Fatigue crack growth behaviour of nickel based superalloys at ambient temperature

The present investigation deals with the study of fatigue crack growth rate (FCGR) behaviour of conventional IN 718 (Ni-0.02%C-19.0%Cr-19.35%Fe-3.0%Mo-5.10%Nb-0.50%Al-1.00%Ti-0.0033%B, all in wt%) and modified IN 718 (Ni-0.02%C-19.04%Cr-19.31%Fe-3.04%Mo-4.73%Nb-1.01%Al-1.16%Ti-0.0033%B, all in wt%) alloys at ambient temperature. Modified IN 718 alloy exhibits enhanced crack growth resistance due to roughness induced crack closure as compared to conventional IN 718 alloy.     

Relative importance of informational units and their role in long-term recall by closed-head-injured patients and control groups.

Applied qualitative analysis to the information recalled by control Ss and closed-head-injured (CHI) patients. The Logical Memory subtest of the Wechsler Memory Scale (WMS) was administered to 40 CHI and 40 control Ss. Recall was tested immediately after administration, 40 min later, and 24 hrs later. The analysis took into account the importance of recalled information as determined by a prior rating according to 3 levels of importance. Results suggest that CHI patients have difficulty selectively retrieving the most important information after a long delay. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Update on the management of hepatitis C

BACKGROUND: Hepatitis C is common and most patients with hepatitis C will develop chronic hepatitis. A significant proportion of patients develop cirrhosis and there is a definite but unquantified risk of hepatocellular carcinoma. OBJECTIVE: This article examines the latest treatments available for hepatitis C. DISCUSSION: Interferon alfa is the only currently proven treatment but recent trials suggest that combination therapy with Ribavirin improves sustained long term response rate. Patients should be counselled regarding the mode of transmission of the virus. Patients with cirrhosis should be screened for hepatocellular carcinoma and liver transplantation should be considered for patients with decompensated disease.     

Interpretation of facial expressions of affect in children with learning disabilities with verbal or nonverbal deficits

The ability to identify facial expressions of happiness, sadness, anger, surprise,fear, and disgust was studied in 48 nondisabled children and 76 children with learning disabilities aged 9 through 12. On the basis of their performance on the Rey Auditory-Verbal Learning Test and the Benton Visual Retention Test, the LD group was divided into three subgroups: those with verbal deficits (VD), nonverbal deficits (NVD), and both verbal and nonverbal (BD) deficits. The measure of ability to interpret facial expressions of affect was a shortened version of Ekman and Friesen's Pictures of Facial Affect. Overall, the nondisabled group had better interpretive ability than the three learning disabled groups and the VD group had better ability than the NVD and BD groups. Although the identification level of the nondisabled group differed from that of the VD group only for surprise, it was superior to that of the NVD and BD groups for four of the six emotions. Happiness was the easiest to identify, and the remaining emotions in ascending order of difficulty were anger, surprise, sadness, fear, and disgust. Older subjects did better than younger ones only for fear and disgust, and boys and girls did not differ in interpretive ability. These findings are discussed in terms of the need to take note of the heterogeneity of the learning disabled population and the particular vulnerability to social imperception of children with nonverbal deficits.     

Crosslinked epoxies: Network structure characterization and physical–mechanical properties

A homologous series of epoxy resins, based on the digylcidyl ether of bisphenol-A, were reacted with stoichiometric quantities of m-phenylenediamine (mPDA) to form networks with varying crosslink densities. Infrared spectroscopic analyses revealed that the networks were formed predominantly by the epoxy—amine addition reactions with little or no OH-etherification. The ultimate glass transition temperatures were inversely proportional to the epoxy chain mol wt, as predicted by a model based on the assumptions of additivity and redistributivity of free volume. The average mol wt between crosslinks, M?_c, determined from the dynamic mechanical shear moduli, agreed to within 15 to 18% with the values predicted by the reaction stoichiometry. The glassy-state modulus did not exhibit any M?_c dependence above room temperature, however, the modulus—temperature plot for all the networks exhibited a discontinuity near ?50°C with a steeper slope below ?50°C than above it. The change in slope occurred over the same temperature interval as the β-transition temperature of the networks. The discontinuity in the modulus—temperature plot can be attributed to the freezing of the localized motions of the molecular groups responsible for the β-transition. © 1992 John Wiley & Sons, Inc.     

Evolution of aluminide coating microstructure on nickel-base cast superalloy CM-247 in a single-step high-activity aluminizing process

This study deals with the aluminizing of a directionally cast Ni-base superalloy, namely CM-247, by a single-step process using a high-activity pack. It is observed that significant incorporation of Al into the substrate surface during aluminizing continues over a period of about 1 hour and is not restricted merely to the first few minutes, as reported in the literature. Based on the microstructural details of the coatings formed at various stages of aluminizing, it is concluded that the coating growth in the above process takes place primarily by inward Al diffusion initially, followed by an intermediate stage when the growth involves both inward Al and outward Ni diffusion. In the final stages, the outward diffusion of Ni dominates the coating formation process. The above mechanism of coating formation is different from the one that prevails in the conventional two-step high-activity coating process in that the reaction front for the formation of NiAl remains spatially stationary despite the outward diffusion of nickel during the intermediate stage. It is also shown in the present study that the content of the Al source in the pack affects the coating structure significantly. It is further demonstrated that the microstructure of the aluminide coatings depends not only on the amount of Al incorporated in the sample during aluminizing but also on the time over which the uptake of this Al takes place.     

Causal end-effector inversion of a flexible link manipulator

A new method to obtain the required base torque for the rest-to-rest manoeuvre of a single flexible link manipulator as its end-effector moves along a desired trajectory is introduced. Contrary to available causal and non-causal end-effector inversion techniques, this new approach does not require pre- and/or post-actuation and works even in the presence of the purely imaginary zeros for the transfer function. In this approach, the desired end-effector trajectory is divided into a finite number of segments. In each segment, but the last one, the desired trajectory is redefined so that a bounded continuous torque can be obtained using causal dynamic inversion. For the last segment the desired trajectory is redefined so that not only the causal inversion is achieved but also the final conditions are satisfied; that is, the end-effector reaches its desired position and the manipulator comes to rest at a given time. The redefinition of the desired trajectory at each segment employs summation of the stable exponential functions, which leads to a family of possible answers for the redefined trajectory. To obtain the best member of this family which minimizes the difference between the desired trajectory and redefined trajectory, an efficient search algorithm is proposed and used. Simulation results show the effectiveness of this new method.     

The Pyloritek test and the CLO test: accuracy and incremental cost analysis

Malpractice lawsuits affect most physicians at some point in their career. Proving that malpractice has been committed is based on substantiation of a variety of elements, including that the patient was rendered care that was "below the standard" of care. While many physicians believe that the "standard" will be judged objectively on the basis of published scientific sources and accepted conventions, the standard is established rather by the testimony of expert witness(es). It is the expert testimony that sets the standard and is proof of the standard. The testimony is open for acceptance or rejection by the judge or jury for a variety of nonscientific reasons. We review what the defendant doctor might expect regarding proof required to establish breach of the standard of care and what the prudent expert should be obliged to demonstrate.     

Effect of H+ ion irradiation on surface morphology of Fe40Ni40B20 metallic glass

The effect of irradiation by H⁺ ions on surface modifications of metallic glass Fe₄₀Ni₄₀B₂₀, in the as-quenched, structurally related and crystallized state, has been studied. Swollen regions develop on the surface of the as-quenched and structurally relaxed specimens, whereas blisters form on the surface of the crystallized specimen, under identical conditions of irradiation. The results are explained in terms of the distribution of hydrogen in the amorphous and crystallized conditions.