The random phase transducer: a new technique for incoherent processing-experimental results

Ultrasonic speckle is an inherent consequence of the stochastic nature of the reflectivity of biological tissues. Speckle is a source of noise on envelope detected echoes as well as on the power spectra. A technique where the spatial coherence of the transducer is controlled by moving a random phase screen (RPS) through the ultrasonic beam is described. An RPS that is a rough surface generating phase shifts that are randomly distributed between 0 and 2pi is presented. Measurements with unfocused and focused transducers working in broadband pulse-echo mode were performed. Experimental results on the directivity pattern and the ability of the system to obtain uncorrelated speckle patterns are presented. The performance of the RPS in SNR improvements is discussed. Experimental results are in good agreement with theoretical predictions.     

Palmqvist Crack Extension and the Center-Loaded Penny Crack Analogy

Palmqvist crack extension in WC-Co can be described using the center-loaded penny crack analogy. When Palmqvist cracks are represented by semicircles of diameter l (l=crack length measured from an impression corner), the stress intensity factor which controls crack extension differs from that of a half-penny crack of radius l+a (2a = impression size) by only a slowly varying factor m=2^1/2 (l/a)^1/2; m≅1.0 to 2.4 for WC-Co and m≅0.8 to 1.4 for ceramics.     

Intrinsic stress in thin films of Ag,Al, ZnS and LiF

The intrinsic force per unit width, S, in thin films of Ag, Al, ZnS and LiF prepared by vacuum evaporation at pressures of less than 5×10^–5 Torr, has been investigated using a sensitive bending plate technique with capacitative detection. In each case the intrinsic force S was found to vary linearly with film thickness f, for thicknesses greater than about 100 Å, leading to a constant intrinsic stress =dS/df. Both S and were found to be compressive for ZnS and Al, and tensile for Ag and LiF.     

Analysis of the most energetic late arrival in axially transmitted signals in cortical bone

Axial transmission techniques are particularly suitable for the ultrasonic assessment of cortical bone. The generic term "axial transmission technique" indicates a measurement configuration in which emitters and receivers are placed on the same side of the skeletal site, along the bone axis. Whereas axially transmitted signals are composed of several contributions, only the first arriving signal was shown to be a robust indicator of bone status, because its velocity discriminates osteoporotic from healthy patients in clinical studies. Later arrivals may provide additional bone indicators enhancing diagnostic value, but the precise determination of their velocities is challenging. In this paper, we focus on the most energetic contribution and we applied a singular-valuedecomposition- based extraction method not yet employed in the domain of bone assessment with the aim of determining the velocity of this contribution. Signals acquired in vitro on human radii, together with academic models, were used to reveal the relationship between the velocity of the most energetic component and bone properties. The velocity of the most energetic component is highly correlated to cortical layer thickness in the in vitro database (R² = 0.6, P < 10^-5; compared with R² = 0.20, P < 10^-2 for the first arriving signal), consistent with a flexural type of wave on regular tubes or plates. Conclusions are in agreement with published papers based on other axial transmission and signal processing approaches.     

Measurement of the intrinsic stress in thin films of silver by a new cantilevered plate technique

The intrinsic force per unit width S_Int in evaporated thin films of silver was determined from the instantaneous deformation of a cantilevered plate during film deposition from the early growth stages until a thickness of 800 Å was reached. The experimentally determined total bending force S_Tot is analysed as a sum of thermal bending forces and a bending force due to momentum transfer from the vapour. Formulae developed earlier are used to relate the thermal bending forces to the experimentally determined substrate temperature T and temperature differential ΔT between substrate faces, both of which are monitored during film deposition by means of thin film thermocouples. The bending force due to momentum transfer is obtained by simple calculation. The intrinsic bending force S_Int is then determined by subtraction. The results obtained by the present continuous technique are compared with earlier results obtained using a more usual sequential deposition technique.     

Analyse des fonctions des protocoles ipsec et leur intégration dans un réseau privé virtuel

Many approaches may lead to integrate security functions in the intranet/internet services. These functions may be placed at the application layer or at lower OSI layers. IPsec suite protocols were specified by IETF in order to integrate security functionality at network layer. This paper describes the features of IPESC protocols and identifies the aspects which are not standardized. The network translation address (nat) functionality used by routers and firewalls is not always compatible with IPESC. We describe and discuss some solutions for the compatibility of ipsec and nat. The last part of this paper describes a typical architecture for ip vpn based on IPSec technology.     

Quality control in the optical industry: From a work analysis of lens inspection to a training programme, an experimental case study

A cognitive work analysis of quality inspection in the optical industry has been carried out in order to devise a training programme. The task concerned the inspection of high quality human eyeglass lenses. We conducted an experimental investigation of defect detection and acceptability decision-making tasks in 18 experts and novice inspectors. Detection and decision-making were investigated together and separately in two experimental sessions. We showed the effect of expertise on reaction times and errors, and we described the cognitive processes of novice inspectors. On the basis of the processing differences between the two groups, a training programme for new inspectors was devised and described. Finally, training effects were tested.     

Impact of Ethanol on Benzene Plume Lengths: Microbial and Modeling Studies

Recent legislation in several states has called for the removal of methyl tert-butyl ether (MTBE) from gasoline. In order to comply with Federal Clean Air Act requirements for carbon monoxide and ozone attainment, ethanol is being considered as a replacement for MTBE. The objective of this study is to evaluate the potential impact of ethanol on benzene plume lengths in subsurface environments following accidental spills of ethanol-blended gasoline. Two types of studies were conducted here. First, laboratory studies were performed using a pure culture indigenous to a gasoline-contaminated aquifer to evaluate the effect of ethanol on the rate of benzene biodegradation under aerobic conditions. Results from microbial studies showed that the biodegradation of 25 mg/L benzene was severely inhibited in the presence of 25 mg/L ethanol. While the enzymes responsible for benzene biodegradation by the culture were inducible, ethanol degradation appeared to be constitutive. Second, a two-dimensional model was developed to quantify the impact of ethanol on benzene plume lengths using weighted-average aerobic and anaerobic biodegradation rates for benzene in the presence and absence of ethanol. Model simulations indicated that benzene plume lengths are likely to increase by 16–34% in the presence of ethanol.