28,866 research outputs found
Thermal Abundances of Heavy Particles
Matsumoto and Yoshimura [hep-ph/9910393] have argued that there are loop
corrections to the number density of heavy particles (in thermal equilibrium
with a gas of light particles) that are not Boltzmann suppressed by a factor of
e^(-M/T) at temperatures T well below the mass M of the heavy particle. We
argue, however, that their definition of the number density does not correspond
to a quantity that could be measured in a realistic experiment. We consider a
model where the heavy particles carry a conserved U(1) charge, and the light
particles do not. The fluctuations of the net charge in a given volume then
provide a measure of the total number of heavy particles in that same volume.
We show that these charge fluctuations are Boltzmann suppressed (to all orders
in perturbation theory). Therefore, we argue, the number density of heavy
particles is also Boltzmann suppressed.Comment: 9 pages, 1 figure; minor improvements in revised versio
Catharine E. Davis, Plaintiff, -against- NYC Department of Education, Lisa Linder, Defendants.
Pathogen-host reorganization during Chlamydia invasion revealed by cryo-electron tomography
Invasion of host cells is a key early event during bacterial infection, but the underlying pathogen-host interactions are yet to be fully visualised in three-dimensional detail. We have captured snapshots of the early stages of bacterial-mediated endocytosis in situ by exploiting the small size of chlamydial elementary bodies (EBs) for whole cell cryo-electron tomography. Chlamydiae are obligate intracellular bacteria that infect eukaryotic cells and cause sexually transmitted infections and trachoma, the leading cause of preventable blindness. We demonstrate that Chlamydia trachomatis LGV2 EBs are intrinsically polarised. One pole is characterised by a tubular inner membrane invagination, while the other exhibits asymmetric periplasmic expansion to accommodate an array of type III secretion systems (T3SSs). Strikingly, EBs orient with their T3SS-containing pole facing target cells, enabling the T3SSs to directly contact the cellular plasma membrane. This contact induces enveloping macropinosomes, actin-rich filopodia and phagocytic cups to zipper tightly around the internalising bacteria. Once encapsulated into tight early vacuoles, EB polarity and the T3SSs are lost. Our findings reveal previously undescribed structural transitions in both pathogen and host during the initial steps of chlamydial invasion
Generalized -conformal change and special Finsler spaces
In this paper, we investigate the change of Finslr metrics which we refer to as a
generalized -conformal change. Under this change, we study some special
Finsler spaces, namely, quasi C-reducible, semi C-reducible, C-reducible,
-like, -like and -like Finsler spaces. We also obtain the
transformation of the T-tensor under this change and study some interesting
special cases. We then impose a certain condition on the generalized
-conformal change, which we call the b-condition, and investigate the
geometric consequences of such condition. Finally, we give the conditions under
which a generalized -conformal change is projective and generalize some
known results in the literature.Comment: References added, some modifications are performed, LateX file, 24
page
Bose-Einstein condensation of magnons in TlCuCl
A quantitative study of the field-induced magnetic ordering in TlCuCl in
terms of a Bose-Einstein condensation (BEC) of magnons is presented. It is
shown that the hitherto proposed simple BEC scenario is in quantitative and
qualitative disagreement with experiment. It is further shown that even very
small Dzyaloshinsky-Moriya interactions or a staggered tensor component of
a certain type can change the BEC picture qualitatively. Such terms lead to a
nonzero condensate density for all temperatures and a gapped quasiparticle
spectrum. Including this type of interaction allows us to obtain good agreement
with experimental data.Comment: 2 pages, 2 figures, submitted to SCES'0
Patterns on a Roll: A Method for Continuous Feed Nanoprinting
Exploiting elastic instability in thin films has proven a robust method for
creating complex patterns and structures across a wide range of lengthscales.
Even the simplest of systems, an elastic membrane with a lattice of pores,
under mechanical strain, generates complex patterns featuring long-range
orientational order. When we promote this system to a curved surface, in
particular, a cylindrical membrane, a novel set of features, patterns and
broken symmetries appears. The newfound periodicity of the cylinder allows for
a novel continuous method for nanoprinting.Comment: 4 pages, 4 figure
Uncertainty principle for proper time and mass
We review Bohr's reasoning in the Bohr-Einstein debate on the photon box
experiment. The essential point of his reasoning leads us to an uncertainty
relation between the proper time and the rest mass of the clock. It is shown
that this uncertainty relation can be derived if only we take the fundamental
point of view that the proper time should be included as a dynamic variable in
the Lagrangian describing the system of the clock. Some problems and some
positive aspects of our approach are then discussed.Comment: 15 pages, accepted for publication in J. Math. Phy
New Kinetic Equation for Pair-annihilating Particles: Generalization of the Boltzmann Equation
A convenient form of kinetic equation is derived for pair annihilation of
heavy stable particles relevant to the dark matter problem in cosmology. The
kinetic equation thus derived extends the on-shell Boltzmann equation in a most
straightforward way, including the off-shell effect. A detailed balance
equation for the equilibrium abundance is further analyzed. Perturbative
analysis of this equation supports a previous result for the equilibrium
abundance using the thermal field theory, and gives the temperature power
dependence of equilibrium value at low temperatures. Estimate of the relic
abundance is possible using this new equilibrium abundance in the sudden
freeze-out approximation.Comment: 19 pages, LATEX file with 2 PS figure
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