Effect of radiation damage on luminescence of erbium-implanted SiO2/Si studied by slow positron beam

The effect of damage on 1.54 μm luminescence for 30 keV-Er-implanted SiO₂ films has been studied by positron annihilation and cathodoluminescence. It was found that S-parameter in the films decreased after implantation, indicating the suppression of positronium formation. The luminescence appeared with the recovery of the S-parameter after 600°C annealing. The intensity reached a maximum at 900°C annealing whereas the S-parameter did not change significantly. It seems that most damages recover at 600°C and thereafter Er ions transform to an optically active state at 900°C.     

Transient thermo-mechanical interactions during high-speed slip at metal-on-metal interfaces

The paper describes results obtained from plate-impact pressure-shear friction experiments to investigate the phenomena of high-speed slip at metal-on-metal interfaces. Using a CH tool-steel/Ti-6Al-4V tribo-pair the authors have studied the effects of normal pressure, slip-speed, temperature and surface roughness on the evolution of the dynamic slip-resistance. Moreover, a finite-element procedure is developed to simulate the evolution of thermo-mechanical fields and understand their relationship to the observed slip response.Next, the pressure-shear friction experiments are extended to investigate the behavior of CH tool-steel/7075-T6 Al alloy tribo-pair. This material combination allows dynamic friction characteristics to be studied in the near-melt and the fully melt temperature regime of the lower-melting-point metal (7075-T6 Al alloy) comprising the tribo-pair. Besides providing information on the slip-velocity versus friction-stress relationship under extreme interfacial conditions, the experiments provides critical information on the shearing resistance of confined molten metal films under high pressures and extremely high shearing rates.     

Replication of tobamovirus RNA

Tobamovirus is a positive-strand RNA virus of plants. Its single-stranded RNA genome replicates via the negative-strand RNA. In this review, we describe our current knowledge about viral and host factors associated with tobamovirus RNA replication and discuss the replication mechanisms. We also mention the usefulness of tobamovirus genomes as vectors.     

Two Dimensional Rotational Temperature Measurement by Multiline Laser Induced Fluorescence of Nitric Oxide in Combustion Flame

Two-dimensional rotational temperature measurement was performed in a stable combustion flame of premixed butane and oxygen using multiline laser induced fluorescence (LIF) of nitric oxide molecules. Multiple rotational absorption lines of A²∑⁺Π;X²II(0,0) Q₁ and Q₂ lines were excited by laser light around 226 nm, and the LIF signal was observed by an image-intensified digital camera. Temperature was determined through least squares fitting correlation between LIF intensity and excitation rotational quantum number for the Boltzmann distribution function. The measured LIF intensity was approximated by the Boltzmann distribution with good accuracy, and the temperature obtained was between 500 K and 1800 K for the test flame. The measuring error of the temperature was evaluated and found to be 80 K, which corresponded to 8% of the measured fluorescence intensity. The two-line LIF scheme was evaluated by different pairs of excitation lines (Q₁(31.5)/Q₁(16.5) and Q₁(18.5)/Q₁(16.5)) for comparison with the multiline LIF approach. Temperature which was obtained by two-line LIF scheme corresponded well with multiline LIF results for Q₁(31.5)/Q₁(16.5) excitation. However, for Q₁(18.5)/Q₁(16.5) excitation, the obtained temperature did not agree with the multiline LIF result because the population of rotational states J=18.5 and J=16.5 is similar at high temperatures. We found that two-line LIF temperature measurement was reliable when excitation lines were suitably selected.     

Analysis of Light Propagation in a Three-Dimensional Realistic Head Model for Topographic Imaging by Finite Difference Method

Near infrared topographic imaging is a novel non-invasive technique to obtain the activated region in the brain cortex. The light propagation in the head is strongly scattered and this causes results in poor spatial resolution and contrast in the topographic images. Adequate modelling of light propagation in the head in order to deduce the volume of tissue interrogated by a source-detector pair for topographic imaging is very important to improve the quality of image of brain activity. In this study, the light propagation in a three-dimensional realistic head model is calculated by the finite difference method. The geometry of the model is generated from axial slices of an MRI scan. The topographic image is obtained from the change in intensity detected by source-detector pairs caused by the brain activity. The images obtained by two types of source-detector arrangement are compared to evaluate the efficiency of source-detector arrangement. The results show that the double-density arrangement improves the quality of the topographic image of the brain activity.     

Development of high grade fiber-optic gyroscopes

Tokimec has been developing high grade interferometric fiber-optic gyroscopes (I-FOGs) for useful applications. The I-FOG consists of a sensing coil module, a light emitting module and an electronics circuits module. We achieved the bias stability of 0.003 deg/h and the angular random walk of 0.001 deg/√h and the scale factor error of 10 ppm (1σ). Then the azimuth error of the strapdown gyrocompass system with the high grade I-FOGs was less than ±0.05 s λ (deg) under the environmental temperature condition 23±5(°C).     

Yukawa coupling structure in intersecting D-brane models

The structure of Yukawa coupling matrices is investigated in type IIA T ⁶/(Z₂ x Z₂) orientifold models with intersecting D-branes. Yukawa coupling matrices are difficult to be made realistic in conventional models in which the generation structure emerges by the multiple intersection of D-branes in the factorized T ⁶ = T ² x T ² x T ². We study the new type of flavor structure, where Yukawa couplings are dynamically generated, and show this type of models lead to non-trivial structures of Yukawa coupling matrices, which can be realistic.Received: 8 December 2004, Revised: 22 December 2004, Published online: 9 March 2005     

Absolute photoionization cross sections with ultra-high energy resolution for Ar, Kr, Xe and N2 in inner-shell ionization regions

The high-resolution absolute photoionization cross sections for Ar, Kr, Xe and N₂ in the inner-shell ionization region have been measured using a multi-electrode ion chamber and monochromatized synchrotron radiation. The energy ranges of the incident photons for the target gases were as follows: Ar: 242–252 eV (2p Rydberg excitation), Kr: 1650–1770 eV (near the 2p ionization thresholds), Xe: 665–720 eV (near the 3d ionization thresholds) and 880–1010 eV (near the 3p ionization thresholds), N₂: 400–425 eV (N 1s excitation and ionization). It is the first time to measure the absolute ionization cross sections of Ar, Kr, Xe and N₂ over the present energy ranges with the energy resolution of over 10,000. The natural lifetime widths of , , and resonances for Ar, resonance for Xe, and resonance for N₂ have been obtained based on the cross sections determined. The ionization energies into the Ar⁺ (), Ar⁺ () and Xe⁺ () ionic states are also determined using the Rydberg formula.     

Grouping and adding method for calculating light scattering by large fluffy aggregates

We present a method to derive the light scattering properties of very porous fractal aggregates composed of a large number of monomers where the size parameter of monomer is larger than unity. Our new method is based on the grouping of the aggregate: The aggregate is divided into groups, where each group is located along a line of the incident light, and the scattering properties of the group are calculated taking into account multiple scattering with monomers located inside the group, as well as those in a buffer region around the group. The scattering and absorption efficiencies are obtained by adding the resultant scattering properties for all the groups. We have shown that the method effectively works when the monomer scatters the incident lights predominantly in the forward direction, which is the case if the monomer size is large compared to the wavelength of the incident light.The errors in resulting scattering and absorption efficiencies for porous aggregates are investigated for various refractive indices and sizes of monomers. We found that the errors are larger for low absorbing materials and they can be reduced by expanding the buffer region. In the case of the buffer region for each group consisting of 1/8 of the total number of monomers, the results show errors less than 15% and 10% for absorption and scattering, respectively. It is also shown that the errors have a small standard deviation (i.e., 2%) for different directions of the incident light.