845 research outputs found
Flux Discharge Cascades in Various Dimensions
We study the dynamics of electric flux discharge by charged particle pair or
spherical string or membrane production in various dimensions. When electric
flux wraps at least one compact cycle, we find that a single "pair" production
event can initiate a cascading decay in real time that "shorts out" the flux
and discharges many units of it. This process arises from local dynamics in the
compact space, and so is invisible in the dimensionally-reduced truncation. It
occurs in theories as simple as the Schwinger model on a circle, and has
implications for any theory with compact dimensions and electric flux,
including string theories and the string landscape.Comment: 19+8 pages, 3 figures, 3 appendice
Optimal control models of the goal-oriented human locomotion
In recent papers it has been suggested that human locomotion may be modeled
as an inverse optimal control problem. In this paradigm, the trajectories are
assumed to be solutions of an optimal control problem that has to be
determined. We discuss the modeling of both the dynamical system and the cost
to be minimized, and we analyze the corresponding optimal synthesis. The main
results describe the asymptotic behavior of the optimal trajectories as the
target point goes to infinity
Systematic reviews of complementary therapies - an annotated bibliography. Part 1: Acupuncture
Background Complementary therapies are widespread but controversial. We aim to provide a comprehensive collection and a summary of systematic reviews of clinical trials in three major complementary therapies (acupuncture, herbal medicine, homeopathy). This article is dealing with acupuncture. Potentially relevant reviews were searched through the register of the Cochrane Complementary Medicine Field, the Cochrane Library, Medline, and bibliographies of articles and books. To be included articles had to review prospective clinical trials of acupuncture; had to describe review methods explicitly; had to be published; and had to focus on treatment effects. Information on conditions, interventions, methods, results and conclusions was extracted using a pretested form and summarized descriptively. Results From a total of 48 potentially relevant reviews preselected in a screeening process 39 met the inclusion criteria. 22 were on various pain syndromes or rheumatic diseases. Other topics addressed by more than one review were addiction, nausea, asthma and tinnitus. Almost unanimously the reviews state that acupuncture trials include too few patients. Often included trials are heterogeneous regarding patients, interventions and outcome measures, are considered to have insufficient quality and contradictory results. Convincing evidence is available only for postoperative nausea, for which acupuncture appears to be of benefit, and smoking cessation, where acupuncture is no more effective than sham acupuncture. Conclusions A large number of systematic reviews on acupuncture exists. What is most obvious from these reviews is the need for (the funding of) well-designed, larger clinical trials
The CMB and the measure of the multiverse
In the context of eternal inflation, cosmological predictions depend on the
choice of measure to regulate the diverging spacetime volume. The spectrum of
inflationary perturbations is no exception, as we demonstrate by comparing the
predictions of the fat geodesic and causal patch measures. To highlight the
effect of the measure---as opposed to any effects related to a possible
landscape of vacua---we take the cosmological model, including the model of
inflation, to be fixed. We also condition on the average CMB temperature
accompanying the measurement. Both measures predict a 1-point expectation value
for the gauge-invariant Newtonian potential, which takes the form of a
(scale-dependent) monopole, in addition to a related contribution to the
3-point correlation function, with the detailed form of these quantities
differing between the measures. However, for both measures both effects are
well within cosmic variance. Our results make clear the theoretical relevance
of the measure, and at the same time validate the standard inflationary
predictions in the context of eternal inflation.Comment: 28 pages; v2: reference added, some clarification
Soft branes in supersymmetry-breaking backgrounds
We revisit the analysis of effective field theories resulting from
non-supersymmetric perturbations to supersymmetric flux compactifications of
the type-IIB superstring with an eye towards those resulting from the
backreaction of a small number of anti-D3-branes. Independently of the
background, we show that the low-energy Lagrangian describing the fluctuations
of a stack of probe D3-branes exhibits soft supersymmetry breaking, despite
perturbations to marginal operators that were not fully considered in some
previous treatments. We take this as an indication that the breaking of
supersymmetry by anti-D3-branes or other sources may be spontaneous rather than
explicit. In support of this, we consider the action of an anti-D3-brane
probing an otherwise supersymmetric configuration and identify a candidate for
the corresponding goldstino.Comment: 36+5 pages. References added, minor typos correcte
D3-brane Potentials from Fluxes in AdS/CFT
We give a comprehensive treatment of the scalar potential for a D3-brane in a
warped conifold region of a compactification with stabilized moduli. By
studying general ultraviolet perturbations in supergravity, we systematically
incorporate `compactification effects' sourced by supersymmetry breaking in the
compact space. Significant contributions to the D3-brane potential, including
the leading term in the infrared, arise from imaginary anti-self-dual (IASD)
fluxes. For an arbitrary Calabi-Yau cone, we determine the most general IASD
fluxes in terms of scalar harmonics, then compute the resulting D3-brane
potential. Specializing to the conifold, we identify the operator dual to each
mode of flux, and for chiral operators we confirm that the potential computed
in the gauge theory matches the gravity result. The effects of four-dimensional
curvature, including the leading D3-brane mass term, arise directly from the
ten-dimensional equations of motion. Furthermore, we show that gaugino
condensation on D7-branes provides a local source for IASD flux. This flux
precisely encodes the nonperturbative contributions to the D3-brane potential,
yielding a promising ten-dimensional representation of four-dimensional
nonperturbative effects. Our result encompasses all significant contributions
to the D3-brane potential discussed in the literature, and does so in the
single coherent framework of ten-dimensional supergravity. Moreover, we
identify new terms with irrational scaling dimensions that were inaccessible in
prior works. By decoupling gravity in a noncompact configuration, then
systematically reincorporating compactification effects as ultraviolet
perturbations, we have provided an approach in which Planck-suppressed
contributions to the D3-brane effective action can be computed.Comment: 70 page
Stress related epigenetic changes may explain opportunistic success in biological invasions in Antipode mussels
Different environmental factors could induce epigenetic changes, which are likely involved in the biological invasion process. Some of these factors are driven by humans as, for example, the pollution and deliberate or accidental introductions and others are due to natural conditions such as salinity. In this study, we have analysed the relationship between different stress factors: time in the new location, pollution and salinity with the methylation changes that could be involved in the invasive species tolerance to new environments. For this purpose, we have analysed two different mussels’ species, reciprocally introduced in antipode areas: the Mediterranean blue mussel Mytilus galloprovincialis and the New Zealand pygmy mussel Xenostrobus securis, widely recognized invaders outside their native distribution ranges. The demetylathion was higher in more stressed population, supporting the idea of epigenetic is involved in plasticity process. These results can open a new management protocols, using the epigenetic signals as potential pollution monitoring tool. We could use these epigenetic marks to recognise the invasive status in a population and determine potential biopollutants
Effects of quantum gravity on the inflationary parameters and thermodynamics of the early universe
The effects of generalized uncertainty principle (GUP) on the inflationary
dynamics and the thermodynamics of the early universe are studied. Using the
GUP approach, the tensorial and scalar density fluctuations in the inflation
era are evaluated and compared with the standard case. We find a good agreement
with the Wilkinson Microwave Anisotropy Probe data. Assuming that a quantum gas
of scalar particles is confined within a thin layer near the apparent horizon
of the Friedmann-Lemaitre-Robertson-Walker universe which satisfies the
boundary condition, the number and entropy densities and the free energy
arising form the quantum states are calculated using the GUP approach. A
qualitative estimation for effects of the quantum gravity on all these
thermodynamic quantities is introduced.Comment: 15 graghes, 7 figures with 17 eps graph
The Cosmological Constant
This is a review of the physics and cosmology of the cosmological constant.
Focusing on recent developments, I present a pedagogical overview of cosmology
in the presence of a cosmological constant, observational constraints on its
magnitude, and the physics of a small (and potentially nonzero) vacuum energy.Comment: 50 pages. Submitted to Living Reviews in Relativity
(http://www.livingreviews.org/), December 199
Are All Placebo Effects Equal? Placebo Pills, Sham Acupuncture, Cue Conditioning and Their Association
Placebo treatments and healing rituals have been used to treat pain throughout history. The present within-subject crossover study examines the variability in individual responses to placebo treatment with verbal suggestion and visual cue conditioning by investigating whether responses to different types of placebo treatment, as well as conditioning responses, correlate with one another. Secondarily, this study also examines whether responses to sham acupuncture correlate with responses to genuine acupuncture. Healthy subjects were recruited to participate in two sequential experiments. Experiment one is a five-session crossover study. In each session, subjects received one of four treatments: placebo pills (described as Tylenol), sham acupuncture, genuine acupuncture, or no treatment rest control condition. Before and after each treatment, paired with a verbal suggestion of positive effect, each subject's pain threshold, pain tolerance, and pain ratings to calibrated heat pain were measured. At least 14 days after completing experiment one, all subjects were invited to participate in experiment two, during which their analgesic responses to conditioned visual cues were tested. Forty-eight healthy subjects completed experiment one, and 45 completed experiment two. The results showed significantly different effects of genuine acupuncture, placebo pill and rest control on pain threshold. There was no significant association between placebo pills, sham acupuncture and cue conditioning effects, indicating that individuals may respond to unique healing rituals in different ways. This outcome suggests that placebo response may be a complex behavioral phenomenon that has properties that comprise a state, rather than a trait characteristic. This could explain the difficulty of detecting a signature for “placebo responders.” However, a significant association was found between the genuine and sham acupuncture treatments, implying that the non-specific effects of acupuncture may contribute to the analgesic effect observed in genuine acupuncture analgesia.National Center for Complementary and Alternative Medicine (U.S.) (R01AT005280
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