19,928 research outputs found
Stopping distance for high energy jets in weakly-coupled quark-gluon plasmas
We derive a simple formula for the stopping distance for a high-energy quark
traveling through a weakly-coupled quark gluon plasma. The result is given to
next-to-leading-order in an expansion in inverse logarithms ln(E/T), where T is
the temperature of the plasma. We also define a stopping distance for gluons
and give a leading-log result. Discussion of stopping distance has a
theoretical advantage over discussion of energy loss rates in that stopping
distances can be generalized to the case of strong coupling, where one may not
speak of individual partons.Comment: 20 pages, 4 figures [change from v1: fixed embarrassing reference
error
Political preferences and threat perception: opportunities for neuroimaging and developmental research
People have preferences for how their social environment is organized and governed. One influential explanation of variation in these preferences focuses on individual differences in sensitivity to threats. Recent research demonstrates that this relationship is a function not only of the degree of sensitivity (greater or lesser), but also of the danger in question (i.e. immigration or climate change) and the kind of potential harm it poses (i.e. physical pain or contamination). Since many political issues are not unambiguously of one kind, the structure of an individual's reactions to perceived political threats is also uncertain. We argue that future research should (i) use functional neuroimaging to test these structures and (ii) investigate the role of social learning in their transmission
Three-dimensional Roton-Excitations and Supersolid formation in Rydberg-excited Bose-Einstein Condensates
We study the behavior of a Bose-Einstein condensate in which atoms are weakly
coupled to a highly excited Rydberg state. Since the latter have very strong
van der Waals interactions, this coupling induces effective, nonlocal
interactions between the dressed ground state atoms, which, opposed to dipolar
interactions, are isotropically repulsive. Yet, one finds partial attraction in
momentum space, giving rise to a roton-maxon excitation spectrum and a
transition to a supersolid state in three-dimensional condensates. A detailed
analysis of decoherence and loss mechanisms suggests that these phenomena are
observable with current experimental capabilities.Comment: 4 pages, 5 figure
Relativistic viscoelastic fluid mechanics
A detailed study is carried out for the relativistic theory of
viscoelasticity which was recently constructed on the basis of Onsager's linear
nonequilibrium thermodynamics. After rederiving the theory using a local
argument with the entropy current, we show that this theory universally reduces
to the standard relativistic Navier-Stokes fluid mechanics in the long time
limit. Since effects of elasticity are taken into account, the dynamics at
short time scales is modified from that given by the Navier-Stokes equations,
so that acausal problems intrinsic to relativistic Navier-Stokes fluids are
significantly remedied. We in particular show that the wave equations for the
propagation of disturbance around a hydrostatic equilibrium in Minkowski
spacetime become symmetric hyperbolic for some range of parameters, so that the
model is free of acausality problems. This observation suggests that the
relativistic viscoelastic model with such parameters can be regarded as a
causal completion of relativistic Navier-Stokes fluid mechanics. By adjusting
parameters to various values, this theory can treat a wide variety of materials
including elastic materials, Maxwell materials, Kelvin-Voigt materials, and (a
nonlinearly generalized version of) simplified Israel-Stewart fluids, and thus
we expect the theory to be the most universal description of single-component
relativistic continuum materials. We also show that the presence of strains and
the corresponding change in temperature are naturally unified through the
Tolman law in a generally covariant description of continuum mechanics.Comment: 52pages, 11figures; v2: minor corrections; v3: minor corrections, to
appear in Physical Review E; v4: minor change
Relativistic magnetohydrodynamics in one dimension
We derive a number of solution for one-dimensional dynamics of relativistic
magnetized plasma that can be used as benchmark estimates in relativistic
hydrodynamic and magnetohydrodynamic numerical codes.
First, we analyze the properties of simple waves of fast modes propagating
orthogonally to the magnetic field in relativistically hot plasma. The magnetic
and kinetic pressures obey different equations of state, so that the system
behaves as a mixture of gases with different polytropic indices. We find the
self-similar solutions for the expansion of hot strongly magnetized plasma into
vacuum.
Second, we derive linear hodograph and Darboux equations for the relativistic
Khalatnikov potential, which describe arbitrary one-dimensional isentropic
relativistic motion of cold magnetized plasma and find their general and
particular solutions. The obtained hodograph and Darboux equations are very
powerful: system of highly non-linear, relativistic, time dependent equations
describing arbitrary (not necessarily self-similar) dynamics of highly
magnetized plasma reduces to a single linear differential equation.Comment: accepted by Phys. Rev.
The Nazi holocaust
The Nazi Holocaust represents an original, interdisciplinary contribution to the field of education, with special reference to the teaching of the humanities in general, and history in particular. Its claim to originality lies in its overall educational conception, in its approach to understanding and transmitting the memory' and lessons of the Holocaust and in its filling a palpable gap.
Before the publication of my work, despite hundreds of volumes devoted at various levels to the subject - from fields as disparate as history, psychology, sociology, theology, moral philosophy, literature and jurisprudence - there was no single accessible, multidimensional volume for the many hundreds of teachers who were faced - often suddenly, as in the case of Britain - with the intimidating task of teaching this
most complex of subjects; under-informed and under-resourced, they were often resigned to teaching it badly or not at all.
Those works that were available were either too simplistic or were too narrowly focused, over-scholasticised and sometimes shrouded in mystification: they generally
failed to take sufficient stock of the fact that the Holocaust had historical and ideological antecedents, such decontextualisation being, perhaps, the single most
glaring educational problem I identified; virtually all 'historical' works failed even to ask, let alone address, the serious moral and psychological questions raised by the subject, and - most seriously - often formed part of an extremist, partisan and passionate literature, seemingly unable or unwilling to grapple with its broader educational meaning [a meaning that I would argue in my book went way beyond the
world of its Jewish victims].
My work set out to make good these shortcomings, and to attempt a breakthrough in the transmission of its most salient messages for all. In a clear, educationally provocative, yet scholarly fashion, I sought to mediate between a vast, often
unapproachable literature, and the hard-pressed teacher and student who wrestle with its meaning. By examining it from different disciplinary perspectives, I also wanted to demonstrate that no one discipline can claim an educational monopoly on this subject.
My work aimed to break new ground in the educational sphere by locating theHolocaust within a number of historically important and educationally desirable
contexts: namely Jewish history, modem German history, genocide in the modem age, and the larger story of human indifference, bigotry and the triumph of ideology over conscience. It examined the impact and aftermath of the Holocaust, considering its implications not only for the surviving Jewish world (including the State of Israel) but for all humanity.
In such a highly-charged emotional and intellectual arena, my work aimed, uniquely, to strike an enlightened balance between various Scyllas and Charybdises, standing, as it were, in the educational and historiographical crossfire of often diametrically opposed views.
The philosophical starting-point of my work is that the Holocaust, though unquestionably a unique historical event, should not be cordoned off from the rest of human experience and imprisoned within the highly-charged realm of 'Jewish
experience' . It offers a new educational perspective by stressing that the attempt to understand even so appalling a tragedy as the Holocaust is, like all good education, ultimately about the making, and not the breaking, of connections. In short, the Holocaust as educational theme is both unique and universal
Equilibrium topology of the intermediate state in type-I superconductors of different shapes
High-resolution magneto-optical technique was used to analyze flux patterns
in the intermediate state of bulk Pb samples of various shapes - cones,
hemispheres and discs. Combined with the measurements of macroscopic
magnetization these results allowed studying the effect of bulk pinning and
geometric barrier on the equilibrium structure of the intermediate state.
Zero-bulk pinning discs and slabs show hysteretic behavior due to geometric
barrier that results in a topological hysteresis -- flux tubes on penetration
and lamellae on flux exit. (Hemi)spheres and cones do not have geometric
barrier and show no hysteresis with flux tubes dominating the intermediate
field region. It is concluded that flux tubes represent the equilibrium
topology of the intermediate state in reversible samples, whereas laminar
structure appears in samples with magnetic hysteresis (either bulk or
geometric). Real-time video is available in
http://www.cmpgroup.ameslab.gov/supermaglab/video/Pb.html
NOTE: the submitted images were severely downsampled due to Arxiv's
limitations of 1 Mb total size
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