汽车发动机用粉末冶金主轴承盖

粉末冶金主轴承盖(MBC)于1993年第一次用于GM的3100与3800V6发动机.该零件一年消耗粉末5 000多t,是北美粉末冶金零件中应用量最大者.选择粉末冶金材料替代传统的铸铁,是因为其有利于零件的功能,而且因为粉末冶金工艺能成形为最终形状,从而使GM可节省下对主轴承盖的切削加工生产线的大部分投资.由于灰铸铁强度不够高,球墨铸铁的价格高又难切削加工,因此,为这种零件开发了一种强度高、成本低的粉末冶金合金钢.这篇论文说明了主轴承盖的功能要求,比较了铸铁与粉末冶金的材料和生产工艺,说明了粉末冶金的设计利益;此外,还讨论了粉末冶金主轴承盖要求的强度、一致性、完善性(无缺陷)及切削性,其中包括试验与试验验证.     

Melter Feed Reactions at T ≤ 700°C for Nuclear Waste Vitrification

To understand feed‐to‐glass conversion for the vitrification of nuclear waste, we investigated batch reactions and phase transitions in a simulated nuclear waste glass melter feed heated at 5 K/min up to 700°C using optical microscopy, scanning electron microscopy with energy‐dispersive X‐ray spectroscopy, and X‐ray diffraction. To determine the content and composition of leachable phases, we performed leaching tests; the leachates were analyzed by inductively coupled plasma atomic emission spectroscopy. By 400°C, gibbsite and sodium borates lost water and converted to amorphous phase, whereas other metallic hydroxides dehydrated to oxides. Between 400°C and 700°C, carbonates decomposed before 500°C; amorphous aluminum oxide and calcium oxide reacted with the sodium borate and formed the more durable amorphous borate phase along with intermediate crystalline products; above 500°C, quartz began to dissolve, and hematite started to convert to trevorite.     

Multiple Frame Flash Photomicrography in Living Animals

The equipment described consists of a micro-camera, flash tube unit, microscope substage optical system and stage. The foot-controlled camera embodies a reflecting single leaf electric shutter. The camera can be used for single frame photography at intervals down to l1/2 seconds or multiple frame photography from 2 to 45 frames per second, using continuously moving 35mm. film. This method obviates vibration problems. The short flash duration "freezes" the film movement during exposure. The camera is used in conjunction with a flash tube, designed for photomicrography. It utilizes mercury electrodes in argon at atmospheric pressure, and gives a light source 3mm. in diameter of great intrinsic brilliance, in which the yellow wavelengths predominate. The spectral output is suitable for use with achromatic objectives. The energy dissipation, which can be varied from 2 to 8 joules per flash, gives ample light for high power photomicrography, with an exposure of approximately 5 micro-seconds. The tube operates at 950 volts D.C. The flash unit embodies an auxiliary illuminating system for viewing before photography commences. During photography, 10 per cent of the flash illumination is used for viewing. The microscope substage and stage can be used in place of the quartz rod technique in the study of transilluminated organs and tissues of living animals. It transmits ten times more light than the latter, and allows the maximum resolution that the objective is capable of giving.     

Behavior of Dilative Sand Interfaces in a Geotribology Framework

Frictional resistance along the exterior of an embedded structure or structural element develops through relative displacement at the interface. An understanding of how surface topography influences interface strength and deformation behavior is required to develop comprehensive interface models for soil-structure analyses, to develop interface design methods and for producing enhanced construction materials. This paper presents the results of an investigation to quantify the influence of surface topography on shear stress and volume change behavior of dilative granular material interface systems. The root spacing, asperity spacing, asperity height, and asperity angle of machined, idealized surfaces are systematically varied. Direct interface shear test results using Ottawa 20/30 sand and glass microbeads show that maximum interface efficiency for these materials is achieved for a asperity spacing to median grain diameter ratio between 1.0 and 3.0, and an asperity height to median grain diameter ratio greater than 0.9. An asperity angle of 50 degrees or greater yields maximum efficiency for any given asperity spacing or height. The results suggest that interface behavior is governed by predictable geometric and mechanical relationships that are applicable to more complex manufactured surfaces.     

Direct resistance comparisons from the QHR to100 M/spl Omega/ using a cryogenic current comparator

Measurements of room-temperature 100 M/spl Omega/ standard resistors and cryogenic thin-film resistors based directly on a quantized Hall resistance standard have been made with a cryogenic current comparator (CCC) bridge. This 15 496:2 ratio CCC attains a current sensitivity of 10.7 fA/Hz/sup 1/2/ in measurements of cryogenic thin-film resistors, without extensive shielding or filtering. A resistive primary winding helps the CCC maintain stability in the presence of external noise. The resistive-winding technique may be useful for the absolute measurement of small currents delivered by single-electron tunneling devices.     

Age-dependent sparing of visual function after bilateral lesions of primary visual cortex.

Bilateral lesions of primary visual cortex (PVC) sustained early in life induce the visual system to undergo structural and functional reorganization and produce modified neuronal networks capable of mediating visual abilities that would be impaired if the lesions occurred in adulthood. Reorganization after early lesion is also accompanied by degeneration of the lateral geniculate nucleus of the thalamus, and 90% of beta retinal ganglion cells die via retrograde degeneration. It is unclear whether the high potential of the system to reorganize after early lesion could overcome the effects of beta retinal ganglion cell death. Visual acuity, which depends on an intact beta-cell array, was impaired in cats that underwent PVC lesions on postnatal day 1 and indicated that neuroplastic potential was insufficient to overcome early lesion-induced maladaptive plasticity. Animals with lesions made at 1 month of age, a stage accompanied by high levels of neuroplastic potential but no death of beta cells, achieved acuity measures equivalent to intact animals. The authors conclude that visual signals are rerouted to subserve functionality when the lesion is made at 1 month of age, but not at 1 day of age. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lack of involvement of known oncogenic DNA viruses in Epstein-Barr virus-negative Hodgkin's disease

Epstein-Barr virus (EBV) is associated with around one-third of cases, but young adult cases are rarely EBV associated. In this study, known oncogenic DNA viruses, including human adenoviruses, papovaviruses and the human herpesviruses-6 (HHV-6) and -8 (HHV-8) were not detected in Hodgkin's disease lesions. These results suggest that an as yet unidentified infectious agent is involved in the pathogenesis of non-EBV-associated Hodgkin's disease.     

Dose-response functions for the soiling of heritage materials due to air pollution exposure

A set of materials (Portland limestone, white painted steel, white plastic and polycarbonate filter material) was exposed at locations in London, Athens and Krakow. Regular measurements of reflectance were taken over a period of twelve months. Co-located measurements of PM₁₀ concentrations were available. Based on these results, the relationship between soiling (measured as loss of reflectance) and ambient PM₁₀ concentrations was quantified leading to the development of dose–response functions for the soiling of materials. The results for limestone revealed too much scatter for a prediction to be made. Implications for air quality management and for the conservation of cultural heritage buildings are considered, including public acceptability and economic factors.