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At least 487 records · Page 27

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DOE OSTI2015

SR2067 reveals a unique kinetic and structural signature for PPARγ partial agonism

Here, synthetic full agonists of PPARγ have been prescribed for the treatment of diabetes due to their ability to regulate glucose homeostasis and insulin sensitization. While the use of full agonists of PPARγ has been hampered due to severe side effects, partial agonists have shown promise due to their decreased incidence of such side effects in preclinical models. No kinetic information has been forthcoming in regard to the mechanism of full versus partial agonism of PPARγ to date. In this paper, we describe the discovery of a partial agonist, SR2067. A co-crystal structure obtained at 2.2 Å resolution demonstrates that interactions with the β-sheet are driven exclusively via hydrophobic interactions mediated through a naphthalene group, an observation that is unique from other partial agonists. Finally, surface plasmon resonance revealed that SR2067 binds to the receptor with higher affinity (K D = 513 nM) as compared to that of full agonist rosiglitazone, yet it has a much slower off rate compared to that of rosiglitazone.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1986

Parameter estimation problems for distributed systems using a multigrid method

The problem of estimating spatially varying coefficients of partial differential equations is considered from observation of the solution and of the right hand side of the equation. It is assumed that the observations are distributed in the domain and that enough observations are given. A method of discretization and an efficient multigrid method for solving the resulting discrete systems are described. Numerical results are presented for estimation of coefficients in an elliptic and a parabolic partial differential equation.

Taasan, S.↗

NASA NTRS1990

Parameter estimation problems for distributed systems using a multigrid method

Ta'asan, Shlomo↗

DOE OSTI2017

Multiple-Satellite Observation of Magnetic Dip Event During the Substorm on 10 October 2013

Here, we present a multiple-satellite observation of the magnetic dip event during the substorm on 10 October 2013. The observation illustrates the temporal and spatial evolution of the magnetic dip and gives a compelling evidence that ring current ions induce the magnetic dip by enhanced plasma beta. The dip moves with the energetic ions in a comparable drift velocity and affects the dynamics of relativistic electrons in the radiation belt. In addition, the magnetic dip provides a favorable condition for the electromagnetic ion cyclotron (EMIC) wave generation based on the linear theory analysis. The calculated proton diffusion coefficients show that the observed EMIC wave can lead to the pitch angle scattering losses of the ring current ions, which in turn partially relax the magnetic dip in the observations. This study enriches our understanding of magnetic dip evolution and demonstrates the important role of the magnetic dip for the coupling of radiation belt and ring current.

58 GEOSCIENCES↗

DOE OSTI2015

SU-F-303-05: DCE-MRI Before and During Treatment for Prediction of Concurrent Chemotherapy and Radiation Therapy Response in Head and Neck Cancer

Purpose: To determine the ability of pharmacokinetic parameters derived from dynamic contrast-enhanced MRI (DCE- MRI) acquired before and during concurrent chemotherapy and radiation therapy to predict clinical response in patients with head and neck cancer. Methods: Eleven patients underwent a DCE-MRI scan at three time points: 1–2 weeks before treatment, 4–5 weeks after treatment initiation, and 3–4 months after treatment completion. Post-processing of MRI data included correction to reduce motion artifacts. The arterial input function was obtained by measuring the dynamic tracer concentration in the jugular veins. The volume transfer constant (Ktrans), extracellular extravascular volume fraction (ve), rate constant (Kep; Kep = Ktrans/ve), and plasma volume fraction (vp) were computed for primary tumors and cervical nodal masses. Patients were categorized into two groups based on response to therapy at 3–4 months: responders (no evidence of disease) and partial responders (regression of disease). Responses of the primary tumor and nodes were evaluated separately. A linear classifier and receiver operating characteristic curve analyses were used to determine the best model for discrimination of responders from partial responders. Results: When the above pharmacokinetic parameters of the primary tumor measured before and during treatment were incorporated into the linear classifier, a discriminative accuracy of 88.9%, with sensitivity =100% and specificity = 66.7%, was observed between responders (n=6) and partial responders (n=3) for the primary tumor with the corresponding accuracy = 44.4%, sensitivity = 66.7%, and specificity of 0% for nodal masses. When only pre-treatment parameters were used, the accuracy decreased to 66.7%, with sensitivity = 66.7% and specificity = 66.7% for the primary tumor and decreased to 33.3%, sensitivity of 50%, and specificity of 0% for nodal masses. Conclusion: Higher accuracy, sensitivity, and specificity were obtained using DCE-MRI-derived pharmacokinetic parameters acquired before and during treatment as compared with those derived from the pre-treatment time-point, exclusively.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2025

Characterizing Stress Roughness at Utah FORGE Through Simulation of Hydraulic Fracture Growth During 16A Stage 3 Stimulation

In most geologic formations, the vertical gradient of the minimum horizontal stress (𝜎 h ) exceeds the hydrostatic gradient, often driving hydraulic fractures to propagate upward. However, observations indicate that the upward growth of real hydraulic fractures is less pronounced than theoretical predictions based on smoothly varying 𝜎 h fields. In fact, the layered structure of sedimentary rocks hinders fracture propagation across layers, partially explaining the limited height growth observed in practice (Zoback et al., 2022). While crystalline rocks lack the pervasive layered fabric of sedimentary formations, they still possess structural fabric formed over their geologic history, resulting in inherently "rough" in situ stress fields. Recent studies have identified another key factor: the "roughness" of in situ stress, characterized by temporal, relatively short-wavelength fluctuations superimposed on the overall stress gradient. This stress roughness leads to apparent toughness anisotropy, where the vertical toughness appears significantly larger than the horizontal toughness (P. Fu et al., 2019; Dontsov & Suarez-Rivera, 2021). Neglecting the effects of rock fabric and stress roughness can yield inaccurate predictions of hydraulic fracture geometry and growth rates at larger length scales.

58 GEOSCIENCES↗

NASA NTRS1990

Observational constraints on the global atmospheric CO2 budget

Observed atmospheric concentrations of CO2 and data on the partial pressures of CO2 in surface ocean waters are combined to identify globally significant sources and sinks of CO2. The atmospheric data are compared with boundary layer concentrations calculated with the transport fields generated by a general circulation model (GCM) for specified source-sink distributions. In the model the observed north-south atmospheric concentration gradient can be maintained only if sinks for CO2 are greater in the Northern than in the Southern Hemisphere. The observed differences between the partial pressure of CO2 in the surface waters of the Northern Hemisphere and the atmosphere are too small for the oceans to be the major sink of fossil fuel CO2. Therefore, a large amount of the CO2 is apparently absorbed on the continents by terrestrial ecosystems.

Tans, Pieter P.↗

DOE OSTI2019

A regularized deconvolution method for turbulent closure modeling in implicitly filtered large-eddy simulation

Turbulence closure models that are based on a regularized deconvolution method (RDM) are proposed for application to implicitly filtered Large-Eddy Simulation (LES). This method reconstructs sub-grid scale contributions by approximately recovering filtered quantities through an optimization approach. Physical principles on the boundedness and conservation of reconstructed quantities are preserved by constraining the optimization problem. Further, to account for effects of scales that are not resolved in implicitly filtered LES, a reconstruction method is proposed that combines sub-grid projection and energy-similarity to enrich unresolved scales. With this method, closure models are developed for turbulent scalar fluxes and turbulence–chemistry interaction that are intrinsically consistent with the LES formulation. These closure models are evaluated in application to a piloted turbulent jet flame with inhomogeneous inlet composition, in which combustion is represented by a two-scalar manifold model. The RDM-formulation is benchmarked against simulations obtained using a presumed PDF method and eddy diffusivity closure model. In partially-premixed flame regions, it is observed that RDM improves the prediction of turbulent mixing, and faster grid convergence is observed for results with RDM compared to simulations employing a presumed PDF method.

42 ENGINEERING↗

NASA NTRS1977

Use of sensitivity analysis to predict pilot performance as a function of different displays

A technique for objectively evaluating different displays by sensitivity analysis is described. First, the mathematical model used to analyze static displays is developed. The technique is based on formulating functional relationships between the state variables and the variables observable in the display. The matrix of the partial derivatives of the display variables with respect to the state variables, together with the observer's acuity function, is used to calculate expected errors in the state vector estimation. The technique is expanded by the use of Kalman filtering to process a time series of observation vectors. This provides a tool for analyzing displays of dynamic processes by means of a dynamic display evaluation computer program. Results are reported using this program to simulate an Instrument Landing System approach.

Mout, M. L.↗

DOE OSTI2019

RF sheath modeling of experimentally observed plasma surface interactions with the JET ITER-Like Antenna

Waves in the Ion Cyclotron Range of Frequencies (ICRF) enhance local Plasma-Surface Interactions (PSI) near the wave launchers and magnetically-connected objects via Radio-Frequency (RF) sheath rectification. ITER will use 20MW of ICRF power over long pulses, questioning the long-term impact of RF-enhanced localized erosion on the lifetime of its Beryllium (Be) wall. Recent dedicated ICRF-heated L-mode discharges documented this process on JET for different types of ICRF antennas. Using visible spectroscopy in JET ICRF-heated L-mode discharges, poloidally-localized regions of enhanced (by ~2–4x) Be I and Be II light emission were observed on two outboard limiters magnetically connected to the bottom of the active ITER-Like Antenna (ILA). The observed RF-PSI induced by the ILA was qualitatively comparable to that induced by the JET standard, type-A2 antennas, for similar strap toroidal phasing and connection geometries. The Be II line emission was found more intense when powering the bottom half of the ILA rather than its top half. Conversely, more pronounced SOL density modifications were observed with only top array operation, on field lines connected to the top half of the ILA. So far the near-field modeling of the ILA with antenna code TOPICA (Torino Polytechnic Ion Cyclotron Antenna), using curved antenna model, was partially able to reproduce qualitatively the observed phenomena. A quantitative discrepancy persisted between the observed Be source amplification and the calculated, corresponding increases in E // field at the magnetically connected locations to the ILA when changing from only top to only bottom half antenna operation. This paper revisits these current drive phased and half-ILA powered cases using for the new simulations flat model of the ILA and more realistic antenna feeding to calculate the E// field maps with TOPICA code. Further, the Self-consistent Sheaths and Waves for Ion Cyclotron Heating Slow Wave (SSWICH-SW) code, which couples slow wave evanescence with DC Scrape-Off Layer (SOL) biasing, is used to estimate the poloidal distribution of rectified RF-sheath Direct Current (DC) potential V DC in the private SOL between the ILA poloidal limiters. The approach so far was limited to correlating the observed, enhanced emission regions at the remote limiters to the antenna near-electric fields, as calculated by TOPICA. The present approach includes also a model for the rectification of these near-fields in the private SOL of the ILA. With the improved approach, when comparing only top and only bottom half antenna feeding, we obtained good qualitative correlation between all experimental measurements and the calculated local variations in the E // field and V DC potential.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2022

Monte Carlo study of the pseudogap and superconductivity emerging from quantum magnetic fluctuations

Abstract The origin of the pseudogap behavior, found in many high- T c superconductors, remains one of the greatest puzzles in condensed matter physics. One possible mechanism is fermionic incoherence, which near a quantum critical point allows pair formation but suppresses superconductivity. Employing quantum Monte Carlo simulations of a model of itinerant fermions coupled to ferromagnetic spin fluctuations, represented by a quantum rotor, we report numerical evidence of pseudogap behavior, emerging from pairing fluctuations in a quantum-critical non-Fermi liquid. Specifically, we observe enhanced pairing fluctuations and a partial gap opening in the fermionic spectrum. However, the system remains non-superconducting until reaching a much lower temperature. In the pseudogap regime the system displays a “gap-filling" rather than “gap-closing" behavior, similar to the one observed in cuprate superconductors. Our results present direct evidence of the pseudogap state, driven by superconducting fluctuations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

NASA NTRS2004

Aura Atmospheric Data Products and Their Availability from NASA Goddard Earth Sciences DAAC

NASA's EOS-Aura spacecraft was launched successfully on July 15, 2004. The four instruments onboard the spacecraft are the Microwave Limb Sounder (MLS), the Ozone Monitoring Instrument (OMI), the Tropospheric Emission Spectrometer (TES), and the High Resolution Dynamics Limb Sounder (HBDLS). The Aura instruments are designed to gather earth sciences measurements across the ultraviolet, visible, infra-red, thermal and microwave regions of the electromagnetic spectrum. Aura will provide over 70 distinct standard atmospheric data products for use in ozone layer and surface UV-B monitoring, air quality forecast, and atmospheric chemistry and climate change studies (http://eosaura.gsfc.nasa.gov/). These products include earth-atmosphere radiances and solar spectral irradiances; total column, tropospheric, and profiles of ozone and other trace gases, surface W-B flux; clouds and aerosol characteristics; and temperature, geopotential height, and water vapor profiles. The MLS, OMI, and HIRDLS data products will be archived at the NASA Goddard Earth Sciences (GES) Distributed Active Archive Center (DAAC), while data from TES will be archived at NASA Langley Research Center DAAC. Some of the standard products which have gone through quick preliminary checks are already archived at the GES DAAC (http://daac.nsfc.nasa.gov/) and are available to the Aura science team and data validation team members for data validation; and to the application and visualization software developers, for testing their application modules. Once data are corrected for obvious calibration problems and partially validated using in-situ observations, they would be made available to the broader user community. This presentation will provide details of the whole suite of Aura atmospheric data products, and the time line of the availability of the rest of the preliminary products and of the partially validated provisional products. Software and took available for data access, visualization, and data mining will also be discussed.

Ahmad, S.↗

NASA NTRS2004

Toward a Global Map of Raindrop Size Distributions: Rain-Type Classification and Its Implications for Validating Global Rainfall Products - Part 1

Variability in the global distribution of precipitation is recognized as a key element in assessing the impact of climate change for life on earth. The response of precipitation to climate forcings is, however, poorly understood because of discrepancies in the magnitude and sign of climatic trends in satellite-based rainfall estimates. Quantifying and ultimately removing these biases is critical for studying the response of the hydrologic cycle to climate change. In addition, estimates of random errors owing to variability in algorithm assumptions on local spatial and temporal scales are critical for establishing how strongly their products should be weighted in data assimilation or model validation applications and for assigning a level of confidence to climate trends diagnosed from the data. This paper explores the potential for refining assumed drop size distributions (DSDs) in global radar rainfall algorithms by establishing a link between satellite observables and information gleaned from regional validation experiments where polarimetric radar, Doppler radar, and disdrometer measurements can be used to infer raindrop size distributions. By virtue of the limited information available in the satellite retrieval framework, the current method deviates from approaches adopted in the ground-based radar community that attempt to relate microphysical processes and resultant DSDs to local meteorological conditions. Instead, the technique exploits the fact that different microphysical pathways for rainfall production are likely to lead to differences in both the DSD of the resulting raindrops and the three-dimensional structure of associated radar reflectivity profiles. Objective rain-type classification based on the complete three-dimensional structure of observed reflectivity profiles is found to partially mitigate random and systematic errors in DSDs implied by differential reflectivity measurements. In particular, it is shown that vertical and horizontal reflectivity structure obtained from spaceborne radar can be used to reproduce significant differences in Z(sub dr) between the easterly and westerly climate regimes observed in the Tropical Rainfall Measuring Mission Large-scale Biosphere-Atmosphere (TRMM-LBA) field experiment as well as the even larger differences between Amazonian rainfall and that observed in eastern Colorado. As such, the technique offers a potential methodology for placing locally observed DSD information into a global framework.

L'Ecuyer, Tristan S.↗

DOE OSTI2016

Dislocation Structure and Mobility in hcp He 4

We assess the core structure and mobility of the screw and edge basal-plane dislocations in hcp 4 He using path-integral Monte Carlo simulations. Our findings provide key insights into recent interpretations of giant plasticity and mass flow junction experiments. First, both dislocations are dissociated into nonsuperfluid Shockley partial dislocations separated by ribbons of stacking fault, suggesting that they are unlikely to act as one-dimensional channels that may display Lüttinger-liquid-like behavior. Second, the centroid positions of the partial cores are found to fluctuate substantially, even in the absence of applied shear stresses. This implies that the lattice resistance to motion of the partial dislocations is negligible, consistent with the recent experimental observations of giant plasticity. Our results indicate that both the structure of the partial cores and the zero-point fluctuations play a role in this extreme mobility.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2021

Asynchronous quadratic control for constrained hidden markov jump linear systems with incomplete MTPM and MOCPM

Abstract This paper investigates the quadratic optimal control problem for constrained Markov jump linear systems with incomplete mode transition probability matrix (MTPM). Considering original system mode is not accessible, observed mode is utilized for asynchronous controller design where mode observation conditional probability matrix (MOCPM), which characterizes the emission between original modes and observed modes is assumed to be partially known. An LMI optimization problem is formulated for such constrained hidden Markov jump linear systems with incomplete MTPM and MOCPM. Based on this, a feasible state-feedback controller can be designed with the application of free-connection weighting matrix method. The desired controller, dependent on observed mode, is an asynchronous one which can minimize the upper bound of quadratic cost and satisfy restrictions on system states and control variables. Furthermore, clustering observation where observed modes recast into several clusters, is explored for simplifying the computational complexity. Numerical examples are provided to illustrate the validity.

Zhu, Jin↗

NASA NTRS2007

Oxidation of C/SiC Composites at Reduced Oxygen Partial Pressures

T-300 carbon fibers and T-300 carbon fiber reinforced silicon carbide composites (C/SiC) were oxidized in flowing reduced oxygen partial pressure environments at a total pressure of one atmosphere (0.5 atm O2, 0.05 atm O2 and 0.005 atm O2, balance argon). Experiments were conducted at four temperatures (816deg, 1149deg, 1343deg, and 1538 C). The oxidation kinetics were monitored using thermogravimetric analysis. T-300 fibers were oxidized to completion for times between 0.6 and 90 h. Results indicated that fiber oxidation kinetics were gas phase diffusion controlled. Oxidation rates had an oxygen partial pressure dependence with a power law exponent close to one. In addition, oxidation rates were only weakly dependent on temperature. The C/SiC coupon oxidation kinetics showed some variability, attributed to differences in the number and width of cracks in the SiC seal coat. In general, weight losses were observed indicating oxidation of the carbon fibers dominated the oxidation behavior. Low temperatures and high oxygen pressures resulted in the most rapid consumption of the carbon fibers. At higher temperatures, the lower oxidation rates were primarily attributed to crack closure due to SiC thermal expansion, rather than oxidation of SiC since these reduced rates were observed even at the lowest oxygen partial pressures where SiC oxidation is minimal.

Opila, E. J.↗

DOE OSTI2020

Mapping the Temperature-dependent and network site-specific onset of spectral diffusion at the surface of a water cluster cage

We explore the kinetic processes that sustain equilibrium in a microscopic, finite system. This is accomplished by monitoring the spontaneous, time-dependent frequency evolution (the frequency autocorrelation) of a single OH oscillator, embedded in a water cluster held in a temperature-controlled ion trap. The measurements are carried out by applying two-color, IR-IR photodissociation mass spectrometry to the D3O+?(HDO)(D2O)19 isotopologue of the “magic number” protonated water cluster, H+?(H2O)21. The OH group can occupy any one of the five spectroscopically distinct sites in the distorted pentagonal dodecahedron cage structure. The OH frequency is observed to evolve over tens of milliseconds in the temperature range (90-120 K). Starting at 100 K, large “jumps” are observed between two OH frequencies separated by ~300 cm-1 indicating migration of the OH group from the bound OH site at 3350 cm-1 to the free position at 3686 cm-1. Increasing the temperature to 110 K leads to partial interconversion among many sites. All sites are observed to interconvert at 120 K such that the distribution of the unique OH group among them adopts the form one would expect for a canonical ensemble. The spectral dynamics displayed by the clusters thus offer an unprecedented view into the molecular-level processes that drive spectral diffusion in an extended network of water molecules.

Yang, Nan↗

DOE OSTI2014

Tri-peptide reference structures for the calculation of relative solvent accessible surface area in protein amino acid residues

Relative amino acid residue solvent accessibility values allow the quantitative comparison of atomic solvent-accessible surface areas in different residue types and physical environments in proteins and in protein structural alignments. Geometry-optimised tri-peptide structures in extended solvent-exposed reference conformations have been obtained for 43 amino acid residue types at a high level of quantum chemical theory. Significant increases in side-chain solvent accessibility, offset by reductions in main-chain atom solvent exposure, were observed for standard residue types in partially geometry-optimised structures when compared to non-minimised models built from identical sets of proper dihedral angles abstracted from the literature. Optimisation of proper dihedral angles led most notably to marked increases of up to 54% in proline main-chain atom solvent accessibility compared to literature values. Similar effects were observed for fully-optimised tri-peptides in implicit solvent. The relief of internal strain energy was associated with systematic variation in N, C α and C β atom solvent accessibility across all standard residue types. The results underline the importance of optimisation of ‘hard’ degrees of freedom (bond lengths and valence bond angles) and improper dihedral angle values from force field or other context-independent reference values, and impact on the use of standardised fixed internal co-ordinate geometry in sampling approaches to the determination of absolute values of protein amino acid residue solvent accessibility. Finally, quantum chemical methods provide a useful and accurate alternative to molecular mechanics methods to perform energy minimisation of peptides containing non-standard (chemically modified) amino acid residues frequently present in experimental protein structure data sets, for which force field parameters may not be available. Reference tri-peptide atomic co-ordinate sets including hydrogen atoms are made freely available.

59 BASIC BIOLOGICAL SCIENCES↗