纳米钨合金材料的研究与应用

采用纳米粉末制备的纳米钨合金块体材料具有非常优越的潜在物理力学性能。用作高性能结构件和高性能电子、微电子等功能材料等方面都将具有很大的潜在优势,可以更好地满足高性能新型材料的要求。本文综述了近几年国内外纳米难溶钨合金材料的研究状况,详细地介绍了数种纳米钨合金粉末制备和制备技术和纳米钨合金材料制备中所取得的成绩,分析了纳米钨合金在粉末制备和烧结中存在的问题。针对纳米粉末烧结时的晶粒长大问题,介绍了可能的几种纳米块体材料的烧结技术和今后纳米难熔钨合金材料的研究发展方向,并指出了今后该种新型材料的的应用发展前景。     

纳米钨合金材料的研究与应用

采用纳米粉末制备的纳米钨合金块体材料具有非常优越的潜在物理力学性能,用作高性能结构件和高性能电子、微电子等功能材料等方面都将具有很大的潜在优势,可以更好地满足高性能新型材料的要求.本文综述了近几年国内外纳米难熔钨合金材料的研究状况,详细地介绍了数种纳米钨合金粉末制备的制备技术和在纳米钨合金材料制备中所取得的成绩,分析了纳米钨合金在粉末制备和烧结中存在的问题.针对纳米粉末烧结时的晶粒长大问题,介绍了可能的几种纳米块体材料的烧结技术和今后纳米难熔钨合金材料的研究发展方向,并指出了今后该种新型材料的应用发展前景.     

钨的冶金及其加工技术

简要综述了钨的冶金和加工技术。除了用于制备高纯金属以及单晶等场合之外,钨及其合金的制备仍以粉末冶金方法为主,但近些年来在纳米钨粉的制备、掺杂钨合金的研究、钨合金的注射成形和复合材料的制备方面有很快地发展。     

纳米晶难熔高比重钨合金的研究现状及应用前景

综述了近几年来纳米晶难熔钨合金的研究状况,分析了纳米晶钨合金在粉末制备和烧结过程中存在的问题,指出了该种新型材料的应用前景.     

美国开发新型穿甲弹钨合金有望取代贫铀合金

正据中国国防科技信息网报道,美国开发出有望取代穿甲弹贫铀合金的新型钨铬铁合金。美国麻省理工大学(MIT)的研究人员开发出一种新型钨铬铁粉末冶金合金W-7Cr-9Fe,可以取代穿甲弹中的贫铀合金。测试结果表明,W-7Cr-9Fe合金纳米压痕硬度高达21吉帕,约是纳米晶体铁基合金或粗晶钨的2倍,远高于目前的商用钨合金。     

纳米晶钨合金粉末常压烧结的致密化和晶粒长大

高比重合金由于具有密度和强度高、延性好等一系列优异的性能,在军工上被用作动能穿甲弹材料.纳米材料被认为是21世纪应用前景最为广阔的新型材料.采用纳米粉末可望大大细化钨合金晶粒,显著提高合金的强度、延性和硬度等力学性能,因而是制备新型高强韧、高比重钨合金的一个很重要的研究方向.作者采用机械合金化(MA)工艺制备了纳米晶钨合金复合粉末,研究了纳米晶钨合金粉末在常压氢气气氛中的烧结致密化和在烧结过程中的钨晶粒长大行为.研究结果表明,MA纳米晶粉末促进了致密化,使致密化温度降低约100～200℃.在一般固相烧结温度时可以得到晶粒尺寸为3～5μm的细晶高强度合金.同时,指出了在液相烧结时存在的问题,即钨晶粒加速重排、产生晶粒聚集与合并,迅速发生钨晶粒长大,在较短时间内液相烧结时,钨晶粒尺寸又长大到接近传统高比重合金水平.     

难熔钨合金与硬质合金的研究新动向

难熔钨合金和硬质合金在工业中应用很广泛,本文主要介绍近年来在超细/纳米钨合金和硬质合金粉末和合金制备技术方面的研究新进展,重点阐述了注射成形、喷雾转换、溶胶-喷雾干燥-热还原以及合金的晶粒控制等技术,并指出了今后钨合金和硬质合金的研究发展方向。     

大直径钨镧合金锻造棒材性能研究

采用纳米掺杂方法制备了大直径钨镧合金棒坯,通过与纯钨对比,研究了不同氧化镧质量分数的钨镧合金棒坯烧结性能以及含质量分数1.0%纳米氧化镧粉掺杂的钨镧合金锻造棒材的室温性能和高温再结晶性能。结果表明:采用质量分数1.0%、1.5%和2.0%三种含量的纳米氧化镧粉掺杂烧结后,合金掺杂分布和晶粒组织均匀,随着氧化镧含量的增高,棒坯密度逐渐降低、晶粒数逐渐越多;1.0%氧化镧粉掺杂钨镧合金棒坯经过78.7%锻造变形量后,较纯钨棒材硬度值更高,金相组织更细、更均匀,车加工后车削较长,表面光洁度较高,再结晶温度比纯钨高约150℃。     

美国开发新型穿甲弹钨合金有望取代贫铀合金

<正>美国麻省理工大学(MIT)的研究人员开发出一种新型钨铬铁粉末冶金合金W-7Cr一9Fe,可以取代穿甲弹中的贫铀合金。测试结果表明,W-7Cr-9Fe合金纳米压痕硬度高达21吉帕,约是纳米晶体铁基合金或粗晶钨的2倍,远高于目前的商用钨合金。这种合金的制备过程是:首先制备纳米晶体粉末,再制成所需形状。其中,粉末是采用高能球磨粉末冶金工艺制备的,包括反复的剪切促使合金粉末混合,同时伴随热激活恢复过程,使合金恢复到平衡状态。     

纳米晶高密度钨合金的研究进展

介绍了近几年来纳米晶钨基高密度合金的研究状况,讨论了粉末制备的机械合金化法、喷雾干燥法和反应喷射工艺法,同时详细讨论了粉末的注射成形以及包括固相烧结、二步烧结在内的烧结工艺.最后,从这些方面分析了影响纳米晶钨合金性能的具体因素,以及对高密度钨合金今后的发展方向提出了建议.     

Three-dimensional model of the fibrin(ogen) molecule and fibrin fibril

The paper deals with the three-dimensional model of fibrin(ogen) molecule and fibrin fibril, based on the electron microscopy data on fibrin(ogen) molecule and on fibrin fibril structure, data on symmetry of fibrinogen primary structure, on domain structure of molecule, on location of sites of polymerization and on the data on polymerization mechanism of fibrin.     

Proliferation and differentiation of human trabecular osteoblastic cells on hydroxyapatite

In order to evaluate whether human osteoblastic cells differentiate normally on hydroxyapatite, we have compared the adhesion, proliferation, and differentiation of human trabecular (HT) osteoblastic cells on synthetic-dense hydroxyapatite and on standard plastic culture. We show here that initial HT cell attachment was 4-fold lower on hydroxyapatite than on plastic after 4 h of culture, and that normal cell attachment on hydroxyapatite was restored after 18 h of culture. HT cell proliferation was similar on the two substrates at 2-8 days of culture, but was lower on hydroxyapatite compared to plastic after 15 and 28 days of culture, as evaluated by DNA synthesis or cell number. HT cells cultured on both substrates produced an abundant extracellular matrix which immunostained for Type I collagen. The levels of carboxyterminal propeptide of Type I procollagen (P1CP) in the medium were lower in HT cell cultures on hydroxyapatite than on plastic. In addition, (3H)-proline incorporation into matrix proteins and the mean thickness of matrix layers were 52% and 26% lower, respectively, on hydroxyapatite compared to plastic after 4 weeks of culture, indicating that the total collagenous matrix synthesized by HT cells was lower on hydroxyapatite. However, (3H)-proline and calcium uptake expressed per cell was higher on hydroxyapatite than on plastic. The results show that human osteoblastic cells attach, proliferate, and differentiate on dense hydroxyapatite with a sequence similar to that of plastic. However, the growth of human osteoblastic cells is lower on hydroxyapatite in long-term culture, which results in a reduced amount of extracellular matrix, although matrix production per cell may be increased.     

Expression of HLA-ABC and -DR locus antigens on human kidney, endothelial, tubular and glomerular cells

The distribution of the major histocompatibility complex antigens on the various cellular structures of the human kidney was analysed by using a modified Staphylococcus aureus Cowan 1 method. Conventional alloantisera and heterologous antisera raised against isolated molecules were used for the HLA-ABC antigens, whereas the HLA-DR (Ia) antigens were detected with heterologous antisera only. The HLA-ABC antigens were expressed on all types of kidney passenger leucocytes, on vascular endothelial cells, and on kidney tubular cells, but not substantially on the glomerular podocytes. The DR antigens were strongly expressed on (a fraction of) the passenger lymphocytes and on the kidney vascular endothelial cells, weakly on the passenger monocytes, but not measurably on the urine-producing apparatus of the kidney--that is, on the glomerular and tubular cells.     

Oxidative stress is found in amyloid deposits in systemic amyloidosis

PURPOSE: To investigate a method of diagnosing angiomyolipoma that contains minimal fat. MATERIALS AND METHODS: In six cases of angiomyolipoma with minimal fat, the attenuation on contrast material-enhanced and unenhanced computed tomographic (CT) images, the echogenicity on sonograms, the signal intensity on T2-weighted magnetic resonance (MR) images, and the gross configuration of the lesion were retrospectively analyzed. In 100 cases of renal cell carcinoma, the same parameters were analyzed, and results were compared with those of angiomyolipoma. RESULTS: When compared with the surrounding renal parenchyma, all six angiomyolipomas showed homogeneously high attenuation on unenhanced CT images, homogeneous enhancement on contrast-enhanced CT images, and homogeneous isoechogenicity on sonograms. Of the five angiomyolipomas examined with MR imaging, four were hypointense and one was isointense on T2-weighted images. All six angiomyolipomas protruded from the renal margin. None of the 100 renal cell carcinomas showed homogeneously high attenuation on unenhanced CT images, homogeneous enhancement on contrast-enhanced CT images, or homogeneous isoechogenicity on sonograms. CONCLUSION: In the kidney, homogeneously high attenuation on unenhanced CT images, homogeneous enhancement on contrast-enhanced CT images, and homogeneous isoechogenicity on sonograms are suggestive of angiomyolipoma that contains abundant muscle and minimal fat.     

炼钢厂生产管理信息系统的设计与实现

炼钢厂生产管理信息系统包括制造命令管理子系统、生产辅助管理子系统和工艺质量管理子系统.本文从软件工程理论出发,围绕数据库应用系统的开发,结合制造命令管理子系统的具体实现,主要介绍了生产管理系统在Oracle Developer中的设计思想及开发方法.     

利用自身优势谋求最大的发展空间

面对激烈竞争的市场,阐述了企业图生存发展必须发挥自身优势,走科技创新之路,不断进行技术改造与更新,实施产品的规模化、系统化和配套化生产,运用正确的经营战略开拓市场,靠质量和品种占领市场,靠技术进步扩大市场,靠严格的管理赢得市场,靠售后服务巩固市场,从而使企业不断发展壮大,永远立于不败之地。     

Delaying colostrum intake by one day has important effects on metabolic traits and on gastrointestinal and metabolic hormones in neonatal calves

Effects on metabolic and endocrine traits of feeding colostrum on d 1 and 2, then mature milk up to d 7, or glucose or water on d 1, colostrum on d 2 and 3 and then mature milk up to d 7 were studied in calves. Calves fed colostrum within the first 24 h after birth had significantly higher rectal temperatures, heart rates and respiratory frequencies than calves provided only water or glucose. Significantly elevated plasma nonesterified fatty acid and bilirubin concentrations on d 1 and 2 of life in calves fed only water on d 1 compared with calves of the other groups mirrored reduced energy intake. Fecal consistency was significantly higher during wk 1 of life, and gastrin and glucose-dependent insulinotropic polypeptide increased only on d 1 and/or 2 of life in calves already fed colostrum on d 1, expressing improved functioning of the gastrointestinal tract. Significantly higher plasma globulin levels up to d 7 in calves fed colostrum on d 1 than in those starting colostrum intake only on d 2 demonstrated significantly enhanced efficiency of gamma-globulin absorption. Furthermore, significantly higher circulating glucose, albumin, insulin, insulin-like growth factor-I concentrations and significantly lower urea levels in calves fed colostrum on d 1 compared with those fed colostrum starting on d 2 of life indicated stimulation of anabolic processes. In conclusion, colostrum intake by calves within the first 24 h of life is needed not only for an adequate immune status, but also to produce the additional important and favorable effects on metabolic and endocrine traits and on vitality.     

Effects of ionizing radiation on cartilage: emphasis on effects on the extracellular matrix

In this report, we review data dealing with radiation effects on cartilage. More specifically, we emphasize on alterations caused in the extra-cellular cartilage matrix. Although radiation studies predominantly describe the effect on the structure of DNA and on the mitotic activity of cells, alterations caused by the effect on the non-mitotic activity can also be important. Cartilage, having an extracellular matrix composed of 2 major components, aggrecan and collagen, provides a good model to study this kind of radiation effects. The following topics concerning literature data are summarized: effects on the amount of matrix synthesized, effects on the activity of certain enzymes and effects on the structure and morphology of the matrix. Some new findings concerning the radiation effect on the size distribution of aggrecan-aggregate populations, de novo synthesized by chondrocyte cultures, either derived from calcifying or from non-calcifying cartilage, are given.     

Office laboratory procedures, office economics, patient and parent education, and urinary tract infection

This review provides an update on four important areas in office pediatrics: office laboratory procedures, office economics, patient and parent education, and urinary tract infection. Ball reviews new information about physician office laboratories, with updates on the Clinical Laboratory Improvement Amendments, streptococcal pharyngitis, urinalyses, office stool examination, and information on Helicobacter pylori serology. Shapiro reports on office economics, highlighting new office technologies, physician operated networks, managed care, recent legislation, and the "cost versus quality" debate. Duncan provides a very thought provoking essay on parent and patient education, focusing on improving parenting skills. Wahl reviews the recent literature on urinary tract infections, with emphasis on host-bacteria interactions, diagnostic evaluations, pyelonephritis, renal cortical scarring, and long term follow-up of vesicoureteral reflux. We hope we have provided pediatricians with useful and practical information for their office practices.     

Effects of parturition and lactation on blood and milk cell concentrations, corticosteroids, and neutrophil phagocytosis in the cow

Blood differential leukocytes, erythrocytes, milk somatic cells, and neutrophil phagocytosis in 14 Holstein-Friesian cows were measured at 2-day intervals for 2 weeks before parturition, on the day of parturition, on postpartum days 1,2,5,10,15, and 30, and at monthly intervals throughout lactation. Circulating corticosteroids were measured in 6 cows on days -6, -4, -2, on the day of parturition, and on days +1, +2, +5, +10, +15, +30, and +60. Circulating neutrophils on day -2 on the day of parturition, on days 2, 10, and 15 averaged 3,363, 5,889, 3,085, 4,116, and 3,558/mm, respectively. The increase in neutrophils at parturition was accompanined by an increase in corticosteroids (2.7, 9.0, 11.1, 6.1, and 5.4 ng/ml of blood plasma on days -4 and -2, on the day of parturition, and on days +1 and +2, respectively). The phagocytic ability of circulating neutrophils was determined by incubating yeast cells with whole blood (30 minutes, 37 C) and microscopically counting yeast cells per neutrophil. Mean yeast cells per neutrophil decreased (P less than 0.01) during the 2nd week after parturition (7.4, 6.5, 6.6, and 7.2 on days +2, +10, +15, and +30, respectively). But this decrease was compensated for by an increase in circulating neutrophils during the same period.