Observation by soft X-ray laser interferometry of Nb cathodesurface evolution during very high electric field application

We present the very first experiment allowing in situ observation of surface evolution during very high electric field application. This has been achieved by soft (λ=21.2 nm) X-ray laser Fresnel two-mirror interferometry. The surface under study was a niobium planar cathode opposite to a stainless steel blade-like anode. The applied field range on the cathode was F≈0 to 50 MV/m. The interferograms were single shots of 80 ps duration, allowing to probe the surface morphology quasi-instantaneously. The delay between two shots was 20 min while the electric field was kept on. The comparison of successive interferograms gives the Nb surface evolution over ~2 h. Thus, we observed the appearance of defects of ~3 nm high and their evolution with time. These may be the precursors of the minute breakdown which occurred later on. This technique thus makes it possible to detect the preliminary stages of a discharge     

Scenarios and Covert Channels: Another Game...

Covert channels are information leaks in systems that use resources to transfer secretly a message. They are a threat for security, performance, but also for a system's profitability. This paper proposes a new approach to detect covert channels from scenario models of protocols. The problem of finding covert channels in scenarios is first modeled as a game, in which a pair of malicious users S,R is trying to transfer information while the rest of the protocol tries to prevent it. The messages transferred are encoded by behavioral choices at some precise moments, and decoded by a transducer whose input vocabulary is an observation of the system. We then characterize the presence of a covert channel as the existence of a winning strategy for S,R and of a decoder.     

Small fluctuation solution of infinite beam on random Winkler foundation

An analysis of an infinite beam on random Winkler foundation is presented. The solution is based on the small fluctuation approximation which is similar to a first order perturbation procedure. The displacement of the beam is found to be a nonhomogeneous random function with a space dependent spectrum. Explicit expression is presented for the spatial distribution of the standard deviation of the displacement along the beam.Statistical characterization of the small fluctuation approximation makes it possible to derive the spatial distribution of the error introduced by this approximation. It is shown that this error increases exponentially near the zeros of the deterministic solution, but the range of x values where the error exceeds an acceptable value is quite limited. If it is assumed that such local violation of the small fluctuation approximation do not have a significant effect on the solution in the vicinity of the loading point, then it is possible to establish the zone of validity (in the x space) of this approximation. Based on this argument, it is shown that the small fluctuation approximation is valid in the zone of major engineering interest, i.e. from the loading point, down to the point where the deterministic displacement reduces to approximately 20% of its maximum value.In the random variable limit when the autocorrelation distance is very large in comparison with the characteristic length of the beam support system, the present procedure yields results that are identical with the first order Cornell approximation. In general the error introduced by the small fluctuation assumption is less than or equal to the error associated with the first order Cornell approximation; this error decreases with the autocorrelation distance of the coefficient of subgrade reaction. In the zero correlation limit the displacement become deterministic and the error introduced by the small fluctuation approximation vanishes.     

A Venturi microregulator array module for distributed pressure control

Pressure-driven flow control systems are a critical component in many microfluidic devices. Compartmentalization of this functionality into a stand-alone module possessing a simple interface would allow reduction of the number of pneumatic interconnects required for fluidic control. Ideally, such a module would also be sufficiently compact for implementation in portable platforms. In our current work, we show the feasibility of using a modular array of Venturi pressure microregulators for coordinated droplet manipulation. The arrayed microregulators share a single pressure input and are capable of outputting electronically controlled pressures that can be independently set between ±1.3 kPa. Because the Venturi microregulator operates by thermal perturbation of a choked gas flow, this output range corresponds to a temperature variation between 20 and 95°C. Using the array, we demonstrate loading, splitting, merging, and independent movement of multiple droplets in a valveless microchannel network.     

Effect of triacylglycerol composition and structures on oxidative stability of oils from selected soybean germplasm

The oxidative stability of soybean oil triacylglycerols was studied with respect to composition and structure. Crude soybean oils of various fatty acid and triacylglycerol composition, hexane-extracted from ground beans, were chromatographed to remove non-triacylglycerol components. Purified triacylglycerols were oxidized at 60°C, in air, in the dark. The oxidative stability or resistance of the substrate to reaction with oxygen was measured by determination of peroxide value and headspace analysis of volatiles of the oxidized triacylglycerols (at less than 1% oxidation). The correlation coefficients (r) for rates of peroxide formation (r=0.85) and total headspace volatiles (r=0.87) were related positively to oxidizability. Rate of peroxide formation showed a positive correlation with average number of double bonds (r=0.81), linoleic acid (r=0.63), linolenic acid (r=0.85). Rate of peroxide formation also showed a positive correlation with linoleic acid (r=0.72) at the 2-position of the glycerol moiety. A negative correlation was observed between rate of peroxide formation and oleic acid (r=−0.82). Resistance of soybean triacylglycerols to reaction with oxygen was decreased by linolenic (r=0.87) and increased by oleic acid (r=−0.76)-containing triacylglycerols. Volatile formation was increased by increased concentration of linolenic acid at exterior glycerol carbons 1,3 and by linoleic acid at the interior carbon 2. Headspace analysis of voltiles and high-performance liquid chromatography of hydroperoxides indicated that as oxidation proceeded there was a slight decrease in the linolenic acid-derived hydroperoxides and an increase in the linoleic acid-derived hydroperoxides. The oxidative stability of soybean oil triacylclycerols with respect to composition and structure is of interest to the development of soybean varieties with oils of improved odor and flavor stability. Presented at the 81st Annual American Oil Chemists' Society Meeting, Baltimore, MD, April 18–21, 1990.     

-Arthrography and computed tomography arthrography of the wrist-

A five-generation family is here reported in which several members developed malignant melanoma, dysplastic naevi, astrocytoma in all grades, benign or malignant schwannoma, neurofibroma, or meningioma in a single instance. Significant cosegregation of skin and nervous tumours, preclusion of allelism to type 1 neurofibromatosis and phenotypic departure from known syndromes of hereditary proneness to cancer make one suggest an original familial predisposition to both malignant melanoma and central/peripheral nervous tumours.     

Numerical study of conduction and convection heat losses from a half-insulated air-filled annulus of the receiver of a parabolic trough collector

Grid-quality parabolic trough collectors utilize expensive receivers that maintain vacuum in their annuli to reduce convection losses. On the other hand, receivers with air-filled annuli, currently used mainly for process heat applications, are significantly less expensive, but their thermal performance is inferior to evacuated receivers. A promising technique that can bridge the cost and performance gap between the two types of receivers is introduced in this work. A heat-resistant thermal insulation material is fitted into the portion of the receiver annulus that does not receive concentrated sunlight. The presence of this insulation material is expected to reduce not only convection heat losses, but also radiation losses. This study focuses on the calculation of conduction and convection heat losses from the proposed receiver using numerical modeling. The performance of the proposed concept is compared to that of a conventional receiver with an air-filled annulus. The results have shown that the combined conduction and convection heat loss from the proposed receiver can be smaller than that from a receiver with an air-filled annulus by as much as 25% when fiberglass insulation is used. However, the fact that the thermal conductivity of the insulating material increases with temperature reduces the benefit of the proposed concept at high temperatures. As a result, the proposed receiver is expected to be suitable as a replacement for receivers with air-filled annuli or as an economical alternative to evacuated receivers that are used at the lower temperature end of utility-scale solar power plants.     

The effect of treatment with buffered lactic acid on microbial decontamination and on shelf life of poultry

The use of buffered lactic acid systems compared with unbuffered lactic acid solutions enhances the decontaminating effect and increases shelf life of chicken legs. A reduction of about 2 pH units of the chicken skin is obtained by treatment with 10% lactic acid buffer. The buffer keeps the pH of the skin lower than that of untreated legs. Legs treated with 10% lactic acid buffer have a shelf life of 12 days at 6 degrees C, which means an increase of 6 days compared with the shelf life of untreated legs.