295 research outputs found
Nonlinear stabilitty for steady vortex pairs
In this article, we prove nonlinear orbital stability for steadily
translating vortex pairs, a family of nonlinear waves that are exact solutions
of the incompressible, two-dimensional Euler equations. We use an adaptation of
Kelvin's variational principle, maximizing kinetic energy penalised by a
multiple of momentum among mirror-symmetric isovortical rearrangements. This
formulation has the advantage that the functional to be maximized and the
constraint set are both invariant under the flow of the time-dependent Euler
equations, and this observation is used strongly in the analysis. Previous work
on existence yields a wide class of examples to which our result applies.Comment: 25 page
Cosmic D--term Strings as Wrapped D3 Branes
We describe cosmic D--term strings as D3 branes wrapped on a resolved
conifold. The matter content that gives rise to D--term strings is shown to
describe the world--volume theory of a space--filling D3 brane transverse to
the conifold which itself is a wrapped D5 brane. We show that, in this brane
theory, the tension of the wrapped D3 brane mathces that of the D--term string.
We argue that there is a new type of cosmic string which arises from fractional
D1 branes on the world--volume of a fractional D3 brane.Comment: 13 pages in phyzzx.tex; eq. (17) corrected, other minor corrections;
v3: more minor correction
Inflation on Fractional Branes: D--Brane Inflation as D--Term Inflation
We describe a D--brane inflation model which consists of two fractional D3
branes separated on a transverse . Inflation arises due to the
resolved orbifold singularity of which corresponds to an anomalous D--term
on the brane. We show that D--brane inflation in the bulk corresponds to
D--term inflation on the brane. The inflaton and the trigger field parametrize
the interbrane distances on an respectively. After inflation the
branes reach a supersymmetric configuration in which they are at the origin of
but separated along the directions.Comment: 15 pages in phyzzx.tex; minor corrections including all factors of
2\pi; v3: more minor correction
Power of Black Hole Physics: Seeing through the Vacuum Landscape
In this paper we generalize the black hole bound of arXiv:0706.2050 to de
Sitter spaces, and apply it to various vacua in the landscape, with a special
emphasis on slow-roll inflationary vacua. Non-trivial constraints on the
lifetime and the Hubble expansion rate emerge. For example, the general
tendency is, that for the fixed number and the increasing mass of the species,
vacua must become more curved and more unstable, either classically or quantum
mechanically. We also discuss the constraints on the lifetime of vacua in the
landscape, due to decay into the neighboring states.Comment: 33 page
Electromagnetic field angular momentum in condensed matter systems
Various electromagnetic systems can carry an angular momentum in their {\bf
E} and {\bf B} fields. The electromagnetic field angular momentum (EMAM) of
these systems can combine with the spin angular momentum to give composite
fermions or composite bosons. In this paper we examine the possiblity that an
EMAM could provide an explanation of the fractional quantum Hall effect (FQHE)
which is complimentary to the Chern-Simons explanation. We also examine a toy
model of a non-BCS superconductor (e.g. high superconductors) in terms of
an EMAM. The models presented give a common, simple picture of these two
systems in terms of an EMAM. The presence of an EMAM in these systems might be
tested through the observation of the decay modes of a charged, spin zero
unstable particle inside one of these systems.Comment: 17 pages, no figures, to be published in Phys. Rev.
Fusion of secretory vesicles isolated from rat liver
Secretory vesicles isolated from rat liver were found to fuse after exposure to Ca2+. Vescle fusion is characterized by the occurrence of twinned vesicles with a continuous cleavage plane between two vesicles in freeze-fracture electron microscopy. The number of fused vesicles increases with increasing Ca2+-concentrations and is half maximal around 10–6 m. Other divalent cations (Ba2+, Sr2+, and Mg2+) were ineffective. Mg2+ inhibits Ca2+-induced fusion. Therefore, the fusion of secretory vesiclesin vitro is Ca2+ specific and exhibits properties similar to the exocytotic process of various secretory cells.
Various substances affecting secretionin vivo (microtubular inhibitors, local anethetics, ionophores) were tested for their effect on membrane fusion in our system.
The fusion of isolated secretory vesicles from liver was found to differ from that of pure phospholipid membranes in its temperature dependence, in its much lower requirement for Ca2+, and in its Ca2+-specificity. Chemical and enzymatic modifications of the vesicle membrane indicate that glycoproteins may account for these differences
The state of tranquility: Subjective perception is shaped by contextual modulation of auditory connectivity
In this study, we investigated brain mechanisms for the generation of subjective experience from objective sensory inputs. Our experimental construct was subjective tranquility. Tranquility is a mental state more likely to occur in the presence of objective sensory inputs that arise from natural features in the environment. We used functional magnetic resonance imaging to examine the neural response to scenes that were visually distinct (beach images vs. freeway images) and experienced as tranquil (beach) or non-tranquil (freeway). Both sets of scenes had the same auditory component because waves breaking on a beach and vehicles moving on a freeway can produce similar auditory spectral and temporal characteristics, perceived as a constant roar. Compared with scenes experienced as non-tranquil, we found that subjectively tranquil scenes were associated with significantly greater effective connectivity between the auditory cortex and medial prefrontal cortex, a region implicated in the evaluation of mental states. Similarly enhanced connectivity was also observed between the auditory cortex and posterior cingulate gyrus, temporoparietal cortex and thalamus. These findings demonstrate that visual context can modulate connectivity of the auditory cortex with regions implicated in the generation of subjective states. Importantly, this effect arises under conditions of identical auditory input. Hence, the same sound may be associated with different percepts reflecting varying connectivity between the auditory cortex and other brain regions. This suggests that subjective experience is more closely linked to the connectivity state of the auditory cortex than to its basic sensory inputs
Haloperidol and Ziprasidone for Treatment of Delirium in Critical Illness
BACKGROUND:
There are conflicting data on the effects of antipsychotic medications on delirium in patients in the intensive care unit (ICU).
METHODS:
In a randomized, double-blind, placebo-controlled trial, we assigned patients with acute respiratory failure or shock and hypoactive or hyperactive delirium to receive intravenous boluses of haloperidol (maximum dose, 20 mg daily), ziprasidone (maximum dose, 40 mg daily), or placebo. The volume and dose of a trial drug or placebo was halved or doubled at 12-hour intervals on the basis of the presence or absence of delirium, as detected with the use of the Confusion Assessment Method for the ICU, and of side effects of the intervention. The primary end point was the number of days alive without delirium or coma during the 14-day intervention period. Secondary end points included 30-day and 90-day survival, time to freedom from mechanical ventilation, and time to ICU and hospital discharge. Safety end points included extrapyramidal symptoms and excessive sedation.
RESULTS:
Written informed consent was obtained from 1183 patients or their authorized representatives. Delirium developed in 566 patients (48%), of whom 89% had hypoactive delirium and 11% had hyperactive delirium. Of the 566 patients, 184 were randomly assigned to receive placebo, 192 to receive haloperidol, and 190 to receive ziprasidone. The median duration of exposure to a trial drug or placebo was 4 days (interquartile range, 3 to 7). The median number of days alive without delirium or coma was 8.5 (95% confidence interval [CI], 5.6 to 9.9) in the placebo group, 7.9 (95% CI, 4.4 to 9.6) in the haloperidol group, and 8.7 (95% CI, 5.9 to 10.0) in the ziprasidone group (P=0.26 for overall effect across trial groups). The use of haloperidol or ziprasidone, as compared with placebo, had no significant effect on the primary end point (odds ratios, 0.88 [95% CI, 0.64 to 1.21] and 1.04 [95% CI, 0.73 to 1.48], respectively). There were no significant between-group differences with respect to the secondary end points or the frequency of extrapyramidal symptoms.
CONCLUSIONS:
The use of haloperidol or ziprasidone, as compared with placebo, in patients with acute respiratory failure or shock and hypoactive or hyperactive delirium in the ICU did not significantly alter the duration of delirium. (Funded by the National Institutes of Health and the VA Geriatric Research Education and Clinical Center; MIND-USA ClinicalTrials.gov number, NCT01211522 .)
Complex structure moduli stability in toroidal compactifications
In this paper we present a classification of possible dynamics of closed
string moduli within specific toroidal compactifications of Type II string
theories due to the NS-NS tadpole terms in the reduced action. They appear as
potential terms for the moduli when supersymmetry is broken due to the presence
of D-branes. We particularise to specific constructions with two, four and
six-dimensional tori, and study the stabilisation of the complex structure
moduli at the disk level. We find that, depending on the cycle on the compact
space where the brane is wrapped, there are three possible cases: i) there is a
solution inside the complex structure moduli space, and the configuration is
stable at the critical point, ii) the moduli fields are driven towards the
boundary of the moduli space, iii) there is no stable solution at the minimum
of the potential and the system decays into a set of branes.Comment: 24 pages, JHEP3.cls, 19 figures. A few references adde
Inflationary Scenarios from Branes at Angles
We describe a simple mechanism that can lead to inflation within string-based
brane-world scenarios. The idea is to start from a supersymmetric configuration
with two parallel static Dp-branes, and slightly break the supersymmetry
conditions to produce a very flat potential for the field that parametrises the
distance between the branes, i.e. the inflaton field. This breaking can be
achieved in various ways: by slight relative rotations of the branes with small
angles, by considering small relative velocities between the branes, etc. If
the breaking parameter is sufficiently small, a large number of e-folds can be
produced within the D-brane, for small changes of the configuration in the
compactified directions. Such a process is local, i.e. it does not depend very
strongly on the compactification space nor on the initial conditions. Moreover,
the breaking induces a very small velocity and acceleration, which ensures very
small slow-roll parameters and thus an almost scale invariant spectrum of
metric fluctuations, responsible for the observed temperature anisotropies in
the microwave background. Inflation ends as in hybrid inflation, triggered by
the negative curvature of the string tachyon potential. In this paper we
elaborate on one of the simplest examples: two almost parallel D4-branes in a
flat compactified space.Comment: 29 pages, 9 eps figures, using JHEP3.cls, published in JHE
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