Direct modulation of InGaAsP/InP double heterostructure lasers

Direct modulation of an InGaAsP/InP double heterostructure laser was investigated experimentally. Sinusoidal modulation up to 2.5 GHz was achieved with almost constant modulation efficiency. Pulse responses showed that the damped relaxation oscillation in light output was well suppressed.     

Synchronous firing and higher-order interactions in neuron pool

The stochastic mechanism of synchronous firing in a population of neurons is studied from the point of view of information geometry. Higher-order interactions of neurons, which cannot be reduced to pairwise correlations, are proved to exist in synchronous firing. In a neuron pool where each neuron fires stochastically, the probability distribution q(r) of the activity r, which is the fraction of firing neurons in the pool, is studied. When q(r) has a widespread distribution, in particular, when q(r) has two peaks, the neurons fire synchronously at one time and are quiescent at other times. The mechanism of generating such a probability distribution is interesting because the activity r is concentrated on its mean value when each neuron fires independently, because of the law of large numbers. Even when pairwise interactions, or third-order interactions, exist, the concentration is not resolved. This shows that higher-order interactions are necessary to generate widespread activity distributions. We analyze a simple model in which neurons receive common overlapping inputs and prove that such a model can have a widespread distribution of activity, generating higher-order stochastic interactions.     

Lipid peroxidation-derived cytotoxic aldehyde, 4-hydroxy-2-nonenal in smoked pork

The contents of 4-Hydroxy-2-nonenal (HNE), cytotoxic aldehyde, in smoked meat products (ham, bacon and sausage) were analyzed. All the samples analyzed contained HNE, although large differences in the contents between the different samples were observed. In one lot of ham (H1) and wiener sausage (WS1) a high level in HNE was observed. The changes of HNE contents of pork meats containing 0, 0.1, 0.5 and 1% Sugi wood vinegar (SWV) stored at 0?°C were also analyzed for 7 days. As an index of lipid peroxidation level, malonaldehyde (MA) contents were also analyzed in these samples. After 7 days of storage, HNE was detected only in pork meats containing 1% SWV and the level was similar to those of H1 and WS1. Judging from MA contents, SWV may act as a pro-oxidant in pork meats and HNE may accumulate in pork in which lipid peroxidation is in progress.     

Ice clouds and Asian dust studied with lidar measurements of particle extinction-to-backscatter ratio, particle depolarization, and water-vapor mixing ratio over Tsukuba

The tropospheric particle extinction-to-backscatter ratio, the depolarization ratio, and the water-vapor mixing ratio were measured by use of a Raman lidar and a polarization lidar during the Asian dust seasons in 2001 and 2002 in Tsukuba, Japan. The apparent (not corrected for multiple-scattering effects) extinction-to-backscatter ratios (Sp) showed a dependence on the relative humidity with respect to ice (RHice) obtained from the lidar-derived water-vapor mixing ratio and radiosonde-derived temperature; they were mostly higher than 30 sr in dry air (RHice < 50%), whereas they were mostly lower than 30 sr in ice-supersaturated air (RHice > or = 100%), where the apparent extinction coefficients were larger than 0.036 km(-1). Both regions showed mean particle depolarization ratios of 20%-22%. Comparisons with theoretical calculations and the previous experiments suggest that the observed dependence of Sp on RHice is attributed to the difference in the predominant particles: nonspherical aerosols (mainly the Asian dust) in dry air and cloud particles in ice-supersaturated air.     

Aqueous chromatography utilizing pH-/temperature-responsive polymer stationary phases to separate ionic bioactive compounds

Cross-linked poly(N-isopropylacrylamide-co-acrylic acid) (poly(IPAAm-co-AAc))-grafted silica bead surfaces were prepared and applied as new column matrix materials that exploit temperature-responsive anionic chromatography to separate basic bioactive compounds, specifically catecholamine derivatives, in aqueous mobile phases. Since poly(IPAAm-co-AAc) has a well-known temperature-responsive phase transition and apparent pKa shift, polymer-grafted silica bead surfaces are expected to exhibit simultaneous hydrophilic/hydrophobic and charge density alterations under thermal stimuli. Elution behavior of catecholamine derivatives from a copolymer-modified bead packed column was monitored using aqueous mobile-phase HPLC under varying temperature and pH. Catecholamine derivatives had higher retention times on poly(IPAAm-co-AAc) columns at higher pH in comparison with those on noncharged PIPAAm reference columns, suggesting an electrostatic interaction as a separation mode. Temperature also affected the retention behavior of catecholamine derivatives. Optimal separation of four catecholamine derivatives was achieved at elevated temperature, 50 degrees C, and at pH 7.0. This is due to the increased hydrophobicity of the stationary phase as evidenced by the elution of a nonionic hydrophobic steroid. From these results, mutual influences of both electrostatic and hydrophobic interactions between basic catecholamine derivatives and pH-/temperature-responsive surfaces are noted. Consequently, elution of weakly charged bioactive compounds is readily regulated through the modulation of stationary-phase thermoresponsive hydrophilic/hydrophobic and charge density changes.     

Novel vitamin E derivative with 4-substituted resorcinol moiety has both antioxidant and tyrosinase inhibitory properties

A novel vitamin E derivative, (6″-hydroxy-2″,5″,7″,8″-tetramethylchroman-2″-yl) methyl 3-(2′,4′-dihydroxyphenyl)propionate (TM4R), which has a chromanoxyl ring and 4-substituted resorcinol moieties, was synthesized; and its inhibitory effects on tyrosinase, antioxidant ability, and lightening effect of ultraviolet B (UVB)-induced hyperpigmentation were estimated. TM4R showed potent inhibitory activity on tyrosinase, which is the rate-limiting enzyme in melanogenesis. The scavenging activities of TM4R on 1,1-diphenyl-2-picrylhydrazyl and hydroxyl radicals were found to be nearly the same as those of α-tocopherol. Furthermore, an efficient lightening effect was observed following topical application of TM4R to UVB-stimulated hyperpigmented dorsal skin of brownish guinea pigs. These results suggest that TM4R may be a candidate for an efficient whitening agent, possibly by inhibiting tyrosinase activity and biological reactions caused by reactive oxygen species.     

The Effect of the Oxygen Exchange at Electrodes on the High-Voltage Electrocoloration of Fe-Doped SrTiO3 Single Crystals: A Combined SIMS and Microelectrode Impedance Study

The effect of the electrode material on the high voltage stoichiometry-polarization (electrocoloration) of Fe-doped SrTiO₃ single crystals has been studied. For different electrode materials (150-nm Ag/15-nm Cr and 150-nm Au/15-nm Cr) secondary ion mass spectrometry (SIMS) was used to measure the depth profile of the ¹⁸O-isotope after high-field stress. The results were compared with spatially resolved impedance measurements on electrocolored Fe-doped SrTiO₃ single crystals. For Au/Cr as well as Ag/Cr electrodes a large dc voltage leads to moving color fronts which are usually correlated with a pronounced stoichiometry polarization of the samples due to electrodes blocking the ionic current. However, the local impedance measurements demonstrate that the conductivity profiles near the cathode depend on the electrode material. This finding is in accordance with the SIMS measurements which indicate that the Ag/Cr-electrodes are, in contrast to Au/Cr-electrodes not completely inactive for the oxygen incorporation into the Fe-doped SrTiO₃. The results are discussed in terms of defect chemical models.     

Analysis of alcohol oxidase isozymes in gene-disrupted strains of methylotrophic yeast Pichia methanolica

A cell-free extract of methanol-grown Pichia methanolica cells was found to contain nine alcohol oxidase (AOD) isozymes by active staining of a native polyacrylamide electrophoresis gel. Our previous study revealed that AOD in P. methanolica was encoded by two genes, MOD1 and MOD2, and the results of an experiment involving Candida boidinii as an expression host suggested that the AOD isozymes observed in P. methanolica were due to random association of Mod1p and Mod2p into an active octamer [Nakagawa et al., Yeast, 15, 1223-1230 (1999)]. This study was conducted using P. methanolica MOD1- and/or MOD2-gene disrupted strains to confirm a previous hypothesis. While the cell-free extract of the wild-type strain gave nine ladder bands, the mod1delta and mod2delta strains gave a single active AOD band corresponding to the mobilities of Mod2p and Mod1p on a native electrophoresis gel, respectively. The cell-free extract of glyceorl-grown wild-type cells gave a single band corresponding to Mod1p, showing that only MOD1 is expressed in glycerol-grown cells. While the expression of both MOD1 and MOD2 was induced by methanol, this finding and our previous observations indicated that the expression of MOD1 and MOD2 was controlled by a distinct regulatory mechanism in P. methanolica.     

On one- and two-parameter analyses of short fatigue crack growth

Recent data on short fatigue crack growth in two cast and hot isostatically pressed (hipped) aluminum alloys obtained by Shyam, Allison and Jones have been analyzed in terms of a previously proposed one-parameter short crack model which includes consideration of elastic–plastic effects, the Kitagawa effect and the development of crack closure in the wake of a newly formed crack. The material constants obtained in a prior investigation of short crack growth behavior in a cast aluminum alloy tested under fully reversed loading were used as a basis for the present analysis. The predicted rates of fatigue crack propagation are in accord with the experimental results. In the discussion, aspects of the two-parameter approach presented by Shyam et al. are compared with those of the one-parameter method of analysis used herein.     

Cover Picture: Assembly and Photoinduced Organization of Mono‐ and Oligopeptide Molecules Containing an Azobenzene Moiety (Adv. Funct. Mater. 9/2007)

An illustration of the phototriggered organization and dispersion of tri‐peptide‐substituted azobenzene derivatives, as reported on p. 1507 by Yoko Matsuzawa and co‐workers. The tri‐peptide units form a beta‐sheet structure through hydrogen bonding to assemble a fibrous network system. Cis–trans photoisomerization of the azobenzene moiety leads to a large polarity change of the component molecule to break and re‐form hydrogen bonds between the tri‐peptide units. Assembled systems consisting of an azobenzene moiety as the photofunctional component and valyl units as the network backbone are investigated. The molecular ordering of these assemblies is examined by spectroscopy and theoretical calculations. The number of valyl units greatly influences the molecular order in the organized systems. Only N‐(L ‐valyl‐L ‐valyl‐L ‐valyl)azobenzene‐4‐carboxamide ( 3 ) forms a complete β‐sheet structure in this artificial assembly. Upon photoirradiation, the azobenzene moieties isomerize completely, revealing the reversibility in the structural organization through the flexibility of the β‐sheet network in this system.