Propagation of stress waves in viscoelastic media

A new method for the determination of the characteristic parameters of the stress wave propagation, such as attenuation coefficient, wave velocity, Young's modulus and the viscosity coefficient, at various frequencies in viscoelastic rods is presented. The method is based on the propagation of an arbitrary pulse in such a rod and the determination of the characteristic wave propagation parameters of each term of the Fourier series expansion of the propagating pulse. Since each term corresponds to a definite frequency, the characteristic properties of the wave propagation over a wide frequency range can be determined, by means of one test only. The analysis is based on the assumption that the viscoelastic material obeys a Kelvin-Voigt model. The stress pulse was created by means of a steel ball, projected by an air-gun, and was recorded by a transient recorder with digital memory. Two typical viscoelastic materials were tested, namely a poly(methyl methacrylate) (plexiglas) and a polycarbonate of bisphenol A (lexan). The characteristic wave propagation parameters were determined in a frequency range between 3 and 35 kHz and the results obtained agreed satisfactorily with corresponding results of previous investigators.     

Development and characterization of silica-based membranes for hydrogen separation

The method of chemical vapor deposition (CVD) in the counter current configuration was employed in the present study for the development of composite silica membranes. The experiments were carried out in a horizontal CVD reactor under controlled temperature conditions and at various reaction times and differential pressures across the substrate sides. Tetraethylorthosilicate (TEOS) and ozone were used as deposition precursors. Two types of substrates were employed: a porous Vycor tube and an alumina (γ-Al₂O₃) nanofiltration (NF) tube. Measurements with a novel mercury intrusion technique showed that significant reduction of the initial pore size of the γ-Al₂O₃ substrates was achieved, which reached 76% in the cases of extended silica deposition. Additionally, by appropriately interpreting the Knudsen type O₂ permeance results, acquired during the CVD treatment of Vycor tubes, a pore radius reduction even down to the 30% of the initial value was concluded. The permeance of Η₂ and other gases (Ηe, Ν₂, Αr, CO₂) on the developed membranes was measured in a home-made apparatus. The separation capability of the composite membranes was determined by calculating the selectivity of hydrogen over helium, nitrogen, argon and carbon dioxide.     

The Effect of Fines on Critical State and Liquefaction Resistance Characteristics of Non-Plastic Silty Sands

Monotonic and cyclic triaxial tests were carried out on sand-silt mixtures for the investigation of the effect of fines content on their critical state and liquefaction resistance characteristics. Both the undrained and the drained monotonic tests produce a unique critical state line for each tested mixture, which moves downwards with increasing fines content up to a threshold value of 35% and then upwards. At a given void ratio and mean effective stress, the liquefaction resistance ratio decreases with increasing fines content up to the same threshold value of 35%, and increases thereafter with further increasing fines content. However, at a given intergranular void ratio, defined as the ratio of the volume of fines plus voids to that of sand particles, liquefaction resistance ratio increases with increasing fines content up to the threshold value. The threshold fines content value, which is an important parameter in determining the transition from the sand dominated to the silt dominated behaviour of sand-silt mixtures, is related to their particle packing. An expression is proposed for the estimation of the threshold fines content as a function of the mean diameter ratio, d₅₀/D₅₀, and the void ratio. The results, presented herein, also show that for each tested mixture the liquefaction resistance ratio is related to the state parameter and that this relation is influenced by the effective stress level and fines content. The results on the sand-silt mixtures are supported by similar results on natural silty sands.     

E‐CLEMA: A cross‐layer design for improved quality of service in mobile WiMAX networks

In this paper, an efficient cross‐layer design that performs joint adaptation of the physical (PHY) and application layers of a mobile WiMAX network is proposed. The design takes into account channel state and performance information from the PHY and medium access control (MAC) layers, respectively. It uses a decision algorithm to evaluate this information, specify unfavorable conditions regarding low channel quality and increased congestion, and take measures by coordinating modulation order, transmission power, and media encoding rate, toward improved overall quality of service (QoS) offered to the user. Extensive simulation results show that the proposed design achieves considerably reduced packet loss and power consumption, combined with increased throughput as compared to a typical mobile WiMAX system. Copyright © 2008 John Wiley & Sons, Ltd.     

Uncertainty and method limitations in a short-time measurement of the effective thermal transmittance on a building envelope using an infrared camera

Buildings' thermal insulation has received a lot of attention these past years, in an effort to reduce the sector's high energy consumptions. A number of non-destructive methods have been used in order to evaluate in situ the building envelope's effective thermal transmittance, characterised, however, by long-lasting measurement periods. This paper examines the uncertainty and method limitations to use short-time measurements using an infrared camera for this purpose, but also within real environmental conditions that are inevitably unsteady during the measurement series. Experimental measurements were realised with three different infrared cameras, and the results show that a value of effective thermal transmittance could be estimated in situ by a relative uncertainty that does not exceed 20% (coverage factor?=?2), a reliable estimation as long as all systematic errors are identified and diminished through calculations.     

Rapid Detection of Chemical Hazards (Toxins,Dioxins, and PCBs) in Seafood

Among the various hazards occurring in fish and seafood chemical hazards and in particular toxins (ciguatera, scombroid fish poisoning, paralytic shellfish poisoning, neurotoxic (brevetoxic) shellfish poisoning, puffer fish poisoning, diarrhetic shellfish poisoning) have an important place in food poisoning cases. On the other hand, some of the chemical hazards are often due to the pollution of the environment (heavy metals, dioxins, polychlorinated biphenyls, and halogenated aromatic hydrocarbons) and their detection is neither rapid nor facile. As a result there was a great need for developing new rapid and effective methods toward the chemical hazards determination mainly because of their high toxicity. The aim of this review is to provide the information about the new up-to-date detection techniques (Immunological, Chemical and Biochemical, and Molecular assays) in conjunction with detection limits. The latter is made possible by means of inclusion of seven comprehensive and, in most case cases, very extended tables. A reference is also made on the risk characterization of toxins as regards their importance to food contamination or poisoning.     

An ATP-dependent As(III)-glutathione transport system in membrane vesicles of Leishmania tarentolae

Membrane preparations enriched in plasma membrane vesicles prepared from promastigotes of Leishmania tarentolae were shown to accumulate thiolate derivatives of 73As(III). Free arsenite was transported at a low rate, but rapid accumulation was observed after reaction with reduced glutathione (GSH) conditions that favor the formation of As(GS)3. Accumulation required ATP but not electrochemical energy, indicating that As(GS)3 is transported by an ATP-coupled pump. Pentostam, a Sb(V)-containing drug that is one of the first-line therapeutic agents for treatment of leishmaniasis, inhibited uptake after reaction with GSH. Vesicles prepared from a strain in which both copies of the pgpA genes were disrupted accumulated As(GS)3 at wild-type levels, demonstrating that the PgpA protein is not the As(GS)3 pump. These results have important implications for the mechanism of drug resistance in the trypanosomatidae, suggesting that a plasma membrane As(GS)3 pump catalyzes active extrusion of metal thiolates, including the Pentostam-glutathione conjugate.     

The fate of human sperm-derived mtDNA in somatic cells

Inheritance of animal mtDNA is almost exclusively maternal, most likely because sperm-derived mitochondria are actively eliminated from the ovum, either at or soon after fertilization. How such elimination occurs is currently unknown. We asked whether similar behavior could be detected in somatic cells, by following the fate of mitochondria and mtDNAs after entry of human sperm into transformed cells containing mitochondria but lacking endogenous mtDNAs (rho0 cells). We found that a high proportion (10%-20%) of cells contained functioning sperm mitochondria soon after sperm entry. However, under selective conditions permitting only the survival of cells harboring functional mtDNAs, only approximately 1/10(5) cells containing sperm mitochondria survived and proliferated. These data imply that mitochondria in sperm can enter somatic cells relatively easily, but they also suggest that mechanisms exist to eliminate sperm-derived mtDNA from somatic cells, mechanisms perhaps similar to those presumed to operate in the fertilized oocyte.     

Investigation of occupational radiation exposure during interventional cardiac catheterisations performed via radial artery

The purpose of this study was to determine the thyroid, sternum and hand radiation doses of radiologists who perform angiographies and angioplasties via the radial artery. Staff radiation dose was estimated for 21 cardiac interventional catheterisations. Thermoluminescence dosemeters (TLDs) were used to determine radiation dose for each procedure at the right and left wrist, at the sternum and the thyroid. A dose area product (DAP) meter was also attached to give a direct value in Gy cm2 for each procedure. Staff radiation doses varied between 34 and 235 microGy per procedure at the left wrist, 28 and 172 microGy at the right wrist, 16 and 106 microGy at the level of the thyroid and 16 and 154 microGy at the level of the sternum. The DAP values varied between 25 and 167 Gy cm2. Radiation doses in this study are comparable to those reported in previous studies. Moreover, good correlation was found between the DAP values and the occupational dose measured with TLDs.