10,255 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
Kinetics, Activation Parameters, and Mechanism of the Acid Hydrolysis of tert-Butyl Acetate in Aqueous DMSO
The rate of the acid-catalysed hydrolysis of tert-butyl acetate
was found to decrease pronouncly in the presence of increasing
amounts of DMSO. The observed activation energy decreased progressively
with increasing DMSO content of the medium and the
change was attributed to a gradual interconversion of the two
concurrent and competing reaction mechanisms AALl and AAc2.
The overall reaction rate was analysed theoretically as two individual
rate constants corresponding to the respective mechanisms.
The percentage contribution of each mechanism was then estimated
and found to be concordant with the values determined experimentally
by others using 180 tracer technique. The proportion of
the AALl mechanism was found to increase both with increasing
temperature and decreasing DMSO content. The relative abundance
of the transition state belonging to each of the involved mechanisms
was discussed in the light of the solvating power of the binary DMSO-H20 solvent system. The effect of the molar concentration of water as well as the dielectric constant of the medium on the reaction kinetics was studied. The thermodynamic parameters of activation showed strong dependence on solvent composition and their values were determined by the relative contributions of the two mechanistic routes of the reaction
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
Programmed buckling by controlled lateral swelling in a thin elastic sheet
Recent experiments have imposed controlled swelling patterns on thin polymer
films, which subsequently buckle into three-dimensional shapes. We develop a
solution to the design problem suggested by such systems, namely, if and how
one can generate particular three-dimensional shapes from thin elastic sheets
by mere imposition of a two-dimensional pattern of locally isotropic growth.
Not every shape is possible. Several types of obstruction can arise, some of
which depend on the sheet thickness. We provide some examples using the
axisymmetric form of the problem, which is analytically tractable.Comment: 11 pages, 9 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
Changes in parents' psychotropic medication use following child's cancer diagnosis : A fixed-effects register-study in Finland
Background Symptoms of depression and anxiety are elevated among parents of children with cancer. However, knowledge of parents' psychotropic medication use following child's cancer diagnosis is scarce. Methods We use longitudinal Finnish register data on 3266 mothers and 2687 fathers whose child (aged 0-19) was diagnosed with cancer during 2000-2016. We record mothers' and fathers' psychotropic medication use (at least one annual purchase of anxiolytics, hypnotics, sedatives, or antidepressants) 5 years before and after the child's diagnosis and assess within-individual changes in medication use by time since diagnosis, cancer type, child's age, presence of siblings, and parent's living arrangements and education using linear probability models with the individual fixed-effects estimator. The fixed-effects models compare each parent's annual probability of psychotropic medication use after diagnosis to their annual probability of medication use during the 5-year period before the diagnosis. Results Psychotropic medication use was more common among mothers than fathers already before the child's diagnosis, 11.2% versus 7.3%. Immediately after diagnosis, psychotropic medication use increased by 6.0 (95% CI 4.8-7.2) percentage points among mothers and by 3.2 (CI 2.1-4.2) percentage points among fathers. Among fathers, medication use returned to pre-diagnosis level by the second year, except among those whose child was diagnosed with acute lymphoblastic leukemia or lymphoblastic lymphoma. Among mothers of children with a central nervous system cancer, medication use remained persistently elevated during the 5-year follow-up. For mothers with other under-aged children or whose diagnosed child was younger than 10 years, the return to pre-diagnosis level was also slow. Conclusions Having a child with cancer clearly increases parents' psychotropic medication use. The increase is smaller and more short-lived among fathers, but among mothers its duration depends on both cancer type and family characteristics. Our results suggest that an increased care burden poses particular strain to the long-term mental well-being of mothers.Peer reviewe
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
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