Related Publications

  • Census-independent population mapping in northern Nigeria

    Although remote sensing has long been used to aid in the estimation of population, it has usually been in the context of spatial disaggregation of national census data, with the census counts serving both as observational data for specifying models and as constraints on model outputs. Here we present a framework for estimating populations from the bottom up, entirely independently of national census data, a critical need in areas without recent and reliable census data. To make observations of population density, we replace national census data with a microcensus, in which we enumerate...
  • Multigroup Monte Carlo on GPUs: Comparison of history- and event-based algorithms

    This paper presents an investigation of the performance of different multigroup Monte Carlo transport algorithms on GPUs with a discussion of both history-based and event-based approaches. Several algorithmic improvements are introduced for both approaches. By modifying the history-based algorithm that is traditionally favored in CPU-based MC codes to occasionally filter out dead particles to reduce thread divergence, performance exceeds that of either the pure history-based or event-based approaches. The impacts of several algorithmic choices are discussed, including performance studies on...
  • Substrate Binding Induces Conformational Changes in a Class A β-lactamase That Prime It for Catalysis

    The emergence and dissemination of bacterial resistance to β-lactam antibiotics via β-lactamase enzymes is a serious problem in clinical settings, often leaving few treatment options for infections resulting from multidrug-resistant superbugs. Understanding the catalytic mechanism of β-lactamases is important for developing strategies to overcome resistance. Binding of a substrate in the active site of an enzyme can alter the conformations and pKas of catalytic residues, thereby contributing to enzyme catalysis. Here we report X-ray and neutron crystal structures of the class A Toho-1 β-...
  • Building with ions: towards direct write of platinum nanostructures using in situ liquid cell helium ion microscopy

    Direct write with a liquid precursor using an ion beam in situ, allows fabrication of nanostructures with higher purity than using gas phase deposition. Specifically, positively charged helium ions, when compared to electrons, localize the reaction zone to a single-digit nanometer scale. However, to control the interaction of the ion beam with the liquid precursor, as well as enable single digit fabrication, a comprehensive understanding of the radiolytic process, and the role of secondary electrons has to be developed. Here, we demonstrate an approach for directly writing platinum...
  • Catalytic Exhaust Gas Recirculation-Loop Reforming for High Efficiency in a Stoichiometric Spark-Ignited Engine through Thermochemical Recuperation and Dilution Limit Extension, Part 2: Engine Performance

    This is the second part of a two-part investigation of on-board catalytic fuel reforming to increase the brake efficiency of a multicylinder, stoichiometric spark-ignited (SI) engine. In Part 1 of the investigation, we analytically and experimentally characterized the energetics and kinetics of a candidate reforming catalyst over a range of reforming equivalence ratios and oxygen concentration conditions to identify the best conditions for efficient reforming. In the present part of our investigation, we studied an engine strategy that combined exhaust gas recirculation (EGR)–loop reforming...
  • Kinetics of Methylmercury Production Revisited

    Laboratory measurements of the biologically mediated methylation of mercury (Hg) to the neurotoxin monomethylmercury (MMHg) often exhibit kinetics that are inconsistent with first-order kinetic models. Using time-resolved measurements of filter passing Hg and MMHg during methylation/demethylation assays, a multisite kinetic sorption model, and reanalyses of previous assays, we show that competing kinetic sorption reactions can lead to time-varying availability and apparent non-first-order kinetics in Hg methylation and MMHg demethylation. The new model employing a multisite kinetic sorption...
  • A magnetic topological semimetal Sr1−yMn1−zSb2 (y, z < 0.1)

    Weyl (WSMs) evolve from Dirac semimetals in the presence of broken time-reversal symmetry (TRS) or space-inversion symmetry. The WSM phases in TaAs-class materials and photonic crystals are due to the loss of space-inversion symmetry. For TRS-breaking WSMs, despite numerous theoretical and experimental efforts, few examples have been reported. In this Article, we report a new type of magnetic semimetal Sr1−yMn1−zSb2 (y, z < 0.1) with nearly massless relativistic fermion behaviour (m∗ =  0.04 − 0.05m0, where m0 is the free-electron mass). This material exhibits a ferromagnetic order...
  • Uncertainty in Estimates of Bioenergy‐Induced Land Use Change: The Impact of Inconsistent Land Cover Data Sets and Land Class Definitions

    While many data sets are increasingly available to describe land cover characteristics, these data require careful analysis and supplemental research before conclusions can be drawn about the scope, magnitude, and drivers of change. Land cover data, typically derived from remote sensing, are frequently analyzed to estimate land use change (LUC) that may be attributable to policies such as the U.S. Renewable Fuel Standard, which encourages bioenergy. However, land cover classifications such as grassland do not clearly differentiate among multiple land uses (pasture, fodder, crop, yard,...
  • "To Be or Not to Be" Protonated: Atomic Details of Human Carbonic Anhydrase-Clinical Drug Complexes by Neutron Crystallography and Simulation

    Human carbonic anhydrases (hCAs) play various roles in cells, and have been drug targets for decades. Sequence similarities of hCA isoforms necessitate designing specific inhibitors, which requires detailed structural information for hCA-inhibitor complexes. We present room temperature neutron structures of hCA II in complex with three clinical drugs that provide in-depth analysis of drug binding, including protonation states of the inhibitors, hydration water structure, and direct visualization of hydrogen-bonding networks in the enzyme's active site. All sulfonamide inhibitors studied bind...
  • Constraint-Based Routing Models for the Transport of Radioactive Materials

    The Department of Energy (DOE) has a historic programmatic interest in the safe and secure routing, tracking, and transportation risk analysis of radiological materials in the United States. In order to address these program goals, DOE has funded the development of several tools and related systems designed to provide insight to planners and other professionals handling radioactive materials shipments. These systems include the WebTRAGIS (Transportation Routing Analysis Geographic Information System) platform. WebTRAGIS is a browser-based routing application developed at Oak Ridge National...
  • A rule-based expert system applied to moisture durability of building envelopes

    The moisture durability of an envelope component such as a wall or roof is difficult to predict. Moisture durability depends on all the construction materials used, as well as the climate, orientation, air tightness, and indoor conditions. Modern building codes require more insulation and tighter construction but provide little guidance about how to ensure these energy-efficient assemblies remain moisture durable. Furthermore, as new products and materials are introduced, builders are increasingly uncertain about the long-term durability of their building envelope designs. Oak Ridge National...
  • Supertough PLA-Silane Nanohybrids by in Situ Condensation and Grafting

    Brittleness is a key barrier for poly(lactic acid) (PLA) toward broader applications. Supertough PLA was achieved by simply mixing a low amount (0.5–1 wt %) of organoalkoxysilane with PLA. Three organosilanes, (3-aminopropyl)triethoxysilane (APTES), 3-(triethoxysilyl)propyl isocyanate (ICPTES), and trimethoxymethylsilane (MTMS), were selected for this study to understand how the functional group on a silane affects the behavior of the PLA-silane hybrids. Remarkable improvements in ultimate tensile strain (up to 12 folds) and tensile toughness (up to 10 folds) were observed in APTES- and...
  • Quantum Accelerators for High-Performance Computing Systems

    We define some of the programming and system-level challenges facing the application of quantum processing to high-performance computing. Alongside barriers to physical integration, prominent differences in the execution of quantum and conventional programs challenges the intersection of these computational models. Following a brief overview of the state of the art, we discuss recent advances in programming and execution models for hybrid quantum-classical computing. We discuss a novel quantum-accelerator framework that uses specialized kernels to offload select workloads while integrating...
  • The SCALE 6.2 ORIGEN API for High Performance Depletion

    In recent years, the SCALE 6.2 development efforts have included modernization of key components of the modular SCALE code system. The ORIGEN depletion/decay module has received extensive improvements, including the addition of an application programming interface (API) for both C++ and Fortran with modern object-oriented design and various solver enhancements. This paper highlights the API capabilities that are currently available in beta release for embedding ORIGEN depletion calculations in other codes (e.g., for coupled transport/depletion calculations). The capabilities of the API are...
  • Community proteogenomics reveals the systemic impact of phosphorus availability on microbial functions in tropical soil

    Phosphorus is a scarce nutrient in many tropical ecosystems, yet how soil microbial communities cope with growth-limiting phosphorus deficiency at the gene and protein levels remains unknown. Here, we report a metagenomic and metaproteomic comparison of microbial communities in phosphorus-deficient and phosphorus-rich soils in a 17-year fertilization experiment in a tropical forest. The large-scale proteogenomics analyses provided extensive coverage of many microbial functions and taxa in the complex soil communities. A greater than fourfold increase in the gene abundance of 3-phytase was the...
  • Experimental frequency splitter and tritter setup.

    Electro-optic frequency beam splitters and tritters for high-fidelity photonic quantum information processing

    We report experimental realization of high-fidelity photonic quantum gates for frequency-encoded qubits and qutrits based on electro-optic modulation and Fourier-transform pulse shaping. Our frequency version of the Hadamard gate offers near-unity fidelity (0.99998 + or -0.00003), requires only a single microwave drive tone for near-ideal performance, functions across the entire C-band (1530-1570 nm), and can operate concurrently on multiple qubits spaced as tightly as four frequency modes apart, with no observable degradation in the fidelity. For qutrits we implement a 3 x 3 extension of the...
  • Destabilization of Magnetic Order in a Dilute Kitaev Spin Liquid Candidate

    The insulating honeycomb magnet α−RuCl3 exhibits fractionalized excitations that signal its proximity to a Kitaev quantum spin liquid state; however, at T=0 , fragile long-range magnetic order arises from non-Kitaev terms in the Hamiltonian. Spin vacancies in the form of Ir3+ substituted for Ru are found to destabilize this long-range order. Neutron diffraction and bulk characterization of Ru1−xIrxCl3 show that the magnetic ordering temperature is suppressed with increasing x , and evidence of zizag magnetic order is absent for x>0.3 . Inelastic neutron scattering demonstrates that the...
  • An Acrylonitrile–Butadiene–Lignin Renewable Skin with Programmable and Switchable Electrical Conductivity for Stress/Strain-Sensing Applications

    We report an approach for programming electrical conductivity of a bio-based leathery skin devised with a layer of 60 nm metallic nanoparticles. Lignin-based renewable shape-memory materials were made, for the first time, to program and restore the materials’ electrical conductivity after repeated deformation up to 100% strain amplitude, at a temperature 60–115 °C above the glass transition temperature (Tg) of the rubbery matrix. We cross-linked lignin macromolecules with an acrylonitrile–butadiene rubbery melt in high quantities ranging from 40 to 60 wt % and processed the resulting...
  • Spontaneous imbibition of water and determination of effective contact angles in the Eagle Ford Shale Formation using neutron imaging

    Understanding of fundamental processes and prediction of optimal parameters during the horizontal drilling and hydraulic fracturing process results in economically effective improvement of oil and natural gas extraction. Although modern analytical and computational models can capture fracture growth, there is a lack of experimental data on spontaneous imbibition and wettability in oil and gas reservoirs for the validation of further model development. In this work, we used neutron imaging to measure the spontaneous imbibition of water into fractures of Eagle Ford shale with known geometries...
  • Memristive Mixed-Signal Neuromorphic Systems: Energy-Efficient Learning at the Circuit-Level

    Neuromorphic computing is a non-von Neumann computer architecture for the post Moore’s law era of computing. Since a main focus of the post Moore’s law era is energy-efficient computing with fewer resources and less area, neuromorphic computing contributes effectively in this research. In this paper we present a memristive neuromorphic system for improved power and area efficiency. Our particular mixed-signal approach implements neural networks with spiking events in a synchronous way. Moreover, the use of nano-scale memristive devices saves both area and power in the system. We also provide...
  • Reproductive Microbiomes: Using the Microbiome as a Novel Diagnostic Tool for Endometriosis

    Background: Endometriosis is a chronic inflammatory disease which results in significant pain and long term reproductive consequences for up to 50% of infertile women. This study was focused to understand how endometriosis altered the uterine and cervical bacterial community. Methods and findings: Urogenital swabs and uterine washes were collected from 19 pre-menopausal women undergoing laparoscopic surgery for pelvic pain, suspected endometriosis (experimental n=10), and women undergoing laparoscopic surgery for benign ovarian/uterine conditions (control n=9). Patients were followed for the...
  • Seeing real-space dynamics of liquid water through inelastic x-ray scattering

    Water is ubiquitous on earth, but we know little about the real-space motion of molecules in liquid water. We demonstrate that high-resolution inelastic x-ray scattering measurement over a wide range of momentum and energy transfer makes it possible to probe real-space, real-time dynamics of water molecules through the so-called Van Hove function. Water molecules are found to be strongly correlated in space and time with coupling between the first and second nearest-neighbor molecules. The local dynamic correlation of molecules observed here is crucial to a fundamental understanding of the...
  • Long-term strategic planning of inter-city fast charging infrastructure for battery electric vehicles

    This study introduces a multistage chance-constrained stochastic model for strategic planning of battery electric vehicle (BEV) inter-city fast charging infrastructure. A mixed integer programming model is developed to determine where and when charging stations are opened, and how many chargers are required for each station to meet the growing BEV inter-city demand. The model is applied to a case study in California and solved by genetic algorithm. This study showed that investment in inter-city charging infrastructure is vital to alleviate the range anxiety. Also, planning decisions depend...
  • High performance aluminum–cerium alloys for high-temperature applications

    Light-weight high-temperature alloys are important to the transportation industry where weight, cost, and operating temperature are major factors in the design of energy efficient vehicles. Aluminum alloys fill this gap economically but lack high-temperature mechanical performance. Alloying aluminum with cerium creates a highly castable alloy, compatible with traditional aluminum alloy additions, that exhibits dramatically improved high-temperature performance. These compositions display a room temperature ultimate tensile strength of 400 MPa and yield strength of 320 MPa, with 80% mechanical...
  • Purinyl-cobamide is a native prosthetic group of reductive dehalogenases

    Cobamides such as vitamin B12 are structurally conserved, cobalt-containing tetrapyrrole biomolecules that have essential biochemical functions in all domains of life. In organohalide respiration, a vital biological process for the global cycling of natural and anthropogenic organohalogens, cobamides are the requisite prosthetic groups for carbon–halogen bond-cleaving reductive dehalogenases. This study reports the biosynthesis of a new cobamide with unsubstituted purine as the lower base and assigns unsubstituted purine a biological function by demonstrating that Coα-purinyl-cobamide (...