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At least 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Stimulated Raman scattering of laser dye mixtures dissolved in multiple scattering media

Stimulated Raman scattering (SRS) of a mixture of rhodamine 6G and pyrromethene 605 laser dyes in vesicular films is studied. It is shown that a peculiar interaction of dyes occurs under conditions of multiple scattering of light from vesicles. This interaction manifests itself as SRS excitation of one of the dyes by random lasing of the other dye, provided that the random lasing spectrum overlaps the Stokes lines of the first dye. In addition, there is energy transfer between molecules of these dyes if their luminescence and absorption spectra overlap. The results obtained confirm that the mechanism of SRS from laser dyes in multiple scattering media is similar to that in coherent-active Raman spectroscopy. These results extend the possibility of determining the vibrational spectrum of dye molecules from their secondary radiation in these media. (nonlinear optical phenomena)

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Spectral multiplicity for powers of weakly mixing automorphisms

We study the behaviour of the maximal spectral multiplicity m(R{sup n}) for the powers of a weakly mixing automorphism R. For some particular infinite sets A we show that there exists a weakly mixing rank-one automorphism R such that m(R{sup n})=n and m(R{sup n+1})=1 for all positive integers n element of A. Moreover, the cardinality cardm(R{sup n}) of the set of spectral multiplicities for the power R{sup n} is shown to satisfy the conditions cardm(R{sup n+1})=1 and cardm(R{sup n})=2{sup m(n)}, m(n){yields}{infinity}, n element of A. We also construct another weakly mixing automorphism R with the following properties: all powers R{sup n} have homogeneous spectra and the set of limit points of the sequence {l_brace}m(R{sup n})/n:n element of N{r_brace} is infinite. Bibliography: 17 titles.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2020

Application of Neutron Multiplicity Counting Experiments to Optimal Cross-Section Adjustments

This paper presents the first application of model calibration to neutron multiplicity counting (NMC) experiments for cross-section optimization that is informed by adjoint-based sensitivity analysis (SA) and first-order uncertainty quantification (UQ). We summarize previous work on SA applied to NMC and describe notable modifications and additions. We give the procedure for first-order UQ and Bayesian-inference-based parameter estimation (PE). We then discuss model calibration applied to NMC of a 4.5-kg sphere of weapons-grade, alpha-phase plutonium metal (the BeRP ball) with the nPod neutron multiplicity counter. For the BeRP ball in bare and polyethylene-reflected configurations, we discuss the sensitivity of the first- and second-moment detector responses (i.e., first and second moments of the NMC distribution, respectively) to the cross sections. We describe the sources of uncertainty in the measured and simulated responses. Specifically, uncertainty in the measured responses is due to both random and systematic sources. Uncertainty in the simulated responses is due to the cross-section covariances. We describe in detail the adjustment to the cross sections and cross-section covariances due to the optimization. Due to the contribution of systematic uncertainties to the measured response uncertainties, the adjustment to the cross sections is similar in trend but larger in magnitude compared to that recommended by previous work. We compare the measured responses to responses simulated with nominal and optimized cross sections, demonstrating that the best-estimate cross sections produce simulations of NMC experiments that are more accurate with reduced uncertainty.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Space-Dependent Calculation of the Multiplicity Moments for Shells With the Inclusion of Scattering

In recent work, we extended the methodology of multiplicity counting in nuclear safeguards by elaborating the one-speed stochastic transport theory of the calculation of the so-called multiplicity moments, i.e., the factorial moments of the number of neutrons emitted from a fissile item, following a source event from an internal neutron source [spontaneous fission and (α; n) reactions]. Calculations were made for solid spheres and cylinders, with the source being homogeneously distributed within the item. Recent measurements of the Rocky Flats Shells during the Measurement of Uranium Subcritical and Critical (MUSIC) campaign conducted by Los Alamos National Laboratory and assisted by the University of Michigan inspired us to extend the model to spherical shell geometry with a point source in the middle of the central cavity. Comparison of the calculated results with the experimental ones indicated that accounting for fission as the only neutron reaction (the standard procedure in the point model, adapted also in our work so far) was not sufficient for reaching good agreement with measurements. The model was therefore extended to include elastic scattering into the one speed formalism, whereas the effect of inelastic scattering was accounted for in an empirical way. After these extensions, good agreement was found between the calculated and the measured values. The paper describes the extension of the theory and provides concrete quantitative results.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

From binaries to multiples. I. Data on F and G dwarfs within 67 pc of the Sun

Data on the multiplicity of F- and G-type dwarf stars within 67 pc of the Sun are presented. This distance-limited sample based on the Hipparcos catalog contains 4847 primary stars (targets) with 0.5 < V – I{sub C} < 0.8 and is >90% complete. There are 2196 known stellar pairs; some of them belong to 361 hierarchical systems from triples to quintuples. Models of companion detection by radial velocity, astrometric acceleration, direct resolution, and common proper motion are developed. They serve to compute completeness for each target, using the information on its coverage collected here. About 80% of companions to the primary stars are detected, but the census of subsystems in the secondary components is only about 30%. Masses of binary components are estimated from their absolute magnitudes or by other methods; the periods of wide pairs are evaluated from their projected separations. A third of binaries with periods shorter than ∼100 yr are spectroscopic and/or astrometric pairs with yet unknown periods and mass ratios. These data are used in the accompanying Paper II to derive unbiased statistics of hierarchical multiple systems.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The multiplicity of massive stars: A high angular resolution survey with the HST fine guidance sensor

We present the results of an all-sky survey made with the Fine Guidance Sensor on the Hubble Space Telescope to search for angularly resolved binary systems among massive stars. The sample of 224 stars is comprised mainly of Galactic O- and B-type stars and luminous blue variables, plus a few luminous stars in the Large Magellanic Cloud. The FGS TRANS mode observations are sensitive to the detection of companions with an angular separation between 0.″01 and 1.″0 and brighter than △m=5. The FGS observations resolved 52 binary and 6 triple star systems and detected partially resolved binaries in 7 additional targets (43 of these are new detections). These numbers yield a companion detection frequency of 29% for the FGS survey. We also gathered literature results on the numbers of close spectroscopic binaries and wider astrometric binaries among the sample, and we present estimates of the frequency of multiple systems and the companion frequency for subsets of stars residing in clusters and associations, field stars, and runaway stars. These results confirm the high multiplicity fraction, especially among massive stars in clusters and associations. We show that the period distribution is approximately flat in increments of logP. We identify a number of systems of potential interest for long-term orbital determinations, and we note the importance of some of these companions for the interpretation of the radial velocities and light curves of close binaries that have third companions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

A SURVEY OF THE HIGH ORDER MULTIPLICITY OF NEARBY SOLAR-TYPE BINARY STARS WITH Robo-AO

We conducted a survey of nearby binary systems composed of main sequence stars of spectral types F and G in order to improve our understanding of the hierarchical nature of multiple star systems. Using Robo-AO, the first robotic adaptive optics instrument, we collected high angular resolution images with deep and well-defined detection limits in the Sloan Digital Sky Survey i' band. A total of 695 components belonging to 595 systems were observed. We prioritized observations of faint secondary components with separations over 10'' to quantify the still poorly constrained frequency of their subsystems. Of the 214 secondaries observed, 39 contain such subsystems; 19 of those were discovered with Robo-AO. The selection-corrected frequency of secondary subsystems with periods from 10{sup 3.5} to 10{sup 5} days is 0.12 ± 0.03, the same as the frequency of such companions to the primary. Half of the secondary pairs belong to quadruple systems where the primary is also a close pair, showing that the presence of subsystems in both components of the outer binary is correlated. The relatively large abundance of 2+2 quadruple systems is a new finding, and will require more exploration of the formation mechanism of multiple star systems. We also targeted close binaries with periods less than 100 yr, searching for their distant tertiary components, and discovered 17 certain and 2 potential new triples. In a subsample of 241 close binaries, 71 have additional outer companions. The overall frequency of tertiary components is not enhanced, compared to all (non-binary) targets, but in the range of outer periods from 10{sup 6} to 10{sup 7.5} days (separations on the order of 500 AU), the frequency of tertiary components is 0.16 ± 0.03, exceeding the frequency of similar systems among all targets (0.09) by almost a factor of two. Measurements of binary stars with Robo-AO allowed us to compute first orbits for 9 pairs and to improve orbits of another 11 pairs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Multiplicity of the galactic senior citizens: A high-resolution search for cool subdwarf companions

Cool subdwarfs are the oldest members of the low-mass stellar population. Mostly present in the galactic halo, subdwarfs are characterized by their low-metallicity. Measuring their binary fraction and comparing it to solar-metallicity stars could give key insights into the star formation process early in the Milky Way’s history. However, because of their low luminosity and relative rarity in the solar neighborhood, binarity surveys of cool subdwarfs have suffered from small sample sizes and incompleteness. Previous surveys have suggested that the binary fraction of red subdwarfs is much lower than for their main-sequence cousins. Using the highly efficient Robo-AO system, we present the largest high-resolution survey of subdwarfs, sensitive to angular separations (ρ ⩾ 0.″ 15) and contrast ratios (Δm{sub i} ⩽ 6) invisible in past surveys. Of 344 target cool subdwarfs, 43 are in multiple systems, 19 of which are newly discovered, for a binary fraction of 12.5 ± 1.9%. We also discovered seven triple star systems for a triplet fraction of 2.0 ± 0.8%. Comparisons to similar surveys of solar-metallicity dwarf stars gives a ∼3σ disparity in luminosity between companion stars, with subdwarfs displaying a shortage of low-contrast companions. We also observe a lack of close subdwarf companions in comparison to similar-mass dwarf multiple systems.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

MULTIPLICITY AMONG F-TYPE STARS. II

In continuation of our previous study we present an updated census of new companions and model atmosphere analyses for some 50 southern dwarfs, mostly in the mass range 0.90⩽M⩽1.10 M{sub ⊙}. For the common-proper-motion companions μ Vir B, HR 2225 B, HD 67199 B, and HD 114853 B, we confirm their physical association from their radial velocities. We report the discovery of the F-type visual binary α For as a field blue straggler and confirm (ζ Ret, HR 5864) or identify (HD 67199, HR 4013, HR 8843) another five mass transfer systems or candidates. For the F stars τ{sup 1} Eri and 111 Tau, we present 10σ and 7σ cases for astrometric binaries by virtue of the very accurate van Leeuwen Hipparcos parallaxes. Following the work of Shaya and Olling, we suggest the F-type star ι Vir to be a wide (0.37 pc) hierarchical quadruple system. We confirm the visual binary NLTT 23781/2 as a common-proper-motion object to the very wide (0.54 pc) F star 40 Leo, but discard the G star HD 128987 as an ultra-wide (1.01 pc) physical companion to the α Lib quadruple system on account of a diverse metallicity. The improved statistics of our sample establishes the previously discovered positive correlation of stellar multiplicities with primary mass. For the F star multiplicity census in the mass range 1.10⩽M⩽1.70 M{sub ⊙}, we find that at least a quarter consists of triple or higher level systems and at least two out of three F stars are non-single.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

Tracing multiple scattering patterns in absolute (e,2e) cross sections for H{sub 2} and He over a 4{pi} solid angle

Absolutely normalized (e,2e) measurements for H{sub 2} and He covering the full solid angle of one ejected electron are presented for 16 eV sum energy of both final state continuum electrons. For both targets rich cross-section structures in addition to the binary and recoil lobes are identified and studied as a function of the fixed electron's emission angle and the energy sharing among both electrons. For H{sub 2} their behavior is consistent with multiple scattering of the projectile as discussed before [Al-Hagan et al., Nature Phys. 5, 59 (2009)]. For He the binary and recoil lobes are significantly larger than for H{sub 2} and partly cover the multiple scattering structures. To highlight these patterns we propose a alternative representation of the triply differential cross section. Nonperturbative calculations are in good agreement with the He results and show discrepancies for H{sub 2} in the recoil peak region. For H{sub 2} a perturbative approach reasonably reproduces the cross-section shape but deviates in absolute magnitude.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2010

Nanometric resolution using far-field optical tomographic microscopy in the multiple scattering regime

The resolution of optical far-field microscopes is classically diffraction-limited to half the illumination wavelength. We show experimentally that this fundamental limit does not apply in the multiple scattering regime. We used tomographic diffractive microscopy at 633 nm to image two pairs of closely spaced rods (with a width and interdistance of 50 nm) of widely different diffractive properties. Using an inversion algorithm accounting for multiple scattering, only the pair of highly diffracting rods could be clearly visualized with a resolution similar to that of an atomic force microscope.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2010

Rapidity scaling of multiplicity and flow in weakly and strongly interacting systems

We examine the 'naturalness' of the scaling of multiplicity and elliptic flow v{sub 2} with rapidity in weakly and strongly coupled systems. We argue that multiplicity scaling is relatively straightforward to incorporate in existing ansatz, and that this scaling is insensitive to the transport properties of the system. On the other hand, we argue that the observed scaling of elliptic flow is problematic to describe within a hydrodynamic model (the Knudsen number K<<1), but arises more naturally within weakly coupled systems (where the Knudsen number {approx}1). We conclude with an overview of ways proposed to make weakly coupled systems compatible with the absolute value of elliptic flow, and we indicate experimental probes that could clarify these issues.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Disentangling correlations in multiple parton interactions

Multiple Parton Interactions are the tool to obtain information on the correlations between partons in the hadron structure. Partons may be correlated in all degrees of freedom and all different correlation terms contribute to the cross section. The contributions due to the different parton flavors can be isolated, at least to some extent, by selecting properly the final state. In the case of high energy proton-proton collisions, the effects of correlations in the transverse coordinates and in fractional momenta are, on the contrary, unavoidably mixed in the final observables. The standard way to quantify the strength of double parton interactions is by the value of the effective cross section and a small value of the effective cross section may be originated both by the relatively short transverse distance between the pairs of partons undergoing the double interaction and by a large dispersion of the distribution in multiplicity of the multiparton distributions. The aim of the present paper is to show how the effects of longitudinal and transverse correlations may be disentangled by taking into account the additional information provided by double parton interactions in high energy proton-deuteron collisions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Macromolecular phasing using diffraction from multiple crystal forms

A phasing algorithm for macromolecular crystallography is proposed that utilizes diffraction data from multiple crystal forms – crystals of the same molecule with different unit-cell packings (different unit-cell parameters or space-group symmetries). The approach is based on the method of iterated projections, starting with no initial phase information. The practicality of the method is demonstrated by simulation using known structures that exist in multiple crystal forms, assuming some information on the molecular envelope and positional relationships between the molecules in the different unit cells. With incorporation of new or existing methods for determination of these parameters, the approach has potential as a method for ab initio phasing.

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

Fast multiplicity counter featuring stilbene detectors for special nuclear material assay

The Treaty on the Nonproliferation of Nuclear Weapons demands for new instruments to prevent diversion of fissile material and safeguard controls. We present a fast neutron multiplicity counting system based on organic scintillators, i.e. liquid EJ-309 and stilbene. The system is able to detect fission correlated counts and photon and neutron multiplets, needed to quantify fissile mass, without the need of complex electronic circuitry and unfolding procedures, required in moderated systems. Moderated system, typically based on helium-3 detectors, feature a gate time of hundreds of microseconds. Conversely, the use of organic scintillators allows an exceptionally short gate time of hundreds of nanoseconds. This results in a reduction of accidental neutron coincidence. In our system, the superior gamma-neutron discrimination capabilities of stilbene scintillators allow to measure high-order multiplicities (> 3) and the inspection of complex source terms. This counter is thus also suitable for the assay of newer fuels containing plutonium and other fissionable actinides. A prototypal version of the well-counter was assembled and tested at the University of Michigan, using a spontaneous fission and an (a,n) neutron source, i.e. 252Cf and PuBe respectively. Presented measured results show excellent agreement with simulations. The viability of the system to discriminate time-correlated fission neutrons from random, uncorrelated neutrons was proved. An experimental campaign will be carried out at Idaho National Laboratory in August 2015 to characterize weapon grade plutonium samples.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Decentralizing Network Inference Problems With Multiple-Description Fusion Estimation (MDFE)

Network inference (or tomography) problems, such as traffic matrix estimation or completion and link loss inference, have been studied rigorously in different networking applications. These problems are often posed as under-determined linear inverse (UDLI) problems and solved in a centralized manner, where all the measurements are collected at a central node, which then applies a variety of inference techniques to estimate the attributes of interest. This paper proposes a novel framework for decentralizing these large-scale under-determined network inference problems by intelligently partitioning it into smaller subproblems and solving them independently and in parallel. The resulting estimates, referred to as multiple descriptions, can then be fused together to compute the global estimate. We apply this Multiple Description and Fusion Estimation (MDFE) framework to three classical problems: traffic matrix estimation, traffic matrix completion, and loss inference. Using real topologies and traces, we demonstrate how MDFE can speed up computation while maintaining (even improving) the estimation accuracy and how it enhances robustness against noise and failures. In conclusion, we also show that our MDFE framework is compatible with a variety of existing inference techniques used to solve the UDLI problems.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2022

Traffic Signal Control With Adaptive Online-Learning Scheme Using Multiple-Model Neural Networks

This article proposes a new traffic signal control algorithm to deal with unknown-traffic-system uncertainties and reduce delays in vehicle travel time. Unknown-traffic-system dynamics are approximated using a recurrent neural network (NN). To accurately identify the traffic system model, an online-learning scheme is developed to switch among a set of candidate NNs (i.e., multiple-model NNs) based on their estimation errors. Then, a bank of optimal signal-timing controllers is designed based on the online identification of the traffic system. Simulation studies have been carried out for the obtained control strategies using multiple-model NNs, and the desired results have been obtained. Moreover, compared with the widely used actuated traffic signal control schemes, it is shown that the proposed method can reduce vehicle travel delays and improve traffic system robustness.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2020

A Plutonium Mass Uncertainty Assessment Using a Cherenkov-Based Neutron Multiplicity Water Detector

We present a new analysis of the sensitivity of a water Cherenkov-based neutron multiplicity counter for nondestructive assay of trace quantities of 240 Pu. The multiplicity counter [water-based neutron detector (WaND)] contains 1.0 m 3 of water doped with 0.2% gadolinium in the form of a gadolinium salt (0.4% GdCl 3 ). It can be used for testing the presence of trace quantities of 240 Pu within a sample of unknown material by observing the correlated timing behavior of neutron capture candidates in the detector. The new analysis takes advantage of the fact that the detector is comprised almost entirely of a homogeneous medium, which permits the use of a simple model to reproduce the observed neutron capture timing behavior. Finally, the results of this analysis indicate that the detector has an absolute neutron detection efficiency of 23.4 ± 1.1% and is sensitive to a 240 Pu mass as small as 2.3 mg (at 1σ) after a 1-h data acquisition.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗