Showing papers on "Scattering published in 2000"

High-field electrical transport in single-wall carbon nanotubes

Abstract: Using low-resistance electrical contacts, we have measured the intrinsic high-field transport properties of metallic single-wall carbon nanotubes. Individual nanotubes appear to be able to carry currents with a density exceeding 10(9) A/cm(2). As the bias voltage is increased, the conductance drops dramatically due to scattering of electrons. We show that the current-voltage characteristics can be explained by considering optical or zone-boundary phonon emission as the dominant scattering mechanism at high field.

Smoke, Dust, and Haze: Fundamentals of Aerosol Dynamics

Abstract: 1. AEROSOL CHARACTERIZATION Parameters Determining Aerosol Behavior Particle Size Particle Concentration Size Distribution Function Moments of the Distribution Function Examples of Size Distribution Functions Chemical Composition Aerosol Dynamics: Relation to Characterization 2. PARTICLE TRANSPORT PROPERTIES Equation of Diffusion Coefficient of Diffusion Friction Coefficient Agglomerate Diffusion Coefficients Path Length of a Brownian Particle Migration in an External Force Field Electrical Migration Thermophoresis London-van der Waals Forces Boundary Condition for Particle Diffusion 3. CONVECTIVE DIFFUSION: EFFECTS OF FINITE PARTICLE DIAMETER AND EXTERNAL FORCE FIELDS Equation of Convective Diffusion Similitude Considerations for Aerosol Diffusion Concentration Boundary Layer Diffusion to Cylinders at Low Reynolds Numbers: Concentration Boundary Layer Equation Diffusion at Low Reynolds Numbers: Similitude Law for Particles of Finite Diameter Low Re Deposition: Comparison of Theory with Experiment Single Element Particle Capture by Diffusion and Interception at High Reynolds Numbers High Re Deposition: Application to Deposition on Rough Surfaces Diffusion from a Laminar Pipe Flow Diffusion from a Turbulent Pipe Flow Particle Deposition from Rising Bubbles Convective Diffusion in an External Force Field: Electrical Precipitation Thermophoresis: "Dust Free Space" 4. INERTIAL TRANSPORT AND DEPOSITION Particle-Surface Interactions: Low Speeds Particle-Surface Interactions: Rebound Particle Acceleration at Low Reynolds Numbers: Stop Distance Similitude Law for Impaction: Stokesian Particles Impaction of Stokesian Particles on Cylinders and Spheres Impaction of Non-Stokesian Particles Deposition from a Rotating Flow: Cyclone Separator Particle Eddy Diffusion Coefficient Turbulent Deposition Aerodynamic Focusing: Aerosol Beams Transition from the Diffusion to Inertial Ranges 5. LIGHT SCATTERING Scattering by Single Particles: General Considerations Scattering by Particles Small Compared to the Wavelength Scattering by Large Particles: The Extinction Paradox Scattering in the Intermediate Size Range: Mie Theory Scattering by Aerosol Clouds Scattering over the Visible Wavelength Range: Aerosol Contributions by Volume Rayleigh Scattering: Self-Similar Size Distributions Mie Scattering: Power Law Distributions Quasi-Elastic Light Scattering Specific Intensity: Equation of Radiative Transfer Equation of Radiative Transfer: Formal Solution Light Transmission Through the Atmosphere: Visibility Inelastic Scattering: Raman Effect 6. EXPERIMENTAL METHODS Sampling Microscopy Mass Concentration: Filtration Total Number Concentration: Condensation Particle Counter Total Light Scattering and Extinction Coefficients Size Distribution Function Mass and Chemical Species Distribution: The Cascade Impactor Aerosol Chemical Analysis Summary Classification of Measurment Instruments Monodisperse Aerosol Generators 7. COLLISION AND COAGULATION: COALESCING PARTICLES Introduction Collision Frequency Function Brownian Coagulation Brownian Coagulation: Dynamics of Discrete Distribution for an Intially Monodisperse Aerosol Brownian Coagulation: Effect of Particle Force Fields Effect of van der Waals Forces Effect of Coulomb Forces Collision Frequency for Laminar Shear Simultaneous Laminar Shear and Brownian Motion Turbulent Coagulation Equation of Coagulation: Continuous Distribution Function Similarity Solution: Coagulation in the Continuum Regime Similarity Solution for Brownian Coagulation Similarity Solution: Coagulation in the Free Molecule Region Time to Reach the Self-Preserving Distribution (SPD) 8. DYNAMICS OF AGGLOMERATE FORMATION AND RESTRUCTURING Agglomerate Morphology: Scaling Laws Computer Simulation of Agglomerate Formation Langevin Simulations of Agglomeration Smoluchowski Equation: Collision Kernals for Power Law Aggregates Self-Preserving Agglomerate Size Distributions Effect of Primary Particle Size on Agglomerate Growth Effect of Df on Agglomearte Growth Agglomerate Restructuring 9. THERMODYNAMICS PROPERTIES The Vapor Pressure Curve and the Supersaturated State Effects of Solutes on Vapor Pressure Vapor Pressure of a Small Particle Hygroscopic Particle-Vapor Equilibrium Charged Particle-Vapor Equilibria Solid Particle-Vapor Equilibrium Effect of Particle Size on the Equilibrium of a Heterogeneous Chemical Reaction Molecular Clusters 10. GAS-TO-PARTICLE CONVERSION Condensation by Adiabatic Expansion: The Experiments of C.T.R. Wilson Kinetics of Homogeneous Nucleation Experimental Test of Nucleation Theory Heterogeneous Condensation Growth Laws Dynamics of Growth: Continuity Relation in v Space Measurement of Growth Rates: Homogeneous Gas-Phase Reactions Simultaneous Homogeneous and Heterogeneous Condensation Effects of Turbulence on Homogeneous Nucleation 11. THE GENERAL DYNAMIC EQUATION FOR THE PARTICLE SIZE DISTRIBUTION FUNCTION General Dynamic Equation for the Discrete Distribution Function Coagulation and Nucleation as Limiting Processes in Gas-to-Particle Conversion General Dynamic Equation for the Continuous Distribution Function The Dynamic Equation for the Number Concentration N The Dynamic Equation for the Volume Fraction Simultaneous Coagulation and Diffusional Growth: Similarity Solution for Continuum Regime Simultaneous Coagulation and Growth: Experimental Results The GDE for Turbulent Flow The GDE for Turbulent Stack Plumes Coagulation and Stirred Settling Coagulation and Deposition by Convective Diffusion Continuously Stirred Tank Reactor 12. SYNTHESIS OF SUBMICRON SOLID PARTICLES: AEROSOL REACTORS Aerosol Reactors: Commercial and Pilot Scale The Collision-Coalescence Mechanism of Primary Particle Formation Extension of the Smouluchowski Equation to Colliding, Coalescing Particles Rate Equation for Particle Coalescence Solid-State Diffusion Coefficient Estimation of Average Primary Particle Size: Method of Characteristic Times Primary Particle Size: Effects of Aerosol Material Properties Particle Neck Formation Particle Crystal Structure 13. ATMOSPHERIC AEROSOL DYNAMICS Atmospheric Aerosol Size Distribution Aerosol Dynamics in Power Plant Plumes Chemical Composition of Urban Aerosols Distributions of Chemical Species with Particle Size Morphological Characteristics of the Submicron Aerosol Common Measures of Air Quality for Particulate Matter: Federal Standards Receptor Modeling: Source Apportionment Statistical Variations of Ambient Aerosol Chemical Components EACH CHAPTER ENDS WITH PROBLEMS AND REFERENCES Common Symbols Index

Methods of X-ray and Neutron Scattering in Polymer Science

Abstract: This book presents the basic theories underlying x-ray and neutron scattering, as well as the various techniques that have been developed for their application to the study of polymers. The two scattering methods are discussed together from the beginning, so as to allow readers to gain a unified view of the scattering phenomena. The book is introductory and may be used as a textbook in polumer science class or for self-study by polymer scientists new in scattering techniques.

Angle-resonant stimulated polariton amplifier

Abstract: We experimentally demonstrate resonant coupling between photons and excitons in microcavities which can efficiently generate enormous single-pass optical gains approaching 100. This new parametric phenomenon appears as a sharp angular resonance of the incoming pump beam, at which the moving excitonic polaritons undergo very large changes in momentum. Ultrafast stimulated scattering is clearly identified from the exponential dependence on pump intensity. This device utilizes boson amplification induced by stimulated energy relaxation.

Light Scattering by Nonspherical Particles: Theory, Measurements, and Applications

Abstract: Almost all solid particles and very many liquid drops are not spherical. In addition, particles may have internal structure, both homogeneous and heterogeneous, and there may be agglomeration. It has long been recognized that the well-known Mie theory for homogeneous spheres, and similar theories for simple shapes such as the infinite cylinder, are not adequate representations of the scattering by more complex shapes and structures. There may be significant differences in the calculated phase function to that in reality, and a theory for homogeneous spheres will completely fail to predict polarization effects. In the absence of rigorous analytical solutions for particles of general shape and structure, recourse is made to numerical techniques. The development of powerful computers has enabled these calculations to be performed rapidly and accurately for a wide range of particle types and sizes. The growth in numerical techniques has been exponential. For these reasons this book has come at a very opportune time, and is a welcome review of a large field of expertise. Authors who are recognized masters review each subject, and all the major methods are covered. For completeness there are also sections dealing with examples of practical applications of the calculations to nature. The book opens with a foreword by the renowned H C van de Hulst, who provides an interesting historical review and perspective. An introductory section of three chapters follows, dealing with fundamental concepts and definitions. The first of these deals with scattering by single particles and moves on to multiple scattering and radiative transfer. The second chapter is concerned with methods for nonspherical particles. It briefly reviews the limited exact theories available and then covers numerical and approximate methods. Finally, there is a chapter covering the basic properties of the scattering matrix for small particles. Overall, this section provides a most welcome review and grounding in the necessary basics of the subject. The next two sections form the backbone of the book and are concerned with reviewing developments in numerical techniques. The first of these has chapters covering the method of separation of variables, the discrete dipole approximation, the T-matrix method and the finite difference time domain (FDTD) technique. The second section pursues inhomogeneous particles with refractive index profiles, heterogeneous particles with inclusions, multiple interacting particles and aggregates. At the end of this section is a chapter reviewing developments to date in the theory of scattering by statistically irregular particles. This is very welcome in light of the fact that the bulk of natural particles are not regular in the sense that their shapes can be predicted. The latter part of the book is the province of measurements and applications. Here it is slightly less satisfactory, being perhaps a little narrower in scope. Under measurements there is a description of one experimental method for the determination of the elements of the Stokes matrix and a description of one microwave facility for large scale modelling of particles. The final section is a review of applications. This is largely concerned with environmental situations, covering LIDAR and radiative transfer methods for studies of clouds, microwave measurements of precipitation, scattering in marine environments and interplanetary dust. The book ends with a short chapter of biological applications. These are all interesting and useful illustrative examples, but I wonder whether a wider view may have been appropriate. Applications in industrial situations come to mind. In summary this is a very worthwhile research publication. It is attractively presented and comprehensive. It will prove to be a most useful addition to the literature in the ever-expanding field of light scattering. A R Jones

Spatial confinement of laser light in active random media

Abstract: We have observed spatial confinement of laser light in micrometer-sized random media. The optical confinement is attributed to the disorder-induced scattering and interference. Our experimental data suggest that coherent amplification of the scattered light enhances the interference effect and helps the spatial confinement. Using the finite-difference time-domain method, we simulate lasing with coherent feedback in the active random medium.

Scattering of Electromagnetic Waves: Theories and Applications

Abstract: Introduction to Electromagnetic Scattering by a Single Particle. Basic Theory of Electromagnetic Scattering. Fundamentals of Random Scattering. Characteristics of Discrete Scatterers and Rough Surfaces. Scattering and Emission by Layered Media. Single Scattering and Applications. Radiative Transfer Theory. Solution Techniques of Radiative Transfer Theory. One-Dimensional Random Rough Surface Scattering. Index.

SAXS experiments on absolute scale with Kratky systems using water as a secondary standard

Abstract: For small-angle scattering, of X-rays (SAXS) and neutrons (SANS), the importance of absolute calibration has been recognized since the inception of the technique. The work reported here focuses on SAXS measurements using Kratky slit systems. In former days, only molecular weights or scattering per particle were determined, but today absolute calibration implies the use of the unit of cm−1 for the scattering curve. It is necessary to measure the so-called absolute intensity, which is the ratio of the scattering intensity to the primary intensity P0. Basically there are two possible ways to determine the absolute intensity. The first one is the direct method, which involves the mechanical attenuation of the primary beam by a rotating disc or a moving slit. The second is the indirect method, using secondary standards. Water is well suited as a calibration standard because of the angle-independent scattering. The essential advantage is that the scattering of water only depends on the physical property of isothermal compressibility. Before presenting an example of the practical performance of this method, the most important theoretical equations for an SAS experiment on the absolute scale are summarized. With the slit collimation system, the scattering curve of water can be measured with high enough statistical accuracy. As a first example, the scattering curve of the protein lysozyme on the absolute scale is presented. The second example is the determination of the aggregation number of a triblock copolymer P94 (EO17–PO42–EO17). Taking into account that at least 10% of the polymer sample consists of diblocks, the accuracy of around 10% for the determined aggregation number is rather good. The data of P94 are also considered on the particle scale in order to obtain the radial scattering-length density distribution.

Structural information from multilamellar liposomes at full hydration: full q-range fitting with high quality x-ray data

Abstract: We present a method for analyzing small angle x-ray scattering data on multilamellar phospholipid bilayer systems at full hydration. The method utilizes a modified Caille theory structure factor in combination with a Gaussian model representation of the electron density profile such that it accounts also for the diffuse scattering between Bragg peaks. Thus the method can retrieve structural information even if only a few orders of diffraction are observed. We further introduce a procedure to derive fundamental parameters, such as area per lipid, membrane thickness, and number of water molecules per lipid, directly from the electron density profile without the need of additional volumetric measurements. The theoretical apparatus is applied to experimental data on 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, and 1, 2-dipalmitoyl-sn-glycero-3-phosphoethanolamine liposome preparations.

Rayleigh scattering in high-Q microspheres

Abstract: The Rayleigh scattering has to be largely suppressed in high-Q whispering-gallery modes in microspheres because of restrictions imposed on scattering angles by cavity confinement. Earlier estimates of the fundamental limit for the quality factor in fused-silica microspheres are revisited, and Q≃1012 is predicted in few-millimeter-size fused-silica spheres, if the surface hydration problem is ovecome. Particular effects of surface scattering losses are analyzed, and the manifestation of scattering in the form of intermode coupling is calculated. The predominant effect of counterpropagating mode coupling (intracavity backscattering) is analyzed in the presence of a mode-matched traveling-wave coupler. As much as 100% resonance reflection regime is shown to be feasible.

What can x-ray scattering tell us about the radial distribution functions of water?

Abstract: We present an analysis of the Advanced Light Source (ALS) x-ray scattering experiment on pure liquid water at ambient temperature and pressure described in the preceding article. The present study discusses the extraction of radial distribution functions from the x-ray scattering of molecular fluids. It is proposed that the atomic scattering factors used to model water be modified to include the changes in the intramolecular electron distribution caused by chemical bonding effects. Based on this analysis we present a gOO(r) for water consistent with our recent experimental data gathered at the ALS, which differs in some aspects from the gOO(r) reported by other x-ray and neutron scattering experiments. Our gOO(r) exhibits a taller and sharper first peak, and systematic shifts in all peak positions to smaller r. Based on experimental uncertainties, we discuss what features of gOO(r) should be reproduced by classical simulations of nonpolarizable and polarizable water models, as well as ab initio simulations of water, at ambient conditions. We directly compare many water models and simulations to the present data, and discuss possible improvements in both classical and ab initio simulation approaches in the future.

Continuous wave observation of massive polariton redistribution by stimulated scattering in semiconductor microcavities

Abstract: A massive redistribution of the polariton occupancy to two specific wave vectors is observed under conditions of continuous wave excitation of a semiconductor microcavity. The “condensation” of the polaritons to the two specific states arises from stimulated scattering at final state occupancies of order unity. The stimulation phenomena, arising due to the bosonic character of the polariton quasiparticles, occur for conditions of resonant excitation of the lower polariton branch. High energy nonresonant excitation, as in most previous work, instead leads to conventional lasing in the vertical cavity structure.

CONUSS and PHOENIX: Evaluation of nuclear resonant scattering data

Abstract: Evaluation methods for data obtained by nuclear resonant scattering techniques are discussed. The CONUSS software package for the interpretation of time or energy spectra from coherent elastic nuclear resonant scattering, i.e., forward scattering and Bragg/Laue scattering, is presented. The analysis of phonon spectra obtained by incoherent nuclear resonant scattering is demonstrated using the PHOENIX software.

Multiple Scattering, Parton Energy Loss and Modified Fragmentation Functions in Deeply Inelastic eA Scattering

Abstract: Modified quark fragmentation functions in deeply inelastic $\mathrm{eA}$ collisions and their QCD evolution equations are derived for the first time in the framework of multiple parton scattering. Induced radiation gives rise to additional terms in the evolution equations and thus softens the modified quark fragmentation functions. The results in the next-leading-twist depend on both diagonal and off-diagonal twist-four parton distributions and the combination of which clearly manifests the LPM interference pattern. The predicted modification depends quadratically on the nuclear size ( ${A}^{2/3}$). Generalization to the case of hot QCD medium is also discussed.

User Guide for the Discrete Dipole Approximation Code DDSCAT (Version 5a10)

Abstract: DDSCAT.5a is a freely available software package which applies the "discrete dipole approximation" (DDA) to calculate scattering and absorption of electromagnetic waves by targets with arbitrary geometries and complex refractive index. The DDA approximates the target by an array of polarizable points. DDSCAT.5a requires that these polarizable points be located on a cubic lattice. DDSCAT.5a10 allows accurate calculations of electromagnetic scattering from targets with "size parameters" 2 pi a/lambda < 15 provided the refractive index m is not large compared to unity (|m-1| < 1). The DDSCAT package is written in Fortran and is highly portable. The program supports calculations for a variety of target geometries (e.g., ellipsoids, regular tetrahedra, rectangular solids, finite cylinders, hexagonal prisms, etc.). Target materials may be both inhomogeneous and anisotropic. It is straightforward for the user to import arbitrary target geometries into the code, and relatively straightforward to add new target generation capability to the package. DDSCAT automatically calculates total cross sections for absorption and scattering and selected elements of the Mueller scattering intensity matrix for specified orientation of the target relative to the incident wave, and for specified scattering directions. This User Guide explains how to use DDSCAT.5a10 to carry out EM scattering calculations. CPU and memory requirements are described.

Time-resolved X-Ray diffraction from coherent phonons during a laser-induced phase transition

Abstract: Time-resolved x-ray diffraction with picosecond temporal resolution is used to observe scattering from impulsively generated coherent acoustic phonons in laser-excited InSb crystals. The observed frequencies and damping rates are in agreement with a model based on dynamical diffraction theory coupled to analytic solutions for the laser-induced strain profile. The results are consistent with a 12 ps thermal electron-acoustic phonon coupling time together with an instantaneous component from the deformation-potential interaction. Above a critical laser fluence, we show that the first step in the transition to a disordered state is the excitation of large amplitude, coherent atomic motion.

Elastic Wave Scattering by Periodic Structures of Spherical Objects: Theory and Experiment

Abstract: We extend the multiple-scattering theory for elastic waves by taking into account the full vector character. The formalism for both the band structure calculation and the reflection and transmission calculations for finite slabs is presented. The latter is based on a double-layer scheme which obtains the reflection and transmission matrix elements for the multilayer slab from those of a single layer. As a demonstration of applications of the formalism, we calculate the band structures of elastic waves propagating in a three-dimensional periodic arrangement of spherical particles and voids, as well as the transmission coefficients through finite slabs. In contrast with the plane-wave method, the multiple-scattering approach exhibits advantages in handling specialized geometries (spherical geometry in the present case). We also present a comparison between theory and ultrasound experiment for a hexagonal-close-packed array of steel balls immersed in water. Excellent agreement is obtained.

Organic light-emitting device with an ordered monolayer of silica microspheres as a scattering medium

Abstract: Periodic dielectric structures, consisting of hexagonally closed-packed arrays of silica microspheres with the diameter of 550 nm, were incorporated into organic light-emitting devices with a conventional two-layer structure made with vacuum-sublimation The arrays acted as a two-dimensional diffraction lattice which behaved as a light scattering medium for the light propagated in waveguiding modes within the device Strongly scattered light emission through the front surface of the devices was observed An increase in the device coupling-out factor for electroluminescent efficiency by using the scattering structure is demonstrated

Calculation of the amplitude matrix for a nonspherical particle in a fixed orientation.

Abstract: General equations are derived for computing the amplitude matrix for a nonspherical particle in an arbitrary orientation and for arbitrary illumination and scattering directions with respect to the laboratory reference frame, provided that the scattering problem can be solved with respect to the particle reference frame. These equations are used along with the T-matrix method to provide benchmark results for homogeneous, dielectric, rotationally symmetric particles. The computer code is publicly available on the World-Wide Web at http://www.giss.nasa.gov/~crmim.

A high-quality x-ray scattering experiment on liquid water at ambient conditions

Abstract: We report a new, high-quality x-ray scattering experiment on pure ambient water using a synchrotron beam line at the Advanced Light Source at Lawrence Berkeley National Laboratory. Several factors contribute to the improved quality of our intensity curves including use of a highly monochromatic source, a well-characterized polarization correction, a Compton scattering correction that includes electron correlation, and more accurate intensities using a modern charge coupled device (CCD) detector. We provide a comprehensive description of the data processing that we have used for correcting systematic errors, and we provide an estimate of our remaining random errors. The resulting error estimates of our data are smaller then the discrepancies between data sets collected in past x-ray experiments. We find that the older x-ray curves support a family of gOO(r)’s that exhibit a smaller first peak (∼2.2), while the current data is better fit with a family of gOO(r)’s with a first peak height of 2.8, and systema...

Scattering-theory analysis of waveguide-resonator coupling

Abstract: Using a formalism similar to the quantum scattering theory, we analyze the problem of coupling between optical waveguides and high Q resonators. We give the optical transmission and reflection coefficients as functions of the waveguide-resonator coupling, cavity loss (gain), and cavity resonant frequency. Based on these results, the recently proposed concept of "critical coupling" is discussed. Using a matrix formalism based on the scattering analysis, we find the dispersion relation of indirectly coupled resonator optical waveguides. The coupling between waveguides and multiple cavities is investigated and the reflection and transmission coefficients are derived.

Parameterization of the scattering and absorption properties of individual ice crystals

Abstract: We present parameterizations of the single-scattering properties for individual ice crystals of various habits based on the results computed from the accurate light scattering calculations. The projected area, volume, and single-scattering properties of ice crystals with various shapes and sizes are computed for 56 narrow spectral bands covering 0.2–5 μm. The ice crystal habits considered in this study are hexagonal plates, solid and hollow columns, planar and spatial bullet rosettes, and aggregates that are commonly observed in cirrus clouds. Using the observational relationships between the aspect ratios and the sizes of ice crystals, we can define the three-dimensional structure of these ice crystal habits with respect to their maximum dimensions for light scattering calculations. The volume and projected area of ice crystals, expressed in terms of the diameters of the corresponding equivalent spheres, are first parameterized by employing the ice crystal maximum dimensions. Further, various analytical expressions as functions of the effective dimensions of ice crystals have been developed to parameterize the extinction and absorption efficiencies, asymmetry factor, and the truncation of the forward peak energy in the phase function. The present parameterization scheme provides an efficient approach to obtain the basic scattering and absorption properties of nonspherical ice crystals.

Size effects in the electrical resistivity of polycrystalline nanowires

Abstract: Grain-boundary and surface scattering are known to increase the electrical resistivity of thin metallic films and wires. The length scale at which these produce appreciable effects is of the order of the electronic mean free path. For the well-studied case of thin films, both mechanisms can, in principle, be used to explain the observed thickness dependence on resistivity. In order to evaluate which of these mechanisms is more relevant, we have carried out an experimental study of the width dependence of the resistivity of narrow thin-film polycrystalline gold wires (nanowires), and computed the expected behavior on the basis of both surface and grain-boundary scattering mechanisms independently. We find that the resistivity increases as wire width decreases in a manner which is dependent on the mean grain size and cannot be explained adequately by either model alone. We propose a modification to the well-known model of Mayadas and Shatzkes, incorporating the variation of mean grain size on wire dimensions.

Electronic transport properties of single-crystal bismuth nanowire arrays

Abstract: We present here a detailed study of the electrical transport properties of single-crystal bismuth nanowire arrays embedded in a dielectric matrix. Measurements of the resistance of Bi nanowire arrays with different wire diameters (60\char21{}110 nm) have been carried out over a wide range of temperatures (2.0\char21{}300 K) and magnetic fields (0\char21{}5.4 T). The transport properties of a heavily Te-doped Bi nanowire array have also been studied. At low temperatures, we show that the wire boundary scattering is the dominant scattering process for carriers in the undoped single-crystal Bi nanowires, while boundary scattering is less important for a heavily Te-doped sample, consistent with general theoretical considerations. The temperature dependences of the zero-field resistivity and of the longitudinal magneto-coefficient of the Bi nanowires were also studied and were found to be sensitive to the wire diameter. The quantum confinement of carriers is believed to play an important role in determining the overall temperature dependence of the zero-field resistivity. Theoretical considerations of the quantum confinement effects on the electronic band structure and on the transport properties of Bi nanowires are discussed. Despite the evidence for localization effects and diffusive electron interactions at low temperatures $(Tl~4.0\mathrm{K}),$ localization effects are not the dominant mechanisms affecting the resistivity or the magnetoresistance in the temperature range of this study.

Scattering of elastic waves by periodic arrays of spherical bodies

Abstract: We develop a formalism for the calculation of the frequency band structure of a phononic crystal consisting of nonoverlapping elastic spheres, characterized by Lam\'e coefficients which may be complex and frequency dependent, arranged periodically in a host medium with different mass density and Lam\'e coefficients. We view the crystal as a sequence of planes of spheres, parallel to and having the two-dimensional periodicity of a given crystallographic plane, and obtain the complex band structure of the infinite crystal associated with this plane. The method allows one to calculate, also, the transmission, reflection, and absorption coefficients for an elastic wave (longitudinal or transverse) incident, at any angle, on a slab of the crystal of finite thickness. We demonstrate the efficiency of the method by applying it to a specific example.

Light scattering from cells: the contribution of the nucleus and the effects of proliferative status

Abstract: As part of our ongoing efforts to understand the fundamental nature of light scattering from cells and tissues, we present data on elastic light scattering from isolated mammalian tumor cells and nuclei. The contribution of scattering from internal structures and in particular from the nuclei was compared to scattering from whole cells. Roughly 55% of the elastic light scattering at high-angles (> 40 degrees) comes from intracellular structures. An upper limit of 40% on the fractional contribution of nuclei to scattering from cells in tissue was determined. Using cell suspensions isolated from monolayer cultures at different stages of growth, we have also found that scattering at angles greater than about 110 degrees was correlated with the DNA content of the cells. Based on model calculations and the relative size difference of nuclei from cells in different stages of growth, we argue that this difference in scattering results from changes in the internal structures of the nucleus. This interpretation is consistent with our estimate of 0.2 micron as the mean size of the scattering centers in cells. Additionally, we find that while scattering from the nucleus accounts for a majority of internal scattering, a significant portion must result from scattering off of cytoplasmic structures such as mitochondria.