Photonic band gaps in 12-fold symmetric quasicrystals

The 12-fold symmetric quasicrystal shows great potential as a novel photonic band gap (PBG) structure exhibiting a band gap for relatively low filling fractions and dielectric contrasts. The band gaps are highly homogeneous with respect to the angle of incidence of the incoming light due to the crystal's high degree of rotational symmetry. These crystals have been analyzed using a finite element method developed specifically for modelling PBG structures. We present and discuss quasicrystal structures and their optical properties.     

Dynamic crack propagation with cohesive elements: a methodology to address mesh dependency

In this paper, two brittle fracture problems are numerically simulated: the failure of a ceramic ring under centrifugal loading and crack branching in a PMMA strip. A three‐dimensional finite element package in which cohesive elements are dynamically inserted has been developed. The cohesive elements' strength is chosen to follow a modified weakest link Weibull distribution. The probability of introducing a weak cohesive element is set to increase with the cohesive element size. This reflects the physically based effect according to which larger elements are more likely to contain defects. The calculations illustrate how the area dependence of the Weibull model can be used to effectively address mesh dependency. On the other hand, regular Weibull distributions have failed to reduce mesh dependency for the examples shown in this paper. The ceramic ring calculations revealed that two distinct phenomena appear depending on the magnitude of the Weibull modulus. For low Weibull modulus, the fragmentation of the ring is dominated by heterogeneities. Whereas many cracks were generated, few of them could propagate to the outer surface. Monte Carlo simulations revealed that for highly heterogeneous rings, the number of small fragments was large and that few large fragments were generated. For high Weibull modulus, signifying that the ring is close to being homogeneous, the fragmentation process was very different. Monte Carlo simulations highlighted that a larger number of large fragments are generated due to crack branching. Copyright © 2003 John Wiley & Sons, Ltd.     

Sliding wear of austenitic and austenitic-ferritic stainless steels

The dry sliding behavior of a 304L austenitic stainless steel and a duplex 2205 austenitic-ferritic stainless was investigated. The evolution of wear was characterized by the existence of a sliding-distance transition. In particular, wear passed from delamination to tribo-oxidation, with a reduction in wear rate. The occurrence of such a transition was interpreted with reference to a theory of sliding wear based on the formation, by subsurface plastic deformation, of a tribological layer and its detachment during sliding. It has been found that the transition is controlled by the ability of the tribological system to form, on its outer part, a protective oxide-rich scale. This introduces a kinetic limitation, which is particularly important in the case of the duplex 2205, because of its lower ductility in comparison to the 304L steel. In this frame, the influence of sliding velocity, the particular frictional behavior, the role of chromium in the oxidative wear, and the surface temperature evolution during sliding could be explained.     

Effect of geometry and green density on the anisotropic sintering shrinkage of axisymmetric iron parts

Sintering shrinkage of prior cold compacted iron rings with different geometry (height to wall thickness ratio) and green density in the 6.5–7.3?g/cm³ range was investigated. It displays a minimum at an intermediate green density. Axial, tangential and radial shrinkages are different, due to the gradients of green density along the axial and the radial directions. Therefore, the effect of height on shrinkage and its anisotropy is the result of their effect on the stress distribution in the green parts during cold compaction, and the resulting green density and deformation experienced by the powder. Anisotropy decreases on increasing shrinkage.     

Postdoctoral training in professional geropsychology: A survey of fellowship graduates.

Have psychologists who have pursued postdoctoral training in geropsychology viewed such training as a worthwhile professional investment? As the population is aging, psychologists are increasingly working with older adults. For many psychologists, competent practice with the elderly will require some continuing education, whereas other psychologists may choose to secure specialty-level training in the field. A survey of psychologists who completed such specialized postdoctoral training found a high level of satisfaction with the training and a sense of professional competence in most of the geropsychology competency areas set forth by the American Psychological Association. The need for increased opportunities for both proficiency and specialty-level training in applied geropsychology is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

HIV, health care workers and patients: how to ensure safety in the dental office

What can be done to preserve the high standards of patient care, give reasonable assurances to patients and acknowledge the rights of health care workers? Conscientious adherence to infection control is the most responsible option available.     

Creep Failure Analysis of Bars Sustaining Constant Tensile Loads

Life time and failure modes are predicted for metallic barssustaining tensile creep. Experimental results show that a ductile or a`brittle' mode of fracture occurs depending respectively on whether thenominal applied stress is large or small. The analysis is based on amodeling of void nucleation and growth in which damage evolution iscontrolled by two mechanisms of plastic flow in the matrix material.Fracture is supposed to occur when the porosity attains a critical valuewhich depends on the mode of fracture considered. Experimental resultsare explained and described in terms of the proposed model.     

Cross-reactivity of anti-10kD heat shock protein antibodies in leprosy and tuberculosis patients

The response to recombinant 10-kD heat shock protein (HSP) of Mycobacterium leprae (rML10) was evaluated by indirect ELISA in sera from leprosy patients, household contacts, tuberculosis patients and healthy controls in a leprosy-endemic area in the North East of Argentina. Some technical parameters were analyzed: within-assay and between-assay variability, dose-response curves and detectability indexes (specificity and sensitivity) of ELISA applied to measure anti-10 kDa antibodies. High levels of these antibodies have already been reported in positive bacilloscopy patients; herein we have also demonstrated that tuberculosis patients sera cross-react with this M. leprae antigen. This test seems to have a low sensitivity and specificity for leprosy detection; it confirms that antibodies against highly conserved HSP antigens are important in the polyclonal response against mycobacterial epitopes in leprosy as well as in tuberculosis.     

A Novel In Situ Method for Producing a Dispersion of a Ceramic Phase into Copper That Remains Stable at 0.9T M

We apply an in situ approach, whereby a polymer is incorporated into copper and evolves within the metal into the ceramic phase, to create a dispersion of hard particles in a metal. All constituents for the ceramic phase are contained within the organic polymer. The temperature for this polymer to ceramic conversion lies in the 1073 K to 1273 K (800 °C to 1000 °C) range. The process produces a nanoscale dispersion of the ceramic, which leads to high microhardness that remains unaltered at temperatures up to 1223 K (950 °C) (0.9T _M). Apparently, the introduction of the ceramic phase leads to the retention of copper crystallite size of a few hundred nm, despite exposure to heat treatments at these very high temperatures. We call these materials polymer-derived metal-matrix composites.