Electro-precipitation of Fe3O4 nanoparticles in ethanol

The preparation of superparamagnetic magnetite (Fe₃O₄) nanoparticles by electro-precipitation in ethanol is proposed. Particle average size can be set from 4.4 to 9 nm with a standard deviation around 20%. Combination of wide-angle X-ray scattering (WAXS), Electron energy loss spectroscopy (EELS) and Mössbauer spectroscopy characterizations clearly identifies the particles as magnetite single-crystals (Fe₃O₄).     

Radiative transfer in a multi-layer medium subject to Fresnel boundary and interface conditions and uniform illumination by obliquely incident parallel rays

The ADO (analytical discrete ordinates) method, a pre-processing procedure, and the break-point analysis developed for azimuthally symmetric problems in a previous work are generalized and used to solve a radiative-transfer problem defined by a finite, plane–parallel, multi-layer medium subject to Fresnel boundary and interface conditions and uniform illumination in the form of obliquely incident parallel rays. Illumination is modeled by Dirac distributions in each of the two angles (polar and azimuthal) that define the direction of propagation of the incident rays. Accurate numerical results are tabulated for two sets of test problems.     

Is space-time symmetry a suitable generalization of parity-time symmetry?

We discuss space-time symmetric Hamiltonian operators of the form H=H₀+igH^′$H=H_0+ig{H}^{\prime }$, where H₀$H_0$ is Hermitian and g$g$ real. H₀$H_0$ is invariant under the unitary operations of a point group G$G$ while H^′$H^{\prime }$ is invariant under transformation by elements of a subgroup G^′$G^{\prime }$ of G$G$. If G$G$ exhibits irreducible representations of dimension greater than unity, then it is possible that H$H$ has complex eigenvalues for sufficiently small nonzero values of g$g$. In the particular case that H$H$ is parity-time symmetric then it appears to exhibit real eigenvalues for all 0<g<g_c$0<g<g_c$, where g_c$g_c$ is the exceptional point closest to the origin. Point-group symmetry and perturbation theory enable one to predict whether H$H$ may exhibit real or complex eigenvalues for g>0$g>0$. We illustrate the main theoretical results and conclusions of this paper by means of two- and three-dimensional Hamiltonians exhibiting a variety of different point-group symmetries.     

eta-->gammagamma decay width via the Primakoff cross section

Incoherent eta photoproduction in nuclei is evaluated at forward angles within 4 to 9 GeV using a multiple scattering Monte Carlo cascade calculation with full eta-nucleus final-state interactions. The Primakoff, nuclear coherent and nuclear incoherent components of the cross sections fit remarkably well previous measurements for Be and Cu from Cornell, suggesting a destructive interference between the Coulomb and nuclear coherent amplitudes for Cu. The inelastic background of the data is consistently attributed to the nuclear incoherent part, which is clearly not isotropic as previously considered in Cornell's analysis. The respective Primakoff cross sections from Be and Cu give Gamma(eta-->gammagamma)=0.476(62) keV, where the quoted error is only statistical. This result is consistent with the Particle Data Group average of 0.510(26) keV and in sharp contrast (approximately 50%) with the value of 0.324(46) keV obtained at Cornell.     

Lightest isotope of Bh produced via the 209Bi(52Cr,n)260Bh reaction

The lightest isotope of Bh was produced in the new 209Bi(52Cr,n)260Bh reaction at the Lawrence Berkeley National Laboratory's 88-Inch Cyclotron. Positive identification was made by observation of eight correlated alpha particle decay chains in the focal plane detector of the Berkeley Gas-Filled Separator. 260Bh decays with a 35(-9)(+19) ms half-life by alpha particle emission mainly by a group at 10.16 MeV. The measured cross section of 59(-20)(+29) pb is compared to model predictions. The influence of the N=152 and Z=108 shells on alpha decay properties is discussed.     

Shock initiation of composition B and C-4 explosives: Experiments and modeling

Shock initiation experiments with composition B and C-4 HE were performed to obtain in situ pressure gauge data for the purpose of providing the ignition and growth reactive flow model with proper modeling parameters. A 100-mm-bore propellant-driven gas gun was utilized to initiate the explosive charges containing manganin piezoresistive pressure gauge packages embedded in the explosive sample. Experimental data provided new information on the shock velocity-particle velocity relationship for each of the investigated material in their respective pressure range. The run-to-detonation distance points in the pop plot for these experiments showed agreement with previously published data, and ignition and growth modeling calculations resulted in a good fit to the experimental data. Identical ignition and growth reaction rate parameters were used for C-4 and composition B, and the composition B model also included a third reaction rate to simulate the completion of reaction by the TNT component. This model can be applied to shock initiation scenarios that have not or cannot be tested experimentally with a high level of confidence in its predictions. This paper was presented at the International Conference “Shock Waves in Condensed Media,” St. Petersburg, September, 2006. The text was submitted by the authors in English.     

Crystallographic determination of metal surfaces with helium scattering

Helium-surface diffraction data has been used to construct the interaction potential between a Helium atom and a metal surface. The constructed potential fits experimental data for all beam energies and angles of incidence and more importantly is independent of beam energy. Such a potential essentially consists of two parts: a short range repulsive corrugated potential due to electronic overlap, and a long range attractive potential due to dispersion forces. We have generated potentials for He scattering for Ni, Cu and Au and in all cases found excellent agreement with experiments. We also report that the repulsive part of the He scattering potential can be obtained rather simply from first principles without adjustable parameters. This suggests that one can determine surface crystallography from first principles without adjustable parameters.     

Critical Casimir effect in dilute He–He mixture films

Recently, we have found that ⁴He films thin near the lambda point. Based on our measurements, the thinning appears to be caused by the confinement of superfluid order parameter fluctuations in the films. The phenomenon of the thinning is believed to be analogous to the Casimir effect in electromagnetism where the confinement of electromagnetic fluctuations causes the vacuum layer that separates two metal plates to thin. In this paper, we report the result of an experiment extending our previous study to ³He–⁴He mixture films. Thinning is found near the new lambda points and the characteristics of the thinning are similar to that found in pure ⁴He films.     

Lasing action assisted by long‐range surface plasmons

It is shown that lasing action at subwavelength scales can be achieved in realistic plasmonic systems supporting long‐range surface plasmons (LRSPPs). To this end, a general numerical framework has been developed that is able to accurately account for the full spatio‐temporal lasing dynamics and the vastly different length‐ and time‐scales featured by this class of systems. Starting from a loss compensation regime for propagating LRSPPs, it is shown how the introduction of an optical feedback mechanism induces the formation of a self‐sustained laser oscillation at moderate pump intensities. The simplicity of the proposed subwavelength scale laser offers significant potential as a novel class of planar light sources in complex plasmonic circuits.