An update of the Amsterdam Light Scattering Database

We present an update of the Amsterdam Light Scattering Database located at http://www.astro.uva.nl/scatter. We give a detailed explanation and clarification of the nature of the scattering matrices in the database. Measured scattering matrix elements are presented as functions of the scattering angle, for aerosol particles in random orientation at 632.8 nm. They pertain to seven volcanic dust samples from three different volcanoes, two samples with extreme refractive indices (hematite and rutile), and three forsterite samples with identical compositions, but different size distributions. For 15 phytoplankton species and two types of silt suspended in water, the database now contains two matrix elements, F₁₁ and -F₁₂/F₁₁ as functions of the scattering angle at 632.8 nm. Lastly, we have included all scattering matrix elements as functions of the scattering angle for spherical micron-sized water droplets, which may be used for testing purposes.     

Jahn–Teller coupled charge density wave in a double exchange system

In a two orbital model, we formulate Jahn–Teller coupled charge density wave in one electron per lattice site limit. Softening of Jahn–Teller phonons corresponding to distortion modes Q₂ or Q₃ associated with perfect nesting of Fermi surface leads to this instability at low temperature. The gap equation for charge density wave state and its dependences on electron–lattice coupling are calculated explicitly when any one of the Jahn–Teller modes is excited cooperatively. We find that the Q₂ distortion mode yields lowest free energy. Effect of electron–lattice interaction on collective mode, such as amplitude mode, is more pronounced when the excited mode is Q₂.     

Exact Hamiltonian for an analytic correlated ground-state wave function for He-like ions

A correlated three-parameter variational ground-state Ψ(r₁,r₂,r₁₂) proposed by Chandrasekhar for helium-like ions gives a high percentage of the electron correlation energy resulting from the interaction energy e²/r₁₂ and also yields an analytic ground-state electron density ρ(r). Here, we extract via Schrödinger equation an exact Hamiltonian for which the Chandrasekhar wave function is the ground-state. Properties of the potential energy function in this Hamiltonian are quantified. Finally, kinetic energy densities are plotted and related to the Laplacian of ρ(r).     

The intruder orbitals in superdeformed bands and alignment additivity of odd–odd nuclei in the region

The particle-number conserving (PNC) method for treating the cranked shell model with monopole and quadrupole pairing correlations is used to study the superdeformed (SD) bands observed in odd–odd nuclei in the A190 mass region. Spins are assigned to the levels in these bands. The microscopic mechanism of the ω evolution of the dynamic moment of inertia J⁽²⁾ for these SD bands are analyzed. In particular, the major roles of the j_15/2 neutron and i_13/2 proton orbitals played in the SD bands are investigated in detail by contributions to J⁽²⁾ from each cranked orbital and interference terms between two cranked orbitals. Additivity in the A190 mass region is investigated. The experimental evidence for additivity of alignments in ¹⁹²Tl can be reproduced by our calculations.     

Can particle shape information be retrieved from light-scattering observations using spheroidal model particles?

We address the question if and how observations of scattered intensity and polarisation can be employed for retrieving particle shape information beyond a simple classification into spherical and nonspherical particles. To this end, we perform several numerical experiments, in which we attempt to retrieve shape information of complex particles with a simple nonspherical particle model based on homogeneous spheroids. The discrete dipole approximation is used to compute reference phase matrices for a cube, a Gaussian random sphere, and a porous oblate and prolate spheroid as a function of size parameter. Phase matrices for the model particles, homogeneous spheroids, are computed with the T-matrix method. By assuming that the refractive index and the size distribution is known, an optimal shape distribution of model particles is sought that best matches the reference phase matrix. Both the goodness of fit and the optimal shape distribution are analysed. It is found that the phase matrices of cubes and Gaussian random spheres are well reproduced by the spheroidal particle model, while the porous spheroids prove to be challenging. The “retrieved” shape distributions, however, do not correlate well with the shape of the target particle even when the phase matrix is closely reproduced. Rather, they tend to exaggerate the aspect ratio and always include multiple spheroids. A most likely explanation why spheroids succeed in mimicking phase matrices of more irregularly shaped particles, even if their shape distributions display little similarity to those of the target particles, is that by varying the spheroids’ aspect ratio one covers a large range of different phase matrices. This often makes it possible to find a shape distribution of spheroids that matches the phase matrix of more complex particles.     

Porous irregular aggregates of sub-micron sized grains to reproduce cometary dust light scattering observations

The present study intends to interpret some of the characteristic features of the light scattered by cometary dust, such as phase angle and wavelength dependence of its polarization, through simulations using Ballistic Cluster-Cluster Aggregation (BCCA) or Ballistic Particle-Cluster Aggregation (BPCA) aggregates of up to 128 sub-micron sized grains (spherical and spheroidal with a possible size distribution) of various composition (silicates, organics, silicates core with organics mantle). The dependence of the linear polarization with the size parameter is shown to depend highly on the size and composition of the constitutive grains. Internal interactions induced by shape or orientation averaging of the grains may lessen this dependence, leading to results comparable to those observed on cometary dust for fluffy aggregates of grains with a size parameter in the 1.3–1.8 range. A size distribution of realistically shaped particles (aggregates of spheroids and larger spheroids) following a power law size distribution with a power index of -3, the smallest grains radius by 0.03– and the largest spheroids effective radius by , gives a very good fit to the Hale-Bopp observed phase curves. The best silicates–organics ratio ranges from about 50–75% organics and 25–50% silicates in volume considering the eventual presence of core-mantle grains.     

A simplified model to predict the effects of aggregation on the absorption properties of soot particles

An exact electrostatics formulation for sphere clusters is used to predict the Rayleigh-limit radiative absorption properties of soot aggregates. In the near to mid IR wavelengths, it is shown that aggregation can result in absorption cross sections that are significantly larger than that predicted by an independent-sphere (Rayleigh–Gans) model. The relative increase in absorption increases with the number of spheres in the aggregate, and reaches an asymptote for aggregates containing 100–200 spheres. A simplified correlation is developed to predict the aggregate absorption cross section as a function of number of spheres and refractive index. Implications of the effects of aggregation on absorption and emission of thermal radiation by soot in flame and atmospheric environments are discussed.     

Study of the decay

Using data from the FOCUS (E831) experiment at Fermilab, we present a new measurement for the Cabibbo-suppressed decay mode D⁰→K⁺K⁻π⁺π⁻. We measure: Γ(D⁰→K⁺K⁻π⁺π⁻)/Γ(D⁰→K⁻π⁻π⁺π⁺)=0.0295±0.0011±0.0008. An amplitude analysis has been performed in order to determine the resonant substructure of this decay mode. The dominant components are the decays D⁰→K₁(1270)⁺K⁻, D⁰→K₁(1400)⁺K⁻ and D⁰→ρ(770)⁰(1020).     

Size-dependent linear and non-linear optical response of single carrier two-dimensional quantum dots

We explore the pattern of size dependence of linear and non-linear optical (NLO) responses of one-electron quantum dots in two dimensions with or without anharmonicity in the confinement potential. For some fixed values of transverse magnetic field strength (ω_c) and harmonic confinement potential (ω₀), the influence of the size of the dot on the linear (), the first (β) and the second (γ) NLO responses of the system computed through a finite field linear variational route is analysed. Size-dependent maximization is predicted to be feasible for the quadratic hyperpolarizability.     

Materials with a desired refraction coefficient can be made by embedding small particles

A method is proposed to create materials with a desired refraction coefficient, possibly negative one. The method consists of embedding into a given material small particles. Given n₀(x), the refraction coefficient of the original material in a bounded domain , and a desired refraction coefficient n(x), one calculates the number N(x) of small particles, to be embedded in D around a point xD per unit volume of D, in order that the resulting new material has refraction coefficient n(x).     

Long range disorder and Anderson transition in systems with chiral symmetry

We study the spectral properties of a chiral random banded matrix (chRBM) with elements decaying as a power-law H_ij|i−j|⁻. This model is equivalent to a chiral 1D Anderson Hamiltonian with long range power-law hopping. In the weak disorder limit we obtain explicit nonperturbative analytical results for the density of states (DoS) and the two-level correlation function (TLCF) by mapping the chRBM onto a nonlinear σ model. We also put forward, by exploiting the relation between the chRBM at =1 and a generalized chiral random matrix model, an exact expression for the above correlation functions. We give compelling analytical and numerical evidence that for this value the chRBM reproduces all the features of an Anderson transition. Finally we discuss possible applications of our results to quantum chromodynamics (QCD).     

Visible light scattering study at 470, 550, and 660 nm of components of mineral dust aerosol: Hematite and goethite

Iron oxides, usually in the form of hematite or goethite, comprise an important component of atmospheric mineral dust aerosol. Because these minerals are strong visible absorbers they play a critical role in determining the overall impact of dust aerosol on climate forcing. In this work, results from light scattering measurements from hematite and goethite dust aerosol are presented for three visible wavelengths, λ=470, 550, and 660 nm. We observe important systematic differences in the scattering between these different iron oxide samples, as well as significant wavelength dependence across the visible region of the spectrum. Aerosol size distributions are measured simultaneously with the light scattering, enabling a rigorous comparison between theoretical light scattering models and experimental data. Theoretical simulations of the scattering are carried out using both Mie and T-Matrix theories. Simulations are in reasonably good agreement with experimental data for hematite; thus, our data offer a useful check on tabulated optical constants for hematite. However, simulations show very poor agreement for goethite. The poor agreement in the goethite case is likely the result of particle shape effects related to the rod-like morphology of the goethite particles. This study demonstrates how particle mineralogy and morphology play an important role in dictating the optical properties of mineral dust aerosol, a major component of tropospheric dust.     

Surface structure of low-coveraged Cs on Si(0 0 1)-() system

Alkali metals (AM) on semiconductors have been investigated as a simple model system for the metal-semiconductor interfaces due to their simple electronic structures. Especially, cesium (Cs) on Si(0 0 1) surface has been studied with various experimental techniques. In this study, we investigated the atomic structure of initial Cs adsorption on Si(0 0 1)-(2×1) surface using coaxial impact collision ion scattering spectroscopy. When Cs atoms are adsorbed on Si(0 0 1)-(2×1) up to 0.2 ML at room temperature, the initial adsorption site is on-top T3 site with poor periodicity and the length of Si dimer is reserved as in the clean Si(0 0 1) surface. It is also found that Cs atoms adsorbed on Si(0 0 1) surface with a height of 2.83±0.05 Å from the second layer of Si(0 0 1) surface.     

Energy of formation for and liquid binary alloys

We have investigated the free energy of formation for Ag_xIn_1-x and Ag_xSn_1-x liquid binary alloys at temperatures 1173 and 1250 K, respectively. A microscopic theory based on the first order perturbation has been applied. The interionic interaction and a reference liquid are the fundamental components of the theory. The interionic interaction is described by a local pseudopotential. A liquid of hard spheres (HS) of two different effective diametres and charges is used to describe the reference system. The results of the calculations for energy of formation agree very well with the available experimental data. Our calculations also reveal that a simple perturbative approach along with appropriate effective pair potentials can produce nearly quantitative results for the concerned alloys.     

The study of the influence of uniaxial stress on impurity complexes in silicon

The influence of external uniaxial stress on the different indium-donor complexes in silicon has been studied using the perturbed γ –γ angular correlation (PAC) method. Such effect of an applied stress is detected by means of the probe atoms situated at different complexes in the sample. The current results showed that the responses of the probes in an extrinsic silicon samples are found to be dissimilar for the same value of stress. Such change in the local environments of the probe atoms could be associated with the various strain field created by the implantations of varied size of impurities. The phosphorous implantation in silicon has even lead to the complete absence of observable effect of the applied stress suggesting significant lose of the elasticity of the sample.     

The finite-size scaling study of the specific heat and the Binder parameter for the six-dimensional Ising model

The six-dimensional Ising model with nearest-neighbor pair interactions is simulated on the Creutz cellular automaton by using the finite-size lattices with the linear dimensions L=4,6,8,10. The temperature variations and the finite-size scaling plots of the specific heat and Binder parameter verify the theoretically predicted expression near the infinite lattice critical temperature. The approximate values for the critical temperature of the infinite lattice T_C=10.838(1), T_C=10.836(20) and T_C=10.835(1) are obtained from the intersection points of specific heat curves, Binder parameter curves and the straight line fit of specific heat maxima, respectively. These results are in agreement with the more precise value of T_C=10.835(5). The value obtained for the critical exponent of the specific heat, i.e., =0.012(2) is also in agreement with =0 predicted by the theory.     

Measurements of decays into and

Based on a sample of 5.8×10⁷ J/ψ events taken with the BESII detector, the branching fractions of J/ψ→2(π⁺π⁻)η and J/ψ→3(π⁺π⁻)η are measured for the first time to be (2.26±0.08±0.27)×10⁻³ and (7.24±0.96±1.11)×10⁻⁴, respectively.     

QCD sum rule study of the masses of light tetraquark scalar mesons

We study the low-lying scalar mesons of light u, d, s flavors in the QCD sum rule. Having all possible combinations of tetraquark currents in the local form, QCD sum rule analysis has been carefully performed. We found that using the appropriate tetraquark currents, the masses of σ, κ, f₀ and a₀ mesons appear in the region of 0.6–1 GeV with the expected ordering. The results are compared with that of the conventional currents, where the masses are considerably larger.     

Evidence for particle size–shape correlations in the optical properties of silicate clay aerosol

Accurate modeling of the optical properties of atmospheric mineral dust is important for climate modeling calculations and remote sensing data retrievals. Atmospheric mineral dust in the accumulation mode size range is often rich in silicate clays including kaolinite and illite. This is important because dust optical properties depend on particle shape, and fundamental clay particles are known to consist of very thin flakes.In this combined laboratory and modeling study, we investigate the optical properties (IR extinction and visible light scattering) of two samples of silicate clay dust aerosol, kaolinite and illite. Particle size distributions are measured simultaneously with the optical properties. T-Matrix theory based simulations using a spheroidal particle approximation are compared with experimental data. We find that the full range of visible scattering and polarimetry data, and IR extinction profiles are not well fit by assuming a single size–shape distribution for the aerosol. In contrast, a simple bimodal distribution model that treats small particles (fundamental clay flakes) in the distribution as highly eccentric oblate spheroids with axial ratio parameters ≥5, but approximates larger particles by a more moderate shape distribution with axial ratio parameters <3, gives better agreement with the full range of experimental data. These conclusions are consistent with mineralogical data on the dimensions of fundamental clay particles.     

Chiral dynamics and antikaon-nuclear quasibound states

Recent developments are summarised concerning low-energy interactions as they relate to the possible existence of antikaon-nuclear quasibound states. An exploratory study of antikaons bound to finite nuclei is performed, with emphasis on the evolution of such states from light to heavy nuclei (A = 16–208). The energy dependent, driving attractive interactions are constructed using the s-wave coupled-channel amplitudes involving the Λ(1405) and resulting from chiral SU(3) dynamics, plus p-wave amplitudes dominated by the Σ(1385). Effects of Pauli and short-range correlations are discussed. The decay width induced by K⁻NN two-body absorption is estimated and found to be substantial. It is concluded that -nuclear quasibound states can possibly exist with binding energies ranging from 60 to 100 MeV, but with short life times corresponding to decay widths of similar magnitudes.