Carrier scattering by Auger mechanism in a single quantum wire

We report on time-resolved microphotoluminescence experiments in a single GaAs/GaAlAs V-shaped quantum wire as a function of optical excitation intensity. At low pump power we observe that excitons are localized in quantum boxes formed by the local potential minima existing along the wire axis. As the pump power is increased, state filling of the lowest lying levels of the boxes appears. When two carriers occupy the first excited level of the box, a very efficient Auger scattering occurs, leading to a transfer of carriers from one box to another neighbouring one. The intradot Auger scattering time has been measured and is of the same order of magnitude as the LA-phonon emission rate. Received 5 February 2001     

Nuclear Spin Alignment of 12,13B Produced in Heavy Ion Collisions

The nuclear spin alignments of the β-emitting fragments ¹²B(I ^π=1⁺, T _1/2=20.2 ms) and ¹³B(I ^π=3/2⁻, T _1/2=17.4 ms) produced in the 100A-MeV ¹³C, ¹⁵N + ⁹Be collisions respectively have been observed for the first time detecting asymmetric β-ray emission from these nuclei. By means of the spin manipulation technique based on the hyperfine interaction of B isotopes in TiO₂, both the polarization P and the alignment A were determined reliably. The obtained P and A were significantly smaller than the expectation from the kinematical model. From the fact that the quenching factors for P and A are almost the same, there may be some depolarization mechanism in the collision process itself. This revised version was published online in September 2006 with corrections to the Cover Date.     

Precise Quadrupole Moment of the Doubly Closed Shell Plus One Proton Nucleus 41Sc

In order to precisely determine the |eqQ(⁴¹Sc)/h| of ⁴¹Sc(I ^π=7/2⁻, T _1/2=0.596 s) implanted in a TiO₂ single crystal the electric field gradient tensor and anisotropic chemical shift were determined by detecting the Fourier Transformed Pulse-NMR of ⁴⁵Sc(I ^π=7/2⁻, stable) in the crystal at a high field of 7.0 T and 9.4 T. Combining the new |eqQ(⁴¹Sc)/h| value with the Q(⁴⁵Sc)=−(23.6±0.2) fm², also renewed by using the known atomic hyperfine interaction constants and Sternheimer polarization effect, the |Q(⁴¹Sc;I ^π=7/2⁻,T _1/2=0.596 s)|=(15.6±0.3) fm² has been precisely determined. The value is compared with the theoretical Q(⁴¹Sc) given by a shell model code. This revised version was published online in September 2006 with corrections to the Cover Date.     

Prototype Demonstration of Discrete Correlation Processor-2 Based on High-Speed Optical Image Steering for Large-Fan-Out Reconfigurable Optical Interconnections

We present a discrete correlation processor-2 (DCP-2), which is an optical processor with reconfigurability of interconnection patterns for large-fan-out optical interconnection systems. To our knowledge, there is no reconfigurable optical processor satisfying the requirements for large fan-outs such as high-speed reconfiguration of interconnection pattern, high optical efficiency, and high contrast ratio, because existing spatial light modulators (SLM#x0027;s) lack at least one of these features. The DCP-2 architecture fulfills the requirements by using a hybrid configuration composed of a high-speed image steerer and a spatial light modulator, which work in a complementary manner to shorten the setup time of the SLM. We constructed two kinds of prototype demonstrators based on this architecture. In the experiment, reconfiguration speed of the DCP-2 prototype with shift-invariant optical interconnections, in which a liquid crystal SLM cooperated with a two-dimensional acousto-optic beam deflector, was about 26,000 times faster than that of the standalone SLM at the cost of 50#x0025; energy loss by the deflector.     

Estimation of the latent track size of CR-39 using atomic force microscope

As a frame work of the study for the latent track size measurement using atomic force microscope, we have measured the minute etch pits and the extremely small amount of bulk etch of CR-39 at the beginning of chemical etching, and obtained its growth curves in nanometer dimensions. The pieces of CR-39 were exposed to 6 MeV/nC and Fe ions with normal incidence angle and were etched in 70°C 7 N NaOH solution for 0.5,1,2,3,5 min. The diameters of latent track were estimated to be 17 nm for Fe ions and 8 nm for C ions, respectively. These values are comparable to the experimental data on the average ‘track core diameters’ that have been obtained by various experimental techniques.     

Magnetic Properties and the Electric Field Gradients of Fe4N and Fe4C

The magnetic properties and the hyperfine interactions of Fe₄N and Fe₄C under high pressures are discussed on the basis of first-principles electronic structure calculations performed by the KKR Green's function method and its extention into a full potential scheme (FP-KKR). The results show that both Fe₄N and Fe₄C undergo a weak first order transition from high to low spin states under pressure. This transition is sensitively reflected not only by H _hf but also by EFG. The calculated Curie temperature, magnetic moments and H _hf well reproduce the experimental observations.     

An improved synthesis of pyrido[2,3-d]pyrimidines

An improved and efficient synthesis of 1,3-dialkylpyrido[2,3-d]pyrimidine-2,4-(1H,3H)-diones from 6-methylaminouracils and methyl propiolate or diethyl ethoxymethylenemalonate is described.     

Studies on sialic acids. XIII. Isolation of 3-deoxy-D-glycero-D-galacto-2-nonulopyranosonic acid (KDN) from chum salmon, Oncorhynchus keta

A method for analysis of 3-deoxy-D-glycero-D-galacto-2-nonulopyranosonic acid (KDN) by high-performance liquid chromatography (HPLC) with a strongly basic anion-exchange resin was developed. The method was applied to detect free KDN in water used to rinse of fertilized eggs of chum salmon, Oncorhynchus keta. Furthermore, KDN was isolated from the water as a fully protected derivative.     

Electric Field Gradients of Light Impurities in TiO2 Calculated by the Full Potential KKR Green's Function Method

The electric field gradients (EFGs) of B, N, O and Na in TiO₂ were calculated by the full potential Korringa–Kohn–Rostoker (KKR) Greens function method in the framework of the density functional theory. The agreement with the experiments was much improved from the previous calculations that were based on the muffin-tin potential model.