Formal Foundations of Operational Semantics

In this paper we report on the results of a sophisticated and substantial use of PVS to establish a recent result in operational semantics. The result we establish is a context lemma for operational equivalence for very wide class of programming languages, known as the CIU theorem. The proof uses the annotated holes technique to represent contexts and compute with them. Thus this paper demonstrates that that it is possible to use PVS as a tool in the development of modern operational techniques, and a productive tool at that. The process of formalizing the CIU theorem revealed several gaps in published proof. The proof of the CIU theorem in PVS took approximately six months to develop. The actual machine checked proof involves the proving of around one thousand facts, and takes PVS slightly less than three hours of CPU time running on a Linux machine configured with 2 GBytes of main memory and four 550 MHz Xeon PIII processors.     

Ovarian gonadotrophin surge-attenuating factor (GnSAF): where are we after 20 years of research?

When gonadotrophin-stimulated IVF methods were being developed in the 1970s and 1980s, understanding of the physiology of FSH improved. In addition to its classic actions of stimulating aromatase activity and oestradiol secretion by ovarian granulosa cells, FSH was found to stimulate the ovarian production of an uncharacterized hormone known by its specific effect of reducing pituitary responsiveness to GnRH. This hormone has been called gonadotrophin surge-attenuating factor (GnSAF), gonadotropin surge-inhibiting factor (GnSIF), various abbreviations (GnSAF/IF, GnSIF/AF) and also attenuin. Although first described in the 1980s, GnSAF has still not been convincingly characterized and no published candidate amino acid sequences conclusively relate to GnSAF bioactivity. On the basis of superovulation studies and in vitro experimentation into the roles of steroids in regulating LH, GnRH and GnRH self-priming, the concept that GnSAF has a role in the regulation of LH secretion, the timing of the LH surge and the prevention of premature luteinization developed. For at least a decade, understanding of the specific GnSAF effects of reducing pituitary sensitivity to GnRH, especially GnRH self-priming and antagonizing the stimulatory effects of oestradiol on GnRH-induced LH secretion, supported this concept. However, improved knowledge of the changes in GnSAF bioactivity in follicular fluid and serum in women requires revision of this concept. The present authors propose that the main role of GnSAF is probably the negative regulation of pulsatile LH secretion, mainly during the first half of the follicular phase, indicating a critical role in the regulation of folliculogenesis and oestradiol secretion.     

Immobilized enzyme electron spin resonance: a method for detecting enzymatically generated transient radicals

The study of enzymatically generated, transient radicals provides valuable information about radical reactivity as well as enzyme function. ESR methods to detect transient radicals are generally based on continuous flow and have the potential to consume large quantities of enzyme, substrate, and buffer. Experimental approaches have been pursued to minimize sample volumes, although none have made the continuous-flow ESR approach generally applicable for enzymes and substrates available in limited quantities. We have developed an alternative approach to the traditional continuous-flow ESR method that provides the same high-resolution ESR spectra, but does not consume large quantities of enzyme, substrate, or buffer. The method utilizes enzyme immobilized onto an inert substrate packed directly into an ESR flat cell. Flowing substrate solution over the immobilized enzyme generates in situ, transient radicals, which can then be observed on the submillisecond time scale. We have termed this method "immobilized enzyme ESR," abbreviated IE-ESR. In this paper, we have described the details of the IE-ESR technique and have presented data collected using the IE-ESR technique for transient radicals from limited quantity enzymes, limited quantity substrates, and D2O buffers. An extension of this technique to ESR spin trapping has also been discussed.     

An ergonomic intervention to reduce back strain among apple harvest workers in New York State

The impact of modifications to the apple picking bucket on common picking postures, self-reported comfort, ease of use, and speed of harvest were measured. Fourteen apple pickers wore an intervention hip belt, were interviewed and measured using posture-activities-tools-handling methodology. The use of hip belt did not significantly alter time spent in various postures. 78.6% of interviewed workers preferred the modified bag, 71.4% noted a difference in the back, neck, or shoulder, while 64.3% said regular use of modified bag would slow their work. Major themes in worker comments are discussed. The hip belt modification to apple harvest bag seems generally acceptable to workers, but needs further development to overcome unintended effects. Although work sampling demonstrates that the bag does not affect work practices, workers appear somewhat concerned that productivity will be negatively impacted. Further training of workers in the use and potential benefits of bag are needed.     

Impedance/Dielectric Spectroscopy of Electroceramics–Part 1: <Emphasis Type="Italic">Evaluation of Composite Models for Polycrystalline Ceramics</Emphasis>

In the microcrystalline regime, the electrical (impedance/dielectric) behavior of grain boundary-controlled electroceramics is well described by the brick-layer model (BLM). In the nanocrystalline regime, however, grain boundary layers can represent a significant volume fraction of the overall microstructure. Simple boundary-layer models no longer adequately describe the electrical properties of nanocrystalline ceramics. The present work describes the development of a pixel-based finite-difference approach to treat a nested-cube model (NCM), which is used to investigate the validity of existing models for describing the electrical properties of polycrystalline ceramics over the entire range of grain core vs. grain boundary volume fractions, from the nanocrystalline regime to the microcrystalline regime. The NCM is shown to agree closely with the Maxwell-Wagner effective medium theory.     

How to prepare membrane proteins for solid-state NMR: A case study on the alpha-helical integral membrane protein diacylglycerol kinase from E. coli

Several studies have demonstrated that it is viable to use microcrystalline preparations of water-soluble proteins as samples in solid-state NMR experiments [1-5]. Here, we investigate whether this approach holds any potential for studying water-insoluble systems, namely membrane proteins. For this case study, we have prepared proteoliposomes and small crystals of the alpha-helical membrane-protein diacylglycerol kinase (DGK). Preparations were characterised by 13C- and 15N-cross-polarization magic-angle spinning (CPMAS) NMR. It was found that crystalline samples produce better-resolved spectra than proteoliposomes. This makes them more suitable for structural NMR experiments. However, reconstitution is the method of choice for biophysical studies by solid-state NMR. In addition, we discuss the identification of lipids bound to membrane-protein crystals by 31P-MAS NMR.     

Variability in EMF permittivity values: implications for SAR calculations

Digital anatomical models of man and animals are available for use in numerical calculations to predict electromagnetic field (EMF)-induced specific absorption rate (SAR) values. To use these models, permittivity values are assigned to the various tissues for the EMF frequencies of interest. There is, as yet, no consensus on what are the best permittivity data. This study analyzed the variability in published permittivity data and investigated the effects of permittivity values that are proportional on SAR calculations. Whole-sphere averaged and localized SAR values along the diameter of a 4-cm sphere are calculated for EMF exposures in the radio frequency range of 1 MHz to 1 GHz. When the dimensions of a sphere are small compared to the wavelength (i.e., wavelength inside the material is greater than ten times the dimensions of the object), the whole-sphere averaged SAR is inversely proportional to the permittivity of the material composing the sphere. However, the localized SAR values generally do not have the same relation and, as a matter of fact, vary greatly depending on the location within the sphere. These results indicate that care must be taken in choosing the permittivity values used in calculating SAR values and some estimate of the dependence of the calculated SAR values on variability in permittivity should be determined.     

Letter legibility and visual word recognition

Word recognition performance varies systematically as a function of where the eyes fixate in the word. Performance is maximal with the eye slightly left of the center of the word and decreases drastically to both sides of this optimal viewing position. While manipulations of lexical factors have only marginal effects on this phenomenon, previous studies have pointed to a relation between the viewing position effect (VPE) and letter legibility: When letter legibility drops, the VPE becomes more exaggerated. To further investigate this phenomenon, we improved letter legibility by magnifying letter size in a way that was proportional to the distance from fixation (e.g., TABLE). Contrary to what would be expected if the VPE were due to limits of acuity, improving the legibility of letters has only a restricted influence on performance. In particular, for long words, a strong VPE remains even when letter legibility is equalized across eccentricities. The failure to neutralize the VPE is interpreted in terms of perceptual learning: Since normally, because of acuity limitations, the only information available in parafoveal vision concerns low-resolution features of letters; even when magnification provides better information, readers are unable to make use of it.