Direct activity measurements in liquid Ag−Cu alloys using a valved knudsen cell-mass spectrometer system

The primary objective of this investigation was to demonstrate a new method of measuring activities. The mass spectrometric analysis of effusates from a unique valved Knudsen cell was used to determine the activity of Ag in the liquid Ag−Cu system at 1400 K. The alloy compositions were varied from one composition extreme to the otherin situ. The system exhibits positive deviation from ideal behavior, and the results are in agreement with previous investigations and are summarized by the equation

Standing up to the big squeeze

Consumer confidence is at its lowest ebb since 1980. Economic growth is at a standstill & unemployment & inflation are both rising. Here's a front-line report from more than three dozen operators who are fending off the recession's dual pressures of slow sales & rising costs. They are using discount pricing, partnering with vendors, setting pay for performance standards & a variety of other recession-beating practices.     

Mechanical properties of certain oriented crystalline polymers

The yield stress is a simple function of the deformation ratio in the direction of testing for specimens oriented by uniaxial or biaxial stretching or rolling. Unless the yield stress increases more rapidly than in proportion to the deformation ratio, there will be instability during tensile creep under high loads. The relative merit of various polymers differs for creep and stress relaxation. Fatigue and bend recovery are also related to the molecular structure.     

Cuticular hydrocarbons ofReticulitermes virginicus (Banks) and their role as potential species- and caste-recognition cues

The cuticular hydrocarbon components of four castes ofReticulitermes virginicus (Banks) have been identified and quantitated. Components identified includen-alkanes; 2-, 3-, 11-, 13-, and 15-methyl-alkanes; 11,15-dimethylalkanes, (Z)-9-alkenes; (Z,Z)-7,9-dienes; and (E/Z)-6,9-dienes ranging in carbon number from C₂₁ to C₄₀. All caste forms ofR.virginicus contained the same components, but showed caste-specific proportions. Comparison of these hydrocarbons with those of the sympatric termiteR. flavipes (Kollar) suggest that cuticular hydrocarbons might serve as species- and caste-recognition cues. A bioassay was developed to test this species-recognition hypothesis, with the experimental results supporting the hypothesis.Isoptera: Rhinotermitidae.     

Analysing neurobiological models using communicating automata

Two important issues in computational modelling in cognitive neuroscience are: first, how to formally describe neuronal networks (i.e. biologically plausible models of the central nervous system), and second, how to analyse complex models, in particular, their dynamics and capacity to learn. We make progress towards these goals by presenting a communicating automata perspective on neuronal networks. Specifically, we describe neuronal networks and their biological mechanisms using Data-rich Communicating Automata, which extend classic automata theory with rich data types and communication. We use two case studies to illustrate our approach. In the first case study, we model a number of learning frameworks, which vary in respect of their biological detail, for instance the Backpropagation (BP) and the Generalized Recirculation (GeneRec) learning algorithms. We then used the SPIN model checker to investigate a number of behavioral properties of the neural learning algorithms. SPIN is a well-known model checker for reactive distributed systems, which has been successfully applied to many non-trivial problems. The verification results show that the biologically plausible GeneRec learning is less stable than BP learning. In the second case study, we presented a large scale (cognitive-level) neuronal network, which models an attentional spotlight mechanism in the visual system. A set of properties of this model was verified using Uppaal, a popular real-time model checker. The results show that the asynchronous processing supported by concurrency theory is not only a more biologically plausible way to model neural systems, but also provides a better performance in cognitive modelling of the brain than conventional artificial neural networks that use synchronous updates. Finally, we compared our approach with several other related theories that apply formal methods to cognitive modelling. In addition, the practical implications of the approach are discussed in the context of neuronal network based controllers.     

All-glass system for preparative gas chromatography using capillary columns

A zero dead-volume all-glass-lined stainless-steel effluent splitter with a modified thermal gradient collector was designed for preparative gas chromatography using glass capillary columns. This system gives efficient collection of extremely pure samples of the 1-ng to 10-g range for spectral analysis and biological testing.Approved as TA 15656 by the director of the Texas Agricultural Experiment Station in cooperation with ARS, USDA. Supported by the Texas Department of Agriculture interagency agreement IAC-0487 (78-79).     

Mandibular gland secretions of the male beewolvesPhilanthus crabroniformis,P. barbatus,andP. pulcher (Hymenoptera: Sphecidae)

The composition of the territorial marking pheromones from mandibular glands of males of the beewolvesPhilanthus crabroniformis, P. barbatus, andP. pulcher have been determined. The structures of the components were elucidated by gas chromatography-mass spectrometry and gas chromatography-Fourier transform infrared spectroscopy. The major compound ofP. crabroniformis is isopropyl tetradecanoate, with somewhat lesser amounts of 2-tridecanone, 3-methyl-3-butenyl tetradecanoate, and 928 (Z)(E)-11-eicosen-1-ol. The major compounds ofP. barbatus are ethyl tetradecanoate and hexadecanal, which are present in approximately a 6040 ratio. These two compounds comprise over 95% of the neutral lipids. Also present in lesser amounts are ethyl dodecanoate, tetradecanal, hexadecan-1-ol, a ^x -octadecen-1-ol, and octadecan-1-ol. The major compounds ofP. pulcher are ethyl (Z)-7-hexadecenoate and geranylgeraniol acetate, which comprise nearly 90% of the neutral lipid fraction, with smaller amounts of tetradecanal, pentadecanal, and ethyl hexadecanoate; trace amounts of ^x hexadecenal, hexadecanal, and octadecanal are also present.     

Partitioning of polymers into pores with surface interactions at dilute solution limit

The partitioning of a single polymer chain into a slit in a good solvent with different surface interactions is examined through Monte Carlo simulations from subcritical regime to adsorptive regime. The chain conformation in the subcritical regime is not perturbed by the surface interactions significantly. In the adsorptive regime, the conformation of the chain is strongly perturbed by the surface interactions. The confinement free energy in the two regimes maybe written in a uniform formula, βΔμ_conf∼c₁N(a/D)^xε_w+c₂N(a/D)^1/ν with x∼2.0 or larger in the subcritical regime and ∼1.0 in the adsorptive regime, where ν is the Flory exponent, D is the slit width, N is the chain length, a is the monomer size, and ε_w is the surface interaction energy between the polymer beads and the slit. This formula is valid for a long chain in the narrow slit in the subcritical regime or when the adsorption layer h>D in the adsorptive regime. A critical behavior occurs when ε_w is at the critical adsorption point and x=1/ν, then Δμ_conf will have little dependence on N or D. Higher order terms that are neglected in the above equation, however, may be present that could lead to a weak dependence of K on N and D even in the critical adsorption point.     

Free fatty acids in cultured cells

A method for isolation and quantitation of cellular free fatty acid has been developed. When this method was used to quantitate the free fatty acid content of various cells and tissues, their levels of free fatty acids were found to vary over a wide range. In comparing tissue culture cells having different levels of free fatty acid, it was demonstrated that the conditions of culture and the type of serum in the medium are not responsible for the difference in levels. Isotopic studies have shown that the cellular free fatty acid is not biosynthesized, but is derived from the free fatty acid of the medium. Preliminary studies on the fate of the intracellular free fatty acid and a discussion of possible factors controlling the level of this compound in cells are presented.