The effect of residual stresses induced by prestraining on fatigue life of notched specimens

The effect of tensile prestraining-induced residual stress on the fatigue life of notched steel parts was investigated. The study was performed on AISI 4140 steel. Rotating bending fatigue tests were carried out on semicircular notched specimens with different notch radii in the as-quenched and tempered conditions. Metallography of the specimens was performed by means of light optical microscopy. The finite-element method was used to evaluate the residual stress distribution near the notch region. Fatigue tests revealed fatigue life improvement for notched specimens, which changes depending on the notch radii and applied stress. Scanning electron microscopy was used to examine the fracture surfaces of the specimens.     

Moderate head injuries in children as compared to other age groups, including the cases who had talked and deteriorated

Patients defined as having a moderate head injury on the basis of Glasgow Coma Scale scores within the ranges of 9 to 13 after acute nonsurgical procedures were selected. Almost 1600 cases were hospitalized in the Neurosurgery Department. The cases were admitted through the Emergency Unit of Gaz University Medical School, Ankara, Turkey during the period between 1979 and 1992. The group studied consisted of 231 selected patients assessed separately in paediatric, adult and elderly age groups. Possible risk factors such as: GCS score, anisocoria, unilateral or bilateral fixed pupils, impaired oculocephalic reflexes, presence of multiple systemic injuries, aetiology of head trauma, presence of linear or depressed skull fractures, space occupying mass on CT or operation was also assessed. Subarachnoid haemorrhage turned out to be the only independent significant risk factor in predicting mortality. The data about the patients who have "talked and deteriorated" were also reported so as to assisst physicians charged with the care of trauma victims.     

Fatigue behavior of X40CrMoV 51 at high temperatures

The fatigue characteristics of the hot work tool steel X40CrMoV 51 (UNS number T20811) at high temperatures is presented. The temperatures for the experiments were chosen between 50–600 °C. The experiments used B-type cylindrical specimens machined from X40CrMoV in an R.R. Moore rotating bending type fatigue test machine obeying the high cycle principle. The temperature intervals for the experiments were chosen as 50, 100, 200, 300, 400, 500, and 600 °C, for which the fatigue limit for each interval at 2 × 10⁶ cycles was determined. The fatigue limit of the material at room temperature (RT) is observed as 432 MPa, whereas it drops to 383 MPa at 400 °C. On the other hand, it stays almost constant between 400–600 °C, indicating that the material includes the elements forming strong carbides such as V, Mo, and Cr, which prevent the decrease of the fatigue limit due to higher temperatures.     

Transmission Congestion and Competition on Power Generation Expansion

Generation expansion planning involves decisions on location and capacity of new generation, which may lead to adding or relieving congestion in transmission lines and to increasing or reducing competition in deregulated markets. Generation expansion may encounter congestion in the transmission network by constrained single-line flows as well as flowgate transfer capabilities. In this paper, a model to study the interaction between competition and transmission congestion on power generation expansion is proposed. The generation expansion problem is modeled as a Cournot competition game. Network transmission constraints are included in the optimal generation expansion problem to comply with power flow limits. Results from a five-bus power network and the IEEE 24-bus system are presented and discussed     

Predictors of left atrial thrombus and spontaneous echo contrast in rheumatic valve disease before and after mitral valve replacement

In this study we aimed to analyze, with reference to mitral regurgitation (MR), the incidence and predictors of left atrial (LA) thrombus and spontaneous echo contrast in patients with rheumatic valve disease before and after mitral valve replacement. The incidence of LA thrombus is known to be less in patients with MR. The impact of mitral valve replacement on this beneficial effect has not been studied in detail. The study included 169 consecutive patients (59 men and 110 women, average age 40 +/- 13 years) with rheumatic mitral valve disease who underwent transesophageal echocardiographic examination 1 to 3 days before and within 7 days (mean 4.0 +/- 1.3) after mitral valve replacement using mechanical prostheses in a single institution. The preoperative incidence of echocardiographic LA spontaneous echo contrast (SEC) was 1.1%, 30%, and 54%, and the incidence of thrombus was 1.1%, 13%, and 17% in the groups with MR, combined mitral stenosis + MR, and isolated mitral stenosis, respectively. In the MR group, SEC and thrombus incidence increased significantly after surgery. The independent predictors for postoperative thrombus development were atrial fibrillation, postoperative SEC, and preoperative thrombus. Thrombus recurred after surgery in 64% of 14 patients who had surgical thrombectomy. The presence of postoperative MR was associated with decreased risk of postoperative SEC and thrombus development. The interaction between MR and SEC and thrombus both before and after surgery provides further support for the protective effect of MR against LA thrombus formation.     

Fretting fatigue properties of plasma nitrided AISI 316 L stainless steel: Experiments and finite element analysis

This study investigates the effects of thickness, hardness and composition of modified layer on the plain and fretting fatigue properties of the nitrided 316 L steel plasma nitrided under various processing conditions. Fretting fatigue behaviour of untreated and nitrided material is also analysed with the finite element method. Experimental and theoretical fatigue life results are compared. The result indicates that the nitriding process improved the fretting fatigue properties of 316 L stainless steel. The experimental test results are close to theoretical fretting fatigue life results, thus it yields that the established model in the numerical analysis is consistent in this regard.     

Reactions of anti-immunoglobulin sera with synthetic T cell receptor peptides: implications for the three-dimensional structure and function of the TCR beta chain

The derived amino acid sequence of the human TCR beta chain shows considerable homology to lg lambda light chains in its variable (V) and constant (C) domains, and in its joining segment (J). We assessed the cross-reactivity between TCR beta chains and lg light chains by synthesizing a set of nested, overlapping 16-mer peptides that duplicated the sequence that corresponds to the continuous VDJC sequence of TCR beta chain and determining the capacity of rabbit antisera to human or murine lgs to react with these peptides. The reactivities we observed were consistent with homologies to lambda and kappa light chains. The strongest reactivity in ELISA binding and competitive inhibition was with a peptide that corresponds to the 'switch peptide' of light chains. The sequence is encoded by the C-terminal region of the J segment (Fr4) and the N-terminus of the C region. Other regions reactive with anti-light chain sera corresponded respectively to CDR1 and Fr3 segments of the V region, and a segment of the constant region predicted to loop out of the tight globular structure. The peptide immunochemical results, coupled with the identification of specific regions of sequence correspondence between TCR beta and the characterized lambda light chain Mcg, allowed us to develop a three-dimensional model of the beta chain consistent with its role in antigen recognition and response to superantigens.     

Control of a Thermoelectric Brain Cooler by Adaptive Neuro-Fuzzy Inference System

Abstract

In this study, neuro-fuzzy control of a thermoelectric head cooler system (thermoelectric helmet) is developed for brain hypothermia applications. Hypothermia is a medical treatment method of protecting the brain, in which the temperature of the brain drops below the critical level for reducing oxygen consumption of tissues. The brain should be kept at a certain temperature by a suitable control for hypothermia applications. The temperature of the thermoelectric head cooler system changes according to the current intensity supplied. The control of the thermoelectric head cooler system was performed according to the initial membership functions, which was determined by an expert using fuzzy logic control. The system was modeled by an adaptive neuro-fuzzy inference system (ANFIS). The data were then entered into the system and new membership functions were determined. By this way, learning ability of the artificial neural network and the abilities of fuzzy logic, such as decision making, were combined and a more effective solution was developed. The system software can be reprogrammed with the new membership functions.     

Application of kriging method to structural reliability problems

Approximation methods are widely used to alleviate the computational burden of engineering analyses. For structural reliability analyses, the common approach is to use the response surface method (RSM) based on the least square regression. However, another approximation method based on kriging has gained popularity especially in the field of deterministic optimization. However, the application of the kriging method to structural reliability problems has not been realized until recently. Therefore, this paper investigates the use of the kriging method for structural reliability problems by comparing it with the most common RSM. The effects of the kriging parameters are also examined on the basis of the β computation and fitting behavior. It can be deduced from the results given in this paper that using the most common approach in the literature to find the kriging parameters does not guarantee a good result for the structural reliability problems. As a result, some advantages as well as disadvantages of the kriging method are reported, based on the results obtained from the application of the kriging method to the examples from the literature. Finally, this paper suggests the points for which the kriging model could be improved to get better results for structural reliability problems.     

A response surface method based on weighted regression for structural reliability analysis

Approximation methods such as the response surface method (RSM) are widely used to alleviate the computational burden of engineering analyses. For reliability analysis, the common approach in the RSM is to use regression methods based on least square methods. However, for structural reliability problems, RSMs should approximate the performance function around the design point where its value is close to zero. Therefore, in this study, a new response surface called ADAPRES is proposed, in which a weighted regression method is applied in place of normal regression. The experimental points are also selected from the region where the design point is most likely to exist. Examples are given to demonstrate the benefit of the proposed method for both numerical and implicit performance functions.