8,691 research outputs found
Ultrasonic detection of flaws in fusion butt welds
Reliable and accurate Delta technique, a nondestructive ultrasonics method, uses redirection of energy to detect randomly oriented imperfections in fusion butt welds. Data on flaws can be read from either an oscilloscope or a printout
Evolution of the bilayer nu = 1 quantum Hall state under charge imbalance
We use high-mobility bilayer hole systems with negligible tunneling to
examine how the bilayer nu = 1 quantum Hall state evolves as charge is
transferred from one layer to the other at constant total density. We map
bilayer nu = 1 state stability versus imbalance for five total densities
spanning the range from strongly interlayer coherent to incoherent. We observe
competition between single-layer correlations and interlayer coherence. Most
significantly, we find that bilayer systems that are incoherent at balance can
develop spontaneous interlayer coherence with imbalance, in agreement with
recent theoretical predictions.Comment: 4 pages, 4 figure
Feshbach resonances in the 6Li-40K Fermi-Fermi mixture: Elastic versus inelastic interactions
We present a detailed theoretical and experimental study of Feshbach
resonances in the 6Li-40K mixture. Particular attention is given to the
inelastic scattering properties, which have not been considered before. As an
important example, we thoroughly investigate both elastic and inelastic
scattering properties of a resonance that occurs near 155 G. Our theoretical
predictions based on a coupled channels calculation are found in excellent
agreement with the experimental results. We also present theoretical results on
the molecular state that underlies the 155G resonance, in particular concerning
its lifetime against spontaneous dissociation. We then present a survey of
resonances in the system, fully characterizing the corresponding elastic and
inelastic scattering properties. This provides the essential information to
identify optimum resonances for applications relying on interaction control in
this Fermi-Fermi mixture.Comment: Submitted to EPJD, EuroQUAM special issues "Cold Quantum Matter -
Achievements and Prospects", v2 with updated calibration of magnetic field
(+4mG correction) and updated figures 4 and
Optically trapped atom interferometry using the clock transition of large Rb-87 Bose-Einstein condensates
We present a Ramsey-type atom interferometer operating with an optically
trapped sample of 10^6 Bose-condensed Rb-87 atoms. The optical trap allows us
to couple the |F =1, mF =0>\rightarrow |F =2, mF =0> clock states using a
single photon 6.8GHz microwave transition, while state selective readout is
achieved with absorption imaging. Interference fringes with contrast
approaching 100% are observed for short evolution times. We analyse the process
of absorption imaging and show that it is possible to observe atom number
variance directly, with a signal-to-noise ratio ten times better than the
atomic projection noise limit on 10^6 condensate atoms. We discuss the
technical and fundamental noise sources that limit our current system, and
outline the improvements that can be made. Our results indicate that, with
further experimental refinements, it will be possible to produce and measure
the output of a sub-shot-noise limited, large atom number BEC-based
interferometer.
In an addendum to the original paper, we attribute our inability to observe
quantum projection noise to the stability of our microwave oscillator and
background magnetic field. Numerical simulations of the Gross-Pitaevskii
equations for our system show that dephasing due to spatial dynamics driven by
interparticle interactions account for much of the observed decay in fringe
visibility at long interrogation times. The simulations show good agreement
with the experimental data when additional technical decoherence is accounted
for, and suggest that the clock states are indeed immiscible. With smaller
samples of 5 \times 10^4 atoms, we observe a coherence time of {\tau} =
(1.0+0.5-0.3) s.Comment: 22 pages, 6 figures Addendum: 11 pages, 6 figure
Emerging Adults with Type 1 Diabetes during the First Year Post-High School: Perceptions of Parental Behaviors
Among 182 emerging adults with type 1 diabetes (93% White and 57% female), changes during the year post-high school were examined in perceptions of diabetes-specific conflict with parents, parent–youth shared responsibility, parental tangible aid, and parental autonomy support, as well as the moderating effects of living situation, gender, years with diabetes, and glycemic control. A linear mixed effects model, controlling for baseline values, tested the changes in and relationships among these variables over time. Changes over time in parent–youth conflict were moderated by living independently of parents; autonomy support and shared responsibility were moderated by years with diabetes; and tangible aid was moderated by glycemic control. Future longitudinal research needs to examine whether changes in parental behaviors lead to positive or negative diabetes outcomes among these emerging adults with diabetes
An Alternative Prior Process for Nonparametric Bayesian Clustering
Prior distributions play a crucial role in Bayesian approaches to clustering.
Two commonly-used prior distributions are the Dirichlet and Pitman-Yor
processes. In this paper, we investigate the predictive probabilities that
underlie these processes, and the implicit "rich-get-richer" characteristic of
the resulting partitions. We explore an alternative prior for nonparametric
Bayesian clustering -- the uniform process -- for applications where the
"rich-get-richer" property is undesirable. We also explore the cost of this
process: partitions are no longer exchangeable with respect to the ordering of
variables. We present new asymptotic and simulation-based results for the
clustering characteristics of the uniform process and compare these with known
results for the Dirichlet and Pitman-Yor processes. We compare performance on a
real document clustering task, demonstrating the practical advantage of the
uniform process despite its lack of exchangeability over orderings
Association of Self-Efficacy and Self-Regulation with Nutrition and Exercise Behaviors in a Community Sample of Adults
This study examined the association of self-efficacy and self-regulation with nutrition and exercise behaviors. The study used a cross-sectional design and included 108 participants (54 men, 54 women). Nutrition behaviors (fruit/vegetable consumption, dinner cooking, and restaurant eating) and exercise were measured using total days in last week a behavior was reported. Instruments measuring self-efficacy and self-regulation demonstrated excellent Cronbach’s alphas (.93–.95). Path analysis indicated only fruit/vegetable consumption and exercise were associated with self-efficacy and self-regulation. Self-regulation showed direct association with fruit/vegetable consumption and exercise, but self-efficacy had direct association only with exercise. Self-efficacy and self-regulation should be strategically used to promote health behaviors
Gate-Voltage Studies of Discrete Electronic States in Al Nanoparticles
We have investigated the spectrum of discrete electronic states in single,
nm-scale Al particles incorporated into new tunneling transistors, complete
with a gate electrode. The addition of the gate has allowed (a) measurements of
the electronic spectra for different numbers of electrons in the same particle,
(b) greatly improved resolution and qualitatively new results for spectra
within superconducting particles, and (c) detailed studies of the gate-voltage
dependence of the resonance level widths, which have directly demonstrated the
effects of non-equilibrium excitations.Comment: 4 pages, 7 figure
Diabetes-related quality of life and the demands and burdens of diabetes care among emerging adults with type 1 diabetes in the year after high school graduation
The roles of glycemic control, diabetes management, diabetes care responsibility, living independently of parents, and time since high school graduation in predicting diabetes-related quality of life (DQOL) were examined in 184 emerging adults with type 1 diabetes. Data were collected at graduation and 1 year later. Analyses controlling for selected covariates were completed using generalized linear mixed models. Better diabetes management was associated with more positive responses on all four dimensions of DQOL. Impact and worry of DQOL were greater in the presence of depressive symptoms, and life satisfaction was lower. DQOL life satisfaction was lower in those living independently of parents. Young women reported poorer diabetes-related health status than did young men. Time since graduation was not linked to DQOL. Further research is needed on ways to improve DQOL in conjunction with diabetes management and on ways that families can support DQOL when youth live independently
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