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At least 1,405 records · Page 78
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

A possible mass distribution of primordial black holes implied by LIGO-Virgo

The LIGO-Virgo Collaboration has so far detected around 90 black holes, some of which have masses larger than what were expected from the collapse of stars. The mass distribution of LIGO-Virgo black holes appears to have a peak at ~ 30 M ⊙ and two tails on the ends. By assuming that they all have a primordial origin, we analyze the GWTC-1 (O1&O2) and GWTC-2 (O3a) datasets by performing maximum likelihood estimation on a broken power law mass function f ( m ), with the result f ∝ m 1.2 for m < 35 M ⊙ and f ∝ m -4 for m > 35 M ⊙ . This appears to behave better than the popular log-normal mass function. Surprisingly, such a simple and unique distribution can be realized in our previously proposed mechanism of PBH formation, where the black holes are formed by vacuum bubbles that nucleate during inflation via quantum tunneling. Moreover, this mass distribution can also provide an explanation to supermassive black holes formed at high redshifts.

Astronomy & Astrophysics↗
NASA NTRS1997

Soot Volume Fraction Maps for Normal and Reduced Gravity Laminar Acetylene Jet Diffusion Flames

The study of soot particulate distribution inside gas jet diffusion flames is important to the understanding of fundamental soot particle and thermal radiative transport processes, as well as providing findings relevant to spacecraft fire safety, soot emissions, and radiant heat loads for combustors used in air-breathing propulsion systems. Compared to those under normal gravity (1-g) conditions, the elimination of buoyancy-induced flows is expected to significantly change the flow field in microgravity (O g) flames, resulting in taller and wider flames with longer particle residence times. Work by Bahadori and Edelman demonstrate many previously unreported qualitative and semi-quantitative results, including flame shape and radiation, for sooting laminar zas jet diffusion flames. Work by Ku et al. report soot aggregate size and morphology analyses and data and model predictions of soot volume fraction maps for various gas jet diffusion flames. In this study, we present the first 1-g and 0-g comparisons of soot volume fraction maps for laminar acetylene and nitrogen-diluted acetylene jet diffusion flames. Volume fraction is one of the most useful properties in the study of sooting diffusion flames. The amount of radiation heat transfer depends directly on the volume fraction and this parameter can be measured from line-of-sight extinction measurements. Although most Soot aggregates are submicron in size, the primary particles (20 to 50 nm in diameter) are in the Rayleigh limit, so the extinction absorption) cross section of aggregates can be accurately approximated by the Rayleigh solution as a function of incident wavelength, particles' complex refractive index, and particles' volume fraction.

Greenberg, Paul S.↗
DOE OSTI2014

Quantifying the Combined Effect of Radiation Therapy and Hyperthermia in Terms of Equivalent Dose Distributions

Purpose: To develop a method to quantify the therapeutic effect of radiosensitization by hyperthermia; to this end, a numerical method was proposed to convert radiation therapy dose distributions with hyperthermia to equivalent dose distributions without hyperthermia. Methods and Materials: Clinical intensity modulated radiation therapy plans were created for 15 prostate cancer cases. To simulate a clinically relevant heterogeneous temperature distribution, hyperthermia treatment planning was performed for heating with the AMC-8 system. The temperature-dependent parameters α (Gy{sup −1}) and β (Gy{sup −2}) of the linear–quadratic model for prostate cancer were estimated from the literature. No thermal enhancement was assumed for normal tissue. The intensity modulated radiation therapy plans and temperature distributions were exported to our in-house-developed radiation therapy treatment planning system, APlan, and equivalent dose distributions without hyperthermia were calculated voxel by voxel using the linear–quadratic model. Results: The planned average tumor temperatures T90, T50, and T10 in the planning target volume were 40.5°C, 41.6°C, and 42.4°C, respectively. The planned minimum, mean, and maximum radiation therapy doses were 62.9 Gy, 76.0 Gy, and 81.0 Gy, respectively. Adding hyperthermia yielded an equivalent dose distribution with an extended 95% isodose level. The equivalent minimum, mean, and maximum doses reflecting the radiosensitization by hyperthermia were 70.3 Gy, 86.3 Gy, and 93.6 Gy, respectively, for a linear increase of α with temperature. This can be considered similar to a dose escalation with a substantial increase in tumor control probability for high-risk prostate carcinoma. Conclusion: A model to quantify the effect of combined radiation therapy and hyperthermia in terms of equivalent dose distributions was presented. This model is particularly instructive to estimate the potential effects of interaction from different treatment modalities.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
NASA NTRS2002

Induction of chromatin damage and distribution of isochromatid breaks in human fibroblast cells exposed to heavy ions

The frequency of chromatid breaks and the distribution of isochromatid breaks were measured in G2-phase normal human fibroblasts prematurely condensed a short time after exposure to low- or high-LET radiations. The average number of isochromatid breaks from a single particle traversal increased with increasing LET values, while the average number of chromatid-type breaks appeared to reach a plateau. The distribution of isochromatid breaks after high-LET iron particles exposure was overdispersed compared to gamma-rays, indicating that a single iron particle traversal through a cell nucleus can produce multiple isochromatid breaks.

NASA Center JSC↗
DOE OSTI2015

Insights into acetone photochemistry on rutile TiO₂(110). 2. new photodesorption channel with CH₃ ejection along the surface normal

Angle-resolved photon stimulated desorption (PSD) combined with infrared reflection-adsorption spectroscopy and temperature programmed desorption reveal two distinct channels in the photochemistry of acetone on rutile TiO₂(110) surface. During UV irradiation of co-adsorbed oxygen and acetone molecules, methyl radicals (CH₃) are ejected in two different directions: i) normal to the surface and ii) off-normal at ~±66° to the surface normal in the azimuth (i.e. perpendicular to the rows of bridging oxygen and Ti atoms). Both components are relatively narrow and non-cosine, indicating non-thermal evolution of CH₃ radicals. The direction of the “off-normal” PSD component is consistent with orientation of the C–CH₃ bonds in the n²-acetone diolate—a photoactive form of acetone chemisorption on the oxidized TiO₂(110) surface proposed earlier from experimental and theoretical studies. The direction of the “normal” PSD component requires an orientation of a C–CH₃ bond which is not consistent with the n²-acetone diolate structure. The angular distribution of the CH₃ PSD depends on the acetone coverage. The “off-normal” PSD component dominates at lower acetone coverage (< 0.2 ML), but does not increase at higher coverages in accord with the acetone diolate peak intensity in the infrared reflection-absorption spectra. The “normal” PSD component grows with the acetone coverage up to 0.6 ML. The newly discovered “normal” PSD channel is tentatively assigned to a photo-produced n²- acetone enolate as a potential precursor based on the H/D exchange experiments

Environmental Molecular Sciences Laboratory↗
DOE OSTI2023

Improved quality metrics for association and reproducibility in chromatin accessibility data using mutual information

Correlation metrics are widely utilized in genomics analysis and often implemented with little regard to assumptions of normality, homoscedasticity, and independence of values. This is especially true when comparing values between replicated sequencing experiments that probe chromatin accessibility, such as assays for transposase-accessible chromatin via sequencing (ATAC-seq). Such data can possess several regions across the human genome with little to no sequencing depth and are thus non-normal with a large portion of zero values. Despite distributed use in the epigenomics field, few studies have evaluated and benchmarked how correlation and association statistics behave across ATAC-seq experiments with known differences or the effects of removing specific outliers from the data. Here, we developed a computational simulation of ATAC-seq data to elucidate the behavior of correlation statistics and to compare their accuracy under set conditions of reproducibility. Using these simulations, we monitored the behavior of several correlation statistics, including the Pearson’s R and Spearman’s ρ coefficients as well as Kendall’s τ and Top–Down correlation. We also test the behavior of association measures, including the coefficient of determination R 2 , Kendall’s W, and normalized mutual information. Our experiments reveal an insensitivity of most statistics, including Spear man’s ρ, Kendall’s τ, and Kendall’s W, to increasing differences between simulated ATAC-seq replicates. The removal of co-zeros (regions lacking mapped sequenced reads) between simulated experiments greatly improves the estimates of correlation and association. After removing co-zeros, the R 2 coefficient and normalized mutual information display the best performance, having a closer one-to-one relationship with the known portion of shared, enhanced loci between simulated replicates. When comparing values between experimental ATAC-seq data using a random forest model, mutual information best predicts ATAC-seq replicate relationships. Collectively, this study demonstrates how measures of correlation and association can behave in epigenomics experiments. We provide improved strategies for quantifying relationships in these increasingly prevalent and important chromatin accessibility assays.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

TU-H-CAMPUS-JeP3-04: Factors Predicting a Need for Treatment Replanning with Proton Radiotherapy for Lung Cancer

Purpose: Proton dose distribution is sensitive to tumor regression and tissue and normal anatomy changes. Replanning is sometimes necessary during treatment to ensure continue tumor coverage or avoid overtreatment of organs at risk (OARs). We investigated action thresholds for replanning and identified both dosimetric and non-dosimetric metrics that would predict a need for replan. Methods: All consecutive lung cancer patients (n = 188) who received definitive proton radiotherapy and had more than two evaluation CT scans at the Roberts Proton Therapy Center (Philadelphia, USA) from 2011 to 2015 were included in this study. The cohort included a variety of tumor sizes, locations, histology, beam angles, as well as radiation-induced tumor and lung change. Dosimetric changes during therapy were characterized by changes in the dose volume distribution of PTV, ITV, and OARs (heart, cord, esophagus, brachial plexus and lungs). Tumor and lung change were characterized by changes in sizes, and in the distribution of Hounsfield numbers and water equivalent thickness (WET) along the beam path. We applied machine learning tools to identify both dosimetric and non-dosimetric metrics that predicted a replan. Results: Preliminary data showed that clinical indicators (n = 54) were highly correlated; thus, a simple indicator may be derived to guide the action threshold for replanning. Additionally, tumor regression alone could not predict dosimetric changes in OARs; it required further information about beam angles and tumor locations. Conclusion: Both dosimetric and non-dosimetric factors are predictive of the need for replanning during proton treatment.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

The emergence of nonuniform spatiotemporal fractionation schemes within the standard BED model

Purpose: Nonuniform spatiotemporal radiotherapy fractionation schemes, i.e., delivering distinct dose distributions in different fractions can potentially improve the therapeutic ratio. This is possible if the dose distributions are designed such that similar doses are delivered to normal tissues (exploit the fractionation effect) while hypofractionating subregions of the tumor. In this paper, the authors develop methodology for treatment planning with nonuniform fractions and demonstrate this concept in the context of intensity-modulated proton therapy (IMPT). Methods: Treatment planning is performed by simultaneously optimizing (possibly distinct) IMPT dose distributions for multiple fractions. This is achieved using objective and constraint functions evaluated for the cumulative biologically equivalent dose (BED) delivered at the end of treatment. BED based treatment planning formulations lead to nonconvex optimization problems, such that local gradient based algorithms require adequate starting positions to find good local optima. To that end, the authors develop a combinatorial algorithm to initialize the pencil beam intensities. Results: The concept of nonuniform spatiotemporal fractionation schemes is demonstrated for a spinal metastasis patient treated in two fractions using stereotactic body radiation therapy. The patient is treated with posterior oblique beams with the kidneys being located in the entrance region of the beam. It is shown that a nonuniform fractionation scheme that hypofractionates the central part of the tumor allows for a skin and kidney BED reduction of approximately 10%–20%. Conclusions: Nonuniform spatiotemporal fractionation schemes represent a novel approach to exploit fractionation effects that deserves further exploration for selected disease sites.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1991

Dust properties around evolved stars from far-infrared size limits

High angular resolution far-infrared scans were obtained of six stars surrounded by circumstellar dust shells believed to result from mass loss by the central star. None of the dust shells was clearly resolved at either 50 or 100 microns; the upper limits are in the range 4 to 10 arcsec. These size limits place constraints on the far-IR dust emissivity and dust density distribution. For one of the objects, AFGL 2343, larger than normal grains are almost certainly required. For several other stars, the size limits are much more consistent with dust having an emissivity law no steeper than 1/lambda in the 1-100-micron spectral region. For IRC + 10216, an earlier suggestion is confirmed that, assuming reasonable grain properties, a smooth radial dust distribution is not consistent with the scans and the energy distribution of the object.

Harvey, Paul M.↗
DOE OSTI2015

SU-E-T-233: Cyberknife Versus Linac IMRT for Dose Comparision in Hypofractionated Hemi Larynx Irradiation of Early Stage True Vocal Cord Cancer: A Dosimetric Study

Purpose: To compare dosimetric data of patients treated for early-stage larynx cancer on Cyberknife and Linac IMRT. Methods: Nine patients were treated with Cyberknife to a dose of 45 Gy in 10 fractions of the involved hemilarynx. The prescription dose provided at least 95% of PTV coverage. After Cyberknife treatment, the CT images and contours were sent to Pinnacle treatment planning system for IMRT planning on a regular SBRT linac with same dose prescription and constrains. Dose to target and normal tissue, including the arytenoids, cord, carotid arteries, thyroid, and skin, were analyzed using dose volume histograms. Results: For Cyberknife plan, the conformity indices are within 1.11–1.33. The average dose to the contralateral arytenoids for Cyberknife plans was 28.9±6.5Gy), which is lower than the same mean dose for IMRT plans (34.0±5.2 Gy). The average maximum dose to the ipsilateral and contralateral carotid artery were 20.6 ±9.1 Gy and 10.2±6.0 Gy respectively for Cybeknife comparing with 22.1±8.0 Gy and 12.0±5.1 Gy for IMRT. The mean dose to the thyroid was 3.6±2.2 Gy for Cyberknife and 3.4±2.4 Gy for IMRT. As shown in DVH, the Cyberknife can deliver less dose to the normal tissue which is close to target area comparing with IMRT Plans. However, IMRT plan’s can give more sparing for the critical organs which is far away from the target area. Conclusion: We have compared the dosimetric parameters of Cyberknife and linac IMRT plans for patients with early-stage larynx cancer. Both Cyberknife and IMRT plans can achieve conformal dose distribution to the target area. Cyberknife was able to reduce normal tissue dose in high doses region while IMRT plans can reduce the dose of the normal tissue at the low dose region. These dosimetric parameters can be used to guide future prospective protocols using SBRT for larynx cancer.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1999

Highlights of Part I: Propagation Through Mars Environment: Propagation through Mars Environment - Part 1

We recommend using the dayside Martian ionosphere as a reflector for global communication, because it has a stable density peak and usable critical frequency. This is very crucial for the future Mars ground to ground communication. The dayside ionosphere has been well modeled as a Chapman layer. We suggest performing the Martian nightside ionosphere modeling study. Because the nightside ionosphere has very little measurements available, we propose to drop a digital ionosound instrument into the Mars surface for data collection. Even though the Martian tropospheric radio refractivity had a small value, it still can cause ray bending and multipath effects. We recommend performing an accurate calculation on excess phase and group delays (range and time delays). Other effects, such as range rate errors, appearance angle deviation, defocusing loss on Mars, etc. should be estimated. Ice depolarization effects due to Martian clouds on radio waves are unknown yet, but they are expected to be small, because of lower optical depth and the thinner layer of cloud. Total Martian atmospheric gaseous attenuation is expected to be less than 1 dB on microwaves and, because the Martian atmosphere had very low concentration in uncondensed H2O and O2. An accurate calculation for zenith opacity requires the information about scale heights of H2O and O2 distribution. An accurate water vapor altitude profile at Mars is not available et. Under the normal condition, CO2 and N2 gases ddo not have electric or magnetic dipoles and do not absorb electromagnetic energy from the waves. However, they may generate the dipoles through a collision and interact with waves under a high density condition and absorb electromagnetic waves in the infrared and visible band. Dust storm is the most dominant factor on the radio wave attenuation. Large Martian dust storms can cause at least 3 dB or higher loss to Ka band wave. For a normal dust storm, the attenuation is about 1 dB. The attenuation much depends on dust mass loading, dust size distribution, etc. Most large dust storms occur in the southern hemisphere during later spring and early summer when the southern hemisphere becomes suddenly hot.

Ho, Christian↗
NASA NTRS1999

Radio Wave Propagation for Communication on and around Mars: Highlights: Propagation Through Mars Environment - Part 1

We recommend to use the dayside Martian ionosphere as a reflector for global communication, because the dayside ionosphere has stable density peak and usable critic frequency. This is very crucial for the future Mars ground to around communication. The dayside ionosphere has been well modeled as a Chapman layer. We suggest to perform the Martian nightside ionospheric modeling study. Because the nightside ionosphere has very little measurements available, we propose to drop a digital ionosond instrument into the Mars surface for data collection. Even though the Martian tropospheric radio refractivity has small value, it still can cause the ray bending and multipath effects. We recommend to perform an accurate calculation on excess phase and group delays (range and time delays). Other effects, such as range rate errors, appearance angle deviation, defocusing loss on Mars, etc. are also needed to be estimated. Ice depolarization effects due to Martian clouds on radio waves is unknown yet, which is expected to be small, because lower optical depth and thinner layer of cloud: Total Martian atmospheric gaseous attenuation is expected to be less than 1 dB on microwaves band, because the Martian atmosphere has very low concentration in uncondensed H2O and O2. An accurate calculation for zenith opacity requires the information about scale heights of H2O and O2 distribution. An accurate water vapor altitude profile at Mars is not available yet. Under the normal condition, CO2 and N2 gases do not have electric or magnetic dipoles and do not absorb electromagnetic energy from the waves. However, they may generate the dipoles through a collision and interact with waves under a high density condition and absorb electromagnetic waves in the infrared and visible band. Dust storm is most dominant factor to the radio wave attenuation. Large Martian dust storm can cause at least 3 dB or higher loss to Ka band wave. For a normal dust storm, the attenuation is about 1 dB. The attenuation much depends on dust mass loading, dust size distribution, etc. Most large dust storm occur in the southern hemisphere during later spring and early summer when the southern hemisphere become suddenly hot.

Ho, Christian↗
NASA NTRS1989

Flow-field characteristics and normal-force correlations for delta wings from Mach 2.4 to 4.6

An experimental investigation has been conducted to determine the upper-surface flowfield types and the normal-force characteristics of a series of delta wing models at supersonic speeds. Flow-visualization data were used to classify the flowfields into seven primary types: shockless attached flow, separation bubble, classical vortex, vortex with shock, shock with no separation, shock-induced separation, and separation bubble with shock. The pressure distributions were integrated to obtain upper and lower surface normal-force loadings. A minimal effect of sweep was observed on the upper-surface normal force at constant Mach number and a minimal effect of Mach number was noted for the 75 deg delta wing lower-surface normal force. The normal-force coefficients for all test conditions were correlated, and a single empirical equation was formulated from which the normal-force coefficient could be calculated as a function of Mach number, angle of attack, and wing aspect ratio.

Covell, Peter F.↗
NASA NTRS1989

Effects of microgravity on growth hormone concentration and distribution in plants

On earth, gravity affects the distribution of the plant growth hormone, indole-3-acetic acid (IAA), in a manner such that the plant grows into a normal vertical orientation (shoots up, roots down). How the plant controls the amount and distribution of IAA is only partially understood and is currently under investigation in this laboratory. The question to be answered in the flight experiment concerns the effect of gravity on the concentration, turn over, and distribution of the growth hormone. The answer to this question will aid in understanding the mechanism by which plants control the amount and distribution of growth hormone. Such knowledge of a plant's hormonal metabolism may aid in the growth of plants in space and will lead to agronomic advances.

Schulze, Aga↗
DOE OSTI2014

SU-E-T-580: Comparison of Cervical Carcinoma IMRT Plans From Four Commercial Treatment Planning Systems (TPS)

Purpose: Different treatment planning systems (TPS) use different treatment optimization and leaf sequencing algorithms. This work compares cervical carcinoma IMRT plans optimized with four commercial TPSs to investigate the plan quality in terms of target conformity and delivery efficiency. Methods: Five cervical carcinoma cases were planned with the Corvus, Monaco, Pinnacle and Xio TPSs by experienced planners using appropriate optimization parameters and dose constraints to meet the clinical acceptance criteria. Plans were normalized for at least 95% of PTV to receive the prescription dose (Dp). Dose-volume histograms and isodose distributions were compared. Other quantities such as Dmin(the minimum dose received by 99% of GTV/PTV), Dmax(the maximum dose received by 1% of GTV/PTV), D100, D95, D90, V110%, V105%, V100% (the volume of GTV/PTV receiving 110%, 105%, 100% of Dp), conformity index(CI), homogeneity index (HI), the volume of receiving 40Gy and 50 Gy to rectum (V40,V50) ; the volume of receiving 30Gy and 50 Gy to bladder (V30,V50) were evaluated. Total segments and MUs were also compared. Results: While all plans meet target dose specifications and normal tissue constraints, the maximum GTVCI of Pinnacle plans was up to 0.74 and the minimum of Corvus plans was only 0.21, these four TPSs PTVCI had significant difference. The GTVHI and PTVHI of Pinnacle plans are all very low and show a very good dose distribution. Corvus plans received the higer dose of normal tissue. The Monaco plans require significantly less segments and MUs to deliver than the other plans. Conclusion: To deliver on a Varian linear-accelerator, the Pinnacle plans show a very good dose distribution. Corvus plans received the higer dose of normal tissue. The Monaco plans have faster beam delivery.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Towards a data-driven model of hadronization using normalizing flows

We introduce a model of hadronization based on invertible neural networks that faithfully reproduces a simplified version of the Lund string model for meson hadronization. Additionally, we introduce a new training method for normalizing flows, termed MAGIC, that improves the agreement between simulated and experimental distributions of high-level (macroscopic) observables by adjusting single-emission (microscopic) dynamics. Our results constitute an important step toward realizing a machine-learning based model of hadronization that utilizes experimental data during training. Finally, we demonstrate how a Bayesian extension to this normalizing-flow architecture can be used to provide analysis of statistical and modeling uncertainties on the generated observable distributions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Can a quantum critical state represent a blackbody?

The blackbody theory of Planck played a seminal role in the development of quantum theory at the turn of the past century. A blackbody cavity is generally thought to be a collection of photons in thermal equilibrium; the radiation emitted is at all wavelengths, and the intensity follows a scaling law, which is Planck’s characteristic distribution law. These photons arise from non-interacting normal modes. Here we suggest that certain quantum critical states when heated emit “radiation” at all wavelengths and satisfy all the criteria of a blackbody. An important difference is that the “radiation” does not necessarily consist of non-interacting photons, but also emergent relativistic bosons or fermions. The examples we provide include emergent relativistic fermions at a topological quantum critical point. This perspective on a quantum critical state may be illuminating in many unforeseen ways.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2000

Inverse Bremsstrahlung in Shocked Astrophysical Plasmas

There has recently been interest in the role of inverse bremsstrahlung, the emission of photons by fast suprathermal ions in collisions with ambient electrons possessing relatively low velocities, in tenuous plasmas in various astrophysical contexts. This follows a long hiatus in the application of suprathermal ion bremsstrahlung to astrophysical models since the early 1970s. The potential importance of inverse bremsstrahlung relative to normal bremsstrahlung, i.e. where ions are at rest, hinges upon the underlying velocity distributions of the interacting species. In this paper, we identify the conditions under which the inverse bremsstrahlung emissivity is significant relative to that for normal bremsstrahlung in shocked astrophysical plasmas. We determine that, since both observational and theoretical evidence favors electron temperatures almost comparable to, and certainly not very deficient relative to proton temperatures in shocked plasmas, these environments generally render inverse bremsstrahlung at best a minor contributor to the overall emission. Hence inverse bremsstrahlung can be safely neglected in most models invoking shock acceleration in discrete sources such as supernova remnants. However, on scales approximately > 100 pc distant from these sources, Coulomb collisional losses can deplete the cosmic ray electrons, rendering inverse bremsstrahlung, and perhaps bremsstrahlung from knock-on electrons, possibly detectable.

Baring, Matthew G.↗