Case Study in Digital Simulation

This paper presents a study of numerical methods for the simulation of continuous systems described by n— order differential equations. The methods are applied to a wide spectrum of problems with the emphasis being on the practical rather than the theoretical results. The paper is directed toward the reader who is interested in comparative results of the application of various methods rather than derivations which can be found in a number of available texts. The methods considered are Euler, modified Euler, classical Runge-Kutta, Milne\u27s fourth-order predictor-corrector, Hamming\u27s fourth-order predictor-corrector, a second-order predictorcorrector, Adams-Moulton, state variable, 2 transform, and 2 form. The methods are compared with respect to accuracy, computational efficiency, convenience of application and ease of programming. The results of this case study should be helpful to the practicing engineer in selecting an appropriate digital simulation technique for his particular application

Quantum Smoluchowski equation: Escape from a metastable state

We develop a quantum Smoluchowski equation in terms of a true probability distribution function to describe quantum Brownian motion in configuration space in large friction limit at arbitrary temperature and derive the rate of barrier crossing and tunneling within an unified scheme. The present treatment is independent of path integral formalism and is based on canonical quantization procedure.Comment: 10 pages, To appear in the Proceedings of Statphys - Kolkata I

Porcine Head Response to Blast

Recent studies have shown an increase in the frequency of traumatic brain injuries related to blast exposure. However, the mechanisms that cause blast neurotrauma are unknown. Blast neurotrauma research using computational models has been one method to elucidate that response of the brain in blast, and to identify possible mechanical correlates of injury. However, model validation against experimental data is required to ensure that the model output is representative of in vivo biomechanical response. This study exposes porcine subjects to primary blast overpressures generated using a compressed-gas shock tube. Shock tube blasts were directed to the unprotected head of each animal while the lungs and thorax were protected using ballistic protective vests similar to those employed in theater. The test conditions ranged from 110 to 740 kPa peak incident overpressure with scaled durations from 1.3 to 6.9 ms and correspond approximately with a 50% injury risk for brain bleeding and apnea in a ferret model scaled to porcine exposure. Instrumentation was placed on the porcine head to measure bulk acceleration, pressure at the surface of the head, and pressure inside the cranial cavity. Immediately after the blast, 5 of the 20 animals tested were apneic. Three subjects recovered without intervention within 30 s and the remaining two recovered within 8 min following respiratory assistance and administration of the respiratory stimulant doxapram. Gross examination of the brain revealed no indication of bleeding. Intracranial pressures ranged from 80 to 390 kPa as a result of the blast and were notably lower than the shock tube reflected pressures of 300–2830 kPa, indicating pressure attenuation by the skull up to a factor of 8.4. Peak head accelerations were measured from 385 to 3845 G’s and were well correlated with peak incident overpressure (R2 = 0.90). One SD corridors for the surface pressure, intracranial pressure (ICP), and head acceleration are presented to provide experimental data for computer model validation

Recruitment of mud clam Polymesoda erosa (Solander, 1876) in a mangrove habitat of Chorao island, Goa

Habitat-specific settlement success results either from active habitat selection or differential mortality after non-selective settlement. The mud clam Polymesoda erosa (Solander, 1876) is an ecologically and economically important benthic invertebrate with high abundance in the mangrove forests of Chorao Island, Goa, India. A one-year study (Jul 2004-Jul 2005) was conducted to characterize the patterns of post-larval settlement and survival of P. erosa in the mangrove habitat. The mean density of settling post-larvae was 28 no.m-2 with a majority of settlers during Sept 04. The density of adult clams in the landward zone ranged from 7-12 no.m-2 (mean: 9 ± 6 sd; n=122). In the seaward region, adults were completely absent at the low tide level. Higher densities of juveniles observed at the low- and mid-tide levels were assumed to be due to frequent inundation which allowed the young individuals to feed adequately and attain the critical sizes at which vulnerability to physical and biological constraints is substantially reduced, whereas, at high-tide level, increased desiccation may account for the mortality of settlers. It is speculated that initially the settlers settle according to the hydrodynamic conditions for sedimentation; however, adult survival is affected by their recruitment in a suitable habitat (e.g. substrates near Avicennia sp.). Thus, habitat dependent viability during the post-settlement phase could be the best explanation for the non-random, patchy distribution of P. erosa observed in the Chorao mangrove swamp.Um assentamento larval bem sucedido resulta da seleção ativa do habitat pelas larvas ou da mortalidade diferencial destas após o assentamento não seletivo. Nos manguezais da ilha Chorao, Goa, India, a ostra do lodo Polymesoda erosa (Solander, 1876) é um invertebrado muito abundante e de importância econômica. O presente trabalho, realizado durante um ano (julho de 2004 a julho de 2005), visou caracterizar os padrões de assentamento pós-larval e a sobrevivência de P. erosa no ambiente do mangue. Os resultados mostraram que a densidade de larvas pós-assentadas foi de 28 indiv.m-2, com a maioria dos assentamentos ocorrendo em setembro de 2004. A densidade de adultos fixados no lado terrestre variou de 7 a 12 indiv.m-2 (média: 9 ± 6 dp; n = 122). Na região voltada ao mar, os adultos estiveram ausentes no nível da maré baixa. As altas densidades de juvenis observadas nos níveis de maré baixa e média estão provavelmente relacionadas à inundação frequente da área, o que permite aos indivíduos jovens alimentarem-se adequadamente e atingirem os tamanhos críticos em que a vulnerabilidade aos estresses físicos e biológicos são substancialmente reduzidos. Além disso, na maré alta, o aumento da dissecação pode favorecer a mortalidade dos indivíduos recém-assentados. É lançada a hipótese de que o assentamento ocorre inicialmente devido às condições hidrodinâmicas da sedimentação, mas a sobrevivência do adulto é afetada pelo recrutamento em ambiente favorável (p. ex., em substratos próximos a Avicenia sp.). Desta forma, a viabilidade do habitat durante o período pós-assentamento pode ser a melhor explicação para a distribuição não randômica, em manchas, observada para P. erosa no manguezal da ilha Chorao

Writing User-Friendly Energy Audit Reports

Energy audits don't save money and energy for companies unless the recommendations are implemented. Audit reports should be designed to encourage implementation, but often they impede it instead. In this paper, the authors discuss their experience with writing industrial energy audit reports and suggest some ways to make the reports more user-friendly. The goal in writing an audit report should not be the report itself; rather, it should be to achieve implementation of the report recommendations and thus achieve increased energy efficiency and energy cost savings for the customer