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At least 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
DOE OSTI2010

WHERE DO WET, DRY, AND MIXED GALAXY MERGERS OCCUR? A STUDY OF THE ENVIRONMENTS OF CLOSE GALAXY PAIRS IN THE DEEP2 GALAXY REDSHIFT SURVEY

We study the environments of wet, dry, and mixed galaxy mergers at 0.75 < z < 1.2 using close pairs in the DEEP2 Galaxy Redshift Survey. We find that the typical environment of dry and mixed merger candidates is denser than that of wet mergers, mostly due to the color-density relation. While the galaxy companion rate (N{sub c}) is observed to increase with overdensity, using N-body simulations, we find that the fraction of pairs that will eventually merge decreases with the local density, predominantly because interlopers are more common in dense environments. After taking into account the merger probability of pairs as a function of local density, we find only marginal environment dependence of the galaxy merger rate for wet mergers. On the other hand, the dry and mixed merger rates increase rapidly with local density due to the increased population of red galaxies in dense environments, implying that the dry and mixed mergers are most effective in overdense regions. We also find that the environment distribution of K+A galaxies is similar to that of wet mergers alone and of wet+mixed mergers, suggesting a possible connection between K+A galaxies and wet and/or wet+mixed mergers. Based on our results, we therefore expect that the properties, including structures and masses, of red-sequence galaxies should be different between those in underdense regions and those in overdense regions since the dry mergers are significantly more important in dense environments. We conclude that, as early as z {approx} 1, high-density regions are the preferred environment in which dry mergers occur, and that present-day red-sequence galaxies in overdense environments have, on average, undergone 1.2 {+-} 0.3 dry mergers since this time, accounting for (38 {+-} 10)% of their mass accretion in the last 8 billion years. The main uncertainty in this finding is the conversion from the pair fraction to the galaxy merger rate, which is possibly as large as a factor of 2. Our findings suggest that dry mergers are crucial in the mass assembly of massive red galaxies in dense environments, such as brightest cluster galaxies in galaxy groups and clusters.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Dark-matter halo assembly bias: Environmental dependence in the non-Markovian excursion-set theory

In the standard excursion-set model for the growth of structure, the statistical properties of halos are governed by the halo mass and are independent of the larger-scale environment in which the halos reside. Numerical simulations, however, have found the spatial distributions of halos to depend not only on their mass but also on the details of their assembly history and environment. Here we present a theoretical framework for incorporating this 'assembly bias' into the excursion-set model. Our derivations are based on modifications of the path-integral approach of Maggiore and Riotto that models halo formation as a non-Markovian random-walk process. The perturbed density field is assumed to evolve stochastically with the smoothing scale and exhibits correlated walks in the presence of a density barrier. We write down conditional probabilities for multiple barrier crossings and derive from them analytic expressions for descendant and progenitor halo mass functions and halo merger rates as a function of both halo mass and the linear overdensity δ {sub e} of the larger-scale environment of the halo. Our results predict a higher halo merger rate and higher progenitor halo mass function in regions of higher overdensity, consistent with the behavior seen in N-body simulations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Bayesian mass estimates of the Milky Way: the dark and light sides of parameter assumptions

We present mass and mass profile estimates for the Milky Way (MW) Galaxy using the Bayesian analysis developed by Eadie et al. and using globular clusters (GCs) as tracers of the Galactic potential. The dark matter and GCs are assumed to follow different spatial distributions; we assume power-law model profiles and use the model distribution functions described in Evans et al. and Deason et al. We explore the relationships between assumptions about model parameters and how these assumptions affect mass profile estimates. We also explore how using subsamples of the GC population beyond certain radii affect mass estimates. After exploring the posterior distributions of different parameter assumption scenarios, we conclude that a conservative estimate of the Galaxy’s mass within 125 kpc is 5.22×10{sup 11} M{sub ⊙}, with a 50% probability region of (4.79,5.63)×10{sup 11} M{sub ⊙}. Extrapolating out to the virial radius, we obtain a virial mass for the MW of 6.82×10{sup 11} M{sub ⊙} with 50% credible region of (6.06,7.53)×10{sup 11} M{sub ⊙}(r{sub vir}=185{sub −7}{sup +7} kpc). If we consider only the GCs beyond 10 kpc, then the virial mass is 9.02 (5.69,10.86)×10{sup 11} M{sub ⊙} (r{sub vir}=198{sub −24}{sup +19} kpc). We also arrive at an estimate of the velocity anisotropy parameter β of the GC population, which is β=0.28 with a 50% credible region (0.21, 0.35). Interestingly, the mass estimates are sensitive to both the dark matter halo potential and visible matter tracer parameters, but are not very sensitive to the anisotropy parameter.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

THE X-RAY POWER SPECTRAL DENSITY FUNCTION OF THE SEYFERT ACTIVE GALACTIC NUCLEUS NGC 7469

We present the broadband X-ray power spectral density (PSD) function of the X-ray-luminous Seyfert 1.2 NGC 7469, measured from Rossi X-ray Timing Explorer monitoring data and two XMM-Newton observations. We find significant evidence for a turnover in the 2-10 keV PSD at a temporal frequency of 2.0{sup +3.0}{sub -0.8} x 10{sup -6} Hz or 1.0{sup +3.0}{sub -0.6} x 10{sup -6} Hz, depending on the exact form of the break (sharply broken or slowly bending power law, respectively). The 'surrogate' Monte Carlo method of Press et al. was used to map out the probability distributions of PSD model parameters and obtain reliable uncertainties (68% confidence limits quoted here). The corresponding break timescale of 5.8 {+-} 3.5 days or 11.6{sup +17.5}{sub -8.7} days, respectively, is consistent with the empirical relation between PSD break timescale, black hole mass, and bolometric luminosity of McHardy et al. Compared to the 2-10 keV PSD, the 10-20 keV PSD has a much flatter shape at high temporal frequencies, and no PSD break is significantly detected, suggesting an energy-dependent evolution not unlike that exhibited by several Galactic black hole systems.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Modeling of the Flows of Admixtures in a Random Layered Strip with Probable Arrangement of Inclusions Near the Boundaries of the Body

We study the random flow of admixtures in a two-phase stochastically inhomogeneous strip with the most probable arrangement of inclusions in the vicinity of the surfaces of the body. A mathematical model is formulated for the function of diffusion flow with nonzero constant initial concentration. A random diffusion flow is represented in the form of a Neumann series. The procedure of averaging of the random mass flow over the ensemble of phase configurations with arcsine distribution function is performed. The influence of the characteristics of the medium on the distribution of mass flow is analyzed. It is shown that if the diffusion coefficient of admixtures in the inclusion is higher than for the matrix, then the increase in the characteristic thickness of the layers causes a decrease in the value of the diffusion flow, whereas the mass flow in the entire body increases with the volume fraction of the inclusions.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

Sequential experimental design based generalised ANOVA

Over the last decade, surrogate modelling technique has gained wide popularity in the field of uncertainty quantification, optimization, model exploration and sensitivity analysis. This approach relies on experimental design to generate training points and regression/interpolation for generating the surrogate. In this work, it is argued that conventional experimental design may render a surrogate model inefficient. In order to address this issue, this paper presents a novel distribution adaptive sequential experimental design (DA-SED). The proposed DA-SED has been coupled with a variant of generalised analysis of variance (G-ANOVA), developed by representing the component function using the generalised polynomial chaos expansion. Moreover, generalised analytical expressions for calculating the first two statistical moments of the response, which are utilized in predicting the probability of failure, have also been developed. The proposed approach has been utilized in predicting probability of failure of three structural mechanics problems. It is observed that the proposed approach yields accurate and computationally efficient estimate of the failure probability.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

THE TRANSITION LAYER BETWEEN THE THIN ACCRETION DISK AND THE HOT CORONA: CONSTRAINTS FROM THE THERMAL X-RAY LINE EMISSION

The observed continuum spectra in the low-luminosity active galactic nuclei, M81, can be reproduced by the advection-dominated accretion flow (ADAF)+thin disk/corona accretion flow model. We find that the best fit to the spectral energy distribution of M81 requires accretion rate m-dot =3 Multiplication-Sign 10{sup -4} for R {sub tr} = 60 R {sub S}. The observed H-like and He-like iron lines may probably be emitted from the transition layer between the vertically connected hot corona and cold thin disk. We model a power-law function of height z for the electron temperature in the transition layer, and calculate the thermal H-like and He-like iron line emission from M81. Combining the observations with our results, we find that the thickness of the transition layer is {approx}14%-23% of the thickness of the corona at the same radius. We discuss that the observed stronger H-like line emission than He-like line emission cannot be explained with the pure ADAF model. Our results provide useful constraints on the theoretical model for disk-corona connection.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Framework for discrete-time quantum walks and a symmetric walk on a binary tree

We formulate a framework for discrete-time quantum walks, motivated by classical random walks with memory. We present a specific representation of the classical walk with memory 2, on which this is based. The framework has no need for coin spaces, it imposes no constraints on the evolution operator other than unitarity, and is unifying of other approaches. As an example we construct a symmetric discrete-time quantum walk on the semi-infinite binary tree. The generating function of the amplitude at the root is computed in closed form, as a function of time and the initial level n in the tree, and we find the asymptotic and a full numerical solution for the amplitude. It exhibits a sharp interference peak and a power-law tail, as opposed to the exponentially decaying tail of a broadly peaked distribution of the classical symmetric random walk on a binary tree. The probability peak is orders of magnitude larger than it is for the classical walk (already at small n). The quantum walk shows a polynomial algorithmic speedup in n over the classical walk, which we conjecture to be of the order 2/3, based on strong trends in data.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

The DESI One-Percent Survey: Constructing Galaxy–Halo Connections for ELGs and LRGs Using Auto and Cross Correlations

In the current Dark Energy Spectroscopic Instrument (DESI) survey, emission line galaxies (ELGs) and luminous red galaxies (LRGs) are essential for mapping the dark matter distribution at z ~ 1. We measure the auto and cross correlation functions of ELGs and LRGs at 0.8 < z ≤ 1.0 from the DESI One-Percent survey. Following Gao et al., we construct the galaxy–halo connections for ELGs and LRGs simultaneously. With the stellar–halo mass relation for the whole galaxy population (i.e., normal galaxies), LRGs can be selected directly by stellar mass, while ELGs can also be selected randomly based on the observed number density of each stellar mass, once the probability P sat of a satellite galaxy becoming an ELG is determined. We demonstrate that the observed small scale clustering prefers a halo mass-dependent P sat model rather than a constant. With this model, we can well reproduce the auto correlations of LRGs and the cross correlations between LRGs and ELGs at r p > 0.1 Mpc h –1 . We can also reproduce the auto correlations of ELGs at r p > 0.3 Mpc h –1 (s > 1 Mpc h –1 ) in real (redshift) space. Although our model has only seven parameters, we show that it can be extended to higher redshifts and reproduces the observed auto correlations of ELGs in the whole range of 0.8 < z ≤ 1.6, which enables us to generate a lightcone ELG mock for DESI. With the above model, we further derive halo occupation distributions for ELGs, which can be used to produce ELG mocks in coarse simulations without resolving subhalos.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Neutral Current Elastic Scattering and the Strange Spin Structure of the Proton

Neutrinos can be used as a unique and informative probe of the structure within nucleons. This thesis presents the tools and methodology for studying the strange quark spin in the nucleon through neutral current elastic neutrino-proton scattering in the MicroBooNE experiment located at the Fermi National Accelerator Lab. An automated boosted decision tree based proton identification algorithm is used to select proton in liquid argon TPC data with a 70\% efficiency. After a set of protons are selected, a logistic regression model is used to select neutral current elastic proton interactions in MicroBooNE. Neutral current elastic proton interactions are selected with an 11\% efficiency and 30\% purity. The number of selected events measured in MicroBooNE data as a function of $Q^2$ is compared directly to the number of selected events in MicroBooNE simulation. An event reweighting scheme is used to vary the expected number of eventsin MicroBooNE simulation based on the values o f the physics parameters of interest. The likelihood for any given value of the physical parameters can then be easily calculated and the probability distributions of the physics parameters can be sampled using Markov Chain Monte Carlo. Future improvements to the detector physics models in MicroBooNE are required for a precise determination of the strange quark spin structure in the proton. With the current level of uncertainty on the detector physics models, we are only able to constrain the net strange quark spin, $\Delta s$ to the range $-1.8 < \Delta s < 3.8$ with 95\% confidence.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

General Description of Fission Observables: GEF Model Code

The GEF (“GEneral description of Fission observables”) model code is documented. It describes the observables for spontaneous fission, neutron-induced fission and, more generally, for fission of a compound nucleus from any other entrance channel, with given excitation energy and angular momentum. The GEF model is applicable for a wide range of isotopes from Z = 80 to Z = 112 and beyond, up to excitation energies of about 100 MeV. The results of the GEF model are compared with fission barriers, fission probabilities, fission-fragment mass- and nuclide distributions, isomeric ratios, total kinetic energies, and prompt-neutron and prompt-gamma yields and energy spectra from neutron-induced and spontaneous fission. Derived properties of delayed neutrons and decay heat are also considered. The GEF model is based on a general approach to nuclear fission that explains a great part of the complex appearance of fission observables on the basis of fundamental laws of physics and general properties of microscopic systems and mathematical objects. The topographic theorem is used to estimate the fission-barrier heights from theoretical macroscopic saddle-point and ground-state masses and experimental ground-state masses. Motivated by the theoretically predicted early localisation of nucleonic wave functions in a necked-in shape, the properties of the relevant fragment shells are extracted. These are used to determine the depths and the widths of the fission valleys corresponding to the different fission channels and to describe the fission-fragment distributions and deformations at scission by a statistical approach. A modified composite nuclear-level-density formula is proposed. It respects some features in the superfluid regime that are in accordance with new experimental findings and with theoretical expectations. These are a constant-temperature behaviour that is consistent with a considerably increased heat capacity and an increased pairing condensation energy that is consistent with the collective enhancement of the level density. The exchange of excitation energy and nucleons between the nascent fragments on the way from saddle to scission is estimated according to statistical mechanics. As a result, excitation energy and unpaired nucleons are predominantly transferred to the heavy fragment in the superfluid regime. This description reproduces some rather peculiar observed features of the prompt-neutron multiplicities and of the even-odd effect in fission-fragment Z distributions. For completeness, some conventional descriptions are used for calculating pre-equilibrium emission, fission probabilities and statistical emission of neutrons and gamma radiation from the excited fragments. Preference is given to simple models that can also be applied to exotic nuclei compared to more sophisticated models that need precise empirical input of nuclear properties, e.g. spectroscopic information. The approach reveals a high degree of regularity and provides a considerable insight into the physics of the fission process. Fission observables can be calculated with a precision that complies with the needs for applications in nuclear technology without specific adjustments to measured data of individual systems. The GEF executable runs out of the box with no need for entering any empirical data. This unique feature is of valuable importance, because the number of systems and energies of potential significance for fundamental and applied science will never be possible to be measured. The relevance of the approach for examining the consistency of experimental results and for evaluating nuclear data is demonstrated.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Interaction of intermediate-energy protons with {sup 20}Ne and {sup 24}Mg nuclei within the multiple-scattering model

Observables of the elastic and inelastic scattering of 800- and 250-MeV protons on {sup 20}Ne and {sup 24}Mg nuclei were calculated on the basis of the theory of multiple diffractive scattering and the dispersive {alpha}-cluster model. The {sup 20}Ne and {sup 24}Mg nuclei were assumed to consist of a core ({sup 16}O nucleus) and additional alpha-particle clusters, which could be situated with the highest probability both in the vicinity of the center of mass of the core and outside the core. The multiparticle densities of these nuclei and single-particle nucleon-distribution densities as obtained from the dispersive {alpha}-cluster model were used in the calculations. The differential cross sections and polarizations for elastic and inelastic p{sup 20}Ne and p{sup 24}Mg scattering at the energy of 800 MeV are in better agreement with experimental data than the analogous calculations at the energy of 250 MeV. The spin-rotation functions calculated in the singleparticle approximation for elastic p{sup 20}Ne and p{sup 24}Mg scattering at these two energy values differ qualitatively from their counterparts calculated on the basis of the dispersive {alpha}-cluster model.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Asymptotic inconsistency of the cumulative algorithm for laser-induced damage probability analysis

The “cumulative algorithm” is a data analysis method that has been proposed to provide an objective, nonparametric determination of laser-induced damage probability as a function of fluence from experimental data that contain both damaged sites and undamaged sites (i.e., 1-on-1 or S-on-1 testing protocols). In this work, the limitations of this approach are explored by considering the asymptotic limit of a large number of test sites. It is shown that the cumulative algorithm does not converge to the true probability distribution and significantly underestimates the damage probability near the damage onset. Here, based on the results of this work, the cumulative algorithm is not recommended for accurate estimation of damage probability.

Computational methods↗
DOE OSTI2014

de Gennes narrowing describes the relative motion of protein domains

The relative motion of structural domains is essential for the biological function of many proteins. Here, by analyzing neutron scattering data and performing molecular dynamics simulations, we find that interdomain motion in several proteins obeys the principle of de Gennes narrowing, in which the wave vector dependence of the interdomain diffusion coefficient is inversely proportional to the interdomain structure factor. Furthermore, the rate of interdomain motion is inversely proportional to the probability distribution of the spatial configurations of domains.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Simulating sticky particles: A Monte Carlo method to sample a stratification

Many problems in materials science and biology involve particles interacting with strong, short-ranged bonds that can break and form on experimental timescales. Treating such bonds as constraints can significantly speed up sampling their equilibrium distribution, and there are several methods to sample probability distributions subject to fixed constraints. We introduce a Monte Carlo method to handle the case when constraints can break and form. More generally, the method samples a probability distribution on a stratification: a collection of manifolds of different dimensions, where the lower-dimensional manifolds lie on the boundaries of the higher-dimensional manifolds. We show several applications of the method in polymer physics, self-assembly of colloids, and volume calculation in high dimensions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

A Data-Driven Framework for Residential Electric Vehicle Charging Load Profile Generation

Residential electric vehicle charging load profile is indispensable to achieve reliable control strategies for mitigating negative effects on power distribution system due to emerging electrified transportation. This paper introduces a data-driven framework of charging load profile generation for residential plug-in electric vehicles. Real world historical residential charging behavior data is utilized to construct empirical charging decision making model by using machine learning algorithm. A multiple channels method with kernel density estimation is proposed to construct probability density functions for estimating charging duration based on parking duration. A generation algorithm considering parking time and travel demand dependency is introduced to generate residential charging behaviors. This framework is extensible to generate various charging load profiles and simulate varied residential charging scenarios under different number of households and charging rates. This will be crucial for designing and validating residential charging control strategies.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2018

Probability of Loss of Assured Safety in Systems with Multiple Time-Dependent Failure Modes: Incorporation of Delayed Link Failure in the Presence of Aleatory Uncertainty.

Probability of loss of assured safety (PLOAS) is modeled for weak link (WL)/strong link (SL) systems in which one or more WLs or SLs could potentially degrade into a precursor condition to link failure that will be followed by an actual failure after some amount of elapsed time. The following topics are considered: (i) Definition of precursor occurrence time cumulative distribution functions (CDFs) for individual WLs and SLs, (ii) Formal representation of PLOAS with constant delay times, (iii) Approximation and illustration of PLOAS with constant delay times, (iv) Formal representation of PLOAS with aleatory uncertainty in delay times, (v) Approximation and illustration of PLOAS with aleatory uncertainty in delay times, (vi) Formal representation of PLOAS with delay times defined by functions of link properties at occurrence times for failure precursors, (vii) Approximation and illustration of PLOAS with delay times defined by functions of link properties at occurrence times for failure precursors, and (viii) Procedures for the verification of PLOAS calculations for the three indicated definitions of delayed link failure.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2012

Using spatial information about recurrence risk for robust optimization of dose-painting prescription functions

Purpose: To develop a robust method for deriving dose-painting prescription functions using spatial information about the risk for disease recurrence. Methods: Spatial distributions of radiobiological model parameters are derived from distributions of recurrence risk after uniform irradiation. These model parameters are then used to derive optimal dose-painting prescription functions given a constant mean biologically effective dose. Results: An estimate for the optimal dose distribution can be derived based on spatial information about recurrence risk. Dose painting based on imaging markers that are moderately or poorly correlated with recurrence risk are predicted to potentially result in inferior disease control when compared the same mean biologically effective dose delivered uniformly. A robust optimization approach may partially mitigate this issue. Conclusions: The methods described here can be used to derive an estimate for a robust, patient-specific prescription function for use in dose painting. Two approximate scaling relationships were observed: First, the optimal choice for the maximum dose differential when using either a linear or two-compartment prescription function is proportional to R, where R is the Pearson correlation coefficient between a given imaging marker and recurrence risk after uniform irradiation. Second, the predicted maximum possible gain in tumor control probability for any robust optimization technique is nearly proportional to the square of R.

61 RADIATION PROTECTION AND DOSIMETRY↗