110 research outputs found
Quantum integrability of quadratic Killing tensors
Quantum integrability of classical integrable systems given by quadratic
Killing tensors on curved configuration spaces is investigated. It is proven
that, using a "minimal" quantization scheme, quantum integrability is insured
for a large class of classic examples.Comment: LaTeX 2e, no figure, 35 p., references added, minor modifications. To
appear in the J. Math. Phy
Covariant analysis of Newtonian multi-fluid models for neutron stars: I Milne-Cartan structure and variational formulation
This is the first of a series of articles showing how 4 dimensionally
covariant analytical procedures developed in the context of General Relativity
can be usefully adapted for application in a purely Newtonian framework where
they provide physical insights (e.g. concerning helicity currents) that are not
so easy to obtain by the traditional approach based on a 3+1 space time
decomposition. After an introductory presentation of the relevant Milne
spacetime structure and the associated Cartan connection, the essential
principles are illustrated by application to the variational formulation of
simple barotropic perfect fluid models. This variational treatment is then
extended to conservative multiconstituent self gravitating fluid models of the
more general kind that is needed for treating the effects of superfluidity in
neutron stars.Comment: 35 pages Latex, with typo corrections and updated reference
Exactly Soluble Sector of Quantum Gravity
Cartan's spacetime reformulation of the Newtonian theory of gravity is a
generally-covariant Galilean-relativistic limit-form of Einstein's theory of
gravity known as the Newton-Cartan theory. According to this theory, space is
flat, time is absolute with instantaneous causal influences, and the degenerate
`metric' structure of spacetime remains fixed with two mutually orthogonal
non-dynamical metrics, one spatial and the other temporal. The spacetime
according to this theory is, nevertheless, curved, duly respecting the
principle of equivalence, and the non-metric gravitational connection-field is
dynamical in the sense that it is determined by matter distributions. Here,
this generally-covariant but Galilean-relativistic theory of gravity with a
possible non-zero cosmological constant, viewed as a parameterized gauge theory
of a gravitational vector-potential minimally coupled to a complex
Schroedinger-field (bosonic or fermionic), is successfully cast -- for the
first time -- into a manifestly covariant Lagrangian form. Then, exploiting the
fact that Newton-Cartan spacetime is intrinsically globally-hyperbolic with a
fixed causal structure, the theory is recast both into a constraint-free
Hamiltonian form in 3+1-dimensions and into a manifestly covariant reduced
phase-space form with non-degenerate symplectic structure in 4-dimensions.
Next, this Newton-Cartan-Schroedinger system is non-perturbatively quantized
using the standard C*-algebraic technique combined with the geometric procedure
of manifestly covariant phase-space quantization. The ensuing unitary quantum
field theory of Newtonian gravity coupled to Galilean-relativistic matter is
not only generally-covariant, but also exactly soluble.Comment: 83 pages (TeX). A note is added on the early work of a remarkable
Soviet physicist called Bronstein, especially on his insightful contribution
to "the cube of theories" (Fig. 1) -- see "Note Added to Proof" on pages 71
and 72, together with the new references [59] and [61
Broad targeting of resistance to apoptosis in cancer
Apoptosis or programmed cell death is natural way of removing aged cells from the body. Most of the anti-cancer therapies trigger apoptosis induction and related cell death networks to eliminate malignant cells. However, in cancer, de-regulated apoptotic signaling, particularly the activation of an anti-apoptotic systems, allows cancer cells to escape this program leading to uncontrolled proliferation resulting in tumor survival, therapeutic resistance and recurrence of cancer. This resistance is a complicated phenomenon that emanates from the interactions of various molecules and signaling pathways. In this comprehensive review we discuss the various factors contributing to apoptosis resistance in cancers. The key resistance targets that are discussed include (1) Bcl-2 and Mcl-1 proteins; (2) autophagy processes; (3) necrosis and necroptosis; (4) heat shock protein signaling; (5) the proteasome pathway; (6) epigenetic mechanisms; and (7) aberrant nuclear export signaling. The shortcomings of current therapeutic modalities are highlighted and a broad spectrum strategy using approaches including (a) gossypol; (b) epigallocatechin-3-gallate; (c) UMI-77 (d) triptolide and (e) selinexor that can be used to overcome cell death resistance is presented. This review provides a roadmap for the design of successful anti-cancer strategies that overcome resistance to apoptosis for better therapeutic outcome in patients with cancer
Thoughts on Tachyon Cosmology
After a pedagogical review of elementary cosmology, I go on to discuss some
obstacles to obtaining inflationary or accelerating universes in M/String
Theory. In particular, I give an account of an old No-Go Theorem to this
effect. I then describe some recent ideas about the possible r\^ole of the
tachyon in cosmology. I stress that there are many objections to a naive
inflationary model based on the tachyon, but there remains the possiblity that
the tachyon was important in a possible pre-inflationary Open-String Era
preceding our present Closed String Era.Comment: 34 pages, no figures. This is the written version of a lecture
delivered at the Workshop on the Quantum Structure of Spacetime and the
Geometric Nature of Fundamental Interactions held in Leuven from Sept 13th to
Sept 19th(2002) which is to appear in the Proceedings in a special issue of
Quantum and Classical Gravit
Association between TCF7L2 gene polymorphisms and susceptibility to Type 2 Diabetes Mellitus: a large Human Genome Epidemiology (HuGE) review and meta-analysis
<p>Abstract</p> <p>Background</p> <p>Transcription factor 7-like 2 (<it>TCF7L2</it>) has been shown to be associated with type 2 diabetes mellitus (T2MD) in multiple ethnic groups in the past two years, but, contradictory results were reported for Chinese and Pima Indian populations. The authors then performed a large meta-analysis of 36 studies examining the association of type 2 diabetes mellitus (T2DM) with polymorphisms in the <it>TCF7L2 </it>gene in various ethnicities, containing rs7903146 C-to-T (IVS3C>T), rs7901695 T-to-C (IVS3T>C), a rs12255372 G-to-T (IVS4G>T), and rs11196205 G-to-C (IVS4G>C) polymorphisms and to evaluate the size of gene effect and the possible genetic mode of action.</p> <p>Methods</p> <p>Literature-based searching was conducted to collect data and three methods, that is, fixed-effects, random-effects and Bayesian multivariate mete-analysis, were performed to pool the odds ratio (<it>OR</it>). Publication bias and study-between heterogeneity were also examined.</p> <p>Results</p> <p>The studies included 35,843 cases of T2DM and 39,123 controls, using mainly primary data. For T2DM and IVS3C>T polymorphism, the Bayesian <it>OR </it>for TT homozygotes and TC heterozygotes versus CC homozygote was 1.968 (95% credible interval (<it>CrI</it>): 1.790, 2.157), 1.406 (95% <it>CrI</it>: 1.341, 1.476), respectively, and the population attributable risk (PAR) for the TT/TC genotypes of this variant is 16.9% for overall. For T2DM and IVS4G>T polymorphism, TT homozygotes and TG heterozygotes versus GG homozygote was 1.885 (95%<it>CrI</it>: 1.698, 2.088), 1.360 (95% <it>CrI</it>: 1.291, 1.433), respectively. Four <it>OR</it>s among these two polymorphisms all yielded significant between-study heterogeneity (P < 0.05) and the main source of heterogeneity was ethnic differences. Data also showed significant associations between T2DM and the other two polymorphisms, but with low heterogeneity (<it>P </it>> 0.10). Pooled <it>OR</it>s fit a codominant, multiplicative genetic model for all the four polymorphisms of <it>TCF7L2 </it>gene, and this model was also confirmed in different ethnic populations when stratification of IVS3C>T and IVS4G>T polymorphisms except for Africans, where a dominant, additive genetic mode is suggested for IVS3C>T polymorphism.</p> <p>Conclusion</p> <p>This meta-analysis demonstrates that four variants of <it>TCF7L2 </it>gene are all associated with T2DM, and indicates a multiplicative genetic model for all the four polymorphisms, as well as suggests the <it>TCF7L2 </it>gene involved in near 1/5 of all T2MD. Potential gene-gene and gene-environmental interactions by which common variants in the <it>TCF7L2 </it>gene influence the risk of T2MD need further exploration.</p
LIF-Dependent Signaling: New Pieces in the Lego
LIF, a member of the IL6 family of cytokine, displays pleiotropic effects on various cell types and organs. Its critical role in stem cell models (e.g.: murine ES, human mesenchymal cells) and its essential non redundant function during the implantation process of embryos, in eutherian mammals, put this cytokine at the core of many studies aiming to understand its mechanisms of action, which could benefit to medical applications. In addition, its conservation upon evolution raised the challenging question concerning the function of LIF in species in which there is no implantation. We present the recent knowledge about the established and potential functions of LIF in different stem cell models, (embryonic, hematopoietic, mesenchymal, muscle, neural stem cells and iPSC). We will also discuss EVO-DEVO aspects of this multifaceted cytokine
Search for Eccentric Black Hole Coalescences during the Third Observing Run of LIGO and Virgo
Despite the growing number of confident binary black hole coalescences
observed through gravitational waves so far, the astrophysical origin of these
binaries remains uncertain. Orbital eccentricity is one of the clearest tracers
of binary formation channels. Identifying binary eccentricity, however, remains
challenging due to the limited availability of gravitational waveforms that
include effects of eccentricity. Here, we present observational results for a
waveform-independent search sensitive to eccentric black hole coalescences,
covering the third observing run (O3) of the LIGO and Virgo detectors. We
identified no new high-significance candidates beyond those that were already
identified with searches focusing on quasi-circular binaries. We determine the
sensitivity of our search to high-mass (total mass ) binaries
covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to
compare model predictions to search results. Assuming all detections are indeed
quasi-circular, for our fiducial population model, we place an upper limit for
the merger rate density of high-mass binaries with eccentricities at Gpc yr at 90\% confidence level.Comment: 24 pages, 5 figure
- …