Random vibration analysis of space flight hardware using NASTRAN

During liftoff and ascent flight phases, the Space Transportation System (STS) and payloads are exposed to the random acoustic environment produced by engine exhaust plumes and aerodynamic disturbances. The analysis of payloads for randomly fluctuating loads is usually carried out using the Miles' relationship. This approximation technique computes an equivalent load factor as a function of the natural frequency of the structure, the power spectral density of the excitation, and the magnification factor at resonance. Due to the assumptions inherent in Miles' equation, random load factors are often over-estimated by this approach. In such cases, the estimates can be refined using alternate techniques such as time domain simulations or frequency domain spectral analysis. Described here is the use of NASTRAN to compute more realistic random load factors through spectral analysis. The procedure is illustrated using Spacelab Life Sciences (SLS-1) payloads and certain unique features of this problem are described. The solutions are compared with Miles' results in order to establish trends at over or under prediction

Transient loads analysis for space flight applications

A significant part of the flight readiness verification process involves transient analysis of the coupled Shuttle-payload system to determine the low frequency transient loads. This paper describes a methodology for transient loads analysis and its implementation for the Spacelab Life Sciences Mission. The analysis is carried out using two major software tools - NASTRAN and an external FORTRAN code called EZTRAN. This approach is adopted to overcome some of the limitations of NASTRAN's standard transient analysis capabilities. The method uses Data Recovery Matrices (DRM) to improve computational efficiency. The mode acceleration method is fully implemented in the DRM formulation to recover accurate displacements, stresses, and forces. The advantages of the method are demonstrated through a numerical example

Study of malaria in febrile patients attending tertiary health care center and evaluation of peripheral smear examination, quantitative buffy coat and rapid diagnostic test in the diagnosis of malaria

Background: The objective was to study the prevalence of malaria in febrile patients attending the hospital and to evaluate peripheral smear examination, quantitative buffy coat and rapid diagnostic test in the diagnosis of malaria.Methods: The study group includes 208 patients presenting with fever with chills and rigor and other suggestive symptoms of malaria attending the tertiary care center. 5 ml of venous blood was collected in ethylene diamine tetra acetate (EDTA) tube from each patient and the samples were processed for peripheral blood smear examination, quantitative buffy coat (QBC) and antigen detection by rapid diagnostic test (RDT).Results: Out of 208 suspected cases of malaria, 3 (1.44%) were positive for malaria and 205 (98.55%) were negative, the prevalence of malaria was found to be 1.44%. Of total 208 cases tested, 3 cases (1.44%) were positive for malaria by peripheral blood smear examination and by QBC and with rapid diagnostic test only 2 cases (0.96%) were positive. P. vivax was detected in all 3 positive cases.Conclusions: Peripheral smear examination is considered as gold standard method for diagnosis of malaria. QBC can be helpful when an experienced microscopist is not available. Rapid diagnostic tests are simple, rapid, do not need expertise, interpretation of results is easy and objective and useful in routine diagnosis.

Analyzing the effects of surface distribution of pores in cell electroporation for a cell membrane containing cholesterol

This paper presents a model and numerical analysis (simulations) of transmembrane potential induced in biological cell membrane under the influence of externally applied electric field (i.e., electroporation). This model differs from the established models of electroporation in two distinct ways. Firstly, it incorporates the presence of cholesterol (~20% mole-fraction) in biological membrane. Secondly, it considers the distribution of pores as a function of the variation of transmembrane potential from one region of the cell to another. Formulation is based on the role of membrane tension and electrical forces in the formation of pores in a cell membrane, which is considered as an infinitesimally thin insulator. The model has been used to explore the process of creation and evolution of pores and to determine the number and size of pores as a function of applied electric field (magnitude and duration). Results show that the presence of cholesterol enhances poration by changing the membrane tension. Analyses indicate that the number of pores and average pore radii differ significantly from one part of the cell to the other. While some regions of the cell membrane undergo rapid and dense poration, others remain unaffected. The method can be a useful tool for a more realistic prediction of pore formation in cells subjected to electroporation.Comment: 11 pages, 3 figures. v2: added new references, grammatical changes, corrected typo

Information Processing view of Electricity Demand Response Systems: A Comparative Study Between India and Australia

Background: In recent years, demand response (DR) has gained increased attention from utilities, regulators, and market aggregators to meet the growing demands of electricity. The key aspect of a successful DR program is the effective processing of data and information to gain critical insights. This study aims to identify information processing needs and capacity that interact to improve energy DR effectiveness. To this end, organizational information processing theory (OIPT) is employed to understand the role of Information Systems (IS) resources in achieving desired DR program performance. This study also investigates how information processing for DR systems differ between developing (India) and developed (Australia) countries. Method: This work adopts a case study methodology to propose a theoretical framework using OIPT for information processing in DR systems. The study further employs a comparative case data analyses between Australian and Indian DR initiatives. Results: Our cross case analysis identifies variables of value creation in designing DR programs - pricing structure for demand side participation, renewable integration at supply side, reforms in the regulatory instruments, and emergent technology. This research posits that the degree of information processing capacity mediates the influence of information processing needs on energy DR effectiveness. Further, we develop five propositions on the interaction between task based information processing needs and capacity, and their influence on DR effectiveness. Conclusions: The study generates insights on the role of IS resources that can help stakeholders in the electricity value chain to take informed and intelligent decisions for improved performance of DR programs

Stochastic modeling of discontinuous dynamic recrystallization at finite strains in hcp metals

We present a model that aims to describe the effective, macroscale material response as well as the underlying mesoscale processes during discontinuous dynamic recrystallization under severe plastic deformation. Broadly, the model brings together two well-established but distinct approaches – first, a continuum crystal plasticity and twinning approach to describe complex deformation in the various grains, and second, a discrete Monte-Carlo-Potts approach to describe grain boundary migration and nucleation. The model is implemented within a finite-strain Fast Fourier Transform-based framework that allows for efficient simulations of recrystallization at high spatial resolution, while the grid-based Fourier treatment lends itself naturally to the Monte-Carlo approach. The model is applied to pure magnesium as a representative hexagonal closed packed metal, but is sufficiently general to admit extension to other material systems. Results demonstrate the evolution of the grain architecture in representative volume elements and the associated stress–strain history during the severe simple shear deformation typical of equal channel angular extrusion. We confirm that the recrystallization kinetics converge with increasing grid resolution and that the resulting model captures the experimentally observed transition from single- to multi-peak stress–strain behavior as a function of temperature and rate