The effect of ambient temperature on the sensitivity of hot-cathode ionization gauges

We measured the sensitivities of five hot-cathode ionization gauges for ambient laboratory temperatures between 23 and 31 °C. All of the ionization gauges exhibited very similar behavior, and the sensitivity could be adequately modeled with a linear function of temperature. The slopes of the fits were smaller than one would expect due to changes in the calibration chamber number density. The thermal transpiration effect, due to local heating of the gauge structures, can account for this, and a characteristic gauge tube temperature can be inferred from the temperature dependence of the sensitivity. A recent comparison of the high vacuum standards of several National Metrology Institutes (NMIs) was performed over the range of 10⁻⁶-10⁻³ Pa using hot-cathode and spinning rotor gauges as transfer standards. Among the participants, laboratory temperatures varied by as much as 5 °C. It is necessary to know how laboratory temperature affects the sensitivity of the hot-cathode transfer standards (spinning rotor gauges explicitly account for the gas temperature) so that individual laboratory results can be corrected to a common temperature.     

Nerve conduction velocity and H-reflex recovery in bipolar illness

Bipolar illness may be characterized by dysregulation and dysfunction of biologically active ions and ion pumps, respectively. In an effort to examine whether purported physiologic abnormalities may have functional counterparts, nerve conduction velocities (NCVs) and H-reflex recovery were examined in 7 acutely manic, 11 euthymic bipolar, 13 remitted schizophrenic, and 6 normal control individuals. All electrophysiologic tests were clinically normal. However, euthymic bipolar patients had significantly slower NCVs than either manic or normal individuals. Percent decrement of H-reflex recovery was nonsignificantly increased in manic versus euthymic bipolar subjects. Data analysis suggests lithium was not responsible for these changes. These data indicate that different mood states in bipolar illness are associated with alterations in electroneurophysiologic function.     

Effect of curing characteristics on residual stress generation in polymethyl methacrylate bone cements

Residual stresses resulting from the shrinkage of polymethyl methacrylate (PMMA) bone cement have been implicated in the formation of cracks in cement mantles following total hip arthroplasty. This study investigates whether two such cements, with differentiated solidification characteristics (i.e. working and setting times), display significant differences in their residual stress characteristics in an experiment designed to replicate the physical conditions of total hip arthroplasty. Experiments were performed using a representative femoral construct to measure and compare the temperatures and residual strains developed for standard PMMA cement mantles (CMW 1 Gentamicin) and slow curing cement mantles (SmartSet HV Gentamicin) during and following polymerization. These experimental results revealed no statistically significant difference (t-test, p > 0.05) for peak exotherm temperature and residual strain levels between the cements (measured after 3 h). The tailored polymerization characteristics of the slow-curing cement do not significantly affect residual stress generation, compared with the standard cement. It is often considered that residual stresses significantly relax following polymerization and before biomechanical loads are first applied during rehabilitation (up to 3 days later). This was examined for durations of 18 h to 3 days. Axial strains in the model femur and stem reduced by averages of 5.5 and 7.9 per cent respectively, while hoop strains in the stem exhibited larger reductions. An axisymmetric transient thermoelastic finite element model of the experiment was developed, allowing residual stresses to be predicted based on differential scanning calorimetry (DSC) measurements of the heat released throughout the exothermic curing reaction. The model predictions closely replicated the experimental measurements of both temperature and residual strain at 3 h, suggesting that residual strains can be fully accounted for by the thermal contraction mechanism associated with cooling after solidification.     

Pulsed, single-mode cavity ringdown spectroscopy

We discuss the use of single-mode cavity ringdown spectroscopy with pulsed lasers for quantitative gas density and line strength measurements. The single-mode approach to cavity ringdown spectroscopy gives single exponential decay signals without mode beating, which allows measurements with uncertainties near the shot-noise limit. The technique is demonstrated with a 10-cm-long ringdown cavity and a pulsed, frequency-stabilized optical parametric oscillator as the light source. A noise-equivalent absorption coefficient of 5 x 10(-10) cm(-1) Hz(-1/2) is demonstrated, and the relative standard deviation in the ringdown time (varsigma(tau)/tau) extracted from a fit to an individual ringdown curve is found to be the same as that for an ensemble of hundreds of independent measurements. Repeated measurement of a line strength is shown to have a standard deviation <0.3%. The effects of normally distributed noise on quantities measured using cavity ringdown spectroscopy are discussed, formulas for the relative standard deviation in the ringdown time are given in the shot- and technical-noise limits, and the noise-equivalent absorption coefficient in these limits are compared for pulsed and continuous-wave light sources.     

Aerobic exercise equipment preferences among older adults: a preliminary investigation

The purpose of this study was to develop an instrument that would measure the aerobic exercise equipment preferences of a frail older population and to see, despite a small sample size, if a many-facet Rasch analysis would provide useful information concerning the construct validity of the instrument and the equipment preferences of the sample. Sixteen ambulatory seniors (M = 82.0 yr +/- 6.6; 4 males and 12 females), who resided in a local retirement community and were involved in a structured fitness program, evaluated the following exercise equipment: Schwinn Air-Dyne, Nu-Step Recumbent Stepper; Monark bicycle ergometer; Stairmaster; and PTS Turbo Recumbent Bicycle. Participants used the equipment for 5 min. and then completed the survey via a structured interview technique. Test-retest reliability coefficients indicated the participants' responses were stable across days for each piece of exercise equipment (proportions of agreement >.83; km >.77). A many-facet (equipment, items, participants) Rasch analysis verified that 12 closed format items defined a linear construct of equipment preference (separation = 1.8; reliability =.77). The pieces of equipment were placed on the linear continuum according to their equipment preference measures (separation = 3.21; reliability =.91) derived from the participants' response patterns to the items (separation = 1.43; reliability =.67). Although the MNSQ infit and outfit statistics were acceptable for each facet, the items did not target the equipment very well. Suggested changes to the instrument include converting questions to statements to use with Likert response categories; converting negative wording to positive phrasing, and adding items related to seat comfort, foot pedal placement, and visibility of display panel. The Nu-Step and Schwinn were the most preferred pieces of equipment while the Stairmaster was the least preferred. This preliminary investigation illustrates how useful information can be obtained from a many-facet Rasch analysis to guide instrument revision and better understand exercise equipment preferences among a frail older population.     

Silver sulfide as a staining agent for scanning electron microscopy of nylon 6/MXD6 blends

BACKGROUND: In transmission and scanning electron microscopy imaging, the ability to obtain sufficient contrast between the components of a blend when they are both of a similar chemical structure still remains problematic. This paper investigates the domain morphology of a polymer blend containing two polyamides, nylon 6 and the semi‐aromatic polyamide poly(m‐xylene adipamide) (MXD6), using scanning electron microscopy in backscattered electron imaging mode. The efficiency of three staining agents, ruthenium tetroxide, phosphotungstic acid and silver sulfide, in obtaining optimum phase contrast between the two polymers is discussed. RESULTS: The use of silver sulfide as a staining agent was found to be a fast and reliable approach which required basic sample preparation and provided excellent compositional contrast between the phases present in the nylon 6/MXD6 blends compared to the other staining agents. CONCLUSIONS: The technique described in this paper is believed to be a novel and versatile method that has the potential to further improve the ability to study complex polymer blends where one polymer contains an aromatic ring. Copyright © 2009 Society of Chemical Industry     

Advances in feedforward neural networks: demystifying knowledgeacquiring black boxes

We survey research of recent years on the supervised training of feedforward neural networks. The goal is to expose how the networks work, how to engineer them so they can learn data with less extraneous noise, how to train them efficiently, and how to assure that the training is valid. The scope covers gradient descent and polynomial line search, from backpropagation through conjugate gradients and quasi Newton methods. There is a consensus among researchers that adaptive step gains (learning rates) can stabilize and accelerate convergence and that a good starting weight set improves both the training speed and the learning quality. The training problem includes both the design of a network function and the fitting of the function to a set of input and output data points by computing a set of coefficient weights. The form of the function can be adjusted by adjoining new neurons and pruning existing ones and setting other parameters such as biases and exponential rates. Our exposition reveals several useful results that are readily implementable     

Retardation of jump-up escape responding in rats pretreated with different frequencies of noncontingent electric shock.

Pretreated 5 groups of 5 male albino Sprague-Dawley rats each with either 0, 10, 40, 80, or 160 5-sec, 1.5-ma pulsed shocks. Ss were then given escape training in a jump-up box. The number of failures to escape was an increasing function of pretreatment shock frequency. Ss that showed the retardation effect escaped irregularly with short latencies on some trials and failures to escape on others. After escape training, Ss in the 0-shock pretreatment group were given 80 5-sec, 1.5-ma pulsed shocks and then exposed to additional escape training in the jump-up box. These Ss did not show the retardation effect. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

CXCR4 is required by a nonprimate lentivirus: heterologous expression of feline immunodeficiency virus in human, rodent, and feline cells

A heterologous feline immunodeficiency virus (FIV) expression system permitted high-level expression of FIV proteins and efficient production of infectious FIV in human cells. These results identify the FIV U3 element as the sole restriction to the productive phase of replication in nonfeline cells. Heterologous FIV expression in a variety of human cell lines resulted in profuse syncytial lysis that was FIV env specific, CD4 independent, and restricted to cells that express CXCR4, the coreceptor for T-cell-line-adapted strains of human immunodeficiency virus. Stable expression of human CXCR4 in CXCR4-negative human and rodent cell lines resulted in extensive FIV Env-mediated, CXCR4-dependent cell fusion and infection. In feline cells, stable overexpression of human CXCR4 resulted in increased FIV infectivity and marked syncytium formation during FIV replication or after infection with FIV Env-expressing vectors. The use of CXCR4 is a fundamental feature of lentivirus biology independent of CD4 and a shared cellular link to infection and cytopathicity for distantly related lentiviruses that cause AIDS. Their conserved use implicates chemokine receptors as primordial lentivirus receptors.