Radiation-induced reactions of ring-substituted polystyrenes analyzed by radiolysis of low molecular-weight model compounds

Radiation-induced reactions of polystyrene derivatives have been studied by the radiolysis of ring-substituted isopropylbenzene derivatives, i. e., 4-amino. 4-hydroxy, 4-methoxy, 4-methyl, 4-chloromethyl, 4-chloro, and 4-acetyl derivatives. Low-temperature ESR analyses measured at 77 K indicate that. In general, the a-position is the most sensitive site to radiation and that thus a-radicals are produced through a-hydrogen removal. However, among these derivatives, the amino, acetyl, chloromethyl, and. chloro derivatives undergo different reactions from the other derivatives. A phCO? CH₃ cleavage from the- acetyl derivative and N? H cleavage from the amino derivative occur, and chlorine removal takes place from the chloro-methyl and chloro derivatives. Final products detected by gas chromatography-mass spectrometry indicate not only that radiation-induced free radical recombination occurs. but also that if chlorine is produced by radiation, hydrogen abstraction by radiation-induced chlorine takes place prior to the free radical recombination. The susceptibility of each derivative to hydrogen abstraction by radiation-induced active chlorine increases, as the electron-donation of ring-substituents is increased. Based on the clarified reaction mechanism, the design of polystyrene derivatives as resist materials is discussed and two new types of resist systems are described. One is a new chloromethylstyrene based blend resist, which is formulated from poly(4-meth-oxystyrene) and poly(4-chloromethylstyrene). The other is a new non-swelling alkaline developable negative resist, which is formulated from poly(4-hydroxystyrene) and a chlorine-releasing compound.     

Acute renal failure in renal allograft recipients and patients with native kidneys

Techniques for the separation/concentration of micro-organisms from background food matrices can be applied to increase the speed of analysis and ease of isolation and detection of target micro-organisms. One recent example of such a technique is the immunomagnetic separation (IMS) procedure that has been used for the separation of specific micro-organisms from foods. This paper describes the use of a novel biosorbent consisting of a Salmonella-specific bacteriophage (phage) immobilized to a solid phase that was used for the separation and concentration of Salmonella from food materials. This work has shown that a Salmonella-specific phage-based biosorbent could remove Salmonella from culture fluid and separate Salmonella from suspensions of other Enterobacteriaceae. The ease of production of phage, high affinity of phage-cell interaction and the ability of phage to infect host cells in heterogeneous environments indicates the potential of such a biosorbent as the basis for a reliable separation system in food microbiological analysis.     

Effect of impurity hydrogen on the deformation and fracture in an Al-5 mass Pct Mg alloy

Air-melted and argon-melted Al-5 mass pct Mg alloy specimens containing impurity hydrogen of 0.27 and 0.04 mass ppm, respectively, were tensile-tested at ambient temperature. The ductility and fracture processes were compared in the two specimens, and hydrogen evolution behavior during the test was also compared using a special testing machine equipped with a mass spectrometer and ultra high vacuum chamber. The air-melted specimen, containing a higher amount of hydrogen, had less reduction in area (RA) and a higher amount of evolved hydrogen gas on fracture. This implied that the impurity hydrogen was in the transgranular voids, which appeared as dimples on the fracture surface. Fracture process analysis involving fractography, load-displacement curve analysis, and optical microscopy on a cross section of the deformed test piece demonstrated that the impurity hydrogen reduces nonuniform elongation by accelerating the nucleation of transgranular voids produced under triaxial tensile stress after necking. Hydrogen evolution was also detected corresponding to each load drop in the serrated flow of the air-melted specimen, supporting the idea that hydrogen atoms are transported with moving dislocations.     

Not Oligomers but Amyloids are Cytotoxic in the Membrane‐Mediated Amyloidogenesis of Amyloid‐β Peptides

The formation of neurotoxic aggregates by amyloid‐β peptide (Aβ) is considered to be a key step in the onset of Alzheimer's disease. It is widely accepted that oligomers are more neurotoxic than amyloid fibrils in the aqueous‐phase aggregation of Aβ. Membrane‐mediated amyloidogenesis is also relevant to the pathology, although the relationship between the aggregate size and cytotoxicity has remained elusive. Here, aggregation processes of Aβ on living cells and cytotoxic events were monitored by fluorescence techniques. Aβ formed amyloids after forming oligomers composed of ≈10 Aβ molecules. The formation of amyloids was necessary to activate apoptotic caspase‐3 and reduce the ability of the cell to proliferate; this indicated that amyloid formation is a key event in Aβ‐induced cytotoxicity.     

类金刚石纤维砂轮的开发及其磨削特性

为了获得高精度加工表面，最近磨具市场上有一种Al2O3纤维砂轮问世^[1]。该砂轮克服了磨粒砂轮中磨粒易于脱落的缺点，但其硬度仍受到一定限制。近十年来，由于类金刚石薄膜具有接近金刚石的硬度、高耐磨性和很低的摩擦系数等优良的机械、物理、化学和光电特性，因而被广泛地应用于精密零部件和涂附刃具的制造^[2]。如果能将类金刚石薄膜形成类金刚石纤维，然后将其代替Al2O3纤维作为磨料，就可以满足纤维砂轮的硬度要求。因此，1999年以来，日本山口胜美教授和中国魏源迁教授成功地将类金刚石纤维植入基体并与树脂结合剂结合，开发了一种类金刚石纤维砂轮^[3-5]。该砂轮中的类金刚石纤维按同一方向排列且与砂轮磨削面相垂直，纤维的端部可用作为切削刃。为了考察这种新型砂轮的磨削特性，本文作者对难加工材料如模具钢SKD11及硬脆材料如硅片、光学玻璃、石英和大理石进行了大量的磨削试验。试验结果表明能获得纳米级加工表面，例如被磨硅片和模具钢的表面粗糙度分别为Ra2nm(Ryl5nm)和Ra2nm(Ry23nm)。     

Performance evaluation of candidate appointment schedules using clearing functions

This study is concerned with the problem of reducing the waiting times of outpatients. Both scheduled patients and walk-ins are included among the outpatients to reflect the typical medical environment in Japan. The consultation time of a hospital is divided into several blocks, and each scheduled patient is given the start time of a block as his or her scheduled time of the consultation as an appointment. It is assumed that all scheduled patients arrive at the hospital at their scheduled times, while walk-ins arrive randomly. A set of candidate appointment schedules is given, and the process of selecting promising schedules in terms of average waiting times is the focus of the work. To support the selection process without conducting a conventional simulation, the notion of a clearing function is adopted to evaluate each candidate schedule. The clearing function of a system gives the expected output or throughput of the system under varying levels of workload of the system. Although it is necessary to conduct exploratory experiments in advance to obtain the clearing function, the expected waiting time can be estimated by simple calculations with the aid of the clearing function. The average waiting times of four schedules in two scenarios are calculated and compared with those obtained from conventional simulations. It is revealed that the proposed procedure based on the clearing function gives acceptable estimated average values.     

Hydrogen production by oxidative methanol reforming on Pd/ZnO: Catalyst preparation and supporting materials

Pd and Pd–Zn alloy were supported on various supporting materials using impregnation, co-precipitation and microemulsion methods, and their catalytic performances in oxidative methanol reforming (OMR) were investigated. Pd/ZnO exhibited much higher selectivity than either Pd/Al₂O₃ or Pd/ZrO₂ in the OMR for hydrogen production. This was attributed to the presence of Pd–Zn alloy on the ZnO support. Elemental Pd on Al₂O₃ or ZrO₂ promotes methanol decomposition reaction and increases CO formation. Using a microemulsion method, a highly selective Pd/ZnO can be obtained with much lower Pd loading than that in samples prepared by co-precipitation. Modification of Al₂O₃ with ZnO produced a ZnAl₂O₄ phase, which was found to be a good support for the Pd/ZnO catalyst. Highly active and selective Pd/ZnO/ZnAl₂O₄ catalysts for the OMR reaction, containing much lower Pd loadings have been developed by impregnation of the supports with an aqueous solution of Pd(NO₃)₂ + Zn(NO₃)₂.     

Two-stage drawing of poly(ethylene 2,6-naphthalate)

Initially amorphous and semicrystalline films of poly(ethylene 2,6-naphthalate) with different molecular weights were drawn by two-stage drawing, that is, coextrusion at low temperatures (25–160°C) followed by tensile drawing at high temperatures (200–245°C). Both films could be drawn up to a draw ratio of 8–10 by this method under controlled conditions. The tensile modulus and strength of drawn samples were greatly affected by the draw temperature for the first stage, predrawn morphology, and molecular weight. The remarkable effects of these variables on the tensile properties are closely related to the difference in the resultant amorphous chain orientation of the samples, reflecting the disentanglements and chain slippage during drawing, and the dissipation of chain orientation after processing.     

环氧化天然橡胶/二胺硫化胶在轮胎胎面中的应用

含二胺的环氧化天然橡胶（ＥＮＲ）与炭黑的硫化胶，其橡胶区内的ｔｇδ较低，业已证实，其潘恩效应也降低。人们推测，基于与二胺的交联和ＥＮＲ与炭黑之间强烈的相互作用；才使得这种硫化胶的ｔｇδ值较低。考察了不同二胺对轮胎胎胶料性能的影响，发现伯胺和脂肪胺改善胎面滚动阻力的效果优于叔胺和芳香胺。