Elastic properties of Pu metal and Pu-Ga alloys (open access)

Elastic properties of Pu metal and Pu-Ga alloys

We present elastic properties, theoretical and experimental, of Pu metal and Pu-Ga ({delta}) alloys together with ab initio equilibrium equation-of-state for these systems. For the theoretical treatment we employ density-functional theory in conjunction with spin-orbit coupling and orbital polarization for the metal and coherent-potential approximation for the alloys. Pu and Pu-Ga alloys are also investigated experimentally using resonant ultrasound spectroscopy. We show that orbital correlations become more important proceeding from {alpha} {yields} {beta} {yields} {gamma} plutonium, thus suggesting increasing f-electron correlation (localization). For the {delta}-Pu-Ga alloys we find a softening with larger Ga content, i.e., atomic volume, bulk modulus, and elastic constants, suggest a weakened chemical bonding with addition of Ga. Our measurements confirm qualitatively the theory but uncertainties remain when comparing the model with experiments.
Date: January 5, 2010
Creator: Soderlind, P; Landa, A; Klepeis, J E; Suzuki, Y & Migliori, A
Object Type: Article
System: The UNT Digital Library
Dihadron Azimuthal Correlation from Collins Effect in Unpolarized Hadron Collisions (open access)

Dihadron Azimuthal Correlation from Collins Effect in Unpolarized Hadron Collisions

We study the dihadron azimuthal correlation produced nearly back-to-back in unpolarized hadron collisions, arising from the product of two Collins fragmentation functions. Using the latest Collins fragmentation functions extracted from the global analysis of available experimental data, we make predictions for the azimuthalcorrelation of two-pion production in pp collisions at RHIC energies. We find that the correlation is sizable in the mid-rapidity region for moderate jet transverse momentum.
Date: January 5, 2010
Creator: Yuan, Feng
Object Type: Article
System: The UNT Digital Library
Systemsize dependence of associated yields in hadron-triggered jets (open access)

Systemsize dependence of associated yields in hadron-triggered jets

We present results on the system size dependence of high transverse momentum di-hadron correlations at {radical}s{sub NN} = 200 GeV as measured by STAR at RHIC. Measurements in d+Au, Cu+Cu and Au+Au collisions reveal similar jet-like correlation yields at small angular separation ({Delta}{phi} {approx} 0, {Delta}{eta} {approx} 0) for all systems and centralities. Previous measurements have shown that the away-side yield is suppressed in heavy-ion collisions. We present measurements of the away-side suppression as a function of transverse momentum and centrality in Cu+Cu and Au+Au collisions. The suppression is found to be similar in Cu+Cu and Au+Au collisions at a similar number of participants. The results are compared to theoretical calculations based on the parton quenching model and the modified fragmentation model. The observed differences between data and theory indicate that the correlated yields presented here will provide important constraints on medium density profile and energy loss model parameters.
Date: July 5, 2010
Creator: STAR Collaboration
Object Type: Article
System: The UNT Digital Library
Phases of Augmented Hadronic Light-Front Wave Functions (open access)

Phases of Augmented Hadronic Light-Front Wave Functions

It is an important question whether the final/initial state gluonic interactions which lead to naive-time-reversal-odd single-spin asymmetries and diffraction at leading twist can be associated in a definite way with the light-front wave function hadronic eigensolutions of QCD. We use light-front time-ordered perturbation theory to obtain augmented light-front wave functions which contain an imaginary phase which depends on the choice of advanced or retarded boundary condition for the gauge potential in light-cone gauge. We apply this formalism to the wave functions of the valence Fock states of nucleons and pions, and show how this illuminates the factorization properties of naive-time-reversal-odd transverse momentum dependent observables which arise from rescattering. In particular, one calculates the identical leading-twist Sivers function from the overlap of augmented light-front wavefunctions that one obtains from explicit calculations of the single-spin asymmetry in semi-inclusive deep inelastic lepton-polarized nucleon scattering where the required phases come from the final-state rescattering of the struck quark with the nucleon spectators.
Date: January 5, 2010
Creator: Yuan, Feng; Brodsky, S.J.; Pasquini, B. & Xiao, B.-W.
Object Type: Article
System: The UNT Digital Library
Control of Toxic Chemicals in Puget Sound, Phase 3: Study of Atmospheric Deposition of Air Toxics to the Surface of Puget Sound (open access)

Control of Toxic Chemicals in Puget Sound, Phase 3: Study of Atmospheric Deposition of Air Toxics to the Surface of Puget Sound

The results of the Phase 1 Toxics Loading study suggested that runoff from the land surface and atmospheric deposition directly to marine waters have resulted in considerable loads of contaminants to Puget Sound (Hart Crowser et al. 2007). The limited data available for atmospheric deposition fluxes throughout Puget Sound was recognized as a significant data gap. Therefore, this study provided more recent or first reported atmospheric deposition fluxes of PAHs, PBDEs, and select trace elements for Puget Sound. Samples representing bulk atmospheric deposition were collected during 2008 and 2009 at seven stations around Puget Sound spanning from Padilla Bay south to Nisqually River including Hood Canal and the Straits of Juan de Fuca. Revised annual loading estimates for atmospheric deposition to the waters of Puget Sound were calculated for each of the toxics and demonstrated an overall decrease in the atmospheric loading estimates except for polybrominated diphenyl ethers (PBDEs) and total mercury (THg). The median atmospheric deposition flux of total PBDE (7.0 ng/m2/d) was higher than that of the Hart Crowser (2007) Phase 1 estimate (2.0 ng/m2/d). The THg was not significantly different from the original estimates. The median atmospheric deposition flux for pyrogenic PAHs (34.2 ng/m2/d; without TCB) shows …
Date: July 5, 2010
Creator: Brandenberger, Jill M.; Louchouarn, Patrick; Kuo, Li-Jung; Crecelius, Eric A.; Cullinan, Valerie I.; Gill, Gary A. et al.
Object Type: Report
System: The UNT Digital Library
Identified high-pT spectra in Cu+Cu collisions at sqrt sNN=200 GeV (open access)

Identified high-pT spectra in Cu+Cu collisions at sqrt sNN=200 GeV

We report new results on identified (anti)proton and charged pion spectra at large transverse momenta (3 < p{sub T} < 10 GeV/c) from Cu+Cu collisions at {radical}s{sub NN} = 200 GeV using the STAR detector at the Relativistic Heavy Ion Collider (RHIC). This study explores the system size dependence of two novel features observed at RHIC with heavy ions: the hadron suppression at high-p{sub T} and the anomalous baryon to meson enhancement at intermediate transverse momenta. Both phenomena could be attributed to the creation of a new form of QCD matter. The results presented here bridge the system size gap between the available pp and Au+Au data, and allow the detailed exploration for the on-set of the novel features. Comparative analysis of all available 200 GeV data indicates that the system size is a major factor determining both the magnitude of the hadron spectra suppression at large transverse momenta and the relative baryon to meson enhancement.
Date: July 5, 2010
Creator: STAR Collaboration
Object Type: Article
System: The UNT Digital Library
Analytical Validation of Accelerator Mass Spectrometry for Pharmaceutical Development: the Measurement of Carbon-14 Isotope Ratio. (open access)

Analytical Validation of Accelerator Mass Spectrometry for Pharmaceutical Development: the Measurement of Carbon-14 Isotope Ratio.

Accelerator mass spectrometry (AMS) is an isotope based measurement technology that utilizes carbon-14 labeled compounds in the pharmaceutical development process to measure compounds at very low concentrations, empowers microdosing as an investigational tool, and extends the utility of {sup 14}C labeled compounds to dramatically lower levels. It is a form of isotope ratio mass spectrometry that can provide either measurements of total compound equivalents or, when coupled to separation technology such as chromatography, quantitation of specific compounds. The properties of AMS as a measurement technique are investigated here, and the parameters of method validation are shown. AMS, independent of any separation technique to which it may be coupled, is shown to be accurate, linear, precise, and robust. As the sensitivity and universality of AMS is constantly being explored and expanded, this work underpins many areas of pharmaceutical development including drug metabolism as well as absorption, distribution and excretion of pharmaceutical compounds as a fundamental step in drug development. The validation parameters for pharmaceutical analyses were examined for the accelerator mass spectrometry measurement of {sup 14}C/C ratio, independent of chemical separation procedures. The isotope ratio measurement was specific (owing to the {sup 14}C label), stable across samples storage conditions for at …
Date: February 5, 2010
Creator: Keck, B D; Ognibene, T & Vogel, J S
Object Type: Article
System: The UNT Digital Library
Observation of pi+pi-pi+pi- photoproduction in ultraperipheral heavy-ion collisions at sqrt sNN = 200 GeV at the STAR detector (open access)

Observation of pi+pi-pi+pi- photoproduction in ultraperipheral heavy-ion collisions at sqrt sNN = 200 GeV at the STAR detector

We present a measurement of {pi}{sup +}{pi}{sup -}{pi}{sup +}{pi}{sup -} photonuclear production in ultra-peripheral Au-Au collisions at {radical}s{sub NN} = 200 GeV from the STAR experiment. The {pi}{sup +}{pi}{sup -}{pi}{sup +}{pi}{sup -} final states are observed at low transverse momentum and are accompanied by mutual nuclear excitation of the beam particles. The strong enhancement of the production cross section at low transverse momentum is consistent with coherent photoproduction. The {pi}{sup +}{pi}{sup -}{pi}{sup +}{pi}{sup -} invariant mass spectrum of the coherent events exhibits a broad peak around 1540 {+-} 40 MeV/c{sup 2} with a width of 570 {+-} 60 MeV/c{sup 2}, in agreement with the photoproduction data for the {rho}{sup 0}(1700). We do not observe a corresponding peak in the {pi}{sup +}{pi}{sup -} final state and measure an upper limit for the ratio of the branching fractions of the {rho}{sup 0}(1700) to {pi}{sup +}{pi}{sup -} and {pi}{sup +}{pi}{sup -}{pi}{sup +}{pi}{sup -} of 2.5% at 90% confidence level. The ratio of {rho}{sup 0}(1700) and {rho}{sup 0}(770) coherent production cross sections is measured to be 13.4 {+-} 0.8{sub stat.} {+-} 4.4{sub syst.}%.
Date: July 5, 2010
Creator: STAR Collaboration
Object Type: Article
System: The UNT Digital Library
Long range rapidity correlations and jet production in high energy nuclear collisions (open access)

Long range rapidity correlations and jet production in high energy nuclear collisions

The STAR Collaboration at RHIC presents a systematic study of high transverse momentum charged di-hadron correlations at small azimuthal pair separation {Delta}{phi}, in d+Au and central Au+Au collisions at {radical}s{sub NN} = 200 GeV. Significant correlated yield for pairs with large longitudinal separation {Delta}{eta} is observed in central Au+Au, in contrast to d+Au collisions. The associated yield distribution in {Delta}{eta} x {delta}{phi} can be decomposed into a narrow jet-like peak at small angular separation which has a similar shape to that found in d+Au collisions, and a component which is narrow in {Delta}{phi} and depends only weakly on {Delta}{eta}, the 'ridge'. Using two systematically independent analyses, finite ridge yield is found to persist for trigger p{sub t} > 6 GeV/c, indicating that it is correlated with jet production. The transverse momentum spectrum of hadrons comprising the ridge is found to be similar to that of bulk particle production in the measured range (2 < p{sub t} < 4 GeV/c).
Date: July 5, 2010
Creator: STAR Collaboration
Object Type: Article
System: The UNT Digital Library
Thermal Degradation Studies of Polyurethane/POSS Nanohybrid Elastomers (open access)

Thermal Degradation Studies of Polyurethane/POSS Nanohybrid Elastomers

Reported here is the synthesis of a series of Polyurethane/POSS nanohybrid elastomers, the characterization of their thermal stability and degradation behavior at elevated temperatures using a combination of Thermal Gravimetric Analysis (TGA) and Thermal Volatilization Analysis (TVA). A series of PU elastomers systems have been formulated incorporating varying levels of 1,2-propanediol-heptaisobutyl-POSS (PHIPOSS) as a chain extender unit, replacing butane diol. The bulk thermal stability of the nanohybrid systems has been characterized using TGA. Results indicate that covalent incorporation of POSS into the PU elastomer network increase the non-oxidative thermal stability of the systems. TVA analysis of the thermal degradation of the POSS/PU hybrid elastomers have demonstrated that the hybrid systems are indeed more thermally stable when compared to the unmodified PU matrix; evolving significantly reduced levels of volatile degradation products and exhibiting a {approx}30 C increase in onset degradation temperature. Furthermore, characterization of the distribution of degradation products from both unmodified and hybrid systems indicate that the inclusion of POSS in the PU network is directly influencing the degradation pathways of both the soft and hard block components of the elastomers: The POSS/PU hybrid systems show reduced levels of CO, CO2, water and increased levels of THF as products of …
Date: March 5, 2010
Creator: Lewicki, J P; Pielichowski, K; TremblotDeLaCroix, P; Janowski, B; Todd, D & Liggat, J J
Object Type: Article
System: The UNT Digital Library
Simulations of a stretching bar using a plasticity model from the shear transformation zone theory (open access)

Simulations of a stretching bar using a plasticity model from the shear transformation zone theory

An Eulerian simulation is developed to study an elastoplastic model of amorphous materials that is based upon the shear transformation zone theory developed by Langer and coworkers. In this theory, plastic deformation is controlled by an effective temperature that measures the amount of configurational disorder in the material. The simulation is used to model ductile fracture in a stretching bar that initially contains a small notch, and the effects of many of the model parameters are examined. The simulation tracks the shape of the bar using the level set method. Within the bar, a finite difference discretization is employed that makes use of the essentially non-oscillatory (ENO) scheme. The system of equations is moderately stiff due to the presence of large elastic constants, and one of the key numerical challenges is to accurately track the level set and construct extrapolated field values for use in boundary conditions. A new approach to field extrapolation is discussed that is second order accurate and requires a constant amount of work per gridpoint.
Date: June 5, 2010
Creator: Rycroft, Chris H. & Gibou, Frederic
Object Type: Article
System: The UNT Digital Library
Application for Permit to Operate a Class III Solid Waste Disposal Site at the Nevada Test Site - U10c Disposal Site (open access)

Application for Permit to Operate a Class III Solid Waste Disposal Site at the Nevada Test Site - U10c Disposal Site

The NTS is located approximately 105 km (65 mi) northwest of Las Vegas, Nevada. NNSA/NSO is the federal lands management authority for the NTS and NSTec is the Management & Operations contractor. Access on and off the NTS is tightly controlled, restricted, and guarded on a 24-hour basis. The NTS is posted with signs along its entire perimeter. NSTec is the operator of all solid waste disposal sites on the NTS. The U10C Disposal Site is located in the northwest corner of Area 9 at the NTS (Figure 1) and is located in a subsidence crater created by two underground nuclear events, one in October 1962 and another in April 1964. The disposal site opened in 1971 for the disposal of rubbish, refuse, pathological waste, asbestos-containing material, and industrial solid waste. A Notice of Intent form to operate the disposal site as a Class II site was submitted to the state of Nevada on January 26, 1994, and was acknowledged in a letter to the DOE on February 8, 1994. It operated as a state of Nevada Class II Solid Waste Disposal Site (SWDS) until it closed on October 5, 1995, for retrofit as a Class III SWDS. The retrofit …
Date: August 5, 2010
Creator: Programs, NSTec Environmental
Object Type: Report
System: The UNT Digital Library
Paleoclimatic implications of glacial and postglacial refugia for Pinus pumila in western Beringia (open access)

Paleoclimatic implications of glacial and postglacial refugia for Pinus pumila in western Beringia

Palynological results from Julietta Lake currently provide the most direct evidence to support the existence of a glacial refugium for Pinus pumila in mountains of southwestern Beringia. Both percentages and accumulation rates indicate the evergreen shrub survived until at least {approx}19,000 14C yr B.P. in the Upper Kolyma region. Percentage data suggest numbers dwindled into the late glaciation, whereas pollen accumulation rates point towards a more rapid demise shortly after {approx}19,000 14C yr B.P. Pinus pumila did not re-establish in any great numbers until {approx}8100 14C yr B.P., despite the local presence {approx}9800 14C yr B.P. of Larix dahurica, which shares similar summer temperature requirements. The postglacial thermal maximum (in Beringia {approx}11,000-9000 14C yr B.P.) provided Pinus pumila shrubs with equally harsh albeit different conditions for survival than those present during the LGM. Regional records indicate that in this time of maximum warmth Pinus pumila likely sheltered in a second, lower-elevation refugium. Paleoclimatic models and modern ecology suggest that shifts in the nature of seasonal transitions and not only seasonal extremes have played important roles in the history of Pinus pumila over the last {approx}21,000 14C yr B.P.
Date: February 5, 2010
Creator: Anderson, P M; Lozhkin, A V; Solomatkina, T B & Brown, T A
Object Type: Article
System: The UNT Digital Library
Fighting Fire with Fire: Superlattice Cooling of Silicon Hotspots to Reduce Global Cooling Requirements (open access)

Fighting Fire with Fire: Superlattice Cooling of Silicon Hotspots to Reduce Global Cooling Requirements

The running costs of data centers are dominated by the need to dissipate heat generated by thousands of server machines. Higher temperatures are undesirable as they lead to premature silicon wear-out; in fact, mean time to failure has been shown to decrease exponentially with temperature (Black's law). Although other server components also generate heat, microprocessors still dominate in most server configurations and are also the most vulnerable to wearout as the feature sizes shrink. Even as processor complexity and technology scaling have increased the average energy density inside a processor to maximally tolerable levels, modern microprocessors make extensive use of hardware structures such as the load-store queue and other CAM-based units, and the peak temperatures on chip can be much worse than even the average temperature of the chip. In recent studies, it has been shown that hot-spots inside a processor can generate {approx} 800W/cm{sup 2} heat flux whereas the average heat flux is only 10-50W/cm{sup 2}, and due to this disparity in heat generation, the temperature in hot spots may be up to 30 C more than average chip temperature. The key problem processor hot-spots create is that in order to prevent some critical hardware structures from wearing out …
Date: October 5, 2010
Creator: Biswas, S; Tiwari, M; Sherwood, T; Theogarajan, L & Chong, F T
Object Type: Article
System: The UNT Digital Library
Observation of charge-dependent azimuthal correlations and possible local strong parity violation in heavy-ion collisions (open access)

Observation of charge-dependent azimuthal correlations and possible local strong parity violation in heavy-ion collisions

Parity-odd domains, corresponding to non-trivial topological solutions of the QCD vacuum, might be created during relativistic heavy-ion collisions. These domains are predicted to lead to charge separation of quarks along the orbital momentum of the system created in non-central collisions. To study this effect, we investigate a three particle mixed harmonics azimuthal correlator which is a {Rho}-even observable, but directly sensitive to the charge separation effect. We report measurements of this observable using the STAR detector in Au+Au and Cu+Cu collisions at {radical}s{sub NN} = 200 and 62 GeV. The results are presented as a function of collision centrality, particle separation in rapidity, and particle transverse momentum. A signal consistent with several of the theoretical expectations is detected in all four data sets. We compare our results to the predictions of existing event generators, and discuss in detail possible contributions from other effects that are not related to parity violation.
Date: July 5, 2010
Creator: STAR Collaboration
Object Type: Article
System: The UNT Digital Library
Pressure-induced isostructural transition in PdN2 (open access)

Pressure-induced isostructural transition in PdN2

We show that a synthesized Pd-N compound crystallize into the pyrite structure by comparison of experimental and calculated Raman intensities. The decreasing Raman intensities with decreasing pressure is explained by a closing of the fundamental band gap. We further discuss the experimental decomposition of this compound at 11 GPa in terms of an isostructural transition within the pyrite structure.
Date: March 5, 2010
Creator: Aberg, D; Erhart, P; Crowhurst, J; Zaug, J M; Goncharov, A F & Sadigh, B
Object Type: Article
System: The UNT Digital Library
US PRACTICE FOR INTERIM WET STORAGE OF RRSNF (open access)

US PRACTICE FOR INTERIM WET STORAGE OF RRSNF

Aluminum research reactor spent nuclear fuel is currently being stored or is anticipated to be returned to the United States and stored at Department of Energy storage facilities at the Savannah River Site and the Idaho Nuclear Technology and Engineering Center. This paper summarizes the current practices to provide for continued safe interim wet storage in the U.S. Aluminum fuel stored in poor quality water is subject to aggressive corrosion attack and therefore water chemistry control systems are essential to maintain water quality. Fuel with minor breaches are safely stored directly in the basin. Fuel pieces and heavily damaged fuel is safely stored in isolation canisters.
Date: August 5, 2010
Creator: Vinson, D.
Object Type: Report
System: The UNT Digital Library
3D Simulations of the NIF Indirect Drive Ignition Target Design (open access)

3D Simulations of the NIF Indirect Drive Ignition Target Design

The radiation hydrodynamics code Hydra is used to quantify the sensitivity of different NIF ignition point designs to several 3D effects. Each of the 48 NIF quads is included in the calculations and is allowed to have different power. With this model they studied the effect on imploded core symmetry of discrete laser spots (as opposed to idealized azimuthally-averaged rings) and random variations in laser power.
Date: January 5, 2010
Creator: Jones, O. S.; Milovich, J. L.; Callahan, D. A.; Edwards, M. J.; Landen, O. L.; Salmonson, J. D. et al.
Object Type: Article
System: The UNT Digital Library
Towards the understanding of PETN initiation by a fast, high power arc source (open access)

Towards the understanding of PETN initiation by a fast, high power arc source

We present a thorough characterization of a capacitor driven arc source that can deliver up to 200 mJ of energy to the arc and high explosive in a well-controlled, repeatable manner on the hundreds of nanoseconds time-scale. Our ultimate purpose is to create a platform to study high explosive kinetics under extreme conditions of high-temperature. In the current paper, we characterize the behavior of our arc source by electrical discharge over a thin PETN film. Temperature and density are determined by time-resolved atomic emission spectroscopy on the nano- to microsecond time scale along with fast photographic imaging to capture time-resolved images of the expanding plasma. We also discuss preliminary simulations of arc plasma using a 1-D hydrodynamic model. Comparisons of these simulations with experimental data are presented. Ultimately our goal is to create a platform that will generate conditions of high temperature in order to study high explosive kinetics. We believe that our arc source platform can be further combined with a time-resolved vibrational spectroscopy (e.g. IR or Raman) to study chemical kinetics under extreme conditions. High temperature conditions may access novel reactive pathways that are different from either shock or slower thermal processes that are substantially lower in temperature.
Date: March 5, 2010
Creator: Grant, C D; Tang, V; Glascoe, E A & McCarrick, J F
Object Type: Article
System: The UNT Digital Library
Frequency stabilization via the mixed mode in three mode HeNe lasers (open access)

Frequency stabilization via the mixed mode in three mode HeNe lasers

This paper describes a three mode HeNe laser frequency stabilization technique using the mixed mode frequency to obtain a fractional frequency stability of 2 x 10{sup -11}. The mixed mode frequency occurs due to optical nonlinear interactions with the adjacent modes at each of the three modes. In precision displacement interferometry systems, the laser source frequency must be stabilized to provide an accurate conversion ratio between phase change and displacement. In systems, such as lithography applications, which require high speed, high accuracy and low data age uncertainty, it is also desirable to avoid periodic nonlinearities, which reduces computation time and errors. One method to reduce periodic nonlinearity is to spatially separate the measurement and reference beams to prevent optical mixing, which has been shown for several systems. Using spatially separated beams and the proper optical configuration, the interferometer can be fiber fed, which can increase the interferometer's stability by reducing the number of beam steering optical elements. Additionally, as the number of measurement axes increases, a higher optical power from the laser source is necessary.
Date: February 5, 2010
Creator: Ellis, J D; Joo, K; Buice, E S; Spronck, J W & Munnig Schmidt, R H
Object Type: Article
System: The UNT Digital Library
Growth of Long Range Forward-Backward Multiplicity Correlations with Centrality in Au+Au Collisions at sqrt sNN = 200 GeV (open access)

Growth of Long Range Forward-Backward Multiplicity Correlations with Centrality in Au+Au Collisions at sqrt sNN = 200 GeV

Forward-backward multiplicity correlation strengths have been measured with the STAR detector for Au+Au and p+p collisions at {radical}s{sub NN} = 200 GeV. Strong short and long range correlations (LRC) are seen in central Au+Au collisions. The magnitude of these correlations decrease with decreasing centrality until only short range correlations are observed in peripheral Au+Au collisions. Both the Dual Parton Model (DPM) and the Color Glass Condensate (CGC) predict the existence of the long range correlations. In the DPM the fluctuation in the number of elementary (parton) inelastic collisions produces the LRC. In the CGC longitudinal color flux tubes generate the LRC. The data is in qualitative agreement with the predictions from the DPM and indicates the presence of multiple parton interactions.
Date: July 5, 2010
Creator: STAR Collaboration
Object Type: Article
System: The UNT Digital Library
Bacterial Microcompartments (open access)

Bacterial Microcompartments

Bacterialmicrocompartments (BMCs) are organelles composed entirely of protein. They promote specific metabolic processes by encapsulatingand colocalizing enzymes with their substrates and cofactors, by protecting vulnerable enzymes in a defined microenvironment, and bysequestering toxic or volatile intermediates. Prototypes of the BMCsare the carboxysomes of autotrophic bacteria. However, structures of similarpolyhedral shape are being discovered in an ever-increasing number of heterotrophic bacteria, where they participate in the utilization ofspecialty carbon and energy sources.Comparative genomics reveals that the potential for this type of compartmentalization is widespread acrossbacterial phyla and suggests that genetic modules encoding BMCs are frequently laterally transferred among bacteria. The diverse functionsof these BMCs suggest that they contribute to metabolic innovation in bacteria in a broad range of environments.
Date: June 5, 2010
Creator: Kerfeld, Cheryl A.; Heinhorst, Sabine & Cannon, Gordon C.
Object Type: Article
System: The UNT Digital Library
The FERMI@Elettra free-electron-laser source for coherent X-ray physics: photon properties, beam transport system, and applications (open access)

The FERMI@Elettra free-electron-laser source for coherent X-ray physics: photon properties, beam transport system, and applications

FERMI@Elettra is comprised of two free electron lasers (FELs) that will generate short pulses (tau ~;; 25 to 200 fs) of highly coherent radiation in the XUV and soft X-ray region. The use of external laser seeding together with a harmonic upshift scheme to obtain short wavelengths will give FERMI@Elettra the capability to produce high quality, longitudinal coherent photon pulses. This capability together with the possibilities of temporal synchronization to external lasers and control of the output photon polarization will open new experimental opportunities not possible with currently available FELs. Here we report on the predicted radiation coherence properties and important configuration details of the photon beam transport system. We discuss the several experimental stations that will be available during initial operations in 2011, and we give a scientific perspective on possible experiments that can exploit the critical parameters of this new light source.
Date: April 5, 2010
Creator: Allaria, Enrico; Callegari, Carlo; Cocco, Daniele; Fawley, William M.; Kiskinova, Maya; Masciovecchio, Claudio et al.
Object Type: Article
System: The UNT Digital Library
Comparison of the Growth of Pore and Shear Band Driven Detonations (open access)

Comparison of the Growth of Pore and Shear Band Driven Detonations

The authors examine the effect of ignition site topology on the rate of reaction of a detonating material. The hot plane, hot line, and hot finite patch topologies are added to previous work on hot spot ignition. The hot plane and hot patch ignition forms would arise from ignition due to shear banding, and the hot line ignition form is shown to complete the topological set. The limiting behavior of instantaneous ignition is considered and used to construct simple reaction rate vs. extent of reaction forms. they fit simple form factor reaction rates, as might be available in most hydro codes with reactive flow modes, to the simple topologies. The difference between the rate vs. extent forms are examined with the objective that one should be able to use this information to distinguish between the different topological ignition forms.
Date: March 5, 2010
Creator: Nichols, A. L.
Object Type: Article
System: The UNT Digital Library