Experimental studies of transition radiation and optical bremsstrahlung

This report summarizes research on the optical emission from thin films and bulk metals bombarded by 25 to 120 keV electrons carried out at Oak Ridge National Laboratory. Details concerning the experimental apparatus and theoretical calculations may be found in the references listed in this paper. Measurements have been carried out on the dependence of the emitted spectra on angle of observation, polarization, sample thickness, surface roughness, surface contamination, and incident electron energy. 13 refs

Analytical solutions to zeroth-order dispersion relations of a cylindrical metallic nanowire

Zeroth-order complex dispersion relations of a cylindrical metallic nanowire have been solved out analytically with approximate methods. The analytical solutions are valid for the sections of the dispersion relations whose frequencies are close to the Surface Plasmon frequency. The back bending of the Surface Plasmon-Polaritons(SPPs) can be well described by the analytical solutions, confirming that the back bending is originated from the metal Ohmic loss. The utility of the back bending point in the dispersion relation for the measurement of the metallic Ohimc loss has also been suggested.Comment: 6pages, 3figure

Discovery of widespread transcription initiation at microsatellites predictable by sequence-based deep neural network

Using the Cap Analysis of Gene Expression (CAGE) technology, the FANTOM5 consortium provided one of the most comprehensive maps of transcription start sites (TSSs) in several species. Strikingly, ~72% of them could not be assigned to a specific gene and initiate at unconventional regions, outside promoters or enhancers. Here, we probe these unassigned TSSs and show that, in all species studied, a significant fraction of CAGE peaks initiate at microsatellites, also called short tandem repeats (STRs). To confirm this transcription, we develop Cap Trap RNA-seq, a technology which combines cap trapping and long read MinION sequencing. We train sequence-based deep learning models able to predict CAGE signal at STRs with high accuracy. These models unveil the importance of STR surrounding sequences not only to distinguish STR classes, but also to predict the level of transcription initiation. Importantly, genetic variants linked to human diseases are preferentially found at STRs with high transcription initiation level, supporting the biological and clinical relevance of transcription initiation at STRs. Together, our results extend the repertoire of non-coding transcription associated with DNA tandem repeats and complexify STR polymorphism

Optical, mass, and auger spectra from e-bombarded KBr

We have measured the mass spectrum and optical emission lines of neutral potassium atoms ejected from KBr at T = 300/degree/K and 443/degree/K bombarded by 2-keV electrons. The room-temperature data may be complicated by the nonstoichiometry of the alkali-enriched sample surface and seem difficult to interpret. The high-temperature sample, which maintains the proper stoichiometry, produces data in support of gas-phase excitation of alkali atoms desorbed from the surface. 15 refs., 4 figs

PHOTOACOUSTIC STUDY OF GUIDED MODES IN LiF THIN FILMS

Des modes lumineux sont excités dans des films de LiF. Des mesures photoacoustiques permettent de déterminer l'indice de réfraction, l'anisotropie optique, l'épaisseur et la rugosité des films.Light modes are excited in LiF films. Photoacoustic measurements allow to determine refractive index, optical anisotropy, thickness and roughness of the films

Photoemission from oblate silver spheroids with polarized vacuum uv excitation

A 3 nm thick silver film was evaporated on a quartz slide and then heated for 60 s at 400/sup 0/C. The resulting spheroids were 60 nm in diameter with average center-to-center distance of 110 nm. These particles were flattened out along the substrate normal with a typical ratio of minor axis length to major axis length being 0.2. Photoemission measurements were made using a Seya-Namioka monochromator with an air discharge lamp. The dependence of the photo yield on the polarization of the incident light was determined with a VUV transmission polarizer made of cleaved LiF plates. (WRF

Optical properties of metals by spectroscopic ellipsometry

The use of spectroscopic ellipsometry for the accurate determination of the optical properties of liquid and solid metals is discussed and illustrated with previously published data for Li and Na. New data on liquid Sn and Hg from 0.6 to 3.7 eV are presented. Liquid Sn is Drude-like. The optical properties of Hg deviate from the Drude expressions, but simultaneous measurements of reflectance and ellipsometric parameters yield consistent results with no evidence for vectorial surface effects

Soft x-ray transmission gratings

A technique was developed for producing transmission diffraction gratings suitable for use in the soft x-ray region. Thin self-supporting films of a transparent material are overlaid with several thousand opaque metallic strips per mm. Gratings with 2100, 2400, and 5600 1/mm have been produced and tested. Representative spectra over the wavelength range from 17.2 to 40.0 nm are given for a grating consisting of a 120-nm-thick Al support layer overlaid with 2400, 34-nm-thick, Ag strips/mm. The absolute transmittance is approx. 13% at 30 nm, and the efficiency in the first order is approx. 16%. The observed resolution of approx. 2A is acceptable for many of the potential applications. These gratings have several advantages over the two presently available alternatives in the soft x-ray region (i.e., reflection gratings used at grazing incidence and free-standing metallic wire transmission gratings). Fabrication is relatively quick, simple, and cheap. The support layer can also serve as a filter and help conduct excessive heat away. Higher line densities and hence higher resolutions are possible, and when used at normal incidence the spectra are aberration free. Suitable materials, component thicknesses, and line densities can be chosen to produce a grating of optimum characteristics for a particular application