Plastic working of laminated composite materials

Conclusions Plastic working can be successfully employed for increasing the strength of the joint in a laminated composite material whose components react with each other during high-speed cladding, with the formation of brittle intermetallic compouds. At the same time, by suitable choice of reduction and mismatch, it is possible to produce straight bimetallic strips by rolling them with mismatched peripheral roll velocities.Translated from Poroshkovaya Metallurgiya, No. 12(240), pp. 47–50, December, 1982.     

The use of meditation--relaxation techniques for the management of stress in a working population

The efficacy of meditation-relaxation techniques has been widely researched in the laboratory, but their effectiveness for management of stress in organizational settings is still relatively unexplored. The present study compared relaxation and control conditions as part of a program of stress-reduction in industry. A total of 154 New York Telephone employees self-selected for stress learned one of three techniques--clinically standardized meditation (CSM), respiratory one method meditation (ROM) or progressive relaxation (PMR)--or served as waiting list controls. At 5.5 months, the treatment groups showed clinical improvement in self-reported symptoms of stress, but only the meditation groups (not the PMR group) showed significantly more symptom reduction than the controls. The meditation groups had a 78% compliance rate at 5.5 months with treatment effect seen whether subjects practiced their techniques frequently or occasionally. The safe and inexpensive semi-automated meditation training has considerable value for stress-management programs in organizational settings.     

Pelvic floor exercises versus vaginal weight cones in genuine stress incontinence

BACKGROUND: Anomalous origin of coronary arteries (AOCA) is a rare congenital disease. Although it may have a benign course, it has been identified as a frequent cause of sports-related sudden death. Unfortunately, in vivo detection of AOCA is not easy, as individuals with this anomaly often are asymptomatic and show no signs of myocardial ischemia. Presently, transthoracic two-dimensional echocardiography (TTE) is the only noninvasive, widely available tool to visualize the ostia and first tracts of coronary arteries. OBJECTIVE: To assess the efficacy of TTE in the screening of AOCA in a large athletic population. STUDY DESIGN: In a prospective study, we assessed the ostia and first tracts of coronary arteries in 3,650 subjects (mean age, 30+/-12 years) practicing different sports at various competitive levels. Subjects underwent a TTE examination in our laboratory for scientific or diagnostic purposes. RESULTS: Technically satisfactory echocardiograms were obtained in 3,504 subjects (96%); a clear visualization of the ostia and first tracts of both coronary arteries was obtained in 3,150 cases (90%). Three asymptomatic athletes (0.09%) were suspected to have an AOCA; two with a right coronary artery origin from the left sinus, and one with a left coronary artery origin from the right sinus. Diagnosis was confirmed by coronary angiography. CONCLUSIONS: Our study indicated that AOCA is rare in asymptomatic athletes. Systematic and accurate exploration of coronary anatomy in athletes referred for a diagnostic TTE examination may be useful in identifying those with AOCA.     

Friction properties of composite materials with a macro- and microheterogeneous working surface

Conclusions High friction parameters can be ensured using the composite materials with the working surface in the form of alternating micro- or macrovolumes of the high-strength and ductile components: the former ensures sufficiently high wear resistance whereas the latter component promotes the formation of screening films reducing the losses due to friction. The laboratory and service tests confirm the high performance parameters of these materials.Translated from Poroshkovaya Metallurgiya, No. 7(283), pp. 78–83, July, 1986.     

铜钨复合材料及在热加工中的应用

铜钨复合材料是以铜，钨元素为主组成的一种两相结构假合金，以往多应用于高压电器触头等方面，近年来，增加耐磨相和添加其它元素，同时调整制造工艺，经过改性的铜钨金属复合材料，应用于热加工方面取得较好效果。     

Crack closure and residual stress effects in fatigue of a particle-reinforced metal matrix composite

A study of the influence of macroscopic quenching stresses on long fatigue crack growth in an aluminium alloy-SiC composite has been made. Direct comparison between quenched plate, where high residual stresses are present, and quenched and stretched plate, where they have been eliminated, has highlighted their rôle in crack closure. Despite similar strength levels and identical crack growth mechanisms, the stretched composite displays faster crack growth rates over the complete range of ΔK, measured at R = 0.1, with threshold being displaced to a lower nominal ΔK value. Closure levels are dependent upon crack length, but are greater in the unstretched composite, due to the effect of surface compressive stresses acting to close the crack tip. These result in lower values of ΔK_eff in the unstretched material, explaining the slower crack growth rates. Effective ΔK_th values are measured at 1.7 MPa√m, confirmed by constant K_max testing. In the absence of residual stress, closure levels of approximately 2.5 MPa√m are measured and this is attributed to a roughness mechanism.     

Polymerization contraction stress in thin resin composite layers as a function of layer thickness

OBJECTIVES: In the present study, the effect of layer thickness on the curing stress in thin resin composite layers was investigated. Since the value of the contraction stress is dependent on the compliance of the measuring equipment (especially for thin films), a method to determine the compliance of the test apparatus was tested. METHODS: A chemically initiated resin composite (Clearfil F2, Kuraray) was inserted between two sandblasted and silane-coated stainless steel discs in a tensilometer. The curing contraction of the cylindrical samples was continuously counteracted by feedback displacement of the tensilometer crosshead, and the curing stress development was registered. After 20 min, the samples were loaded in tension until fracture. The curing stress was determined for layer thicknesses of 50, 100, 200, 300, 400, 500, 600, 700 microns, 1.4 mm and 2.7 mm. The compliance of the apparatus was calculated with the aid of a non-linear regression analysis, using an equation derived from Hooke's Law as the model. RESULTS: None of the samples fractured due to contraction stress prior to tensile loading. The contraction stress after 20 min decreased from 23.3 +/- 5.3 MPa for the 50 microns layer to 5.5 +/- 0.6 MPa for the 2.7 mm layer. The compliance on the apparatus was 0.029 mm/MPa. SIGNIFICANCE: A measuring method was developed which was found to be suitable for the determination of axial polymerization contraction stress in this films of chemically initiated resin composites. The method makes it possible to estimate the stress levels that occur in resin composite films in the clinical situation.     

Effect of the working medium and the particle size of the strengthening phase on tribological properties of a metal—Ceramic composite

We present data from tribological tests of composite materials in a metal-ceramic system in various working media. We have found that introduction of hard particles (silicon carbide) into a tin bronze matrix has a positive effect on the tribological properties of the composite. The size of the particles of strengthening phase must be larger than the depth of the working layer subjected to plastic deformation.     

工艺条件对铝电解NiFe2O4基惰性阳极热应力的影响

近年来惰性阳极已成为铝电解工业中的研究热点.以有限元软件ANSYS为开发平台,建立了单个惰性阳极实际工作条件下的有限元模型,以降低热应力,优化热应力分布为目标,研究了工艺条件包括电解质温度、电流强度、极距、阳极浸入电解质深度、环境温度、阳极与环境的换热系数等参数对惰性阳极热应力分布的影响.结果表明,在实际的工作条件下,阳极与电解质相接触的界面附近存在的轴向拉应力,是阳极开裂的主要原因.电解质温度和阳极浸入电解质深度是影响阳极热应力的两个最主要因素.温度升高、阳极浸入电解质深度增加都会使阳极的热应力分布变差.当电解温度由750℃上升到970℃时,第1主应力最大值和最小值绝对值分别上升了29.7%和29.6%,阳极浸入电解质深度由0.01 m变化至0.10 m时,第一主应力最大值和最小值绝对值分别上升了52.1%和65%.其他参数对阳极热应力分布影响很小.     

Effect of plastic working on the structural stability of composite (nickel-chromium alloy)-tungsten materials

Conclusions The character of diffusional interaction of the components of tungsten-reinforced heat-resisting sheet composite materials produced by hot forging with subsequent plastic working depends on the latter's degree of plastic deformation. The loss of chromium from the surface of such a CM varies depending on the degree of plastic deformation and on the composition of the matrix alloy. Tungsten fibers stabilize the composition of a CM by acting as obstacles in the paths of chromium diffusion fluxes.Translated from Poroshkovaya Metallurgiya, No. 3(255), pp. 40–44, March, 1984.     

Spectral sensitivity of cones in the goldfish, Carassius auratus

The spectral sensitivities of retinal cones isolated from goldfish (Carassius auratus) retinas were measured in the range 277-737 nm by recording membrane photocurrents with suction pipette electrodes (SPE). Cones were identified with lambda max (+/- S.D.) at 623 +/- 6.9 nm, 537 +/- 4.7 nm, 447 +/- 7.7 nm, and about 356 nm (three cells). Two cells (lambda max 572 and 576 nm) possibly represent genetic polymorphism. A single A2 template fits the alpha-band of P447(2), P537(2), and P623(2). HPLC analysis showed 4% retinal:96% 3-dehydroretinal. Sensitivity at 280 nm is nearly half that at the lambda max in the visible. The lambda max of the beta-band (in nm) is a linear function of the lambda max of the alpha-band and follows the same relation as found for A1-based cone pigments of a cyprinid fish.     

Hardiness, Type A behavior, and the stress–illness relation in working women.

Hardiness has been proposed as a stress-resistance resource in maintaining health. This construct has been shown to act in conjunction with the Type A behavior pattern in affecting illness. In this study, we examined this relation in women (N?=?82) with the use of the Structured Interview and the Jenkins Activity Survey to assess Type A behavior. As expected, there was a strong stress–illness association. However, there were no hardiness main effects nor interactions between stress, Type A behavior, and hardiness. Hardiness was significantly associated with age, education level, and marital status. No differences in hardiness composition were found between high stress/high illness and high stress/low illness groups. Only the Powerlessness scale of hardiness was related to illness. These results are discussed in comparison with other hardiness studies. Particular attention is focused on possible sex differences, and implications for future research are suggested. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Internal recording of the early receptor potential in turtle cones

1. Early receptor potentials (E.R.P.s) were recorded with internal electrodes in turtle cones by applying brief flashes from a xenon tube with a maximum photon density equivalent to 2-3 x 10(8) photons micronm-2 at the optimum wave-length. 2. The E.R.P. was separated from the late receptor potential (L.R.P.) by superposing in flash on a step of light which was strong enough to saturate the L.R.P. 3. In red-sensitive cones the E.R.P. consisted of a brief depolarizing phase (R1) followed by a hyperpolarizing phase (R2) of maximum amplitude 10 mV and duration 30-40 msec. R1 was small or absent in green-sensitive cones. 4. With flashes of increasing intensity the E.R.P. approached its maximum exponentially with an exponential constant Q of about 10(8) photons micronm-2 which is of the same order as the reciprocal of the photosensitivity of porphyropsin; the implication of this result, which is considered in the theoretical section, is the the E.R.P. is proportional to the number of photoisomerizations. 5. When tested with a constant xenon flash at varying times after the beginning of a bleaching light the E.R.P. declined exponentially with a similar value of Q. 6. After prolonged bleaches the E.R.P. recovered with a time constant of about 100 sec but much quicker recoveries were observed after relatively brief bleaches. 7. The form and size of the E.R.P. are consistent with the accepted view that it arises from a redistribution of charge in the cone pigment molecule. 8. The effect of a single photoisomerization in an isolated cone was estimated as about 10(-10) V or one electronic charge through about 10% of the membrane.     

A composite model for the grain-size dependence of yield stress of nanograined materials

Based on the observation that, in a nanograined material, a significant portion of atoms resides in the grain-boundary region and grain-boundary activity plays a key role for its plastic behavior, a micromechanics-based composite model is developed to calculate the transition of yield stress as the grain size decreases from the coarse grain to the nanograin regime. The development makes use of a generalized self-consistent scheme in conjunction with the secant moduli of the constituent phases and a field-fluctuation approach. The constituent grains are modeled by inclusions with a grain-size-dependent plastic property and, in order to reflect the atomic sliding inside the grain boundaries observed in molecular dynamic simulations, the grain-boundary phase is modeled as a soft, ductile material with a pressure-dependent property. Applications of the developed model to a high-density copper showed the distinctive—some experimentally observed—features: (1) the yield stress initially increases following the Hall-Petch equation, but as the grain size reduces to the nanorange, it will depart and decrease; (2) when the grain size drops to a critical value (called the critical equicohesive grain size), the slope turns negative, (3) there is a tension-compression asymmetry (or strength-differential effect) in the yield stress, and (4) parametric calculations for materials whose grains deform only elastically indicate that the Hall-Petch plot will exhibit a continuously decreasing negative slope over the entire range of grain size. Further application of the theory to palladium in the nanorange shows a continuous decrease of the yield strength with decreasing grain size. It can be generally concluded that the range following the Hall-Petch equation is dominated by the deformation of the grains, and the range with a negative slope is controlled by the plasticity of the grain boundaries. During the transitional stage, both grains and grain boundaries deform competitively.