Effect of postischemic reperfusion on microcirculation and lipid metabolism of skeletal muscle

To study the effect of ischemia reperfusion injury on microvascular reactivity and tissue metabolism in skeletal muscle, a Sprague-Dawley rat cremaster muscle was prepared as a tourniquet ischemia model and subjected to 2 hr ischemia followed by 1 hr reperfusion to simulate the timing of ischemia during microvascular surgery. The dose-response curve of arteriolar reactivity to norepinephrine, lipid peroxidation, and ultrastructure of capillaries was determined in both the control and postischemic reperfusion stages. Judging from the results, we summarize our observations as follows: (1) Postischemic reperfusion significantly increased arteriolar reactivity to norepinephrine, in which the EC50 for vasoconstriction decreased in all three orders of arterioles. These results suggest that reperfusion could have impaired the vasodilation control mechanism, possibly being endothelium dependent. (2) Lipid peroxidation increased sixfold in the reperfusion group, suggesting that oxygen free radicals have produced significant tissue damage under the created conditions. (3) Significant endothelial damage in the capillaries shown by electron microscope observation supports these studies, indicating that ischemia/reperfusion in clinically transplanted skeletal muscles could cause significant damage to the tissue microcirculation both physiologically and metabolically.     

The geometry effects for stress intensity factor of sandwich specimen for measuring interfacial fracture toughness

The interfacial stress intensity factors for three types of sandwich specimens: the single edge crack tensile specimen, the three point bend specimen and the four point shear specimen were obtained by the finite element analysis and compared with the asymptotic solutions. The results show that the geometric effect for mode II specimen is larger than mode I specimen. The limit curves for geometry factor equal to 1.05 were obtained to indicate the usable range of validity of the asymptotic solution.     

Role of conserved Asn-Tyr-Asp-Tyr sequence in bacterial copper/2,4, 5-trihydroxyphenylalanyl quinone-containing histamine oxidase

Copper amine oxidase contains a covalently bound quinonoid cofactor, 2,4,5-trihydroxyphenylalanyl quinone (TPQ), which is synthesized by post-translational modification of a specific tyrosyl residue occurring in the highly conserved sequence, Asn-Tyr-(Asp/Glu)-Tyr. To elucidate the role(s) of the conserved sequence in the biogenesis of TPQ, each of the corresponding residues at positions 401-404 in the recombinant histamine oxidase from Arthrobacter globiformis has been replaced with other amino acids by site-directed mutagenesis. When Asn-401 was changed to Asp or Gln, the rate of TPQ formation by copper-dependent self-processing was 10(3)- to 10(4)-fold slower than in the wild-type enzyme. When Tyr-402 was replaced by Phe, TPQ was not formed at all, showing that Tyr-402 is essential as the precursor to TPQ. In contrast, Asp-403 could be replaced by Glu without changes in the rate of TPQ formation, whereas its replacement by Asn led to a marked decrease. Furthermore, when Tyr-404 was changed to Phe, TPQ was formed swiftly on incubation with copper ions, but the TPQ enzyme exhibited very low activity with altered substrate specificity. These results collectively indicate that a very rigorous structural motif is required for efficient formation of TPQ and for the catalytic activity in the active site of copper amine oxidases.     

2-D dopant profiling in VLSI devices using dopant-selectiveetching: an atomic force microscopy study

We report a detailed mapping of a 2-D dopant profile on a fully processed industrial sample with large dynamic range and high spatial resolution by utilizing a dopant-selective etching process and Atomic Force Microscopy. The experimental results show excellent agreement with those obtained from SRP and SIMS as corroborative methods. We also discuss the most critical factors which influence the applicability, reproducibility, and reliability of this method     

Effect of nitrogen ion implantation on impact wear

The effect of nitrogen ion implantation on the impact wear of several metals and alloys with different hardnesses was studied. An impact testing machine was built for this study. In this machine, bullet-shaped projectiles are bounced against a metal surface which is either stationary or rotating. Wear was determined by weight loss measurements. Scanning electron microscopy pictures were taken to study the surface damage. It was found that nitrogen ion implantation improved the impact wear of most of the materials studied. With sliding motion added during the impact, nitrogen ion implantation has little effect.     

Adaptive 2D finite element simulation of metal forming processes

The development and integration of available current methods and the development of new methods for an adaptive finite element analysis of metal forming processes are presented. The analysis includes large-strain, elastic–plastic, and thermal effects. Many numerical methods such as mesh generation, simulation of the contact between the workpiece and tool and die, and optimization of the finite element mesh are integrated and incorporated. In addition, an algorithm is developed which can detect certain severely distorted elements where the area of integration is approaching zero. The advantage of correcting these regions of locally distorted elements is demonstrated. These numerical methods are implemented in a finite element program developed for simulating metal forming processes, with the emphasis on automating the analysis. Examples include an axisymmetric stress simulation of a coldheading process, a plane strain simulation of an extrusion process and a plane strain simulation of orthogonal metal cutting, all with noticeable thermal effects. The orthogonal cutting forces and feed forces calculated are compared with two sets of experimental data, with good agreement.     

Microwave plasma enhanced chemical vapor deposition diamond synthesis from high carbon content source

To synthesize diamond films by microwave plasma enhanced chemical vapor deposition (MPECVD), the methane concentration (CH₄/H₂)plays a crucial role. It is well-known that there always exists a critical methane concentration (≤0.6%) only below which a good quality diamond film can be obtained. In this study, however, the phenomena of diamond synthesis resulting from high carbon concentration conditions were observed. The molten metals, e.g., Ag, Cu, were used as the deposition substrates on which crystalline diamonds can be achieved from a methane content of CH₄/H₂≥6% or even from solid carbon sources. These results suggest that there may exist a low methane content boundary layer (<0.6%) in the proximity of molten metal surface on which suitable species, CH, CH⁺, H_α and H_β are composed for the diamond nucleation and growth similar to the condition as in the conventional low methane contents. The molten metal inclines to dissolve other forms of carbonaceous materials other than diamond, and thus keeps a much higher steady supply of carbon atoms that enhances the quality as well as the growth rate of the forming diamonds. Received: 23 June 2001 / Accepted: 23 July 2001     

A new precipitate phase in Al-4wt. % Cu thin-film interconnects

We report here the identification of a new precipitate phase in thin-film Al-4wt.%Cu metallization used for interconnects on integrated circuits. The phase is based on a trigonal distortion of a face centered cubic lattice. Computer simulation of electron diffraction intensities suggests that the basis structure is isomorphous with Al₂Ca but with a large and ordered population of vacancies on Cu sites. The reason for the formation of the new phase and its implications for electromigration reliability are discussed.     

Microstructure and thermal behavior of Sn-Zn-Ag solders

The microstructure and thermal behavior of the Sn-Zn-Ag solder were investigated for 8.73–9% Zn and 0–3.0% Ag. The scanning electron microscopy (SEM) analysis shows the Ag-Zn compound when the solder contains 0.1% Ag. X-ray diffraction (XRD) analysis results indicate that Ag₅Zn₈ and AgZn₃ become prominent when the Ag content is 0.3% and above. Meanwhile, the Zn-rich phase is refined, and the Zn orientations gradually diminish upon increase in Ag content. The morphology of the Ag-Zn compound varies from nodular to dendrite structure when the Ag content increases. The growth of the Ag-Zn compounds is accompanied by the diminishing of the eutectic structure of the Sn-9Zn solder. Differential scanning calorimetry (DSC) investigation reveals that the solidus temperature of these solders exists at around 198°C. A single, sharp exothermic peak was found for the solders with Ag content less than 0.5%. Liquidus temperatures were identified with the DSC analysis to vary from 206°C to 215°C when the Ag content ranges from 1.0% to 3.0%