The Neutron Scatter Camera (NSC) is a neutron spectrometer and imager that has been developed and improved by the Sandia National Laboratories for several years. Built for special nuclear material searches, the instrument was configured by the design to reconstruct neutron sources within the fission energy range 1–10 MeV. In this work, we present modifications that attempt to extend the NSC sensitivity to neutron energies in the range ~10–200 MeV and discuss the corresponding consequences for the event processing. We present simulation results that manifest important aspects of the NSC response to those intermediate energy neutrons. The simulation results also evidence that the instrument’s spectroscopic capabilities severely deteriorate at those energies, mainly due to the uncertainties in measuring energy, time, and distance between the two neutron scattering interactions. Furthermore, this work is motivated by the need to characterize neutron fluxes at particle accelerators as they may represent important backgrounds for neutrino experiments.
Scaling arrays of non-volatile memory devices from academic demonstrations to reliable, manufacturable systems requires a better understanding of variability at array and wafer-scale levels. CrossSim models the accuracy of neural networks implemented on an analog resistive memory accelerator using the cycle-to-cycle variability of a single device. In this work, we extend this modeling tool to account for device-to-device variation in a realistic way, and evaluate the impact of this reliability issue in the context of neuromorphic online learning tasks.
We report on the position, timing, and energy resolution of a range of plastic scintillator bars and reflector treatments using dual-ended silicon photomultiplier readout. These measurements are motivated by the upcoming construction of an optically segmented single-volume neutron scatter camera, in which neutron elastic scattering off of hydrogen is used to kinematically reconstruct the location and energy of a neutron-emitting source. For this application, interaction position resolutions of about 10 mm and timing resolutions of about 1 ns are necessary to achieve the desired efficiency for fission-energy neutrons. The results presented here indicate that this is achievable with an array of 5×5×190mm 3 bars of EJ-204 scintillator wrapped in Teflon tape, read out with SensL's J-series 6×6mm 2 silicon photomultipliers. With two independent setups, we also explore the systematic variability of the position resolution, and show that, in general, using the difference in the pulse arrival time at the two ends is less susceptible to systematic variation than using the log ratio of the charge amplitude of the two ends. Finally, we measure a bias in the absolute time of interactions as a function of position along the bar: the measured interaction time for events at the center of the bar is ∼100 ps later than interactions near the SiPM.
A stable explicit time-scale splitting algorithm for stiff chemical Langevin equations (CLEs) is developed, based on the concept of computational singular perturbation. The drift term of the CLE is projected onto basis vectors that span the fast and slow subdomains. The corresponding fast modes exhaust quickly, in the mean sense, and the system state then evolves, with a mean drift controlled by slow modes, on a random manifold. The drift-driven time evolution of the state due to fast exhausted modes is modeled algebraically as an exponential decay process, while that due to slow drift modes and diffusional processes is integrated explicitly. This allows time integration step sizes much larger than those required by typical explicit numerical methods for stiff stochastic differential equations. The algorithm is motivated and discussed, and extensive numerical experiments are conducted to illustrate its accuracy and stability with a number of model systems.
Modern computational validation efforts rely on comparison of known experimental quantities such as current, voltage, particle densities, and other plasma properties with the same values determined through simulation. A discrete photon approach for radiation transport was recently incorporated into a particle-in-cell/direct simulation Monte Carlo code. As a result, spatially and temporally resolved synthetic spectra may be generated even for non-equilibrium plasmas. The generation of this synthetic spectra lends itself to potentially new validation opportunities. In this work, initial comparisons of synthetic spectra are made with experimentally gathered optical emission spectroscopy. A custom test apparatus was constructed that contains a 0.5 cm gap distance parallel plane discharge in ultra high purity helium gas (99.9999%) at a pressure of 75 Torr. Plasma generation is initiated with the application of a fast rise-time, 100 ns full-width half maximum, 2.0 kV voltage pulse. Transient electrical diagnostics are captured along with time-resolved emission spectra. A one-dimensional simulation is run under the same conditions and compared against the experiment to determine if sufficient physics are included to model the discharge. To sync the current measurements from experiment and simulation, significant effort was undertaken to understand the kinetic scheme required to reproduce the observed features. Additionally, the role of the helium molecule excimer emission and atomic helium resonance emission on photocurrent from the cathode are studied to understand which effect dominates photo-feedback processes. Results indicate that during discharge development, atomic helium resonance emission dominates the photo-flux at the cathode even though it is strongly self-absorbed. A comparison between the experiment and simulation demonstrates that the simulation reproduces observed features in the experimental discharge current waveform. Furthermore, the synthesized spectra from the kinetic method produces more favorable agreement with the experimental data than a simple local thermodynamic equilibrium calculation and is a first step towards using spectra generated from a kinetic method in validation procedures. The results of this study produced a detailed compilation of important helium plasma chemistry reactions for simulating transient helium plasma discharges.
Willsey, Graham G.; Eckstrom, Korin; Labauve, Annette E.; Hinkel, Lauren A.; Schutz, Kristin; Meagher, Robert J.; Lipuma, John J.; Wargo, Matthew J.
Stenotrophomonas maltophilia is a Gram-negative opportunistic pathogen that can infect the lungs of people with cystic fibrosis (CF). The highly viscous mucus in the CF lung, expectorated as sputum, serves as the primary nutrient source for microbes colonizing this site and induces virulence-associated phenotypes and gene expression in several CF pathogens. Here, we characterized the transcriptional responses of three S. maltophilia strains during exposure to synthetic CF sputum media (SCFM2) to gain insight into how this organism interacts with the host in the CF lung. These efforts led to the identification of 881 transcripts differentially expressed by all three strains, many of which reflect the metabolic pathways used by S. maltophilia in sputum, as well as altered stress responses. The latter correlated with increased resistance to peroxide exposure after pre-growth in SCFM2 for two of the strains. We also compared the SCFM2 transcriptomes of two S. maltophilia CF isolates to that of the acute infection strain, S. maltophilia K279a, allowing us to identify CF isolate-specific signatures in differential gene expression. Expression of genes from the accessory genomes was also differentially altered in response to SCFM2. Finally, a number of biofilm-associated genes were differentially induced in SCFM2, particularly in K279a, which corresponded to increased aggregation and biofilm formation in this strain relative to both CF strains. Collectively, this work details the response ofS. maltophiliato an environment that mimics important aspects of the CF lung, identifying potential survival strategies and metabolic pathways used byS. maltophiliaduring infections.ImportanceStenotrophomonas maltophilia is an important infecting bacterium in the airways of people with cystic fibrosis (CF). However, compared to the other CF pathogens, S. maltophilia has been relatively understudied. The significance of our research is to provide insight into the global transcriptomic changes of S. maltophilia in response to a medium that was designed to mimic important aspects of the CF lung. This work allows us to understand the overall metabolic changes that occur when S. maltophilia encounters the CF lung, and generates a roadmap of candidate genes to test using in vitro and in vivo models of CF.
The advent of fabrication techniques such as additive manufacturing has focused attention on the considerable variability of material response due to defects and other microstructural aspects. This variability motivates the development of an enhanced design methodology that incorporates inherent material variability to provide robust predictions of performance. In this work, we develop plasticity models capable of representing the distribution of mechanical responses observed in experiments using traditional plasticity models of the mean response and recently developed uncertainty quantification (UQ) techniques. To account for material response variability through variations in physical parameters, we adapt a recent Bayesian embedded modeling error calibration technique. We use Bayesian model selection to determine the most plausible of a variety of plasticity models and the optimal embedding of parameter variability. To expedite model selection, we develop an adaptive importance-sampling-based numerical integration scheme to compute the Bayesian model evidence. In conclusion, we demonstrate that the new framework provides predictive realizations that are superior to more traditional ones, and how these UQ techniques can be used in model selection and assessing the quality of calibrated physical parameters.
In the first auto-magnetizing liner implosion experiments on the Z Facility, precompressed internal axial fields near 150 T were measured and 7.2-keV radiography indicated a high level of cylindrical uniformity of the imploding liner's inner surface. An auto-magnetizing (AutoMag) liner is made of discrete metallic helical conductors encapsulated in insulating material. Here, the liner generates internal axial magnetic field as a 1–2 MA, 100–200 ns current prepulse flows through the helical conductors. After the prepulse, the fast-rising main current pulse causes the insulating material between the metallic helices to break down ceasing axial field production. After breakdown, the helical liner, nonuniform in both density and electrical conductivity, implodes in 100 ns. In-flight radiography data demonstrate that while the inner wall maintains cylindrical uniformity, multiple new helically oriented structures are self-generated within the outer liner material layers during the implosion; this was not predicted by simulations. Furthermore, liner stagnation was delayed compared to simulation predictions. An analytical implosion model is compared with experimental data and preshot simulations to explore how changes in the premagnetization field strength and drive current affect the liner implosion trajectory. Both the measurement of >100 T internal axial field production and the demonstration of cylindrical uniformity of the imploding liner's inner wall are encouraging for promoting the use of AutoMag liners in future MagLIF experiments.
Magnesium-based materials provide some of the highest capacities for solid-state hydrogen storage. However, efforts to improve their performance rely on a comprehensive understanding of thermodynamic and kinetic limitations at various stages of (de)hydrogenation. Part of the complexity arises from the fact that unlike interstitial metal hydrides that retain the same crystal structures of the underlying metals, MgH 2 and other magnesium-based hydrides typically undergo dehydrogenation reactions that are coupled to a structural phase transformation. As a first step towards enabling molecular dynamics studies of thermodynamics, kinetics, and (de)hydrogenation mechanisms of Mg-based solid-state hydrogen storage materials with changing crystal structures, we have developed an analytical bond order potential for Mg−H systems. We demonstrate that our potential accurately reproduces property trends of a variety of elemental and compound configurations with different coordinations, including small clusters and bulk lattices. More importantly, we show that our potential captures the relevant (de)hydrogenation chemical reactions 2H (gas)→H 2 (gas) and 2H (gas)+Mg (hcp)→MgH 2 (rutile) within molecular dynamics simulations. This verifies that our potential correctly prescribes the lowest Gibbs free energies to the equilibrium H 2 and MgH 2 phases as compared to other configurations. It also indicates that our molecular dynamics methods can directly reveal atomic processes of (de)hydrogenation of the Mg−H systems.
Complex light metal hydrides are promising candidates for efficient, compact solid-state hydrogen storage. (De)hydrogenation of these materials often proceeds via multiple reaction intermediates, the energetics of which determine reversibility and kinetics. At the solid-state reaction front, molecular-level chemistry eventually drives the formation of bulk product phases. Therefore, a better understanding of realistic (de)hydrogenation behavior requires considering possible reaction products along all stages of morphological evolution, from molecular to bulk crystalline. Here, we use first-principles calculations to explore the interplay between intermediate morphology and reaction pathways. Employing representative complex metal hydride systems, we investigate the relative energetics of three distinct morphological stages that can be expressed by intermediates during solid-state reactions: i) dispersed molecules; ii) clustered molecular chains; and iii) condensed-phase crystals. Our results verify that the effective reaction energy landscape strongly depends on the morphological features and associated chemical environment, offering a possible explanation for observed discrepancies between X-ray diffraction and nuclear magnetic resonance measurements. Our theoretical understanding also provides physical and chemical insight into phase nucleation kinetics upon (de)hydrogenation of complex metal hydrides.
The ability of nanoporous metals to avoid accumulation of damage under ion beam irradiation has been the focus of several studies in recent years. The width of the interconnected ligaments forming the network structure typically is on the order of tens of nanometers. In such confined volumes with high amounts of surface area, the accumulation of damage (defects such as stacking-fault tetrahedra and dislocation loops) can be mitigated via migration and annihilation of these defects at the free surfaces. In this work, in situ characterization of radiation damage in nanoporous gold (np-Au) was performed in the transmission electron microscope. Several samples with varying average ligament size were subjected to gold ion beams having three different energies (10 MeV, 1.7 MeV and 46 keV). The inherent radiation tolerance of np-Au was directly observed in real time, for all ion beam conditions, and the degree of ion-induced damage accumulation in np-Au ligaments is discussed here.
Detection of radiological iodine gas after nuclear accidents or in nuclear fuel reprocessing is necessary for the safety of human life and the environment. The development of sensors for the detection of iodine benefits from the incorporation of nanoporous materials with high selectivity for I2 from common competing gases in air. Silver mordenite zeolite (Ag-MOR) is widely-used material for capture of gaseous iodine (I2). Herein, thin film zeolite coatings were applied to Pt interdigitated electrodes (IEDs) to fabricate iodine gas sensors with direct electrical readout responses. Correlations between occluded ion, exposure to iodine gas, resultant AgI nanoparticle polymorphs and location in zeolite with resultant impedance spectroscopy (IS) properties are described. Furthermore, IS is leveraged to elucidate the changes in charge conduction pathways as determined by the cation-zeolite film incorporated in the sensor. Silver mordenite reveals a significant change in impedance upon exposure to gaseous I2 at 70 °C, and the magnitude and direction of the response is dependent on whether the Ag+-mordenite is reduced (Ag0) before I2 exposure. An equivalent circuit model is developed to describe the movement of charge along the surface and through the pores of the mordenite grains. Relative changes in the impedance of these conduction pathways are related to the chemical changes from Ag+ or Ag0 to resultant AgI polymorph phase. Together, these results inform design of a compact Ag-mordenite sensor for direct electrical detection of gaseous I2.
We report transport measurements of electrons on helium in a microchannel device where the channels are 200 nm deep and 3μm wide. The channels are fabricated above amorphous metallic Ta 40 W 40 Si 20 , which has surface roughness below 1 nm and minimal variations in work function across the surface due to the absence of polycrystalline grains. We are able to set the electron density in the channels using a ground plane. We estimate a mobility of 300cm2/Vs and electron densities as high as 2.56×109cm-2. We demonstrate control of the transport using a barrier which enables pinch-off at a central microchannel connecting two reservoirs. The conductance through the central microchannel is measured to be 10 nS for an electron density of 1.58×109cm-2. Our work extends transport measurements of surface electrons to thin helium films in microchannel devices above metallic substrates.
We present a so-called "split-well direct-phonon" active region design for terahertz quantum cascade lasers (THz-QCLs). Lasers based on this scheme profit from both elimination of high-lying parasitic bound states and resonant-depopulation of the lower laser level. Negative differential resistance is observed at room temperature, which indicates that each module behaves as a clean 3-level system. We further use this design to investigate the impact of temperature on the dephasing time of GaAs/AlGaAs THz-QCLs.
The TED-GC–MS analysis is a two-step method. A sample is first decomposed in a thermogravimetric analyzer (TGA) and the gaseous decomposition products are then trapped on a solid-phase adsorber. Subsequently, the solid-phase adsorber is analyzed with thermal desorption gas chromatography mass spectrometry (TDU-GC–MS). This method is ideally suited for the analysis of polymers and their degradation processes. Here, a new entirely automated system is introduced which enables high sample throughput and reproducible automated fractioned collection of decomposition products. The fractionated collection together with low temperatures reduces the risk of contamination, improves instrumental stability and minimizes maintenance efforts. Through variation of the two main parameters (purge gas flow and heating rate) it is shown how the extraction process can be optimized. By measuring the decomposition products of polyethylene it is demonstrated that compounds with masses of up to 434 Da can be detected. This is achieved despite the low temperature (˜40 °C) of the solid-phase adsorber and the low thermal desorption temperature of 200 °C in the TDU unit. It is now shown that automated TED-GC–MS represents a new flexible multi-functional method for comprehensive polymer analyses. Comparable polymer characterization was previously only achievable through a combination of multiple independent analytical methods. This is demonstrated by three examples focused on practical challenges in materials analysis and identification: The first one is the analysis of wood plastic composites for which the decomposition processes of the polymer and the bio polymer (wood) could be clearly distinguished by fractionated collection using sequential adsorbers. Secondly, a fast quantitative application is shown by determining the weight concentrations of an unknown polyolefin blend through comparison with a reference material. Additionally, the determination of microplastic concentrations in environmental samples is becoming an increasingly important analytical necessity. It is demonstrated that with TED-GC–MS calibration curves showing good linearity for the most important precursors for microplastic, even complex matrix materials (suspended particulate matter) can be successfully analyzed.
In this paper, we investigate the coupling from external electromagnetic (EM) fields to the interior EM fields of a high-quality factor cylindrical cavity through a small perturbing slot. We illustrate the shielding effectiveness versus frequency, highlighting bounds on the penetrant power through the slot. Because internal fields may become larger than external ones, we then introduce a small amount of microwave absorbing materials decorating the slot to improve shielding effectiveness considerably, as shown by both simulations and experiments. Although the cylindrical cavity is used for demonstration purposes in this paper, the conclusions presented here can be leveraged for use with more complex cavity structures.
The oxidation mechanisms of exfoliated Gallium Selenide (GaSe) are strongly influenced by humidity. We have observed that the presence of water molecules leads to formation of Ga2O3, SeO2, and Se via sequence of intermediate reactions which include generation of aqueous solution of selenic acid. Raman spectra of GaSe flakes undergoing oxidation in a humidity-controlled environment reveal formation of selenic acid-related species causing Raman scattering signal in the regions around 830 cm-1 and around 1230 cm-1. This observation sheds light on the path of chemical reactions, going via an intermediate stage of formation of gallium hydroxide and selenium oxide-water complexes with further decompositions of these compounds to Ga2O3, SeO2, and amorphous selenium.
Ducted fuel injection (DFI) has been proposed as a strategy to enhance the fuel/charge gas mixing within the combustion chamber of a direct-injection mixing-controlled compression ignition engine. The concept involves injecting each fuel spray through a small tube within the combustion chamber to facilitate the creation of a leaner mixture in the autoignition zone, relative to a conventional free-spray configuration (i.e., a fuel spray that is not surrounded by a duct). While previous experiments demonstrated that DFI lowers both soot incandescence and soot mass in a constant-volume combustion vessel with a single-component normal-alkane fuel (n-dodecane), this study provides the first evidence that the technology provides similar benefits in an engine application using a commercial diesel fuel containing ~30 wt% aromatics. The present study investigates the effects on engine-out emissions and efficiency with a two-orifice injector tip for charge gas mixtures containing 16 and 21 mol% oxygen. The result is that DFI is confirmed to be effective at curtailing engine-out soot emissions. It also breaks the tradeoff between emissions of soot and nitrogen oxides (NOx) by simultaneously attenuating soot and NOx with increasing dilution.
In this paper, we investigate the coupling from external electromagnetic (EM) fields to the interior EM fields of a high-quality factor cylindrical cavity through a small perturbing slot. We illustrate the shielding effectiveness versus frequency, highlighting bounds on the penetrant power through the slot. Because internal fields may become larger than external ones, we then introduce a small amount of microwave absorbing materials decorating the slot to improve shielding effectiveness considerably, as shown by both simulations and experiments. Although the cylindrical cavity is used for demonstration purposes in this paper, the conclusions presented here can be leveraged for use with more complex cavity structures.
Our work extends the concepts and tools of Hamiltonian Surface Shaping and Power Flow Control (HS SPFC) for electro-mechanical (EM) systems(i.e., adiabatic irreversible work processes and Hamiltonian natural systems)to Exergy Surface Shaping and Thermodynamic Flow Control (ESSTFC) for electro-mechanical-thermal (EMT) systems (i.e., irreversible work processes with heat and mass flows). The extension of HSSPFC requires the development of exergy potential functions, irreversible entropy production terms of the entropy balance equation to obtain the exergy destruction terms for inclusion in the exergy balance equation, and variational principles for producing consistent equations of motion for coupled EMT systems. The Hamiltonian for natural EM systems is an exergy potential function which leaves the development of exergy potential functions for the thermal part of the coupled models. This development is completed by integrating the exergy function over the control volume subject to the modeling assumptions. The irreversible entropy production terms are the exergy destruction terms of the exergy balance equation and the generalization of the mechanical dissipation and electrical resistance within EM systems. These generalized dissipation terms enable the derivation of a consistent set of coupled equations of motion for EMT systems. For this paper, Extended Irreversible Thermodynamics will be utilized to produce consistent thermal equations of motion that directly include the exergy destruction terms. There are several variational principles that are available for application to EMT systems. We focus on the variational principles developed by Biot and Fung [1, 2]. Furthermore, a simplified EMT system that models the EMT dynamics of a Navy ship equipped with a railgun is used to demonstrate the application of ESSTFC for designing high performance, stable nonlinear controllers for EMT systems.
Dance, Tess; LaForce, Tara; Glubokovskikh, Stanislav; Ennis-King, Jonathan; Pevzner, Roman
Proper site characterisation is essential in the planning stages of a CO2 storage project; but we can also learn a good deal about the reservoir once the injection is underway or has been completed. During CO2CRC Otway Project Stage 2C, sources of valuable information about storage performance have been generated as a consequence of the staged injection of 15,000 t of CO2 rich gas, as well as observations from time-lapse seismic surveys and well monitoring data. Now that injection has ceased for Stage 2C, the geological model is compared against field observations for the period spanning injection and 23 months after injection ended. The post-injection reservoir characterisation has proven critical to refine the static and dynamic models for future field development and added assurance about the long-term stabilisation of the CO2 plume. The south-eastern progress of plume development, as seen on the time-lapse seismic data, has led to a review of the structural interpretation and horizon-fault geometry represented in the models. The developing plume has illuminated the extent of splay faults previously unresolved on the baseline seismic data. Saturation profiles interpreted from pulsed-neutron logs at the injection and observation wells show a preference for higher saturations occurring in high permeability distributary channels penetrated by each of the wells. This has reduced the uncertainty in predicting connectivity of this facies between the wells. The pressure data from numerous injection events has been used to refine the characterisation of the average horizontal permeability of the reservoir zone, and the vertical permeability of the intra-formational seal. Furthermore, it has been used to infer near-field bounding conditions of the interior splay fault, which in turn improves our understanding of containment at the site.
This research applies nonlinear ultrasonic techniques for the quantitative characterization of additively manufactured materials. The characterization focuses on identifying the dislocation density produced during the additive constructive process in order to increase confidence on a part's performance and the success of the manufacturing process. Second harmonic generation techniques based on the transmission of Rayleigh surface waves are used to measure the ultrasonic nonlinearity parameter, β, which has proven a quantitative indicator of dislocations but has not been fully proven in additive manufactured materials. 316L and 304L stainless steel parts made from Powder Bed Fusion and Laser Engineered Net Shaping are compared between AM techniques and with wrought manufactured counterparts. β is consistently higher for additive manufactured parts. An annealing heat treatment is applied to each specimen to reduce dislocation density. β expectedly decreases by annealing in all specimens. A linear ultrasonic measurement is made to evaluate the effectiveness of using nonlinear techniques. The ultrasonic attenuation is higher for additive manufactured parts and increases at higher frequencies.
Sandia National Laboratories is developing a laboratory-based x-ray phase contrast imaging (XPCI) computed tomography (CT) system. This system utilizes a Talbot-Lau interferometer based on in-house fabricated gratings and a conventional x-ray system. Initial work has focused on adding CT capabilities to a 28 keV XPCI system. A new set of gratings tuned for an x-ray energy of 100 keV is being developed. This new grating set will facilitate imaging denser components. System configuration details will be presented as well as a discussion of the challenges associated with building an XPCI CT system. Additionally, initial imaging results will be presented.
In the chemical transport field, such as petro-chemicals or food processing, there is a need to quantify the spatially varying temperature and phase state of the material within a cylindrical vessel, such as a pipeline, using non-invasive techniques. Using ultrasonic signals, which vary in time-of-flight, intensity, and wave characteristics based on the temperature and phase of a material, an automated technique is presented which can provide a non-axisymmetric map of the phase and temperature inside a cylindrical vessel within a single plane using exclusively information from the through-transmission wave and the external temperature profile. This research demonstrates the approach using an amorphous wax, due to its stable nature and ability to be reheated many times without changing the properties of the wax. Due to its amorphous nature, the wax transitions from a solid to a low-viscosity fluid over a range of temperatures. This behavior is similar to that of a thermoplastic and a slurry experiencing curing. As the spatial temperature within a container of wax increases the time of flight for an ultrasonic signal will change. Results presented indicate the ability of the investigated technique to map the temperature and phase change of the wax based solely on the ultrasonic signals and knowledge of the external temperature on the outer edge of the vessel.
Additively manufactured (AM) components often exhibit significant discontinuities and indications without a clear understanding of how they might affect the mechanical properties of a part during qualification and service. This uncertainty is unacceptable for the design and manufacturing of most aerospace components. Current research in both mechanical testing and nondestructive evaluation involves developing methods for characterizing and inspecting AM components as the use of such materials continues to rise. Although several AM manufacturing methods have been developed in recent decades, this paper focuses on AM production-ready processes for a direct metal laser sintering (DMLS) powder bed fusion machine and will provide background on Sandia National Laboratories' research efforts in this area. Tensile bar samples manufactured using the DMLS powder bed fusion method were inspected in this study, and the results of ultrasonic spectroscopy for assessing internal flaws will be presented. A combination of material property evaluation, microstructural characterization, and nondestructive inspection techniques will also be described. The results obtained from these material evaluation methods assist in determining inspection limits and methods for qualifying AM materials.
Terahertz (THz) photoconductive devices are used for generation, detection, and modulation of THz waves, and they rely on the ability to switch electrical conductivity on a subpicosecond time scale using optical pulses. However, fast and efficient conductivity switching with high contrast has been a challenge, because the majority of photoexcited charge carriers in the switch do not contribute to the photocurrent due to fast recombination. Here, we improve efficiency of electrical conductivity switching using a network of electrically connected nanoscale GaAs resonators, which form a perfectly absorbing photoconductive metasurface. We achieve perfect absorption without incorporating metallic elements, by breaking the symmetry of cubic Mie resonators. As a result, the metasurface can be switched between conductive and resistive states with extremely high contrast using an unprecedentedly low level of optical excitation. We integrate this metasurface with a THz antenna to produce an efficient photoconductive THz detector. The perfectly absorbing photoconductive metasurface opens paths for developing a wide range of efficient optoelectronic devices, where required optical and electronic properties are achieved through nanostructuring the resonator network.
A small, consumable-free, low-power, ultra-high-speed comprehensive GC×GC system consisting of microfabricated columns, nanoelectromechanical system (NEMS) cantilever resonators for detection, and a valve-based stop-flow modulator is demonstrated. The separation of a highly polar 29-component mixture covering a boiling point range of 46 to 253 °C on a pair of microfabricated columns using a Staiger valve manifold in less than 7 seconds, and just over 4 seconds after the ensemble holdup time is demonstrated with a downstream FID. The analysis time of the second dimension was 160 ms, and peak widths in the second dimension range from 10-60 ms. A peak capacity of just over 300 was calculated for a separation of just over 6 s. Data from a continuous operation testing over 40 days and 20000 runs of the GC×GC columns with the NEMS resonators using a 4-component test set is presented. The GC×GC-NEMS resonator system generated second-dimension peak widths as narrow as 8 ms with no discernable peak distortion due to under-sampling from the detector.
The room temperature electronic transport properties of 1 μm thick Bi0.4Sb1.6Te3 (BST) films correlate with overall microstructural quality. Films with homogeneous composition are deposited onto fused silica substrates, capped with SiN to stop both oxidation and Te loss, and postannealed to temperatures ranging from 200 to 450 °C. BST grain sizes and (00l) orientations improve dramatically with annealing to 375 °C, with smaller increases to 450 °C. Tiny few-nanometer-sized voids in the as-deposited film grain boundaries coalesce into larger void sizes up to 300 nm with annealing to 350 °C; the smallest voids continue coalescing with annealing to 450 °C. These voids are decorated with few-nanometer-sized Sb clusters that increase in number with increasing annealing temperatures, reducing the Sb content of the remaining BST film matrix. Resistivity decreases linearly with increasing temperature over the entire range studied, consistent with improving crystalline quality. The Seebeck coefficient also improves with crystalline quality to 350 °C, above which void coalescence and reduced Sb content from the BST matrix correlate with a decrease in the Seebeck coefficient. Yet, a plateau exists for an optimal power factor between 350 and 450 °C, implying thermal stability to higher temperatures than previously reported.
There are currently (as of January, 2019) more than 2,700 dual-purpose canisters (DPCs) loaded with spent nuclear fuel (SNF) across the United States. DPCs continue to be loaded at a rate of more than 200 per year by mid-century there are likely to be more than 8,160 DPCs in service. Options for disposing of SNF loaded in DPCs include repackaging into specialized disposal canisters, directly disposing of the loaded DPCs (with or without modification), or some combination of the two. The main technical challenges for direct disposal of loaded DPCs are thermal management, handling and emplacement operations for the large, heavy packages, and postclosure criticality control. This report focuses on postclosure criticality control which is the most challenging. The challenge lies in determining how to modify DPCs so as to minimize the probability that a criticality event might occur in a repository, or if the DPCs are not modified, to understand the nature and consequences of postclosure criticality events. There are several approaches that could facilitate direct disposal of loaded DPCs with acceptable repository performance. This report describes these approaches and presents comparative analysis of the rough-order-of-magnitude (ROM) costs. Repackaging SNF in DPCs into specialized disposal canisters could be financially and operationally costly with additional radiological, operational safety, and management risks. A disposition approach that would not involve repackaging or modifications to DPCs (future or already loaded) is development of a new licensing strategy that addresses the risk (probability and consequence) from criticality events. A different approach would modify existing loaded DPCs (some or all of them), and change the loading or design of future DPCs, to decrease the probability of a criticality event in a repository below levels of concern. This report investigates the cost to modify existing loaded DPCs, and the cost to modify the loading or design of future DPCs to facilitate direct disposal. It establishes the ROM cost for repackaging SNF that has been loaded into DPCs, into specialized canisters for disposal. It also identifies technical and regulatory challenges associated with the potential design modifications and loading considerations. It is left to future analyses to compare radiological, operational safety, and management risks associated with the available approaches.
Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science
Adams, David P.; Brown, Donald W.; Balogh, L.; Carpenter, John S.; Clausen, Bjorn; Livescu, Veronica; Martinez, Ramon M.; Morrow, Benjamin M.; Palmer, T.A.; Pokharel, Reeju; Strantza, M.; Vogel, S.C.
Additive manufacturing of metal components results in unique microstructures with, necessarily, mechanical properties that are distinct from conventionally produced components. In this paper, four distinct microstructural features associated with directed energy deposition of 304L stainless steels, their stability, and their influences on flow strength were examined. These were (1) high dislocation density comparable with deformed materials, (2) increased ferrite content, (3) local chemical heterogeneity, and (4) tortuous grain morphology. In situ neutron diffraction measurements were used to monitor the evolution of the as-built microstructure during post-build heat treatment and relate the specific microstructural features to the strength behavior of the material following the heat treatment. The increased flow strength of the additively manufactured material relative to wrought counterparts is found to be due primarily to an increased dislocation density in the as-built material. However, the increased dislocation density does not completely account for the increased strength and it is hypothesized that some of the additional strength is related to the unique AM grain structure.
Traffic cameras are becoming a popular form of surveillance in traffic bodies across the country. With recent advances in computer vision and deep learning, there is a great opportunity to leverage these images to provide real-time traffic estimates and other public services. In this report, we detail some of the challenges, current interests of the research community, and our early efforts in using traffic cameras for vehicle detection and traffic estimation. We also discuss a benchmark traffic dataset that we are assembling and plan to release to the research community to motivate further work in this area.
The historical subsidence surveys shot over the U.S. Strategic Petroleum Reserve Big Hill site, located in southeastern Texas, have indicated surface uplift since 2002. In order to better understand and substantiate the surface behavior inferred from annual elevation measurements, InSAR (interferometric synthetic aperture radar) data was acquired. InSAR involves the processing of multiple satellite synthetic aperture radar scenes acquired across the same location of the Earth's surface at different times to map surface deformation. The analysis of the data can detect millimeters of motion spanning days, months, year and decades, across specific sites. The InSAR analysis indicates the fastest subsidence rates are over the north central region of the site, specifically centered over caverns 104 and 103. Subsidence rates decrease towards both the west and east, with the western side subsiding at greater rate than the eastern edge. There is some uplift noted, off the site and off the dome to the east. Overall, the subsidence pattern is in line with subsidence behavior expected over a cavern field. In investigating the validity of the uplift measured during the ground surveys it was discovered that reference location can impact results. An exercise was conducted that took the current InSAR data and presented two varying results dependent on the reference location, either on or off the dome. The conclusion was that if the reference is located on the dome, as it has been for years for the ground surveys, the reference location is moving too, giving the appearance of uplift.
Ductile materials fail through mechanisms of void nucleation and coalescence. A tensile test of a ductile metal begins with reversible elastic deformation, proceeds through permanent plastic deformation, and ends with rupture. Dislocations in the grains of a metal do not slip in the elastic range but begin moving in the plastic range. As the dislocations interact with grain boundaries and each other, they cause increasing resistance to plastic deformation, termed work hardening. The applied load and the true stress rise together during this process. When the dislocations have no room to move, voids open up in the material. As these voids coalesce into cracks, the true stress rises rapidly and the sustained load decreases. Rupture occurs when the cracks propagate through the specimen and it loses all load-carrying capacity. The complexity of the ductile fracture phenomenon continues to attract substantial attention from researchers. Sharp objects in a production environment can puncture fragile components made from ductile metals. Non-linear dynamic simulations help engineers to plan processes such that these components do not fail when an accident happens. The projectile is termed a probe, and the component is the target. The surface of the probe that contacts the target may be sharp, blunt, or flat. Probes are typically cylindrical for simplicity, but other shapes that exist in the production environment are equally applicable.
The following document is Sandia National Laboratories Facilities Site and Strategic Partnerships methodology and assumptions used in the assembly of programming, planning, and budgeting level cost range for early capital acquisition needs development and communication. This basis of estimate summary is specific to the Combined Radiation Environments for Survivability Testing (CREST) Line Item proposal, and reflects updated estimates provided by the Subject Matter Experts (SME) team as indicated.
Sandia National Laboratories conducted a reliability analysis on the Alertus mass notification system to determine if improvements need to be made to the system to increase reliability. The Alertus mass notification system for Building 803 was analyzed with a set number of components. The components, their associated failure modes and failure mode rates were inputted into a fault tree in the SAPHIRE software which calculated the reliability of the system to be 0.998269.
This report uses the CMIP5 series of climate model simulations to produce country- level uncertainty distributions for use in socioeconomic risk assessments of climate change impacts. It provides appropriate probability distributions, by month, for 169 countries and autonomous-areas on temperature, precipitation, maximum temperature, maximum wind speed, humidity, runoff, soil moisture and evaporation for the historical period (1976-2005), and for decadal time periods to 2100. It also provides historical and future distributions for the Arctic region on ice concentration, ice thickness, age of ice, and ice ridging in 15-degree longitude arc segments from the Arctic Circle to 80 degrees latitude, plus two polar semicircular regions from 80 to 90 degrees latitude. The report provides simplified algorithms with which anyone on any country can determine their risk from climate change and to include in resilience evaluations. The full report is contained in 27 volumes.
Radiation Protection (628) in conjunction with Nuclear Facility Operations (1381) completed a comprehensive radiological conditions characterization of the ACRR facility between August 2015 and January 2017 to better understand the radiological environment in and around the ACRR High-Bay. The overall goals of the characterization, as identified by 1381 and 628, were to determine potential dose to workers during routine reactor operations, areas of potential elevated dose in and around the ACRR High-Bay, the relationship between reactor power and dose during steady-state operations, and the dose per pulse for pulsed operations. To accomplish this, eight configurations were identified of interest for characterization based on increased dose potential for which field surveys were completed to include assessment of the neutron spectra for each, determination of neutron dose conversion factors (Neutron Codes) based on defined neutron spectra, mapped dose surveys for each configuration, as well as determination of the relationship between dose and reactor power level during steady-state reactor operations. Steady-state survey data was also used to calculate dose per pulse approximations during pulsed reactor operations.
This report documents additional evaluations of Thermal Shock-Resistant Cement (TSRC) developed by Brookhaven National Laboratory (BNL). Our work focused on thermal expansion, and fluid flow through the TSRC, and the application of thermal shock to a steel/TSRC sheathed sample. The key contributions of this work to the geothermal community are: 1) Development of a test system to make measurements of material properties at elevated temperature and pressure. 2) Measurements of thermal expansion and permeability of TSRC at elevated temperature and pressure conditions relevant to in situ geothermal conditions. 3) Development of a test system to thermally shock a steel/TSRC sheathed sample at elevated temperature and pressure conditions relevant to in situ geothermal conditions. Herein we report the results of the study of repeated testing upon 3 cylindrical samples supplied by BNL, one steel, one TSRC, and one steel/TSRC sheathed sample.
Prestressed concrete containment structures are subject to performance loss primarily due to aging and degradation. Many nuclear power plants (NPPs) have extended operating licenses beyond the design life of 40 years and some are considering operation for up to 80 years. The focus of this review is to determine which modes of performance loss, or 'failure modes', are most applicable to prestressed concrete containment vessels (PCCVs) beyond the age of 40 years. A list of failure modes taken from Crystal River Nuclear Plant Special Inspection Report is analyzed for applicability to aging nuclear containment structures. Each failure mode is described and discussed in detail. A table is provided to highlight the severity of each failure mode. This page left blank
This report presents a complete listing, as of May 2019, of the damping controller (DCON) project accomplishments including a project overview, project innovations, awards, patent application, journal papers, conference papers, project reports, and project presentations. The purpose of the DCON is to mitigate inter-area oscillations in the WI by active improvement of oscillatory mode damping using phasor measurement unit (PMU) feedback to modulate power flow in the PDCI. The DCON project is the result of a collaboration between Sandia National Laboratories (SNL), Montana Technological University (MTU), Bonneville Power Administration (BPA), and the Department of Energy Office of Electricity (DOE-OE).
Schoenwald, David A.; Pierre, Brian J.; Wilches Bernal, Felipe; Elliott, Ryan T.; Byrne, Raymond H.; Neely, Jason C.; Trudnowski, Daniel J.
This report presents the results from testing of the Pacific DC Intertie (PDCI) wide-area damping controller (DCON) on the actual electric power grid in the western region of North America known as the Western Interconnection (WI). In addition, this report summarizes the key contributions and development strategy of the DCON. Therefore, this report also serves as the final report for the DCON project, which is known as TIP (Technology Innovation Project) no. 289. The purpose of the DCON is to mitigate inter-area oscillations in the WI by active improvement of oscillatory mode damping using phasor measurement unit (PMU) feedback to modulate power flow in the PDCI. This report describes the tests conducted, analysis of the results, and conclusions drawn as to the performance and safety of the DCON in the improvement of damping for inter-area oscillations in the WI. The DCON is the result of a collaboration between Sandia National Laboratories (SNL), Bonneville Power Administration (BPA), Montana Technological University (MTU), and the Department of Energy Office of Electricity (DOE-OE).
The dynamic behavior of an elastic peridynamic material with a nonconvex bond potential is studied. In spite of the material's inherently unstable nature, initial value problems can be solved using essentially the same techniques as with conventional materials. In a suitably constructed material model, small perturbations grow exponentially over time until the material fails. The time for this growth is computed explicitly for a stretching bar that passes from the stable to the unstable phase of the material model. This time to failure represents an incubation time for the nucleation of a crack. The finiteness of the failure time in effect creates a rate dependence in the failure properties of the material. Thus, the unstable nature of the elastic material leads to a rate effect even though it does not contain any terms that explicitly include a strain rate dependence.
Sculpt is a companion application to Cubit designed to run in parallel for generating all-hex meshes of complex geometry. It uses a unique overlay-grid procedure that extracts surfaces from a volume-fraction representation of the geometry. This allows for fast, automatic, fault-tolerant meshing in a high-performance computing (HPC) environment. Although Sculpt can be driven from Cubit as a GUI front-end, Sculpt was developed as a separate application so that it can be run independently from Cubit on HPC computing platforms. It was also designed as a separable software library so it can be easily integrated as an in-situ meshing solution within other codes. This work provides a brief technical discussion of the algorithms used in Sculpt as well as a complete user's manual. It includes details of the Cubit interface to Sculpt and the complete manual for the stand-alone application, including examples.
Wave energy converters (WECs) must survive in a wide variety of conditions while minimizing structural costs, so as to deliver power at cost-competitive rates. Although engineering design and analysis tools used for other ocean systems, such as offshore structures and ships, can be applied, the unique nature and limited historical experience of WEC design necessitates assessment of the effectiveness of these methods for this specific application. This paper details a study to predict extreme loading in a two-body WEC using a combination of mid-fidelity and high-fidelity numerical modeling tools. Here, the mid-fidelity approach is a time-domain model based on linearized potential flow hydrodynamics and the high-fidelity modeling tool is an unsteady Reynolds-averaged Navier–Stokes model. In both models, the dynamics of the WEC power take-off and mooring system have been included. For the high-fidelity model, two design wave approaches (an equivalent regular wave and a focused wave) are used to estimate the worst case wave forcing within a realistic irregular sea state.These simplified design wave approaches aim to capture the extreme response of the WEC within a feasible amount of computational effort. When compared to the mid-fidelity model results in a long-duration irregular sea, the short-duration design waves simulated in CFD produce upper percentile load responses, hinting at the suitability of these two approaches.
Due to a number of recent events where access control into or out of a hazardous area or operation was a factor, the Environment, Safety, and Health (ES&H) director requested a review of access control events occurring at Sandia National Laboratories from 2015 to January 2019. The purpose of the review was to determine the extent of access control as an ES&H issue, draw preliminary conclusions from the data, and identify recommendations for improvement, if appropriate. Using the Occurrence Reporting and Processing System (ORPS) database, nine events from 2015 through January 2019 were identified as situations involving access control of personnel into or out of a hazardous area or operation. Supplemental records from the Assurance Information System (AIS) database and the occurrence management team's repository in Electronic Integrated Management System (EIMS) were sought to confirm this dataset of access control events and to gather details concerning the causal factors associated with each event.
We present a new method for boundary detection within sequential data using compression-based analytics. Our approach is to approximate the information distance between two adjacent sliding windows within the sequence. Large values in the distance metric are indicative of boundary locations. A new algorithm is developed, referred to as sliding information distance (SLID), that provides a fast, accurate, and robust approximation to the normalized information distance. A modified smoothed z-score algorithm is used to locate peaks in the distance metric, indicating boundary locations. A variety of data sources are considered, including text and audio, to demonstrate the efficacy of our approach.
Extended-MHD simulations of power flow along a pulsed-power transmission line are performed in a 2-D axisymmetric geometry, in particular looking at the influence of Hall physics for a transmission line coupled to the liner used in a magnetized liner inertial fusion experiment at Sandia National Labs. It was recently shown by the authors that, for a coaxial transmission line, when Hall physics is included, significantly more blow-off occurs from plasma initialized against the anode compared to the cathode. The mechanism of this blow-off was traced to electron {text{E}}× {text{B}} drift modeled by the Hall term. This result is also observed for the present simulations, and it is shown that the anode blow-off significantly delays the coupling of current to the liner. It is also found that Hall MHD and MHD results are sensitive to the treatment of density floors and the plasma-vacuum interface. Although MHD shows more sensitivity than Hall MHD, correct modeling of the transition from plasma to vacuum remains an unsolved problem that must be addressed in order to improve the predictive capability of fluid-based power flow simulations with regard to energy coupling.
Attaining high performance with MPI applications requires efficient message matching to minimize message processing overheads and the latency these overheads introduce into application communication. In this paper, we use a validated simulation-based approach to examine the relationship between MPI message matching performance and application time-to-solution. Specifically, we examine how the performance of several important HPC workloads is affected by the time required for matching. Our analysis yields several important contributions: (i) the performance of current workloads is unlikely to be significantly affected by MPI matching unless match queue operations get much slower or match queues get much longer; (ii) match queue designs that provide sublinear performance as a function of queue length are unlikely to yield much benefit unless match queue lengths increase dramatically; and (iii) we provide guidance on how long the mean time per match attempt may be without significantly affecting application performance. The results and analysis in this paper provide valuable guidance on the design and development of MPI message match queues.
The Sandia National Laboratories (SNL) Advanced Technology Development and Mitigation (ATDM) project focuses on R&D for exascale computational science and engineering (CSE) software. Exascale application (APP) codes are co-developed and integrated with a large number of 2^nd generation Trilinos packages built on top of Kokkos for achieving portable performance. These efforts are challenged by needing to develop and test on many unstable and constantly changing pre-exascale platforms using immature compilers and other system software. Challenges, experiences, and lessons learned are presented for creating stable development and integration workflows for these types of difficult projects. In particular, we describe automated workflows, testing, and integration processes as well as new tools and multi-team collaboration processes for effectively keeping a large number of automated builds and tests working on these unstable platforms.
An increasing number of experiments are being conducted to study the design and performance of wave energy converters. Often in these tests, a real-time realization of prospective control algorithms is applied in order to assess and optimize energy absorption as well as other factors. This paper details the design and execution of an experiment for evaluating the capability of a model-scale WEC to execute basic control algorithms. Model-scale hardware, system, and experimental design are considered, with a focus on providing an experimental setup capable of meeting the dynamic requirements of a control system. To more efficiently execute such tests, a dry bench testing method is proposed and utilized to allow for controller tuning and to give an initial assessment of controller performance; this is followed by wave tank testing. The trends from the dry bench test and wave tank test results show good agreement with theory and confirm the ability of a relatively simple feedback controller to substantially improve energy absorption. Additionally, the dry bench testing approach is shown to be an effective and efficient means of designing and testing both controllers and actuator systems for wave energy converters.
Staphylococcus aureus is a major human pathogen of the skin. The global burden of diabetes is high, with S. aureus being a major complication of diabetic wound infections. We investigated how the diabetic environment influences S. aureus skin infection and observed an increased susceptibility to infection in mouse models of both type I and type II diabetes. A dual gene expression approach was taken to investigate transcriptional alterations in both the host and bacterium after infection. While analysis of the host response revealed only minor changes between infected control and diabetic mice, we observed that S. aureus isolated from diabetic mice had significant increases in the levels of genes associated with translation and posttranslational modification and chaperones and reductions in the levels of genes associated with amino acid transport and metabolism. One family of genes upregulated in S. aureus isolated from diabetic lesions encoded the Clp proteases, associated with the misfolded protein response. The Clp proteases were found to be partially glucose regulated as well as influencing the hemolytic activity of S. aureus. Strains lacking the Clp proteases ClpX, ClpC, and ClpP were significantly attenuated in our animal model of skin infection, with significant reductions observed in dermonecrosis and bacterial burden. In particular, mutations in clpP and clpX were significantly attenuated and remained attenuated in both normal and diabetic mice. Our data suggest that the diabetic environment also causes changes to occur in invading pathogens, and one of these virulence determinants is the Clp protease system.
In this paper, we test Si vertical-junction disk modulators and waveguide-integrated Ge p-i-n photodiodes (PDs) to see how the key performance metrics are affected by 60Co gamma radiation (total ionizing dose), a common proxy for simulating a mix of high-energy ion particle flux. It is found that reverse bias dark current increases significantly for both devices after 1-Mrad(Si) exposure. As the bandwidth of the Si disk modulator decreases by 6.5% after 1-Mrad(Si) dose, the bandwidth of the Ge p-i-n PD appears to be unaffected. The increased sensitivity of the Si disk modulator bandwidth to gamma radiation is hypothesized to be caused by a decrease in the carrier concentration of the junction with a resulting increase in the p-n junction RC time constant. The Ge p-i-n PD is relatively insensitive to the surface effects, because the absorption happens away from the SiO2-Ge interface and the gamma radiation has a minimal effect on carrier mobility.
Contact probing of gaging surfaces is used throughout dimensional metrology. Probe tips such as ruby, sapphire, or diamond are commonly employed as styli for universal length measuring machines (ULMs) and coordinate measuring machines (CMMs) due to the hardness, durability, and wear resistance. Gaging surfaces of gage blocks are precision ground or lapped, with very low surface roughness to enable wringing. Damage or contamination of these surfaces can prevent wringing and lead to measurement error. Experimental investigations using a horizontal ULM and CMM have revealed that even at low force settings (≤0.16 N), probe materials such as ruby and sapphire can cause plastic deformation to hardened carbon chrome steel (such as AISI 52,100) gage block surfaces at the microscale, likely attributed to fretting-associated wear. Under some conditions, permanent transfer of material from the probe stylus to the gaging surface is possible. Results demonstrate irreversible changes and damage to gaging surfaces with repeated probe contact on a ULM and CMM. Optical microscopy, optical profilometry, and scanning electron microscopy (SEM) provide a semi-quantitative assessment of microscale plastic deformation and material transfer. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and Raman techniques confirm chemical constituency of reference materials used (gage blocks and probes) and also identify makeup of deposits on gaging surfaces following probe contact.
Copp, David C.; Vamvoudakis, Kyriakos G.; Hespanha, Joao P.
We propose a distributed output-feedback model predictive control approach for achieving consensus among multiple agents. Each agent computes a distributed control action based on an output-feedback measurement of a local neighborhood tracking error and communicates information only to its neighbors, according to a communication network modeled as a directed graph. Each agent computes its distributed control action by solving a local min–max optimization problem that simultaneously computes a local state estimate and control input under worst-case assumptions on unmeasured input disturbances and measurement noise. Under easily verified controllability and observability assumptions, this distributed output-feedback model predictive control approach provides an upper bound on the group consensus error, thereby ensuring practical consensus in the presence of unmeasured disturbances and noise. A numerical example with four agents connected in a directed graph is given to illustrate the results.
We numerically analyze the role of carrier mobility in transparent conducting oxides in epsilon-near-zero phase modulators. High-mobility materials such as cadmium oxide enable compact photonic phase modulators with a modulation figure of merit > 29-{\circ}/\mathrm{dB}.
We use GaAs metasurfaces with (111) crystal orientation to channel the second harmonic generation (SHG) into the zero-diffraction order that is suppressed for SHG obtained from GaAs metasurfaces with (100) orientation.
Phase errors in large optical phased arrays degrade beam quality and must be actively corrected. Using a novel, low-power electro-optic design with matched pathlengths, we demonstrate simplified optimization and reduced sensitivity to wavelength and temperature.
There is growing interest in nexus research: energy-water, energy-water-land, and more recently food-energy-water. Motivating this movement is the recognition that the dynamics and feedbacks that constitute these nexuses have been overlooked in the past but are critical to the planning and management of these interacting elements. Formal reviews have identified gaps in current studies. In this commentary, we highlight additional oversights that are hindering integration of findings in nexus studies, notably usage of imprecise terminology to describe analyses, a failure to close the loop by linking production with corresponding waste streams, and exclusion of dynamics linking diverse constituent elements. Equally lacking from current nexus studies is a consistent protocol for communicating the conceptual basis of our studies. To fill this gap, we draw on diverse perspectives and fields to propose a comprehensive and systematic framework that can guide the model conceptualization phase of nexus studies. We also present a standardized documentation practice (similar to one utilized by the agent-based modeling community) to facilitate communication of nexus studies. These initiatives can improve our ability to account for and communicate the nuanced, food-energy-water nexus interactions in a consistent manner, which is necessary to better inform risk analysis and avoid decisions with unintended consequences and hidden costs to society.
Nanowire transistors are typically undoped devices whose characteristics depend strongly on the injection of carriers from the electrical contacts. In this letter, we fabricate and characterize SiGe nanowire transistors with an n-p-n doping profile and with a top gate covering only the p-doped section of the nanowire. For each device, we locate the p-segment with scanning capacitance microscopy, where the p-segment position varies along the channel due to the stochastic nature of our dropcast fabrication technique. The current-voltage characteristics for a series of transistors with different gate positions reveal that the on/off ratios for electrons is the highest when the gated p-type section is closest to the source contact, whereas the on/off ratios for holes is the highest when the gated p-type section is closest to the drain contact.
We demonstrate the first silicon photonic single-sideband (SSB)modulator with dual-parallel Mach-Zehnder modulators (MZMs)operating near 1550 nm with a measured carrier suppression of 27 dB and at least 12 dB sideband suppression at 1 GHz.
We demonstrate ultrafast tuning of Fano resonances in a broken symmetry III-V metasurface using optical pumping. The resonance is spectrally shifted by 10 nm under low pump fluences of < 100 uJ.cm-2.
Contemporary parallel scientific codes often rely on message passing for inter-process communication. However, inefficient coding practices or multithreading (e.g., via MPI-THREAD-MULTIPLE) can severely stress the underlying message processing infrastructure, resulting in potentially un-acceptable impacts on application performance. In this article, we propose and evaluate a novel method for addressing this issue: 'Fuzzy Matching'. This approach has two components. First, it exploits the fact most server-class CPUs include vector operations to parallelize message matching. Second, based on a survey of point-to-point communication patterns in representative scientific applications, the method further increases parallelization by allowing matches based on 'partial truth', i.e., by identifying probable rather than exact matches. We evaluate the impact of this approach on memory usage and performance on Knight's Landing and Skylake processors. At scale (262,144 Intel Xeon Phi cores), the method shows up to 1.13 GiB of memory savings per node in the MPI library, and improvement in matching time of 95.9%; smaller-scale runs show run-time improvements of up to 31.0% for full applications, and up to 6.1% for optimized proxy applications.