Wear Mechanisms of Glass-Infiltrated Alumina Sliding Against Alumina in Water

Glass-infiltrated alumina is now commonly used as a core material in dental restorations. If the veneer layer, which covers the core, is broken or damaged through use, a direct contact between the core and the opposing restorative material or human enamel can occur. The wear behavior in simulated contacts with human enamel has already been studied. In the present work, we have investigated the wear mechanisms of glass-infiltrated alumina in contact with a high-purity alumina as an opposing ceramic restoration. Wear tests were performed in a pin-on-disk tribometer under conditions that roughly resemble those in the oral environment. The wear rates of the alumina balls and the glass-infiltrated disks sliding in water increased linearly with load. No wear transition (i.e., a sudden increase in wear) was observed as either the load or the sliding distance was increased. Examination of the wear debris in the SEM suggested the presence of wear particles that are often attributed to the formation of hydrated aluminum oxide through tribochemical reactions between water and alumina. While tribochemical wear was the dominating wear mechanism for the alumina balls, microfracture and delamination governed the wear behavior of the glass-infiltrated alumina disks. Examination of the surface layers formed on the disk wear tracks confirmed the presence of amorphous hydrated alumina on the wear track. It is suggested that these reaction products smear on the wear track filling the pores produced by microfracture and delamination. The high wear resistance of glass-infiltrated alumina is attributed to the presence of hydrated alumina in the third body layer that accommodates the interfacial shear stresses and the high strength due to strong bonding between the glass phase and alumina grains. Based on the observed wear resistance of glass-infiltrated alumina in the present study, this material should be evaluated for applications in addition to dental restorations.     

The tribological performance of DLC coatings under oil-lubricated fretting conditions

Whether or not the process of fretting occurs is to a large extent dependent on the coefficient of friction, because the coefficient of friction directly affects the amount of shear stress. As a result, the key factor when it comes to reducing the amount of fretting damage is to reduce the coefficient of friction. Various surface coatings, and especially hard, diamond-like carbon (DLC) coatings, are known to be able to produce surfaces with a low level of friction. Despite some such attempts in the past, which did not result in major improvements, the developments and improvements in DLC coatings in recent years suggest the need for a re-evaluation of these coatings for fretting applications. Another way to reduce the amount of friction in mechanical components is to apply lubricants, and recent studies on the lubrication of DLC coatings suggest that this combination could be very successful in preventing failures under boundary-lubrication conditions. Therefore, in this work we present the results of friction and wear measurements from three types of fretting contacts: steel/steel, steel/DLC and DLC/DLC. Boundary oil-lubrication conditions were investigated and a wide range of displacement amplitudes, i.e., from 25 to 500 μm, were selected to assess the fretting and sliding behaviours. The results show a significant difference between the fretting and sliding regimes. In the fretting regime, the DLC-containing contacts, and especially the self-mated DLC/DLC contacts, performed much better than the steel/steel contacts, and significantly reduced both the wear (a 3–10 times reduction with steel/DLC and DLC/DLC) and the friction (a more-than-two-times reduction with DLC/DLC). In the sliding regime, the lubrication effects governed the tribological performance, making the results for all three material combinations very similar.     

Formation of Helium Porosity in Different Materials during Post-Radiation Annealing

The characterisitics of the development of helium porosity in bcc and fcc alloys and structural steel after irradiation with 40-keV He⁺ up to dose 5⋅10²⁰ m⁻² at 20°C and subsequent annealing at 650°C for 1 h and 5 h are studied by transmission electron microscopy. It it found that under these conditions smaller bubbles with high density are formed in bcc than in fcc materials. It is shown that for an annealing time of 5 h higher porosity is formed in all materials, except nickel, than with 1 h annealing. This is due to the inflow of thermal vacancies from the free surface. The data obtained are discussed from the standpoint of the formation of various helium-containing complexes, their thermal stability, and the diffusion mobility of the matrix atoms. __________ Translated from Atomnaya Energiya, Vol. 99, No. 2, pp. 115–120, August 2005.     

Helium-porosity evolution in He+-irradiated Ni-C and Ni-C-Ti model alloys

Moscow Engineering Physics Institute. Translated from Atomnaya Énergiya, Vol. 73, No. 3, pp. 203–209, September, 1992.     

电子束辐照对中华管鞭虾原肌球蛋白免疫原性及其构象的影响

提取中华管鞭虾肉中的原肌球蛋白（tropomyosin,TM）,采用不同电子束辐照剂量（0、1、3、5、7、9?kGy）处理,分别用免疫印迹法和间接酶联免疫吸附测定法检测TM与免疫球蛋白G（immunoglobulin G,IgG）的结合能力,采用圆二色光谱和荧光光谱法检测TM二级结构及其表面疏水性,探究电子束辐照引发的TM结构变化与免疫原性的关系。结果显示：电子束辐照会降低TM的含量;随辐照剂量的增加,TM分子中的α-螺旋含量降低,β-折叠和无规卷曲含量增加,分子表面疏水性增强,同时TM与IgG的结合能力下降。电子束辐照处理能改变中华管鞭虾TM的构象,从而降低其免疫原性。本研究结果为应用电子束辐照降低中华管鞭虾肉的潜在致敏性提供理论依据。     

Corticotropin-releasing factor modulates defensive-withdrawal and exploratory behavior in rats.

The role of corticotropin-releasing factor (CRF), an endogenous neuropeptide, in modulating species-typical responses was examined in an unfamiliar open field containing a small chamber. Rats placed in this small chamber spent most of their time withdrawn in it. However, rats given an icv injection (20 μg) of α-helical CRF(9–41), a CRF receptor antagonist, emerged from the chamber and explored the unfamiliar open field. Results of additional studies with vehicle-treated rats suggest that reexposure reduces the threatening impact of an unfamiliar open field. CRF (300 ng) injected centrally, but not peripherally, before reexposure to the test environment significantly reduced exploration in the open field and increased a pattern of defensive-withdrawal into the chamber. Data suggest that whether defensive-withdrawal or exploratory behavior is exhibited may depend on CRF actions in brain systems that mediate the perception of threat in the environment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)