UNT Libraries Government Documents Department - 64 Matching Results

Search Results

Modeling the Reactions of Energetic Materials in the Condensed Phase

Description: High explosive (HE) materials are unique for having a strong exothermic reactivity, which has made them desirable for both military and commercial applications. Although the history of HE materials is long, condensed-phase properties are poorly understood. Understanding the condensed-phase properties of HE materials is important for determining stability and performance. Information regarding HE material properties (for example, the physical, chemical, and mechanical behaviors of the constituents in plastic-bonded explosive, or PBX, formulations) is necessary in efficiently building the next generation of explosives as the quest for more powerful energetic materials (in terms of energy per volume) moves forward. In addition, understanding the reaction mechanisms has important ramifications in disposing of such materials safely and cheaply, as there exist vast stockpiles of HE materials with corresponding contamination of earth and groundwater at these sites, as well as a military testing sites The ability to model chemical reaction processes in condensed phase energetic materials is rapidly progressing. Chemical equilibrium modeling is a mature technique with some limitations. Progress in this area continues, but is hampered by a lack of knowledge of condensed phase reaction mechanisms and rates. Atomistic modeling is much more computationally intensive, and is currently limited to very short time scales. Nonetheless, this methodology promises to yield the first reliable insights into the condensed phase processes responsible for high explosive detonation. Further work is necessary to extend the timescales involved in atomistic simulations. Recent work in implementing thermostat methods appropriate to shocks may promise to overcome some of these difficulties. Most current work on energetic material reactivity assumes that electronically adiabatic processes dominate. The role of excited states is becoming clearer, however. These states are not accessible in perfect crystals under realistic pressures and temperatures, but may still be accessed through defects or other energy localization mechanisms.
Date: December 3, 2003
Creator: Fried, L. E.; Manaa, M. R. & Lewis, J. P.

DETECTION OF TOPOLOGICAL PATTERNS IN PROTEIN NETWORKS.

Description: Complex networks appear in biology on many different levels: (1) All biochemical reactions taking place in a single cell constitute its metabolic network, where nodes are individual metabolites, and edges are metabolic reactions converting them to each other. (2) Virtually every one of these reactions is catalyzed by an enzyme and the specificity of this catalytic function is ensured by the key and lock principle of its physical interaction with the substrate. Often the functional enzyme is formed by several mutually interacting proteins. Thus the structure of the metabolic network is shaped by the network of physical interactions of cell's proteins with their substrates and each other. (3) The abundance and the level of activity of each of the proteins in the physical interaction network in turn is controlled by the regulatory network of the cell. Such regulatory network includes all of the multiple mechanisms in which proteins in the cell control each other including transcriptional and translational regulation, regulation of mRNA editing and its transport out of the nucleus, specific targeting of individual proteins for degradation, modification of their activity e.g. by phosphorylation/dephosphorylation or allosteric regulation, etc. To get some idea about the complexity and interconnectedness of protein-protein regulations in baker's yeast Saccharomyces Cerevisiae in Fig. 1 we show a part of the regulatory network corresponding to positive or negative regulations that regulatory proteins exert on each other. (4) On yet higher level individual cells of a multicellular organism exchange signals with each other. This gives rise to several new networks such as e.g. nervous, hormonal, and immune systems of animals. The intercellular signaling network stages the development of a multicellular organism from the fertilized egg. (5) Finally, on the grandest scale, the interactions between individual species in ecosystems determine their food webs. An interesting property of many biological ...
Date: November 17, 2003
Creator: MASLOV,S. SNEPPEN,K.

LARGE-SCALE TOPOLOGICAL PROPERTIES OF MOLECULAR NETWORKS.

Description: Bio-molecular networks lack the top-down design. Instead, selective forces of biological evolution shape them from raw material provided by random events such as gene duplications and single gene mutations. As a result individual connections in these networks are characterized by a large degree of randomness. One may wonder which connectivity patterns are indeed random, while which arose due to the network growth, evolution, and/or its fundamental design principles and limitations? Here we introduce a general method allowing one to construct a random null-model version of a given network while preserving the desired set of its low-level topological features, such as, e.g., the number of neighbors of individual nodes, the average level of modularity, preferential connections between particular groups of nodes, etc. Such a null-model network can then be used to detect and quantify the non-random topological patterns present in large networks. In particular, we measured correlations between degrees of interacting nodes in protein interaction and regulatory networks in yeast. It was found that in both these networks, links between highly connected proteins are systematically suppressed. This effect decreases the likelihood of cross-talk between different functional modules of the cell, and increases the overall robustness of a network by localizing effects of deleterious perturbations. It also teaches us about the overall computational architecture of such networks and points at the origin of large differences in the number of neighbors of individual nodes.
Date: November 17, 2003
Creator: MASLOV,S. SNEPPEN,K.

Statistical Modeling of Large-Scale Scientific Simulation Data

Description: With the advent of massively parallel computer systems, scientists are now able to simulate complex phenomena (e.g., explosions of a stars). Such scientific simulations typically generate large-scale data sets over the spatio-temporal space. Unfortunately, the sheer sizes of the generated data sets make efficient exploration of them impossible. Constructing queriable statistical models is an essential step in helping scientists glean new insight from their computer simulations. We define queriable statistical models to be descriptive statistics that (1) summarize and describe the data within a user-defined modeling error, and (2) are able to answer complex range-based queries over the spatiotemporal dimensions. In this chapter, we describe systems that build queriable statistical models for large-scale scientific simulation data sets. In particular, we present our Ad-hoc Queries for Simulation (AQSim) infrastructure, which reduces the data storage requirements and query access times by (1) creating and storing queriable statistical models of the data at multiple resolutions, and (2) evaluating queries on these models of the data instead of the entire data set. Within AQSim, we focus on three simple but effective statistical modeling techniques. AQSim's first modeling technique (called univariate mean modeler) computes the ''true'' (unbiased) mean of systematic partitions of the data. AQSim's second statistical modeling technique (called univariate goodness-of-fit modeler) uses the Andersen-Darling goodness-of-fit method on systematic partitions of the data. Finally, AQSim's third statistical modeling technique (called multivariate clusterer) utilizes the cosine similarity measure to cluster the data into similar groups. Our experimental evaluations on several scientific simulation data sets illustrate the value of using these statistical models on large-scale simulation data sets.
Date: November 15, 2003
Creator: Eliassi-Rad, T.; Baldwin, C.; Abdulla, G. & Critchlow, T.

Improving Compressed Air System Performance: A Sourcebook for Industry

Description: NREL will produce this sourcebook for DOE's Industrial Technologies Office as part of a series of documents on industrial energy equipment. The sourcebook is a reference for industrial compressed air system users, outlining opportunities to improve system efficiency.
Date: November 1, 2003

Radiation Hydrodynamics

Description: The discipline of radiation hydrodynamics is the branch of hydrodynamics in which the moving fluid absorbs and emits electromagnetic radiation, and in so doing modifies its dynamical behavior. That is, the net gain or loss of energy by parcels of the fluid material through absorption or emission of radiation are sufficient to change the pressure of the material, and therefore change its motion; alternatively, the net momentum exchange between radiation and matter may alter the motion of the matter directly. Ignoring the radiation contributions to energy and momentum will give a wrong prediction of the hydrodynamic motion when the correct description is radiation hydrodynamics. Of course, there are circumstances when a large quantity of radiation is present, yet can be ignored without causing the model to be in error. This happens when radiation from an exterior source streams through the problem, but the latter is so transparent that the energy and momentum coupling is negligible. Everything we say about radiation hydrodynamics applies equally well to neutrinos and photons (apart from the Einstein relations, specific to bosons), but in almost every area of astrophysics neutrino hydrodynamics is ignored, simply because the systems are exceedingly transparent to neutrinos, even though the energy flux in neutrinos may be substantial. Another place where we can do ''radiation hydrodynamics'' without using any sophisticated theory is deep within stars or other bodies, where the material is so opaque to the radiation that the mean free path of photons is entirely negligible compared with the size of the system, the distance over which any fluid quantity varies, and so on. In this case we can suppose that the radiation is in equilibrium with the matter locally, and its energy, pressure and momentum can be lumped in with those of the rest of the fluid. That is, it ...
Date: October 16, 2003
Creator: Castor, J. I.

Geothermal Today: 2003 Geothermal Technologies Program Highlights (Covers Highlights from 2002)

Description: This outreach publication highlights milestones and accomplishments of the DOE Geothermal Technologies Program for 2002. Included in this publication are discussions of geothermal fundamentals, enhanced geothermal systems, direct-use applications, geothermal potential in Idaho, coating technology, energy conversion R&D, and the GeoPowering the West initiative.
Date: September 1, 2003

A History of the Fitzner/Eberhardt Arid Lands Ecology Reserve: Four Decades of Environmental Research

Description: This book describes the history of the Fitzner/Eberhardt Arid Lands Ecology Reserve. It briefly describes the setting; outlines historical land uses of the Reserve; describes its establishments and designations; and provides examples of the types of research and education projects PNNL conducted on the Reserve for over four decades. A comprehensive bibliography also is provided.
Date: September 1, 2003
Creator: O'Connor, Georganne P.; Rickard, William H.; Kennedy, Ellen P.; Dirkes, Roger L. & Feaster-Alley, Kathy

13th Workshop on Crystalline Silicon Solar Cell Materials and Processes: Extended Abstracts and Papers

Description: The 13th Workshop will provide a forum for an informal exchange of technical and scientific information between international researchers in the photovoltaic and relevant non-photovoltaic fields. It will offer an excellent opportunity for researchers in private industry and at universities to prioritize mutual needs for future collaborative research. The workshop is intended to address the fundamental aspects of impurities and defects in silicon: their properties, the dynamics during device processing, and their application for developing low-cost processes for manufacturing high-efficiency silicon solar cells. A combination of oral, poster, and discussion sessions will review recent advances in crystal growth, new cell structures, new processes and process characterization techniques, and cell fabrication approaches suitable for future manufacturing demands.
Date: August 1, 2003
Creator: Sopori, B. L.; Rand, J.; Saitoh, T.; Sinton, R.; Stavola, M.; Swanson, D. et al.