1,417 research outputs found
Do the constants of nature couple to strong gravitational fields?
Recently, white dwarf stars have found a new use in the fundamental physics
community. Many prospective theories of the fundamental interactions of Nature
allow traditional constants, like the fine structure constant , to vary
in some way. A study by Berengut et al. (2013) used the Fe/Ni V line
measurements made by Preval et al. (2013) from the hot DA white dwarf G191-B2B,
in an attempt to detect any variation in . It was found that the Fe V
lines indicated an increasing alpha, whereas the Ni V lines indicated a
decreasing alpha. Possible explanations for this could be misidentification of
the lines, inaccurate atomic data, or wavelength dependent distortion in the
spectrum. We examine the first two cases by using a high S/N reference spectrum
from the hot sdO BD+284211 to calibrate the Fe/Ni V atomic data. With
this new data, we re-evaluate the work of Berengut et al. (2013) to derive a
new constraint on the variation of alpha in a gravitational field.Comment: 4 pages, 2 figures: To appear in the proceedings of the "19th
European White Dwarf Workshop" in Montreal, Canada, 201
Transnuclear TRP1-Specific CD8 T Cells with High or Low Affinity TCRs Show Equivalent Antitumor Activity
We have generated, via somatic cell nuclear transfer, two independent lines of transnuclear (TN) mice, using as nuclear donors CD8 T cells, sorted by tetramer staining, that recognize the endogenous melanoma antigen TRP1. These two lines of nominally identical specificity differ greatly in their affinity for antigen (TRP1(high) or TRP1(low)) as inferred from tetramer dissociation and peptide responsiveness. Ex vivo-activated CD8 T cells from either TRP1(high) or TRP1(low) mice show cytolytic activity in 3D tissue culture and in vivo, and slow the progression of subcutaneous B16 melanoma. Although naïve TRP1(low) CD8 T cells do not affect tumor growth, upon activation these cells function indistinguishably from TRP1(high) cells in vivo, limiting tumor cell growth and increasing mouse survival. The anti-tumor effect of both TRP1(high) and TRP1(low) CD8 T cells is enhanced in RAG-deficient hosts. However, tumor outgrowth eventually occurs, likely due to T cell exhaustion. The TRP1 TN mice are an excellent model for examining the functional attributes of T cells conferred by TCR affinity, and they may serve as a platform for screening immunomodulatory cancer therapies
UNITED STATES-LATIN AMERICAN TRADE RELATIONS: IMPORTANCE TO U.S. AGRICULTURAL POLICY DECISIONS
International Relations/Trade,
Angular momentum and an invariant quasilocal energy in general relativity
Owing to its transformation property under local boosts, the Brown-York
quasilocal energy surface density is the analogue of E in the special
relativity formula: E^2-p^2=m^2. In this paper I will motivate the general
relativistic version of this formula, and thereby arrive at a geometrically
natural definition of an `invariant quasilocal energy', or IQE. In analogy with
the invariant mass m, the IQE is invariant under local boosts of the set of
observers on a given two-surface S in spacetime. A reference energy subtraction
procedure is required, but in contrast to the Brown-York procedure, S is
isometrically embedded into a four-dimensional reference spacetime. This
virtually eliminates the embeddability problem inherent in the use of a
three-dimensional reference space, but introduces a new one: such embeddings
are not unique, leading to an ambiguity in the reference IQE. However, in this
codimension-two setting there are two curvatures associated with S: the
curvatures of its tangent and normal bundles. Taking advantage of this fact, I
will suggest a possible way to resolve the embedding ambiguity, which at the
same time will be seen to incorporate angular momentum into the energy at the
quasilocal level. I will analyze the IQE in the following cases: both the
spatial and future null infinity limits of a large sphere in asymptotically
flat spacetimes; a small sphere shrinking toward a point along either spatial
or null directions; and finally, in asymptotically anti-de Sitter spacetimes.
The last case reveals a striking similarity between the reference IQE and a
certain counterterm energy recently proposed in the context of the conjectured
AdS/CFT correspondence.Comment: 54 pages LaTeX, no figures, includes brief summary of results,
submitted to Physical Review
Chronology Protection and Non-Naked Singularity
We test the chronology protection conjecture in classical general relativity
by investigating finitely vicious space-times. First we present singularity
theorems in finitely vicious space-times by imposing some restrictions on the
chronology violating sets. In the theorems we can refer to the location of an
occurring singularity and do not assume any asymptotic conditions such as the
existence of null infinities. Further introducing the concept of a non-naked
singularity, we show that a restricted class of chronology violations cannot
arise if all occurring singularities are the non-naked singularities. Our
results suggest that the causal feature of the occurring singularities is the
key to prevent the appearance of causality violation.Comment: 17 pages including 3 eps figures. Accepted for publication in
Classical and Quantum Gravit
Quasi-local energy-momentum and two-surface characterization of the pp-wave spacetimes
In the present paper the determination of the {\it pp}-wave metric form the
geometry of certain spacelike two-surfaces is considered. It has been shown
that the vanishing of the Dougan--Mason quasi-local mass , associated
with the smooth boundary of a spacelike
hypersurface , is equivalent to the statement that the Cauchy
development is of a {\it pp}-wave type geometry with pure
radiation, provided the ingoing null normals are not diverging on and the
dominant energy condition holds on . The metric on
itself, however, has not been determined. Here, assuming that the matter is a
zero-rest-mass-field, it is shown that both the matter field and the {\it
pp}-wave metric of are completely determined by the value of the
zero-rest-mass-field on and the two dimensional Sen--geometry of
provided a convexity condition, slightly stronger than above, holds. Thus the
{\it pp}-waves can be characterized not only by the usual Cauchy data on a {\it
three} dimensional but by data on its {\it two} dimensional boundary
too. In addition, it is shown that the Ludvigsen--Vickers quasi-local
angular momentum of axially symmetric {\it pp}-wave geometries has the familiar
properties known for pure (matter) radiation.Comment: 15 pages, Plain Tex, no figure
Post-vaccine epidemiology of serotype 3 pneumococci identifies transformation inhibition through prophage-driven alteration of a non-coding RNA
Background: The respiratory pathogen Streptococcus pneumoniae (the pneumococcus) is a genetically diverse bacterium associated with over 101 immunologically distinct polysaccharide capsules (serotypes). Polysaccharide conjugate vaccines (PCVs) have successfully eliminated multiple targeted serotypes, yet the mucoid serotype 3 has persisted despite its inclusion in PCV13. This capsule type is predominantly associated with a single globally disseminated strain, GPSC12 (clonal complex 180).Methods: A genomic epidemiology study combined previous surveillance datasets of serotype 3 pneumococci to analyse the population structure, dynamics, and differences in rates of diversification within GPSC12 during the period of PCV introductions. Transcriptomic analyses, whole genome sequencing, mutagenesis, and electron microscopy were used to characterise the phenotypic impact of loci hypothesised to affect this strain's evolution.Results: GPSC12 was split into clades by a genomic analysis. Clade I, the most common, rarely underwent transformation, but was typically infected with the prophage phi OXC141. Prior to the introduction of PCV13, this Glade's composition shifted towards a phi OXC141-negative subpopulation in a systematically sampled UK collection. In the post-PCV13 era, more rapidly recombining non-Clade I isolates, also phi OXC141-negative, have risen in prevalence. The low in vitro transformation efficiency of a Clade I isolate could not be fully explained by the similar to 100-fold reduction attributable to the serotype 3 capsule. Accordingly, prophage phi OXC141 was found to modify csRNA3, a non-coding RNA that inhibits the induction of transformation. This alteration was identified in -30% of all pneumococci and was particularly common in the unusually clonal serotype 1 GPSC2 strain. RNA-seq and quantitative reverse transcriptase PCR experiments using a genetically tractable pneumococcus demonstrated the altered csRNA3 was more effective at inhibiting production of the competence-stimulating peptide pheromone. This resulted in a reduction in the induction of competence for transformation.Conclusion: This interference with the quorum sensing needed to induce competence reduces the risk of the prophage being deleted by homologous recombination. Hence the selfish prophage-driven alteration of a regulatory RNA limits cell-cell communication and horizontal gene transfer, complicating the interpretation of post-vaccine population dynamics
Ability of SP12 mutant of S. typhi to effectively induce antibody responses to the mucosal antigen enterotoxigenic E. coli heat labile toxin B subunit after oral delivery to humans
We have evaluated an oral vaccine based on an Salmonella enteric serovar typhi (S. typhi) Ty2 derivative TSB7 harboring deletion mutations in ssaV (SPI-2) and aroC together with a chromosomally integrated copy of eltB encoding the B subunit of enterotoxigenic Escherichia coli heat labile toxin (LT-B) in volunteers. Two oral doses of 108 or 109 CFU were administered to two groups of volunteers and both doses were well tolerated, with no vaccinemia, and only transient stool shedding. Immune responses to LT-B and S. typhi lipopolysaccharide were demonstrated in 67 and 97% of subjects, respectively, without evidence of anti-carrier immunity preventing boosting of LT-B responses in many cases. Further development of this salmonella-based (spi-VEC) system for oral delivery of heterologous antigens appears warranted
Black Hole Interaction Energy
The interaction energy between two black holes at large separation distance
is calculated. The first term in the expansion corresponds to the Newtonian
interaction between the masses. The second term corresponds to the spin-spin
interaction. The calculation is based on the interaction energy defined on the
two black holes initial data. No test particle approximation is used. The
relation between this formula and cosmic censorship is discussed.Comment: 18 pages, 2 figures, LaTeX2
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