A new approach for describing the uncertainty associated with organic material decomposition in an abnormal thermal environment is described. Rather than applying multipliers to the pressure predicted by the simulation, the uncertain parameters are incorporated in a broader Latin hypercube sampling study. The resulting distribution gives more information than the pressure multiplier, but similar uncertainty bounds can be derived from a log-normal fit.
In this study, risk-significant pressurized-water reactor severe accident sequences are examined using MELCOR 1.8.5 to explore the range of fission product releases to the reactor containment building. Advances in the understanding of fission product release and transport behavior and severe accident progression are used to render best estimate analyses of selected accident sequences. Particular emphasis is placed on estimating the effects of high fuel burnup in contrast with low burnup on fission product releases to the containment. Supporting this emphasis, recent data available on fission product release from high-burnup (HBU) fuel from the French VERCOR project are used in this study. The results of these analyses are treated as samples from a population of accident sequences in order to employ approximate order statistics characterization of the results. These trends and tendencies are then compared to the NUREG-1465 alternative source term prescription used today for regulatory applications. In general, greater differences are observed between the state-of-the-art calculations for either HBU or low-burnup (LBU) fuel and the NUREG-1465 containment release fractions than exist between HBU and LBU release fractions. Current analyses suggest that retention of fission products within the vessel and the reactor coolant system (RCS) are greater than contemplated in the NUREG-1465 prescription, and that, overall, release fractions to the containment are therefore lower across the board in the present analyses than suggested in NUREG-1465. The decreased volatility of Cs 2 MoO 4 compared to CsI or CsOH increases the predicted RCS retention of cesium, and as a result, cesium and iodine do not follow identical behaviors with respect to distribution among vessel, RCS, and containment. With respect to the regulatory alternative source term, greater differences are observed between the NUREG-1465 prescription and both HBU and LBU predictions than exist between HBU and LBU analyses. Additionally, current analyses suggest that the NUREG-1465 release fractions are conservative by about a factor of 2 in terms of release fractions and that release durations for in-vessel and late in-vessel release periods are in fact longer than the NUREG-1465 durations. It is currently planned that a subsequent report will further characterize these results using more refined statistical methods, permitting a more precise reformulation of the NUREG-1465 alternative source term for both LBU and HBU fuels, with the most important finding being that the NUREG-1465 formula appears to embody significant conservatism compared to current best-estimate analyses. ACKNOWLEDGEMENTS This work was supported by the United States Nuclear Regulatory Commission, Office of Nuclear Regulatory Research. The authors would like to thank Dr. Ian Gauld and Dr. Germina Ilas, of Oak Ridge National Laboratory, for their contributions to this work. In addition to development of core fission product inventory and decay heat information for use in MELCOR models, their insights related to fuel management practices and resulting effects on spatial distribution of fission products in the core was instrumental in completion of our work.
While arc-faults are rare in electrical installations, many documented events have led to fires that resulted in significant damage to energy-generation, commercial and residential systems, as well as surrounding structures, in both the United States and abroad. Arc-plasma discharges arise over time due to a variety of reliability issues related to cable material degradation, electrical and mechanical stresses or acute conductive wiring dislocations. These may lead to discontinuity between energized conductors, facilitating arcing events and fires. Arc-flash events rapidly release significant energy in a localized volume, where the electric arc experiences a reduction in resistance. This facilitates a reduction in electrical resistance as the arc temperature and pressure can increase rapidly. Strong pressure waves, electromagnetic interference (EMI), and intense light from an arc pose a threat to electrical worker safety and system equipment. This arc-fault primer provides basic fundamental insight into arc-fault plasma discharges, and an overview of direct current (DC) and alternating current (AC) arc-fault phenomena. This primer also covers pressure waves and EMI arc-fault hazard analyses related to incident energy prediction and potential damage analysis. Mitigation strategies are also discussed related to engineering design and employment of protective devices including arc-fault circuit interrupters (AFCIs). Best practices related to worker safety are also covered, especially as they pertain to electrical codes and standards, particularly Institute of Electrical and Electronics Engineers (IEEE) 1584 and National Fire Protection Agency (NFPA) 70E. Throughout the primer various modelling and test capabilities at Sandia National Laboratories are also covered, especially as they relate to novel methods of arc-fault/arc-flash characterization and mitigation approaches. Herein, this work describes methods for producing and characterizing controlled, sustained arcs at atmospheric pressures as well as methods for mitigation with novel materials.
ZrTe5, a topological semimetal, has recently attracted great attention due to its extraordinary electronic properties. Extensive studies have been carried out in ZrTe5 on their charge transport properties. However, there are few studies on their spin properties. One well-developed technique to study spin degeneracy of a Landau level (LL) in a two-dimensional system is by tilting magnetic field. It is known that the Landau level energy is proportional to the magnetic field normal component while the Zeeman energy scales with the total magnetic field. Therefore, these two energy scales can be tuned relatively to each other in a tilted magnetic field.
In this report, we describe some approaches to calculate the non-linear system of equations prescribed by the harmonic balance method (HB), a frequency domain analysis technique for modelling a non-linear system of partial differential equations (PDEs). The approach which we ultimately pursue can be seen as a time-collocation approach, except that the harmonic balance equations are obtained weakly (in the sense used in the calculus of variations). This weak formulation allows us to adapt existing transient or stationary PDEs models in the Panzer/Trilinos framework for frequency domain analysis via the harmonic balance method. We begin with a motivatation for the harmonic balance method and outline its mathematical formulation. We then describe some approaches to calculate the harmonic balance formulae, and their means of implementation through the modification of a Panzer tutorial problem - a stationary Helmholtz equation with a constant Dirichlet boundary condition and a non-linear source. For each of these approaches, we outline the necessary adaptations to solve the corresponding (periodically) transient Helmholtz equation with a (temporally) periodic Dirichlet boundary condition and non-linear source.
Currently there are limitations in computing chatter behavior of small electrical contacts embedded in components using finite element models. Reduced order models (ROM) have been developed of such electrical contact sub-assemblies to assess the chatter behavior of the contacts during vibration and shock environments. The current ROM method requires experimental validation. This ROM also neglects the frequency and damping effects of the viscous fluid that typically surrounds such sub-assemblies. Dynamic ring-down testing of the electrical contacts in air will be performed and will provide a validation data set for the current ROM. Additionally, dynamic ring-down testing of the electrical contact will be performed in fluids of varying viscosities that will help characterize the effect of the fluid on the contact for an improved ROM.
This PRD is developed for multiple delivery options which have yet to be determined: The intent for the options is to allow for a risk analysis to be performed and determine the most appropriate location. Each location has benefits where others may not. These options will be vetted in a workshop December 7 and 8, 2016. Once an option is selected the requirements pertaining to options that are not selected will be removed from this PRD.
When two Landau levels are brought into energy degeneracy, interesting phases and phase transitions can occur. For single-layer 2D electrons, a quantum Hall ferromagnetic transition (QHFT) occurs when Landau levels with opposite spins are made degenerate by an in-plane magnetic field, which enhances the Zeeman splitting but keeps the cyclotron energy constant. At the QHFT, the 2D electron system breaks up into magnetic domains with opposite spins, and a resistance spike is observed as electrons move through the domain wall loops. An alternative way to enhance the ratio of Zeeman splitting to the cyclotron energy, which is proportional to m*g*, is to reduce the carrier density (p). Here we report the observation of a QHFT at ν = 2 in a Ge 2D hole system through modulating p without any in-plane magnetic field. We also report the effects of an in-plane magnetic field to this QHFT.
This is one of a series of reports produced as a result of the Co-Optimization of Fuels & Engines (Co-Optima) project, a Department of Energy (DOE)-sponsored multi-agency project initiated to accelerate the introduction of affordable, scalable, and sustainable biofuels and high-efficiency, low-emission vehicle engines. The simultaneous fuels and vehicles research and development is designed to deliver maximum energy savings, emissions reduction, and on-road performance.
Neural machine learning methods, such as deep neural networks (DNN), have achieved remarkable success in a number of complex data processing tasks. These methods have arguably had their strongest impact on tasks such as image and audio processing – data processing domains in which humans have long held clear advantages over conventional algorithms. In contrast to biological neural systems, which are capable of learning continuously, deep artificial networks have a limited ability for incorporating new information in an already trained network. As a result, methods for continuous learning are potentially highly impactful in enabling the application of deep networks to dynamic data sets. Here, inspired by the process of adult neurogenesis in the hippocampus, we explore the potential for adding new neurons to deep layers of artificial neural networks in order to facilitate their acquisition of novel information while preserving previously trained data representations. Our results on the MNIST handwritten digit dataset and the NIST SD 19 dataset, which includes lower and upper case letters and digits, demonstrate that neurogenesis is well suited for addressing the stability-plasticity dilemma that has long challenged adaptive machine learning algorithms.
Flows of complex materials are not only scientifically intriguing, but can also be visually striking. At the SOR Annual Meeting in Denver this fall, you will have the opportunity to have your work recognized as the most engaging image or movie of rheology for 2017.
The Sandia Data Archive (SDA) format is special implementation the HDF5 (Hierarchal Data Format, version 5) standard. Archive files store data in records identified with a unique text label. Primitive records store numeric, logical, and character arrays of arbitrary size and dimensionality. Compound records store composite MAT- LAB variables--cell arrays, structures, and objects--with arbitrary nesting. External records allow text/binary files to be stored alongside archived data or division of a large file into smaller archives for transmission. This report documents version 1.1 of the SDA standard, which adds support for structure and object arrays. The basic principles of SDA remain unchanged from version 1.0, with minor enhancements and bug fixes. The Sandia Mat lab AnalysiS Hierarchy (SMASH) toolbox uses SDA extensively; support utilities from the toolbox are highlighted here. Although the SDA format is designed around MATLAB, its use of HDF5 allows adoption in other computer languages.
The Memory Management Unit (MMU) is one of the most important parts of any modern computing system. It can be thought of as the hardware support for virtual memory, which enforces access permissions, and manages the translation of processes' virtual addresses into real memory physical addresses. The operating system (OS) allocates the physical memory in a small granularity frames that can be accessed by processes with appropriate permissions. Each process has the illusion of having an entire memory space, however, the actual addresses issued by the process, (`virtual addresses'), are translated into the physical frame address allocated by the OS through virtual memory.
Electromagnetic responses reflect the interaction between applied electromagnetic fields and heterogeneous geoelectrical structures. Here by quantifying the relationship between multi-scale electrical properties and the observed electromagnetic response is therefore important for meaningful geologic interpretation. Furthermore, we present here examples of near-surface electromagnetic responses whose spatial fluctuations appear on all length scales, are repeatable and fractally distributed, suggesting that the spatial fluctuations may be considered as “geologic noise”.
The selective partitioning of lipid components in phase-separated membranes is essential for domain formation involved in cellular processes. Identifying and tracking the movement of lipids in cellular systems would be improved if we understood how to achieve selective affinity between fluorophore-labeled lipids and membrane assemblies. Here, we investigated the structure and chemistry of membrane lipids to evaluate lipid designs that partition to the liquid ordered (Lo) phase. A range of fluorophores at the headgroup position and lengths of PEG spacer between the lipid backbone and fluorophore were examined. On a lipid body with saturated palmityl or palmitoyl tails, we found that although the lipid tails can direct selective partitioning to the Lo phase through favorable packing interactions, headgroup hydrophobicity can override the partitioning behavior and direct the lipid to the disordered membrane phase (Ld). The PEG spacer can serve as a buffer to mute headgroup-membrane interactions and thus improve Lo phase partitioning, but its effect is limited with strongly hydrophobic fluorophore headgroups. We present a series of lipid designs leading to the development of novel fluorescently labeled lipids with selective affinity for the Lo phase.
A two-part silicon photonic variable optical attenuator is demonstrated in a compact footprint which can provide a high extinction ratio at wavelengths between 1520 nm and 1620 nm. The device was made by following the conventional p-i-n waveguide section by a high-extinction-ratio second-order microring filter section. The rings provide additional on-off contrast by utilizing a thermal resonance shift, which harvested the heat dissipated by current injection in the p-i-n junction. We derive and discuss a simple thermal-resistance model in explanation of these effects.
There exists significant demand for improved Reynolds-Averaged Navier-Stokes (RANS) turbulence models that are informed by and can represent a richer set of turbulence physics. This paper presents a method of using deep neural networks to learn a model for the Reynolds stress anisotropy tensor from high-fidelity simulation data. A novel neural network architecture is proposed which uses a multiplicative layer with an invariant tensor basis to embed Galilean invariance into the predicted anisotropy tensor. It is demonstrated that this neural network architecture provides improved prediction accuracy compared with a generic neural network architecture that does not embed this invariance property. The Reynolds stress anisotropy predictions of this invariant neural network are propagated through to the velocity field for two test cases. For both test cases, significant improvement versus baseline RANS linear eddy viscosity and nonlinear eddy viscosity models is demonstrated.
Osborn, David L.; Bourgalais, J.; Spencer, Michael; Goulay, F.; Le Picard, S.D.
Product detection studies of C(3P) atom reactions with butene (C4H8) isomers (but-1-ene, cis-but-2-ene, trans-but-2-ene) are carried out in a flow tube reactor at 353 K and 4 Torr under multiple collision conditions. Ground state carbon atoms are generated by 248 nm laser photolysis of tetrabromomethane, CBr4, in a buffer of helium. Thermalized reaction products are detected using synchrotron tunable VUV photoionization and time-of-flight mass spectrometry. The temporal profiles of the detected ions are used to discriminate products from side or secondary reactions. For the C(3P) + trans-but-2-ene and C(3P) + cis-but-2-ene reactions, various isomers of C4H5 and C5H7 are identified as reaction products formed via CH3 and H elimination. Assuming equal ionization cross sections for all C4H5 and C5H7 isomers, C4H5:C5H7 branching ratios of 0.63:1 and 0.60:1 are derived for the C(3P) + trans-but-2-ene and the C(3P) + cis-but-2-ene reactions, respectively. For the C(3P) + but-1-ene reaction, two reaction channels are observed: the H-elimination channel, leading to the formation of the ethylpropargyl isomer, and the C3H3 + C2H5 channel. Assuming equal ionization cross sections for ethylpropargyl and C3H3 radicals, a branching ratio of 1:0.95 for the C3H3 + C2H5 and H + ethylpropargyl channels is derived. The experimental results are compared to previous H atom branching ratios and used to propose the most likely mechanisms for the reaction of ground state carbon atoms with butene isomers. (Chemical Equation Presented).
When diethanolamine (DEA) is used as a curative for a DGEBA epoxy, a rapid “adduct-forming” reaction of epoxide with the secondary amine of DEA is followed by a slow “gelation” reaction of epoxide with hydroxyl and with other epoxide. Through an extensive review of previous investigations of simpler, but chemically similar, reactions, it is deduced that at low temperature the DGEBA/DEA gelation reaction is “activated” (shows a pronounced induction time, similar to autocatalytic behavior) by the tertiary amine in the adduct. At high temperature, the activated nature of the reaction disappears. The impact of this mechanism change on the kinetics of the gelation reaction, as resolved with differential scanning calorimetry, infrared spectroscopy, and isothermal microcalorimetry, is presented. It is shown that the kinetic characteristics of the gelation-reaction of the DGEBA/DEA system are similar to other tertiary-amine activated epoxy reactions and consistent with the anionic polymerization model previously proposed for this class of materials. Principle results are the time-temperature-transformation diagram, the effective activation energy, and the upper stability temperature of the zwitterion initiator of the activated gelation reaction. It is established that the rate of epoxide consumption cannot be generically represented as a function only of temperature and degree of epoxy conversion. The complex chemistry active in the material requires specific consideration of the dilute intermediates in the reaction sequence in order to define a model of the reaction kinetics applicable to all time-temperature cure histories.
Consideration of water supply in transmission expansion planning (TEP) provides a valuable means of managing impacts of thermoelectric generation on limited water resources. Toward this opportunity, thermoelectric water intensity factors and water supply availability (fresh and non-fresh sources) were incorporated into a recent TEP exercise conducted for the electric interconnection in the Western United States. The goal was to inform the placement of new thermoelectric generation so as to minimize issues related to water availability. Although freshwater availability is limited in the West, few instances across five TEP planning scenarios were encountered where water availability impacted the development of new generation. This unexpected result was related to planning decisions that favored the development of low water use generation that was geographically dispersed across the West. These planning decisions were not made because of their favorable influence on thermoelectric water demand; rather, on the basis of assumed future fuel and technology costs, policy drivers and the topology of electricity demand. Results also projected that interconnection-wide thermoelectric water consumption would increase by 31% under the business-as-usual case, while consumption would decrease by 42% under a scenario assuming a low-carbon future. Except in a few instances, new thermoelectric water consumption could be accommodated with less than 10% of the local available water supply; however, limited freshwater supplies and state-level policies could increase use of non-fresh water sources for new thermoelectric generation. Results could have been considerably different if scenarios favoring higher-intensity water use generation technology or potential impacts of climate change had been explored. Conduct of this exercise highlighted the importance of integrating water into all phases of TEP, particularly joint management of decisions that are both directly (e.g., water availability constraint) and indirectly (technology or policy constraints) related to future thermoelectric water demand, as well as, the careful selection of scenarios that adequately bound the potential dimensions of water impact.
Proceedings of the 2016 IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining, ASONAM 2016
Soundarajan, Sucheta; Eliassi-Rad, Tina; Gallagher, Brian; Pinar, Ali P.
Real-world network datasets are often incomplete. Subsequently, any analysis on such networks is likely to produce skewed results. We examine the following problem: given an incomplete network, which b nodes should be probed to bring as many new nodes as possible into the observed network? For instance, consider someone who has observed a portion (say 1%) of the Twitter network. How should she use a limited budget to reduce the incompleteness of the network? In this work, we propose a novel algorithm, called MAXREACH, which uses a budget b to increase the number of nodes in the observed network. Our experiments, across a range of datasets and conditions, demonstrate the efficacy of MAXREACH.
Here, first-principles molecular dynamics simulations were used to investigate the dissociation of sarin (GB) on the calcium silicate hydrate (CSH) mineral tobermorite (TBM), a surrogate for cement. CSH minerals (including TBM) and amorphous materials of similar composition are the major components of Portland cement, the binding agent of concrete. Metadynamics simulations were used to investigate the effect of the TBM surface and confinement in a microscale pore on the mechanism and free energy of dissociation of GB. Our results indicate that both the adsorption site and the humidity of the local environment significantly affect the sarin dissociation energy. In particular, sarin dissociation in a low-water environment occurs via a dealkylation mechanism, which is consistent with previous experimental studies.
Here, the insertion/extraction of lithium into/from various host materials is the basic process by which lithium-ion batteries reversible store charge. This process is generally accompanied by strain in the host material, inducing stress which can lead to capacity loss. Therefore, understanding of both the structural changes and the associated stress – investigated almost exclusively separate to date – is a critical factor for developing high-performance batteries. Here, we report an in situ method, which utilizes Raman spectroscopy in parallel with optical interferometry to study effects of varying charging rates (C-rates) on the structure and stress in a V2O5 thin film cathode. Abrupt stress changes at specific crystal phase transitions in the Li—V—O system are observed and the magnitude of the stress changes with the amount of lithium inserted into the electrode are correlated. A linear increase in the stress as a function of x in LixV2O5 is observed, indicating that C-rate does not directly contribute to larger intercalation stress. However, a more rapid increase in disorder within the LixV2O5 layers is correlated with higher C-rate. Ultimately, these experiments demonstrate how the simultaneous stress/Raman in situ approach can be utilized as a characterization platform for investigating various critical factors affecting lithium-ion battery performance.
Alkali metal borohydrides can reversibly store hydrogen; however, the materials display poor cyclability, oftentimes linked to the occurrence of stable closo-polyborate intermediate species. In an effort to understand the role of such intermediates on the hydrogen storage properties of metal borohydrides, several alkali metal dodecahydro-closo-dodecaborate salts were isolated in anhydrous form and characterized by diffraction and spectroscopic techniques. Mixtures of Li2B12H12, Na2B12H12, and K2B12H12 with the corresponding alkali metal hydrides were subjected to hydrogenation conditions known to favor partial or full reversibility in metal borohydrides. The stoichiometric mixtures of MH and M2B12H12 salts form the corresponding metal borohydrides MBH4 (M = Li, Na, K) in almost quantitative yield at 100 MPa H2 and 500°C. In addition, stoichiometric mixtures of Li2B12H12 and MgH2 were found to form MgB2 at 500°C and above upon desorption in vacuum. The two destabilization strategies outlined above suggest that metal polyhydro-closo-polyborate species can be converted into the corresponding metal borohydrides or borides, albeit under rather harsh conditions of hydrogen pressure and temperature. (Chemical Equation Presented).
A central control algorithm was developed to utilize photovoltaic system advanced inverter functions, specifically fixed power factor and constant reactive power, to provide distribution system voltage regulation and to mitigate voltage regulator tap operations by using voltage measurements at the regulator. As with any centralized control strategy, the capabilities of the control require a reliable and fast communication infrastructure. These communication requirements were evaluated by varying the interval at which the controller sends dispatch commands and evaluating the effectiveness to mitigate tap operations. The control strategy was demonstrated to perform well for communication intervals faster than the delay on the voltage regulator (30 seconds). The communication reliability, latency, and bandwidth requirements were also evaluated.
Oil adsorbs to carbonate reservoirs indirectly through a relatively thick separating water layer, and directly to the surface through a relatively thin intervening water layer. Whereas directly sorbed oil desorbs slowly and incompletely in response to changes in reservoir conditions, indirectly sorbed oil can be rapidly desorbed by changing the chemistry of the separating water layer. The additional recovery might be as much as 30% original oil in place (OOIP) above the ∼30% OOIP recovered from carbonates through reservoir depressurization (primary production) and viscous displacement (waterflooding). Electrostatic adhesive forces are the dominant control over carbonate reservoir wettability. A surface complexation model that quantifies electrostatic adhesion accurately predicts oil recovery trends for carbonates. The approach should therefore be useful for estimating initial wettability and designing fluids that improve oil recovery.
Optimal control theory is applied to compute control for a single-degree-of-freedom heave wave energy converter. The goal is to maximize the energy extraction per cycle. Both constrained and unconstrained optimal control problems are presented. Both periodic and non-periodic excitation forces are considered. In contrast to prior work, it is shown that for this non-autonomous system, the optimal control, in general, includes both singular arc and bang-bang modes. Conditions that determine the switching times to/from the singular arc are derived. Simulation results show that the proposed optimal control solution matches the solution obtained using the complex conjugate control. A generic linear dynamic model is used in the simulations. In conclusion, the main advantage of the proposed control is that it finds the optimal control without the need for wave prediction; it only requires the knowledge of the excitation force and its derivatives at the current time.
Friction stir welded steel pipelines were tested in high pressure hydrogen gas to examine the effects of hydrogen accelerated fatigue crack growth. Fatigue crack growth rate (da/dN) vs. stress-intensity factor range (ΔK) relationships were measured for an X52 friction stir welded pipe tested in 21 MPa hydrogen gas at a frequency of 1 Hz and R = 0.5. Tests were performed on three regions: base metal (BM), center of friction stir weld (FSW), and 15 mm off-center of the weld. For all three material regions, tests in hydrogen exhibited accelerated fatigue crack growth rates that exceeded an order of magnitude compared to companion tests in air. Among tests in hydrogen, fatigue crack growth rates were modestly higher in the FSW than the BM and 15 mm off-center tests. Select regions of the fracture surfaces associated with specified ΔK levels were examined which revealed intergranular fracture in the BM and 15 mm off-center specimens but an absence of intergranular features in the FSW specimens. In conclusion, the X52 friction stir weld and base metal tested in hydrogen exhibited fatigue crack growth rate relationships that are comparable to those for conventional arc welded steel pipeline of similar strength found in the literature.
Power distribution upgrades that include: A new PMH-5, 12KV/208, Delta/WYE transformer. 600A Main Switchboard (MSB) with 600A LSI Main CB and push button capability. New feeders from transformer to MSB. New panels with NEMA 1 enclosures, door-in-door, with 4" gutter space on each side, New NEMA 4X CT Cabinet and meter socket. New 300A & 150A LSI circuit breakers, Trenching for grounding and an allowance of $12,000 for grounding system provided by SNL electrical Operations Engineer.
Etampawala, Thusitha N.; Aryal, Dipak; Osti, Naresh C.; He, Lilin; Heller, William T.; Willis, Carl L.; Grest, Gary S.; Perahia, Dvora
The self-assembly of multiblock copolymers in solutions is controlled by a delicate balance between inherent phase segregation due to incompatibility of the blocks and the interaction of the individual blocks with the solvent. The current study elucidates the association of pentablock copolymers in a mixture of selective solvents which are good for the hydrophobic segments and poor for the hydrophilic blocks using small angle neutron scattering (SANS). The pentablock consists of a center block of randomly sulfonated polystyrene, designed for transport, tethered to poly-ethylene-r-propylene and end-capped by poly-t-butyl styrene, for mechanical stability. We find that the pentablock forms ellipsoidal core-shell micelles with the sulfonated polystyrene in the core and Gaussian decaying chains of swollen poly-ethylene-r-propylene and poly-t-butyl styrene tertiary in the corona. With increasing solution concentration, the size of the micelle, the thickness of the corona, and the aggregation number increase, while the solvent fraction in the core decreases. In dilute solution the micelle increases in size as the temperature is increased, however, temperature effects dissipate with increasing solution concentration.
IEEE International Conference on Automation Science and Engineering
Sundar, Kaarthik; Qin, Jianglei; Rathinam, Sivakumar; Ntaimo, Lewis; Darbha, Swaroop; Valicka, Christopher G.
Remote sensing systems such as a constellation of satellites periodically observe regions on the surface of the earth to collect visual imagery and other sensory data that is both spatial and temporal. Efficiently scheduling sensing activities on a constellation of satellites is a natural problem that arises while managing these systems. Given a set of satellites, a set of sensing activities with their priorities and timing constraints, the objective of the problem is to assign activities to the satellites over a given time period such that at most one activity is assigned to a satellite at any time and the quality of information collected by the satellites is maximized. This problem is computationally challenging to solve and is NP-Hard. In this research, heuristics are first developed to find feasible solutions based on a greedy approach and by dividing the given time period into smaller blocks of time. To determine the quality of a feasible solution, an integer linear programming approach is also developed. Numerical results show that good feasible solutions can be obtained in the order of seconds on a standard computer for a constellation of up to eight satellites and thousand activities using the proposed algorithms.
Chan, Chun W.I.; Albo, Asaf; Hu, Qing; Reno, John L.
Contemporary research into diagonal active region terahertz quantum cascade lasers for high temperature operation has yielded little success. We present evidence that the failure of high diagonality alone as a design strategy is due to a fundamental trade-off between large optical oscillator strength and long upper-level lifetime. We hypothesize that diagonality needs to be paired with increased doping in order to succeed, and present evidence that highly diagonal designs can benefit from much higher doping than normally found in terahertz quantum cascade lasers. In assuming the benefits of high diagonality paired with high doping, we also highlight important challenges that need to be overcome, specifically the increased importance of carrier induced band-bending and impurity scattering.
Magnetically driven implosions of solid metal shells are an effective vehicle to compress materials to extreme pressures and densities. Rayleigh-Taylor instabilities (RTI) are ubiquitous, yet typically undesired features in all such experiments where solid materials are rapidly accelerated to high velocities. In cylindrical shells ("liners"), the magnetic field driving the implosion can exacerbate the RTI. We suggest an approach to implode solid metal liners enabling a remarkable reduction in the growth of magnetized RTI (MRTI) by employing a magnetic drive with a tilted, dynamic polarization, forming a dynamic screw pinch. Our calculations, based on a self-consistent analytic framework, demonstrate that the cumulative growth of the most deleterious MRTI modes may be reduced by as much as 1 to 2 orders of magnitude. One key application of this technique is to generate increasingly stable, higher-performance implosions of solid metal liners to achieve fusion [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)]. We weigh the potentially dramatic benefits of the solid liner dynamic screw pinch against the experimental tradeoffs required to achieve the desired drive field history and identify promising designs for future experimental and computational studies.
As PV penetration on the distribution system increases, there is growing concern about how much PV each feeder can handle. A total of 216 medium-voltage distributions feeders have been analyzed in detail for their individual PV hosting capacity and the locational PV hosting capacity at all the buses on the feeder. A statistical analysis is performed on the hosting capacity results in order to compare correlation with feeder load, percent of issues caused, and the variation for different feeder voltages. Due to the large number of distribution systems simulated, the analysis provides novel insights into each of these areas. Investigating the locational PV hosting capacity also expands the conventional analytical methods that study only the worst-case PV scenario.
FERC order 755 and FERC order 784 provide pay-for-performance requirements and direct utilities and independent system operators to consider speed and accuracy when purchasing frequency regulation. Independent System Operators (ISOs) have differing implementations of pay-for-performance. This paper focuses on the PJM implementation. PJM is a regional transmission organization in the northeastern United States that serves 13 states and the District of Columbia. PJM's implementation employs a two part payment based on the Regulation Market Capability Clearing price (RMCCP) and the Regulation Market Performance Clearing Price (RMPCP). The performance credit includes a mileage ratio. Both the RMCCP and RMPCP employ an actual performance score. Using the PJM remuneration model, this paper outlines the calculations required to estimate the maximum potential revenue from participation in arbitrage and regulation in day-ahead markets using linear programming. Historical PJM data from 2014 and 2015 was then used to evaluate the maximum potential revenue from a 5 MWh, 20 MW system based on the Beacon Power Hazle Township flywheel plant. Finally, a heuristic trading algorithm that does not require perfect foresight was evaluated against the results of the optimization algorithm.
We present simulation and experimental results showing circular polarization is more tolerant of optical collection geometry (field of view and collection area) variations than linear polarization for forward-scattering environments. Circular polarization also persists superiorly in the forward-scattering environment compared to linear polarization by maintaining its degree of polarization better through increasing optical thicknesses. In contrast, both linear and circular polarizations are susceptible to collection geometry variations for isotropic-scattering (Rayleigh regime) environments, and linear polarization maintains a small advantage in polarization persistence. Simulations and measurements are presented for laboratory-based environments of polystyrene microspheres in water. Particle diameters were 0.0824 μm (for isotropic-scattering) and 1.925 μm (for forward-scattering) with an illumination wavelength of 543.5 nm.
Background: Successful implementation of modified cyanobacteria as hosts for industrial applications requires the development of a cyanobacterial chassis. The cyanobacterium Synechococcus sp. PCC 7002 embodies key attributes for an industrial host, including a fast growth rate and high salt, light, and temperature tolerances. This study addresses key limitations in the advancement of Synechococcus sp. PCC 7002 as an industrial chassis. Results: Tools for genome integration were developed and characterized, including several putative neutral sites for genome integration. The minimum homology arm length for genome integration in Synechococcus sp. PCC 7002 was determined to be approximately 250 bp. Three fluorescent protein reporters (hGFP, Ypet, and mOrange) were characterized for gene expression, microscopy, and flow cytometry applications in Synechococcus sp. PCC 7002. Of these three proteins, the yellow fluorescent protein (Ypet) had the best optical properties for minimal interference with the native photosynthetic pigments and for detection using standard microscopy and flow cytometry optics. Twenty-five native promoters were characterized as tools for recombinant gene expression in Synechococcus sp. PCC 7002 based on previous RNA-seq results. This characterization included comparisons of protein and mRNA levels as well as expression under both continuous and diurnal light conditions. Promoters A2520 and A2579 were found to have strong expression in Synechococcus sp. PCC 7002 while promoters A1930, A1961, A2531, and A2813 had moderate expression. Promoters A2520 and A2813 showed more than twofold increases in gene expression under light conditions compared to dark, suggesting these promoters may be useful tools for engineering diurnal regulation. Conclusions: The genome integration, fluorescent protein, and promoter tools developed in this study will help to advance Synechococcus sp. PCC 7002 as a cyanobacterial chassis. The long minimum homology arm length for Synechococcus sp. PCC 7002 genome integration indicates native exonuclease activity or a low efficiency of homologous recombination. Low correlation between transcript and protein levels in Synechococcus sp. PCC 7002 suggests that transcriptomic data are poor selection criteria for promoter tool development. Lastly, the conventional strategy of using promoters from photosynthetic operons as strong promoter tools is debunked, as promoters from hypothetical proteins (A2520 and A2579) were found to have much higher expression levels.
Talin, Albert A.; Ruzmetov, Dmitry; Kolmakov, Andrei; Mckelvey, Kim; El Gabaly, Farid; Ware, Nicholas; Dunn, Bruce; White, Henry
Realization of safe, long cycle life and simple to package solid-state rechargeable batteries with high energy and power density has been a long-standing goal of the energy storage community.[1,2] Much of the research activity has been focused on developing new solid electrolytes with high Li ionic conductivity. In addition, LiPON, the only solid electrolyte currently used in commercial thin film solid state Li-ion batteris (SSLIBs), has a conductivity of ~10-6 S/cm, compared to ~0.01 S/cm typically observed for liquid organic electrolytes[3].
Sparse matrix-matrix multiplication (or SpGEMM) is a key primitive for many high-performance graph algorithms as well as for some linear solvers, such as algebraic multigrid. The scaling of existing parallel implementations of SpGEMM is heavily bound by communication. Even though 3D (or 2.5D) algorithms have been proposed and theoretically analyzed in the flat MPI model on Erdös--Rényi matrices, those algorithms had not been implemented in practice and their complexities had not been analyzed for the general case. In this work, we present the first implementation of the 3D SpGEMM formulation that exploits multiple (intranode and internode) levels of parallelism, achieving significant speedups over the state-of-the-art publicly available codes at all levels of concurrencies. We extensively evaluate our implementation and identify bottlenecks that should be subject to further research.
For decades, neural networks have shown promise for next-generation computing, and recent breakthroughs in machine learning techniques, such as deep neural networks, have provided state-of-the-art solutions for inference problems. However, these networks require thousands of training processes and are poorly suited for the precise computations required in scientific or similar arenas. The emergence of dedicated spiking neuromorphic hardware creates a powerful computational paradigm which can be leveraged towards these exact scientific or otherwise objective computing tasks. We forego any learning process and instead construct the network graph by hand. In turn, the networks produce guaranteed success often with easily computable complexity. We demonstrate a number of algorithms exemplifying concepts central to spiking networks including spike timing and synaptic delay. We also discuss the application of cross-correlation particle image velocimetry and provide two spiking algorithms; one uses time-division multiplexing, and the other runs in constant time.
We describe the challenge of implementing optical interconnect for beyond Moore's electronic devices. In particular, we developed a simple link model and calculated the optical communications energy for logic voltages down to 10 mV. The results of this link model show a limit to the minimum communications energy that depends on the achievable extinction ratio of the devices. This work gives some insight into the tact that should be taken for improved optical devices to have an impact in future computing systems using ultra-low voltage transistor devices.
We address practical limits of energy efficiency scaling for logic and memory. Scaling of logic will end with unreliable operation, making computers probabilistic as a side effect. The errors can be corrected or tolerated, but overhead will increase with further scaling. We address the tradeoff between scaling and error correction that yields minimum energy per operation, finding new error correction methods with energy consumption limits about 2× below current approaches. The maximum energy efficiency for memory depends on several other factors. Adiabatic and reversible methods applied to logic have promise, but overheads have precluded practical use. However, the regular array structure of memory arrays tends to reduce overhead and makes adiabatic memory a viable option. This paper reports an adiabatic memory that has been tested at about 85× improvement over standard designs for energy efficiency. Combining these approaches could set energy efficiency expectations for processor-in-memory computing systems.
Amidst the rising impact of machine learning and the popularity of deep neural networks, learning theory is not a solved problem. With the emergence of neuromorphic computing as a means of addressing the von Neumann bottleneck, it is not simply a matter of employing existing algorithms on new hardware technology, but rather richer theory is needed to guide advances. In particular, there is a need for a richer understanding of the role of adaptivity in neural learning to provide a foundation upon which architectures and devices may be built. Modern machine learning algorithms lack adaptive learning, in that they are dominated by a costly training phase after which they no longer learn. The brain on the other hand is continuously learning and provides a basis for which new mathematical theories may be developed to greatly enrich the computational capabilities of learning systems. Game theory provides one alternative mathematical perspective analyzing strategic interactions and as such is well suited to learning theory.
Continuing to improve computational energy efficiency will soon require developing and deploying new operational paradigms for computation that circumvent the fundamental thermodynamic limits that apply to conventionally-implemented Boolean logic circuits. In particular, Landauer's principle tells us that irreversible information erasure requires a minimum energy dissipation of kT ln 2 per bit erased, where k is Boltzmann's constant and T is the temperature of the available heat sink. However, correctly applying this principle requires carefully characterizing what actually constitutes "information erasure" within a given physical computing mechanism. In this paper, we show that abstract combinational logic networks can validly be considered to contain no information beyond that specified in their input, and that, because of this, appropriately-designed physical implementations of even multi-layer networks can in fact be updated in a single step while incurring no greater theoretical minimum energy dissipation than is required to update their inputs. Furthermore, this energy can approach zero if the network state is updated adiabatically via a reversible transition process. Our novel operational paradigm for updating logic networks suggests an entirely new class of hardware devices and circuits that can be used to reversibly implement Boolean logic with energy dissipation far below the Landauer limit.
2016 IEEE International Conference on Rebooting Computing, ICRC 2016 - Conference Proceedings
Debenedictis, Erik; Frank, Michael P.; Ganesh, Natesh; Anderson, Neal G.
At roughly kT energy dissipation per operation, the thermodynamic energy efficiency "limits" of Moore's Law were unimaginably far off in the 1960s. However, current computers operate at only 100-10,000 times this limit, forming an argument that historical rates of efficiency scaling must soon slow. This paper reviews the justification for the ∼kT per operation limit in the context of processors for von Neumann-class computer architectures of the 1960s. We then reapply the fundamental arguments to contemporary applications and identify a new direction for future computing in which the ultimate efficiency limits would be much further out. New nanodevices with high-level functions that aggregate the functionality of several logic gates and some local memory may be the right building blocks for much more energy efficient execution of emerging applications - such as neural networks.
We discuss the engineering of p-AlGaN cladding layers for achieving efficient tunnel-injected III-Nitride ultraviolet light emitting diodes (UV LEDs) in the UV-A spectral range. We show that the capacitance-voltage measurements can be used to estimate the compensation and doping in the p-AlGaN layers located between the multi-quantum well region and the tunnel junction layer. By increasing the p-type doping concentration to overcome the background compensation, on-wafer external quantum efficiency and wall-plug efficiency of 3.37% and 1.62%, respectively, were achieved for the tunnel-injected UV LEDs emitting at 325 nm. We also show that interband tunneling hole injection can be used to realize UV LEDs without any acceptor doping. The work discussed here provides new understanding of hole doping and transport in AlGaN-based UV LEDs and demonstrates the excellent performance of tunnel-injected LEDs for the UV-A wavelength range.
We use fluorescence microscopy to examine the dynamics of the crowding-induced mixing transition of liquid ordered (Lo)-liquid disordered (Ld) phase separated lipid bilayers when the following particles of increasing size bind to either the Lo or Ld phase: Ubiquitin, green fluorescent protein (GFP), and nanolipoprotein particles (NLPs) of two diameters. These proteinaceous particles contained histidine-tags, which were phase targeted by binding to iminodiacetic acid (IDA) head groups, via a Cu2+ chelating mechanism, of lipids that specifically partition into either the Lo phase or Ld phase. The degree of steric pressure was controlled by varying the size of the bound particle (10-240 kDa) and the amount of binding sites present (i.e., DPIDA concentrations of 9 and 12 mol%) in the supported lipid multibilayer platform used here. We develop a mass transfer-based diffusional model to analyze the observed Lo phase domain dissolution that, along with visual observations and activation energy calculations, provides insight into the sequence of events in crowding-induced mixing. Our results suggest that the degree of steric pressure and target phase influence not only the efficacy of steric-pressure induced mixing, but the rate and controlling mechanism for which it occurs.
The pulsed photolytic chlorine-initiated oxidation of diethyl ketone [DEK; (CH3CH2)2CO], 2,2,4,4-d4-DEK [d4-DEK; (CH3CD2)2CO], and 1,1,1,5,5,5-d6-DEK [d6-DEK; (CD3CH2)2CO] is studied at 8 torr and 1−2 atm and from 400−625 K. Cl atoms produced by laser photolysis react with diethyl ketone to form either primary (3-pentan-on-1-yl, RP) or secondary (3-pentan-on-2-yl, RS) radicals, which in turn react with O2. Multiplexed time-of-flight mass spectrometry, coupled to either a hydrogen discharge lamp or tunable synchrotron photoionizing radiation, is used to detect products as a function of mass, time, and photon energy. At 8 torr, the nature of the chain propagating cyclic ether + OH channel changes as a function of temperature. At 450 K, the production of OH is mainly in conjunction with formation of 2,4-dimethyloxetan-3-one, resulting from reaction of the resonance-stabilized secondary RS with O2. In contrast, at 550 K and 8 torr, 2-methyl-tetrahydrofuran-3-one, originating from oxidation of the primary radical (RP), is observed as the dominant cyclic ether product. Formation of both of these cyclic ether production channels proceeds via a resonance-stabilized hydroperoxy alkyl (QOOH) intermediate. Little or no ketohydroperoxide (KHP) is observed under the low-pressure conditions. At higher O2 concentrations and higher pressures (1−2 atm), a strong KHP signal appears as the temperature is increased above 450 K. Definitive isomeric identification from measurements on the deuterated DEK isotopologues indicates the favored pathway produces a γ-KHP via resonance-stabilized alkyl, QOOH, and HOOPOOH radicals. Time-resolved measurements reveal the KHP formation becomes faster and signal more intense upon increasing temperature from 450 to 575 K before intensity drops significantly at 625 K. The KHP time profile also shows a peak followed by a gradual depletion for the extent of experiment. Several tertiary products exhibit a slow accumulation in coincidence with the observed KHP decay. These products can be associated with decomposition of KHP by β-scission pathways or via isomerization of a γ-KHP into a cyclic peroxide intermediate (Korcek mechanism). The oxidation of d4-DEK, where kinetic isotope effects disfavor γ-KHP formation, shows greatly reduced KHP formation and associated signatures from KHP decomposition products.
Bouchard, Kristofer E.; Aimone, James B.; Chun, Miyoung; T, Dean; Denker, Michael; Diesmann, Markus; Donofrio, David D.; Frank, Loren M.; Kasthuri, Narayanan; C, Koch; Ruebel, Oliver; Simon, Horst D.; Sommer, Friedrich T.; Prabhat, None
Opportunities offered by new neuro-technologies are threatened by lack of coherent plans to analyze, manage, and understand the data. High-performance computing will allow exploratory analysis of massive datasets stored in standardized formats, hosted in open repositories, and integrated with simulations.
In 2 experiments, we examined the impact of foveal semantic expectancy and congruity on parafoveal word processing during reading. Experiment 1 utilized an eye-tracking gaze-contingent display change paradigm, and Experiment 2 measured event-related brain potentials (ERPs) in a modified flanker rapid serial visual presentation (RSVP) paradigm. Eye-tracking and ERP data converged to reveal graded effects of foveal load on parafoveal processing. In Experiment 1, when word n was highly expected, and thus foveal load was low, there was a large parafoveal preview benefit to word n + 1. When word n was unexpected but still plausible, preview benefits to n + 1 were reduced in magnitude, and when word n was semantically incongruent, the preview benefit to n + 1 was unreliable in early pass measures. In Experiment 2, ERPs indicated that when word n was expected, and thus foveal load was low, readers successfully discriminated between valid and orthographically invalid previews during parafoveal perception. However, when word n was unexpected, parafoveal processing of n + 1 was reduced, and it was eliminated when word n was semantically incongruent. Taken together, these findings suggest that sentential context modulates the allocation of attention in the parafovea, such that covert allocation of attention to parafoveal processing is disrupted when foveal words are inconsistent with expectations based on various contextual constraints.
To address the transport and trapping of hydrogen isotopes, several permeation experiments are being pursued at both Sandia National Laboratories (deuterium gas-driven permeation) and Idaho National Laboratories (tritium gas- and plasma-driven tritium permeation). These experiments are in part a collaboration between the US and Japan to study the performance of tungsten at divertor relevant temperatures (PHENIX). Here we report on the development of a high temperature (≤1150 °C) gas-driven permeation cell and initial measurements of deuterium permeation in several types of tungsten: high purity tungsten foil, ITER-grade tungsten (grains oriented through the membrane), and dispersoid-strengthened ultra-fine grain (UFG) tungsten being developed in the US. Experiments were performed at 500–1000 °C and 0.1–1.0 atm D2 pressure. Permeation through ITER-grade tungsten was similar to earlier W experiments by Frauenfelder (1968–69) and Zaharakov (1973). Data from the UFG alloy indicates marginally higher permeability (< 10×) at lower temperatures, but the permeability converges to that of the ITER tungsten at 1000 °C. The permeation cell uses only ceramic and graphite materials in the hot zone to reduce the possibility for oxidation of the sample membrane. Sealing pressure is applied externally, thereby allowing for elevation of the temperature for brittle membranes above the ductile-to-brittle transition temperature.
Allendorf, Mark; Fischer, Roland A.; Medishetty, Raghavender
The well-known synthetic versatility of metal-organic frameworks (MOFs) is rooted in the ability to predict the metal-ion coordination geometry and the vast possibilities to use organic chemistry to modify the linker groups. However, the use of molecules occupying the pores as a component of framework design has been largely ignored. Recent reports show that the presence of these so-called guests can have dramatic effects, even when they are a seemingly innocuous species such as water or polar solvents. We term these guests non-innocent when their presence alters the MOF in such a way as to create a new material with properties different from the MOF without the guests. Advantages of using guest molecules to impart new properties to MOFs include the relative ease of introducing new functionalities, the ability to modify the material properties at will by removing the guest or inserting different ones, and avoidance of the difficulties associated with synthesizing new frameworks, which can be challenging even when the basic topology remains constant. In this article, we describe the Guest@MOF concept and provide examples illustrating its potential as a new MOF design element.
Transition metal oxide (TMO) memristors have recently attracted special attention from the semiconductor industry and academia. Memristors are one of the strongest candidates to replace flash memory, and possibly DRAM and SRAM in the near future. Moreover, memristors have a high potential to enable beyond-CMOS technology advances in novel architectures for high performance computing (HPC). The utility of memristors has been demonstrated in reprogrammable logic (cross-bar switches), brain-inspired computing and in non-CMOS complementary logic. Indeed, the potential use of memristors as logic devices is especially important considering the inevitable end of CMOS technology scaling that is anticipated by 2025. In order to aid the on-going Sandia memristor fabrication effort with a memristor design tool and establish a clear physical picture of resistance switching in TMO memristors, we have created and validated with experimental data a simulation tool we name the Memristor Charge Transport (MCT) Simulator.
The World Water and Agriculture Model has been used to simulate water, hydropower, and food sector effects in Egypt, Sudan, and Ethiopia during the filling of the Grand Ethiopian Renaissance Dam reservoir. This unique capability allows tradeoffs to be made between filling policies for the Grand Ethiopian Renaissance Dam reservoir. This Nile River Basin study is presented to illustrate the capacity to use the World Water and Agriculture Model to simulate regional food security issues while keeping a global perspective. The study uses runoff data from the Intergovernmental Panel for Climate Change Coupled Model Inter-comparison Project Phase 5 and information from the literature in order to establish a reasonable set of hydrological initial conditions. Gross Domestic Product and population growth are modelled exogenously based on a composite projection of United Nations and World Bank data. The effects of the Grand Ethiopian Renaissance Dam under various percentages of water withheld are presented.
In this report we address the challenge of designing efficient protection system for inverter- dominated microgrids. These microgrids are characterised with limited fault current capacity as a result of current-limiting protection functions of inverters. Typically, inverters limit their fault contribution in sub-cycle time frame to as low as 1.1 per unit. As a result, overcurrent protection could fail completely to detect faults in inverter-dominated microgrids. As part of this project a detailed literature survey of existing and proposed microgrid protection schemes were conducted. The survey concluded that there is a gap in the available microgrid protection methods. The only credible protection solution available in literature for low- fault inverter-dominated microgrids is the differential protection scheme which represents a robust transmission-grade protection solution but at a very high cost. Two non-overcurrent protection schemes were investigated as part of this project; impedance-based protection and transient-based protection. Impedance-based protection depends on monitoring impedance trajectories at feeder relays to detect faults. Two communication-based impedance-based protection schemes were developed. the first scheme utilizes directional elements and pilot signals to locate the fault. The second scheme depends on a Central Protection Unit that communicates with all feeder relays to locate the fault based on directional flags received from feeder relays. The later approach could potentially be adapted to protect networked microgrids and dynamic topology microgrids. Transient-based protection relies on analyzing high frequency transients to detect and locate faults. This approach is very promising but its implementation in the filed faces several challenges. For example, high frequency transients due to faults can be confused with transients due to other events such as capacitor switching. Additionally, while detecting faults by analyzing transients could be doable, locating faults based on analyzing transients is still an open question.
The Spent Fuel and Waste Science and Technology (SFWST) Campaign of the U.S. Department of Energy (DOE) Office of Nuclear Energy (NE) is conducting research and development (R&D) on generic deep geologic disposal systems (i.e., repositories). This report describes specific activities in FY 2016 associated with the development of a Defense Waste Repository (DWR)a for the permanent disposal of a portion of the HLW and SNF derived from national defense and research and development (R&D) activities of the DOE.
Using metalorganic vapor phase epitaxy, a comprehensive study of BxGa1-xN growth on GaN and AlN templates is described. BGaN growth at high-temperature and high-pressure results in rough surfaces and poor boron incorporation efficiency, while growth at low-temperature and low-pressure (750–900 °C and 20 Torr) using nitrogen carrier gas results in improved surface morphology and boron incorporation up to ~7.4% as determined by nuclear reaction analysis. However, further structural analysis by transmission electron microscopy and x-ray pole figures points to severe degradation of the high boron composition films, into a twinned cubic structure with a high density of stacking faults and little or no room temperature photoluminescence emission. Films with <1% triethylboron (TEB) flow show more intense, narrower x-ray diffraction peaks, near-band-edge photoluminescence emission at ~362 nm, and primarily wurtzite-phase structure in the x-ray pole figures. For films with >1% TEB flow, the crystal structure becomes dominated by the cubic phase. As a result, only when the TEB flow is zero (pure GaN), does the cubic phase entirely disappear from the x-ray pole figure, suggesting that under these growth conditions even very low boron compositions lead to mixed crystalline phases.
Water utilities are vulnerable to a wide variety of human-caused and natural disasters. These disruptive events can result in loss of water service, contaminated water, pipe breaks, and failed equipment. Furthermore, long term changes in water supply and customer demand can have a large impact on the operating conditions of the network. The ability to maintain drinking water service during and following these types of events is critical. Simulation and analysis tools can help water utilities explore how their network will respond to disruptive events and plan effective mitigation strategies. The U.S. Environmental Protection Agency and Sandia National Laboratories are developing new software tools to meet this need. The Water Network Tool for Resilience (WNTR, pronounced winter) is a Python package designed to help water utilities investigate resilience of water distribution systems over a wide range of hazardous scenarios and to evaluate resilience-enhancing actions. The following documentation includes installation instructions and examples, description of software features, and software license. It is assumed that the reader is familiar with the Python Programming Language.
Current discriminator designs are based on historical designs and traditional manufacturing methods. The goal of this project was to form non-traditional groups to create novel discriminator designs by taking advantage of additive manufacturing. These designs would expand current discriminator designs and provide insight on the applicability of additive manufacturing for future projects. Our design stretched the current abilities of additive manufacturing and noted desired improvements for the future. Through collaboration with NSC, we noted several additional technologies which work well with additive manufacturing such as topology optimization and CT scanning and determined how these technologies could be improved to better combine with additive manufacturing.
Vanadium dioxide (VO2) is an attractive material for a variety of applications due to its metal-to-insulator transition (MIT) observed at modest temperatures. This transition takes VO2 from its low temperature insulating monoclinic phase to a high temperature (above 68°C) metallic rutile phase. This transition gives rise to a change in resistivity up to 5 orders of magnitude and a change in complex refractive index (especially at IR wavelengths), which is of interest for radar circuit protection and tunable control of infrared signature. Recently, collaborations have been initiated between CINT scientists and external university programs. The Enhanced Surveillance funds help fund this work which enabled synthesis of VO2 films for several collaborations with internal and external researchers.
We begin with a model of 20 LTD modules, connected in parallel. We assume each LTD module consists of 10 LTD cavities, connected in series. We assume each cavity includes 20 LTD bricks, in parallel. Each brick is assumed to have a 40-nF capacitance and a 160-nH inductance. We use for this calculation the RLC-circuit model of an LTD system that was developed by Mazarakis and colleagues.
Modern semiconductor devices rely on the transport of minority charge carriers. Direct examination of minority carrier lifetimes in real devices with nanometer-scale features requires a measurement method with simultaneously high spatial and temporal resolutions. Achieving nanometer spatial resolutions at sub-nanosecond temporal resolution is possible with pump-probe methods that utilize electrons as probes. Recently, a stroboscopic scanning electron microscope was developed at Caltech, and used to study carrier transport across a Si p-n junction [ 1 , 2 , 3 ] . In this report, we detail our development of a prototype scanning ultrafast electron microscope system at Sandia National Laboratories based on the original Caltech design. This effort represents Sandia's first exploration into ultrafast electron microscopy.
Concentrating solar power (CSP) utilizes solar thermal energy to drive a thermal power cycle for the generation of electricity. CSP systems are facilitated as large, centralized power plants , such as power towers and trough systems, to take advantage of ec onomies of scale through dispatchable thermal energy storage, which is a principle advantage over other energy generation systems . Additionally, the combination of large solar concentration ratios with high solar conversion efficiencies provides a strong o pportunity of employment of specific power cycles such as the Brayton gas cycle that utilizes super critical fluids such as supercritical carbon dioxide (s CO 2 ) , compared to other sola r - fossil hybrid power plants. A comprehensive thermal - fluids examination is provided by this work of various heat transfer phenomena evident in CSP technologies. These include sub - systems and heat transfer fundamental phenomena evident within CSP systems , which include s receivers, heat transfer fluids (HTFs), thermal storage me dia and system designs , thermodynamic power block systems/components, as well as high - temperature materials. This work provides literature reviews, trade studies, and phenomenological comparisons of heat transfer media (HTM) and components and systems, all for promotion of high performance and efficient CSP systems. In addition, f urther investigations are also conducted that provide advanced heat transfer modeling approaches for gas - particle receiver systems , as well as performance/efficiency enhancement re commendations, particularly for solarized supercritical power systems .