3,167 research outputs found
Gravitational Waves in Open de Sitter Space
We compute the spectrum of primordial gravitational wave perturbations in
open de Sitter spacetime. The background spacetime is taken to be the
continuation of an O(5) symmetric instanton saddle point of the Euclidean no
boundary path integral. The two-point tensor fluctuations are computed directly
from the Euclidean path integral. The Euclidean correlator is then analytically
continued into the Lorentzian region where it describes the quantum mechanical
vacuum fluctuations of the graviton field. Unlike the results of earlier work,
the correlator is shown to be unique and well behaved in the infrared. We show
that the infrared divergence found in previous calculations is due to the
contribution of a discrete gauge mode inadvertently included in the spectrum.Comment: 17 pages, compressed and RevTex file, including one postscript figure
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Relationship of global assessment of change to AUSCAN and pinch and grip strength among individuals with hand osteoarthritis
SummaryObjectiveThis study assessed the utility and construct validity of a new patient global assessment of symptom change for hand osteoarthritis (OA) by examining its associations with change over time in grip strength, pinch strength, and AUStralian CANadian Osteoarthritis Hand Index (AUSCAN).MethodsParticipants (N=531, 80% female, mean age=68) were part of a study on the Genetics of Generalized Osteoarthritis (GOGO) and completed two assessments (average 4 years apart). At the second assessment, participants described change in their right and left hand pain, aching, and stiffness on a 15-point scale with descriptors ranging from âGreat deal worseâ to âGreat deal betterâ. Linear regression models examined associations of global change scores with changes in hand strength and AUSCAN, controlling for age, gender, number of hand joints with OA, and time between assessments.ResultsBoth right and left hand global assessment of change scores were significantly associated with change in AUSCAN, grip strength, and right hand pinch strength (P<0.05), and approached significance for left hand pinch strength (P=0.06). The strongest associations were between global change scores and AUSCAN change (right hand: ÎČ=0.29, P<0.001; left hand: ÎČ=0.27, P<0.001). Associations of change scores with grip and pinch strength were stronger among participants with greater radiographic OA severity at baseline.ConclusionResults support the validity of this new global assessment of symptom change. This measure is particularly useful for assessing change over time when no baseline data are available. Additional research should examine this measure's responsiveness in the context of clinical trials
Changing the operation of small geometrically complex EBG-based antennas with micron-sized particles that respond to magneto-static fields
As the usage of wireless technology grows, there are evermore demands on the antennas that support these platforms. This need has led to the design of unique antennas with improved bandwidth, agile frequency capabilities, compact size and greater efficiencies. In part though, the trade-off for such capabilities is antenna complexity. This paper presents a new technique for simplifying the method of changing the operation of a printed antenna using micron-sized silver coated particles that respond to magneto-static fields. More specifically, a structure consisting of a low-loss dielectric material with a cylindrical cavity containing micro-sized particles is developed. The overall size of the dielectric material is 1.5 mm Ă 1.5 mm Ă 0.5 mm and the cavity has a diameter of 0.9 mm. Furthermore, the top and bottom of the cavity with the micron-sized particles is capped with copper foil. Then, to manipulate the enclosed particles, a static magnet is placed near the structure. The enclosed particles columnize and orientate in the direction of the field-lines, connecting the top and bottom copper foil plates. To disconnect the plates then, the field is simply removed and the columns collapse. Macroscopically, the structure has the behavior of a switch. The structures presented in this work are denoted as Magneto-static Field Responsive Structures (MRSs). The MRSs have an additional benefit of not requiring a direct connection to a biasing circuit. This is very useful because there are many antenna designs that make it difficult to embed biasing circuitry to reconfigure printed antennas using MEMS and PIN diodes, for example. Finally, a new frequency reconfigurable Electromagnetic Band Gap (EBG) antenna is presented. This design is unique because the complex layout does not allow for traditional biasing circuitry and the operation is changed using the new MRSs presented in this paper
Walking the Walk or Just Talk?: A Global Examination of Menâs Intentions to Take Violence Preventative Action
Given the increasing prominence of both bystander-based approaches to gender-based violence (GBV) prevention and of proactively engaging men and boys to join efforts to end GBV, understanding the factors that support menâs antiviolence bystander behavior is important. This study examined correlates of willingness to engage in violence preventative bystander behavior in a global sample of 299 adult men engaged in GBV prevention events or work. Participants came from over 50 countries and provided data via an online, anonymous survey available in English, Spanish, and French. Path analysis was used to model participantsâ willingness to engage in a variety of violence-preventative behaviors in the future, with variable selection guided by the Theory of Planned Behavior (TPB) and by research implicating gender-related attitudes in bystander willingness and behavior. Findings suggest that bystander willingness was supported by past bystander behavior, self-efficacy to engage in bystander behavior, positive beliefs about the contributions of antiviolence involvement, and by an awareness of male privilege. Social network support for GBV prevention work, and support for gender equity were not significant correlates of bystander willingness in the full path model. These findings held across participants from the Global North and Global South, suggesting that self-efficacy, an awareness of male privilege, and positive attitudes toward antiviolence work are factors which may support menâs violence preventative actions across broad regional contexts. © 2018 Taylor & Franci
Montecarlo simulation of the role of defects as the melting mechanism
We study in this paper the melting transition of a crystal of fcc structure
with the Lennard-Jones potential, by using isobaric-isothermal Monte Carlo
simulations.
Local and collective updates are sequentially used to optimize the
convergence. We show the important role played by defects in the melting
mechanism in favor of modern melting theories.Comment: 6 page, 10 figures included. Corrected version to appear in Phys.
Rev.
Detecting a stochastic background of gravitational radiation: Signal processing strategies and sensitivities
We analyze the signal processing required for the optimal detection of a
stochastic background of gravitational radiation using laser interferometric
detectors. Starting with basic assumptions about the statistical properties of
a stochastic gravity-wave background, we derive expressions for the optimal
filter function and signal-to-noise ratio for the cross-correlation of the
outputs of two gravity-wave detectors. Sensitivity levels required for
detection are then calculated. Issues related to: (i) calculating the
signal-to-noise ratio for arbitrarily large stochastic backgrounds, (ii)
performing the data analysis in the presence of nonstationary detector noise,
(iii) combining data from multiple detector pairs to increase the sensitivity
of a stochastic background search, (iv) correlating the outputs of 4 or more
detectors, and (v) allowing for the possibility of correlated noise in the
outputs of two detectors are discussed. We briefly describe a computer
simulation which mimics the generation and detection of a simulated stochastic
gravity-wave signal in the presence of simulated detector noise. Numerous
graphs and tables of numerical data for the five major interferometers
(LIGO-WA, LIGO-LA, VIRGO, GEO-600, and TAMA-300) are also given. The treatment
given in this paper should be accessible to both theorists involved in data
analysis and experimentalists involved in detector design and data acquisition.Comment: 81 pages, 30 postscript figures, REVTE
Proximity effect in ultrathin Pb/Ag multilayers within the Cooper limit
We report on transport and tunneling measurements performed on ultra-thin
Pb/Ag (strong coupled superconductor/normal metal) multilayers evaporated by
quench condensation. The critical temperature and energy gap of the
heterostructures oscillate with addition of each layer, demonstrating the
validity of the Cooper limit model in the case of multilayers. We observe
excellent agreement with a simple theory for samples with layer thickness
larger than 30\AA . Samples with single layers thinner than 30\AA deviate from
the Cooper limit theory. We suggest that this is due to the "inverse proximity
effect" where the normal metal electrons improve screening in the
superconducting ultrathin layer and thus enhance the critical temperature.Comment: 4 pages, 4 figure
Relationship of limb length inequality with radiographic knee and hip osteoarthritis
SummaryObjectiveThis study examined the relationship of limb length inequality (LLI) with radiographic hip and knee osteoarthritis (OA) in a large, community-based sample.MethodsThe total study group comprised 926 participants with radiographic knee OA, 796 with radiographic hip OA, and 210 (6.6%) with LLIÂ â„2cm. The presence of radiographic OA was defined as Kellgren/Lawrence (K/L) grade â„2. Multiple logistic regression models were used to examine the relationship of LLI with hip and knee OA, while controlling for age, gender, race, body mass index, and history of hip or knee problems (joint injury, fracture, surgery, or congenital anomalies).ResultsIn unadjusted analyses, participants with LLI were more likely than those without LLI to have radiographic knee OA (45.1% vs 28.3%, P<0.001) and radiographic hip OA (35.2% vs 28.7%, P=0.063). In multiple logistic regression models, knee OA was significantly associated with presence of LLI (adjusted Odds Ratio [aOR]=1.80, 95% Confidence Interval [95% CI] 1.29â2.52), but there was no significant relationship between hip OA and LLI (aOR=1.20, 95% CI 0.86â1.67). Among participants with LLI, right hip OA was more common when the contralateral limb was longer than when the ipsilateral limb was longer (30.3% vs 17.5%, P=0.070).ConclusionLLI was associated with radiographic knee OA, controlling for other important variables. Future research should examine the relationship of LLI with hip or knee OA incidence, progression, and symptom severity, as well as the efficacy for LLI corrective treatments in OA
Extreme Electron-Phonon Coupling in Boron-based Layered Superconductors
The phonon-mode decomposition of the electron-phonon coupling in the
MgB2-like system Li_{1-x}BC is explored using first principles calculations. It
is found that the high temperature superconductivity of such systems results
from extremely strong coupling to only ~2% of the phonon modes. Novel
characteristics of E_2g branches include (1) ``mode lambda'' values of 25 and
greater compared to a mean of for other modes, (2) a precipitous
Kohn anomaly, and (3) E_2g phonon linewidths within a factor of ~2 of the
frequency itself, indicating impending breakdown of linear electron-phonon
theory. This behavior in borne out by recent inelastic x-ray scattering studies
of MgB2 by Shukla et al.Comment: 4 two-column pages, 4 figures. Equations simplified. Figure 4
changed. Comparison with new data include
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