螺旋齿轮与正齿轮的表面致密化

过去几十年,用于汽车的粉末冶金零件不断增长,对零件性能的要求也越来越高.汽车用的变速器齿轮的形状复杂,按照齿轮质量要求(DIN,ISO,AGMA等)几何精度很高,按齿面与齿根的耐久性要求力学性能也很高.对于制造复杂形状零件,粉末冶金法对控制成本很有效.通过增加对齿的选择性致密化,在增加很少费用下就能满足精度与力学性能要求.由压制、烧结、碾压致密化及最后热处理组成的工艺路线,可评估用粉末冶金制造的变速器齿轮的可行性.在研究中所用的螺旋齿轮与正齿轮,对致密化及所得到的齿轮的质量与齿根疲劳都进行了试验.     

High‐Affinity Carbohydrate Binding by Trimeric Benzoboroxoles Measured on Carbohydrate Arrays

Carbohydrates are involved in a wide range of biological processes of pharmaceutical relevance. The selective recognition of carbohydrates is therefore of great interest in biology and medicine. In this study we present the synthesis of fluorescent multimeric benzoboroxoles and the analysis of multivalent binding processes to immobilized carbohydrate arrays by fluorescence spectroscopy. We observed high binding affinities of trimeric benzoboroxoles by determination of K_Dsurf values for their interaction with α‐Gal on glass chips. The observed K_Dsurf values were in the mid‐nM range (49 and 104 nM ) and are comparable to the K_Dsurf values for binding of natural lectins, such as that of ConA to immobilized α‐Man (79 nM ). The array technology was found to be an excellent tool for studying the binding processes of multivalent lectin mimetics with respect to profiling and quantitation.     

Soft factors and their impact on time to market

Time to market is considered to be one of the most important quality attributes for an organization to retain its competitive edge. Soft factors are at least as important as technical issues in improving and controlling the time to market. Soft factors are used as a collective term for factors that are difficult to quantify exactly, i.e. non-technical aspects. Based on the identified importance of the soft factors, a method, incorporating the soft factors, has been developed to increase the predictability of time to market. The method consists of three main parts: model development, model usage and model maintenance. The proposed method is general, while the actual model is primarily useful for the organization for which data have been collected. The objective is two-fold: first to prevent a general method of incorporating soft factors into the prediction of the time to market, and secondly to identify a set of critical soft factors for the organization in which data have been collected. The model is based on data collection from 12 large software projects. Time to market, effort (manhours) and a grade for ten soft factors have been collected. The model is derived from a set of eight projects and it is evaluated using the remaining four projects. The method is shown to be superior to the prediction made without taking the soft factors into account. The need to maintain the model is stressed as the model will evolve with time through new experiences gained. The proposed method can be applied in practice to help software engineers and managers to plan and control time to market and soft factors in software projects.     

Motor development as the development of systems: Comments on the special section.

Two systems approaches to motor development represented in this special section are discussed. One of them is more focused on functional questions and stresses the tight coupling between motor development and perceptual development. It is here called perception-action approach. The second one is more concerned with morphological questions and the emergence of form. It is here referred to as the dynamic-systems approach. As a guide to continuing progress in this area, the importance of understanding the development of the brain is pointed out. Without such knowledge, little insight into the process of motor development is possible. The importance of longitudinal studies for a deeper understanding of motor development is also pointed out. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Regional localization of two genes for nonspecific X-linked mental retardation to Xp22.3-p22.2 (MRX49) and Xp11.3-p11.21 (MRX50)

Nine human ovarian cancer cell lines that express wild-type (wt) or mutated (mut) p53 were used to evaluate the cytotoxicity induced by cisplatin (DDP). The concentrations inhibiting the growth by 50% (IC50) were calculated for each cell line, and no differences were found between cells expressing wt p53 and mut p53. Using, for each cell line, the DDP IC50, we found that these concentrations were able to induce an increase in p53 levels in all four wt-p53-expressing cell lines and in one out of five mut-p53-expressing cell lines. WAF1 and GADD45 mRNAs were also increased by DDP treatment, independently of the presence of a wt p53. Bax levels were only marginally affected by DDP, and this was observed in both wt-p53- and mut-p53-expressing cells. DDP-induced apoptosis was evident 72 h after treatment, and the percentage of cells undergoing apoptosis was slightly higher for wt-p53-expressing cells. However, at doses near the IC50, the percentage of apoptotic cells was less than 20% in all the cell lines investigated. We conclude that the presence of wt p53 is not a determinant for the cytotoxicity induced by DDP in human ovarian cancer cell lines.     

Influence of the partial pressure of oxygen on the redox chemistry of multivalent elements in molten sodium tetraborate

Voltammetric determinations based on current measurements have been developed in order to allow anin situ evaluation of the redox ratios of multivalent elements in molten sodium tetraborate. The same technique has been used to study the influence of the partial pressure of oxygen in the gaseous atmosphere on the redox properties of sodium tetraborate melts. Experiments were carried out at 1273 K in solutions of chromium with oxidation states VI and III and of antimony with oxidation states V and III; the values ranged from 5×10^–5 atm to 1 atm. Log [Ox]/[Red] plotted against log shows linear relationships with slopes of 0.72 and 0.54 in the case of chromium and antimony solutions, respectively. These values lie close to the theoretical values of 0.75 and 0.50, respectively, which are deduced assuming conditions of equilibrium between oxygen and the solute. In agreement with these results, voltammetric and potentiometric determinations confirm Nernstian behaviour of the oxygen-oxide redox system.     

Realization of Wurtzite GaSb Using InAs Nanowire Templates

The crystal structure of a material has a large impact on the electronic and material properties such as band alignment, bandgap energy, and surface energies. Au‐seeded III–V nanowires are promising structures for exploring these effects, since for most III–V materials they readily grow in either wurtzite or zinc blende crystal structure. In III–Sb nanowires however, wurtzite crystal structure growth has proven difficult. Therefore, other methods must be developed to achieve wurtzite antimonides. For GaSb, theoretical predictions of the band structure diverge significantly, but the absence of wurtzite GaSb material has prevented any experimental verification of the properties. Having access to this material is a critical step toward clearing the uncertainty in the electronic properties, improving the theoretical band structure models and potentially opening doors toward application of this material. This work demonstrates the use of InAs wurtzite nanowires as templates for realizing GaSb wurtzite shell layers with varying thicknesses. The properties of the axial and radial heterointerfaces are studied at the atomic scale by means of aberration‐corrected scanning transmission electron microscopy, revealing their sharpness and structural quality. The transport characterizations point toward a positive offset in the valence bandedge of wurtzite compared to zinc blende.     

Multi robot collision avoidance in a shared workspace

This paper presents a decentralised human-aware navigation algorithm for shared human–robot work-spaces based on the velocity obstacles paradigm. By extending our previous work on collision avoidance, we are able to include and avoid static and dynamic obstacles, no matter whether they are induced by other robots and humans passing through. Using various cost maps and Monte Carlo sampling with different cost factors accounting for humans and robots, the approach allows human workers to use the same navigation space as robots. It does not rely on any external positioning sensors and shows its feasibility even in densely packed environments.     

Effect of Product Microstructure and Process Parameters on Modified Atmosphere Packaged Bread

The objective of this study was to examine bread microstructure, oxygen diffusion properties, and gas exchange between bread and headspace after packaging in modified atmosphere (MA). Breads were produced at laboratory scale, and industrially produced breads were included as a reference. X-ray microtomography was applied to characterize the microstructure of the bread samples. For each sample type, oxygen diffusivity was calculated based on microstructural parameters. The samples for gas analyses were packaged under MA using vacuum compensation, using two vacuum strengths during the air evacuation step. The total porosity of all laboratory samples was above 75%, except for the side and bottom crusts which had a lower porosity (<70%). The porosities of the crumb and the side crust of the commercial bread were 80 and 76%, respectively. The connectivity density of the crumbs of the laboratory and commercial breads was 8 and 10 mm^?3, respectively. The crust showed a larger resistance to oxygen diffusion than the crumb, but for both bread regions, the diffusivity was maximally ten times smaller than that of oxygen in air. When considering all data obtained from the gas analysis in the headspace immediately after packaging, oxygen levels of 0.1 ± 0.1% for strong vacuum and 3.8 ± 2.9% for weak vacuum were obtained, which differed significantly (p < 0.05). The results of the laboratory samples corresponded well to those of industrially baked breads. It was concluded that vacuum strength during packaging determines gas transport in bread after packaging.     

Properties of mixtures of zinc chloride and N-methylpyridinium chloride in the molten state—II. Specific mass, electrical conductivity and viscosity

The concentration and temperature dependences of the specific mass and of the transport properties of molten mixtures of zinc chloride of N-methylpyridinium chloride have been investigated. The specific mass linearly decreases with the temperature at all compositions of the mixture. In the limited temperature range available in this study (423–473 K), the temperature dependence of the transport properties is adequately described by the Arrhenius law. The specific mass regularly increases from pure N-methylpyridinium chloride to pure zinc chloride. The equivalent conductance generally decreases with the concentration of zinc chloride in the melt but remains practically constant from X_ZnCl2 = 0.33 to X_ZnCl2 = 0.50. The viscosity isotherms show a maximum value at X_ZnCl2 = 0.33 and a minimum for X_ZnCl2 = 0.45. The discussion of the results is founded upon the structural properties of the melts and takes into account the Walden's relation between the viscosity and the equivalent conductance.