Size Distribution by Light Scattering from Individual Particles

The particle size distribution of a polystyrene latex has been determined using a new light-scattering photometer which measures the scattered radiance as .a function of scattering angle of single aerosolized particles as they are levitated in a laser beam. The results are in agreement with those obtained by conventional light scattering and by electron microscopy. In addition to the main population, two classes of smaller particles were observed. This single particle light-scattering technique offers the possibility of analyzing broader size distributions than heretofore amenable to light scattering and has the added advantage of not requiring any a priori assumptions about the form of the particle size distribution

Size Distribution by Light Scattering from Individual Particles

The particle size distribution of a polystyrene latex has been determined using a new light-scattering photometer which measures the scattered radiance as .a function of scattering angle of single aerosolized particles as they are levitated in a laser beam. The results are in agreement with those obtained by conventional light scattering and by electron microscopy. In addition to the main population, two classes of smaller particles were observed. This single particle light-scattering technique offers the possibility of analyzing broader size distributions than heretofore amenable to light scattering and has the added advantage of not requiring any a priori assumptions about the form of the particle size distribution

Epsilons Near Zero limits in the Mie scattering theory

The classical Mie theory - electromagnetic radiation scattering by the homogeneous spherical particles - is considered in the epsilon near zero limits separately for the materials of the particles and the surrounding medium. The maxima of a scattered transverse electrical (TE) field for the surrounding medium materials with the epsilon near zero limits are revealed. The effective multipole polarizabilities of the corresponding scattering particles are investigated. The possibility to achieve magnetic dipole resonance and accordingly to construct metamaterials with negative refractive index for the aggregates spherical particles in surrounding medium with the epsilon near zero limits is considered.Comment: 8 pages, 6 figure

Brownian coagulation of aerosols in the transition regime

Earlier experimental studies of Brownian coagulation of aerosols have been extended into the transition regime, i.e. Knudsen number values 0.8-1.6. This was done by working with the same range of particle size as earlier, but at a reduced pressure. A number of modffications were made in the experimental technique, including the use of diethylhexylsebacate instead of dibutylphthalate in order to avoid the possibility of loss to the walls by evaporation. The rate of coagulation at Kn = 0.2 agreed closely with that predicted, using Smoluchowski's coagulation constant for the continuum regime as modified by the Cunningham correction. The rate at higher Knudsen numbers (Kn = 0.8-1.6) was somewhat lower (about 20%) than that predicted by Fuchs' formula for interpolation between the continuum and free molecule regimes

Multiangle static and dynamic light scattering in the intermediate scattering angle range

We describe a light scattering apparatus based on a novel optical scheme covering the scattering angle range 0.5\dg \le \theta \le 25\dg, an intermediate regime at the frontier between wide angle and small angle setups that is difficult to access by existing instruments. Our apparatus uses standard, readily available optomechanical components. Thanks to the use of a charge-coupled device detector, both static and dynamic light scattering can be performed simultaneously at several scattering angles. We demonstrate the capabilities of our apparatus by measuring the scattering profile of a variety of samples and the Brownian dynamics of a dilute colloidal suspension

Notes on Conformal Invisibility Devices

As a consequence of the wave nature of light, invisibility devices based on isotropic media cannot be perfect. The principal distortions of invisibility are due to reflections and time delays. Reflections can be made exponentially small for devices that are large in comparison with the wavelength of light. Time delays are unavoidable and will result in wave-front dislocations. This paper considers invisibility devices based on optical conformal mapping. The paper shows that the time delays do not depend on the directions and impact parameters of incident light rays, although the refractive-index profile of any conformal invisibility device is necessarily asymmetric. The distortions of images are thus uniform, which reduces the risk of detection. The paper also shows how the ideas of invisibility devices are connected to the transmutation of force, the stereographic projection and Escheresque tilings of the plane

Light scattering Q-space analysis of irregularly shaped particles

Citation: Heinson, Y. W., Maughan, J. B., Heinson, W. R., Chakrabarti, A., & Sorensen, C. M. (2016). Light scattering Q-space analysis of irregularly shaped particles. Journal of Geophysical Research-Atmospheres, 121(2), 682-691. doi:10.1002/2015jd024171We report Q-space analysis of light scattering phase function data for irregularly shaped dust particles and of theoretical model output to describe them. This analysis involves plotting the scattered intensity versus the magnitude of the scattering wave vector q=(4/)sin(/2), where is the optical wavelength and is the scattering angle, on a double-logarithmic plot. In q-space all the particle shapes studied display a scattering pattern which includes a q-independent forward scattering regime; a crossover, Guinier regime when q is near the inverse size; a power law regime; and an enhanced backscattering regime. Power law exponents show a quasi-universal functionality with the internal coupling parameter . The absolute value of the exponents start from 4 when <1, the diffraction limit, and decreases as increases until a constant 1.750.25 when 10. The diffraction limit exponent implies that despite their irregular structures, all the particles studied have mass and surface scaling dimensions of D-m=3 and D-s=2, respectively. This is different from fractal aggregates that have a power law equal to the fractal dimension D-f because D-f=D-m=D-s<3. Spheres have D-m=3 and D-s=2 but do not show a single power law nor the same functionality with . The results presented here imply that Q-space analysis can differentiate between spheres and these two types of irregularly shaped particles. Furthermore, they are applicable to analysis of the contribution of aerosol radiative forcing to climate change and of aerosol remote sensing data

Creating atom-number states around tapered optical fibres by loading from an optical lattice

We describe theoretically a setup in which a tapered optical nanofibre is introduced into an optical lattice potential for cold atoms. Firstly, we consider the disturbance to the geometry of the lattice potential due to scattering of the lattice lasers from the dielectric fibre surface and show that the resulting distortion to the lattice can be minimized by placing the fibre at an appropriate position in the lattice. We then calculate the modifications of the local potentials that are achievable by transmitting off-resonant light through the fibre. The availability of such a technique holds the potential to deterministically create and address small well-defined samples of atoms in the evanescent field of the tapered nanofibre.Comment: 7 pages. 6 figure

Identification of Violence in the Home - Pediatric and Parental Reports

Objectives: To compare the rates of domestic violence reported by mothers with those identified by physicians, to compare the rates of harsh discipline practices reported by mothers with the rates of abuse identified by physicians, and to examine the relationship between reported domestic violence and harsh discipline practices. Design: Interviews with parents and pediatricians to compare pediatric detection of domestic violence and child abuse with parental reports of domestic violence and harsh discipline practices. Setting: Community-based pediatric practices in the 13-town greater New Haven, Conn, area. Participants: Of the 23 practices invited, 19 agreed to participate. Of the 2006 parents of eligible 4- to 8-year-olds asked to participate, 1886 (94%) completed the Child Behavior Checklist. Of those invited into the interview portion, 1148 (83%) completed the 90-minute in-person interview. Main Outcome Measures: Percentages of cases of domestic violence identified by pediatricians and reported by mothers. Percentages of cases of child abuse detected by pediatricians and percentages of mothers reporting that they have hit their children and left a mark. Results: Pediatricians detected domestic violence in 0.3% of the cases, but parents reported domestic violence in 4.2% (kappa = 0.106 [95% confidence interval, -0.007 to 0.219]). Pediatricians identified physical abuse of children in 0.5% of the cases, while mothers reported hitting their children and leaving a mark in 21.6% (kappa = 0.003 [95% confidence interval, -0.018 to 0.024]). Mothers reporting domestic violence were significantly more likely to report hitting hard enough to leave a mark (relative risk, 1.6 ([95% confidence interval, 1.09-2.38]) compared with those not reporting domestic violence. Physicians identifying domestic violence were not significantly more likely to report child abuse than those not identifying domestic violence. Conclusions: Parents report more cases of violence than pediatricians detect. Pediatricians should ask parents directly about domestic violence and harsh discipline

Forces on Dust Grains Exposed to Anisotropic Interstellar Radiation Fields

Grains exposed to anisotropic radiation fields are subjected to forces due to the asymmetric photon-stimulated ejection of particles. These forces act in addition to the ``radiation pressure'' due to absorption and scattering. Here we model the forces due to photoelectron emission and the photodesorption of adatoms. The ``photoelectric'' force depends on the ambient conditions relevant to grain charging. We find that it is comparable to the radiation pressure when the grain potential is relatively low and the radiation spectrum is relatively hard. The calculation of the ``photodesorption'' force is highly uncertain, since the surface physics and chemsitry of grain materials are poorly understood at present. For our simple yet plausible model, the photodesorption force dominates the radiation pressure for grains with size >~0.1 micron exposed to starlight from OB stars. We find that the anisotropy of the interstellar radiation field is ~10% in the visible and ultraviolet. We estimate size-dependent drift speeds for grains in the cold and warm neutral media and find that micron-sized grains could potentially be moved across a diffuse cloud during its lifetime.Comment: LaTeX(41 pages, 19 figures), submitted to Ap