Precise comparison of experimental and theoretical SNRs in CO2 laser heterodyne systems

A detailed comparison of experimental and theoretical SNR in an IR laser heterodyne system has been made with three different signal analyzers. Good agreement, considerably better than a factor of 1.5, is reported. Accurate allowance was made for transmission in the receiver optics, the effective quantum efficiency of the detector due to shot noise domination by the local oscillator, and for coherent speckle effects across the collection aperture. The evaluation of SNR with a surface acoustic wave spectrum analyzer and digital integrator is described in some detail. As an illustration an absolute measurement of backscattering strength in the atmosphere from an airborne equipment at altitudes up to 13.1 km is provided.     

Experimental electrocoagulation of dog esophageal and duodenal mucosa

The per review system for the assessment of research proposals is widely respected by working scientists. Nevertheless two problems associated with the operation of this system by the US National Institutes of Health are identified. First the scientist has no control over which committee will review an application and it may be considered by a quite inappropriate group. Second analysis of the committee composition suggests that in some of the groups several members are not active scientists and therefore not the "peers" of the applicant.     

Cortisol in physiological concentrations acts within minutes to modify effects of prolactin and growth hormone on prostaglandin secretion: importance of effect in modulating cellular responses to calcium and cyclic nucleotides

We propose that intracellular prostaglandins (PGs) are essential for the final expression of the effects of second messengers in most cells. We suggest that the amounts of PGs required are very small (in the picomolar range) and are much lower than those used in most current PG studies. We suggest that while therapeutic levels of inhibitors of PG synthetase may be adequate to block the overflow of PGs from cells, they are in most cases unlikely to reduce intracellular PGs sufficiently to test the role of such PGs. We propose that there is a basal level of PG synthesis unaffected by hormones but that above this level PG synthesis is regulated by the interplay between physiological levels of cortisol, prolactin, growth hormone and thyroid hormones. For the most part prolactin seems to stimulate PG synthesis and cortisol to inhibit it: cortisol has, however, no inhibitory effect on basal PG synthesis. In reducing prolactin-stimulated PG synthesis cortisol is 1000-2000 times more potent than indomethacin on a molar basis. We suggest that the regulation of intracellular PG levels is the mechanism of the so-called "permissive" actions of these hormones. These concepts could prove important in the understanding of many aspects of physiology and pathophysiology including diurnal and seasonal changes in hormone responsiveness. They are also relevant to the use of established drugs and the design of new ones.     

Occurrence of gastric ulcer after Nissen fundoplication

Of 160 patients who underwent Nissen fundoplication for treatment of symptomatic peptic reflux esophagitis, five patients (3.1%) developed gastric ulcers. Four of these five patients experienced the "gas-bloat" syndrome. All ulcers were located on the lesser curvature of the stomach. Analyses of our experience with use of various types of hiatal hernia repair suggests that creation of the valvuloplastic mechanism unique to the Nissen procedure may be of etiologic significance in the development of gastric ulcers following this procedure.     

Acceptability of three convenience chicken products

Three convenience products--frozen, precooked chicken apple fritters, chicken breast fillets, and chicken patties--provided by one processor were subjectively evaluated by two taste panels of older adults, ranging in age from the sixties to middle eighties. The panelists represented a middle-income group maintaining private homes and a low-income group living in public housing. Both panels rated each product above "good" (score=4) or "fair" (score=3) on four acceptability factors and the overall score. Although mean scores of the low-income taste panel on all factors were generally higher for all products, the only significant difference (P less than .01) pertained to the appearance factor. Both panels indicated willingness to buy all three products.     

Occlusion pressures in men rebreathing CO2 under methoxyflurane anesthesia

The effect of general anesthesia on control of breathing was studied by CO2 rebreathing and occlusion pressure measurements in six normal human subjects under methoxyflurane anesthesia. CO2 was found to increase the amplitude of the occlusion pressure wave without changing its shape, so that CO2 responses in terms of the occlusion pressure developed 100 ms after the onset of inspiration (Po/0.1) gave results equivalent to the responses in terms of Po/1.o or any other parameter of the pressure wave. Methoxyflurane depressed the ventilatory response to CO2 but not the occlusion pressure response, implying that the most important action of the anesthetic was to increase the effective elastance of the respiratory system rather than to depress the respiratory centers. The elastance was further increased by CO2, and this mechanical change had the effect of shifting the "apneic threshold" extrapolated from the ventilatory response curve to a lower PAco2. Frequency of breathing, inspiratory and expiratory times were not altered by CO2 in anesthetized subjects.     

A Raman microprobe study of electrical treeing in polyethylene

The chemical nature of electrical tree growth in a blend of high and low density polyethylene has been studied by confocal Raman microprobe spectroscopy. The observed spectra, which are easily perturbed by the Raman probe beam, can be described in terms of three components, the relative intensities of which vary from place-to-place on the sample. Throughout the body of the tree, the usual Raman bands of polyethylene are seen, but superimposed upon a pronounced fluorescent background. This suggests a degree of material degradation throughout the structure, even where there is no visible evidence of electrical discharge damage or ageing. The individual channels that make up the fractal structure of the tree can then be divided into two distinct categories. Within the core of the tree, their Raman spectra are made up of two elements; fluorescence, plus the G and D bands of sp² hybridized carbon. Here, the tree channels are best thought of as hollow tubules surrounded by a carbonaceous shell. At the tips, the channels are characterized simply by the Raman bands of polyethylene superimposed upon a reduced fluorescent background, irrespective of their size. That is, in this region, the tree channels are simply hollow tubules within the dielectric. The transition between these two structures occurs relatively abruptly. These observations are related to the treeing process.     

Radio Echo Sounding of Pine Island Glacier, West Antarctica: Aperture Synthesis Processing and Analysis of Feasibility From Space

Airborne radio echo sounding of the West Antarctic Ice Sheet over Pine Island Glacier was performed in the austral summer of 2004/2005 under the National Science Foundation's West Antarctic Ice Sheet Initiative. The British Antarctic Survey flew its newly developed 150-MHz ice-sounding radar over Pine Island Glacier and collected approximately 35 000 km of sounding data. The synthetic aperture radar (SAR) technique was applied to process those data in order to enhance radar signatures from the bed. As a matter of fact, airborne ice-sounding radar systems are generally affected by surface clutter returns, masking the echoes of internal layers and ice-bedrock transition at a large depth. Focused and unfocused (Doppler filtering) SAR techniques were compared, and their respective advantages/disadvantages were analyzed. Enhancement of bedrock detection at a large depth (> 2000 m) through SAR processing is demonstrated. Finally, a simulation analysis was performed for assessing the feasibility of ice-sheet sounding from space. It is shown that the gain in bed detection threshold is marginal in the satellite sounding geometry. Airborne radar, Antarctica, ice sounding, satellite remote sensing, subglacial topography, synthetic aperture radar (SAR) processing, West Antarctic Ice Sheet.     

Secondary emission formulas

A minor revision is made to the author's `A New Formula for Secondary Emission Yield' (ibid., vol.36, no.9, p.1963-7, September 1989) based on the work of A. Shih and C. Hor reported elsewhere in this issue (ibid. vol.40, no.4, p.824-9, Apr. 1993)