Showing papers on "Scattering published in 2004"
TL;DR: The symmetry–imposed selection rules for double–resonant Raman scattering in graphite are developed and an excellent agreement is found between the graphite phonon dispersion from double– ResonantRaman scattering and other experimental methods.
Abstract: We present a review of the Raman spectra of graphite from an experimental and theoretical point of view. The disorder-induced Raman bands in this material have been a puzzling Raman problem for almost 30 years. Double-resonant Raman scattering explains their origin as well as the excitation-energy dependence, the overtone spectrum and the difference between Stokes and anti-Stokes scattering. We develop the symmetry-imposed selection rules for double-resonant Raman scattering in graphite and point out misassignments in previously published works. An excellent agreement is found between the graphite phonon dispersion from double-resonant Raman scattering and other experimental methods.
1,132 citations
TL;DR: It is demonstrated that in both model systems, a combination of short-range attraction and long-range repulsion results in the formation of small equilibrium clusters, which is relevant for nucleation processes during protein crystallization, protein or DNA self-assembly.
Abstract: Controlling interparticle interactions, aggregation and cluster formation is of central importance in a number of areas, ranging from cluster formation in various disease processes to protein crystallography and the production of photonic crystals. Recent developments in the description of the interaction of colloidal particles with short-range attractive potentials have led to interesting findings including metastable liquid-liquid phase separation and the formation of dynamically arrested states (such as the existence of attractive and repulsive glasses, and transient gels). The emerging glass paradigm has been successfully applied to complex soft-matter systems, such as colloid-polymer systems and concentrated protein solutions. However, intriguing problems like the frequent occurrence of cluster phases remain. Here we report small-angle scattering and confocal microscopy investigations of two model systems: protein solutions and colloid-polymer mixtures. We demonstrate that in both systems, a combination of short-range attraction and long-range repulsion results in the formation of small equilibrium clusters. We discuss the relevance of this finding for nucleation processes during protein crystallization, protein or DNA self-assembly and the previously observed formation of cluster and gel phases in colloidal suspensions.
967 citations
TL;DR: Numerical studies show that optical tweezers using radial polarization can stably trap metallic particles in 3-dimension due to the spatial separation of the gradient force and scattering/absorption forces.
Abstract: Metallic particles are generally considered difficult to trap due to strong scattering and absorption forces. In this paper, numerical studies show that optical tweezers using radial polarization can stably trap metallic particles in 3-dimension. The extremely strong axial component of a highly focused radially polarized beam provides a large gradient force. Meanwhile, this strong axial field component does not contribute to the Poynting vector along the optical axis. Consequently, it does not create axial scattering/absorption forces. Owing to the spatial separation of the gradient force and scattering/absorption forces, a stable 3-D optical trap for metallic particles can be formed.
747 citations
TL;DR: Using electrodynamics calculations, one dimensional array structures built from spherical silver nanoparticles that produce remarkably narrow plasmon resonance spectra upon irradiation with light that is polarized perpendicular to the array axis are discovered.
Abstract: Using electrodynamics calculations, we have discovered one dimensional array structures built from spherical silver nanoparticles that produce remarkably narrow (∼ meV or less) plasmon resonance spectra upon irradiation with light that is polarized perpendicular to the array axis. The narrow lines require a minimum particle radius of about 30 nm to achieve. Variations of the plasmon resonance wavelength, extinction efficiency and width with particle size, array structure, interparticle distance and polarization direction are examined, and conditions which lead to the smallest widths are demonstrated. A simple analytical expression valid for infinite lattices shows that the sharp resonance arises from cancellation between the single particle width and the imaginary part of the radiative dipolar interaction.
710 citations
TL;DR: In this article, the mean-free path of single-walled carbon nanotubes was inferred from the scaling of the resistance of the same nanotube with length in the low and high-bias regimes.
Abstract: Electron scattering rates in metallic single-walled carbon nanotubes are studied using an atomic force microscope as an electrical probe. From the scaling of the resistance of the same nanotube with length in the low- and high-bias regimes, the mean-free paths for both regimes are inferred. The observed scattering rates are consistent with calculations for acoustic-phonon scattering at low biases and zone boundary/optical phonon scattering at high biases.
687 citations
TL;DR: In this article, two opposing tip-to-tip Au triangles have been fabricated with triangle lengths of 75 nm and gaps ranging from 16 to 488 nm, and the plasmon scattering resonance first blue shifts with increasing gap, and then red shifts as the particles become more and more uncoupled, while perpendicularly polarized excitation shows little dependence upon gap size.
Abstract: Metallic “bowtie” nanoantennas consisting of two opposing tip-to-tip Au triangles have been fabricated with triangle lengths of 75 nm and gaps ranging from 16 to 488 nm. For light polarized along the line between the two triangles, the plasmon scattering resonance first blue-shifts with increasing gap, and then red-shifts as the particles become more and more uncoupled, while perpendicularly polarized excitation shows little dependence upon gap size. This behavior may be approximately understood in a coupled-dipole approximation as changes in the phase between static dipole−dipole interactions and dipole radiative interaction effects.
645 citations
TL;DR: This investigation details the properties of a passive, dispersive metamaterial that is matched to free space and has an index of refraction equal to zero, and shows that in both the source and scattering configurations the electromagnetic fields in a matched zero-index medium take on a static character in space, yet remain dynamic in time.
Abstract: Planar metamaterials that exhibit a zero index of refraction have been realized experimentally by several research groups. Their existence stimulated the present investigation, which details the properties of a passive, dispersive metamaterial that is matched to free space and has an index of refraction equal to zero. Thus, unlike previous zero-index investigations, both the permittivity and permeability are zero here at a specified frequency. One-, two-, and three-dimensional source problems are treated analytically. The one- and two-dimensional source problem results are confirmed numerically with finite difference time domain (FDTD) simulations. The FDTD simulator is also used to treat the corresponding one- and two-dimensional scattering problems. It is shown that in both the source and scattering configurations the electromagnetic fields in a matched zero-index medium take on a static character in space, yet remain dynamic in time, in such a manner that the underlying physics remains associated with propagating fields. Zero phase variation at various points in the zero-index medium is demonstrated once steady-state conditions are obtained. These behaviors are used to illustrate why a zero-index metamaterial, such as a zero-index electromagnetic band-gap structured medium, significantly narrows the far-field pattern associated with an antenna located within it. They are also used to show how a matched zero-index slab could be used to transform curved wave fronts into planar ones.
613 citations
TL;DR: Tip-enhanced Raman spectroscopy is reported on with smooth single crystalline surfaces as substrates, based on the optical excitation of localized surface plasmons in the tip-substrate cavity, which provides a large but local field enhancement near the tip apex.
Abstract: Tip-enhanced Raman spectroscopy (TERS) is based on the optical excitation of localized surface plasmons in the tip-substrate cavity, which provides a large but local field enhancement near the tip apex. We report on TERS with smooth single crystalline surfaces as substrates. The adsorbates were CN- ions at Au(111) and malachite green isothiocyanate (MGITC) molecules at Au(111) and Pt(110) using either Au or Ir tips. The data analysis yields Raman enhancements of about 4 x 10(5) for CN- and up to 10(6) for MGITC at Au(111) with a Au tip, probing an area of less than 100 nm radius.
561 citations
TL;DR: The structure of temperature-sensitive poly(N-isopropylacrylamide) microgels in dilute suspension was investigated by means of small-angle neutron scattering and clearly showed that the segment density in the swollen state is not homogeneous, but gradually decays at the surface.
Abstract: The structure of temperature-sensitive poly(N-isopropylacrylamide) microgels in dilute suspension was investigated by means of small-angle neutron scattering. A direct modeling expression for the scattering intensity distribution was derived which describes very well the experimental data at all temperatures over an extensive q range. The overall particle form as well as the internal structure of the microgel network is described by the model. The influence of temperature, cross-linking density, and particle size on the structure was revealed by radial density profiles and clearly showed that the segment density in the swollen state is not homogeneous, but gradually decays at the surface. The density profile reveals a box profile only when the particles are collapsed at elevated temperatures. An increase of the cross-linking density resulted in both an increase of the polymer volume fraction in the inner region of the particle and a reduction of the smearing of the surface. The polymer volume fraction inside the colloid decreased with increasing particle size. The structural changes are in good agreement with the kinetics of the emulsion copolymerization used to prepare the microgel colloids.
488 citations
TL;DR: In this paper, a new fundamental understanding of ballistic transport, optical phonon scattering and potential interfacial scattering mechanisms in nanotubes has been obtained, and the authors showed that the electrical transport in these miniature transistors is near ballistic up to high biases at both room and low temperatures.
Abstract: Carbon nanotube field-effect transistors with structures and properties near the scaling limit with short (down to 50 nm) channels, self aligned geometries, palladium electrodes with low contact resistance and high-k dielectric gate insulators are realized. Electrical transport in these miniature transistors is near ballistic up to high biases at both room and low temperatures. Atomic layer deposited (ALD) high-k films interact with nanotube sidewalls via van der Waals interactions without causing weak localization at 4 K. New fundamental understanding of ballistic transport, optical phonon scattering and potential interfacial scattering mechanisms in nanotubes are obtained.
482 citations
TL;DR: Extinction, scattering, and absorption cross sections and efficiencies were experimentally measured for chemically clean silver nanoparticles in water for 16 different sizes ranging from 29 to 136 nm in this article.
Abstract: Extinction, scattering, and absorption cross sections and efficiencies were experimentally measured for chemically clean silver nanoparticles in water for 16 different sizes ranging from 29 to 136 nm. The measured efficiencies indicate that particles interact with light 4−10 times stronger than the geometric cross section suggests. Absorption and scattering components of the plasmon resonance were separately measured across the visible spectral range. A method, termed standard subtraction, is suggested for the simple and reliable determination of particle concentrations independent of their size, shape, and aggregation state.
TL;DR: An unsupervised terrain and land-use classification algorithm using polarimetric synthetic aperture radar data using a combination of a scattering model-based decomposition developed by Freeman and Durden and the maximum-likelihood classifier based on the complex Wishart distribution is proposed.
Abstract: In this paper, we proposed an unsupervised terrain and land-use classification algorithm using polarimetric synthetic aperture radar data. Unlike other algorithms that classify pixels statistically and ignore their scattering characteristics, this algorithm not only uses a statistical classifier, but also preserves the purity of dominant polarimetric scattering properties. This algorithm uses a combination of a scattering model-based decomposition developed by Freeman and Durden and the maximum-likelihood classifier based on the complex Wishart distribution. The first step is to apply the Freeman and Durden decomposition to divide pixels into three scattering categories: surface scattering, volume scattering, and double-bounce scattering. To preserve the purity of scattering characteristics, pixels in a scattering category are restricted to be classified with other pixels in the same scattering category. An efficient and effective class initialization scheme is also devised to initially merge clusters from many small clusters in each scattering category by applying a merge criterion developed based on the Wishart distance measure. Then, the iterative Wishart classifier is applied. The stability in convergence is much superior to that of the previous algorithm using the entropy/anisotropy/Wishart classifier. Finally, an automated color rendering scheme is proposed, based on the classes' scattering category to code the pixels to resemble their natural color. This algorithm is also flexible and computationally efficient. The effectiveness of this algorithm is demonstrated using the Jet Propulsion Laboratory's AIRSAR and the German Aerospace Center's (DLR) E-SAR L-band polarimetric synthetic aperture radar images.
TL;DR: The mechanism of surfactant-assisted dispersion of single-walled carbon nanotubes in water is studied by small-angle neutron scattering and the scattering data favor a random structureless adsorption model for the dispersive of the nanot tubes.
Abstract: The mechanism of surfactant-assisted dispersion of single-walled carbon nanotubes in water is studied by small-angle neutron scattering. The previously hypothesized formation of cylindrical micelles with the nanotubes forming the core of cylinders is inconsistent with the data presented. The scattering data favor a random structureless adsorption model for the dispersion of the nanotubes.
TL;DR: In this paper, the authors measured the dispersion of graphite optical phonons in the in-plane Brillouin zone by inelastic x-ray scattering and showed that first-principles calculations describe very well the vibrational properties of graphene once the long-range character of the dynamical matrix is taken into account.
Abstract: We measured the dispersion of the graphite optical phonons in the in-plane Brillouin zone by inelastic x-ray scattering. The longitudinal and transverse optical branches cross along the � -K as well as the � -M direction. The dispersion of the optical phonons was, in general, stronger than expected from the literature. At the K point the transverse optical mode has a minimum and is only � 70 cm � 1 higher in frequency than the longitudinal mode. We show that first-principles calculations describe very well the vibrational properties of graphene once the long-range character of the dynamical matrix is taken into account.
TL;DR: In this paper, the gamma-ray attenuation due to photon-photon scattering in high-redshift sources has been studied for three observed TeV-blazars (Mkn501, Mkn421, H1426+428).
Abstract: Bearing on the model for the time-dependent metagalactic radiation field developed in the first paper of this series, we compute the gamma-ray attenuation due to pair production in photon-photon scattering. Emphasis is on the effects of varying the star formation rate and the fraction of UV radiation assumed to escape from the star forming regions, the latter being important mainly for high-redshift sources. Conversely, we investigate how the metagalactic radiation field can be measured from the gamma-ray pair creation cutoff as a function of redshift, the Fazio-Stecker relation. For three observed TeV-blazars (Mkn501, Mkn421, H1426+428) we study the effects of gamma-ray attenuation on their spectra in detail.
TL;DR: In this paper, a dipole-limit calculation based on confocal ellipsoids was used to simulate the spectra of the core/shell nanorods using bulk dielectric functions.
Abstract: Au/Ag core/shell nanorods with different shell thickness were synthesized in aqueous solution by chemically depositing silver on gold nanorods surface. With the silver coating, the longitudinal plasmon mode of the nanorods shifted blue and was enhanced. A dipole-limit calculation, based on confocal ellipsoids, simulates the spectra of the core/shell nanorods using bulk dielectric functions. Good agreement with the experimental result was achieved. Light scattering spectra of single nanorods were taken by dark-field microscopy to measure the homogeneous line width. The scattering spectra of single gold nanorods are less than 10% broader than the theoretical value, while the spectra of silver-coated nanorods are systematically 40−50% broader. The additional damping of the plasmon was modeled as the extra scattering at the Au−Ag interface and the nanorods surface. A model for evaluating the plasmon damping in inhomogeneous metallic systems with interfaces is presented.
TL;DR: In this article, the resistivity of thin Cu films depends on film thickness as the dimensions approach the electron mean-free-path for Cu of 39 nm, and the key size-dependent contributions are from electron-surface scattering, grain boundary scattering, and surface roughness-induced scattering.
Abstract: The resistivity of thin Cu films depends on film thickness as the dimensions approach the electron mean-free-path for Cu of 39 nm. The key size-dependent contributions are from electron–surface scattering, grain boundary scattering, and surface roughness-induced scattering. Measurements with pseudoepitaxial Cu films deposited on Si have been undertaken to reduce effects of grain boundaries and surface roughness and suggest an electron-scattering parameter of p=0.12. Overlayers of metal films on the Cu generally increase the resistivity for Ta and Pt overlayers, and may reduce the resistivity for Au and Al. The resistivity increase may also be reversed if the overlayer oxidizes.
01 Jan 2004
TL;DR: The first € price and the £ and $ price are net prices, subject to local VAT as discussed by the authors, and the first £ and £ price is net price subject to the local VAT.
Abstract: The first € price and the £ and $ price are net prices, subject to local VAT. Prices indicated with * include VAT for books; the €(D) includes 7% for Germany, the €(A) includes 10% for Austria. Prices indicated with ** include VAT for electronic products; 19% for Germany, 20% for Austria. All prices exclusive of carriage charges. Prices and other details are subject to change without notice. All errors and omissions excepted. U. Pietsch, V. Holy, T. Baumbach High-Resolution X-Ray Scattering
TL;DR: In this paper, an incoherent particle model was developed to calculate the phonon thermal conductivity of superlattice nanowires, which is an extension of the photon net-radiation method and Schuster-Schwarzschild approximation.
Abstract: An incoherent particle model has been developed to calculate the phonon thermal conductivity of superlattice nanowires. This is an extension of the photon net-radiation method and Schuster–Schwarzschild approximation to dispersive acoustic phonons in a gray medium. By comparing the roughness and geometric variations of typical nanowires to the characteristic phonon wavelength (∼1 nm at 300 K), diffuse scattering and incoherent three-dimensional dispersion are justified. An isotropic sine-type (Born–von Karman) dispersion is used, which requires only the sound velocity, atomic number density, and bulk conductivity to fully describe a material. A simple picture is also given in terms of Matthiessen’s rule and three effective mean free paths. Agreement with available experimental data is poor at the smallest diameters, but good above 30 nm diameter. Compared to a conventional superlattice, calculations show that the additional sidewall scattering in a superlattice nanowire can reduce the thermal conductivity...
TL;DR: In this article, the authors used a CLEAN-based algorithm to deconvolve interstellar pulse broadening from the measured pulse shapes, and employed two distinct pulse-broadening functions (PBFs): PBF1 is appropriate for a thin screen of scattering material between the Earth and a pulsar, while PBF2 was appropriate for scattering material uniformly distributed along the line of sight from the Earth to a pulsars.
Abstract: We have made observations of 98 low Galactic latitude pulsars to measure pulse broadening caused by multipath propagation through the interstellar medium. Data were collected with the 305 m Arecibo telescope at four radio frequencies between 430 and 2380 MHz. We used a CLEAN-based algorithm to deconvolve interstellar pulse broadening from the measured pulse shapes. We employed two distinct pulse-broadening functions (PBFs): PBF1 is appropriate for a thin screen of scattering material between the Earth and a pulsar, while PBF2 is appropriate for scattering material uniformly distributed along the line of sight from the Earth to a pulsar. We found that some observations were better fitted by PBF1 and some by PBF2. Pulse-broadening times (τd) are derived from fits of PBFs to the data and are compared with the predictions of a smoothed model of the Galactic electron distribution. Several lines of sight show excess broadening, which we model as clumps of high-density scattering material. A global analysis of all available data finds that the pulse broadening scales with frequency, ν, as τd ν-α, where α ~ 3.9 ± 0.2. This is somewhat shallower than the value α = 4.4 expected from a Kolmogorov medium but could arise if the spectrum of turbulence has an inner cutoff at ~300-800 km. A few objects follow particularly shallow scaling laws (the mean scaling index α ~ 3.1 ± 0.1 and ~3.8 ± 0.2, respectively, for PBF1 and PBF2), which may arise from large-scale refraction or from the truncation of scattering screens transverse to the Earth-pulsar line of sight.
TL;DR: In this article, the authors describe the characteristics of synchrotron-based X-ray scattering techniques that make them uniquely powerful probes of mineral-water interfacial structures and discuss the new insights that have been derived from their application.
Book•
27 Aug 2004
TL;DR: In this paper, the authors present an X-ray diffraction experiment using Diffractometers and reflectometers. But they do not consider the effects of scattering from volume defects in thin layers and multilayers.
Abstract: 1 Elements for Designing an X-Ray Diffraction Experiment.- 2 Diffractometers and Reflectometers.- 3 Scans and Resolution in Angular and Reciprocal Space.- 4 Basic Principles.- 5 Kinematical Theory.- 6 Dynamical Theory.- 7 Semikinematical Theory.- 8 Determination of Layer Thicknesses of Single Layers and Multilayers.- 9 Lattice Parameters and Strains in Epitaxial Layers and Multilayers.- 10 Diffuse Scattering From Volume Defects in Thin Layers.- 11 X-Ray Scattering by Rough Multilayers.- 12 X-Ray Scattering by Artificially Lateral Semiconductor Nanostructures.- 13 Strain Analysis in Periodic Nanostructures.- 14 X-Ray Scattering from Self-Organized Structures.- References.
TL;DR: In this paper, a generalized index of polydispersity for symmetric particles, PDI = BRg4/(1.62G), where G is the Guinier prefactor, is introduced and compared with other approaches to describe particle size distributions in SAXS, specifically the maximumentropy method.
Abstract: Control and quantification of particle size distribution is of importance in the application of nanoscale particles. For this reason, polydispersity in particle size has been the focus of many simulations of particle growth, especially for nanoparticles synthesized from aerosols such as fumed silica, titania and alumina. Single-source aerosols typically result in close to a log-normal distribution in size and micrograph evidence generally supports close to spherical particles, making such particles ideal candidates for considerations of polydispersity. Small-angle X-ray scattering (SAXS) is often used to measure particle size in terms of the radius of gyration, Rg, using Guinier's law, as well as particle surface area, S/V, from the Porod constant B and the scattering invariant Q. In this paper, the unified function is used to obtain these parameters and various moments of the particle size distribution are calculated. The particle size obtained from BET analysis of gas adsorption data directly agrees with the moment calculated from S/V. Scattering results are also compared with TEM particle-counting results. The potential of scattering to distinguish between polydisperse single particles and polydisperse particles in aggregates is presented. A generalized index of polydispersity for symmetric particles, PDI = BRg4/(1.62G), where G is the Guinier prefactor, is introduced and compared with other approaches to describe particle size distributions in SAXS, specifically the maximum-entropy method.
TL;DR: In this paper, a 3D quantum simulator for the silicon nanowire transistor (SNWT) is presented, where the authors use Buttiker probes to simulate the effects of scattering on both internal device characteristics and terminal currents.
Abstract: The silicon nanowire transistor (SNWT) is a promising device structure for future integrated circuits, and simulations will be important for understanding its device physics and assessing its ultimate performance limits. In this work, we present a three-dimensional quantum mechanical simulation approach to treat various SNWTs within the effective-mass approximation. We begin by assuming ballistic transport, which gives the upper performance limit of the devices. The use of a mode space approach (either coupled or uncoupled) produces high computational efficiency that makes our 3D quantum simulator practical for extensive device simulation and design. Scattering in SNWTs is then treated by a simple model that uses so-called Buttiker probes, which was previously used in metal-oxide-semiconductor field effect transistor (MOSFET) simulations. Using this simple approach, the effects of scattering on both internal device characteristics and terminal currents can be examined, which enables our simulator to be used for the exploration of realistic performance limits of SNWTs.
TL;DR: In this paper, the optical properties of metallodielectric nanostructures, variations of a core−shell geometry, are investigated using the finite difference time domain method, which provides a convenient, systematic and general approach for calculating the optical response of a nanostructure of arbitrary symmetry and geometry to an incident light wave.
Abstract: The optical properties of metallodielectric nanostructures, variations of a core−shell geometry, are investigated using the finite difference time domain method. This method provides a convenient, systematic, and general approach for calculating the optical response of a nanostructure of arbitrary symmetry and geometry to an incident light wave. Properties such as the optical absorption and scattering cross sections as well as the local electromagnetic fields and induced charge densities at the surfaces of the nanostructures can be obtained by this method. Issues of convergence with grid size and other simulation parameters are discussed in detail. The method is applied to uniform single nanoshells, nanoshells with surface defects, and nanoshells with shape distortions from a spherical geometry. The results show that, while defects can significantly affect local surface field enhancements, far field properties such as optical absorption and scattering spectra can be remarkably insensitive to defects and d...
TL;DR: The results show that the narrow lines are remarkably robust to array disorder, but vacancy defects can easily destroy the effect, and it is shown that the arrays have greater sensitivity than isolated nanoparticles.
Abstract: The interaction of light with silver nanoparticle arrays can in some cases produce mixed plasmonic/photonic bands that have extremely narrow (<1 meV) line shapes in extinction and scattering. In this paper we extend computational electrodynamics results of a recent communication [S. Zou, N. Janel, and G. C. Schatz, J. Chem. Phys. 120, 10871 (2004)] where this effect was first described to study how these narrow bands are influenced by a number of structural factors, and to determine how useful these arrays might be for sensing applications. Included are studies of the effect of disorder in the array structure on plasmon intensity and width, of the effect of orientation of the array relative to the polarization and propagation direction of the incident light, and of the effect of particle shape (comparing results for silver spheres and cylindrical disks). Our results show that the narrow lines are remarkably robust to array disorder, but vacancy defects can easily destroy the effect. The narrowest lines are associated with one dimensional arrays in which both polarization and wave vectors are perpendicular to the array axis. For two dimensional arrays, the narrowest lines are associated with the wave vector perpendicular to the plane of the array and polarization in the plane. Arrays composed of oblate cylinders generate more intense and more redshifted plasmon/photonic peaks than do prolate or spherical particles under comparable conditions. Finally, for sensing applications in which analyte binding is determined by the plasmon wavelength shift associated with change in the surface refractive index, we show that the arrays have greater sensitivity than isolated nanoparticles.
TL;DR: In this article, the authors present the scattering lengths for the pi-pi processes in the three flavour Chiral Perturbation Theory (ChPT) framework at next-to-next-to leading order.
Abstract: We present the scattering lengths for the pi-pi processes in the three flavour Chiral Perturbation Theory (ChPT) framework at next-to-next-to-leading order. We then combine this calculation with the determination of the parameters from $Ke4 and the masses and decay constants and compare with the results of a dispersive analysis of pi-pi scattering. The comparison indicates a small but nonzero value for the 1/Nc suppressed NLO low energy constants L4r and L6r.
TL;DR: In this article, the buckling instability was investigated by both small angle light scattering and atomic force microscopy, demonstrating that a tunable phase grating can be created with a mechanical instability.
Abstract: We investigate a buckling instability by both small angle light scattering and atomic force microscopy, demonstrating that a tunable phase grating can be created with a mechanical instability. The instability is realized in a prestressed silicone sheet coated with a glassy polymer film. Compression of the sample results in a sinusoidally wrinkled surface where the amplitude is controlled by the degree of compression and the wavelength by film thickness. We model the system with Fourier optics, explaining the positions and relative intensities of the diffraction orders.
01 Dec 2004
TL;DR: The optimal detector in the Neyman-Pearson sense is developed and analyzed for the statistical MIMO radar, and an optimal detector invariant to the signal and noise levels is also developed and analyze.
Abstract: Inspired by recent advances in multiple-input multiple-output (MIMO) communications, this paper introduces the statistical MIMO radar concept. The fundamental difference between statistical MIMO and other radar array systems is that the latter seek to maximize the coherent processing gain, while statistical MIMO radar capitalizes on the diversity of target scattering to improve radar performance. Coherent processing is made possible by highly correlated signals at the receiver array, whereas in statistical MIMO radar, the signals received by the array elements are uncorrelated. It is well known that in conventional radar, slow fluctuations of the target radar cross-section (RCS) result in target fades that degrade radar performance. By spacing the antenna elements at the transmitter and at the receiver such that the target angular spread is manifested, the MIMO radar can exploit the spatial diversity of target scatterers opening the way to a variety of new techniques that can improve radar performance. In this paper, we focus on the application of the target spatial diversity to improve detection performance. The optimal detector in the Neyman-Pearson sense is developed and analyzed for the statistical MIMO radar. An optimal detector invariant to the signal and noise levels is also developed and analyzed. In this case as well, statistical MIMO radar provides great improvements over other types of array radars.
TL;DR: In this paper, single particle dark field spectroscopy has been combined with high-resolution scanning electron and atomic force microscopy to study the scattering spectra of single gold/silica nanoshells.
Abstract: Single particle dark field spectroscopy has been combined with high-resolution scanning electron and atomic force microscopy to study the scattering spectra of single gold/silica nanoshells. The plasmon resonant peak energies match those calculated by Mie theory based on the nanoshell geometry. The resonance line widths fit Mie theory without the inclusion of a size-dependent surface scattering term, which is often included to fit ensemble measurements. These results suggest that plasmon spectral measurements of nanoparticle ensembles are broadened due to particle inhomogeneity.