17,485 research outputs found
Dilaton Stabilization and Inflation in the D-brane World
We study the dilaton stabilization in the D-brane world in which a D-brane
constitutes our universe. The dilaton can be stabilized due to the interplay
between the D-brane tension and the negative scalar curvature of extra
dimensions. Cosmic evolution of the dilaton is investigated with the obtained
dilaton potential and it is found that inflation can be realized before the
settlement of the dilaton.Comment: 10 pages, abstract correcte
Breakdown of the lattice polaron picture in La0.7Ca0.3MnO3 single crystals
When heated through the magnetic transition at Tc, La0.7Ca0.3MnO3 changes
from a band metal to a polaronic insulator. The Hall constant R_H, through its
activated behavior and sign anomaly, provides key evidence for polaronic
behavior. We use R_H and the Hall mobility to demonstrate the breakdown of the
polaron phase. Above 1.4Tc, the polaron picture holds in detail, while below,
the activation energies of both R_H and the mobility deviate strongly from
their polaronic values. These changes reflect the presence of metallic,
ferromagnetic fluctuations, in the volume of which the Hall effect develops
additional contributions tied to quantal phases.Comment: 11 pages, 3 figures, final version to appear in Phys. Rev. B Rapi
200 A GeV Au+Au collisions serve a nearly perfect quark-gluon liquid
The specific shear viscosity (eta/s)_QGP of a Quark-Gluon-Plasma (QGP) at
temperatures T_c < T < 2T_c is extracted from the centrality dependence of the
eccentricity-scaled elliptic flow measured in ultra-relativistic heavy-ion
collisions. Coupling viscous fluid dynamics for the QGP with a microscopic
transport model for hadronic freeze-out we find that the eccentricity-scaled
elliptic flow is a universal function of charged multiplicity per unit overlap
area, (1/S)(dN_ch/dy), that depends only on the viscosity but not on the model
used for computing the initial fireball eccentricity. Comparing with
measurements we find 1 < (4pi)(eta/s)_QGP < 2.5 where the uncertainty range is
dominated by model uncertainties for the eccentricity values used to normalize
the measured elliptic flow.Comment: 4 pages, 2 figures, accepted by PR
Chemicals having estrogenic activity can be released from some bisphenol a-free, hard and clear, thermoplastic resins
Background: Chemicals that have estrogenic activity (EA) can potentially cause adverse health effects in mammals
including humans, sometimes at low doses in fetal through juvenile stages with effects detected in adults.
Polycarbonate (PC) thermoplastic resins made from bisphenol A (BPA), a chemical that has EA, are now often
avoided in products used by babies. Other BPA-free thermoplastic resins, some hypothesized or advertised to be
EA-free, are replacing PC resins used to make reusable hard and clear thermoplastic products such as baby bottles.
Methods: We used two very sensitive and accurate in vitro assays (MCF-7 and BG1Luc human cell lines) to quantify
the EA of chemicals leached into ethanol or water/saline extracts of fourteen unstressed or stressed (autoclaving,
microwaving, UV radiation) thermoplastic resins. Estrogen receptor (ER)-dependent agonist responses were confirmed
by their inhibition with the ER antagonist ICI 182,780.
Results: Our data showed that some (4/14) unstressed and stressed BPA-free thermoplastic resins leached chemicals
having significant levels of EA, including one polystyrene (PS), and three Tritan™ resins, the latter reportedly
EA-free. Exposure to UV radiation in natural sunlight resulted in an increased release of EA from Tritan™ resins.
Triphenyl-phosphate (TPP), an additive used to manufacture some thermoplastic resins such as Tritan™, exhibited
EA in both MCF-7 and BG1Luc assays. Ten unstressed or stressed glycol-modified polyethylene terephthalate
(PETG), cyclic olefin polymer (COP) or copolymer (COC) thermoplastic resins did not release chemicals with detectable
EA under any test condition.
Conclusions: This hazard survey study assessed the release of chemicals exhibiting EA as detected by two sensitive,
widely used and accepted, human cell line in vitro assays. Four PC replacement resins (Tritan™ and PS) released
chemicals having EA. However, ten other PC-replacement resins did not leach chemicals having EA (EA-free-resins).
These results indicate that PC-replacement plastic products could be made from EA-free resins (if appropriate EA-free
additives are chosen) that maintain advantages of re-usable plastic items (price, weight, shatter resistance) without
releasing chemicals having EA that potentially produce adverse health effects on current or future generations.This work was supported by the following NIH/NIEHS grants: R44 ES011469, 01–03 (CZY);
1R43/44 ES014806, 01–03 (CZY); subcontract (CZY, PI) on an NIH Grant 01–03
43/44ES018083-01. This work was also supported by NIH grants to MSD (P42
ES004699), and DJK and SIY (1R43ES018083-01-03, NIEHS 1R44ES019442-01-03
and NIEHS 2R44ES016964-01-03).Neuroscienc
Berry's phase contribution to the anomalous Hall effect of gadolinium
When conduction electrons are forced to follow the local spin texture, the
resulting Berry phase can induce an anomalous Hall effect (AHE). In gadolinium,
as in double-exchange magnets, the exchange interaction is mediated by the
conduction electrons and the AHE may therefore resemble that of chromium
dioxide and other metallic double-exchange ferromagnets. The Hall resistivity,
magnetoresistance, and magnetization of single crystal gadolinium were measured
in fields up to 30 T. Measurements between 2 K and 400 K are consistent with
previously reported data. A scaling analysis for the Hall resistivity as a
function of the magnetization suggests the presence of a Berry's-phase
contribution to the anomalous Hall effect.Comment: 6 pages, 7 figures, submitted to Phys. Rev.
Relation between phase and dwell times for quantum tunneling of a relativistically propagating particle
The general and explicit relation between the phase time and the dwell time
for quantum tunneling of a relativistically propagating particle is
investigated and quantified. In analogy with previously obtained
non-relativistic results, it is shown that the group delay can be described in
terms of the dwell time and a self-interference delay. Lessons concerning the
phenomenology of the relativistic tunneling are drawn
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