Propagation of transverse bulk and surface acoustic waves in LiNbO (3) variable time-delay devices

Experimental measurements are reported on voltage-controlled acoustic time-delay lines operating at 1 GHz in the nearly pure shear-horizontal (S-H) mode in 38 degrees rotated Y-cut LiNbO(3). The high-acoustic velocity (4800 m/s) in conjunction with the large electroacoustic effect exhibited by this orientation allows high-frequency operation and optimum time-delay tuning sensitivity with a planar, single surface, device geometry. The authors demonstrate fractional time delay of 0.3x10(-6) V(-1 ) for surface electrodes that produce an in-plane E-field. However, the simultaneous excitation and propagation of both a leaky surface-acoustic wave (LSAW) and surface skimming bulk wave (SSBW), both as (nearly pure) S-H waves in these devices, seriously restricts the extent to which it is possible to maximize the time delay modulation sensitivity by reducing electrode gap spacing as done in similar SAW devices. The LSAW and surface-skimming body wave (SSBW) propagate at nearly the same velocity on a free surface, and perturbation of their velocity and relative attenuation rates by surface electrodes causes pronounced interference effects between the two modes for some device geometries.     

Experimental determination of dynamic Young's modulus and mechanical damping,and theoretical prediction of dislocation density for depleted uranium-0.75 wt% titanium using the PUCOT

Dynamic Young's modulus (E) and mechanical damping (Q ^–1) measurements were made for three microstructures (, + , and ) of a depleted uranium-0.75 wt% titanium alloy. The temperature range covered was 298 to 1123 K. The apparatus was the piezoelectric ultrasonic composite oscillator technique (PUCOT) operated at 80 kHz. The ranges of values for E and Q ^–1 were 193 to 99 GPa and 3×10^–3 to 8×10^–2, respectively. Correlations for E of each heat treatment as functions of temperature are presented. In addition, the mechanical damping against strain amplitude plots generated from PUCOT data were analysed using the Granato-Luecke zero Kelvin and high-temperature theories of dislocation damping. Computed dislocation densities ranged up to 10¹⁶m^–2.     

A comparison of neutron-induced SEU rates in Si and GaAs devices

The single-event-upset rates due to neutron-induced nuclear recoils have been calculated for Si and GaAs components using the HETC and MCNP codes and the ENDF data base for (n, p) and (n, alpha) reactions. For the same critical charge and sensitive volume, the upset rate in Si exceeds that of GaAs by a factor of about 1.7, mainly because more energy is transferred in neutron interactions with lighter Si nuclei. The upset rates due to neutrons are presented as functions of critical charge and atmospheric altitude. Upsets induced by cosmic-ray nuclei, secondary protons and neutrons are compared.     

On the concept of relative and plastic spins and its implications to large deformation theories. Part II: Anisotropic hardening plasticity

Summary By resorting to both microscopic and macroscopic considerations, including the concept of single slip, dislocation stress, and a scale invariance argument we show that the notion and formalism of the relative spin introduced in Part I reduces to that of plastic spin previously recognized in the literature. The central feature of this reduction is the possibility of obtaining physically based constitutive equations for the plastic spin along with appropriate evolution equations for the dislocation or back stress. When these constitutive models are incorporated in the analysis of existing data on tension-torsion tests, we find satisfactory agreement between theory and experiment. In particular, a theoretical interpretation of the torsionally induced axial strain, as observed for example by Swift, Bailey et al., Hart and Chang, and others, is provided. Moreover, the recent experiments of Montheillet et al. on torsionally induced axial stresses are discussed in the light of the presently proposed models of large inelastic deformation inelasticity accounting for anisotropy and texture effects.

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With 12 Figures     

Considerations on speed selection and risk homeostasis in driving

Risk-taking behavior by drivers is put within the context of a general model of utility maximization by speed choice. It is shown that so-called "risk homeostasis" is possible only under very restrictive conditions. Under more general conditions, risk compensation can occur; that is, the safety effects expected from engineering measures will be discounted to a considerable degree by shifts in behavior.     

Effect of pre-scalding brushing on contamination level of pork carcasses during the slaughtering process

The number of aerobic bacteria on the skin of pork carcasses was measured at seven different points on the slaughtering line in order to study the hygienic effect of pre-scalding brushing on the contamination level of carcasses. Eighty carcasses were investigated, of which 40 were brushed before scalding and 40 served as controls. Samples were excised from three sites: back, abdomen and ham. The total number of samples was 1368. The cleaning monitoring of the pre-scalding brushing machine and the blackscraping machine was done at the same time. After singeing and blackscraping there were significant differences (P<0·05) between brushed and non-brushed ham sites. After singeing, brushed ham sites had a contamination level of 2·11 (log(10) cm(-2)) and non-brushed ham sites a level of 1·57. After blackscraping the contamination of brushed ham sites was 3·45 (log(10) cm(-2)) and that of non-brushed ham sites 3·26. At the end of the slaughtering line brushed carcasses were more contaminated than those not brushed, although this difference was not significant.     

Storage life of frozen salmonoids Effect of light and packaging conditions on carotenoid oxidation and lipid oxidation

Summary The combined effect of oxygen transmission of packaging material and of exposure to light with different spectral distribution on the oxidative degradation of carotenoids and lipids in frozen salmonoids has been characterized in a storage experiment with steaks of rainbow trout. The degradation of the carotenoid astaxanthin, as followed by HPLC analysis and tristimulus colorimetric measurement, was sensitive to the radiant flux density of UV light and less sensitive to the oxygen transmission rate of the packaging material, in agreement with previous findings for photooxidation of carotenoids in food model systems. This is in contrast to the lipid oxidation, which was found to be dependent on the accessability of oxygen rather than on exposure to UV light. Formation of peroxides in the product culminated after 3 months of storage (up to 8.4 mEq kg^–1 oil), and preceded the formation of thiobarbituric-acid-reactive substances. The product in packaging material with a high oxygen transmission rate (60 cm³ m^–2 bar^–1 per 24 h) reached a level of approximately 5 mol malonaldhyde/kg^–1 product, when stored exposed to standard fluorescent light or fluorescent light with a high UV component. Rancid taste was not detected by sensory evaluation for any of the products after 6 months of storage, whereas a bitter taste was noted for the product exposed to UV light.

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Die Haltbarkeit von Lachsforellen Einfluß von Licht und Verpackung auf die Carotenoid- und Fettoxydation

Zusammenfassung Der kombinierte Effekt von Sauerstoffdurchgang durch Verpackungsmaterial und der Lichteinwirkung verschiedener spektraler Verteilung auf den oxidativen Abbau der Carotinoide und Fette in gefrorenen Lachsforellen wurde in einem Lagerungsversuch untersucht. Der Abbau des Carotenoids Astaxanthin wurde mit HPLC undTristimulus-Calorimetrie beobachtet, und war empfindlich gegenüber UV-Licht und weniger empfindlich gegenüber der Sauerstoffdurchlässigkeit der Verpackung, was mit früheren Ergebnissen für Photooxidation der Carotinoide in Modellsystemen übereinstimmt. Dies widerspricht der Fettoxidation, die mehr von Sauerstoffzugang abhängig ist als von der Entwicklung des UV-Lichtes. Die Bildung von Peroxiden des Produktes kuliminierte nach 3monatiger Lagerung (bis 8,4 meq/kg Öl) und ging der Bildung von Thiobarbitursäure-aktiven Substanzen voraus. Das Produkt im Material mit hohem Sauerstoffdurchgang (60 cm³ m^–2 bar^–1 pro 24 h), das bei normalen fluorescierendem Licht oder bei fluorescierendem Licht mit hohem UV-Anteil aufbewahrt wurde, erreichte einen TBS-Wert von ungefähr 5 mol Malonaldehyd/kg Fleisch. Ein ranziger Geschmack wurde durch sensorische Bewertung nach 6monatiger Lagerung nicht erkannt, wohl aber ein bitterer Geschmack bei dem UV-Licht ausgesetzten Proben.

     

Health resort treatment of eye diseases caused by ischemia]

The authors discuss the results of ophthalmodynamometric tests used for the assessment of cerebro-retinal vessels reactivity following carbon dioxide baths and "peat collars". An analysis of systemic and local blood pressure in the ophthalmic artery measured with Weigelin and Lobstein technique enables to assess changes in blood pressures following a/m balneologic procedures. It was found that blood pressure does not change parallelly due to the mechanism of cerebral autoregulation. Transient decrease in blood pressure in the ophthalmic artery is produced by the dilatation of the internal carotid artery indicating a potent vasodilating action of carbon dioxide.