Optical measurements of thermal diffusivity of a material

The measurement of thermal diffusivity of a material (in particular, a thin film) is important for various reasons, e.g., to predict the heat transfer in the solid subjected to a thermal process, to monitor surface composition or morphology, or to detect invisible subsurface defects like delaminations. This measurement can be done in a noncontact manner using various photothermal methods. Such methods typically involve pulsed heating of the surface by small amounts using a laser source; the decay of the surface temperature after this pulsed photothermal heating is then probed to provide the thermal diffusivity. Various probing methods have been developed in the literature, including the probing of reflection, refraction, and diffraction from the pulsed heated area, infrared thermal radiometry, and surface deformation. This paper provides an overview of such techniques and some examples of their applications.     

Degradation of junction leakage in devices subjected to gateoxidation in nitrous oxide [MOS transistors]

Nitrided gate oxides offer several electrical and reliability advantages over conventional oxides and also provide a good barrier against impurity diffusion. Oxidation in nitrous oxide (N₂O) has been very successful in overcoming some of the problems associated with nitridation in ammonia. The authors have observed that the extent of N₂O oxidation has a strong detrimental effect on the drain leakage current of MOS transistors in the off state. This phenomenon has been identified to be caused by an increase in the active area junction leakage current     

Measles, polio and tetanus toxoid antibody levels in Gambian children aged 3 to 4 years following routine vaccination

A nation-wide cross-sectional survey of 816 children 3-4 years old was carried out in The Gambia between September 1990 and July 1991 to assess the seroprevalence of antibodies against 3 diseases included in the expanded programme on immunization: measles, poliomyelitis and tetanus. Among 689 children whose records were available, 94.5% were fully immunized. Measles vaccine was administered to 97% of the children and 91% of these had detectable antibodies at the time of the survey. Antibodies against type 1 and type 3 polioviruses, after up to 6 doses of oral polio vaccine, were present in 88.1% and 89.3% of the children respectively. Ninety-seven percent of the children who had received 4 doses of diphtheria-pertussis-tetanus vaccine (DPT) and 91% of those who received 3 doses had detectable tetanus toxoid antibodies at the age of 3-4 years. This study shows that serological responses to EPI vaccines given in infancy persist at very satisfactory levels throughout early childhood.     

Recent advances in raisingT c and establishing the gap-symmetry of high-T c cuprate superconductors

The most recent attempts in raising T_c of cuprate superconductors were successful by synthesizing new Hg-based cuprate materials. We discuss some properties of materials from this series with varying numbers of Cu-O planes per unit cell, including the considerable rise of the critical temperature under the influence of external pressure.In the second part of this contribution, various attempts to directly determine the symmetry of the superconducting order parameter of high-T_c cuprates are mentioned and set into perspective. The experimental approaches are all based on probing the phase of the order parameter in suitably connected closed superconducting loops. The evidence for unconventional order-parameter symmetry in these materials is growing.     

Ischemia‐reperfusion injury. A phenomenon,that also occurs in the bone

Ischemia‐reperfusion injury of the bone occurs due to traumatic and non‐traumatic alterations affecting blood supply to the bone. It is likely to occur also upon insertion of an implant. Ischemia‐reperfusion injury of the bone has been studied by interruption of blood supply in situ, in limb replantation/transplantation models, in revascularized bone grafts and non‐vascularized bone fragments, as well as in isolated cultured cells. All cells of the bone are affected, including osteoblasts, osteocytes, osteoclasts, chondrocytes, and bone marrow cells. Critical ischemia times for induction of bone cell death, either in the ischemic period or following reperfusion, are in the range of 3 to 7 h. These critical ischemia times are significantly increased by decreasing the temperature from 37 °C to 0–4 °C. Anoxia is the most likely trigger of cell injury in the ischemic phase. In the reperfusion phase, reactive oxygen species are decisively involved in the injurious process. In general, however, the available information on the mechanism of ischemia‐reperfusion injury of the bone is relatively sparse. On the other hand, there are clear similarities to the mechanisms of ischemia‐reperfusion injury known from other organs, and there is a clear potential for protection against ischemia‐reperfusion injury of the bone.     

Knight Shift Data and Superconducting T c Modeling Based on an Effective Hole Model

The superconducting T _c of cuprates have been modeled on a linear scaling with hole concentration per CuO₂ plane and a deleterious influence of bond resonance with the apical system (effective hole formalism). In cases where distribution between various hole reservoirs is not trivial, Knight shift can provide actual hole concentrations. It is shown here that when Knight shift data are used in an effective hole algorithm, satisfactory T _c predictions can be made, corroborating the deleterious influence on T _c of apical O and earlier assumptions concerning hole distributions. For the case of stacking of more than two CuO₂ planes, the inner plane has to be treated as an infinite layer analog in the effective hole model. A separation into inner and outer planes with different dopings is indeed observed by Knight shift, with higher doping in the latter. This is explained here as being due to a tendency to equalize an effective doping degree, as the outer planes lose holes in resonance of bonding with the apical system.