384 research outputs found
Drude model and Lifshitz formula
Since nearly 10 years, it is known that inserting the permittivity of the
Drude model into the Lifshitz formula for free energy causes a violation of the
third law of thermodynamics. In this paper we show that the standard Matsubara
formulation for free energy contains a contribution that is non-perturbative in
the relaxation parameter. We argue that the correct formula must have a
perturbative expansion and conclude that the standard Matsubara formulation
with the permittivity of the Drude model inserted is not correct. We trace the
non-perturbative contribution in the complex frequency plane, where it shows up
as a self-intersection or a bifurcation of the integration path.Comment: accepted for publication in EPJ
The students' view
This year UKSG awarded six sponsored delegate places to students who had answered the call for applications.The following is an amalgam of excerpts from their reports on impressions and experiences of the 27th UKSG Annual Conference and Exhibition
Geometry and material effects in Casimir physics - Scattering theory
We give a comprehensive presentation of methods for calculating the Casimir
force to arbitrary accuracy, for any number of objects, arbitrary shapes,
susceptibility functions, and separations. The technique is applicable to
objects immersed in media other than vacuum, to nonzero temperatures, and to
spatial arrangements in which one object is enclosed in another. Our method
combines each object's classical electromagnetic scattering amplitude with
universal translation matrices, which convert between the bases used to
calculate scattering for each object, but are otherwise independent of the
details of the individual objects. This approach, which combines methods of
statistical physics and scattering theory, is well suited to analyze many
diverse phenomena. We illustrate its power and versatility by a number of
examples, which show how the interplay of geometry and material properties
helps to understand and control Casimir forces. We also examine whether
electrodynamic Casimir forces can lead to stable levitation. Neglecting
permeabilities, we prove that any equilibrium position of objects subject to
such forces is unstable if the permittivities of all objects are higher or
lower than that of the enveloping medium; the former being the generic case for
ordinary materials in vacuum.Comment: 44 pages, 11 figures, to appear in upcoming Lecture Notes in Physics
volume in Casimir physic
Effects of exercise on physical and mental health, and cognitive and brain functions in schizophrenia: clinical and experimental evidence
Exercise promotes several health benefits, such as cardiovascular, musculoskeletal and cardiorespiratory improvements. It is believed that the practice of exercise in individuals with psychiatric disorders, e.g. schizophrenia, can cause significant changes. Schizophrenic patients have problematic lifestyle habits compared with general population; this may cause a high mortality rate, mainly caused by cardiovascular and metabolic diseases. Thus, the aim of this study is to investigate changes in physical and mental health, cognitive and brain functioning due to the practice of exercise in patients with schizophrenia. Although still little is known about the benefits of exercise on mental health, cognitive and brain functioning of schizophrenic patients, exercise training has been shown to be a beneficial intervention in the control and reduction of disease severity. Type of training, form of execution, duration and intensity need to be better studied as the effects on physical and mental health, cognition and brain activity depend exclusively of interconnected factors, such as the combination of exercise and medication. However, one should understand that exercise is not only an effective nondrug alternative, but also acts as a supporting linking up interventions to promote improvements in process performance optimization. In general, the positive effects on mental health, cognition and brain activity as a result of an exercise program are quite evident. Few studies have been published correlating effects of exercise in patients with schizophrenia, but there is increasing evidence that positive and negative symptoms can be improved. Therefore, it is important that further studies be undertaken to expand the knowledge of physical exercise on mental health in people with schizophrenia, as well as its dose-response and the most effective type of exercise
4pi Models of CMEs and ICMEs
Coronal mass ejections (CMEs), which dynamically connect the solar surface to
the far reaches of interplanetary space, represent a major anifestation of
solar activity. They are not only of principal interest but also play a pivotal
role in the context of space weather predictions. The steady improvement of
both numerical methods and computational resources during recent years has
allowed for the creation of increasingly realistic models of interplanetary
CMEs (ICMEs), which can now be compared to high-quality observational data from
various space-bound missions. This review discusses existing models of CMEs,
characterizing them by scientific aim and scope, CME initiation method, and
physical effects included, thereby stressing the importance of fully 3-D
('4pi') spatial coverage.Comment: 14 pages plus references. Comments welcome. Accepted for publication
in Solar Physics (SUN-360 topical issue
Observational tests of the galaxy formation process
The mutual feedback between star formation and nuclear activity in large
spheroidal galaxies may be a key ingredient to overcome several difficulties
plaguing current semi-analytic models for galaxy formation. We discuss some
observational implications of the model by Granato et al. (2003) for the
co-evolution of galaxies and active nuclei at their centers and stress the
potential of the forthcoming surveys of the Sunyaev-Zeldovich effect on
arcminute scales, down to K levels, to investigate the early galaxy
formation phases, difficult to access by other means.Comment: 6, pages, 1 figure, to appear in proc. of the meeting "Baryons on
Cosmic Structures", Roma, October 20-21, 200
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