Impact resistance of Transitions Plus spectacle lenses

Although it has been shown that photochromic glass industrial lenses do not provide adequate occupational impact protection, they are frequently requested by outdoor workers wanting sunglasses. The recent introduction of Transitions Plus (TP), a photochromic plastic lens, may meet the needs of these workers. The impact resistance of 60 TP lenses of dress thickness was studied using a ballistic test. Lenses were edged and mounted in metal industrial frames. The completed spectacles were placed on a headform for ballistic testing using a 6.5 mm (1/4 in) steel ball propelled from an airgun. The lenses were divided into test groups that received: (1) a single impact at the geometrical center by a ball traveling at 18 m/s (59 ft/s) and (2) 50 consecutive impacts at 18 m/s, or (3) a single impact at 46.5 m/s (152 ft/s). All lenses passed the single impact test at 18 m/s. Four lenses broke under repeated impact. All lenses subjected to the high-speed impact test failed, either breaking or being dislodged from the frame. These findings show that dress thickness TP lenses provide impact protection from small blunt missiles traveling at moderate speed, and that they are durable under repeated low energy impact. However, thicker lenses must be used when the wearer has a high risk of ocular exposure to small high-speed missiles in the workplace. It can be concluded that TP lenses may be used in occupational eyewear for many outdoor workers who want photochromic sunglass lenses, provided that other needs for vision and occupational safety are also satisfied.     

Surface topography and frictional characteristics of ceramic brackets

The surface topography and frictional characteristics of single crystal sapphire and polycrystalline alumina brackets were evaluated in both the dry and the wet state as a function of the four basic wire alloy compositions. On the premise that a particular combination of bracket, wire, and environment must be attained so that the efficiency and reproducibility of tooth movement is improved, a significant reduction in the coefficients of friction was sought. Viscometric measurements were used to show that the characteristics of saliva remained unchanged throughout the investigation. Scanning electron micrographs and laser specular reflection were studied to illustrate the general appearance and quantitative magnitude of roughnesses. Frictional measurements of couples in the dry, the wet, and again in the dry state were evaluated at five different normal loads. The outcomes of the virgin materials show that arch wire alloy, rather than bracket product type or surface roughness, influence the frictional characteristics the most and that titanium wires generally cause higher frictional resistances than either stainless steel or cobalt-chromium wires. Friction tests of specimens that were run multiple times suggest that couples comprised of nickel titanium arch wires against ceramic brackets may actually improve as a result of a break-in period.     

Fracture resistance of fiber-reinforced ceramic matrix composites

The influence of the properties of the fibers, the matrix and the interface on the mechanical properties of fiber reinforced ceramics is analyzed by a simplified method previously developed by the authors for cohesive materials. The method parts from the assumption that crack displacements are known a priori and furnishes, in a simple and easy way, the fracture resistance curves versus crack length. The numerical results from the model are compared with experimental data from the literature. Finally, the model is used to assess the influence of fiber strength, interface slipping shear stress, fiber radius and fiber defect distribution on the fracture resistance and ductility of fiber-reinforced ceramic composites.     

Polymorphic structural features of modelled HLA-DQ molecules segregate according to susceptibility or resistance to IDDM

The structural features of HLA-DQ alleles which are susceptible and resistant to insulin-dependent diabetes mellitus (IDDM) have been examined using a model of their three-dimensional structure obtained by energy minimisation, based on the published structure of HLA-DR1. The model shows DQ molecules to have an overall shape nearly identical to that of DR molecules, but with significant differences in the fine structure: 1) the antigen-binding groove of DQ molecules has a polymorphic first pocket; this pocket can be either amphiphilic or hydrophilic, 2) The beta 49-56 dimerisation domain of DQ is polymorphic: hydrophobic, or amphiphilic, or hydrophilic and positively charged, leading to spontaneous or T-cell receptor-induced homodimer formation, or T-cell receptor-induced homodimer formation, or difficulty of the formation of such dimers, respectively; 3) a prominent Arg-Gly-Asp loop is formed by some DQ alleles (beta 167-169) and probably functions in cell adhesion. There are also small differences in the residues and sequences implicated in CD4 binding (mostly in DQ beta 134-148) but the significance of these differences cannot be evaluated at present. All seven DQ alleles which confer susceptibility to IDDM possess a hydrophilic first pocket in the antigen-binding groove, a hydrophobic or amphiphilic beta 49-56 dimerisation patch that allows for spontaneous or T-cell receptor-induced dimerisation, and the Arg-Gly-Asp loop. By contrast, in the protective alleles at least one of these three features is absent. This segregation of phenotypes according to susceptibility or resistance can well explain the model of tighter autoantigen binding by the protective alleles compared to the susceptible alleles, previously proposed for the pathogenesis of IDDM.     

Clinical and statistical standards of therapeutic and diagnostic process in patients with ophthalmic diseases]

Rehabilitation professionals contributing to the plan of care for a patient with a wound must be aware of and follow the rules promulgated by regulators, surveyors, and payers. Certain regulations are of particular importance. When establishing functional outcomes, the rehabilitation professional should ask whether the outcomes are meaningful, practical, and sustainable. By becoming part of the multidisciplinary team, rehabilitation professionals can help to improve cost-effectiveness of wound care and patient outcomes.     

ZrB2-SiC复相陶瓷的制备及其耐热冲击性能的研究

以Zr-B2O3-Mg为反应体系,利用自蔓延高温合成法(SHS)制备ZrB2粉体.分别在反应前和反应后掺入(体积分数)20%SiC,利用放电等离子烧结技术(SPS)制备ZrB2-SiC超高温陶瓷.采用SEM观察显微组织,利用阿基米德法测定密度,用氧炔焰进行热冲击试验.结果表明:与在自蔓延生成ZrB2后再掺入SiC的粉体相比,在自蔓延体系中直接掺入SiC粉体能够改善SiC的烧结活性及分散均匀程度,从而使相同烧结工艺下制备的ZrB2-SiC复相陶瓷具有较高的致密度和更好的抗热冲击性能.     

Wear resistance of silicon carbide and nitride based ceramic materials

Various factors that affect the nature of wear in SiC and Si₃N4₂ based ceramics have been analyzed. It is shown that adhesion, mechanochemical and diffusion interactions in the contact zone and wear due to fatigue, thermal stresses and abrasion are the predominant factors. Ceramics based on SiC and Si₃N₄ are shown to have excellent wear resistance. Poreless silicon nitride materials that have good chemical stability, heat and crack resistance appear promising as ceramic—metal friction couples and for metal machining. Silicon carbide based poreless materials are efficient ceramic—ceramic friction couples and for service under severe hydro and gas abrasive media attack.Translated from Poroshkovaya Metallurgiya, No. 5, pp. 3–8, May, 1993.     

The fracture resistance of a model metal/ceramic interface

Crack propagation has been measured for the Al₂O₃/Au interface subject to conditions that exclude stress corrosion. Crack growth has been shown to occur with a rising resistance, governed by intact metal ligaments in the crack wake. The level of resistance also increases as the metal layer thickness increases. Crack extension occurs by a combination of plastic void growth and interface debonding. The fracture energies are much larger than the work of adhesion, but appreciably smaller than those expected for ductile interface fracture. The fracture energy is nevertheless dominated by plastic dissipation, which increases at larger metal layer thicknesses.     

Impact of genetics on disease resistance

PURPOSE: To evaluate the safety and efficacy of phacoemulsification, primary posterior capsulorhexis (PCCC), and primary intraocular lens (IOL) implantation for uveitic cataracts. SETTING: Institutional practice. METHODS: Fifteen consecutive eyes of 13 patients with various causes of uveitis received anterior capsulorhexis, phacoemulsification, PCCC, and in-the-bag implantation of a heparin-surface-modified IOL for visually disabling cataract. The safety and efficacy of the combined operation were studied prospectively. RESULTS: At a mean follow-up of 16.9 months (range 8 to 30 months), all eyes had a clear central visual area. Fourteen of 15 eyes (93.3%) had good visual improvement after surgery. Eight eyes (53%) achieved a best corrected visual acuity (BCVA) of 20/30 or better and 6 (40%), 20/20 or better. Seventy-three percent of eyes attained a BCVA of 20/80 or better. The mean improvement in visual acuity was 5.2 Snellen lines (range 0 to 11 lines). No cases of uveitis flare-up or other major complications related to the cataract surgery occurred. CONCLUSIONS: The study's preliminary results are encouraging and indicate that phacoemulsification, PCCC, and IOL implantation can be considered in patients with visually disabling uveitic cataract.     

The ex vivo effect of ligation technique on the static frictional resistance of stainless steel brackets and archwires

This ex vivo investigation compared the effect of various orthodontic ligation techniques on the static frictional resistance of stainless steel brackets and archwires under both dry and wet conditions. The techniques studied were: elastomeric modules tied conventionally and in a 'figure of 8' pattern, stainless steel ligatures, and Teflon-coated ligatures. The first part of the investigation involved the construction of calibration curves for each of the materials, so an estimate of the normal force exerted by the ligatures could be ascertained. Secondly, a pair of ligature locking pliers were modified so that ligatures could be placed with a standardized force. Finally, the four methods of ligation were directly compared on a specially constructed testing apparatus. Results revealed that elastomeric modules tied in a 'figure of 8' pattern produced significantly more friction than any other method tested, under both dry and wet conditions. No significant differences in frictional resistance were found between conventionally tied elastomeric modules and stainless steel ligatures. Teflon-coated ligatures, however, were associated with the lowest frictional forces. The results of the calibration tests indicated that the normal forces exerted by all four methods of ligation may be higher than previously estimated.     

TiB2-HfC陶瓷的高温抗氧化性能

为了研究TiB₂-HfC陶瓷的高温抗氧化性能, 分析了TiB₂-HfC陶瓷在1100 ℃下分别氧化1、4、7、10 h后的氧化行为; 根据材料氧化后的微观结构, 对陶瓷氧化层进行了划分, 将其分为外氧化层、次氧化层及过渡层。实验结果表明: 外氧化层的氧化物为TiO₂、B₂O₃、HfO₂、NiO和CoO; 随着氧化时间的延长, 材料发生了严重氧化, 氧化层逐渐变厚, 材料保有的抗弯强度逐渐减小, 材料的氧化增重与氧化时间呈抛物线规律; 氧化1h后, 材料表面形成了约为12 μm的致密氧化层, 此时材料具有较好的抗氧化性能, 且仍保有较高的抗弯强度, 其值为823.6 MPa。     

The effect of different ceramic materials on the fracture resistance of dentin-bonded crowns

Using stereomicroscopy, light microscopy, and scanning electron microscopy, we investigated the development of vasa vasorum in the proliferated neointima of the autovein graft and its anastomoses implanted in the canine femoral artery against a background of poor distal runoff. In the stereomicroscopic examination, a microfil silicone rubber compound (MF) was injected transluminally or via perivascular vasa, and the vascular specimen was prepared for clearing by immersion in a methyl-salicylate solution. Vessel interstices filled with MF were found adjacent to the suture materials within 5 days of grafting. Fourteen days after implantation, luminally originating vasa vasorum were often visible in the neointima along the suture line and distributed into the media and adventitia connecting to the original vasa vasorum. At 6 months or more after grafting, many orifices of luminally originating vasa vasorum were seen along the suture line of both proximal end-to-end and distal end-to-side anastomoses and distributed into the thickened neointima forming a vasa network when the neointima had proliferated to over 250 microm in depth. On the other hand, some clefts filled with MF were found in mural thrombi deposited on the vascular sinus of the graft within 5 days, and these appeared to be one of the sources of luminally originating vasa vasorum on the graft distant from the suture line. Moreover, the development of numerous vasa vasorum was constantly demonstrated in the neointima when it had proliferated to over 250 microm in depth.     

钨粉颗粒级配对氧化铝陶瓷金属化方阻的影响

选取3种平均粒径分别为0.2、0.5和1μm的钨粉,将任意2种钨粉按一定的质量比混合后与氧化铝陶瓷共烧,得到氧化铝陶瓷的金属化层,研究钨粉颗粒级配对氧化铝陶瓷金属化方阻的影响。结果表明,钨金属化层的方阻与其烧结致密化程度直接相关,钨金属化层越致密,其表面方阻越低。单独使用其中1种粒度的钨粉与氧化铝陶瓷共烧时,金属化方阻较高。将0.5μm和1μm钨粉混合能显著降低方阻,当两者质量比为45:55时得到的金属化方阻最小(12.10 m/□)。混合钨粉的累积分布曲线符合Dinger-Funk粉体堆积公式,分布模数n越接近0.37,其烧结致密化程度越高,金属化方阻越低。     

Crack resistance of modern ceramics and ceramic composites. II. EF method

The procedure and test results are for crack resistance are presented for various monolithic and composite oxide and nonoxide ceramics by chipping the rectangular edge of a polished specimen. The main difference of the test method suggested (EF method) with an arbitrary point of fracture for a specimen edge from the well-known similar method with a fixed point of fracture is demonstrated. Tests are performed with Rockwell, Vickers and Knoop indenters, and the Rockwell indenter is chosen as the optimum. On the basis of statistically reliable experimental data a direct relationship is established between edge toughness and critical fracture toughness determined in the same ceramic specimens based on scandium oxide, aluminum oxide, zirconium dioxide, silicon carbide and silicon nitride. The EF method, whose use does not require special equipment, may be used effectively in a normal metallurgy test laboratory, particularly when specimens for evaluating ceramic breaking resistance may only be prepared in smaller sizes than those required for standard crack resistance tests. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(450), pp. 39–49, July–August, 2006.