The computation of Pareto-optimal set in multicriterial optimization of rapid prototyping processes

The purpose of this research is the multicriterial optimization of rapid prototyping processes. The mathematical model of the optimization problem takes into consideration as optimization criteria, surface quality of the prototype and the time of manufacturing. Based on the mathematical model, a practical method to find the Pareto-optimal set is developed, as a main goal. To solve the optimization problem, a computer program for rapid prototyping processes simulation was designed. The program calculates the geometry of successive layers, as well as the necessary time for their materialization. Depending on the importance degree of each optimization criterion, the program offers the optimal solution. In addition, when it is necessary, the program allows the user intervention in solving the problem optimization.The theoretical concepts presented in this research are very suggestively illustrated on a comprehensive case study. Starting from the Pareto-optimal set diagrams for the cases of LOM and SLS technologies, the optimal solutions are graphically illustrated in a very suggestive manner.     

Measures of localized spinal muscle fatigue

The objective of this study was to determine the best variable, if any, to indicate the level of localized muscle fatigue. Six male and six female subjects were studied while they exerted their maximal voluntary contraction and 40% of maximal voluntary contraction of spinal extensors in an isometric lifting activity. The electromyography (EMG) of erectores spinae at thoracic and lumbar levels was measured bilaterally. Also, the muscle bed blood volume, level of blood oxygenation to erector spinae at L3 level and heart rate were measured. The initial and final values of subjective feelings of fatigue through visual analogue score, rate of perceived exertions and body part discomfort rating were recorded. The mean maximal voluntary contraction forces for males and females were 899 (238) N and 431 (135) N respectively. The mean durations of hold in maximal voluntary fatiguing contraction were 68.1 (39.9) s and 72.3 (37.0) s for men and women respectively. By the end of the hold the force declined to 52% for males and 62% for females. The EMG amplitudes and median frequencies also progressively declined (p < 0.01). ANOVA revealed that the task percentile values of all variables were significantly different (p < 0.01). Gender had a significant main effect (p < 0.01). The correlation coefficients between force and other individual variables were weak to modest, but significant (p < 0.001). None of the single variables predicted fatigue reliably for either gender and levels of contraction. The regression equations developed were highly significant (p < 0.01) and they explained 96 to 98% of variance in both genders and contractions.     

Electronic image formation in high-voltage TEM by sequential pixel acquisition

We describe a complete hybrid imaging system for the electronic detection and manipulation of high-voltage TEM images. The system includes a recently incorporated two-dimensional beam deflector for dissecting the image into pixels by displacing it in a raster in front of an aperture leading to an electron detector. The characteristics of images thus formed by sequential pixel acquisition and displayed on a CRT are discussed and illustrated. Absorption or thickness profiles are also obtained by displaying the scanned pixel intensity in Y-modulation. Similarly, the displacement of an entire diffraction pattern allows the intensities of individual diffraction spots to be quantitated directly over a wide dynamic range. The direct splitting of the image into electronically controlled pixels can be applied to local mass measurements and to energy-loss analysis by means of a simple magnetic prism that can also provide energy filtering in lieu of a more elaborate electron-optical, image-preserving system.     

THE ENERGETIC STABILITY OF TORI AND SINGLE-WALL TUBES

Tessellated tori, generated here from square-like tiled lattices, are closely related to cylinders and capped tubes. This way of building them enables the orientation of their bonds, and so the geometric proportions of the torus, to be specified for molecular mechanics calculations and, along with their transformation into capped tubes this is illustrated and discussed in the light of their energetic stability.     

Promising Therapies for Atrial Fibrillation and Ventricular Tachycardia

Sudden cardiac death due to arrhythmias, such as atrial fibrillation or ventricular tachycardia, account for 15–20% of all deaths. Myocardial infarction increases the burden of atrial fibrillation and ventricular tachycardia by structural and electrical remodeling of the heart. The current management of new-onset atrial fibrillation includes electric cardioversion with very high conversion rates and pharmacologic cardioversion, with less a than 50% conversion rate. If atrial fibrillation cannot be converted, the focus becomes the control of the symptoms ensuring a constant rhythm and rate control, without considering other contributory factors such as autonomic imbalance. Recently, a huge success was obtained by developing ablation techniques or addressing the vagal nerve stimulation. On the other hand, ventricular tachycardia is more sensitive to drug therapies. However, in cases of non-responsiveness to drugs, the usual therapeutic choice is represented by stereotactic ablative therapy or catheter ablation. This review focuses on these newly developed strategies for treatment of arrhythmias in clinical practice, specifically on vernakalant and low-level tragus stimulation for atrial fibrillation and stereotactic ablative therapy for drug-refractory ventricular tachycardia. These therapies are important for the significant improvement of the management of atrial fibrillation and ventricular tachycardia, providing: (1) a safer profile than current therapies, (2) higher success rate than current solutions, (3) low cost of delivery.     

Solidification of a PEG 1500-epoxy nanocomposite around a horizontal pipe

A PCM-epoxy phase change material composite (polyethylene glycol 1500-epoxy) was developed as heat storage building element for houses with low energy consumption. The PCM component, polyethylene glycol 1500, was integrated in an epoxy matrix, and presents a phase change interval of 34-42 °C and an enthalpy of solidification of 103.411 kJ/kg. Experiments on solidification were conducted using a Plexiglas test cell filled with the PEG 1500-epoxy nanocomposite material (P15-E) for further implementation of this material in buildings. The forwarded solidification model assumes negligible convection in the liquid region and predicts the time for radial formation of two regions: a mushy-zone and a solid, annular one around the pipe during solidification. The heat transfer during solidification can be also characterized by the time evolution of both liquid and solid radial fronts. The model was analytically solved using Megerlin approximation concerning “solidification with mushy zone”, with the third order condition at the external frontier. The experimental values are in agreement with the calculated theoretical curves.     

On a simplified system for steam production in nuclear power plants with pressurized water reactors

The paper develops the idea of a new system of steam production (Simplified System for Steam Production, SSSP) in nuclear power plants (NPPs) with PWR reactors, which is simplified as compared to the system used in the classical NPP of this type where steam is produced by steam generators (SGs). With the SSSP, expanders are used instead of SGs. The particularities of a NPP with a SSSP are analyzed in comparison to the classical NPP equipped with PWR and BWR reactors, which are used almost exclusively at present to produce electric energy at the industrial level.     

Spontaneous copolymerization of 2-methyl-2-oxazoline and N-phenyl maleimide

Summary The copolymerizations of 2-methyl-2-oxazoline and N-phenyl maleimide in bulk or in solution,at 60°C or room temperature are reported. The initiation is spontaneous and is due to the formation of zwitterion by interaction of the two monomers. The copolymers are statistical,more rich in maleimide units and propagation reaction can take place both by anions and zwitterions.