school teachers in finding strategies and methodologies that can minimize the impact of such behaviors on normal class
Force balance and membrane shedding at the Red Blood Cell surface
During the aging of the red-blood cell, or under conditions of extreme
echinocytosis, membrane is shed from the cell plasma membrane in the form of
nano-vesicles. We propose that this process is the result of the
self-adaptation of the membrane surface area to the elastic stress imposed by
the spectrin cytoskeleton, via the local buckling of membrane under increasing
cytoskeleton stiffness. This model introduces the concept of force balance as a
regulatory process at the cell membrane, and quantitatively reproduces the rate
of area loss in aging red-blood cells.Comment: 4 pages, 3 figure
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