Spectroscopy of F 3 + -color centers in lithium fluoride crystals (review)

Results of investigations of radiative F ₃ ⁺ -color centers in lithium fluoride obtained by the methods of one- and two-photon absorption, polarization spectroscopy, and luminescence in singlet, triplet and triplet-singlet channels are reported. The scheme of energy levels of the F ₃ ⁺ -center is revised. The probabilities of singlet-triplet conversion and the rates of depletion of the lower triplet state in the range of 80–350 K are presented. Recommendations are given on the technology of radiative LiF coloration that provide an increase in the F ₃ ⁺ -center concentration and a decrease in the concentration of some other centers that prevent lasing on the LiF:F ₃ ⁺ active medium from being obtained. The phototransformations of color centers in LiF are analyzed. The parameters of lasers with LiF:F ₃ ⁺ active media that provide generation of radiation tunable in the green region of the spectrum are considered. Based on spectroscopic data the maximum attainable time characteristics of such lasers are discussed. The prospects for further investigations of LiF:F ₃ ⁺ lasers are outlined in brief. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 5, pp. 745–760, September–October, 1998.     

Thermal expansion and magnetostriction in an anomalous Gd intermetallic compound

Thermal expansion and forced magnetostriction measurements are reported on two Gd intermetallic compounds which order magnetically below 10 K. The relative influence of the electronic, lattice and magnetic degrees of freedom was determined using results obtained on a non-magnetic isostructural compound. A Grüneisen analysis revealed that whilst the magnetic contribution to the specific heat is similar for both Pd₂GdIn and Cu₂GdIn the spontaneous magnetostriction was significantly smaller in the Pd compound. Forced magnetostriction measurements suggest that the thermal expansion in Pd₂GdIn is primarily associated with spin fluctuations in the Pd 4d band. It is suggested that these additional degrees of freedom give rise to the enhanced specific heat observed in Pd₂GdIn. Received 28 July 1999     

Chromatic Properties of Si02-BaO-TiO2-K2O Series Radial Gradient-Index Material

Chromatic properties of SiO₂-BaO-TiO₂-K₂O series radial gradient-index material in the range of visible wavelengths are presented and the possibility of apochromatic microscope objectives is considered.     

Color Constancy in a Photograph Perceived as a Three-Dimensional Space

It is known that color constancy does not hold in a photograph. This could be because the photograph is recognized as a two-dimensional paper. Based on the concept of the recognized visual space of illumination (RVSI), it is predicted that color constancy holds in the photograph if it is perceived as a 3-D scene. We examined whether the color constancy held under a special viewing condition. A photograph of a room under incandescent illumination was shown under daylight illumination. We tested the neutral color perception of a stimulus on the photograph both with and without a dimension-up viewing box showing the photograph alone monocularly. The results showed good color constancy when a subject observed the photograph with the viewing box. It was also shown that the degree of color constancy decreased for a jumbled photograph without 3-D information. Our results suggest that the recognition of a space and illumination are important in color perception.     

Time-resolved optical absorption in YAlO3 crystals

The present work is devoted to the investigation of transient absorption (TA) induced by a pulsed electron beam (E=250 keV) in pure and doped YAlO₃ (YAP) single crystals. The nature of centers responsible for TA is discussed.     

Color Correction of Pathological Images Based on Dye Amount Quantification

Pathological images are color images of stained tissue slides, the color of which varies depending on staining conditions. For reliable diagnosis, the color variation must be corrected in these images. This paper proposes a color correction method for hematoxylin and eosin (H&E) stained pathological images in which the amounts of H&E dyes are estimated based on multispectral imaging technique and Beer Lambert law, and the color image is generated corresponding to the adjusted amount of dyes. This enables us to correct an image to an arbitrary or specified optimal staining-condition image. Through experiments using H&E stained human liver slide images, the effectiveness of the proposed method was confirmed.     

Effects of perceived listeners on speakers''vocal intensity

The purpose of this study was to determine the amount of change in speakers' vocal intensity when a listener is located at various perceived versus actual physical distances from a speaker. Twelve men and 12 women with normal voices were asked to read a passage at three interspeaker distances in one of two conditions. In the perceived listener condition, participants were asked to “imagine” that the listener was located 3, 15, or 30 ft away. In the actual listener condition, one of the experimenters stood at each one of the three experimental distances. Conditions were counterbalanced. The results showed that men and women increased vocal intensity levels for all three interspeaker distances regardless of the type of condition. However, women showed larger increases than men at all interspeaker distances in both conditions. Data for both men and women combined showed that the amount of increase is <6 dB, which indicates that speakers do not follow the inverse square law when raising vocal intensity. Clinical implications of the results are discussed.     

Blue metal complex pigments involved in blue flower color

The blue pigment of cornflower, protocyanin, has been investigated for a long time, but its precise structure was not entirely explained until recently. The molecular structure of the pigment was recently shown to be a metal complex of six molecules each of anthocyanin and flavone glycoside, with one ferric iron, one magnesium and two calcium ions by X-ray crystallographic analysis. The studies provided the answer to the question posed in the early part of the last century, “why is the cornflower blue and rose red when both flowers contain the same anthocyanin?” This work was achieved on the basis of the results of long years of the studies made by many researchers. In this review, the author focuses on the investigations of the blue metal complex pigments involved in the bluing of flowers, commelinin from Commelina commusis, protocyanin from Centaurea cyanus, protodelphin from Salvia patens and hydrangea blue pigment.     

Geometry and electronic properties of single vacancies in achiral carbon nanotubes

An ideal single vacancy can be formed by removing one carbon atom from a hexagonal network. The vacancy is one of the most important defect structures in carbon nanotubes (CNTs). Vacancies can affect the mechanical, chemical, and electronic properties of CNTs. We have systematically investigated single vacancies and their related point defects for achiral, single-walled carbon nanotubes (SWNTs) using first-principles calculations. The structures around single vacancies undergo reconstruction without constraint, forming ground-stateor metastable-state structures. The 5-1DB and 3DB point defects can be formed in armchair CNTS, while the 5-1DB-P and 5-1DB-T point defects can be formed in zigzag CNTs. The related point defects can transform into each other under certain conditions. The formation energies of armchair CNTs change smoothly with the tube radius, while in the case of the 3DB defect, as the radius get larger, the formation energies tend towards a constant value.