Visualization of Magnetization Transfer Effect in Polyethylene Glycol Impregnated Waterlogged Wood

To visualize the condition of impregnation of polyethylene glycol (PEG) in waterlogged wood, we demonstrated magnetic transfer (MT) magnetic resonance imaging (MRI) through a series of process of PEG impregnation. Three different samples were examined; reference wood, 10 cm cut wood, and 5 cm cut wood. During this study, the upper section sample was kept immersed in water, for the middle and lower sections the concentration of PEG solution was changed at 20 wt% intervals from 20 to 100 wt%. The impregnated periods of each PEG solution concentration were 14 days. Then, MR imaging were performed with/without MT pulse. The MTR value for both 10 cm- and 5 cm-samples were shown to decrease at 20 wt% PEG at peak concentration. When the sample volume was large, e.g., 10 cm-sample, the MTR value decreased to 100 wt% PEG concentration. In contrast, when a sample volume was small, e.g., 5 cm-sample, MTR value decreased to 60 wt% PEG concentration. In conclusion, MTR analysis makes it possible to nondestructively visualize and evaluate the inner condition concerning the PEG impregnation method for waterlogged wood.     

Error analysis for rotating active Stokes-Mueller imaging polarimeters

Retrieval of Mueller matrices from intensity measurements is a noise-sensitive process. In addition, the choice of the method used for extracting Mueller matrix elements greatly influences the precision of the final results. Among available procedures, three have been tested and their robustness analyzed by adding Gaussian noise to computer synthesized data and have been verified by comparing experimental data. As expected, the methods based on classical matrix inversion reach their noise reduction limit even if more data are considered. In contrast, the discrete Fourier transform approach features a remarkable stability. The identified reason is that the retrieval process corresponds to filtering with a periodic kernel.     

Optical resonance in a narrow slit in a thick metallic screen.

Interaction of TM-polarized waves with a subwavelength thick metallic slit has been analyzed. A Fabry-Pérot-like behavior is reported. The resonance peaks, however, have very low magnitude and a systematic shift towards longer wavelengths is observed. The slit being narrow, this shift can be interpreted as the result of an aperture effect. Spectral transmission from a periodic array of such slits features the same peaks with a high increase in their magnitude, confirming that a grating acts as an amplifier of those resonances. Such a mechanism might explain the enhancement of the transmission observed in recent experiments [T. W. Ebbesen, H. J. Lezec, H. F. Ghaemi, T. Thio, and P. A. Wolff, Nature (London) 391, 667 (1998)].     

Detection efficiency improvement of a large volume scintillation cell

A large volume scintillation cell (LVSC) for radon activity concentration measurements has been reported at MARC-IV. The present paper describes improvements in the detection efficiency of the LVSC and results of the radon activity concentration measurements for indoor air that were performed using the improved LVSC. The cell is a cylindrical shape and has two photomultiplier tubes that are attached to a condensing lens on the photocathode so as to provide good light collection. Individual counting efficiencies were determined to be 0.48 for ²²²Rn, 0.55 for ²¹⁸Po, and 0.61 for ²¹⁴Po. The average counting efficiency per alpha-particle from the radon and its short half-life progenies was 0.55. This value is smaller than the original value reported by LUCAS of 0.86. However, the sensitivity is approximately eight times higher than that of the Lucas cell, which has a smaller volume. A background counting rate of 0.015 cps was obtained. The lower limit of detection (LLD) for the measurements was estimated using the average background counts, the detection efficiency and measurement time. The LLD at 80% statistics confidence limits was less than 10 Bq/m³ when counted within two hours.     

Radon-Nikodým theorem for biweights and regular biweights on partial *-algebras

The first purpose of this paper is to investigate Radon-Nikodym theorem for biweights on partial *-algebra. Secondly, we study regularity of biweights on partial *-algebraA and show that a biweightϕ onA is decomposed intoϕ=ϕ _r+ϕ _s, whereϕ _r is a regular biweight onA andϕ _s is a singular biweight onA.     

Preparation of composition-controlled silicon oxynitride films by sputtering; deposition mechanism,and optical and surface properties

Silicon oxynitride films have been grown on silicon by current-controlled reactive sputtering. The content of oxygen in the films could be well controlled by regulating the sputtering current under the reactive gas of Ar+ N₂ with an oxygen content of around 3%. The atomic ratio of oxygen to nitrogen in the silicon oxynitride film became larger with increasing sputtering current. It has been found that electron irradiation of the silicon substrate induces adsorption of oxygen and nitrogen. The degree of oxygen adsorption was about ten times larger than that of nitrogen. This phenomenon is a key mechanism in controlling the film composition. The adsorptive mechanism might be explained by the phenomenon of surface activation by the electron bombardment. Utilizing this technique, wettability by germanium of silicon oxynitride films could be controlled by varying their oxygen and nitrogen contents. A better wetting condition was obtained from films with large atomic ratio of nitrogen to oxygen in the silicon oxynitride film.     

Degeneration of Riemann surfaces and intermediate polarization of the moduli space of flat connections

We construct a family of polarizations of the moduli space of flat SU(n)-connections on a closed 2-manifold of genus g(≧2). These are generalizations of various polarizations known until now. That is, our family of polarizations includes Weitsman’s real polarizations in the case of n=2 [17], as well as the Kahler polarizations which are well known since [2] and [18]. Our construction is based on an original formulation of degeneration of Riemann surfaces. The relation between our polarizations and the complex structures of the moduli Spaces of parabolic bundles are also studied.