Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “LEADING ABSTRACT”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

The Microphysical Roles of Lower-Tropospheric versus Midtropospheric Aerosol Particles in Mature-Stage MCS Precipitation

Abstract Simulations of two leading-line, trailing-stratiform mesoscale convective system (MCS) events that occurred during the Midlatitude Continental Convective Clouds Experiment (MC3E) have been used to understand the relative microphysical impacts of lower- versus midtropospheric aerosol particles (APs) on MCS precipitation. For each MCS event, four simulations were conducted in which the initial vertical location and concentrations of cloud droplet nucleating APs were varied. These simulations were used to determine the precipitation response to AP vertical location. Importantly, the total integrated number and mass of the initial aerosol profiles used in the sensitivity simulations remained constant, such that differences in the simulations could be directly attributable to changes in the vertical location of cloud droplet nucleating APs. These simulations demonstrate that lower-tropospheric APs largely influenced the precipitation response directly rearward of the leading cold pool boundary. However, farther rearward in the MCS, the relative impact of lower- versus midtropospheric APs largely depended on the MCS structure, which varied between the two events because of differences in line-normal wind shear. Midtropospheric APs were able to activate new cloud droplets in the midtropospheric levels of convective updrafts and to enhance mixed-phase precipitation through increased cloud riming, and this microphysical pathway had a more significant impact on mixed-phase precipitation in weaker line-normal wind shear conditions. This result exposes the importance of properly representing midtropospheric APs when assessing aerosol effects on clouds. This study also demonstrates the utility of assessing aerosol effects within the different regions of MCSs.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Coupled Gel/Seeded Growth of Cs2AgBiBr6 Single Crystals for Radiation Detection

Abstract— The all-inorganic lead free Cs2AgBiBr6 perovskite represents a highly promising environment-friendly radiation detector material. The first attempt to grow Cs2AgBiBr6 single crystals using the unique gel growth method is reported in this study. This technique enables controlled reagent diffusion in a gel medium at room temperature, fostering the growth of visible single crystals. It offers advantages over conventional methods, leading to fewer equilibrium and non-equilibrium defects and simplified execution. Interestingly, the as-grown crystals exhibited variations in size and colors within the gel matrix, indicating the influence of Bi solutes in Bi-poor and Bi-rich Cs2AgBiBr6 crystals. Once the crystals were confirmed by powder xray diffraction, a series of comprehensive material characterizations was performed. The resistivity of Cs2AgBiBr6 single crystals was measured at 1.12x107 Ω•cm. Trap density analysis yielded a value of 2.82 x1010 cm-3. The charge carrier mobility was determined to be 32.9 cm2V-1S-1, suggesting the suitability for radiation detector applications. Additional growth optimization is going on and further characterization will be reported during the presentation. Our work helps accelerate the development of lead-free perovskite materials toward radiation detector applications.

James, Ralph B.↗
DOE OSTI2022

Persistent, extensive channelized drainage modeled beneath Thwaites Glacier, West Antarctica

Abstract. Subglacial hydrology is a leading control on basal friction and the dynamics of glaciers and ice sheets. At low discharge, subglacial water flows through high-pressure, sheet-like systems that lead to low effective pressures. However, at high discharge, subglacial water melts the overlying ice into localized channels that efficiently remove water from the bed, thereby increasing effective pressure and basal friction. Recent observations suggest channelized subglacial flow exists beneath Thwaites Glacier, yet it remains unclear if stable channelization is feasible in West Antarctica, where surface melting is nonexistent and water at the bed is limited. Here, we use the MPAS-Albany Land Ice model to run a suite of over 130 subglacial hydrology simulations of Thwaites Glacier across a wide range of physical parameter choices to assess the likelihood of channelization. We then narrow our range of viable simulations by comparing modeled water thicknesses to previously observed radar specularity content, which indicates flat, spatially extensive water bodies at the bed. In all of our data-compatible simulations, stable channels reliably form within 100–200 km of the grounding line and reach individual discharge rates of 35–110 m3 s−1 at the ice–ocean boundary. While only one to two channels typically form across the 200 km width of the glacier in our simulations, their high efficiency drains water across the entire lateral extent of the glacier. We posit the large catchment size of Thwaites Glacier, its funnel-like geometry, and high basal melt rates together accumulate enough water to form stable channels. No simulations resembled observed specularity content when channelization was disabled. Our results suggest channelized subglacial hydrology has two consequences for Thwaites Glacier dynamics: (i) amplifying submarine melting of the terminus and ice shelf while (ii) simultaneously raising effective pressure within 100 km of the grounding line and increasing basal friction. The distribution of effective pressure implied from our modeling differs from parameterizations typically used in large-scale ice sheet models, suggesting the development of more process-based parameterizations may be necessary.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1997

An Automated Method for Identifying Inconsistencies within Diagrammatic Software Requirements Specifications

The development of large-scale, composite software in a geographically distributed environment is an evolutionary process. Often, in such evolving systems, striving for consistency is complicated by many factors, because development participants have various locations, skills, responsibilities, roles, opinions, languages, terminology and different degrees of abstraction they employ. This naturally leads to many partial specifications or viewpoints. These multiple views on the system being developed usually overlap. From another aspect, these multiple views give rise to the potential for inconsistency. Existing CASE tools do not efficiently manage inconsistencies in distributed development environment for a large-scale project. Based on the ViewPoints framework the WHERE (Web-Based Hypertext Environment for requirements Evolution) toolkit aims to tackle inconsistency management issues within geographically distributed software development projects. Consequently, WHERE project helps make more robust software and support software assurance process. The long term goal of WHERE tools aims to the inconsistency analysis and management in requirements specifications. A framework based on Graph Grammar theory and TCMJAVA toolkit is proposed to detect inconsistencies among viewpoints. This systematic approach uses three basic operations (UNION, DIFFERENCE, INTERSECTION) to study the static behaviors of graphic and tabular notations. From these operations, subgraphs Query, Selection, Merge, Replacement operations can be derived. This approach uses graph PRODUCTIONS (rewriting rules) to study the dynamic transformations of graphs. We discuss the feasibility of implementation these operations. Also, We present the process of porting original TCM (Toolkit for Conceptual Modeling) project from C++ to Java programming language in this thesis. A scenario based on NASA International Space Station Specification is discussed to show the applicability of our approach. Finally, conclusion and future work about inconsistency management issues in WHERE project will be summarized.

Zhang, Zhong↗
DOE OSTI2021

Fermi-Hubbard Transport Solver v. 1.0

SAND2021-1511 O. The code takes a description of a system comprised of two leads that are sources and sinks of electrons, a set of abstract sites that those electrons can occupy, and their connectivity. It then predicts the current passing between the two leads through the set of abstract sites. There are numerical parameters that define the rate at which electrons tunnel between sites and another parameter that determines the energy of having two electrons on the same site. When the ratio of these energies and biases are set just right, they can be used to predict the existence of Coulomb blockade in which no current flows because the energetic penalty would be too high. That is, the code predicts a current and the absence of a current which is predictive of Coulomb blockade. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Brickson, MitchellI↗
DOE OSTI2015

Compositional dependence of optical band gap and refractive index in lead and bismuth borate glasses

Highlights: • Refractive indices increase with increasing PbO/Bi{sub 2}O{sub 3} content. • Optical band gap arises due to direct forbidden transition. • Optical band gaps decrease with increasing PbO/Bi{sub 2}O{sub 3} content. • New empirical relation between the optical band gap and the refractive index. - Abstract: We prepared a series of lead and bismuth borate glasses by varying PbO/Bi{sub 2}O{sub 3} content and studied refractive index and optical band gap as a function of glass composition. Refractive indices were measured very accurately using a Brewster’s angle set up while the optical band gaps were determined by analyzing the optical absorption edge using the Mott–Davis model. Using the Lorentz–Lorentz method and the effective medium theory, we calculated the refractive indices and then compared them with the measured values. Bismuth borate glasses show better agreement between the calculated values of the refractive index and experimental values. We used a differential method based on Mott–Davis model to obtain the type of transition and optical band gap (E{sub opt}) which in turn was compared with the value of E{sub opt} obtained using the extinction coefficient. Our analysis shows that in both lead and bismuth borate glasses, the optical band gap arises due to direct forbidden transition. With increasing PbO/Bi{sub 2}O{sub 3} content, the absorption edge shifts toward longer wavelengths and the optical band gap decreases. This behavior can be explained in terms of changes to the Pb−O/Bi−O chemical bonds with glass composition. We obtained a new empirical relation between the optical band gap and the refractive index which can be used to accurately determine the electronic oxide polarizability in lead and bismuth oxide glasses.

36 MATERIALS SCIENCE↗
NASA NTRS1993

(abstract) A Brief, Selective Review of Thermal Cycling Fatigue in Eutectic Tin-Lead Solder

This paper reviews selected parts of the current literature relevant to thermo-mechanical fatigue mechanisms in eutectic tin-lead solder, and suggests a general outline to account for some observed failures. The field is found to be complex. One recent experimental study finds some failure modes to be sensitive to joint geometry. Attempts to extrapolate from test environments to service environments have had only limited success. Much work remains to be done before fatigue failures in this material can be considered as under practical control.

environments↗
DOE OSTI2024

Two-loop master integrals for leading-color $$ pp\to t\overline{t}H $$ amplitudes with a light-quark loop

Abstract We compute the two-loop master integrals for leading-color QCD scattering amplitudes including a closed light-quark loop in$$ t\overline{t}H $$ t t ¯ H production at hadron colliders. Exploiting numerical evaluations in modular arithmetic, we construct a basis of master integrals satisfying a system of differential equations inϵ-factorized form. We present the analytic form of the differential equations in terms of a minimal set of differential one-forms. We explore properties of the function space of analytic solutions to the differential equations in terms of iterative integrals which can be exploited for studying the analytic form of related scattering amplitudes. Finally, we solve the differential equations using generalized series expansions to numerically evaluate the master integrals in physical phase space. As the first computation of a set of two-loop seven-scale master integrals, our results provide valuable input for analytic studies of scattering amplitudes in processes involving massive particles and a large number of kinematic scales.

Physics↗
DOE OSTI2015

SB6.0: The 6th International meeting on Synthetic Biology, July 9-11, 2013

The Synthetic Biology conference series (SBx.0) is the preeminent academic meeting in synthetic biology. Organized by the BioBricks Foundation, the SBx.0 conference series brings together leading researchers, students, industry executives, and policy makers from around the world to share, consider, debate, and plan efforts to make biology easier to engineer. Historically held every two years, the SBx.0 conferences are held in alternating locations in the United States, Europe, and Asia to encourage global participation and collaboration so that the ramifications of synthetic biology research and development are most likely to be safe ethical, and beneficial. On 9-11 July 2013, the 6th installment of the synthetic biology conference series (SB6.0) was held on the campus of Imperial College London (http://sb6.biobricks.org). The SB6.0 conference was attended by over 700 people, and many more were able to participate via video digital conference (http://sb6.biobricks.org/digital-conference/). Over the course of three days, the SB6.0 conference agenda included plenary sessions, workshops, and poster presentations covering topics ranging from the infrastructure needs arising when “Systematic Engineering Meets Biological Complexity” and design-led considerations for “Connecting People and Technologies” to discussions on “Engineering Biology for New Materials,” “Assessing Risk and Managing Biocontainment,” and “New Directions for Energy and Sustainability.” The $10,150 grant awarded by the U.S. Department of Energy (DE-SC0010233) to the BioBricks Foundation was used to provide partial reimbursement for the travel expenses of leading researchers from the United States to speak at the SB6.0 conference. A total of $9,450 was used to reimburse U.S. speakers for actual expenses related to the SB6.0 conference, including airfare (economy or coach only), ground transportation, hotel, and registration fees. In addition, $700 of the grant was used to offset direct administrative costs associated with selecting speakers (preparing announcements, evaluating abstract submissions) and handling travel arrangements. Leading U.S. researchers selected to speak at the SB6.0 conference included: Adam Arkin, Ph.D. Division Director of the Physical Biosciences Division at the Lawrence Berkeley National Laboratory and Professor in the Department of Bioengineering at UC Berkeley Jay Keasling, Ph.D. Professor in the Department of Bioengineering at Berkeley, Senior Faculty Scientist and Associate Laboratory Director of the Lawrence Berkeley National Laboratory, and Chief Executive Officer of the Joint BioEnergy Institute. Debra Mathews, Ph.D. Assistant Director for Science Programs for the Johns Hopkins Berman Institute of Bioethics, Assistant Professor in the Department of Pediatrics, and Affiliate Faculty in the McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins School of Medicine. Richard Murray, Ph.D. Thomas E. and Doris Everhart Professor of Control & Dynamical Systems and Bioengineering at Caltech. Sarah Richardson, Ph.D. Distinguished Postdoctoral Fellow in Genomics at the Lawrence Berkeley National Laboratory and the Department of Energy Joint Genome Institute. and others (for a complete listing of speakers presenting at the SB6.0 conference see http://sb6.biobricks.org/speakers/) The SB6.0 conference was the largest synthetic biology conference to date, and highlights of the SB6.0 conference have been published in a special issue of ACS Synthetic Biology (http://pubs.acs.org/toc/asbcd6/3/3). The BioBricks Foundation appreciates the support of the U.S. Department of Energy in helping to make this most influential and important conference in the field of synthetic biology a success.

42 ENGINEERING↗
DOE OSTI2020

Pacific decadal oscillation remotely forced by the equatorial Pacific and the Atlantic Oceans

Abstract The Pacific Decadal Oscillation (PDO), the leading mode of Pacific decadal sea surface temperature variability, arises mainly from combinations of regional air-sea interaction within the North Pacific Ocean and remote forcing, such as from the tropical Pacific and the Atlantic. Because of such a combination of mechanisms, a question remains as to how much PDO variability originates from these regions. To better understand PDO variability, the equatorial Pacific and the Atlantic impacts on the PDO are examined using several 3-dimensional partial ocean data assimilation experiments conducted with two global climate models: the CESM1.0 and MIROC3.2m. In these partial assimilation experiments, the climate models are constrained by observed temperature and salinity anomalies, one solely in the Atlantic basin and the other solely in the equatorial Pacific basin, but are allowed to evolve freely in other regions. These experiments demonstrate that, in addition to the tropical Pacific’s role in driving PDO variability, the Atlantic can affect PDO variability by modulating the tropical Pacific climate through two proposed processes. One is the equatorial pathway, in which tropical Atlantic sea surface temperature (SST) variability causes an El Niño-like SST response in the equatorial Pacific through the reorganization of the global Walker circulation. The other is the north tropical pathway, where low-frequency SST variability associated with the Atlantic Multidecadal Oscillation induces a Matsuno-Gill type atmospheric response in the tropical Atlantic-Pacific sectors north of the equator. These results provide a quantitative assessment suggesting that 12–29% of PDO variance originates from the Atlantic Ocean and 40–44% from the tropical Pacific. The remaining 27–48% of the variance is inferred to arise from other processes such as regional ocean-atmosphere interactions in the North Pacific and possibly teleconnections from the Indian Ocean.

Meteorology & Atmospheric Sciences↗
NASA NTRS2011

Graph Theory Roots of Spatial Operators for Kinematics and Dynamics

Spatial operators have been used to analyze the dynamics of robotic multibody systems and to develop novel computational dynamics algorithms. Mass matrix factorization, inversion, diagonalization, and linearization are among several new insights obtained using such operators. While initially developed for serial rigid body manipulators, the spatial operators and the related mathematical analysis have been shown to extend very broadly including to tree and closed topology systems, to systems with flexible joints, links, etc. This work uses concepts from graph theory to explore the mathematical foundations of spatial operators. The goal is to study and characterize the properties of the spatial operators at an abstract level so that they can be applied to a broader range of dynamics problems. The rich mathematical properties of the kinematics and dynamics of robotic multibody systems has been an area of strong research interest for several decades. These properties are important to understand the inherent physical behavior of systems, for stability and control analysis, for the development of computational algorithms, and for model development of faithful models. Recurring patterns in spatial operators leads one to ask the more abstract question about the properties and characteristics of spatial operators that make them so broadly applicable. The idea is to step back from the specific application systems, and understand more deeply the generic requirements and properties of spatial operators, so that the insights and techniques are readily available across different kinematics and dynamics problems. In this work, techniques from graph theory were used to explore the abstract basis for the spatial operators. The close relationship between the mathematical properties of adjacency matrices for graphs and those of spatial operators and their kernels were established. The connections hold across very basic requirements on the system topology, the nature of the component bodies, the indexing schemes, etc. The relationship of the underlying structure is intimately connected with efficient, recursive computational algorithms. The results provide the foundational groundwork for a much broader look at the key problems in kinematics and dynamics. The properties of general graphs and trees of nodes and edge were examined, as well as the properties of adjacency matrices that are used to describe graph connectivity. The nilpotency property of such matrices for directed trees was reviewed, and the adjacency matrices were generalized to the notion of block weighted adjacency matrices that support block matrix elements. This leads us to the development of the notion of Spatial Kernel Operator SKO kernels. These kernels provide the basis for the development of SKO resolvent operators.

Jain, Abhinandan↗
DOE OSTI2018

Bandgap Narrowing in Non‐Fullerene Acceptors: Single Atom Substitution Leads to High Optoelectronic Response Beyond 1000 nm

Abstract Two narrow bandgap non‐fullerene acceptors (NBG‐NFAs), namely, COTIC‐4F and SiOTIC‐4F, are designed and synthesized for the fabrication of efficient near‐infrared organic solar cells (OSCs). The chemical structures of the NBG‐NFAs contain a D′‐D‐D′ electron‐rich internal core based on a cyclopentadithiophene (or dithienosilole) (D) and alkoxythienyl (D′) core, end‐capped with the highly electron‐deficient unit 2‐(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene)malononitrile (A), ultimately providing a A‐D′‐D‐D′‐A molecular configuration that enhances the intramolecular charge transfer characteristics of the excited states. One can thereby reduce the optical bandgap ( E g opt ) to as low as ≈1.10 eV, one of the smallest values for NFAs reported to date. In bulk‐heterojunction (BHJ) OSCs, NBG‐NFA blends with the polymer donor PTB7‐Th yield power conversion efficiencies (PCE) of up to 9.0%, which is particularly high when compared against a range of NBG BHJ blends. Most significantly, it is found that, despite the small energy loss ( E g opt − e V OC ) of 0.52 eV, the PTB7‐Th/NBG‐NFA bulk heterojunction blends can yield short‐circuit current densities of up to 22.8 mA cm −2 , suggesting that the design and application of NBG‐NFA materials have substantial potential to further improve the PCE of OSCs.

Lee, Jaewon↗
DOE OSTI2022

Tuning Phonon Energies in Lanthanide‐doped Potassium Lead Halide Nanocrystals for Enhanced Nonlinearity and Upconversion

Abstract Optical applications of lanthanide‐doped nanoparticles require materials with low phonon energies to minimize nonradiative relaxation and promote nonlinear processes like upconversion. Heavy halide hosts offer low phonon energies but are challenging to synthesize as nanocrystals. Here, we demonstrate the size‐controlled synthesis of low‐phonon‐energy KPb 2 X 5 (X=Cl, Br) nanoparticles and the ability to tune nanocrystal phonon energies as low as 128 cm −1 . KPb 2 Cl 5 nanoparticles are moisture resistant and can be efficiently doped with lighter lanthanides. The low phonon energies of KPb 2 X 5 nanoparticles promote upconversion luminescence from higher lanthanide excited states and enable highly nonlinear, avalanche‐like emission from KPb 2 Cl 5 : Nd 3+ nanoparticles. The realization of nanoparticles with tunable, ultra‐low phonon energies facilitates the discovery of nanomaterials with phonon‐dependent properties, precisely engineered for applications in nanoscale imaging, sensing, luminescence thermometry and energy conversion.

Zhang, Zhuolei↗
DOE OSTI2019

Interplay between Short and Long-Ranged Forces Leading to the Formation of Ag Nanoparticle Superlattice

Nanoparticle (NP) superlattices have attracted increasing attention due to their unique properties. However, key questions remain for predicting the nanoparticle behavior from interparticle forces, especially the role of hydration force (Fhyd) and its correlation to other forces, regarding the transient and final superlattice configurations. Here we investigated the self-assembly of Ag NPs in aqueous solution by employing in situ liquid cell transmission electron microscopy, combined with atomic force microscopy based force measurements and theoretical calculations. In spite of instantaneous Brownian motion of NPs, a correlation between velocity and van der Waals force (FvdW) on average was observed during the later self-assembly process. In the post-assembly state, a delicate balance between Fhyd and FvdW gives rise to ~ 0.6~0.9 nm separation be-tween NPs in the superlattice. Our study demonstrates pivotal roles of interparticle forces, enabling the control of the separation which is critical for tailoring the properties of superlattices.

Lee, Jaewon↗