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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.

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All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

1612 MHz OH maser emission from axisymmetric circumstellar envelopes - Miras

Radiative transfer calculations are performed using a modified form of the Sobolev approximation to determine the inversion of the 1612 MHz line of OH in axisymmetric circumstellar envelopes around Miras. The mass loss is assumed to be occurring in the form of a smooth wind. Line profiles and maps are presented for three models of varying degrees of asymmetry and for various orientations of the envelopes. It is concluded that the axisymmetric models can reproduce many of the features of observed profiles and maps which both the standard, spherically symmetric model and the discrete emission model cannot easily explain. The model profiles reproduce all of the general features seen in the line profiles of real sources.

Collison, Alan J.↗
NASA NTRS1998

Global Surface Ultraviolet Radiation Climatology from TOMS and ERBE Data

The overall goal of this project has been to develop a method for calculating the distribution of solar ultraviolet radiation (UVR) over most of the earth's surface using NASA's Total Ozone Mapping Spectrometer (TOMS) and Earth Radiation Budget Experiment (ERBE) data, and to use this method to develop a UVR climatology that is useful in the context of the global ozone depletion issue. The research carried out with this support has resulted the following accomplishments: (1) a radioactive transfer method. based on the delta-Eddington approximation, was successfully developed; (2) the method was applied to the five years of overlapping TOMS and ERBE Monthly-Hourly data to examine the impact of global variability in cloud cover on trends in surface UVR; (3) a presentation was made on effects of stratospheric ozone depletion; (4) the radioactive transfer model was finally applied to all daylight hours to make a through study of the global effect of cloud cover;and (6) a five-year global climatology of surface UVR based on all of the research has been prepared for general distribution.

Lubin, Dan↗
NASA NTRS1999

GHRS Observations of Cool, Low-Gravity Stars: The Outer Atmosphere and Wind of the Nearby K Supergiant Lambda Velorum - 5

UV spectra of lambda Velorum taken with the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope are used to probe the structure of the outer atmospheric layers and wind and to estimate the mass-loss rate from this K5 lb-II supergiant. VLA radio observations at lambda = 3.6 cm are used to obtain an independent check on the wind velocity and mass-loss rate inferred from the UV observations, Parameters of the chromospheric structure are estimated from measurements of UV line widths, positions, and fluxes and from the UV continuum flux distribution. The ratios of optically thin C II] emission lines indicate a mean chromospheric electron density of log N(sub e) approximately equal 8.9 +/- 0.2 /cc. The profiles of these lines indicate a chromospheric turbulence (v(sub 0) approximately equal 25-36 km/s), which greatly exceeds that seen in either the photosphere or wind. The centroids of optically thin emission lines of Fe II and of the emission wings of self-reversed Fe II lines indicate that they are formed in plasma approximately at rest with respect to the photosphere of the star. This suggests that the acceleration of the wind occurs above the chromospheric regions in which these emission line photons are created. The UV continuum detected by the GHRS clearly traces the mean flux-formation temperature as it increases with height in the chromosphere from a well-defined temperature minimum of 3200 K up to about 4600 K. Emission seen in lines of C III] and Si III] provides evidence of material at higher than chromospheric temperatures in the outer atmosphere of this noncoronal star. The photon-scattering wind produces self-reversals in the strong chromospheric emission lines, which allow us to probe the velocity field of the wind. The velocities to which these self-absorptions extend increase with intrinsic line strength, and thus height in the wind, and therefore directly map the wind acceleration. The width and shape of these self-absorptions reflect a wind turbulence of approximately equal 9-21 km/s. We further characterize the wind by comparing the observations with synthetic profiles generated with the Lamers et al. Sobolev with Exact Integration (SEI) radiative transfer code, assuming simple models of the outer atmospheric structure. These comparisons indicate that the wind in 1994 can be described by a model with a wind acceleration parameter beta approximately 0.9, a terminal velocity of 29-33 km/s, and a mass-loss rate approximately 3 x 10(exp -9) solar M/yr. Modeling of the 3.6 cm radio flux observed in 1997 suggests a more slowly accelerating wind (higher beta) and/or a higher mass-loss rate than inferred from the UV line profiles. These differences may be due to temporal variations in the wind or from limitations in one or both of the models. The discrepancy is currently under investigation.

Carpenter, Kenneth G.↗
DOE OSTI2016

Assessment of DR-55 as a Drop-In Replacement for R-410A

R410A has no ozone depletion potential (ODP), and is the most commonly used refrigerant in vapor compression systems for space cooling and heating applications. However, it has significant global warming potential with GWP higher than 1900. To mitigate the global warming effect, industry and research institutes are actively pursuing a replacement for R-410A with the following attributes, much lower GWP along with similar or higher efficiency and capacity. DR-55 (aka R452B) is a design-compatible refrigerant replacement for R-410A. It decreases the GWP by 70%, and has lower working pressure, comparable discharge temperature, and uses the same lubricant, tubing, and valves. In this study, we experimentally evaluated the performance of DR-55 as a drop-in replacement for R-410A in a high efficiency rooftop air conditioning unit. The experimental results demonstrated that DR-55 led to 5% higher efficiency at the working conditions of Integrated Energy Efficiency Rating (IEER). DR-55 also showed significantly better high ambient performance from 95 F to 125 F. In addition to the experimental study, we used the DOE/ORNL Heat Pump Design Model to model the RTU using R-410A and DR-55, respectively. The model results were compared to the laboratory measurements. The model validation demonstrates that the refrigerant heat transfer and pressure drop correlations, developed for conventional refrigerants like R-410A, are usable for DR-55. Also, a converted compressor model for DR-55, i.e. reducing volumetric and isentropic efficiencies as a function of the suction and discharge pressures from an R-410A compressor map can predict the compressor mass flow rate and power accurately.

DR-55↗
DOE OSTI2014

The active site of hen egg-white lysozyme: flexibility and chemical bonding

Chemical bonding at the active site of lysozyme is analyzed on the basis of a multipole model employing transferable multipole parameters from a database. Large B factors at low temperatures reflect frozen-in disorder, but therefore prevent a meaningful free refinement of multipole parameters. Chemical bonding at the active site of hen egg-white lysozyme (HEWL) is analyzed on the basis of Bader’s quantum theory of atoms in molecules [QTAIM; Bader (1994 ▶), Atoms in Molecules: A Quantum Theory. Oxford University Press] applied to electron-density maps derived from a multipole model. The observation is made that the atomic displacement parameters (ADPs) of HEWL at a temperature of 100 K are larger than ADPs in crystals of small biological molecules at 298 K. This feature shows that the ADPs in the cold crystals of HEWL reflect frozen-in disorder rather than thermal vibrations of the atoms. Directly generalizing the results of multipole studies on small-molecule crystals, the important consequence for electron-density analysis of protein crystals is that multipole parameters cannot be independently varied in a meaningful way in structure refinements. Instead, a multipole model for HEWL has been developed by refinement of atomic coordinates and ADPs against the X-ray diffraction data of Wang and coworkers [Wang et al. (2007), Acta Cryst. D63, 1254–1268], while multipole parameters were fixed to the values for transferable multipole parameters from the ELMAM2 database [Domagala et al. (2012), Acta Cryst. A68, 337–351] . Static and dynamic electron densities based on this multipole model are presented. Analysis of their topological properties according to the QTAIM shows that the covalent bonds possess similar properties to the covalent bonds of small molecules. Hydrogen bonds of intermediate strength are identified for the Glu35 and Asp52 residues, which are considered to be essential parts of the active site of HEWL. Furthermore, a series of weak C—H⋯O hydrogen bonds are identified by means of the existence of bond critical points (BCPs) in the multipole electron density. It is proposed that these weak interactions might be important for defining the tertiary structure and activity of HEWL. The deprotonated state of Glu35 prevents a distinction between the Phillips and Koshland mechanisms.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Investigations of Polymethacrylate Tribochemical Films Using X-Ray Spectroscopy and Optical Profilometry

This study investigates the elemental composition and surface morphology of solid tribochemical films formed on steel surfaces. The reversible addition-fragmentation chain transfer (RAFT) method was used to synthesize nine different metal-free polymers, which were blended into commercial base oils. The polymers were either homopolymers of dodecyl methacrylate and ethylhexyl methacrylate or were co-polymers of these monomers with six polar monomers. After tribological testing at 100 degrees C using the ball-on-flat geometry, the resulting tribochemical films were imaged using scanning electron microscopy (SEM) and optical microscopy. The resulting tribochemical films have thicknesses around 50-100 nm. Two of the films corresponding to small (P1-imidazole-containing copolymer) and large (P3-less polar homopolymer) wear were cross-sectioned using focused ion beam (FIB) and analyzed for elemental composition using energy-dispersive X-Ray (EDX) mapping. Oxygen and nitrogen enrichment was observed, consistent with the relative chemical composition of the precursor polymers. Transmission electron microscopy (TEM) evidence suggests that at the worn surface, some organic elements penetrate or are mixed into the steel substrate giving an interlocking appearance. The two samples examined with TEM showed that P1 tribofilm is diffused or mixed with the steel substrate more so than P3, suggesting a stronger affinity and contact during tribofilm formation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

FIRST ZEEMAN DOPPLER IMAGING OF A COOL STAR USING ALL FOUR STOKES PARAMETERS

Magnetic fields are ubiquitous in active cool stars, but they are in general complex and weak. Current Zeeman Doppler imaging (ZDI) studies of cool star magnetic fields chiefly employ circular polarization observations because linear polarization is difficult to detect and requires a more sophisticated radiative transfer modeling to interpret. But it has been shown in previous theoretical studies, and in the observational analyses of magnetic Ap stars, that including linear polarization in the magnetic inversion process makes it possible to correctly recover many otherwise lost or misinterpreted magnetic features. We have obtained phase-resolved observations in all four Stokes parameters of the RS CVn star II Peg at two separate epochs. Here we present temperature and magnetic field maps reconstructed for this star using all four Stokes parameters. This is the very first such ZDI study of a cool active star. Our magnetic inversions reveal a highly structured magnetic field topology for both epochs. The strength of some surface features is doubled or even quadrupled when linear polarization is taken into account. The total magnetic energy of the reconstructed field map also becomes about 2.1–3.5 times higher. The overall complexity is also increased as the field energy is shifted toward higher harmonic modes when four Stokes parameters are used. As a consequence, the potential field extrapolation of the four Stokes parameter ZDI results indicates that magnetic field becomes weaker at a distance of several stellar radii due to a decrease of the large-scale field component.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Simultaneous differential spinning disk fluorescence optical sectioning microscopy and nanomechanical mapping atomic force microscopy

Combined microscopy techniques offer the life science research community a powerful tool to investigate complex biological systems and their interactions. Here, we present a new combined microscopy platform based on fluorescence optical sectioning microscopy through aperture correlation microscopy with a Differential Spinning Disk (DSD) and nanomechanical mapping with an Atomic Force Microscope (AFM). The illumination scheme of the DSD microscope unit, contrary to standard single or multi-point confocal microscopes, provides a time-independent illumination of the AFM cantilever. This enables a distortion-free simultaneous operation of fluorescence optical sectioning microscopy and atomic force microscopy with standard probes. In this context, we discuss sample heating due to AFM cantilever illumination with fluorescence excitation light. Integration of a DSD fluorescence optical sectioning unit with an AFM platform requires mitigation of mechanical noise transfer of the spinning disk. We identify and present two solutions to almost annul this noise in the AFM measurement process. The new combined microscopy platform is applied to the characterization of a DOPC/DOPS (4:1) lipid structures labelled with a lipophilic cationic indocarbocyanine dye deposited on a mica substrate.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Feedback on Forty-year Long Clean-up Operations of a Contaminated Soil for Environmental Purpose - 20026

One of the CEA facilities in France is the place of miscellaneous mapping and clean-up operations since the 1980's. The final purpose of the conducted work deals with the environmental remediation of the building. In France, the absence of a regulatory framework for the management of sites polluted by radioactive substances, especially as the lack of release thresholds, has led to develop different approaches of soil radiological characterization. The geostatistical approach is part of them. Preliminary investigations are an unavoidable step prior to clearance and remediation. First, historical analysis enables to define site perimeters to investigate as well as to precisely locate expected contaminated parts. For radioactive pollutants, the media (water, soil, air) and transfer routes participate in the definition of the investigation perimeter and thus also need to be identified through a geological study. At the same time, functional analysis leads to choose the best measurement means which could provide useful information when combined with visual inspection. An equipment well adapted to easy-to-measure radionuclides as gamma emitters, such as gamma probe or on-site gamma spectrometry, is usually selected as a non-destructive assay. Coupled with spatial positions, processed on-site radiological data can be mapped. Data processing consists in mapping and kriging before a geostatistical analysis in order to identify the zones of interest to be targeted. Selected zones are not only linked to high level count rates but also to low level ones so that a pollution-free reference is known in the area. This data processing also enables to categorize waste types according to their origin and contamination levels. An expected volume of different waste then follows as well as the waste characterization equipments. In-depth investigations, e.g. core drillings and samplings, naturally ensue to aim at remediation optimization through the assessment of environmental impact. After clean-up operations, non-destructive assays as well as destructive samplings enable to check the effective clearance. Following this methodology in the present remediation work, results of the first non-destructive assay campaign highlighted a long-lived transuranic radionuclides contamination in the concrete flagstone. Successive non-destructive assays were then performed in the defined zones of interest. Count rates measured with a surface probe were first mapped. The best localization of destructive assays, i.e. core drillings at a 1 meter depth, came from this surface mapping followed by a geostatistical analysis. The concrete flagstone was totally removed. Then, the depth of soil to remove under the flagstone was optimized from the results of radiological activities measured in core drillings samples. A new surface mapping was then drawn after this partial soil excavation. The sand and demolition rubble samples, homogeneously constituted from the flagstone fragments, were analyzed by gamma spectrometry. Meanwhile, waste drums and other containers were also measured by gamma spectrometry and passive neutron measurement devices. All these results have brought miscellaneous pieces of information. In this context, major issues appear in terms of physical constraints such as the premises tininess as well as of soil sampling techniques and in terms of measurement performances assessment and the representativeness of homogeneous samples. The choice of radiological soil and waste characterization devices is described in the light of enhanced performances by keeping in mind radiation protection requirements and a willing to always optimize waste categories (very low level waste) and volume. The improvement of the characterization methods appears through this forty-year long work while sharing the feedback of encountered difficulties. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2026

A hybrid CNN-LSTM surrogate model for hyper-resolution spatiotemporal flood forecasting in Norfolk, Virginia

Study region: Norfolk, Virginia, United States Study focus: Accurate and timely flood forecasting is essential for enhancing resilience in coastal urban areas in the context of increasing frequency and intensity of rainfall, sea level rise and urbanization. This study presents a hybrid deep learning-based surrogate model that integrates Convolutional Neural Networks (CNN) and Long Short-Term Memory (LSTM) networks to enable real-time spatiotemporal flood forecasting. The model leverages CNN to capture spatial features from inputs such as elevation and Topographic Wetness Index (TWI), while LSTM processes time-series inputs of rainfall and tide data to capture temporal features. New hydrologic insights for the region: The hybrid CNN-LSTM model was trained using the physics-based hydrodynamic model simulations obtained from the Two-dimensional Unsteady FLOW (TUFLOW) model for Norfolk, Virginia, and achieved high predictive accuracy across diverse flood-prone areas. The reduced computational time from four to six hours using TUFLOW to 3.2 min per event using CNN-LSTM enables rapid flood inundation mapping and early warning applications. The model effectively captured both spatial flood extents and their temporal evolution across different flooding scenarios, providing forecasts at a 2.5-m spatial resolution and 15-min temporal resolution and a one-hour-ahead prediction horizon. While challenges remain in terms of transferability to new regions and real-time data assimilation, this approach demonstrates strong potential for supporting operational flood risk management in coastal urban environments.

Coastal urban flooding↗
DOE OSTI2011

Turbine adapted maps for turbocharger engine matching

This paper presents a new representation of the turbine performance maps oriented for turbocharger characterization. The aim of this plot is to provide a more compact and suited form to implement in engine simulation models and to interpolate data from turbocharger test bench. The new map is based on the use of conservative parameters as turbocharger power and turbine mass flow to describe the turbine performance in all VGT positions. The curves obtained are accurately fitted with quadratic polynomials and simple interpolation techniques give reliable results. Two turbochargers characterized in an steady flow rig were used for illustrating the representation. After being implemented in a turbocharger submodel, the results obtained with the model have been compared with success against turbine performance evaluated in engine tests cells. A practical application in turbocharger matching is also provided to show how this new map can be directly employed in engine design. (author)

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2022

ESS-DIVE Reporting Format for Amplicon Abundance Table

While standardized sequencing data is available in public repositories and efforts such as MIxS for common sample collection and processing metadata are well established, the lack of common bioinformatic processing metadata has hindered the ability to do large-scale metaanalyses and the potential for data re-use by non-experts such as ecosystem, watershed, or earth system modelers. To address this need for Department of Energy researchers, we have developed an amplicon reporting format which captures both sample preparation and bioinformatic processing metadata and stores processed amplicon data as a paired abundance table and sequencing file to maximize the potential for re-use of these data. To aid in the adoption of accessible and reproducible analysis workflows, this reporting format was developed in concert with amplicon functionality within the Department of Energy’s Systems Biology Knowledgebase (KBase) to ensure common data and metadata requirements and facilitate seamless transfer between these platforms.This dataset contains support documentation for the amplicon reporting format (README.md and instructions.md), templates for both bioinformatic and sequencing metadata (amplicon_bioinformatic_metadata_template_2021_10_03.csv and amplicon_sequencing_metadata_template_2021_10_03.csv), a crosswalk indicating how this reporting format relates to the current MIxS format (ESSDIVE-MIxS_crosswalk.csv), a list of available instrument terms (amplicon_seq_instrument_terms_2021_10_03.csv), a map between QIIME2 parameter settings and metadata fields (amplicon_qiime2_plugin_metadata_map.csv), a data dictionary (amplicon_CSV_dd.csv), and file-level metadata (amplicon_FLMD.csv).

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

A Comprehensive Library of X-Ray Pulsars in the Small Magellanic Cloud: Time Evolution of Their Luminosities and Spin Periods

We have collected and analyzed the complete archive of XMM-Newton (116), Chandra (151), and RXTE (952) observations of the Small Magellanic Cloud (SMC), spanning 1997–2014. The resulting observational library provides a comprehensive view of the physical, temporal, and statistical properties of the SMC pulsar population across the luminosity range of L{sub X}=10{sup 31.2}--10{sup 38} erg s{sup −1}. From a sample of 65 pulsars we report ∼1654 individual pulsar detections, yielding ∼1260 pulse-period measurements. Our pipeline generates a suite of products for each pulsar detection: spin period, flux, event list, high time-resolution light curve, pulse profile, periodogram, and spectrum. Combining all three satellites, we generated complete histories of the spin periods, pulse amplitudes, pulsed fractions, and X-ray luminosities. Some pulsars show variations in pulse period due to the combination of orbital motion and accretion torques. Long-term spin-up/spin-down trends are seen in 12/11 pulsars, respectively, pointing to sustained transfer of mass and angular momentum to the neutron star on decadal timescales. Of the sample, 30 pulsars have a relatively very small spin period derivative and may be close to equilibrium spin. The distributions of pulse detection and flux as functions of spin period provide interesting findings: mapping boundaries of accretion-driven X-ray luminosity and showing that fast pulsars (P < 10 s) are rarely detected, which as of yet are more prone to giant outbursts. Accompanying this paper is an initial public release of the library so that it can be used by other researchers. We intend the library to be useful in driving improved models of neutron star magnetospheres and accretion physics.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2021

3D Cloud Tomography and Droplet Size Retrieval from Multi-Angle Polarimetric Imaging of Scattered Sunlight from Above

Tomography aims to recover a three-dimensional (3D) density map of a medium or an object. In medical imaging,it is extensively used for diagnostics via X-ray computed tomography (CT). We define and derive a tomographyof cloud droplet distributions via passive remote sensing. We use multi-view polarimetric images to fit a 3Dpolarized radiative transfer (RT) forward model. Our motivation is 3D volumetric probing of vertically-developedconvectively-driven clouds that are ill-served by current methods in operational passive remote sensing. Currenttechniques are indeed based on strictly 1D RT modeling and applied to a single cloudy pixel, where cloud geometrydefaults to that of a plane-parallel slab. Incident unpolarized sunlight, once scattered by cloud droplets, changesits polarization state according to droplet size. Therefore, polarimetric measurements in the rainbow and gloryangular regions can be used to infer the droplet size distribution. This work defines and derives a framework for afull 3D tomography of cloud droplets for both their mass concentration in space and their distribution across arange of sizes. This gridded 3D retrieval of key microphysical properties is made tractable by our novel approachthat involves a restructuring and partial linearization of an open-source polarized 3D RT code to accommodate aspecial two-step iterative optimization technique. Physically-realistic synthetic clouds are used to demonstrate themethodology with rigorous uncertainty quantification, while a real-world cloud imaged by AirMSPI is processedto illustrate the new remote sensing capability

Schechner, Yoav Y.↗
NASA NTRS2024

Machine Learning Based Aerosol and Ocean Color Joint Retrieval Algorithm for Multiangle Polarimeters over Coastal Waters

NASA’s Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission, recently launched in February 2024, carries two multiangle polarimeters (MAPs): the UMBC Hyper-Angular Rainbow Polarimeter (HARP2) and SRON Spectropolarimeter for Planetary Exploration One (SPEXone). Measurements from these MAPs will greatly advance ocean ecosystem and aerosol studies as their measurements contain rich information on microphysical properties of aerosols and hydrosols. The Multi-Angular Polarimetric Ocean coLor (MAPOL) joint retrieval algorithm has been developed to retrieve aerosol and ocean color information, which uses a vector radiative transfer (RT) model as the forward model. The RT model is computationally expensive, which makes processing a large amount of data challenging. FastMAPOL was developed to expedite retrieval using neural networks to replace the RT forward models. As a prototype study, FastMAPOL was initially limited to open ocean applications where the ocean Inherent Optical Properties (IOPs) were parameterized in terms of one parameter: chlorophyll-a concentration (Chla). In this study we further expand the FastMAPOL joint retrieval algorithm to incorporate NN based forward models for coastal waters, which use multi-parameter bio-optical models. In addition, aerosols are represented by six components, i.e., fine mode non absorbing insoluble (FNAI), brown carbon (BrC), black carbon (BC), fine mode non absorbing soluble (FNAS), sea salt (SS) and non-spherical dust (Dust). Sea salt and dust are coarse mode aerosols, while the other components are in the fine mode. The sizes and spectral refractive indices are fixed for each aerosol component, while their abundances are retrievable. The multi-parameter bio-optical model and aerosol components are chosen to represent the coastal marine environment. The retrieval algorithm is applied to synthetic measurements in three different configurations ofMAPs in the PACE mission: HARP2 observations only, SPEXone observations only and combined HARP2 and SPEXone observations. The retrieval results from synthetic measurements show that for aerosol retrieval the SPEXone-only configuration works equally well with the HAPR2-only configuration. On the other hand, for ocean color retrieval the SPEXone instrument provides better information due to its larger spectral coverage. For the surface parameters (wind speed), HARP2 measurements provide better information due to its wide field of view. Combined measurement configuration HARP2+SPEXone performed the best to retrieve all aerosol, ocean color and surface parameters. We also studied the impact of sun glint to aerosol and ocean color retrievals. The retrieval test revealed that wind speed and absorbing aerosol retrieval improves significantly when including measurements at glint geometries. Furthermore, the retrieval algorithm is equipped with modules for atmospheric correction and bidirectional reflectance distribution (BRDF) correction to obtain the remote sensing reflectance, which enables ocean biogeochemistry studies using the PACE polarimeter data.

PACE↗
DOE OSTI2016

Measurement-based performance profiles and dynamics of UDT over dedicated connections

Wide-area data transfers in high-performance computing and big data scenarios are increasingly being carried over dedicated network connections that provide high capacities at low loss rates. UDP-based transport protocols are expected to be particularly well-suited for such transfers but their performance is relatively unexplored over a wide range of connection lengths, compared to TCP over shared connections. We present extensive throughput measurements of UDP-based Data Transfer (UDT) over a suite of physical and emulated 10 Gbps connections. In sharp contrast to current UDT analytical models, these measurements indicate much more complex throughput dynamics that are sensitive to the connection modality, protocol parameters, and round-trip times. Lyapunov exponents estimated from the Poincare maps of UDT traces clearly indicate regions of instability and complex dynamics. We propose a simple model based on the ramp-up and sustainment regimes of a generic transport protocol, which qualitatively illustrates the dominant monotonicity and concavity properties of throughput profiles and relates them to Lyapunov exponents. These measurements and analytical results together enable us to comprehensively evaluate UDT performance and select parameters to achieve high throughput, and they also provide guidelines for designing effective transport protocols for dedicated connections.

Foster, Ian↗
DOE OSTI2016

PRINCIPAL COMPONENT ANALYSIS STUDIES OF TURBULENCE IN OPTICALLY THICK GAS

In this work we investigate the sensitivity of principal component analysis (PCA) to the velocity power spectrum in high-opacity regimes of the interstellar medium (ISM). For our analysis we use synthetic position–position–velocity (PPV) cubes of fractional Brownian motion and magnetohydrodynamics (MHD) simulations, post-processed to include radiative transfer effects from CO. We find that PCA analysis is very different from the tools based on the traditional power spectrum of PPV data cubes. Our major finding is that PCA is also sensitive to the phase information of PPV cubes and this allows PCA to detect the changes of the underlying velocity and density spectra at high opacities, where the spectral analysis of the maps provides the universal −3 spectrum in accordance with the predictions of the Lazarian and Pogosyan theory. This makes PCA a potentially valuable tool for studies of turbulence at high opacities, provided that proper gauging of the PCA index is made. However, we found the latter to not be easy, as the PCA results change in an irregular way for data with high sonic Mach numbers. This is in contrast to synthetic Brownian noise data used for velocity and density fields that show monotonic PCA behavior. We attribute this difference to the PCA's sensitivity to Fourier phase information.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

AROUND THE RING WE GO: THE COLD, DENSE RING OF MOLECULAR GAS IN NGC 1614

We present high-resolution archival Atacama Large Millimeter/submillimeter Array (ALMA) {sup 12}CO J = 3-2 and J = 6-5 and HCO{sup +} J = 4-3 observations and new CARMA {sup 12}CO and {sup 13}CO J = 1-0 observations of the luminous infrared galaxy NGC 1614. The high-resolution maps show the previously identified ring-like structure while the {sup 12}CO J = 3-2 map shows extended emission that traces the extended dusty features. We combined these new observations with previously published Submillimeter Array {sup 12}CO and {sup 13}CO J = 2-1 observations to constrain the physical conditions of the molecular gas at a resolution of 230 pc using a radiative transfer code and a Bayesian likelihood analysis. At several positions around the central ring-like structure, the molecular gas is cold (20-40 K) and dense (>10{sup 3.0} cm{sup –3}). The only region that shows evidence of a second molecular gas component is the ''hole'' in the ring. The {sup 12}CO-to-{sup 13}CO abundance ratio is found to be greater than 130, more than twice the local interstellar medium value. We also measure the CO-to-H{sub 2} conversion factor, α{sub CO}, to range from 0.9 to 1.5 M {sub ☉} (K km s{sup –1} pc{sup 2}){sup –1}.

79 ASTRONOMY AND ASTROPHYSICS↗