21,631 research outputs found
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
Why Two Renormalization Groups are Better than One
The advantages of using more than one renormalization group (RG) in problems
with more than one important length scale are discussed. It is shown that: i)
using different RG's can lead to complementary information, i.e. what is very
difficult to calculate with an RG based on one flow parameter may be much more
accessible using another; ii) using more than one RG requires less physical
input in order to describe via RG methods the theory as a function of its
parameters; iii) using more than one RG allows one to solve problems with more
than one diverging length scale. The above points are illustrated concretely in
the context of both particle physics and statistical physics using the
techniques of environmentally friendly renormalization. Specifically, finite
temperature theory, an Ising-type system in a film geometry, an
Ising-type system in a transverse magnetic field, the QCD coupling constant at
finite temperature and the crossover between bulk and surface critical
behaviour in a semi-infinite geometry are considered.Comment: 17 pages LaTex; to be published in the Proceedings of RG '96, Dubn
Variation of the broad X-ray iron line in MCG-6-30-15 during a flare
We report results on the broad iron emission line of the Seyfert galaxy
MCG-6-30-15, obtained from the second long ASCA observation in 1997. The
time-averaged profile of the broad line is very similar to that seen with ASCA
in 1994, so confirming the detailed model fit then obtained. A bright flare is
seen in the light curve, during which the continuum was soft. At that time the
emission line peaks around 5 keV and most of its emission is shifted below 6
keV with no component detected at 6.4 keV (EW<60 eV). This can be interpreted
as the result of an extraordinarily large gravitational redshift due to a
dominant flare occurring very close to the black hole at a radius of <5m.Comment: 5 pages, accepted or publication in MNRAS Letter
Quantum multiparty key distribution protocol without use of entanglement
We propose a quantum key distribution (QKD) protocol that enables three
parties agree at once on a shared common random bit string in presence of an
eavesdropper without use of entanglement. We prove its unconditional security
and analyze the key rate.Comment: 8 pages, no figur
Self-discharge characteristics of spacecraft nickel-cadmium cells at elevated temperatures
The effects of heat generation were determined in NiCd cells during high temperature storage on open circuits. The testing was designed to determine the extent to which thermal stability is a valid concern, at temperature of exposure (externally effected) between 40 and 120 C
Boltzmann Suppression of Interacting Heavy Particles
Matsumoto and Yoshimura have recently argued that the number density of heavy
particles in a thermal bath is not necessarily Boltzmann-suppressed for T << M,
as power law corrections may emerge at higher orders in perturbation theory.
This fact might have important implications on the determination of WIMP relic
densities. On the other hand, the definition of number densities in a
interacting theory is not a straightforward procedure. It usually requires
renormalization of composite operators and operator mixing, which obscure the
physical interpretation of the computed thermal average. We propose a new
definition for the thermal average of a composite operator, which does not
require any new renormalization counterterm and is thus free from such
ambiguities. Applying this definition to the model of Matsumoto and Yoshimura
we find that it gives number densities which are Boltzmann-suppressed at any
order in perturbation theory. We discuss also heavy particles which are
unstable already at T=0, showing that power law corrections do in general
emerge in this case.Comment: 7 pages, 5 figures. New section added, with the discussion of the
case of an unstable heavy particle. Version to appear on Phys. Rev.
On the Bloch Theorem Concerning Spontaneous Electric Current
We study the Bloch theorem which states absence of the spontaneous current in
interacting electron systems. This theorem is shown to be still applicable to
the system with the magnetic field induced by the electric current. Application
to the spontaneous surface current is also examined in detail. Our result
excludes the possibility of the recently proposed -wave superconductivity
having the surface flow and finite total current.Comment: 12 pages, LaTeX, 3 Postscript figure
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