2,206 Matching Results

Search Results

Advanced search parameters have been applied.

Radiolysis of Organic Fluids, Annual Progress Report: October 1, 1961-September 30, 1962

Description: From introduction: This report reviews the Susie program (particularly reactor dosimetry and data analysis) as well as other items that represent a smaller share of the total effort.
Date: January 15, 1963
Creator: Bolt, R. O.; Burrous, M. L.; Carroll, J. G.; Hall, K. L.; Sweeney, M. A. & Tobriner, M. W.
Partner: UNT Libraries Government Documents Department

Ionization of Water Clusters is Mediated by Exciton Energy Transfer from Argon Clusters

Description: The exciton energy deposited in an argon cluster, (Arn ,< n=20>) using VUV radiation is transferred to softly ionize doped water clusters, ((H2O)n, n=1-9) leading to the formation of non-fragmented clusters. Following the initial excitation, electronic energy is channeled to ionize the doped water cluster while evaporating the Ar shell, allowing identification of fragmented and complete water cluster ions. Examination of the photoionization efficiency curve shows that cluster evaporation from excitons located above 12.6 eV are not enough to cool the energized water cluster ion, and leads to their dissociation to (H2O)n-2H+ (protonated) clusters.
Date: January 25, 2012
Creator: Golan, Amir & Ahmed, Musahid
Partner: UNT Libraries Government Documents Department

Conformational Studies of Myosin and Actin with Calibrated Resonance Energy Transfer

Description: Resonance energy transfer was employed to study the conformational changes of actomyosin during ATP hydrolysis. To calibrate the technique, the parameters for resonance energy transfer were defined. With conformational searching algorithms to predict probe orientation, the distances measured by resonance energy transfer are highly consistent with the atomic models, which verified the accuracy and feasibility of resonance energy transfer for structural studies of proteins and oligonucleotides. To study intramyosin distances, resonance energy transfer probes were attached to skeletal myosin's nucleotide site, subfragment-2, and regulatory light chain to examine nucleotide analog-induced structural transitions. The distances between the three positions were measured in the presence of different nucleotide analogs. No distance change was considered to be statistically significant. The measured distance between the regulatory light chain and nucleotide site was consistent with either the atomic model of skeletal myosin subfragment-1 or an average of the three models claimed for different ATP hydrolysis states, which suggested that the neck region was flexible in solution. To examine the participation of actin in the powerstroke process, resonance energy transfer between different sites on actin and myosin was measured in the presence of nucleotide analogs. The efficiencies of energy transfer between myosin catalytic domain and actin were consistent with the actoS1 docking model. However, the neck region was much closer to the actin filament than predicted by static atomic models. The efficiency of energy transfer between Cys 374 and the regulatory light chain was much greater in the presence of ADP-AlF4, ADP-BeFx, and ADP-vanadate than in the presence of ADP or no nucleotide. These data detect profound differences in the conformations of the weakly and strongly attached crossbridges which appear to result from a conformational selection that occurs during the weak binding of the myosin head to actin. The resonance energy transfer data exclude a number ...
Access: This item is restricted to UNT Community Members. Login required if off-campus.
Date: May 2000
Creator: Xu, Jin
Partner: UNT Libraries

Hindrance of the Myosin Power Stroke Posed by the Proximity to the Troponin Complex Identified Using a Novel LRET Fluorescent Nanocircuit

Description: A novel luminescence resonance energy transfer (LRET) nanocircuit assay involving a donor and two acceptors in tandem was developed to study the dynamic interaction of skeletal muscle contraction proteins. The donor transmits energy relayed to the acceptors distinguishing myosin subfragment-1 (S1) lever arm orientations. The last acceptor allows the detection of S1's bound near or in between troponin complexes on the thin filament. Additionally, calcium related changes between troponin T and myosin were detected. Based on this data, the troponin complex situated every 7 actin monomers, hinders adjacently bound myosins to complete their power stroke; whereas myosins bound in between troponin complexes undergo complete power strokes.
Date: May 2007
Creator: Coffee Castro-Zena, Pilar G.
Partner: UNT Libraries

Luminescence Resonance Energy Transfer-Based Modeling of Troponin in the Presence of Myosin and Troponin/Tropomyosin Defining Myosin Binding Target Zones in the Reconstituted Thin Filament

Description: Mechanistic details on the regulation of striated muscle contraction still need to be determined, particularly the specific structural locations of the elements comprising the thick and thin filaments. Of special interest is the location of the regulatory component, troponin, on the actin filament and how its presence influences the behavior of myosin binding to the thin filament. In the present study: (1) Luminescence resonance energy transfer was used to monitor potential conformational changes in the reconstituted thin filament between the C-terminal region of troponin T and myosin subfragment 1; (2) Location of troponin in previously derived atomic models of the acto-myosin complex was mapped to visualize specific contacts; and (3) Shortened tropomyosin was engineered and protein binding and ATPase assays were performed to study the effect of myosin binding close to the troponin complex. Analysis of the results suggest the following: (1) Irrespective of calcium levels, the C-terminal region of troponin T is located close to myosin loop 3 and a few actin helices that may perturb strong acto-myosin interactions responsible for force production. (2) Atomic models indicate myosin subfragment 1 cannot attain the post- powerstroke state due to the full motion of the lever arm being sterically hindered by troponin. (3) A shortened tropomyosin with five actin binding modules (instead of the native seven in muscle cells) binds actin contiguously in a head-to-tail manner and serves to increase the periodicity of troponin complexes on the actin filament. Such behavior eliminates the structure of the actin filament being responsible for the binding location of tropomyosin. (4) Differential behavior of myosin subfragment 1 i.e. (a) binding adjacent to troponin and (b) binding further away from troponin, is apparent as tropomyosin and troponin appear to govern the regions or "target zones" where myosin can bind productively along the actin filament. Physiologically, myosins ...
Date: May 2009
Creator: Patel, Dipesh A.
Partner: UNT Libraries

Importance of electronic relaxation for inter-coulombic decay in aqueous systems

Description: Inspired by recent photoelectron spectroscopy (PES) experiments on hydroxide solutions, we have examined the conditions necessary for enhanced (and, in the case of solutions, detectable) intercoulombic decay (ICD)--Auger emission from an atomic site other than that originally excited. We present general guidelines, based on energetic and spatial overlap of molecular orbitals, for this enhancement of ICDbased energy transfer in solutions. These guidelines indicate that this decay process should be exhibited by broad classes of biomolecules and suggest a design criterion for targeted radiooncology protocols. Our findings show that PES cannot resolve the current hydroxide coordination controversy.
Date: October 1, 2010
Creator: Schwartz, Craig P.; Fatehi, Shervin; Saykally, Richard J. & Prendergast, David
Partner: UNT Libraries Government Documents Department

Observation of resonant energy transfer between identical-frequency laser beams

Description: Enhanced transmission of a low intensity laser beam is observed when crossed with an identical-frequency beam in a plasma with a flow velocity near the ion sound speed. The time history of the enhancement and the dependence on the flow velocity strongly suggest that this is due to energy transfer between the beams via a resonant ion wave with zero frequency in the laboratory frame. The maximum energy transfer has been observed when the beams cross in a region with Mach 1 flow. The addition of frequency modulation on the crossing beams is seen to reduce the energy transfer by a factor of two. Implications for indirect-drive fusion schemes are discussed.
Date: December 9, 1998
Creator: Afeyan, B. B.; Cohen, B. I.; Estabrook, K. G.; Glenzer, S. H.; Joshi, C.; Kirkwood, R. K. et al.
Partner: UNT Libraries Government Documents Department

Screening and Degradation Tests of Linear-Polymer Additives for District Heating Applications

Description: In closed-loop district heating and cooling (DHC) systems, the addition of a friction-reducing additive to the working fluid conveying energy between the energy sources and end users would allow increased load-handling capability (in an existing system) or the use of much smaller pipes and/or pumps (in a new system). As the first step in identifying friction-reducing additives that have a reasonable lifetime at DHC temperatures, two high-molecular-weight linear-polymer additives have been tested at two different temperatures (25.0 C and 87.8 C). The additives are Polyox WSR-301 and Separan AP-273 at 200 wppm in deionized water. Results of capillary tube screening tests with fresh solutions show that both polymers can give more than 60% friction reduction. However, Separan is effective at high temperatures, whereas Polyox undergoes thermal degradation. Degradation tests in a closed recirculatory flow system show that (1) friction reduction is always accompanied by heat transfer reduction regardless of the hours of shear, (2) Polyox cannot be used in recirculatory systems because it is very sensitive to mechanical degradation, and (3) although Separan does degrade under high flow shear conditions, it does not degrade completely; it achieves a plateau value of friction reduction even under continuous shear. This is an important discovery and implies that Separan is still a good candidate for closed-loop DH systems.
Date: December 1987
Creator: Choi, U. S.; Cho, Young I. & Kasza, Kenneth Edmund
Partner: UNT Libraries Government Documents Department

Predicted Heat-Transfer Performance of an Evacuated Glass-Jacketed CPC Receiver : Countercurrent Flow Design

Description: The heat-transfer performance of an evacuated glass-jacketed CPC-receiver facility, free on one end and fixed onto the glass jacket at the other, was carried out using heat-transfer relationships and the best information available in the literature. Specifically, the collector examined was a 3x-CPC facility, 8 ft long, with an entrance aperture 4.5 in. wide covered with a single glass cover, and provided with an aluminum reflecting surface (rho = 0.88). To maximize heat retention, a selectively treated receiver surface, epsilon = 0.11, was used. The optical efficiency of this CPC collector facility was calculated to be eta₀ = 0.536.
Date: May 1976
Creator: Thodos, George
Partner: UNT Libraries Government Documents Department

Analysis of Heat-Pipe Absorbers in Evacuated-Tube Solar Collectors

Description: Heat transfer in evacuated-tube solar collectors with heat-pipe absorbers is compared with that for similar collectors with flow-through absorbers. In systems that produce hot water or other heated fluids, the heat-pipe absorber suffers a heat transfer penalty compared with the flow-through absorber, but in many cases the penalty can be minimized by proper design at the heat-pipe condenser and system manifold. The heat transfer penalty decreases with decreasing collector heat loss coefficient, suggesting that evacuated tubes with optical concentration are more appropriate for use with heat pipes than evacuated or non-evacuated flat-plate collectors. When the solar collector is used to drive an absorption chiller, the heat-pipe absorber has better heat transfer characteristics than the flow-through absorbers.
Date: February 1986
Creator: Hull, John R.; Schertz, William W. & Allen, John W.
Partner: UNT Libraries Government Documents Department

A General Model for Turbulent Momentum and Heat Transport in Liquid Metals

Description: This report develops a general single-point closure scheme for calculating the local levels of turbulent fluxes of momentum and heat in liquid-metal flows. Transport effects are accounted for by way of the three scalar quantities: turbulent kinetic energy; turbulence-energy dissipation rate; and scalar energy (or half the mean temperature variance). Their values at any point in the flow are obtained from the solution of conservation equations of transport type for each of the three quantities. The turbulent momentum fluxes (Reynolds stresses) and heat-transport rates are then obtained from the algebraic formulas containing the above scalar quantities and the mean velocity and temperature fields.
Date: March 1979
Creator: Sha, William T. & Launder, Brian E.
Partner: UNT Libraries Government Documents Department

A Model for Turbulent Momentum and Heat Transport in Large Rod Bundles

Description: A quasi-continuum model for turbulent momentum and heat transport in large rod bundles has been developed. This model has been derived from a sub-channel analysis and adapted to a quasi-continuum form by introducing concepts of porosity and distributed resistance. The effects of turbulent kinetic energy generation due to shear, viscosity, diffusion, geometric effects, buoyancy, and Reynolds number are explicitly included. The proposed model of turbulence is relatively simple, yet it is believed to provide a framework for taking account of important turbulent mechanisms in rod bundles.
Date: January 1979
Creator: Sha, William T. & Launder, Brian E.
Partner: UNT Libraries Government Documents Department

Boiling Heat Transfer of Refrigerant R-113 in a Small-Diameter, Horizontal Tube

Description: Results of a study of boiling heat transfer from refrigerant R-113 in a small-diameter (2.92-mm) tube are reported. Local heat transfer coefficients over a range of heat fluxes, mass fluxes, and equilibrium mass qualities were measured. The measured coefficients were used to evaluate eight different heat transfer correlations, some of which have been developed specifically for refrigerants. High heat fluxes and low flow rates are inherent in small channels, and this combination results in high boiling numbers. The high boiling number of the collected data shows that the nucleation mechanism was dominant. As a result, the two-phase correlations that predicted this dominance also predicted the data best if they also properly modeled the physical parameters. The correlations of Lazarek and Black and of Shah, as modified in this study, predicted the data very well. It is also shown that a simple form, suggested by Stephan and Abdelsalam for nucleate boiling, correlates the data equally well. This study is part of a research program in multiphase flow and heat transfer, with the overall objective of developing validated design correlations and predictive methods that will facilitate the design and optimization of compact heat exchangers for use with environmentally acceptable alternatives for chlorofluorocarbon (CFC) refrigerants and refrigerant mixtures.
Date: January 1992
Creator: Wambsganss, M. W.; France, D. M.; Jendrzejczyk, J. A. & Tran, T. N.
Partner: UNT Libraries Government Documents Department

Energy Transfer of Excitons Between Quantum Wells Separated by a Wide Barrier

Description: We present a microscopic theory of the excitonic Stokes and anti-Stokes energy transfer mechanisms between two widely separated unequal quantum wells with a large energy mismatch ({Delta}) at low temperatures (T). Exciton transfer through dipolar coupling, photon-exchange coupling and over-barrier ionization of the excitons through exciton-exciton Auger processes are examined. The energy transfer rate is calculated as a function of T and the center-to-center distance d between the two wells. The rates depend sensitively on T for plane-wave excitons. For located excitons, the rates depend on T only through the T-dependence of the localization radius.
Date: December 6, 1999
Partner: UNT Libraries Government Documents Department

Energy transfer properties and mechanisms. Technical progress report

Description: Collisional energy transfer is the controlling factor in many nonequilibrium chemical systems: combustion, laser-induced chemical reactions, shock-heated gases, atmospheric chemistry, etc. During this period, efforts were made in 3 areas: large molecule energy transfer experiments (organic compounds); triatomic V-T/R energy transfer (memory effects); and energy transfer in extreme environments (shock tube data on norbornene). Results are described very briefly.
Date: February 3, 1995
Creator: Barker, J.R.
Partner: UNT Libraries Government Documents Department

Intramolecular Charge and Energy Transfer in Multichromophoric Aromatic Systems

Description: A concerted experimental and computational study of energy transfer in nucleic acid bases and charge transfer in dialkylaminobenzonitriles, and related electron donor-acceptor molecules, indicate that the ultrafast photoprocesses occur through three-state conical interactions involving an intermediate state of biradical character.
Date: September 9, 2008
Creator: Lim, Edward C.
Partner: UNT Libraries Government Documents Department

Graphene Layer Growth: Collision of Migrating Five-MemberRings

Description: A reaction pathway is explored in which two cyclopenta groups combine on the zigzag edge of a graphene layer. The process is initiated by H addition to a five-membered ring, followed by opening of that ring and the formation of a six-membered ring adjacent to another five-membered ring. The elementary steps of the migration pathway are analyzed using density functional theory to examine the region of the potential energy surface associated with the pathway. The calculations are performed on a substrate modeled by the zigzag edge of tetracene. Based on the obtained energetics, the dynamics of the system are analyzed by solving the energy transfer master equations. The results indicate energetic and reaction-rate similarity between the cyclopenta combination and migration reactions. Also examined in the present study are desorption rates of migrating cyclopenta rings which are found to be comparable to cyclopenta ring migration.
Date: December 2, 2005
Creator: Whitesides, Russell; Kollias, Alexander C.; Domin, Dominik; Lester Jr., William A. & Frenklach, Michael
Partner: UNT Libraries Government Documents Department

2010 Atomic & Molecular Interactions Gordon Research Conference

Description: The Atomic and Molecular Interactions Gordon Conferences is justifiably recognized for its broad scope, touching on areas ranging from fundamental gas phase and gas-condensed matter collision dynamics, to laser-molecule interactions, photophysics, and unimolecular decay processes. The meeting has traditionally involved scientists engaged in fundamental research in gas and condensed phases and those who apply these concepts to systems of practical chemical and physical interest. A key tradition in this meeting is the strong mixing of theory and experiment throughout. The program for 2010 conference continues these traditions. At the 2010 AMI GRC, there will be talks in 5 broadly defined and partially overlapping areas of intermolecular interactions and chemical dynamics: (1) Photoionization and Photoelectron Dynamics; (2) Quantum Control and Molecules in Strong Fields; (3) Photochemical Dynamics; (4) Complex Molecules and Condensed Phases; and (5) Clusters and Reaction Dynamics. These areas encompass many of the most productive and exciting areas of chemical physics, including both reactive and nonreactive processes, intermolecular and intramolecular energy transfer, and photodissociation and unimolecular processes. Gas phase dynamics, van der Waals and cluster studies, laser-matter interactions and multiple potential energy surface phenomena will all be discussed.
Date: July 23, 2010
Creator: Martinez, Todd
Partner: UNT Libraries Government Documents Department


Description: Fatty acids have a reversible inhibitory effect on respiration and on photosynthetic action. They investigated the influence of octanoic acid on the photosynthetic bacteria Rhodopseudomonas spheroids R-26. From the spectroscopic data they conclude that a less efficient energy transfer and decoupling of the light harvesting pigment system from the energy converting reaction center is responsible for the inhibitory effect.
Date: May 1, 1971
Creator: Steffea, Hans & Calvin, Melvin.
Partner: UNT Libraries Government Documents Department