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At least 1,747 records · Page 97

Data mining and statistical inference in selective laser melting

Selective laser melting (SLM) is an additive manufacturing process that builds a complex three-dimensional part, layer-by-layer, using a laser beam to fuse fine metal powder together. The design freedom afforded by SLM comes associated with complexity. As the physical phenomena occur over a broad range of length and time scales, the computational cost of modeling the process is high. At the same time, the large number of parameters that control the quality of a part make experiments expensive. In this paper, we describe ways in which we can use data mining and statistical inference techniques to intelligently combine simulations and experiments to build parts with desired properties. We start with a brief summary of prior work in finding process parameters for high-density parts. We then expand on this work to show how we can improve the approach by using feature selection techniques to identify important variables, data-driven surrogate models to reduce computational costs, improved sampling techniques to cover the design space adequately, and uncertainty analysis for statistical inference. Here, our results indicate that techniques from data mining and statistics can complement those from physical modeling to provide greater insight into complex processes such as selective laser melting.

36 MATERIALS SCIENCE↗

Linkages between Policy and Business Innovation in the Development of China’s Energy Performance Contracting Market

China has a large and growing energy performance contracting (EPC) market, which has played a significant role in driving energy efficiency retrofits and improvements This paper evaluates how policies and business innovations have worked synergistically to expand China’s EPC market. We analyze the interconnected roles of four key factors: incentive policies, China’s Five-Year Plans, and business innovations in diversifying contract models and strengthening measurement and verification. We use multiple data sources for the analysis, including detailed information on business choices in 21 pilot projects, industry-wide surveys, and policy information. Our study indicates that supportive policies were important for the initial market development. As the market was established and continued to grow, the private sector started to take initiatives to address the issues that are left out of the policies, which helped overcome certain market barriers and enabled the sustainable growth of the market. Future policies could incorporate the successful innovations from the businesses to ensure long-term development of China’s EPC market. Understanding these policy and business drivers in a holistic way is critical to understanding how China was able to leverage its relatively small policy investments into much larger transformation of its existing buildings and industrial facilities through energy efficiency retrofits. This in turn can be informative for other countries seeking to achieve large-scale energy efficiency improvements.

Zhou, Yuanrong↗

On the proper derivation of the Floquet-based quantum classical Liouville equation and surface hopping describing a molecule or material subject to an external field

We investigate different approaches to derive the proper Floquet-based quantum–classical Liouville equation (F-QCLE) for laser-driven electron-nuclear dynamics. The first approach projects the operator form of the standard QCLE onto the diabatic Floquet basis and then transforms to the adiabatic representation. The second approach directly projects the QCLE onto the Floquet adiabatic basis. Both approaches yield a form that is similar to the usual QCLE with two modifications: (1) The electronic degrees of freedom are expanded to infinite dimension and (2) the nuclear motion follows Floquet quasi-energy surfaces. However, the second approach includes an additional cross derivative force due to the dual dependence on time and nuclear motion of the Floquet adiabatic states. Our analysis and numerical tests indicate that this cross derivative force is a fictitious artifact, suggesting that one cannot safely exchange the order of Floquet state projection with adiabatic transformation. Our results are in accord with similar findings by Izmaylov et al., [J. Chem. Phys. 140, 084104 (2014)] who found that transforming to the adiabatic representation must always be the last operation applied, although now we have extended this result to a time-dependent Hamiltonian. Finally, this paper and the proper derivation of the F-QCLE should lay the basis for further improvements of Floquet surface hopping.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Enhancing the accuracy of XPS calculations: Exploring hybrid basis set schemes for CVS-EOMIP-CCSD calculations

Reliable computational methodologies and basis sets for modeling x-ray spectra are essential for extracting and interpreting electronic and structural information from experimental x-ray spectra. In particular, the trade-off between numerical accuracy and computational cost due to the size of the basis set is a major challenge, since molecular orbitals undergo extreme relaxation in the core-hole state. To gain clarity on the changes in electronic structure induced by the formation of a core-hole, the use of sufficiently flexible basis for expanding the orbitals, particularly for the core region, has been shown to be essential. This work focuses on the refinement of core-hole ionized state calculations using the equation-of-motion coupled cluster family of methods through an extensive analysis on the effectiveness of “hybrid” and mixed basis sets. In this investigation, we utilize the CVS-EOMIP-CCSD method in combination and construct hybrid basis sets piecewise from readily available Dunning’s correlation consistent basis sets in order to calculate x-ray ionization energies (IEs) for a set of small gas phase molecules. Our results provide insights into the impact of basis sets on the CVS-EOMIP-CCSD calculations of K-edge IEs of first-row p-block elements. Furthermore, these insights enable us to understand more about the basis set dependence of the core IEs computed and allow us to establish a protocol for deriving reliable and cost-effective theoretical estimates for computing IEs of small molecules containing such elements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Time-resolved x-ray imaging of a laser-induced nanoplasma and its neutral residuals

The evolution of individual, large gas-phase xenon clusters, turned into a nanoplasma by a high power infrared laser pulse, is tracked from femtoseconds up to nanoseconds after laser excitation via coherent diffractive imaging, using ultra-short soft x-ray free electron laser pulses. A decline of scattering signal at high detection angles with increasing time delay indicates a softening of the cluster surface. Here we demonstrate, for the first time a representative speckle pattern of a new stage of cluster expansion for xenon clusters after a nanosecond irradiation. The analysis of the measured average speckle size and the envelope of the intensity distribution reveals a mean cluster size and length scale of internal density fluctuations. Furthermore, the measured diffraction patterns were reproduced by scattering simulations which assumed that the cluster expands with pronounced internal density fluctuations hundreds of picoseconds after excitation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Rest frame of bubble nucleation

Vacuum bubbles nucleate at rest with a certain critical size and subsequently expand. But what selects the rest frame of nucleation? This question has been recently addressed in [1] in the context of Schwinger pair production in 1+1 dimensions, by using a model detector in order to probe the nucleated pairs. The analysis in [1] showed that, for a constant external electric field, the adiabatic ''in'' vacuum of charged particles is Lorentz invariant, (and in this) case pairs tend to nucleate preferentially at rest with respect to the detector. Here, we sharpen this picture by showing that the typical relative velocity between the frame of nucleation and that of the detector is at most of order Δv ∼ S{sub E}{sup −1/3} << 1. Here, S{sub E} >> 1 is the action of the instanton describing pair creation. The bound Δv coincides with the minimum uncertainty in the velocity of a non-relativistic charged particle embedded in a constant electric field. A velocity of order Δv is reached after a time interval of order Δt ∼ S{sub E}{sup −1/3}r{sub 0} << r{sub 0} past the turning point in the semiclassical trajectory, where r{sub 0} is the size of the instanton. If the interaction takes place in the vicinity of the turning point, the semiclassical description of collision does not apply. Nonetheless, we find that even in this case there is still a strong asymmetry in the momentum transferred from the nucleated particles to the detector, in the direction of expansion after the turning point. We conclude that the correlation between the rest frame of nucleation and that of the detector is exceedingly sharp.

79 ASTRONOMY AND ASTROPHYSICS↗

Inducing optimally directed non-routine designs

Non-routine designs are characterized by the creation of new variables and thus an expansion of the design space. These differ from routine designs in that the latter are restricted to a fixed set of variables and thus a pre-defined design space. In previous papers, the 1stPRINCE non-routine design methodology that expands the design space in such a way that optimal trends dictate the direction and form of this expansion is described. How inductive techniques can determine these optimal trends are examined. The induction techniques in 1stPRINCE utilize constraint information from monotonicity analysis to determine how to mutate the design space. The process observes the constraint information of mutated designs and induces trends from those constraints. Application of 1stPRINCE to a beam under flexural load leads to an optimally directed tapered beam. An interesting application of 1stPRINCE to determine the optimally directed shape of a spinning square block such that resistance to spinning is minimized leads to the discovery of a circular wheel.

Cagan, Jonathan↗

SeaWiFS technical report series. Volume 25: Ocean optics protocols for SeaWiFS validation, revision 1

This report presents protocols for measuring optical properties, and other environmental variables, to validate the radiometric performance of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), and to develop and validate bio-optical algorithms for use with SeaWiFS data. The protocols are intended to establish foundations for a measurement strategy to verify the challenging SeaWiFS uncertainty goals of 5 percent in water-leaving radiances and 35 percent in chlorophyll alpha concentration. The protocols first specify the variables which must be measured, and briefly review the rationale for measuring each variable. Subsequent chapters cover detailed protocols for instrument performance specifications, characterizing and calibrating instruments, methods of making measurements in the field, and methods of data analysis. These protocols were developed at a workshop sponsored by the SeaWiFS Project Office (SPO) and held at the Naval Postgraduate School in Monterey, California (9-12 April 1991). This report began as the proceedings of the workshop, as interpreted and expanded by the authors and reviewed by workshop participants and other members of the bio-optical research community. The protocols are an evolving prescription to allow the research community to approach the unprecedented measurement uncertainties implied by the SeaWiFS goals; research and development are needed to improve the state-of-the-art in specific areas. These protocols should be periodically revised to reflect technical advances during the SeaWiFS Project cycle. The present edition (Revision 1) incorporates new protocols in several areas, including expanded protocol descriptions for Case-2 waters and other improvements, as contributed by several members of the SeaWiFS Science Team.

Hooker, Stanford B.↗

Rapid Calculation of Spacecraft Trajectories Using Efficient Taylor Series Integration

A variable-order, variable-step Taylor series integration algorithm was implemented in NASA Glenn's SNAP (Spacecraft N-body Analysis Program) code. SNAP is a high-fidelity trajectory propagation program that can propagate the trajectory of a spacecraft about virtually any body in the solar system. The Taylor series algorithm's very high order accuracy and excellent stability properties lead to large reductions in computer time relative to the code's existing 8th order Runge-Kutta scheme. Head-to-head comparison on near-Earth, lunar, Mars, and Europa missions showed that Taylor series integration is 15.8 times faster than Runge- Kutta on average, and is more accurate. These speedups were obtained for calculations involving central body, other body, thrust, and drag forces. Similar speedups have been obtained for calculations that include J2 spherical harmonic for central body gravitation. The algorithm includes a step size selection method that directly calculates the step size and never requires a repeat step. High-order Taylor series integration algorithms have been shown to provide major reductions in computer time over conventional integration methods in numerous scientific applications. The objective here was to directly implement Taylor series integration in an existing trajectory analysis code and demonstrate that large reductions in computer time (order of magnitude) could be achieved while simultaneously maintaining high accuracy. This software greatly accelerates the calculation of spacecraft trajectories. At each time level, the spacecraft position, velocity, and mass are expanded in a high-order Taylor series whose coefficients are obtained through efficient differentiation arithmetic. This makes it possible to take very large time steps at minimal cost, resulting in large savings in computer time. The Taylor series algorithm is implemented primarily through three subroutines: (1) a driver routine that automatically introduces auxiliary variables and sets up initial conditions and integrates; (2) a routine that calculates system reduced derivatives using recurrence relations for quotients and products; and (3) a routine that determines the step size and sums the series. The order of accuracy used in a trajectory calculation is arbitrary and can be set by the user. The algorithm directly calculates the motion of other planetary bodies and does not require ephemeris files (except to start the calculation). The code also runs with Taylor series and Runge-Kutta used interchangeably for different phases of a mission.

Scott, James R.↗

ALH84001: The Key to Unlocking Secrets About Mars-15 Years and Counting

From the December 27, 1984 discovery of ALH84001, and its subsequent identification as a sample of Mars in 1993, mystery and debate has surrounded the meteorite. With the realization that the ALH84001 sample was a orthopyroxenite and one of the oldest SNC meteorites (~4.09 Ga) available to study, important and critical information about the Martian hydrosphere and atmosphere along with the early history and evolution of the planet could be obtained by studying the unique carbonate globules (~3.9 Ga) in the sample. The initial work showed the carbonate globules were deposited within fractures and cracks in the host-orthopyroxene by low-temperature aqueous fluids. Ideas that the carbonates were formed at temperatures approaching 800oC were ruled out by later experiments. The 1996 announcement by McKay et al. that ALH84001 contained features which could be interpreted as having a biogenic origin generated considerable excitement and criticism. The NASA Administrator Dan Golden said the 1996 ALH84001 announcement saved NASA s Mars planetary exploration program and injected $6 billion dollars over five years into the scientific research and analysis efforts. All of the original four lines of evidence for possible biogenic features within ALH84001 offered by McKay et al. have withstood the test of time. Criticism has been directed at the interpretation of the 1996 analytical data. Research has expanded to other SNC meteorites. Despite the numerous attacks on the ideas, the debate continues after 15 years. The 2009 paper by Thomas-Keprta et al. on the origins of a suite of magnetites within the ALH84001 has offered strong arguments that some of the magnetites can only be formed by biogenic processes and not from thermal decomposition or shock events which happened to the meteorite. NASA s Astrobiology Institute was formed from the foundation laid by the ALH84001 hypothesis of finding life beyond the Earth. The strong astrobiology outreach programs have expanded because of the work done on the Martian meteorites. Despite the criticism on the biogenic-like features in ALH84001, the meteorite has opened a window into the early history of Mars. Clearly low-temperature fluids have left their signatures within the ALH84001 meteorite and subsequent cratering events on Mars have been recorded on observable features within the meteorite. The 15 years of detailed study on ALH84001 and its unique carbonate globules have clearly shown formational and secondary processes at work on Mars. The evidence for biogenic processes operating on early Mars along with ground water activity within the last 15% of the life of Mars offers clear evidence that another niche for life may be possible within our solar system. Now we need a well-documented Mars sample return mission.

Gibson, Everett K.↗

DESIGN AND TESTING OF A 275 BAR 700 DEGREE CELSIUS EXPANDER FOR AN INTEGRALLY GEARED SUPERCRITICAL CO2 COMPANDER

An integrally-geared (IG) compressor-expander (compander) for use in a nominal 10 MW-scale concentrated solar power (CSP) supercritical carbon dioxide (sCO2) plant application was designed, manufactured, and tested. The integrally-geared compander (IGC) developed for this application comprises multiple pinion shafts interacting through a single bull gear to create a compact package and utilize a lowcost, low-speed driver. The present work will detail the design of the high-pressure high-temperature expander casing on an integrally geared frame, and illustrate how the project successfully mitigated the risk of fatigue and creep while allowing for rapid thermal transients in the design. Furthermore, test data from the test campaign will be presented supporting the analysis. Test results also show temperature profiles during operation exceeding 720° Celsius.

wilkes, jason↗

Smoothed particle hydrodynamics modeling and analysis of oxide reduction process for uranium oxides

A common kinetic feature for oxide reduction chemical/electrochemical processes is oxygen transport via a porous metallic layer, which has been considered as a rate-determining step for reducing uranium oxides to metallic uranium. Accounting this kinetic behavior must involve the resolution of the moving reactive interface between shrinking oxide and expanding metal phases. This study presents a numerical model using smoothed particles hydrodynamics (SPH) to effectively deal with the evolution of the shrinking core reaction interface and oxygen transport via mass transfer of lithium oxide (Li 2 O) species in multiple mass transfer domains. We successfully validated the proposed model against a theoretical derivation for the oxide reduction process handling a shrinking oxide core with molten salt and metal ash medium on a simple planar geometry. Armed with successful validation results, the model examined a realistic reactant geometry to extend the arguments beyond the one-dimensional analyses, allowing the proposed model to apply to general application scenarios with multi-dimensional geometry. Here, this study demonstrated that the proposed model could simulate and evaluate an arbitrary reaction basket design without iterative experimental trials, which is prohibitive for a scaled high-temperature molten salt study in an inert environment. The construct potentially provides not only deep insights on multiphysics behaviors governing the process dynamics but also a robust framework for evaluating and screening candidate basket designs in the most cost-effective manner.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

Ablation, Thermal Response, and Chemistry Program for Analysis of Thermal Protection Systems

In previous work, the authors documented the Multicomponent Ablation Thermochemistry (MAT) and Fully Implicit Ablation and Thermal response (FIAT) programs. In this work, key features from MAT and FIAT were combined to create the new Fully Implicit Ablation, Thermal response, and Chemistry (FIATC) program. FIATC is fully compatible with FIAT (version 2.5) but has expanded capabilities to compute the multispecies surface chemistry and ablation rate as part of the surface energy balance. This new methodology eliminates B' tables, provides blown species fractions as a function of time, and enables calculations that would otherwise be impractical (e.g. 4+ dimensional tables) such as pyrolysis and ablation with kinetic rates or unequal diffusion coefficients. Equations and solution procedures are presented, then representative calculations of equilibrium and finite-rate ablation in flight and ground-test environments are discussed.

Milos, Frank S.↗

US Navy Submarine Sea Trial of NASA developed Multi-Gas Monitor

During a successful 2 year technology demonstration of the tunable diode laser spectroscopy (TDLS) based Multi-Gas Monitor (MGM) on the International Space Station (ISS), we began discussing with the US Navy the possibility of conducting a sea trial of an MGM on a submarine. The sea trial would also include a gas chromatography/differential mobility spectrometer based Air Quality Monitor (AQM), which is used operationally on ISS for volatile organic compound analysis. AQM preparation and results will be the subject of a separate paper. The Navy's interest in testing NASA equipment in general relates to their ongoing search for better air monitoring technology. NASA's goal is studying submarines as closed environment analogs to spacecraft. MGM's core technology was developed by Vista Photonics Inc. using Small Business Innovation Research (SBIR) grants and expanded for various applications using NASA program funding. The MGM measures oxygen, carbon dioxide, ammonia and water vapor in ambient air, displays concentrations with temperature and pressure, and stores 30 second moving averages. The sea trial involves collocating the instrument with the Central Atmosphere Monitoring System (CAMS Mk II) of the submarine, connecting it to rack power prior to departure, and letting it run during the entire 90 day patrol. All data is stored within MGM, with no connection to the vessel data bus. Crew intervention is limited to checking MGM periodically to see that it is working and power cycling if necessary. After the trial is over, the unit with its data will be retrieved. Post sea trial calibration check and data analysis are planned and results will be compared with both CAMS Mk II data and results from MGM's ISS technology demonstration. Since the sea trial itself has been delayed, this paper describes the preparation of MGM for the sea trial and also provides a summary of the latest data from the ISS MGM technology demonstration.

Mudgett, Paul D.↗

Advanced Fuel Cycle Cost Basis Report: Module D1-4 and Module D1-5 Ceramic Pelletized Sodium-Cooled Fast Reactor (SFR) Fuel Fabrication Ceramic Vibrocompacted Fuel Fabrication

This is a cost module that is part of the Advanced Fuel Cycle -- Cost Basis Report. Module D1-4: Nature of this module update (Rev 1) from previous advanced fuel cycle cost basis reports (AFCCBRs): new life cycle cost data on U,Pu SFR mixed oxide (MOX) fuels is derived from the Nonproliferation Assessment Systems Analysis Program (NASAP) conducted in the late 1970s. Highassay low-enriched uranium (HALEU) ceramic fuel is also discussed in more detail compared to earlier AFC-CBRs, since some advanced SFR concepts currently under development will require this HALEU fuel type for startup. Module D1-5: Nature of this FY-21 module update from previous AFC-CBRs: this module includes a few new references and a somewhat expanded discussion of vibrocompaction fuel fabrication technology. The WIT values for VIPAC are pegged directly to those for conventional LWR and SFR pelletized U,Pu MOX (note that this module now includes VIPAC MOX fuel for LWRs in addition to SFRs). Based on information from Russia, where VIPAC has been studied extensively, the unit costs are expressed as a percentage of those in the new updated Module D1-2 (pelletized U,Pu MOX) and new updated Module D1-4 (pelletized U,Pu MOX) for large NOAK fabrication facilities of the same production capacity. Since both ceramic pelletized MOX Modules D1-2 and D1-4 benefitted from analysis of 1970s NASAP data, by extension this Module D1-5 also benefits.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

Computer-aided design of stability enhanced nicotinamide cofactor biomimetics for cell-free biocatalysis

Cell-free biocatalysis (CFB) is an efficient and environmentally friendly method to synthesize molecules such as pharmaceuticals, biochemicals, and biofuels through the in vitro use of enzyme cascades. These enzymes often require redox cofactors to drive chemical reactions. Natural redox cofactors (NAD(P)H) are expensive to isolate, motivating synthetic nicotinamide cofactor biomimetics (NCBs) as a cost-effective solution. A select handful of NCBs have been identified as potential NAD(P)H alternatives with comparable or improved redox capabilities, however, they display a tendency to degrade in common buffers. In this study, a library of 132 NCB candidates is systematically generated, over 85% of which have not been characterized in the literature, to expand the diversity of currently explored NCBs. The decomposition mechanism of NCBs in phosphate is evaluated using density functional theory (DFT), revealing protonation at the nicotinamide C5 position as a reporter of cofactor stability. Based on this result, we trained a linear regression model on DFT calculated descriptors to predict NCB stability in phosphate buffer, achieving mean absolute error (MAE) and root mean squared error (RMSE) values within computational accuracy. Analysis of key atomic descriptors and qualitative trends in our dataset informed the design of novel NCB candidates we propose with optimized stability. This work enables researchers to predict the relative stability of NCBs before synthesis, thereby streamlining the process to make CFB more affordable and viable at industry scales.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Improving Estimation of the Koopman Operator with Kolmogorov–Smirnov Indicator Functions

It has become common to perform kinetic analysis using approximate Koopman operators that transform high-dimensional timeseries of observables into ranked dynamical modes. The key to the practical success of the approach is the identification of a set of observables that form a good basis on which to expand the slow relaxation modes. Good observables are, however, difficult to identify a priori and suboptimal choices can lead to significant underestimations of characteristic time scales. Leveraging the representation of slow dynamics in terms of Hidden Markov Models (HMM), we propose a simple and computationally efficient clustering procedure to infer surrogate observables that form a good basis for slow modes. Here, we apply the approach to an analytically solvable model system as well as on three protein systems of different complexities. We consistently demonstrate that the inferred indicator functions can significantly improve the estimation of the leading eigenvalues of Koopman operators and correctly identify key states and transition time scales of stochastic systems, even when good observables are not known a priori.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Thermodynamic and Kinetic Activity Descriptors for the Catalytic Hydrogenation of Ketones

Activity descriptors are a powerful tool for the design of catalysts than can efficiently utilize H 2 with minimal energy losses. In this study, we develop the use of hydricity and H - self-exchange rates as thermodynamic and kinetic descriptors for the hydrogenation of ketones by molecular catalysts. Two complexes with known hydricity, HRh(dmpe) 2 and HCo(dmpe) 2 , were investigated for the catalytic hydrogenation of ketones under mild conditions (1.5 atm, 25 °C). The rhodium catalyst proved to be an efficient catalyst for a wide range of ketones, whereas the cobalt catalyst could only hydrogenate electron-deficient ketones. Using a combination of experiment and electronic structure theory, thermodynamic hydricity values were established for 46 alkoxide/ketone pairs in both MeCN and THF solvent. Through comparison of the hydricities of the catalysts and substrates, it was determined that catalysis was only observed for catalyst/ketone pairs with an exergonic H - transfer step. Mechanistic studies revealed that H - transfer was rate-limiting step for catalysis, allowing for the experimental and computation construction of linear free-energy relationships (LFERs) for H - transfer. Further analysis revealed the LFERs could be reproduced using Marcus theory, in which the H - self-exchange rates for the HRh/Rh + and ketone/alkoxide pairs were used to predict the experimentally measured catalytic barriers within 2 kcal mol -1 . Finally, these studies significantly expand the scope of catalytic reactions that can be analyzed with a thermodynamic hydricity descriptor and firmly establish Marcus theory as a valid approach to develop kinetic descriptors for designing catalysts for H - transfer reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗