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