2,851 research outputs found
Evolution of replication efficiency following infection with a molecularly cloned feline immunodeficiency virus of low virulence
The development of an effective vaccine against human immunodeficiency virus is considered to be the most practicable means of controlling the advancing global AIDS epidemic. Studies with the domestic cat have demonstrated that vaccinal immunity to infection can be induced against feline immunodeficiency virus (FIV); however, protection is largely restricted to laboratory strains of FIV and does not extend to primary strains of the virus. We compared the pathogenicity of two prototypic vaccine challenge strains of FIV derived from molecular clones; the laboratory strain PET<sub>F14</sub> and the primary strain GL8<sub>414</sub>. PET<sub>F14</sub> established a low viral load and had no effect on CD4<sup>+</sup>- or CD8<sup>+</sup>- lymphocyte subsets. In contrast, GL8<sub>414</sub> established a high viral load and induced a significant reduction in the ratio of CD4<sup>+</sup> to CD8<sup>+</sup> lymphocytes by 15 weeks postinfection, suggesting that PET<sub>F14</sub> may be a low-virulence-challenge virus. However, during long-term monitoring of the PET<sub>F14</sub>-infected cats, we observed the emergence of variant viruses in two of three cats. Concomitant with the appearance of the variant viruses, designated 627<sub>W135</sub> and 628<sub>W135</sub>, we observed an expansion of CD8<sup>+</sup>-lymphocyte subpopulations expressing reduced CD8 ß-chain, a phenotype consistent with activation. The variant viruses both carried mutations that reduced the net charge of the V3 loop (K409Q and K409E), giving rise to a reduced ability of the Env proteins to both induce fusion and to establish productive infection in CXCR4-expressing cells. Further, following subsequent challenge of naïve cats with the mutant viruses, the viruses established higher viral loads and induced more marked alterations in CD8<sup>+</sup>-lymphocyte subpopulations than did the parent F14 strain of virus, suggesting that the E409K mutation in the PET<sub>F14</sub> strain contributes to the attenuation of the virus
Simulating spin-3/2 particles at colliders
Support for interactions of spin-3/2 particles is implemented in the
FeynRules and ALOHA packages and tested with the MadGraph 5 and CalcHEP event
generators in the context of three phenomenological applications. In the first,
we implement a spin-3/2 Majorana gravitino field, as in local supersymmetric
models, and study gravitino and gluino pair-production. In the second, a
spin-3/2 Dirac top-quark excitation, inspired from compositness models, is
implemented. We then investigate both top-quark excitation and top-quark
pair-production. In the third, a general effective operator for a spin-3/2
Dirac quark excitation is implemented, followed by a calculation of the angular
distribution of the s-channel production mechanism.Comment: 20 pages, 7 figure
Stealth Dark Matter: Dark scalar baryons through the Higgs portal
We present a new model of "Stealth Dark Matter": a composite baryonic scalar
of an strongly-coupled theory with even . All mass scales
are technically natural, and dark matter stability is automatic without
imposing an additional discrete or global symmetry. Constituent fermions
transform in vector-like representations of the electroweak group that permit
both electroweak-breaking and electroweak-preserving mass terms. This gives a
tunable coupling of stealth dark matter to the Higgs boson independent of the
dark matter mass itself. We specialize to , and investigate the
constraints on the model from dark meson decay, electroweak precision
measurements, basic collider limits, and spin-independent direct detection
scattering through Higgs exchange. We exploit our earlier lattice simulations
that determined the composite spectrum as well as the effective Higgs coupling
of stealth dark matter in order to place bounds from direct detection,
excluding constituent fermions with dominantly electroweak-breaking masses. A
lower bound on the dark baryon mass GeV is obtained from the
indirect requirement that the lightest dark meson not be observable at LEP II.
We briefly survey some intriguing properties of stealth dark matter that are
worthy of future study, including: collider studies of dark meson production
and decay; indirect detection signals from annihilation; relic abundance
estimates for both symmetric and asymmetric mechanisms; and direct detection
through electromagnetic polarizability, a detailed study of which will appear
in a companion paper.Comment: 15 pages, 3 figures, citations added, typos fixed, minor
clarification
Lattice simulations with eight flavors of domain wall fermions in SU(3) gauge theory
We study an SU(3) gauge theory with Nf=8 degenerate flavors of light fermions
in the fundamental representation. Using the domain wall fermion formulation,
we investigate the light hadron spectrum, chiral condensate and electroweak S
parameter. We consider a range of light fermion masses on two lattice volumes
at a single gauge coupling chosen so that IR scales approximately match those
from our previous studies of the two- and six-flavor systems. Our results for
the Nf=8 spectrum suggest spontaneous chiral symmetry breaking, though fits to
the fermion mass dependence of spectral quantities do not strongly disfavor the
hypothesis of mass-deformed infrared conformality. Compared to Nf=2 we observe
a significant enhancement of the chiral condensate relative to the symmetry
breaking scale F, similar to the situation for Nf=6. The reduction of the S
parameter, related to parity doubling in the vector and axial-vector channels,
is also comparable to our six-flavor results
Cosmic cookery : making a stereoscopic 3D animated movie.
This paper describes our experience making a short stereoscopic movie visualizing the development of structure in
the universe during the 13.7 billion years from the Big Bang to the present day. Aimed at a general audience for
the Royal Society's 2005 Summer Science Exhibition, the movie illustrates how the latest cosmological theories
based on dark matter and dark energy are capable of producing structures as complex as spiral galaxies and
allows the viewer to directly compare observations from the real universe with theoretical results. 3D is an
inherent feature of the cosmology data sets and stereoscopic visualization provides a natural way to present the
images to the viewer, in addition to allowing researchers to visualize these vast, complex data sets.
The presentation of the movie used passive, linearly polarized projection onto a 2m wide screen but it was
also required to playback on a Sharp RD3D display and in anaglyph projection at venues without dedicated
stereoscopic display equipment. Additionally lenticular prints were made from key images in the movie. We
discuss the following technical challenges during the stereoscopic production process; 1) Controlling the depth
presentation, 2) Editing the stereoscopic sequences, 3) Generating compressed movies in display speci¯c formats.
We conclude that the generation of high quality stereoscopic movie content using desktop tools and equipment
is feasible. This does require careful quality control and manual intervention but we believe these overheads
are worthwhile when presenting inherently 3D data as the result is signi¯cantly increased impact and better
understanding of complex 3D scenes
A Double Sigma Model for Double Field Theory
We define a sigma model with doubled target space and calculate its
background field equations. These coincide with generalised metric equation of
motion of double field theory, thus the double field theory is the effective
field theory for the sigma model.Comment: 26 pages, v1: 37 pages, v2: references added, v3: updated to match
published version - background and detail of calculations substantially
condensed, motivation expanded, refs added, results unchange
The RING-CH ligase K5 antagonizes restriction of KSHV and HIV-1 particle release by mediating ubiquitin-dependent endosomal degradation of tetherin
Tetherin (CD317/BST2) is an interferon-induced membrane protein that inhibits the release of diverse enveloped viral particles. Several mammalian viruses have evolved countermeasures that inactivate tetherin, with the prototype being the HIV-1 Vpu protein. Here we show that the human herpesvirus Kaposi's sarcoma-associated herpesvirus (KSHV) is sensitive to tetherin restriction and its activity is counteracted by the KSHV encoded RING-CH E3 ubiquitin ligase K5. Tetherin expression in KSHV-infected cells inhibits viral particle release, as does depletion of K5 protein using RNA interference. K5 induces a species-specific downregulation of human tetherin from the cell surface followed by its endosomal degradation. We show that K5 targets a single lysine (K18) in the cytoplasmic tail of tetherin for ubiquitination, leading to relocalization of tetherin to CD63-positive endosomal compartments. Tetherin degradation is dependent on ESCRT-mediated endosomal sorting, but does not require a tyrosine-based sorting signal in the tetherin cytoplasmic tail. Importantly, we also show that the ability of K5 to substitute for Vpu in HIV-1 release is entirely dependent on K18 and the RING-CH domain of K5. By contrast, while Vpu induces ubiquitination of tetherin cytoplasmic tail lysine residues, mutation of these positions has no effect on its antagonism of tetherin function, and residual tetherin is associated with the trans-Golgi network (TGN) in Vpu-expressing cells. Taken together our results demonstrate that K5 is a mechanistically distinct viral countermeasure to tetherin-mediated restriction, and that herpesvirus particle release is sensitive to this mode of antiviral inhibition
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