30,099 research outputs found
Non-BPS D8-branes and Dynamic Domain Walls in Massive IIA Supergravities
We study the D8-branes of the Romans massive IIA supergravity theory using
the coupled supergravity and worldvolume actions. D8 branes can be regarded as
domain walls with the jump in the extrinsic curvature at the brane given by the
Israel matching conditions. We examine the restrictions that these conditions
place on extreme and non-extreme solutions and find that they rule out some of
the supersymmetric solutions given by Bergshoeff {\em et al}. We consider what
happens when the dilaton varies on the worldvolume of the brane, which implies
that the brane is no longer static. We obtain a family of D8-brane solutions
parametrized by a non-extremality term on each side of the brane and the
asymptotic values of the 10-form field. The non-extremality parameters can be
related to the velocity of the brane. We also study 8-brane solutions of a
massive IIA supergravity theory introduced by Howe, Lambert and West. This
theory also admits a 10-form formulation, but the 10-form is not a R-R sector
field and so these 8-branes are not D-branes.Comment: 23 pages REVTeX, 2 .eps figures. This paper completely replaces and
extends an earlier paper (hep-th/9712112) by Chamblin and Perr
Pressure study of nematicity and quantum criticality in SrRuO for an in-plane field
We study the relationship between the nematic phases of SrRuO and
quantum criticality. At ambient pressure, one nematic phase is associated with
a metamagnetic quantum critical end point (QCEP) when the applied magnetic
field is near the \textit{c}-axis. We show, however, that this metamagnetic
transition does not produce the same nematic signatures when the QCEP is
reached by hydrostatic pressure with the field applied in the
\textit{ab}-plane. Moreover, a second nematic phase, that is seen for field
applied in the \textit{ab}-plane close to, but not right at, a second
metamagnetic anomaly, persists with minimal change to the highest applied
pressure, 16.55 kbar. Taken together our results suggest that metamagnetic
quantum criticality may not be necessary for the formation of a nematic phase
in SrRuO
Recommended from our members
Composite drill stem of epoxy fiber glass reinforced with boron filaments and a retrievable core liner/sample return container for the Apollo lunar surface drill
Composite drill stem of epoxy fiber glass and boron filaments and lunar core sampling system for Apollo lunar surface dril
The predominant relationship between sexual environment characteristics and HIV-serodiscordant condomless anal sex among HIV-positive men who have sex with men (MSM)
In some studies, situational factors have been shown to be stronger predictors of condomless sex than individual risk factors. Cross-sectional relationships between condomless anal sex (CAS) with HIV-serodiscordant partners and risk factors across ecological levels (individual, sexual environment) were examined using a sample (N = 60) of HIV-positive men who have sex with men (MSM) who reported multiple recent episodes of CAS. Negative binomial regressions were used to evaluate the association of contextual risk factors (e.g., substance use during sex, transactional sex, public sex, sex at a sex party) with recent condomless sex, controlling for demographics and mental health. Results demonstrated that sexual environment factors, particularly sex under the influence of drugs or alcohol (B = .019, p < .05), transactional sex (B = .035, p < .01), and public sex (B = .039, p < .01) explained a large proportion of the variance in CAS. Only sex at a sex party was not related to CAS (p = .39). For each additional sexual environment in which men engaged, their rates of CAS increased (B = .39, p < .01). Secondary prevention interventions that are tailored to the proximal sexual environment could be maximally effective, particularly if they address substance use and other challenging sexual situations.We are very grateful to the participants for their time and efforts in the study. Support for the current study came from a feasibility grant (PI: Conall O'Cleirigh) from the Harvard University Center for AIDS Research (Parent Grant: P30AI060354, PI: Bruce Walker, MD) awarded to Dr. Conall O'Cleirigh. Investigator support for Dr. Steven Safren also came from NIH Grant K24MH094214. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. (P30AI060354 - Harvard University Center for AIDS Research; K24MH094214 - NIH)Accepted manuscrip
Are low-energy nuclear observables sensitive to high-energy phase shifts?
Conventional nucleon-nucleon potentials with strong short-range repulsion
require contributions from high-momentum wave function components even for
low-energy observables such as the deuteron binding energy. This can lead to
the misconception that reproducing high-energy phase shifts is important for
such observables. Interactions derived via the similarity renormalization group
decouple high-energy and low-energy physics while preserving the phase shifts
from the starting potential. They are used to show that high-momentum
components (and high-energy phase shifts) can be set to zero when using
low-momentum interactions, without losing information relevant for low-energy
observables.Comment: 13 pages, 5 figures; reference and acknowledgment adde
An Investigation of the Overlap Between the Statistical Discrete Gust and the Power Spectral Density Analysis Methods
The results of a NASA investigation of a claimed Overlap between two gust response analysis methods: the Statistical Discrete Gust (SDG) Method and the Power Spectral Density (PSD) Method are presented. The claim is that the ratio of an SDG response to the corresponding PSD response is 10.4. Analytical results presented for several different airplanes at several different flight conditions indicate that such an Overlap does appear to exist. However, the claim was not met precisely: a scatter of up to about 10 percent about the 10.4 factor can be expected
Formation of a Nematic Fluid at High Fields in Sr3Ru2O7
In principle, a complex assembly of strongly interacting electrons can
self-organise into a wide variety of collective states, but relatively few such
states have been identified in practice. We report that, in the close vicinity
of a metamagnetic quantum critical point, high purity Sr3Ru2O7 possesses a
large magnetoresistive anisotropy, consistent with the existence of an
electronic nematic fluid. We discuss a striking phenomenological similarity
between our observations and those made in high purity two-dimensional electron
fluids in GaAs devices.Comment: 14 pages, 3 figures, 11 extra pages of supplementary informatio
A possible explanation for the inconsistency between the Giotto grain mass distribution and ground-based observations
Giotto measured the in situ Halley dust grain mass distribution with 2 instruments, Particle Impact Analyzer and Dust Impact Detection System (DIDSY), as well as the total intercepted mass from the deceleration of the spacecraft (Giotto Radio-Science Experiment, GRE). Ground based observations made shortly before encounter have fluxes much higher than would be predicted from Giotto data. It is concluded that Giotto DIDSY and GRE data represent observations of dust originating from a narrow track along the nucleus. They are consistent with ground based data, if assumptions are made about the level of activity along this track. The actual size distribution that should be used for modeling of the whole coma should not include the large mass excess actually observed by Giotto. Extrapolation of the small grain data should be used, since for these grains the velocity dispersion is low and temporal changes at the nucleus would not affect the shape of the mass distribution
Near--K-edge double and triple detachment of the F- negative ion: observation of direct two-electron ejection by a single photon
Double and triple detachment of the F-(1s2 2s2 2p6) negative ion by a single
photon have been investigated in the photon energy range 660 to 1000 eV. The
experimental data provide unambiguous evidence for the dominant role of direct
photo-double-detachment with a subsequent single-Auger process in the reaction
channel leading to F2+ product ions. Absolute cross sections were determined
for the direct removal of a (1s+2p) pair of electrons from F- by the absorption
of a single photon
The NMR of High Temperature Superconductors without Anti-Ferromagnetic Spin Fluctuations
A microscopic theory for the NMR anomalies of the planar Cu and O sites in
superconducting La_1.85Sr_0.15CuO_4 is presented that quantitatively explains
the observations without the need to invoke anit-ferromagnetic spin
fluctuations on the planar Cu sites and its significant discrepancy with the
observed incommensurate neutron spin fluctuations. The theory is derived from
the recently published ab-initio band structure calculations that correct LDA
computations tendency to overestimate the self-coulomb repulsion for the
half-filled Cu d_x2-y2 orbital for these ionic systems. The new band structure
leads to two bands at the Fermi level with holes in the Cu d_z2 and apical O
p_z orbitals in addition to the standard Cu d_x2-y2 and planar O p_sigma
orbitals. This band structure is part of a new theory for the cuprates that
explains a broad range of experiments and is based upon the formation of Cooper
pairs comprised of a k up spin electron from one band and a -k down spin
electron from another band (Interband Pairing Model).Comment: In Press, Journal of Physical Chemistry. See also
http://www.firstprinciples.com. Minor changes to references and figure
readabilit
- …