Sound extinction by fish schools: forward scattering theory and data analysis.

PubMed

Raveau, M; Feuillade, C

2015-02-01

A model used previously to study collective back scattering from fish schools [Feuillade et al., J. Acoust. Soc. Am. 99(1), 196-208 (1996)], is used to analyze the forward scattering properties of these objects. There is an essential physical difference between back and forward scattering from fish schools. Strong frequency dependent interference effects, which affect the back scattered field amplitude, are absent in the forward scattering case. This is critically important for data analysis. There is interest in using back scattering and transmission data from fish schools to study their size, the species and abundance of fish, and fish behavior. Transmission data can be processed to determine the extinction of the field by a school. The extinction of sound depends on the forward scattering characteristics of the school, and data inversion to provide information about the fish should be based upon a forward scattering paradigm. Results are presented of an analysis of transmission data obtained in September 1995 during an experiment performed in the Gulf of Lion in the Mediterranean Sea [Diachok, J. Acoust. Soc. Am. 105(4), 2107-2128 (1999)]. The analysis shows that using forward scattering leads to significantly larger estimates of fish abundance than previous analysis based upon back scattering approaches.

Transport and breakdown analysis for improved figure-of-merit for AlGaN power devices

NASA Astrophysics Data System (ADS)

Coltrin, Michael E.; Kaplar, Robert J.

2017-02-01

Mobility and critical electric field for bulk AlxGa1-xN alloys across the full composition range (0 ≤ x ≤ 1) are analyzed to address the potential application of this material system for power electronics. Calculation of the temperature-dependent electron mobility includes the potential limitations due to different scattering mechanisms, including alloy, optical polar phonon, deformation potential, and piezoelectric scattering. The commonly used unipolar figure of merit (appropriate for vertical-device architectures), which increases strongly with increasing mobility and critical electric field, is examined across the alloy composition range to estimate the potential performance in power electronics applications. Alloy scattering is the dominant limitation to mobility and thus also for the unipolar figure of merit. However, at higher alloy compositions, the limitations due to alloy scattering are overcome by increased critical electric field. These trade-offs, and their temperature dependence, are quantified in the analysis.

New evaluation of thermal neutron scattering libraries for light and heavy water

NASA Astrophysics Data System (ADS)

Marquez Damian, Jose Ignacio; Granada, Jose Rolando; Cantargi, Florencia; Roubtsov, Danila

2017-09-01

In order to improve the design and safety of thermal nuclear reactors and for verification of criticality safety conditions on systems with significant amount of fissile materials and water, it is necessary to perform high-precision neutron transport calculations and estimate uncertainties of the results. These calculations are based on neutron interaction data distributed in evaluated nuclear data libraries. To improve the evaluations of thermal scattering sub-libraries, we developed a set of thermal neutron scattering cross sections (scattering kernels) for hydrogen bound in light water, and deuterium and oxygen bound in heavy water, in the ENDF-6 format from room temperature up to the critical temperatures of molecular liquids. The new evaluations were generated and processable with NJOY99 and also with NJOY-2012 with minor modifications (updates), and with the new version of NJOY-2016. The new TSL libraries are based on molecular dynamics simulations with GROMACS and recent experimental data, and result in an improvement of the calculation of single neutron scattering quantities. In this work, we discuss the importance of taking into account self-diffusion in liquids to accurately describe the neutron scattering at low neutron energies (quasi-elastic peak problem). To improve modeling of heavy water, it is important to take into account temperature-dependent static structure factors and apply Sköld approximation to the coherent inelastic components of the scattering matrix. The usage of the new set of scattering matrices and cross-sections improves the calculation of thermal critical systems moderated and/or reflected with light/heavy water obtained from the International Criticality Safety Benchmark Evaluation Project (ICSBEP) handbook. For example, the use of the new thermal scattering library for heavy water, combined with the ROSFOND-2010 evaluation of the cross sections for deuterium, results in an improvement of the C/E ratio in 48 out of 65 international benchmark cases calculated with the Monte Carlo code MCNP5, in comparison with the existing library based on the ENDF/B-VII.0 evaluation.

Analysis of hyperspectral scattering profiles using a generalized Gaussian distribution function for prediction of apple firmness and soluble solids content

USDA-ARS?s Scientific Manuscript database

Hyperspectral scattering provides an effective means for characterizing light scattering in the fruit and is thus promising for noninvasive assessment of apple firmness and soluble solids content (SSC). A critical problem encountered in application of hyperspectral scattering technology is analyzing...

Critical behavior of the order-disorder phase transition in β -brass investigated by x-ray scattering

NASA Astrophysics Data System (ADS)

Madsen, A.; Als-Nielsen, J.; Hallmann, J.; Roth, T.; Lu, W.

2016-07-01

β -brass exhibits an archetypical example of an order-disorder transition with a critical behavior that was previously investigated by neutron scattering. The data were well described by the three-dimensional (3d) Ising model but the relatively crude experimental resolution prevented an in-depth examination of the single-length scaling hypothesis, a cornerstone in the theory of critical phenomena. With the development of synchrotron x-ray experiments, high-resolution data could be recorded and surprisingly it was found that the single-length scaling did not hold in most critical systems, possibly due to strain originating from surface defects and/or impurities. In this paper we demonstrate single-length critical behavior using high-resolution x-ray scattering in β -brass. The investigations confirm that β -brass behaves like a 3d Ising system over a wide range of length scales comprising correlated clusters of millions of atoms. To vary the surface sensitivity, experiments have been performed both in Bragg reflection and Laue transmission geometries but without any substantial differences observed in the scaling and critical behavior.

Details of the disorder-induced transition between s ± and s ++ states in the two-band model for Fe-based superconductors

NASA Astrophysics Data System (ADS)

Shestakov, V. A.; Korshunov, M. M.; Togushova, Yu N.; Efremov, D. V.; Dolgov, O. V.

2018-07-01

Irradiation of superconductors with different particles is one of many ways to investigate the effects of disorder. Here we study the disorder-induced transition between s ± and s ++ states in the two-band model for Fe-based superconductors with nonmagnetic impurities. Specifically, we investigate the important question of whether the superconducting gaps during the transition change smoothly or abruptly. We show that the behavior can be of either type and is controlled by the ratio of intraband to interband impurity scattering potentials, and by a parameter σ , that represents scattering strength and ranges from zero (Born approximation) to one (unitary limit). For the pure interband scattering potential and the scattering strength σ ≲ 0.11, the {s}+/- \\to {s}++ transition is accompanied by steep changes in the gaps, while for larger values of σ , the gaps change smoothly. The behavior of the gaps is characterized by steep changes at low temperatures, T< 0.1{T}{{c}0} with T c0 being the critical temperature in the clean limit, otherwise it changes gradually. The critical temperature T c is always a smooth function of the scattering rate in spite of the steep changes in the behavior of the gaps.

Quantum Critical Quasiparticle Scattering within the Superconducting State of CeCoIn_{5}.

PubMed

Paglione, Johnpierre; Tanatar, M A; Reid, J-Ph; Shakeripour, H; Petrovic, C; Taillefer, Louis

2016-07-01

The thermal conductivity κ of the heavy-fermion metal CeCoIn_{5} was measured in the normal and superconducting states as a function of temperature T and magnetic field H, for a current and field parallel to the [100] direction. Inside the superconducting state, when the field is lower than the upper critical field H_{c2}, κ/T is found to increase as T→0, just as in a metal and in contrast to the behavior of all known superconductors. This is due to unpaired electrons on part of the Fermi surface, which dominate the transport above a certain field. The evolution of κ/T with field reveals that the electron-electron scattering (or transport mass m^{⋆}) of those unpaired electrons diverges as H→H_{c2} from below, in the same way that it does in the normal state as H→H_{c2} from above. This shows that the unpaired electrons sense the proximity of the field-tuned quantum critical point of CeCoIn_{5} at H^{⋆}=H_{c2} even from inside the superconducting state. The fact that the quantum critical scattering of the unpaired electrons is much weaker than the average scattering of all electrons in the normal state reveals a k-space correlation between the strength of pairing and the strength of scattering, pointing to a common mechanism, presumably antiferromagnetic fluctuations.

Experimental Approaches for Solution X-Ray Scattering and Fiber Diffraction

PubMed Central

Irving, T. C.

2008-01-01

X-ray scattering and diffraction from non-crystalline systems have gained renewed interest in recent years, as focus shifts from the structural chemistry information gained by high-resolution studies to the context of structural physiology at larger length scales. Such techniques permit the study of isolated macromolecules as well as highly organized macromolecular assemblies as a whole under near-physiological conditions. Time-resolved approaches, made possible by advanced synchrotron instrumentation, add a critical dimension to many of these investigations. This article reviews experimental approaches in non-crystalline x-ray scattering and diffraction that may be used to illuminate important scientific questions such as protein/nucleic acid folding and structure-function relationships in large macromolecular assemblies. PMID:18801437

Strain heterogeneity in sheared colloids revealed by neutron scattering

DOE PAGES

Chen, Kevin; Wu, Bin; He, Lilin; ...

2018-02-07

Recent computational and theoretical studies have shown that the deformation of colloidal suspensions under a steady shear is highly heterogeneous at the particle level and demonstrate a critical influence on the macroscopic deformation behavior. Despite its relevance to a wide variety of industrial applications of colloidal suspensions, scattering studies focusing on addressing the heterogeneity of the non-equilibrium colloidal structure are scarce thus far. Here in this paper, we report the first experimental result using small-angle neutron scattering. From the evolution of strain heterogeneity, we conclude that the shear-induced deformation transforms from nearly affine behavior at low shear rates, to plasticmore » rearrangements when the shear rate is high.« less

Connected and disconnected contractions in pion-pion scattering

NASA Astrophysics Data System (ADS)

Acharya, Neramballi Ripunjay; Guo, Feng-Kun; Meißner, Ulf-G.; Seng, Chien-Yeah

2017-09-01

We show that the interplay of chiral effective field theory and lattice QCD can be used in the evaluation of so-called disconnected diagrams, which appear in the study of the isoscalar and isovector channels of pion-pion scattering and have long been a major challenge for the lattice community. By means of partially-quenched chiral perturbation theory, we distinguish and analyze the effects from different types of contraction diagrams to the pion-pion scattering amplitude, including its scattering lengths and the energy-dependence of its imaginary part. Our results may be used to test the current degree of accuracy of lattice calculation in the handling of disconnected diagrams, as well as to set criteria for the future improvement of relevant lattice computational techniques that may play a critical role in the study of other interesting QCD matrix elements.

Scattering from Rock and Rock Outcrops

DTIC Science & Technology

2015-09-30

Scattering from Rock and Rock Outcrops Derek R. Olson The Pennsylvania State University Applied Research Laboratory, P.O. Box 30 State...In terms of target detection and classification, scattering from exposed rock on the seafloor, (i.e., individual rocks and rock outcrops) presents...levels, and other statistical measures of acoustic scattering from rocks and rock outcrops is therefore critical. Unfortunately (and curiously

Energy-loss spectrum for inelastic scattering of charged particles in disordered systems near the critical point

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gerasimov, O. I.; Adamian, V. M.

The behavior of the theoretically predicted correlational ''fine''energy-loss spectrum of inelastic electron scattering in disordered systemsclose to single resonance is investigated near the critical point. In extendingour earlier work, it is shown that the relation of the statistical expressionof the cross section of energy loss to the function which describes the lineshape in an ideal gas asymptotically increases near the critical point as apower law. ''Fracton'' interpretation of display of the localization of asingle excitation in disordered systems in the resonance-line shape of theenergy-loss spectrum is suggested. The possibility of direct determination ofthe pair distribution function (without Fourier transformation ofmore » the structurefactor) using the method of charged-particle scattering is discussed.« less

Thermodynamics of Hydrophobic Amino Acids in Solution: A Combined Experimental–Computational Study

DOE PAGES

Song, Lingshuang; Yang, Lin; Meng, Jie; ...

2016-12-29

Here, we present a joint experimental-computational study to quantitatively describe the thermodynamics of hydrophobic leucine amino acids in aqueous solution. X-ray scattering data were acquired at a series of solute and salt concentrations to effectively measure inter-leucine interactions, indicating that a major scattering peak is observed consistently at q = 0.83 Å -1. Atomistic molecular dynamics simulations were then performed and compared with the scattering data, achieving high consistency at both small and wider scattering angles (q = 0$-$1.5 Å -1). This experimental-computational consistence enables a first glimpse of the leucineleucine interacting landscape, where two leucine molecules are aligned mostlymore » in a parallel fashion, as opposed to anti-parallel, but also allows us to derive effective leucine-leucine interactions in solution. Collectively, this combined approach of employing experimental scattering and molecular simulation enables a quantitative characterization on effective inter-molecular interactions of hydrophobic amino acids, critical for protein function and dynamics such as protein folding.« less

Thermodynamics of Hydrophobic Amino Acids in Solution: A Combined Experimental–Computational Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, Lingshuang; Yang, Lin; Meng, Jie

Here, we present a joint experimental-computational study to quantitatively describe the thermodynamics of hydrophobic leucine amino acids in aqueous solution. X-ray scattering data were acquired at a series of solute and salt concentrations to effectively measure inter-leucine interactions, indicating that a major scattering peak is observed consistently at q = 0.83 Å -1. Atomistic molecular dynamics simulations were then performed and compared with the scattering data, achieving high consistency at both small and wider scattering angles (q = 0$-$1.5 Å -1). This experimental-computational consistence enables a first glimpse of the leucineleucine interacting landscape, where two leucine molecules are aligned mostlymore » in a parallel fashion, as opposed to anti-parallel, but also allows us to derive effective leucine-leucine interactions in solution. Collectively, this combined approach of employing experimental scattering and molecular simulation enables a quantitative characterization on effective inter-molecular interactions of hydrophobic amino acids, critical for protein function and dynamics such as protein folding.« less

Pretransitional diffuse neutron scattering in the mixed perovskite relaxor K1-xLixTaO3

NASA Astrophysics Data System (ADS)

Yong, Grace; Toulouse, Jean; Erwin, Ross; Shapiro, Stephen M.; Hennion, Bernard

2000-12-01

Several previous studies of K1-xLixTaO3 (KLT) have revealed the presence, above the structural transition, of polar nanoregions. Recently, these have been shown to play an essential role in the relaxor behavior of KLT. In order to characterize these regions, we have performed a neutron-scattering study of KLT crystals with different lithium concentrations, both above and below the critical concentration. This study reveals the existence of diffuse scattering that appears upon formation of these regions. The rodlike distribution of the diffuse scattering along cubic directions indicates that the regions form in the shape of discs in the various cubic planes. From the width of the diffuse scattering we extract values for a correlation length or size of the regions as a function of temperature. Finally, on the basis of the reciprocal lattice points around which the diffuse scattering is most intense, we conclude that the regions have tetragonal symmetry. The large increase in Bragg intensities at the first-order transition suggests that the polar regions freeze to form large structural domains and the transition is triggered by the percolation of strain fields through the crystals.

Spectral statistics and scattering resonances of complex primes arrays

NASA Astrophysics Data System (ADS)

Wang, Ren; Pinheiro, Felipe A.; Dal Negro, Luca

2018-01-01

We introduce a class of aperiodic arrays of electric dipoles generated from the distribution of prime numbers in complex quadratic fields (Eisenstein and Gaussian primes) as well as quaternion primes (Hurwitz and Lifschitz primes), and study the nature of their scattering resonances using the vectorial Green's matrix method. In these systems we demonstrate several distinctive spectral properties, such as the absence of level repulsion in the strongly scattering regime, critical statistics of level spacings, and the existence of critical modes, which are extended fractal modes with long lifetimes not supported by either random or periodic systems. Moreover, we show that one can predict important physical properties, such as the existence spectral gaps, by analyzing the eigenvalue distribution of the Green's matrix of the arrays in the complex plane. Our results unveil the importance of aperiodic correlations in prime number arrays for the engineering of gapped photonic media that support far richer mode localization and spectral properties compared to usual periodic and random media.

Study of density distribution in a near-critical simple fluid (19-IML-1)

NASA Technical Reports Server (NTRS)

Michels, Teun

1992-01-01

This experiment uses visual observation, interferometry, and light scattering techniques to observe and analyze the density distribution in SF6 above and below the critical temperature. Below the critical temperature, the fluid system is split up into two coexisting phases, liquid and vapor. The spatial separation of these phases on earth, liquid below and vapor above, is not an intrinsic property of the fluid system; it is merely an effect of the action of the gravity field. At a fixed temperature, the density of each of the coexisting phases is in principle fixed. However, near T sub c where the fluid is strongly compressible, gravity induced hydrostatic forces will result in a gradual decrease in density with increasing height in the sample container. This hydrostatic density profile is even more pronounced in the one phase fluid at temperatures slightly above T sub c. The experiment is set up to study the intrinsic density distributions and equilibration rates of a critical sample in a small container. Interferometry will be used to determine local density and thickness of surface and interface layers. The light scattering data will reveal the size of the density fluctuations on a microscopic scale.

X-ray near-field speckle: implementation and critical analysis

PubMed Central

Lu, Xinhui; Mochrie, S. G. J.; Narayanan, S.; Sandy, A. R.; Sprung, M.

2011-01-01

The newly introduced coherence-based technique of X-ray near-field speckle (XNFS) has been implemented at 8-ID-I at the Advanced Photon Source. In the near-field regime of high-brilliance synchrotron X-rays scattered from a sample of interest, it turns out that, when the scattered radiation and the main beam both impinge upon an X-ray area detector, the measured intensity shows low-contrast speckles, resulting from interference between the incident and scattered beams. A micrometer-resolution XNFS detector with a high numerical aperture microscope objective has been built and its capability for studying static structures and dynamics at longer length scales than traditional far-field X-ray scattering techniques is demonstrated. Specifically, the dynamics of dilute silica and polystyrene colloidal samples are characterized. This study reveals certain limitations of the XNFS technique, especially in the characterization of static structures, which is discussed. PMID:21997906

Spin waves in full-polarized state of Dzyaloshinskii-Moriya helimagnets: Small-angle neutron scattering study

NASA Astrophysics Data System (ADS)

Grigoriev, S. V.; Sukhanov, A. S.; Altynbaev, E. V.; Siegfried, S.-A.; Heinemann, A.; Kizhe, P.; Maleyev, S. V.

2015-12-01

We develop the technique to study the spin-wave dynamics of the full-polarized state of the Dzyaloshinskii-Moriya helimagnets by polarized small-angle neutron scattering. We have experimentally proven that the spin-waves dispersion in this state has the anisotropic form. We show that the neutron scattering image displays a circle with a certain radius which is centered at the momentum transfer corresponding to the helix wave vector in helimagnetic phase ks, which is oriented along the applied magnetic field H . The radius of this circle is directly related to the spin-wave stiffness of this system. This scattering depends on the neutron polarization showing the one-handed nature of the spin waves in Dzyaloshinskii-Moriya helimagnets in the full-polarized phase. We show that the spin-wave stiffness A for MnSi helimagnet decreased twice as the temperature increases from zero to the critical temperature Tc.

Quantum critical quasiparticle scattering within the superconducting state of CeCoIn 5

DOE PAGES

Paglione, Johnpierre; Tanatar, M. A.; Reid, J.-Ph.; ...

2016-06-27

Here, the thermal conductivity κ of the heavy-fermion metal CeCoIn 5 was measured in the normal and superconducting states as a function of temperature T and magnetic field H, for a current and field parallel to the [100] direction. Inside the superconducting state, when the field is lower than the upper critical field H c2, κ/T is found to increase as T→0, just as in a metal and in contrast to the behavior of all known superconductors. This is due to unpaired electrons on part of the Fermi surface, which dominate the transport above a certain field. The evolution ofmore » κ/T with field reveals that the electron-electron scattering (or transport mass m*) of those unpaired electrons diverges as H→H c2 from below, in the same way that it does in the normal state as H→H c2 from above. This shows that the unpaired electrons sense the proximity of the field-tuned quantum critical point of CeCoIn 5 at H*=H c2 even from inside the superconducting state. In conclusion, the fact that the quantum critical scattering of the unpaired electrons is much weaker than the average scattering of all electrons in the normal state reveals a k-space correlation between the strength of pairing and the strength of scattering, pointing to a common mechanism, presumably antiferromagnetic fluctuations.« less

Conductivity of Weakly Disordered Metals Close to a "Ferromagnetic" Quantum Critical Point

NASA Astrophysics Data System (ADS)

Kastrinakis, George

2018-05-01

We calculate analytically the conductivity of weakly disordered metals close to a "ferromagnetic" quantum critical point in the low-temperature regime. Ferromagnetic in the sense that the effective carrier potential V(q,ω ), due to critical fluctuations, is peaked at zero momentum q=0. Vertex corrections, due to both critical fluctuations and impurity scattering, are explicitly considered. We find that only the vertex corrections due to impurity scattering, combined with the self-energy, generate appreciable effects as a function of the temperature T and the control parameter a, which measures the proximity to the critical point. Our results are consistent with resistivity experiments in several materials displaying typical Fermi liquid behaviour, but with a diverging prefactor of the T^2 term for small a.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Demidov, V. E.; Dzyapko, O.; Demokritov, S. O.

The room-temperature dynamics of a magnon gas driven by short microwave pumping pulses is studied. An overpopulation of the lowest energy level of the system following the pumping is observed. Using the sensitivity of the Brillouin light scattering technique to the coherence degree of the scattering magnons we demonstrate the spontaneous emergence of coherence of the magnons at the lowest level, if their density exceeds a critical value. This finding is clear proof of the quantum nature of the observed phenomenon and direct evidence of Bose-Einstein condensation of magnons at room temperature.

Distribution of an Acoustic Scattering Layer, Petermann Fjord, Northwest Greenland

NASA Astrophysics Data System (ADS)

Heffron, E.; Mayer, L. A.; Jakobsson, M.; Hogan, K.; Jerram, K.

2017-12-01

The Petermann 2015 Expedition was a comprehensive paleoceanographic and paleoclimatological study of the marine-terminating Petermann Glacier and its outlet system in Northwest Greenland carried out July-August 2015. The purpose was the reconstruction of glacial history and current glacial processes in Petermann Fjord to better understand the fate of the Petermann Glacier and its floating ice tongue that acts as a critical buttressing force to the outlet glacier draining about 4% of the Greenland Ice Sheet. Seafloor mapping was a critical component of the study and an EM122 multibeam sonar was utilized for this purpose; additionally, water column data were acquired with this sonar and an EK80 split-beam echosounder. During the expedition, the mapping team noted an acoustic scattering layer in the EK80 and EM122 water column data which was observed to change depth in a spatially consistent manner that appeared to be related to location. Initial onboard processing revealed what appears to be a strong spatial coherence in the layer distribution that corresponds to our understanding of the complex circulation pattern in the study area, including inflow of warmer Atlantic waters and outflow of subglacial waters. This initial processing was limited to observations at 46 discrete locations that corresponded to CTD stations, a very small subset of the 4800 line kilometers of data collected by each sonar. Both sonars were run 24 hours per day over the 30-day expedition, providing continuous time-varying acoustic coverage of the study area. Post-cruise additional data has been processed to extract the acoustic returns from the scattering layer using a combination of commercial sonar processing software and specialized MATLAB and Python routines. 3-D surfaces have been generated from the extracted points in order to visualize the continuous spatial and temporal distribution of the scattering layer across the entire study area. Multiple crossings of the same location at different times of day address the question of the temporal stability of the scattering layer while the detailed map of the spatial distribution demonstrates the relationship of the scattering layer to the water masses and implies that continuous acoustic coverage may be a powerful proxy for oceanography.

Stray Light Analyis With The HP-41C/CV Calculator

NASA Astrophysics Data System (ADS)

Bamberg, Jack A.

1983-10-01

A stray radiation analysis program (nicknamed MINI-APART after its namesake: APART) suitable for use on the HP-41C/CV calculator is described. The program is ideally suited for quick estimates of stray light performance in well-baffled optical systems, which are limited by scatter from the first optical element. Critical path models are described, including single scatter, double scatter, diffraction-scatter, and thermal emission-scatter. Program use is illustrated, and several comparisons are made with the results obtained by the large stray radiation programs, GUERAP-3 and APART/PADE.

Polarized neutron scattering studies of chiral criticality, and new universality classes of phase transitions

NASA Astrophysics Data System (ADS)

Plakhty, V. P.; Wosnitza, J.; Kulda, J.; Brückel, Th.; Schweika, W.; Visser, D.; Gavrilov, S. V.; Moskvin, E. V.; Kremer, R. K.; Banks, M. G.

2006-11-01

Using a novel polarised neutron scattering technique, the critical exponents for the spin chirality and chiral susceptibility are determined for the triangular lattice antiferromagnet (TLA) CsMnBr 3 in the ranges of reduced temperature τ>10 -3 and τ>7×10 -3, respectively. Their values, βC=0.44(2) and γC=0.85(3), together with the scaling relation α+2β+γ=2.13(9), including the critical exponent where α for the specific heat, prove that the spin-ordering transition belongs to the XY chiral universality class. In the case of helimagnet Ho, it is found that β-2β=0.14(4), where β is the staggered magnetisation exponent. The scaling relation α+2β+γ=2 could be fulfilled with a reasonable α=0.23(4), although for the chiral critical exponents βC=0.90(2) and γC=0.69(5) one needs α=-0.49(5) in contradiction with any experimental data. As the scaling relation always holds, we assume that the spin-ordering transition in Ho is of the first order. In the quantum antiferromagnet CsCuCl 3, a triangular spin order coexists with a long-period Dzyaloshinskii helix. The Dzyaloshinskii axial vector should remove the helix chiral degeneracy, which has not been observed in reality. The critical exponent β=0.22(2) is found to be in agreement with the XY chiral scenario for a TLA. Chiral scattering above TN is very weak, probably being masked by zero-point quantum fluctuations. A modulation of the crystal structure with the periodicity of the helix is observed, indicating strong coupling of the Dzyaloshinskii-Moriya interaction with the lattice.

Scattering theory for the defocusing fourth-order Schrödinger equation

NASA Astrophysics Data System (ADS)

Miao, Changxing; Zheng, Jiqiang

2016-02-01

In this paper, we study the global well-posedness and scattering theory for the defocusing fourth-order nonlinear Schrödinger equation (FNLS) \\text{i}{{u}t}+{{Δ }2}u +\\mid u{{\\mid}p}u=0 in dimensions d≥slant 8 . We prove that if the solution u is apriorily bounded in the critical Sobolev space, that is, u\\in Lt∞≤ft(I;\\overset{\\centerdot}{\\mathop{H}} x{{sc}}≤ft({{{R}}d}\\right)\\right) with all {{s}c}:=\\frac{d}{2}-\\frac{4}{p}≥slant 1 if p is an even integer or {{s}c}\\in ≤ft[1,2+p\\right) otherwise, then u is global and scatters. We will give a uniform way to treat the energy-subcritical, energy-critical and energy-supercritical FNLS by making use of the strategy derived from concentration compactness ideas, and we are able to overcome the logarithmic blowup in the double Duhamel trick in dimension eight by exploiting the refined dispersive estimate which is in sharp contrast to the Schrödinger equation.

Interband coupling and transport interband scattering in s ± superconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kogan, Vladimir; Prozorov, Ruslan

A two-band model with repulsive interband coupling and interband transport (potential) scattering is considered to elucidate their effects on material properties. In agreement with previous work, we find that the bands order parameters Δ 1,2 differ and the large is at the band with a smaller normal density of states (DOS), N n2 < N n1. However, the bands energy gaps, as determined by the energy dependence of the DOS, are equal due to scattering. For each temperature, the gaps turn zero at a certain critical interband scattering rate, i.e. for strong enough scattering the model material becomes gappless. Inmore » the gapless state, the DOS at the band 2 is close to the normal state value, whereas at the band 1 it has a V-shape with non-zero minimum. When the normal bands DOS' are mismatched, N n1 6= N n2, the critical temperature T c is suppressed even in the absence of interband scattering, T c(N n1) has a dome-like shape. With increasing interband scattering, the London penetration depth at low temperatures evolves from being exponentially at to the powerlaw and even to near linear behavior in the gapless state, the latter being easily misinterpreted as caused by order parameter nodes.« less

The self-association of acebutolol: Conductometry and light scattering

NASA Astrophysics Data System (ADS)

Ruso, Juan M.; López-Fontán, José L.; Prieto, Gerardo; Sarmiento, Félix

2003-04-01

The association characteristics of an amphiphilic beta-blocker drug, acebutolol hydrochloride, in aqueous solution containing high concentrations of electrolyte and at different temperatures have been examined by static and dynamic light scattering and electrical conductivity. Time averaged light scattering measurements on aqueous solutions of acebutolol at 298.15 K in the presence of added electrolyte (0.4-1.0 mol kg-1 NaCl) have shown discontinuities which reflect the appearance of aggregates. The critical micelle concentration, aggregation numbers, effective micelle charges, and degree of micellar ionization were calculated. Dynamic light scattering has shown an increase in micellar size with increase in concentration of added electrolyte. Data have been interpreted using the DLVO theory to quantify the interaction between the drug aggregates and the colloidal stability. Critical micelle concentrations in water have been calculated from conductivity measurements over the temperature range 288.15-313.15 K. The variation in critical concentration with temperature passes through a minimum close to 294 K. Thermodynamic parameters of aggregate formation (ΔGm0,ΔHm0,ΔSm0) were obtained from a variation of the mass action model applicable to systems of low aggregation number.

Magnetic scattering effects in two-band superconductor: the ferromagnetic dopants in MgB₂.

PubMed

Li, W X; Zeng, R; Poh, C K; Li, Y; Dou, S X

2010-04-07

This paper demonstrates the magnetic scattering effects on the electron-phonon interaction in two-band superconductors based on the transition-metal-doped MgB₂ to clarify the effects of magnetic dopants on multi-band superconductivity. The phonon properties of polycrystalline Mg(1-x)M(x)B₂ (M = Fe, Ni and Co), with x up to 0.05, were studied, with the investigation based on the normal state Raman spectra, especially the variation of the E(2g) mode. The magnetic scattering effect of Fe is much weaker than that of Mn in MgB₂, while it is stronger than that of Ni. The weak magnetic scattering effects are responsible for the superconducting behaviors of Mg(1 - x)Fe(x)B₂ and Mg(1 - x)Ni(x)B₂. Co shows almost no magnetic scattering effects on the superconductivity, while the depression of the critical temperature, T(c), in Mg(1 - x)Co(x)B₂ is attributed to the phonon behavior and is independent of the ferromagnetic nature of cobalt.

Ocean-atmosphere interface: its influence on radiation.

PubMed

Plass, G N; Humphreys, T J; Kattawar, G W

1981-03-15

The influence of the ocean-atmosphere interface on the radiance distribution in both the ocean and atmosphere is investigated. At visible wavelengths in the real ocean just below the surface, the downwelling radiance is a maximum within the critical angle and drops off by 1 or 2 orders of magnitude toward the horizon. The usual explanation that this is due to the sky radiation concentrated within the critical angle and the total internal reflection of the weak upward radiance at the ocean surface at angles outside the critical angle is too simplistic. There are two other important factors: (1) the atmosphere must have sufficient optical thickness so that appreciable sky (multiple scattered) radiation develops at all angles in the downward direction; (2) the water must have appreciable absorption so that the upwelling radiance just below the ocean surface is only a small fraction of the downwelling radiance entering the ocean. Examples show that, if either one of these conditions is not satisfied, an entirely different radiance distribution develops. The variation of the following quantities with depth is studied: radiance; vector and scalar irradiance; distribution function; reflectance; and heating rate. The radiance distribution in a homogeneous medium is compared with that in the same medium with an atmosphere-ocean interface at various depths within the medium. Most of the calculations are done for Rayleigh scattering centers, but some results are given for Mie-type scattering.

Scattering of the double sine-Gordon kinks

NASA Astrophysics Data System (ADS)

Gani, Vakhid A.; Marjaneh, Aliakbar Moradi; Askari, Alidad; Belendryasova, Ekaterina; Saadatmand, Danial

2018-04-01

We study the scattering of kink and antikink of the double sine-Gordon model. There is a critical value of the initial velocity v_{{cr}} of the colliding kinks, which separates different regimes of the collision. At v_{in}>v_{cr} we observe kinks reflection, while at v_{in}

Finite Density Condensation and Scattering Data: A Study in ϕ4 Lattice Field Theory

NASA Astrophysics Data System (ADS)

Gattringer, Christof; Giuliani, Mario; Orasch, Oliver

2018-06-01

We study the quantum field theory of a charged ϕ4 field in lattice regularization at finite density and low temperature in 2 and 4 dimensions with the goal of analyzing the connection of condensation phenomena to scattering data in a nonperturbative way. The sign problem of the theory at nonzero chemical potential μ is overcome by using a worldline representation for the Monte Carlo simulation. At low temperature we study the particle number as a function of μ and observe the steps for 1-, 2-, and 3-particle condensation. We determine the corresponding critical values μncrit , n =1 , 2, 3 and analyze their dependence on the spatial extent L of the lattice. Linear combinations of the μncrit give the interaction energies in the 2- and 3-particle sectors and their dependence on L is related to scattering data by Lüscher's formula and its generalizations to three particles. For two dimensions we determine the scattering phase shift and for four dimensions the scattering length. We cross-check our results with a determination of the mass and the 2- and 3-particle energies from conventional 2-, 4-, and 6-point correlators at zero chemical potential. The letter demonstrates that the physics of condensation at finite density and low temperature is closely related to scattering data of a quantum field theory.

Lecture Notes on Criticality Safety Validation Using MCNP & Whisper

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, Forrest B.; Rising, Michael Evan; Alwin, Jennifer Louise

Training classes for nuclear criticality safety, MCNP documentation. The need for, and problems surrounding, validation of computer codes and data area considered first. Then some background for MCNP & Whisper is given--best practices for Monte Carlo criticality calculations, neutron spectra, S(α,β) thermal neutron scattering data, nuclear data sensitivities, covariance data, and correlation coefficients. Whisper is computational software designed to assist the nuclear criticality safety analyst with validation studies with the Monte Carlo radiation transport package MCNP. Whisper's methodology (benchmark selection – C k's, weights; extreme value theory – bias, bias uncertainty; MOS for nuclear data uncertainty – GLLS) and usagemore » are discussed.« less

Body Temperature-Related Structural Transitions of Monotremal and Human Hemoglobin

PubMed Central

Digel, I.; Maggakis-Kelemen, Ch.; Zerlin, K. F.; Linder, Pt.; Kasischke, N.; Kayser, P.; Porst, D.; Temiz Artmann, A.; Artmann, G. M.

2006-01-01

In this study, temperature-related structural changes were investigated in human, duck-billed platypus (Ornithorhynchus anatinus, body temperature Tb = 31–33°C), and echidna (Tachyglossus aculeatus, body temperature Tb = 32–33°C) hemoglobin using circular dichroism spectroscopy and dynamic light scattering. The average hydrodynamic radius (Rh) and fractional (normalized) change in the ellipticity (Fobs) at 222 ± 2 nm of hemoglobin were measured. The temperature was varied stepwise from 25°C to 45°C. The existence of a structural transition of human hemoglobin at the critical temperature Tc between 36–37°C was previously shown by micropipette aspiration experiments, viscosimetry, and circular dichroism spectroscopy. Based on light-scattering measurements, this study proves the onset of molecular aggregation at Tc. In two different monotremal hemoglobins (echidna and platypus), the critical transition temperatures were found between 32–33°C, which are close to the species' body temperature Tb. The data suggest that the correlation of the structural transition's critical temperature Tc and the species' body temperature Tb is not mere coincidence but, instead, is a more widespread structural phenomenon possibly including many other proteins. PMID:16844747

Body temperature-related structural transitions of monotremal and human hemoglobin.

PubMed

Digel, I; Maggakis-Kelemen, Ch; Zerlin, K F; Linder, Pt; Kasischke, N; Kayser, P; Porst, D; Temiz Artmann, A; Artmann, G M

2006-10-15

In this study, temperature-related structural changes were investigated in human, duck-billed platypus (Ornithorhynchus anatinus, body temperature T(b) = 31-33 degrees C), and echidna (Tachyglossus aculeatus, body temperature T(b) = 32-33 degrees C) hemoglobin using circular dichroism spectroscopy and dynamic light scattering. The average hydrodynamic radius (R(h)) and fractional (normalized) change in the ellipticity (F(obs)) at 222 +/- 2 nm of hemoglobin were measured. The temperature was varied stepwise from 25 degrees C to 45 degrees C. The existence of a structural transition of human hemoglobin at the critical temperature T(c) between 36-37 degrees C was previously shown by micropipette aspiration experiments, viscosimetry, and circular dichroism spectroscopy. Based on light-scattering measurements, this study proves the onset of molecular aggregation at T(c). In two different monotremal hemoglobins (echidna and platypus), the critical transition temperatures were found between 32-33 degrees C, which are close to the species' body temperature T(b). The data suggest that the correlation of the structural transition's critical temperature T(c) and the species' body temperature T(b) is not mere coincidence but, instead, is a more widespread structural phenomenon possibly including many other proteins.

Regional Cerebral Abnormalities Measured by Frequency-Domain Near-Infrared Spectroscopy in Pediatric Patients During Extracorporeal Membrane Oxygenation.

PubMed

Tian, Fenghua; Jenks, Christopher; Potter, Donald; Miles, Darryl; Raman, Lakshmi

Extracorporeal membrane oxygenation (ECMO) is a form of advanced cardiorespiratory support provided to critically ill patients with severe respiratory or cardiovascular failure. While children undergoing ECMO therapy have significant risk for neurological morbidity, currently there is a lack of reliable bedside tool to detect the neurologic events for patients on ECMO. This study assessed the feasibility of frequency-domain near-infrared spectroscopy (NIRS) for detection of intracranial complications during ECMO therapy. The frequency-domain NIRS device measured the absorption coefficient (µa) and reduced scattering coefficient (µs') at six cranial positions from seven pediatric patients (0-16 years) during ECMO support and five healthy controls (2-14 years). Regional abnormalities in both absorption and scattering were identified among ECMO patients. A main finding in this study is that the abnormalities in scattering appear to be associated with lower-than-normal µs' values in regional areas of the brain. Because light scattering originates from the intracellular structures (such as nuclei and mitochondria), a reduction in scattering primarily reflects loss or decreased density of the brain matter. The results from this study indicate a potential to use the frequency-domain NIRS as a safe and complementary technology for detection of intracranial complications during ECMO therapy.

Nonlinear optical response in graphene nanoribbons: The critical role of electron scattering

NASA Astrophysics Data System (ADS)

Karimi, F.; Davoody, A. H.; Knezevic, I.

2018-06-01

Nonlinear nanophotonics has many potential applications, such as in mode locking, frequency-comb generation, and all-optical switching. The development of materials with large nonlinear susceptibility is key to realizing nonlinear nanophotonics. Nanostructured graphene systems, such as graphene nanoribbons and nanoislands, have been predicted to have a strong plasmon-enhanced nonlinear optical behavior in the nonretarded regime. Plasmons concentrate the light field down to subwavelength scales and can enhance the nonlinear optical effects; however, plasmon resonances are narrowband and sensitive to the nanostructure geometry. Here we show that graphene nanoribbons, particularly armchair graphene nanoribbons, have a remarkably strong nonlinear optical response in the long-wavelength regime and over a broad frequency range, from terahertz to the near infrared. We use a quantum-mechanical master equation with a detailed treatment of scattering and show that, in the retarded regime, electron scattering has a critical effect on the optical nonlinearity of graphene nanoribbons, which cannot be captured via the commonly used relaxation-time approximation. At terahertz frequencies, where intraband optical transitions dominate, the strong nonlinearity (in particular, third-order Kerr nonlinearity) stems from the jagged shape of the electron energy distribution, caused by the interband electron scattering mechanisms along with the intraband inelastic scattering mechanisms. We show that the relaxation-time approximation fails to capture this quantum-mechanical phenomenon and results in a significant underestimation of the intraband nonlinearity. At the midinfrared to near infrared frequencies, where interband optical transitions dominate, the Kerr nonlinearity is significantly overestimated within the relaxation-time approximation. These findings unveil the critical effect of electron scattering on the optical nonlinearity of nanostructured graphene, and also underscore the capability of this class of materials for nonlinear nanophotonic applications.

Diffusion and cellular uptake of drugs in live cells studied with surface-enhanced Raman scattering probes

NASA Astrophysics Data System (ADS)

Bálint, Štefan; Rao, Satish; Sánchez, Mónica Marro; Huntošová, Veronika; Miškovský, Pavol; Petrov, Dmitri

2010-03-01

An understanding of the mechanisms of drug diffusion and uptake through cellular membranes is critical for elucidating drug action and in the development of effective drug delivery systems. We study these processes for emodin, a potential anticancer drug, in live cancer cells using surface-enhanced Raman scattering. Micrometer-sized silica beads covered by nanosized silver colloids are passively embedded into the cell and used as sensors of the drug. We demonstrate that the technique offers distinct advantages: the possibility to study the kinetics of drug diffusion through the cellular membrane toward specific cell organelles, the detection of lower drug concentrations compared to fluorescence techniques, and less damage imparted on the cell.

Advanced Stimulated Scattering Measurements in Supercritical Fluids

DTIC Science & Technology

2006-09-01

supercritical fluid measurement techniques. Ajay Agrawal, optical diagnostics. Mel Roquemore, turbine engines. Fred Schauer, pulse detonation propulsion...Lett. 87, 233902 (2001). 11. R. W. Gammon, H. L. Swinney, and H. Z. Cummins, "Brillouin scattering in carbon dioxide in the critical region," Phys. Rev...Stimulated Scattering Measurements in Supercritical F49620-03-C-0015 Fluids 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 61102F 6. AUTHOR(S) 5d

Pitch angle scattering in three-dimensional "critical balance" MHD turbulence.

NASA Astrophysics Data System (ADS)

Forman, Miriam; Oughton, Sean; Horbury, Tim

2004-11-01

We calculated the dependence of the quasi-linear particle pitch angle scattering coefficient in general 3-dimensional turbulence axi-symmetric about the mean magnetic field. We integrate over the power spectrum tensor of the turbulence in terms of the scalar functions E, F, C, and H of the wavevector k, as described by Oughton, et al. for incompressible MHD. The application to a "slab+ 2.5D" model is trivial, and reproduces Bieber, et al.'s extremely important previous result that the 2.5D part does not do any pitch-angle scattering. However, the "slab + 2D" is a highly idealized model. One wonders how its two parts are related to actual turbulence, as observed in space or in simulations, and to the calculation of the particle scattering. Here we update the "slab + 2D" model to a more realistic distribution in k-space, specifically a modification of the inertial-range "critical balance" form introduced by Goldreich and Sridhar, and developed further by Cho, Lazarian and Vishniac. We apply the 3D quasi-linear method to calculate D and the spatial diffusion coefficient parallel to the local mean magnetic field, in the "critical balance" anisotropic turbulence. We thank the International Space Science Institute (Bern, Switzerland) for support of this work.

Quantum Enhancement of the Index of Refraction in a Bose-Einstein Condensate.

PubMed

Bons, P C; de Haas, R; de Jong, D; Groot, A; van der Straten, P

2016-04-29

We study the index of refraction of an ultracold bosonic gas in the dilute regime. Using phase-contrast imaging with light detuned from resonance by several tens of linewidths, we image a single cloud of ultracold atoms for 100 consecutive shots, which enables the study of the scattering rate as a function of temperature and density using only a single cloud. We observe that the scattering rate is increased below the critical temperature for Bose-Einstein condensation by a factor of 3 compared to the single-atom scattering rate. We show that current atom-light interaction models to second order of the density show a similar increase, where the magnitude of the effect depends on the model that is used to calculate the pair-correlation function. This confirms that the effect of quantum statistics on the index of refraction is dominant in this regime.

Imaging Molecular Motion: Femtosecond X-Ray Scattering of an Electrocyclic Chemical Reaction

NASA Astrophysics Data System (ADS)

Minitti, M. P.; Budarz, J. M.; Kirrander, A.; Robinson, J. S.; Ratner, D.; Lane, T. J.; Zhu, D.; Glownia, J. M.; Kozina, M.; Lemke, H. T.; Sikorski, M.; Feng, Y.; Nelson, S.; Saita, K.; Stankus, B.; Northey, T.; Hastings, J. B.; Weber, P. M.

2015-06-01

Structural rearrangements within single molecules occur on ultrafast time scales. Many aspects of molecular dynamics, such as the energy flow through excited states, have been studied using spectroscopic techniques, yet the goal to watch molecules evolve their geometrical structure in real time remains challenging. By mapping nuclear motions using femtosecond x-ray pulses, we have created real-space representations of the evolving dynamics during a well-known chemical reaction and show a series of time-sorted structural snapshots produced by ultrafast time-resolved hard x-ray scattering. A computational analysis optimally matches the series of scattering patterns produced by the x rays to a multitude of potential reaction paths. In so doing, we have made a critical step toward the goal of viewing chemical reactions on femtosecond time scales, opening a new direction in studies of ultrafast chemical reactions in the gas phase.

Imaging Molecular Motion: Femtosecond X-Ray Scattering of an Electrocyclic Chemical Reaction.

PubMed

Minitti, M P; Budarz, J M; Kirrander, A; Robinson, J S; Ratner, D; Lane, T J; Zhu, D; Glownia, J M; Kozina, M; Lemke, H T; Sikorski, M; Feng, Y; Nelson, S; Saita, K; Stankus, B; Northey, T; Hastings, J B; Weber, P M

2015-06-26

Structural rearrangements within single molecules occur on ultrafast time scales. Many aspects of molecular dynamics, such as the energy flow through excited states, have been studied using spectroscopic techniques, yet the goal to watch molecules evolve their geometrical structure in real time remains challenging. By mapping nuclear motions using femtosecond x-ray pulses, we have created real-space representations of the evolving dynamics during a well-known chemical reaction and show a series of time-sorted structural snapshots produced by ultrafast time-resolved hard x-ray scattering. A computational analysis optimally matches the series of scattering patterns produced by the x rays to a multitude of potential reaction paths. In so doing, we have made a critical step toward the goal of viewing chemical reactions on femtosecond time scales, opening a new direction in studies of ultrafast chemical reactions in the gas phase.

Transport relaxation processes in supercritical fluids

NASA Astrophysics Data System (ADS)

Jonas, J.

The technique for solubility measurements of solids in compressed supercritical fluids using NMR and theoretical analysis of experimental data on collision induced scattering were examined. Initial tests for a determination of solid solubilities in supercritical fluids without mixing were previously described and these preparations have continued. Super critical carbon dioxide dissolving naphthalene, for which solubility data is already available (M. McHugh, M.E. Paulaitis, J. Chem. Eng. Data, Vol. 25 (4), 1980) is being studied. This initial testing of the NMR technique for measuring solubilities in a well characterized system should prove very valuable for our later determinations with the proposed mixing probe. Systematic experimental studies of collision induced spectra in several supercritical fluids using both Raman and Rayleigh scattering are continued. The experimental work on SF6 and CH4 was finished and the experimental data testing of the various theoretical models for collision induced scattering is being analyzed.

Rebuttal to comment on “Modeling of opposition effects with ensembles of clusters: Interplay of various scattering mechanisms” by Elena V. Petrova, Victor P. Tishkovets, Klaus Jockers, 2007 [Icarus 188, 233 245

NASA Astrophysics Data System (ADS)

Petrova, Elena V.; Tishkovets, Victor P.; Jockers, Klaus

2008-04-01

Shkuratov and Zubko [Shkuratov, Yu.G., Zubko, E., 2008. Icarus 194, 850-852] criticize our paper [Petrova, E.V., Tishkovets, V.P., Jockers, K., 2007. Icarus 188, 233-245]. With this comment we reply to this criticism. We show that the experimental data and the modeling calculations presented by these authors cannot disprove the near-field effect as an important contributor to the scattering mechanisms considered in our paper.

Coherent forward scattering as a signature of Anderson metal-insulator transitions

NASA Astrophysics Data System (ADS)

Ghosh, Sanjib; Miniatura, Christian; Cherroret, Nicolas; Delande, Dominique

2017-04-01

We show that the coherent forward scattering (CFS) interference peak amplitude sharply jumps from zero to a finite value upon crossing a metal-insulator transition. Extensive numerical simulations reveal that the CFS peak contrast obeys the one-parameter scaling hypothesis and gives access to the critical exponents of the transition. We also discover that the critical CFS peak directly controls the spectral compressibility at the transition where eigenfunctions are multifractal, and we demonstrate the universality of this property with respect to various types of disorder.

Neutron and x-ray scattering study of phonon dispersion and diffuse scattering in (Na ,Bi ) Ti O3-x BaTi O3 single crystals near the morphotropic phase boundary

NASA Astrophysics Data System (ADS)

Luo, Chengtao; Bansal, Dipanshu; Li, Jiefang; Viehland, Dwight; Winn, Barry; Ren, Yang; Li, Xiaobing; Luo, Haosu; Delaire, Olivier

2017-11-01

Neutron and x-ray scattering measurements were performed on (N a1 /2B i1 /2 ) Ti O3-x at %BaTi O3 (NBT-x BT ) single crystals (x =4 , 5, 6.5, and 7.5) across the morphotropic phase boundary (MPB), as a function of both composition and temperature, and probing both structural and dynamical aspects. In addition to the known diffuse scattering pattern near the Γ points, our measurements revealed new, faint superlattice peaks, as well as an extensive diffuse scattering network, revealing a short-range ordering of polar nanoregions (PNR) with a static stacking morphology. In samples with compositions closest to the MPB, our inelastic neutron scattering investigations of the phonon dynamics showed two unusual features in the acoustic phonon branches, between the superlattice points, and between the superlattice points and Γ points, respectively. These critical elements are not present in the other compositions away from the MPB, which suggests that these features may be related to the tilt modes coupling behavior near the MPB.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pirlepesov, F.; Shin, J.; Moskvin, V. P.

Purpose: Dose weighted Linear Energy Transfer (LETd) analysis of critical structures may be useful in understanding the side effects of the proton therapy. The objective is to analyze the differences between LETd and dose distributions in brain tumor patients receiving double scattering proton therapy, to quantify LETd variation in critical organs, and to identify beam arrangements contributing to high LETd in critical organs. Methods: Monte Carlo simulations of 9 pediatric brain tumor patients were performed. The treatment plans were reconstructed with the TOPAS Monte Carlo code to calculate LETd and dose. The beam data were reconstructed proximal to the aperturemore » of the double scattering nozzle. The dose and LETd to target and critical organs including brain stem, optic chiasm, lens, optic nerve, pituitary gland, and hypothalamus were computed for each beam. Results: Greater variability in LETd compared to dose was observed in the brainstem for patients with a variety of tumor types including 5 patients with tumors located in the posterior fossa. Approximately 20%–44% brainstem volume received LETd of 5kev/µm or greater from beams within gantry angles 180°±30° for 5 patients treated with a 3 beam arrangement. Critical organs received higher LETd when located in the vicinity of the beam distal edge. Conclusion: This study presents a novel strategy in the evaluation of the proton treatment impact on critical organs. While the dose to critical organs is confined below the required limits, the LETd may have significant variation. Critical organs in the vicinity of beam distal edge receive higher LETd and depended on beam arrangement, e.g. in posterior fossa tumor treatment, brainstem receive higher LETd from posterior-anterior beams. This study shows importance of the LETd analysis of the radiation impact on the critical organs in proton therapy and may be used to explain clinical imaging observations after therapy.« less

Attenuation analysis of long-haul NLOS atmospheric optical scattering communication

NASA Astrophysics Data System (ADS)

Zhang, Shihua; Wang, Jingyuan; Xu, Zhiyong; Song, Chao; Wang, Rong; Chen, Yiwang; Zhao, Jiyong; Wei, Yimei

2016-06-01

The attenuation characteristics of ultraviolet (UV) and infrared transmitting in the atmosphere is analyzed, when long-haul Non-Line-of-Sight (NLOS) optical scattering communication is considered. The effects of Rayleigh and Mie scattering to link performance are presented. Under given geometric configurations, a critical range RC is found. When communication range is shorter than RC, the attenuation of UV is lower than that of infrared. But the path loss of UV increases rapidly, while the path loss of infrared increases much slower. When communication range is longer than RC, the attenuation of UV is higher than that of infrared. Numerical values of RC under different geometries are analyzed. It is also indicated that, under arbitrary geometric configurations, the impact of the Rayleigh scattering to infrared scattering communication is weak, but to UV scattering, the Rayleigh scattering effect cannot be ignored.

The Beginning of String Theory: A Historical Sketch

NASA Astrophysics Data System (ADS)

Vecchia, P. Di; Schwimmer, A.

In this note we follow the historical development of the ideas that led to the formulation of String Theory. We start from the inspired guess of Veneziano and its extension to the scattering of N scalar particles, then we describe how the study of its factorization properties allowed to identify the physical spectrum, and finally we discuss how the critical values of the intercept of the Regge trajectory and of the critical dimension were fixed to be α_0 =1 and d=26.

Zero-Field Ambient-Pressure Quantum Criticality in the Stoichiometric Non-Fermi Liquid System CeRhBi

NASA Astrophysics Data System (ADS)

Anand, Vivek K.; Adroja, Devashibhai T.; Hillier, Adrian D.; Shigetoh, Keisuke; Takabatake, Toshiro; Park, Je-Geun; McEwen, Keith A.; Pixley, Jedediah H.; Si, Qimiao

2018-06-01

We present the spin dynamics study of a stoichiometric non-Fermi liquid (NFL) system CeRhBi, using low-energy inelastic neutron scattering (INS) and muon spin relaxation (μSR) measurements. It shows evidence for an energy-temperature (E/T) scaling in the INS dynamic response and a time-field (t/Hη) scaling of the μSR asymmetry function indicating a quantum critical behavior in this compound. The E/T scaling reveals a local character of quantum criticality consistent with the power-law divergence of the magnetic susceptibility, logarithmic divergence of the magnetic heat capacity and T-linear resistivity at low temperature. The occurrence of NFL behavior and local criticality over a very wide dynamical range at zero field and ambient pressure without any tuning in this stoichiometric heavy fermion compound is striking, making CeRhBi a model system amenable to in-depth studies for quantum criticality.

Similarity of scattering rates in metals showing T-linear resistivity.

PubMed

Bruin, J A N; Sakai, H; Perry, R S; Mackenzie, A P

2013-02-15

Many exotic compounds, such as cuprate superconductors and heavy fermion materials, exhibit a linear in temperature (T) resistivity, the origin of which is not well understood. We found that the resistivity of the quantum critical metal Sr(3)Ru(2)O(7) is also T-linear at the critical magnetic field of 7.9 T. Using the precise existing data for the Fermi surface topography and quasiparticle velocities of Sr(3)Ru(2)O(7), we show that in the region of the T-linear resistivity, the scattering rate per kelvin is well approximated by the ratio of the Boltzmann constant to the Planck constant divided by 2π. Extending the analysis to a number of other materials reveals similar results in the T-linear region, in spite of large differences in the microscopic origins of the scattering.

Accurate in situ measurement of complex refractive index and particle size in intralipid emulsions

NASA Astrophysics Data System (ADS)

Dong, Miao L.; Goyal, Kashika G.; Worth, Bradley W.; Makkar, Sorab S.; Calhoun, William R.; Bali, Lalit M.; Bali, Samir

2013-08-01

A first accurate measurement of the complex refractive index in an intralipid emulsion is demonstrated, and thereby the average scatterer particle size using standard Mie scattering calculations is extracted. Our method is based on measurement and modeling of the reflectance of a divergent laser beam from the sample surface. In the absence of any definitive reference data for the complex refractive index or particle size in highly turbid intralipid emulsions, we base our claim of accuracy on the fact that our work offers several critically important advantages over previously reported attempts. First, our measurements are in situ in the sense that they do not require any sample dilution, thus eliminating dilution errors. Second, our theoretical model does not employ any fitting parameters other than the two quantities we seek to determine, i.e., the real and imaginary parts of the refractive index, thus eliminating ambiguities arising from multiple extraneous fitting parameters. Third, we fit the entire reflectance-versus-incident-angle data curve instead of focusing on only the critical angle region, which is just a small subset of the data. Finally, despite our use of highly scattering opaque samples, our experiment uniquely satisfies a key assumption behind the Mie scattering formalism, namely, no multiple scattering occurs. Further proof of our method's validity is given by the fact that our measured particle size finds good agreement with the value obtained by dynamic light scattering.

Accurate in situ measurement of complex refractive index and particle size in intralipid emulsions.

PubMed

Dong, Miao L; Goyal, Kashika G; Worth, Bradley W; Makkar, Sorab S; Calhoun, William R; Bali, Lalit M; Bali, Samir

2013-08-01

A first accurate measurement of the complex refractive index in an intralipid emulsion is demonstrated, and thereby the average scatterer particle size using standard Mie scattering calculations is extracted. Our method is based on measurement and modeling of the reflectance of a divergent laser beam from the sample surface. In the absence of any definitive reference data for the complex refractive index or particle size in highly turbid intralipid emulsions, we base our claim of accuracy on the fact that our work offers several critically important advantages over previously reported attempts. First, our measurements are in situ in the sense that they do not require any sample dilution, thus eliminating dilution errors. Second, our theoretical model does not employ any fitting parameters other than the two quantities we seek to determine, i.e., the real and imaginary parts of the refractive index, thus eliminating ambiguities arising from multiple extraneous fitting parameters. Third, we fit the entire reflectance-versus-incident-angle data curve instead of focusing on only the critical angle region, which is just a small subset of the data. Finally, despite our use of highly scattering opaque samples, our experiment uniquely satisfies a key assumption behind the Mie scattering formalism, namely, no multiple scattering occurs. Further proof of our method's validity is given by the fact that our measured particle size finds good agreement with the value obtained by dynamic light scattering.

Scattering theory for the radial H˙1/2-critical wave equation with a cubic convolution

NASA Astrophysics Data System (ADS)

Miao, Changxing; Zhang, Junyong; Zheng, Jiqiang

2015-12-01

In this paper, we study the global well-posedness and scattering for the wave equation with a cubic convolution ∂t2u - Δu = ± (| x | - 3 *| u | 2) u in dimensions d ≥ 4. We prove that if the radial solution u with life-span I obeys (u ,ut) ∈ Lt∞ (I H˙x 1 / 2 (Rd) × H˙x-1/2 (Rd)), then u is global and scatters. By the strategy derived from concentration compactness, we show that the proof of the global well-posedness and scattering is reduced to disprove the existence of two scenarios: soliton-like solution and high to low frequency cascade. Making use of the No-waste Duhamel formula and double Duhamel trick, we deduce that these two scenarios enjoy the additional regularity by the bootstrap argument of [7]. This together with virial analysis implies the energy of such two scenarios is zero and so we get a contradiction.

Time-of-flight scattering and recoiling spectrometry (TOF-SARS) analysis of Pt{110}. I. Quantitative structural study of the clean (1 × 2) surface

NASA Astrophysics Data System (ADS)

Masson, F.; Rabalais, J. W.

1991-08-01

The technique of time-of-flight scattering and recoiling spectrometry (TOF-SARS) is used for quantitative structural characterization of the reconstructed (1 × 2) missing-row Pt{110} clean surface. The results are presented as scans of scattered intensity versus incident angle at two scattering angles and are interpreted in terms of simple classical concepts (shadowing, blocking, focusing). Measured critical incident and exit angles corresponding to interatomic spacings unaffected by reconstruction are used to calibrate the screening constant of the interaction potential employed in the trajectory simulations. Analysis of the surface reconstruction is performed by combining experimental data and calibrated computations. The results indicate a contraction of the first-to-second interlayer spacing (-0.22 ± 0.07 Å, i.e., -16 ± 5%), a buckling of amplitude 0.19 ± 0.13 Å in the third layer and, possibly, a row-pairing in the second layer. These observations are in agreement with LEED, MEIS, GXRD, and RHEED experiments.

Monte-Carlo simulation of soil carbon measurements by inelastic neutron scattering

USDA-ARS?s Scientific Manuscript database

Measuring soil carbon is critical for assessing the potential impact of different land management practices on carbon sequestration. The inelastic neutron scattering (INS) of fast neutrons (with energy around 14 MeV) on carbon-12 nuclei produces gamma rays with energy of 4.43 MeV; this gamma flux ca...

Resonances, radiation pressure and optical scattering phenomena of drops and bubbles

NASA Technical Reports Server (NTRS)

Marston, P. L.; Goosby, S. G.; Langley, D. S.; Loporto-Arione, S. E.

1982-01-01

Acoustic levitation and the response of fluid spheres to spherical harmonic projections of the radiation pressure are described. Simplified discussions of the projections are given. A relationship between the tangential radiation stress and the Konstantinov effect is introduced and fundamental streaming patterns for drops are predicted. Experiments on the forced shape oscillation of drops are described and photographs of drop fission are displayed. Photographs of critical angle and glory scattering by bubbles and rainbow scattering by drops are displayed.

Light-scattering signal may indicate critical time zone to rescue brain tissue after hypoxia

NASA Astrophysics Data System (ADS)

Kawauchi, Satoko; Sato, Shunichi; Uozumi, Yoichi; Nawashiro, Hiroshi; Ishihara, Miya; Kikuchi, Makoto

2011-02-01

A light-scattering signal, which is sensitive to cellular/subcellular structural integrity, is a potential indicator of brain tissue viability because metabolic energy is used in part to maintain the structure of cells. We previously observed a unique triphasic scattering change (TSC) at a certain time after oxygen/glucose deprivation for blood-free rat brains; TSC almost coincided with the cerebral adenosine triphosphate (ATP) depletion. We examine whether such TSC can be observed in the presence of blood in vivo, for which transcranial diffuse reflectance measurement is performed for rat brains during hypoxia induced by nitrogen gas inhalation. At a certain time after hypoxia, diffuse reflectance intensity in the near-infrared region changes in three phases, which is shown by spectroscopic analysis to be due to scattering change in the tissue. During hypoxia, rats are reoxygenated at various time points. When the oxygen supply is started before TSC, all rats survive, whereas no rats survive when the oxygen supply is started after TSC. Survival is probabilistic when the oxygen supply is started during TSC, indicating that the period of TSC can be regarded as a critical time zone for rescuing the brain. The results demonstrate that light scattering signal can be an indicator of brain tissue reversibility.

Diffraction-controlled backscattering threshold and application to Raman gap

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rose, Harvey A.; Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87544; Mounaix, Philippe

2011-04-15

In most classic analytical models of linear stimulated scatter, light diffraction is omitted, a priori. However, modern laser optic typically includes a variant of the random phase plate [Y. Kato et al., Phys. Rev. Lett. 53, 1057 (1984)], resulting in diffraction limited laser intensity fluctuations - or localized speckles - which may result in explosive reflectivity growth as the average laser intensity approaches a critical value [H. A. Rose and D. F. DuBois, Phys. Rev. Lett. 72, 2883 (1994)]. Among the differences between stimulated Raman scatter (SRS) and stimulated Brillouin scatter is that the SRS scattered light diffracts more stronglymore » than the laser light with increase of electron density. This weakens the tendency of the SRS light to closely follow the most amplified paths, diminishing gain. Let G{sub 0} be the one-dimensional power gain exponent of the stimulated scatter. In this paper we show that differential diffraction gives rise to an increase of G{sub 0} at the SRS physical threshold with increase of electron density up to a drastic disruption of SRS as electron density approaches one fourth of its critical value from below. For three wave interaction lengths not small compared to a speckle length, this is a physically robust Raman gap mechanism.« less

Neutron scattering studies of nano-scale wood-water interactions

Treesearch

Nayomi Z. Plaza Rodriguez

2017-01-01

Understanding and controlling water in wood is critical to both improving forest products moisture durability and developing new sustainable forest products-based technologies. While wood is known to be hygroscopic, there is still a lack of understanding of the nanoscale wood-water interactions necessary for increased moisture-durability and dimensional stability. My...

CRITICAL MICELLIZATION DENSITY; A SMALL-ANGLE SCATTERING STRUCTURAL STUDY OF THE MONOMER-AGGREGATE TRANSITION OF BLOCK COPOLYMERS IN SUPERCRITICAL CO2. (R826115)

EPA Science Inventory

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

Geometric capture and escape of a microswimmer colliding with an obstacle.

PubMed

Spagnolie, Saverio E; Moreno-Flores, Gregorio R; Bartolo, Denis; Lauga, Eric

2015-05-07

Motivated by recent experiments, we consider the hydrodynamic capture of a microswimmer near a stationary spherical obstacle. Simulations of model equations show that a swimmer approaching a small spherical colloid is simply scattered. In contrast, when the colloid is larger than a critical size it acts as a passive trap: the swimmer is hydrodynamically captured along closed trajectories and endlessly orbits around the colloidal sphere. In order to gain physical insight into this hydrodynamic scattering problem, we address it analytically. We provide expressions for the critical trapping radius, the depth of the "basin of attraction," and the scattering angle, which show excellent agreement with our numerical findings. We also demonstrate and rationalize the strong impact of swimming-flow symmetries on the trapping efficiency. Finally, we give the swimmer an opportunity to escape the colloidal traps by considering the effects of Brownian, or active, diffusion. We show that in some cases the trapping time is governed by an Ornstein-Uhlenbeck process, which results in a trapping time distribution that is well-approximated as inverse-Gaussian. The predictions again compare very favorably with the numerical simulations. We envision applications of the theory to bioremediation, microorganism sorting techniques, and the study of bacterial populations in heterogeneous or porous environments.

Anomalous frequency and temperature-dependent scattering and Hund's coupling in the almost quantum critical heavy-fermion system CeFe2Ge2

NASA Astrophysics Data System (ADS)

Bossé, G.; Pan, LiDong; Li, Yize S.; Greene, L. H.; Eckstein, J.; Armitage, N. P.

2016-02-01

We present THz range optical conductivity data of a thin film of the near quantum critical heavy-fermion compound CeFe2Ge2 . Our complex conductivity measurements find a deviation from conventional Drude-like transport in a temperature range previously reported to exhibit unconventional behavior. We calculate the frequency-dependent effective mass and scattering rate using an extended Drude model analysis. We find the inelastic scattering rate can be described by a temperature-dependent power law ωn (T ), where n (T ) approaches ˜1.0 ±0.2 at 1.5 K. This is compared to the ρ ˜T1.5 behavior claimed in dc resistivity data and the ρ ˜T2 expected from Fermi-liquid theory. In addition to a low-temperature mass renormalization, we find an anomalous mass renormalization that persists to high temperature. We attribute this to a Hund's coupling in the Fe states in a manner similar to that recently proposed in the ferropnictides. CeFe2Ge2 appears to be a very interesting system where one may study the interplay between the usual 4 f lattice Kondo effect and this Hund's enhanced Kondo effect in the 3 d states.

Optimizing Nanoscale Quantitative Optical Imaging of Subfield Scattering Targets

PubMed Central

Henn, Mark-Alexander; Barnes, Bryan M.; Zhou, Hui; Sohn, Martin; Silver, Richard M.

2016-01-01

The full 3-D scattered field above finite sets of features has been shown to contain a continuum of spatial frequency information, and with novel optical microscopy techniques and electromagnetic modeling, deep-subwavelength geometrical parameters can be determined. Similarly, by using simulations, scattering geometries and experimental conditions can be established to tailor scattered fields that yield lower parametric uncertainties while decreasing the number of measurements and the area of such finite sets of features. Such optimized conditions are reported through quantitative optical imaging in 193 nm scatterfield microscopy using feature sets up to four times smaller in area than state-of-the-art critical dimension targets. PMID:27805660

Laser scattering in a hanging drop vapor diffusion apparatus for protein crystal growth in a microgravity environment

NASA Technical Reports Server (NTRS)

Casay, G. A.; Wilson, W. W.

1992-01-01

One type of hardware used to grow protein crystals in the microgravity environment aboard the U.S. Space Shuttle is a hanging drop vapor diffusion apparatus (HDVDA). In order to optimize crystal growth conditions, dynamic control of the HDVDA is desirable. A critical component in the dynamically controlled system is a detector for protein nucleation. We have constructed a laser scattering detector for the HDVDA capable of detecting the nucleation stage. The detector was successfully tested for several scatterers differing in size using dynamic light scattering techniques. In addition, the ability to detect protein nucleation using the HDVDA was demonstrated for lysozyme.

EXPERIMENTAL STUDIES OF IBS (INTRA-BEAM SCATTERING) IN RHIC AND COMPARISON WITH THEORY.

DOE Office of Scientific and Technical Information (OSTI.GOV)

FEDOTOV, A.V.; FISCHER, W.; TEPIKIAN, S.

A high-energy electron cooling system is presently being developed to overcome emittance growth due to Intra-beam Scattering (IBS) in RHIC. A critical item for choosing appropriate parameters of the cooler is an accurate description of the IBS. The analytic models were verified vs dedicated IBS measurements. Analysis of the 2004 data with the Au ions showed very good agreement for the longitudinal growth rates but significant disagreement with exact IBS models for the transverse growth rates. Experimental measurements were improved for the 2005 run with the Cu ions. Here, we present comparison of the 2005 data with theoretical models.

The conformation of Pluronic block copolymers adsorbed on carbon nanotubes and their interaction with water studied by small-angle neutron scattering

NASA Astrophysics Data System (ADS)

Cohen, Yachin; Granite, Meirav; Pyckhout-Hintzen, Wim; Radulescu, Aurel

2010-03-01

Amphiphilic block copolymers are particularly useful in dispersing single-walled carbon nanotubes (SWCNT) in water. Small-angle neutron scattering measurements conducted at different D2O/H2O content of the dispersing medium provide quantitative information on the adsorption density and conformation of the polymer interacting with the nanotube surface. Data is presented on Pluronic F108 - (EO)132(PO)50(EO)132 and F127 (EO)100(PO)65(EO)100, where EO-ethylene oxide and PO-propylene oxide, well below the critical micellization temperature of the polymer. A dense coating of the PPO blocks on the nanotube surface is determined with the PEO chains extended from the cylindrical core-shell structure. The data from the two Pluronic systems show minimal scattering at about 70% D2O in the dispersing water, which exhibit a q -1 power law of the scattering vector (q ). This indicates near matching of the polymer chains at a surprisingly high scattering length density. The model fit required considerations of tight association of water molecules around PEO chains and slight isotopic selectivity.

Neutron and x-ray scattering study of phonon dispersion and diffuse scattering in ( Na , Bi ) Ti O 3 - x BaTi O 3 single crystals near the morphotropic phase boundary

DOE PAGES

Luo, Chengtao; Bansal, Dipanshu; Li, Jiefang; ...

2017-11-10

Neutron and x-ray scattering measurements were performed on (Na 1/2Bi 1/2)TiO 3-x at % BaTiO 3 (NBT-xBT) single crystals (x = 4, 5, 6.5, and 7.5) across the morphotropic phase boundary (MPB), as a function of both composition and temperature, and probing both structural and dynamical aspects. In addition to the known diffuse scattering pattern near the gamma points, our measurements revealed new, faint superlattice peaks, as well as an extensive diffuse scattering network, revealing a short-range ordering of polar nanoregions (PNR) with a static stacking morphology. Furthermore, in samples with compositions closest to the MPB, our inelastic neutron scatteringmore » investigations of the phonon dynamics showed two unusual features in the acoustic phonon branches, between the superlattice points, and between the superlattice points and gamma points, respectively. Finally, these critical elements are not present in the other compositions away from the MPB, which suggests that these features may be related to the tilt modes coupling behavior near the MPB.« less

Neutron and x-ray scattering study of phonon dispersion and diffuse scattering in ( Na , Bi ) Ti O 3 - x BaTi O 3 single crystals near the morphotropic phase boundary

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, Chengtao; Bansal, Dipanshu; Li, Jiefang

Neutron and x-ray scattering measurements were performed on (Na 1/2Bi 1/2)TiO 3-x at % BaTiO 3 (NBT-xBT) single crystals (x = 4, 5, 6.5, and 7.5) across the morphotropic phase boundary (MPB), as a function of both composition and temperature, and probing both structural and dynamical aspects. In addition to the known diffuse scattering pattern near the gamma points, our measurements revealed new, faint superlattice peaks, as well as an extensive diffuse scattering network, revealing a short-range ordering of polar nanoregions (PNR) with a static stacking morphology. Furthermore, in samples with compositions closest to the MPB, our inelastic neutron scatteringmore » investigations of the phonon dynamics showed two unusual features in the acoustic phonon branches, between the superlattice points, and between the superlattice points and gamma points, respectively. Finally, these critical elements are not present in the other compositions away from the MPB, which suggests that these features may be related to the tilt modes coupling behavior near the MPB.« less

Design of a collective scattering system for small scale turbulence study in Korea Superconducting Tokamak Advanced Research

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, W., E-mail: woochanglee@unist.ac.kr; Lee, D. J.; Park, H. K.

The design characteristics of a multi-channel collective (or coherent) scattering system for small scale turbulence study in Korea Superconducting Tokamak Advanced Research (KSTAR), which is planned to be installed in 2017, are given in this paper. A few critical issues are discussed in depth such as the Faraday and Cotton-Mouton effects on the beam polarization, radial spatial resolution, probe beam frequency, polarization, and power. A proper and feasible optics with the 300 GHz probe beam, which was designed based on these issues, provides a simultaneous measurement of electron density fluctuations at four discrete poloidal wavenumbers up to 24 cm{sup −1}.more » The upper limit corresponds to the normalized wavenumber k{sub θ}ρ{sub e} of ∼0.15 in nominal KSTAR plasmas. To detect the scattered beam power and extract phase information, a quadrature detection system consisting of four-channel antenna/detector array and electronics will be employed.« less

Effects of mixing states on the multiple-scattering properties of soot aerosols.

PubMed

Cheng, Tianhai; Wu, Yu; Gu, Xingfa; Chen, Hao

2015-04-20

The radiative properties of soot aerosols are highly sensitive to the mixing states of black carbon particles and other aerosol components. Light absorption properties are enhanced by the mixing state of soot aerosols. Quantification of the effects of mixing states on the scattering properties of soot aerosol are still not completely resolved, especially for multiple-scattering properties. This study focuses on the effects of the mixing state on the multiple scattering of soot aerosols using the vector radiative transfer model. Two types of soot aerosols with different mixing states such as external mixture soot aerosols and internal mixture soot aerosols are studied. Upward radiance/polarization and hemispheric flux are studied with variable soot aerosol loadings for clear and haze scenarios. Our study showed dramatic changes in upward radiance/polarization due to the effects of the mixing state on the multiple scattering of soot aerosols. The relative difference in upward radiance due to the different mixing states can reach 16%, whereas the relative difference of upward polarization can reach 200%. The effects of the mixing state on the multiple-scattering properties of soot aerosols increase with increasing soot aerosol loading. The effects of the soot aerosol mixing state on upwelling hemispheric flux are much smaller than in upward radiance/polarization, which increase with increasing solar zenith angle. The relative difference in upwelling hemispheric flux due to the different soot aerosol mixing states can reach 18% when the solar zenith angle is 75°. The findings should improve our understanding of the effects of mixing states on the optical properties of soot aerosols and their effects on climate. The mixing mechanism of soot aerosols is of critical importance in evaluating the climate effects of soot aerosols, which should be explicitly included in radiative forcing models and aerosol remote sensing.

Apparent Negative Reflection with the Gradient Acoustic Metasurface by Integrating Supercell Periodicity into the Generalized Law of Reflection.

PubMed

Liu, Bingyi; Zhao, Wenyu; Jiang, Yongyuan

2016-12-05

As the two dimensional version of the functional wavefront manipulation metamaterial, metasurface has become a research hot spot for engineering the wavefront at will with a subwavelength thickness. The wave scattered by the gradient metasurface, which is composed by the periodic supercells, is governed by the generalized Snell's law. However, the critical angle that derived from the generalized Snell's law circles the domain of the incident angles that allow the occurrence of the anomalous reflection and refraction, and no free space scattering waves could exist when the incident angle is beyond the critical angle. Here we theoretically demonstrate that apparent negative reflection can be realized by a gradient acoustic metasurface when the incident angle is beyond the critical angle. The underlying mechanism of the apparent negative reflection is understood as the higher order diffraction arising from the interaction between the local phase modulation and the non-local effects introduced by the supercell periodicity. The apparent negative reflection phenomena has been perfectly verified by the calculated scattered acoustic waves of the reflected gradient acoustic metasurface. This work may provide new freedom in designing functional acoustic signal modulation devices, such as acoustic isolator and acoustic illusion device.

Global Solutions for the zero-energy Novikov–Veselov equation by inverse scattering

NASA Astrophysics Data System (ADS)

Music, Michael; Perry, Peter

2018-07-01

Using the inverse scattering method, we construct global solutions to the Novikov–Veselov equation for real-valued decaying initial data q 0 with the property that the associated Schrödinger operator is nonnegative. Such initial data are either critical (an arbitrarily small perturbation of the potential makes the operator nonpositive) or subcritical (sufficiently small perturbations of the potential preserve non-negativity of the operator). Previously, Lassas, Mueller, Siltanen and Stahel proved global existence for critical potentials, also called potentials of conductivity type. We extend their results to include the much larger class of subcritical potentials. We show that the subcritical potentials form an open set and that the critical potentials form the nowhere dense boundary of this open set. Our analysis draws on previous work of the first author and on ideas of Grinevich and Manakov.

Advancing X-ray scattering metrology using inverse genetic algorithms.

PubMed

Hannon, Adam F; Sunday, Daniel F; Windover, Donald; Kline, R Joseph

2016-01-01

We compare the speed and effectiveness of two genetic optimization algorithms to the results of statistical sampling via a Markov chain Monte Carlo algorithm to find which is the most robust method for determining real space structure in periodic gratings measured using critical dimension small angle X-ray scattering. Both a covariance matrix adaptation evolutionary strategy and differential evolution algorithm are implemented and compared using various objective functions. The algorithms and objective functions are used to minimize differences between diffraction simulations and measured diffraction data. These simulations are parameterized with an electron density model known to roughly correspond to the real space structure of our nanogratings. The study shows that for X-ray scattering data, the covariance matrix adaptation coupled with a mean-absolute error log objective function is the most efficient combination of algorithm and goodness of fit criterion for finding structures with little foreknowledge about the underlying fine scale structure features of the nanograting.

Optimization design of spectral discriminator for high-spectral-resolution lidar based on error analysis.

PubMed

Di, Huige; Zhang, Zhanfei; Hua, Hangbo; Zhang, Jiaqi; Hua, Dengxin; Wang, Yufeng; He, Tingyao

2017-03-06

Accurate aerosol optical properties could be obtained via the high spectral resolution lidar (HSRL) technique, which employs a narrow spectral filter to suppress the Rayleigh or Mie scattering in lidar return signals. The ability of the filter to suppress Rayleigh or Mie scattering is critical for HSRL. Meanwhile, it is impossible to increase the rejection of the filter without limitation. How to optimize the spectral discriminator and select the appropriate suppression rate of the signal is important to us. The HSRL technology was thoroughly studied based on error propagation. Error analyses and sensitivity studies were carried out on the transmittance characteristics of the spectral discriminator. Moreover, ratwo different spectroscopic methods for HSRL were described and compared: one is to suppress the Mie scattering; the other is to suppress the Rayleigh scattering. The corresponding HSRLs were simulated and analyzed. The results show that excessive suppression of Rayleigh scattering or Mie scattering in a high-spectral channel is not necessary if the transmittance of the spectral filter for molecular and aerosol scattering signals can be well characterized. When the ratio of transmittance of the spectral filter for aerosol scattering and molecular scattering is less than 0.1 or greater than 10, the detection error does not change much with its value. This conclusion implies that we have more choices for the high-spectral discriminator in HSRL. Moreover, the detection errors of HSRL regarding the two spectroscopic methods vary greatly with the atmospheric backscattering ratio. To reduce the detection error, it is necessary to choose a reasonable spectroscopic method. The detection method of suppressing the Rayleigh signal and extracting the Mie signal can achieve less error in a clear atmosphere, while the method of suppressing the Mie signal and extracting the Rayleigh signal can achieve less error in a polluted atmosphere.

Surface periodicity of Ir(110) from time-of-flight scattering and recoiling spectrometry (TOF-SARS)

NASA Astrophysics Data System (ADS)

Bu, H.; Shi, M.; Rabalais, J. W.

1991-03-01

The surface periodicity of the Ir(110) surface in both the clean reconstructed (1×3) and oxygen stabilized unreconstructed (1×1) phases have been investigated using time-of-flight scattering and recoiling spectrometry (TOF-SARS). A pulsed 4 keV Ar + ion beam is directed at a grazing incident angle to the surface and the scattered neutral plus ion flux is monitored as a function of beam exit angle and crystal azimuthal angle. It is demonstrated that either maxima or minima are obtained in the scattered flux along the low-index crystallographic directions depending on whether near-specular or off-specular scattering conditions, respectively, are used. These scattering intensity patterns as a function of crystal azimuthal angle provide a direct measure of the surface periodicity. These intensity variations are explained in terms of the Lindhard critical angle, semichannel focusing effects, and trajectory simulations.

Relativistic scattered wave calculations on UF6

NASA Technical Reports Server (NTRS)

Case, D. A.; Yang, C. Y.

1980-01-01

Self-consistent Dirac-Slater multiple scattering calculations are presented for UF6. The results are compared critically to other relativistic calculations, showing that the results of all molecular orbital calculations are in qualitative agreement, as measured by energy levels, population analyses, and spin-orbit splittings. A detailed comparison is made to the relativistic X alpha(RX alpha) method of Wood and Boring, which also uses multiple scattering theory, but incorporates relativistic effects in a more approximate fashion. For the most part, the RX alpha results are in agreement with the present results.

Imaging complex objects using learning tomography

NASA Astrophysics Data System (ADS)

Lim, JooWon; Goy, Alexandre; Shoreh, Morteza Hasani; Unser, Michael; Psaltis, Demetri

2018-02-01

Optical diffraction tomography (ODT) can be described using the scattering process through an inhomogeneous media. An inherent nonlinearity exists relating the scattering medium and the scattered field due to multiple scattering. Multiple scattering is often assumed to be negligible in weakly scattering media. This assumption becomes invalid as the sample gets more complex resulting in distorted image reconstructions. This issue becomes very critical when we image a complex sample. Multiple scattering can be simulated using the beam propagation method (BPM) as the forward model of ODT combined with an iterative reconstruction scheme. The iterative error reduction scheme and the multi-layer structure of BPM are similar to neural networks. Therefore we refer to our imaging method as learning tomography (LT). To fairly assess the performance of LT in imaging complex samples, we compared LT with the conventional iterative linear scheme using Mie theory which provides the ground truth. We also demonstrate the capacity of LT to image complex samples using experimental data of a biological cell.

Light Scattering in Exoplanet Transits

NASA Astrophysics Data System (ADS)

Robinson, Tyler D.; Fortney, Jonathan J.

2016-10-01

Transit spectroscopy is currently the leading technique for studying exoplanet atmospheric composition, and has led to the detection of molecular species, clouds, and/or hazes for numerous worlds outside the Solar System. The field of exoplanet transit spectroscopy will be revolutionized with the anticipated launch of NASA's James Webb Space Telescope (JWST) in 2018. Over the course of the design five year mission for JWST, the observatory is expected to provide in-depth observations of many tens of transiting exoplanets, including some worlds in the poorly understood 2-4 Earth-mass regime. As the quality of transit spectrum observations continues to improve, so should models of exoplanet transits. Thus, certain processes initially thought to be of second-order importance should be revisited and possibly added to modeling tools. For example, atmospheric refraction, which was commonly omitted from early transit spectrum models, has recently been shown to be of critical importance in some terrestrial exoplanet transits. Beyond refraction, another process that has seen little study with regards to exoplanet transits is light multiple scattering. In most cases, scattering opacity in exoplanet transits has been treated as equivalent to absorption opacity. However, this equivalence cannot always hold, such as in the case of a strongly forward scattering, weakly absorbing aerosol. In this presentation, we outline a theory of exoplanet transit spectroscopy that spans the geometric limit (used in most modern models) to a fully multiple scattering approach. We discuss a new technique for improving model efficiency that effectively separates photon paths, which tend to vary slowly in wavelength, from photon absorption, which can vary rapidly in wavelength. Using this newly developed approach, we explore situations where cloud or haze scattering may be important to JWST observations of gas giants, and comment on the conditions necessary for scattering to become a major influence on an exoplanet transit spectrum.

NEUTRON PHYSICS DIVISION ANNUAL PROGRESS REPORT. Period Ending September 1, 1962

DOE Office of Scientific and Technical Information (OSTI.GOV)

None

1963-01-11

A total of 74 subsections are included in the report. The information in 4 subsections was previously abstracted in NSA. Separate abstracts were prepared for 38 of the subsections. Those sections for which no abstracts were prepared contain information on prompt neutron lifetime, Rover critical experiments, Pu/sup 239/ fission, neutron decay, the O5R code, alpha scattering, 8 and P wavelengths, proton scattering, deuteron scattering, local optical potentials, N. S. Savamah radiation leakage, reactor shielding, cross section data analysis, gamma transport, gamma energy deposition, gaussian integration, data interpolation, neutron scattering, neutron energy deposition, space vehicles, computer analyses, shielding, positron sources, andmore » secondary particles. (J.R.D.)« less

Topographic measurement of buried thin-film interfaces using a grazing resonant soft x-ray scattering technique

NASA Astrophysics Data System (ADS)

Gann, Eliot; Watson, Anne; Tumbleston, John R.; Cochran, Justin; Yan, Hongping; Wang, Cheng; Seok, Jaewook; Chabinyc, Michael; Ade, Harald

2014-12-01

The internal structures of thin films, particularly interfaces between different materials, are critical to system properties and performance across many disciplines, but characterization of buried interface topography is often unfeasible. In this work, we demonstrate that grazing resonant soft x-ray scattering (GRSoXS), a technique measuring diffusely scattered soft x rays from grazing incidence, can reveal the statistical topography of buried thin-film interfaces. By controlling and predicting the x-ray electric field intensity throughout the depth of the film and simultaneously the scattering contrast between materials, we are able to unambiguously identify the microstructure at different interfaces of a model polymer bilayer system. We additionally demonstrate the use of GRSoXS to selectively measure the topography of the surface and buried polymer-polymer interface in an organic thin-film transistor, revealing different microstructure and markedly differing evolution upon annealing. In such systems, where only indirect control of interface topography is possible, accurate measurement of the structure of interfaces for feedback is critically important. While we demonstrate the method here using organic materials, we also show that the technique is readily extendable to any thin-film system with elemental or chemical contrasts exploitable at absorption edges.

Using seismic coda waves to resolve intrinsic and scattering attenuation

NASA Astrophysics Data System (ADS)

Wang, W.; Shearer, P. M.

2016-12-01

Seismic attenuation is caused by two factors, scattering and intrinsic absorption. Characterizing scattering and absorbing properties and the power spectrum of crustal heterogeneity is a fundamental problem for informing strong ground motion estimates at high frequencies, where scattering and attenuation effects are critical. Determining the relative amount of attenuation caused by scattering and intrinsic absorption has been a long-standing problem in seismology. The wavetrain following the direct body wave phases is called the coda, which is caused by scattered energy. Many studies have analyzed the coda of local events to constrain crustal and upper-mantle scattering strength and intrinsic attenuation. Here we examine two popular attenuation inversion methods, the Multiple Lapse Time Window Method (MLTWM) and the Coda Qc Method. First, based on our previous work on California attenuation structure, we apply an efficient and accurate method, the Monte Carlo Approach, to synthesize seismic envelope functions. We use this code to generate a series of synthetic data based on several complex and realistic forward models. Although the MLTWM assumes a uniform whole space, we use the MLTWM to invert for both scattering and intrinsic attenuation from the synthetic data to test how accurately it can recover the attenuation models. Results for the coda Qc method depend on choices for the length and starting time of the coda-wave time window. Here we explore the relation between the inversion results for Qc, the windowing parameters, and the intrinsic and scattering Q structure of our synthetic model. These results should help assess the practicality and accuracy of the Multiple Lapse Time Window Method and Coda Qc Method when applied to realistic crustal velocity and attenuation models.

Correlation between light scattering signal and tissue reversibility in rat brain exposed to hypoxia

NASA Astrophysics Data System (ADS)

Kawauchi, Satoko; Sato, Shunichi; Uozumi, Yoichi; Nawashiro, Hiroshi; Ishihara, Miya; Kikuchi, Makoto

2010-02-01

Light scattering signal is a potential indicator of tissue viability in brain because cellular and subcellular structural integrity should be associated with cell viability in brain tissue. We previously performed multiwavelength diffuse reflectance measurement for a rat global ischemic brain model and observed a unique triphasic change in light scattering at a certain time after oxygen and glucose deprivation. This triphasic scattering change (TSC) was shown to precede cerebral ATP exhaustion, suggesting that loss of brain tissue viability can be predicted by detecting scattering signal. In the present study, we examined correlation between light scattering signal and tissue reversibility in rat brain in vivo. We performed transcranial diffuse reflectance measurement for rat brain; under spontaneous respiration, hypoxia was induced for the rat by nitrogen gas inhalation and reoxygenation was started at various time points. We observed a TSC, which started at 140 +/- 15 s after starting nitrogen gas inhalation (mean +/- SD, n=8). When reoxygenation was started before the TSC, all rats survived (n=7), while no rats survived when reoxygenation was started after the TSC (n=8). When reoxygenation was started during the TSC, rats survived probabilistically (n=31). Disability of motor function was not observed for the survived rats. These results indicate that TSC can be used as an indicator of loss of tissue reversibility in brains, providing useful information on the critical time zone for treatment to rescue the brain.

Loading and testing a light scattering cell with a binary fluid mixture near its critical composition

NASA Technical Reports Server (NTRS)

Jacobs, Donald T.; Becker, James S.

1993-01-01

Critical phenomena has been the subject of physics research for many years. However, only in recent years has the research effort become intense. The current intensity has caused the study of critical phenomena to be grouped into a previous older era and a present contemporary era. Turbidity cell filling with methanol cyclohexane is one of the first steps toward a further understanding of critical phenomena. Work performed during the research period is outlined. During this period, research was spent developing apparatus and techniques that will make it possible to study critical phenomena through turbidity measurements on methanol cyclohexane. Topics covered range from the orientation of turbidity cell parts for assembly to the filling apparatus and procedure used when th cell is built. The last section will briefly cover some of the observations made when viewing the cell in a controlled water bath. However, before mention is made of the specifics of the summer research, a short introduction to critical phenomena and turbidity and how they relate to this experiment is provided.

Monitoring muscle optical scattering properties during rigor mortis

NASA Astrophysics Data System (ADS)

Xia, J.; Ranasinghesagara, J.; Ku, C. W.; Yao, G.

2007-09-01

Sarcomere is the fundamental functional unit in skeletal muscle for force generation. In addition, sarcomere structure is also an important factor that affects the eating quality of muscle food, the meat. The sarcomere structure is altered significantly during rigor mortis, which is the critical stage involved in transforming muscle to meat. In this paper, we investigated optical scattering changes during the rigor process in Sternomandibularis muscles. The measured optical scattering parameters were analyzed along with the simultaneously measured passive tension, pH value, and histology analysis. We found that the temporal changes of optical scattering, passive tension, pH value and fiber microstructures were closely correlated during the rigor process. These results suggested that sarcomere structure changes during rigor mortis can be monitored and characterized by optical scattering, which may find practical applications in predicting meat quality.

User's manual for University of Arizona APART program (Analysis Program - Arizona Radiation Trace)

NASA Technical Reports Server (NTRS)

Breault, R. P.

1975-01-01

A description and operating instructions for the Analysis Program Arizona Radiation Trace (APART) are given. This is a computer program that is able to efficiently and accurately predict the off-axis rejection characteristics of unwanted stray radiation for complex rotationally symmetric optical systems. The program first determines the critical objects or areas that scatter radiation to the image plane either directly or through imaging elements: this provides the opportunity to modify, if necessary, the design so that the number of critical areas seen by the image plane is reduced or the radiation to these critical areas is minimized. Next, the power distribution reaching the image plane and a sectional power map of all internal surfaces are computed. Angular information is also provided that relates the angle by which the radiation came into a surface to the angle by which the radiation is scattered out of the surface.

Turbidity very near the critical point of methanol-cyclohexane mixtures

NASA Technical Reports Server (NTRS)

Kopelman, R. B.; Gammon, R. W.; Moldover, M. R.

1984-01-01

The turbidity of a critical mixture of methanol and cyclohexane has been measured extremely close to the consolute point. The data span the reduced-temperature range between 10 to the -7th and 10 to the -3d, which is two decades closer to Tc than previous measurements. In this temperature range, the turbidity varies approximately as 1nt, as expected from the integrated form for Ornstein-Zernike scattering. A thin cell (200-micron optical path) with a very small volume (0.08 ml) was used to avoid multiple scattering. A carefully controlled temperature history was used to mix the sample and to minimize the effects of critical wetting layers. The data are consistent with a correlation-length amplitude of 3.9 plus or minus 1.0 A, in agreement with the value 3.5 A calculated from two-scale-factor universality and heat-capacity data from the literature.

Turbidity very near the critical point of methanol-cyclohexane mixtures

NASA Astrophysics Data System (ADS)

Kopelman, R. B.; Gammon, R. W.; Moldover, M. R.

1984-04-01

The turbidity of a critical mixture of methanol and cyclohexane has been measured extremely close to the consolute point. The data span the reduced-temperature range between 10 to the -7th and 10 to the -3d, which is two decades closer to Tc than previous measurements. In this temperature range, the turbidity varies approximately as 1nt, as expected from the integrated form for Ornstein-Zernike scattering. A thin cell (200-micron optical path) with a very small volume (0.08 ml) was used to avoid multiple scattering. A carefully controlled temperature history was used to mix the sample and to minimize the effects of critical wetting layers. The data are consistent with a correlation-length amplitude of 3.9 plus or minus 1.0 A, in agreement with the value 3.5 A calculated from two-scale-factor universality and heat-capacity data from the literature.

SU-E-T-375: Passive Scattering to Pencil-Beam-Scanning Comparison for Medulloblastoma Proton Therapy: LET Distributions and Radiobiological Implications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Giantsoudi, D; MacDonald, S; Paganetti, H

2014-06-01

Purpose: To compare the linear energy transfer (LET) distributions between passive scattering and pencil beam scanning proton radiation therapy techniques for medulloblastoma patients and study the potential radiobiological implications. Methods: A group of medulloblastoma patients, previously treated with passive scattering (PS) proton craniospinal irradiation followed by prosterior fossa or involved field boost, were selected from the patient database of our institution. Using the beam geometry and planning computed tomography (CT) image sets of the original treatment plans, pencil beam scanning (PBS) treatment plans were generated for the cranial treatment for each patient, with average beam spot size of 8mm (sigmamore » in air at isocenter). 3-dimensional dose and LET distributions were calculated by Monte Carlo methods (TOPAS) both for the original passive scattering and new pencil beam scanning treatment plans. LET volume histograms were calculated for the target and OARs and compared for the two delivery methods. Variable RBE weighted dose distributions and volume histograms were also calculated using a variable dose and LET-based model. Results: Better dose conformity was achieved with PBS planning compared to PS, leading to increased dose coverage for the boost target area and decreased average dose to the structures adjacent to it and critical structures outside the whole brain treatment field. LET values for the target were lower for PBS plans. Elevated LET values for OARs close to the boosted target areas were noticed, due to end of range of proton beams falling inside these structures, resulting in higher RBE weighted dose for these structures compared to the clinical RBE value of 1.1. Conclusion: Transitioning from passive scattering to pencil beam scanning proton radiation treatment can be dosimetrically beneficial for medulloblastoma patients. LET–guided treatment planning could contribute to better decision making for these cases, especially for critical structures at close proximity to the boosted target area.« less

Scattering of In-Plane Waves by Elastic Wedges

NASA Astrophysics Data System (ADS)

Mohammadi, K.; Asimaki, D.; Fradkin, L.

2014-12-01

The scattering of seismic waves by elastic wedges has been a topic of interest in seismology and geophysics for many decades. Analytical, semi-analytical, experimental and numerical studies on idealized wedges have provided insight into the seismic behavior of continental margins, mountain roots and crustal discontinuities. Published results, however, have almost exclusively focused on incident Rayleigh waves and out-of-plane body (SH) waves. Complementing the existing body of work, we here present results from our study on the res­ponse of elastic wedges to incident P or SV waves, an idealized pro­blem that can provide valuable insight to the understanding and parameterization of topographic ampli­fication of seismic ground mo­tion. We first show our earlier work on explicit finite difference simulations of SV-wave scattering by elastic wedges over a wide range of internal angles. We next present a semi-analytical solution that we developed using the approach proposed by Gautesen, to describe the scattered wavefield in the immediate vicinity of the wedge's tip (near-field). We use the semi-analytical solution to validate the numerical analyses, and improve resolution of the amplification factor at the wedge vertex that spikes when the internal wedge angle approaches the critical angle of incidence.

Root-cause estimation of ultrasonic scattering signatures within a complex textured titanium

NASA Astrophysics Data System (ADS)

Blackshire, James L.; Na, Jeong K.; Freed, Shaun

2016-02-01

The nondestructive evaluation of polycrystalline materials has been an active area of research for many decades, and continues to be an area of growth in recent years. Titanium alloys in particular have become a critical material system used in modern turbine engine applications, where an evaluation of the local microstructure properties of engine disk/blade components is desired for performance and remaining life assessments. Current NDE methods are often limited to estimating ensemble material properties or detecting localized voids, inclusions, or damage features within a material. Recent advances in computational NDE and material science characterization methods are providing new and unprecedented access to heterogeneous material properties, which permits microstructure-sensing interactions to be studied in detail. In the present research, Integrated Computational Materials Engineering (ICME) methods and tools are being leveraged to gain a comprehensive understanding of root-cause ultrasonic scattering processes occurring within a textured titanium aerospace material. A combination of destructive, nondestructive, and computational methods are combined within the ICME framework to collect, holistically integrate, and study complex ultrasound scattering using realistic 2-dimensional representations of the microstructure properties. Progress towards validating the computational sensing methods are discussed, along with insight into the key scattering processes occurring within the bulk microstructure, and how they manifest in pulse-echo immersion ultrasound measurements.

Apparent Negative Reflection with the Gradient Acoustic Metasurface by Integrating Supercell Periodicity into the Generalized Law of Reflection

PubMed Central

Liu, Bingyi; Zhao, Wenyu; Jiang, Yongyuan

2016-01-01

As the two dimensional version of the functional wavefront manipulation metamaterial, metasurface has become a research hot spot for engineering the wavefront at will with a subwavelength thickness. The wave scattered by the gradient metasurface, which is composed by the periodic supercells, is governed by the generalized Snell’s law. However, the critical angle that derived from the generalized Snell’s law circles the domain of the incident angles that allow the occurrence of the anomalous reflection and refraction, and no free space scattering waves could exist when the incident angle is beyond the critical angle. Here we theoretically demonstrate that apparent negative reflection can be realized by a gradient acoustic metasurface when the incident angle is beyond the critical angle. The underlying mechanism of the apparent negative reflection is understood as the higher order diffraction arising from the interaction between the local phase modulation and the non-local effects introduced by the supercell periodicity. The apparent negative reflection phenomena has been perfectly verified by the calculated scattered acoustic waves of the reflected gradient acoustic metasurface. This work may provide new freedom in designing functional acoustic signal modulation devices, such as acoustic isolator and acoustic illusion device. PMID:27917909

A Fourier-based total-field/scattered-field technique for three-dimensional broadband simulations of elastic targets near a water-sand interface.

PubMed

Shao, Yu; Wang, Shumin

2016-12-01

The numerical simulation of acoustic scattering from elastic objects near a water-sand interface is critical to underwater target identification. Frequency-domain methods are computationally expensive, especially for large-scale broadband problems. A numerical technique is proposed to enable the efficient use of finite-difference time-domain method for broadband simulations. By incorporating a total-field/scattered-field boundary, the simulation domain is restricted inside a tightly bounded region. The incident field is further synthesized by the Fourier transform for both subcritical and supercritical incidences. Finally, the scattered far field is computed using a half-space Green's function. Numerical examples are further provided to demonstrate the accuracy and efficiency of the proposed technique.

Neutron Scattering Studies of the Interplay of Amyloid β Peptide(1–40) and An Anionic Lipid 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol

DOE PAGES

Rai, Durgesh K.; Sharma, Veerendra K.; Anunciado, Divina; ...

2016-08-09

The interaction between lipid bilayers and Amyloid β peptide (Aβ) plays a critical role in proliferation of Alzheimer’s disease (AD). AD is expected to affect one in every 85 humans by 2050, and therefore, deciphering the interplay of Aβ and lipid bilayers at the molecular level is of profound importance. In this work, we applied an array of neutron scattering methods to study the structure and dynamics of Aβ(1–40) interacting 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) bilayers. In the structural investigations of lipid bilayer’s response to Aβ binding, Small Angle Neutron Scattering and Neutron Membrane Diffraction revealed that the Aβ anchors firmly to themore » highly charged DMPG bilayers in the interfacial region between water and hydrocarbon chain, and it doesn’t penetrate deeply into the bilayer. This association mode is substantiated by the dynamics studies with high resolution Quasi-Elastic Neutron Scattering experiments, showing that the addition of Aβ mainly affects the slower lateral motion of lipid molecules, especially in the fluid phase, but not the faster internal motion. The results revealed that Aβ associates with the highly charged membrane in surface with limited impact on the structure, but the altered membrane dynamics could have more influence on other membrane processes.« less

New Frontier in Probing Fluid Transport in Low-Permeability Geomedia: Applications of Elastic and Inelastic Neutron Scattering

NASA Astrophysics Data System (ADS)

Ding, M.; Hjelm, R.; Sussman, A. J.

2016-12-01

Low-permeability geomedia are prevalent in subsurface environments. They have become increasingly important in a wide range of applications such as CO2-sequestration, hydrocarbon recovery, enhanced geothermal systems, legacy waste stewardship, high-level radioactive waste disposal, and global security. The flow and transport characteristics of low-permeability geomedia are dictated by their exceedingly low permeability values ranging from 10-6 to 10-12 darcy with porosities dominated by nanoscale pores. Developing new characterization methods and robust computational models that allow estimation of transport properties of low-permeability geomedia has been identified as a critical basic research and technology development need for controlling subsurface and fluids flow. Due to its sensibility to hydrogen and flexible sample environment, neutron based elastic and inelastic scattering can, through various techniques, interrogate all the nanoscale pores in the sample whether they are fluid accessible or not, and readily characterize interfacial waters. In this presentation, we will present two studies revealing the effects of nanoscale pore confinement on fluid dynamics in geomedia. In one study, we use combined (ultra-small)/small-angle elastic neutron scatterings to probe nanoporous features responses in geological materials to transport processes. In the other study, incoherent inelastic neutron scattering was used to distingwish between intergranular pore water and fluid inclusion moisture in bedded rock salt, and to explore their thermal stablibility. Our work demonstrates that neutron based elastic and inelastic scatterings are techniques of choice for in situ probing hydrocarbon and water behavior in nanoporous materials, providing new insights into water-rock interaction and fluids transport in low-permeability geomaterials.

Probing mesoscopic crystals with electrons: One-step simultaneous inelastic and elastic scattering theory

NASA Astrophysics Data System (ADS)

Nazarov, Vladimir U.; Silkin, Vyacheslav M.; Krasovskii, Eugene E.

2017-12-01

Inelastic scattering of the medium-energy (˜10 -100 eV) electrons underlies the method of the high-resolution electron energy-loss spectroscopy (HREELS), which has been successfully used for decades to characterize pure and adsorbate-covered surfaces of solids. With the emergence of graphene and other quasi-two-dimensional (Q2D) crystals, HREELS could be expected to become the major experimental tool to study this class of materials. We, however, identify a critical flaw in the theoretical picture of the HREELS of Q2D crystals in the context of the inelastic scattering only ("energy-loss functions" formalism), in contrast to its justifiable use for bulk solids and surfaces. The shortcoming is the neglect of the elastic scattering, which we show is inseparable from the inelastic one, and which, affecting the spectra dramatically, must be taken into account for the meaningful interpretation of the experiment. With this motivation, using the time-dependent density functional theory for excitations, we build a theory of the simultaneous inelastic and elastic electron scattering at Q2D crystals. We apply this theory to HREELS of graphene, revealing an effect of the strongly coupled excitation of the π +σ plasmon and elastic diffraction resonances. Our results open a path to the theoretically interpretable study of the excitation processes in crystalline mesoscopic materials by means of HREELS, with its supreme resolution on the meV energy scale, which is far beyond the capacity of the now overwhelmingly used EELS in transmission electron microscopy.

Scattering engineering in continuously shaped metasurface: An approach for electromagnetic illusion

PubMed Central

Guo, Yinghui; Yan, Lianshan; Pan, Wei; Shao, Liyang

2016-01-01

The control of electromagnetic waves scattering is critical in wireless communications and stealth technology. Discrete metasurfaces not only increase the design and fabrication complex but also cause difficulties in obtaining simultaneous electric and optical functionality. On the other hand, discontinuous phase profiles fostered by discrete systems inevitably introduce phase noises to the scattering fields. Here we propose the principle of a scattering-harness mechanism by utilizing continuous gradient phase stemming from the spin-orbit interaction via sinusoidal metallic strips. Furthermore, by adjusting the amplitude and period of the sinusoidal metallic strip, the scattering characteristics of the underneath object can be greatly changed and thus result in electromagnetic illusion. The proposal is validated by full-wave simulations and experiment characterization in microwave band. Our approach featured by continuous phase profile, polarization independent performance and facile implementation may find widespread applications in electromagnetic wave manipulation. PMID:27439474

Scattering engineering in continuously shaped metasurface: An approach for electromagnetic illusion

NASA Astrophysics Data System (ADS)

Guo, Yinghui; Yan, Lianshan; Pan, Wei; Shao, Liyang

2016-07-01

The control of electromagnetic waves scattering is critical in wireless communications and stealth technology. Discrete metasurfaces not only increase the design and fabrication complex but also cause difficulties in obtaining simultaneous electric and optical functionality. On the other hand, discontinuous phase profiles fostered by discrete systems inevitably introduce phase noises to the scattering fields. Here we propose the principle of a scattering-harness mechanism by utilizing continuous gradient phase stemming from the spin-orbit interaction via sinusoidal metallic strips. Furthermore, by adjusting the amplitude and period of the sinusoidal metallic strip, the scattering characteristics of the underneath object can be greatly changed and thus result in electromagnetic illusion. The proposal is validated by full-wave simulations and experiment characterization in microwave band. Our approach featured by continuous phase profile, polarization independent performance and facile implementation may find widespread applications in electromagnetic wave manipulation.

What Is Actually Affected by the Scrambling of Objects When Localizing the Lateral Occipital Complex?

PubMed

Margalit, Eshed; Biederman, Irving; Tjan, Bosco S; Shah, Manan P

2017-09-01

The lateral occipital complex (LOC), the cortical region critical for shape perception, is localized with fMRI by its greater BOLD activity when viewing intact objects compared with their scrambled versions (resembling texture). Despite hundreds of studies investigating LOC, what the LOC localizer accomplishes-beyond distinguishing shape from texture-has never been resolved. By independently scattering the intact parts of objects, the axis structure defining the relations between parts was no longer defined. This led to a diminished BOLD response, despite the increase in the number of independent entities (the parts) produced by the scattering, thus indicating that LOC specifies interpart relations, in addition to specifying the shape of the parts themselves. LOC's sensitivity to relations is not confined to those between parts but is also readily apparent between objects, rendering it-and not subsequent "place" areas-as the critical region for the representation of scenes. Moreover, that these effects are witnessed with novel as well as familiar intact objects and scenes suggests that the relations are computed on the fly, rather than being retrieved from memory.

Quenched Magnon excitations by oxygen sublattice reconstruction in (SrCuO2)n/(SrTiO3)2 superlattices.

PubMed

Dantz, M; Pelliciari, J; Samal, D; Bisogni, V; Huang, Y; Olalde-Velasco, P; Strocov, V N; Koster, G; Schmitt, T

2016-09-12

The recently discovered structural reconstruction in the cuprate superlattice (SrCuO2)n/(SrTiO3)2 has been investigated across the critical value of n = 5 using resonant inelastic x-ray scattering (RIXS). We find that at the critical value of n, the cuprate layer remains largely in the bulk-like two-dimensional structure with a minority of Cu plaquettes being reconstructed. The partial reconstruction leads to quenching of the magnons starting at the Γ-point due to the minority plaquettes acting as scattering points. Although comparable in relative abundance, the doped charge impurities in electron-doped cuprate superconductors do not show this quenching of magnetic excitations.

JNK-associated scattered growth of YD-10B oral squamous carcinoma cells while maintaining the epithelial phenotype

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Gayoung; Kim, Hyun-Man

Cell scattering of epithelial carcinoma cancer cells is one of the critical event in tumorigenesis. Cells losing epithelial cohesion detach from aggregated epithelial cell masses and may migrate to fatal organs through metastasis. The present study investigated the molecular mechanism by which squamous cell carcinoma cells grow scattered at the early phase of transformation while maintaining the epithelial phenotype. We studied YD-10B cells, which are established from human oral squamous cell carcinoma, because the cells grow scattered without the development of E-cadherin junctions (ECJs) under routine culture conditions despite the high expression of functional E-cadherin. The functionality of their E-cadherinmore » was demonstrated in that YD-10B cells developed ECJs, transiently or persistently, when they were cultured on substrates coated with a low amount of fibronectin or to confluence. The phosphorylation of JNK was up-regulated in YD-10B cells compared with that in human normal oral keratinocyte cells or human squamous cell carcinoma cells, which grew aggregated along with well-organized ECJs. The suppression of JNK activity induced the aggregated growth of YD-10B cells concomitant with the development of ECJs. These results indicate for the first time that inherently up-regulated JNK activity induces the scattered growth of the oral squamous cell carcinoma cells through down-regulating the development of ECJ despite the expression of functional E-cadherin, a hallmark of the epithelial phenotype. - Highlights: • JNK dissociates YD-10B oral squamous cell carcinoma cells. • JNK suppresses the development of E-cadherin junctions of oral carcinoma cells. • Suppression of JNK activity reverses the scattered growth of oral carcinoma cells.« less

The Role of Support Staff as People Move from Congregated Settings to Group Homes and Personalized Arrangements in Ireland

ERIC Educational Resources Information Center

García Iriarte, Edurne; Stockdale, Janine; McConkey, Roy; Keogh, Fiona

2016-01-01

The movement of people with intellectual disabilities into the community is increasingly endorsed by public policy. Whilst staff are critical to a successful transition to the community, there is only scattered research on their role in supporting people to move. In this study, 32 staff and the 16 people with intellectual disabilities they…

Core–Shell Structure and Aggregation Number of Micelles Composed of Amphiphilic Block Copolymers and Amphiphilic Heterografted Polymer Brushes Determined by Small-Angle X-ray Scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Szymusiak, Magdalena; Kalkowski, Joseph; Luo, Hanying

2017-08-31

A large group of functional nanomaterials employed in biomedical applications, including targeted drug delivery, relies on amphiphilic polymers to encapsulate therapeutic payloads via self-assembly processes. Knowledge of the micelle structures will provide critical insights into design of polymeric drug delivery systems. Core–shell micelles composed of linear diblock copolymers poly(ethylene glycol)-b-poly(caprolactone) (PEG-b-PCL), poly(ethylene oxide)-b-poly(lactic acid) (PEG-b-PLA), as well as a heterografted brush consisting of a poly(glycidyl methacrylate) backbone with PEG and PLA branches (PGMA-g-PEG/PLA) were characterized by dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) measurements to gain structural information regarding the particle morphology, core–shell size, and aggregation number. Themore » structural information at this quasi-equilibrium state can also be used as a reference when studying the kinetics of polymer micellization.« less

Core–Shell Structure and Aggregation Number of Micelles Composed of Amphiphilic Block Copolymers and Amphiphilic Heterografted Polymer Brushes Determined by Small-Angle X-ray Scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Szymusiak, Magdalena; Kalkowski, Joseph; Luo, Hanying

2017-08-16

A large group of functional nanomaterials employed in biomedical applications, including targeted drug delivery, relies on amphiphilic polymers to encapsulate therapeutic payloads via self-assembly processes. Knowledge of the micelle structures will provide critical insights into design of polymeric drug delivery systems. Core–shell micelles composed of linear diblock copolymers poly(ethylene glycol)-b-poly(caprolactone) (PEG-b-PCL), poly(ethylene oxide)-b-poly(lactic acid) (PEG-b-PLA), as well as a heterografted brush consisting of a poly(glycidyl methacrylate) backbone with PEG and PLA branches (PGMA-g-PEG/PLA) were characterized by dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) measurements to gain structural information regarding the particle morphology, core–shell size, and aggregation number. Themore » structural information at this quasi-equilibrium state can also be used as a reference when studying the kinetics of polymer micellization.« less

Stability of Weyl metals under impurity scattering

NASA Astrophysics Data System (ADS)

Huang, Zhoushen; Das, Tanmoy; Balatsky, Alexander V.; Arovas, Daniel P.

2013-04-01

We investigate the effects of bulk impurities on the electronic spectrum of Weyl semimetals, a recently identified class of Dirac-type materials. Using a T-matrix approach, we study resonant scattering due to a localized impurity in tight-binding versions of the continuum models recently discussed by [Burkov, Hook, and Balents, Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.84.235126 84, 235126 (2011)], describing perturbed four-component Dirac fermions in the vicinity of a critical point. The impurity potential is described by a strength g as well as a matrix structure Λ. Unlike the case in d-wave superconductors, where a zero energy resonance can always be induced by varying the scalar and/or magnetic impurity strength, we find that for certain types of impurity (Λ), the Weyl node is protected and that a scalar impurity will induce an intragap resonance over a wide range of scattering strength. A general framework is developed to address this question, as well as to determine the dependence of resonance energy on the impurity strength.

Electronic Raman scattering as an ultra-sensitive probe of strain effects in semiconductors

DOE PAGES

Fluegel., Brian; Mialitsin, Aleksej V.; Beaton, Daniel A.; ...

2015-05-28

In this study, the semiconductor strain engineering has become a critical feature of high-performance electronics because of the significant device performance enhancements that it enables. These improvements, which emerge from strain-induced modifications to the electronic band structure, necessitate new ultra-sensitive tools to probe the strain in semiconductors. Here, we demonstrate that minute amounts of strain in thin semiconductor epilayers can be measured using electronic Raman scattering. We applied this strain measurement technique to two different semiconductor alloy systems using coherently strained epitaxial thin films specifically designed to produce lattice-mismatch strains as small as 10 –4. Comparing our strain sensitivity andmore » signal strength in Al xGa 1–xAs with those obtained using the industry-standard technique of phonon Raman scattering, we found that there was a sensitivity improvement of 200-fold and a signal enhancement of 4 × 10 3, thus obviating key constraints in semiconductor strain metrology.« less

Relativistic Eulerian Vlasov simulations of the amplification of seed pulses by Brillouin backscattering in plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shoucri, M., E-mail: Shoucri.Magdi@ireq.ca; Matte, J.-P.; Vidal, F.

We apply an Eulerian Vlasov code to study the amplification by Brillouin scattering of a short seed laser pulse by a long pump laser pulse in an underdense plasma. The stimulated Brillouin backscattering interaction is the coupling of the pump and seed electromagnetic waves propagating in opposite directions, and the ion plasma wave. The code solves the one-dimensional relativistic Vlasov-Maxwell set of equations. Large amplitude ion waves are generated. In the simulations we present, the density plateau of the plasma is n{sub e}=0.3 n{sub c} (n{sub c} is the critical density), which excludes spurious stimulated Raman scattering amplification (which can occurmore » only if n{sub e}« less

Laser Speckle Contrast Imaging: theory, instrumentation and applications.

PubMed

Senarathna, Janaka; Rege, Abhishek; Li, Nan; Thakor, Nitish V

2013-01-01

Laser Speckle Contrast Imaging (LSCI) is a wide field of view, non scanning optical technique for observing blood flow. Speckles are produced when coherent light scattered back from biological tissue is diffracted through the limiting aperture of focusing optics. Mobile scatterers cause the speckle pattern to blur; a model can be constructed by inversely relating the degree of blur, termed speckle contrast to the scatterer speed. In tissue, red blood cells are the main source of moving scatterers. Therefore, blood flow acts as a virtual contrast agent, outlining blood vessels. The spatial resolution (~10 μm) and temporal resolution (10 ms to 10 s) of LSCI can be tailored to the application. Restricted by the penetration depth of light, LSCI can only visualize superficial blood flow. Additionally, due to its non scanning nature, LSCI is unable to provide depth resolved images. The simple setup and non-dependence on exogenous contrast agents have made LSCI a popular tool for studying vascular structure and blood flow dynamics. We discuss the theory and practice of LSCI and critically analyze its merit in major areas of application such as retinal imaging, imaging of skin perfusion as well as imaging of neurophysiology.

Attenuation of Scattered Thermal Energy Atomic Oxygen

NASA Technical Reports Server (NTRS)

Banks, Bruce a.; Seroka, Katelyn T.; McPhate, Jason B.; Miller, Sharon K.

2011-01-01

The attenuation of scattered thermal energy atomic oxygen is relevant to the potential damage that can occur within a spacecraft which sweeps through atomic oxygen in low Earth orbit (LEO). Although there can be significant oxidation and resulting degradation of polymers and some metals on the external surfaces of spacecraft, there are often openings on a spacecraft such as telescope apertures, vents, and microwave cavities that can allow atomic oxygen to enter and scatter internally to the spacecraft. Atomic oxygen that enters a spacecraft can thermally accommodate and scatter to ultimately react or recombine on surfaces. The atomic oxygen that does enter a spacecraft can be scavenged by use of high erosion yield polymers to reduce its reaction on critical surfaces and materials. Polyoxymethylene and polyethylene can be used as effective atomic oxygen scavenging polymers.

Critical behavior in trapped strongly interacting Fermi gases

NASA Astrophysics Data System (ADS)

Taylor, E.

2009-08-01

We investigate the width of the Ginzburg critical region and experimental signatures of critical behavior in strongly interacting trapped Fermi gases close to unitarity, where the s -wave scattering length diverges. Despite the fact that the width of the critical region is of the order unity, evidence of critical behavior in the bulk thermodynamics of trapped gases is strongly suppressed by their inhomogeneity. The specific heat of a harmonically confined gas, for instance, is linear in the reduced temperature t=(T-Tc)/Tc above Tc . We also discuss the prospects of observing critical behavior in the local compressibility from measurements of the density profile.

Driving a Superconductor to Insulator Transition with Random Gauge Fields.

PubMed

Nguyen, H Q; Hollen, S M; Shainline, J; Xu, J M; Valles, J M

2016-11-30

Typically the disorder that alters the interference of particle waves to produce Anderson localization is potential scattering from randomly placed impurities. Here we show that disorder in the form of random gauge fields that act directly on particle phases can also drive localization. We present evidence of a superfluid bose glass to insulator transition at a critical level of this gauge field disorder in a nano-patterned array of amorphous Bi islands. This transition shows signs of metallic transport near the critical point characterized by a resistance , indicative of a quantum phase transition. The critical disorder depends on interisland coupling in agreement with recent Quantum Monte Carlo simulations. We discuss how this disorder tuned SIT differs from the common frustration tuned SIT that also occurs in magnetic fields. Its discovery enables new high fidelity comparisons between theoretical and experimental studies of disorder effects on quantum critical systems.

Laser-induced stimulated Raman scattering in the forward direction of a droplet - Comparison of Mie theory with geometrical optics

NASA Technical Reports Server (NTRS)

Srivastava, Vandana; Jarzembski, Maurice A.

1991-01-01

This paper uses Mie theory to treat electromagnetic scattering and to evaluate field enhancement in the forward direction of a small droplet irradiated by a high-energy beam and compares the results of calculations with the field-enhancement evaluation obtained via geometrical optics treatment. Results of this comparison suggest that the field enhancement located at the critical ring region encircling the axis in the forward direction of the droplet can support laser-induced Raman scattering. The results are supported by experimental observations of the interaction of a 120-micron-diam water droplet with a high-energy Nd:YAG laser beam.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaminsky, G.; Belanger, David P.; Ye, Feng

We use polarized neutron scattering to characterize the Bragg scattering intensity below T C=89.5 K at the (1,0,0) pseudocubic nuclear Bragg point of LaCoO 3. Upon cooling in a field (FC), a net magnetic moment is apparent in Bragg scattering intensity, just as it was in previous magnetization measurements. Critical behavior associated with the net moment near T C upon cooling in small applied fields rapidly rounds with increasing field strength. We show, using a mean-field calculation, that this net moment can develop in a metastable state that forms upon FC, even when all the interactions in the system aremore » antiferromagnetic.« less

Origin of the net magnetic moment in LaCoO3

NASA Astrophysics Data System (ADS)

Kaminsky, G. M.; Belanger, D. P.; Ye, F.; Fernandez-Baca, J. A.; Wang, J.; Matsuda, M.; Yan, J.-Q.

2018-01-01

We use polarized neutron scattering to characterize the Bragg scattering intensity below TC=89.5 K at the (1,0,0) pseudocubic nuclear Bragg point of LaCoO3. Upon cooling in a field (FC), a net magnetic moment is apparent in Bragg scattering intensity, just as it was in previous magnetization measurements. Critical behavior associated with the net moment near TC upon cooling in small applied fields rapidly rounds with increasing field strength. We show, using a mean-field calculation, that this net moment can develop in a metastable state that forms upon FC, even when all the interactions in the system are antiferromagnetic.

On-the-Fly Generation of Differential Resonance Scattering Probability Distribution Functions for Monte Carlo Codes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davidson, Eva E.; Martin, William R.

Current Monte Carlo codes use one of three models: (1) the asymptotic scattering model, (2) the free gas scattering model, or (3) the S(α,β) model, depending on the neutron energy and the specific Monte Carlo code. This thesis addresses the consequences of using the free gas scattering model, which assumes that the neutron interacts with atoms in thermal motion in a monatomic gas in thermal equilibrium at material temperature, T. Most importantly, the free gas model assumes the scattering cross section is constant over the neutron energy range, which is usually a good approximation for light nuclei, but not formore » heavy nuclei where the scattering cross section may have several resonances in the epithermal region. Several researchers in the field have shown that the exact resonance scattering model is temperaturedependent, and neglecting the resonances in the lower epithermal range can under-predict resonance absorption due to the upscattering phenomenon mentioned above, leading to an over-prediction of keff by several hundred pcm. Existing methods to address this issue involve changing the neutron weights or implementing an extra rejection scheme in the free gas sampling scheme, and these all involve performing the collision analysis in the center-of-mass frame, followed by a conversion back to the laboratory frame to continue the random walk of the neutron. The goal of this paper was to develop a sampling methodology that (1) accounted for the energydependent scattering cross sections in the collision analysis and (2) was performed in the laboratory frame,avoiding the conversion to the center-of-mass frame. The energy dependence of the scattering cross section was modeled with even-ordered polynomials (2nd and 4th order) to approximate the scattering cross section in Blackshaw’s equations for the moments of the differential scattering PDFs. These moments were used to sample the outgoing neutron speed and angle in the laboratory frame on-the-fly during the random walk of the neutron. Results for criticality studies on fuel pin and fuel assembly calculations using methods developed in this dissertation showed very close comparison to results using the reference Dopplerbroadened rejection correction (DBRC) scheme.« less

On-the-Fly Generation of Differential Resonance Scattering Probability Distribution Functions for Monte Carlo Codes

DOE PAGES

Davidson, Eva E.; Martin, William R.

2017-05-26

Current Monte Carlo codes use one of three models: (1) the asymptotic scattering model, (2) the free gas scattering model, or (3) the S(α,β) model, depending on the neutron energy and the specific Monte Carlo code. This thesis addresses the consequences of using the free gas scattering model, which assumes that the neutron interacts with atoms in thermal motion in a monatomic gas in thermal equilibrium at material temperature, T. Most importantly, the free gas model assumes the scattering cross section is constant over the neutron energy range, which is usually a good approximation for light nuclei, but not formore » heavy nuclei where the scattering cross section may have several resonances in the epithermal region. Several researchers in the field have shown that the exact resonance scattering model is temperaturedependent, and neglecting the resonances in the lower epithermal range can under-predict resonance absorption due to the upscattering phenomenon mentioned above, leading to an over-prediction of keff by several hundred pcm. Existing methods to address this issue involve changing the neutron weights or implementing an extra rejection scheme in the free gas sampling scheme, and these all involve performing the collision analysis in the center-of-mass frame, followed by a conversion back to the laboratory frame to continue the random walk of the neutron. The goal of this paper was to develop a sampling methodology that (1) accounted for the energydependent scattering cross sections in the collision analysis and (2) was performed in the laboratory frame,avoiding the conversion to the center-of-mass frame. The energy dependence of the scattering cross section was modeled with even-ordered polynomials (2nd and 4th order) to approximate the scattering cross section in Blackshaw’s equations for the moments of the differential scattering PDFs. These moments were used to sample the outgoing neutron speed and angle in the laboratory frame on-the-fly during the random walk of the neutron. Results for criticality studies on fuel pin and fuel assembly calculations using methods developed in this dissertation showed very close comparison to results using the reference Dopplerbroadened rejection correction (DBRC) scheme.« less

Critical Reflectance Derived from MODIS: Application for the Retrieval of Aerosol Absorption over Desert Regions

NASA Technical Reports Server (NTRS)

Wells, Kelley C.; Martins, J. Vanderlei; Remer, Lorraine A.; Kreidenweis, Sonia M.; Stephens, Graeme L.

2012-01-01

Aerosols are tiny suspended particles in the atmosphere that scatter and absorb sunlight. Smoke particles are aerosols, as are sea salt, particulate pollution and airborne dust. When you look down at the earth from space sometimes you can see vast palls of whitish smoke or brownish dust being transported by winds. The reason that you can see these aerosols is because they are reflecting incoming sunlight back to the view in space. The reason for the difference in color between the different types of aerosol is that the particles arc also absorbing sunlight at different wavelengths. Dust appears brownish or reddish because it absorbs light in the blue wavelengths and scatters more reddish light to space, Knowing how much light is scattered versus how much is absorbed, and knowin that as a function of wavelength is essential to being able to quantify the role aerosols play in the energy balance of the earth and in climate change. It is not easy measuring the absorption properties of aerosols when they are suspended in the atmosphere. People have been doing this one substance at a time in the laboratory, but substances mix when they are in the atmosphere and the net absorption effect of all the particles in a column of air is a goal of remote sensing that has not yet been completely successful. In this paper we use a technique based on observing the point at which aerosols change from brightening the surface beneath to darkening it. If aerosols brighten a surface. they must scatter more light to space. If they darken the surface. they must be absorbing more. That cross over point is called the critical reflectance and in this paper we show that critical reflectance is a monotonic function of the intrinsic absorption properties of the particles. This parameter we call the single scattering albedo. We apply the technique to MODIS imagery over the Sahara and Sahel regions to retrieve the single scattering albedo in seven wavelengths, compare these retrievals to ground-based retrievals from AERONET instruments and compute error bars on each retrieval. The results show that we can retrieve single scattering albedo for pure dust to within +/-0.02 and mixtures of dust and smoke to within +/-0.03. No other space based instrument has achieved a retrieval of single scattering albedo that spans the spectrum from 0.47 microns to 2.13 microns and produces regional maps of aerosol absorption showing gradients and changes. Applied in a more operational fashion, such information will narrow uncertainties in estimating aerosol forcing on climate.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grebogi, C.; Yorke, J.A.

This report discusses the following topics: controlling chaotic dynamical systems; embedding of experimental data; effect of noise on critical exponents of crises; transition to chaotic scattering; and distribution of floaters on a fluid surface. (LSP)

Structural studies of Neurospora crassa LPMO9D and redox partner CDHIIA using neutron crystallography and small-angle scattering.

PubMed

Bodenheimer, Annette M; O'Dell, William B; Stanley, Christopher B; Meilleur, Flora

2017-08-07

Sensitivity to hydrogen/deuterium and lack of observable radiation damage makes cold neutrons an ideal probe the structural studies of proteins with highly photosensitive groups such as the copper center of lytic polysaccharide monooxygenases (LPMOs) and flavin adenine dinucleotide (FAD) and heme redox cofactors of cellobiose dehydrogenases (CDHs). Here, neutron crystallography and small-angle neutron scattering are used to investigate Neurospora crassa LPMO9D (NcLPMO9D) and CDHIIA (NcCDHIIA), respectively. The presence of LPMO greatly enhances the efficiency of commercial glycoside hydrolase cocktails in the depolymerization of cellulose. LPMOs can receive electrons from CDHs to activate molecular dioxygen for the oxidation of cellulose resulting in chain cleavage and disruption of local crystallinity. Using neutron protein crystallography, the hydrogen/deuterium atoms of NcLPMO9D could be located throughout the structure. At the copper active site, the protonation states of the side chains of His1, His84, His157 and Tyr168, and the orientation of water molecules could be determined. Small-angle neutron scattering measurements provided low resolution models of NcCDHIIA with both the dehydrogenase and cytochrome domains in oxidized states that exhibited elongated conformations. This work demonstrates the suitability of neutron diffraction and scattering for characterizing enzymes critical to oxidative cellulose deconstruction. Copyright © 2017 Elsevier Ltd. All rights reserved.

A conservative spectral method for the Boltzmann equation with anisotropic scattering and the grazing collisions limit

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gamba, Irene M.; ICES, The University of Texas at Austin, 201 E. 24th St., Stop C0200, Austin, TX 78712; Haack, Jeffrey R.

2014-08-01

We present the formulation of a conservative spectral method for the Boltzmann collision operator with anisotropic scattering cross-sections. The method is an extension of the conservative spectral method of Gamba and Tharkabhushanam [17,18], which uses the weak form of the collision operator to represent the collisional term as a weighted convolution in Fourier space. The method is tested by computing the collision operator with a suitably cut-off angular cross section and comparing the results with the solution of the Landau equation. We analytically study the convergence rate of the Fourier transformed Boltzmann collision operator in the grazing collisions limit tomore » the Fourier transformed Landau collision operator under the assumption of some regularity and decay conditions of the solution to the Boltzmann equation. Our results show that the angular singularity which corresponds to the Rutherford scattering cross section is the critical singularity for which a grazing collision limit exists for the Boltzmann operator. Additionally, we numerically study the differences between homogeneous solutions of the Boltzmann equation with the Rutherford scattering cross section and an artificial cross section, which give convergence to solutions of the Landau equation at different asymptotic rates. We numerically show the rate of the approximation as well as the consequences for the rate of entropy decay for homogeneous solutions of the Boltzmann equation and Landau equation.« less

Structural studies of Neurospora crassa LPMO9D and redox partner CDHIIA using neutron crystallography and small-angle scattering

DOE PAGES

Bodenheimer, Annette M.; O'Dell, William B.; Stanley, Christopher B.; ...

2017-03-04

Sensitivity to hydrogen/deuterium and lack of observable radiation damage makes cold neutrons an ideal probe the structural studies of proteins with highly photosensitive groups such as the copper center of lytic polysaccharide monooxygenases (LPMOs) and flavin adenine dinucleotide (FAD) and heme redox cofactors of cellobiose dehydrogenases (CDHs). In this paper, neutron crystallography and small-angle neutron scattering are used to investigate Neurospora crassa LPMO9D (NcLPMO9D) and CDHIIA (NcCDHIIA), respectively. The presence of LPMO greatly enhances the efficiency of commercial glycoside hydrolase cocktails in the depolymerization of cellulose. LPMOs can receive electrons from CDHs to activate molecular dioxygen for the oxidation ofmore » cellulose resulting in chain cleavage and disruption of local crystallinity. Using neutron protein crystallography, the hydrogen/deuterium atoms of NcLPMO9D could be located throughout the structure. At the copper active site, the protonation states of the side chains of His1, His84, His157 and Tyr168, and the orientation of water molecules could be determined. Small-angle neutron scattering measurements provided low resolution models of NcCDHIIA with both the dehydrogenase and cytochrome domains in oxidized states that exhibited elongated conformations. Finally, this work demonstrates the suitability of neutron diffraction and scattering for characterizing enzymes critical to oxidative cellulose deconstruction.« less

Structural studies of Neurospora crassa LPMO9D and redox partner CDHIIA using neutron crystallography and small-angle scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bodenheimer, Annette M.; O'Dell, William B.; Stanley, Christopher B.

Sensitivity to hydrogen/deuterium and lack of observable radiation damage makes cold neutrons an ideal probe the structural studies of proteins with highly photosensitive groups such as the copper center of lytic polysaccharide monooxygenases (LPMOs) and flavin adenine dinucleotide (FAD) and heme redox cofactors of cellobiose dehydrogenases (CDHs). In this paper, neutron crystallography and small-angle neutron scattering are used to investigate Neurospora crassa LPMO9D (NcLPMO9D) and CDHIIA (NcCDHIIA), respectively. The presence of LPMO greatly enhances the efficiency of commercial glycoside hydrolase cocktails in the depolymerization of cellulose. LPMOs can receive electrons from CDHs to activate molecular dioxygen for the oxidation ofmore » cellulose resulting in chain cleavage and disruption of local crystallinity. Using neutron protein crystallography, the hydrogen/deuterium atoms of NcLPMO9D could be located throughout the structure. At the copper active site, the protonation states of the side chains of His1, His84, His157 and Tyr168, and the orientation of water molecules could be determined. Small-angle neutron scattering measurements provided low resolution models of NcCDHIIA with both the dehydrogenase and cytochrome domains in oxidized states that exhibited elongated conformations. Finally, this work demonstrates the suitability of neutron diffraction and scattering for characterizing enzymes critical to oxidative cellulose deconstruction.« less

Metastability versus collapse following a quench in attractive Bose-Einstein condensates

NASA Astrophysics Data System (ADS)

Golde, Jake; Ruhl, Joanna; Olshanii, Maxim; Dunjko, Vanja; Datta, Sumita; Malomed, Boris A.

2018-05-01

We consider a Bose-Einstein condensate (BEC) with attractive two-body interactions in a cigar-shaped trap, initially prepared in its ground state for a given negative scattering length, which is quenched to a larger absolute value of the scattering length. Using the mean-field approximation, we compute numerically, for an experimentally relevant range of aspect ratios and initial strengths of the coupling, two critical values of quench. One corresponds to the weakest attraction strength, the quench to which causes the system to collapse before completing even a single return from the narrow configuration (pericenter) in its breathing cycle. The other is a similar critical point for the occurrence of collapse before completing two returns. In the latter case, we also compute the limiting value, as we keep increasing the strength of the postquench attraction towards its critical value, of the time interval between the first two pericenters. We also use a Gaussian variational model to estimate the critical quenched attraction strength below which the system is stable against the collapse for long times. These time intervals and critical attraction strengths, apart from being fundamental properties of nonlinear dynamics of self-attractive BECs, may provide clues to the design of upcoming experiments that are trying to create robust BEC breathers.

Differential and integral cross sections for the rotationally inelastic scattering of methyl radicals with H2 and D2

NASA Astrophysics Data System (ADS)

Tkáč, Ondřej; Ma, Qianli; Rusher, Cassandra A.; Greaves, Stuart J.; Orr-Ewing, Andrew J.; Dagdigian, Paul J.

2014-05-01

Comparisons are presented of experimental and theoretical studies of the rotationally inelastic scattering of CD3 radicals with H2 and D2 collision partners at respective collision energies of 680 ± 75 and 640 ± 60 cm-1. Close-coupling quantum-mechanical calculations performed using a newly constructed ab initio potential energy surface (PES) provide initial-to-final CD3 rotational level (n, k → n', k') integral and differential cross sections (ICSs and DCSs). The DCSs are compared with crossed molecular beam and velocity map imaging measurements of angular scattering distributions, which serve as a critical test of the accuracy of the new PES. In general, there is very good agreement between the experimental measurements and the calculations. The DCSs for CD3 scattering from both H2 and D2 peak in the forward hemisphere for n' = 2-4 and shift more to sideways and backward scattering for n' = 5. For n' = 6-8, the DCSs are dominated by backward scattering. DCSs for a particular CD3 n → n' transition have a similar angular dependence with either D2 or H2 as collision partner. Any differences between DCSs or ICSs can be attributed to mass effects because the PES is unchanged for CD3-H2 and CD3-D2 collisions. Further comparisons are drawn between the CD3-D2 scattering and results for CD3-He presented in our recent paper [O. Tkáč, A. G. Sage, S. J. Greaves, A. J. Orr-Ewing, P. J. Dagdigian, Q. Ma, and M. H. Alexander, Chem. Sci. 4, 4199 (2013)]. These systems have the same reduced mass, but are governed by different PESs.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, H; Medin, P; Jiang, S

Purpose: In-treatment tumor localization is critical for the management of tumor motion in lung cancer radiotherapy. Conventional tumor-tracking methods using a kV or MV x-ray projection has limited contrast. To facilitate real-time, marker-less and low-dose in-treatment image tumor tracking, we propose a novel scheme using Compton scatter imaging. This study reports Monte Carlo (MC) simulations on this scheme for the purpose of proof-of-principle. Methods: A slit x-ray beam along the patient superior-inferior (SI) direction is directed to the patient, intersecting the patient lung at a 2D plane containing majority part of the tumor motion trajectory. X-ray photons are scattered duemore » to Compton effect from this plane, which are spatially collimated by, e.g., a pinhole, on one side of the plane and then captured by a detector behind it. The captured image, after correcting for x-ray attenuation and scatter angle variation, reflects the electron density, which allows visualization of the instantaneous anatomy on this plane. We performed MC studies on a phantom and a patient case for the initial test of this proposed method. Results: In the phantom case, the contrast-resolution calculated using tumor/lung as foreground/background for kV fluoroscopy, cone-beam CT, and scattering image were 0.0625, 0.6993, and 0.5290, respectively. In the patient case, tumor motion can be clearly observed in the scatter images. Compared to fluoroscopy, scattering imaging also significantly reduced imaging dose because of its narrower beam design. Conclusion: MC simulation studies demonstrated the potential of the proposed scheme in terms of capturing the instantaneous anatomy of a patient on a 2D plane. Clear visualization of the tumor will probably facilitate ‘marker-less’ and ‘real-time’ tumor tracking with low imaging dose. NIH (1R01CA154747-01, 1R21CA178787-01A1 and 1R21EB017978-01A1)« less

Scattering of acoustic evanescent waves by circular cylinders: Partial wave series solution

NASA Astrophysics Data System (ADS)

Marston, Philip L.

2002-05-01

Evanescent acoustical waves occur in a variety of situations such as when sound is incident on a fluid interface beyond the critical angle and when flexural waves on a plate are subsonic with respect to the surrounding fluid. The scattering by circular cylinders at normal incidence was calculated to give insight into the consequences on the scattering of the evanescence of the incident wave. To analyze the scattering, it is necessary to express the incident wave using a modified expansion involving cylindrical functions. For plane evanescent waves, the expansion becomes a double summation with products of modified and ordinary Bessel functions. The resulting modified series is found for the scattering by a fluid cylinder in an unbounded medium. The perfectly soft and rigid cases are also examined. Unlike the case of an ordinary incident wave, the counterpropagating partial waves of the same angular order have unequal magnitudes when the incident wave is evanescent. This is a consequence of the exponential dependence of the incident wave amplitude on the transverse coordinate. The associated exponential dependence of the scattering on the location of a scatterer was previously demonstrated [T. J. Matula and P. L. Marston, J. Acoust. Soc. Am. 93, 1192-1195 (1993)].

Diffuse scattering in relaxor ferroelectrics: true three-dimensional mapping, experimental artefacts and modelling.

PubMed

Bosak, A; Chernyshov, D; Vakhrushev, Sergey; Krisch, M

2012-01-01

The available body of experimental data in terms of the relaxor-specific component of diffuse scattering is critically analysed and a collection of related models is reviewed; the sources of experimental artefacts and consequent failures of modelling efforts are enumerated. Furthermore, it is shown that the widely used concept of polar nanoregions as individual static entities is incompatible with the experimental diffuse scattering results. Based on the synchrotron diffuse scattering three-dimensional data set taken for the prototypical ferroelectric relaxor lead magnesium niobate-lead titanate (PMN-PT), a new parameterization of diffuse scattering in relaxors is presented and a simple phenomenological picture is proposed to explain the unusual properties of the relaxor behaviour. The model assumes a specific slowly changing displacement pattern, which is indirectly controlled by the low-energy acoustic phonons of the system. The model provides a qualitative but rather detailed explanation of temperature, pressure and electric-field dependence of diffuse neutron and X-ray scattering, as well as of the existence of a hierarchy in the relaxation times of these materials.

Determination of the pion-nucleon coupling constant and scattering lengths

NASA Astrophysics Data System (ADS)

Ericson, T. E.; Loiseau, B.; Thomas, A. W.

2002-07-01

We critically evaluate the isovector Goldberger-Miyazawa-Oehme (GMO) sum rule for forward πN scattering using the recent precision measurements of π-p and π-d scattering lengths from pionic atoms. We deduce the charged-pion-nucleon coupling constant, with careful attention to systematic and statistical uncertainties. This determination gives, directly from data, g2c(GMO)/ 4π=14.11+/-0.05(statistical)+/-0.19(systematic) or f2c/4π=0.0783(11). This value is intermediate between that of indirect methods and the direct determination from backward np differential scattering cross sections. We also use the pionic atom data to deduce the coherent symmetric and antisymmetric sums of the pion-proton and pion-neutron scattering lengths with high precision, namely, (aπ-p+aπ-n)/2=[- 12+/-2(statistical)+/-8(systematic)]×10-4 m-1π and (aπ-p-aπ- n)/2=[895+/-3(statistical)+/-13 (systematic)]×10-4 m-1π. For the need of the present analysis, we improve the theoretical description of the pion-deuteron scattering length.

Analysis of small crack behavior for airframe applications

NASA Technical Reports Server (NTRS)

Mcclung, R. C.; Chan, K. S.; Hudak, S. J., Jr.; Davidson, D. L.

1994-01-01

The small fatigue crack problem is critically reviewed from the perspective of airframe applications. Different types of small cracks-microstructural, mechanical, and chemical-are carefully defined and relevant mechanisms identified. Appropriate analysis techniques, including both rigorous scientific and practical engineering treatments, are briefly described. Important materials data issues are addressed, including increased scatter in small crack data and recommended small crack test methods. Key problems requiring further study are highlighted.

Sphere-to-rod transition of non-surface-active amphiphilic diblock copolymer micelles: a small-angle neutron scattering study.

PubMed

Kaewsaiha, Ploysai; Matsumoto, Kozo; Matsuoka, Hideki

2007-08-28

Micellization behavior of amphiphilic diblock copolymers with strong acid groups, poly(hydrogenated isoprene)-block-poly(styrenesulfonate), was investigated by small-angle neutron scattering (SANS). We have reported previously (Kaewsaiha, P.; Matsumoto, K.; Matsuoka, H. Langmuir 2005, 21, 9938) that this strongly ionic amphiphilic diblock copolymer shows almost no surface activity but forms micelles in water. In this study, the size, shape, and internal structures of the micelles formed by these unique copolymers in aqueous solution were duly investigated. The SANS data were well described by the theoretical form factor of a core-shell model and the Pedersen core-corona model. The micellar shape strongly depends on the hydrophobic chain length of the block copolymer. The polymer with the shortest hydrophobic chain was suggested to form spherical micelles, whereas the scattering curves of the longer hydrophobic chain polymers showed a q-1 dependence, reflecting the formation of rodlike micelles. Furthermore, the addition of salt at high concentration also induced the sphere-to-rod transition in micellar shape as a result of the shielding effect of electrostatic repulsion. The corona thickness was almost constant up to the critical salt concentration (around 0.2 M) and then decreased with further increases in salt concentration, which is in qualitatively agreement with existing theories. The spherical/rodlike micelle ratio was also constant up to the critical salt concentration and then decreased. The micelle size and shape of this unique polymer could be described by the common concept of the packing parameter, but the anomalously stable nature of the micelle (up to 1 M NaCl) is a special characteristic.

Small-angle neutron scattering study of magnetic ordering and inhomogeneity across the martensitic phase transformation in Ni 50–xCo xMn₄₀Sn₁₀ alloys

DOE PAGES

Bhatti, Kanwal Preet; El-Khatib, S.; Srivastava, Vijay; ...

2012-04-27

The Heusler-derived multiferroic alloy Ni 50–xCo xMn₄₀Sn₁₀ has recently been shown to exhibit, at just above room temperature, a highly reversible martensitic phase transformation with an unusually large magnetization change. In this work the nature of the magnetic ordering above and below this transformation has been studied in detail in the critical composition range x = 6–8 via temperature-dependent (5–600 K) magnetometry and small-angle neutron scattering (SANS). We observe fairly typical paramagnetic to long-range-ordered ferromagnetic phase transitions on cooling to 420–430 K, with the expected critical spin fluctuations, followed by first-order martensitic phase transformations to a nonferromagnetic state below 360–390more » K. The static magnetization reveals complex magnetism in this low-temperature nonferromagnetic phase, including a Langevin-like field dependence, distinct spin freezing near 60 K, and significant exchange bias effects, consistent with superparamagnetic blocking of ferromagnetic clusters of nanoscopic dimensions. We demonstrate that these spin clusters, whose existence has been hypothesized in a variety of martensitic alloys exhibiting competition between ferromagnetic and antiferromagnetic exchange interactions, can be directly observed by SANS. The scattering data are consistent with a liquidlike spatial distribution of interacting magnetic clusters with a mean center-to-center spacing of 12 nm. Considering the behavior of the superparmagnetism, cooling-field and temperature-dependent exchange bias, and magnetic SANS, we discuss in detail the physical form and origin of these spin clusters, their intercluster interactions, the nature of the ground-state magnetic ordering in the martensitic phase, and the implications for our understanding of such alloy systems.« less

Tunable dielectric response, resistive switching, and unconventional transport in SrTiO3

NASA Astrophysics Data System (ADS)

Mikheev, Evgeny

The first section of this thesis discusses integration of SR TiO3 grown by molecular beam epitaxy (MBE) in vertical device structures. One target application is as a tunable dielectric. Parallel plate capacitors based on epitaxial Pt(001) bottom electrodes and (Ba,Sr)TiO 3 dielectric layers grown by MBE are demonstrated. Optimization of structural quality of the vertical stack is shown to produce very low dielectric loss combined with very high tunability of the dielectric constant by DC bias. This results in considerable improvement of common figures of merit for varactor performance in comparison to previous reports. Another target application for transition metals oxides is in resistive switching memories, which are based on the hysteretic current-voltage response observed in many oxide-based Schottky junctions and capacitors. A study on the role of metal/oxide interface quality is presented. In particular, the use of epitaxial Pt(001) as Schottky contacts to Nb:SRTiO 3 is shown to suppress resistive switching hysteresis by eliminating unintentional contributions to interface capacitance. Such uncontrolled factors are discussed as a probable root cause for poor reproducibility in resistive switching memories, currently a ubiquitous challenge in the field. Potential routes towards stabilizing reproducible switching through intentional control of defect densities in high-quality structures are discussed, including a proof of concept demonstration using Schottky junctions incorporating intentionally non-stoichiometric SRTiO3 interlayers grown by MBE. The second section of this thesis is concerned with unconventional electronic transport in SRTiO3. A systematic description of scattering mechanisms will be presented for three related material systems: uniformly-doped SRTiO3, two-dimensional electron liquids (2DEL) at SRTiO3/RTiO 3 interfaces (R = Gd, Sm) and confined 2DELs in RTiO3/SRTiO3/ RTiO3 quantum wells. In particular, the prevalence of a well-defined T2 scattering rate in doped SRTiO3 will be discussed as being incompatible with its traditional assignment as electron-electron scattering in a Fermi liquid. In the case of ultrathin SRTiO3 quantum wells bound by RTiO3, evidence will be presented for the existence of a quantum critical point. This refers to a quantum phase transition at zero temperature towards an ordered phase in SRTiO 3. This transition is driven by increasing confinement of the 2DEL, with a critical point located at the 5 SrO layer thickness of SRTiO 3. It is manifested in anomalous temperature exponents of the power law resistivity. Additionally, a well-defined trend for the separation of the Hall and longitudinal scattering rates will be presented, analogously to a similar effect observed in the normal state of high-Tc superconductors. In particular, a unique pattern of residual scattering separation was documented, consistent with a quantum critical correction to the Hall lifetime that is divergent at the quantum critical point.

The GMO Sumrule and the πNN Coupling Constant

NASA Astrophysics Data System (ADS)

Ericson, T. E. O.; Loiseau, B.; Thomas, A. W.

The isovector GMO sumrule for forward πN scattering is critically evaluated using the precise π-p and π-d scattering lengths obtained recently from pionic atom measurements. The charged πNN coupling constant is then deduced with careful analysis of systematic and statistical sources of uncertainties. This determination gives directly from data gc2(GMO)/4π = 14.17±0.09 (statistic) ±0.17 (systematic) or fc2/ 4π=0.078(11). This value is half-way between that of indirect methods (phase-shift analyses) and the direct evaluation from from backward np differential scattering cross sections (extrapolation to pion pole). From the π-p and π-d scattering lengths our analysis leads also to accurate values for (1/2)(aπ-p+aπ-n) and (1/2) (aπ-p-aπ-n).

Scattering of matter waves in spatially inhomogeneous environments

DOE PAGES

Tsitoura, F.; Krüger, P.; Kevrekidis, P. G.; ...

2015-03-30

In this article, we study scattering of quasi-one-dimensional matter waves at an interface of two spatial domains, one with repulsive and one with attractive interatomic interactions. It is shown that the incidence of a Gaussian wave packet from the repulsive to the attractive region gives rise to generation of a soliton train. More specifically, the number of emergent solitons can be controlled, e.g., by the variation of the amplitude or the width of the incoming wave packet. Furthermore, we study the reflectivity of a soliton incident from the attractive region to the repulsive one. We find the reflection coefficient numericallymore » and employ analytical methods, which treat the soliton as a particle (for moderate and large amplitudes) or a quasilinear wave packet (for small amplitudes), to determine the critical soliton momentum (as a function of the soliton amplitude) for which total reflection is observed.« less

Electric Field Induced Interfacial Instabilities

NASA Technical Reports Server (NTRS)

Kusner, Robert E.; Min, Kyung Yang; Wu, Xiao-Lun; Onuki, Akira

1996-01-01

The study of the interface in a charge-free, nonpolar, critical and near-critical binary fluid in the presence of an externally applied electric field is presented. At sufficiently large fields, the interface between the two phases of the binary fluid should become unstable and exhibit an undulation with a predefined wavelength on the order of the capillary length. As the critical point is approached, this wavelength is reduced, potentially approaching length-scales such as the correlation length or critical nucleation radius. At this point the critical properties of the system may be affected. In zero gravity, the interface is unstable at all long wavelengths in the presence of a field applied across it. It is conjectured that this will cause the binary fluid to break up into domains small enough to be outside the instability condition. The resulting pattern formation, and the effects on the critical properties as the domains approach the correlation length are of acute interest. With direct observation, laser light scattering, and interferometry, the phenomena can be probed to gain further understanding of interfacial instabilities and the pattern formation which results, and dimensional crossover in critical systems as the critical fluctuations in a particular direction are suppressed by external forces.

Criteria of backscattering in chiral one-way photonic crystals

NASA Astrophysics Data System (ADS)

Cheng, Pi-Ju; Chang, Shu-Wei

2016-03-01

Optical isolators are important devices in photonic circuits. To reduce the unwanted reflection in a robust manner, several setups have been realized using nonreciprocal schemes. In this study, we show that the propagating modes in a strongly-guided chiral photonic crystal (no breaking of the reciprocity) are not backscattering-immune even though they are indeed insensitive to many types of scatters. Without the protection from the nonreciprocity, the backscattering occurs under certain circumstances. We present a perturbative method to calculate the backscattering of chiral photonic crystals in the presence of chiral/achiral scatters. The model is, essentially, a simplified analogy to the first-order Born approximation. Under reasonable assumptions based on the behaviors of chiral photonic modes, we obtained the expression of reflection coefficients which provides criteria for the prominent backscattering in such chiral structures. Numerical examinations using the finite-element method were also performed and the results agree well with the theoretical prediction. From both our theory and numerical calculations, we find that the amount of backscattering critically depends on the symmetry of scatter cross sections. Strong reflection takes place when the azimuthal Fourier components of scatter cross sections have an order l of 2. Chiral scatters without these Fourier components would not efficiently reflect the chiral photonic modes. In addition, for these chiral propagating modes, disturbances at the most significant parts of field profiles do not necessarily result in the most effective backscattering. The observation also reveals what types of scatters or defects should be avoided in one-way applications of chiral structures in order to minimize the backscattering.

BIM-Sim: Interactive Simulation of Broadband Imaging Using Mie Theory

NASA Astrophysics Data System (ADS)

Berisha, Sebastian; van Dijk, Thomas; Bhargava, Rohit; Carney, P. Scott; Mayerich, David

2017-02-01

Understanding the structure of a scattered electromagnetic (EM) field is critical to improving the imaging process. Mechanisms such as diffraction, scattering, and interference affect an image, limiting the resolution and potentially introducing artifacts. Simulation and visualization of scattered fields thus plays an important role in imaging science. However, the calculation of scattered fields is extremely time-consuming on desktop systems and computationally challenging on task-parallel systems such as supercomputers and cluster systems. In addition, EM fields are high-dimensional, making them difficult to visualize. In this paper, we present a framework for interactively computing and visualizing EM fields scattered by micro and nano-particles. Our software uses graphics hardware for evaluating the field both inside and outside of these particles. We then use Monte-Carlo sampling to reconstruct and visualize the three-dimensional structure of the field, spectral profiles at individual points, the structure of the field at the surface of the particle, and the resulting image produced by an optical system.

A Small Angle Scattering Sensor System for the Characterization of Combustion Generated Particulate

NASA Technical Reports Server (NTRS)

Feikema, Douglas A.; Kim, W.; Sivathanu, Yudaya

2007-01-01

One of the critical issues for the US space program is fire safety of the space station and future launch vehicles. A detailed understanding of the scattering signatures of particulate is essential for the development of a false alarm free fire detection system. This paper describes advanced optical instrumentation developed and applied for fire detection. The system is being designed to determine four important physical properties of disperse fractal aggregates and particulates including size distribution, number density, refractive indices, and fractal dimension. Combustion generated particulate are the primary detection target; however, in order to discriminate from other particulate, non-combustion generated particles should also be characterized. The angular scattering signature is measured and analyzed using two photon optical laser scattering. The Rayleigh-Debye-Gans (R-D-G) scattering theory for disperse fractal aggregates is utilized. The system consists of a pulsed laser module, detection module and data acquisition system and software to analyze the signals. The theory and applications are described.

Interactions between sodium dodecyl sulphate and non-ionic cellulose derivatives studied by size exclusion chromatography with online multi-angle light scattering and refractometric detection.

PubMed

Wittgren, Bengt; Stefansson, Morgan; Porsch, Bedrich

2005-08-05

The novel approach described allows to characterise the surfactant-polymer interaction under several sodium dodecyl sulphate (SDS) concentrations (0-20 mM) using size exclusion chromatography (SEC) with online multi-angle light scattering (MALS) and refractometric (RI) detection. Three different cellulose derivatives, hydroxypropyl cellulose (HPC), hydroxypropyl methyl cellulose (HPMC) and hydroxyethyl cellulose (HEC), have been studied in solution containing 10 mM NaCl and various concentrations of sodium dodecyl sulphate. It is shown that this approach is well suited for successful application of both Hummel-Dreyer and multi-component light scattering principles and yields reliable molecular masses of both the polymer complex and the polymer itself within the complex, the amount of surfactant bound into the complex as well as appropriate values of the refractive index increment (dn/dc)micro, of both the complex and the polymer in question. The more hydrophobic derivatives HPC and HPMC adsorbed significantly more SDS than HEC. The inter-chain interactions close to critical aggregation concentration (cac) were clearly seen for HPC and HPMC as an almost two-fold average increase in polymer molecular mass contained in the complex.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rai, Durgesh K.; Sharma, Veerendra K.; Anunciado, Divina

The interaction between lipid bilayers and Amyloid β peptide (Aβ) plays a critical role in proliferation of Alzheimer’s disease (AD). AD is expected to affect one in every 85 humans by 2050, and therefore, deciphering the interplay of Aβ and lipid bilayers at the molecular level is of profound importance. In this work, we applied an array of neutron scattering methods to study the structure and dynamics of Aβ(1–40) interacting 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) bilayers. In the structural investigations of lipid bilayer’s response to Aβ binding, Small Angle Neutron Scattering and Neutron Membrane Diffraction revealed that the Aβ anchors firmly to themore » highly charged DMPG bilayers in the interfacial region between water and hydrocarbon chain, and it doesn’t penetrate deeply into the bilayer. This association mode is substantiated by the dynamics studies with high resolution Quasi-Elastic Neutron Scattering experiments, showing that the addition of Aβ mainly affects the slower lateral motion of lipid molecules, especially in the fluid phase, but not the faster internal motion. The results revealed that Aβ associates with the highly charged membrane in surface with limited impact on the structure, but the altered membrane dynamics could have more influence on other membrane processes.« less

Origin of the net magnetic moment in LaCoO 3

DOE PAGES

Kaminsky, G.; Belanger, David P.; Ye, Feng; ...

2018-01-19

We use polarized neutron scattering to characterize the Bragg scattering intensity below T C=89.5 K at the (1,0,0) pseudocubic nuclear Bragg point of LaCoO 3. Upon cooling in a field (FC), a net magnetic moment is apparent in Bragg scattering intensity, just as it was in previous magnetization measurements. Critical behavior associated with the net moment near T C upon cooling in small applied fields rapidly rounds with increasing field strength. We show, using a mean-field calculation, that this net moment can develop in a metastable state that forms upon FC, even when all the interactions in the system aremore » antiferromagnetic.« less

Precision determination of the πN scattering lengths and the charged πNN coupling constant

NASA Astrophysics Data System (ADS)

Ericson, T. E. O.; Loiseau, B.; Thomas, A. W.

2000-01-01

We critically evaluate the isovector GMO sumrule for the charged πNN coupling constant using recent precision data from π-p and π-d atoms and with careful attention to systematic errors. From the π-d scattering length we deduce the pion-proton scattering lengths 1/2(aπ-p + aπ-n) = (-20 +/- 6(statistic)+/-10 (systematic) .10-4m-1πc and 1/2(aπ-p - aπ-n) = (903 +/- 14) . 10-4m-1πc. From this a direct evaluation gives g2c(GMO)/4π = 14.20 +/- 0.07 (statistic)+/-0.13(systematic) or f2c/4π = 0.0786 +/- 0.0008.

Quantitative long term measurements of burns in a rat model using Spatial Frequency Domain Imaging (SFDI) and Laser Speckle Imaging (LSI)

PubMed Central

Ponticorvo, Adrien; Burmeister, David M.; Rowland, Rebecca; Baldado, Melissa; Kennedy, Gordon T.; Saager, Rolf; Bernal, Nicole; Choi, Bernard; Durkin, Anthony J.

2017-01-01

The current standard for diagnosis of burn severity and subsequent wound healing is through clinical examination, which is highly subjective. Several new technologies are shifting focus to burn care in an attempt to help quantify not only burn depth but also the progress of healing. While accurate early assessment of partial thickness burns is critical for dictating the course of treatment, the ability to quantitatively monitor wound status over time is critical for understanding treatment efficacy. SFDI and LSI are both non-invasive imaging modalities that have been shown to have great diagnostic value for burn severity, but have yet to be tested over the course of wound healing. In this study, a hairless rat model (n=6, 300-450g) was used with a four pronged comb to create four identical partial thickness burns (superficial n=3 and deep n=3) that were used to monitor wound healing over a 28 day period. Weekly biopsies were taken for histological analysis to verify wound progression. Both SFDI and LSI were performed weekly to track the evolution of hemodynamic (blood flow and oxygen saturation) and structural (reduced scattering coefficient) properties for the burns. LSI showed significant changes in blood flow from baseline to 220% in superficial and 165% in deep burns by day 7. In superficial burns, blood flow returned to baseline levels by day 28, but not for deep burns where blood flow remained elevated. Smaller increases in blood flow were also observed in the surrounding tissue over the same time period. Oxygen saturation values measured with SFDI showed a progressive increase from baseline values of 66% to 74% in superficial burns and 72% in deep burns by day 28. Additionally, SFDI showed significant decreases in the reduced scattering coefficient shortly after the burns were created. The scattering coefficient progressively decreased in the wound area, but returned towards baseline conditions at the end of the 28 day period. Scattering changes in the surrounding tissue remained constant despite the presence of hemodynamic changes. Here we show that LSI and SFDI are capable of monitoring changes in hemodynamic and scattering properties in burn wounds over a 28 day period. These results highlight the potential insights that can be gained by using noninvasive imaging technologies to study wound healing. Further development of these technologies could be revolutionary for wound monitoring and studying the efficacy of different treatments. PMID:28220508

The influence of material and mesh characteristics on transmission mode desorption electrospray ionization.

PubMed

Chipuk, Joseph E; Brodbelt, Jennifer S

2009-04-01

Adaptation of desorption electrospray ionization to a transmission mode (TM-DESI) entails passing an electrospray plume through a sample that has been deposited onto a mesh substrate. A combination of mass spectrometry and fluorescence microscopy studies is used to illustrate the critical role material composition, mesh open space, and mesh fiber diameter play on the transmission, desorption, and ionization process. Substrates with open spaces less than 150 microm and accompanying minimal strand diameters produce less scattering of the plume and therefore favor transmission. Larger strand diameters typically encompass larger open spaces, but the increase in the surface area of the strand increases plume scattering as well as solvent and analyte spreading on the mesh. Polypropylene (PP), ethylene tetrafluoroethylene (ETFE), and polyetheretherketone (PEEK) materials afford much better desorption than similarly sized polyethylene terephthalate (PETE) or nylon-6,6 (PA66) substrates. Ultimately, the manner in which the electrospray plume interacts with the mesh as it is transmitted through the substrate is shown to be critical to performing and optimizing TM-DESI analyses. In addition, evidence is presented for analyte dependent variations in the desorption mechanisms of dry and solvated samples.

Quantum critical point revisited by dynamical mean-field theory

NASA Astrophysics Data System (ADS)

Xu, Wenhu; Kotliar, Gabriel; Tsvelik, Alexei M.

2017-03-01

Dynamical mean-field theory is used to study the quantum critical point (QCP) in the doped Hubbard model on a square lattice. The QCP is characterized by a universal scaling form of the self-energy and a spin density wave instability at an incommensurate wave vector. The scaling form unifies the low-energy kink and the high-energy waterfall feature in the spectral function, while the spin dynamics includes both the critical incommensurate and high-energy antiferromagnetic paramagnons. We use the frequency-dependent four-point correlation function of spin operators to calculate the momentum-dependent correction to the electron self-energy. By comparing with the calculations based on the spin-fermion model, our results indicate the frequency dependence of the quasiparticle-paramagnon vertices is an important factor to capture the momentum dependence in quasiparticle scattering.

Quantum critical point revisited by dynamical mean-field theory

DOE PAGES

Xu, Wenhu; Kotliar, Gabriel; Tsvelik, Alexei M.

2017-03-31

Dynamical mean-field theory is used to study the quantum critical point (QCP) in the doped Hubbard model on a square lattice. We characterize the QCP by a universal scaling form of the self-energy and a spin density wave instability at an incommensurate wave vector. The scaling form unifies the low-energy kink and the high-energy waterfall feature in the spectral function, while the spin dynamics includes both the critical incommensurate and high-energy antiferromagnetic paramagnons. Here, we use the frequency-dependent four-point correlation function of spin operators to calculate the momentum-dependent correction to the electron self-energy. Furthermore, by comparing with the calculations basedmore » on the spin-fermion model, our results indicate the frequency dependence of the quasiparticle-paramagnon vertices is an important factor to capture the momentum dependence in quasiparticle scattering.« less

Phonon Scattering in Silicon by Multiple Morphological Defects: A Multiscale Analysis

NASA Astrophysics Data System (ADS)

Lorenzi, Bruno; Dettori, Riccardo; Dunham, Marc T.; Melis, Claudio; Tonini, Rita; Colombo, Luciano; Sood, Aditya; Goodson, Kenneth E.; Narducci, Dario

2018-05-01

Ideal thermoelectric materials should possess low thermal conductivity κ along with high electrical conductivity σ . Thus, strategies are needed to impede the propagation of phonons mostly responsible for thermal conduction while only marginally affecting charge carrier diffusion. Defect engineering may provide tools to fulfill this aim, provided that one can achieve an adequate understanding of the role played by multiple morphological defects in scattering thermal energy carriers. In this paper, we study how various morphological defects such as grain boundaries and dispersed nanovoids reduce the thermal conductivity of silicon. A blended approach has been adopted, using data from both simulations and experiments in order to cover a wide range of defect densities. We show that the co-presence of morphological defects with different characteristic scattering length scales is effective in reducing the thermal conductivity. We also point out that non-gray models (i.e. models with spectral resolution) are required to improve the accuracy of predictive models explaining the dependence of κ on the density of morphological defects. Finally, the application of spectral models to Matthiessen's rule is critically addressed with the aim of arriving at a compact model of phonon scattering in highly defective materials showing that non-local descriptors would be needed to account for lattice distortion due to nanometric voids.

Application of modern radiative transfer tools to model laboratory quartz emissivity

NASA Astrophysics Data System (ADS)

Pitman, Karly M.; Wolff, Michael J.; Clayton, Geoffrey C.

2005-08-01

Planetary remote sensing of regolith surfaces requires use of theoretical models for interpretation of constituent grain physical properties. In this work, we review and critically evaluate past efforts to strengthen numerical radiative transfer (RT) models with comparison to a trusted set of nadir incidence laboratory quartz emissivity spectra. By first establishing a baseline statistical metric to rate successful model-laboratory emissivity spectral fits, we assess the efficacy of hybrid computational solutions (Mie theory + numerically exact RT algorithm) to calculate theoretical emissivity values for micron-sized α-quartz particles in the thermal infrared (2000-200 cm-1) wave number range. We show that Mie theory, a widely used but poor approximation to irregular grain shape, fails to produce the single scattering albedo and asymmetry parameter needed to arrive at the desired laboratory emissivity values. Through simple numerical experiments, we show that corrections to single scattering albedo and asymmetry parameter values generated via Mie theory become more necessary with increasing grain size. We directly compare the performance of diffraction subtraction and static structure factor corrections to the single scattering albedo, asymmetry parameter, and emissivity for dense packing of grains. Through these sensitivity studies, we provide evidence that, assuming RT methods work well given sufficiently well-quantified inputs, assumptions about the scatterer itself constitute the most crucial aspect of modeling emissivity values.

Investigation of the leading and subleading high-energy behavior of hadron-hadron total cross sections using a best-fit analysis of hadronic scattering data

NASA Astrophysics Data System (ADS)

Giordano, M.; Meggiolaro, E.; Silva, P. V. R. G.

2017-08-01

In the present investigation we study the leading and subleading high-energy behavior of hadron-hadron total cross sections using a best-fit analysis of hadronic scattering data. The parametrization used for the hadron-hadron total cross sections at high energy is inspired by recent results obtained by Giordano and Meggiolaro [J. High Energy Phys. 03 (2014) 002, 10.1007/JHEP03(2014)002] using a nonperturbative approach in the framework of QCD, and it reads σtot˜B ln2s +C ln s ln ln s . We critically investigate if B and C can be obtained by means of best-fits to data for proton-proton and antiproton-proton scattering, including recent data obtained at the LHC, and also to data for other meson-baryon and baryon-baryon scattering processes. In particular, following the above-mentioned nonperturbative QCD approach, we also consider fits where the parameters B and C are set to B =κ Bth and C =κ Cth, where Bth and Cth are universal quantities related to the QCD stable spectrum, while κ (treated as an extra free parameter) is related to the asymptotic value of the ratio σel/σtot. Different possible scenarios are then considered and compared.

Design of a facility for the in situ measurement of catalytic reaction by neutron scattering spectroscopy

NASA Astrophysics Data System (ADS)

Tan, Shuai; Cheng, Yongqiang; Daemen, Luke L.; Lutterman, Daniel A.

2018-01-01

Catalysis is a critical enabling science for future energy needs. The next frontier of catalysis is to evolve from catalyst discovery to catalyst design, and for this next step to be realized, we must develop new techniques to better understand reaction mechanisms. To do this, we must connect catalytic reaction rates and selectivities to the kinetics, energetics, and dynamics of individual elementary steps and relate these to the structure and dynamics of the catalytic sites involved. Neutron scattering spectroscopies offer unique capabilities that are difficult or impossible to match by other techniques. The current study presents the development of a compact and portable instrumental design that enables the in situ investigation of catalytic samples by neutron scattering techniques. The developed apparatus was tested at the Spallation Neutron Source (SNS) in Oak Ridge National Laboratory and includes a gas handling panel that allows for computer hookups to control the panel externally and online measurement equipment such as coupled GC-FID/TCD (Gas Chromatography-Flame Ionization Detector/Thermal Conductivity Detector) and MS (Mass Spectrometry) to characterize offgassing while the sample is in the neutron scattering spectrometer. This system is flexible, modular, compact, and portable enabling its use for many types of gas-solid and liquid-solid reactions at the various beamlines housed at the SNS.

Structure of guar in solutions of H{sub 2}O and D{sub 2}O: An ultra-small-angle light-scattering study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gittings, M.R.; Cipelletti, L.; Trappe, V.

2000-05-11

The authors examine the structure of guar as a function of concentration in both H{sub 2}O and D{sub 2}O using several different scattering techniques. The range of scattering vectors spans 5 decades (143 cm{sup {minus}1} < q < 10.3 x 10{sup 6} cm{sup {minus}1}), providing insight into the supramolecular and local organization of the chains. This allows direct characterization of the large-scale aggregate structure of the guar, which can be on the order of 100 {micro}m. The aggregates are most likely loosely interconnected with single chains and other aggregates, and the structure and organization are critical in determining solution viscoelasticmore » properties. The solubility is poorer in D{sub 2}O as evidenced by larger aggregates, higher scattering intensities, a slightly higher fractal dimension, and a sublinear concentration dependence of the intensity. Aggregates were found in dilute neutral guar solutions as well as in cationic guar solutions (in H{sub 2}O), whether screened or unscreened. The presence of aggregates at all concentrations for neutral and charged guar indicates the difficulty in determining a molecular weight of the guar molecule.« less

Photoinduced Domain Pattern Transformation in Ferroelectric-Dielectric Superlattices

DOE PAGES

Ahn, Youngjun; Park, Joonkyu; Pateras, Anastasios; ...

2017-07-31

The nanodomain pattern in ferroelectric/dielectric superlattices transforms to a uniform polarization state under above-bandgap optical excitation. X-ray scattering reveals a disappearance of domain diffuse scattering and an expansion of the lattice. Furthermore, the reappearance of the domain pattern occurs over a period of seconds at room temperature, suggesting a transformation mechanism in which charge carriers in long-lived trap states screen the depolarization field. A Landau-Ginzburg-Devonshire model predicts changes in lattice parameter and a critical carrier concentration for the transformation.

Photoinduced Domain Pattern Transformation in Ferroelectric-Dielectric Superlattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahn, Youngjun; Park, Joonkyu; Pateras, Anastasios

2017-07-01

The nanodomain pattern in ferroelectric/dielectric superlattices transforms to a uniform polarization state under above-bandgap optical excitation. X-ray scattering reveals a disappearance of domain diffuse scattering and an expansion of the lattice. The reappearance of the domain pattern occurs over a period of seconds at room temperature, suggesting a transformation mechanism in which charge carriers in long-lived trap states screen the depolarization field. A Landau-Ginzburg-Devonshire model predicts changes in lattice parameter and a critical carrier concentration for the transformation.

Superamphiphilic nanocontainers based on the resorcinarene - Cationic surfactant system: Synergetic self-assembling behavior

NASA Astrophysics Data System (ADS)

Gaynanova, Gulnara A.; Bekmukhametova, Alina M.; Kashapov, Ruslan R.; Ziganshina, Albina Yu.; Zakharova, Lucia Ya.

2016-05-01

Self-organization in the mixed system based on water-soluble aminomethylated calix[4]arene with sulfonatoethyl groups at the lower rim and classical cationic surfactant cetyltrimethylammonium bromide has been studied by the methods of tensiometry, conductometry, spectrophotometry, dynamic and electrophoretic light scattering. The values of the critical association concentration, the size and zeta potential values, and the solubilization capacity of mixed aggregates toward the hydrophobic probe (Sudan I) were determined.

Results From the Physics of Colloids Experiment on ISS

NASA Technical Reports Server (NTRS)

Weitz, David; Bailey, Arthur; Manley, Suliana; Prasad, Vikram; Christianson, Rebecca; Sankaran, Subramanian; Doherty, Michael; Jankovsky, Amy; Lorik, Tibor; Shiley, William

2002-01-01

The Physics of Colloids in Space (PCS) experiment was accommodated within International Space Station (ISS) EXpedite the PRocessing of Experiments to Space Station (EXPRESS) Rack 2 and was remotely operated from early June 2001 until February 2002 from NASA Glenn Research Center's Telescience Support Center (TSC) in Cleveland, Ohio, and from the remote site at Harvard University in Cambridge, Massachusetts. PCS was launched on 4/19/2001 on Space Shuttle STS-100. The experiment was activated on 5/31/2001. The entire experimental setup performed remarkably well, and accomplished 2400 hours of science operations on-orbit. The sophisticated instrumentation in PCS is capable of dynamic and static light scattering from 11 to 169 degrees, Bragg scattering over the range from 10 to 60 degrees, dynamic and static light scattering at low angles from 0.3 to 6.0 degrees, and color imaging. The long duration microgravity environment on the ISS facilitated extended studies on the growth and coarsening characteristics of binary crystals. The de-mixing of the colloid-polymer critical-point sample was also studied as it phase-separated into two phases. Further, aging studies on a col-pol gel, gelation rate studies in extremely low concentration fractal gels over several days, and studies on a glass sample, all provided valuable information. Several exciting and unique aspects of these results are discussed here.

Surfactant-based critical phenomena in microgravity

NASA Technical Reports Server (NTRS)

Kaler, Eric W.; Paulaitis, Michael E.

1994-01-01

The objective of this research project is to characterize by experiment and theoretically both the kinetics of phase separation and the metastable structures produced during phase separation in a microgravity environment. The particular systems we are currently studying are mixtures of water, nonionic surfactants, and compressible supercritical fluids at temperatures and pressures where the coexisting liquid phases have equal densities (isopycnic phases). In this report, we describe experiments to locate equilibrium isopycnic phases and to determine the 'local' phase behavior and critical phenomena at nearby conditions of temperature, pressure, and composition. In addition, we report the results of preliminary small angle neutron scattering (SANS) experiments to characterize microstructures that exist in these mixtures at different fluid densities.

BIM-Sim: Interactive Simulation of Broadband Imaging Using Mie Theory

PubMed Central

Berisha, Sebastian; van Dijk, Thomas; Bhargava, Rohit; Carney, P. Scott; Mayerich, David

2017-01-01

Understanding the structure of a scattered electromagnetic (EM) field is critical to improving the imaging process. Mechanisms such as diffraction, scattering, and interference affect an image, limiting the resolution, and potentially introducing artifacts. Simulation and visualization of scattered fields thus plays an important role in imaging science. However, EM fields are high-dimensional, making them time-consuming to simulate, and difficult to visualize. In this paper, we present a framework for interactively computing and visualizing EM fields scattered by micro and nano-particles. Our software uses graphics hardware for evaluating the field both inside and outside of these particles. We then use Monte-Carlo sampling to reconstruct and visualize the three-dimensional structure of the field, spectral profiles at individual points, the structure of the field at the surface of the particle, and the resulting image produced by an optical system. PMID:29170738

Proton dynamics in oxides: insight into the mechanics of proton conduction from quasielastic neutron scattering.

PubMed

Karlsson, Maths

2015-01-07

This article is concerned with the use of quasielastic neutron scattering as a technique for investigation of the dynamical properties of proton conducting oxides. Currently, the main interest in these materials comes from their promise as electrolytes in future electrochemical devices and particularly through their use as electrolytes in next-generation, intermediate-temperature, fuel cells. However, the realization of such devices depends critically on the development of new, more highly proton conducting oxides. Such a development depends on increasing the current understanding of proton conduction in oxides and for this purpose quasielastic neutron scattering is an important mean. The aim of this article is to introduce the non-specialist reader to the basic principles of quasielastic neutron scattering, its advantages and disadvantages, to summarize the work that has been done on proton conducting oxides using this technique, as well as to discuss future opportunities within this field of research.

Effects of periodic forcing in chaotic scattering

NASA Astrophysics Data System (ADS)

Blesa, Fernando; Seoane, Jesús M.; Barrio, Roberto; Sanjuán, Miguel A. F.

2014-04-01

The effects of a periodic forcing on chaotic scattering are relevant in certain situations of physical interest. We investigate the effects of the forcing amplitude and the external frequency in both the survival probability of the particles in the scattering region and the exit basins associated to phase space. We have found an exponential decay law for the survival probability of the particles in the scattering region. A resonant-like behavior is uncovered where the critical values of the frequencies ω ≃1 and ω ≃2 permit the particles to escape faster than for other different values. On the other hand, the computation of the exit basins in phase space reveals the existence of Wada basins depending of the frequency values. We provide some heuristic arguments that are in good agreement with the numerical results. Our results are expected to be relevant for physical phenomena such as the effect of companion galaxies, among others.

Predicting scattering scanning near-field optical microscopy of mass-produced plasmonic devices

NASA Astrophysics Data System (ADS)

Otto, Lauren M.; Burgos, Stanley P.; Staffaroni, Matteo; Ren, Shen; Süzer, Özgün; Stipe, Barry C.; Ashby, Paul D.; Hammack, Aeron T.

2018-05-01

Scattering scanning near-field optical microscopy enables optical imaging and characterization of plasmonic devices with nanometer-scale resolution well below the diffraction limit. This technique enables developers to probe and understand the waveguide-coupled plasmonic antenna in as-fabricated heat-assisted magnetic recording heads. In order to validate and predict results and to extract information from experimental measurements that is physically comparable to simulations, a model was developed to translate the simulated electric field into expected near-field measurements using physical parameters specific to scattering scanning near-field optical microscopy physics. The methods used in this paper prove that scattering scanning near-field optical microscopy can be used to determine critical sub-diffraction-limited dimensions of optical field confinement, which is a crucial metrology requirement for the future of nano-optics, semiconductor photonic devices, and biological sensing where the near-field character of light is fundamental to device operation.

Uranium nitride: a cubic antiferromagnet with anisotropic critical behavior

DOE Office of Scientific and Technical Information (OSTI.GOV)

Buyers, W J.L.; Holden, T M; Svensson, E C

1977-11-01

Highly anisotropic critical scattering associated with the transition at T/sub N/ = 49.5 K to the type-I antiferromagnetic structure has been observed in uranium nitride. The transverse susceptibility is found to be unobservably small. The longitudinal susceptibility diverges at T/sub N/ and its anisotropy shows that the spins within the (001) ferromagnetic sheets of the (001) domain are much more highly correlated than they are with the spins lying in adjacent (001) sheets. The correlation range within the sheets is much greater than that expected for a Heisenberg system with the same T/sub N/. The rod-like scattering extended along themore » spin and domain direction is reminiscent of two-dimensional behavior. The results are inconsistent with a simple localized model and may reflect the itinerant nature of the 5f electrons.« less

Reactivity impact of {sup 16}O thermal elastic-scattering nuclear data for some numerical and critical benchmark systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kozier, K. S.; Roubtsov, D.; Plompen, A. J. M.

2012-07-01

The thermal neutron-elastic-scattering cross-section data for {sup 16}O used in various modern evaluated-nuclear-data libraries were reviewed and found to be generally too high compared with the best available experimental measurements. Some of the proposed revisions to the ENDF/B-VII.0 {sup 16}O data library and recent results from the TENDL system increase this discrepancy further. The reactivity impact of revising the {sup 16}O data downward to be consistent with the best measurements was tested using the JENDL-3.3 {sup 16}O cross-section values and was found to be very small in MCNP5 simulations of the UO{sub 2} and reactor-recycle MOX-fuel cases of the ANSmore » Doppler-defect numerical benchmark. However, large reactivity differences of up to about 14 mk (1400 pcm) were observed using {sup 16}O data files from several evaluated-nuclear-data libraries in MCNP5 simulations of the Los Alamos National Laboratory HEU heavy-water solution thermal critical experiments, which were performed in the 1950's. The latter result suggests that new measurements using HEU in a heavy-water-moderated critical facility, such as the ZED-2 zero-power reactor at the Chalk River Laboratories, might help to resolve the discrepancy between the {sup 16}O thermal elastic-scattering cross-section values and thereby reduce or better define its uncertainty, although additional assessment work would be needed to confirm this. (authors)« less

Surface Brillouin scattering study of the surface excitations in amorphous silicon layers produced by ion bombardment

NASA Astrophysics Data System (ADS)

Zhang, X.; Comins, J. D.; Every, A. G.; Stoddart, P. R.; Pang, W.; Derry, T. E.

1998-11-01

Thin amorphous silicon layers on crystalline silicon substrates have been produced by argon-ion bombardment of (001) silicon surfaces. Thermally induced surface excitations characteristic of this example of a soft-on-hard system have been investigated by surface Brillouin scattering (SBS) as a function of scattering-angle and amorphous-layer thickness. At large scattering angles or for sufficiently large layer thickness, a second peak is present in the SBS spectrum near the low-energy threshold for the continuum of bulk excitations of the system. The measured spectra are analyzed on the basis of surface elastodynamic Green's functions, which successfully simulate their detailed appearance and identify the second peak as either a Sezawa wave (true surface wave) or a pseudo-Sezawa wave (attenuated surface wave) depending on the scattering parameters. The attributes of the pseudo-Sezawa wave are described; these include its asymmetrical line shape and variation in intensity with k∥d (the product of the surface excitation wave vector and the layer thickness), and its emergence as the Sezawa wave from the low-energy side of the Lamb shoulder at a critical value of k∥d. Furthermore, the behavior of a pronounced minimum in the Lamb shoulder near the longitudinal wave threshold observed in the experiments is reported and is found to be in good agreement with the calculated spectra. The elastic constants of the amorphous silicon layer are determined from the velocity dispersion of the Rayleigh surface acoustic wave and the minimum in the Lamb shoulder.

In situ control of industrial processes using laser light scattering and optical rotation

NASA Astrophysics Data System (ADS)

Mendoza Sanchez, Patricia Judith; López Echevarria, Daniel; Huerta Ruelas, Jorge Adalberto

2006-02-01

We present results of optical measurements in products or processes usually found in industrial processes, which can be used to control them. Laser light scattering was employed during semiconductor epitaxial growth by molecular beam epitaxy. With this technique, it was possible to determine growth rate, roughness and critical temperatures related to substrate degradation. With the same scattering technique, oil degradation as function of temperature was monitored for different automotive lubricants. Clear differences can be studied between monograde and multigrade oils. Optical rotation measurements as function of temperature were performed in apple juice in a pasteurization process like. Average variations related to optical rotation dependence of sugars were measured and monitored during heating and cooling process, finding a reversible behavior. As opposite behavior, sugar-protein solution was measured in a similar heating and cooling process. Final result showed a non-reversible behavior related to protein denaturation. Potential applications are discussed for metal-mechanic, electronic, food, and pharmaceutical industry. Future improvements in optical systems to make them more portable and easily implemented under typical industry conditions are mentioned.

Effects of Carrier Confinement and Intervalley Scattering on Photoexcited Electron Plasma in Silicon.

PubMed

Sieradzki, A; Kuznicki, Z T

2013-01-01

The ultrafast reflectivity of silicon, excited and probed with femtosecond laser pulses, is studied for different wavelengths and energy densities. The confinement of carriers in a thin surface layer delimited by a nanoscale Si-layered system buried in a Si heavily-doped wafer reduces the critical density of carriers necessary to create the electron plasma by a factor of ten. We performed two types of reflectivity measurements, using either a single beam or two beams. The plasma strongly depends on the photon energy density because of the intervalley scattering of the electrons revealed by two different mechanisms assisted by the electron-phonon interaction. One mechanism leads to a negative differential reflectivity that can be attributed to an induced absorption in X valleys. The other mechanism occurs, when the carrier population is thermalizing and gives rise to a positive differential reflectivity corresponding to Pauli-blocked intervalley gamma to X scattering. These results are important for improving the efficiency of Si light-to-electricity converters, in which there is a possibility of multiplying carriers by nanostructurization of Si.

Stability of Weyl metals under imuurity scattering

NASA Astrophysics Data System (ADS)

Huang, Zhoushen; Das, Tanmoy; Balatsky, Alexander V.; Arovas, Daniel P.

2013-03-01

We investigate the effects of bulk impurities on the electronic spectrum of Weyl semimetals, a recently identified class of Dirac-type materials. Using a T-matrix approach, we study resonant scattering due to a localized impurity in tight binding versions of the continuum models recently discussed by Burkov, Hook, and Balents, describing perturbed four-component Dirac fermions in the vicinity of a critical point. The impurity potential is described by a strength g as well as a matrix structure Λ. Unlike the case in d-wave superconductors, where a zero energy resonance can always be induced by varying the impurity scalar and/or magnetic impurity strength, we find that for certain types of impurity (Λ), the Weyl node is protected, and that a scalar impurity will induce an intragap resonance over a wide range of scattering stength. A general framework is developed to address this question, as well as to determine the dependence of resonance energy on the impurity strength. This work is supported in part by the NSF through grant DMR-1007028. Work at LANL was supported by US DoE.

Ultraviolet Thomson Scattering from Direct-Drive Coronal Plasmas

NASA Astrophysics Data System (ADS)

Henchen, R. J.; Goncharov, V. N.; Michel, D. T.; Follett, R. K.; Katz, J.; Froula, D. H.

2013-10-01

Ultraviolet (λ4 ω = 263 nm) Thomson scattering (TS) was used to probe ion-acoustic waves (IAW's) and electron plasma waves (EPW's) from direct-drive coronal plasmas. Fifty-nine drive beams (λ3 ω = 351 nm) illuminate a spherical target with a radius of ~860 μm. Advances in the ultraviolet (UV) TS diagnostic at the Omega Laser Facility provide the ability to detect deep UV photons (~190 nm) and allow access to scattered light from EPW's propagating near the 3 ω quarter-critical surface (~2.5 × 1021 cm-3) . A series of experiments studied the effects of ablator materials on coronal plasma conditions. Electron temperatures and densities were measured from 150 μm to 400 μm from the initial target surface. Standard CH shells were compared to three-layered shells consisting of Si doped CH, Si, and Be. Early analysis indicates that these multilayered targets have less hot-electron energy as a result of higher electron temperature in the coronal plasma. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Critical behavior of a chiral superfluid in a bipartite square lattice

NASA Astrophysics Data System (ADS)

Okamoto, Junichi; Huang, Wen-Min; Höppner, Robert; Mathey, Ludwig

2018-01-01

We study the critical behavior of Bose-Einstein condensation in the second band of a bipartite optical square lattice in a renormalization group framework at one-loop order. Within our field theoretical representation of the system, we approximate the system as a two-component Bose gas in three dimensions. We demonstrate that the system is in a different universality class than the previously studied condensation in a frustrated triangular lattice due to an additional Umklapp scattering term, which stabilizes the chiral superfluid order at low temperatures. We derive the renormalization group flow of the system and show that this order persists in the low energy limit. Furthermore, the renormalization flow suggests that the phase transition from the thermal phase to the chiral superfluid state is first order.

The stimulated Brillouin scattering during the interaction of picosecond laser pulses with moderate- scale-length plasmas

NASA Astrophysics Data System (ADS)

Gaeris, Andres Claudio

The Stimulated Brillouin Scattering (SBS) instability is studied in moderately short scale-length plasmas. The backscattered and specularly reflected light resulting from the interaction of a pair of high power picosecond duration laser pulses with solid Silicon, Gold and Parylene-N (CH) strip targets was spectrally resolved. The first, weaker laser pulse forms a short scale-length plasma while the second delayed one interacts with the isothermally expanded, underdense region of the plasma. The pulses are generated by the Table Top Terawatt (TTT) laser operating at 1054 nm (infrared) with intensities up to 5.10 16 W/cm2. Single laser pulses only show Lambertian scattering on the target critical surface. Pairs of pulses with high intensity in the second pulse show an additional backscattered, highly blueshifted feature, associated with SBS. Increasing this second pulse intensity even more leads to the appearance of a third feature, even more blueshifted than the second, resulting from the Brillouin sidescattering of the laser pulse reflected on the critical surface. The SBS threshold intensities and enhanced reflectivities for P-polarized light are determined for different plasma density scale-lengths. These measurements agree with the convective thresholds predicted by the SBS theory of Liu, Rosenbluth, and White using plasma profiles simulated by the LILAC code. The spectral position of the Brillouin back- and sidescattered features are determined. The SBS and Doppler shifts are much too small to explain the observed blueshifts. The refractive index shift is of the right magnitude, although more detailed verification is required in the future.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jeon, Byung-Gu; Koteswararao, B.; Park, C. B.

Thermal transport of quantum magnets has elucidated the nature of low energy elementary excitations and complex interplay between those excited states via strong scattering of thermal carriers. BiCu 2PO 6 is a unique frustrated spin-ladder compound exhibiting highly anisotropic spin excitations that contain both itinerant and localized dispersion characters along the b- and a-axes respectively. Here, we investigate thermal conductivity κ of BiCu 2PO 6 under high magnetic fields (H) of up to 30 tesla. A dip-feature in κ, located at ~15K at zero-H along all crystallographic directions, moves gradually toward lower temperature (T) with increasing H, thus resulting inmore » giant suppression by a factor of ~30 near the critical magnetic field of H c≅23.5 tesla. The giant H- and T-dependent suppression of κ can be explained by the combined result of resonant scattering of phononic heat carriers with magnetic energy levels and increased phonon scattering due to enhanced spin fluctuation at H c, unequivocally revealing the existence of strong spin-phonon coupling. Moreover, we find an experimental indication that the remaining magnetic heat transport along the b-axis becomes almost gapless at the magnetic quantum critical point realized at H c.« less

Flow-through compression cell for small-angle and ultra-small-angle neutron scattering measurements

NASA Astrophysics Data System (ADS)

Hjelm, Rex P.; Taylor, Mark A.; Frash, Luke P.; Hawley, Marilyn E.; Ding, Mei; Xu, Hongwu; Barker, John; Olds, Daniel; Heath, Jason; Dewers, Thomas

2018-05-01

In situ measurements of geological materials under compression and with hydrostatic fluid pressure are important in understanding their behavior under field conditions, which in turn provides critical information for application-driven research. In particular, understanding the role of nano- to micro-scale porosity in the subsurface liquid and gas flow is critical for the high-fidelity characterization of the transport and more efficient extraction of the associated energy resources. In other applications, where parts are produced by the consolidation of powders by compression, the resulting porosity and crystallite orientation (texture) may affect its in-use characteristics. Small-angle neutron scattering (SANS) and ultra SANS are ideal probes for characterization of these porous structures over the nano to micro length scales. Here we show the design, realization, and performance of a novel neutron scattering sample environment, a specially designed compression cell, which provides compressive stress and hydrostatic pressures with effective stress up to 60 MPa, using the neutron beam to probe the effects of stress vectors parallel to the neutron beam. We demonstrate that the neutron optics is suitable for the experimental objectives and that the system is highly stable to the stress and pressure conditions of the measurements.

Dynamic light scattering study on phase separation of a protein-water mixture: Application on cold cataract development in the ocular lens

NASA Astrophysics Data System (ADS)

Petta, V.; Pharmakakis, N.; Papatheodorou, G. N.; Yannopoulos, S. N.

2008-06-01

We present a detailed dynamic light scattering study of the phase separation in the ocular lens emerging during cold cataract development. Cold cataract is a phase separation effect that proceeds via spinodal decomposition of the lens cytoplasm with cooling. The intensity autocorrelation functions of the lens protein content are analyzed with the aid of two methods, providing information on the populations and dynamics of the scattering elements associated with cold cataract. It is found that the temperature dependence of many measurable parameters changes appreciably at the characteristic temperature ˜16±1°C which is associated with the onset of cold cataract. By extending the temperature range of this work to previously inaccessible regimes, i.e., well below the phase separation or coexistence curve at Tcc , we have been able to accurately determine the temperature dependence of the collective and self-diffusion coefficients of proteins near the spinodal. The analysis showed that the dynamics of proteins bears some resemblance to the dynamics of structural glasses, where the apparent activation energy for particle diffusion increases below Tcc , indicating a highly cooperative motion. Application of ideas developed for studying the critical dynamics of binary protein-solvent mixtures, as well as the use of a modified Arrhenius equation, enabled us to estimate the spinodal temperature Tsp of the lens nucleus. The applicability of dynamic light scattering as a noninvasive, early-diagnostic tool for ocular diseases is also demonstrated in light of the findings of the present paper.

Shadowgraph Study of Gradient Driven Fluctuations

NASA Technical Reports Server (NTRS)

Cannell, David; Nikolaenko, Gennady; Giglio, Marzio; Vailati, Alberto; Croccolo, Fabrizio; Meyer, William

2002-01-01

A fluid or fluid mixture, subjected to a vertical temperature and/or concentration gradient in a gravitational field, exhibits greatly enhanced light scattering at small angles. This effect is caused by coupling between the vertical velocity fluctuations due to thermal energy and the vertically varying refractive index. Physically, small upward or downward moving regions will be displaced into fluid having a refractive index different from that of the moving region, thus giving rise to the enhanced scattering. The scattered intensity is predicted to vary with scattering wave vector q, as q(sup -4), for sufficiently large q, but the divergence is quenched by gravity at small q. In the absence of gravity, the long wavelength fluctuations responsible for the enhanced scattering are predicted to grow until limited by the sample dimensions. It is thus of interest to measure the mean-squared amplitude of such fluctuations in the microgravity environment for comparison with existing theory and ground based measurements. The relevant wave vectors are extremely small, making traditional low-angle light scattering difficult or impossible because of stray elastically scattered light generated by optical surfaces. An alternative technique is offered by the shadowgraph method, which is normally used to visualize fluid flows, but which can also serve as a quantitative tool to measure fluctuations. A somewhat novel shadowgraph apparatus and the necessary data analysis methods will be described. The apparatus uses a spatially coherent, but temporally incoherent, light source consisting of a super-luminescent diode coupled to a single-mode optical fiber in order to achieve extremely high spatial resolution, while avoiding effects caused by interference of light reflected from the various optical surfaces that are present when using laser sources. Results obtained for a critical mixture of aniline and cyclohexane subjected to a vertical temperature gradient will be presented. The sample was confined between two horizontal parallel sapphire plates with a vertical spacing of 1 mm. The temperatures of the sapphire plates were controlled by independent circulating water loops that used Peltier devices to add or remove heat from the room air as required. For a mixture with a temperature gradient, two effects are involved in generating the vertical refractive index gradient, namely thermal expansion and the Soret effect, which generates a concentration gradient in response to the applied temperature gradient. For the aniline/cyclohexane system, the denser component (aniline) migrates toward the colder surface. Consequently, when heating from above, both effects result in the sample density decreasing with altitude and are stabilizing in the sense that no convective motion occurs regardless of the magnitude of the applied temperature gradient. The Soret effect is strong near a binary liquid critical point, and thus the dominant effect is due to the induced concentration gradient. The results clearly show the divergence at low q and the predicted gravitational quenching. Results obtained for different applied temperature gradients at varying temperature differences from the critical temperature, clearly demonstrate the predicted divergence of the thermal diffusion ratio. Thus, the more closely the critical point is approached, the smaller becomes the temperature gradient required to generate the same signal. Two different methods have been used to generate pure concentration gradients. In the first, a sample cell was filled with a single fluid, ethylene glycol, and a denser miscible fluid, water, was added from below thus establishing a sharp interface to begin the experiment. As time went on the two fluids diffused into each other, and large amplitude fluctuations were clearly observed at low q. The effects of gravitational quenching were also evident. In the second method, the aniline/cyclohexane sample was used, and after applying a vertical temperature gradient for several hours, the top and bottom temperatures were set equal and the thermal gradient died on a time scale of seconds, leaving the Soret induced concentration gradient in place. Again, large-scale fluctuations were observed and died away slowly in amplitude as diffusion destroyed the initial concentration gradient.

Spinodal assisted growing dynamics of critical nucleus in polymer blends

NASA Astrophysics Data System (ADS)

Zhang, Xinghua; Qi, Shuanhu; Yan, Dadong

2012-11-01

In metastable polymer blends, nonclassical critical nucleus is not a drop of stable phase in core wrapped with a sharp interface, but a diffuse structure depending on the metastability. Thus, forming a critical nucleus does not mean the birth of a new phase. In the present work, the nonclassical growing dynamics of the critical nucleus is addressed in the metastable polymer blends by incorporating self-consistent field theory and external potential dynamics theory, which leads to an intuitionistic description for the scattering experiments. The results suggest that the growth of nonclassical critical nucleus is controlled by the spinodal-decomposition which happens in the region surrounding the nucleus. This leads to forming the shell structures around the nucleus.

Two-component scattering model and the electron density spectrum

NASA Astrophysics Data System (ADS)

Zhou, A. Z.; Tan, J. Y.; Esamdin, A.; Wu, X. J.

2010-02-01

In this paper, we discuss a rigorous treatment of the refractive scintillation caused by a two-component interstellar scattering medium and a Kolmogorov form of density spectrum. It is assumed that the interstellar scattering medium is composed of a thin-screen interstellar medium (ISM) and an extended interstellar medium. We consider the case that the scattering of the thin screen concentrates in a thin layer represented by a δ function distribution and that the scattering density of the extended irregular medium satisfies the Gaussian distribution. We investigate and develop equations for the flux density structure function corresponding to this two-component ISM geometry in the scattering density distribution and compare our result with the observations. We conclude that the refractive scintillation caused by this two-component ISM scattering gives a more satisfactory explanation for the observed flux density variation than does the single extended medium model. The level of refractive scintillation is strongly sensitive to the distribution of scattering material along the line of sight (LOS). The theoretical modulation indices are comparatively less sensitive to the scattering strength of the thin-screen medium, but they critically depend on the distance from the observer to the thin screen. The logarithmic slope of the structure function is sensitive to the scattering strength of the thin-screen medium, but is relatively insensitive to the thin-screen location. Therefore, the proposed model can be applied to interpret the structure functions of flux density observed in pulsar PSR B2111 + 46 and PSR B0136 + 57. The result suggests that the medium consists of a discontinuous distribution of plasma turbulence embedded in the interstellar medium. Thus our work provides some insight into the distribution of the scattering along the LOS to the pulsar PSR B2111 + 46 and PSR B0136 + 57.

Hollow-fiber flow field-flow fractionation and multi-angle light scattering investigation of the size, shape and metal-release of silver nanoparticles in aqueous medium for nano-risk assessment.

PubMed

Marassi, Valentina; Casolari, Sonia; Roda, Barbara; Zattoni, Andrea; Reschiglian, Pierluigi; Panzavolta, Silvia; Tofail, Syed A M; Ortelli, Simona; Delpivo, Camilla; Blosi, Magda; Costa, Anna Luisa

2015-03-15

Due to the increased use of silver nanoparticles in industrial scale manufacturing, consumer products and nanomedicine reliable measurements of properties such as the size, shape and distribution of these nano particles in aqueous medium is critical. These properties indeed affect both functional properties and biological impacts especially in quantifying associated risks and identifying suitable risk-mediation strategies. The feasibility of on-line coupling of a fractionation technique such as hollow-fiber flow field flow fractionation (HF5) with a light scattering technique such as MALS (multi-angle light scattering) is investigated here for this purpose. Data obtained from such a fractionation technique and its combination thereof with MALS have been compared with those from more conventional but often complementary techniques e.g. transmission electron microscopy, dynamic light scattering, atomic absorption spectroscopy, and X-ray fluorescence. The combination of fractionation and multi angle light scattering techniques have been found to offer an ideal, hyphenated methodology for a simultaneous size-separation and characterization of silver nanoparticles. The hydrodynamic radii determined by fractionation techniques can be conveniently correlated to the mean average diameters determined by multi angle light scattering and reliable information on particle morphology in aqueous dispersion has been obtained. The ability to separate silver (Ag(+)) ions from silver nanoparticles (AgNPs) via membrane filtration during size analysis is an added advantage in obtaining quantitative insights to its risk potential. Most importantly, the methodology developed in this article can potentially be extended to similar characterization of metal-based nanoparticles when studying their functional effectiveness and hazard potential. Copyright © 2014 Elsevier B.V. All rights reserved.

Resolving the Framework Position of Organic Structure-Directing Agents in Hierarchical Zeolites via Polarized Stimulated Raman Scattering.

PubMed

Fleury, Guillaume; Steele, Julian A; Gerber, Iann C; Jolibois, F; Puech, P; Muraoka, Koki; Keoh, Sye Hoe; Chaikittisilp, Watcharop; Okubo, Tatsuya; Roeffaers, Maarten B J

2018-04-05

The direct synthesis of hierarchically intergrown silicalite-1 can be achieved using a specific diquaternary ammonium agent. However, the location of these molecules in the zeolite framework, which is critical to understand the formation of the material, remains unclear. Where traditional characterization tools have previously failed, herein we use polarized stimulated Raman scattering (SRS) microscopy to resolve molecular organization inside few-micron-sized crystals. Through a combination of experiment and first-principles calculations, our investigation reveals the preferential location of the templating agent inside the linear pores of the MFI framework. Besides illustrating the attractiveness of SRS microscopy in the field of material science to study and spatially resolve local molecular distribution as well as orientation, these results can be exploited in the design of new templating agents for the preparation of hierarchical zeolites.

Initial characterization of mudstone nanoporosity with small angle neutron scattering using caprocks from carbon sequestration sites.

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCray, John; Navarre-Sitchler, Alexis; Mouzakis, Katherine

Geological carbon sequestration relies on the principle that CO{sub 2} injected deep into the subsurface is unable to leak to the atmosphere. Structural trapping by a relatively impermeable caprock (often mudstone such as a shale) is the main trapping mechanism that is currently relied on for the first hundreds of years. Many of the pores of the caprock are of micrometer to nanometer scale. However, the distribution, geometry and volume of porosity at these scales are poorly characterized. Differences in pore shape and size can cause variation in capillary properties and fluid transport resulting in fluid pathways with different capillarymore » entry pressures in the same sample. Prediction of pore network properties for distinct geologic environments would result in significant advancement in our ability to model subsurface fluid flow. Specifically, prediction of fluid flow through caprocks of geologic CO{sub 2} sequestration reservoirs is a critical step in evaluating the risk of leakage to overlying aquifers. The micro- and nanoporosity was analyzed in four mudstones using small angle neutron scattering (SANS). These mudstones are caprocks of formations that are currently under study or being used for carbon sequestration projects and include the Marine Tuscaloosa Group, the Lower Tuscaloosa Group, the upper and lower shale members of the Kirtland Formation, and the Pennsylvanian Gothic shale. Total organic carbon varies from <0.3% to 4% by weight. Expandable clay contents range from 10% to {approx}40% in the Gothic shale and Kirtland Formation, respectively. Neutrons effectively scatter from interfaces between materials with differing scattering length density (i.e. minerals and pores). The intensity of scattered neutrons, I(Q), where Q is the scattering vector, gives information about the volume of pores and their arrangement in the sample. The slope of the scattering data when plotted as log I(Q) vs. log Q provides information about the fractality or geometry of the pore network. Results from this study, combined with high-resolution TEM imaging, provide insight into the differences in volume and geometry of porosity between these various mudstones.« less

Scattering by multiple cylinders located on both sides of an interface

NASA Astrophysics Data System (ADS)

Lee, Siu-Chun

2018-07-01

The solution for scattering by multiple parallel infinite cylinders located in adjacent half spaces with dissimilar refractive index is presented in this paper. The incident radiation is an arbitrarily polarized plane wave propagating in the upper half space in the plane perpendicular to the axis of the cylinders. The formulation of the electromagnetic field vectors utilized Hertz potentials that are expressed in terms of an expansion of cylindrical wave functions. It accounts for the near-field multiple scattering, Fresnel effect at the interface, and interaction between cylinders in both half spaces. Analytical formulas are derived for the electromagnetic field and Poynting vector in the far-field. The present solution provides the theoretical framework for deducing the solutions for scattering by cylinders located on either side of an interface irradiated by a propagating or an evanescent incident wave. Deduction of these solutions from the present formulation is demonstrated. Numerical results are presented to illustrate the frustration of total internal reflection and scattering of light beyond the critical angle by nanocylinders located in either or both half spaces.

Identification of the low-energy excitations in a quantum critical system

NASA Astrophysics Data System (ADS)

Heitmann, Tom; Lamsal, Jagat; Watson, Shannon; Erwin, Ross; Chen, Wangchun; Zhao, Yang; Montfrooij, Wouter

2017-05-01

We have identified low-energy magnetic excitations in a doped quantum critical system by means of polarized neutron scattering experiments. The presence of these excitations could explain why Ce(Fe0.76Ru0.24)2Ge2 displays dynamical scaling in the absence of local critical behavior or long-range spin-density wave criticality. The low-energy excitations are associated with the reorientations of the superspins of fully ordered, isolated magnetic clusters that form spontaneously upon lowering the temperature. The system houses both frozen clusters and dynamic clusters, as predicted by Hoyos and Vojta [Phys. Rev. B 74, 140401(R) (2006)].

Determining the unique refractive index properties of solid polystyrene aerosol using broadband Mie scattering from optically trapped beads.

PubMed

Jones, Stephanie H; King, Martin D; Ward, Andrew D

2013-12-21

A method is described to measure the refractive index dispersion with wavelength of optically trapped solid particles in air. Knowledge of the refraction properties of solid particles is critical for the study of aerosol; both in the laboratory and in the atmosphere for climate studies. Single micron-sized polystyrene beads were optically trapped in air using a vertically aligned counter-propagating configuration of focussed laser beams. Each bead was illuminated using white light from a broadband light emitting diode (LED) and elastic scattering within the bead was collected onto a spectrograph. The resulting Mie spectra were analysed to accurately determine polystyrene bead radii to ±0.4 nm and values of the refractive index to ±0.0005 over a wavelength range of 480-700 nm. We demonstrate that optical trapping combined with elastic scattering can be used to both accurately size polystyrene beads suspended in air and determine their wavelength dependent refractive index. The refractive index dispersions are in close agreement with reported values for polystyrene beads in aqueous dispersion. Our results also demonstrate a variation in the refractive index of polystyrene, from bead to bead, in a commercial sample. The measured variation highlights that care must be taken when using polystyrene beads as a calibration aerosol.

Signal broadening in the laser Doppler velocimeter.

NASA Technical Reports Server (NTRS)

Angus, J. C.; Edwards, R. V.; Dunning, J. W., Jr.

1971-01-01

Critical review of a recent paper in which Denison, Stevenson, and Fox (1971) discussed the sources of spectral broadening in the laser Doppler velocimeter. It is pointed out that, in their discussion, the above-mentioned authors indicated that the spread in wave vectors of the incident and detected fields and the finite length of time a scattering center stayed in the sample volume each contributed separately and independently to the observed spectral width of the scattered radiation. This statement is termed incorrect, and it is shown that the two effects are one and the same.

Observation of the enhanced backscattering of light by the end of a tilted dielectric cylinder owing to the caustic merging transition

NASA Astrophysics Data System (ADS)

Marston, Philip L.; Zhang, Yibing; Thiessen, David B.

2003-01-01

The scattering of light by obliquely illuminated circular dielectric cylinders was previously demonstrated to be enhanced by a merger of Airy caustics at a critical tilt angle. [Appl. Opt. 37, 1534 (1998)]. A related enhancement is demonstrated here for backward and near-backward scattering for cylinders cut with a flat end perpendicular to the cylinder's axis. It is expected that merged caustics will enhance the backscattering by clouds of randomly oriented circular cylinders that have appropriately flat ends.

Fukushima Daiichi Muon Imaging

NASA Astrophysics Data System (ADS)

Miyadera, Haruo

2015-10-01

Japanese government announced cold-shutdown condition of the reactors at Fukushima Daiichi by the end of 2011, and mid- and long-term roadmap towards decommissioning has been drawn. However, little is known for the conditions of the cores because access to the reactors has been limited by the high radiation environment. The debris removal from the Unit 1 - 3 is planned to start as early as 2020, but the dismantlement is not easy without any realistic information of the damage to the cores, and the locations and amounts of the fuel debris. Soon after the disaster of Fukushima Daiichi, several teams in the US and Japan proposed to apply muon transmission or scattering imagings to provide information of the Fukushima Daiichi reactors without accessing inside the reactor building. GEANT4 modeling studies of Fukushima Daiichi Unit 1 and 2 showed clear superiority of the muon scattering method over conventional transmission method. The scattering method was demonstrated with a research reactor, Toshiba Nuclear Critical Assembly (NCA), where a fuel assembly was imaged with 3-cm resolution. The muon scattering imaging of Fukushima Daiichi was approved as a national project and is aiming at installing muon trackers to Unit 2. A proposed plan includes installation of muon trackers on the 2nd floor (operation floor) of turbine building, and in front of the reactor building. Two 7mx7m detectors were assembled at Toshiba and tested.

Consistent Pl Analysis of Aqueous Uranium-235 Critical Assemblies

NASA Technical Reports Server (NTRS)

Fieno, Daniel

1961-01-01

The lethargy-dependent equations of the consistent Pl approximation to the Boltzmann transport equation for slowing down neutrons have been used as the basis of an IBM 704 computer program. Some of the effects included are (1) linearly anisotropic center of mass elastic scattering, (2) heavy element inelastic scattering based on the evaporation model of the nucleus, and (3) optional variation of the buckling with lethargy. The microscopic cross-section data developed for this program covered 473 lethargy points from lethargy u = 0 (10 Mev) to u = 19.8 (0.025 ev). The value of the fission neutron age in water calculated here is 26.5 square centimeters; this value is to be compared with the recent experimental value given as 27.86 square centimeters. The Fourier transform of the slowing-down kernel for water to indium resonance energy calculated here compared well with the Fourier transform of the kernel for water as measured by Hill, Roberts, and Fitch. This method of calculation has been applied to uranyl fluoride - water solution critical assemblies. Theoretical results established for both unreflected and fully reflected critical assemblies have been compared with available experimental data. The theoretical buckling curve derived as a function of the hydrogen to uranium-235 atom concentration for an energy-independent extrapolation distance was successful in predicting the critical heights of various unreflected cylindrical assemblies. The critical dimensions of fully water-reflected cylindrical assemblies were reasonably well predicted using the theoretical buckling curve and reflector savings for equivalent spherical assemblies.

The application of the principles of invariance to the radiative transfer equation in plant canopies

NASA Technical Reports Server (NTRS)

Ganapol, B. D.; Myneni, R. B.

1992-01-01

Solutions of the radiative transfer equation describing photon interactions with vegetation canopies are important in remote sensing since they provide the canopy reflectance distribution required in the interpretation of satellite acquired information. The general one-dimensional two-angle transport problem for a finite copy of arbitrary leaf angle distribution is considered. Analytical solutions are obtained in terms of generalized Chandrasekhar's X- and Y-functions by invoking the principles of invariance. A critical step in the formulation involves the decomposition of the integral of the scattering phase function into a product of known functions of the incident and scattered photon directions. Several simplified cases previously considered in the literature are derived from the generalized solution. Various symmetries obeyed by the scattering operator and reciprocity relations are formally proved.

Evaluation of beam halo from beam-gas scattering at the KEK Accelerator Test Facility

NASA Astrophysics Data System (ADS)

Yang, R.; Naito, T.; Bai, S.; Aryshev, A.; Kubo, K.; Okugi, T.; Terunuma, N.; Zhou, D.; Faus-Golfe, A.; Kubytskyi, V.; Liu, S.; Wallon, S.; Bambade, P.

2018-05-01

In circular colliders, as well as in damping rings and synchrotron radiation light sources, beam halo is one of the critical issues limiting the performance as well as potentially causing component damage and activation. It is imperative to clearly understand the mechanisms that lead to halo formation and to test the available theoretical models. Elastic beam-gas scattering can drive particles to large oscillation amplitudes and be a potential source of beam halo. In this paper, numerical estimation and Monte Carlo simulations of this process at the ATF of KEK are presented. Experimental measurements of beam halo in the ATF2 beam line using a diamond sensor detector are also described, which clearly demonstrate the influence of the beam-gas scattering process on the transverse halo distribution.

A string theory which isn't about strings

NASA Astrophysics Data System (ADS)

Lee, Kanghoon; Rey, Soo-Jong; Rosabal, J. A.

2017-11-01

Quantization of closed string proceeds with a suitable choice of worldsheet vacuum. A priori, the vacuum may be chosen independently for left-moving and right-moving sectors. We construct ab initio quantized bosonic string theory with left-right asymmetric worldsheet vacuum and explore its consequences and implications. We critically examine the validity of new vacuum and carry out first-quantization using standard operator formalism. Remarkably, the string spectrum consists only of a finite number of degrees of freedom: string gravity (massless spin-two, Kalb-Ramond and dilaton fields) and two massive spin-two Fierz-Pauli fields. The massive spin-two fields have negative norm, opposite mass-squared, and provides a Lee-Wick type extension of string gravity. We compute two physical observables: tree-level scattering amplitudes and one-loop cosmological constant. Scattering amplitude of four dilatons is shown to be a rational function of kinematic invariants, and in D = 26 factorizes into contributions of massless spin-two and a pair of massive spin-two fields. The string one loop partition function is shown to perfectly agree with one loop Feynman diagram of string gravity and two massive spin-two fields. In particular, it does not exhibit modular invariance. We critically compare our construction with recent studies and contrast differences.

Are metastable, precrystallisation, density-fluctuations a universal phenomena?

PubMed

Heeley, Ellen L; Poh, C Kit; Li, Wu; Maidens, Anna; Bras, Wim; Dolbnya, Igor P; Gleeson, Anthony J; Terrill, Nicolas J; Fairclough, J Patrick A; Olmsted, Peter D; Ristic, Rile I; Hounslow, Micheal J; Ryan, Anthony J

2003-01-01

In-situ observations of crystallisation in minerals and organic polymers have been made by simultaneous, time-resolved small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) techniques. In isotactic polypropylene slow quiescent crystallisation shows the onset of large scale ordering prior to crystal growth. Rapid crystallisations studied by melt extrusion indicate the development of well resolved oriented SAXS patterns associated with long range order before the development of crystalline peaks in the WAXS region. Block copolymers self-assemble into mesophases in polymer melts above a critical chain length (or above a critical temperature) and this self-assembly process is shown to be susceptible to an incipient crystallisation. Mesophase formation is observed at anomalously high temperatures in ethylene-oxide containing block copolymers below the normal melting point of the polyoxy ethylene chains. Formation of calcium carbonate from aqueous solutions of sodium carbonate and calcium nitrate is observed to be a two-stage process and precipitation proceeds by the production of an amorphous metastable phase. This phase grows until it is volume filling and leads to the formation of the two polymorphs Calcite and Vaterite. These three sets of results suggest pre-nucleation density fluctuations, leading to a metastable phase, play an integral role in all three classes of crystallisation. In due course, this phase undergoes transformation to "normal" crystals.

Nonlinear coupled mode approach for modeling counterpropagating solitons in the presence of disorder-induced multiple scattering in photonic crystal waveguides

NASA Astrophysics Data System (ADS)

Mann, Nishan; Hughes, Stephen

2018-02-01

We present the analytical and numerical details behind our recently published article [Phys. Rev. Lett. 118, 253901 (2017), 10.1103/PhysRevLett.118.253901], describing the impact of disorder-induced multiple scattering on counterpropagating solitons in photonic crystal waveguides. Unlike current nonlinear approaches using the coupled mode formalism, we account for the effects of intraunit cell multiple scattering. To solve the resulting system of coupled semilinear partial differential equations, we introduce a modified Crank-Nicolson-type norm-preserving implicit finite difference scheme inspired by the transfer matrix method. We provide estimates of the numerical dispersion characteristics of our scheme so that optimal step sizes can be chosen to either minimize numerical dispersion or to mimic the exact dispersion. We then show numerical results of a fundamental soliton propagating in the presence of multiple scattering to demonstrate that choosing a subunit cell spatial step size is critical in accurately capturing the effects of multiple scattering, and illustrate the stochastic nature of disorder by simulating soliton propagation in various instances of disordered photonic crystal waveguides. Our approach is easily extended to include a wide range of optical nonlinearities and is applicable to various photonic nanostructures where power propagation is bidirectional, either by choice, or as a result of multiple scattering.

Nonlinear Scattering of VLF Waves in the Radiation Belts

NASA Astrophysics Data System (ADS)

Crabtree, Chris; Rudakov, Leonid; Ganguli, Guru; Mithaiwala, Manish

2014-10-01

Electromagnetic VLF waves, such as whistler mode waves, control the lifetime of trapped electrons in the radiation belts by pitch-angle scattering. Since the pitch-angle scattering rate is a strong function of the wave properties, a solid understanding of VLF wave sources and propagation in the magnetosphere is critical to accurately calculate electron lifetimes. Nonlinear scattering (Nonlinear Landau Damping) is a mechanism that can strongly alter VLF wave propagation [Ganguli et al. 2010], primarily by altering the direction of propagation, and has not been accounted for in previous models of radiation belt dynamics. Laboratory results have confirmed the dramatic change in propagation direction when the pump wave has sufficient amplitude to exceed the nonlinear threshold [Tejero et al. 2014]. Recent results show that the threshold for nonlinear scattering can often be met by naturally occurring VLF waves in the magnetosphere, with wave magnetic fields of the order of 50-100 pT inside the plasmapause. Nonlinear scattering can then dramatically alter the macroscopic dynamics of waves in the radiation belts leading to the formation of a long-lasting wave-cavity [Crabtree et al. 2012] and, when amplification is present, a multi-pass amplifier [Ganguli et al. 2012]. By considering these effects, the lifetimes of electrons can be dramatically reduced. This work is supported by the Naval Research Laboratory base program.

Mathematical filtering minimizes metallic halation of titanium implants in MicroCT images.

PubMed

Ha, Jee; Osher, Stanley J; Nishimura, Ichiro

2013-01-01

Microcomputed tomography (MicroCT) images containing titanium implant suffer from x-rays scattering, artifact and the implant surface is critically affected by metallic halation. To improve the metallic halation artifact, a nonlinear Total Variation denoising algorithm such as Split Bregman algorithm was applied to the digital data set of MicroCT images. This study demonstrated that the use of a mathematical filter could successfully reduce metallic halation, facilitating the osseointegration evaluation at the bone implant interface in the reconstructed images.

Anomalous time delays and quantum weak measurements in optical micro-resonators

PubMed Central

Asano, M.; Bliokh, K. Y.; Bliokh, Y. P.; Kofman, A. G.; Ikuta, R.; Yamamoto, T.; Kivshar, Y. S.; Yang, L.; Imoto, N.; Özdemir, Ş.K.; Nori, F.

2016-01-01

Quantum weak measurements, wavepacket shifts and optical vortices are universal wave phenomena, which originate from fine interference of multiple plane waves. These effects have attracted considerable attention in both classical and quantum wave systems. Here we report on a phenomenon that brings together all the above topics in a simple one-dimensional scalar wave system. We consider inelastic scattering of Gaussian wave packets with parameters close to a zero of the complex scattering coefficient. We demonstrate that the scattered wave packets experience anomalously large time and frequency shifts in such near-zero scattering. These shifts reveal close analogies with the Goos–Hänchen beam shifts and quantum weak measurements of the momentum in a vortex wavefunction. We verify our general theory by an optical experiment using the near-zero transmission (near-critical coupling) of Gaussian pulses propagating through a nano-fibre with a side-coupled toroidal micro-resonator. Measurements demonstrate the amplification of the time delays from the typical inverse-resonator-linewidth scale to the pulse-duration scale. PMID:27841269

Elastic and inelastic scattering of neutrons on 238U nucleus

NASA Astrophysics Data System (ADS)

Capote, R.; Trkov, A.; Sin, M.; Herman, M. W.; Soukhovitskiĩ, E. Sh.

2014-04-01

Advanced modelling of neutron induced reactions on the 238U nucleus is aimed at improving our knowledge of neutron scattering. Capture and fission channels are well constrained by available experimental data and neutron standard evaluation. A focus of this contribution is on elastic and inelastic scattering cross sections. The employed nuclear reaction model includes - a new rotational-vibrational dispersive optical model potential coupling the low-lying collective bands of vibrational character observed in even-even actinides; - the Engelbrecht-Weidenmüller transformation allowing for inclusion of compound-direct interference effects; - and a multi-humped fission barrier with absorption in the secondary well described within the optical model for fission. Impact of the advanced modelling on elastic and inelastic scattering cross sections including angular distributions and emission spectra is assessed both by comparison with selected microscopic experimental data and integral criticality benchmarks including measured reaction rates (e.g. JEMIMA, FLAPTOP and BIG TEN). Benchmark calculations provided feedback to improve the reaction modelling. Improvement of existing libraries will be discussed.

Crustal Seismic Attenuation in Germany Measured with Acoustic Radiative Transfer Theory

NASA Astrophysics Data System (ADS)

Gaebler, Peter J.; Eulenfeld, Tom; Wegler, Ulrich

2017-04-01

This work is carried out in the context of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). As part of this treaty a verification regime was introduced to detect, locate and characterize nuclear explosion testings. The study of seismology can provide essential information in the form of broadband waveform recordings for the identification and verification of these critical events. A profound knowledge of the Earth's subsurface between source and receiver is required for a detailed description of the seismic wave field. In addition to underground parameters such as seismic velocity or anisotropy, information about seismic attenuation values of the medium are required. Goal of this study is the creation of a comprehensive model of crustal seismic attenuation in Germany and adjacent areas. Over 20 years of earthquake data from the German Central Seismological Observatory data archive is used to estimate the spatial dependent distribution of seismic intrinsic and scattering attenuation of S-waves for frequencies between 0.5 and 20 Hz. The attenuation models are estimated by fitting synthetic seismogram envelopes calculated with acoustic radiative transfer theory to observed seismogram envelopes. This theory describes the propagation of seismic S-energy under the assumption of multiple isotropic scattering, the crustal structure of the scattering medium is hereby represented by a half-space model. We present preliminary results of the spatial distribution of intrinsic attenuation represented by the absorption path length, as well as of scattering attenuation in terms of the mean free path and compare the outcomes to results from previous studies. Furthermore catalog magnitudes are compared to moment magnitudes estimated during the inversion process. Additionally site amplification factors of the stations are presented.

Molecular characterization of multivalent bioconjugates by size-exclusion chromatography with multiangle laser light scattering.

PubMed

Pollock, Jacob F; Ashton, Randolph S; Rode, Nikhil A; Schaffer, David V; Healy, Kevin E

2012-09-19

The degree of substitution and valency of bioconjugate reaction products are often poorly judged or require multiple time- and product-consuming chemical characterization methods. These aspects become critical when analyzing and optimizing the potency of costly polyvalent bioactive conjugates. In this study, size-exclusion chromatography with multiangle laser light scattering was paired with refractive index detection and ultraviolet spectroscopy (SEC-MALS-RI-UV) to characterize the reaction efficiency, degree of substitution, and valency of the products of conjugation of either peptides or proteins to a biopolymer scaffold, i.e., hyaluronic acid (HyA). Molecular characterization was more complete compared to estimates from a protein quantification assay, and exploitation of this method led to more accurate deduction of the molecular structures of polymer bioconjugates. Information obtained using this technique can improve macromolecular engineering design principles and help to better understand multivalent macromolecular interactions in biological systems.

Molecular characterization of multivalent bioconjugates by size-exclusion chromatography (SEC) with multi-angle laser light scattering (MALS)

PubMed Central

Pollock, Jacob F.; Ashton, Randolph S.; Rode, Nikhil A.; Schaffer, David V.; Healy, Kevin E.

2013-01-01

The degree of substitution and valency of bioconjugate reaction products are often poorly judged or require multiple time- and product- consuming chemical characterization methods. These aspects become critical when analyzing and optimizing the potency of costly polyvalent bioactive conjugates. In this study, size-exclusion chromatography with multi-angle laser light scattering was paired with refractive index detection and ultraviolet spectroscopy (SEC-MALS-RI-UV) to characterize the reaction efficiency, degree of substitution, and valency of the products of conjugation of either peptides or proteins to a biopolymer scaffold, i.e., hyaluronic acid (HyA). Molecular characterization was more complete compared to estimates from a protein quantification assay, and exploitation of this method led to more accurate deduction of the molecular structures of polymer bioconjugates. Information obtained using this technique can improve macromolecular engineering design principles and better understand multivalent macromolecular interactions in biological systems. PMID:22794081

Nanoscale electron transport at the surface of a topological insulator.

PubMed

Bauer, Sebastian; Bobisch, Christian A

2016-04-21

The use of three-dimensional topological insulators for disruptive technologies critically depends on the dissipationless transport of electrons at the surface, because of the suppression of backscattering at defects. However, in real devices, defects are unavoidable and scattering at angles other than 180° is allowed for such materials. Until now, this has been studied indirectly by bulk measurements and by the analysis of the local density of states in close vicinity to defect sites. Here, we directly measure the nanoscale voltage drop caused by the scattering at step edges, which occurs if a lateral current flows along a three-dimensional topological insulator. The experiments were performed using scanning tunnelling potentiometry for thin Bi2Se3 films. So far, the observed voltage drops are small because of large contributions of the bulk to the electronic transport. However, for the use of ideal topological insulating thin films in devices, these contributions would play a significant role.

Nanoscale electron transport at the surface of a topological insulator

NASA Astrophysics Data System (ADS)

Bauer, Sebastian; Bobisch, Christian A.

2016-04-01

The use of three-dimensional topological insulators for disruptive technologies critically depends on the dissipationless transport of electrons at the surface, because of the suppression of backscattering at defects. However, in real devices, defects are unavoidable and scattering at angles other than 180° is allowed for such materials. Until now, this has been studied indirectly by bulk measurements and by the analysis of the local density of states in close vicinity to defect sites. Here, we directly measure the nanoscale voltage drop caused by the scattering at step edges, which occurs if a lateral current flows along a three-dimensional topological insulator. The experiments were performed using scanning tunnelling potentiometry for thin Bi2Se3 films. So far, the observed voltage drops are small because of large contributions of the bulk to the electronic transport. However, for the use of ideal topological insulating thin films in devices, these contributions would play a significant role.

Fingerprint Stimulated Raman Scattering Imaging Reveals Retinoid Coupling Lipid Metabolism and Survival.

PubMed

Chen, Andy Jing; Li, Junjie; Jannasch, Amber; Ozseker, Sena; Wang, Meng C; Cheng, Ji-Xin

2018-06-17

Retinoids play critical roles in development, immunity and lipid metabolism, and their deficiency leads to various human disorders. Yet, tools for sensing retinoids in vivo are lacking, which limits the understanding of retinoid distribution, dynamics and functions in living organisms. Here, using hyperspectral stimulated Raman scattering microscopy, we discover a previously unknown cytoplasmic store of retinoids in Caenorahbditis elegans. Following the temporal dynamics of retinoids, we reveal that their levels are positively correlated with fat storage, and their supplementation slows down fat loss during dauer starvation. We also discover that retinoids promote fat unsaturation in response to high-glucose stress, and improve organism survival. Together, our studies report a new method for tracking the spatiotemporal dynamics of retinoids in living organisms, and suggest the crucial roles of retinoids in maintaining metabolic homeostasis and enhancing organism fitness upon developmental and dietary stresses. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Near Infrared Light Scattering Changes Following Acute Brain Injury

PubMed Central

Highton, David; Tachtsidis, Ilias; Tucker, Alison; Elwell, Clare; Smith, Martin

2018-01-01

Acute brain injury (ABI) is associated with changes in near infrared light absorption reflecting haemodynamic and metabolic status via changes in cerebral oxygenation (haemoglobin oxygenation and cytochrome-c-oxidase oxidation). Light scattering has not been comprehensively investigated following ABI and may be an important confounding factor in the assessment of chromophore concentration changes, and/or a novel non-invasive optical marker of brain tissue morphology, cytostructure, hence metabolic status. The aim of this study is to characterize light scattering following adult ABI. Time resolved spectroscopy was performed as a component of multimodal neuromonitoring in critically ill brain injured patients. The scattering coefficient (μ′s), absorption coefficient and cerebral haemoglobin oxygen saturation (SO2) were derived by fitting the time resolved data. Cerebral infarction was subsequently defined on routine clinical imaging. In total, 21 patients with ABI were studied. Ten patients suffered a unilateral frontal infarction, and mean μ′s was lower over infarcted compared to non-infarcted cortex (injured 6.9/cm, non-injured 8.2/cm p = 0.002). SO2 did not differ significantly between the two sides (injured 69.3 %, non-injured 69.0 % p = 0.7). Cerebral infarction is associated with changes in μ′s which might be a novel marker of cerebral injury and will interfere with quantification of haemoglobin/cytochrome c oxidase concentration. Although further work combining optical and physiological analysis is required to elucidate the significance of these results, μ′s may be uniquely placed as a non-invasive biomarker of cerebral energy failure as well as gross tissue changes. PMID:26782205

Giant suppression of phononic heat transport in a quantum magnet BiCu2PO6

NASA Astrophysics Data System (ADS)

Jeon, Byung-Gu; Koteswararao, B.; Park, C. B.; Shu, G. J.; Riggs, S. C.; Moon, E. G.; Chung, S. B.; Chou, F. C.; Kim, Kee Hoon

2016-11-01

Thermal transport of quantum magnets has elucidated the nature of low energy elementary excitations and complex interplay between those excited states via strong scattering of thermal carriers. BiCu2PO6 is a unique frustrated spin-ladder compound exhibiting highly anisotropic spin excitations that contain both itinerant and localized dispersion characters along the b- and a-axes respectively. Here, we investigate thermal conductivity κ of BiCu2PO6 under high magnetic fields (H) of up to 30 tesla. A dip-feature in κ, located at ~15 K at zero-H along all crystallographic directions, moves gradually toward lower temperature (T) with increasing H, thus resulting in giant suppression by a factor of ~30 near the critical magnetic field of Hc ≅ 23.5 tesla. The giant H- and T-dependent suppression of κ can be explained by the combined result of resonant scattering of phononic heat carriers with magnetic energy levels and increased phonon scattering due to enhanced spin fluctuation at Hc, unequivocally revealing the existence of strong spin-phonon coupling. Moreover, we find an experimental indication that the remaining magnetic heat transport along the b-axis becomes almost gapless at the magnetic quantum critical point realized at Hc.

Giant suppression of phononic heat transport in a quantum magnet BiCu2PO6.

PubMed

Jeon, Byung-Gu; Koteswararao, B; Park, C B; Shu, G J; Riggs, S C; Moon, E G; Chung, S B; Chou, F C; Kim, Kee Hoon

2016-11-15

Thermal transport of quantum magnets has elucidated the nature of low energy elementary excitations and complex interplay between those excited states via strong scattering of thermal carriers. BiCu 2 PO 6 is a unique frustrated spin-ladder compound exhibiting highly anisotropic spin excitations that contain both itinerant and localized dispersion characters along the b- and a-axes respectively. Here, we investigate thermal conductivity κ of BiCu 2 PO 6 under high magnetic fields (H) of up to 30 tesla. A dip-feature in κ, located at ~15 K at zero-H along all crystallographic directions, moves gradually toward lower temperature (T) with increasing H, thus resulting in giant suppression by a factor of ~30 near the critical magnetic field of H c  ≅ 23.5 tesla. The giant H- and T-dependent suppression of κ can be explained by the combined result of resonant scattering of phononic heat carriers with magnetic energy levels and increased phonon scattering due to enhanced spin fluctuation at H c , unequivocally revealing the existence of strong spin-phonon coupling. Moreover, we find an experimental indication that the remaining magnetic heat transport along the b-axis becomes almost gapless at the magnetic quantum critical point realized at H c .

Bio-Optics of the Chesapeake Bay from Measurements and Radiative Transfer Calculations

NASA Technical Reports Server (NTRS)

Tzortziou, Maria; Herman, Jay R.; Gallegos, Charles L.; Neale, Patrick J.; Subramaniam, Ajit; Harding, Lawrence W., Jr.; Ahmad, Ziauddin

2005-01-01

We combined detailed bio-optical measurements and radiative transfer (RT) modeling to perform an optical closure experiment for optically complex and biologically productive Chesapeake Bay waters. We used this experiment to evaluate certain assumptions commonly used when modeling bio-optical processes, and to investigate the relative importance of several optical characteristics needed to accurately model and interpret remote sensing ocean-color observations in these Case 2 waters. Direct measurements were made of the magnitude, variability, and spectral characteristics of backscattering and absorption that are critical for accurate parameterizations in satellite bio-optical algorithms and underwater RT simulations. We found that the ratio of backscattering to total scattering in the mid-mesohaline Chesapeake Bay varied considerably depending on particulate loading, distance from land, and mixing processes, and had an average value of 0.0128 at 530 nm. Incorporating information on the magnitude, variability, and spectral characteristics of particulate backscattering into the RT model, rather than using a volume scattering function commonly assumed for turbid waters, was critical to obtaining agreement between RT calculations and measured radiometric quantities. In situ measurements of absorption coefficients need to be corrected for systematic overestimation due to scattering errors, and this correction commonly employs the assumption that absorption by particulate matter at near infrared wavelengths is zero.

Giant suppression of phononic heat transport in a quantum magnet BiCu2PO6

PubMed Central

Jeon, Byung-Gu; Koteswararao, B.; Park, C. B.; Shu, G. J.; Riggs, S. C.; Moon, E. G.; Chung, S. B.; Chou, F. C.; Kim, Kee Hoon

2016-01-01

Thermal transport of quantum magnets has elucidated the nature of low energy elementary excitations and complex interplay between those excited states via strong scattering of thermal carriers. BiCu2PO6 is a unique frustrated spin-ladder compound exhibiting highly anisotropic spin excitations that contain both itinerant and localized dispersion characters along the b- and a-axes respectively. Here, we investigate thermal conductivity κ of BiCu2PO6 under high magnetic fields (H) of up to 30 tesla. A dip-feature in κ, located at ~15 K at zero-H along all crystallographic directions, moves gradually toward lower temperature (T) with increasing H, thus resulting in giant suppression by a factor of ~30 near the critical magnetic field of Hc ≅ 23.5 tesla. The giant H- and T-dependent suppression of κ can be explained by the combined result of resonant scattering of phononic heat carriers with magnetic energy levels and increased phonon scattering due to enhanced spin fluctuation at Hc, unequivocally revealing the existence of strong spin-phonon coupling. Moreover, we find an experimental indication that the remaining magnetic heat transport along the b-axis becomes almost gapless at the magnetic quantum critical point realized at Hc. PMID:27845377

Giant suppression of phononic heat transport in a quantum magnet BiCu 2PO 6

DOE PAGES

Jeon, Byung-Gu; Koteswararao, B.; Park, C. B.; ...

2016-11-15

Thermal transport of quantum magnets has elucidated the nature of low energy elementary excitations and complex interplay between those excited states via strong scattering of thermal carriers. BiCu 2PO 6 is a unique frustrated spin-ladder compound exhibiting highly anisotropic spin excitations that contain both itinerant and localized dispersion characters along the b- and a-axes respectively. Here, we investigate thermal conductivity κ of BiCu 2PO 6 under high magnetic fields (H) of up to 30 tesla. A dip-feature in κ, located at ~15K at zero-H along all crystallographic directions, moves gradually toward lower temperature (T) with increasing H, thus resulting inmore » giant suppression by a factor of ~30 near the critical magnetic field of H c≅23.5 tesla. The giant H- and T-dependent suppression of κ can be explained by the combined result of resonant scattering of phononic heat carriers with magnetic energy levels and increased phonon scattering due to enhanced spin fluctuation at H c, unequivocally revealing the existence of strong spin-phonon coupling. Moreover, we find an experimental indication that the remaining magnetic heat transport along the b-axis becomes almost gapless at the magnetic quantum critical point realized at H c.« less

Studies of Current Induced Magnetization reversal and generation of GHz radiation in magnetic nanopillars

NASA Astrophysics Data System (ADS)

Alhajdarwish, Mustafa Yousef

This thesis describes studies of two phenomena: Current-Induced Magnetization Switching (CIMS), and Current-Induced Generation of GHz Radiation. The CIMS part contains results of measurements of current-perpendicular-to-plane (CPP) magnetoresistance (MR) and CIMS behavior on Ferromagnetic/Nonmetal/Ferromagnetic (F1/N/F2) nanopillars. Judicious combinations of F1 and F2 metals with different bulk scattering asymmetries, and with F1/N and N/F2 interfaces having different interfacial scattering asymmetries, are shown to be able to controllably, and independently, 'invert' both the CPP-MR and the CIMS. In 'normal' CPP-MR, R(AP) > R(P), where R(AP) and R(P) are the nanopillar resistances for the anti-parallel (AP) and parallel (P) orientations of the Fi and F2 magnetic moments. In 'inverse' CPP-MR, R(P) > R(AP). In 'normal' CIMS, positive current switches the nanopillar from the P to the AP state. In 'inverse' CIMS, positive current switches the nanopillar from AP to P. All four possible combinations of CPP-MR and CIMS---(a) 'normal'-'normal', (b) 'normal'- 'inverse', 'inverse'-'normal', and (d) 'inverse'-'inverse' are shown and explained. These results rule out the self-Oersted field as the switching source, since the direction of that field is independent of the bulk or interfacial scattering asymmetries. Successful use of impurities to reverse the bulk scattering asymmetry shows the importance of scattering off of impurities within the bulk F1 and F2 metals---i.e. that the transport must be treated as 'diffusive' rather than 'ballistic'. The GHz studies consist of five parts: (1) designing a sample geometry that allows reliable measurements; (2) making nanopillar samples with this geometry; (3) constructing a system for measuring frequencies up to 12 GHz and measuring current-driven GHz radiation data with it; (4) showing 'scaling' behavior of GHz data with the critical fields and currents for nominally identical (but actually slightly different) samples, and justifying such scaling; and (5) designing and constructing a system for frequency domain studies up to 40 GHz and for time domain studies.

A Hydrodynamic Theory for Spatially Inhomogeneous Semiconductor Lasers. 2; Numerical Results

NASA Technical Reports Server (NTRS)

Li, Jianzhong; Ning, C. Z.; Biegel, Bryan A. (Technical Monitor)

2001-01-01

We present numerical results of the diffusion coefficients (DCs) in the coupled diffusion model derived in the preceding paper for a semiconductor quantum well. These include self and mutual DCs in the general two-component case, as well as density- and temperature-related DCs under the single-component approximation. The results are analyzed from the viewpoint of free Fermi gas theory with many-body effects incorporated. We discuss in detail the dependence of these DCs on densities and temperatures in order to identify different roles played by the free carrier contributions including carrier statistics and carrier-LO phonon scattering, and many-body corrections including bandgap renormalization and electron-hole (e-h) scattering. In the general two-component case, it is found that the self- and mutual- diffusion coefficients are determined mainly by the free carrier contributions, but with significant many-body corrections near the critical density. Carrier-LO phonon scattering is dominant at low density, but e-h scattering becomes important in determining their density dependence above the critical electron density. In the single-component case, it is found that many-body effects suppress the density coefficients but enhance the temperature coefficients. The modification is of the order of 10% and reaches a maximum of over 20% for the density coefficients. Overall, temperature elevation enhances the diffusive capability or DCs of carriers linearly, and such an enhancement grows with density. Finally, the complete dataset of various DCs as functions of carrier densities and temperatures provides necessary ingredients for future applications of the model to various spatially inhomogeneous optoelectronic devices.

Diffusion studies with synchrotron Mössbauer spectroscopy

NASA Astrophysics Data System (ADS)

Jackson, J. M.

2011-12-01

Knowledge of diffusion properties is critical for understanding many physical and chemical processes in planetary interiors. For example, diffusion behavior provides constraints on chemical exchange and viscosity. Nuclear resonances open the window for observing diffusion properties under the extreme conditions that exist deep inside the Earth. Synchrotron Mössbauer spectroscopy (viz. nuclear forward scattering) makes use of synchrotron radiation coherently scattered in the forward direction after nuclear resonant excitation. The decay of the forward-scattered radiation is faster when atoms move on the time scale of the excited-state lifetime because of a loss of coherence. Such diffusion-activated processes lead to accelerated decay and line broadening in the measured signal. In the case of the Mössbauer active isotope 57Fe, the nuclear resonance at 14.4 keV has a natural lifetime of 141 ns. Therefore, one can observe diffusion events ranging from approximately one-sixth to 100 times the natural lifetime of 57Fe, which corresponds to diffusion coefficients of 10-16 and 10-13 m2/s, respectively and a two to three order of magnitude range of suitability. In this contribution, we will describe such measurements that access the microscopic details of the diffusion process for iron-bearing phases.

Potential enhancements to the performance of ASDE radars derived from multistatic radar principles

DOT National Transportation Integrated Search

2001-10-14

Airport surface surveillance systems, such as airport surface detection equipment (ASDE) radars, are susceptible to multipath propagation and scattering effects that can result in the placement of false targets located at critical locations on airpor...

Measurement of the main and critical parameters for optimal laser treatment of heart disease

NASA Astrophysics Data System (ADS)

Kabeya, FB; Abrahamse, H.; Karsten, AE

2017-10-01

Laser light is frequently used in the diagnosis and treatment of patients. As in traditional treatments such as medication, bypass surgery, and minimally invasive ways, laser treatment can also fail and present serious side effects. The true reason for laser treatment failure or the side effects thereof, remains unknown. From the literature review conducted, and experimental results generated we conclude that an optimal laser treatment for coronary artery disease (named heart disease) can be obtained if certain critical parameters are correctly measured and understood. These parameters include the laser power, the laser beam profile, the fluence rate, the treatment time, as well as the absorption and scattering coefficients of the target treatment tissue. Therefore, this paper proposes different, accurate methods for the measurement of these critical parameters to determine the optimal laser treatment of heart disease with a minimal risk of side effects. The results from the measurement of absorption and scattering properties can be used in a computer simulation package to predict the fluence rate. The computing technique is a program based on the random number (Monte Carlo) process and probability statistics to track the propagation of photons through a biological tissue.

Is the nuclear refractive index lower than cytoplasm? Validation of phase measurements and implications for light scattering technologies.

PubMed

Steelman, Zachary A; Eldridge, Will J; Weintraub, Jacob B; Wax, Adam

2017-12-01

The refractive index (RI) of biological materials is a fundamental parameter for the optical characterization of living systems. Numerous light scattering technologies are grounded in a quantitative knowledge of the refractive index at cellular and subcellular scales. Recent work in quantitative phase microscopy (QPM) has called into question the widely held assumption that the index of the cell nucleus is greater than that of the cytoplasm, a result which disagrees with much of the current literature. In this work, we critically examine the measurement of the nuclear and whole-cell refractive index using QPM, validating that nuclear refractive index is lower than that of cytoplasm in four diverse cell lines and their corresponding isolated nuclei. We further examine Mie scattering and phase-wrapping as potential sources of error in these measurements, finding they have minimal impact. Finally, we use simulation to examine the effects of incorrect RI assumptions on nuclear morphology measurements using angle-resolved scattering information. Despite an erroneous assumption of the nuclear refractive index, accurate measurement of nuclear morphology was maintained, suggesting that light scattering modalities remain effective. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

On the Interpretation of Supernova Light Echo Profiles and Spectra

NASA Astrophysics Data System (ADS)

Rest, A.; Sinnott, B.; Welch, D. L.; Foley, R. J.; Narayan, G.; Mandel, K.; Huber, M. E.; Blondin, S.

2011-05-01

The light echo (LE) systems of historical supernovae in the Milky Way and local group galaxies provide an unprecedented opportunity to reveal the effects of asymmetry on observables, particularly optical spectra. Scattering dust at different locations on the LE ellipsoid witnesses the supernova from different perspectives, and the light consequently scattered toward Earth preserves the shape of line profile variations introduced by asymmetries in the supernova photosphere. However, the interpretation of supernova LE spectra to date has not involved a detailed consideration of the effects of outburst duration and geometrical scattering modifications due to finite scattering dust filament dimension, inclination, and image point-spread function and spectrograph slit width. In this paper, we explore the implications of these factors and present a framework for future-resolved supernova LE spectra interpretation, and test it against Cas A and SN 1987A LE spectra. We conclude that the full modeling of the dimensions and orientation of the scattering dust using the observed LEs at two or more epochs is critical for the correct interpretation of LE spectra. Indeed, without doing so one might falsely conclude that differences exist when none are actually present.

Faraday effect on stimulated Raman scattering in the linear region

NASA Astrophysics Data System (ADS)

Liu, Z. J.; Li, B.; Xiang, J.; Cao, L. H.; Zheng, C. Y.; Hao, L.

2018-04-01

The paper presents the effect of Faraday rotation on stimulated Raman scattering (SRS). When light propagates along the magnetic field upon plasma, Faraday rotation occurs. The rotation angle can be expressed as {{d}}θ /{{d}}{s}=2.93× {10}-4B\\tfrac{{n}e/{n}c}{\\sqrt{1-{n}e/{n}c}} {cm}}-1 approximately, where θ is the rotation angle and s is distance, n e is the electron density, n c is the critical density and B is magnetic field in unit of Gauss. Both the incident light and Raman light have Faraday effects. The angle between the polarization directions of incident light and Raman light changes with position. The driven force of electron plasma wave also reduces, and then SRS scattering level is reduced. Faraday rotation effect can increase the laser intensity threshold of Raman scattering, even if the magnetic field strength is small. The circularly polarized light incident case is also compared with that of the linearly polarized light incident. The Raman scattering level of linearly polarized light is much smaller than that of circularly polarized light in the magnetized plasma. The difference between linearly and circularly polarized lights is also discussed.

Notes on Experiments.

ERIC Educational Resources Information Center

Physics Education, 1983

1983-01-01

An experiment on cooling by convection, holographic processes achieved using optical fibers and observation of magnetic domains are described. Also describes four demonstrations: mechanical resonance on air track, independence of horizontal/vertical motion, motion of sphere in fluid medium, and light scattering near the critical point. (JN)

Spin chirality and polarised neutron scattering

NASA Astrophysics Data System (ADS)

Plakhty, V. P.; Maleyev, S. V.; Kulda, J.; Visser, E. D.; Wosnitza, J.; Moskvin, E. V.; Brückel, Th.; Kremer, R. K.

2001-03-01

Possibilities of polarised neutrons in studies of chiral criticality are discussed. The critical exponents β C of the average chirality below TN, as well as φ C=β C+γ C and, therefore, γ C of the chiral susceptibility above TN are determined for a XY triangular lattice antiferromagnet (TLA) CsMnBr3: β C=0.44(2) , γ C=0.84(7) . The critical behaviour of the chirality that orders at TN with a relative precision of 5×10 -4 proves that the phase transition belongs to a new chiral universality class. For the TLA CsNiCl 3 ( S=1) we found in the XY region ( B=3 T) φ C=1.24(7) in agreement with the Monte-Carlo value φ C=1.22(6) for the chiral universality class. In the easy-axis region at B=1 T, φ C=0.54(4) , and the Haldane excitations are observed in the polarisation-dependent inelastic cross section above TN. The helimagnet holmium exhibits a different chiral criticality with φ C=1.56(5) , essentially higher than for TLAs.

Coherent generation of symmetry-forbidden phonons by light-induced electron-phonon interactions in magnetite

NASA Astrophysics Data System (ADS)

Borroni, S.; Baldini, E.; Katukuri, V. M.; Mann, A.; Parlinski, K.; Legut, D.; Arrell, C.; van Mourik, F.; Teyssier, J.; Kozlowski, A.; Piekarz, P.; Yazyev, O. V.; Oleś, A. M.; Lorenzana, J.; Carbone, F.

2017-09-01

Symmetry breaking across phase transitions often causes changes in selection rules and emergence of optical modes which can be detected via spectroscopic techniques or generated coherently in pump-probe experiments. In second-order or weakly first-order transitions, fluctuations of the ordering field are present above the ordering temperature, giving rise to intriguing precursor phenomena, such as critical opalescence. Here, we demonstrate that in magnetite (Fe3O4 ) light excitation couples to the critical fluctuations of the charge order and coherently generates structural modes of the ordered phase above the critical temperature of the Verwey transition. Our findings are obtained by detecting coherent oscillations of the optical constants through ultrafast broadband spectroscopy and analyzing their dependence on temperature. To unveil the coupling between the structural modes and the electronic excitations, at the origin of the Verwey transition, we combine our results from pump-probe experiments with spontaneous Raman scattering data and theoretical calculations of both the phonon dispersion curves and the optical constants. Our methodology represents an effective tool to study the real-time dynamics of critical fluctuations across phase transitions.

Split Dirac cones in HgTe/CdTe quantum wells due to symmetry-enforced level anticrossing at interfaces

NASA Astrophysics Data System (ADS)

Tarasenko, S. A.; Durnev, M. V.; Nestoklon, M. O.; Ivchenko, E. L.; Luo, Jun-Wei; Zunger, Alex

2015-02-01

HgTe is a band-inverted compound which forms a two-dimensional topological insulator if sandwiched between CdTe barriers for a HgTe layer thickness above the critical value. We describe the fine structure of Dirac states in the HgTe/CdTe quantum wells of critical and close-to-critical thicknesses and show that the necessary creation of interfaces brings in another important physical effect: the opening of a significant anticrossing gap between the tips of the Dirac cones. The level repulsion driven by the natural interface inversion asymmetry of zinc-blende heterostructures considerably modifies the electron states and dispersion but preserves the topological transition at the critical thickness. By combining symmetry analysis, atomistic calculations, and extended k .p theory with interface terms, we obtain a quantitative description of the energy spectrum and extract the interface mixing coefficient. We discuss how the fingerprints of the predicted zero-magnetic-field splitting of the Dirac cones could be detected experimentally by studying magnetotransport phenomena, cyclotron resonance, Raman scattering, and THz radiation absorption.

Elastic pp-bar and pp scattering up to. sqrt. s = 546 GeV and the flavored perturbative Reggeon field theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dash, J.W.; Jones, S.T.

We show that the perturbative Reggeon field theory (RFT) with flavoring corrections added reproduces the pp and pp-bar differential cross sections from Fermilab to the CERN SPS collider (Spp-bar S). This completes a long program of phenomenology which is now capable of providing a unified framework for soft hadronic scattering at current energies. Our scenario of data being influenced by finite scales at least up to ..sqrt..s = 546 GeV is compatible with the truly asymptotic limit being described by the critical RFT scaling laws.

Multibeam Stimulated Raman Scattering in Inertial Confinement Fusion Conditions.

PubMed

Michel, P; Divol, L; Dewald, E L; Milovich, J L; Hohenberger, M; Jones, O S; Hopkins, L Berzak; Berger, R L; Kruer, W L; Moody, J D

2015-07-31

Stimulated Raman scattering from multiple laser beams arranged in a cone sharing a common daughter wave is investigated for inertial confinement fusion (ICF) conditions in a inhomogeneous plasma. It is found that the shared electron plasma wave (EPW) process, where the lasers collectively drive the same EPW, can lead to an absolute instability when the electron density reaches a matching condition dependent on the cone angle of the laser beams. This mechanism could explain recent experimental observations of hot electrons at early times in ICF experiments, at densities well below quarter critical when two plasmon decay is not expected to occur.

Development of a Technique for Separating Raman Scattering Signals from Background Emission with Single-Shot Measurement Potential

NASA Technical Reports Server (NTRS)

Hartfield, Roy J., Jr.; Dobson, Chris; Eskridge, Richard; Wehrmeyer, Joseph A.

1997-01-01

A novel technique for extracting Q-branch Raman signals scattered by a diatomic species from the emission spectrum resulting from the irradiation of combustion products using a broadband excimer laser has been developed. This technique is based on the polarization characteristics of vibrational Raman scattering and can be used for both single-shot Raman extraction and time-averaged data collection. The Q-branch Raman signal has a unique set of polarization characteristics which depend on the direction of the scattering while fluorescence signals are unpolarized. For the present work, a calcite crystal is used to separate the horizonal component of a collected signal from the vertical component. The two components are then sent through a UV spectrometer and imaged onto an intensified CCD camera separately. The vertical component contains both the Raman signal and the interfering fluorescence signal. The horizontal component contains the fluorescence signal and a very weak component of the Raman signal; hence, the Raman scatter can be extracted by taking the difference between the two signals. The separation of the Raman scatter from interfering fluorescence signals is critically important to the interpretation of the Raman for cases in which a broadband ultraviolet (UV) laser is used as an excitation source in a hydrogen-oxygen flame and in all hydrocarbon flames. The present work provides a demonstration of the separation of the Raman scatter from the fluorescence background in real time.

Physics of debris clouds from hypervelocity impacts

NASA Technical Reports Server (NTRS)

Zee, Ralph

1993-01-01

The protection scheme developed for long duration space platforms relies primarily upon placing thin metal plates or 'bumpers' around flight critical components. The effectiveness of this system is highly dependent upon its ability to break up and redistribute the momentum of any particle which might otherwise strike the outer surface of the spacecraft. Therefore it is of critical importance to design the bumpers such that maximum dispersion of momentum is achieved. This report is devoted to an in-depth study into the design and development of a laboratory instrument which would permit the in-situ monitoring of the momentum distribution as the impact event occurs. A series of four designs were developed, constructed and tested culminating with the working instrument which is currently in use. Each design was individually tested using the Space Environmental Effects Facility (SEEF) at the Marshall Space Flight Center in Huntsville, Alabama. Along with the development of the device, an experimental procedure was developed to assist in the investigation of various bumper materials and designs at the SEEF. Preliminary results were used to compute data which otherwise were not experimentally obtainable. These results were shown to be in relative agreement with previously obtained values derived through other methods. The results of this investigation indicated that momentum distribution could in fact be measured in-situ as the impact event occurred thus giving a more accurate determination of the effects of experimental parameters on the momentum spread. Data produced by the instrument indicated a Gaussian-type momentum distribution. A second apparatus was developed and it was placed before the shield in the line of travel utilized a plate to collect impact debris scattered backwards. This plate had a passage hole in the center to allow the particle to travel through it and impact the proposed shield material. Applying the law of conservation of angular momentum a backward momentum vector was determined from the angular velocity of the plate. The forward scattered and backward scattered momentum values were then analyzed to judge the distribution of debris. Loss of momentum was attributed to the inaccuracies of the means of measurement. Assumptions of symmetrical debris for the forward and backward scattered directions also contributed to this loss.

Target parameter estimation

NASA Technical Reports Server (NTRS)

Hocking, W. K.

1989-01-01

The objective of any radar experiment is to determine as much as possible about the entities which scatter the radiation. This review discusses many of the various parameters which can be deduced in a radar experiment, and also critically examines the procedures used to deduce them. Methods for determining the mean wind velocity, the RMS fluctuating velocities, turbulence parameters, and the shapes of the scatterers are considered. Complications with these determinations are discussed. It is seen throughout that a detailed understanding of the shape and cause of the scatterers is important in order to make better determinations of these various quantities. Finally, some other parameters, which are less easily acquired, are considered. For example, it is noted that momentum fluxes due to buoyancy waves and turbulence can be determined, and on occasions radars can be used to determine stratospheric diffusion coefficients and even temperature profiles in the atmosphere.

Initial results of the high resolution edge Thomson scattering upgrade at DIII-D.

PubMed

Eldon, D; Bray, B D; Deterly, T M; Liu, C; Watkins, M; Groebner, R J; Leonard, A W; Osborne, T H; Snyder, P B; Boivin, R L; Tynan, G R

2012-10-01

Validation of models of pedestal structure is an important part of predicting pedestal height and performance in future tokamaks. The Thomson scattering diagnostic at DIII-D has been upgraded in support of validating these models. Spatial and temporal resolution, as well as signal to noise ratio, have all been specifically enhanced in the pedestal region. This region is now diagnosed by 20 view-chords with a spacing of 6 mm and a scattering length of just under 5 mm sampled at a nominal rate of 250 Hz. When mapped to the outboard midplane, this corresponds to ~3 mm spacing. These measurements are being used to test critical gradient models, in which pedestal gradients increase in time until a threshold is reached. This paper will describe the specifications of the upgrade and present initial results of the system.

The complex of optical methods for study of gas-liquid jets

NASA Astrophysics Data System (ADS)

Poplavski, S. V.; Boiko, V. M.

2017-10-01

A set of optical methods for studying the dispersion and dynamics of liquids in high-speed gas jets was realized. Four optical methods were used: shadow imaging, PIV method, Laser Doppler Anemometer (LDA), a method for recording the dispersity of a spray by angular scattering of light. With the example of a supersonic coaxial jet with a central fluid supply, a technique is developed that makes it possible to obtain not only the sum of the data by four methods but new critical data on the structure of the two-phase flow, such as the concentration distributions of the spray.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Wenhu; Kotliar, Gabriel; Tsvelik, Alexei M.

Dynamical mean-field theory is used to study the quantum critical point (QCP) in the doped Hubbard model on a square lattice. We characterize the QCP by a universal scaling form of the self-energy and a spin density wave instability at an incommensurate wave vector. The scaling form unifies the low-energy kink and the high-energy waterfall feature in the spectral function, while the spin dynamics includes both the critical incommensurate and high-energy antiferromagnetic paramagnons. Here, we use the frequency-dependent four-point correlation function of spin operators to calculate the momentum-dependent correction to the electron self-energy. Furthermore, by comparing with the calculations basedmore » on the spin-fermion model, our results indicate the frequency dependence of the quasiparticle-paramagnon vertices is an important factor to capture the momentum dependence in quasiparticle scattering.« less

Aerosol Direct Radiative Effects Over the Northwest Atlantic, Northwest Pacific, and North Indian Oceans: Estimates Based on In-situ Chemical and Optical Measurements and Chemical Transport Modeling

NASA Astrophysics Data System (ADS)

Bates, T. S.; Anderson, T. L.; Baynard, T.; Bond, T.; Boucher, O.; Carmichael, G.; Clarke, A.; Erlick, C.; Guo, H.; Horowitz, L.; Howell, S.; Kulkarni, S.; Maring, H.; McComiskey, A.; Middlebrook, A.; Noone, K.; O'Dowd, C. D.; Ogren, J. A.; Penner, J.; Quinn, P. K.; Ravishankara, A. R.; Savoie, D. L.; Schwartz, S. E.; Shinozuka, Y.; Tang, Y.; Weber, R. J.; Wu, Y.

2005-12-01

The largest uncertainty in the radiative forcing of climate change over the industrial era is that due to aerosols, a substantial fraction of which is the uncertainty associated with scattering and absorption of shortwave (solar) radiation by anthropogenic aerosols in cloud-free conditions. Quantifying and reducing the uncertainty in aerosol influences on climate is critical to understanding climate change over the industrial period and to improving predictions of future climate change for assumed emission scenarios. Measurements of aerosol properties during major field campaigns in several regions of the globe during the past decade are contributing to an enhanced understanding of atmospheric aerosols and their effects on light scattering and climate. The present study, which focuses on three regions downwind of major urban/population centers (North Indian Ocean during INDOEX, the Northwest Pacific Ocean during ACE-Asia, and the Northwest Atlantic Ocean during ICARTT), incorporates understanding gained from field observations of aerosol distributions and properties into calculations of perturbations in radiative fluxes due to these aerosols. This study evaluates the current state of observations and of two chemical transport models (STEM and MOZART). Measurements of burdens, extinction optical depth, and direct radiative effect of aerosols (change in radiative flux due to total aerosols) are used as measurement-model check points to assess uncertainties. In-situ measured and remotely sensed aerosol properties for each region (mixing state, mass scattering efficiency, single scattering albedo, and angular scattering properties and their dependences on relative humidity) are used as input parameters to two radiative transfer models (GFDL and University of Michigan) to constrain estimates of aerosol radiative effects, with uncertainties in each step propagated through the analysis. Such comparisons with observations and resultant reductions in uncertainties are essential for improving and developing confidence in climate model calculations incorporating aerosol forcing.

Investigating biomass burning aerosol morphology using a laser imaging nephelometer

NASA Astrophysics Data System (ADS)

Manfred, Katherine M.; Washenfelder, Rebecca A.; Wagner, Nicholas L.; Adler, Gabriela; Erdesz, Frank; Womack, Caroline C.; Lamb, Kara D.; Schwarz, Joshua P.; Franchin, Alessandro; Selimovic, Vanessa; Yokelson, Robert J.; Murphy, Daniel M.

2018-02-01

Particle morphology is an important parameter affecting aerosol optical properties that are relevant to climate and air quality, yet it is poorly constrained due to sparse in situ measurements. Biomass burning is a large source of aerosol that generates particles with different morphologies. Quantifying the optical contributions of non-spherical aerosol populations is critical for accurate radiative transfer models, and for correctly interpreting remote sensing data. We deployed a laser imaging nephelometer at the Missoula Fire Sciences Laboratory to sample biomass burning aerosol from controlled fires during the FIREX intensive laboratory study. The laser imaging nephelometer measures the unpolarized scattering phase function of an aerosol ensemble using diode lasers at 375 and 405 nm. Scattered light from the bulk aerosol in the instrument is imaged onto a charge-coupled device (CCD) using a wide-angle field-of-view lens, which allows for measurements at 4-175° scattering angle with ˜ 0.5° angular resolution. Along with a suite of other instruments, the laser imaging nephelometer sampled fresh smoke emissions both directly and after removal of volatile components with a thermodenuder at 250 °C. The total integrated aerosol scattering signal agreed with both a cavity ring-down photoacoustic spectrometer system and a traditional integrating nephelometer within instrumental uncertainties. We compare the measured scattering phase functions at 405 nm to theoretical models for spherical (Mie) and fractal (Rayleigh-Debye-Gans) particle morphologies based on the size distribution reported by an optical particle counter. Results from representative fires demonstrate that particle morphology can vary dramatically for different fuel types. In some cases, the measured phase function cannot be described using Mie theory. This study demonstrates the capabilities of the laser imaging nephelometer instrument to provide realtime, in situ information about dominant particle morphology, which is vital for understanding remote sensing data and accurately describing the aerosol population in radiative transfer calculations.

Generalized model screening potentials for Fermi-Dirac plasmas

NASA Astrophysics Data System (ADS)

Akbari-Moghanjoughi, M.

2016-04-01

In this paper, some properties of relativistically degenerate quantum plasmas, such as static ion screening, structure factor, and Thomson scattering cross-section, are studied in the framework of linearized quantum hydrodynamic theory with the newly proposed kinetic γ-correction to Bohm term in low frequency limit. It is found that the correction has a significant effect on the properties of quantum plasmas in all density regimes, ranging from solid-density up to that of white dwarf stars. It is also found that Shukla-Eliasson attractive force exists up to a few times the density of metals, and the ionic correlations are seemingly apparent in the radial distribution function signature. Simplified statically screened attractive and repulsive potentials are presented for zero-temperature Fermi-Dirac plasmas, valid for a wide range of quantum plasma number-density and atomic number values. Moreover, it is observed that crystallization of white dwarfs beyond a critical core number-density persists with this new kinetic correction, but it is shifted to a much higher number-density value of n0 ≃ 1.94 × 1037 cm-3 (1.77 × 1010 gr cm-3), which is nearly four orders of magnitude less than the nuclear density. It is found that the maximal Thomson scattering with the γ-corrected structure factor is a remarkable property of white dwarf stars. However, with the new γ-correction, the maximal scattering shifts to the spectrum region between hard X-ray and low-energy gamma-rays. White dwarfs composed of higher atomic-number ions are observed to maximally Thomson-scatter at slightly higher wavelengths, i.e., they maximally scatter slightly low-energy photons in the presence of correction.

Impact of calcification state on the inherent optical properties of Emiliania huxleyi coccoliths and coccolithophores

NASA Astrophysics Data System (ADS)

Bi, Lei; Yang, Ping

2015-04-01

Understanding the inherent optical properties (IOPs) of coccoliths and coccolithophores is important in oceanic radiative transfer simulations and remote sensing implementations. In this study, the invariant imbedding T-matrix method (II-TM) is employed to investigate the IOPs of coccoliths and coccolithophores. The Emiliania huxleyi (Ehux) coccolith and coccolithophore models are built based on observed biometric parameters including the eccentricity, the number of slits, and the rim width of detached coccoliths. The calcification state that specifies the amount of calcium of a single coccolith is critical in the determination of the size-volume/mass relationship (note, the volume/mass of coccoltihs at different calcification states are different although the diameters are the same). The present results show that the calcification state, namely, under-calcification, normal-calcification, or over-calcification, significantly influences the backscattering cross section and the phase matrix. Furthermore, the linear depolarization ratio of the light scattered by coccoliths is sensitive to the degree of calcification, and provides a potentially valuable parameter for interpreting oceanic remote sensing data. The phase function of an ensemble of randomly oriented coccolithophores has a similar pattern to that of individual coccoliths, but the forward scattering is dominant in the coccolithophores due to the large geometric cross sections. The linear depolarization ratio associated with coccolithophores is found to be larger than that for coccoliths as polarization is more sensitive to multiple scattering than the phase function. The simulated coccolithophore phase matrix numerical results are compared with laboratory measurements. For scattering angles larger than 100°, an increase of the phase function with respect to the scattering angle is confirmed based on the present coccolithophore model while the spherical approximation fails.

Self-association of analgesics in aqueous solution: micellar properties of dextropropoxyphene hydrochloride and methadone hydrochloride.

PubMed

Attwood, D; Tolley, J A

1980-08-01

The solution properties of several analgesics including dextropropoxyphene hydrochloride, methadone hydrochloride, dextromoramide acid tartrate and dipipanone hydrochloride have been examined using light scattering, conductivity, vapour pressure osmometry and surface tension techniques. A micellar pattern of association was established for dextropropoxyphene hydrochloride and methadone hydrochloride and critical micelle concentrations and aggregation numbers are reported. The hydrophobic contribution to the free energy of micellization of dextropropoxyphene was determined from measurement of the critical micelle concentration in the presence of added electrolyte.

Bose-Einstein condensation of spin wave quanta at room temperature.

PubMed

Dzyapko, O; Demidov, V E; Melkov, G A; Demokritov, S O

2011-09-28

Spin waves are delocalized excitations of magnetic media that mainly determine their magnetic dynamics and thermodynamics at temperatures far below the critical one. The quantum-mechanical counterparts of spin waves are magnons, which can be considered as a gas of weakly interacting bosonic quasi-particles. Here, we discuss the room-temperature kinetics and thermodynamics of the magnon gas in yttrium iron garnet films driven by parametric microwave pumping. We show that for high enough pumping powers, the thermalization of the driven gas results in a quasi-equilibrium state described by Bose-Einstein statistics with a non-zero chemical potential. Further increases of the pumping power cause a Bose-Einstein condensation documented by an observation of the magnon accumulation at the lowest energy level. Using the sensitivity of the Brillouin light scattering spectroscopy to the degree of coherence of the scattering magnons, we confirm the spontaneous emergence of coherence of the magnons accumulated at the bottom of the spectrum, occurring if their density exceeds a critical value.

Universal patterns of equilibrium cluster growth in aqueous sugars observed by dynamic light scattering.

PubMed

Sidebottom, D L; Tran, Tri D

2010-11-01

Dynamic light scattering performed on aqueous solutions of three sugars (glucose, maltose and sucrose) reveal a common pattern of sugar cluster formation with a narrow cluster size distribution. In each case, equilibrium clusters form whose size increases with increasing sugar content in an identical power law manner in advance of a common, critical-like, percolation threshold near 83 wt % sugar. The critical exponent of the power law divergence of the cluster size varies with temperature, increasing with decreasing temperature, due to changes in the strength of the intermolecular hydrogen bond and appears to vanish for temperatures in excess of 90 °C. Detailed analysis of the cluster growth process suggests a two-stage process: an initial cluster phase formed at low volume fractions, ϕ, consisting of noninteracting, monodisperse sugar clusters whose size increases ϕ(1/3) followed by an aggregation stage, active at concentrations above about ϕ=40%, where cluster-cluster contact first occurs.

Dynamic Light Scattering Study of Inhibition of Nucleation and Growth of Hydroxyapatite Crystals by Osteopontin

PubMed Central

de Bruyn, John R.; Goiko, Maria; Mozaffari, Maryam; Bator, Daniel; Dauphinee, Ron L.; Liao, Yinyin; Flemming, Roberta L.; Bramble, Michael S.; Hunter, Graeme K.; Goldberg, Harvey A.

2013-01-01

We study the effect of isoforms of osteopontin (OPN) on the nucleation and growth of crystals from a supersaturated solution of calcium and phosphate ions. Dynamic light scattering is used to monitor the size of the precipitating particles and to provide information about their concentration. At the ion concentrations studied, immediate precipitation was observed in control experiments with no osteopontin in the solution, and the size of the precipitating particles increased steadily with time. The precipitate was identified as hydroxyapatite by X-ray diffraction. Addition of native osteopontin (nOPN) extracted from rat bone caused a delay in the onset of precipitation and reduced the number of particles that formed, but the few particles that did form grew to a larger size than in the absence of the protein. Recombinant osteopontin (rOPN), which lacks phosphorylation, caused no delay in initial calcium phosphate precipitation but severely slowed crystal growth, suggesting that rOPN inhibits growth but not nucleation. rOPN treated with protein kinase CK2 to phosphorylate the molecule (p-rOPN) produced an effect similar to that of nOPN, but at higher protein concentrations and to a lesser extent. These results suggest that phosphorylations are critical to OPN’s ability to inhibit nucleation, whereas the growth of the hydroxyapatite crystals is effectively controlled by the highly acidic OPN polypeptide. This work also demonstrates that dynamic light scattering can be a powerful tool for delineating the mechanism of protein modulation of mineral formation. PMID:23457612

Wave Turning and Flow Angle in the E-Region Ionosphere

NASA Astrophysics Data System (ADS)

Young, M.; Oppenheim, M. M.; Dimant, Y. S.

2016-12-01

This work presents results of particle-in-cell (PIC) simulations of Farley-Buneman (FB) turbulence at various altitudes in the high-latitude E-region ionosphere. In that region, the FB instability regularly produces meter-scale plasma irregularities. VHF radars observe coherent echoes via Bragg scatter from wave fronts parallel or anti-parallel to the radar line of sight (LoS) but do not necessarily measure the mean direction of wave propagation. Haldoupis (1984) conducted a study of diffuse radar aurora and found that the spectral width of back-scattered power depends critically on the angle between the radar LoS and the true flow direction, called the flow angle. Knowledge of the flow angle will allow researchers to better interpret observations of coherent back-scatter. Experiments designed to observe meter-scale irregularities in the E-region ionosphere created by the FB instability typically assume that the predominant flow direction is the E×B direction. However, linear theory of Dimant and Oppenheim (2004) showed that FB waves should turn away from E×B and particle-in-cell simulations by Oppenheim and Dimant (2013) support the theory. The present study comprises a quantitative analysis of the dependence of back-scattered power, flow velocity, and spectral width as functions of the flow angle. It also demonstrates that the mean direction of meter-scale wave propagation may differ from the E×B direction by tens of degrees. The analysis includes 2-D and 3-D simulations at a range of altitudes in the auroral ionosphere. Comparison between 2-D and 3-D simulations illustrates the relative importance to the irregularity spectrum of a small but finite component in the direction parallel to B. Previous work has shown this small parallel component to be important to turbulent electron heating and nonlinear transport.

Optical Study of the Critical Behaviour of Pure Fluids and Binary Mixtures.

NASA Astrophysics Data System (ADS)

Narger, Ulrike

1990-01-01

Optical techniques were used to study the critical behaviour of the pure fluids CHF_3, CClF_3 and Xe, and binary mixtures He-Xe and nicotine + water. We find that for all these substances, the order parameter is described by a power law in the reduced temperature t = (T _{c} - T)/T_{c} with a leading exponent beta = 0.327 +/- 0.002. Also, we determine the first correction to scaling exponent to be Delta = 0.43 +/- 0.02 for the pure fluids and Delta = 0.50 +/- 0.02 for the He-Xe system. The coexistence curve diameter in CHF _3 and CClF_3 exhibits a deviation from recti-linear diameter, in agreement with a modern theory which interprets this behaviour as resulting from three-body effects. In contrast, no such deviation is observed in Xe where, according to that theory, it should be more pronounced than in other substances. In the polar fluid CHF_3, the order parameter, isothermal compressibility and the chemical potential along the critical isotherm were simultaneously measured in the same experiment in an effort to ensure self-consistency of the results. From the data, two amplitude ratios which are predicted to be universal are determined: Gamma_sp{0}{+} /Gamma_sp{0}{ -} = 4.8 +/- 0.6 and D_0 Gamma_sp{0}{+ } B_sp{0}{delta-1} = 1.66 +/- 0.14. In the binary liquid system nicotine + water, the diffusivity was measured both by light scattering and by interferometry. The results agree qualitatively, but differ by a factor of ~2. From the light scattering data, the critical exponent of the viscosity is found to be z_{eta } = 0.044 +/- 0.008. The interferometric experiments on Xe and He-Xe furnish a direct way to measure the effects of wetting: From the data, the exponent of the surface tension is found to be n = 1.24 +/- 0.06. The similarity of the order parameter and compressibility in Xe and a He-Xe mixture containing 5% He indicate that the phase transition in this He-Xe mixture is of the liquid -gas type rather than the binary liquid type.

Response to ``Comment on `Indications of energetic consequences of decoherence at short times for scattering from open quantum systems''' [AIP Advances 1, 049101 (2011)

NASA Astrophysics Data System (ADS)

Chatzidimitriou-Dreismann, C. A.; Gray, E. MacA.; Blach, T. P.

2011-12-01

The Comment by Mayers and Reiter criticizes our work on two counts. Firstly, it is claimed that the quantum decoherence effects that we report in consequence of our experimental analysis of neutron Compton scattering from H in gaseous H2 are not, as we maintain, outside the framework of conventional neutron scattering theory. Secondly, it is claimed that we did not really observe such effects, owing to a faulty analysis of the experimental data, which are claimed to be in agreement with conventional theory. We focus in this response on the critical issue of the reliability of our experimental results and analysis. Using the same standard Vesuvio instrument programs used by Mayers et al., we show that, if the experimental results for H in gaseous H2 are in agreement with conventional theory, then those for D in gaseous D2 obtained in the same way cannot be, and vice-versa. We expose a flaw in the calibration methodology used by Mayers et al. that leads to the present disagreement over the behaviour of H, namely the ad hoc adjustment of the measured H peak positions in TOF during the calibration of Vesuvio so that agreement is obtained with the expectation of conventional theory. We briefly address the question of the necessity to apply the theory of open quantum systems.

Reflected scatterometry for noninvasive interrogation of bacterial colonies

NASA Astrophysics Data System (ADS)

Kim, Huisung; Doh, Iyll-Joon; Sturgis, Jennifer; Bhunia, Arun K.; Robinson, J. Paul; Bae, Euiwon

2016-10-01

A phenotyping of bacterial colonies on agar plates using forward-scattering diffraction-pattern analysis provided promising classification of several different bacteria such as Salmonella, Vibrio, Listeria, and E. coli. Since the technique is based on forward-scattering phenomena, light transmittance of both the colony and the medium is critical to ensure quality data. However, numerous microorganisms and their growth media allow only limited light penetration and render the forward-scattering measurement a challenging task. For example, yeast, Lactobacillus, mold, and several soil bacteria form colorful and dense colonies that obstruct most of the incoming light passing through them. Moreover, blood agar, which is widely utilized in the clinical field, completely blocks the incident coherent light source used in forward scatterometry. We present a newly designed reflection scatterometer and validation of the resolving power of the instrument. The reflectance-type instrument can acquire backward elastic scatter patterns for both highly opaque media and colonies and has been tested with three different bacterial genera grown on blood agar plates. Cross-validation results show a classification rate above 90% for four genera.

The effect of interface hopping on inelastic scattering of oppositely charged polarons in polymers

NASA Astrophysics Data System (ADS)

Di, Bing; Wang, Ya-Dong; Zhang, Ya-Lin; An, Zhong

2013-06-01

The inelastic scattering of oppositely charge polarons in polymer heterojunctions is believed to be of fundamental importance for the light-emitting and transport properties of conjugated polymers. Based on the tight-binding SSH model, and by using a nonadiabatic molecular dynamic method, we investigate the effects of interface hopping on inelastic scattering of oppositely charged polarons in a polymer heterojunction. It is found that the scattering processes of the charge and lattice defect depend sensitively on the hopping integrals at the polymer/polymer interface when the interface potential barrier and applied electric field strength are constant. In particular, at an intermediate electric field, when the interface hopping integral of the polymer/polymer heterojunction material is increased beyond a critical value, two polarons can combine to become a lattice deformation in one of the two polymer chains, with the electron and the hole bound together, i.e., a self-trapped polaron—exciton. The yield of excitons then increases to a peak value. These results show that interface hopping is of fundamental importance and facilitates the formation of polaron—excitons.

Focused fluorescence excitation with time-reversed ultrasonically encoded light and imaging in thick scattering media

NASA Astrophysics Data System (ADS)

Lai, Puxiang; Suzuki, Yuta; Xu, Xiao; Wang, Lihong V.

2013-07-01

Scattering dominates light propagation in biological tissue, and therefore restricts both resolution and penetration depth in optical imaging within thick tissue. As photons travel into the diffusive regime, typically 1 mm beneath human skin, their trajectories transition from ballistic to diffusive due to the increased number of scattering events, which makes it impossible to focus, much less track, photon paths. Consequently, imaging methods that rely on controlled light illumination are ineffective in deep tissue. This problem has recently been addressed by a novel method capable of dynamically focusing light in thick scattering media via time reversal of ultrasonically encoded (TRUE) diffused light. Here, using photorefractive materials as phase conjugate mirrors, we show a direct visualization and dynamic control of optical focusing with this light delivery method, and demonstrate its application for focused fluorescence excitation and imaging in thick turbid media. These abilities are increasingly critical for understanding the dynamic interactions of light with biological matter and processes at different system levels, as well as their applications for biomedical diagnosis and therapy.

Surface finish measurement studies

NASA Technical Reports Server (NTRS)

Teague, E. C.

1983-01-01

The performance of stylus instruments for measuring the topography of National Transonic Facility (NTF) model surfaces both for monitoring during fabrication and as an absolute measurement of topography was evaluated. It was found that the shop-grade instruments can damage the surface of models and that their use for monitoring fabrication procedures can lead to surface finishes that are substantially out of range in critical areas of the leading edges. The development of a prototype light-scattering instrument which would allow for rapid assessment of the surface finish of a model is also discussed.

The role of water in the formation of reversed micelles: An antimicellization agent

USGS Publications Warehouse

Yu, Z.-J.; Zhou, N.-F.; Neuman, R.D.

1992-01-01

Micellization of sodium bis(2-ethylhexyl) phosphate in n-heptane has been studied under controlled environmental conditions by dynamic and static light scattering. The results clearly show that a trace amount of water has a very dramatic effect on reversed micellization. In contrast with results in the literature, water can function as an antimicellization agent. The generality of and the evidence for supporting the current view that water is a prerequisite for the formation of reversed micelles are discussed and criticized. ?? 1992 American Chemical Society.

Interplay of Structure and Dynamics in Biomaterials

NASA Astrophysics Data System (ADS)

Vodnala, Preeti

Study of structure and dynamic behavior is essential to understand molecular motions in biological systems. In this work, two biomaterials were studied to address membrane properties and protein diffusion. For the first project, we studied the structure of liposomes, artificial vesicles that are used for drug encapsulation and administration of pharmaceuticals or cellular nutrients. Small-angle x-ray scattering (SAXS) was used to determine the structural properties of different liposomes composed of egg-PC and cholesterol bilayer. We examined the location of cholesterol by labelling cholesterol with bromine molecule and reveal that cholesterol is located one side of the leaflet adjusting itself to the curvature of a liposome. In my second project, we studied the dynamics of concentrated suspensions of alpha crystallin, one of the most abundant proteins in the human eye lens using X-ray photon correlation spectroscopy (XPCS). An improved understanding of dynamics could point the way towards treatments presbyopia and cataract. The dynamics were measured at volume fraction close to the critical volume fraction for the glass transition, where the intermediate scattering function, ƒ(q,T) could be well fit using a double exponential decay. The measured relaxation is in reasonable agreement with published molecular dynamics simulations for the relaxation times of hard-sphere colloids.

Classification of fracture and non-fracture groups by analysis of coherent X-ray scatter

PubMed Central

Dicken, A. J.; Evans, J. P. O.; Rogers, K. D.; Stone, N.; Greenwood, C.; Godber, S. X.; Clement, J. G.; Lyburn, I. D.; Martin, R. M.; Zioupos, P.

2016-01-01

Osteoporotic fractures present a significant social and economic burden, which is set to rise commensurately with the aging population. Greater understanding of the physicochemical differences between osteoporotic and normal conditions will facilitate the development of diagnostic technologies with increased performance and treatments with increased efficacy. Using coherent X-ray scattering we have evaluated a population of 108 ex vivo human bone samples comprised of non-fracture and fracture groups. Principal component fed linear discriminant analysis was used to develop a classification model to discern each condition resulting in a sensitivity and specificity of 93% and 91%, respectively. Evaluating the coherent X-ray scatter differences from each condition supports the hypothesis that a causal physicochemical change has occurred in the fracture group. This work is a critical step along the path towards developing an in vivo diagnostic tool for fracture risk prediction. PMID:27363947

Electromagnetic Scattering by a Morphologically Complex Object: Fundamental Concepts and Common Misconceptions

NASA Technical Reports Server (NTRS)

Mischenko, Michael I.; Travis, Larry D.; Cairns, Brian; Tishkovets, Victor P.; Dlugach, Janna M.; Rosenbush, Vera K.; Kiselev, Nikolai N.

2011-01-01

Following Keller(Proc Symp Appl Math 1962;13:227:46), we classify all theoretical treatments of electromagnetic scattering by a morphologically complex object into first- principle (or "honest" in Keller s terminology) and phenomenological (or "dishonest") categories. This helps us identify, analyze, and dispel several profound misconceptions widespread in the discipline of electromagnetic scattering by solitary particles and discrete random media. Our goal is not to call for a complete renunciation of phenomenological approaches but rather to encourage a critical and careful evaluation of their actual origin, virtues, and limitations. In other words, we do not intend to deter creative thinking in terms of phenomenological short-cuts, but we do want to raise awareness when we stray (often for practical reasons) from the fundamentals. The main results and conclusions are illustrated by numerically-exact data based on direct numerical solutions of the macroscopic Maxwell equations.

Evidence for a common scale O(0.1) m that controls seabed scattering and reverberation in shallow water.

PubMed

Holland, Charles W

2012-10-01

Analysis of the spectral content of long-range reverberation yields two observations. First, there is a remarkably similar scale, O(0.1) m, between three diverse continental shelf regions. This is surprising given the complexity and diversity of geologic processes. Second, there is strong evidence that the scale is associated with heterogeneities within the sediment. Thus, sediment volume scattering, not interface scattering, controls long-range reverberation from a few hundred hertz to several kilohertz. This is also unexpected given that at long ranges the vertical grazing angles are less than the critical angle, and hence the penetration of the acoustic field into the sub-bottom is expected to be modest. The consistency of the scale, O(0.1) m, suggests an underlying feature or mechanism that is consistent across many ostensibly diverse geological settings. Neither the feature nor mechanism is known at this time.

Femtosecond resolution of soft mode dynamics in structural phase transitions

NASA Technical Reports Server (NTRS)

Dougherty, Thomas P.; Wiederrecht, Gary P.; Nelson, Keith A.; Garrett, Mark H.; Jensen, Hans P.; Warde, Cardinal

1992-01-01

The microscopic pathway along which ions or molecules in a crystal move during structural phase transition can often be described in terms of a collective vibrational mode of the lattice. In many cases, this mode, called a 'soft' phonon mode because of its characteristically low frequency near the phase transition temperature, is difficult to characterize through conventional frequency-domain spectroscopies such as light or neutron scattering. A femtosecond time-domain analog of light-scattering spectroscopy called impulsive stimulated Raman scattering (ISRS) has been used to examine the soft modes of two perovskite ferroelectric crystals. The low-frequency lattice dynamics of KNbO3 and BaTiO3 are clarified in a manner that permits critical evaluation of microscopic models for their ferroelectric transitions. The results illustrate the advantages of ISRS over conventional Raman spectroscopy of low-frequency, heavily damped soft modes.

Electronic Raman scattering as an ultra-sensitive probe of strain effects in semiconductors.

PubMed

Fluegel, Brian; Mialitsin, Aleksej V; Beaton, Daniel A; Reno, John L; Mascarenhas, Angelo

2015-05-28

Semiconductor strain engineering has become a critical feature of high-performance electronics because of the significant device performance enhancements that it enables. These improvements, which emerge from strain-induced modifications to the electronic band structure, necessitate new ultra-sensitive tools to probe the strain in semiconductors. Here, we demonstrate that minute amounts of strain in thin semiconductor epilayers can be measured using electronic Raman scattering. We applied this strain measurement technique to two different semiconductor alloy systems using coherently strained epitaxial thin films specifically designed to produce lattice-mismatch strains as small as 10(-4). Comparing our strain sensitivity and signal strength in Al(x)Ga(1-x)As with those obtained using the industry-standard technique of phonon Raman scattering, we found that there was a sensitivity improvement of 200-fold and a signal enhancement of 4 × 10(3), thus obviating key constraints in semiconductor strain metrology.

Electronic Raman scattering as an ultra-sensitive probe of strain effects in semiconductors

PubMed Central

Fluegel, Brian; Mialitsin, Aleksej V.; Beaton, Daniel A.; Reno, John L.; Mascarenhas, Angelo

2015-01-01

Semiconductor strain engineering has become a critical feature of high-performance electronics because of the significant device performance enhancements that it enables. These improvements, which emerge from strain-induced modifications to the electronic band structure, necessitate new ultra-sensitive tools to probe the strain in semiconductors. Here, we demonstrate that minute amounts of strain in thin semiconductor epilayers can be measured using electronic Raman scattering. We applied this strain measurement technique to two different semiconductor alloy systems using coherently strained epitaxial thin films specifically designed to produce lattice-mismatch strains as small as 10−4. Comparing our strain sensitivity and signal strength in AlxGa1−xAs with those obtained using the industry-standard technique of phonon Raman scattering, we found that there was a sensitivity improvement of 200-fold and a signal enhancement of 4 × 103, thus obviating key constraints in semiconductor strain metrology. PMID:26017853

Imaging the 'mosaic' structure of ICB by pre-critical PcP-PKiKP phases

NASA Astrophysics Data System (ADS)

Shen, Z.; Ai, Y.; He, Y.; Jiang, M.

2013-12-01

Slowly growing in highly homogeneous liquid outer core, earth inner core has been thought lacking of significant heterogeneous structure. However, seismic observations of recent decades have demonstrated hierarchical heterogeneous structure as hemispherical longitudinal dichotomy superimposed by coda-generating scattering heterogeneities with diameters of tens of kilometers, indicating complicity of inner core crystallizing environment and related dynamic process. Furthermore, as boundary of phase transform and energy-material exchange, ICB has been unveiled as patchy mosaic-like surface, based on high variety of global pre-critical PcP-PKiKP amplitude ratios. From dense arrays deployed across East and South China in the year 2005~2011 and 13 earthquakes of west Pacific subduction zone, we have collected over 150 clear pre-critical PcP-PKiKP waveforms of epicenter distance range between 14~35°, providing an ideal sampling to detect possible ICB regional variation of the East Asia area. The amplitude observation exhibits good geographical coherency which is characterized as region of high density contrast (>1.0g/cm3) located beneath East China demarcated by the low (around or lower than 0.6g/cm3) on the periphery, except the southeastward stretching. This contrasting depicts vividly the claimed 'mosaic' ICB and bridges the gap between hemispherical (~1000km order) and scatter-inducing (~10km order or less) scales of heterogeneity. On the other hand, travel time residues of PcP-PKiKP in our study reveal a complex pattern north of ~18°N perturbed strongly by shallow (crust and mantle) anomalies and remarkable delay of PKiKP in the south, implicating effects of undetected ULVZ below Celebes Sea. This research is supported by the National Natural Science Foundation of China (NSFC, grant 90914011, 41125015). Distribution of PcP-PKiKP relative amplitude ratio

Prior image constrained image reconstruction in emerging computed tomography applications

NASA Astrophysics Data System (ADS)

Brunner, Stephen T.

Advances have been made in computed tomography (CT), especially in the past five years, by incorporating prior images into the image reconstruction process. In this dissertation, we investigate prior image constrained image reconstruction in three emerging CT applications: dual-energy CT, multi-energy photon-counting CT, and cone-beam CT in image-guided radiation therapy. First, we investigate the application of Prior Image Constrained Compressed Sensing (PICCS) in dual-energy CT, which has been called "one of the hottest research areas in CT." Phantom and animal studies are conducted using a state-of-the-art 64-slice GE Discovery 750 HD CT scanner to investigate the extent to which PICCS can enable radiation dose reduction in material density and virtual monochromatic imaging. Second, we extend the application of PICCS from dual-energy CT to multi-energy photon-counting CT, which has been called "one of the 12 topics in CT to be critical in the next decade." Numerical simulations are conducted to generate multiple energy bin images for a photon-counting CT acquisition and to investigate the extent to which PICCS can enable radiation dose efficiency improvement. Third, we investigate the performance of a newly proposed prior image constrained scatter correction technique to correct scatter-induced shading artifacts in cone-beam CT, which, when used in image-guided radiation therapy procedures, can assist in patient localization, and potentially, dose verification and adaptive radiation therapy. Phantom studies are conducted using a Varian 2100 EX system with an on-board imager to investigate the extent to which the prior image constrained scatter correction technique can mitigate scatter-induced shading artifacts in cone-beam CT. Results show that these prior image constrained image reconstruction techniques can reduce radiation dose in dual-energy CT by 50% in phantom and animal studies in material density and virtual monochromatic imaging, can lead to radiation dose efficiency improvement in multi-energy photon-counting CT, and can mitigate scatter-induced shading artifacts in cone-beam CT in full-fan and half-fan modes.

Nematic fluctuations and resonance in iron-based superconductors

NASA Astrophysics Data System (ADS)

Gallais, Yann

The spontaneous appearance of nematicity, a state of matter that breaks rotation but not translation symmetry, is ubiquitous in many iron based superconductors (Fe SC), and has relevance for the cuprates as well. Here I will review recent electronic Raman scattering experiments which report the presence of critical nematic fluctuations in the charge channel in the tetragonal phase of several Fe SC systems. In electron doped Co-BaFe2As2 (Co-Ba122), these fluctuations extend over most of the superconducting dome. Their associated nematic susceptibility shows Curie-Weiss behavior, and its doping dependence suggests the presence of a nematic quantum critical point near optimal TC Similar nematic fluctuations are also observed in FeSe despite the absence of magnetic order, raising the question of the link between nematicity and magnetism in Fe SC. In FeSe I will further contrast the evolution of nematic fluctuations under isoelectronic S substitution and hydrostatic pressures up to 8 GPa, with only the former showing evidence for a nematic quantum critical point. In the superconducting state of Co-Ba122, I will show that a resonance emerges in the Raman spectra near the nematic quantum critical point. This nematic resonance is a clear fingerprint of the coupling between nematic fluctuations and Bogoliubov quasiparticles, and can be thought as the nematic counterpart of the spin resonance observed in neutron scattering experiments. Support from Agence Nationale de la Recherche via ANR Grant ''Pnictides'' is acknowledged.

Neutron-19C scattering: Emergence of universal properties in a finite range potential

NASA Astrophysics Data System (ADS)

Shalchi, M. A.; Yamashita, M. T.; Hadizadeh, M. R.; Frederico, T.; Tomio, Lauro

2017-01-01

The low-energy properties of the elastic s-wave scattering for the n-19C are studied near the critical condition for the occurrence of an excited Efimov state in n-n-18C. It is established to which extent the universal scaling laws, strictly valid in the zero-range limit, survive when finite range potentials are considered. By fixing the two-neutrons separation energy in 20C with available experimental data, it is studied the scaling of the real (δ0R) and imaginary parts of the s-wave phase-shift with the variation of the n-18C binding energy. We obtain some universal characteristics given by the pole-position of kcot ⁡ (δ0R) and effective-range parameters. By increasing the n-18C binding energy, it was verified that the excited state of 20C goes to a virtual state, resembling the neutron-deuteron behavior in the triton. It is confirmed that the analytical structure of the unitary cut is not affected by the range of the potential or mass asymmetry of the three-body system.

Polarimetric passive remote sensing of periodic surfaces

NASA Technical Reports Server (NTRS)

Veysoglu, Murat E.; Yueh, H. A.; Shin, R. T.; Kong, J. A.

1991-01-01

The concept of polarimetry in active remote sensing is extended to passive remote sensing. The potential use of the third and fourth Stokes parameters U and V, which play an important role in polarimetric active remote sensing, is demonstrated for passive remote sensing. It is shown that, by the use of the reciprocity principle, the polarimetric parameters of passive remote sensing can be obtained through the solution of the associated direct scattering problem. These ideas are applied to study polarimetric passive remote sensing of periodic surfaces. The solution of the direct scattering problem is obtained by an integral equation formulation which involves evaluation of periodic Green's functions and normal derivative of those on the surface. Rapid evaluation of the slowly convergent series associated with these functions is observed to be critical for the feasibility of the method. New formulas, which are rapidly convergent, are derived for the calculation of these series. The study has shown that the brightness temperature of the Stokes parameter U can be significant in passive remote sensing. Values as high as 50 K are observed for certain configurations.

An in situ USAXS-SAXS-WAXS study of precipitate size distribution evolution in a model Ni-based alloy.

PubMed

Andrews, Ross N; Serio, Joseph; Muralidharan, Govindarajan; Ilavsky, Jan

2017-06-01

Intermetallic γ' precipitates typically strengthen nickel-based superalloys. The shape, size and spatial distribution of strengthening precipitates critically influence alloy strength, while their temporal evolution characteristics determine the high-temperature alloy stability. Combined ultra-small-, small- and wide-angle X-ray scattering (USAXS-SAXS-WAXS) analysis can be used to evaluate the temporal evolution of an alloy's precipitate size distribution (PSD) and phase structure during in situ heat treatment. Analysis of PSDs from USAXS-SAXS data employs either least-squares fitting of a preordained PSD model or a maximum entropy (MaxEnt) approach, the latter avoiding a priori definition of a functional form of the PSD. However, strong low- q scattering from grain boundaries and/or structure factor effects inhibit MaxEnt analysis of typical alloys. This work describes the extension of Bayesian-MaxEnt analysis methods to data exhibiting structure factor effects and low- q power law slopes and demonstrates their use in an in situ study of precipitate size evolution during heat treatment of a model Ni-Al-Si alloy.

An in situ USAXS–SAXS–WAXS study of precipitate size distribution evolution in a model Ni-based alloy1

PubMed Central

Andrews, Ross N.; Serio, Joseph; Muralidharan, Govindarajan; Ilavsky, Jan

2017-01-01

Intermetallic γ′ precipitates typically strengthen nickel-based superalloys. The shape, size and spatial distribution of strengthening precipitates critically influence alloy strength, while their temporal evolution characteristics determine the high-temperature alloy stability. Combined ultra-small-, small- and wide-angle X-ray scattering (USAXS–SAXS–WAXS) analysis can be used to evaluate the temporal evolution of an alloy’s precipitate size distribution (PSD) and phase structure during in situ heat treatment. Analysis of PSDs from USAXS–SAXS data employs either least-squares fitting of a preordained PSD model or a maximum entropy (MaxEnt) approach, the latter avoiding a priori definition of a functional form of the PSD. However, strong low-q scattering from grain boundaries and/or structure factor effects inhibit MaxEnt analysis of typical alloys. This work describes the extension of Bayesian–MaxEnt analysis methods to data exhibiting structure factor effects and low-q power law slopes and demonstrates their use in an in situ study of precipitate size evolution during heat treatment of a model Ni–Al–Si alloy. PMID:28656039

Heterogeneous Mixtures as NLO Christiansen Filters for Optical Limiting

DOE Office of Scientific and Technical Information (OSTI.GOV)

Exarhos, Gregory J.; Ferris, Kim F.; Samuels, William D.

Mixtures of two non-absorbing and index-matched materials with contrasting nonlinear optical response have been shown to optically limit above a critical fluence of pulsed nanosecond laser light. Under these conditions, index mismatch is induced between the disparate phases leading to strong Tyndall scattering. The effect has been demonstrated previously by the authors in both solid-liquid mixtures (hexadecane and calcium fluoride), and surfactant-stabilized liquid-liquid emulsions consisting of dichloroethane as the organic phase and a concentrated aqueous phase of sodium thiocyanate (NaSCN). Materials used in these studies exhibit low absorption coefficients over extended wavelength regions allowing for a broadband response of themore » limiter. Recently, limiting has been observed at 532 nm in a polymer composite consisting of barium fluoride and poly-(n-butyl acrylate). A modified open-aperture z-scan method was used to quantify optical limiter performance in this system. Modeling studies provide the basis for designing optical limiters based upon this light scattering mechanism and show the importance of size resonance and constituent optical properties on limiter performance.« less

Stress path dependent hydromechanical behaviour of heterogeneous carbonate rock

NASA Astrophysics Data System (ADS)

Gland, N.; Dautriat, J.; Dimanov, A.; Raphanel, J.

2010-06-01

The influence of stress paths, representative of reservoir conditions, on the hydromechanical behavior of a moderately heterogeneous carbonate has been investigated. Multiscale structural heterogeneities, common for instance in carbonate rocks, can strongly alter the mechanical response and significantly influence the evolution of flow properties with stress. Using a triaxial cell, the permeability evolutions during compression and the effects of brittle (fracture) and plastic (pore collapse) deformations at yield, were measured. A strong scattering was observed on the mechanical response both in term of compressibility and failure threshold. Using the porosity scaling predicted by an adapted effective medium theory (based on crack growth under Hertzian contact), we have rescaled the critical pressures by the normalized porosity deviation. This procedure reduces efficiently the scattering, revealing in the framework of proportional stress path loading, a linear relation between the critical pressures and the stress path parameter through all the deformation regimes. It leads to a new formulation for the critical state envelope in the 'mean stress, deviatoric stress' diagram. The attractive feature of this new yield envelope formulation relies on the fact that only the two most common different mechanical tests 'Uniaxial Compression' and 'Hydrostatic Compression', are needed to define entirely the yield envelope. Volumic strains and normalized permeabilities are finally mapped in the stresses diagram and correlated.

Perfect and broadband acoustic absorption by critically coupled sub-wavelength resonators.

PubMed

Romero-García, V; Theocharis, G; Richoux, O; Merkel, A; Tournat, V; Pagneux, V

2016-01-19

Perfect absorption is an interdisciplinary topic with a large number of applications, the challenge of which consists of broadening its inherently narrow frequency-band performance. We experimentally and analytically report perfect and broadband absorption for audible sound, by the mechanism of critical coupling, with a sub-wavelength multi-resonant scatterer (SMRS) made of a plate-resonator/closed waveguide structure. In order to introduce the role of the key parameters, we first present the case of a single resonant scatterer (SRS) made of a Helmholtz resonator/closed waveguide structure. In both cases the controlled balance between the energy leakage of the several resonances and the inherent losses of the system leads to perfect absorption peaks. In the case of the SMRS we show that systems with large inherent losses can be critically coupled using resonances with large leakage. In particular, we show that in the SMRS system, with a thickness of λ/12 and diameter of λ/7, several perfect absorption peaks overlap to produce absorption bigger than 93% for frequencies that extend over a factor of 2 in audible frequencies. The reported concepts and methodology provide guidelines for the design of broadband perfect absorbers which could contribute to solve the major issue of noise reduction.

Perfect and broadband acoustic absorption by critically coupled sub-wavelength resonators

NASA Astrophysics Data System (ADS)

Romero-García, V.; Theocharis, G.; Richoux, O.; Merkel, A.; Tournat, V.; Pagneux, V.

2016-01-01

Perfect absorption is an interdisciplinary topic with a large number of applications, the challenge of which consists of broadening its inherently narrow frequency-band performance. We experimentally and analytically report perfect and broadband absorption for audible sound, by the mechanism of critical coupling, with a sub-wavelength multi-resonant scatterer (SMRS) made of a plate-resonator/closed waveguide structure. In order to introduce the role of the key parameters, we first present the case of a single resonant scatterer (SRS) made of a Helmholtz resonator/closed waveguide structure. In both cases the controlled balance between the energy leakage of the several resonances and the inherent losses of the system leads to perfect absorption peaks. In the case of the SMRS we show that systems with large inherent losses can be critically coupled using resonances with large leakage. In particular, we show that in the SMRS system, with a thickness of λ/12 and diameter of λ/7, several perfect absorption peaks overlap to produce absorption bigger than 93% for frequencies that extend over a factor of 2 in audible frequencies. The reported concepts and methodology provide guidelines for the design of broadband perfect absorbers which could contribute to solve the major issue of noise reduction.

Perfect and broadband acoustic absorption by critically coupled sub-wavelength resonators

PubMed Central

Romero-García, V.; Theocharis, G.; Richoux, O.; Merkel, A.; Tournat, V.; Pagneux, V.

2016-01-01

Perfect absorption is an interdisciplinary topic with a large number of applications, the challenge of which consists of broadening its inherently narrow frequency-band performance. We experimentally and analytically report perfect and broadband absorption for audible sound, by the mechanism of critical coupling, with a sub-wavelength multi-resonant scatterer (SMRS) made of a plate-resonator/closed waveguide structure. In order to introduce the role of the key parameters, we first present the case of a single resonant scatterer (SRS) made of a Helmholtz resonator/closed waveguide structure. In both cases the controlled balance between the energy leakage of the several resonances and the inherent losses of the system leads to perfect absorption peaks. In the case of the SMRS we show that systems with large inherent losses can be critically coupled using resonances with large leakage. In particular, we show that in the SMRS system, with a thickness of λ/12 and diameter of λ/7, several perfect absorption peaks overlap to produce absorption bigger than 93% for frequencies that extend over a factor of 2 in audible frequencies. The reported concepts and methodology provide guidelines for the design of broadband perfect absorbers which could contribute to solve the major issue of noise reduction. PMID:26781863

Millimeter wave scattering characteristics and radar cross section measurements of common roadway objects

NASA Astrophysics Data System (ADS)

Zoratti, Paul K.; Gilbert, R. Kent; Majewski, Ronald; Ference, Jack

1995-12-01

Development of automotive collision warning systems has progressed rapidly over the past several years. A key enabling technology for these systems is millimeter-wave radar. This paper addresses a very critical millimeter-wave radar sensing issue for automotive radar, namely the scattering characteristics of common roadway objects such as vehicles, roadsigns, and bridge overpass structures. The data presented in this paper were collected on ERIM's Fine Resolution Radar Imaging Rotary Platform Facility and processed with ERIM's image processing tools. The value of this approach is that it provides system developers with a 2D radar image from which information about individual point scatterers `within a single target' can be extracted. This information on scattering characteristics will be utilized to refine threat assessment processing algorithms and automotive radar hardware configurations. (1) By evaluating the scattering characteristics identified in the radar image, radar signatures as a function of aspect angle for common roadway objects can be established. These signatures will aid in the refinement of threat assessment processing algorithms. (2) Utilizing ERIM's image manipulation tools, total RCS and RCS as a function of range and azimuth can be extracted from the radar image data. This RCS information will be essential in defining the operational envelope (e.g. dynamic range) within which any radar sensor hardware must be designed.

Cotton fiber quality characterization with light scattering and fourier transform infrared techniques.

PubMed

Thomasson, J A; Manickavasagam, S; Mengüç, M P

2009-03-01

Fiber quality measurement is critical to assessing the value of a bale of cotton for various textile purposes. An instrument that could measure numerous cotton quality properties by optical means could be made simpler and faster than current fiber quality measurement instruments, and it might be more amenable to on-line measurement at processing facilities. To that end, a laser system was used to investigate cotton fiber samples with respect to electromagnetic scattering at various wavelengths, polarization angles, and scattering angles. A Fourier transform infrared (FT-IR) instrument was also used to investigate the transmission of electromagnetic energy at various mid-infrared wavelengths. Cotton samples were selected to represent a wide range of micronaire values. Varying the wavelength of the laser at a fixed polarization resulted in little variation in scattered light among the cotton samples. However, varying the polarization at a fixed wavelength produced notable variation, indicating that polarization might be used to differentiate among cotton samples with respect to certain fiber properties. The FT-IR data in the 12 to 22 microm range produced relatively large differences in the amount of scattered light among all samples, and FT-IR data at certain combinations of fixed wavelengths were highly linearly related to certain measures of cotton quality including micronaire.

On the connection between the Koppel-Young and the Nelkin Models for thermal neutron scattering in water molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Markovic, M.I.

1982-10-01

A critical analysis of the Koppel-Young model is presented and compared with Nelkin's model and their equivalence is asserted. It is shown that the only distinction between the two models is in the orientational averaging of the rotational-vibrational intermedial scattering function. Based on total cross sections, the Krieger-Nelkin orientation averaging has been confirmed to give excellent agreement with the Koppel-Young orientation averaging. However, significant quasi-periodical differences are observed when calculating differential cross sections. As a result of these insights, a new unified model is proposed for microdynamics of water molecules.

Optical coherence refractometry.

PubMed

Tomlins, Peter H; Woolliams, Peter; Hart, Christian; Beaumont, Andrew; Tedaldi, Matthew

2008-10-01

We introduce a novel approach to refractometry using a low coherence interferometer at multiple angles of incidence. We show that for plane parallel samples it is possible to measure their phase refractive index rather than the group index that is usually measured by interferometric methods. This is a significant development because it enables bulk refractive index measurement of scattering and soft samples, not relying on surface measurements that can be prone to error. Our technique is also noncontact and compatible with in situ refractive index measurements. Here, we demonstrate this new technique on a pure silica test piece and a highly scattering resin slab, comparing the results with standard critical angle refractometry.

Incomplete immunity to backscattering in chiral one-way photonic crystals.

PubMed

Cheng, Pi-Ju; Tien, Chung-Hao; Chang, Shu-Wei

2015-04-20

We show that the propagating modes in a strongly-guided chiral one-way photonic crystal are not backscattering-immune even though they are indeed insensitive to many kinds of scatters. Since these modes are not protected by the nonreciprocity, the backscattering does occur under certain circumstances. We use a perturbative method to derive criteria for the prominent backscattering in such chiral structures. From both our theory and numerical examinations, we find that the amount of backscattering critically depends on the symmetry of scatters. Additionally, for these chiral photonic modes, disturbances at the most intense parts of field profiles do not necessarily lead to the most effective backscattering.

A survey of light-scattering techniques used in the remote monitoring of atmospheric aerosols

NASA Technical Reports Server (NTRS)

Deirmendjian, D.

1980-01-01

A critical survey of the literature on the use of light-scattering mechanisms in the remote monitoring of atmospheric aerosols, their geographical and spatial distribution, and temporal variations was undertaken to aid in the choice of future operational systems, both ground based and air or space borne. An evaluation, mainly qualitative and subjective, of various techniques and systems is carried out. No single system is found to be adequate for operational purposes. A combination of earth surface and space-borne systems based mainly on passive techniques involving solar radiation with active (lidar) systems to provide auxiliary or backup information is tentatively recommended.

Classification of Stellar Orbits in Axisymmetric Galaxies

NASA Astrophysics Data System (ADS)

Li, Baile; Holley-Bockelmann, Kelly; Khan, Fazeel Mahmood

2015-09-01

It is known that two supermassive black holes (SMBHs) cannot merge in a spherical galaxy within a Hubble time; an emerging picture is that galaxy geometry, rotation, and large potential perturbations may usher the SMBH binary through the critical three-body scattering phase and ultimately drive the SMBH to coalesce. We explore the orbital content within an N-body model of a mildly flattened, non-rotating, SMBH-embedded elliptical galaxy. When used as the foundation for a study on the SMBH binary coalescence, the black holes bypassed the binary stalling often seen within spherical galaxies and merged on gigayear timescales. Using both frequency-mapping and angular momentum criteria, we identify a wealth of resonant orbits in the axisymmetric model, including saucers, that are absent from an otherwise identical spherical system and that can potentially interact with the binary. We quantified the set of orbits that could be scattered by the SMBH binary, and found that the axisymmetric model contained nearly six times the number of these potential loss cone orbits compared to our equivalent spherical model. In this flattened model, the mass of these orbits is more than three times that of the SMBH, which is consistent with what the SMBH binary needs to scatter to transition into the gravitational wave regime.

CLASSIFICATION OF STELLAR ORBITS IN AXISYMMETRIC GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Baile; Holley-Bockelmann, Kelly; Khan, Fazeel Mahmood, E-mail: baile.li@vanderbilt.edu, E-mail: k.holley@vanderbilt.edu, E-mail: khanfazeel.ist@gmail.com

2015-09-20

It is known that two supermassive black holes (SMBHs) cannot merge in a spherical galaxy within a Hubble time; an emerging picture is that galaxy geometry, rotation, and large potential perturbations may usher the SMBH binary through the critical three-body scattering phase and ultimately drive the SMBH to coalesce. We explore the orbital content within an N-body model of a mildly flattened, non-rotating, SMBH-embedded elliptical galaxy. When used as the foundation for a study on the SMBH binary coalescence, the black holes bypassed the binary stalling often seen within spherical galaxies and merged on gigayear timescales. Using both frequency-mapping andmore » angular momentum criteria, we identify a wealth of resonant orbits in the axisymmetric model, including saucers, that are absent from an otherwise identical spherical system and that can potentially interact with the binary. We quantified the set of orbits that could be scattered by the SMBH binary, and found that the axisymmetric model contained nearly six times the number of these potential loss cone orbits compared to our equivalent spherical model. In this flattened model, the mass of these orbits is more than three times that of the SMBH, which is consistent with what the SMBH binary needs to scatter to transition into the gravitational wave regime.« less

Quantum interference in multi-branched molecules: The exact transfer matrix solutions.

PubMed

Jiang, Yu

2017-12-07

We present a transfer matrix formalism for studying quantum interference in a single molecule electronic system with internal branched structures. Based on the Schrödinger equation with the Bethe ansatz and employing Kirchhoff's rule for quantum wires, we derive a general closed-form expression for the transmission and reflection amplitudes of a two-port quantum network. We show that the transport through a molecule with complex internal structures can be reduced to that of a single two-port scattering unit, which contains all the information of the original composite molecule. Our method allows for the calculation of the transmission coefficient for various types of individual molecular modules giving rise to different resonant transport behaviors such as the Breit-Wigner, Fano, and Mach-Zehnder resonances. As an illustration, we first re-derive the transmittance of the Aharonov-Bohm ring, and then we apply our formulation to N identical parity-time (PT)-symmetric potentials, connected in series as well as in parallel. It is shown that the spectral singularities and PT-symmetric transitions of single scattering cells may be observed in coupled systems. Such transitions may occur at the same or distinct values of the critical parameters, depending on the connection modes under which the scattering objects are coupled.

Molecular Packing of Amphiphilic Nanosheets Resolved by X-ray Scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harutyunyan, Boris; Dannenhoffer, Adam; Kewalramani, Sumit

2016-12-29

Molecular packing in light harvesting 2D assemblies of photocatalytic materials is a critical factor for solar-to-fuel conversion efficiency. However, structure–function correlations have yet to be fully established. This is partly due to the difficulties in extracting the molecular arrangements from the complex 3D powder averaged diffraction patterns of 2D lattices, obtained via in situ wide-angle X-ray scattering. Here, we develop a scattering theory formalism and couple it with a simple geometrical model for the molecular shape of chromophore 9-methoxy-N-(sodium hexanoate)perylene-3,4-dicarboximide (MeO-PMI) used in our study. This generally applicable method fully reproduces the measured diffraction pattern including the asymmetric line shapesmore » for the Bragg reflections and yields the molecular packing arrangement within a 2D crystal structure with a remarkable degree of detail. We find an approximate edge-centered herringbone structure for the PMI fused aromatic rings and ordering of the carboxypentyl chains above and below the nanosheets. Such a packing arrangement differs from the more symmetric face-to-face orientation of the unsubstituted PMI rings. This structural difference is correlated to our measurement of the reduced catalytic performance of MeO-PMI nanosheets as compared to the mesoscopically similar unsubstituted PMI assemblies.« less

Characterization of the shape and line-edge roughness of polymer gratings with grazing incidence small-angle X-ray scattering and atomic force microscopy

DOE PAGES

Suh, Hyo Seon; Chen, Xuanxuan; Rincon-Delgadillo, Paulina A.; ...

2016-04-22

Grazing-incidence small-angle X-ray scattering (GISAXS) is increasingly used for the metrology of substrate-supported nanoscale features and nanostructured films. In the case of line gratings, where long objects are arranged with a nanoscale periodicity perpendicular to the beam, a series of characteristic spots of high-intensity (grating truncation rods, GTRs) are recorded on a two-dimensional detector. The intensity of the GTRs is modulated by the three-dimensional shape and arrangement of the lines. Previous studies aimed to extract an average cross-sectional profile of the gratings, attributing intensity loss at GTRs to sample imperfections. Such imperfections are just as important as the average shapemore » when employing soft polymer gratings which display significant line-edge roughness. Herein are reported a series of GISAXS measurements of polymer line gratings over a range of incident angles. Both an average shape and fluctuations contributing to the intensity in between the GTRs are extracted. Lastly, the results are critically compared with atomic force microscopy (AFM) measurements, and it is found that the two methods are in good agreement if appropriate corrections for scattering from the substrate (GISAXS) and contributions from the probe shape (AFM) are accounted for.« less

Three-dimensional light-tissue interaction models for bioluminescence tomography

NASA Astrophysics Data System (ADS)

Côté, D.; Allard, M.; Henkelman, R. M.; Vitkin, I. A.

2005-09-01

Many diagnostic and therapeutic approaches in medical physics today take advantage of the unique properties of light and its interaction with tissues. Because light scatters in tissue, our ability to develop these techniques depends critically on our knowledge of the distribution of light in tissue. Solutions to the diffusion equation can provide such information, but often lack the flexibility required for more general problems that involve, for instance, inhomogeneous optical properties, light polarization, arbitrary three-dimensional geometries, or arbitrary scattering. Monte Carlo techniques, which statistically sample the light distribution in tissue, offer a better alternative to analytical models. First, we discuss our implementation of a validated three-dimensional polarization-sensitive Monte Carlo algorithm and demonstrate its generality with respect to the geometry and scattering models it can treat. Second, we apply our model to bioluminescence tomography. After appropriate genetic modifications to cell lines, bioluminescence can be used as an indicator of cell activity, and is often used to study tumour growth and treatment in animal models. However, the amount of light escaping the animal is strongly dependent on the position and size of the tumour. Using forward models and structural data from magnetic resonance imaging, we show how the models can help to determine the location and size of tumour made of bioluminescent cancer cells in the brain of a mouse.

Finite-temperature spin dynamics in a perturbed quantum critical Ising chain with an E₈ symmetry.

PubMed

Wu, Jianda; Kormos, Márton; Si, Qimiao

2014-12-12

A spectrum exhibiting E₈ symmetry is expected to arise when a small longitudinal field is introduced in the transverse-field Ising chain at its quantum critical point. Evidence for this spectrum has recently come from neutron scattering measurements in cobalt niobate, a quasi-one-dimensional Ising ferromagnet. Unlike its zero-temperature counterpart, the finite-temperature dynamics of the model has not yet been determined. We study the dynamical spin structure factor of the model at low frequencies and nonzero temperatures, using the form factor method. Its frequency dependence is singular, but differs from the diffusion form. The temperature dependence of the nuclear magnetic resonance (NMR) relaxation rate has an activated form, whose prefactor we also determine. We propose NMR experiments as a means to further test the applicability of the E₈ description for CoNb₂O₆.

Advanced in-situ measurement of soil carbon content using inelastic neutron scattering

USDA-ARS?s Scientific Manuscript database

Measurement and mapping of natural and anthropogenic variations in soil carbon stores is a critical component of any soil resource evaluation process. Emerging modalities for soil carbon analysis in the field is the registration of gamma rays from soil under neutron irradiation. The inelastic neutro...

A Critical Comparison of Some Methods for Interpolation of Scattered Data

DTIC Science & Technology

1979-12-01

because faster evaluation of the local interpolants is possible. KAll things considered, the method of choice here seems to be the Modified Quadratic...topography and other irregular surfaces," J. of Geophysical Research 76 ( 1971 ) 1905-1915I’ [23) HARDY, Rolland L. - "Analytical topographic surfaces by

Large enhancement of second harmonic generation from transition-metal dichalcogenide monolayer on grating near bound states in the continuum.

PubMed

Wang, Tiecheng; Zhang, Shihao

2018-01-08

Second harmonic generation from the two-layer structure where a transition-metal dichalcogenide monolayer is put on a one-dimensional grating has been studied. This grating supports bound states in the continuum which have no leakage lying within the continuum of radiation modes, we can enhance the second harmonic generation from the transition-metal dichalcogenide monolayer by more than four orders of magnitude based on the critical field enhancement near the bound states in the continuum. In order to complete this calculation, the scattering matrix theory has been extended to include the nonlinear effect and the scattering matrix of a two-dimensional material including nonlinear terms; furthermore, two methods to observe the bound states in the continuum are considered, where one is tuning the thickness of the grating and the other is changing the incident angle of the electromagnetic wave. We have also discussed various modulation of the second harmonic generation enhancement by adjusting the azimuthal angle of the transition-metal dichalcogenide monolayer.

Analysis and modeling of localized heat generation by tumor-targeted nanoparticles (Monte Carlo methods)

NASA Astrophysics Data System (ADS)

Sanattalab, Ehsan; SalmanOgli, Ahmad; Piskin, Erhan

2016-04-01

We investigated the tumor-targeted nanoparticles that influence heat generation. We suppose that all nanoparticles are fully functionalized and can find the target using active targeting methods. Unlike the commonly used methods, such as chemotherapy and radiotherapy, the treatment procedure proposed in this study is purely noninvasive, which is considered to be a significant merit. It is found that the localized heat generation due to targeted nanoparticles is significantly higher than other areas. By engineering the optical properties of nanoparticles, including scattering, absorption coefficients, and asymmetry factor (cosine scattering angle), the heat generated in the tumor's area reaches to such critical state that can burn the targeted tumor. The amount of heat generated by inserting smart agents, due to the surface Plasmon resonance, will be remarkably high. The light-matter interactions and trajectory of incident photon upon targeted tissues are simulated by MIE theory and Monte Carlo method, respectively. Monte Carlo method is a statistical one by which we can accurately probe the photon trajectories into a simulation area.

Microwave Dielectric and Propagation Properties of Vegetation Canopies

NASA Technical Reports Server (NTRS)

Ulaby, F. T. (Principal Investigator)

1985-01-01

A vegetation canopy is a highly inhomogeneous medium at microwave frequencies, and because the scattering elements (leaves, stalks, fruits, and branches) have a nonuniform distribution in orientation, the canopy is likely to exhibit nonisotropic attenuation properties. In some canopies, the stalk may contain the overwhelming majority of the plant's biomass, which suggests that an incident radar wave would be differentially attenuated by the canopy depending on the direction of the incident electric field relative to the stalks' orientation. The propagation properties of a vegetation canopy play a central role in modeling both the backscattering behavior observed by an imaging radar and the emission observed by a radiometer. These propagation properties are in turn governed by the dielectric properties and the size, shape, and slope distributions of the scatteres. In spite of the critical need for canopy propagation models and experimental data, very few investigations had been conducted (prior to this study) to determine the extinction properties of vegetation canopies, either by constituent type (leaves, stalks, etc.) or as a whole.

Ultraviolet Thomson Scattering from Direct-Drive Coronal Plasmas in Multilayer Targets

NASA Astrophysics Data System (ADS)

Henchen, R. J.; Goncharov, V. N.; Michel, D. T.; Follett, R. K.; Katz, J.; Froula, D. H.

2014-10-01

Ultraviolet (λ4 ω = 263 nm) Thomson scattering (TS) was used to probe ion-acoustic waves (IAW's) and electron plasma waves (EPW's) from direct-drive coronal plasmas. Fifty-nine drive beams (λ3 ω = 351 nm) illuminate a spherical target with a radius of ~ 860 μ m. A series of experiments studied the effect of higher electron temperature near the 3 ω quarter-critical surface (~ 2 . 5 ×1021 cm-3) on laser-plasma interactions resulting from a Si layer in the target. Electron temperatures and densities were measured from 150 to 400 μm from the initial target surface. Standard CH shells were compared to two-layered shells of CH and Si and three-layered shells of CH, Si, and CH. These multilayer targets have less hot-electron energy than standard CH shells as a result of higher electron temperature in the coronal plasmas. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Optical Limiting by Index-Matched Phase-Segregated Mixtures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Exarhos, Gregory J.; Ferris, Kim F.; Manijeh Razeghi, Gail J. Brown

The nonlinear optical response for index-matched, non-absorbing immiscible phases (liquid-solid, liquid-liquid, solid-solid) has been determined by means of open aperture z-scan measurements. In mixtures where one constituent shows a relatively high optical nonlinearity, rapid and reversible transformation to a light-scattering state is observed under conditions where a critical incident light fluence is exceeded. This passive broadband response is induced by a transient change in the dispersive part of the refractive index, and is based upon the Christiansen-Shelyubskii filter that at one time was used as a means to monitor the temperature of glass melts. Modeling studies are used to simulatemore » scattering intensities in such textured composites as a function of composition, microstructure, and constituent optical properties. Results provide a rational approach to the selection of materials for use in these limiters. Challenges to preparing dispersed phase mixtures and their response to 532 nm nanosecond pulsed laser irradiation are described.« less

A review of laser-plasma interaction physics of indirect-drive fusion

NASA Astrophysics Data System (ADS)

Kirkwood, R. K.; Moody, J. D.; Kline, J.; Dewald, E.; Glenzer, S.; Divol, L.; Michel, P.; Hinkel, D.; Berger, R.; Williams, E.; Milovich, J.; Yin, L.; Rose, H.; MacGowan, B.; Landen, O.; Rosen, M.; Lindl, J.

2013-10-01

The National Ignition Facility (NIF) has been designed, constructed and has recently begun operation to investigate the ignition of nuclear fusion with a laser with up to 1.8 MJ of energy per pulse. The concept for fusion ignition on the NIF, as first proposed in 1990, was based on an indirectly driven spherical capsule of fuel in a high-Z hohlraum cavity filled with low-Z gas (Lindl et al 2004 Phys. Plasmas 11 339). The incident laser energy is converted to x-rays with keV energy on the hohlraums interior wall. The x-rays then impinge on the surface of the capsule, imploding it and producing the fuel conditions needed for ignition. It was recognized at the inception that this approach would potentially be susceptible to scattering of the incident light by the plasma created in the gas and the ablated material in the hohlraum interior. Prior to initial NIF operations, expectations for laser-plasma interaction (LPI) in ignition-scale experiments were based on experimentally benchmarked simulations and models of the plasma effects that had been carried out as part of the original proposal for NIF and expanded during the 13-year design and construction period. The studies developed the understanding of the stimulated Brillouin scatter, stimulated Raman scatter and filamentation that can be driven by the intense beams. These processes produce scatter primarily in both the forward and backward direction, and by both individual beams and collective interaction of multiple beams. Processes such as hot electron production and plasma formation and transport were also studied. The understanding of the processes so developed was the basis for the design and planning of the recent experiments in the ignition campaign at NIF, and not only indicated that the plasma instabilities could be controlled to maximize coupling, but predicted that, for the first time, they would be beneficial in controlling drive symmetry. The understanding is also now a critical component in the worldwide effort to produce a fusion energy source with a laser (Lindl et al 2011 Nucl. Fusion 51 094024, Collins et al 2012 Phys. Plasmas 19 056308) and has recently received its most critical test yet with the inception of the NIF experiments with ignition-scale indirect-drive targets (Landen et al 2010 Phys. Plasmas 17 056301, Edwards et al 2011 Phys. Plasmas 18 051003, Glenzer et al 2011 Phys. Rev. Lett. 106 085004, Haan et al 2011 Phys. Plasmas 18 051001, Landen et al 2011 Phys. Plasmas 18 051001, Lindl et al 2011 Nucl. Fusion 51 094024). In this paper, the data obtained in the first complete series of coupling experiments in ignition-scale hohlraums is reviewed and compared with the preceding work on the physics of LPIs with the goal of recognizing aspects of our understanding that are confirmed by these experiments and recognizing and motivating areas that need further modeling. Understanding these hohlraum coupling experiments is critical as they are only the first step in a campaign to study indirectly driven implosions under the conditions of ignition by inertial confinement at NIF, and in the near future they are likely to further influence ignition plans and experimental designs.

Lifetimes in Te 124 : Examining critical-point symmetry in the Te nuclei

DOE PAGES

Hicks, S. F.; Vanhoy, J. R.; Burkett, P. G.; ...

2017-03-27

The Doppler-shift attenuation method following inelastic neutron scattering was used to determine the lifetimes of nuclear levels to 3.3-MeV excitation in 124Te. Level energies and spins, γ -ray energies and branching ratios, and multipole-mixing ratios were deduced from measured γ-ray angular distributions at incident neutron energies of 2.40 and 3.30 MeV, γ-ray excitation functions, and γγ coincidence measurements. The newly obtained reduced transition probabilities and level energies for 124Te were compared to critical-point symmetry model predictions. The E(5) and β 4 potential critical-point symmetries were also investigated in 122Te and 126Te.

Compressibility, isothermal titration calorimetry and dynamic light scattering analysis of the aggregation of the amphiphilic phenothiazine drug thioridazine hydrochloride in water/ethanol mixed solvent

NASA Astrophysics Data System (ADS)

Cheema, Mohammad Arif; Siddiq, Mohammad; Barbosa, Silvia; Castro, Emilio; Egea, José A.; Antelo, Luis T.; Taboada, Pablo; Mosquera, Víctor

2007-07-01

Thioridazine hydrochloride is a drug used in treatment of mental illness that shows side effects. Therefore, it is interesting to study the change of the physico-chemical properties of the drug in different environments to understand the mechanism of action of the drug. Thioridazine can be considered as a hydrotrope if we considered that the term comprise hydrophilic and hydrophobic moieties that form aggregates by a stacking mechanism as it is the case of all the phenothiazine tranquillizing drugs. The association properties of the amphiphilic phenothiazine drug thioridazine hydrochloride were investigated by density, ultrasound, isothermal titration calorimetry and dynamic light scattering (DLS), yielding values of the critical concentration, adiabatic apparent compressibilities and hydrodynamic radius. The DLS data were analyzed according to the treatment of the Derjaguin, Landau, Verwey and Overbeek (DLVO) theory to study the stability of the system. The aim of the study is to obtain information about the physico-chemical characterization of the drug in aqueous solution and the effect of ethanol on the aggregate stability of this amphiphilic drug. The phenothiazine tranquillizing drugs have interesting association characteristics that derive from their rigid, tricyclic hydrophobic groups.

A novel method for study of the aggregation of protein induced by metal ion aluminum(III) using resonance Rayleigh scattering technique

NASA Astrophysics Data System (ADS)

Long, Xiufen; Zhang, Caihua; Cheng, Jiongjia; Bi, Shuping

2008-01-01

We present a novel method for the study of the aggregation of protein induced by metal ion aluminum(III) using resonance Rayleigh scattering (RRS) technique. In neutral Tris-HCl medium, the effect of this aggregation of protein results in the enhancement of RRS intensity and the relationship between the enhancement of the RRS signal and the Al concentration is nonlinear. On this basis, we established a new method for the determination of the critical induced-aggregation concentrations ( CCIAC) of metal ion Al(III) inducing the protein aggregation. Our results show that many factors, such as, pH value, anions, salts, temperature and solvents have obvious effects. We also studied the extent of aggregation and structural changes using ultra-violet spectrometry, protein intrinsic fluorescence and circular dichroism to further understand the exact mechanisms of the aggregation characteristics of proteins induced by metal ion Al(III) at the molecular level, to help us to develop effective methods to investigate the toxicity of metal ion Al, and to provide theoretical and quantitative evidences for the development of appropriate treatments for neurodementia such as Parkinson's disease, Alzheimer's disease and dementia related to dialysis.

Minimizing scatter-losses during pre-heat for magneto-inertial fusion targets

NASA Astrophysics Data System (ADS)

Geissel, Matthias; Harvey-Thompson, Adam J.; Awe, Thomas J.; Bliss, David E.; Glinsky, Michael E.; Gomez, Matthew R.; Harding, Eric; Hansen, Stephanie B.; Jennings, Christopher; Kimmel, Mark W.; Knapp, Patrick; Lewis, Sean M.; Peterson, Kyle; Schollmeier, Marius; Schwarz, Jens; Shores, Jonathon E.; Slutz, Stephen A.; Sinars, Daniel B.; Smith, Ian C.; Speas, C. Shane; Vesey, Roger A.; Weis, Matthew R.; Porter, John L.

2018-02-01

The size, temporal and spatial shape, and energy content of a laser pulse for the pre-heat phase of magneto-inertial fusion affect the ability to penetrate the window of the laser-entrance-hole and to heat the fuel behind it. High laser intensities and dense targets are subject to laser-plasma-instabilities (LPI), which can lead to an effective loss of pre-heat energy or to pronounced heating of areas that should stay unexposed. While this problem has been the subject of many studies over the last decades, the investigated parameters were typically geared towards traditional laser driven Inertial Confinement Fusion (ICF) with densities either at 10% and above or at 1% and below the laser's critical density, electron temperatures of 3-5 keV, and laser powers near (or in excess of) 1 × 1015 W/cm2. In contrast, Magnetized Liner Inertial Fusion (MagLIF) [Slutz et al., Phys. Plasmas 17, 056303 (2010) and Slutz and Vesey, Phys. Rev. Lett. 108, 025003 (2012)] currently operates at 5% of the laser's critical density using much thicker windows (1.5-3.5 μm) than the sub-micron thick windows of traditional ICF hohlraum targets. This article describes the Pecos target area at Sandia National Laboratories using the Z-Beamlet Laser Facility [Rambo et al., Appl. Opt. 44(12), 2421 (2005)] as a platform to study laser induced pre-heat for magneto-inertial fusion targets, and the related progress for Sandia's MagLIF program. Forward and backward scattered light were measured and minimized at larger spatial scales with lower densities, temperatures, and powers compared to LPI studies available in literature.

Critical behavior in graphene with Coulomb interactions.

PubMed

Wang, Jianhui; Fertig, H A; Murthy, Ganpathy

2010-05-07

We demonstrate that, in the presence of Coulomb interactions, electrons in graphene behave like a critical system, supporting power law correlations with interaction-dependent exponents. An asymptotic analysis shows that the origin of this behavior lies in particle-hole scattering, for which the Coulomb interaction induces anomalously close approaches. With increasing interaction strength the relevant power law changes from real to complex, leading to an unusual instability characterized by a complex-valued susceptibility in the thermodynamic limit. Measurable quantities, as well as the connection to classical two-dimensional systems, are discussed.

Identifying the theory of dark matter with direct detection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gluscevic, Vera; Gresham, Moira I.; McDermott, Samuel D.

2015-12-01

Identifying the true theory of dark matter depends crucially on accurately characterizing interactions of dark matter (DM) with other species. In the context of DM direct detection, we present a study of the prospects for correctly identifying the low-energy effective DM-nucleus scattering operators connected to UV-complete models of DM-quark interactions. We take a census of plausible UV-complete interaction models with different low-energy leading-order DM-nuclear responses. For each model (corresponding to different spin–, momentum–, and velocity-dependent responses), we create a large number of realizations of recoil-energy spectra, and use Bayesian methods to investigate the probability that experiments will be able tomore » select the correct scattering model within a broad set of competing scattering hypotheses. We conclude that agnostic analysis of a strong signal (such as Generation-2 would see if cross sections are just below the current limits) seen on xenon and germanium experiments is likely to correctly identify momentum dependence of the dominant response, ruling out models with either 'heavy' or 'light' mediators, and enabling downselection of allowed models. However, a unique determination of the correct UV completion will critically depend on the availability of measurements from a wider variety of nuclear targets, including iodine or fluorine. We investigate how model-selection prospects depend on the energy window available for the analysis. In addition, we discuss accuracy of the DM particle mass determination under a wide variety of scattering models, and investigate impact of the specific types of particle-physics uncertainties on prospects for model selection.« less

Identifying the theory of dark matter with direct detection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gluscevic, Vera; Gresham, Moira I.; McDermott, Samuel D.

2015-12-29

Identifying the true theory of dark matter depends crucially on accurately characterizing interactions of dark matter (DM) with other species. In the context of DM direct detection, we present a study of the prospects for correctly identifying the low-energy effective DM-nucleus scattering operators connected to UV-complete models of DM-quark interactions. We take a census of plausible UV-complete interaction models with different low-energy leading-order DM-nuclear responses. For each model (corresponding to different spin–, momentum–, and velocity-dependent responses), we create a large number of realizations of recoil-energy spectra, and use Bayesian methods to investigate the probability that experiments will be able tomore » select the correct scattering model within a broad set of competing scattering hypotheses. We conclude that agnostic analysis of a strong signal (such as Generation-2 would see if cross sections are just below the current limits) seen on xenon and germanium experiments is likely to correctly identify momentum dependence of the dominant response, ruling out models with either “heavy” or “light” mediators, and enabling downselection of allowed models. However, a unique determination of the correct UV completion will critically depend on the availability of measurements from a wider variety of nuclear targets, including iodine or fluorine. We investigate how model-selection prospects depend on the energy window available for the analysis. In addition, we discuss accuracy of the DM particle mass determination under a wide variety of scattering models, and investigate impact of the specific types of particle-physics uncertainties on prospects for model selection.« less

Critical temperature transitions in laser-mediated cartilage reshaping

NASA Astrophysics Data System (ADS)

Wong, Brian J.; Milner, Thomas E.; Kim, Hong H.; Telenkov, Sergey A.; Chew, Clifford; Kuo, Timothy C.; Smithies, Derek J.; Sobol, Emil N.; Nelson, J. Stuart

1998-07-01

In this study, we attempted to determine the critical temperature [Tc] at which accelerated stress relaxation occurred during laser mediated cartilage reshaping. During laser irradiation, mechanically deformed cartilage tissue undergoes a temperature dependent phase transformation which results in accelerated stress relaxation. When a critical temperature is attained, cartilage becomes malleable and may be molded into complex new shapes that harden as the tissue cools. Clinically, reshaped cartilage tissue can be used to recreate the underlying cartilaginous framework of structures such as the ear, larynx, trachea, and nose. The principal advantages of using laser radiation for the generation of thermal energy in tissue are precise control of both the space-time temperature distribution and time- dependent thermal denaturation kinetics. Optimization of the reshaping process requires identification of the temperature dependence of this phase transformation and its relationship to observed changes in cartilage optical, mechanical, and thermodynamic properties. Light scattering, infrared radiometry, and modulated differential scanning calorimetry (MDSC) were used to measure temperature dependent changes in the biophysical properties of cartilage tissue during fast (laser mediated) and slow (conventional calorimetric) heating. Our studies using MDSC and laser probe techniques have identified changes in cartilage thermodynamic and optical properties suggestive of a phase transformation occurring near 60 degrees Celsius.

Anisotropy and multiband superconductivity in Sr 2 RuO 4 determined by small-angle neutron scattering studies of the vortex lattice [Anisotropy and multiband superconductivity in Sr 2 RuO 4

DOE PAGES

Kuhn, S. J.; Morgenlander, W.; Louden, E. R.; ...

2017-11-14

Despite numerous studies the exact nature of the order parameter in superconducting Sr 2RuO 4 remains unresolved. We have extended previous small-angle neutron scattering studies of the vortex lattice in this material to a wider field range, higher temperatures, and with the field applied close to both the <100> and <110> basal plane directions. Measurements at high field were made possible by the use of both spin polarization and analysis to improve the signal-to-noise ratio. Rotating the field towards the basal plane causes a distortion of the square vortex lattice observed for H // <001> and also a symmetry changemore » to a distorted triangular symmetry for fields close to <100>.The vortex lattice distortion allows us to determine the intrinsic superconducting anisotropy between the c axis and the Ru-O basal plane, yielding a value of ~60 at low temperature and low to intermediate fields. This greatly exceeds the upper critical field anisotropy of ~20 at low temperature, reminiscent of Pauli limiting. Indirect evidence for Pauli paramagnetic effects on the unpaired quasiparticles in the vortex cores are observed, but a direct detection lies below the measurement sensitivity. The superconducting anisotropy is found to be independent of temperature but increases for fields > 1 T, indicating multiband superconductvity in Sr 2RuO 4. Lastly, the temperature dependence of the scattered intensity provides further support for gap nodes or deep minima in the superconducting gap.« less

Anisotropy and multiband superconductivity in Sr 2 RuO 4 determined by small-angle neutron scattering studies of the vortex lattice [Anisotropy and multiband superconductivity in Sr 2 RuO 4

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuhn, S. J.; Morgenlander, W.; Louden, E. R.

Despite numerous studies the exact nature of the order parameter in superconducting Sr 2RuO 4 remains unresolved. We have extended previous small-angle neutron scattering studies of the vortex lattice in this material to a wider field range, higher temperatures, and with the field applied close to both the <100> and <110> basal plane directions. Measurements at high field were made possible by the use of both spin polarization and analysis to improve the signal-to-noise ratio. Rotating the field towards the basal plane causes a distortion of the square vortex lattice observed for H // <001> and also a symmetry changemore » to a distorted triangular symmetry for fields close to <100>.The vortex lattice distortion allows us to determine the intrinsic superconducting anisotropy between the c axis and the Ru-O basal plane, yielding a value of ~60 at low temperature and low to intermediate fields. This greatly exceeds the upper critical field anisotropy of ~20 at low temperature, reminiscent of Pauli limiting. Indirect evidence for Pauli paramagnetic effects on the unpaired quasiparticles in the vortex cores are observed, but a direct detection lies below the measurement sensitivity. The superconducting anisotropy is found to be independent of temperature but increases for fields > 1 T, indicating multiband superconductvity in Sr 2RuO 4. Lastly, the temperature dependence of the scattered intensity provides further support for gap nodes or deep minima in the superconducting gap.« less

The use of silver nanorod array based surface enhanced Raman scattering sensor for food safety applications

USDA-ARS?s Scientific Manuscript database

For the advancement of preventive strategies, it is critical to develop rapid and sensitive detection methods with nanotechnology for food safety applications. This article reports the recent development on the use of aligned silver nanorod (AgNR) arrays prepared by oblique angle deposition, as surf...

An improved radiation metric. [for radiation pressure in strong gravitational fields

NASA Technical Reports Server (NTRS)

Noerdlinger, P. D.

1976-01-01

An improved radiation metric is obtained in which light rays make a small nonzero angle with the radius, thus representing a source of finite size. Kaufmann's previous solution is criticized. The stabilization of a scatterer near a source of gravitational field and radiation is slightly enhanced for sources of finite size.

An Alternative Retrieval Algorithm for the Ozone Mapping and Profiler Suite Limb Profiler

DTIC Science & Technology

2012-05-01

behavior of aerosol extinction from the upper troposphere through the stratosphere is critical for retrieving ozone in this region. Aerosol scattering is......include area code) b. ABSTRACT c. THIS PAGE 18. NUMBER OF PAGES 17. LIMITATION OF ABSTRACT An Alternative Retrieval Algorithm for the Ozone Mapping and

The application of polyethylene glycol (PEG) to electron microscopy

PubMed Central

1980-01-01

The cytoplasm of cells from a variety of tissues has been viewed in sections (0.25-1 micrometers) devoid of any embedding resin. Glutaraldehyde- and osmium tetroxide-fixed tissues were infiltrated and embedded in a water-miscible wax, polyethylene glycol (PEG), and subsequently sectioned on dry glass or diamond knives. The PEG matrix was removed and the sections were placed on Formvarcarbon-polylysine- coated grids, dehydrated, dried by the critical-point method, and observed in either the high- or low-voltage electron microscope. Stereoscopic views of cells devoid of embedding resin present an image of cell utrastructure unobscured by electron-scattering resins similar to the image of whole, unembedded critical-point-dried or freeze-dried cultured cells observed by transmission electron microscopy. All organelles, including the cytoskeletal structures, are identified and appear not to have been damaged during processing, although membrane components appear somewhat less distinct. The absence of an embedding matrix eliminates the need for additional staining to increase contrast, unlike the situation with specimens embedded in standard electron-scattering resins. The PEG technique thus appears to be a valuable adjunct to conventional methods for ultrastructural analysis. PMID:7400222

The application of polyethylene glycol (PEG) to electron microscopy.

PubMed

Wolosewick, J J

1980-08-01

The cytoplasm of cells from a variety of tissues has been viewed in sections (0.25-1 micrometers) devoid of any embedding resin. Glutaraldehyde- and osmium tetroxide-fixed tissues were infiltrated and embedded in a water-miscible wax, polyethylene glycol (PEG), and subsequently sectioned on dry glass or diamond knives. The PEG matrix was removed and the sections were placed on Formvarcarbon-polylysine-coated grids, dehydrated, dried by the critical-point method, and observed in either the high- or low-voltage electron microscope. Stereoscopic views of cells devoid of embedding resin present an image of cell utrastructure unobscured by electron-scattering resins similar to the image of whole, unembedded critical-point-dried or freeze-dried cultured cells observed by transmission electron microscopy. All organelles, including the cytoskeletal structures, are identified and appear not to have been damaged during processing, although membrane components appear somewhat less distinct. The absence of an embedding matrix eliminates the need for additional staining to increase contrast, unlike the situation with specimens embedded in standard electron-scattering resins. The PEG technique thus appears to be a valuable adjunct to conventional methods for ultrastructural analysis.

Multidimensional analysis of fast-spectrum material replacement measurements for systematic estimation of cross section uncertainties

NASA Technical Reports Server (NTRS)

Klann, P. G.; Lantz, E.; Mayo, W. T.

1973-01-01

A series of central core and core-reflector interface sample replacement experiments for 16 materials performed in the NASA heavy-metal-reflected, fast spectrum critical assembly (NCA) were analyzed in four and 13 groups using the GAM 2 cross-section set. The individual worths obtained by TDSN and DOT multidimensional transport theory calculations showed significant differences from the experimental results. These were attributed to cross-section uncertainties in the GAM 2 cross sections. Simultaneous analysis of the measured and calculated sample worths permitted separation of the worths into capture and scattering components which systematically provided fast spectrum averaged correction factors to the magnitudes of the GAM 2 absorption and scattering cross sections. Several Los Alamos clean critical assemblies containing Oy, Ta, and Mo as well as one of the NCA compositions were reanalyzed using the corrected cross sections. In all cases the eigenvalues were significantly improved and were recomputed to within 1 percent of the experimental eigenvalue. A comparable procedure may be used for ENDF cross sections when these are available.

Pharmaceutical Perspective on Opalescence and Liquid-Liquid Phase Separation in Protein Solutions.

PubMed

Raut, Ashlesha S; Kalonia, Devendra S

2016-05-02

Opalescence in protein solutions reduces aesthetic appeal of a formulation and can be an indicator of the presence of aggregates or precursor to phase separation in solution signifying reduced product stability. Liquid-liquid phase separation of a protein solution into a protein-rich and a protein-poor phase has been well-documented for globular proteins and recently observed for monoclonal antibody solutions, resulting in physical instability of the formulation. The present review discusses opalescence and liquid-liquid phase separation (LLPS) for therapeutic protein formulations. A brief discussion on theoretical concepts based on thermodynamics, kinetics, and light scattering is presented. This review also discusses theoretical concepts behind intense light scattering in the vicinity of the critical point termed as "critical opalescence". Both opalescence and LLPS are affected by the formulation factors including pH, ionic strength, protein concentration, temperature, and excipients. Literature reports for the effect of these formulation factors on attractive protein-protein interactions in solution as assessed by the second virial coefficient (B2) and the cloud-point temperature (Tcloud) measurements are also presented. The review also highlights pharmaceutical implications of LLPS in protein solutions.

Percolation Thresholds in Angular Grain media: Drude Directed Infiltration

NASA Astrophysics Data System (ADS)

Priour, Donald

Pores in many realistic systems are not well delineated channels, but are void spaces among grains impermeable to charge or fluid flow which comprise the medium. Sparse grain concentrations lead to permeable systems, while concentrations in excess of a critical density block bulk fluid flow. We calculate percolation thresholds in porous materials made up of randomly placed (and oriented) disks, tetrahedrons, and cubes. To determine if randomly generated finite system samples are permeable, we deploy virtual tracer particles which are scattered (e.g. specularly) by collisions with impenetrable angular grains. We hasten the rate of exploration (which would otherwise scale as ncoll1 / 2 where ncoll is the number of collisions with grains if the tracers followed linear trajectories) by considering the tracer particles to be charged in conjunction with a randomly directed uniform electric field. As in the Drude treatment, where a succession of many scattering events leads to a constant drift velocity, tracer displacements on average grow linearly in ncoll. By averaging over many disorder realizations for a variety of systems sizes, we calculate the percolation threshold and critical exponent which characterize the phase transition.

Laser pulsing in linear Compton scattering

DOE PAGES

Krafft, G. A.; Johnson, E.; Deitrick, K.; ...

2016-12-16

Previous work on calculating energy spectra from Compton scattering events has either neglected considering the pulsed structure of the incident laser beam, or has calculated these effects in an approximate way subject to criticism. In this paper, this problem has been reconsidered within a linear plane wave model for the incident laser beam. By performing the proper Lorentz transformation of the Klein-Nishina scattering cross section, a spectrum calculation can be created which allows the electron beam energy spread and emittance effects on the spectrum to be accurately calculated, essentially by summing over the emission of each individual electron. Such anmore » approach has the obvious advantage that it is easily integrated with a particle distribution generated by particle tracking, allowing precise calculations of spectra for realistic particle distributions in collision. The method is used to predict the energy spectrum of radiation passing through an aperture for the proposed Old Dominion University inverse Compton source. In addition, as discussed in the body of the paper, many of the results allow easy scaling estimates to be made of the expected spectrum. A misconception in the literature on Compton scattering of circularly polarized beams is corrected and recorded.« less

Stimulated Rayleigh-Bragg scattering in a three-photon absorbing medium and its phase-conjugation property

NASA Astrophysics Data System (ADS)

He, Guang S.; Zheng, Qingdong; Prasad, Paras N.

2007-05-01

We show that the backward-stimulated Rayleigh-Bragg scattering (SRBS) can be efficiently generated in a three-photon absorbing medium. Compared with all other known stimulated (such as Brillouin and Raman) scattering effects, the observed effect exhibits the following three features: (i) no frequency shift, (ii) a lower pump threshold, and (iii) no critical requirement for pump spectral linewidths within a range of Δv¯≤1cm-1. The specific nonlinear scattering medium is a three-photon absorbing chromophore solution (PRL-OT04 in chloroform), pumped by 1064nm laser pulses of nanoseconds duration but with three different spectral linewidths. The mechanism for generating backward SRBS in a three-photon active medium is the formation of a stationary Bragg grating enhanced by three-photon-absorption-associated refractive index changes. A superior optical phase-conjugation property of the backward SRBS beam has been experimentally demonstrated by employing two different optical setups. In both cases, a specially introduced aberration influence of 4-5 mrad can be basically removed by the backward SRBS beam that retains a much smaller beam divergence of ≤0.4 mrad.

Model-Based Detection of Radioactive Contraband for Harbor Defense Incorporating Compton Scattering Physics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Candy, J V; Chambers, D H; Breitfeller, E F

2010-03-02

The detection of radioactive contraband is a critical problem is maintaining national security for any country. Photon emissions from threat materials challenge both detection and measurement technologies especially when concealed by various types of shielding complicating the transport physics significantly. This problem becomes especially important when ships are intercepted by U.S. Coast Guard harbor patrols searching for contraband. The development of a sequential model-based processor that captures both the underlying transport physics of gamma-ray emissions including Compton scattering and the measurement of photon energies offers a physics-based approach to attack this challenging problem. The inclusion of a basic radionuclide representationmore » of absorbed/scattered photons at a given energy along with interarrival times is used to extract the physics information available from the noisy measurements portable radiation detection systems used to interdict contraband. It is shown that this physics representation can incorporated scattering physics leading to an 'extended' model-based structure that can be used to develop an effective sequential detection technique. The resulting model-based processor is shown to perform quite well based on data obtained from a controlled experiment.« less

Quantum random bit generation using energy fluctuations in stimulated Raman scattering.

PubMed

Bustard, Philip J; England, Duncan G; Nunn, Josh; Moffatt, Doug; Spanner, Michael; Lausten, Rune; Sussman, Benjamin J

2013-12-02

Random number sequences are a critical resource in modern information processing systems, with applications in cryptography, numerical simulation, and data sampling. We introduce a quantum random number generator based on the measurement of pulse energy quantum fluctuations in Stokes light generated by spontaneously-initiated stimulated Raman scattering. Bright Stokes pulse energy fluctuations up to five times the mean energy are measured with fast photodiodes and converted to unbiased random binary strings. Since the pulse energy is a continuous variable, multiple bits can be extracted from a single measurement. Our approach can be generalized to a wide range of Raman active materials; here we demonstrate a prototype using the optical phonon line in bulk diamond.

Efficient modeling of Bragg coherent x-ray nanobeam diffraction

DOE PAGES

Hruszkewycz, S. O.; Holt, M. V.; Allain, M.; ...

2015-07-02

X-ray Bragg diffraction experiments that utilize tightly focused coherent beams produce complicated Bragg diffraction patterns that depend on scattering geometry, characteristics of the sample, and properties of the x-ray focusing optic. In this paper, we use a Fourier-transform-based method of modeling the 2D intensity distribution of a Bragg peak and apply it to the case of thin films illuminated with a Fresnel zone plate in three different Bragg scattering geometries. Finally, the calculations agree well with experimental coherent diffraction patterns, demonstrating that nanodiffraction patterns can be modeled at nonsymmetric Bragg conditions with this approach—a capability critical for advancing nanofocused x-raymore » diffraction microscopy.« less

High-speed wavefront modulation in complex media (Conference Presentation)

NASA Astrophysics Data System (ADS)

Turtaev, Sergey; Leite, Ivo T.; Cizmár, TomáÅ.¡

2017-02-01

Using spatial light modulators(SLM) to control light propagation through scattering media is a critical topic for various applications in biomedical imaging, optical micromanipulation, and fibre endoscopy. Having limited switching rate, typically 10-100Hz, current liquid-crystal SLM can no longer meet the growing demands of high-speed imaging. A new way based on binary-amplitude holography implemented on digital micromirror devices(DMD) has been introduced recently, allowing to reach refreshing rates of 30kHz. Here, we summarise the advantages and limitations in speed, efficiency, scattering noise, and pixel cross-talk for each device in ballistic and diffusive regimes, paving the way for high-speed imaging through multimode fibres.

Instrumentation on Multi-Scaled Scattering of Bio-Macromolecular Solutions

PubMed Central

Chu, Benjamin; Fang, Dufei; Mao, Yimin

2015-01-01

The design, construction and initial tests on a combined laser light scattering and synchrotron X-ray scattering instrument can cover studies of length scales from atomic sizes in Angstroms to microns and dynamics from microseconds to seconds are presented. In addition to static light scattering (SLS), dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and wide angle X-ray diffraction (WAXD), the light scattering instrument is being developed to carry out studies in mildly turbid solutions, in the presence of multiple scattering. Three-dimensional photon cross correlation function (3D-PCCF) measurements have been introduced to couple with synchrotron X-ray scattering to study the structure, size and dynamics of macromolecules in solution. PMID:25946340

Short- and long-range magnetic order in LaMnAsO

DOE Office of Scientific and Technical Information (OSTI.GOV)

McGuire, Michael A.; Garlea, Vasile Ovidiu

2016-02-02

The magnetic properties of the layered oxypnictide LaMnAsO have been revisited using neutron scattering and magnetization measurements. The present measurements identify the Néel temperature T N = 360(1) K. Below T N the critical exponent describing the magnetic order parameter is β=0.33–0.35 , consistent with a three-dimensional Heisenberg model. Above this temperature, diffuse magnetic scattering indicative of short-range magnetic order is observed, and this scattering persists up to T SRO = 650(10) K. Morevoer, the magnetic susceptibility shows a weak anomaly at T SRO and no anomaly at T N. Analysis of the diffuse scattering data using a reverse Montemore » Carlo algorithm indicates that above T N nearly two-dimensional, short-range magnetic order is present with a correlation length of 9.3(3) Å within the Mn layers at 400 K. The inelastic scattering data reveal a spin gap of 3.5 meV in the long-range ordered state, and strong, low-energy (quasielastic) magnetic excitations emerging in the short-range ordered state. When we compared it with other related compounds correlates the distortion of the Mn coordination tetrahedra to the sign of the magnetic exchange along the layer-stacking direction, and suggests that short-range order above T N is a common feature in the magnetic behavior of layered Mn-based pnictides and oxypnictides.« less

Crossover in growth laws for phase-separating binary fluids: molecular dynamics simulations.

PubMed

Ahmad, Shaista; Das, Subir K; Puri, Sanjay

2012-03-01

Pattern and dynamics during phase separation in a symmetrical binary (A+B) Lennard-Jones fluid are studied via molecular dynamics simulations after quenching homogeneously mixed critical (50:50) systems to temperatures below the critical one. The morphology of the domains, rich in A or B particles, is observed to be bicontinuous. The early-time growth of the average domain size is found to be consistent with the Lifshitz-Slyozov law for diffusive domain coarsening. After a characteristic time, dependent on the temperature, we find a clear crossover to an extended viscous hydrodynamic regime where the domains grow linearly with time. Pattern formation in the present system is compared with that in solid binary mixtures, as a function of temperature. Important results for the finite-size and temperature effects on the small-wave-vector behavior of the scattering function are also presented.

BEC-BCS crossover and the liquid-gas phase transition in hot and dense nuclear matter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin Meng; Urban, Michael; Schuck, Peter

2010-08-15

The effect of nucleon-nucleon correlations in symmetric nuclear matter at finite temperature is studied beyond BCS theory. Starting from a Hartree-Fock description of nuclear matter with the Gogny effective interaction, we add correlations corresponding to the formation of preformed pairs and scattering states above the superfluid critical temperature within the in-medium T-matrix approach, which is analogous to the Nozieres-Schmitt-Rink theory. We calculate the critical temperature for a BEC superfluid of deuterons, of a BCS superfluid of nucleons, and in the crossover between these limits. The effect of the correlations on thermodynamic properties (equation of state, energy, entropy) and the liquid-gasmore » phase transition is discussed. Our results show that nucleon-nucleon correlations beyond BCS play an important role for the properties of nuclear matter, especially in the low-density region.« less

Relaxation of the resistive superconducting state in boron-doped diamond films

NASA Astrophysics Data System (ADS)

Kardakova, A.; Shishkin, A.; Semenov, A.; Goltsman, G. N.; Ryabchun, S.; Klapwijk, T. M.; Bousquet, J.; Eon, D.; Sacépé, B.; Klein, Th.; Bustarret, E.

2016-02-01

We report a study of the relaxation time of the restoration of the resistive superconducting state in single crystalline boron-doped diamond using amplitude-modulated absorption of (sub-)THz radiation (AMAR). The films grown on an insulating diamond substrate have a low carrier density of about 2.5 ×1021cm-3 and a critical temperature of about 2 K . By changing the modulation frequency we find a high-frequency rolloff which we associate with the characteristic time of energy relaxation between the electron and the phonon systems or the relaxation time for nonequilibrium superconductivity. Our main result is that the electron-phonon scattering time varies clearly as T-2, over the accessible temperature range of 1.7 to 2.2 K. In addition, we find, upon approaching the critical temperature Tc, evidence for an increasing relaxation time on both sides of Tc.

Critical examination of quantum oscillations in SmB6

NASA Astrophysics Data System (ADS)

Riseborough, Peter S.; Fisk, Z.

2017-11-01

We critically review the results of magnetic torque measurements on SmB6 that show quantum oscillations. Similar studies have been given two different interpretations. One interpretation is based on the existence of metallic surface states, while the second interpretation is in terms of a three-dimensional Fermi surface involving neutral fermionic excitations. We suggest that the low-field oscillations that are seen by both groups for B fields as small as 6 T might be due to metallic surface states. The high-field three-dimensional oscillations are only seen by one group for fields B >18 T. The phenomenon of magnetic breakthrough occurs at high fields and involves the formation of Landau orbits that produces a directional-dependent suppression of Bragg scattering. We argue that the measurements performed under higher-field conditions are fully consistent with expectations based on a three-dimensional semiconducting state with magnetic breakthrough.

Ultrafast electronic dynamics in unipolar n-doped indium gallium arsenide/gallium arsenide self-assembled quantum dots

NASA Astrophysics Data System (ADS)

Wu, Zong-Kwei J.

2006-12-01

Photodetectors based on intraband infrared absorption in the quantum dots have demonstrated improved performance over its quantum well counterpart by lower dark current, relative temperature insensitivity, and its ability for normal incidence operation. Various scattering processes, including phonon emission/absorption and carrier-carrier scattering, are critical in understanding device operation on the fundamental level. In previous studies, our group has investigated carrier dynamics in both low- and high-density regime. Ultrafast electron-hole scattering and the predicted phonon bottleneck effect in intrinsic quantum dots have been observed. Further examination on electron dynamics in unipolar structures is presented in this thesis. We used n-doped quantum dot in mid-infrared photodetector device structure to study the electron dynamics in unipolar structure. Differential transmission spectroscopy with mid-infrared intraband pump and optical interband probe was implemented to measure the electron dynamics directly without creating extra electron-hole pair, Electron relaxation after excitation was measured under various density and temperature conditions. Rapid capture into quantum dot within ˜ 10 ps was observed due to Auger-type electron-electron scattering. Intradot relaxation from the quantum dot excited state to the ground state was also observed on the time scale of 100 ps. With highly doped electron density in the structure, the inter-sublevel relaxation is dominated by Auger-type electron-electron scattering and the phonon bottleneck effect is circumvented. Nanosecond-scale recovery in larger-sized quantum dots was observed, not intrinsic to electron dynamics but due to band-bending and built-in voltage drift. An ensemble Monte Carlo simulation was also established to model the dynamics in quantum dots and in goad agreement with the experimental results. We presented a comprehensive picture of electron dynamics in the unipolar quantum dot structure. Although the phonon bottleneck is circumvented with high doped electron density, relaxation processes in unipolar quantum dots have been measured with time scales longer than that of bipolar systems. The results explain the operation principles of the quantum dot infrared photodetector on a microscopic level and provide basic understanding for future applications and designs.

PCS: The First Fluid Physics Payload on ISS

NASA Technical Reports Server (NTRS)

Doherty, M.; Sankaran, S.

2002-01-01

The Physics of Colloids in Space (PCS) experiment was accommodated within International Space Station (ISS) EXpedite the PRocessing of Experiments to Space Station (EXPRESS) Rack 2 and was remotely operated from early June 2001 until February 2002 from NASA Glenn Research Center's Telescience Support Center in Cleveland, Ohio and from a remote site at Harvard University in Cambridge, Massachusetts. PCS is an experiment conceived by Professor David A. Weitz of Harvard University (the Principal Investigator), focusing on the behavior of three different classes of colloid mixtures. The sophisticated light scattering instrumentation comprising PCS is capable of color imaging, and dynamic and static light scattering from 11 to 169 degrees, Bragg scattering over the range from 10 to 60 degrees, and laser light scattering at low angles from 0.3 to 6.0 degrees. The PCS instrumentation performed remarkably well, demonstrating a flexibility that enabled experiments to be performed that had not been envisioned prior to launch. While on-orbit, PCS accomplished 2400 hours of science operations, and was declared a resounding success. Each of the eight sample cells worked well and produced interesting and important results. Crystal nucleation and growth and the resulting structures of two binary colloidal crystal alloys were studied, with the long duration microgravity environment of the ISS facilitating extended studies on the growth and coarsening characteristics of the crystals. In another experiment run, the de-mixing of the colloid-polymer critical-point sample was studied as it phase-separates into two phases, one that resembles a gas and one that resembles a liquid. This process was studied over four decades of length scale, from 1 micron to 1 centimeter, behavior that cannot be observed in this sample on Earth because sedimentation would cause the colloids to fall to the bottom of the cell faster than the de-mixing process could occur. Similarly, the study of gelation and aging of another colloid-polymer sample, the colloid-polymer gel, also provided valuable information on gelation mechanisms, as did investigations on the extremely the low concentration silica and polystyrene fractal gel samples.

Blood flow and vascular reactivity during attacks of classic migraine--limitations of the Xe-133 intraarterial technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Skyhoj Olsen, T.; Lassen, N.A.

1989-01-01

The present study reports cerebral blood flow (CBF) measurements in 11 patients during attacks of classic migraine (CM)--migraine with aura. In 6 and 7 patients, respectively, cerebral vascular reactivity to increased blood pressure and to hypocapnia was also investigated during the CM attacks. The Xenon-133 intraarterial injection technique was used to measure CBF. In this study, based in part on previously published data, methodological limitations, in particular caused by scattered radiation (Compton scatter), are critically analysed. Based on this analysis and the results of the CBF studies it is concluded: During CM attacks CBF appears to decrease focally in themore » posterior part of the brain to a level around 20 ml/100 g/min which is consistent with a mild degree of ischemia. Changes of CBF in focal low flow areas are difficult to evaluate accurately with the Xe-133 technique. In most cases true CBF may change 50% or more in the low flow areas without giving rise to significantly measurable changes of CBF. This analysis suggests that the autoregulation response cannot be evaluated in the low flow areas with the technique used while the observations are compatible with the concept that a vasoconstrictive state, unresponsive to hypocapnia, prevails in the low flow areas during CM attacks. The gradual increase in size of the low flow area seen in several cases may be interpreted in two different ways. A spreading process may actually exist. However, due to Compton scatter, a gradual decrease of CBF in a territory that does not increase in size will also appear as a gradually spreading low flow area when studied with the Xe-133 intracarotid technique.« less

Doses to organs and tissues from concomitant imaging in radiotherapy: a suggested framework for clinical justification.

PubMed

Harrison, R M

2008-12-01

The increasing use of imaging for localization and verification in radiotherapy has raised issues concerning the justifiable doses to critical organs and tissues from concomitant exposures, particularly when extensive image-guided radiotherapy is indicated. Doses at positions remote from the target volume include components from high-energy leakage and scatter, as well as from concomitant imaging. In this paper, simulated prostate, breast and larynx treatments are used to compare doses from both high-energy and concomitant exposures as a function of distance from the target volume. It is suggested that the fraction, R, of the total dose at any point within the patient that is attributable to concomitant exposures may be a useful aid in their justification. R is small within the target volume and at large distances from it. However, there is a critical region immediately adjacent to the planning target volume where the dose from concomitant imaging combines with leakage and scatter to give values of R that approach 0.5 in the examples given here. This is noteworthy because the regions just outside the target volume will receive total doses in the order of 1 Gy, where commensurately high risk factors may not be substantially reduced because of cell kill. Other studies have identified these regions as sites of second cancers. The justification of an imaging regimen might therefore usefully take into account the maximum value of R encountered from the combination of imaging and radiotherapy for particular treatment sites.

Evolution of magnetic and orbital properties in the magnetically diluted A -site spinel Cu1 -xZnxRh2O4

NASA Astrophysics Data System (ADS)

Zakrzewski, A. V.; Gangopadhyay, S.; MacDougall, G. J.; Aczel, A. A.; Calder, S.; Williams, T. J.

2018-06-01

In frustrated spinel antiferromagnets, dilution with nonmagnetic ions can be a powerful strategy for probing unconventional spin states or uncovering interesting phenomena. Here, we present x-ray, neutron scattering, and thermodynamic studies of the effects of magnetic dilution of the tetragonally distorted A -site spinel antiferromagnet, CuRh2O4 , with nonmagnetic Zn2 + ions. Our data confirm the helical spin order recently identified at low temperatures in this material, and further demonstrate a systematic suppression of the associated Néel temperature with increasing site dilution towards a continuous transition with critical doping of xspin˜0.44 . Interestingly, this critical doping is demonstrably distinct from a second structural critical point at xJ T˜0.6 , which is consistent with the suppression of orbital order on the A site through a classical percolative mechanism. This anomalously low value for xspin is confirmed via multiple measurements, and is inconsistent with predictions of classical percolation theory, suggesting that the spin transition in this material is driven by an enhancement of preexisting spin fluctuations with weak dilution.

Inability to empathize: brain lesions that disrupt sharing and understanding another’s emotions

PubMed Central

2014-01-01

Emotional empathy—the ability to recognize, share in, and make inferences about another person’s emotional state—is critical for all social interactions. The neural mechanisms underlying emotional empathy have been widely studied with functional imaging of healthy participants. However, functional imaging studies reveal correlations between areas of activation and performance of a task, so that they can only reveal areas engaged in a task, rather than areas of the brain that are critical for the task. Lesion studies complement functional imaging, to identify areas necessary for a task. Impairments in emotional empathy have been mostly studied in neurological diseases with fairly diffuse injury, such as traumatic brain injury, autism and dementia. The classic ‘focal lesion’ is stroke. There have been scattered studies of patients with impaired empathy after stroke and other focal injury, but these studies have included small numbers of patients. This review will bring together data from these studies, to complement evidence from functional imaging. Here I review how focal lesions affect emotional empathy. I will show how lesion studies contribute to the understanding of the cognitive and neural mechanisms underlying emotional empathy, and how they contribute to the management of patients with impaired emotional empathy. PMID:24293265

Scattering and Diffraction of Electromagnetic Radiation: An Effective Probe to Material Structure

NASA Technical Reports Server (NTRS)

Xu, Yu-Lin

2016-01-01

Scattered electromagnetic waves from material bodies of different forms contain, in an intricate way, precise information on the intrinsic, geometrical and physical properties of the objects. Scattering theories, ever deepening, aim to provide dependable interpretation and prediction to the complicated interaction of electromagnetic radiation with matter. There are well-established multiple-scattering formulations based on classical electromagnetic theories. An example is the Generalized Multi-particle Mie-solution (GMM), which has recently been extended to a special version ? the GMM-PA approach, applicable to finite periodic arrays consisting of a huge number (e.g., >>106) of identical scattering centers [1]. The framework of the GMM-PA is nearly complete. When the size of the constituent unit scatterers becomes considerably small in comparison with incident wavelength, an appropriate array of such small element volumes may well be a satisfactory representation of a material entity having an arbitrary structure. X-ray diffraction is a powerful characterization tool used in a variety of scientific and technical fields, including material science. A diffraction pattern is nothing more than the spatial distribution of scattered intensity, determined by the distribution of scattering matter by way of its Fourier transform [1]. Since all linear dimensions entered into Maxwell's equations are normalized by wavelength, an analogy exists between optical and X-ray diffraction patterns. A large set of optical diffraction patterns experimentally obtained can be found in the literature [e.g., 2,3]. Theoretical results from the GMM-PA have been scrutinized using a large collection of publically accessible, experimentally obtained Fraunhofer diffraction patterns. As far as characteristic structures of the patterns are concerned, theoretical and experimental results are in uniform agreement; no exception has been found so far. Closely connected with the spatial distribution of scattered intensities are cross sections, such as for extinction, scattering, absorption, and radiation pressure, as a critical type of key quantity addressed in most theoretical and experimental studies of radiative scattering. Cross sections predicted from different scattering theories are supposed to be in general agreement. For objects of irregular shape, the GMM-PA solutions can be compared with the highly flexible Discrete Dipole Approximation (DDA) [4,5] when dividing a target to no more than 106 unit cells. Also, there are different ways to calculate the cross sections in the GMM-PA, providing an additional means to examine the accuracy of the numerical solutions and to unveil potential issues concerning the theoretical formulations and numerical aspects. To solve multiple scattering by an assembly of material volumes through classical theories such as the GMM-PA, the radiative properties of the component scatterers, the complex refractive index in particular, must be provided as input parameters. When using a PA to characterize a material body, this involves the use of an adequate theoretical tool, an effective medium theory, to connect Maxwell's phenomenogical theory with the atomistic theory of matter. In the atomic theory, one regards matter as composed of interacting particles (atoms and molecules) embedded in the vacuum [6]. However, the radiative properties of atomic-scaled particles are known to be substantially different from bulk materials. Intensive research efforts in the fields of cluster science and nanoscience attempt to bridge the gap between bulk and atom and to understand the transition from classical to quantum physics. The GMM-PA calculations, which place virtually no restriction on the component-particle size, might help to gain certain insight into the transition.

Laboratory studies of the growth, sublimation, and light- scattering properties of single levitated ice particles

NASA Astrophysics Data System (ADS)

Bacon, Neil Julian

2001-12-01

I describe experiments to investigate the properties of microscopic ice particles. The goal of the work was to measure parameters that are important in cloud processes and radiative transfer, using a novel technique that avoids the use of substrates. The experiments were conducted in two separate electrodynamic balance chambers. Single, charged ice particles were formed from frost particles or from droplets frozen either homogeneously or heteroge neously with a bionucleant. The particles were trapped at temperatures between -38°C and -4°C and grown or sublimated according to the temperature gradient in the cham ber. I describe observations of breakup of sublimating frost particles, measurements of light scattering by hexagonal crystals, and observations of the morphology of ice particles grown from frozen water droplets and frost particles. The breaking strength of frost particles was an order of magnitude less than that of bulk ice. Light scattering features not previously observed were analyzed and related to crystal dimension. Initial results from a computer model failed to reproduce these features. The widths of scattering peaks suggest that surface roughness may play a role in determining the angular distribution of scattered light. Ice particle mass evolution was found to be consistent with diffusion- limited growth. Crystals grown slowly from frozen droplets adopted isometric habits, while faster growth resulted in thin side-planes, although there was not an exact correspondence between growth conditions and particle morphology. From the morphological transition, I infer lower limits for the critical supersaturation for layer nucleation on the prism face of 2.4% at -15°C, 4.4% at -20°C, and 3.1% at -25°C. Analytic expressions for the size dependence of facet stability are developed, indicating a strong dependence of stability on both crystal size and surface kinetics, and compared with data. I discuss the role of complex particle morphologies in radiative transfer and highlight the need for further measurements.

Volume-energy parameters for heat transfer to supercritical fluids

NASA Technical Reports Server (NTRS)

Kumakawa, A.; Niino, M.; Hendricks, R. C.; Giarratano, P. J.; Arp, V. D.

1986-01-01

Reduced Nusselt numbers of supercritical fluids from different sources were grouped by several volume-energy parameters. A modified bulk expansion parameter was introduced based on a comparative analysis of data scatter. Heat transfer experiments on liquefied methane were conducted under near-critical conditions in order to confirm the usefulness of the parameters. It was experimentally revealed that heat transfer characteristics of near-critical methane are similar to those of hydrogen. It was shown that the modified bulk expansion parameter and the Gibbs-energy parameter grouped the heat transfer data of hydrogen, oxygen and methane including the present data on near-critical methane. It was also indicated that the effects of surface roughness on heat transfer were very important in grouping the data of high Reynolds numbers.

Experimental physics characteristics of a heavy-metal-reflected fast-spectrum critical assembly

NASA Technical Reports Server (NTRS)

Heneveld, W. H.; Paschall, R. K.; Springer, T. H.; Swanson, V. A.; Thiele, A. W.; Tuttle, R. J.

1971-01-01

A zero-power critical assembly was designed, constructed, and operated for the purpose of conducting a series of benchmark experiments dealing with the physics characteristics of a UN-fueled, Li-7 cooled, Mo-reflected, drum-controlled compact fast reactor for use with a space-power electric conversion system. The experimental program consisted basically of measuring the differential neutron spectra and the changes in critical mass that accompanied the stepwise addition of (Li-7)3N, Hf, Ta, and W to a basic core fueled with U metal in a pin-type Ta honeycomb structure. In addition, experimental results were obtained on power distributions, control characteristics, neutron lifetime, and reactivity worths of numerous absorber, structural, and scattering materials.

On the failure load and mechanism of polycrystalline graphene by nanoindentation

PubMed Central

Sha, Z. D.; Wan, Q.; Pei, Q. X.; Quek, S. S.; Liu, Z. S.; Zhang, Y. W.; Shenoy, V. B.

2014-01-01

Nanoindentation has been recently used to measure the mechanical properties of polycrystalline graphene. However, the measured failure loads are found to be scattered widely and vary from lab to lab. We perform molecular dynamics simulations of nanoindentation on polycrystalline graphene at different sites including grain center, grain boundary (GB), GB triple junction, and holes. Depending on the relative position between the indenter tip and defects, significant scattering in failure load is observed. This scattering is found to arise from a combination of the non-uniform stress state, varied and weakened strengths of different defects, and the relative location between the indenter tip and the defects in polycrystalline graphene. Consequently, the failure behavior of polycrystalline graphene by nanoindentation is critically dependent on the indentation site, and is thus distinct from uniaxial tensile loading. Our work highlights the importance of the interaction between the indentation tip and defects, and the need to explicitly consider the defect characteristics at and near the indentation site in polycrystalline graphene during nanoindentation. PMID:25500732

ENDF/B-VIII.0: The 8th Major Release of the Nuclear Reaction Data Library with CIELO-project Cross Sections, New Standards and Thermal Scattering Data

NASA Astrophysics Data System (ADS)

Brown, D. A.; Chadwick, M. B.; Capote, R.; Kahler, A. C.; Trkov, A.; Herman, M. W.; Sonzogni, A. A.; Danon, Y.; Carlson, A. D.; Dunn, M.; Smith, D. L.; Hale, G. M.; Arbanas, G.; Arcilla, R.; Bates, C. R.; Beck, B.; Becker, B.; Brown, F.; Casperson, R. J.; Conlin, J.; Cullen, D. E.; Descalle, M.-A.; Firestone, R.; Gaines, T.; Guber, K. H.; Hawari, A. I.; Holmes, J.; Johnson, T. D.; Kawano, T.; Kiedrowski, B. C.; Koning, A. J.; Kopecky, S.; Leal, L.; Lestone, J. P.; Lubitz, C.; Márquez Damián, J. I.; Mattoon, C. M.; McCutchan, E. A.; Mughabghab, S.; Navratil, P.; Neudecker, D.; Nobre, G. P. A.; Noguere, G.; Paris, M.; Pigni, M. T.; Plompen, A. J.; Pritychenko, B.; Pronyaev, V. G.; Roubtsov, D.; Rochman, D.; Romano, P.; Schillebeeckx, P.; Simakov, S.; Sin, M.; Sirakov, I.; Sleaford, B.; Sobes, V.; Soukhovitskii, E. S.; Stetcu, I.; Talou, P.; Thompson, I.; van der Marck, S.; Welser-Sherrill, L.; Wiarda, D.; White, M.; Wormald, J. L.; Wright, R. Q.; Zerkle, M.; Žerovnik, G.; Zhu, Y.

2018-02-01

We describe the new ENDF/B-VIII.0 evaluated nuclear reaction data library. ENDF/B-VIII.0 fully incorporates the new IAEA standards, includes improved thermal neutron scattering data and uses new evaluated data from the CIELO project for neutron reactions on 1H, 16O, 56Fe, 235U, 238U and 239Pu described in companion papers in the present issue of Nuclear Data Sheets. The evaluations benefit from recent experimental data obtained in the U.S. and Europe, and improvements in theory and simulation. Notable advances include updated evaluated data for light nuclei, structural materials, actinides, fission energy release, prompt fission neutron and γ-ray spectra, thermal neutron scattering data, and charged-particle reactions. Integral validation testing is shown for a wide range of criticality, reaction rate, and neutron transmission benchmarks. In general, integral validation performance of the library is improved relative to the previous ENDF/B-VII.1 library.

Orbitally-driven giant phonon anharmonicity in SnSe

DOE PAGES

Li, Chen W.; Hong, Jiawang; May, Andrew F.; ...

2015-10-19

We understand that elementary excitations and their couplings in condensed matter systems is critical to develop better energy-conversion devices. In thermoelectric materials, the heat-to-electricity conversion efficiency is directly improved by suppressing the propagation of phonon quasiparticles responsible for macroscopic thermal transport. The material with the current record for thermoelectric conversion efficiency, SnSe, achieves an ultra-low thermal conductivity, but the mechanism enabling this strong phonon scattering remains largely unknown. Using inelastic neutron scattering measurements and first-principles simulations, we mapped the four-dimensional phonon dispersion surfaces of SnSe, and revealed the origin of ionic-potential anharmonicity responsible for the unique properties of SnSe. Wemore » show that the giant phonon scattering arises from an unstable electronic structure, with orbital interactions leading to a ferroelectric-like lattice instability. Our results provide a microscopic picture connecting electronic structure and phonon anharmonicity in SnSe, and offers precious insights on how electron-phonon and phononphonon interactions may lead to the realization of ultra-low thermal conductivity.« less

Orbitally driven giant phonon anharmonicity in SnSe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, C. W.; Hong, J.; May, A. F.

Understanding elementary excitations and their couplings in condensed matter systems is critical for developing better energy-conversion devices. In thermoelectric materials, the heat-to-electricity conversion efficiency is directly improved by suppressing the propagation of phonon quasiparticles responsible for macroscopic thermal transport. The current record material for thermoelectric conversion efficiency, SnSe, has an ultralow thermal conductivity, but the mechanism behind the strong phonon scattering remains largely unknown. From inelastic neutron scattering measurements and first-principles simulations, we mapped the four-dimensional phonon dispersion surfaces of SnSe, and found the origin of the ionic-potential anharmonicity responsible for the unique properties of SnSe. We show that themore » giant phonon scattering arises from an unstable electronic structure, with orbital interactions leading to a ferroelectric-like lattice instability. The present results provide a microscopic picture connecting electronic structure and phonon anharmonicity in SnSe, and offers new insights on how electron–phonon and phonon–phonon interactions may lead to the realization of ultralow thermal conductivity.« less

Hydraulic Properties of Closely Spaced Dipping Open Fractures Intersecting a Fluid-Filled Borehole Derived From Tube Wave Generation and Scattering

NASA Astrophysics Data System (ADS)

Minato, Shohei; Ghose, Ranajit; Tsuji, Takeshi; Ikeda, Michiharu; Onishi, Kozo

2017-10-01

Fluid-filled fractures and fissures often determine the pathways and volume of fluid movement. They are critically important in crustal seismology and in the exploration of geothermal and hydrocarbon reservoirs. We introduce a model for tube wave scattering and generation at dipping, parallel-wall fractures intersecting a fluid-filled borehole. A new equation reveals the interaction of tube wavefield with multiple, closely spaced fractures, showing that the fracture dip significantly affects the tube waves. Numerical modeling demonstrates the possibility of imaging these fractures using a focusing analysis. The focused traces correspond well with the known fracture density, aperture, and dip angles. Testing the method on a VSP data set obtained at a fault-damaged zone in the Median Tectonic Line, Japan, presents evidences of tube waves being generated and scattered at open fractures and thin cataclasite layers. This finding leads to a new possibility for imaging, characterizing, and monitoring in situ hydraulic properties of dipping fractures using the tube wavefield.

TERRESTRIAL PLANET FORMATION AROUND THE CIRCUMBINARY HABITABLE ZONE: INWARD MIGRATION IN THE PLANETESIMAL SWARM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gong Yanxiang; Zhou Jilin; Xie Jiwei, E-mail: yxgong@nju.edu.cn, E-mail: zhoujl@nju.edu.cn

2013-01-20

According to the core accretion theory, circumbinary embryos can form only beyond a critical semimajor axis (CSMA). However, due to the relatively high density of solid materials in the inner disk, a significant amount of small planetesimals must exist in the inner zone when embryos form outside this CSMA. Thus, embryo migration induced by the planetesimal swarm is possible after gas disk depletion. Through numerical simulations, we found that (1) the scattering-driven inward migration of embryos is robust and planets can form in the habitable zone if we adopt a mass distribution of an MMSN-like disk; (2) the total massmore » of the planetesimals in the inner region and continuous embryo-embryo scattering are two key factors that cause significant embryo migrations; and (3) the scattering-driven migration of embryos is a natural water-delivery mechanism. We propose that planet detections should focus on the close binary with its habitable zone near CSMA.« less

Observation of a continuous modulation in a shape-memory alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lashley, Jason C; Smith, James L; Mihaila, Bogdan

2008-01-01

Elastic neutron-scattering, inelastic x-ray scattering, specific-heat, and pressure-dependent electrical transport measurements have been made on single crystals of AuZn and Au{sub 0.52}Zn{sub 0.48}. Elastic neutron scattering detects new commensurate Bragg peaks (modulation) appearing at Q = (1.33,0.67,0) at temperatures corresponding to each sample's transition temperature (T{sub M} = 64 and 45 K, respectively). Although the new Bragg peaks appear in a discontinuous manner in the Au{sub 0.52}Zn{sub 0.48} sample, they appear in a continuous manner in AuZn. Surprising us, the temperature dependence of the AuZn Bragg peak intensity and the specific-heat jump near T{sub M} are in favorable accord withmore » a continuous transition. A fit to the pressure dependence of T{sub M} suggests the presence of a critical end point in the AuZn phase diagram located at T*{sub M} = 2.7 K and p* = 3.1 GPa.« less

Control of Porosity in Ladder Polymers by Solvent-induced Aggregation

NASA Astrophysics Data System (ADS)

Brady, Michael; Gamo, Eri; Wang, Cheng; Xia, Yan

Porous polymers hold promise as materials for gas absorption, membranes, and organic electronics. In all of these applications, attaining in-plane ordering of backbones and thus porous free volume impacts the ability to adsorb gas, selectively filter molecules, and conduct charges. In this work, hard and soft x-ray scattering and soft x-ray spectroscopy are of focus to study the pore structure, induced by the solution-driven aggregation of ladder polymer thin films made of LP-1 and LP-2. Using GISAXS and AFM it is shown that thermal annealing drives the growth of crystallites in thin films. Due to the completely sp2nature of the ladder polymer backbones, it is expected that backbones are extremely stiff and thus preventing them from packing once left in a metastable state following casting. Therefore, the combination of GIWAXS and GISAXS will be shown to be critical in correctly understanding how pores develop in this 700 m2/g sorbent (N2). Finally, application in CO2/N2 separation membranes towards carbon sequestration will be presented that show gas selectivity is achieved through heteroatom incorporation and polymer blending. In this talk, focus will be placed on state-of-the-art x-ray scattering and spectroscopy, highlighting the importance of chemically sensitive structural information enabled by the combination of spectroscopy and scattering at play with the use of resonant soft x-rays.

Comparison of Interferometric Time-Series Analysis Techniques with Implications for Future Mission Design

NASA Astrophysics Data System (ADS)

Werner, C. L.; Wegmuller, U.; Strozzi, T.; Wiesmann, A.

2006-12-01

Principle contributors to the noise in differential SAR interferograms are temporal phase stability of the surface, geometry relating to baseline and surface slope, and propagation path delay variations due to tropospheric water vapor and the ionosphere. Time series analysis of multiple interferograms generated from a stack of SAR SLC images seeks to determine the deformation history of the surface while reducing errors. Only those scatterers within a resolution element that are stable and coherent for each interferometric pair contribute to the desired deformation signal. Interferograms with baselines exceeding 1/3 the critical baseline have substantial geometrical decorrelation for distributed targets. Short baseline pairs with multiple reference scenes can be combined using least-squares estimation to obtain a global deformation solution. Alternately point-like persistent scatterers can be identified in scenes that do not exhibit geometrical decorrelation associated with large baselines. In this approach interferograms are formed from a stack of SAR complex images using a single reference scene. Stable distributed scatter pixels are excluded however due to the presence of large baselines. We apply both point- based and short-baseline methodologies and compare results for a stack of fine-beam Radarsat data acquired in 2002-2004 over a rapidly subsiding oil field near Lost Hills, CA. We also investigate the density of point-like scatters with respect to image resolution. The primary difficulty encountered when applying time series methods is phase unwrapping errors due to spatial and temporal gaps. Phase unwrapping requires sufficient spatial and temporal sampling. Increasing the SAR range bandwidth increases the range resolution as well as increasing the critical interferometric baseline that defines the required satellite orbital tube diameter. Sufficient spatial sampling also permits unwrapping because of the reduced phase/pixel gradient. Short time intervals further reduce the differential phase due to deformation when the deformation is continuous. Lower frequency systems (L- vs. C-Band) substantially improve the ability to unwrap the phase correctly by directly reducing both interferometric phase amplitude and temporal decorrelation.

Feasibility study of full-reactor gas core demonstration test

NASA Technical Reports Server (NTRS)

Kunze, J. F.; Lofthouse, J. H.; Shaffer, C. J.; Macbeth, P. J.

1973-01-01

Separate studies of nuclear criticality, flow patterns, and thermodynamics for the gas core reactor concept have all given positive indications of its feasibility. However, before serious design for a full scale gas core application can be made, feasibility must be shown for operation with full interaction of the nuclear, thermal, and hydraulic effects. A minimum sized, and hence minimum expense, test arrangement is considered for a full gas core configuration. It is shown that the hydrogen coolant scattering effects dominate the nuclear considerations at elevated temperatures. A cavity diameter of somewhat larger than 4 ft (122 cm) will be needed if temperatures high enough to vaporize uranium are to be achieved.

A comparative study on methods of improving SCR for ship detection in SAR image

NASA Astrophysics Data System (ADS)

Lang, Haitao; Shi, Hongji; Tao, Yunhong; Ma, Li

2017-10-01

Knowledge about ship positions plays a critical role in a wide range of maritime applications. To improve the performance of ship detector in SAR image, an effective strategy is improving the signal-to-clutter ratio (SCR) before conducting detection. In this paper, we present a comparative study on methods of improving SCR, including power-law scaling (PLS), max-mean and max-median filter (MMF1 and MMF2), method of wavelet transform (TWT), traditional SPAN detector, reflection symmetric metric (RSM), scattering mechanism metric (SMM). The ability of SCR improvement to SAR image and ship detection performance associated with cell- averaging CFAR (CA-CFAR) of different methods are evaluated on two real SAR data.

Future utilization of space: Silverton Conference on material science and phase transformations in zero-gravity, summary of proceeding

NASA Technical Reports Server (NTRS)

Eisner, M. (Editor)

1975-01-01

The importance of zero gravity environment in the development and production of new and improved materials is considered along with the gravitational effects on phase changes or critical behavior in a variety of materials. Specific experiments discussed include: fine scale phase separation in zero gravity; glass formation in zero gravity; effects of gravitational perturbations on determination of critical exponents; and light scattering from long wave fluctuations in liquids in zero gravity. It is concluded that the space shuttle/spacelab system is applicable to various fields of interest.

Size, Shape and Impurity Effects on Superconducting critical temperature.

NASA Astrophysics Data System (ADS)

Umeda, Masaki; Kato, Masaru; Sato, Osamu

Bulk superconductors have their own critical temperatures Tc. However, for a nano-structured superconductor, Tc depends on size and shape of the superconductor. Nishizaki showed that the high pressure torsion on bulks of Nb makes Tc higher, because the torsion makes many nano-sized fine grains in the bulks. However the high pressure torsion on bulks of V makes Tc lower, and Nishizaki discussed that the decrease of Tc is caused by impurities in the bulks of V. We studied size, shape, and impurity effects on Tc, by solving the Gor'kov equations, using the finite element method. We found that smaller and narrower superconductors show higher Tc. We found how size and shape affects Tc by studying spacial order parameter distributions and quasi-particle eigen-energies. Also we studied the impurity effects on Tc, and found that Tc decreases with increase of scattering rate by impurities. This work was supported in part of KAKENHI Grant Number JP26400367 and JP16K05460, and program for leading graduate schools of ministry of education, culture, sports, science and technology-Japan.

Dark Matter Ignition of Type Ia Supernovae.

PubMed

Bramante, Joseph

2015-10-02

Recent studies of low redshift type Ia supernovae (SN Ia) indicate that half explode from less than Chandrasekhar mass white dwarfs, implying ignition must proceed from something besides the canonical criticality of Chandrasekhar mass SN Ia progenitors. We show that 1-100 PeV mass asymmetric dark matter, with imminently detectable nucleon scattering interactions, can accumulate to the point of self-gravitation in a white dwarf and collapse, shedding gravitational potential energy by scattering off nuclei, thereby heating the white dwarf and igniting the flame front that precedes SN Ia. We combine data on SN Ia masses with data on the ages of SN Ia-adjacent stars. This combination reveals a 2.8σ inverse correlation between SN Ia masses and ignition ages, which could result from increased capture of dark matter in 1.4 vs 1.1 solar mass white dwarfs. Future studies of SN Ia in galactic centers will provide additional tests of dark-matter-induced type Ia ignition. Remarkably, both bosonic and fermionic SN Ia-igniting dark matter also resolve the missing pulsar problem by forming black holes in ≳10  Myr old pulsars at the center of the Milky Way.

c-Met and its ligand hepatocyte growth factor/scatter factor regulate mature B cell survival in a pathway induced by CD74.

PubMed

Gordin, Maya; Tesio, Melania; Cohen, Sivan; Gore, Yael; Lantner, Frida; Leng, Lin; Bucala, Richard; Shachar, Idit

2010-08-15

The signals regulating the survival of mature splenic B cells have become a major focus in recent studies of B cell immunology. Durable B cell persistence in the periphery is dependent on survival signals that are transduced by cell surface receptors. In this study, we describe a novel biological mechanism involved in mature B cell homeostasis, the hepatocyte growth factor/scatter factor (HGF)/c-Met pathway. We demonstrate that c-Met activation by HGF leads to a survival cascade, whereas its blockade results in induction of mature B cell death. Our results emphasize a unique and critical function for c-Met signaling in the previously described macrophage migration inhibitory factor/CD74-induced survival pathway. Macrophage migration inhibitory factor recruits c-Met to the CD74/CD44 complex and thereby enables the induction of a signaling cascade within the cell. This signal results in HGF secretion, which stimulates the survival of the mature B cell population in an autocrine manner. Thus, the CD74-HGF/c-Met axis defines a novel physiologic survival pathway in mature B cells, resulting in the control of the humoral immune response.

Transferable Calibration Standard Developed for Quantitative Raman Scattering Diagnostics in High-Pressure Flames

NASA Technical Reports Server (NTRS)

Nguyen, Quang-Viet; Kojima, Jun

2005-01-01

Researchers from NASA Glenn Research Center s Combustion Branch and the Ohio Aerospace Institute (OAI) have developed a transferable calibration standard for an optical technique called spontaneous Raman scattering (SRS) in high-pressure flames. SRS is perhaps the only technique that provides spatially and temporally resolved, simultaneous multiscalar measurements in turbulent flames. Such measurements are critical for the validation of numerical models of combustion. This study has been a combined experimental and theoretical effort to develop a spectral calibration database for multiscalar diagnostics using SRS in high-pressure flames. However, in the past such measurements have used a one-of-a-kind experimental setup and a setup-dependent calibration procedure to empirically account for spectral interferences, or crosstalk, among the major species of interest. Such calibration procedures, being non-transferable, are prohibitively expensive to duplicate. A goal of this effort is to provide an SRS calibration database using transferable standards that can be implemented widely by other researchers for both atmospheric-pressure and high-pressure (less than 30 atm) SRS studies. A secondary goal of this effort is to provide quantitative multiscalar diagnostics in high pressure environments to validate computational combustion codes.

First principles study of Al and C-doped MgB2: evolution of two gaps and critical temperature

NASA Astrophysics Data System (ADS)

de La Peña-Seaman, Omar; de Coss, Romeo; Heid, Rolf; Bohnen, Klaus-Peter

2008-03-01

We have studied the electron-phonon and superconducting properties of the Mg1-xAlxB2 and MgB2(1-x)C2x alloys within the framework of density functional perturbation theory, using a mixed-basis pseudopotential method and the virtual crystal approximation (VCA) for modeling the alloys. For both systems, the Eliashberg spectral function (2̂F(φ)) and the electron-phonon coupling parameter (λ) have been calculated in the two band model (σ,π) for several concentrations until x(Al)=0.55 and x(C)=0.175. Using the calculated 2̂ijF(φ) and a diagonal expression for the Coulomb pseudopotential matrix, &*circ;, we solved numerically the Eliashberg gap equations in the two band model without interband scattering. We reproduce the experimental decreasing behavior of δσ(x), δπ(x), and Tc(x) for both alloy systems. The role of the interband scattering in the observed behavior of the superconducting gaps and Tc in the Al- and C-MgB2 alloys is discussed. This research was supported by Consejo Nacional de Ciencia y Tecnolog'ia (Conacyt) under Grant No. 43830-F.

Critical state of sand matrix soils.

PubMed

Marto, Aminaton; Tan, Choy Soon; Makhtar, Ahmad Mahir; Kung Leong, Tiong

2014-01-01

The Critical State Soil Mechanic (CSSM) is a globally recognised framework while the critical states for sand and clay are both well established. Nevertheless, the development of the critical state of sand matrix soils is lacking. This paper discusses the development of critical state lines and corresponding critical state parameters for the investigated material, sand matrix soils using sand-kaolin mixtures. The output of this paper can be used as an interpretation framework for the research on liquefaction susceptibility of sand matrix soils in the future. The strain controlled triaxial test apparatus was used to provide the monotonic loading onto the reconstituted soil specimens. All tested soils were subjected to isotropic consolidation and sheared under undrained condition until critical state was ascertain. Based on the results of 32 test specimens, the critical state lines for eight different sand matrix soils were developed together with the corresponding values of critical state parameters, M, λ, and Γ. The range of the value of M, λ, and Γ is 0.803-0.998, 0.144-0.248, and 1.727-2.279, respectively. These values are comparable to the critical state parameters of river sand and kaolin clay. However, the relationship between fines percentages and these critical state parameters is too scattered to be correlated.

Critical State of Sand Matrix Soils

PubMed Central

Marto, Aminaton; Tan, Choy Soon; Makhtar, Ahmad Mahir; Kung Leong, Tiong

2014-01-01

The Critical State Soil Mechanic (CSSM) is a globally recognised framework while the critical states for sand and clay are both well established. Nevertheless, the development of the critical state of sand matrix soils is lacking. This paper discusses the development of critical state lines and corresponding critical state parameters for the investigated material, sand matrix soils using sand-kaolin mixtures. The output of this paper can be used as an interpretation framework for the research on liquefaction susceptibility of sand matrix soils in the future. The strain controlled triaxial test apparatus was used to provide the monotonic loading onto the reconstituted soil specimens. All tested soils were subjected to isotropic consolidation and sheared under undrained condition until critical state was ascertain. Based on the results of 32 test specimens, the critical state lines for eight different sand matrix soils were developed together with the corresponding values of critical state parameters, M, λ, and Γ. The range of the value of M, λ, and Γ is 0.803–0.998, 0.144–0.248, and 1.727–2.279, respectively. These values are comparable to the critical state parameters of river sand and kaolin clay. However, the relationship between fines percentages and these critical state parameters is too scattered to be correlated. PMID:24757417

Nano- to Formation-Scale Estimates of Mineral-Specific Reactive Surface Area

NASA Astrophysics Data System (ADS)

Cole, D. R.; Swift, A.; Sheets, J.; Anovitz, L. M.

2017-12-01

Predictions of changes in fluid composition, coupled with the evolution of the solid matrix, include the generation and testing of reactive transport models. However, translating a heterogeneous natural system into physical and chemical model parameters, including the critical but poorly-constrained metric of fluid-accessible surface area, continues to challenge Earth scientists. Studies of carbon storage capacity, permeability, rock strain due to mineral dissolution and precipitation, or the prediction of rock evolution through diagenesis and weathering each consider macroscale outcomes of processes that often are critically impacted by rock surface geometry at the nanoscale. The approach taken here is to consider the whole vertical extent of a saline reservoir and then to address two questions. First, what is the accessible surface area for each major mineral, and for all adjacent pore sizes from <2 nm on up, within each major lithofacies in that formation? Second, with the formation thus divided into units of analysis, parameterized, and placed into geologic context, what constraints can be placed on reactive surface area as a function of mineral composition? A complex sandstone covering a substantial fraction of the quartz-K-feldspar-illite ternary is selected and mineral-specific surface area quantified using neutron scattering, nitrogen and mercury porosimetry, multi-signal high-resolution mineral mapping, and other techniques. For neutron scattering, scale-specific pore geometries enable more accurate translation of volume into surface area. By applying this workflow to all end-member lithologies of this reservoir formation, equations and maps of surface area as a function of position on a quartz-feldspar-clay ternary plot are developed for each major mineral. Results from this work therefore advance our ability to parameterize models not just for the particular formation studied, but for similar geologic units as well.

Frequency-independent approach to calculate physical optics radiations with the quadratic concave phase variations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Yu Mao, E-mail: yumaowu@fudan.edu.cn; Teng, Si Jia, E-mail: sjteng12@fudan.edu.cn

In this work, we develop the numerical steepest descent path (NSDP) method to calculate the physical optics (PO) radiations with the quadratic concave phase variations. With the surface integral equation method, the physical optics (PO) scattered fields are formulated and further reduced to the surface integrals. The high frequency physical critical points contributions, including the stationary phase points, the boundary resonance points and the vertex points are comprehensively studied via the proposed NSDP method. The key contributions of this work are twofold. One is that together with the PO integrals taking the quadratic parabolic and hyperbolic phase terms, this workmore » makes the NSDP theory be complete for treating the PO integrals with quadratic phase variations. Another is that, in order to illustrate the transition effect of the high frequency physical critical points, in this work, we consider and further extend the NSDP method to calculate the PO integrals with the coalescence of the high frequency critical points. Numerical results for the highly oscillatory PO integral with the coalescence of the critical points are given to verify the efficiency of the proposed NSDP method. The NSDP method could achieve the frequency independent computational workload and error controllable accuracy in all the numerical experiments, especially for the case of the coalescence of the high frequency critical points.« less

Improved Convergence Rate of Multi-Group Scattering Moment Tallies for Monte Carlo Neutron Transport Codes

NASA Astrophysics Data System (ADS)

Nelson, Adam

Multi-group scattering moment matrices are critical to the solution of the multi-group form of the neutron transport equation, as they are responsible for describing the change in direction and energy of neutrons. These matrices, however, are difficult to correctly calculate from the measured nuclear data with both deterministic and stochastic methods. Calculating these parameters when using deterministic methods requires a set of assumptions which do not hold true in all conditions. These quantities can be calculated accurately with stochastic methods, however doing so is computationally expensive due to the poor efficiency of tallying scattering moment matrices. This work presents an improved method of obtaining multi-group scattering moment matrices from a Monte Carlo neutron transport code. This improved method of tallying the scattering moment matrices is based on recognizing that all of the outgoing particle information is known a priori and can be taken advantage of to increase the tallying efficiency (therefore reducing the uncertainty) of the stochastically integrated tallies. In this scheme, the complete outgoing probability distribution is tallied, supplying every one of the scattering moment matrices elements with its share of data. In addition to reducing the uncertainty, this method allows for the use of a track-length estimation process potentially offering even further improvement to the tallying efficiency. Unfortunately, to produce the needed distributions, the probability functions themselves must undergo an integration over the outgoing energy and scattering angle dimensions. This integration is too costly to perform during the Monte Carlo simulation itself and therefore must be performed in advance by way of a pre-processing code. The new method increases the information obtained from tally events and therefore has a significantly higher efficiency than the currently used techniques. The improved method has been implemented in a code system containing a new pre-processor code, NDPP, and a Monte Carlo neutron transport code, OpenMC. This method is then tested in a pin cell problem and a larger problem designed to accentuate the importance of scattering moment matrices. These tests show that accuracy was retained while the figure-of-merit for generating scattering moment matrices and fission energy spectra was significantly improved.

A Study of the Efficiency of Spatial Indexing Methods Applied to Large Astronomical Databases

NASA Astrophysics Data System (ADS)

Donaldson, Tom; Berriman, G. Bruce; Good, John; Shiao, Bernie

2018-01-01

Spatial indexing of astronomical databases generally uses quadrature methods, which partition the sky into cells used to create an index (usually a B-tree) written as database column. We report the results of a study to compare the performance of two common indexing methods, HTM and HEALPix, on Solaris and Windows database servers installed with a PostgreSQL database, and a Windows Server installed with MS SQL Server. The indexing was applied to the 2MASS All-Sky Catalog and to the Hubble Source catalog. On each server, the study compared indexing performance by submitting 1 million queries at each index level with random sky positions and random cone search radius, which was computed on a logarithmic scale between 1 arcsec and 1 degree, and measuring the time to complete the query and write the output. These simulated queries, intended to model realistic use patterns, were run in a uniform way on many combinations of indexing method and indexing level. The query times in all simulations are strongly I/O-bound and are linear with number of records returned for large numbers of sources. There are, however, considerable differences between simulations, which reveal that hardware I/O throughput is a more important factor in managing the performance of a DBMS than the choice of indexing scheme. The choice of index itself is relatively unimportant: for comparable index levels, the performance is consistent within the scatter of the timings. At small index levels (large cells; e.g. level 4; cell size 3.7 deg), there is large scatter in the timings because of wide variations in the number of sources found in the cells. At larger index levels, performance improves and scatter decreases, but the improvement at level 8 (14 min) and higher is masked to some extent in the timing scatter caused by the range of query sizes. At very high levels (20; 0.0004 arsec), the granularity of the cells becomes so high that a large number of extraneous empty cells begin to degrade performance. Thus, for the use patterns studied here the database performance is not critically dependent on the exact choices of index or level.

Normal and Anomalous Diffusion: An Analytical Study Based on Quantum Collision Dynamics and Boltzmann Transport Theory.

PubMed

Mahakrishnan, Sathiya; Chakraborty, Subrata; Vijay, Amrendra

2016-09-15

Diffusion, an emergent nonequilibrium transport phenomenon, is a nontrivial manifestation of the correlation between the microscopic dynamics of individual molecules and their statistical behavior observed in experiments. We present a thorough investigation of this viewpoint using the mathematical tools of quantum scattering, within the framework of Boltzmann transport theory. In particular, we ask: (a) How and when does a normal diffusive transport become anomalous? (b) What physical attribute of the system is conceptually useful to faithfully rationalize large variations in the coefficient of normal diffusion, observed particularly within the dynamical environment of biological cells? To characterize the diffusive transport, we introduce, analogous to continuous phase transitions, the curvature of the mean square displacement as an order parameter and use the notion of quantum scattering length, which measures the effective interactions between the diffusing molecules and the surrounding, to define a tuning variable, η. We show that the curvature signature conveniently differentiates the normal diffusion regime from the superdiffusion and subdiffusion regimes and the critical point, η = ηc, unambiguously determines the coefficient of normal diffusion. To solve the Boltzmann equation analytically, we use a quantum mechanical expression for the scattering amplitude in the Boltzmann collision term and obtain a general expression for the effective linear collision operator, useful for a variety of transport studies. We also demonstrate that the scattering length is a useful dynamical characteristic to rationalize experimental observations on diffusive transport in complex systems. We assess the numerical accuracy of the present work with representative experimental results on diffusion processes in biological systems. Furthermore, we advance the idea of temperature-dependent effective voltage (of the order of 1 μV or less in a biological environment, for example) as a dynamical cause of the perpetual molecular movement, which eventually manifests as an ordered motion, called the diffusion.

Memory and the hippocampus in food-storing birds: a comparative approach.

PubMed

Clayton, N S

1998-01-01

Comparative studies provide a unique source of evidence for the role of the hippocampus in learning and memory. Within birds and mammals, the hippocampal volume of scatter-hoarding species that cache food in many different locations is enlarged, relative to the remainder of the telencephalon, when compared with than that of species which cache food in one larder, or do not cache at all. Do food-storing species show enhanced memory function in association with the volumetric enlargement of the hippocampus? Comparative studies within the parids (titmice and chickadees) and corvids (jays, nutcrackers and magpies), two families of birds which show natural variation in food-storing behavior, suggest that there may be two kinds of memory specialization associated with scatter-hoarding. First, in terms of spatial memory, several scatter-hoarding species have a more accurate and enduring spatial memory, and a preference to rely more heavily upon spatial cues, than that of closely related species which store less food, or none at all. Second, some scatter-hoarding parids and corvids are also more resistant to memory interference. While the most critical component about a cache site may be its spatial location, there is mounting evidence that food-storing birds remember additional information about the contents and status of cache sites. What is the underlying neural mechanism by which the hippocampus learns and remembers cache sites? The current mammalian dogma is that the neural mechanisms of learning and memory are achieved primarily by variations in synaptic number and efficacy. Recent work on the concomitant development of food-storing, memory and the avian hippocampus illustrates that the avian hippocampus may swell or shrivel by as much as 30% in response to presence or absence of food-storing experience. Memory for food caches triggers a dramatic increase in the total number of number of neurons within the avian hippocampus by altering the rate at which these cells are born and die.

Investigation of scattering coefficients and anisotropy factors of human cancerous and normal prostate tissues using Mie theory

NASA Astrophysics Data System (ADS)

Pu, Yang; Chen, Jun; Wang, Wubao

2014-02-01

The scattering coefficient, μs, the anisotropy factor, g, the scattering phase function, p(θ), and the angular dependence of scattering intensity distributions of human cancerous and normal prostate tissues were systematically investigated as a function of wavelength, scattering angle and scattering particle size using Mie theory and experimental parameters. The Matlab-based codes using Mie theory for both spherical and cylindrical models were developed and applied for studying the light propagation and the key scattering properties of the prostate tissues. The optical and structural parameters of tissue such as the index of refraction of cytoplasm, size of nuclei, and the diameter of the nucleoli for cancerous and normal human prostate tissues obtained from the previous biological, biomedical and bio-optic studies were used for Mie theory simulation and calculation. The wavelength dependence of scattering coefficient and anisotropy factor were investigated in the wide spectral range from 300 nm to 1200 nm. The scattering particle size dependence of μs, g, and scattering angular distributions were studied for cancerous and normal prostate tissues. The results show that cancerous prostate tissue containing larger size scattering particles has more contribution to the forward scattering in comparison with the normal prostate tissue. In addition to the conventional simulation model that approximately considers the scattering particle as sphere, the cylinder model which is more suitable for fiber-like tissue frame components such as collagen and elastin was used for developing a computation code to study angular dependence of scattering in prostate tissues. To the best of our knowledge, this is the first study to deal with both spherical and cylindrical scattering particles in prostate tissues.

New Neutron Cross-Section Measurements at ORELA for Improved Nuclear Data Calculations

NASA Astrophysics Data System (ADS)

Guber, K. H.; Leal, L. C.; Sayer, R. O.; Koehler, P. E.; Valentine, T. E.; Derrien, H.; Harvey, J. A.

2005-05-01

Many older neutron cross-section evaluations from libraries such as ENDF/B-VI or JENDL-3.2 exhibit deficiencies or do not cover energy ranges that are important for criticality safety applications. These deficiencies may occur in the resolved and unresolved-resonance regions. Consequently, these evaluated data may not be adequate for nuclear criticality calculations where effects such as self-shielding, multiple scattering, or Doppler broadening are important. To support the Nuclear Criticality Predictability Program, neutron cross-section measurements have been initiated at the Oak Ridge Electron Linear Accelerator (ORELA). ORELA is the only high-power white neutron source with excellent time resolution still operating in the United States. It is ideally suited to measure fission, neutron total, and capture cross sections in the energy range from 1 eV to ˜600 keV, which is important for many nuclear criticality safety applications.

Huge critical current density and tailored superconducting anisotropy in SmFeAsO₀.₈F₀.₁₅ by low-density columnar-defect incorporation.

PubMed

Fang, L; Jia, Y; Mishra, V; Chaparro, C; Vlasko-Vlasov, V K; Koshelev, A E; Welp, U; Crabtree, G W; Zhu, S; Zhigadlo, N D; Katrych, S; Karpinski, J; Kwok, W K

2013-01-01

Iron-based superconductors could be useful for electricity distribution and superconducting magnet applications because of their relatively high critical current densities and upper critical fields. SmFeAsO₀.₈F₀.₁₅ is of particular interest as it has the highest transition temperature among these materials. Here we show that by introducing a low density of correlated nano-scale defects into this material by heavy-ion irradiation, we can increase its critical current density to up to 2 × 10⁷ A cm⁻² at 5 K--the highest ever reported for an iron-based superconductor--without reducing its critical temperature of 50 K. We also observe a notable reduction in the thermodynamic superconducting anisotropy, from 8 to 4 upon irradiation. We develop a model based on anisotropic electron scattering that predicts that the superconducting anisotropy can be tailored via correlated defects in semimetallic, fully gapped type II superconductors.

A Comparison of Monte Carlo and Deterministic Solvers for keff and Sensitivity Calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haeck, Wim; Parsons, Donald Kent; White, Morgan Curtis

Verification and validation of our solutions for calculating the neutron reactivity for nuclear materials is a key issue to address for many applications, including criticality safety, research reactors, power reactors, and nuclear security. Neutronics codes solve variations of the Boltzmann transport equation. The two main variants are Monte Carlo versus deterministic solutions, e.g. the MCNP [1] versus PARTISN [2] codes, respectively. There have been many studies over the decades that examined the accuracy of such solvers and the general conclusion is that when the problems are well-posed, either solver can produce accurate results. However, the devil is always in themore » details. The current study examines the issue of self-shielding and the stress it puts on deterministic solvers. Most Monte Carlo neutronics codes use continuous-energy descriptions of the neutron interaction data that are not subject to this effect. The issue of self-shielding occurs because of the discretisation of data used by the deterministic solutions. Multigroup data used in these solvers are the average cross section and scattering parameters over an energy range. Resonances in cross sections can occur that change the likelihood of interaction by one to three orders of magnitude over a small energy range. Self-shielding is the numerical effect that the average cross section in groups with strong resonances can be strongly affected as neutrons within that material are preferentially absorbed or scattered out of the resonance energies. This affects both the average cross section and the scattering matrix.« less

Anomalous quantum critical spin dynamics in YFe2Al10

NASA Astrophysics Data System (ADS)

Huang, K.; Tan, C.; Zhang, J.; Ding, Z.; MacLaughlin, D. E.; Bernal, O. O.; Ho, P.-C.; Baines, C.; Wu, L. S.; Aronson, M. C.; Shu, L.

2018-04-01

We report results of a muon spin relaxation (μ SR ) study of YFe2Al10 , a quasi-two-dimensional (2D) nearly ferromagnetic metal in which unconventional quantum critical behavior is observed. No static Fe2 + magnetism, with or without long-range order, is found down to 19 mK. The dynamic muon spin relaxation rate λ exhibits power-law divergences in temperature and magnetic field, the latter for fields that are too weak to affect the electronic spin dynamics directly. We attribute this to the proportionality of λ (ωμ,T ) to the dynamic structure factor S (ωμ,T ) , where ωμ≈105-107s-1 is the muon Zeeman frequency. These results suggest critical divergences of S (ωμ,T ) in both temperature and frequency. Power-law scaling and a 2D dissipative quantum XY model both yield forms for S (ω ,T ) that agree with neutron scattering data (ω ≈1012s-1 ). Extrapolation to μ SR frequencies agrees semiquantitatively with the observed temperature dependence of λ (ωμ,T ) , but predicts frequency independence for ωμ≪T , in extreme disagreement with experiment. We conclude that the quantum critical spin dynamics of YFe2Al10 is not well understood at low frequencies.

Impacts of variability in geomechanical properties on hydrate bearing sediment responses

NASA Astrophysics Data System (ADS)

Lin, J. S.; Uchida, S.; Choi, J. H.; Seol, Y.

2017-12-01

Hydrate bearing sediments (HBS) may become unstable during the gas production operation, or from natural processes such as change in the landform or temperature. The geomechanical modeling is a rational way to assess HBS stability regardless of the process involved. At the present time, such modeling is laced with uncertainties. The uncertainties come from many sources that include the adequacy of a modeling framework to accurately project the response of HBS, the gap in the available field information, and the variability in the laboratory test results from limited samples. For a reasonable stability assessment, the impact of the various uncertainties have to be addressed. This study looks into one particular aspect of the uncertainty, namely, the uncertainty caused by the scatter in the laboratory tests and the ability of a constitutive model to adequately represent them. Specifically this study focuses on the scatter in the results from laboratory tests on high quality pressured core samples from a marine site, and use a critical state constitutive model to represent them. The study investigates how the HBS responses shift when the parameters of the constitutive model are varied to reflect the different aspects of experimental results. Also investigated are impacts on the responses by altering certain formulations of the constitutive model to suit particular sets of results.

Optical-Based Artificial Palpation Sensors for Lesion Characterization

PubMed Central

Lee, Jong-Ha; Kim, Yoon Nyun; Ku, Jeonghun; Park, Hee-Jun

2013-01-01

Palpation techniques are widely used in medical procedures to detect the presence of lumps or tumors in the soft breast tissues. Since these procedures are very subjective and depend on the skills of the physician, it is imperative to perform detailed a scientific study in order to develop more efficient medical sensors to measure and generate palpation parameters. In this research, we propose an optical-based, artificial palpation sensor for lesion characterization. This has been developed using a multilayer polydimethylsiloxane optical waveguide. Light was generated at the critical angle to reflect totally within the flexible and transparent waveguide. When a waveguide was compressed by an external force, its contact area would deform and cause the light to scatter. The scattered light was captured by a high-resolution camera and saved as an image format. To test the performance of the proposed system, we used a realistic tissue phantom with embedded hard inclusions. The experimental results show that the proposed sensor can detect inclusions and provide the relative value of size, depth, and Young's modulus of an inclusion. PMID:23966198

Laser Speckle Imaging to Monitor Microvascular Blood Flow: A Review.

PubMed

Vaz, Pedro G; Humeau-Heurtier, Anne; Figueiras, Edite; Correia, Carlos; Cardoso, Joao

2016-01-01

Laser speckle is a complex interference phenomenon that can easily be understood, in concept, but is difficult to predict mathematically, because it is a stochastic process. The use of laser speckle to produce images, which can carry many types of information, is called laser speckle imaging (LSI). The biomedical applications of LSI started in 1981 and, since then, many scientists have improved the laser speckle theory and developed different imaging techniques. During this process, some inconsistencies have been propagated up to now. These inconsistencies should be clarified in order to avoid errors in future works. This review presents a review of the laser speckle theory used in biomedical applications. Moreover, we also make a review of the practical concepts that are useful in the construction of laser speckle imagers. This study is not only an exposition of the concepts that can be found in the literature but also a critical analysis of the investigations presented so far. Concepts like scatterers velocity distribution, effect of static scatterers, optimal speckle size, light penetration angle, and contrast computation algorithms are discussed in detail.

Using Neutron Scattering and Mercury Intrusion Techniques to Characterize Micro- and Nano-Pore Structure of Shale

NASA Astrophysics Data System (ADS)

Zhang, Y.; Barber, T.; Hu, Q.; Bleuel, M.

2017-12-01

The micro- and nano-pore structure of oil shale plays a critical role in hydrocarbon storage and migration. This study aims to characterize the pore structure of three Bakken members (i.e., upper organic-rich shale, middle silty/sandy dolomites, and lower organic-rich shale), through small and ultra-small angle neutron scattering (SANS and USANS) techniques, as well as mercury injection capillary pressure (MICP) analyses. SANS/USANS have the capabilities of measuring total porosity (connected and closed porosity) across nm-mm spectrum, not measurable than other fluid-invasion approaches, such as MICP which obtains connected porosity and pore-throat size distribution. Results from both techniques exhibit different features of upper/lower Bakken and middle Bakken, as a result of various mineral composition and organic matter contents. Middle Bakken is primarily dominated by the mineral pores, while in the upper and lower Bakken, organic pores contribute a significant portion of total porosity. A combination of USANS/SANS and MICP techniques gives a comprehensive picture of shale micro- and nano-pore structure.

Resonant x-ray scattering reveals possible disappearance of magnetic order under hydrostatic pressure in the Kitaev candidate γ - Li 2 IrO 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Breznay, Nicholas P.; Ruiz, Alejandro; Frano, Alex

2017-07-05

Honeycomb iridates such as γ-Li 2IrO 3 are argued to realize Kitaev spin-anisotropic magnetic exchange, along with Heisenberg and possibly other couplings. While systems with pure Kitaev interactions are candidates to realize a quantum spin-liquid ground state, in γ-Li 2IrO 3 it has been shown that the presence of competing magnetic interactions leads to an incommensurate spiral spin order at ambient pressure below 38 K. In this paper, we study the pressure sensitivity of this magnetically ordered state in single crystals of γ-Li 2IrO 3 using resonant x-ray scattering (RXS) under applied hydrostatic pressures of up to 3 GPa. Finally,more » RXS is a direct probe of electronic order, and we observe the abrupt disappearance of the q sp = (0.57, 0, 0) spiral order at a critical pressure P c = 1.4 GPa with no accompanying change in the symmetry of the lattice.« less

Room-temperature superfluidity in a polariton condensate

NASA Astrophysics Data System (ADS)

Lerario, Giovanni; Fieramosca, Antonio; Barachati, Fábio; Ballarini, Dario; Daskalakis, Konstantinos S.; Dominici, Lorenzo; de Giorgi, Milena; Maier, Stefan A.; Gigli, Giuseppe; Kéna-Cohen, Stéphane; Sanvitto, Daniele

2017-09-01

Superfluidity--the suppression of scattering in a quantum fluid at velocities below a critical value--is one of the most striking manifestations of the collective behaviour typical of Bose-Einstein condensates. This phenomenon, akin to superconductivity in metals, has until now been observed only at prohibitively low cryogenic temperatures. For atoms, this limit is imposed by the small thermal de Broglie wavelength, which is inversely related to the particle mass. Even in the case of ultralight quasiparticles such as exciton-polaritons, superfluidity has been demonstrated only at liquid helium temperatures. In this case, the limit is not imposed by the mass, but instead by the small binding energy of Wannier-Mott excitons, which sets the upper temperature limit. Here we demonstrate a transition from supersonic to superfluid flow in a polariton condensate under ambient conditions. This is achieved by using an organic microcavity supporting stable Frenkel exciton-polaritons at room temperature. This result paves the way not only for tabletop studies of quantum hydrodynamics, but also for room-temperature polariton devices that can be robustly protected from scattering.

Cross-Section Measurements in the Fast Neutron Energy Range

NASA Astrophysics Data System (ADS)

Plompen, Arjan

2006-04-01

Generation IV focuses research for advanced nuclear reactors on six concepts. Three of these concepts, the lead, gas and sodium fast reactors (LFR, GFR and SFR) have fast neutron spectra, whereas a fourth, the super-critical water reactor (SCWR), can be configured to have a fast spectrum. Such fast neutron spectra are essential to meet the sustainability objective of GenIV. Nuclear data requirements for GenIV concepts will therefore emphasize the energy region from about 1 keV to 10 MeV. Here, the potential is illustrated of the GELINA neutron time-of-flight facility and the Van de Graaff laboratory at IRMM to measure the relevant nuclear data in this energy range: the total, capture, fission and inelastic-scattering cross sections. In particular, measurement results will be shown for lead and bismuth inelastic scattering for which the need was recently expressed in a quantitative way by Aliberti et al. for Accelerator Driven Systems. Even without completion of the quantitative assessment of the data needs for GenIV concepts at ANL it is clear that this particular effort is of relevance to LFR system studies.

Characterization of long-scale-length plasmas produced from plastic foam targets for laser plasma instability (LPI) research

NASA Astrophysics Data System (ADS)

Oh, Jaechul; Weaver, J. L.; Serlin, V.; Obenschain, S. P.

2017-10-01

We report on an experimental effort to produce plasmas with long scale lengths for the study of parametric instabilities, such as two plasmon decay (TPD) and stimulated Raman scattering (SRS), under conditions relevant to fusion plasma. In the current experiment, plasmas are formed from low density (10-100 mg/cc) CH foam targets irradiated by Nike krypton fluoride laser pulses (λ = 248 nm, 1 nsec FWHM) with energies up to 1 kJ. This experiment is conducted with two primary diagnostics: the grid image refractometer (Nike-GIR) to measure electron density and temperature profiles of the coronas, and time-resolved spectrometers with absolute intensity calibration to examine scattered light features of TPD or SRS. Nike-GIR was recently upgraded with a 5th harmonic probe laser (λ = 213 nm) to access plasma regions near quarter critical density of 248 nm light (4.5 ×1021 cm-3). The results will be discussed with data obtained from 120 μm scale-length plasmas created on solid CH targets in previous LPI experiments at Nike. Work supported by DoE/NNSA.

Polarized light scattering by macromolecular self-assembly of J-aggregates

NASA Astrophysics Data System (ADS)

Rebane, Aleksander; Mikhaylov, Alexander

2018-02-01

We have recently reported that by sending a tightly collimated (0.05 - 2 mm diameter) red- or near-IR laser beam through an aqueous solution of pseudoisocyanine (PIC) J-aggregates, a macroscopic tube-like structure is formed surrounding the laser beam on the time scale of minutes. This self-assembled structure is comprised of heterogeneous material containing micrometer-size rod-like strands or microcrystals. Because the illumination wavelength is far redshifted from the linear absorption range of the PIC and J-aggregates, the self-assembly is likely induced by some very weak background absorption or dissipation. Furthermore, strong correlation of the effect with the characteristic Jaggregate peak in the absorption spectrum and critical dependence of the "tube" formation on pH of the solution indicate molecular charge related non-equilibrium nature of the underlying mechanism. Most interestingly, the structure formation is accompanied by strongly polarized scattering. When observed between crossed polarizers, the angular intensity distribution of the scattered light resembles Maltese cross figure, indicating that the scattering rods are arranged in a circular pattern around the beam axis direction. It appears that the illumination is creating in the medium a radially directed gradient of either concentration-, temperature- or other type of parameter that controls the microcrystal formation.

Impact of Snow Grain Shape and Internal Mixing with Black Carbon Aerosol on Snow Optical Properties for use in Climate Models

NASA Astrophysics Data System (ADS)

He, C.; Liou, K. N.; Takano, Y.; Yang, P.; Li, Q.; Chen, F.

2017-12-01

A set of parameterizations is developed for spectral single-scattering properties of clean and black carbon (BC)-contaminated snow based on geometric-optic surface-wave (GOS) computations, which explicitly resolves BC-snow internal mixing and various snow grain shapes. GOS calculations show that, compared with nonspherical grains, volume-equivalent snow spheres show up to 20% larger asymmetry factors and hence stronger forward scattering, particularly at wavelengths <1 mm. In contrast, snow grain sizes have a rather small impact on the asymmetry factor at wavelengths <1 mm, whereas size effects are important at longer wavelengths. The snow asymmetry factor is parameterized as a function of effective size, aspect ratio, and shape factor, and shows excellent agreement with GOS calculations. According to GOS calculations, the single-scattering coalbedo of pure snow is predominantly affected by grain sizes, rather than grain shapes, with higher values for larger grains. The snow single-scattering coalbedo is parameterized in terms of the effective size that combines shape and size effects, with an accuracy of >99%. Based on GOS calculations, BC-snow internal mixing enhances the snow single-scattering coalbedo at wavelengths <1 mm, but it does not alter the snow asymmetry factor. The BC-induced enhancement ratio of snow single-scattering coalbedo, independent of snow grain size and shape, is parameterized as a function of BC concentration with an accuracy of >99%. Overall, in addition to snow grain size, both BC-snow internal mixing and snow grain shape play critical roles in quantifying BC effects on snow optical properties. The present parameterizations can be conveniently applied to snow, land surface, and climate models including snowpack radiative transfer processes.

Structure Formation in Salt-Free Solutions of Amphiphilic Sulfonated Polyelectrolytes

NASA Astrophysics Data System (ADS)

Bockstaller, Michael; Koehler, Werner

2000-03-01

Self-assembled systems have long attracted attention due to their practical importance in many technical and biological fields. Dodecyl-substituted poly(para-phenylen)sulfonates (abbreviated PPPS) are highly charged polyelectrolytes which in the uncharged state have been investigated extensively and an intrinsic persistence length of 15 nm has been reported. Due to their hydrophobic side chains, PPPS are compatible with water only as micellar aggregates and tend to form supramolecular structures even at concentrations as low as 10-5mol_mon.units/l. Because of the rodlike conformation of PPPS, this self-assembly leads to aggregates of anisotropic shape. Therefore, depolarized light scattering was employed to yield complementary information about structure and dynamics of these complex fluids. Aqueous solutions of PPPS at room temperature undergo a structural transition at a critical concentration of c_crit.=0.016 g/l. This transition is characterized by a strong increase of scattered intensity in forward direction and dynamic depolarized scattering. Above c_crit. the cylindrical micelles (L=310 nm, d=3.1 nm, N_radial=12) self assembly into large ellipsoidal clusters of size in the μ m range. Due to the strong increase of depolarized scattered intensity there has to be a preferential orientation of the micelles inside those clusters, which thus represent a lyotropic mesophase. By combining static and dynamic light scattering for the low q-range as well as small angle x-ray scattering for the higher q-range it is possible to determine size and shape of each aggregation step. Decreasing the molecular weight of the PPPS has profound influence on the micellar length and hence on c_crit. which is close to the overlap concentration (c ~ 1/L^3) allowing for the observation of the polyelectrolyte effect.

DNA bubble dynamics as a quantum Coulomb problem.

PubMed

Fogedby, Hans C; Metzler, Ralf

2007-02-16

We study the dynamics of denaturation bubbles in double-stranded DNA. Demonstrating that the associated Fokker-Planck equation is equivalent to a Coulomb problem, we derive expressions for the bubble survival distribution W(t). Below Tm, W(t) is associated with the continuum of scattering states of the repulsive Coulomb potential. At Tm, the Coulomb potential vanishes and W(t) assumes a power-law tail with nontrivial dynamic exponents: the critical exponent of the entropy loss factor may cause a finite mean lifetime. Above Tm (attractive potential), the long-time dynamics is controlled by the lowest bound state. Correlations and finite size effects are discussed.

Doping dependence of low-energy quasiparticle excitations in superconducting Bi2212.

PubMed

Ino, Akihiro; Anzai, Hiroaki; Arita, Masashi; Namatame, Hirofumi; Taniguchi, Masaki; Ishikado, Motoyuki; Fujita, Kazuhiro; Ishida, Shigeyuki; Uchida, Shinichi

2013-12-05

: The doping-dependent evolution of the d-wave superconducting state is studied from the perspective of the angle-resolved photoemission spectra of a high-Tc cuprate, Bi2Sr2CaCu2 O8+δ (Bi2212). The anisotropic evolution of the energy gap for Bogoliubov quasiparticles is parametrized by critical temperature and superfluid density. The renormalization of nodal quasiparticles is evaluated in terms of mass enhancement spectra. These quantities shed light on the strong coupling nature of electron pairing and the impact of forward elastic or inelastic scatterings. We suggest that the quasiparticle excitations in the superconducting cuprates are profoundly affected by doping-dependent screening.

3-dimensional beam scanning system for particle radiation therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leemann, C.; Alonso, J.; Grunder, H.

1977-03-01

In radiation therapy treatment volumes up to several liters have to be irradiated. Today's charged particle programs use ridge filters, scattering foils, occluding rings collimators and boluses to shape the dose distribution. An alternative approach, scanning of a small diameter beam, is analyzed and tentative systems specifications are derived. Critical components are scheduled for fabrication and testing at LBL.

Temperature-dependent micellar structures in poly(styrene-b-isoprene) diblock copolymer solutions near the critical micelle temperature

NASA Astrophysics Data System (ADS)

Bang, Joona; Viswanathan, Karthik; Lodge, Timothy P.; Park, Moon Jeong; Char, Kookheon

2004-12-01

The temperature dependence of the micelle structures formed by poly(styrene-b-isoprene) (SI) diblock copolymers in the selective solvents diethyl phthalate (DEP) and tetradecane (C14), which are selective for the PS and PI blocks, respectively, have been investigated by small angle neutron scattering (SANS). Two nearly symmetric SI diblock copolymers, one with a perdeuterated PS block and the other with a perdeuterated PI block, were examined in both DEP and C14. The SANS scattering length density of the solvent was matched closely to either the core or the corona block. The resulting core and corona contrast data were fitted with a detailed model developed by Pedersen and co-workers. The fits provide quantitative information on micellar characteristics such as aggregation number, core size, overall size, solvent fraction in the core, and corona thickness. As temperature increases, the solvent selectivity decreases, leading to substantial solvent swelling of the core and a decrease in the aggregation number and core size. Both core and corona chains are able to relax their conformations near the critical micelle temperature due to a decrease in the interfacial tension, even though the corona chains are always under good solvent conditions.

Surface areas of fractally rough particles studied by scattering

NASA Astrophysics Data System (ADS)

Hurd, Alan J.; Schaefer, Dale W.; Smith, Douglas M.; Ross, Steven B.; Le Méhauté, Alain; Spooner, Steven

1989-05-01

The small-angle scattering from fractally rough surfaces has the potential to give information on the surface area at a given resolution. By use of quantitative neutron and x-ray scattering, a direct comparison of surface areas of fractally rough powders was made between scattering and adsorption techniques. This study supports a recently proposed correction to the theory for scattering from fractal surfaces. In addition, the scattering data provide an independent calibration of molecular adsorbate areas.

The history of scatter hoarding studies.

PubMed

Brodin, Anders

2010-03-27

In this review, I will present an overview of the development of the field of scatter hoarding studies. Scatter hoarding is a conspicuous behaviour and it has been observed by humans for a long time. Apart from an exceptional experimental study already published in 1720, it started with observational field studies of scatter hoarding birds in the 1940s. Driven by a general interest in birds, several ornithologists made large-scale studies of hoarding behaviour in species such as nutcrackers and boreal titmice. Scatter hoarding birds seem to remember caching locations accurately, and it was shown in the 1960s that successful retrieval is dependent on a specific part of the brain, the hippocampus. The study of scatter hoarding, spatial memory and the hippocampus has since then developed into a study system for evolutionary studies of spatial memory. In 1978, a game theoretical paper started the era of modern studies by establishing that a recovery advantage is necessary for individual hoarders for the evolution of a hoarding strategy. The same year, a combined theoretical and empirical study on scatter hoarding squirrels investigated how caches should be spaced out in order to minimize cache loss, a phenomenon sometimes called optimal cache density theory. Since then, the scatter hoarding paradigm has branched into a number of different fields: (i) theoretical and empirical studies of the evolution of hoarding, (ii) field studies with modern sampling methods, (iii) studies of the precise nature of the caching memory, (iv) a variety of studies of caching memory and its relationship to the hippocampus. Scatter hoarding has also been the subject of studies of (v) coevolution between scatter hoarding animals and the plants that are dispersed by these.

Scatter correction for cone-beam computed tomography using self-adaptive scatter kernel superposition

NASA Astrophysics Data System (ADS)

Xie, Shi-Peng; Luo, Li-Min

2012-06-01

The authors propose a combined scatter reduction and correction method to improve image quality in cone beam computed tomography (CBCT). The scatter kernel superposition (SKS) method has been used occasionally in previous studies. However, this method differs in that a scatter detecting blocker (SDB) was used between the X-ray source and the tested object to model the self-adaptive scatter kernel. This study first evaluates the scatter kernel parameters using the SDB, and then isolates the scatter distribution based on the SKS. The quality of image can be improved by removing the scatter distribution. The results show that the method can effectively reduce the scatter artifacts, and increase the image quality. Our approach increases the image contrast and reduces the magnitude of cupping. The accuracy of the SKS technique can be significantly improved in our method by using a self-adaptive scatter kernel. This method is computationally efficient, easy to implement, and provides scatter correction using a single scan acquisition.

Critical validity assessment of theoretical models: charge-exchange at intermediate and high energies

NASA Astrophysics Data System (ADS)

Belkić, Dževad

1999-06-01

Exact comprehensive computations are carried out by means of four leading second-order approximations yielding differential cross sections dQ/ dΩ for the basic charge exchange process H ++H(1s)→H(1s)+H + at intermediate and high energies. The obtained extensive set of results is thoroughly tested against all the existing experimental data with the purpose of critically assessing the validity of the boundary corrected second-Born (CB2), continuum-distorted wave (CDW), impulse approximation (IA) and the reformulated impulse approximation (RIA). The conclusion which emerges from this comparative study clearly indicates that the RIA agrees most favorably with the measurements available over a large energy range 25 keV-5 MeV. Such a finding reaffirms the few-particle quantum scattering theory which imposes several strict conditions on adequate second-order methods. These requirements satisfied by the RIA are: (i) normalisations of all the scattering wave functions, (ii) correct boundary conditions in both entrance and exit channels, (iii) introduction of a mathematically justified two-center continuum state for the sum of an attractive and a repulsive Coulomb potential with the same interaction strength, (iv) inclusion of the multiple scattering effects neglected in the IA, (v) a proper description of the Thomas double scattering in good agreement with the experiments and without any unobserved peak splittings. Nevertheless, the performed comparative analysis of the above four approximations indicates that none of the methods is free from some basic shortcomings. Despite its success, the RIA remains essentially a high-energy model like the other three methods under study. More importantly, their perturbative character leaves virtually no room for further systematic improvements, since the neglected higher-order terms are prohibitively tedious for practical purposes and have never been computed exactly. To bridge this gap, we presently introduce the variational Padé approximant (VPA) as a novel non-perturbative theory which is valid at all energies. This is a variationally unified T-matrix, T(VPA)i,f= T'i,f+ Si,f, comprised of a selected perturbative model T'i,f and a related stationary non-linear remainder Si,f conceived as an L2-basis set expansion of the total Green's function. The key input Si,f is a double series ∑ n1, n2Cn1n2 with bound-free atomic form factors as rational coefficients Cn1n2. Convergence of this sum is significantly accelerated by the two-dimensional Padé approximant (2D-PA) implemented through the bi-variate Wynn's epsilon ( ɛ) algorithm. The table ɛ( λ) for Si,f( λ) is evaluated at a sufficiently dense grid λ∈ Λ≡[ λmin, λmax] of any chosen variate λ, e.g. scattering angle, incident energy, coupling strength, etc. The roots λk of the inverse function E(λ)=1/ɛ(λ) directly lead to the poles of Si,f( λ) in the complex λ-plane. The availability of all λk's permits an easy obtaining of each of the magnitudes d ɛk=1/ E'(λ k) of the poles of Si,f( λ) by the Cauchy residue calculus and a mere knowledge of the first derivative E'(λ k) of E(λ k) at λk∈ Λ. This is a new signal processing method called the parametric epsilon spectral (P ɛS) estimator which opens an affordable way to powerful numerical investigations of analytical properties of transition and scattering matrices for a general process including resonance phenomena as one of the the most interesting parts of scattering.

Biomass Burning Aerosol Absorption Measurements with MODIS Using the Critical Reflectance Method

NASA Technical Reports Server (NTRS)

Zhu, Li; Martins, Vanderlei J.; Remer, Lorraine A.

2010-01-01

This research uses the critical reflectance technique, a space-based remote sensing method, to measure the spatial distribution of aerosol absorption properties over land. Choosing two regions dominated by biomass burning aerosols, a series of sensitivity studies were undertaken to analyze the potential limitations of this method for the type of aerosol to be encountered in the selected study areas, and to show that the retrieved results are relatively insensitive to uncertainties in the assumptions used in the retrieval of smoke aerosol. The critical reflectance technique is then applied to Moderate Resolution Imaging Spectrometer (MODIS) data to retrieve the spectral aerosol single scattering albedo (SSA) in South African and South American 35 biomass burning events. The retrieved results were validated with collocated Aerosol Robotic Network (AERONET) retrievals. One standard deviation of mean MODIS retrievals match AERONET products to within 0.03, the magnitude of the AERONET uncertainty. The overlap of the two retrievals increases to 88%, allowing for measurement variance in the MODIS retrievals as well. The ensemble average of MODIS-derived SSA for the Amazon forest station is 0.92 at 670 nm, and 0.84-0.89 for the southern African savanna stations. The critical reflectance technique allows evaluation of the spatial variability of SSA, and shows that SSA in South America exhibits higher spatial variation than in South Africa. The accuracy of the retrieved aerosol SSA from MODIS data indicates that this product can help to better understand 44 how aerosols affect the regional and global climate.

An Assessment of Critical Dimension Small Angle X-ray Scattering Metrology for Advanced Semiconductor Manufacturing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Settens, Charles M.

2015-01-01

Simultaneous migration of planar transistors to FinFET architectures, the introduction of a plurality of materials to ensure suitable electrical characteristics, and the establishment of reliable multiple patterning lithography schemes to pattern sub-10 nm feature sizes imposes formidable challenges to current in-line dimensional metrologies. Because the shape of a FinFET channel cross-section immediately influences the electrical characteristics, the evaluation of 3D device structures requires measurement of parameters beyond traditional critical dimension (CD), including their sidewall angles, top corner rounding and footing, roughness, recesses and undercuts at single nanometer dimensions; thus, metrologies require sub-nm and approaching atomic level measurement uncertainty. Synchrotron criticalmore » dimension small angle X-ray scattering (CD-SAXS) has unique capabilities to non-destructively monitor the cross-section shape of surface structures with single nanometer uncertainty and can perform overlay metrology to sub-nm uncertainty. In this dissertation, we perform a systematic experimental investigation using CD-SAXS metrology on a hierarchy of semiconductor 3D device architectures including, high-aspect-ratio contact holes, H2 annealed Si fins, and a series of grating type samples at multiple points along a FinFET fabrication process increasing in structural intricacy and ending with fully fabricated FinFET. Comparative studies between CD-SAXS metrology and other relevant semiconductor dimensional metrologies, particularly CDSEM, CD-AFM and TEM are used to determine physical limits of CD-SAXS approach for advanced semiconductor samples. CD-SAXS experimental tradeoffs, advice for model-dependent analysis and thoughts on the compatibility with a semiconductor manufacturing environment are discussed.« less

Competition of mesoscales and crossover to theta-point tricriticality in near-critical polymer solutions.

PubMed

Anisimov, M A; Kostko, A F; Sengers, J V; Yudin, I K

2005-10-22

The approach to asymptotic critical behavior in polymer solutions is governed by a competition between the correlation length of critical fluctuations diverging at the critical point of phase separation and an additional mesoscopic length scale, the radius of gyration. In this paper we present a theory for crossover between two universal regimes: a regime with Ising (fluctuation-induced) asymptotic critical behavior, where the correlation length prevails, and a mean-field tricritical regime with theta-point behavior controlled by the mesoscopic polymer chain. The theory yields a universal scaled description of existing experimental phase-equilibria data and is in excellent agreement with our light-scattering experiments on polystyrene solutions in cyclohexane with polymer molecular weights ranging from 2 x 10(5) up to 11.4 x 10(6). The experiments demonstrate unambiguously that crossover to theta-point tricriticality is controlled by a competition of the two mesoscales. The critical amplitudes deduced from our experiments depend on the polymer molecular weight as predicted by de Gennes [Phys. Lett. 26A, 313 (1968)]. Experimental evidence for the presence of logarithmic corrections to mean-field tricritical theta-point behavior in the molecular-weight dependence of the critical parameters is also presented.

Polar nephelometer for atmospheric particulate studies

NASA Technical Reports Server (NTRS)

Hansen, M. Z.; Evans, W. H.

1980-01-01

A polar nephelometer for use in studying atmospheric aerosols was developed. The nephelometer detects molecular scatter from air and measures scattering from very clean air using pure molecular scattering for calibration. A compact system using a folded light path with an air cooled argon laser for the light source was designed. A small, sensitive detector unit permits easy angular rotation for changing the scattering angle. A narrow detector field of view of + or - 1/4 degree of scattering along with a single wavelength of incident light is used to minimize uncertainties in the scattering theory. The system is automated for data acquisition of the scattering matrix elements over an angular range from 2 degrees to 178 degrees of scattering. Both laser output and detector sensitivity are monitored to normalize the measured light scattering.

Multiaxial Fatigue Life Prediction Based on Nonlinear Continuum Damage Mechanics and Critical Plane Method

NASA Astrophysics Data System (ADS)

Wu, Z. R.; Li, X.; Fang, L.; Song, Y. D.

2018-04-01

A new multiaxial fatigue life prediction model has been proposed in this paper. The concepts of nonlinear continuum damage mechanics and critical plane criteria were incorporated in the proposed model. The shear strain-based damage control parameter was chosen to account for multiaxial fatigue damage under constant amplitude loading. Fatigue tests were conducted on nickel-based superalloy GH4169 tubular specimens at the temperature of 400 °C under proportional and nonproportional loading. The proposed method was checked against the multiaxial fatigue test data of GH4169. Most of prediction results are within a factor of two scatter band of the test results.

Deorientation of PolSAR coherency matrix for volume scattering retrieval

NASA Astrophysics Data System (ADS)

Kumar, Shashi; Garg, R. D.; Kushwaha, S. P. S.

2016-05-01

Polarimetric SAR data has proven its potential to extract scattering information for different features appearing in single resolution cell. Several decomposition modelling approaches have been developed to retrieve scattering information from PolSAR data. During scattering power decomposition based on physical scattering models it becomes very difficult to distinguish volume scattering as a result from randomly oriented vegetation from scattering nature of oblique structures which are responsible for double-bounce and volume scattering , because both are decomposed in same scattering mechanism. The polarization orientation angle (POA) of an electromagnetic wave is one of the most important character which gets changed due to scattering from geometrical structure of topographic slopes, oriented urban area and randomly oriented features like vegetation cover. The shift in POA affects the polarimetric radar signatures. So, for accurate estimation of scattering nature of feature compensation in polarization orientation shift becomes an essential procedure. The prime objective of this work was to investigate the effect of shift in POA in scattering information retrieval and to explore the effect of deorientation on regression between field-estimated aboveground biomass (AGB) and volume scattering. For this study Dudhwa National Park, U.P., India was selected as study area and fully polarimetric ALOS PALSAR data was used to retrieve scattering information from the forest area of Dudhwa National Park. Field data for DBH and tree height was collect for AGB estimation using stratified random sampling. AGB was estimated for 170 plots for different locations of the forest area. Yamaguchi four component decomposition modelling approach was utilized to retrieve surface, double-bounce, helix and volume scattering information. Shift in polarization orientation angle was estimated and deorientation of coherency matrix for compensation of POA shift was performed. Effect of deorientation on RGB color composite for the forest area can be easily seen. Overestimation of volume scattering and under estimation of double bounce scattering was recorded for PolSAR decomposition without deorientation and increase in double bounce scattering and decrease in volume scattering was noticed after deorientation. This study was mainly focused on volume scattering retrieval and its relation with field estimated AGB. Change in volume scattering after POA compensation of PolSAR data was recorded and a comparison was performed on volume scattering values for all the 170 forest plots for which field data were collected. Decrease in volume scattering after deorientation was noted for all the plots. Regression between PolSAR decomposition based volume scattering and AGB was performed. Before deorientation, coefficient determination (R2) between volume scattering and AGB was 0.225. After deorientation an improvement in coefficient of determination was found and the obtained value was 0.613. This study recommends deorientation of PolSAR data for decomposition modelling to retrieve reliable volume scattering information from forest area.

Studying time of flight imaging through scattering media across multiple size scales (Conference Presentation)

NASA Astrophysics Data System (ADS)

Velten, Andreas

2017-05-01

Light scattering is a primary obstacle to optical imaging in a variety of different environments and across many size and time scales. Scattering complicates imaging on large scales when imaging through the atmosphere when imaging from airborne or space borne platforms, through marine fog, or through fog and dust in vehicle navigation, for example in self driving cars. On smaller scales, scattering is the major obstacle when imaging through human tissue in biomedical applications. Despite the large variety of participating materials and size scales, light transport in all these environments is usually described with very similar scattering models that are defined by the same small set of parameters, including scattering and absorption length and phase function. We attempt a study of scattering and methods of imaging through scattering across different scales and media, particularly with respect to the use of time of flight information. We can show that using time of flight, in addition to spatial information, provides distinct advantages in scattering environments. By performing a comparative study of scattering across scales and media, we are able to suggest scale models for scattering environments to aid lab research. We also can transfer knowledge and methodology between different fields.

Characterizing the behavior of scattered radiation in multi-energy x-ray imaging

NASA Astrophysics Data System (ADS)

Sossin, Artur; Rebuffel, V.; Tabary, J.; Létang, J. M.; Freud, N.; Verger, L.

2017-04-01

Scattered radiation results in various undesirable effects in medical diagnostics, non-destructive testing (NDT) and security x-ray imaging. Despite numerous studies characterizing this phenomenon and its effects, the knowledge of its behavior in the energy domain remains limited. The present study aims at summarizing some key insights on scattered radiation originating from the inspected object. In addition, various simulations and experiments with limited collimation on both simplified and realistic phantoms were conducted in order to study scatter behavior in multi-energy x-ray imaging. Results showed that the spectrum shape of the scatter component can be considered preserved in the first approximation across the image plane for various acquisition geometries and phantoms. The variations exhibited by the scatter spectrum were below 10% for most examined cases. Furthermore, the corresponding spectrum shape proved to be also relatively invariant for different experimental angular projections of one of the examined phantoms. The observed property of scattered radiation can potentially lead to the decoupling of spatial and energy scatter components, which can in turn enable speed ups in scatter simulations and reduce the complexity of scatter correction.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mei, Yang; Ramanathan, Arvind; Glover, Karen

BECN1 is essential for autophagy, a critical eukaryotic cellular homeostasis pathway. Here in this study, we delineate a highly conserved BECN1 domain located between previously characterized BH3 and coiled-coil domains and elucidate its structure and role in autophagy. The 2.0 Å sulfur-single-wavelength anomalous dispersion X-ray crystal structure of this domain demonstrates that its N-terminal half is unstructured while its C-terminal half is helical; hence, we name it the flexible helical domain (FHD). Circular dichroism spectroscopy, double electron–electron resonance–electron paramagnetic resonance, and small-angle X-ray scattering (SAXS) analyses confirm that the FHD is partially disordered, even in the context of adjacent BECN1more » domains. Molecular dynamic simulations fitted to SAXS data indicate that the FHD transiently samples more helical conformations. FHD helicity increases in 2,2,2-trifluoroethanol, suggesting it may become more helical upon binding. Finally, cellular studies show that conserved FHD residues are required for starvation-induced autophagy. Thus, the FHD likely undergoes a binding-associated disorder-to-helix transition, and conserved residues critical for this interaction are essential for starvation-induced autophagy.« less

Large-N solution of the Sp(N) Heisenberg quantum antiferromagnet on the anisotropic triangular lattice in a magnetic field.

NASA Astrophysics Data System (ADS)

Chung, Chung-Hou; Marston, Brad

2002-03-01

We study the Sp(N) generalization of the physical Sp(1) \\cong SU(2) Heisenberg antiferromagnet on the anisotropic triangular lattice( C. H. Chung, J. B. Marston and R. H. McKenzie, Journal of Physics: Condensed Matter 13), 5159 (2001). in a magnetic field. The model is relevant for describing recent experiments on the magnetic phases of the quasi-2D system Cs_2CuCl4 in a magnetic field(R. Coldea, D. A. Tennant, A. M. Tsvelik, and Z. Tylczynski, Phys. Rev. Lett. 86), 1335 (2001).. We solve the model in the large-N limit and study the effect of a magnetic field on the incommensurate magnetic order. Below a critical field the spins form a ``cone'' of polarization, in apparent agreement with neutron scattering experiments when the magnetic field is oriented perpendicular to the lattice. The incommensuration increases with increasing field strength. Above the critical field the spins are fully polarized. We have difficulty treating Dzyaloshinskii-Moriya interactions which are believed to be important for in-plane fields.

Optimization of a simultaneous dual-isotope 201Tl/123I-MIBG myocardial SPECT imaging protocol with a CZT camera for trigger zone assessment after myocardial infarction for routine clinical settings: Are delayed acquisition and scatter correction necessary?

PubMed

D'estanque, Emmanuel; Hedon, Christophe; Lattuca, Benoît; Bourdon, Aurélie; Benkiran, Meriem; Verd, Aurélie; Roubille, François; Mariano-Goulart, Denis

2017-08-01

Dual-isotope 201 Tl/ 123 I-MIBG SPECT can assess trigger zones (dysfunctions in the autonomic nervous system located in areas of viable myocardium) that are substrate for ventricular arrhythmias after STEMI. This study evaluated the necessity of delayed acquisition and scatter correction for dual-isotope 201 Tl/ 123 I-MIBG SPECT studies with a CZT camera to identify trigger zones after revascularization in patients with STEMI in routine clinical settings. Sixty-nine patients were prospectively enrolled after revascularization to undergo 201 Tl/ 123 I-MIBG SPECT using a CZT camera (Discovery NM 530c, GE). The first acquisition was a single thallium study (before MIBG administration); the second and the third were early and late dual-isotope studies. We compared the scatter-uncorrected and scatter-corrected (TEW method) thallium studies with the results of magnetic resonance imaging or transthoracic echography (reference standard) to diagnose myocardial necrosis. Summed rest scores (SRS) were significantly higher in the delayed MIBG studies than the early MIBG studies. SRS and necrosis surface were significantly higher in the delayed thallium studies with scatter correction than without scatter correction, leading to less trigger zone diagnosis for the scatter-corrected studies. Compared with the scatter-uncorrected studies, the late thallium scatter-corrected studies provided the best diagnostic values for myocardial necrosis assessment. Delayed acquisitions and scatter-corrected dual-isotope 201 Tl/ 123 I-MIBG SPECT acquisitions provide an improved evaluation of trigger zones in routine clinical settings after revascularization for STEMI.

Data consistency-driven scatter kernel optimization for x-ray cone-beam CT

NASA Astrophysics Data System (ADS)

Kim, Changhwan; Park, Miran; Sung, Younghun; Lee, Jaehak; Choi, Jiyoung; Cho, Seungryong

2015-08-01

Accurate and efficient scatter correction is essential for acquisition of high-quality x-ray cone-beam CT (CBCT) images for various applications. This study was conducted to demonstrate the feasibility of using the data consistency condition (DCC) as a criterion for scatter kernel optimization in scatter deconvolution methods in CBCT. As in CBCT, data consistency in the mid-plane is primarily challenged by scatter, we utilized data consistency to confirm the degree of scatter correction and to steer the update in iterative kernel optimization. By means of the parallel-beam DCC via fan-parallel rebinning, we iteratively optimized the scatter kernel parameters, using a particle swarm optimization algorithm for its computational efficiency and excellent convergence. The proposed method was validated by a simulation study using the XCAT numerical phantom and also by experimental studies using the ACS head phantom and the pelvic part of the Rando phantom. The results showed that the proposed method can effectively improve the accuracy of deconvolution-based scatter correction. Quantitative assessments of image quality parameters such as contrast and structure similarity (SSIM) revealed that the optimally selected scatter kernel improves the contrast of scatter-free images by up to 99.5%, 94.4%, and 84.4%, and of the SSIM in an XCAT study, an ACS head phantom study, and a pelvis phantom study by up to 96.7%, 90.5%, and 87.8%, respectively. The proposed method can achieve accurate and efficient scatter correction from a single cone-beam scan without need of any auxiliary hardware or additional experimentation.

Investigating the ionosphere response to exhaust products of ``Progress'' cargo spacecraft engines on the basis of Irkutsk Incoherent Scatter Radar data

NASA Astrophysics Data System (ADS)

Shpynev, Boris; Alsatkin, Sergei; Khakhinov, Vitaliy; Lebedev, Valentin

2017-04-01

The FSUE Central Research Institute of Machine Building (TsNIIMash), Rocket and Space Corporation "Energia", and Institute of Solar-Terrestrial Physics of Siberian Branch of Russian Academy of Sciences (ISTP SB RAS) jointly conducted the active space experiment "Radar-Progress" in 2007-2015. During this experiment, we used the Irkutsk Incoherent Scatter Radar to study space-time characteristics of ionospheric disturbances generated by exhaust products of "Progress" cargo spacecraft engines. As the basic effect during exhaust product injection, we consider the formation of new centers for recombination of ambient ionospheric ions O+ on molecules of water and carbon dioxide. This produces an ionization "hole" in the region of injection. In nighttime conditions when the majority of experiments were performed, this hole was filled by hydrogen ions from the plasmasphere, thus the ion composition in the vicinity of the hole and incoherent scatter spectra were changed. For successful observation of the ionization hole dynamics, the critical factors are the degree of radar antenna diagram filling by exhaust products and the velocity of the thermospheric neutral wind, which makes exhaust gases move from the antenna diagram. These two factors lead to the poor repeatability of successful experiments. Successful experiments recorded a decrease in electron density up to 35 % in the hole that existed for 30 min. The lifetime of the region with high concentration of H+ ions can be as long as one hour.

Light fluence dosimetry in lung-simulating cavities

NASA Astrophysics Data System (ADS)

Zhu, Timothy C.; Kim, Michele M.; Padawer, Jonah; Dimofte, Andreea; Potasek, Mary; Beeson, Karl; Parilov, Evgueni

2018-02-01

Accurate light dosimery is critical to ensure consistent outcome for pleural photodynamic therapy (pPDT). Ellipsoid shaped cavities with different sizes surrounded by turbid medium are used to simulate the intracavity lung geometry. An isotropic light source is introduced and surrounded by turbid media. Direct measurements of light fluence rate were compared to Monte Carlo simulated values on the surface of the cavities for various optical properties. The primary component of the light was determined by measurements performed in air in the same geometry. The scattered component was found by submerging the air-filled cavity in scattering media (Intralipid) and absorbent media (ink). The light source was located centrally with the azimuthal angle, but placed in two locations (vertically centered and 2 cm below the center) for measurements. Light fluence rate was measured using isotropic detectors placed at various angles on the ellipsoid surface. The measurements and simulations show that the scattered dose is uniform along the surface of the intracavity ellipsoid geometries in turbid media. One can express the light fluence rate empirically as φ =4S/As*Rd/(1- Rd), where Rd is the diffuse reflectance, As is the surface area, and S is the source power. The measurements agree with this empirical formula to within an uncertainty of 10% for the range of optical properties studied. GPU voxel-based Monte-Carlo simulation is performed to compare with measured results. This empirical formula can be applied to arbitrary geometries, such as the pleural or intraperitoneal cavity.

ENDF/B-VIII.0: The 8 th Major Release of the Nuclear Reaction Data Library with CIELO-project Cross Sections, New Standards and Thermal Scattering Data

DOE PAGES

Brown, D. A.; Chadwick, M. B.; Capote, R.; ...

2018-02-01

We describe the new ENDF/B-VIII.0 evaluated nuclear reaction data library. ENDF/B-VIII.0 fully incorporates the new IAEA standards, includes improved thermal neutron scattering data and uses new evaluated data from the CIELO project for neutron reactions on 1H, 16O, 56Fe, 235U, 238U and 239Pu described in companion papers in the present issue of Nuclear Data Sheets. The evaluations benefit from recent experimental data obtained in the U.S. and Europe, and improvements in theory and simulation. Notable advances include updated evaluated data for light nuclei, structural materials, actinides, fission energy release, prompt fission neutron and γ-ray spectra, thermal neutron scattering data, andmore » charged-particle reactions. Integral validation testing is shown for a wide range of criticality, reaction rate, and neutron transmission benchmarks. In general, integral validation performance of the library is improved relative to the previous ENDF/B-VII.1 library.« less

Phase information contained in meter-scale SAR images

NASA Astrophysics Data System (ADS)

Datcu, Mihai; Schwarz, Gottfried; Soccorsi, Matteo; Chaabouni, Houda

2007-10-01

The properties of single look complex SAR satellite images have already been analyzed by many investigators. A common belief is that, apart from inverse SAR methods or polarimetric applications, no information can be gained from the phase of each pixel. This belief is based on the assumption that we obtain uniformly distributed random phases when a sufficient number of small-scale scatterers are mixed in each image pixel. However, the random phase assumption does no longer hold for typical high resolution urban remote sensing scenes, when a limited number of prominent human-made scatterers with near-regular shape and sub-meter size lead to correlated phase patterns. If the pixel size shrinks to a critical threshold of about 1 meter, the reflectance of built-up urban scenes becomes dominated by typical metal reflectors, corner-like structures, and multiple scattering. The resulting phases are hard to model, but one can try to classify a scene based on the phase characteristics of neighboring image pixels. We provide a "cooking recipe" of how to analyze existing phase patterns that extend over neighboring pixels.

On the evolution of cured voxel in bulk photopolymerization upon focused Gaussian laser exposure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhole, Kiran, E-mail: kirandipali@gmail.com; Gandhi, Prasanna; Kundu, T.

Unconstrained depth photopolymerization is emerging as a promising technique for fabrication of several polymer microstructures such as self propagating waveguides, 3D freeform structures by bulk lithography, and polymer nanoparticles by flash exposure. Experimental observations reveal governing physics beyond Beer Lambert's law and scattering effects. This paper seeks to model unconstrained depth photopolymerization using classical nonlinear Schrödinger equation coupled with transient diffusion phenomenon. The beam propagation part of the proposed model considers scattering effects induced due to spatial variation of the refractive index as a function of the beam intensity. The critical curing energy model is used to further predict profilemore » of polymerized voxel. Profiles of photopolymerized voxel simulated using proposed model are compared with the corresponding experimental results for several cases of exposure dose and duration. The comparison shows close match leading to conclusion that the experimentally observed deviation from Beer Lambert's law is indeed due to combined effect of diffusion of photoinitiator and scattering of light because of change in the refractive index.« less

Large Amplitude Whistler Waves and Electron Acceleration in the Earth's Radiation Belts: A Review of STEREO and Wind Observations

NASA Technical Reports Server (NTRS)

Cattell, Cynthia; Breneman, A.; Goetz, K.; Kellogg, P.; Kersten, K.; Wygant, J.; Wilson, L. B., III; Looper, Mark D.; Blake, J. Bernard; Roth, I.

2012-01-01

One of the critical problems for understanding the dynamics of Earth's radiation belts is determining the physical processes that energize and scatter relativistic electrons. We review measurements from the Wind/Waves and STEREO S/Waves waveform capture instruments of large amplitude whistler-mode waves. These observations have provided strong evidence that large amplitude (100s mV/m) whistler-mode waves are common during magnetically active periods. The large amplitude whistlers have characteristics that are different from typical chorus. They are usually nondispersive and obliquely propagating, with a large longitudinal electric field and significant parallel electric field. We will also review comparisons of STEREO and Wind wave observations with SAMPEX observations of electron microbursts. Simulations show that the waves can result in energization by many MeV and/or scattering by large angles during a single wave packet encounter due to coherent, nonlinear processes including trapping. The experimental observations combined with simulations suggest that quasilinear theoretical models of electron energization and scattering via small-amplitude waves, with timescales of hours to days, may be inadequate for understanding radiation belt dynamics.

Hole mobilities and the effective Hall factor in p-type GaAs

NASA Astrophysics Data System (ADS)

Wenzel, M.; Irmer, G.; Monecke, J.; Siegel, W.

1997-06-01

We prove the effective Hall factor in p-GaAs to be larger than values discussed in the literature up to now. The scattering rates for the relevant scattering mechanisms in p-GaAs have been recalculated after critical testing the existing models. These calculations allow to deduce theoretical drift and theoretical Hall mobilities as functions of temperature which can be compared with measured data. Theoretical Hall factors in the heavy and light hole bands and an effective Hall factor result. The calculated room temperature values of the drift mobility and of the effective Hall factor are 118 cm2/V s and 3.6, respectively. The fitted acoustic deformation potential E1=7.9 eV and the fitted optical coupling constant DK=1.24×1011 eV/m are close to values published before. It is shown that the measured strong dependence of the Hall mobility on the Hall concentration is not mainly caused by scattering by ionized impurities but by the dependence of the effective Hall factor on the hole concentration.

Sharp low-energy feature in single-particle spectra due to forward scattering in d-wave cuprate superconductors.

PubMed

Hong, Seung Hwan; Bok, Jin Mo; Zhang, Wentao; He, Junfeng; Zhou, X J; Varma, C M; Choi, Han-Yong

2014-08-01

There is an enormous interest in the renormalization of the quasiparticle (qp) dispersion relation of cuprate superconductors both below and above the critical temperature T_{c} because it enables the determination of the fluctuation spectrum to which the qp's are coupled. A remarkable discovery by angle-resolved photoemission spectroscopy (ARPES) is a sharp low-energy feature (LEF) in qp spectra well below the superconducting energy gap but with its energy increasing in proportion to T_{c} and its intensity increasing sharply below T_{c}. This unexpected feature needs to be reconciled with d-wave superconductivity. Here, we present a quantitative analysis of ARPES data from Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} (Bi2212) using Eliashberg equations to show that the qp scattering rate due to the forward scattering impurities far from the Cu-O planes is modified by the energy gap below T_{c} and shows up as the LEF. This is also a necessary step to analyze ARPES data to reveal the spectrum of fluctuations promoting superconductivity.

Measuring electron temperature in the extended corona

NASA Technical Reports Server (NTRS)

Hassler, Donald M.; Gardner, L. D.; Kohl, John L.

1992-01-01

A technique for measuring electron temperature in the extended corona from the line profile of the electron scattered component of coronal H I Ly alpha produced by Thomson scattering of chromospheric Ly alpha emission is discussed. Because of the high thermal velocity of electrons at coronal temperatures (approximately 6800 km/s at T(sub e) = 1,500,000 K) the effect of nonthermal velocities and solar wind flows on the electron velocity distribution are negligible. However, the low electron mass which is responsible for the high thermal velocity also results in a very wide profile (approximately equal to 50 A). This wide profile, together with an intensity that is three orders of magnitude weaker than the resonantly scattered component of Ly alpha makes the direct measurement of T(sub e) a challenging observational problem. An evaluation of this technique based on simulated measurements is presented and the subsequent instrumental requirements necessary to make a meaningful determination of the electron temperature are discussed. Estimates of uncertainties in the measured electron temperature are related to critical instrument parameters such as grating stray light suppression.

ENDF/B-VIII.0: The 8 th Major Release of the Nuclear Reaction Data Library with CIELO-project Cross Sections, New Standards and Thermal Scattering Data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, D. A.; Chadwick, M. B.; Capote, R.

We describe the new ENDF/B-VIII.0 evaluated nuclear reaction data library. ENDF/B-VIII.0 fully incorporates the new IAEA standards, includes improved thermal neutron scattering data and uses new evaluated data from the CIELO project for neutron reactions on 1H, 16O, 56Fe, 235U, 238U and 239Pu described in companion papers in the present issue of Nuclear Data Sheets. The evaluations benefit from recent experimental data obtained in the U.S. and Europe, and improvements in theory and simulation. Notable advances include updated evaluated data for light nuclei, structural materials, actinides, fission energy release, prompt fission neutron and γ-ray spectra, thermal neutron scattering data, andmore » charged-particle reactions. Integral validation testing is shown for a wide range of criticality, reaction rate, and neutron transmission benchmarks. In general, integral validation performance of the library is improved relative to the previous ENDF/B-VII.1 library.« less

Gray: a ray tracing-based Monte Carlo simulator for PET

NASA Astrophysics Data System (ADS)

Freese, David L.; Olcott, Peter D.; Buss, Samuel R.; Levin, Craig S.

2018-05-01

Monte Carlo simulation software plays a critical role in PET system design. Performing complex, repeated Monte Carlo simulations can be computationally prohibitive, as even a single simulation can require a large amount of time and a computing cluster to complete. Here we introduce Gray, a Monte Carlo simulation software for PET systems. Gray exploits ray tracing methods used in the computer graphics community to greatly accelerate simulations of PET systems with complex geometries. We demonstrate the implementation of models for positron range, annihilation acolinearity, photoelectric absorption, Compton scatter, and Rayleigh scatter. For validation, we simulate the GATE PET benchmark, and compare energy, distribution of hits, coincidences, and run time. We show a speedup using Gray, compared to GATE for the same simulation, while demonstrating nearly identical results. We additionally simulate the Siemens Biograph mCT system with both the NEMA NU-2 scatter phantom and sensitivity phantom. We estimate the total sensitivity within % when accounting for differences in peak NECR. We also estimate the peak NECR to be kcps, or within % of published experimental data. The activity concentration of the peak is also estimated within 1.3%.

Naturally tuned quantum critical point in the S =1 kagomé YCa3(VO) 3(BO3)4

NASA Astrophysics Data System (ADS)

Silverstein, Harlyn J.; Sinclair, Ryan; Sharma, Arzoo; Qiu, Yiming; Heinmaa, Ivo; Leitmäe, Alexander; Wiebe, Christopher R.; Stern, Raivo; Zhou, Haidong

2018-04-01

Although S =1 /2 kagomé systems have been intensely studied theoretically, and within the past decade been realized experimentally, much less is known about the S =1 analogs. While the theoretical ground state is still under debate, it has been found experimentally that S =1 kagomé systems either order at low temperatures or enter a spin glass state. In this work, YCa3(VO) 3(BO3)4 (YCVBO) is presented, with trivalent vanadium. Owing to its unusual crystal structure, the metal-metal bonding is highly connected along all three crystallographic directions, atypical of other kagomé materials. Using neutron scattering it is shown that YCVBO fails to order down to at least 50 mK and exhibits broad and dispersionless excitations. 11B NMR provides evidence of fluctuating spins at low temperatures while dc magnetization shows critical scaling that is also observed in systems near a quantum critical point such as Herbertsmithite, despite its insulating nature and S =1 magnetism. The evidence shown indicates that YCVBO is naturally tuned to be a quantum disordered magnet in the limit of T =0 K.

Self-assembled vertically aligned Au nanorod arrays for surface-enhanced Raman scattering (SERS) detection of Cannabinol

NASA Astrophysics Data System (ADS)

Milliken, Sarah; Fraser, Jeff; Poirier, Shawn; Hulse, John; Tay, Li-Lin

2018-05-01

Self-assembled multi-layered vertically aligned gold nanorod (AuNR) arrays have been fabricated by a simple preparation process that requires a balance between the particle concentration and the ionic strength of the solvent. An experimentally determined critical AuNR concentration of 2.0 nM and 50 mM NaCl produces well-ordered vertically aligned hexagonally close-packed AuNR arrays. We demonstrate surface treatment via UV Ozone cleaning of such samples to allow introduction of analyte molecules (benzenethiol and cannabinol) for effective surface enhanced Raman scattering detection. This is the first demonstration of the SERS analysis of cannabinol. This approach demonstrates a cost-effective, high-yield and simple fabrication route to SERS sensors with application in the screening for the cannabinoids.

Maximizing fluorescence collection efficiency in multiphoton microscopy

PubMed Central

Zinter, Joseph P.; Levene, Michael J.

2011-01-01

Understanding fluorescence propagation through a multiphoton microscope is of critical importance in designing high performance systems capable of deep tissue imaging. Optical models of a scattering tissue sample and the Olympus 20X 0.95NA microscope objective were used to simulate fluorescence propagation as a function of imaging depth for physiologically relevant scattering parameters. The spatio-angular distribution of fluorescence at the objective back aperture derived from these simulations was used to design a simple, maximally efficient post-objective fluorescence collection system. Monte Carlo simulations corroborated by data from experimental tissue phantoms demonstrate collection efficiency improvements of 50% – 90% over conventional, non-optimized fluorescence collection geometries at large imaging depths. Imaging performance was verified by imaging layer V neurons in mouse cortex to a depth of 850 μm. PMID:21934897

Comment on "Anomalous wave propagation in a one-dimensional acoustic metamaterial having simultaneously negative mass density and Young's modulus" [J. Acoust. Soc. Am. 132, 2887-2895 (2012)].

PubMed

Marston, Philip L

2014-03-01

The phase and group velocities of elastic guided waves are important in the physical interpretation of high frequency scattering by fluid-loaded elastic shells. Outside the context of scattering, those properties are also important for understanding the energy flow in acoustic metamaterials. In a recent investigation of acoustic metamaterials exhibiting anomalous wave propagation [J. Acoust. Soc. Am. 132, 2887-2895 (2012)] criticism of negative group velocity terminology was generalized to elastic waves guided on ordinary materials. Some context and justification for retaining the identification of negative group velocities associated with a type of backscattering enhancement for shells are explained here. The phase evolution direction is determined by the boundary conditions.

A study on scattering correction for γ-photon 3D imaging test method

NASA Astrophysics Data System (ADS)

Xiao, Hui; Zhao, Min; Liu, Jiantang; Chen, Hao

2018-03-01

A pair of 511KeV γ-photons is generated during a positron annihilation. Their directions differ by 180°. The moving path and energy information can be utilized to form the 3D imaging test method in industrial domain. However, the scattered γ-photons are the major factors influencing the imaging precision of the test method. This study proposes a γ-photon single scattering correction method from the perspective of spatial geometry. The method first determines possible scattering points when the scattered γ-photon pair hits the detector pair. The range of scattering angle can then be calculated according to the energy window. Finally, the number of scattered γ-photons denotes the attenuation of the total scattered γ-photons along its moving path. The corrected γ-photons are obtained by deducting the scattered γ-photons from the original ones. Two experiments are conducted to verify the effectiveness of the proposed scattering correction method. The results concluded that the proposed scattering correction method can efficiently correct scattered γ-photons and improve the test accuracy.

Numerical Studies of Scattering Properties of Leaves and Leaf Moisture Influences on the Scattering at Microwave Wavelengths

NASA Technical Reports Server (NTRS)

Lin, Bing; Hu, Yongxiang; Sun, Wenbo; Min, Qilong

2008-01-01

This study uses 3-dimensional finite difference time domain method to accurately calculate single-scattering properties of randomly orientated leaves and evaluate the influences of vegetation water content (VWC) on these properties at 19 and 37 GHz frequencies. The studied leaves are assumed to be thin elliptic disks with two different sizes and have various VWC values. Although the leaf moisture produces considerable absorption during scattering processes, the effective efficiencies of extinction and scattering of leaves still near-linearly increase with VWC. Calculated asymmetry factors and phase functions indicate that there are significant amounts of scattering at large scattering angles in microwave wavelengths, which provides good opportunities for off-nadir microwave remote sensing of forests. This study lays a basic foundation in future quantifications of the relations between satellite measurements and physical properties of vegetation canopies.

Scattering Of Nonplanar Acoustic Waves

NASA Technical Reports Server (NTRS)

Gillman, Judith M.; Farassat, F.; Myers, M. K.

1995-01-01

Report presents theoretical study of scattering of nonplanar acoustic waves by rigid bodies. Study performed as part of effort to develop means of predicting scattering, from aircraft fuselages, of noise made by rotating blades. Basic approach was to model acoustic scattering by use of boundary integral equation to solve equation by the Galerkin method.

Formation and structure of stable aggregates in binary diffusion-limited cluster-cluster aggregation processes

NASA Astrophysics Data System (ADS)

López-López, J. M.; Moncho-Jordá, A.; Schmitt, A.; Hidalgo-Álvarez, R.

2005-09-01

Binary diffusion-limited cluster-cluster aggregation processes are studied as a function of the relative concentration of the two species. Both, short and long time behaviors are investigated by means of three-dimensional off-lattice Brownian Dynamics simulations. At short aggregation times, the validity of the Hogg-Healy-Fuerstenau approximation is shown. At long times, a single large cluster containing all initial particles is found to be formed when the relative concentration of the minority particles lies above a critical value. Below that value, stable aggregates remain in the system. These stable aggregates are composed by a few minority particles that are highly covered by majority ones. Our off-lattice simulations reveal a value of approximately 0.15 for the critical relative concentration. A qualitative explanation scheme for the formation and growth of the stable aggregates is developed. The simulations also explain the phenomenon of monomer discrimination that was observed recently in single cluster light scattering experiments.

Viscoplastic fracture transition of a biopolymer gel.

PubMed

Frieberg, Bradley R; Garatsa, Ray-Shimry; Jones, Ronald L; Bachert, John O; Crawshaw, Benjamin; Liu, X Michael; Chan, Edwin P

2018-06-13

Physical gels are swollen polymer networks consisting of transient crosslink junctions associated with hydrogen or ionic bonds. Unlike covalently crosslinked gels, these physical crosslinks are reversible thus enabling these materials to display highly tunable and dynamic mechanical properties. In this work, we study the polymer composition effects on the fracture behavior of a gelatin gel, which is a thermoreversible biopolymer gel consisting of denatured collagen chains bridging physical network junctions formed from triple helices. Below the critical volume fraction for chain entanglement, which we confirm via neutron scattering measurements, we find that the fracture behavior is consistent with a viscoplastic type process characterized by hydrodynamic friction of individual polymer chains through the polymer mesh to show that the enhancement in fracture scales inversely with the squared of the mesh size of the gelatin gel network. Above this critical volume fraction, the fracture process can be described by the Lake-Thomas theory that considers fracture as a chain scission process due to chain entanglements.

Critical assessment of Pt surface energy - An atomistic study

NASA Astrophysics Data System (ADS)

Kim, Jin-Soo; Seol, Donghyuk; Lee, Byeong-Joo

2018-04-01

Despite the fact that surface energy is a fundamental quantity in understanding surface structure of nanoparticle, the results of experimental measurements and theoretical calculations for the surface energy of pure Pt show a wide range of scattering. It is necessary to further ensure the surface energy of Pt to find the equilibrium shape and atomic configuration in Pt bimetallic nanoparticles accurately. In this article, we critically assess and optimize the Pt surface energy using a semi-empirical atomistic approach based on the second nearest-neighbor modified embedded-atom method interatomic potential. That is, the interatomic potential of pure Pt was adjusted in a way that the surface segregation tendency in a wide range of Pt binary alloys is reproduced in accordance with experimental information. The final optimized Pt surface energy (mJ/m2) is 2036 for (100) surface, 2106 for (110) surface, and 1502 for (111) surface. The potential can be utilized to find the equilibrium shape and atomic configuration of Pt bimetallic nanoparticles more accurately.

An automated analysis workflow for optimization of force-field parameters using neutron scattering data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lynch, Vickie E.; Borreguero, Jose M.; Bhowmik, Debsindhu

Graphical abstract: - Highlights: • An automated workflow to optimize force-field parameters. • Used the workflow to optimize force-field parameter for a system containing nanodiamond and tRNA. • The mechanism relies on molecular dynamics simulation and neutron scattering experimental data. • The workflow can be generalized to any other experimental and simulation techniques. - Abstract: Large-scale simulations and data analysis are often required to explain neutron scattering experiments to establish a connection between the fundamental physics at the nanoscale and data probed by neutrons. However, to perform simulations at experimental conditions it is critical to use correct force-field (FF) parametersmore » which are unfortunately not available for most complex experimental systems. In this work, we have developed a workflow optimization technique to provide optimized FF parameters by comparing molecular dynamics (MD) to neutron scattering data. We describe the workflow in detail by using an example system consisting of tRNA and hydrophilic nanodiamonds in a deuterated water (D{sub 2}O) environment. Quasi-elastic neutron scattering (QENS) data show a faster motion of the tRNA in the presence of nanodiamond than without the ND. To compare the QENS and MD results quantitatively, a proper choice of FF parameters is necessary. We use an efficient workflow to optimize the FF parameters between the hydrophilic nanodiamond and water by comparing to the QENS data. Our results show that we can obtain accurate FF parameters by using this technique. The workflow can be generalized to other types of neutron data for FF optimization, such as vibrational spectroscopy and spin echo.« less

Relating Cirrus Cloud Properties to Observed Fluxes: A Critical Assessment.

NASA Astrophysics Data System (ADS)

Vogelmann, A. M.; Ackerman, T. P.

1995-12-01

The accuracy needed in cirrus cloud scattering and microphysical properties is quantified such that the radiative effect on climate can he determined. Our ability to compute and observe these properties to within needed accuracies is assessed, with the greatest attention given to those properties that most affect the fluxes.Model calculations indicate that computing net longwave fluxes at the surface to within ±5% requires that cloud temperature be known to within as little as ±3 K in cold climates for extinction optical depths greater than two. Such accuracy could be more difficult to obtain than that needed in the values of scattering parameters. For a baseline case (defined in text), computing net shortwave fluxes at the surface to within ±5% requires accuracies in cloud ice water content that, when the optical depth is greater than 1.25, are beyond the accuracies of current measurements. Similarly, surface shortwave flux computations require accuracies in the asymmetry parameter that are beyond our current abilities when the optical depth is greater than four. Unless simplifications are discovered, the scattering properties needed to compute cirrus cloud fluxes cannot be obtained explicitly with existing scattering algorithms because the range of crystal sizes is too great and crystal shapes are too varied to be treated computationally. Thus, bulk cirrus scattering properties might be better obtained by inverting cirrus cloud fluxes and radiances. Finally, typical aircraft broadband flux measurements are not sufficiently accurate to provide a convincing validation of calculations. In light of these findings we recommend a reexamination of the methodology used in field programs such as FIRE and suggest a complementary approach.

High-energy pp and pp-bar forward elastic scattering and total cross sections

DOE Office of Scientific and Technical Information (OSTI.GOV)

Block, M.M.; Cahn, R.N.

1985-04-01

The present status of elastic pp and pp-bar scattering in the high-energy domain is reviewed, with emphasis on the forward and near-forward regions. The experimental techniques for measuring sigma/sub tot/, rho, and B are discussed, emphasizing the importance of the region in which the nuclear and Coulomb scattering interfere. The impact-parameter representation is exploited to give simple didactic demonstrations of important rigorous theorems based on analyticity, and to illuminate the significance of the slope parameter B and the curvature parameter C. Models of elastic scattering are discussed, and a criterion for the onset of ''asymptopia'' is given. A critique ofmore » dispersion relations is presented. Simple analytic functions are used to fit simultaneously the real and imaginary parts of forward scattering amplitudes for both pp and pp-bar, obtained from experimental data for sigma/sub tot/ and rho. It is found that a good fit can be obtained using only five parameters (with a cross section rising as ln/sup 2/s), over the energy range 5 < ..sqrt..s < 62 GeV. The possibilities that (a) the cross section rises only as lns, (b) the cross section rises only locally as ln/sup 2/s, and eventually goes to a constant value, and (c) the cross-section difference between pp and pp-bar does not vanish as s..-->..infinity are examined critically. The nuclear slope parameters B are also fitted in a model-independent fashion. Examination of the fits reveals a new regularity of the pp-bar and the pp systems.« less

Conformal perturbation of off-critical correlators in the 3D Ising universality class

NASA Astrophysics Data System (ADS)

Caselle, M.; Costagliola, G.; Magnoli, N.

2016-07-01

Thanks to the impressive progress of conformal bootstrap methods we have now very precise estimates of both scaling dimensions and operator product expansion coefficients for several 3D universality classes. We show how to use this information to obtain similarly precise estimates for off-critical correlators using conformal perturbation. We discuss in particular the ⟨σ (r )σ (0 )⟩ , ⟨ɛ (r )ɛ (0 )⟩ and ⟨σ (r )ɛ (0 )⟩ two-point functions in the high and low temperature regimes of the 3D Ising model and evaluate the leading and next to leading terms in the s =trΔt expansion, where t is the reduced temperature. Our results for ⟨σ (r )σ (0 )⟩ agree both with Monte Carlo simulations and with a set of experimental estimates of the critical scattering function.

Critical current density and vortex pinning in tetragonal FeS 1 ₋ x Se x ( x = 0 , 0.06 )

DOE PAGES

Wang, Aifeng; Wu, Lijun; Ivanovski, V. N.; ...

2016-09-07

Here we report critical current density (J c) in tetragonal FeS single crystals, similar to iron-based superconductors with much higher superconducting critical temperatures (T c). The J c is enhanced three times by 6% Se doping. We observe scaling of the normalized vortex pinning force as a function of reduced field at all temperatures. Vortex pinning in FeS and FeS 0.94Se 0.06 shows contribution of core-normal surfacelike pinning. Lastly, reduced temperature dependence of J c indicates that dominant interaction of vortex cores and pinning centers is via scattering of charge carriers with reduced mean free path (δl), in contrast tomore » K xFe 2₋ySe 2 where spatial variations in T c (δT c) prevails.« less

Reduction of Raman scattering and fluorescence from anvils in high pressure Raman scattering

NASA Astrophysics Data System (ADS)

Dierker, S. B.; Aronson, M. C.

2018-05-01

We describe a new design and use of a high pressure anvil cell that significantly reduces the Raman scattering and fluorescence from the anvils in high pressure Raman scattering experiments. The approach is particularly useful in Raman scattering studies of opaque, weakly scattering samples. The effectiveness of the technique is illustrated with measurements of two-magnon Raman scattering in La2CuO4.

Quenching star formation with quasar outflows launched by trapped IR radiation

NASA Astrophysics Data System (ADS)

Costa, Tiago; Rosdahl, Joakim; Sijacki, Debora; Haehnelt, Martin G.

2018-06-01

We present cosmological radiation-hydrodynamic simulations, performed with the code RAMSES-RT, of radiatively-driven outflows in a massive quasar host halo at z = 6. Our simulations include both single- and multi-scattered radiation pressure on dust from a quasar and are compared against simulations performed with thermal feedback. For radiation pressure-driving, we show that there is a critical quasar luminosity above which a galactic outflow is launched, set by the equilibrium of gravitational and radiation forces. While this critical luminosity is unrealistically high in the single-scattering limit for plausible black hole masses, it is in line with a ≈ 3 × 10^9 M_⊙ black hole accreting at its Eddington limit, if infrared (IR) multi-scattering radiation pressure is included. The outflows are fast (v ≳ 1000 km s^{-1}) and strongly mass-loaded with peak mass outflow rates ≈ 10^3 - 10^4 M_⊙ yr^{-1}, but short-lived (< 10 Myr). Outflowing material is multi-phase, though predominantly composed of cool gas, forming via a thermal instability in the shocked swept-up component. Radiation pressure- and thermally-driven outflows both affect their host galaxies significantly, but in different, complementary ways. Thermally-driven outflows couple more efficiently to diffuse halo gas, generating more powerful, hotter and more volume-filling outflows. IR radiation, through its ability to penetrate dense gas via diffusion, is more efficient at ejecting gas from the bulge. The combination of gas ejection through outflows with internal pressurisation by trapped IR radiation leads to a complete shut down of star formation in the bulge. We hence argue that radiation pressure-driven feedback may be an important ingredient in regulating star formation in compact starbursts, especially during the quasar's `obscured' phase.

Development of a practical image-based scatter correction method for brain perfusion SPECT: comparison with the TEW method.

PubMed

Shidahara, Miho; Watabe, Hiroshi; Kim, Kyeong Min; Kato, Takashi; Kawatsu, Shoji; Kato, Rikio; Yoshimura, Kumiko; Iida, Hidehiro; Ito, Kengo

2005-10-01

An image-based scatter correction (IBSC) method was developed to convert scatter-uncorrected into scatter-corrected SPECT images. The purpose of this study was to validate this method by means of phantom simulations and human studies with 99mTc-labeled tracers, based on comparison with the conventional triple energy window (TEW) method. The IBSC method corrects scatter on the reconstructed image I(mub)AC with Chang's attenuation correction factor. The scatter component image is estimated by convolving I(mub)AC with a scatter function followed by multiplication with an image-based scatter fraction function. The IBSC method was evaluated with Monte Carlo simulations and 99mTc-ethyl cysteinate dimer SPECT human brain perfusion studies obtained from five volunteers. The image counts and contrast of the scatter-corrected images obtained by the IBSC and TEW methods were compared. Using data obtained from the simulations, the image counts and contrast of the scatter-corrected images obtained by the IBSC and TEW methods were found to be nearly identical for both gray and white matter. In human brain images, no significant differences in image contrast were observed between the IBSC and TEW methods. The IBSC method is a simple scatter correction technique feasible for use in clinical routine.

Modeling of high‐frequency seismic‐wave scattering and propagation using radiative transfer theory

USGS Publications Warehouse

Zeng, Yuehua

2017-01-01

This is a study of the nonisotropic scattering process based on radiative transfer theory and its application to the observation of the M 4.3 aftershock recording of the 2008 Wells earthquake sequence in Nevada. Given a wide range of recording distances from 29 to 320 km, the data provide a unique opportunity to discriminate scattering models based on their distance‐dependent behaviors. First, we develop a stable numerical procedure to simulate nonisotropic scattering waves based on the 3D nonisotropic scattering theory proposed by Sato (1995). By applying the simulation method to the inversion of M 4.3 Wells aftershock recordings, we find that a nonisotropic scattering model, dominated by forward scattering, provides the best fit to the observed high‐frequency direct S waves and S‐wave coda velocity envelopes. The scattering process is governed by a Gaussian autocorrelation function, suggesting a Gaussian random heterogeneous structure for the Nevada crust. The model successfully explains the common decay of seismic coda independent of source–station locations as a result of energy leaking from multiple strong forward scattering, instead of backscattering governed by the diffusion solution at large lapse times. The model also explains the pulse‐broadening effect in the high‐frequency direct and early arriving S waves, as other studies have found, and could be very important to applications of high‐frequency wave simulation in which scattering has a strong effect. We also find that regardless of its physical implications, the isotropic scattering model provides the same effective scattering coefficient and intrinsic attenuation estimates as the forward scattering model, suggesting that the isotropic scattering model is still a viable tool for the study of seismic scattering and intrinsic attenuation coefficients in the Earth.

Temperature-driven Phase Transformation in Y3Co: Neutron Scattering and DFT Studies

NASA Astrophysics Data System (ADS)

Podlesnyak, A.; Ehlers, G.; Cao, H.; Matsuda, M.; Frontzek, M.; Zaharko, O.; Kazantsev, V. A.; Gubkin, A. F.; Baranov, N. V.

2013-03-01

The effects of a crystal structure deformation due to subtle atomic displacements have attracted much attention because they can result in colossal changes of the electronic and magnetic properties of solids. The R3Co binary intermetallic systems exhibit a number of complicated phenomena, including field-induced magnetic phase transitions (R=Er, Ho, Tb), giant magnetoresistance (R=Dy), a substantial magnetocaloric effect (R=Gd) and superconductivity (R=La). Contrary to previous studies that defined the ground state crystal structure of the entire R3Co series as orthorhombic Pnma, we find that Y3Co undergoes a structural phase transition upon cooling around Tc 160K. Density functional theory calculations reveal a dynamical instability of the Pnma structure of Y3Co. Employing inelastic neutron scattering measurements we find a strong damping of the (00 ξ) acoustic phonon mode below the critical temperature Tc. We suggest that some other members of the R3Co series (or even all of them) have ground state crystal symmetry lower than reported Pnma. This raises a question about the true magnetic structures and hence the influence of magnetic properties of the entire R3Co series. The research at ORNL was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy.

Double vibrational collision-induced Raman scattering by SF{sub 6}-N{sub 2}: Beyond the point-polarizable molecule model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Verzhbitskiy, I. A.; Chrysos, M.; Kouzov, A. P.

2010-11-15

Collision-induced Raman bandshapes and zeroth-order spectral moments are calculated both for the depolarized spectrum and for the extremely weak isotropic spectrum of the SF{sub 6}({nu}{sub 1}) +N{sub 2}({nu}{sub 1}) double-Raman-scattering band. A critical comparison is made with experiments conducted recently by the authors [Phys. Rev. A 81, 012702 (2010); 81, 042705 (2010)]. The study of this transition, hitherto restricted to the model framework of two point-polarizable molecules, is now completed to incorporate effects beyond the point-molecule approximation. Whereas the extended model offers a few percent improvement in the depolarized spectrum, it reveals a huge 80% increase in the isotropic spectrummore » and its moment, owing essentially to the polarizability anisotropy of N{sub 2}. For both spectra, agreement between quantum-mechanical calculations and our experiments is found, provided that the best ab initio data for the (hyper)polarizability parameters are used. This refined study shows clearly the need to include all mechanisms and data to a high level of accuracy and allows one to decide between alternatives about difficult and controversial issues such as the intermolecular potential or the sensitive Hamaker force constants.« less

Numerical analysis of the Anderson localization

NASA Astrophysics Data System (ADS)

Markoš, P.

2006-10-01

The aim of this paper is to demonstrate, by simple numerical simulations, the main transport properties of disordered electron systems. These systems undergo the metal insulator transition when either Fermi energy crosses the mobility edge or the strength of the disorder increases over critical value. We study how disorder affects the energy spectrum and spatial distribution of electronic eigenstates in the diffusive and insulating regime, as well as in the critical region of the metal-insulator transition. Then, we introduce the transfer matrix and conductance, and we discuss how the quantum character of the electron propagation influences the transport properties of disordered samples. In the weakly disordered systems, the weak localization and anti-localization as well as the universal conductance fluctuation are numerically simulated and discussed. The localization in the one dimensional system is described and interpreted as a purely quantum effect. Statistical properties of the conductance in the critical and localized regimes are demonstrated. Special attention is given to the numerical study of the transport properties of the critical regime and to the numerical verification of the single parameter scaling theory of localization. Numerical data for the critical exponent in the orthogonal models in dimension 2 < d, ≤ 5 are compared with theoretical predictions. We argue that the discrepancy between the theory and numerical data is due to the absence of the self-averaging of transmission quantities. This complicates the analytical analysis of the disordered systems. Finally, theoretical methods of description of weakly disordered systems are explained and their possible generalization to the localized regime is discussed. Since we concentrate on the one-electron propagation at zero temperature, no effects of electron-electron interaction and incoherent scattering are discussed in the paper.

SU-D-206-07: CBCT Scatter Correction Based On Rotating Collimator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, G; Feng, Z; Yin, Y

2016-06-15

Purpose: Scatter correction in cone-beam computed tomography (CBCT) has obvious effect on the removal of image noise, the cup artifact and the increase of image contrast. Several methods using a beam blocker for the estimation and subtraction of scatter have been proposed. However, the inconvenience of mechanics and propensity to residual artifacts limited the further evolution of basic and clinical research. Here, we propose a rotating collimator-based approach, in conjunction with reconstruction based on a discrete Radon transform and Tchebichef moments algorithm, to correct scatter-induced artifacts. Methods: A rotating-collimator, comprising round tungsten alloy strips, was mounted on a linear actuator.more » The rotating-collimator is divided into 6 portions equally. The round strips space is evenly spaced on each portion but staggered between different portions. A step motor connected to the rotating collimator drove the blocker to around x-ray source during the CBCT acquisition. The CBCT reconstruction based on a discrete Radon transform and Tchebichef moments algorithm is performed. Experimental studies using water phantom and Catphan504 were carried out to evaluate the performance of the proposed scheme. Results: The proposed algorithm was tested on both the Monte Carlo simulation and actual experiments with the Catphan504 phantom. From the simulation result, the mean square error of the reconstruction error decreases from 16% to 1.18%, the cupping (τcup) from 14.005% to 0.66%, and the peak signal-to-noise ratio increase from 16.9594 to 31.45. From the actual experiments, the induced visual artifacts are significantly reduced. Conclusion: We conducted an experiment on CBCT imaging system with a rotating collimator to develop and optimize x-ray scatter control and reduction technique. The proposed method is attractive in applications where a high CBCT image quality is critical, for example, dose calculation in adaptive radiation therapy. We want to thank Dr. Lei Xing and Dr. Yong Yang in the Stanford University School of Medicine for this work. This work was jointly supported by NSFC (61471226), Natural Science Foundation for Distinguished Young Scholars of Shandong Province (JQ201516), and China Postdoctoral Science Foundation (2015T80739, 2014M551949).« less

Highlights of the Zeno Results from the USMP-2 Mission

NASA Technical Reports Server (NTRS)

Gammon, Robert W.; Shaumeyer, J. N.; Briggs, Matthew E.; Boukari, Hacene; Gent, David A.; Wilkinson, R. Allen

1995-01-01

The Zeno instrument, a High-precision, light-scattering spectrometer, was built to measure the decay rates of density fluctuations in xenon near its liquid-vapor critical point in the low-gravity environment of the U.S. Space Shuttle. Eliminating the severe density gradients created in a critical fluid by Earth's gravity, we were able to make measurements to within 100 microKelvin of the critical point. The instrument flew for fourteen days in March, 1994 on the Space Shuttle Columbia, STS-62 flight, as part of the very successful USMP-2 payload. We describe the instrument and document its performance on orbit, showing that it comfortably reached the desired 3 microKelvin temperature control of the sample. Locating the critical temperature of the sample on orbit was a scientific challenge; we discuss the advantages and short-comings of the two techniques we used. Finally we discuss problems encountered with making measurements of the turbidity of the sample, and close with the results of the measurement of the decay rates of the critical-point fluctuations.

Microstructure of Amorphous and Semi-Crystalline Polymers.

DTIC Science & Technology

1981-06-07

of these materials. Further, the occurrence of nodular structures is difficult to reconcile with the results of studies of small angle neutron ...scattering and small angle neutron scattering studies of the same materials. Based on the combined results of these studies , it is suggested that the nodular...relevance here were reviewed by Flory.’ In addition to these, the results of studies using small angle neutron scattering’ and wide angle X-ray scattering

A United Effort for Crystal Growth, Neutron Scattering, and X-ray Scattering Studies of Novel Correlated Electron Materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Young S.

2015-02-12

The research accomplishments during the award involved experimental studies of correlated electron systems and quantum magnetism. The techniques of crystal growth, neutron scattering, x-ray scattering, and thermodynamic & transport measurements were employed, and graduate students and postdoctoral research associates were trained in these techniques.

Damage Effects Identified By Scatter Evaluation Of Supersmooth Surfaces

NASA Astrophysics Data System (ADS)

Stowell, W. K.; Orazio, Fred D.

1983-12-01

The surface quality of optics used in an extremely sensitive laser instrument, such as a Ring Laser Gyro (RLG), is critical. This has led to the development of a Variable Angle Scatterometer at the Air Force Wright Aeronautical Laboratories at Wright-Patterson Air Force Base, which can detect low level light scatter from the high quality optics used in RLG's, without first overcoating with metals. With this instrument we have been able to identify damage effects that occur during the typical processing and handling of optics which cause wide variation in subsequent measurements depending on when, in the process, one takes data. These measurements indicate that techniques such as a Total Integrated Scatter (TIS) may be inadequate for standards on extremely low scatter optics because of the lack of sensitivity of the method on such surfaces. The general term for optical surfaces better than the lowest level of the scratch-dig standards has become "supersmooth", and is seen in technical literature as well as in advertising. A performance number, such as Bidirectional Radiation Distribution Function (BRDF), which can be measured from the uncoated optical surface by equipment such as the Variable Angle Scatterometer (VAS) is proposed as a method of generating better optical surface specifications. Data show that surfaces of average BRDF values near 10 parts per billion per steriadian (0.010 PPM/Sr) for 0-(301 = 0.5, are now possible and measurable.

Damage Effects Identified By Scatter Evaluation Of Supersmooth Surfaces

NASA Astrophysics Data System (ADS)

Stowell, W. K.

1984-10-01

The surface quality of optics used in an extremely sensitive laser instrument, such as a Ring Laser Gyro (RLG), is critical. This has led to the development of a Variable Angle Scatterometer at the Air Force Wright Aeronautical Laboratories at Wright-Patterson Air Force Base, which can detect low level light scatter from the high quality optics used in RLG's, without first overcoating with metals. With this instrument we have been able to identify damage effects that occur during the typical processing and handling of optics which cause wide variation in subsequent measurements depending on when, in the process, one takes data. These measurements indicate that techniques such as a Total Integrated Scatter (TIS) may be inadequate for standards on extremely low scatter optics because of the lack of sensitivity of the method on such surfaces. The general term for optical surfaces better than the lowest level of the scratch-dig standards has become "supersmooth", and is seen in technical literature as well as in advertising. A performance number, such as Bidirectional Radiation Distribution Function (BRDF), which can be measured from the uncoated optical surface by equipment such as the Variable Angle Scatterometer (VAS) is proposed as a method of generating better optical surface specifications. Data show that surfaces of average BRDF values near 10 parts per billion per steriadian (0.010 PPM/Sr) for 0-(301 = 0.5, are now possible and measurable.

Average-atom treatment of relaxation time in x-ray Thomson scattering from warm dense matter.

PubMed

Johnson, W R; Nilsen, J

2016-03-01

The influence of finite relaxation times on Thomson scattering from warm dense plasmas is examined within the framework of the average-atom approximation. Presently most calculations use the collision-free Lindhard dielectric function to evaluate the free-electron contribution to the Thomson cross section. In this work, we use the Mermin dielectric function, which includes relaxation time explicitly. The relaxation time is evaluated by treating the average atom as an impurity in a uniform electron gas and depends critically on the transport cross section. The calculated relaxation rates agree well with values inferred from the Ziman formula for the static conductivity and also with rates inferred from a fit to the frequency-dependent conductivity. Transport cross sections determined by the phase-shift analysis in the average-atom potential are compared with those evaluated in the commonly used Born approximation. The Born approximation converges to the exact cross sections at high energies; however, differences that occur at low energies lead to corresponding differences in relaxation rates. The relative importance of including relaxation time when modeling x-ray Thomson scattering spectra is examined by comparing calculations of the free-electron dynamic structure function for Thomson scattering using Lindhard and Mermin dielectric functions. Applications are given to warm dense Be plasmas, with temperatures ranging from 2 to 32 eV and densities ranging from 2 to 64 g/cc.

Comparison and validation of point spread models for imaging in natural waters.

PubMed

Hou, Weilin; Gray, Deric J; Weidemann, Alan D; Arnone, Robert A

2008-06-23

It is known that scattering by particulates within natural waters is the main cause of the blur in underwater images. Underwater images can be better restored or enhanced with knowledge of the point spread function (PSF) of the water. This will extend the performance range as well as the information retrieval from underwater electro-optical systems, which is critical in many civilian and military applications, including target and especially mine detection, search and rescue, and diver visibility. A better understanding of the physical process involved also helps to predict system performance and simulate it accurately on demand. The presented effort first reviews several PSF models, including the introduction of a semi-analytical PSF given optical properties of the medium, including scattering albedo, mean scattering angles and the optical range. The models under comparison include the empirical model of Duntley, a modified PSF model by Dolin et al, as well as the numerical integration of analytical forms from Wells, as a benchmark of theoretical results. For experimental results, in addition to that of Duntley, we validate the above models with measured point spread functions by applying field measured scattering properties with Monte Carlo simulations. Results from these comparisons suggest it is sufficient but necessary to have the three parameters listed above to model PSFs. The simplified approach introduced also provides adequate accuracy and flexibility for imaging applications, as shown by examples of restored underwater images.

Average-atom treatment of relaxation time in x-ray Thomson scattering from warm dense matter

DOE PAGES

Johnson, W. R.; Nilsen, J.

2016-03-14

Here, the influence of finite relaxation times on Thomson scattering from warm dense plasmas is examined within the framework of the average-atom approximation. Presently most calculations use the collision-free Lindhard dielectric function to evaluate the free-electron contribution to the Thomson cross section. In this work, we use the Mermin dielectric function, which includes relaxation time explicitly. The relaxation time is evaluated by treating the average atom as an impurity in a uniform electron gas and depends critically on the transport cross section. The calculated relaxation rates agree well with values inferred from the Ziman formula for the static conductivity andmore » also with rates inferred from a fit to the frequency-dependent conductivity. Transport cross sections determined by the phase-shift analysis in the average-atom potential are compared with those evaluated in the commonly used Born approximation. The Born approximation converges to the exact cross sections at high energies; however, differences that occur at low energies lead to corresponding differences in relaxation rates. The relative importance of including relaxation time when modeling x-ray Thomson scattering spectra is examined by comparing calculations of the free-electron dynamic structure function for Thomson scattering using Lindhard and Mermin dielectric functions. Applications are given to warm dense Be plasmas, with temperatures ranging from 2 to 32 eV and densities ranging from 2 to 64 g/cc.« less

The Physics of Hard Spheres Experiment on MSL-1: Required Measurements and Instrument Performance

NASA Technical Reports Server (NTRS)

Doherty, Michael P.; Lant, Christian T.; Ling, Jerri S.

1998-01-01

The Physics of HArd Spheres Experiment (PHaSE), one of NASA Lewis Research Center's first major light scattering experiments for microgravity research on complex fluids, flew on board the Space Shuttle's Microgravity Science Laboratory (MSL-1) in 1997. Using colloidal systems of various concentrations of micron-sized plastic spheres in a refractive index-matching fluid as test samples, illuminated by laser light during and after crystallization, investigations were conducted to measure the nucleation and growth rate of colloidal crystals as well as the structure, rheology, and dynamics of the equilibrium crystal. Together, these measurements support an enhanced understanding of the nature of the liquid-to-solid transition. Achievement of the science objectives required an accurate experimental determination of eight fundamental properties for the hard sphere colloidal samples. The instrument design met almost all of the original measurement requirements, but with compromise on the number of samples on which data were taken. The instrument performs 2-D Bragg and low angle scattering from 0.4 deg. to 60 deg., dynamic and single-channel static scattering from 10 deg. to 170 deg., rheology using fiber optics, and white light imaging of the sample. As a result, PHaSE provided a timely microgravity demonstration of critical light scattering measurement techniques and hardware concepts, while generating data already showing promise of interesting new scientific findings in the field of condensed matter physics.

Neutron elastic and inelastic cross section measurements for 28Si

NASA Astrophysics Data System (ADS)

Derdeyn, E. C.; Lyons, E. M.; Morin, T.; Hicks, S. F.; Vanhoy, J. R.; Peters, E. E.; Ramirez, A. P. D.; McEllistrem, M. T.; Mukhopadhyay, S.; Yates, S. W.

2017-09-01

Neutron elastic and inelastic cross sections are critical for design and implementation of nuclear reactors and reactor equipment. Silicon, an element used abundantly in fuel pellets as well as building materials, has little to no experimental cross sections in the fast neutron region to support current theoretical evaluations, and thus would benefit from any contribution. Measurements of neutron elastic and inelastic differential scattering cross sections for 28Si were performed at the University of Kentucky Accelerator Laboratory for incident neutron energies of 6.1 MeV and 7.0 MeV. Neutrons were produced by accelerated deuterons incident on a deuterium gas cell. These nearly mono-energetic neutrons then scattered off a natural Si sample and were detected using liquid deuterated benzene scintillation detectors. Scattered neutron energy was deduced using time-of-flight techniques in tandem with kinematic calculations for an angular distribution. The relative detector efficiency was experimentally determined over a neutron energy range from approximately 0.5 to 7.75 MeV prior to the experiment. Yields were corrected for multiple scattering and neutron attenuation in the sample using the forced-collision Monte Carlo correction code MULCAT. Resulting cross sections will be presented along with comparisons to various data evaluations. Research is supported by USDOE-NNSA-SSAP: NA0002931, NSF: PHY-1606890, and the Donald A. Cowan Physics Institute at the University of Dallas.

Local Criticality and non-Fermi Liquid Behavior in Heavy Fermions

NASA Astrophysics Data System (ADS)

Si, Qimiao

2002-03-01

Quantum criticality provides a means to understand the apparent non-Fermi liquid phenomena in strongly correlated metals. Heavy fermion metals have emerged as a prototype system; many of them explicitly display a magnetic QCP. Experiments have shown that the quantum critical behavior is much richer than expected. One surprise came from neutron scattering, which found that the spin dynamics is anomalous not only near the antiferromagnetic wavevectors but also essentially everywhere in the Brillouin zone. In this talk, I will review the experiments and describe our theoretical work on the subject [1,2,3]. The notion of "local criticality" will be introduced and will be argued to apply to the heavy fermions. Some broader implications of the results will also be discussed. [1] Q. Si, S. Rabello, K. Ingersent, and J. L. Smith, Nature 413, 804 (2001). [2] Q. Si, J. L. Smith and K. Ingersent, Int. Journ. Mod. Phys. B13, 2331 (1999). [3] J. L. Smith and Q. Si, Phys. Rev. B61, 5184 (2000).

Comparison of caprock pore networks which potentially will be impacted by carbon sequestration projects.

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCray, John; Navarre-Sitchler, Alexis; Mouzakis, Katherine

Injection of CO2 into underground rock formations can reduce atmospheric CO2 emissions. Caprocks present above potential storage formations are the main structural trap inhibiting CO2 from leaking into overlying aquifers or back to the Earth's surface. Dissolution and precipitation of caprock minerals resulting from reaction with CO2 may alter the pore network where many pores are of the micrometer to nanometer scale, thus altering the structural trapping potential of the caprock. However, the distribution, geometry and volume of pores at these scales are poorly characterized. In order to evaluate the overall risk of leakage of CO2 from storage formations, amore » first critical step is understanding the distribution and shape of pores in a variety of different caprocks. As the caprock is often comprised of mudstones, we analyzed samples from several mudstone formations with small angle neutron scattering (SANS) and high-resolution transmission electron microscopy (TEM) imaging to compare the pore networks. Mudstones were chosen from current or potential sites for carbon sequestration projects including the Marine Tuscaloosa Group, the Lower Tuscaloosa Group, the upper and lower shale members of the Kirtland Formation, and the Pennsylvanian Gothic shale. Expandable clay contents ranged from 10% to approximately 40% in the Gothic shale and Kirtland Formation, respectively. During SANS, neutrons effectively scatter from interfaces between materials with differing scattering length density (i.e., minerals and pores). The intensity of scattered neutrons, I(Q), where Q is the scattering vector, gives information about the volume and arrangement of pores in the sample. The slope of the scattering data when plotted as log I(Q) vs. log Q provides information about the fractality or geometry of the pore network. On such plots slopes from -2 to -3 represent mass fractals while slopes from -3 to -4 represent surface fractals. Scattering data showed surface fractal dimensions for the Kirtland formation and one sample from the Tuscaloosa formation close to 3, indicating very rough surfaces. In contrast, scattering data for the Gothic shale formation exhibited mass fractal behavior. In one sample of the Tuscaloosa formation the data are described by a surface fractal at low Q (larger pores) and a mass fractal at high Q (smaller pores), indicating two pore populations contributing to the scattering behavior. These small angle neutron scattering results, combined with high-resolution TEM imaging, provided a means for both qualitative and quantitative analysis of the differences in pore networks between these various mudstones.« less

Multi-beam effects on backscatter and its saturation in experiments with conditions relevant to ignition

DOE PAGES

Kirkwood, R. K.; Michel, P.; London, R.; ...

2011-05-26

To optimize the coupling to indirect drive targets in the National Ignition Campaign (NIC) at the National Ignition Facility, a model of stimulated scattering produced by multiple laser beams is used. The model has shown that scatter of the 351 nm beams can be significantly enhanced over single beam predictions in ignition relevant targets by the interaction of the multiple crossing beams with a millimeter scale length, 2.5 keV, 0.02 - 0.05 x critical density, plasma. The model uses a suite of simulation capabilities and its key aspects are benchmarked with experiments at smaller laser facilities. The model has alsomore » influenced the design of the initial targets used for NIC by showing that both the stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) can be reduced by the reduction of the plasma density in the beam intersection volume that is caused by an increase in the diameter of the laser entrance hole (LEH). In this model, a linear wave response leads to a small gain exponent produced by each crossing quad of beams (<~1 per quad) which amplifies the scattering that originates in the target interior where the individual beams are separated and crosses many or all other beams near the LEH as it exits the target. As a result all 23 crossing quads of beams produce a total gain exponent of several or greater for seeds of light with wavelengths in the range that is expected for scattering from the interior (480 to 580 nm for SRS). This means that in the absence of wave saturation, the overall multi-beam scatter will be significantly larger than the expectations for single beams. The potential for non-linear saturation of the Langmuir waves amplifying SRS light is also analyzed with a two dimensional, vectorized, particle in cell code (2D VPIC) that is benchmarked by amplification experiments in a plasma with normalized parameters similar to ignition targets. The physics of cumulative scattering by multiple crossing beams that simultaneously amplify the same SBS light wave is further demonstrated in experiments that benchmark the linear models for the ion waves amplifying SBS. Here, the expectation from this model and its experimental benchmarks is shown to be consistent with observations of stimulated Raman scatter in the first series of energetic experiments with ignition targets, confirming the importance of the multi-beam scattering model for optimizing coupling.« less

Ultrastrong Coupling Few-Photon Scattering Theory

NASA Astrophysics Data System (ADS)

Shi, Tao; Chang, Yue; García-Ripoll, Juan José

2018-04-01

We study the scattering of individual photons by a two-level system ultrastrongly coupled to a waveguide. The scattering is elastic for a broad range of couplings and can be described with an effective U (1 )-symmetric Hamiltonian. This simple model allows the prediction of scattering resonance line shapes, validated up to α =0.3 , and close to the Toulouse point α =1 /2 , where inelastic scattering becomes relevant. Our predictions model experiments with superconducting circuits [P. Forn-Díaz et al., Nat. Phys. 13, 39 (2017), 10.1038/nphys3905] and can be extended to study multiphoton scattering.

Ultrastrong Coupling Few-Photon Scattering Theory.

PubMed

Shi, Tao; Chang, Yue; García-Ripoll, Juan José

2018-04-13

We study the scattering of individual photons by a two-level system ultrastrongly coupled to a waveguide. The scattering is elastic for a broad range of couplings and can be described with an effective U(1)-symmetric Hamiltonian. This simple model allows the prediction of scattering resonance line shapes, validated up to α=0.3, and close to the Toulouse point α=1/2, where inelastic scattering becomes relevant. Our predictions model experiments with superconducting circuits [P. Forn-Díaz et al., Nat. Phys. 13, 39 (2017)NPAHAX1745-247310.1038/nphys3905] and can be extended to study multiphoton scattering.

Optimization-based scatter estimation using primary modulation for computed tomography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Yi; Ma, Jingchen; Zhao, Jun, E-mail: junzhao

Purpose: Scatter reduces the image quality in computed tomography (CT), but scatter correction remains a challenge. A previously proposed primary modulation method simultaneously obtains the primary and scatter in a single scan. However, separating the scatter and primary in primary modulation is challenging because it is an underdetermined problem. In this study, an optimization-based scatter estimation (OSE) algorithm is proposed to estimate and correct scatter. Methods: In the concept of primary modulation, the primary is modulated, but the scatter remains smooth by inserting a modulator between the x-ray source and the object. In the proposed algorithm, an objective function ismore » designed for separating the scatter and primary. Prior knowledge is incorporated in the optimization-based framework to improve the accuracy of the estimation: (1) the primary is always positive; (2) the primary is locally smooth and the scatter is smooth; (3) the location of penumbra can be determined; and (4) the scatter-contaminated data provide knowledge about which part is smooth. Results: The simulation study shows that the edge-preserving weighting in OSE improves the estimation accuracy near the object boundary. Simulation study also demonstrates that OSE outperforms the two existing primary modulation algorithms for most regions of interest in terms of the CT number accuracy and noise. The proposed method was tested on a clinical cone beam CT, demonstrating that OSE corrects the scatter even when the modulator is not accurately registered. Conclusions: The proposed OSE algorithm improves the robustness and accuracy in scatter estimation and correction. This method is promising for scatter correction of various kinds of x-ray imaging modalities, such as x-ray radiography, cone beam CT, and the fourth-generation CT.« less

Radar cross section studies/compact range research

NASA Technical Reports Server (NTRS)

Burnside, W. D.; Dominek, A. K.; Gupta, I. J.; Newman, E. H.; Pathak, P. H.; Peters, L., Jr.

1989-01-01

Achievements in advancing the state-of-the-art in the measurement, control, and analysis of electromagnetic scattering from general aerodynamic targets are summarized. The major topics associated with this study include: (1) electromagnetic scattering analysis; (2) indoor scattering measurement systems; (3) RCS control; (4) waveform processing techniques; (5) material scattering and design studies; (6) design and evaluation of standard targets; and (7) antenna studies. Progress in each of these areas is reported and related publications are listed.

Inferring total canopy APAR from PAR bidirectional reflectances and vegetation indices in tallgrass prairie. [Absorbed Photosynthetically Active Radiation

NASA Technical Reports Server (NTRS)

Middleton, Elizabeth M.

1992-01-01

The fraction of photosynthetically active radiation (PAR) absorbed by a vegetated canopy (APARc) or landscape (APARs) is a critical parameter in climate processes. A grassland study examined: 1) whether APARs can be estimated from PAR bidirectional exitance fractions; and 2) whether APARs is correlated with spectral vegetation indices (SVIs). Data were acquired with a high resolution continuous spectroradiometer at 4 sun angles on grassland sites. APARs was computed from the scattered surface PAR exitance fractions. The nadir APARs value was the most variable diurnally; it provided a good estimate of the average surface APARs at 95 percent. APARc was best represented by exitance factors between 30-60* forward.

Temporal-spatial measurement of electron relaxation time in femtosecond laser induced plasma using two-color pump-probe imaging technique

NASA Astrophysics Data System (ADS)

Pan, Changji; Jiang, Lan; Wang, Qingsong; Sun, Jingya; Wang, Guoyan; Lu, Yongfeng

2018-05-01

The femtosecond (fs) laser is a powerful tool to study ultrafast plasma dynamics, especially electron relaxation in strong ionization of dielectrics. Herein, temporal-spatial evolution of femtosecond laser induced plasma in fused silica was investigated using a two-color pump-probe technique (i.e., 400 nm and 800 nm, respectively). We demonstrated that when ionized electron density is lower than the critical density, free electron relaxation time is inversely proportional to electron density, which can be explained by the electron-ion scattering regime. In addition, electron density evolution within plasma was analyzed in an early stage (first 800 fs) of the laser-material interaction.

Two-plasmon decay instability in inhomogeneous plasmas at oblique laser incidence

DOE PAGES

Wen, H.; Maximov, A. V.; Short, R. W.; ...

2016-09-30

The two-plasmon decay (TPD) and stimulated Raman scattering (SRS) instabilities have been studied in the region near the quarter-critical density in the plasmas of the laser-driven inertial confinement fusion for a wide range of laser angles of incidence. The theoretical analysis of the TPD for oblique laser incidence has been carried out. The theoretical growth rates and thresholds have been compared with the results of the fluid-type simulations, and a good agreement has been found. Here, in the modeling including both TPD and SRS, the spectra of the growing perturbations have multiple peaks, and the maximum growth may be influencedmore » by the interplay between TPD and SRS.« less

The Lamb wave bandgap variation of a locally resonant phononic crystal subjected to thermal deformation

NASA Astrophysics Data System (ADS)

Zhu, Yun; Li, Zhen; Li, Yue-ming

2018-05-01

A study on dynamical characteristics of a ternary locally resonant phononic crystal (PC) plate (i.e., hard scatterer with soft coating periodically disperse in stiff host matrix) is carried out in this paper. The effect of thermal deformation on the structure stiffness, which plays an important role in the PC's dynamical characteristics, is considered. Results show that both the start and the stop frequency of bandgap shift to higher range with the thermal deformation. In particular, the characteristics of band structure change suddenly at critical buckling temperature. The effect of thermal deformation could be utilized for tuning of phononic band structures, which can promote their design and further applications.

Low-dimensional ordering and fluctuations in methanol-{beta}-hydroquinone clathrate studied by x-ray and neutron diffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rheinstaedter, Maikel C.; Enderle, Mechthild; Kloepperpieper, Axel

2005-01-01

Methanol-{beta}-hydroquinone clathrate has been established as a model system for dielectric ordering and fluctuations and is conceptually close to magnetic spin systems. In x-ray and neutron diffraction experiments, we investigated the ordered structure, the one-dimensional (1D) and the three-dimensional critical scattering in the paraelectric phase, and the temperature dependence of the lattice constants. Our results can be explained by microscopic models of the methanol pseudospin in the hydroquinone cage network, in consistency with previous dielectric investigations. A coupling of the 1D fluctuations to local strains leads to an anomalous temperature dependence of the 1D lattice parameter in the paraelectric regime.

Doping dependence of low-energy quasiparticle excitations in superconducting Bi2212

PubMed Central

2013-01-01

The doping-dependent evolution of the d-wave superconducting state is studied from the perspective of the angle-resolved photoemission spectra of a high-Tc cuprate, Bi2Sr2CaCu2 O8+δ (Bi2212). The anisotropic evolution of the energy gap for Bogoliubov quasiparticles is parametrized by critical temperature and superfluid density. The renormalization of nodal quasiparticles is evaluated in terms of mass enhancement spectra. These quantities shed light on the strong coupling nature of electron pairing and the impact of forward elastic or inelastic scatterings. We suggest that the quasiparticle excitations in the superconducting cuprates are profoundly affected by doping-dependent screening. PMID:24314035

Charge-transport anisotropy in black phosphorus: critical dependence on the number of layers.

PubMed

Banerjee, Swastika; Pati, Swapan K

2016-06-28

Phosphorene is a promising candidate for modern electronics because of the anisotropy associated with high electron-hole mobility. Additionally, superior mechanical flexibility allows the strain-engineering of various properties including the transport of charge carriers in phosphorene. In this work, we have shown the criticality of the number of layers to dictate the transport properties of black phosphorus. Trilayer black phosphorus (TBP) has been proposed as an excellent anisotropic material, based on the transport parameters using Boltzmann transport formalisms coupled with density functional theory. The mobilities of both the electron and the hole are found to be higher along the zigzag direction (∼10(4) cm(2) V(-1) s(-1) at 300 K) compared to the armchair direction (∼10(2) cm(2) V(-1) s(-1)), resulting in the intrinsic directional anisotropy. Application of strain leads to additional electron-hole anisotropy with 10(3) fold higher mobility for the electron compared to the hole. Critical strain for maximum anisotropic response has also been determined. Whether the transport anisotropy is due to the spatial or charge-carrier has been determined through analyses of the scattering process of electrons and holes, and their recombination as well as relaxation dynamics. In this context, we have derived two descriptors (S and F(k)), which are general enough for any 2D or quasi-2D systems. Information on the scattering involving purely the carrier states also helps to understand the layer-dependent photoluminescence and electron (hole) relaxation in black phosphorus. Finally, we justify trilayer black phosphorus (TBP) as the material of interest with excellent transport properties.

Coherent Multiple Light Scattering in Ultracold Atomic Rb

NASA Astrophysics Data System (ADS)

Kulatunga, Pasad; Sukenik, C. I.; Balik, Salim; Havey, M. D.; Kupriyanov, D. V.; Sokolov, I. M.

2003-05-01

Wave transport in mesoscopic systems can be strongly influenced by coherent multiple scattering,which can lead to novel magneto-optic, transmission, and backscattering effects of light in atomic vapors. Although related to traditional studies of radiation trapping, in ultracold vapors negligible frequency or phase redistribution takes place in the scattering, and high-order coherent light scattering occurs. Among other things, this leads to enhancement of the influence of otherwise small non-resonant terms in the scattering amplitudes. We report investigation of multiple coherent light scattering from ultracold Rb atoms confined in a magneto-optic trap (MOT). In experimental studies, measurements are made of the angular, spectral, and polarization-dependent coherent backscattering profile of a low-intensity probe beam tuned near the F = 3 - F' = 4 hyperfine transition. The influence of higher probe beam intensity is also studied. In a theoretical study of angular intensity enhancement of backscattered light, we consider scattering orders up to 10 and a realistic and asymmetric Gaussian atom distribution in the MOT. Supported by NSF, NATO, and RFBR.

Cement-based materials' characterization using ultrasonic attenuation

NASA Astrophysics Data System (ADS)

Punurai, Wonsiri

The quantitative nondestructive evaluation (NDE) of cement-based materials is a critical area of research that is leading to advances in the health monitoring and condition assessment of the civil infrastructure. Ultrasonic NDE has been implemented with varying levels of success to characterize cement-based materials with complex microstructure and damage. A major issue with the application of ultrasonic techniques to characterize cement-based materials is their inherent inhomogeneity at multiple length scales. Ultrasonic waves propagating in these materials exhibit a high degree of attenuation losses, making quantitative interpretations difficult. Physically, these attenuation losses are a combination of internal friction in a viscoelastic material (ultrasonic absorption), and the scattering losses due to the material heterogeneity. The objective of this research is to use ultrasonic attenuation to characterize the microstructure of heterogeneous cement-based materials. The study considers a real, but simplified cement-based material, cement paste---a common bonding matrix of all cement-based composites. Cement paste consists of Portland cement and water but does not include aggregates. First, this research presents the findings of a theoretical study that uses a set of existing acoustics models to quantify the scattered ultrasonic wavefield from a known distribution of entrained air voids. These attenuation results are then coupled with experimental measurements to develop an inversion procedure that directly predicts the size and volume fraction of entrained air voids in a cement paste specimen. Optical studies verify the accuracy of the proposed inversion scheme. These results demonstrate the effectiveness of using attenuation to measure the average size, volume fraction of entrained air voids and the existence of additional larger entrapped air voids in hardened cement paste. Finally, coherent and diffuse ultrasonic waves are used to develop a direct relationship between attenuation and water to cement (w/c) ratio. A phenomenological model based on the existence of fluid-filled capillary voids is used to help explain the experimentally observed behavior. Overall this research shows the potential of using ultrasonic attenuation to quantitatively characterize cement paste. The absorption and scattering losses can be related to the individual microstructural elements of hardened cement paste. By taking a fundamental, mechanics-based approach, it should be possible to add additional components such as scattering by aggregates or even microcracks in a systematic fashion and eventually build a realistic model for ultrasonic wave propagation study for concrete.

Nucleation of Bubbles by Electrons in Liquid Helium-4

NASA Astrophysics Data System (ADS)

Yang, Y.; Sirisky, S.; Wei, W.; Seidel, G. M.; Maris, H. J.

2018-02-01

We report on experiments in which we study cavitation resulting from electrons in liquid helium. Electrons are introduced into the liquid by a radioactive source. After an electron comes to rest in the liquid, it forces open a small cavity referred to as an electron bubble. To study cavitation, a sound pulse is generated by means of a hemispherical piezoelectric transducer producing a large-amplitude pressure oscillation at the acoustic focus. If an electron is in the vicinity of the focus and the negative-going pressure swing exceeds a critical value, a cavitation bubble is produced which can be detected by light scattering. Two distinct critical pressures P_{el} and P_{rare} have been measured. The first corresponds to cavitation resulting from the application of a reduced pressure to liquid containing an electron which has already formed an electron bubble. The second is the critical pressure needed to lead to cavitation when an electron enters the liquid at a time and place where there is already a reduced pressure. We have measured these two pressures as a function of temperature and consider possible explanations for the difference between them. In addition to these clearly seen cavitation thresholds, there are some cavitation events that have been detected with a threshold that is at an even smaller negative pressure than P_{el} and P_{rare}.

Resonant soft X-ray scattering on protein solutions

NASA Astrophysics Data System (ADS)

Ye, Dan; Le, Thinh; Wang, Cheng; Zwart, Peter; Gomez, Esther; Gomez, Enrique

Protein structure is crucial for biological function, such that characterizing protein folding and packing is important for the design of therapeutics and enzymes. We propose resonant soft X-ray scattering (RSOXS) as an approach to study proteins and other biological assemblies in solution. Calculations of the scattering contrast suggest that soft X-ray scattering is more sensitive than hard X-ray scattering, because of contrast generated at the absorption edges of constituent elements such as carbon, nitrogen and oxygen. We have examined the structure of bovine serum albumin (BSA) in solution by RSOXS. We find that by varying incident X-ray energies, we are able to achieve higher scattering contrast near the absorption edge. From our RSOXS scattering result we are able to reconstruct the structure of BSA in 3D. These RSOXS results also agree with hard X-ray experiments, including crystallographic data. Our study demonstrates the potential of RSOXS for studying protein structure in solution.

Distinguishing Raman from strongly coupled Brillouin amplification for short pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jia, Qing; Barth, Ido; Edwards, Matthew R.

2016-05-15

Plasma-based amplification by strongly coupled Brillouin scattering has recently been suggested for the compression of a short seed laser to ultrahigh intensities in sub-quarter-critical-density plasmas. However, by employing detailed spectral analysis of particle-in-cell simulations in the same parameter regime, we demonstrate that, in fact, Raman backscattering amplification is responsible for the growth and compression of the high-intensity, leading spike, where most of the energy compression occurs, while the ion mode only affects the low-intensity tail of the amplified pulse. The critical role of the initial seed shape is identified. A number of subtleties in the numerical simulations are also pointedmore » out.« less

Polarized x-ray excitation for scatter reduction in x-ray fluorescence computed tomography.

PubMed

Vernekohl, Don; Tzoumas, Stratis; Zhao, Wei; Xing, Lei

2018-05-25

X-ray fluorescence computer tomography (XFCT) is a new molecular imaging modality which uses x-ray excitation to stimulate the emission of fluorescent photons in high atomic number contrast agents. Scatter contamination is one of the main challenges in XFCT imaging which limits the molecular sensitivity. When polarized x rays are used, it is possible to reduce the scatter contamination significantly by placing detectors perpendicular to the polarization direction. This study quantifies scatter contamination for polarized and unpolarized x-ray excitation and determines the advantages of scatter reduction. The amount of scatter in preclinical XFCT is quantified in Monte Carlo simulations. The fluorescent x rays are emitted isotropically, while scattered x rays propagate in polarization direction. The magnitude of scatter contamination is studied in XFCT simulations of a mouse phantom. In this study, the contrast agent gold is examined as an example, but a scatter reduction from polarized excitation is also expected for other elements. The scatter reduction capability is examined for different polarization intensities with a monoenergetic x-ray excitation energy of 82 keV. The study evaluates two different geometrical shapes of CZT detectors which are modeled with an energy resolution of 1 keV FWHM at an x-ray energy of 80 keV. Benefits of a detector placement perpendicular to the polarization direction are shown in iterative and analytic image reconstruction including scatter correction. The contrast to noise ratio (CNR) and the normalized mean square error (NMSE) are analyzed and compared for the reconstructed images. A substantial scatter reduction for common detector sizes was achieved for 100% and 80% linear polarization while lower polarization intensities provide a decreased scatter reduction. By placing the detector perpendicular to the polarization direction, a scatter reduction by factor up to 5.5 can be achieved for common detector sizes. The image reconstruction showed that for a scatter magnitude decrease by a factor of 2.4, the molecular sensitivity could almost be doubled. Scatter reduction lowers the amount of noise in the projection datasets and reconstructed images which enhance molecular sensitivity at equal dose. The results support the use of linear polarized x rays to reduce scatter in XFCT imaging. © 2018 American Association of Physicists in Medicine.

DARe: Dark Asteroid Rendezvous

NASA Technical Reports Server (NTRS)

Noll, K. S.; McFadden, L. A.; Rhoden, A. R.; Lim, L. F.; Boynton, W. V.; Carter, L. M.; Collins, G.; Englander, J. A.; Goossens, S. A.; Grundy, W. M.;

Channel Modelling and Performance of Non-Line-of-Sight Ultraviolet Scattering Communications

DTIC Science & Technology

2012-01-01

Avalanche photodiode (APD) detectors are also rapidly being developed [6, 7]. These device advances have inspired recent research in LED-based short...response and path loss results for outdoor NLOS UV communication channels in Section 3. The impulse response modelling describes UV pulse broadening via...Both the impulse response and path loss are critical to communication system design and performance assessment. Although pulse broadening creates inter

Cross Sections, relic abundance, and detection rates for neutralino dark matter

NASA Technical Reports Server (NTRS)

Griest, Kim

1988-01-01

Neutralino annihilation and elastic scattering cross sections are derived which differ in important ways from previous work. These are applied to relic abundance calculations and to direct detection of neutralino dark matter from the galactic halo. Assuming the neutralino to be the lightest supersymmetric particle and that it is less massive than the Z sup 0, we find relic densities of neutralinos greater than 4 percent of critical density for almost all values of the supersymmetric parameters. We constrain the parameter space by using results from PETRA (chargino mass less than 23 GeV) and ASP, and then assuming a critical density of neutralinos, display event rates in a cryogenic detector for a variety of models. A new term implies spin independent elastic scattering even for those majorana particles and inclusion of propagator momenta increases detection rates by 10 to 300 percent for pure photinos. Z sup 0-squark interference leads to very low detection rates for some values of the parameters. The new term in the elastic cross section dominates for heavy, mostly spinless materials and mitigates the negative interference cancellations in light materials; except for the pure photino or pure higgsinos cases where it does not contribute. In general, the rates can be substantially different from the pure photino and pure higgsino special cases usually considered.

Pedestrians' vulnerability in floodwaters: sensitivity to gender and age

NASA Astrophysics Data System (ADS)

Arrighi, Chiara; Castelli, Fabio

2017-04-01

Among the causes of fatalities during floods, the loss of stability is an aspect which has been usually investigated with conceptual models and laboratory experiments. The human body geometry has been often simplified to derive mechanical equilibrium conditions for toppling and sliding due to weight and hydrodynamic actions. Experimental activity produced water depth versus velocity diagrams showing the critical conditions for people partly immersed in floodwaters, whose scatter reflects the large variability of tested subjects (i.e. children, men and women with different physical characteristics). Nevertheless, the proposed hazard criteria based on the product number HV are not capable of distinguishing between different subjects. A dimensionless approach with a limited number of parameters and 3D numerical simulations highlight the significance of subject height and quantify the drag forces different subjects are able to withstand. From the mechanical point of view, this approach significantly reduces the experimental scatter. Differences in subjects' height are already an evidence of gender differences; however, many other parameters such as age and skeletal muscle mass may play a significant role in individual responses to floodwater actions, which can be responsible of the residual unexplained variance. In this work, a sensitivity analysis of critical instability conditions with respect to gender/age-related parameters is carried out and results and implications for flood risk management are discussed.

Structure and stabilizing interactions of casein micelles probed by high-pressure light scattering and FTIR.

PubMed

Gebhardt, Ronald; Takeda, Naohiro; Kulozik, Ulrich; Doster, Wolfgang

2011-03-17

Caseins form heterogeneous micelles composed of three types of disordered protein chains (α, β, κ), which include protein-bound calcium phosphate particles. We probe the stability limits of the micelle by applying hydrostatic pressure. The resulting changes of the size distribution and the average molecular weight are recorded in situ with static and dynamic light scattering. Pressure induces irreversible dissociation of the micelles into monomers above a critical value depending on their size. The critical pressure increases with temperature, pH, and calcium concentration due to the interplay of hydrophobic and electrostatic interactions. The pressure transition curves are biphasic, reflecting the equilibrium of two micelle states with different stability, average size, entropy, and calcium bound. The fast process of pressure dissociation is used to probe the slow equilibrium of the two micelle states under various conditions. Binding and release of β-casein from the micelle is suggested as the molecular mechanism of stabilization associated with the two states. In situ FTIR spectroscopy covering the P-O stretching region indicates that bound calcium phosphate particles are released from serine phosphate residues at pressures above 100 MPa. The resulting imbalance of charge triggers the complete decomposition of the micelle. © 2011 American Chemical Society

Thermoresponsive light scattering device utilizing surface behavior effects between polyimide and an ionic liquid-water mixture exhibiting lower critical solution temperature (LCST)-type phase separation

NASA Astrophysics Data System (ADS)

Goda, Kazuya; Takatoh, Kohki; Funasako, Yusuke; Inokuchi, Makoto

2018-06-01

We proposed a thermoresponsive light scattering device that utilizes the surface behavior between polyimide and an ionic liquid-water mixture exhibiting lower critical solution temperature (LCST)-type phase separation. The LCST behavior for an ionic liquid device utilizing the polyimide with and without alkyl side chains was investigated. In the here-reported ionic liquid device that utilized the polyimide with alkyl side chains, [nBu4P][CF3COO] droplets were generated by phase separation—they were predominantly formed at the alkyl surface by a surface pinning effect. A stable transmittance in the opaque state could be obtained with this device. In contrast, an ionic liquid device using polyimide without alkyl side chains deteriorated transmittance in the opaque state because there was no surface pinning effect. Additionally, the viewing angle, contrast ratio, and heat cycle testing of this ionic liquid device with polyimide with alkyl side chains were also investigated. The results indicated that no parallax was obtained and that the ionic liquid device has a stable transmittance (verified by heat cycle testing). This unique device is expected to find use in the smart window applications that are activated by temperature changes.

Micellar Self-Assembly of Recombinant Resilin-/Elastin-Like Block Copolypeptides.

PubMed

Weitzhandler, Isaac; Dzuricky, Michael; Hoffmann, Ingo; Garcia Quiroz, Felipe; Gradzielski, Michael; Chilkoti, Ashutosh

2017-08-14

Reported here is the synthesis of perfectly sequence defined, monodisperse diblock copolypeptides of hydrophilic elastin-like and hydrophobic resilin-like polypeptide blocks and characterization of their self-assembly as a function of structural parameters by light scattering, cryo-TEM, and small-angle neutron scattering. A subset of these diblock copolypeptides exhibit lower critical solution temperature and upper critical solution temperature phase behavior and self-assemble into spherical or cylindrical micelles. Their morphologies are dictated by their chain length, degree of hydrophilicity, and hydrophilic weight fraction of the ELP block. We find that (1) independent of the length of the corona-forming ELP block there is a minimum threshold in the length of the RLP block below which self-assembly does not occur, but that once that threshold is crossed, (2) the RLP block length is a unique molecular parameter to independently tune self-assembly and (3) increasing the hydrophobicity of the corona-forming ELP drives a transition from spherical to cylindrical morphology. Unlike the self-assembly of purely ELP-based block copolymers, the self-assembly of RLP-ELPs can be understood by simple principles of polymer physics relating hydrophilic weight fraction and polymer-polymer and polymer-solvent interactions to micellar morphology, which is important as it provides a route for the de novo design of desired nanoscale morphologies from first principles.

Influence of multiband sign-changing superconductivity on vortex cores and vortex pinning in stoichiometric high- T c   CaKFe 4 As 4

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fente, Anton; Meier, William R.; Kong, Tai

We use a scanning tunneling microscope to study the superconducting density of states and vortex lattice of single crystals of CaKFe 4As 4. This material has a critical temperature of T c = 35 K, one of the highest among stoichiometric iron based superconductors (FeBSCs), and is comparable to T c found near optimal doping in other FeBSCs. We observe quasiparticle scattering from defects with a pattern related to interband scattering between zone centered hole sheets. We measure the tunneling conductance in vortex cores and find a peak due to Caroli–de Gennes–Matricon bound states. The peak is located above themore » Fermi level, showing that CaKFe 4As 4 is a clean superconductor with vortex core bound states close to the so-called extreme quantum limit. We identify locations where the superconducting order parameter is strongly suppressed due to pair breaking. Vortices are pinned at these locations, and the length scale of the suppression of the order parameter is of order of the vortex core size. Finally, as a consequence, the vortex lattice is disordered up to 8 T.« less

Raman and fluorescence contributions to the resonant inelastic soft x-ray scattering on LaAlO3/SrTiO3 heterostructures

NASA Astrophysics Data System (ADS)

Pfaff, F.; Fujiwara, H.; Berner, G.; Yamasaki, A.; Niwa, H.; Kiuchi, H.; Gloskovskii, A.; Drube, W.; Gabel, J.; Kirilmaz, O.; Sekiyama, A.; Miyawaki, J.; Harada, Y.; Suga, S.; Sing, M.; Claessen, R.

2018-01-01

We present a detailed study of the Ti 3 d carriers at the interface of LaAlO3/SrTiO3 heterostructures by high-resolution resonant inelastic soft x-ray scattering (RIXS), with special focus on the roles of overlayer thickness and oxygen vacancies. Our measurements show the existence of interfacial Ti 3 d electrons already below the critical thickness for conductivity. The (total) interface charge carrier density increases up to a LaAlO3 overlayer thickness of 6 unit cells before it levels out. Furthermore, we observe strong Ti 3 d charge carrier doping by oxygen vacancies. The RIXS data combined with photoelectron spectroscopy and transport measurements indicate the simultaneous presence of localized and itinerant charge carriers. At variance with previous interpretations, we show that in our excitation energy dependent RIXS measurements the amounts of localized and itinerant Ti 3 d electrons in the ground state do not scale with the intensities of the Raman and fluorescence peaks, respectively. Rather, we attribute the observation of either Raman components or fluorescence signal to the specific nature of the intermediate state reached in the RIXS excitation process.

Property development for biaxial drawing of ethylene-tetrafluoroehtylene copolymer films and resultant fractural behavior analyzed by in situ X-ray measurements.

PubMed

Uehara, Hiroki; Ono, Yasunori; Kakiage, Masaki; Sakamura, Takumi; Masunaga, Hiroyasu; Yukawa, Yasumasa; Higuchi, Yoshiaki; Kamiya, Hiroki; Yamanobe, Takeshi

2015-03-19

The property development of the ethylene-tetrafluoroethylene copolymer (ETFE) membrane induced by simultaneous biaxial drawing was investigated. Commonly, tensile strength can be increased by drawing; conversely, tear resistance decreases. In this study, the balance between tensile strength and tear resistance for the resultant ETFE membrane was optimized achieved by a combination of lamination of low molecular weight (LMW) and high molecular weight (HMW) layers and subsequent biaxial drawing. The structural factor determining tear resistance of these biaxially drawn membranes was determined based on in situ small-angle X-ray scattering (SAXS) measurement during tensile deformation simulating tearing tests. Lozenge shaped scattering, which indicated inclined lamellae, was observed during such tensile deformation of the resultant membranes. Remarkably, this inclined lamellar structure was observed for the pure LMW membrane; however, it also appeared at the interface between LMW and HMW layers within biaxially drawn membranes. For the membrane exhibiting the highest tearing strength, the fraction of such inclined lamella increased up to the critical strain corresponding to the actual sample breaking. These results confirm that the inclined lamellar structure absorbed strain during membrane tearing.

Influence of multiband sign-changing superconductivity on vortex cores and vortex pinning in stoichiometric high- T c   CaKFe 4 As 4

DOE PAGES

Fente, Anton; Meier, William R.; Kong, Tai; ...

2018-04-02

We use a scanning tunneling microscope to study the superconducting density of states and vortex lattice of single crystals of CaKFe 4As 4. This material has a critical temperature of T c = 35 K, one of the highest among stoichiometric iron based superconductors (FeBSCs), and is comparable to T c found near optimal doping in other FeBSCs. We observe quasiparticle scattering from defects with a pattern related to interband scattering between zone centered hole sheets. We measure the tunneling conductance in vortex cores and find a peak due to Caroli–de Gennes–Matricon bound states. The peak is located above themore » Fermi level, showing that CaKFe 4As 4 is a clean superconductor with vortex core bound states close to the so-called extreme quantum limit. We identify locations where the superconducting order parameter is strongly suppressed due to pair breaking. Vortices are pinned at these locations, and the length scale of the suppression of the order parameter is of order of the vortex core size. Finally, as a consequence, the vortex lattice is disordered up to 8 T.« less

Light Absorption of Stratospheric Aerosols: Long-Term Trend and Contribution by Aircraft

NASA Technical Reports Server (NTRS)

Pueschel , R. F.; Gore, Waren J. Y. (Technical Monitor)

1997-01-01

Measurements of aerosol light-absorption coefficients are useful for studies of radiative transfer and heating rates. Ogren appears to have published the first light- absorption coefficients in the stratosphere in 1981, followed by Clarke in 1983 and Pueschel in 1992. Because most stratospheric soot appears to be due to aircraft operations, application of an aircraft soot aerosol emission index to projected fuel consumption suggests a threefold increase of soot loading and light absorption by 2025. Together, those four data sets indicate an increase in mid-visible light extinction at a rate of 6 % per year. This trend is similar to the increase per year of sulfuric acid aerosol and of commercial fleet size. The proportionality between stepped-up aircraft operations above the tropopause and increases in stratospheric soot and sulfuric acid aerosol implicate aircraft as a source of stratospheric pollution. Because the strongly light-absorbing soot and the predominantly light-scattering sulfuric acid aerosol increase at similar rates, however, the mid-visible stratospheric aerosol single scatter albedo is expected to remain constant and not approach a critical value of 0.98 at which stratospheric cooling could change to warming.

Influence of multiband sign-changing superconductivity on vortex cores and vortex pinning in stoichiometric high-Tc CaKFe4As4

NASA Astrophysics Data System (ADS)

Fente, Antón; Meier, William R.; Kong, Tai; Kogan, Vladimir G.; Bud'ko, Sergey L.; Canfield, Paul C.; Guillamón, Isabel; Suderow, Hermann

2018-04-01

We use a scanning tunneling microscope to study the superconducting density of states and vortex lattice of single crystals of CaKFe4As4 . This material has a critical temperature of Tc=35 K, one of the highest among stoichiometric iron based superconductors (FeBSCs), and is comparable to Tc found near optimal doping in other FeBSCs. We observe quasiparticle scattering from defects with a pattern related to interband scattering between zone centered hole sheets. We measure the tunneling conductance in vortex cores and find a peak due to Caroli-de Gennes-Matricon bound states. The peak is located above the Fermi level, showing that CaKFe4As4 is a clean superconductor with vortex core bound states close to the so-called extreme quantum limit. We identify locations where the superconducting order parameter is strongly suppressed due to pair breaking. Vortices are pinned at these locations, and the length scale of the suppression of the order parameter is of order of the vortex core size. As a consequence, the vortex lattice is disordered up to 8 T.

Structure and self-assembly properties of a new chitosan-based amphiphile.

PubMed

Huang, Yuping; Yu, Hailong; Guo, Liang; Huang, Qingrong

2010-06-17

A new chitosan-based amphiphile, octanoyl-chitosan-polyethylene glycol monomethyl ether (acylChitoMPEG), has been prepared using both hydrophobic octanoyl and hydrophilic polyethylene glycol monomethyl ether (MPEG) substitutions. The success of synthesis was confirmed by Fourier transform infrared (FT-IR) and (1)H NMR spectroscopy. The synthesized acylChitoMPEG exhibited good solubility in either aqueous solution or common organic solvents such as ethanol, acetone, and CHCl(3). The self-aggregation behavior of acylChitoMPEG in solutions was studied by a combination of pyrene fluorescence technique, dynamic light scattering, atomic force microscopy, and small-angle X-ray scattering (SAXS). The critical aggregation concentration (CAC) and hydrodynamic diameter were found to be 0.066 mg/mL and 24.4 nm, respectively. SAXS results suggested a coiled structure of the triple helical acylChitoMPEG backbone with the hydrophobic moieties hiding in the center of the backbone, and the hydrophilic MPEG chains surrounding the acylChitoMPEG backbone in a random Gaussian chain conformation. Cytotoxicity results showed that acylChitoMPEG exhibited negligible cytotoxicity even at concentrations as high as 1.0 mg/mL. All results implied that acylChitoMPEG has the potential to be used for biological or medical applications.

Molecular simulations of self-assembly processes of amphiphiles in dilute solutions: the challenge for quantitative modelling

NASA Astrophysics Data System (ADS)

Jusufi, Arben

2013-11-01

We report on two recent developments in molecular simulations of self-assembly processes of amphiphilic solutions. We focus on the determination of micelle formation of ionic surfactants which exhibit the archetype of self-assembling compounds in solution. The first approach is centred on the challenge in predicting micellisation properties through explicit solvent molecular dynamics simulations. Even with a coarse-grained (CG) approach and the use of highly optimised software packages run on graphics processing unit hardware, it remains in many cases computationally infeasible to directly extract the critical micelle concentration (cmc). However, combined with a recently presented theoretical mean-field model this task becomes resolved. An alternative approach to study self-assembly is through implicit solvent modelling of the surfactants. Here we review some latest results and present new ones regarding capabilities of such a modelling approach in determining the cmc, and the aggregate structures in the dilute regime, that is currently not accessible through explicit solvent simulations, neither through atomistic nor through CG approaches. A special focus is put on surfactant concentration effects and surfactant correlations quantified by scattering intensities that are compared to recently published small-angle X-ray scattering data.

Analytical calculation on the determination of steep side wall angles from far field measurements

NASA Astrophysics Data System (ADS)

Cisotto, Luca; Pereira, Silvania F.; Urbach, H. Paul

2018-06-01

In the semiconductor industry, the performance and capabilities of the lithographic process are evaluated by measuring specific structures. These structures are often gratings of which the shape is described by a few parameters such as period, middle critical dimension, height, and side wall angle (SWA). Upon direct measurement or retrieval of these parameters, the determination of the SWA suffers from considerable inaccuracies. Although the scattering effects that steep SWAs have on the illumination can be obtained with rigorous numerical simulations, analytical models constitute a very useful tool to get insights into the problem we are treating. In this paper, we develop an approach based on analytical calculations to describe the scattering of a cliff and a ridge with steep SWAs. We also propose a detection system to determine the SWAs of the structures.

Spectroscopic observations of nanosized TiO2 by the hydrothermal method

NASA Astrophysics Data System (ADS)

Zikriya, Mohamed; Nadaf, Y. F.; Bharathy, P. Vijai; Renuka, C. G.

2018-05-01

Metal oxides are useful materials that have various applications in advanced field such as, in view of their different properties, hardness, thermal dependability and compound resistance. Novel utilizations of the nanostructures of these oxides are drawing in critical enthusiasm as new preparation process are created and new structures are described. Hydrothermal synthesis is a fruitful procedure to prepare different sensitive structures of metal oxides on the scales from a couple to several nanometres, particularly, the hugely scattered middle structures which are hardly through pyro-preparation. Titanium dioxide nanocrystals are synthesis by a hydrolysis procedure of metatitanic acid. Nano precious crystal of different sizes is procure in the after calcinations from 150 to 225°C. Raman scattering was utilized to examine the advancement of the anatase stage in the nano crystal during calcinations.

Small influence of magnetic ordering on lattice dynamics in TaFe 1.25 Te 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Opačić, M.; Lazarević, N.; Tanasković, D.

2017-11-16

Raman scattering spectra of zigzag spin chain TaFe 1.25Te 3 single crystal are presented in a temperature range from 80 to 300 K. Nine Raman active modes of A g and B g symmetry are clearly observed and assigned by probing different scattering channels, which is confirmed by lattice dynamics calculations. Temperature dependence of the Raman modes linewidth is mainly governed by the lattice anharmonicity. The only deviation from the conventional behavior is observed for A g symmetry modes in a vicinity of the magnetic phase transition at T N ≈ 200 K. This implies that the electron-phonon interaction weaklymore » changes with temperature and magnetic ordering, whereas small changes in the spectra near the critical temperature can be ascribed to spin fluctuations.« less

Impact of Raman scattering on pulse dynamics in a fiber laser with narrow gain bandwidth

NASA Astrophysics Data System (ADS)

Uthayakumar, T.; Alsaleh, M.; Igbonacho, J.; Tchomgo Felenou, E.; Tchofo Dinda, P.; Grelu, Ph; Porsezian, K.

2018-06-01

We examine theoretically the multi-pulse dynamics in a dispersion-managed fiber laser, in which the pulse’s spectral width is controlled by a pass-band filter. We show that in the domain of stable states with very narrow spectral width, i.e. which is one order of magnitude smaller than the bandwidth of the Raman gain of the intra-cavity fiber system, the Raman scattering (RS) significantly alters the multi-pulse dynamics. RS is found to have a greater impact in the immediate vicinity of some critical values of the pump power of the intra-cavity gain medium, where processes of pulse fragmentation occur. As a result, all the borders between the zones of stability of the multi-pulse states are altered, i.e. either shifted or suppressed.

Self-assembled vertically aligned Au nanorod arrays for surface-enhanced Raman scattering (SERS) detection of Cannabinol.

PubMed

Milliken, Sarah; Fraser, Jeff; Poirier, Shawn; Hulse, John; Tay, Li-Lin

2018-05-05

Self-assembled multi-layered vertically aligned gold nanorod (AuNR) arrays have been fabricated by a simple preparation process that requires a balance between the particle concentration and the ionic strength of the solvent. An experimentally determined critical AuNR concentration of 2.0nM and 50mM NaCl produces well-ordered vertically aligned hexagonally close-packed AuNR arrays. We demonstrate surface treatment via UV Ozone cleaning of such samples to allow introduction of analyte molecules (benzenethiol and cannabinol) for effective surface enhanced Raman scattering detection. This is the first demonstration of the SERS analysis of cannabinol. This approach demonstrates a cost-effective, high-yield and simple fabrication route to SERS sensors with application in the screening for the cannabinoids. Copyright © 2018. Published by Elsevier B.V.

Inhibition and Promotion of Heat-Induced Gelation of Whey Proteins in the Presence of Calcium by Addition of Sodium Caseinate.

PubMed

Nguyen, Bach T; Balakrishnan, Gireeshkumar; Jacquette, Boris; Nicolai, Taco; Chassenieux, Christophe; Schmitt, Christophe; Bovetto, Lionel

2016-11-14

Heat-induced aggregation and gelation of aqueous solutions of whey protein isolate (WPI) in the presence of sodium caseinate (SC) and CaCl 2 was studied at pH 6.6. The effect of adding SC (0-100 g/L) on the structure of the aggregates and the gels was investigated by light scattering and confocal laser scanning microscopy at different CaCl 2 concentration ([CaCl 2 ] = 0-30 mM). The gelation process was studied by oscillatory shear rheology. At the whey protein concentrations studied here (34 and 60 g/L), no gels were formed in the absence of CaCl 2 and SC. However, WPI solutions gelled above a critical CaCl 2 concentration that increased with increasing SC concentration. In the absence of CaCl 2 , WPI gels were formed only above a critical SC concentration. The critical SC concentration needed to induce WPI gelation decreased weakly when CaCl 2 was added. In an intermediate range of CaCl 2 concentrations, gels were formed both at low and high SC concentrations, but not at intermediate SC concentrations. Finally, at high CaCl 2 concentrations gels were formed at all SC concentrations. The gelation rate and the gel structure of the gels formed at low and high casein concentrations were very different. The effect of SC on the thermal gelation of WPI was interpreted by competition for Ca 2+ , a chaperon effect, and microphase separation.

Scattering from fractals

NASA Astrophysics Data System (ADS)

Hurd, Alan J.

The realization that structures in Nature often can be described by Mandelbrot's fractals has led to a revolution in many areas of physics. The interaction of waves with fractal systems has, understandably, become intensely studied since scattering is the method of choice to probe delicate fractal structures such as chainlike particle aggregates. Not all of these waves are electromagnetic. Neutron scattering, for example, is an important complementary tool to structural studies by X-ray and light scattering. Since the phenomenology of small-angle neutron scattering (SANS), as it is applied to fractal systems, is identical to that of small-angle X-ray scattering (SAXS), it falls within the scope of this paper.

Acoustic behavior of Halobacterium salinarum gas vesicles in the high frequency range: experiments and modeling

PubMed Central

Cherin, Emmanuel; Melis, Johan M.; Bourdeau, Raymond W.; Yin, Melissa; Kochmann, Dennis M.; Foster, F. Stuart; Shapiro, Mikhail G.

2017-01-01

Gas vesicles are a new and unique class of biologically derived ultrasound contrast agents with sub-micron size whose acoustic properties have not been fully elucidated. In this study, we investigated the acoustic collapse pressure and behavior of Halobacterium salinarum gas vesicles at transmit center frequencies ranging from 12.5 to 27.5 MHz. The acoustic collapse pressure was found to be above 550 kPa at all frequencies, 9 fold higher than the critical pressure observed in hydrostatic conditions. We show that gas vesicles behave non-linearly when exposed to ultrasound at incident pressure ranging from 160 kPa to the collapse pressure, and generate second harmonic amplitudes of −2 to −6 dB below the fundamental in media with viscosities ranging from 0.89 to 8 mPa.s. Simulations performed using a Rayleigh-Plesset type model accounting for buckling, and a dynamic finite element analysis, suggest that buckling is the mechanism behind the generation of harmonics. We found good agreement between the level of second harmonic relative to the fundamental measured at 20 MHz and the Rayleigh-Plesset model predictions. Finite element simulations extended these findings to a non-spherical geometry, confirmed that the acoustic buckling pressure corresponds to the critical pressure in hydrostatic conditions, and support the hypothesis of limited gas flow across the GV shell during the compression phase in the frequency range investigated. From simulations, estimates of GV bandwidth-limited scattering indicate that a single GV has a scattering cross-section comparable to that of a red blood cell. These findings will inform the development of GV-based contrast agents and pulse sequences to optimize their detection with ultrasound. PMID:28258771

Modeling and Studying the Effect of Texture and Elastic Anisotropy of Copper Microstructure in Nanoscale Interconnects on Reliability in Integrated Circuits

NASA Astrophysics Data System (ADS)

Basavalingappa, Adarsh

Copper interconnects are typically polycrystalline and follow a lognormal grain size distribution. Polycrystalline copper interconnect microstructures with a lognormal grain size distribution were obtained with a Voronoi tessellation approach. The interconnect structures thus obtained were used to study grain growth mechanisms, grain boundary scattering, scattering dependent resistance of interconnects, stress evolution, vacancy migration, reliability life times, impact of orientation dependent anisotropy on various mechanisms, etc. In this work, the microstructures were used to study the impact of microstructure and elastic anisotropy of copper on thermal and electromigration induced failure. A test structure with copper and bulk moduli values was modeled to do a comparative study with the test structures with textured microstructure and elastic anisotropy. By subjecting the modeled test structure to a thermal stress by ramping temperature down from 400 °C to 100 °C, a significant variation in normal stresses and pressure were observed at the grain boundaries. This variation in normal stresses and hydrostatic stresses at the grain boundaries was found to be dependent on the orientation, dimensions, surroundings, and location of the grains. This may introduce new weak points within the metal line where normal stresses can be very high depending on the orientation of the grains leading to delamination and accumulation sites for vacancies. Further, the hydrostatic stress gradients act as a driving force for vacancy migration. The normal stresses can exceed certain grain orientation dependent critical threshold values and induce delamination at the copper and cap material interface, thereby leading to void nucleation and growth. Modeled test structures were subjected to a series of copper depositions at 250 °C followed by copper etch at 25 °C to obtain initial stress conditions. Then the modeled test structures were subjected to 100,000 hours ( 11.4 years) of simulated thermal stress at an elevated temperature of 150 °C. Vacancy migration due to concentration gradients, thermal gradients, and mechanical stress gradients were considered under the applied thermal stress. As a result, relatively high concentrations of vacancies were observed in the test structure due to a driving force caused by the pressure gradients resulting from the elastic anisotropy of copper. The grain growth mechanism was not considered in these simulations. Studies with two grain analysis demonstrated that the stress gradients developed will be severe when (100) grains are adjacent to (111) grains, therefore making them the weak points for potentially reliability failures. Ilan Blech discovered that electromigration occurs above a critical product of the current density and metal length, commonly referred as Blech condition. Electromigration stress simulations in this work were carried out by subjecting test structures to scaled current densities to overcome the Blech condition of (jL)crit for small dimensions of test structure and the low temperature stress condition used. Vacancy migration under the electromigration stress conditions was considered along with the vacancy migration induced stress evolution. A simple void growth model was used which assumes voids start to form when vacancies reach a critical level. Increase of vacancies in a localized region increases the resistance of the metal line. Considering a 10% increase in resistance as a failure criterion, the distributions of failure times were obtained for given electromigration stress conditions. Bimodal/multimodal failure distributions were obtained as a result. The sigma values were slightly lower than the ones commonly observed from experiments. The anisotropy of the elastic moduli of copper leads to the development of significantly different stress values which are dependent on the orientation of the grains. This results in some grains having higher normal stress than the others. This grain orientation dependent normal stress can reach a critical stress necessary to induce delamination at the copper and cap interface. Time taken to reach critical stress was considered as time to fail and distributions of failure times were obtained for structures with different grain orientations in the microstructure for different critical stress values. The sigma values of the failure distributions thus obtained for different constant critical stress values had a strong dependence of on the critical stress. It is therefore critical to use the appropriate critical stress value for the delamination of copper and cap interface. The critical stress necessary to overcome the local adhesion of the copper and the cap material interface is dependent on grain orientation of the copper. Simulations were carried out by considering grain orientation dependent critical normal stress values as failure criteria. The sigma value thus obtained with selected critical stress values were comparable to sigma values commonly observed from experiments.

A study of areas of low radio-thermal emissivity on Venus

NASA Astrophysics Data System (ADS)

Wilt, Robert Joseph

1992-01-01

Observations performed by the Magellan radiometer experiment have confirmed previous findings that a few regions on Venus, primarily at higher elevations, possess unexpectedly low values of radiothermal emissivity, occasionally reaching as low as 0.3. Values of emissivity below 0.7 occur over about 1.5 percent of the surface, and are associated with several types of features, including highlands, volcanoes, tectonically uplifted terrain, and impact craters. There is a strong correlation of low emissivity and high elevation, but rather than decreasing gradually with elevation, the emissivity drops rapidly in a small altitude range above a certain 'critical radius'. The altitude at which the change in emissive properties occurs varies from feature to feature; on average, it lies at a planetary radius of about 6054 km. Notable exceptions to the association of low emissivity and high elevation exist; for example, Lakshmi Planum, Maat Mons, and the summits of many volcanoes display high emissivities at high elevations, while in some impact craters and plains areas we find low emissivities at low elevations. Two possible explanations for low emissivities have been advanced: (1) emission from a highly reflective single interface between the atmosphere and a surface material having a bulk dielectric constant of order 80 ('high-dielectric' model); and (2) emission from the surface of a low-loss soil having a more usual permittivity (of order 2) which contains subsurface scatterers composed of ordinary rock materials ('volume scattering' model). Theoretical results and Monte Carlo simulations are used to show that the previously proposed volume scattering model cannot account for the observed emissivities; however, scattering from a material with very low loss (loss factor of order 10-3 or less) containing subsurface voids could produce the observed results. Consideration of the two models in light of the Magellan observations leads us to believe that the low emissivities on Venus result from the creation of a high-dielectic material by surface-atmosphere interaction, probably a loaded dielectric containing a conductive mineral.

Propagation of Gaussian wave packets in complex media and application to fracture characterization

NASA Astrophysics Data System (ADS)

Ding, Yinshuai; Zheng, Yingcai; Zhou, Hua-Wei; Howell, Michael; Hu, Hao; Zhang, Yu

2017-08-01

Knowledge of the subsurface fracture networks is critical in probing the tectonic stress states and flow of fluids in reservoirs containing fractures. We propose to characterize fractures using scattered seismic data, based on the theory of local plane-wave multiple scattering in a fractured medium. We construct a localized directional wave packet using point sources on the surface and propagate it toward the targeted subsurface fractures. The wave packet behaves as a local plane wave when interacting with the fractures. The interaction produces multiple scattering of the wave packet that eventually travels up to the surface receivers. The propagation direction and amplitude of the multiply scattered wave can be used to characterize fracture density, orientation and compliance. Two key aspects in this characterization process are the spatial localization and directionality of the wave packet. Here we first show the physical behaviour of a new localized wave, known as the Gaussian Wave Packet (GWP), by examining its analytical solution originally formulated for a homogenous medium. We then use a numerical finite-difference time-domain (FDTD) method to study its propagation behaviour in heterogeneous media. We find that a GWP can still be localized and directional in space even over a large propagation distance in heterogeneous media. We then propose a method to decompose the recorded seismic wavefield into GWPs based on the reverse-time concept. This method enables us to create a virtually recorded seismic data using field shot gathers, as if the source were an incident GWP. Finally, we demonstrate the feasibility of using GWPs for fracture characterization using three numerical examples. For a medium containing fractures, we can reliably invert for the local parameters of multiple fracture sets. Differing from conventional seismic imaging such as migration methods, our fracture characterization method is less sensitive to errors in the background velocity model. For a layered medium containing fractures, our method can correctly recover the fracture density even with an inaccurate velocity model.

Compactness and robustness: Applications in the solution of integral equations for chemical kinetics and electromagnetic scattering

NASA Astrophysics Data System (ADS)

Zhou, Yajun

This thesis employs the topological concept of compactness to deduce robust solutions to two integral equations arising from chemistry and physics: the inverse Laplace problem in chemical kinetics and the vector wave scattering problem in dielectric optics. The inverse Laplace problem occurs in the quantitative understanding of biological processes that exhibit complex kinetic behavior: different subpopulations of transition events from the "reactant" state to the "product" state follow distinct reaction rate constants, which results in a weighted superposition of exponential decay modes. Reconstruction of the rate constant distribution from kinetic data is often critical for mechanistic understandings of chemical reactions related to biological macromolecules. We devise a "phase function approach" to recover the probability distribution of rate constants from decay data in the time domain. The robustness (numerical stability) of this reconstruction algorithm builds upon the continuity of the transformations connecting the relevant function spaces that are compact metric spaces. The robust "phase function approach" not only is useful for the analysis of heterogeneous subpopulations of exponential decays within a single transition step, but also is generalizable to the kinetic analysis of complex chemical reactions that involve multiple intermediate steps. A quantitative characterization of the light scattering is central to many meteoro-logical, optical, and medical applications. We give a rigorous treatment to electromagnetic scattering on arbitrarily shaped dielectric media via the Born equation: an integral equation with a strongly singular convolution kernel that corresponds to a non-compact Green operator. By constructing a quadratic polynomial of the Green operator that cancels out the kernel singularity and satisfies the compactness criterion, we reveal the universality of a real resonance mode in dielectric optics. Meanwhile, exploiting the properties of compact operators, we outline the geometric and physical conditions that guarantee a robust solution to the light scattering problem, and devise an asymptotic solution to the Born equation of electromagnetic scattering for arbitrarily shaped dielectric in a non-perturbative manner.

SPEAR-induced field-aligned irregularities observed from bi-static HF radio scattering in the polar ionosphere

NASA Astrophysics Data System (ADS)

Blagoveshchenskaya, N. F.; Borisova, T. D.; Kornienko, V. A.; Kalishin, A. S.; Robinson, T. R.; Yeoman, T. K.; Wright, D. M.; Baddeley, L. J.

2009-01-01

Experimental results from SPEAR HF heating experiments in the polar ionosphere are examined. Bi-static scatter measurements of HF diagnostic signals were carried out on the Pori (Finland)-SPEAR-St. Petersburg path at operational frequencies of 11,755 and 15,400 kHz and the London-SPEAR-St. Petersburg path at frequencies of 12,095 and 17,700 kHz, using a Doppler spectral method. The SPEAR HF heating facility generates heater-induced artificial field-aligned small-scale irregularities (AFAIs), which can be detected by HF diagnostic bi-static radio scatter techniques at St. Petersburg at a distance of about 2000 km. In accordance with the Bragg condition, HF bi-static backscatters were sensitive to small-scale irregularities having spatial sizes of the order of 9-13 m across the geomagnetic field line. The properties and behaviour of AFAIs have been considered in the winter and summer seasons under quiet magnetic conditions and under various status of the polar ionosphere (the presence of "thick" and "thin" sporadic Es layers, different structures of the F2 layer). The experimental results obtained have shown that AFAIs can be excited in the F as well as in the E regions of the polar ionosphere. The excitation of a very intense wide-band spectral component with an abrupt increase in the spectral width up to 16-20 Hz has been found in the signals scattered from striations. Along with a wide-band component, a narrow-band spectral component can be also seen in the Doppler sonograms and in the average spectra of the signals scattered from the SPEAR-induced striations. AFAIs were excited even when the HF heater frequency was up to 0.5 MHz larger than the critical frequency. A simulation of the ray geometry for the diagnostic HF radio waves scattered from AFAIs in the polar ionosphere has been made for the geophysical conditions prevailing during experiments carried out in both the winter and summer seasons.

Evaluation of simulation-based scatter correction for 3-D PET cardiac imaging

NASA Astrophysics Data System (ADS)

Watson, C. C.; Newport, D.; Casey, M. E.; deKemp, R. A.; Beanlands, R. S.; Schmand, M.

1997-02-01

Quantitative imaging of the human thorax poses one of the most difficult challenges for three-dimensional (3-D) (septaless) positron emission tomography (PET), due to the strong attenuation of the annihilation radiation and the large contribution of scattered photons to the data. In [/sup 18/F] fluorodeoxyglucose (FDG) studies of the heart with the patient's arms in the field of view, the contribution of scattered events can exceed 50% of the total detected coincidences. Accurate correction for this scatter component is necessary for meaningful quantitative image analysis and tracer kinetic modeling. For this reason, the authors have implemented a single-scatter simulation technique for scatter correction in positron volume imaging. Here, they describe this algorithm and present scatter correction results from human and chest phantom studies.

On the design of experiments for determining ternary mixture free energies from static light scattering data using a nonlinear partial differential equation

PubMed Central

Wahle, Chris W.; Ross, David S.; Thurston, George M.

2012-01-01

We mathematically design sets of static light scattering experiments to provide for model-independent measurements of ternary liquid mixing free energies to a desired level of accuracy. A parabolic partial differential equation (PDE), linearized from the full nonlinear PDE [D. Ross, G. Thurston, and C. Lutzer, J. Chem. Phys. 129, 064106 (2008)10.1063/1.2937902], describes how data noise affects the free energies to be inferred. The linearized PDE creates a net of spacelike characteristic curves and orthogonal, timelike curves in the composition triangle, and this net governs diffusion of information coming from light scattering measurements to the free energy. Free energy perturbations induced by a light scattering perturbation diffuse along the characteristic curves and towards their concave sides, with a diffusivity that is proportional to the local characteristic curvature radius. Consequently, static light scattering can determine mixing free energies in regions with convex characteristic curve boundaries, given suitable boundary data. The dielectric coefficient is a Lyapunov function for the dynamical system whose trajectories are PDE characteristics. Information diffusion is heterogeneous and system-dependent in the composition triangle, since the characteristics depend on molecular interactions and are tangent to liquid-liquid phase separation coexistence loci at critical points. We find scaling relations that link free energy accuracy, total measurement time, the number of samples, and the interpolation method, and identify the key quantitative tradeoffs between devoting time to measuring more samples, or fewer samples more accurately. For each total measurement time there are optimal sample numbers beyond which more will not improve free energy accuracy. We estimate the degree to which many-point interpolation and optimized measurement concentrations can improve accuracy and save time. For a modest light scattering setup, a sample calculation shows that less than two minutes of measurement time is, in principle, sufficient to determine the dimensionless mixing free energy of a non-associating ternary mixture to within an integrated error norm of 0.003. These findings establish a quantitative framework for designing light scattering experiments to determine the Gibbs free energy of ternary liquid mixtures. PMID:22830693

Scatter and crosstalk corrections for {sup 99m}Tc/{sup 123}I dual-radionuclide imaging using a CZT SPECT system with pinhole collimators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fan, Peng; Hutton, Brian F.; Holstensson, Maria

2015-12-15

Purpose: The energy spectrum for a cadmium zinc telluride (CZT) detector has a low energy tail due to incomplete charge collection and intercrystal scattering. Due to these solid-state detector effects, scatter would be overestimated if the conventional triple-energy window (TEW) method is used for scatter and crosstalk corrections in CZT-based imaging systems. The objective of this work is to develop a scatter and crosstalk correction method for {sup 99m}Tc/{sup 123}I dual-radionuclide imaging for a CZT-based dedicated cardiac SPECT system with pinhole collimators (GE Discovery NM 530c/570c). Methods: A tailing model was developed to account for the low energy tail effectsmore » of the CZT detector. The parameters of the model were obtained using {sup 99m}Tc and {sup 123}I point source measurements. A scatter model was defined to characterize the relationship between down-scatter and self-scatter projections. The parameters for this model were obtained from Monte Carlo simulation using SIMIND. The tailing and scatter models were further incorporated into a projection count model, and the primary and self-scatter projections of each radionuclide were determined with a maximum likelihood expectation maximization (MLEM) iterative estimation approach. The extracted scatter and crosstalk projections were then incorporated into MLEM image reconstruction as an additive term in forward projection to obtain scatter- and crosstalk-corrected images. The proposed method was validated using Monte Carlo simulation, line source experiment, anthropomorphic torso phantom studies, and patient studies. The performance of the proposed method was also compared to that obtained with the conventional TEW method. Results: Monte Carlo simulations and line source experiment demonstrated that the TEW method overestimated scatter while their proposed method provided more accurate scatter estimation by considering the low energy tail effect. In the phantom study, improved defect contrasts were observed with both correction methods compared to no correction, especially for the images of {sup 99m}Tc in dual-radionuclide imaging where there is heavy contamination from {sup 123}I. In this case, the nontransmural defect contrast was improved from 0.39 to 0.47 with the TEW method and to 0.51 with their proposed method and the transmural defect contrast was improved from 0.62 to 0.74 with the TEW method and to 0.73 with their proposed method. In the patient study, the proposed method provided higher myocardium-to-blood pool contrast than that of the TEW method. Similar to the phantom experiment, the improvement was the most substantial for the images of {sup 99m}Tc in dual-radionuclide imaging. In this case, the myocardium-to-blood pool ratio was improved from 7.0 to 38.3 with the TEW method and to 63.6 with their proposed method. Compared to the TEW method, the proposed method also provided higher count levels in the reconstructed images in both phantom and patient studies, indicating reduced overestimation of scatter. Using the proposed method, consistent reconstruction results were obtained for both single-radionuclide data with scatter correction and dual-radionuclide data with scatter and crosstalk corrections, in both phantom and human studies. Conclusions: The authors demonstrate that the TEW method leads to overestimation in scatter and crosstalk for the CZT-based imaging system while the proposed scatter and crosstalk correction method can provide more accurate self-scatter and down-scatter estimations for quantitative single-radionuclide and dual-radionuclide imaging.« less

Stimulated Brillouin scattering in the field of a two-dimensionally localized pumping wave

DOE Office of Scientific and Technical Information (OSTI.GOV)

Solikhov, D. K., E-mail: davlat56@mail.ru; Dvinin, S. A., E-mail: dvinin@phys.msu.ru

2016-06-15

Stimulated Brillouin scattering of electromagnetic waves in the field of a two-dimensionally localized pump wave at arbitrary scattering angles in the regime of forward scattering is analyzed. Spatial variations in the amplitudes of interacting waves are studied for different values of the pump field and different dimensions of the pump wave localization region. The intensity of scattered radiation is determined as a function of the scattering angle and the dimensions of the pump wave localization region. It is shown that the intensity increases with increasing scattering angle.