Kunzeanones A, B, and C: novel alkylated phloroglucinol metabolites from Kunzea ambigua

Three new metabolites, kunzeanones A (1), B (2), and C (3), along with three known compounds, cryptostrobin (4), (+)-spathulenol (5), and (−)-globulol (6), were isolated from the non-polar fraction of the dried leaves of Kunzea ambigua (Myrtaceae), which shows ichthyotoxicity toward a small fish, medaka. The structures of these new compounds were elucidated as condensates of alkylated phloroglucinol with methylflavanone and germacrane-type sesquiterpene, respectively, on the basis of spectral analyses including 1-D and 2-D NMR spectra. The stereochemistries of kunzeanones A and B were determined by X-ray crystallographic analysis. A sesquiterpene, (+)-spathulenol (5), among the isolates was characterized as the ichthyotoxic principle of the extract.     

Pseudo-Binary Phase Diagram of LiNH2-MH (M = Na,K) Eutectic Mixture

The hunt for a cleaner energy carrier leads us to consider a source that produces no toxic byproducts. One of the targeted alternatives in this approach is hydrogen energy, which, unfortunately, suffers from a lack of efficient storage media. Solid-state hydrogen absorption systems, such as lithium amide (LiNH₂) systems, may store up to 6.5 weight percent hydrogen. However, the temperature of hydrogenation and dehydrogenation is too high for practical use. Various molar ratios of LiNH₂ with sodium hydride (NaH) and potassium hydride (KH) have been explored in this paper. The temperature of hydrogenation for LiNH₂ combined with KH and NaH was found to be substantially lower than the temperature of individual LiNH₂. This lower temperature operation of both LiNH₂-NaH and LiNH₂-KH systems was investigated in depth, and the eutectic melting phenomenon was observed. Systematic thermal studies of this amide-hydride system in different compositions were carried out, which enabled the plotting of a pseudo-binary phase diagram. The occurrence of eutectic interaction increased atomic mobility, which resulted in the kinetic modification followed by an increase in the reactivity of two materials. For these eutectic compositions, i.e., 0.15LiNH₂-0.85NaH and 0.25LiNH₂-0.75KH, the lowest melting temperature was found to be 307 °C and 235 °C, respectively. Morphological studies were used to investigate and present the detailed mechanism linked with this phenomenon.     

Spontaneous ignition temperature for the compacted mixture of Ni–Al system: Experiment,theory, and comparisons

Spontaneous ignition of compacted mixture has been examined not only experimentally but also theoretically, relevant to materials synthesis for Ni–Al system. Spontaneous ignition temperature, determined from the inflection-point of the temporal variation of surface temperature, is found to decrease at first, reach the minimum, and then increase gradually, with increasing size ratio, being defined as the ratio of compact and particle diameters and reported to be useful in correlating experimental results. The lowest temperature observed is as low as that, more than 200 K below the melting point 934 K of Al, at the size ratio of c.a. 700. While its decrease is attributed to the increase in the particle surface per unit spatial volume of compacted mixture, as reported in the literature, its increase found in the course of the present study can fairly be correlated to an enhancement of heat loss from each particle in the compacted mixture, by conducting a theoretical consideration. As for the dependence of spontaneous ignition temperature on the mixture ratio, a shifting occurs from a decreasing trend with increasing mixture ratio at small size ratios, less than about 700, to an insensitive trend to the mixture ratio, had not been reported in the literature. In addition, a fair degree of agreement, shown in experimental comparisons with theoretical results, indicates that the present formulation has captured the essential features of the spontaneous ignition of compacted mixture, especially for size ratios with large values. Since this kind of particle size effects, relevant to the spontaneous ignition of the compacted mixtures, has not been captured in the previous studies, its elucidation can be considered not only notable but also useful, in manipulating combustion process in materials synthesis, especially, in choosing a specific condition for the lowest spontaneous ignition temperature by varying the size ratio.     

Gamma-ray spectroscopy of the neutron-rich Ni region through heavy-ion deep-inelastic collisions

Nuclei in the neutron-rich Ni region have been studied by γ-ray spectroscopy. Gamma-rays emitted from isomers, with T _1/2 > 1 ns, produced in heavy-ion deep-inelastic collisions were measured with an isomer-scope. The nuclear structure of the doubly magic ⁶⁸Ni and its neighbor ^69,71Cu is discussed on the basis of the shell model. Future experiments for more neutron-rich Ni nuclei are also viewed. Received: 1 May 2001 / Accepted: 4 December 2001     

Diffuse scattering from Ge(111) surface at high temperature

On heating a clean Ge(111) surface above 240°C, Ge(111) 2 × 8 surface structure changes to 1 × 1 one. We have first observed twofold splitting diffuse scattering in RHEED patterns from the Ge(111) 1 × 1 surface at high temperatures. A modulated 2 × 2 structure is proposed as a structural model for the diffuse scattering. The Fermi-surface instability of dangling-bond electrons at the surface is studied as an origin of the formation of the modulated structure.     

Turbulent diffusion for the radial twist map

An analytical tool is given to study the statistical properties of the radial twist map, X_n+1 = X_n + α(Y_n+1) and Y_n+1 = Y_n + Af (X_n), with arbitrary rotation number α(Y) and arbitrary periodic force f(X). The case for which f(X) = sin 2 πX and with arbitrary α is treated in the region of large A. The turbulent diffusion coefficient D for the chaotic orbit relaxes as $\text{t}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$ to $\text{A}{}^2\text{4}$, except for the case of the standard map, where the eventual value of D is different from $\text{A}{}^2\text{4}$.     

High-repetition-rate 12 fs pulse amplification by a Ti:sapphire regenerative amplifier system

We demonstrate the direct generation of 12 fs pulses from a Ti:sapphire regenerative amplifier system at a 1 kHz repetition rate utilizing properly designed broadband components for chirped-pulse amplification. Optimized designs of a regenerative amplifier with a multilayer gain-narrowing compensator and an adaptive dispersion compensator with a spatial light modulator contribute to the shorter pulse amplification.     

Experimental Study on Time-Spread/Wavelength-Hop Optical Code Division Multiplexing with Dispersion-Compensating En/Decoder

10Gbit/s time-spread/wavelength-hop optical code generation and decoding are performed by dispersion-compensating fiber Bragg grating (FBG) en/decoder pair. Error-free 10km single mode fiber (SMF) transmission of 10Gbit/s optical code division multiplexing (OCDM) has been experimentally demonstrated.