Bifurcated Polarization Rotation in Bismuth‐Based Piezoelectrics

ABO₃ perovskite‐type solid solutions display a large variety of structural and physical properties, which can be tuned by chemical composition or external parameters such as temperature, pressure, strain, electric, or magnetic fields. Some solid solutions show remarkably enhanced physical properties including colossal magnetoresistance or giant piezoelectricity. It has been recognized that structural distortions, competing on the local level, are key to understanding and tuning these remarkable properties, yet, it remains a challenge to experimentally observe such local structural details. Here, from neutron pair‐distribution analysis, a temperature‐dependent 3D atomic‐level model of the lead‐free piezoelectric perovskite Na_0.5Bi_0.5TiO₃ (NBT) is reported. The statistical analysis of this model shows how local distortions compete, how this competition develops with temperature, and, in particular, how different polar displacements of Bi³⁺ cations coexist as a bifurcated polarization, highlighting the interest of Bi‐based materials in the search for new lead‐free piezoelectrics.     

Influence of crystallization conditions on the structural characteristics of poly(p-phenylene sulfide): Rietveld refinement

A study was undertaken to obtain more accurate structural information on poly(p-phenylene sulfide) (PPS) through Rietveld analysis. A few samples of PPS crystallized in a relatively wide range of physical conditions were selected with the aim of eventually identifying the occurrence of structural modifications induced by the various crystallization procedures. According to the results, the structural modifications are relatively small and essentially confined to variations of the C–S–C angle, for which values within the range 102°–105° were found close to those proposed by Garbarczyk. In particular, the strong influence of the amorphous phase in determining the crystallographic cell dimension was investigated.     

The ECM: To Scaffold,or Not to Scaffold,That Is the Question

The extracellular matrix (ECM) has pleiotropic effects, ranging from cell adhesion to cell survival. In tissue engineering, the use of ECM and ECM-like scaffolds has separated the field into two distinct areas—scaffold-based and scaffold-free. Scaffold-free techniques are used in creating reproducible cell aggregates which have massive potential for high-throughput, reproducible drug screening and disease modeling. Though, the lack of ECM prevents certain cells from surviving and proliferating. Thus, tissue engineers use scaffolds to mimic the native ECM and produce organotypic models which show more reliability in disease modeling. However, scaffold-based techniques come at a trade-off of reproducibility and throughput. To bridge the tissue engineering dichotomy, we posit that finding novel ways to incorporate the ECM in scaffold-free cultures can synergize these two disparate techniques.     

Performance Evaluation of Space–Time Block Codes Over Keyhole Weibull Fading Channels

It is well known that degenerate channel phenomena known as keyholes may significantly reduce the capacity of multiple-input and multiple-output (mimo) channels. Keyhole mimo channels were predicted theoretically and also observed experimentally. In this paper, a novel method of analyzing the performance of keyhole mimo channels is proposed. The proposed method is based on the assumption that the received signal at the keyhole encompasses an arbitrary number of multipath components and the propagation environment is such that the resulting signal is observed as a non-linear function of the modulus of the sum of these components. Based on this assumption, we initially introduce the double Weibull fading model, constructed by the product of two independent Weibull distributed fading envelopes. Closed-form expressions for its moments-generating function, probability density function, cumulative distribution function, and moments are also derived. Based on these formulas, we analytically evaluate the performance of a 2 × 2 mimo space–time block-coding (stbc) system, where performance metrics such as the average symbol error probability for several modulation schemes, outage probability, amount of fading and ergodic capacity are given in closed form. Various performance evaluation results are presented in order to verify the proposed analysis.

Domain Wall Displacement is the Origin of Superior Permittivity and Piezoelectricity in BaTiO3 at Intermediate Grain Sizes

The dielectric and piezoelectric properties of ferroelectric polycrystalline materials have long been known to be strong functions of grain size and extrinsic effects such as domain wall motion. In BaTiO₃, for example, it has been observed for several decades that the piezoelectric and dielectric properties are maximized at intermediate grain sizes (≈1 μm) and different theoretical models have been introduced to describe the physical origin of this effect. Here, using in situ, high‐energy X‐ray diffraction during application of electric fields, it is shown that 90° domain wall motion during both strong (above coercive) and weak (below coercive) electric fields is greatest at these intermediate grain sizes, correlating with the enhanced permittivity and piezoelectric properties observed in BaTiO₃. This result validates the long‐standing theory in attributing the size effects in polycrystalline BaTiO₃ to domain wall displacement. It is now empirically established that a doubling or more in the piezoelectric and dielectric properties of polycrystalline ferroelectric materials can be achieved through domain wall displacement effects; such mechanisms are suggested for use in the design of new ferroelectric materials with enhanced properties.     

A Longitudinal Examination of Male College Students' Perpetration of Sexual Assault.

Self-administered surveys were completed by 197 men in college at 2 time points, 1 year apart. Men who committed sexual assault at multiple time points (repeat assaulters) had the most extreme scores on measures of hostility toward women, past sexual experiences, drinking in sexual situations, and adolescent delinquency. Nonassaulters had the least extreme scores and men who committed sexual assault at only 1 time point had scores that tended to fall in between. Repeat assaulters also expressed significantly less remorse when they described their sexual assault at Time 1 than did past assaulters who committed sexual assault only at the initial time point. These findings demonstrate the importance of initiating prevention and treatment programs in early adolescence, before longstanding attitudes and behaviors tolerant of sexual assault are established. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Threshold parameter estimation in nonadditive non-Gaussian noise

Threshold or weak-signal locally optimum Bayes estimators (LOBEs) of signal parameters, where the observations are an arbitrary mixture of signal and noise, the latter being independent, are first derived for “simple” as well as quadratic cost functions under the assumption that the signal is present a priori. It is shown that the desired LOBEs are either a linear (simple cost function) or a nonlinear (quadratic cost function) functional of an associated locally optimum and asymptotically optimum Bayes detector. Second, explicit classes of (threshold) optimum estimators are obtained for both cost functions in the coherent as well as in the incoherent reception modes. Third, the general results are applied to amplitude estimation, where two examples are considered: (1) coherent amplitude estimation in multiplicative noise with simple cost function (SCF) and (2) incoherent amplitude estimation with quadratic cost function (QFC) of a narrowband signal arbitrarily mixed with noise. Moreover, explicit estimator structures are given together with desired properties (i.e. efficiency of the unconditional maximum likelihood (ML) estimator) and Bayes' risks. These properties are obtained by employing contiguity-a powerful concept in modern statistics-implied by the locally asymptotically normal character of the detection algorithms     

Streptomyces griseus aminopeptidase: X-ray crystallographic structure at 1.75 A resolution

The X-ray crystal structure of the enzyme Streptomyces griseus aminopeptidase (SGAP) has been determined in its double zinc form to 1.75 A resolution, in its apo-enzyme from (zinc removed) to 2.1 A resolution, and as a mercury replaced derivative to 2.1 A resolution. The structure solution was achieved by single isomorphous replacement with phasing from anomalous scattering (SIRAS), followed by density modification with histogram matching. The protein consists of a central beta-sheet made up of eight parallel and antiparallel strands, surrounded by helices on either side. The active site is located at the carbonyl ends of two middle strands of the beta-sheet region. Two sections of the chain that could not be traced were Glu196 to Arg202, which borders the active site, and the final seven C-terminal residues starting with Gly278. The active site contains two zinc cations, each with similar ligands, at a distance of 3.6 A from each other. An unknown molecule appears to be bound to both zinc ions in the active site at partial occupancy and has been modelled as a phosphate ion. A calcium binding site has also been identified, consistent with the observations that calcium modulates the activity of the enzyme, and increases its heat stability. The mechanism by which the calcium cation modulates enzyme activity is not apparent, since the location of the calcium binding site is approximately 25 A distant from the active site zinc ions. Comparison of the structure of SGAP to other known aminopeptidases shows that the enzyme is most similar to Aeromonas proteolytica aminopeptidase (AAP). Both enzymes share a similar topology, although the overall sequence identity is very low (24% in aligned regions). The coordination of the two active site zinc cations in SGAP resembles that of AAP. These two microbial enzymes differ from bovine lens leucine aminopeptidase (LAP) in both overall structure and in coordination of the two zinc ions.     

Restraint, dieting, and the continuum model of bulimia nervosa.

The authors evaluated the continuity model of bulimia nervosa, which suggests that bulimia results from extreme weight concern and dieting practices. Individuals with bulimia, current dieters, restrained nondieters, and unrestrained nondieters were compared on measures of general psychopathology, eating-disorder-specific psychopathology, and overeating. Multiple methods, including questionnaires, clinical interviews, and food records, were used to collect data. The continuity and discontinuity models were tested with trend and regression analyses. The results of most analyses were consistent with the continuity perspective. However, binge eating behavior exhibited a clear nonlinear trend, which occurred because binge eating was common in bulimic individuals but virtually nonexistent in the other 3 groups. Current dieters scored higher than restrained nondieters on restraint/weight concern, but not on psyhopathology or binge eating. Overall, the results suggest that "normal" dieting is associated with psychological, but not consummatory, symptoms of bulimia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)