超声弯曲工具头的动态特性仿真与实验研究

牙种植超声工具利用弯曲工具头能够制备异型种植窝孔,为了研究工具头弯曲角度对位移响应的影响,利用有限元软件Abaqus对弯曲工具头进行动态仿真,得到不同弯曲角度工具头的位移响应,并通过实验验证有限元分析结果。验证实验表明,有限元分析结果与实验结果基本保持一致,为具有弯曲工具头的牙种植超声工具的设计提供了方法和依据。     

褐藻胶裂解酶在制备海洋寡糖中的应用

褐藻胶裂解酶能裂解褐藻胶制备寡糖,是一种重要的工具酶。本文从酶的分子结构、作用机理等方面介绍了褐藻胶裂解酶的酶学性质,以及该酶在制备海洋寡糖中的应用研究进展。     

褐藻胶裂解酶在制备海洋寡糖中的应用

褐藻胶裂解酶能裂解褐藻胶制备寡糖,是一种重要的工具酶。本文从酶的分子结构、作用机理等方面介绍了褐藻胶裂解酶的酶学性质,以及该酶在制备海洋寡糖中的应用研究进展。      

金刚石工具胎体材料机械性能的概述

金刚石具有高硬度、高强度、高耐磨性等一系列优异特性,被广泛地用来制备金刚石工具。金刚石工具工作寿命和性能的一个重要指标就是金刚石在金刚石工具中的把持强度,其在实际工作中的使用效果在很大程度上取决于胎体材料的性能。文章从固结温度、掺杂、金刚石表面涂层等几个方面对胎体材料机械性能的影响进行了概述,其中包括硬度,屈服强度,弯曲强度和冲击强度。最后指出了金刚石工具胎体材料性能研究存在的问题,并提出了解决对策,为胎体材料的设计提供了理论指导。     

食品采样、制备、样品管理研究中遇到的问题及对策

随着食品安全意识的提升,人们对食品检验提出了更高的要求,其通常包括食品采样、食品制备、样品管理等关键环节.食品采样要保证所采样品具有代表性、时效性、完整性;食品制备要保证制备工具清洁、干燥,不与所制样品发生任何化学反应;样品管理要保证样品存放环境符合相应标准,不同样品按不同储存环境进行存放,其中任何一个环节出现问题,都...     

超硬材料工具用金属预合金粉末的国内发展现状及趋势

文章概要总结了超硬材料工具用金属预合金粉末的种类、制备方法、性能特点、应用范围、存在不足及发展趋势。金属预合金粉末的推广应用是行业的发展趋势,今后将向着多元化、细颗粒、高活性、低松比、高弹性模量的方向发展。     

酶法制备米糠抗氧化生物活性肽的最佳条件的研究

以木瓜蛋白酶为工具酶,在水相体系里水解米糠蛋白,制备具有抗氧化能力的生物活性肽,以其对OH.自由基的清除率为指标,利用响应面试验方法,探讨了温度、时间、加酶量（基于米糠质量）、pH值以及底物浓度对抗氧化生物活性肽制备的影响,所得的最佳反应条件为：温度56℃,时间6.3h,加酶量1.1%,pH值8.7,底物浓度4.83%。研究结果表明：在此条件下制备的米糠生物活性肽对羟自由基具有良好的清除能力。     

制粒剂对无压烧结金刚石工具胎体的性能的影响

为了研究制粒工艺对无压烧结金刚石工具胎体的性能的影响,实验将不同含量的制粒剂加入到合金粉末中通过无压烧结制备金刚石工具胎体试样块,研究了不同制粒剂含量对胎体力学性能的影响。结果表明：在烧结温度为875℃、保温时间为60min的无压烧结工艺下,添加不同含量的制粒剂对胎体的烧结力学性能有着重要的影响。随着制粒剂含量增加,胎体的力学性能都是逐渐下降的。     

金刚石工具用Ni-Co合金粉末的制备及表征

在金刚石工具领域,纯钴基以及钴基金刚石工具具有优良的使用性能,但钴价格很高,使纯钴基以及钴基金刚石工具的使用受到了限制,所以代钴研究具有重大的实际意义。镍和钴同属于过渡族元素,两者物理和化学性质非常接近,故镍代钴有一定的可行性。采用草酸盐共沉淀法得到前驱体,然后将前驱体煅烧还原的工艺制得N i-Co预合金粉末;对前驱体进行了X射线、热(差热和热重)分析,结果表明,通过共沉淀法得到的前驱体是固溶体;对预合金粉末进行了性能表征,所制得的N i-Co预合金粉末氧含量低,形貌近似球形,粒度均匀;通过共沉淀反应前的成分设计,可制备出成分含量连续变化的预合金粉末;通过改变制备工艺参数,可制取不同粒径的粉末。本实验的粉末成分设计是:70N i-30Co(w t%)。     

激光焊接金刚石工具过渡层预合金粉末的试验研究

目前可以用于制备激光焊接金刚石工具过渡层粉末的方法主要有机械混合法、雾化法和化学共沉淀法。化学共沉淀法生产的粉末成分均匀,实现了粉末的预合金化,并且设备简单,生产成本低。此次试验采用草酸盐化学共沉淀法,成功制备了3种不同成分的激光焊接金刚石工具过渡层预合金粉末。焊接强度测试表明,3种粉末的焊接强度均满足欧盟EN13236安全标准,其中2#粉末的焊缝强度最高。X射线物相分析结果表明,3种粉末的主相都是Co3Fe7和CoFe。此外,固定Fe与Co的质量比,加入2wt.%的铜可以有效提高预合金粉末过渡层的焊接强度和稳定性。这是因为,Cu原子完全溶入到Co3Fe7或CoFe晶胞中并形成固溶体,产生了固溶强化。     

39—THE FLOW OF LIQUID FROM A JET THROUGH A COMPRESSIBLE POROUS LAYER. PART III: THE CHARACTERISTICS OF LIQUID FLOW THROUGH A COMPRESSIBLE LAYER OF LOOSE WOOL

The effects on the conditions of flow of the surface and configurational properties of the fibres in a compressible porous layer are discussed. The characteristics of a layer of wool are evaluated, and its compressibility is determined. It is shown that, when a liquid of initial uniform pressure flows through a compressible porous medium, the pressure gradient within the medium increases with the distance of flow. The resulting pressure drop is found to depend on a function of the ratio of the downstream to the upstream porosity of the compressible medium. Experimental results are reported for permeable flow through various layers of loose wool; these indicate that, when the flow is disturbed turbulent, the pressure drop through the layers is proportional to the square of the filter velocity. This result is not readily apparent from the graphs of pressure drop against filter velocity because of the compressibility of the fibres.     

Water–disaccharides interactions in saturated solution and the crystallisation conditions

This paper reports solubility data and measurements of viscosity of the saturated aqueous solutions of sucrose, maltitol, and trehalose. Likewise, the metastable zone width and velocity of nucleation of the three disaccharides are compared. The narrowest metastable zone is observed for maltitol and the largest for trehalose. Such behaviour is due to a higher affinity of trehalose for water. Moreover, the crystallisation of anhydrous disaccharides in aqueous solution necessitates that hydration water be removed and evacuated from crystal integration surface to the bulk of solution to allow the growth of crystals. This step of disassociation and diffusion of hydration water proves to be the controlling step of the crystallisation process. Structural features at the origin of the differences between the three sugars are studied by FTIR spectroscopy. Modifications of frequencies and intensities of the vibrations around the glycosidic bond are interpreted in terms of conformational flexibility. Arguments like H-bond strength or conformational flexibility of the two monomers around the glycosidic oxygen were evoked as possible explanations of the behaviour of disaccharides. Likewise stability of hydration of the disaccharides is derived from the interpretation of FTIR spectra. These structural features help in interpreting the differences in crystallisation conditions and to hypothesize about the cryoprotective ability of the studied molecules.     

基于下肢运动特征的纬编无缝瑜伽裤结构设计

为提升瑜伽裤的功能性和舒适性,研究了纬编无缝瑜伽裤结构设计的方法。首先分析人体下肢围度特征及瑜伽运动中体表皮肤形变,选用氨纶和锦纶编织7种不同组织结构的面料,测量面料的拉伸性能和压力值。最后从围度尺寸和纵向结构进行纬编无缝瑜伽裤分区结构设计,并进行应用举例。结果表明,服装围度尺寸的差异通过调整不同织物的编织针数比例实现;通过织物横向拉伸的压力值,调整服装收缩量;服装纵向设计中,织物拉伸性能与皮肤形变数值的大小呈对应关系;无缝瑜伽裤的结构设计需综合考虑下肢运动特征、织物性能和无缝成形原理。该技术可以应用于其他类型的运动服装设计中,有助于提高服装结构设计的科学性和生产效率。     

21—THE ACETYLATION OF COTTON

An account is given of a study of the effect of the amount of activating agent, the temperature, the catalyst, and the diluents used in the acetylation of cotton with perchloric acid as catalyst. Sulphuric acid was compared with perchloric acid as a catalyst. The effects of traces of water, the amount of acetyl chloride, and the rate of acetylation were studied in the acetylation of cotton with acetyl chloride and pyridine. The conditions in all cases were such that the acetylated cotton retained its fibrous form.     

工商交接备货烟叶等级质量分析

本文根据全国烟叶工商交接等级质量监督检查资料对商业备货烟叶等级质量问题进行了分析。结果表明,不同备货单位间等级质量有很大差异,而且商业企业备货的烟叶等级质量决定工商交接烟叶等级合格率的高低。等级质量问题分析表明,备货烟叶等级合格率不高的主要原因是存在混部位、混颜色、混等级等现象。在原等级中混低的比例远远高于混高的比例,调拨量大、价格较高的烟叶等级合格率较低,中部烟叶等级合格率显著低于上部和下部。本文对提高烟叶等级质量也提出了有关建议。     

Measure the Dissolved Oxygen Consumed by Red Wines in Aging Tanks

The techniques of accelerated wine aging imply the addition of wood pieces of oak to the wine and the use of small doses of oxygen (micro-oxygenation). The dosage of extremely small amounts needs the knowledge of the dissolved oxygen (DO) at every moment in order to assure its correct assimilation. This work presents the first results of a study about the evolution of the dissolved oxygen content in red wines during alternative accelerated aging. Samples were treated in stainless steel vessels with wood pieces and low micro-oxygenation levels. French oak was applied with different toasting levels: light, medium, and high. Quality parameters of the wine were monitored. The knowledge of wine DO levels allowed developing a controlled micro-dosage in the different phases during the accelerated aging. The wine was able to use the whole amount of oxygen provided throughout the process.     

Composition and properties of seeds and pods of the tree legume Prosopis juliflora (DC)

Seeds and whole pods of Prosopis juliflora were analysed for proximate composition, fatty acids, minerals and soluble sugars. Crude protein constituted 35 % and 10 % of the seeds and whole pods, respectively. Nitrogen free extracts (NFE) comprised approximately 45 % of the seeds and whole pods. In the case of the pods, sucrose represented approximately 75 % of the soluble sugars. The lipid of both the seeds and whole pods contained a relatively large proportion of unsaturated fatty acids with linoleic acid as the predominant fatty acid. Levels of the macronutrients Ca, Mg, K and P were relatively low in comparison with cultivated legumes. Alkaline extraction of the seeds and whole pods showed that more than 70 % of the proteins were extractable. Maximum precipitation of the proteins was observed in the pH range 4.0-4.5. Amino acid analysis of the isolated proteins showed relatively high levels of lysine (312mg g^?l N for the seed and 438 mg g^?l N for the pod protein) and adequate levels of valine, leucine, tyrosine and phenylalanine. Methionine was the most limiting amino acid. The in vitro enzymic digestibility of the proteins of Prosopis seed was comparable to that of proteins of other legume seeds.     

Effects of environmental factors and agricultural techniques on antioxidantcontent of tomatoes

Antioxidants are believed to be important in the prevention of diseases such as cancer and cardiovascular disease. Lycopene is one of the main antioxidants to be found in fresh tomatoes and processed tomato products. The lycopene content also accounts for the redness of the fruit, which is one of the main qualities for which industry and consumers now look. Other carotenes (such as β‐carotene), vitamin C, vitamin E and various phenolic compounds are also thought to be health‐promoting factors with antioxidant properties. Since the antioxidant content of tomatoes may depend on genetic factors, the choice of variety cultivated may affect the results at harvest. To be able to control the antioxidant content of tomatoes at the field level when growing a given variety, it is necessary to know the effects of both environmental factors and the agricultural techniques used. Temperatures below 12 °C strongly inhibit lycopene biosynthesis and temperatures above 32 °C stop this process altogether. The effects of the temperature on the synthesis of other antioxidants have not yet been properly assessed. The effects of light have been studied more thoroughly, apart from those on vitamin E. The effects of water availability, mineral nutrients (nitrogen, phosphorus, potassium and calcium) and plant growth regulators have been studied, but results are sometimes contradictory and the data often incomplete. During the ripening period, lycopene content of tomatoes increases sharply from the pink stage onwards, but no sufficient attempts have been made so far to assess the changes in the other antioxidants present in the fruit. This paper reviews the present state of the art. Copyright © 2003 Society of Chemical Industry     

The interactions between oil droplets and gel matrix affect the lubrication properties of sheared emulsion-filled gels

In this work the lubrication behaviour of emulsions, gels, and emulsion-filled gels was studied in relation to their composition and structure. It was found that emulsions had much lower friction coefficients than their continuous phases. Emulsions with 40 wt% oil had the same friction coefficient as the pure oil. The lubrication properties of the gels, sheared by pressing them through a syringe, strongly depended on the molecular properties of the gelling agent and on the breakdown behaviour of the gel matrix. For each type of emulsion-filled gel, the lubrication behaviour was affected by the interactions between oil droplets and matrix. For gels containing oil droplets bound to the matrix, the friction coefficient gradually decreased with increasing oil concentration. For gels containing oil droplets non-bound to the matrix, the friction coefficient of the filled gels was lower than that of the same gel matrix without oil. However, no effect of the oil concentration on friction was observed. The different effects of the oil concentration on the lubrication behaviour of the various gels were explained by the relation between droplet–matrix interactions and the ‘apparent viscosity’ of the sheared gels. For gels with bound droplets, increasing the oil concentration resulted in an increase of the ‘apparent viscosity’ of the sheared gel. For gels with unbound droplets, the oil concentration did not affect the ‘apparent viscosity’. Confocal laser scanning microscopy (CLSM) observations of both emulsions and filled gels did not reveal coalescence of the oil droplets as a result of the shear treatment inherent to friction measurements.