Search results for "Optic"
showing 10 items of 15126 documents
Quadrature effects on the accuracy of flux calculations in realistic atmospheres
1993
Abstract We have investigated the accuracy of five different quadrature methods—equal steps in θ, equal steps in cos θ, Gaussian, double Gaussian and Gauss-Lobatto—on the accuracy of fluxes in realistic aerosol atmospheres, using the Gauss-Seidel method. In addition, a range of Gaussian quadrature stream numbers from two to 32 were compared. The atmospheric models considered are those recently presented by Lenoble, with the exception that we have used Henyey-Greenstein phase functions in place of Mie. Our results should be easily reproduceable by any other workers interested in similar realistic atmospheres. A table of Gauss-Lobatto weights and points is provided as an appendix.
Combining EXAFS and XRay Powder Diffraction to Solve Structures Containing Heavy Atoms
2005
Determination of structures using x-ray powder diffraction is complicated if the reflection intensities are mainly influenced by the scattering from heavy atoms and the atomic coordinates of light atoms remain uncertain. A method like EXAFS, which is sensitive to short range order, gives reliable atomic distances in the surroundings of heavy atoms with a precision of ±0.02 A. The probability for obtaining the complete structure from x-ray powder diffraction increases if one includes parameters derived from EXAFS measurements as restraints during the procedure of structure solving. We demonstrate the potential of combining EXAFS and x-ray powder diffraction by solving the structure UO2[H2AsO…
Digitale Fenster für γ-γ-Koinzidenzmessungen mit Halbleiterdetektoren
1968
Zusammenfassung Digital windows have been designed and built to avoid the disadvantages of normal single channel analysers setting the gate in γ-γ-coincidence experiments with two Ge(Li)-detectors.
First-principles electronic structure of spinelLiCr2O4:A possible half-metal
2004
We have employed first-principles electronic structure calculations to examine the hypothetical (but plausible) oxide spinel, ${\mathrm{LiCr}}_{2}{\mathrm{O}}_{4}$ with the ${d}^{2.5}$ electronic configuration. The cell (cubic) and internal (oxygen position) structural parameters have been obtained for this compound through structural relaxation in the first-principles framework. Within the one-electron band picture, we find that ${\mathrm{LiCr}}_{2}{\mathrm{O}}_{4}$ is magnetic, and a candidate half-metal. The electronic structure is substantially different from the closely related and well-known rutile half-metal ${\mathrm{CrO}}_{2}.$ In particular, we find a smaller conduction-band width…
A penetration depth study on the non-centrosymmetric superconductors Li2(Pd1−xPtx)3B
2008
Abstract We study the superconducting order parameter in the non-centrosymmetric compounds Li 2 (Pd 1− x Pt x ) 3 B ( x =0, 0.3, 0.7 and 1) by measuring magnetic penetration depth λ ( T ). The low temperature λ ( T ) shows a linear temperature dependence for x ⩾0.3, but follows exponential-like behavior for lower Pt contents. These findings suggest that a spin-triplet state might gradually develop with increasing x due to the broken inversion symmetry.
Looking for the dichromatic version of a colour vision model
2004
Different hypotheses on the sensitivity of photoreceptors and post-receptoral mechanisms were introduced in different colour vision models to derive acceptable dichromatic versions. Models with one (Ingling and T'sou, Guth et al, Boynton) and two linear opponent stages (DeValois and DeValois) and with two non-linear opponent stages (ATD95) were used. The L- and M-cone sensitivities of red–green defectives were either set to zero (cone-loss hypothesis) or replaced by that of a different cone-type (cone-replacement hypothesis), whereas for tritanopes the S-cone sensitivity was always assumed to be zero. The opponent mechanisms were either left unchanged or nulled in one or in all the opponent…
Real And Positive Filter Based On Circular Harmonic Expansion
1989
A real and positive filter for pattern recognition is presented. The filter, based on the circular harmonic (CH) expansion of a real function, is partially rotation invariant. As it is real and positive, the filter can be recorded on a transparency as an amplitude filter. Computer simulations of character recognition show a partial rotation invariance of about 40°. Optical experiments agree with these results and with acceptable discrimination between different characters. Nevertheless, due to experimental difficulties, the method is onerous for use in general pattern recognition problems.
Electric hyperfine interaction in199Hg fluorides
1985
With the current integration technique, the Mossbauer effect on the 158 keV, 5/2−→1/2− transition in199Hg was studied using the cubic HgF2 and the tetragonal Hg2F2 as absorbers; in the latter, a quadrupole splittingeQVzz=}- 9.0(2) mm/s was observed. Electron densities were calculated with the self-consistent-charge-extended-Hueckel-molecular-orbital method and δ〈r2〉=(3.26±0.11) fm2 derived. From the quadrupole splitting and the calculation, an effective antishielding factor almost twice that of the neutral Hg atom is derived.
Energy- and time-resolved microscopy using PEEM: recent developments and state-of-the-art
2008
Two novel methods of spectroscopic surface imaging are discussed, both based on photoemission electron microscopy PEEM. They are characterised by a simple electron-optical set up retaining a linear column. An imaging high-pass energy filter has been developed on the basis of lithographically-fabricated microgrids. Owing to a mesh size of only 7μm, no image distortions occur. The present energy resolution is 70 meV. The second approach employs time-of-flight energy dispersion and time-resolved detection using a Delayline Detector. In this case, the drift energy and the time resolution of the detector determine the energy resolution. The present time resolution is 180 ps, giving rise to an en…
Cubic metamaterial crystal supporting broadband isotropic chiral phonons
2021
Chiral metamaterials can support chiral phonons leading to acoustical activity, the acoustical counterpart of optical activity. However, the properties of early metamaterial designs have been very highly anisotropic, and chiral acoustical phonons occurred only for selected high-symmetry directions. The authors propose a novel chiral metamaterial based on ``twisting'' a truncated octahedron in a simple-cubic unit cell. Not supported by crystal symmetry alone but rather by a tuned degeneracy, chiral phonons and large broadband acoustical activity are obtained for all phonon propagation directions in 3D. This result is notable because even isotropic achiral acoustical phonons are rare for crys…