Dose-dependent gingival overgrowth induced by cyclosporin in rats

This study evaluated the effect of dosage on severity of cyclosporin-A (CSA) induced gingival overgrowth. Eighty (80) male Sprague-Dawley rats were randomly distributed into 4 groups. Rats in each group daily received CSA in mineral oil by gastric feeding at dosages of 0 (control), 3, 10, and 30 mg/kg, respectively, for 6 weeks. Stone models of the mandibular incisal region were obtained biweekly and were used for analysis of the gingival dimensions. Animals were sacrificed at the end of week 6 and tissue sections were processed for histopathologic evaluations. Animals were sacrificed at the end of week 6 and tissue sections were processed for histopathologic evaluation Gingival overgrowth including bucco-lingual and mesio-distal width and vertical height were significantly increased with increasing CSA dosage. Furthermore, the gingival dimensions displayed a positive linear relation to dosage and treatment duration. The histopathologic evaluation revealed a granulomatous tissue wedging the tooth-gingival interface in the 3 mg/kg group. This tissue had reached exuberant size in the 10 and 30 mg/kg groups. In summary, the analysis of gingival dimensions the histopathologic evaluation shows a dose-dependent effect on the severity of CSA-induced gingival overgrowth.     

Unloading yield effects in aluminum alloys

A yield effect produced by unloading and reloading during tensile deformation has been observed for several heat treated aluminum alloys. The effect depends on the composition and heat treatment of the material, as well as on the strain (or stress) at which the unloading takes place. Although the effect is independent of the unloading time at room temperature, it is found to be time dependent at 200 K where diffusion of solute elements in aluminum is sluggish. A qualitative model based on the shearing of coherent precipitates during deformation and subsequent healing of the precipitates by rapid short range diffusion in the unloaded state is proposed to explain the effect.     

The effects of doping impurities and substrate crystallin on the formation of nickel suicides on silicon at 200–280° C

Transmission electron microscopy and Auger electron spectroscopy have been applied to investigate the effects of doping impurities and substrate crystallinity on the formation of nickel suicides at 200–280° C in nickel thin films on silicon. The systems investigated included samples with as-implanted BF₂, B, F, As, and P and recrystallized (001) Si as well as P-doped low pressure chemical vapor deposited (LP-P) and B-doped plasma enhanced chemical vapor deposited (PE-B) amorphous silicon substrates. In samples annealed at 220–280° C, substantial amounts of epitaxial NiSi₂ were found to form on crystalline structure of BF₂, B and F implanted samples to various extents at different temperatures. High resolution lattice imagings of cross-sectional samples showed that the epitaxial NiSi₂/Si interfaces are coherent. No NiSi₂ was detected in all nickel thin films deposited on implantation-amorphous specimens. NiSi₂ epitaxy was found to be a sensitive function of annealing temperature. Good correlation was found between the atomic size factor and resulting stress and NiSi₂ epitaxy at low temperature. The formation of Ni₂Si and NiSi was observed to be influenced by the dopant species and crystallinity of the substrates. The vast difference in inducing the formation of nickel suicides in implantation-amorphous and recrystallized samples is likely due to variations in initial structure and/or dopant distribution. The finding that bothn-type andp-type dopants influenced the formation of Ni₂Si and NiSi suggested that they may be related to the electrical activity of the doping species in recrystallized samples. NiSi, possessing one of the lowest resistivity among all metal silicides, was found to be the only phase formed in all implantation-amorphous as well as LP-P and PE-B amorphous silicon samples annealed at 280° C. Nickel thin film appears to be an attractive candidate for the metallization of amorphous silicon devices.     

Characterization of beryllium foil produced by hot rolling

Beryllium foil is important for a number of aerospace applications including honeycomb structures and metal-matrix composites. In this study, a method of producjng beryllium foil directly from powder or flake is demonstrated. A variety of foils were produced in the thickness range 90–300 m, free from defects such as pinholes and excessive surface roughness, and exhibiting sufficient formability for honeycomb manufacture. Foil produced directly from powder or flake exhibits crystallographic texture, microstructure, and formability equivalent to foil produced from more massive precursors.     

Pest disintegration of thin MoSi2 films by oxidation at 500° C

Thin molybdenum disilicide (MoSi₂) films have been produced by magnetron sputter deposition, and subjected to oxidation tests for the study of MoSi₂ pest-a phenomenon showing disintegration of a solid piece of MoSi₂ into powdery products. The as-prepared films were of an amorphous structure. Oxidation of the films in air at 500° C led first to cracking of the films, and then the cracked pieces eventually evolved into disintegrated powders with a yellowish appearance. Secondary electron microscopy and Auger electron spectroscopy revealed that the reaction products consisted of MoO₃ whiskers (platelets), Si-Mo-O fibres, SiO₂ clusters, and some residual MoSi₂. The disintegration of MoSi₂ films appeared to be independent of their crystal structure; a similar phenomenon was also observed in crystallized films, with a metastable hexagonal structure, oxidized under the same conditions. The disintegration of the MoSi₂ films is compared to and correlated with the pest reaction of bulk MoSi₂.     

Analyses of shear band emission in a Mg-based bulk metallic glass deformed at different nanoindentation rates

Nanoindentation behavior of Mg₅₇Cu₃₁Y_6.6Nd_5.4 bulk metallic glass was characterized at different loading rates. The load–displacement curves exhibit significant displacement serrations, apparently associated with discrete shear band emission, at low loading rates but disappear at high rates. Analyses based on displacement serration, strain rate serration and hardness serration were carried out to determine the critical strain rate beyond which the transition from inhomogeneous to homogeneous deformation actually took place. It was concluded that the hardness serration analysis probably provides the most reasonable result as the other two were limited by the instrument noises. Based on a shear band nucleation model, the critical nucleus size was estimated to be a sphere of about 25 nm in diameter.     

Nickel silicidation techniques for strained Si1?xGex, Si1?x?yGexCy, and Si1?yCy alloys material-device applications

A nickel silicide process for Si_1-xGe_x, Si_1-x-yGe_xC_y, and Si_1-yC_y alloy materials compatible with Si technology has been developed. Low-resistivity-phase (12–20 μΘ cm) nickel silicides have been obtained for these alloys with different low sheet-resistance temperature windows. The study shows that thin (15–18 nm) silicide layers with high crystalline quality, smooth silicide surface, and smooth interface between silicide and the underlying material are achievable. The technique could be used to combine the benefits of Ni silicide and Si_1-xGe_x, Si_1-x-yGe_xC_y, and Si_1-yC_y alloys. The technique is promising for Si or Si_1-xGe_x, Si_1-x-yGe_xC_y, and Si_1-yC_y alloy-based metal-oxide semiconductor, field-effect transistors (MOSFETs) or other device applications.     

Electrical characteristics of highly reliable ultrathin hafniumoxide gate dielectric

Electrical and reliability properties of ultrathin HfO₂ have been investigated. Pt electroded MOS capacitors with HfO₂ gate dielectric (physical thickness ~45-135 Å and equivalent oxide thickness ~13.5-25 Å) were fabricated. HfO₂ was deposited using reactive sputtering of a Hf target with O₂ modulation technique. The leakage current of the 45 Å HfO₂ sample was about 1×10^-4 A/cm ² at +1.0 V with a breakdown field ~8.5 MV/cm. Hysteresis was <100 mV after 500°C annealing in N₂ ambient and there was no significant frequency dispersion of capacitance (<1%/dec.). It was also found that HfO₂ exhibits negligible charge trapping and excellent TDDB characteristics with more than ten years lifetime even at V_DD=2.0 V     

Guest Editors' Introduction: Virtual Machines

A system virtual machine is a software implementation of a real computer that can execute unmodified applications and an operating system. This issue contains articles and interviews that explore virtual machine use in pervasive computing.