Micromechanics of seismic wave propagation in granular materials

In this study experimental data on a model soil in a cubical cell are compared with both discrete element (DEM) simulations and continuum analyses. The experiments and simulations used point source transmitters and receivers to evaluate the shear and compression wave velocities of the samples, from which some of the elastic moduli can be deduced. Complex responses to perturbations generated by the bender/extender piezoceramic elements in the experiments were compared to those found by the controlled movement of the particles in the DEM simulations. The generally satisfactory agreement between experimental observations and DEM simulations can be seen as a validation and support the use of DEM to investigate the influence of grain interaction on wave propagation. Frequency domain analyses that considered filtering of the higher frequency components of the inserted signal, the ratio of the input and received signals in the frequency domain and sample resonance provided useful insight into the system response. Frequency domain analysis and analytical continuum solutions for cube vibration show that the testing configuration excited some, but not all, of the system’s resonant frequencies. The particle scale data available from DEM enabled analysis of the energy dissipation during propagation of the wave. Frequency domain analysis at the particle scale revealed that the higher frequency content reduces with increasing distance from the point of excitation.     

Aspects of cardiomyopathy in copper-deficient pigs. Electrocardiography, echocardiography, and ultrastructural findings

Pigs were made copper (Cu)-deficient to evaluate cardiac function and pathology, and electrocardiography. Fifteen-day-old pigs were fed a Cu-restricted diet over an 8 wk period and compared to Cu-adequate diet-fed pigs. Cardiac effects were examined concerning gross morphometry and ultrastructure, echocardiography, and electrocardiography, as well as serum cholesterol levels. The Cu-restricted diet-fed pigs exhibited a marked deceleration of growth and lower hematocrit, hemoglobin, and liver and serum Cu concentrations compared to the Cu-adequate diet-fed pigs. The Cu-restricted diet-fed pigs developed a significantly greater heart weight:body weight ratio, along with greater diastolic measures of ventricular wall and internal dimension relative to body weight. Electrocardiography in the Cu-restricted diet-fed pigs revealed one instance of electrical alternans and an intraventricular conduction disturbance and several instances of T-wave inversion. The Cu-restricted pigs also displayed a prolonged QT interval at the closure of study. Increased mitochondrial volume density and mitochondria:myofibril volume density ratio were observed in the Cu-restricted pig electron micrographs along with excessive lipid and glycogen inclusion and focal degradation of Z-lines, intercalated disk, and sarcomeres. Copper-restriction in young pigs results in cardiac pathology and electrical disturbances. These alterations are similar to those reported for young Cu-restricted rodents. Given then that many cardiac manifestations of developed Cu-deficiency appear conserved across specie lines, the potential for human disturbances in response to severe Cu-deficiency may be plausible.     

Differentiation of normals, neurotics, paranoids, and nonparanoids.

Compared objective tests and symptom ratings in differentiating psychopathology. A univariate and 2 discriminant function analyses were carried out with 30 measures on 61 normals, 45 neurotics, 31 paranoids, and 71 nonparanoid schizophrenics. Considered separately, objective tests of psychomotor speed, cognition, and social perception all differentiate the 4 comparison groups. When symptom ratings are included in the discriminant function analysis, however, only the cognitive tests make a unique contribution not covered by the ratings. Results suggest a basic cognitive deficit, not accounted for entirely by bizarre associations, social isolation, or apathetic motivation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal specificity in serial feature-positive discrimination learning.

Two experiments examined the temporal specificity of learning in operant serial feature positive discriminations (feature?→?target+/target–). Test performance was better when the target cues were presented at their customary times after the features than when they were presented at earlier or later times. When features trained with one feature–target interval were combined with targets trained with another interval, performance was best when the test interval was the same as the interval associated with the feature, suggesting that the temporal information was coded with the feature cue. Finally, the temporal specificity of the responding controlled by occasion setters was unaffected by feature extinction. Implications for the nature of learning in occasion setting are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

G-protein beta gamma subunit genes expressed in olfactory receptor neurons

The expression of genes encoding G-protein beta gamma subunits was investigated in isolated olfactory receptor neurons from channel catfish. DNA sequencing of PCR products showed that the beta 1, beta 2, gamma 2 and gamma 3 genes were expressed in the neurons. Western blotting showed that at least three of these subunit proteins were expressed. This first analysis of the expression of beta gamma genes in olfactory receptor neurons suggests that these subunits may be involved in a variety of transduction events in these cells.     

A multi-technique investigation of the nanoporosity of cement paste

The nanometer-scale structure of cement paste, which is dominated by the colloidal-scale porosity within the C-S-H gel phase, has a controlling effect on concrete properties but is difficult to study due to its delicate structure and lack of long-range order. Here we present results from three experimental techniques that are particularly suited to analyzing disordered nanoporous materials: small-angle neutron scattering (SANS), weight and length changes during equilibrium drying, and nanoindentation. Particular attention is paid to differences between pastes of different ages and cured at different temperatures. The SANS and equilibrium drying results indicate that hydration of cement paste at 20 °C forms a low-density (LD) C-S-H gel structure with a range of gel pore sizes and a relatively low packing fraction of solid particles. This fine structure may persist indefinitely under saturated conditions. However, if the paste is dried or is cured at elevated temperatures (60 °C or greater) the structure collapses toward a denser (less porous) and more stable configuration with fewer large gel pores, resulting in a greater amount of capillary porosity. Nanoindentation measurements of pastes cured at different temperatures demonstrate in all cases the existence of two C-S-H structures with different characteristic values of the indentation modulus. The average value of the modulus of the LD C-S-H is the same for all pastes tested to date, and a micromechanical analysis indicates that this value corresponds to the denser and more stable configuration of LD C-S-H. The experimental results presented here are interpreted in terms of a previously proposed quantitative “colloid” model of C-S-H gel, resulting in an improved understanding of the microstructural changes associated with drying and heat curing.     

Solubility and structure of calcium silicate hydrate

The poorly crystalline calcium silicate hydrate (C-S-H) phases that form near room temperature, which include the technically important C-S-H gel phase formed during the hydration of Portland cement, have a broad similarity to the crystalline minerals tobermorite and jennite, but are characterized by extensive atomic imperfections and structural variations at the nanometer scale. Relationships between the aqueous solubility and chemical structure are reported for specimens formed by different preparation methods and with a broad range of compositions. Both new and previously published data show that these phases generate a family of solubility curves in the CaO-SiO₂-H₂O system at room temperature. As demonstrated by ²⁹Si magic-angle spinning (MAS) NMR data and by charge balance calculations, the observed solubility differences arise from systematic variations in Ca/Si ratio, silicate structure, and Ca-OH content. Based on this evidence, the solubility curves are interpreted as representing a spectrum of metastable phases whose structures range from purely tobermorite-like to largely jennite-like. These findings give an improved understanding of the structure of these phases and reconcile some of the discrepancies in the literature regarding the structure of C-S-H at high Ca/Si ratios.     

Calculation of the Thermal Conductivity and Gas Permeability in a Uniaxial Bundle of Fibers

A model of the local microstructure of a bundle of fibers is simulated and used as the basis for calculations of transport properties. This, in turn, can be used in a macroscopic model of the chemical vapor infiltration process. An expanding/overlapping circle representation of the micro-structure simulates the deposition of matrix in a uniaxial bundle of fibers. An iterative heat conduction algorithm is used to calculate the transverse thermal conductivity based on the thermal conductivities of the solid and gas phases. The permeability of gas through the microstructure is calculated for flow both parallel and transverse to overlapping cylinders using a Stokes equation and assuming a Darcy's law behavior. Both the simulations of the microstructure and associated calculations of the transport properties compare favorably with experimental data. Darcy's law for the behavior of gas in a bundle of fibers is shown to be valid for gas pressures of 5–13 kPa.