Multiple Scattering

Characterization of dense sprays remains one of the challenges of sprays diagnostics. Beam extinction and multiple scattering plague traditional imaging techniques. Advanced techniques under development such as ballistic- and X-ray phase-contrast imaging rely on esoteric illumination sources and/or high-speed detectors. Because both tech- niques exhibit exceptionally large depths-of-field there is ambiguity in the interpretation of the results. In this work the authors demonstrate an imaging strategy appropriate for dense sprays utilizing arrays of consumer- grade electronics for both illumination and sensing. Given the preliminary nature of the work the target in question was static but the method is agnostic to motion. The results are not a two-dimensional image of the target but rather a three- dimensional map of all light scattering sources in a volume. Using a novel illumination scheme that actually benefits from multiply-scattered light the authors demonstrate how an array of ...

We show that, whereas the present log spiral of revolution monochromator works well for Cr edges of 2.8% Cr 2 0 3 in a V 2 0 3 matrix, the device transmits noticeable V extended structure in the case of 0.365% Cr 2 0 3 . We demonstrate that the transmitted V extended structure is due to the V Kp line which is unresolved by the monochromator. It is suggested that this limitation may be overcome by designing a log spiral detector for the Cr Kp line rather than the Cr IQ line. Aspects of the design of this modified log spiral are discussed.

The theory of coherent reflection filtering explains the empirical form of the cochlear reflectance by showing how it emerges from the coherent “backscattering” of forward-traveling waves by impedance perturbations in the mechanics of the cochlear partition. Since the theory was developed using the one-dimensional (1-D) transmission-line model of the cochlea, an obvious logical shortcoming is the failure of the long-wavelength approximation near the peak of the traveling wave, where coherent backscattering is purported to occur. Indeed, existing theory suggests that wave reflection may be strongly suppressed in the short-wave regime. To understand how short-wave behavior near the peak modifies the predictions of the long-wave theory, this paper solves the scattering problem in the 2-D cochlear model. The 2-D problem is reduced to a 1-D wave equation and the solution expressed as an infinite series in which successive terms arise via multiple scattering within the cochlea. The cochle...

The effects of local B-cation ͑Ti, Zr͒ distribution and octahedral tilting on the pre-edge structure in the Ti x-ray absorption K-spectra of the CaTi 1-x Zr x O 3 perovskite solid solutions were investigated. Experimental spectra for the disordered CaTi 1-x Zr x O 3 samples revealed systematic variations of the pre-edge peak intensities with the x values. Multiple-scattering calculations using 75-atom clusters Ti͑TiO 6 ͒ 6-n ͑ZrO 6 ͒ n Ca 8 O 24 were conducted to interpret these differences. The origin of the lowest unoccupied states in the conduction band of the CaTi 1-x Zr x O 3 was determined from the analyses of x-ray absorption near-edge structure of the O K-edge. The calculations reproduced the experimental spectra and demonstrated that the differences in the intensities of certain pre-edge feature are dominated by the probability of finding a Zr atom in the first B-cation coordination sphere around the absorbing Ti. The pre-edge structure appeared to be sensitive to small changes in the value of this probability, so that the pre-edge intensities could be used effectively to compare the extent of local B-site order in perovskite solid solution samples having similar chemical composition but processed differently.

The effects of local B-cation (Ti, Zr) distribution and octahedral tilting on the pre-edge structure in the Ti X-ray absorption K-spectra of the CaTi 1-x Zr x O 3 perovskite solid solutions were investigated. Experimental spectra for the disordered CaTi 1-x Zr x O 3 samples revealed systematic variations of the pre-edge peak intensities with the x-values. Multiple-scattering calculations using 75-atom clusters Ti(TiO 6 ) 6-n (ZrO 6 ) n Ca 8 O 24 were conducted to interpret these differences. The origin of the lowest unoccupied states in the conduction band of the CaTi 1-x Zr x O 3 was determined from the analyses of X-ray absorption near-edge structure of the O K-edge. The calculations reproduced the experimental spectra and demonstrated that the differences in the intensities of certain pre-edge feature are dominated by the probability of finding a Zr atom in the first B-cation coordination sphere around the absorbing Ti. The preedge structure appeared to be sensitive to small changes in the value of this probability, so that the pre-edge intensities could be used effectively to compare the extent of local B-site order in perovskite solid solution samples having similar chemical composition but processed differently.

Diffusive Radiation is a new type of radiation predicted to occur in randomly inhomogeneous media due to the multiple scattering of pseudophotons. This theoretical effect is now observed experimentally. The radiation is generated by the passage of electrons of energy 200KeV -2.2M eV through a random stack of films in the visible light region. The radiation intensity increases resonantly provided the Čerenkov condition is satisfied for the average dielectric constant of the medium. The observed angular dependence and electron resonance energy are in agreement with the theoretical predictions. These observations open a road to application of diffusive radiation in particle detection, astrophysics, soft X-ray generation and etc..

A series of positron-production experiments with crystal tungstens hit by 4 and 8-GeV single-bunch electron beams were carried out at the KEKB 8-GeV injector linac. Three tungsten crystals (<111> axis) with different thicknesses (2.2, 5.3 and 9.0 mm) and those combined with amorphous tungsten plates were tested on a precise goniometer. The positron-production yields were measured with a magnetic spectrometer

The Gigatracker (GTK) is a hybrid silicon pixel detector developed for NA62, the experiment aimed at studying ultra-rare kaon decays at the CERN SPS. Three GTK stations will provide precise momentum and angular measurements on every track of the high intensity NA62 hadron beam with a time-tagging resolution of 150 ps. Multiple scattering and hadronic interactions of beam particles in the GTK have to be minimized to keep background events at acceptable levels, hence the total material budget is fixed to 0.5% X 0 per station. In addition the calculated fluence for 100 days of running is 2 × 10 14 1 MeV n eq /cm 2 , comparable to the one expected for the inner trackers of LHC detectors in 10 years of operation. These requirements pose challenges for the development of an efficient and low-mass cooling system, to be operated in vacuum, and on the thinning of read-out chips to 100 μm or less. The most challenging requirement is represented by the time resolution, which can be achieved by carefully compensating for the discriminator time-walk. For this purpose, two complementary read-out architectures have been designed and produced as small-scale prototypes: the first is based on the use of a Time-over-Threshold circuit followed by a TDC shared by a group of pixels, while the other uses a constant-fraction discriminator followed by an on-pixel TDC. The readout pixel ASICs are produced in 130 nm IBM CMOS technology and bump-bonded to 200 μm thick silicon sensors. The Gigatracker detector system is described with particular emphasis on recent experimental results obtained from laboratory and beam tests of prototype bump-bonded assemblies, which show a time resolution of less than 200 ps for single hits.

A crucial detector of the NA62 experiment is the beam spectrometer named Gigatracker. It consists of three stations of hybrid silicon pixels sensors with 150 ps (rms) of time resolution and 100 µm (rms) of space resolution. In addition the system operates under a high radiation environment and a high density of particles (up to 1.5 MHz/mm 2 in the centre and 0.8 -1 GHz in total). To meet these requirements the readout electronics must compensate the discriminators time-walk and the dead time should be below 1%. In order to evaluate the best solution, two readout chips have been developed. One is based on the constant-fraction discriminator technique and the other one is based on the use of a time-over-threshold circuit. The global architectures of both the front-end ASIC will be discussed.

We propose an empirical model to determine the form of energy loss of charm quarks due to multiple scatterings in quark gluon plasma by demanding a good description of production of D mesons and non-photonic electrons in relativistic collision of heavy nuclei at RHIC and LHC energies. Best results are obtained when we approximate the momentum loss per collision ∆p T = α p T , where α is a constant depending on the centrality and the centre of mass energy. Comparing our results with those obtained earlier for drag coefficients estimated using Langevin equation for heavy quarks we find that up to half of the energy loss of charm quarks at top RHIC energy could be due to collisions while that at LHC energy at 2760 GeV/A the collisional energy loss could be about one third of the total. Estimates are obtained for azimuthal anisotropy in momentum spectra of heavy mesons, due to this energy loss. We further suggest that energy loss of charm quarks may lead to an enhanced production of D-mesons and single electrons at low p T in AA collisions.

Cosmic rays, mostly composed of high energy muons, continuously hit the Earth's surface (at sea level the rate is about 10 000 m -2 min -1 ). Various technologies are adopted for their detection and are widespread in the field of particle and nuclear physics. In this paper, cosmic ray muon detection techniques are assessed for measurement applications in engineering, where these methods could be suitable for several applications, with specific reference to situations where environmental conditions are weakly controlled and/or where the parts to be measured are hardly accessible. Since cosmic ray showering phenomena show statistical nature, the Monte Carlo technique has been adopted to numerically simulate a particular application, where a set of muon detectors are employed for alignment measurements on an industrial press. An analysis has been performed to estimate the expected measurement uncertainty and system resolution, which result to be strongly dependent on the dimensions and geometry of the set-up, on the presence of materials interposed between detectors and, ultimately, on the elapsed time available for the data taking.

Discrete reflection-transmission acoustic models are introduced and analysed regarding their underlying physical properties. Namely, phenomena related to multiple scattering as encountered in the underlying continuous model. Moreover, the discrete models are designed so that computational experiments can be performed efficiently. Each discrete model is expressed through its corresponding reflection-transmission matrix establishing a connection with lattice models encountered in the Physics literature. Their connections with the continuous acoustic model are discussed in detail. In particular we show how a Goupillaud medium can arise from a stable discretization of a more general random medium. Related physical phenomena are studied computationally. In particular reflection-transmission properties of waves in a rapidly varying random medim, which are valid over long propagation distances. By using a long computational domain, in a regime where we have Anderson localization, the energy of an incoherently scattered signal is entirely reflected back and, by time-reversal, completely recompressed into the smooth initial data. Experiments are also performed in a regime where separation of scales fails to hold. Another new result is the time-reversed refocusing, in reflection, of a wave train in the form of a bit stream. The bit stream is scrambled by reflection and unscrambled through time reversal. The robustness of the time-reversed refocusing phenomenon is outstanding.

We report that disordered media made of randomly distributed nanoparticles can be used to overcome the diffraction limit of a conventional imaging system. By developing a method to extract the original image information from the multiple scattering induced by the turbid media, we dramatically increase a numerical aperture of the imaging system. As a result, the resolution is enhanced by more than 5 times over the diffraction limit, and the field of view is extended over the physical area of the camera. Our technique lays the foundation to use a turbid medium as a far-field superlens.

The structure of aluminosilicate melts/glasses plays a key role in the Earth Sciences for the understanding of rock-forming igneous processes, as well as in the Materials Sciences for their technical applications. In particular, the alkaline earth aluminosilicate glasses are an extremely important group of materials, with a wide range of commercial application, as well as serving as analogue for natural basaltic melts. However, definition of their structure and properties is still controversial, and in particular the role and effect of Al has long been a subject of debate. [1-8] Here we report a series of experimental x-ray absorption near-edge structure (XANES) spectra at the Al K edge on a series of synthetic glasses of peralkaline composition in the CaO-Al 2 O 3 -SiO 2 system, together with a general theoretical framework for data analysis based on an ab initio full multiple scattering (MS) theory. We propose an Al/Si tetrahedral network model for aluminosilicate glasses based on distorted polyhedra, with varying both the T-O (T = Al or Si) bond lengths and the T-O-T angles, and with different Al/Si composition. This model achieves a significant agreement between experiments and simulations. In these glasses, experimental data and theoretical results concur to support a model in which Al is network-former with a comparatively well ordered local medium-range order (up to 5 Å).

We develop a theory to study apertureless scanning near-field optical microscopy which takes into account retardation, higher multipoles of the tip, and the multiple scattering between the tip and the surface. We focus on metallic systems and discuss the implication of the formation of tip-induced surface plasmon modes in the tip-surface system. We discuss the effects associated with the shift in energy of those modes as a function of the tip-surface distance. Both the local field and the scattering cross section are enhanced when the tip approaches the surface, but there is no general correspondence between the two enhancements.

The self-interaction corrected local spin density (SIC-LSD) formalism and the standard GGA treatment of the exchange-correlation energy have been applied to study the collapse of the magnetic moment of Fe impurities in MgO. The system Mg_{1-x}Fe_xO is believed to be the second most abundant mineral in the Earth's lower mantle. We confirm the experimentally found increase of the critical pressure

A corrected, first-order solution for modelling acoustic wave scattering in layered halfspaces containing random inhomogeneities is derived. Energy lost to higher order scattering and intrinsic attenuation is included in the correction, which is constructed so that energy is conserved to first order. The complex propagation effects of the layering are overcome by representing the motion as a sum of normal modes. This approach renders the kinematic description of the scattering two dimensional, with the wave vectors of incident and scattered modes lying parallel to the layering. At each level in the halfspace, the inhomogeneities are resolved into two-dimensional Fourier spectra also parallel to the layering. The root mean square (rms) motion of a scattered mode depends on the correlation between spectra at different levels and the group velocity of the mode. To simplify the solution, it is assumed that the inhomogeneity spectra are piecewise constant and that the energy of a normal model propagates only at its group velocity. The final step of the theory establishes a criterion for the source-receiver separations over which the results are accurate. Numerical calculations have been carried out for a single layer of inhomogeneities over a halfspace. The spectra of the inhomogeneities were assumed band limited, and several different spectra were examined. The results suggest the existence of a diagonal selection rule whereby a wavelet of mode order IZ scatters mostly to wavelets of the same order. Moreover, a resonant frequency of scattering occurs, causing the rms signal to appear monochromatic. The frequency of the resonance is controlled by the inhomogeneity spectra band limits. With the aid of the diagonal selection rule, the simplified solution allows for both rapid computation of synthetic signals and inversion of data for scattering cross-section. Existing data suggest the theory may be applied to obtain approximate models of local earthquake codas. The synthetic signals of the single layer cases, for example, have codas similar to published observations. To illustrate the inversion of data with the theory, a preliminary scattering crosssection for the lunar crust is presented.

The polarization properties of any medium are completely described by the sixteen element Mueller matrix that relates the polarization parameters of the light incident on the medium to that emerging from it. Measurement of all the elements of the matrix requires a minimum of sixteen measurements involving both linear and circularly polarized light. However, for many diagnostic applications, it would be useful if the polarization parameters can be quantified with linear polarization measurements alone. In this paper, we present a method based on polar decomposition of Mueller matrix for quantification of the polarization parameters of a scattering medium using the nine element (3 × 3) Mueller matrix that requires linear polarization measurements only. The methodology for decomposition of the 3 × 3 Mueller matrix is based on the previously developed decomposition process for sixteen element (4 × 4) Mueller matrix but with an assumption that the depolarization of linearly polarized light due to scattering is independent of the orientation angle of the incident linear polarization vector. Studies conducted on various scattering samples demonstrated that this assumption is valid for a turbid medium like biological tissue where the depolarization of linearly polarized light primarily arises due to the randomization of the field vector's direction as a result of multiple scattering. For such medium, polar decomposition of 3 × 3 Mueller matrix can be used to quantify the four independent polarization parameters namely, the linear retardance (δ ), the circular retardance (ψ), the linear depolarization coefficient (Δ) and the linear diattenuation (d) with reasonable accuracy. Since this approach requires measurements using linear polarizers only, it considerably simplifies measurement procedure and might find useful applications in tissue diagnosis using the retrieved polarization parameters.

Q -switched Nd:YAG laser ablation of a turbid medium (paint) is studied. The optical properties (absorption coefficient, scattering coefficient, and its anisotropy) of a paint are determined with a multiple scattering model (three-flux model), and from measurements of reflection-transmission of light through thin layers. The energy deposition profiles are calculated at wavelengths of 532nm and 1.064μm. They are different from those described by a Lambert-Beer law. In particular, the energy deposition of the laser beam is not maximum on the surface but at some depth inside the medium. The ablated rate was measured for the two wavelengths and compared with the energy deposition profile predicted by the model. This allows us to understand the evolution of the ablated depth with the wavelength: the more the scattering coefficient is higher, the more the ablated depth and the threshold fluence of ablation decrease.

Dans l'industrie nucléaire, les peintures murales doivent être décontaminées à la fin de vie des installations ou lors d'opération de maintenance. L'ablation par laser de la peinture permet de réduire considérablement le volume de déchets engendrés lors de l'opération, par rapport aux techniques actuelles. Les peintures sont constituées d'une base polymérique dans laquelle des charges et des pigments sont inclus. Le dépôt d'énergie du faisceau laser dans ce milieu diffusant est étudié à l'aide d'un modèle de diffusion multiple, et de mesures de réflexion / transmission de faisceau à travers des couches minces. L'ablation des peintures est analysée avec plusieurs lasers Nd : YAG et un laser TEA-CO2, permettant de faire varier la fluence, la longueur d'onde, la durée de l'impulsion, la cadence de tir et le nombre de tirs appliqué. Des bancs optiques ont été réalisés, et des tests paramétriques permettent de définir les paramètres optimaux de...

Let x be a complex random variable with mean zero and bounded variance σ 2 . Let Nn be a random matrix of order n with entries being i.i.d. copies of x. Let λ 1 , . . . , λn be the eigenvalues of 1 σ √ n Nn. Define the empirical spectral distribution µn of Nn by the formula The following well-known conjecture has been open since the 1950's: Circular law conjecture: µn converges to the uniform distribution µ∞ over the unit disk as n tends to infinity. We prove this conjecture, with strong convergence, under the slightly stronger assumption that the (2 + η)th-moment of x is bounded, for any η > 0. Our method builds and improves upon earlier work of Girko, Bai, Götze-Tikhomirov, and Pan-Zhou, and also applies for sparse random matrices. The new key ingredient in the paper is a general result about the least singular value of random matrices, which was obtained using tools and ideas from additive combinatorics. 1 We are using √ -1 for the imaginary unit, as we wish to reserve i as an index of summation.

BaV 10 O 15 shows a structural phase transition associated with the trimerization of V ions at T s = 123 K. We investigated the orbital states of V trimers using the technique of resonant x-ray scattering (RXS) near the V K-edge absorption energy. The ratio of the intensity between the pre-edge structure (1s to 3d transition) and the main-edge structure (1s to 4p transition) strongly depends on the reciprocal Q position of the scattering. We found that the Q position dependence is consistent with the model of orbital ordering proposed by Pen et al.,

A high-performance Raman lidar operating in the UV portion of the spectrum has been used to acquire, for the first time using a single lidar, simultaneous airborne profiles of the water vapor mixing ratio, aerosol backscatter, aerosol extinction, aerosol depolarization and research mode measurements of cloud liquid water, cloud droplet radius, and number density. The Raman Airborne Spectroscopic Lidar (RASL) system was installed in a Beechcraft King Air B200 aircraft and was flown over the mid-Atlantic United States during July–August 2007 at altitudes ranging between 5 and 8 km. During these flights, despite suboptimal laser performance and subaperture use of the telescope, all RASL measurement expectations were met, except that of aerosol extinction. Following the Water Vapor Validation Experiment—Satellite/Sondes (WAVES_2007) field campaign in the summer of 2007, RASL was installed in a mobile trailer for ground-based use during the Measurements of Humidity and Validation Experim...

A variational retrieval method has been implemented to evaluate the possibility of assimilating rain‐affected microwave radiances in an operational weather forecasting model. The method employs an efficient multiple scattering radiative transfer code and its tangent‐linear and adjoint versions to simulate model state equivalent radiances and their sensitivities to changes in hydrometeor contents. Profiles of temperature and humidity together with the ECMWF model convection and cloud schemes are used to produce first‐guess hydrometeor profiles. The hydrometeor error covariance matrix is calculated from the operational error covariance matrix of temperature and humidity convolved with both convection and cloud scheme for each profile. A sensitivity study is applied to a tropical cyclone using data from the TRMM Microwave Imager where large differences between the first‐guess and observed precipitation fields occurred. The study shows that the approach results in single‐column retrieva...

The Netrmann solution to the scalar equfltion of transfer is obtained numerically for sample phase functions with large forward and backward peaks. The results are presented graphically and are in a homogeneous layer of optical thickness T* C 1 compared with the intensities and albedos computed by approximate methods.

The phase variation with angle of hadronic amplitudes is studied with a view to understanding the underlying physical quantities which control it and how well it can be determined in free space. We find that unitarity forces a moderately accurate determination of the phase in standard amplitude analyses but that the nucleon-nucleon analyses done to date do not give the phase variation needed to achieve a good representation of the data in multiple scattering calculations. Models are examined which suggest its behavior near forward angles is related to the radii of the real and absorptive parts of the interaction. The dependence of this phase on model parameters is such that if these radii are modified in the nuclear medium (in combination with the change due to the shift in energy of the effective amplitude in the medium) then the larger magnitudes of the phase needed to fit the data might be attainable, but only for negative values of the phase variation parameter.

The phase variation with angle of hadronic amplitudes is studied with a view to understanding the underlying physical quantities which control it and how well it can be determined in free space. We find that unitarity forces a moderately accurate determination of the phase in standard amplitude analyses but that the nucleon-nucleon analyses done to date do not give the phase variation needed to achieve a good representation of the data in multiple scattering calculations. Models are examined which suggest its behavior near forward angles is related to the radii of the real and absorptive parts of the interaction. The dependence of this phase on model parameters is such that if these radii are modified in the nuclear medium (in combination with the change due to the shift in energy of the effective amplitude in the medium) then the larger magnitudes of the phase needed to fit the data might be attainable, but only for negative values of the phase variation parameter.

The DØ preshower detector consists of scintillator strips with embedded wavelength-shifting fibers, and a readout using Visible Light Photon Counters. The response to minimum ionizing particles has been tested with cosmic ray muons. We report results on the gain calibration and light-yield distributions. The spatial resolution is investigated taking into account the light sharing between strips, the effects of multiple scattering and various systematic uncertainties. The detection efficiency and noise contamination are also investigated.

The multiple scattering of ultra relativistic electrons in an amorphous matter leads to the suppression of the soft part of radiation spectrum (the Landau-Pomeranchuk-Migdal effect), and also can change essentially the angular distribution of the emitted photons. A similar effect must take place in a crystal for the coherent radiation of relativistic electron. The results of the theoretical investigation of angular distributions and polarization of radiation by a relativistic electron passing through a thin (in comparison with a coherence length) crystal at a small angle to the crystal axis are presented. The electron trajectories in crystal were simulated using the binary collision model which takes into account both coherent and incoherent effects at scattering. The angular distribution of radiation and polarization were calculated as a sum of radiation from each electron. It is shown that there are nontrivial angular distributions of the emitted photons and their polarization that are connected to the superposition of the coherent scattering of electrons by atomic rows ("doughnut scattering" effect) and the suppression of radiation (similar to the Landau-Pomeranchuk-Migdal effect in an amorphous matter). It is also shown that circular polarization of radiation in the considered case is identically zero.

The multiple scattering of ultra relativistic electrons in an amorphous matter leads to the suppression of the soft part of radiation spectrum (the Landau-Pomeranchuk-Migdal effect), and also can change essentially the angular distribution of the emitted photons. A similar effect must take place in a crystal for the coherent radiation of relativistic electron. The results of the theoretical investigation of angular distributions and polarization of radiation by a relativistic electron passing through a thin (in comparison with a coherence length) crystal at a small angle to the crystal axis are presented. The electron trajectories in crystal were simulated using the binary collision model which takes into account both coherent and incoherent effects at scattering. The angular distribution of radiation and polarization were calculated as a sum of radiation from each electron. It is shown that there are nontrivial angular distributions of the emitted photons and their polarization that are connected to the superposition of the coherent scattering of electrons by atomic rows ("doughnut scattering" effect) and the suppression of radiation (similar to the Landau-Pomeranchuk-Migdal effect in an amorphous matter). It is also shown that circular polarization of radiation in the considered case is identically zero.

The atmosphere of Mars significantly attenuates the heavy ion component of the primary galactic cosmic rays (GCR), however increases the fluence of secondary light ions (neutrons, and hydrogen and helium isotopes) because of particle production processes. We describe results of the quantum multiple scattering fragmentation (QMSFRG) model for the production of light nuclei through the distinct mechanisms of nuclear abrasion and ablation, coalescence, and cluster knockout. The QMSFRG model is shown to be in excellent agreement with available experimental data for nuclear fragmentation cross sections. We use the QMSFRG model and the space radiation transport code, HZETRN to make predictions of the light particle environment on the Martian surface at solar minimum and maximum. The radiation assessment detector (RAD) experiment will be launched in 2009 as part of the Mars Science Laboratory (MSL). We make predictions of the expected results for time dependent count-rates to be observed by RAD experiment. Finally, we consider sensitivity assessments of the impact of the Martian atmospheric composition on particle fluxes at the surface.

The number of events for incoherent φ photoproduction is found to have a target mass number dependence of A 0.72±0.07 in the kinematical region of |t| ≤ 0.6 GeV 2 /c 2 . The total cross section of the φ-nucleon interaction, σ φN , has been estimated as 35 +17 -11 mb using the A-dependence of the φ photo-production yield and a Glauber-type multiple scattering theory. This value is much larger than σ φN in free space, suggesting that the φ properties might change in the nuclear medium.

Two-photon excitation laser induced fluorescence (2p-LIF) is used here for imaging an optically dense atomizing spray. The main advantage of the approach is that very little fluorescence interference originating from multiple light scattering is generated. This leads to high image contrast and a faithful description of the imaged fluid structures. While point measurement 2p-LIF imaging is a well-known approach used in life science microscopy, it has, to the best of the authors' knowledge, never been tested for analyzing liquid structures in spray systems. We take advantage of this process, here, at a macroscopic scale (∼ 5 × 5 mm field of view) by imaging the central part of a light sheet of 10 mm height. To generate enough 2p-LIF signal at such a scale and with single-shot detection, ultra-short laser pulses of 25 fs, centered at 800 nm wavelength and having 2.5 mJ pulse energy, have been used. The technique is demonstrated by imaging a single spray plume from a 6 hole commercial Gasoline Direct Injection (GDI) system running at 200 bar injection pressure. The proposed approach is very promising for detailed analysis of liquid breakups in optically dense sprays and can be used for other fluid mechanics related applications.

The combination of radar and lidar in space offers the unique potential to retrieve vertical profiles of ice water content and particle size globally, and two algorithms developed recently claim to have overcome the principal difficulty with this approach—that of correcting the lidar signal for extinction. In this paper “blind tests” of these algorithms are carried out, using realistic 94-GHz radar and 355-nm lidar backscatter profiles simulated from aircraft-measured size spectra, and including the effects of molecular scattering, multiple scattering, and instrument noise. Radiation calculations are performed on the true and retrieved microphysical profiles to estimate the accuracy with which radiative flux profiles could be inferred remotely. It is found that the visible extinction profile can be retrieved independent of assumptions on the nature of the size distribution, the habit of the particles, the mean extinction-to-backscatter ratio, or errors in instrument calibration. Loc...

The number of operations required for conventional density-functional algorithms grows as the cube of the number of atoms, N. For large systems the computing requirements are unattainable. To overcome this limi- tation it is acceptable to approximate those variables with respect to which the free energy is stationary. We show that the stationarity of the free energy with respect to electron density, one-electron potential, chemical potential, occupation function, and temperature allows for very useful approximations leading to rapid and accurate determination of the free energy. Here we discuss approximations involved in calculating the finite temperature electron density needed to evaluate the Harris-Foulkes free energy. Of particular importance are

We argue that, as originally formulated, the ® rst principles spin dynamics of the ® nite-temperature and non-equilibrium properties of itinerant magnets recently proposed by Antropov et al. is not clearly de® ned within density functional theory. We show how constrained density functional theory can be used to provide a formal basis for describing the instantaneous non-collinear states that are being evolved according to the classical equation of motion of spin-dynamics. We propose a constrained local moment (CLM) model in which speci® c orientational con® gurations are maintained by local transverse constraining ® elds that are obtained self-consistently. A general algorithm for ® nding the constraining ® elds is used and the existence of a CLM state is demonstrated for speci® c model problems including a cell of 512 Fe atoms for which the orientations of the magnetic moments are random.

Total energy calculations for Ni-rich ß′-phase NiAl have been performed using the large system multiple scattering (LSMS) method. The large samples used to model the alloys involved up to 128 atoms per cell, and were constructed to have the experimental short range order (SRO) parameters. Both short range ordering and charge transfer effects are automatically taken into account in the calculation. The calculated formation energies of both stoichiometric and non-stoichiometric compounds are in excellent agreement with experiment.

Abstract. Chain of calculations which have to be performed to predict any kind of signal in a deep underwater/ice neutrino detector necessarily includes the lepton propagation through thick layers of matter, as neutrino can be observed only by means of leptons (muons, first of all, due to their large ranges) that are generated in ν N → l N interactions. Thus, the muon propagation plays a key role when analyzing data and it is important to understand clearly how transportation part of simulation chain contributes to total inaccuracy of final results. Here we consider sources of uncertainties that appear in Monte Carlo algorithms for simulation of muon transport. The trivial but effective test is proposed to measure the propagation algorithm accuracy. The test is applied to three MC muon transport codes (PROPMU, MUSIC, MUM) and results are reported. 1

We present a new Monte Carlo muon propagation algorithm MUM (MUons+Medium) which possesses some advantages over analogous algorithms presently in use. The most important features of algorithm are described. Results on the test for accuracy of treatment the muon energy loss with MUM are presented and analyzed. It is evaluated to be of 2×10 -3 or better, depending upon simulation parameters. Contributions of different simplifications which are applied at Monte Carlo muon transportation to the resulting error are considered and ranked. It is shown that when simulating muon propagation through medium it is quite enough to account only for fluctuations in radiative energy loss with fraction of energy lost being as large as 0.05÷0.1. Selected results obtained with MUM are given and compared with ones from other algorithms.

In this paper, the three-dimensional problem of detection and localization of buried metallic objects inside a multilayered medium is studied. Decomposition of the time-reversal operator (DORT) is used as the inversion algorithm in the imaging method. In this approach, one has to analyze the time-reversal (TR) operator obtained by using the multistatic data matrix (MDM) of a TR array. To attain MDM in the forward problem, full-wave simulation results from a commercial simulation software are used. For synthetic retransmission of signals in this inverse problem, determination of the appropriate medium Green's function is required. Here, for the first time the complex images technique is employed in calculating the required Green's functions. The complex images technique gives a closed-form Green's function, instead of evaluating time-consuming numerical integrals resulting in a fast and accurate Green's function calculation. Using singular value decomposition of the MDM at a frequency range of 1-3GHz and synthesized DORT method, images are constructed. Numerical results show the accuracy of the proposed approach in the detection and localization of buried objects. Furthermore, noise effect and sensitivity analysis on layers' permittivity values are studied. The results confirm the robustness of the method against noise and uncertain layers parameters.

A new approach to generate structured grids for two-dimensional multiply connected regions with several holes is proposed. The bounding curves may include corners or cusps. The new algorithm constitutes an extension of the Branch Cut Grid Line Control (BCGC) technique introduced byVillamizar et al. [V. Villamizar, O. Rojas, J. Mabey, Generation of curvilinear coordinates on multiply connected regions with boundary-singularities, J. Comput. Phys. 223 (2007) 571-588] to domains with a finite number of holes. Regions with multiple holes are reduced to several contiguous single hole subregions. Then, the BCGC algorithm is applied to each single hole subregion producing a smooth grid with line control. Finally, the subregions with their respective grids are joined and their interfaces are smoothed resulting a globally smooth grid. The advantages of the novel grids are revealed by employing them to numerically solve acoustic scattering problems in the presence of multiple complexly shaped obstacles.

The applicability of the Dirichlet-to-Neumann technique coupled with finite difference methods is enhanced by extending it to multiple scattering from obstacles of arbitrary shape. The original boundary value problem (BVP) for the multiple scattering problem is reformulated as an interface BVP. A heterogenous medium with variable physical properties in the vicinity of the obstacles is considered. A rigorous proof of the equivalence between these two problems for smooth interfaces in two and three dimensions for any finite number of obstacles is given. The problem is written in terms of generalized curvilinear coordinates inside the computational region. Then, novel elliptic grids conforming to complex geometrical configurations of several two-dimensional obstacles are constructed and approximations of the scattered field supported by them are obtained. The numerical method developed is validated by comparing the approximate and exact far-field patterns for the scattering from two circular obstacles. In this case, for a second order finite difference scheme, a second order convergence of the numerical solution to the exact solution is easily verified.

The effect of multiple scattering on dilepton production in hot equilibrium nuclear matter is studied. In the region of low invariant masses we consider the contribution of both decay and virtual bremsstrahlung mechanisms to the lepton pair production. It is shown that the multiple elastic scattering leads to the increase of the dilepton rate via the particle decays but it results in the suppression of the lepton pair yield due to the virtual bremsstrahlung.

The theory of the low-energy electron point source (LEEPS) microscope is reformulated in matrix form to readily account for multiple scattering. An algorithm is developed for the storage of the structure matrix and an iterative method is used to solve the matrix equation for the structure factor. Examples of small and large clusters of atoms are given to compare single and multiple scattering. A Kirchho2Helmholtz transform is used for the reconstruction. We ®nd that in some cases the multiple scattering is too strong and reconstruction is not possible. We give examples which show that, even when multiple scattering is important, one can still obtain reconstructions that reveal the atomic structure both along and lateral to the optical axis. We also compare our results with those found in LEED.

This article reports the small-angle neutron scattering (SANS) and the transmission electron microscopy (TEM) investigations on solution quenched PH13-8 Mo stainless steel. The metallic carbide precipitates of parallelepiped like morphology, as revealed by TEM, have been mainly responsible for the strong scattering signal in SANS measurements. Scattering signal from the needle like austenites, which have been also identified by TEM, remains insignificant because of the poor scattering contrast between the austenites precipitates and the martensite matrix. Shape of the normalized scattering profile varies significantly with the specimen thickness. These variations of the scattering profiles could arise due to the two factors, namely: (i) the multiple scattering of the neutrons at small-angles and (ii) the double Bragg reflections. In the present case, it has been established that the contribution in the scattering signal due to the double Bragg reflection is quite insignificant compared to that from the multiple scattering. The single scattering profile, extracted from the multiple scattered profiles of the samples, has been analyzed in the light of polydisperse cylindrical particle model as well as with polydisperse parallelepiped particle model, assuming fixed aspect ratio of the precipitates, in order to obtain the size distribution of the precipitates.