285 research outputs found
Reparameterization invariants for anisotropic Bianchi I cosmology with a massless scalar source
Intrinsic time-dependent invariants are constructed for classical, flat,
homogeneous, anisotropic cosmology with a massless scalar material source.
Invariance under the time reparameterization-induced canonical symmetry group
is displayed explicitly.Comment: 28 pages, to appear in General Relativity and Gravitation.
Substantial revisions: added foundational overview section 2, chose new
intrinsic time variable, worked with dimensionless variables, added appendix
with comparison and criticism of other approache
Weak localization and conductance fluctuations of a chaotic quantum dot with tunable spin-orbit coupling
In a two-dimensional quantum dot in a GaAs heterostructure, the spin-orbit
scattering rate is substantially reduced below the rate in a bulk
two-dimensional electron gas [B.I. Halperin et al, Phys. Rev. Lett. 86, 2106
(2001)]. Such a reduction can be undone if the spin-orbit coupling parameters
acquire a spatial dependence, which can be achieved, e.g., by a metal gate
covering only a part of the quantum dot. We calculate the effect of such
spatially non-uniform spin-orbit scattering on the weak localization correction
and the universal conductance fluctuations of a chaotic quantum dot coupled to
electron reservoirs by ballistic point contacts, in the presence of a magnetic
field parallel to the plane of the quantum dot.Comment: 4 pages, RevTeX; 2 figures. Substantial revision
Irreversible fate commitment in the Arabidopsis stomatal lineage requires a Fama and Retinoblastoma-related module
The presumed totipotency of plant cells leads to questions about how specific stem cell lineages and terminal fates could be established. In the Arabidopsis stomatal lineage, a transient self-renewing phase creates precursors that differentiate into one of two epidermal cell types, guard cells or pavement cells. We found that irreversible differentiation of guard cells involves RETINOBLASTOMA-RELATED (RBR) recruitment to regulatory regions of master regulators of stomatal initiation, facilitated through interaction with a terminal stomatal lineage transcription factor, FAMA. Disrupting physical interactions between FAMA and RBR preferentially reveals the role of RBR in enforcing fate commitment over its role in cell-cycle control in this developmental context. Analysis of the phenotypes linked to the modulation of FAMA and RBR sheds new light on the way iterative divisions and terminal differentiation are coordinately regulated in a plant stem-cell lineage. - See more at: http://elifesciences.org/content/3/e03271#sthash.f3srCCrx.dpu
Entanglement transfer from dissociated molecules to photons
We introduce and study the concept of a reversible transfer of the quantum
state of two internally-translationally entangled fragments, formed by
molecular dissociation, to a photon pair. The transfer is based on intracavity
stimulated Raman adiabatic passage and it requires a combination of processes
whose principles are well established.Comment: 5 pages, 3 figure
The 2-Channel Kondo Model I: Review of Experimental Evidence for its Realization in Metal Nanoconstrictions
Certain zero-bias anomalies (ZBAs) in the voltage, temperature and magnetic
field dependence of the conductance of quenched Cu point contacts
have previously been interpreted to be due to non-magnetic 2-channel Kondo
(2CK) scattering from near-degenerate atomic two-level tunneling systems (Ralph
and Buhrman, 1992; Ralph et al. 1994), and hence to represent an experimental
realization of the non-Fermi-liquid physics of the T=0 fixed point of the
2-channel Kondo model. In this, the first in a series of three papers
(I,II,III) devoted to 2-channel Kondo physics, we present a comprehensive
review of the quenched Cu ZBA experiments and their 2CK interpretation,
including new results on ZBAs in constrictions made from Ti or from metallic
glasses. We first review the evidence that the ZBAs are due to electron
scattering from stuctural defects that are not static, but possess internal
dynamics. In order to distinguish between several mechanisms proposed to
explain the experiments, we then analyze the scaling properties of the
conductance at low temperature and voltage and extract from the data a
universal scaling function . The theoretical calculation of the
corresponding scaling function within the 2CK model is the subject of papers II
and III. The main conclusion of our work is that the properties of the ZBAs,
and most notably their scaling behavior, are in good agreement with the 2CK
model and clearly different from several other proposed mechanisms.Comment: 35 pages RevTeX, 19 encapsulated postscript figures; this final
published version features two additional authors, an additional section
reviewing recent experiments on Ti nanoconstrictions that agree very well
with the 2-channel Kondo model, 6 new figures (and is much shorter the
previous 53 page version, due to reformatting
The Hamiltonian formulation of General Relativity: myths and reality
A conventional wisdom often perpetuated in the literature states that: (i) a
3+1 decomposition of space-time into space and time is synonymous with the
canonical treatment and this decomposition is essential for any Hamiltonian
formulation of General Relativity (GR); (ii) the canonical treatment
unavoidably breaks the symmetry between space and time in GR and the resulting
algebra of constraints is not the algebra of four-dimensional diffeomorphism;
(iii) according to some authors this algebra allows one to derive only spatial
diffeomorphism or, according to others, a specific field-dependent and
non-covariant four-dimensional diffeomorphism; (iv) the analyses of Dirac
[Proc. Roy. Soc. A 246 (1958) 333] and of ADM [Arnowitt, Deser and Misner, in
"Gravitation: An Introduction to Current Research" (1962) 227] of the canonical
structure of GR are equivalent. We provide some general reasons why these
statements should be questioned. Points (i-iii) have been shown to be incorrect
in [Kiriushcheva et al., Phys. Lett. A 372 (2008) 5101] and now we thoroughly
re-examine all steps of the Dirac Hamiltonian formulation of GR. We show that
points (i-iii) above cannot be attributed to the Dirac Hamiltonian formulation
of GR. We also demonstrate that ADM and Dirac formulations are related by a
transformation of phase-space variables from the metric to lapse
and shift functions and the three-metric , which is not canonical. This
proves that point (iv) is incorrect. Points (i-iii) are mere consequences of
using a non-canonical change of variables and are not an intrinsic property of
either the Hamilton-Dirac approach to constrained systems or Einstein's theory
itself.Comment: References are added and updated, Introduction is extended,
Subsection 3.5 is added, 83 pages; corresponds to the published versio
Gossip in organisations: Contexts, consequences and controversies
This article examines the key themes surrounding gossip including its contexts, the various outcomes (positive and negative) of gossip as well as a selection of challenges and controversies. The challenges which are highlighted revolve around definitional issues, methodological approaches, and ethical considerations. Our analysis suggests that the characteristics and features of gossip lend itself to a process-oriented approach whereby the beginning and, particularly, end points of gossip are not always easily identified. Gossip about a subject or person can temporarily disappear only for it to re-surface at some later stage. In addition, questions pertaining to the effects of gossip and ethical-based arguments depend on the nature of the relationships within the gossip triad (gossiper, listener/respondent and target)
The blood metabolome of incident kidney cancer: A case-control study nested within the MetKid consortium.
BackgroundExcess bodyweight and related metabolic perturbations have been implicated in kidney cancer aetiology, but the specific molecular mechanisms underlying these relationships are poorly understood. In this study, we sought to identify circulating metabolites that predispose kidney cancer and to evaluate the extent to which they are influenced by body mass index (BMI).Methods and findingsWe assessed the association between circulating levels of 1,416 metabolites and incident kidney cancer using pre-diagnostic blood samples from up to 1,305 kidney cancer case-control pairs from 5 prospective cohort studies. Cases were diagnosed on average 8 years after blood collection. We found 25 metabolites robustly associated with kidney cancer risk. In particular, 14 glycerophospholipids (GPLs) were inversely associated with risk, including 8 phosphatidylcholines (PCs) and 2 plasmalogens. The PC with the strongest association was PC ae C34:3 with an odds ratio (OR) for 1 standard deviation (SD) increment of 0.75 (95% confidence interval [CI]: 0.68 to 0.83, p = 2.6 × 10-8). In contrast, 4 amino acids, including glutamate (OR for 1 SD = 1.39, 95% CI: 1.20 to 1.60, p = 1.6 × 10-5), were positively associated with risk. Adjusting for BMI partly attenuated the risk association for some-but not all-metabolites, whereas other known risk factors of kidney cancer, such as smoking and alcohol consumption, had minimal impact on the observed associations. A mendelian randomisation (MR) analysis of the influence of BMI on the blood metabolome highlighted that some metabolites associated with kidney cancer risk are influenced by BMI. Specifically, elevated BMI appeared to decrease levels of several GPLs that were also found inversely associated with kidney cancer risk (e.g., -0.17 SD change [ßBMI] in 1-(1-enyl-palmitoyl)-2-linoleoyl-GPC (P-16:0/18:2) levels per SD change in BMI, p = 3.4 × 10-5). BMI was also associated with increased levels of glutamate (ßBMI: 0.12, p = 1.5 × 10-3). While our results were robust across the participating studies, they were limited to study participants of European descent, and it will, therefore, be important to evaluate if our findings can be generalised to populations with different genetic backgrounds.ConclusionsThis study suggests a potentially important role of the blood metabolome in kidney cancer aetiology by highlighting a wide range of metabolites associated with the risk of developing kidney cancer and the extent to which changes in levels of these metabolites are driven by BMI-the principal modifiable risk factor of kidney cancer
Old and new physics interpretations of the NuTeV anomaly
We discuss whether the NuTeV anomaly can be explained, compatibly with all other data, by QCD erects (maybe, if the strange sea is asymmetric, or there is a tiny violation of isospin), new physics in propagators or couplings of the vector bosons (not really), loops of supersymmetric particles (no), dimension six operators (yes, for one specific SU(2)(L)-invariant operator), leptoquarks (not in a minimal way), extra U(1) gauge bosons (maybe: an unmixed Z' coupled to B - 3L(mu) also increases the muon g - 2 by about 10(-9) and gives a 'burst' to cosmic rays above the GZK cutoff)
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