Multiple Scattering

Photoelectron diffraction data can, in principle, be regarded as enabling the experimental recording of electron diffraction phases ͑relative to a direct reference wave͒, as well as intensities, thus also permitting the holographic reconstruction of atomic positions. Such holographic photoelectron diffraction patterns have been measured for surface and bulk core-level-shifted W 4 f photoemission from W͑110͒, yielding a data set of unprecedented size and quality. To test the role of experimental uncertainties and of multiple-scattering effects, we have also performed corresponding theoretical calculations at the single-and multiple-scattering levels. The surface and bulk holograms so obtained have been analyzed so as to provide the first parallel comparison of the three-dimensional atomic images that can be directly obtained via the five principal reconstruction algorithms proposed to date. The advantages and disadvantages of each of these methods are discussed. The prospects and limitations of atomic photoelectron holography as an ab initio technique for determining local-surface structures are also explored. ͓S0163-1829͑99͒08207-7͔

The Integral Equation Model with multiple scattering (IEMM) represents a well-established method that provides a theoretical framework for the scattering of electromagnetic waves from rough surfaces. A critical aspect is the long computational time required to run such a complex model. To deal with this problem, a neural network technique is proposed in this work. In particular, we have adopted neural networks to reproduce the backscattering coefficients predicted by IEMM at L-and C-bands, thus making reference to presently operative satellite radar sensors, i.e., that aboard ERS-2, ASAR on board ENVISAT (C-band), and PALSAR aboard ALOS (L-band). The neural network-based model has been designed for radar observations of both flat and tilted surfaces, in order to make it applicable for hilly terrains too. The assessment of the proposed approach has been carried out by comparing neural network-derived backscattering coefficients with IEMM-derived ones. Different databases with respect to those employed to train the networks have been used for this purpose. The outcomes seem to prove the feasibility of relying on a neural network approach to efficiently and reliably approximate an electromagnetic model of surface scattering.

Based on the relation between the theory of light field coherence and theory of radiation transfer in scattering media, a method is proposed for calculating the illumination distribution produced by coherent quasi-diffraction-free beams at different penetration depths of radiation into scattering media such as biological tissues. The method uses the optical transfer function or the point spread function (PSF) of the medium. A simple and convenient analytic PSF model is described. Examples of the illumination distribution produced by a Bessel light beam in a medium with optical parameters typical of real biological tissues are presented. It is shown that the half-width of the axial maximum of a Bessel light beam scattered due to scattering almost does not increase up to optical depths where the contribution of multiple scattering is already considerable.

An accurate multiple-scattering model has been employed to examine the effect of an aerosol layer at 25 mb, corresponding to the El Chichon observations, on the reflection, transmission and absorption of radiation by the stratosphere as a function of latitude, optical thickness and aerosol size distribution. Results are presented and parameterized for each of two wavelength intervals in the shortwave region and 17 wavelength intervals in the longwave region for three models of the aerosol size distribution. They include one model representing the unperturbed stratospheric aerosol plus two models based on measurements of the El Chichon aerosol size distribution. In addition to models of the radiative properties of the aerosol layer, a simple model of the latitudinal distribution of aerosol optical thickness as a function of time is developed, based on diffusive transport in latitude and exponential decay in time. These parameterizations for solar and infrared radiation, together with the dispersion model, permit climate models to account for the evolution of an aerosol size distribution from post-volcanic conditions to background conditions.

[...]
CAPÍTULO XV
AS CONSTITUIÇÕES POLÍTICAS
1 . O regime constitucional . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
2. A constituição da sociedade 127
3. A constituição do estado . . .. . .. . .. .. . . . .. . . . .. . .. . 129 4. O constitucionalismo liberal . . . . . . . . . . . . . . . . . . . . . . . 130
5 . Direito constitucional e realidade constitucional 132
.APÊNDICE
1. Da cidade antiga ao Estado moderno
2. A sociedade política medieval
136
141
X INICIAÇÃO À TEORIA DO ESTADO
3. Idade Média e Renascença . . . . . . . . . . . . . . . . . . . . . . . 146
4. Conseqüências políticas do protestantismo 149
5. O aparecimento do Estado moderno 151
6. O poder absoluto e a centralização . . . . . . . . . . . . . . . . 154
7. Origens revolucionárias do Estado moderno 158
8. Do Estado liberal ao Estado totalitário 160
BIBLIOGRAFIA 167
[...]

In this tutorial, we discuss voxel DAGs and multiresolution hierarchies, which are representations that can encode large volumes of data very efficiently. Despite a significant compression ration, an advantage of these structures is that their content can be efficiently accessed in real-time. This property enables various applications. We begin the tutorial by introducing the concepts of sparsity and of coherency in voxel structures, and explain how a directed acyclic graph (DAG) can be used to represent voxel geometry in a form that exploits both aspects, while remaining usable in its compressed from for e.g. ray casting. In this context, we also discuss extensions that cover the time domain or consider an advanced encoding strategies exploiting symmetries and entropy. We then move on to voxel attributes, such as colors, and explain how to integrate such information with the voxel DAGs. We will provide implementation details and present methods for efficiently constructing the DAGs...

When light waves propagate through disordered photonic lattices, they can eventually become localized due to multiple scattering effects. Here we show experimentally that while the evolution and localization of the photon density distribution is similar in the two cases of diagonal and offdiagonal disorder, the density-density correlation carries a distinct signature of the type of disorder. We show that these differences reflect a symmetry in the spectrum and eigenmodes that exists in off-diagonally disordered lattices but is absent in lattices with diagonal disorder.

In looking for qualitative differences between quaternionic and complex formulations of quantum physical theories, we provide a detailed discussion of the behavior of a wave packet in presence of a quaternionic time-independent potential step. In this paper, we restrict our attention to diffusion phenomena. For the group velocity of the wave packet moving in the potential region and for the reflection and transmission times, the study shows a striking difference between the complex and quaternionic formulations which could be matter of further theoretical discussions and could represent the starting point for a possible experimental investigation.

Thermal infrared (IR) spectra of materials are affected by subpixel surface roughness that increases interactions between surface facets, thereby shifting the spectra toward a blackbody. Roughness also creates directional effects due to differential solar heating and view geometry. Three types of ground-based experiments were conducted to quantify roughness effects at scales of about 10 cm or less. First, a radiosity model was implemented and validated for natural and artificial surfaces using an imaging spectrometer. Area and resolution create practical computational limits so most simulations were performed at a resolution near 1 cm over a 1 m area. Surfaces were specified using laser profilometer data but can be simulated. Second, a well-calibrated radiometer was used to measure radiance for emissivity retrievals of different sized gravels and at different solar and view geometries. Finally, a reflectance spectrometer measured spectra for soft rocks sanded to different roughnesse...

: A new source of radiation has been postulated that occurs when a charged particle, moving with a velocity greater than the velocity of light in a medium, is caused to oscillate about its transverse beam line by means of a static, periodic magnetic or electric field or by means of an incident transverse wave. Experiments were conducted to measure this new source of electromagnetic shock radiation, and compare it to Cerenkov radiation, a known source of electromagnetic shock radiation. The preliminary results agree with predictions of Schneider and Spitzer, but the present accuracy is not sufficient to rule out alternative theories. (Author)

This work reports on x-ray absorption spectroscopy study at the Si K edge of several amorphous SiO x C y H z polymers prepared by plasma-enhanced chemical-vapor deposition with different C / O ratios. SiO 2 and SiC have been used as reference materials. The comparison of the experimental Si K-edge x-ray absorption nearedge structure spectra with theoretical computations based on multiple scattering theory has allowed us to monitor the modification of the local coordination around Si as a function of the overall C / O ratio in this kind of materials.

Inclusive jet production in pPb collisions at a nucleon-nucleon (NN) center-of-mass energy of √ s NN = 5.02 TeV is studied with the CMS detector at the LHC. A data sample corresponding to an integrated luminosity of 30.1 nb -1 is analyzed. The jet transverse momentum spectra are studied in seven pseudorapidity intervals covering the range -2.0 < η CM < 1.5 in the NN center-of-mass frame. The jet production yields at forward and backward pseudorapidity are compared and no significant asymmetry about η CM = 0 is observed in the measured kinematic range. The measurements in the pPb system are compared to reference jet spectra obtained by extrapolation from previous measurements in pp collisions at √ s = 7 TeV. In all pseudorapidity ranges, nuclear modifications in inclusive jet production are found to be small, as predicted by next-to-leading order perturbative QCD calculations that incorporate nuclear effects in the parton distribution functions.

The porosity dependence of the elastic properties of porous silicon in different crystallographic directions is studied. The velocity of longitudinal acoustic waves in porous silicon layers electrochemically etched in (100), (110), and (111) oriented wafers has been measured by acoustic spectroscopy in the gigahertz frequency range. This non-destructive method was used for porous silicon layers with porosity of 25-85% obtaining velocities in the range of about 1 to 7 km s-1. The implication of constant Poisson’s ratio of porous silicon is examined. The effect of velocity dispersion due to multiple scattering is considered. The c11 stiffness constant can be obtained from the velocity measurement in the [100] direction of a cubic crystal. We show that, using the results for velocity in [110] or [111] directions and Keating’s relation, the stiffness constants c12 and c44 can be obtained. The velocity dependence on porosity was fitted as v=v0(1-φ)κ, where v0 is the velocity in bulk sili...

The Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board the ESA/Venus Express mission has technical specifications well suited for many science objectives of Venus exploration. VIRTIS will both comprehensively explore a plethora of atmospheric properties and processes and map optical properties of the surface through its three channels, VIRTIS-M-vis (imaging spectrometer in the 0.3-1 mm range), VIRTIS-M-IR (imaging spectrometer in the 1-5 mm range) and VIRTIS-H (aperture highresolution spectrometer in the 2-5 mm range). The atmospheric composition below the clouds will be repeatedly measured in the night side infrared windows over a wide range of latitudes and longitudes, thereby providing information on Venus's chemical cycles. In particular, CO, H 2 O, OCS and SO 2 can be studied. The cloud structure will be repeatedly mapped from the brightness contrasts in the near-infrared night side windows, providing new insights into Venusian meteorology. The global circulation and local dynamics of Venus will be extensively studied from infrared and visible spectral images. The thermal structure above the clouds will be retrieved in the night

We present radiative transfer modelling of thermal emission from the nightside of Venus in two 'spectral window' regions at 1.51 and 1.55 μm. The first discovery of these windows, reported by Erard et al. 2009, was achieved using a principal component analysis of data from the VIRTIS instrument on Venus Express. These windows are spectrally narrow, with a full-width at half-maximum of ~20 nm, and less bright than the well-known 1.7 and 2.3 μm spectral windows by two orders of magnitude. In this note we present the first radiative transfer analysis of these windows. We conclude that the radiation in these windows originates at an altitude of 20-35 km. As is the case for the other infrared window regions, the brightness of the windows is affected primarily by the optical depth of the overlying clouds; in addition, the 1.51 μm radiance shows a very weak sensitivity to water vapour abundance.

Volcanoes are one of the people favourite scientific issue, and the request of information about them directed to researches involved in volcano studies, are particularly frequent and pressing in active volcanic areas. Education and information programs play an important role among the natural risk mitigation measures. A long-term effort in educational programs is essential to convey simple, clear and complete information able to contribute to a better understanding of peculiar territory features and the related hazard and risk.

diffuseurs elastiques aleatoirement repartis. Cette etude se compose de trois parties. La premiere partie s&#39;interesse a un nombre restreint de diffuseurs. Elle a permis de mettre en evidence un phenomene de couplage resonant entre des diffuseurs cylindriques proches se manifestant par une demultiplication des frequences de resonances associees a l&#39;onde A (onde de Scholte-Stoneley). Ces demultiplications ont ete validees experimentalement. La seconde partie presente deux theories de milieu effectif : celle de Waterman et Truell et celle de Fikioris et Waterman. La philosophie de ces deux theories est de determiner l&#39;onde moyenne resultant d&#39;un moyennage sur les positions des diffuseurs. C&#39;est cette onde que l&#39;on appelle onde coherente. Ces theories aboutissent au calcul d&#39;un nombre d&#39;onde effectif caracterisant l&#39;onde coherente. La difference essentielle entre ces deux theories reside dans la prise en compte de la taille des diffuseurs dans celle d...

The first studies of the polarized sulfur and chlorine x-ray K-edge absorption spectra of the oxy- anions SO4 (sulfate), C103 (chlorate), S203 (thiosulfate), and S206 (dithionate) are presented. To provide a basis for the interpretation of the experimental measurements, extended continuum multiple-scattering Xn computations were carried out. This approach enabled us to identify features in the absorption spectra both by symmetry and final-state type (final bound states or final continuum states). For the thiosulfate anion (which has two nonequivalent sulfur atoms) it proved possible to determine which sulfur atom is responsible for each of a series of well-resolved features in the polarized spectra. In addition, generalizing from the case of the chlorate anion, molecules in which the absorbing atom is not completely surrounded by ligands ("open clusters" ) may have im- portant contributions from the second shell of neighbors manifested as features in the continuum re- gion of the spectrum.

Depolarization lidars are widely used for the study of clouds and aerosols because of their ability to discriminate between spherical particles and particles of irregular shape. Depolarization of cloud backscatter can be caused also by the multiple scattering events. One of the ways to gain information about particle parameters in the presence of strong multiple scattering is the measurement of azimuthally dependent polarization patterns in the focal plane of receiver. In this paper we present an algorithm for the calculation of corresponding polarized patterns in the frame of double scattering approximation. The computations are performed for different parameters of scattering geometry, e.g. cloud base and sounding depth. Intensity distribution of depolarized component is of cross-shape and rotated at 45 dg with respect to laser polarization. The use of a properly oriented cross-shape mask in the receiver focal plane allows removing a significant portion of depolarized component produced by double scattering. To verify it experimentally, cloud depolarization measurements were performed with different orientations of cross-shape mask. Results obtained from measurements are in qualitative agreement with the model prediction.

Depolarization lidars are widely used to study clouds and aerosols because of their ability to discriminate between spherical particles and particles of irregular shape. Depolarization of cloud backscattered radiation can be caused also by multiple scattering events. One of the ways to gain information about particle parameters in the presence of strong multiple scattering is the measurement of radial and azimuthal dependence of the polarization patterns in the focal plane of receiver. We present an algorithm for the calculation of corresponding polarized patterns in the frame of double scattering approximation. Computations are performed for various receiver field of views, for different parameters of the scattering geometry, e.g., cloud base and sounding depth, as well as for different values of cloud particle size and refractive index. As the spatial distribution of cross-polarized radiation is of cross shape and rotated at 45°with respect to laser polarization, the use of a properly oriented cross-shaped mask in the receiver focal plane allows the removal of a significant portion of the depolarized component of the backscattered radiation produced by double scattering. This has been verified experimentally based on cloud depolarization measurements performed at different orientations of the cross-shaped mask. Results obtained from measurements are in agreement with model predictions.

A new computer model, the GCR Event-based Risk Model code (GERMcode), was developed to describe biophysical events from high-energy protons and high charge and energy (HZE) particles that have been studied at the NASA Space Radiation Laboratory (NSRL) for the purpose of simulating space radiation biological effects. In the GERMcode, the biophysical description of the passage of HZE particles in tissue and shielding materials is made with a stochastic approach that includes both particle track structure and nuclear interactions. The GERMcode accounts for the major nuclear interaction processes of importance for describing heavy ion beams, including nuclear fragmentation, elastic scattering, and knockout-cascade processes by using the quantum multiple scattering fragmentation (QMSFRG) model. The QMSFRG model has been shown to be in excellent agreement with available experimental data for nuclear fragmentation cross sections. For NSRL applications, the GERMcode evaluates a set of biophysical properties, such as the Poisson distribution of particles or delta-ray hits for a given cellular area and particle dose, the radial dose on tissue, and the frequency distribution of energy deposition in a DNA volume. By utilizing the ProE/Fishbowl ray-tracing analysis, the GERMcode will be used as a bi-directional radiation transport model for future spacecraft shielding analysis in support of Mars mission risk assessments. Recent radiobiolical experiments suggest the need for new approaches to risk assessment that include time-dependent biological events due to the signaling times for activation and relaxation of biological processes in cells and tissue. Thus, the tracking of the temporal and spatial distribution of events in tissue is a major goal of the GERMcode in support of the simulation of biological processes important in GCR risk assessments. In order to validate our approach, basic radiobiological responses such as cell survival curves, mutation, chromosomal aberrations, and representative mouse tumor induction curves are implemented into the GERMcode. Extension of these descriptions to other endpoints related to non-targeted effects and biochemical pathway responses will be discussed.

The angular momentum independent statistical decay model is often applied using a Monte-Carlo simulation to describe the decay of prefragment nuclei in heavy ion reactions. This paper presents an analytical approach to the decay problem of nuclei with mass numbers less than 60, which is important for galactic cosmic ray (GCR) studies. This decay problem of nuclei with mass number less than 60 incorporates well-known levels of the lightest nuclei (A < 11) to improve convergence and accuracy. A sensitivity study of the model level density function is used to determine the impact on mass and charge distributions in nuclear fragmentation. This angular momentum independent statistical decay model also describes the momentum and energy distribution of emitted particles (n, p, d, t, h, and a) from a prefragment nucleus.

Background: Using optical techniques for tissue diagnostics (so-called 'optical biopsy') has been a subject of extensive research for many years. Various groups have been exploring different spectral and/or imaging modalities (e.g. diffuse reflectance spectroscopy, autofluorescence, Raman spectroscopy, optical coherence tomography (OCT), polarized light microscopy, etc.) for biomedical applications. In this paper, we report on using multi-wavelength imaging Mueller polarimetry combined with an appropriated image post-processing for the detection of tissue malignancy. Methods: We investigate a possibility of complementary analysis of Mueller matrix images obtained for turbid tissue-like scattering phantoms and excised human normal and cancerous colorectal tissue samples embedded in paraffin. Combined application of correlation, fractal and statistical analysis was employed to assess quantitatively the polarization-inhomogeneous scattered fields observed at the surface of tissue samples. Results: The combined analysis of the polarimetric images of paraffin-embedded tissue blocks has proved to be an efficient tool for the unambiguous detection of tissue malignant transformation. A fractal structure was clearly observed at spatial distributions of depolarization of light scattered in healthy tissues in a visible range of spectrum, while corresponding distributions for cancerous tissues did not show such dependence. We demonstrate that paraffin does not destroy a fractal structure of spatial distribution of depolarization. Thus, the loss of fractality in spatial distributions of depolarization for cancerous tissue is related to the structural changes in the tissue sample induced by cancer itself and, therefore, may serve as a marker of the disease. The obtained results emphasize that a combined use of statistical, correlation and fractal analysis for the Mueller-matrix image post-processing is an effective approach for an assessment of variations of optical properties in turbid tissue-like scattering media and biological tissues, with a high potential to be transferred to clinical practice for screening cancerous tissue samples.

Under almost all circumstances, electron diffraction patterns contain information about the phases of structure factors, a consequence of the short wavelength of an electron and its strong Coulombic interaction with matter. However, extracting this information remains a challenge and no generic method exists. In this work, a set of simple analytical expressions is derived for the intensity distribution in convergent-beam electron diffraction (CBED) patterns recorded under three-beam conditions. It is shown that these expressions can be used to identify features in three-beam CBED patterns from which three-phase invariants can be extracted directly, without any iterative refinement processes. The octant, in which the three-phase invariant lies, can be determined simply by inspection of the indexed CBED patterns (i.e. the uncertainty of the phase measurement is ±22.5°). This approach is demonstrated with the experimental measurement of three-phase invariants in two simple test cases: ...

We present a new tomographic method based on the non-linear least-squares inversion of seismograms using the spectral elements method (SEM). The SEM is used for the forward modelling and to compute partial derivatives of seismograms with respect to the model parameters. The main idea of the method is to use a special data reduction scheme to overcome the prohibitive numerical cost of such an inversion. The SEM allows us to trigger several sources at the same time within one simulation with no incremental numerical cost. Doing so, the resulting synthetic seismograms are the sum of seismograms due to each individual source for a common receiver and a common origin time, with no possibility to separate them afterward. These summed synthetics are not directly comparable to data, but using the linearity of the problem with respect to the seismic sources, we can sum all data for a common station and a common zero time, and we perform the same operation on synthetics. Using this data reduction scheme, we can then model the whole data set using a single SEM run, rather than a number of runs equal to the number of events considered, allowing this type of inversion to be feasible on a reasonable size computer. In this paper we present tests that show the feasibility of the method. It appears that this approach can work owing to the combination of two factors: the off-path sensitivity of the long-period waveforms and the presence of multiple-scattering, which compensate for the loss of information in the summation process. We discuss the advantages and drawbacks of such a scheme.

This paper describes new Monte Carlo codes for proton transport simulations in complex geometrical forms and in materials of different composition. The SRNA codes were developed for three dimensional (3D) dose distribution calculation in proton therapy and dosimetry. The model of these codes is based on the theory of proton multiple scattering and a simple model of compound nucleus decay. The developed package consists of two codes: SRNA-2KG and SRNA-VOX. The first code simulates proton transport in combined geometry that can be described by planes and second order surfaces. The second one uses the voxelized geometry of material zones and is specifically adopted for the application of patient computer tomography data. Transition probabilities for both codes are given by the SRNADAT program. In this paper, we will present the models and algorithms of our programs, as well as the results of the numerical experiments we have carried out applying them, along with the results of proton t...

A methodology is introduced for the systematic treatment of electron-electron correlations in solids and other interacting quantum N-particle systems. The method is developed within the framework of electronic structure theory ͑band theory͒ but, in contrast to conventional approaches, which are based on the singleparticle picture, it is formulated within a many-particle picture in which n particles in d-dimensional phase space are treated as a single particle in a phase space of nd dimensions. In this phase space, interparticle interactions appear as external potentials allowing the treatment of the system of particles through the use of single-particle methods, while at the same time allowing a systematic, direct, and nonperturbative treatment of interparticle interactions. The method makes use of the invariance of the Hamiltonian describing an interactingparticle system under partitioning into subsystems of n particles. This treatment leads to exact results in the limit n→N. Based on such partitioning, we propose a generalization of density functional theory and an appropriately defined local density approximation to treat the interactions between the n-particle units in a system of Nуn particles. This approach yields n-particle correlated densities and n-particle states which can be used in an analysis of the electronic properties of materials, such as total energy, phase stability, electronic transport, and others. We use the formal construct of multiple-scattering theory to develop the method for the calculation of the two-particle electronic structure of a solid and the corresponding total energy of the ground state. We also illustrate some of the properties of the method in terms of a Hubbard model Hamiltonian on a linear ring. Various features of the method and further possible applications are presented in a discussion section. ͓S0163-1829͑97͒02240-6͔

Modern optical diagnostics for quantitative characterization of polydisperse sprays and other aerosols which contain a wide range of droplet size encounter difficulties in the dense regions due to the multiple scattering of laser radiation with the surrounding droplets. The accuracy and efficiency of optical measurements can only be improved if the radiative transfer within such polydisperse turbid media is understood. A novel Monte Carlo code has been developed for modeling of optical radiation propagation in inhomogeneous polydisperse scattering media with typical drop size ranging from 2 µm to 200 µm in diameter. We show how strong variations of both particle size distribution and particle concentration within a 3D scattering medium can be taken into account via the Monte Carlo approach. A new approximation which reduces ~20 times the computational memory space required to determine the phase function is described. The approximation is verified by considering four log-normal drop size distributions. It is found valid for particle sizes in the range of 10-200 µm with increasing errors, due to additional photons scattered at large angles, as the number of particles below than 10 µm increases. The technique is applied to the simulation of typical planar Mie imaging of a hollow cone spray. Simulated and experimental images are compared and shown to agree well. The code has application in developing and testing new optical diagnostics for complex scattering media such as dense sprays.

Emulsion or suspension destabilisation is often due to two physical phenomena: (1) particle size increase (coalescence) or particle aggregation (flocculation); (2) particle migration (creaming or sedimentation). Creaming or sedimentation are often considered as reversible while coalescence or flocculation spells disaster for the formulator. Therefore, it is of prime importance to detect at an early stage these phenomena in order to shorten the ageing tests and to improve the formulations. This work thus concerns the optical characterisation of destabilisation of concentrated dispersions. It deals mainly with the independent and anisotropic scattering of light by a suspension or emulsion in a cylindrical glass tube in relation with the optical analyser TURBISCAN MA 1000. Indeed, in dense suspensions or emulsions, photons undergo many scattering events before escaping the medium and entering a receiver aperture. Multiple scattering thus contributes significantly to the measured transmitted and backscattered flux. We present statistical models and numerical simulations for the radiative transfer in suspensions (plane or cylindrical geometry) only involving the photon mean path length, the asymmetry factor and the geometry of the light receivers. We have further developed an imaging method with high grey level resolution for the visualisation and the analysis of the surface flux in the backscattered spot light. We compare the results from physical models and simulations with those of experiments performed using the imagery method and the TURBISCAN MA 1000 analyser for dispersions of latex beads (variable size and particle volume fraction). We then present a few examples of dispersion destabilisation analysis with the TURBISCAN MA 1000. We show that the instrument is able to discriminate concentration and particle or aggregate size variations and to detect those phenomena much earlier than the operator's naked eye, especially for opaque and concentrated systems.

Emulsion or suspension destabilisation often results from coalescence or particle aggregation (flocculation) leading to particle migration (creaming or sedimentation). Creaming and sedimentation are often considered as reversible, while coalescence and flocculation spell disaster for the formulator. Thus, it is of prime importance to detect coalescence or cluster formation at an early stage to shorten the ageing tests and to improve the formulations. This work mainly concerns the independent and anisotropic scattering of light from an emulsion or suspension in a cylindrical glass measurement cell, in relation with the optical analyser TURBISCAN MA 2000. The propagation of light through a concentrated dispersion can be used to characterise the system physico-chemical stability. Indeed, photons undergo many scattering events in an optically thick dispersion before escaping the medium and entering a receiver aperture. Multiple scattering thus contributes significantly to the transmitted and backscattered flux measured by TURBISCAN MA 2000. We present statistical models and numerical simulations for the radiative transfer in a suspension (plane or cylindrical measurement cells) only involving the photon mean path length, the asymmetry factor and the geometry of the light receivers. We further have developed an imaging method with high grey level resolution for the visualisation and the analysis of the surface flux in the backscattered spot light. We compare the results from physical models and numerical simulations with the experiments performed with the imaging method and the optical analyser TURBISCAN MA 2000 for latex beads suspensions (variable size and particle volume fraction). We then present a few examples of concentrated emulsion and suspension instability analysis with TURBISCAN 2000. It is shown that the instrument is able to characterise particle or aggregate size variation and particle/aggregate migration and to detect these phenomena much more earlier than the operator's naked eye, especially for concentrated and optically thick media.

Muon collider luminosity depends on the number of muons in the storage ring and on the transverse size of the beams in collision. Ionization cooling as it is currently envisioned will not cool the beam sizes sufficiently well to provide adequate luminosity without large muon intensities. Six-dimensional cooling schemes will reduce the longitudinal emittance of a muon beam so that smaller high frequency RF cavities can be used for later stages of cooling and for acceleration. However, the bunch length at collision energy is then shorter than needed to match the interaction region beta function. New ideas to shrink transverse beam dimensions by lengthening each bunch will help achieve high luminosity in muon colliders. Analytic expressions for the reverse emittance exchange mechanism were derived, including a new resonant method of beam focusing.

The NOAA-7, GOES-5 and GOES-0 VISSR/VAS solar channels have been calibrated for the periods from October 1983 through January 1985 (NOAA-7, GOES-6) and from October 1983 through July 1984 (GOES-5). The White Sands Monument area in New Mexico, whose relectance properties are well known, and space are used as calibration targets. The shortwave reflected terrestrial irradiance that is measured at satellite altitude is computed using a fairly accurate radiative transfer model which accounts for multiple scattering and bidirectional effects ( T a d et d., 1979). The ground target reflectance and relevant characteristics of the overlying atmosphere are estimated from climatological data (ozone amount, aerosol size-frequency distribution and refractive index) and observations at the nearest meterorological sites (water vapor amount, visibility). The approach is believed to produce accuracies of 8 to 13% depending on the channel considered. The results obtained for the 15-month period do not indicate any drift in the solar channels of both types of instrument. The gain changes, about 15% of the mean values, are largely attributed to inhomogeneities of the ground target (shading effects due to the presence of dunes). No systematic effect of the normalization procedure applied by NOAA to the raw VISSR/VAS data is detected. There is some evidence that the GOES-5 solar channels gradually deteriorated from March 1984 until the failure of the satellite in July 1984. Comparisons of gains determined in orbit with those before launch show that the NOAA-7 solar channels read higher by about 15%. The disparities cannot be explained by model errors and must have occurred before the time period analyzed here.

We discuss, using the Glauber multiple-scattering formalism, the magnitude of the contributions to particle production c r o s s sections from nuclei at high energies which can be attributed to multiple-inelastic-scattering processes involving a number of nucleons. Of particular interest i s the contribution of such processes to the production of particles with high spin or hypercharge, since the beam particle can be "promoted" to these final states as a result of a s e r i e s of collisions, each involving only a relatively small change in i t s spin o r hyperchange. When we compare these "promotional" production cross sections due to multiple scattering within a nucleus with estimates of the corresponding production c r o s s sections due to multiple scattering within a single nucleon, however, we find that there is no overwhelming practical advantage in going to a nuclear target. The basic reason seems to be that the "thickness" of nuclear matter offered to a beam particle passing through the center of an individual nucleon i s not so much smaller in units of mean free paths than that offered by a nucleus.

The Green's function method (GFM) is used to describe the effects of a statistical roughness on the propagation of electromagnetic fields in a circular waveguide. The GFM method, applied to a scalar Helmholtz equation with perturbed boundary conditions, allows us to treat multiple scattering of the field. Theoretical results for azimuthal and longitudinal roughness are reported, and the phase velocity of the field is discussed in both cases.

The electronic structure of complex oxides is important for the understanding of their functional properties. In this paper, the electronic structures of the multiferroic perovskite bismuth ferrite ͑BiFeO 3 ͒ and the related isostructural compounds Bi 0.9 La 0.1 FeO 3 and BiFe 0.7 Mn 0.3 O 3 are investigated through experiments and modeling. Using electron energy loss spectroscopy the oxygen K edge, i.e., the unoccupied O p density of states, is probed. As these states participate in covalent bonding with both Bi and Fe states, insight into the bonding in the materials is obtained. By substituting on both cation sites, it is possible to connect features in the spectrum to chemical bonds to the cations. We compare the experimental results of substituted and unsubstituted BiFeO 3 and apply a multiple-scattering approach as well as density functional theory to interpret the differences in terms of changes in electronic structure and density of states. Specifically, we show that although mainly ionic, both Bi-O and Fe-O bonds have some covalent character, and that Mn substitution on Fe sites is found to alter the Bi-O bonds and reduce the anisotropy of the system. Upon introduction of La on Bi sites, the covalent character of the material is reduced and the ionic interaction increases as the La-O bond is higher in energy and mediated through other cation orbitals ͑La d orbitals͒ than the Bi-O bond ͑Bi p orbitals͒. Also, La substitution is found to influence the Fe electronic structure, showing that the A and B site cations are more coupled than commonly recognized. Thus, we use the electronic structure to confirm that B site cation substitution can influence the ferroelectricity, which is usually almost exclusively attributed to A site cation anisotropy.

X-ray absorption near-edge structure (XANES) calculations of stoichiometric SrBi2Ta2O9 (SBT) and off-stoichiometric Sr0.8Bi2.2Ta2O9 (offstoich-SBT) with space group of A21am have been performed using FEFF 8.2 code, which is based on real space multiple scattering approach. Due to the nature of layered structure of SBT any change in atomic concentration of crystal may cause change in the electronic and magnetic properties. It was observed that lower concentration of Strontium (Sr) lead to an energy shift about 2 eV to higher energies due to the weaker interaction with valency levels of Sr and Oxygen atoms. On the contrary, regarding to offstoich-SBT as a result of higher concentration, Bismuth (Bi) atoms locate closer distances to Oxygen atoms. Hence, Bismuth have energy shifts about 16 eV to lower energy side in M-edge. Such properties lead to change in electronic and ferroelectric properties of SBT.

The structure of TcO2 between 25 and 1000 °C has been determined in situ using X-ray powder diffraction methods and is found to remain monoclinic in space group P21/c. Thermal expansion in TcO2 is highly anisotropic, with negative thermal expansion of the b axis observed above 700 °C. This is the result of an anomalous expansion along the a axis that is a consequence of weakening of the Tc-Tc bonds.

Methanobactin is a small siderophore-like molecule proposed to function in copper sequestration and handling by methanotrophs, methane-oxidizing bacteria that play a key role in the global carbon cycle. 1 Copper is critical to methanotroph metabolism, regulating expression of two methane monooxygenase (MMO) systems, 2,3 soluble MMO (sMMO) 4 and particulate MMO (pMMO) 5 as well as of other metabolic enzymes. 6 In addition, copper is a pMMO cofactor 7-9 and stimulates the formation of intracytoplasmic membranes that house pMMO. 3,10 Methanobactin may not function solely in copper uptake, but could also play a more direct role in pMMO loading and activity. Originally referred to as a copper-binding compound (CBC), methanobactin was first detected a decade ago, 11-13 but difficulties with degradation precluded structural characterization until recently. 14,15 The sequence of methanobactin from Methylosinus trichosporium OB3b is N-2-isopropylester-(4-thionyl-5hydroxyimidazolate)-Gly 1-Ser 2-Cys 3-Tyr 4-pyrrolidine-(4-hydroxy-5-thionylimidazolate)-Ser 5-Cys 6-Met 7 , and the crystal structure shows a single copper ion coordinated by an N 2 S 2 donor set (Scheme 1). 14,15 On the basis of its structural similarity to iron siderophores, 16 methanobactin may have antibacterial properties. 14 Additional practical applications for methanobactin potentially include its use in the semiconductor industry to remove copper from wastewater. 17 Despite its potential broad importance, key information about methanobactin, such as the oxidation state of the chelated copper ion, is lacking. Here we show by electron paramagnetic resonance (EPR) and X-ray absorption (XAS) spectroscopies that methanobactin binds copper in the 1+ oxidation state. Spent media from M. trichosporium OB3b was incubated with CuCl 2 , and methanobactin was isolated and purified by protocols similar to those described by Graham and co-workers. 12, 15 Analysis of the final product by MALDI-MS or ESI-MS gave a single peak at 1215 Da, corresponding to an 1153 Da methanobactin molecule which has lost one or two hydrogen atoms and bound one copper atom. Anaerobic incubation of spent media with CuCl also gave a peak at 1215 Da (Figure S1), indicating that apo methanobactin can be fully loaded with one copper ion by treatment with either Cu(II) or Cu(I). The X-band EPR spectrum of Cu(II)-loaded methanobactin (Figure 1, blue trace) shows a weak, poorly resolved signal with g || = 2.32(2), g ⊥ = 2.07(1), and A || = 420(20) MHz (130 G) (all parameters determined by spectral simulation). A similar sized peptide from M.

During the EASOE campaign in the Arctic, all lidar measurements showed total depolarization values for the Pinatubo stratospheric aerosol layer varying between 2% and 4%. If multiple 'scattering is negligible, the radiation backscattered by a polydispersion of spheres has the same polarization as the incident light. There is always some depolarization of a lidar return because of the anisotropy of the polarizability of the air molecules, but depolarization in the signal returned from aerosols indicates the presence of non-spherical particles. In this paper, we utilize scattering calculations for non-spherical particles to explore interpretations of lidar signals returned by Pinatubo aerosols. Taking into account several particle shapes and lognormal size distributions, calculations show that only slightly-to-moderate deformed spheres with equivalentmean-radius less then.0.2/•m yield depolarization values in the range given by the lidar measurements, if such particles form a substantial fraction of the population. The implications of particle non-sphericity on the retrieval of the aerosol size distribution are discussed.

Experiments with resonant photons at the U M 4 edge have been performed on a sample of USb0.9Te0.1, which has an incommensurate magnetic structure with k = k = 0.596(2) reciprocal lattice units. The reflections of the form kkk , as observed previously in a commensurate k = 1/2 system [N. Bernhoeft et al., Phys. Rev. B 69 174415 (2004)] are observed, removing any doubt that these occur because of multiple scattering or high-order contamination of the incident photon beam. They are clearly connected with the presence of a 3k configuration. Measurements of the kkk reflections from the sample UAs0.8Se0.2 in a magnetic field show that the transition at T * ∼50 K is between a low-temperature 2k and high-temperature 3k state and that this transition is sensitive to an applied magnetic field. These experiments stress the need for quantitative theory to explain the intensities of these kkk reflections.