Thermomechanical characterization of stress localization in glass: An experimental and numerical study

Thermoelastic stress analysis and quantitative calorimetry are full‐field noncontact techniques widely used to study the thermomechanical behaviour of materials. The first one linearly relates the sum of the principal stresses to the temperature variation, and the second one can be used to measure the mechanical dissipation. However, brittle materials such as glass are a priori bad candidates for these techniques. Indeed, their low‐temperature variations under loading lead to very noisy infrared images, and their brittle mechanical behaviour does not allow to deform them significantly. In the present paper, the thermomechanical characterization of a holed glass sample under cyclic loading is performed. A preliminary new filtering methodology has been applied to the thermal movie to remove the noise. The stress field obtained from the thermoelastic stress analysis is well correlated to the finite element model showing that this technique is adapted to study the thermoelastic response of brittle materials. Finally, the corresponding calorimetric response has been determined by using a simplified formulation of the heat diffusion equation. This permits to quantify heat sources and to carry out energy balances.     

Influence of a fine glass powder on the durability characteristics of concrete and its comparison to fly ash

A detailed investigation carried out to ascertain the durability characteristics of fine glass powder modified concretes is reported in this paper. Tests were designed to facilitate comparisons between concretes modified with either glass powder or fly ash at the same cement replacement level. The optimal replacement level of cement by glass powder is determined from strength and hydration tests as 10%. The later age compressive strengths of glass powder and fly ash modified concretes are seen to differ by only 5%. The durability characteristics are ascertained using tests for rapid chloride permeability, alkali–silica reactivity, and moisture transport parameters. The chloride penetrability values indicate some amount of pore refinement. The potential of glass powder to reduce the expansion due to alkali–silica reaction is established from tests conducted in accordance with ASTM C 1260, but fly ash is found to perform better at similar replacement levels. Glass powder–fly ash blends that make up a 20% cement replacement level are found to be as efficient as 20% fly ash in reducing expansion. The control concrete is seen to exhibit the lowest overall moisture intake after 14 days of curing, and fly ash concrete the highest, with the glass powder concrete in between. The trend is reversed at later ages, demonstrating that both the replacement materials contribute to improved durability characteristics. The sorptivity and moisture diffusion coefficient values calculated from the moisture intake-time data also demonstrate a similar trend. These studies show that fine glass powder has the potential to improve the durability of concretes.     

Nicotine does not modulate IL-4 and interferon-gamma release from peripheral blood mononuclear cells and T cell clones activated by phorbol myristate acetate and calcium ionophore

Tobacco smoking induces an increased nonspecific IgE response. IgE synthesis is controlled by IL-4 and IFN-gamma. The effect of nicotine (10(-10) to 10(-5) M), one of the major components of tobacco smoke, were studied on IL-4 and IFN-gamma release by peripheral blood mononuclear cells from 12 allergic patients and 12 nonallergic subjects and 16 T cell clones stimulated by nonspecific agonists (phorbol myristate acetate and calcium ionophore). The release of IL-4 and IFN-gamma was measured by ELISA in supernatants after a 48-hour culture. Nicotine did not modify IL-4 and IFN-gamma release by peripheral blood mononuclear cells or T cell clones. The effects of tobacco smoke on IgE production are unlikely to change in the T cell phenotype by nicotine.     

Buprenorphine versus heroin dependence: comparison of toxicologic and psychopathologic characteristics

Sociodemographic, toxicologic, and psychopathologic characteristics of 22 buprenorphine addicts and 45 heroin addicts admitted for inpatient detoxification were compared. Although the buprenorphine addicts were older, clinically significant differences were not apparent. The availability of buprenorphine may be the main reason for its abuse.     

Time integrated detection of femtosecond laser pulses scattered by small droplets

Scattering of femtosecond laser pulses by small droplets has been measured and compared with predictions, yielding some interesting new applications for time integrated detection of the scattered field. The scattering intensity of integrated detection becomes monotonic with droplet size over large regions of scattering angle and morphology dependent resonances are surpressed, opening the way for particle sizing using the scattered intensity. Furthermore, the ripple structure no longer appears in the rainbow region of scattering, simplifying rainbow refractometry significantly. These scattering proporties of femtosecond laser pulses have been demonstrated in the laboratory using a novel Paul trap for levitating single droplets.     

Effect of temperature on RC elements strengthened with CFRP

The strengthening of RC elements with CFRP is a technique that has been acquiring more and more potential. The bond between the CFRP reinforcement and the concrete support is usually made with epoxy adhesives. However, it is here that the integrity of the system can be affected, namely by exposure to high temperatures. In order to study the effect of an increase of air temperature on the behaviour of the epoxy adhesive, CFRP strengthened RC and reference RC specimens were tested. After cyclical thermal exposures, with temperatures rising between 20 and 80°C, specimens were subjected either to compressive shear tests or bending tests. The results demonstrated that epoxy adhesive exhibits poor behaviour when subjected to increased temperatures, causing important bond deterioration. The improvement achieved with the CFRP reinforcement tends to disappear with an increase of the environment temperature. So, the thermal resistance of this strengthened system cannot be considered very high. However, the inclusion of insulating materials can be a good solution to protect the strengthened RC elements. Among tested materials, the foamed polyurethane showed the best behaviour.     

Experimental study of the viscoelastic properties of green poplar wood during maturation

During the radial growth of trees, internal stresses are created because of wood-cell maturation. Biomechanical models can compute these stresses, but they are currently limited by a lack of knowledge about the viscoelastic behavior of green wood. The aim of the present paper is to study the viscoelastic behavior of green wood and to obtain measurements of viscoelastic parameters. In order to accomplish this, the effect of internal maturation stresses on the studied samples was first eliminated by studying viscoelastic phenomena. Creep tests were then performed on small slats of wood using a cantilever bending test. It is shown that green wood viscoelastic behavior can be modeled with Burgers’ model. The corresponding parameters are estimated with respect to the wood-cells age. No significant difference between tension wood and normal wood is revealed, but it appears that green wood tends to lose its viscoelastic behavior with maturation.     

An efficient memory allocation algorithm and hardware design with VHDL synthesis

This paper presents a hardware-efficient memory allocation technique, called EMA, that detects the existence of any free block of requested size in memory. EMA can allocate a free memory block of any number of chunks in any part of memory without having any internal fragmentation. The gate-level design of the hardware unit, along with its area-time measurements is given in this paper. Simulation results indicate that EMA is fast and flexible enough to allocate/deallocate a free block in any part of memory resulting in efficient utilization of memory spaces. In addition, the VHDL synthesis with FPGA implementation shows that EMA has less complicated hardware, and is faster than the known hardware techniques.