3,485 research outputs found
A theory-based approach to understanding condom errors and problems reported by men attending an STI clinic
The official published version can be accessed from the link below - Copyright @ 2008 Springer VerlagWe employed the information–motivation–behavioral skills (IMB) model to guide an investigation of correlates for correct condom use among 278 adult (18–35 years old) male clients attending a sexually transmitted infection (STI) clinic. An anonymous questionnaire aided by a CD-recording of the questions was administered. Linear Structural Relations Program was used to conduct path analyses of the hypothesized IMB model. Parameter estimates showed that while information did not directly affect behavioral skills, it did have a direct (negative) effect on condom use errors. Motivation had a significant direct (positive) effect on behavioral skills and a significant indirect (positive) effect on condom use errors through behavioral skills. Behavioral skills had a direct (negative) effect on condom use errors. Among men attending a public STI clinic, these findings suggest brief, clinic-based, safer sex programs for men who have sex with women should incorporate activities to convey correct condom use information, instill motivation to use condoms correctly, and directly enhance men’s behavioral skills for correct use of condoms
Extreme positive allometry of animal adhesive pads and the size limits of adhesion-based climbing.
Organismal functions are size-dependent whenever body surfaces supply body volumes. Larger organisms can develop strongly folded internal surfaces for enhanced diffusion, but in many cases areas cannot be folded so that their enlargement is constrained by anatomy, presenting a problem for larger animals. Here, we study the allometry of adhesive pad area in 225 climbing animal species, covering more than seven orders of magnitude in weight. Across all taxa, adhesive pad area showed extreme positive allometry and scaled with weight, implying a 200-fold increase of relative pad area from mites to geckos. However, allometric scaling coefficients for pad area systematically decreased with taxonomic level and were close to isometry when evolutionary history was accounted for, indicating that the substantial anatomical changes required to achieve this increase in relative pad area are limited by phylogenetic constraints. Using a comparative phylogenetic approach, we found that the departure from isometry is almost exclusively caused by large differences in size-corrected pad area between arthropods and vertebrates. To mitigate the expected decrease of weight-specific adhesion within closely related taxa where pad area scaled close to isometry, data for several taxa suggest that the pads' adhesive strength increased for larger animals. The combination of adjustments in relative pad area for distantly related taxa and changes in adhesive strength for closely related groups helps explain how climbing with adhesive pads has evolved in animals varying over seven orders of magnitude in body weight. Our results illustrate the size limits of adhesion-based climbing, with profound implications for large-scale bio-inspired adhesives.We are sincerely grateful to all our colleagues who readily shared published and unpublished data with us: Aaron M. Bauer, Jon Barnes, Niall Crawford, Thomas Endlein, Hanns Hagen Goetzke, Thomas E. Macrini, Anthony P. Russell & Joanna M. Smith. We also thank Casey Gilman, Dylan Briggs, Irina Showalter, Dan King and Mike Imburgia for their assistance with the collection of gecko toepad data. This study was supported by research grants from the UK Biotechnology and Biological Sciences Research Council (BB/I008667/1) to WF, the Human Frontier Science Programme (RGP0034/2012) to DI, AJC and WF, the Denman Baynes Senior Research Fellowship to DL and a Discovery Early Career Research Fellowship (DE120101503) to CJC.This is the author accepted manuscript. The final version is available from the National Academy of Sciences via http://dx.doi.org/ 10.1073/pnas.151945911
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Cavitation in soft matter
Cavitation is the sudden, unstable expansion of a void or bubble within a liquid or solid subjected to a negative hydrostatic stress. Cavitation rheology is a field emerging from the development of a suite of materials characterization, damage quantification, and therapeutic techniques that exploit the physical principles of cavitation. Cavitation rheology is inherently complex and broad in scope with wide-ranging applications in the biology, chemistry, materials, and mechanics communities. This perspective aims to drive collaboration among these communities and guide discussion by defining a common core of high-priority goals while highlighting emerging opportunities in the field of cavitation rheology. A brief overview of the mechanics and dynamics of cavitation in soft matter is presented. This overview is followed by a discussion of the overarching goals of cavitation rheology and an overview of common experimental techniques. The larger unmet needs and challenges of cavitation in soft matter are then presented alongside specific opportunities for researchers from different disciplines to contribute to the field
Long-range interactions of metastable helium atoms
Polarizabilities, dispersion coefficients, and long-range atom-surface
interaction potentials are calculated for the n=2 triplet and singlet states of
helium using highly accurate, variationally determined, wave functions.Comment: RevTeX, epsf, 4 fig
How unique is the Asymptotic Normalisation Coefficient (ANC) method?
The asymptotic normalisation coefficients (ANC) for the vertex B
Be + p is deduced from a set of different proton transfer reactions at
different energies. This set should ensure the peripheral character of the
reaction and availability of data for the elastic channels. The problems
associated with the characteristics of the data and the analysis are discussed.
For a subgroup of the set of available data, the uniqueness property of the
extracted ANC is fulfilled. However, more measurements are needed before a
definite conclusion can be drawn.Comment: 19 pages, 11 figures, to be published in Phys Rev
Pattern formation and selection in quasi-static fracture
Fracture in quasi-statically driven systems is studied by means of a discrete
spring-block model. Developed from close comparison with desiccation
experiments, it describes crack formation induced by friction on a substrate.
The model produces cellular, hierarchical patterns of cracks, characterized by
a mean fragment size linear in the layer thickness, in agreement with
experiments. The selection of a stationary fragment size is explained by
exploiting the correlations prior to cracking. A scaling behavior associated
with the thickness and substrate coupling, derived and confirmed by
simulations, suggests why patterns have similar morphology despite their
disparity in scales.Comment: 4 pages, RevTeX, two-column, 5 PS figures include
Chandra and RXTE Spectra of the Burster GS 1826-238
Using simultaneous observations from Chandra and RXTE, we investigated the
LMXB GS 1826-238 with the goal of studying its spectral and timing properties.
The uninterrupted Chandra observation captured 6 bursts (RXTE saw 3 of the 6),
yielding a recurrence time of 3.54 +/- 0.03 hr. Using the proportional counter
array on board RXTE, we made a probable detection of 611 Hz burst oscillations
in the decaying phases of the bursts with an average rms signal amplitude of
4.8%. The integrated persistent emission spectrum can be described as the dual
Comptonization of ~ 0.3 keV soft photons by a plasma with kT_e ~ 20 keV and an
optical depth of about 2.6 (interpreted as emission from the accretion disk
corona), plus the Comptonization of hotter ~ 0.8 keV seed photons by a ~ 6.8
keV plasma (interpreted as emission from or near the boundary layer). We
discovered evidence for a neutral Fe K\alpha emission line, and we found
interstellar Fe L_II and Fe L_III absorption features. The burst spectrum can
be fit by fixing the disk Comptonization parameters to the persistent emission
best-fit values, and adding a blackbody. The blackbody/seed photon temperature
at the peak of the burst is ~ 1.8 keV and returns to ~ 0.8 keV over 200 s. The
blackbody radius is consistent with R_bb = 10.3-11.7 km assuming a distance of
6 kpc; however, by accounting for the fraction of the surface that is obscured
by the disk as a function of binary inclination, we determined the source
distance must actually be near 5 kpc in order for the stellar radius to lie
within the commonly assumed range of 10-12 km.Comment: Accepted for publication in ApJ; 13 pages, 6 figure
Development and geometry of isotropic and directional shrinkage crack patterns
We have studied shrinkage crack patterns which form when a thin layer of an
alumina/water slurry dries. Both isotropic and directional drying were studied.
The dynamics of the pattern formation process and the geometric properties of
the isotropic crack patterns are similar to what is expected from recent
models, assuming weak disorder. There is some evidence for a gradual increase
in disorder as the drying layer become thinner, but no sudden transition, in
contrast to what has been seen in previous experiments. The morphology of the
crack patterns is influenced by drying gradients and front propagation effects,
with sharp gradients having a strong orienting and ordering effect.Comment: 8 pages, 11 figures, 8 in jpg format, 3 in postscript. See also
http://mobydick.physics.utoronto.ca/mud.htm
Temporal aspects and frequency distributions of solar soft X-ray flares
A statistical analysis of almost 50000 soft X-ray (SXR) flares observed by
GOES during the period 1976-2000 is presented. On the basis of this extensive
data set, statistics on temporal properties of soft X-ray flares, such as
duration, rise and decay times with regard to the SXR flare classes is
presented. Correlations among distinct flare parameters, i.e. SXR peak flux,
fluence and characteristic times, and frequency distributions of flare
occurrence as function of the peak flux, the fluence and the duration are
derived. We discuss the results of the analysis with respect to statistical
flare models, the idea of coronal heating by nanoflares, and elaborate on
implications of the obtained results on the Neupert effect in solar flares.Comment: 11 pages, 7 figure
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