19,265 research outputs found
The Human Thioesterase II Protein Binds to a Site on HIV-1 Nef Critical for CD4 Down-regulation
A HIV-1 Nef affinity column was used to purify a 35-kDa Nef-interacting protein from T-cell lysates. The 35-kDa protein was identified by peptide microsequence analysis as the human thioesterase II (hTE) enzyme, an enzyme previously identified in a yeast two-hybrid screen as a potential Nef-interacting protein. Immunofluorescence studies showed that hTE localizes to peroxisomes and that coexpression of Nef and hTE leads to relocalization of Nef to peroxisomes. Interaction of Nef and hTE was abolished by point mutations in Nef at residues Asp108, Leu112, Phe121, Pro122, and Asp123. All of these mutations also abrogated the ability of Nef to down-regulate CD4 from the surface of HIV-infected cells. Based on the x-ray and NMR structures of Nef, these residues define a surface on Nef critical for CD4 down-regulation. A subset of these mutations also affected the ability of Nef to down-regulate major histocompatibility complex class I. These results, taken together with previous studies, identify a region on Nef critical for most of its known functions. However, not all Nef alleles bind to hTE with high affinity, so the role of hTE during HIV infection remains uncertain
Trends in Elasticity and Electronic Structure of Transition-Metal Nitrides and Carbides from First Principles
The elastic properties of the -structured transition-metal nitrides and
their carbide counterparts are studied using the {\it ab initio\} density
functional perturbation theory. The linear response results of elastic
constants are in excellent agreement with those obtained from numerical
derivative methods, and are also consistent with measured data. We find the
following trends: (1) Bulk moduli and tetragonal shear moduli
, increase and lattice constants decrease
rightward or downward on the Periodic Table for the metal component or if C is
replaced by N; (2) The inequality holds for
; (3) depends strongly on the number of valence electrons per
unit cell (). From the fitted curve of as a function of , we
can predict that MoN is unstable in structure, and transition-metal
carbonitrides ( ZrCN) and di-transition-metal carbides
( HfTaC) have maximum at .Comment: 4 pages, 2 figures, submitted to PRL. 2 typos in ref. 15 were
correcte
Event Horizon Deformations in Extreme Mass-Ratio Black Hole Mergers
We study the geometry of the event horizon of a spacetime in which a small
compact object plunges into a large Schwarzschild black hole. We first use the
Regge-Wheeler and Zerilli formalisms to calculate the metric perturbations
induced by this small compact object, then find the new event horizon by
propagating null geodesics near the unperturbed horizon. A caustic is shown to
exist before the merger. Focusing on the geometry near the caustic, we show
that it is determined predominantly by large-l perturbations, which in turn
have simple asymptotic forms near the point at which the particle plunges into
the horizon. It is therefore possible to obtain an analytic characterization of
the geometry that is independent of the details of the plunge. We compute the
invariant length of the caustic. We further show that among the leading-order
horizon area increase, half arises from generators that enter the horizon
through the caustic, and the rest arises from area increase near the caustic,
induced by the gravitational field of the compact object.Comment: 23 pages, 14 figure
A framework for bounding nonlocality of state discrimination
We consider the class of protocols that can be implemented by local quantum
operations and classical communication (LOCC) between two parties. In
particular, we focus on the task of discriminating a known set of quantum
states by LOCC. Building on the work in the paper "Quantum nonlocality without
entanglement" [BDF+99], we provide a framework for bounding the amount of
nonlocality in a given set of bipartite quantum states in terms of a lower
bound on the probability of error in any LOCC discrimination protocol. We apply
our framework to an orthonormal product basis known as the domino states and
obtain an alternative and simplified proof that quantifies its nonlocality. We
generalize this result for similar bases in larger dimensions, as well as the
"rotated" domino states, resolving a long-standing open question [BDF+99].Comment: 33 pages, 7 figures, 1 tabl
Warped Compactification with an Abelian Gauge Theory
We investigate warped compactification with an abelian gauge theory in six
dimensions. The vanishing cosmological constant in four dimensions can
generically be realized with a regular metric even in a 3-brane background
without fine tuning of couplings.Comment: 6 pages, late
Percolation theory applied to measures of fragmentation in social networks
We apply percolation theory to a recently proposed measure of fragmentation
for social networks. The measure is defined as the ratio between the
number of pairs of nodes that are not connected in the fragmented network after
removing a fraction of nodes and the total number of pairs in the original
fully connected network. We compare with the traditional measure used in
percolation theory, , the fraction of nodes in the largest cluster
relative to the total number of nodes. Using both analytical and numerical
methods from percolation, we study Erd\H{o}s-R\'{e}nyi (ER) and scale-free (SF)
networks under various types of node removal strategies. The removal strategies
are: random removal, high degree removal and high betweenness centrality
removal. We find that for a network obtained after removal (all strategies) of
a fraction of nodes above percolation threshold, . For fixed and close to percolation threshold
(), we show that better reflects the actual fragmentation. Close
to , for a given , has a broad distribution and it is
thus possible to improve the fragmentation of the network. We also study and
compare the fragmentation measure and the percolation measure
for a real social network of workplaces linked by the households of the
employees and find similar results.Comment: submitted to PR
Are autistic traits measured equivalently in individuals with and without an Autism Spectrum Disorder?:An invariance analysis of the Autism Spectrum Quotient Short Form
It is common to administer measures of autistic traits to those without autism spectrum disorders (ASDs) with, for example, the aim of understanding autistic personality characteristics in non-autistic individuals. Little research has examined the extent to which measures of autistic traits actually measure the same traits in the same way across those with and without an ASD. We addressed this question using a multi-group confirmatory factor invariance analysis of the Autism Quotient Short Form (AQ-S: Hoekstra et al. in J Autism Dev Disord 41(5):589-596, 2011) across those with (n = 148) and without (n = 168) ASD. Metric variance (equality of factor loadings), but not scalar invariance (equality of thresholds), held suggesting that the AQ-S measures the same latent traits in both groups, but with a bias in the manner in which trait levels are estimated. We, therefore, argue that the AQ-S can be used to investigate possible causes and consequences of autistic traits in both groups separately, but caution is due when combining or comparing levels of autistic traits across the two group
Detecting Bose-Einstein condensation of exciton-polaritons via electron transport
We examine the Bose-Einstein condensation of exciton-polaritons in a
semiconductor microcavity via an electrical current. We propose that by
embedding a quantum dot p-i-n junction inside the cavity, the tunneling current
through the device can reveal features of condensation due to a one-to-one
correspondence of the photons to the condensate polaritons. Such a device can
also be used to observe the phase interference of the order parameters from two
condensates.Comment: 5 Pages, 3 Figure
Dealing in hope: Does observing hope expressions increase conciliatory attitudes in intergroup conflict?
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