Real-time radioscopy (RTR) of solid rocket motors has revealed information about the propellant burning and cracking. This theoretical study evaluated the viability of real-time radioscopy for measuring propellant cra...
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Real-time radioscopy (RTR) of solid rocket motors has revealed information about the propellant burning and cracking. This theoretical study evaluated the viability of real-time radioscopy for measuring propellant crack propagation speed. The scope included the quantitative interpretation of crack tip velocity from simulated radiographic images of a burning, center-perforated motor. The simplified motor simulation portrayed a bore crack that moved radially at a speed that was 10 times the propellant burning rate. Comparing the image interpretation with the simulation input quantified the accuracy of the crack velocity measurement under favorable, first-order assumptions. The simulation included the effects of system configuration, finite spatial resolution (from video pixels), and (8-bit) intensity digitization. The image digitization and interpretation introduced a +/-20% measurement uncertainty in the crack tip speed for the nominal condition. A +/-10% uncertainty resulted from doubling the camera gain. Using curve-fitting techniques, the result was a constant 2% bias in the crack tip velocity measurement. This best case analysis shows that RTR has the potential for making acceptable measurements under the conditions studied.
An analytical method is proposed for finding numerical values of binary interaction coefficients for the Lee-Kesler-Plocker (LKP) equation of state. The method is based on solving simultaneous equations from Plocker&#...
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An analytical method is proposed for finding numerical values of binary interaction coefficients for the Lee-Kesler-Plocker (LKP) equation of state. The method is based on solving simultaneous equations from Plocker's mixing rules for pseudocritical parameters of a mixture and the Lee-Kesler equation for the saturation line. For mixtures of hydrocarbons containing from two to nine carbon atoms, the divergence between calculated and experimentally based interaction coefficients (ICs) is no more than +/-0.4%. The method is extended to mixtures of polar substances. For polar mixtures, an effective molar composition concept is introduced which takes into account the impact of dipole moments on the process of molecular associations. Formulas for finding the effective molar composition of mixtures containing polar and/or nonpolar constituents and the binary interaction coefficient (kappa(ij)) based on this effective composition and pure component properties are shown. Calculated kappa(ij) values for 12 binary mixtures of polar substances differ by 0.4% or less from corresponding kappa(ij) values obtained by processing experimental data on saturated pressure (P-s) and saturated temperature (T-s) lines for these same mixtures. A simplified alternative kappa(ij) approximation method with an error (2-5%) is also given for mixtures of polar substances.
An automatic algorithm based on inter-residue contacts is presented to identify domains in proteins. The results of the algorithm are compared to an assignment performed by inspection that was guided by the authors...
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An automatic algorithm based on inter-residue contacts is presented to identify domains in proteins. The results of the algorithm are compared to an assignment performed by inspection that was guided by the authors' description in the literature. The authors) and the algorithm's assignments for a chain were considered to agree if the same number of domains were identified and if the assignments were the same for at least 95% of the residues. With this criterion, the algorithm agreed with the authors' assignment for 78% of the 284 non-redundant chains considered, When some of the authors' assignments were re-evaluated based on the results of the algorithm, an agreement of 84% was obtained. The algorithm is therefore a useful tool for data validation in domain assignment. The authors assignments of domains were analysed for structural principles of domains. The number of chains forming one, two, three, four and five domains are 197, 67, 13, 6 and 1 respectively. Most domains in multidomain proteins are formed from continuous segments and adopt the same structural class. Distributions of the number of residues and the ellipticity of domains and chains are presented. The relationship between accessible surface area and molecular weight for domains and chains is examined.
A method is studied that allows the autonomous formation of a ring of satellites. The method uses information of the intersatellite spacing to generate low-thrust radial and transverse control accelerations. Using the...
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A method is studied that allows the autonomous formation of a ring of satellites. The method uses information of the intersatellite spacing to generate low-thrust radial and transverse control accelerations. Using the concept of potential functions, the uniform ring is seen as a minimum energy configuration of the system. The control accelerations ensure that the potential function of the entire system monotonically decreases so that this minimum energy configuration is achieved from any initial configuration. It is believed that such autonomous methods may provide significant operational advantages for future multisatellite rings for global point-to-point communications. (AIAA)
Realizing wider use of ceramic matrix composites requires the development of advanced structural analysis technologies. This article focuses on the use of interactive reliability models to predict component probabilit...
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Realizing wider use of ceramic matrix composites requires the development of advanced structural analysis technologies. This article focuses on the use of interactive reliability models to predict component probability of failure. The deterministic Willam-Warnke failure criterion is the theoretical basis for the reliability model presented herein. The model has been incorporated into a test-bed software program. This computer program is coupled to a general-purpose finite element program. A simple structural problem is presented to illustrate the reliability model and the computer algorithm.
In this paper, the control design problem of linear discrete-time uncertain systems with time-varying uncertainties is considered. A computer algorithm is developed to find the controller gains that asymptotically sta...
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In this paper, the control design problem of linear discrete-time uncertain systems with time-varying uncertainties is considered. A computer algorithm is developed to find the controller gains that asymptotically stabilize the uncertain systems. The stabilization scheme is based on the constructive use of Lyapunov theory. The theoretical results are applied to different examples.
This paper reports on the development of new linearized AC load flow models based on a novel approach. The load flow models have been developed based on the principle of linearizing nonlinear power flow equations arou...
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This paper reports on the development of new linearized AC load flow models based on a novel approach. The load flow models have been developed based on the principle of linearizing nonlinear power flow equations around complete operating range by minimizing the square and integral square errors. The new methods involve the direct solution of linear simultaneous power flow equations and thus are non-iterative in nature. The performance of the proposed linearized models have been tested on IEEE 14-bus and IEEE 30-bus systems and an 89-bus Indian system for analysing both a base case and contingency cases. Their results are compared with the exact load flow and some of the existing approximate load flow solutions. The proposed linearized load flow models are found to be extremely fast and much more accurate, especially for voltage magnitude prediction, than other existing linearized and approximate models. It is envisaged that the new models have great potential for on-line applications in power system studies and contingency simulation for voltage security evaluation.
Acute myocardial infarction results from the cessation of myocardial blood flow caused by thrombotic occlusion of a coronary artery. Rapid restoration of blood flow to the ischemic myocardium minimizes cardiac damage ...
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Acute myocardial infarction results from the cessation of myocardial blood flow caused by thrombotic occlusion of a coronary artery. Rapid restoration of blood flow to the ischemic myocardium minimizes cardiac damage and improves early and long-term morbidity and mortality. Chest pain is the first symptom of myocardial infarction, but in some patients with silent ischemia, the disease can be diagnosed only in retrospect. In symptomatic patients, myocardial infarction should be accurately and promptly diagnosed so that reperfusion therapy can begin immediately. Electrocardiography is the simplest diagnostic modality. Although regional ST-segment elevation is specific, it is not sensitive. In contrast, new computerized algorithms for electrocardiographic analysis and serial monitoring increase sensitivity without decreasing specificity. In the emergency room, echocardiography is used to diagnose patients with no prior history of coronary artery disease whose electrocardiograms proved nondiagnostic. Time-consuming perfusion nuclear studies are inferior to echocardiography but may nevertheless enable physicians to diagnose myocardial infarction in the emergency room. Although the presence of excess creatine kinase is a sign of myocardial necrosis, its increase is delayed for a few hours after coronary occlusion. Doctors can diagnose myocardial infarction as early as two hours after coronary occlusion with the help of simpler automatic assays of MB-creatine kinase mass that use monoclonal antibodies. Other investigational markers of myocardial necrosis include myoglobin and troponin. Elevation of a circulating protein marker also signifies established necrosis, but physicians hope to achieve reperfusion through therapy before irreversible damage occurs.
The automatic identification of moths associated with a given function is an important challenge for molecular sequence analysis. A method is presented for the extraction of such patterns from large sets of unaligned ...
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The automatic identification of moths associated with a given function is an important challenge for molecular sequence analysis. A method is presented for the extraction of such patterns from large sets of unaligned sequences with related but general function, for example, a set of heat shock proteins. In such a set of proteins there can often be several subfamilies each characterized by one or more distinct moths. The aim is to develop computational tools to identify these moths. The algorithm presented locates high frequency words of length k with a given number of positions, r, fixed. statistics for a binomial distribution are used to assess the significance of the words. The high-frequency words are clustered and highly populated clusters retained. The composition of the clusters is displayed graphically. A set of moths associated with the sequence family can automatically be extracted. The method is benchmarked on a set of 106 heat shock sequences and a set of 257 toxin sequences. It is shown to recover previously identified motifs.
The problem of protein structure prediction is formulated here as that of evaluating how well an amino acid sequence fits a hypothetical structure. The simplest and most complicated approaches, secondary structure pre...
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The problem of protein structure prediction is formulated here as that of evaluating how well an amino acid sequence fits a hypothetical structure. The simplest and most complicated approaches, secondary structure prediction and all-atom free energy calculations, can be viewed as sequence-structure fitness problems. Here, an approach of intermediate complexity is described, which involves; (1) description of a protein structure in terms of contact interface vectors, with both intra-protein and protein-solvent contacts counted, (2) derivation of sequence preferences for 2 up to 29 contact interface types, (3) generation of numerous hypothetical model structures by placing the input sequence into a large set of known three-dimensional structures in all possible alignments, (4) evaluation of these models by summing the sequence preferences over all structural positions and (5) choice of predicted three-dimensional structure as that with the best sequence-structure fitness. Evolutionary information is incorporated by using position-dependent core weights derived from multiple sequence alignments. A number of tests of the method are performed: (1) evaluation of cyclic shifts of a sequence in its native structure; (2) alignment of a sequence in its native structure, allowing gaps; (3) alignment search with a sequence or sequence fragment in a database of structures; and (4) alignment search with a structure in a database of sequences. The main results are: (1) a native sequence can very well find its native structure among a large number of alternatives, in correct alignment; (2) substructures, such as (βα)n units, can be detected in spite of very low sequence similarity; (3) remote homologues can be detected, with some dependence on the set of parameters used; (4) contact interface parameters are clearly superior to classical secondary structure parameters; (5) a simple interface description in terms of just two states, protein-protein and protein-water contac
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