13,252 research outputs found
Effect of low-frequency tones and turbulent-boundary-layer noise on annoyance
A laboratory study was conducted to examine annoyance to combinations of low-frequency tones and turbulent-boundary-layer noise. A total of 240 sounds, containing tones in the range from 80 to 315 Hz, were rated by 108 test subjects in an anechoic chamber. The results indicated that tone penalties (defines as the failure of a noise metric to account for the presence of pure tones) are highly dependent on the choice of noise metric. A-weighted sound pressure level underpredicted annoyance by as much as the equivalent of 5 db and unweighted sound pressure level overpredicted by as much as the equivalent of db. Tone penalties were observed to be dependent on the shape of the turbulent boundary-layer noise spectrum
as a discovery tool for bosons at the LHC
The Forward-Backward Asymmetry (AFB) in physics is commonly only
perceived as the observable which possibly allows one to interpret a
signal by distinguishing different models of such (heavy) spin-1 bosons. In
this article, we examine the potential of AFB in setting bounds on or even
discovering a at the Large Hadron Collider (LHC) and show that it
might be a powerful tool for this purpose. We analyze two different scenarios:
s with a narrow and wide width, respectively. We find that in both
cases AFB can complement the cross section in accessing signals.Comment: arXiv admin note: substantial text overlap with arXiv:1503.0267
Thinking territory historically.
BACKGROUND:
While the randomised controlled trial (RCT) is generally regarded as the design of
choice for assessing the effects of health care, within the social sciences there is
considerable debate about the relative suitability of RCTs and non-randomised
studies (NRSs) for evaluating public policy interventions.
// OBJECTIVES:
To determine whether RCTs lead to the same effect size and variance as NRSs of
similar policy interventions; and whether these findings can be explained by other
factors associated with the interventions or their evaluation.
// METHODS:
Analyses of methodological studies, empirical reviews, and individual health and
social services studies investigated the relationship between randomisation and
effect size of policy interventions by:
1) Comparing controlled trials that are identical in all respects other than the use of
randomisation by 'breaking' the randomisation in a trial to create non-randomised
trials (re-sampling studies).
2) Comparing randomised and non-randomised arms of controlled trials mounted
simultaneously in the field (replication studies).
3) Comparing similar controlled trials drawn from systematic reviews that include
both randomised and non-randomised studies (structured narrative reviews and
sensitivity analyses within meta-analyses).
4) Investigating associations between randomisation and effect size using a pool of
more diverse RCTs and NRSs within broadly similar areas (meta-epidemiology).
// RESULTS:
Prior methodological reviews and meta-analyses of existing reviews comparing
effects from RCTs and nRCTs suggested that effect sizes from RCTs and nRCTs
may indeed differ in some circumstances and that these differences may well be
associated with factors confounded with design.
Re-sampling studies offer no evidence that the absence of randomisation directly
influences the effect size of policy interventions in a systematic way. No consistent
explanations were found for randomisation being associated with changes in effect
sizes of policy interventions in field trials
Revisiting the identification of wintertime atmospheric circulation regimes in the Euro-Atlantic sector
Atmospheric circulation is often clustered in so-called circulation regimes, which are persistent and recurrent patterns. For the Euro-Atlantic sector in winter, most studies identify four regimes: the Atlantic Ridge, the Scandinavian Blocking and the two phases of the North Atlantic Oscillation. These results are obtained by applying k-means clustering to the first several empirical orthogonal functions (EOFs) of geopotential height data. Studying the observed circulation in reanalysis data, it is found that when the full field data is used for the k-means cluster analysis instead of the EOFs, the optimal number of clusters is no longer four but six. The two extra regimes that are found are the opposites of the Atlantic Ridge and Scandinavian Blocking, meaning they have a low-pressure area roughly where the original regimes have a high-pressure area. This introduces an appealing symmetry in the clustering result. Incorporating a weak persistence constraint in the clustering procedure is found to lead to a longer duration of regimes, extending beyond the synoptic timescale, without changing their occurrence rates. This is in contrast to the commonly-used application of a time-filter to the data before the clustering is executed, which, while increasing the persistence, changes the occurrence rates of the regimes. We conclude that applying a persistence constraint within the clustering procedure is a superior way of stabilizing the clustering results than low-pass filtering the data
On the existence of dyons and dyonic black holes in Einstein-Yang-Mills theory
We study dyonic soliton and black hole solutions of the
Einstein-Yang-Mills equations in asymptotically anti-de Sitter space. We prove
the existence of non-trivial dyonic soliton and black hole solutions in a
neighbourhood of the trivial solution. For these solutions the magnetic gauge
field function has no zeros and we conjecture that at least some of these
non-trivial solutions will be stable. The global existence proof uses local
existence results and a non-linear perturbation argument based on the (Banach
space) implicit function theorem.Comment: 23 pages, 2 figures. Minor revisions; references adde
Effect of statins on atrial fibrillation: collaborative meta-analysis of published and unpublished evidence from randomised controlled trials
Objective To examine whether statins can reduce the risk of atrial fibrillation.
Design Meta-analysis of published and unpublished results from larger scale statin trials, with comparison of the findings against the published results from smaller scale or shorter duration studies.
Data sources Medline, Embase, and Cochrane's CENTRAL up to October 2010. Unpublished data from longer term trials were obtained through contact with investigators.
Study selection Randomised controlled trials comparing statin with no statin or comparing high dose versus standard dose statin; all longer term trials had at least 100 participants and at least six months' follow-up.
Results In published data from 13 short term trials (4414 randomised patients, 659 events), statin treatment seemed to reduce the odds of an episode of atrial fibrillation by 39% (odds ratio 0.61, 95% confidence interval 0.51 to 0.74; P<0.001), but there was significant heterogeneity (P<0.001) between the trials. In contrast, among 22 longer term and mostly larger trials of statin versus control (105 791 randomised patients, 2535 events), statin treatment was not associated with a significant reduction in atrial fibrillation (0.95, 0.88 to 1.03; P=0.24) (P<0.001 for test of difference between the two sets of trials). Seven longer term trials of more intensive versus standard statin regimens (28 964 randomised patients and 1419 events) also showed no evidence of a reduction in the risk of atrial fibrillation (1.00, 0.90 to 1.12; P=0.99).
Conclusions The suggested beneficial effect of statins on atrial fibrillation from published shorter term studies is not supported by a comprehensive review of published and unpublished evidence from larger scale trials
Sub-milliarcsecond Imaging of Quasars and AGN
We have used the VLBA at 15 GHz to image the structure of 132 strong compact
AGN and quasars with a resolution better than one milliarcsecond and a dynamic
range typically exceeding 1000 to 1. These observations were made as part of a
program to investigate the sub-parsec structure of quasars and AGN and to study
the changes in their structure with time. Many of the sources included in our
study, particularly those located south of +35 degrees, have not been
previously imaged with milliarcsecond resolution. Each of the sources has been
observed at multiple epochs. In this paper we show images of each of the 132
sources which we have observed. For each source we present data at the epoch
which had the best quality data. The milliarcsecond jets generally appear
one-sided but two-sided structure is often found in lower luminosity radio
galaxies and in high luminosity quasars with gigahertz peaked spectra. Usually
the structure is unresolved along the direction perpendicular to the jet, but a
few sources have broad plumes. In some low luminosity radio galaxies, the
structure appears more symmetric at 2 cm than at long wavelengths. The apparent
long wavelength symmetry in these sources is probably due to absorption by
intervening material. A few sources contain only a single component with any
secondary feature at least a thousand times weaker. We find no obvious
correlation of radio morphology and the detection of gamma-ray emission by
EGRET.Comment: 19 pages, 3 tables, 3 figures. Figure 2 (132 contour diagrams) is
long and is omitted here. Figure 2 may be viewed at
http://www.cv.nrao.edu/2cmsurvey/ In press, Astronomical Journal, April 199
Compressible flow structures interaction with a two-dimensional ejector: a cold-flow study
An experimental study has been conducted to examine the interaction of compressible flow structures such as
shocks and vortices with a two-dimensional ejector geometry using a shock-tube facility. Three diaphragm pressure
ratios ofP4
=P1 = 4, 8, and 12 have been employed, whereP4
is the driver gas pressure andP1
is the pressure within
the driven compartment of the shock tube. These lead to incident shock Mach numbers of Ms = 1:34, 1.54, and 1.66,
respectively. The length of the driver section of the shock tube was 700 mm. Air was used for both the driver and
driven gases. High-speed shadowgraphy was employed to visualize the induced flowfield. Pressure measurements
were taken at different locations along the test section to study theflow quantitatively. The induced flow is unsteady
and dependent on the degree of compressibility of the initial shock wave generated by the rupture of the diaphragm
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