Discrete element weld model, phase 2

A numerical method was developed for analyzing the tungsten inert gas (TIG) welding process. The phenomena being modeled include melting under the arc and the flow in the melt under the action of buoyancy, surface tension, and electromagnetic forces. The latter entails the calculation of the electric potential and the computation of electric current and magnetic field therefrom. Melting may occur at a single temperature or over a temperature range, and the electrical and thermal conductivities can be a function of temperature. Results of sample calculations are presented and discussed at length. A major research contribution has been the development of numerical methodology for the calculation of phase change problems in a fixed grid framework. The model has been implemented on CHAM's general purpose computer code PHOENICS. The inputs to the computer model include: geometric parameters, material properties, and weld process parameters

Is slower early growth beneficial for long-term cardiovascular health?

Background - Accelerated neonatal growth increases the later propensity to cardiovascular disease (CVD) in animals, whereas slower growth is thought to have a beneficial effect. To test this hypothesis in humans, we measured flow-mediated endothelium-dependent dilation (FMD) in a population subject to slower early growth and in healthy controls.Methods and Results - High-resolution vascular ultrasound was used to measure the change in brachial artery diameter in response to reactive hyperemia in adolescents age 13 to 16 years who were either part of a cohort born preterm and followed up prospectively (n = 216) or controls born at term ( n = 61). Greater weight gain or linear growth in the first 2 weeks postnatally was associated with lower FMD at adolescence ( regression coefficient, - 0.026-mm change in mean arterial diameter per 100-g increase in weight; 95% CI, - 0.040 to - 0.012 mm; P = 0.0003) independent of birthweight and potential confounding factors. Mean FMD in the half of the preterm population with the lowest rates of early growth was higher than in both the half with the greatest growth ( P = 0.001) and subjects born at term ( P = 0.03).Conclusions - FMD was 4% lower in adolescents with the highest compared with the lowest rate of weight gain in the first 2 weeks after birth, a substantial negative effect similar to that for insulin-dependent diabetes mellitus or smoking in adults. Our findings are consistent with the adverse effects of accelerated neonatal growth on long-term cardiovascular health and suggest that postnatal growth patterns could explain the previously reported association between birthweight and later CVD

Analysis of Metallic Shielding for Reduction of RF Induced Heating of Electrode During MRI for Active Implants

The options available to patients with implantable devices are limited. It is because there are multiple interactions between the MRI environment and the implantable medical devices. The three main components of MRI systems- static magnet, RF coil, and a gradient coil- interact with the implantable medical devices. These interactions can cause force, torque, device vibrations and RF-induced heating. Among all these potential hazards is the heating caused by the RF electromagnetic field. The lead wires of the implants can act as antennas and pick up the electric field generated by the RF coil. This results in the induced current traveling along the length of the device that will dissipate as heat where it is coupled to tissue. The combination of critically sensitive tissues and high heat makes this interaction the most significant risk for patient safety. Hence, there arises a need to design effective techniques that can minimize RF heating induced during an MRI. The technique of shielding has been proven to reduce RF-induced heating. The focus of current research is to provide analysis of shielding technique for reduction of RF-induced heating of electrodes during MRI. Shielded leads have been developed as a method to reduce RF-heating responsible for temperature rise at the electrodes. The purpose of this work is to provide a quantitative understanding of how a conducting metallic shield over a lead will reduce RF heating at the electrode during MRI scans. A physical model and equations for reduction of RF heating by a shielded lead are presented. Temperature rises are calculated for different lengths of shielded and unshielded leads. Confirming measurements are made for a quarter-wavelength coaxial cable model of the lead. Measured temperature rise and transfer function depended on terminations conditions, with the shorted lead exhibiting the temperature rise sixteen times less than an open-ended lead. The information provided by this work is expected to facilitate the development of lead wires with reduced RF-induced heating. The availability of lead wires with reduced heating will allow expanded access to MRI by patients with implantable devices

Study on the Formability & Shape Confirmity of Mg & Al-alloy sheets in Warm condition by Electromagnetic Forming

Electromagnetic forming is a high strain rate process used for shaping metals. Mg-alloys are of interest by virtue of the light weight and potential for application in automotive industries. These alloys have poor formability at room temperature and have to be formed under warm working conditions. Simulations using COMSOL Multiphysics software were carried out to predict the forming behavior of Mg-alloy sheets deformed at high speeds and different temperatures into a die with a corrugated shape. Conformance of the sheet to the die shape is the objective of this study. These sheets are assumed to be externally heated to different temperatures prior to forming. Possible changes in the mechanical and electrical properties of the material with temperature have been incorporated to show their individual and combined effects. A virtual circuit was built to excite the coil, fully coupled with the Solid Mechanics & Magnetic Fields, through related physics in the software. Optimal parameters that ensure good conformance to die shape are sought as the outcome of the simulation of warm electromagnetic forming of magnesium & aluminium alloy sheets. The quality of strain distribution under different clamping constraints was assessed using the strain non-uniformity index (SNI)

Influence of leptin on arterial distensibility - A novel link between obesity and cardiovascular disease?

Background-The mechanisms by which obesity increases the risk of atherosclerotic cardiovascular disease (CVD) are poorly understood. In experimental models, leptin, a hormone produced by adipose tissue, has been shown adversely to affect vascular health. Therefore, we tested the hypothesis that high leptin concentrations are associated with lower arterial distensibility, an index of circulatory function relevant to the atherosclerotic process.Methods and Results-Noninvasive, high-resolution, vascular ultrasound was used to measure brachial artery distensibility in 294 healthy adolescents (aged 13 to 16 years) who had a broad range of body mass indexes. Fat mass was measured by bioelectric impedance analysis; fasting serum leptin concentration by radioimmunoassay; and lipid profile, fasting insulin, glucose, and C-reactive protein concentrations by standard laboratory techniques. Higher leptin concentrations were associated with impaired arterial distensibility (regression coefficient, -1.3% change in arterial distension per 10% increase in leptin; 95% CI, -1.9% to -0.8%; P<0.001). This association was independent of fat mass, blood pressure, and C-reactive protein, fasting insulin, or LDL cholesterol concentrations.Conclusions-Elevation in leptin was associated with impaired vascular function, independent of the metabolic and inflammatory disturbances associated with obesity. Our observations are consistent with data from experimental models and suggest that high leptin concentration is an important mechanism for the adverse influence of body fatness on CVD

Antibody-mediated targeting of liposomes to red cells in vivo

Covalent attachment of anti-rat erythrocyte F(ab')2 to liposomes specifically enhanced their binding to rat erythrocytes in vivo and reduced their uptake by the liver. Furthermore, at least 20-30% of the cell-bound liposomes delivered their contents to the cells. Besides, the liposome binding did not affect the survival time of the target cells at least up to 3 h in the blood circulation. These results demonstrate for the first time that liposomes can be successfully targeted to cells other than liver cells in vivo

Cell-Free Extract Data Variability Reduction in the Presence of Structural Non-Identifiability

The bottom up design of genetic circuits to control cellular behavior is one of the central objectives within Synthetic Biology. Performing design iterations on these circuits in vivo is often a time consuming process, which has led to E. coli cell extracts to be used as simplified circuit prototyping environments. Cell extracts, however, display large batch-to-batch variability in gene expression. In this paper, we develop the theoretical groundwork for a model based calibration methodology for correcting this variability. We also look at the interaction of this methodology with the phenomenon of parameter (structural) non-identifiability, which occurs when the parameter identification inverse problem has multiple solutions. In particular, we show that under certain consistency conditions on the sets of output-indistinguishable parameters, data variability reduction can still be performed, and when the parameter sets have a certain structural feature called covariation, our methodology may be modified in a particular way to still achieve the desired variability reduction

Comparative study of performance of parallel Alpha Beta Pruning for different architectures

Optimization of searching the best possible action depending on various states like state of environment, system goal etc. has been a major area of study in computer systems. In any search algorithm, searching best possible solution from the pool of every possibility known can lead to the construction of the whole state search space popularly called as minimax algorithm. This may lead to a impractical time complexities which may not be suitable for real time searching operations. One of the practical solution for the reduction in computational time is Alpha Beta pruning. Instead of searching for the whole state space, we prune the unnecessary branches, which helps reduce the time by significant amount. This paper focuses on the various possible implementations of the Alpha Beta pruning algorithms and gives an insight of what algorithm can be used for parallelism. Various studies have been conducted on how to make Alpha Beta pruning faster. Parallelizing Alpha Beta pruning for the GPUs specific architectures like mesh(CUDA) etc. or shared memory model(OpenMP) helps in the reduction of the computational time. This paper studies the comparison between sequential and different parallel forms of Alpha Beta pruning and their respective efficiency for the chess game as an application.Comment: 5 pages, 6 figures, Accepted in 2019 IEEE 9th International Advance Computing Conference(IEEE Xplore

Infrared horizon sensor modeling for attitude determination and control: Analysis and mission experience

The work performed by the Attitude Determination and Control Section at the National Aeronautics and Space Administration/Goddard Space Flight Center in analyzing and evaluating the performance of infrared horizon sensors is presented. The results of studies performed during the 1960s are reviewed; several models for generating the Earth's infrared radiance profiles are presented; and the Horizon Radiance Modeling Utility, the software used to model the horizon sensor optics and electronics processing to computer radiance-dependent attitude errors, is briefly discussed. Also provided is mission experience from 12 spaceflight missions spanning the period from 1973 to 1984 and using a variety of horizon sensing hardware. Recommendations are presented for future directions for the infrared horizon sensing technology

POMS initiatives for promoting practice-driven research and research-influenced practice

The Production and Operations Management Society (POMS) and Production and Operations Management (POM) have developed new initiatives with these objectives: (1) to disseminate managerial insights of articles published in POM to practitioners, MBA students, and participants in executive development programs; (2) to solicit descriptions of current and emerging problems from practitioners and share them with academics; and (3) to recognize academic research based on direct work with practitioners