Hysteresis of the stress–strain dependences in Hooke’s region

A procedure is proposed for the construction [with high accuracy (∼ 0.02%)] of the stress–strain diagrams for specimens corresponding to a model of restrained circular plate. On the basis of these diagrams for 40Kh steel, it is shown that the phenomenon of hysteresis, the nonlinearity of the dependence of the amplitude of hysteresis on the mechanical stresses σ, and the initial residual strains appear for low σ (10–20 times lower than the yield strength). These results can serve as a basis for the subsequent development of the procedure of prediction of the strength of structural materials for low strains, much lower than the maximum strains corresponding to the ordinary Hooke’s region.     

Physical contact in interactions between clinicians and young children.

51 child-clinicians reported judged intervention outcomes and frequency of occurrence of 4 types of physical contact (touching, holding hands, sitting on lap, and hugging) for 368 children (mean age 7.71 yrs). Although contact frequencies varied markedly from 89% for touching to 22% for sitting on lap, they were moderately intercorrelated. Girls had more physical contact than boys, especially for hugging. Younger, compared to older, children had significantly more physical contact and more positive outcomes. Female, compared to male, clinicians had more physical contact with children. Doctoral-level clinicians reported fewer physical contacts with children than nondoctoral clinicians. Clinicians in private practice reported fewer physical contacts and more positive outcomes than those in the public sector. Psychiatrists touched children less often than social workers or psychologists. There were no relationships between the frequencies of any physical-contact variable and judged intervention outcome. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Author reactions to the manuscript revision process.

A survey was conducted of 483 authors with articles published in 7 American Psychological Association journals to assess Ss' reactions to the editorial review process. Results indicate that editorial feedback is shaped by both content-related and role-related factors and that de facto editorial practices differ in stringency. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Shape-dependent oriented trapping and scaffolding of plasmonic nanoparticles by topological defects for self-assembly of colloidal dimers in liquid crystals

We demonstrate scaffolding of plasmonic nanoparticles by topological defects induced by colloidal microspheres to match their surface boundary conditions with a uniform far-field alignment in a liquid crystal host. Displacing energetically costly liquid crystal regions of reduced order, anisotropic nanoparticles with concave or convex shapes not only stably localize in defects but also self-orient with respect to the microsphere surface. Using laser tweezers, we manipulate the ensuing nanoparticle-microsphere colloidal dimers, probing the strength of elastic binding and demonstrating self-assembly of hierarchical colloidal superstructures such as chains and arrays.     

Polyblends. I. Mechanical properties of polyblends of butadiene–acrylonitrile elastomers and copolymers of vinyl stearate and vinyl chloride

Several nitrile rubber elastomers were polyblended, across the composition range, with selected polymeric compositions containing vinyl chloride. The compositions incorporated were (a) bulk poly(vinyl chloride) (PVC); (b) copolymers of vinyl stearate and vinyl chloride containing, respectively, 0.21, 0.36, and 0.47 weight fraction of the vinyl ester; and (c) mixtures containing the same weight fractions of di-2-ethylhexyl phthalate (DOP) with PVC. Mechanical, viscoelastic, optical, and volatility properties were studied on all blends in this first paper. To accurately compare the mechanical properties of polyblends of different systems, a criterion of mechanical equivalence was taken as the observance of similar stresses at break for compositions selected to have identical 100% moduli. Optimum mechanical equivalence, therefore, occurred at the largest ratios of 100% modulus to break stress for all systems compared. Optimum mechanical property equivalence was observed for NBR blends with PVC and for similar blends of both internally and externally plasticized systems containing 0.21 weight fraction of plasticizer. However, considerably more nitrile rubber was needed for PVC blends to acquire the properties of the plasticized systems. Mechanical equivalence was observed, but was not optimum for systems having more plasticizer because tensile strengths were lower. Polyblending with NBR improved the toughness and low-temperature properties of starting vinyl stearate copolymers. Improved toughness was indicated by the expansion of areas under stress–strain curves. Refractive index matching appeared to explain the transparency of the best films and their relative freedom from haze. On heating at 85°C, poly(vinyl chloride) and the copolymer polyblends suffered no volatility loss. Volatility of DOP from the blends was 1.5 times greater than for PVC–DOP mixtures. Because modulus–temperature curves and mechanical T_g values of the filler component shifted with composition, the mechanical behavior of these blends was in harmony with an accepted standard of interdomain compatibility.     

Dynamic mechanical properties of polymer–leather composites

The effects of polymer impregnation, moisture, and lubricant oils on the complex modulus of the grain layer of leather have been studied. The impregnated materials were prepared by introducing a mixture of polyurethane oligomer and vinyl monomers into the grain layer and polymerizing by electron-beam irradiation. Synergism was observed in the interaction of the components of the system and analyzed in terms of the adhesion of the polymer to the collagen fibers.     

Application of linear discriminant analysis in prostate cancer research by synchrotron radiation-induced X-ray emission

The ability to visualize an object of interest is one of the cornerstones of advancement in science. For this reason, synchrotron radiation-induced X-ray emission (micro-SRIXE) holds special promise as a imaging technique in structural biology, biochemistry, and medicine. It gives the possibility to image concentration of most of the elements in a sample at high space resolution. Statistical analysis of data obtained for samples of prostate tissues in an experiment at L-beam line HASYLAB (Hamburg, Germany) is presented in this paper. The regions for the measurements were selected according to the histological view of the sample. By histological examination, samples were divided into five groups (from healthy to Gleason4, most advanced stage of cancerogenesis). Data obtained in micro-SRIXE experiments on prostate cancer samples provide information about concentrations of certain elements in these groups. The rising problem is to find out concentrations of which elements allow the researcher to discriminate between different (early mentioned) groups. Linear discriminant analysis, a basic technique for feature extraction, was used in statistical analysis of the data. Our results indicate that the use of synchrotron radiation and discriminant analysis in the study of prostate cancer tissues provide information that can be key to better understanding of biomolecular functions.     

Crown ether bridged homo- and heterodinuclear copper(II) and nickel(II) cyclidene complexes: Interaction with anions

Homodinuclear (3CuCu, 3NiNi) and heterdionuclear (3CuNi) cyclidene complexes linked by two 1,10-diaza-18-crown-6 ethers were synthesized and their properties characterized. For the 3CuCu in the negative potential range the mixed-valence state Cu^I-Cu^II was observed and the comproportionation constants were determined. The redox potentials of M^II/III showed a good correlation with DN of the solvent. In acetonitrile solution containing 0.1 mol dm⁻³ Bu₄NPF₆ reversible M^II/III redox processes were observed. However, in the presence of stronger ion pairing anions (e.g. BF₄⁻ and ClO₄⁻) the “potential inversion” occurred. Redox potentials of dinuclear complexes were compared with mononuclear cyclidene complexes. The influence of selected anions (Cl⁻ and NO₃⁻) on the redox process M^II/III was studied. The effect of Cl⁻ anion was different for 3CuCu and 3NiNi. In 3CuCu coordination of two chloride anions took place after oxidation of copper centers. In the 3NiNi complex two Cl⁻ anions were coordinated to one of the nickel(II) centers facilitating oxidation, at different potentials, of both nickel(II) cations. The behaviour of heteronuclear complex with Cl⁻ anions was similar to 3NiNi. All dinuclear complexes interacted with NO₃⁻ anions and the observed potential shifts were larger for nickel(II) than for copper(II) cations.     

Exploration of the transition temperatures and crystal structure of highly crystalline poly(1,3-cyclohexadiene): An experimental and computational investigation

Experimental determination of transition temperatures for highly crystalline polymers such as poly-1,3-cyclohexadiene (PCHD) can be difficult due to reduced solubility and thermalization processes which occur during data acquisition. In order to facilitate further understanding of these processes for PCHD, density functional theory (DFT) and molecular dynamics (MD) were used in conjunction with differential scanning calorimetry (DSC) and powder X-ray diffraction (XRD) to explore the oligomer microstructures, the crystal structure, and the temperature dependence of the specific volume (1/ρ). DFT geometry minimizations on isolated oligomers were used to identify the lowest energy confirmer; revealing that alternating R,R and S,S chiral bonds between monomer units afford the lowest energy structure. MD simulations of crystalline PCHD were constructed so as to replicate the experimental XRD pattern of crystalline PCHD, with the best fit producing a monoclinic crystal structure. The temperature dependence of the specific volume derived from MD simulations provided insight into the glass/vitrification (T_g) and melting (T_m) transition temperatures. Comparison of the simulation transition temperatures with differential scanning calorimetry data of PCHD polymerized with Ni(acac)₂/MAO shows good agreement and solidifies the fidelity of the newly defined PCHD crystalline structure.     

Sliding Contact Test for Engineered Surfaces

This article describes a test process for engineered surfaces such as surface treatments, surface coatings, and lubricant performance for both liquid and solid lubrication. Test constraints require that it be rapid enough to allow for easy multiple testing and be of low cost. In addition, the test should have a simple geometry for specimen preparation and ease of interpretation of results and provide key data such as friction, temperature, and wear, and interactions of these as a function of time. Besides lubricated contacts, dry contacts should also be easily tested and evaluated. Products of interest that have a wide variety of tribosurfaces would include heavy-duty truck transmissions (such as gears, bearings, synchronizers), high-pressure hydraulic systems (such as pumps, motors, actuators), and automotive components (such as tappets, valves, gears). Since this tribotesting must easily relate to products and product tribocontacts, the test must have a systematic approach to these tribocontacts. The test geometry is a rotating ring on washer (flat-on-flat) with Kingsbury-type lubricant entryways to ensure adequate lubrication. All conditions of testing are controlled, except for varying rotational speeds and applied loads along a programmed path. The product of pressure and velocity (PV factor) is increased in a way that drives the contact interface from hydrodynamic lubrication toward boundary lubrication, following the Stribeck curve. Test results have provided data that distinguish the performance capability of various surface treatments and coatings and data that measure the range of performance capabilities of various lubricant regimes.