76 research outputs found
Dynamic Scaling and Two-Dimensional High-Tc Superconductors
There has been ongoing debate over the critical behavior of two-dimensional
superconductors; in particular for high Tc superconductors. The conventional
view is that a Kosterlitz-Thouless-Berezinskii transition occurs as long as
finite size effects do not obscure the transition. However, there have been
recent suggestions that a different transition actually occurs which
incorporates aspects of both the dynamic scaling theory of Fisher, Fisher, and
Huse and the Kosterlitz-Thouless-Berezinskii transition. Of general interest is
that this modified transition apparently has a universal dynamic critical
exponent. Some have countered that this apparent universal behavior is rooted
in a newly proposed finite-size scaling theory; one that also incorporates
scaling and conventional two-dimensional theory. To investigate these issues we
study DC voltage versus current data of a 12 angstrom thick YBCO film. We find
that the newly proposed scaling theories have intrinsic flexibility that is
relevant to the analysis of the experiments. In particular, the data scale
according to the modified transition for arbitrarily defined critical
temperatures between 0 K and 19.5 K, and the temperature range of a successful
scaling collapse is related directly to the sensitivity of the measurement.
This implies that the apparent universal exponent is due to the intrinsic
flexibility rather than some real physical property. To address this intrinsic
flexibility, we propose a criterion which would give conclusive evidence for
phase transitions in two-dimensional superconductors. We conclude by reviewing
results to see if our criterion is satisfied.Comment: 14 page
Velocity-force characteristics of an interface driven through a periodic potential
We study the creep dynamics of a two-dimensional interface driven through a
periodic potential using dynamical renormalization group methods. We find that
the nature of weak-drive transport depends qualitatively on whether the
temperature is above or below the equilibrium roughening transition
temperature . Above , the velocity-force characteristics is Ohmic,
with linear mobility exhibiting a jump discontinuity across the transition. For
, the transport is highly nonlinear, exhibiting an interesting
crossover in temperature and weak external force . For intermediate drive,
, we find near a power-law velocity-force characteristics
, with , and well-below ,
, with . In the limit
of vanishing drive () the velocity-force characteristics crosses over
to , and is controlled by soliton nucleation.Comment: 18 pages, submitted to Phys. Rev.
Triggering Threshold Spacecraft Charging with Changes in Electron Emission from Materials
Modest changes in spacecraft charging conditions can lead to abrupt changes in the spacecraft equilibrium, from small positive potentials to large negative potentials relative to the space plasma; this phenomenon is referred to as threshold charging. It is well known that temporal changes of the space plasma environment (electron plasma temperature or density) can cause threshold charging. Threshold charging can also result from by temporal changes in the juxtaposition of the spacecraft to the environment, including spacecraft orbit, orientation, and geometry. This study focuses on the effects of possible changes in electron emission properties of representative spacecraft materials. It is found that for electron-induced emission, the possible threshold scenarios are very rich, since this type of electron emission can cause either positive or negative charging. Alternately, modification of photon- or ion-induced electron emission is found to induce threshold charging only in certain favorable cases. Changes of emission properties discussed include modifications due to: contamination, degradation and roughening of surfaces and layered materials; biasing and charge accumulation; bandstructure occupation and density of states caused by heat, optical or particle radiation; optical reflectivity and absorptivity; and inaccuracies and errors in measurements and parameterization of materials properties. An established method is used here to quantitatively gauge the relative extent to which these various changes in electron emission alter a spacecraft’s charging behavior and possibly lead to threshold charging. The absolute charging behavior of a hypothetical flat, two-dimensional satellite panel of a single material (either polycrystalline conductor Au or the polymeric polyimide Kapton™ H) is modeled as it undergoes modification and concomitant changes in spacecraft charging in three representative geosynchronous orbit environments, from full sunlight to full shade (eclipse) are considered
Coping with overload and stress: Men and women in dual-earner families
This study tested gender differences in a model positing relationships between work and family demands, overload, 4 coping mechanisms, and stress. The coping mechanisms were hypothesized to moderate the relationship between overload and stress. The sample consisted of 1,404 men and 1,623 women in dual-earner families. Respondents relied on 2 coping strategies: scaling back and restructuring family roles. Men were more likely than women to respond to overload by scaling back and less likely to respond by work-role restructuring. Coping by family-role restructuring moderated the relationship between role overload and stress for both groups; however, the gender difference was not significant. Coping by work-role restructuring moderated the relationship between overload and stress only for men. Copyrigh
A comparison of the values and commitment of private sector, public sector, and parapublic sector employees
This study investigated differences in general values, work values and organizational commitment among 549 private sector, public sector, and parapublic sector knowledge workers. No differences in general values were observed across sectors, although five significant work value differences were revealed: parapublic employees value work that contributes to society more than public servants, who value it more than private sector employees; parapublic employees value opportunities for advancement less than both public and private sector employees; public servants value intellectually stimulating and challenging work more than parapublic employees; and private sector employees value prestigious work more than public servants. Private sector employees displayed greater organizational commitment than the employees in the other two sectors. Overall, the findings suggest only limited value differences among employees of the various sectors. The finding of some work value differences between employees in the public and parapublic sectors suggests that these two groups merit separate consideration in comparative studies such as this one
Incentive-based treatments to promote smoking abstinence during pregnancy: Findings from the vermont center on behavior and health
Lifetime Substance Use and HIV Sexual Risk Behaviors Predict Treatment Response to Contingency Management Among Homeless, Substance-Dependent MSM
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