The photoexcited spin-aligned state of high-density exciton magnetic polarons and the effect of magnetic field in semimagnetic semiconductor Cd(0.8)Mn(0.2)Te

In Cd(0.8)Mn(0.2)Te, nonlinear photoluminescence (PL) appears only when localized excitons are selectively excited to high-density states. Here, the effect of a magnetic field is compared between nonlinear PL and PL due to localized magnetic polarons. Nonlinear PL shows a shift towards lower energy under an applied magnetic field, whereas PL of a localized magnetic polaron band shows a slight shift towards higher energy. The experimental results support the hypothesis that the origin of the nonlinear PL is a spin-aligned state of high-density exciton magnetic polarons. In the spin-aligned state, most spins of electrons (holes) in many magnetic polarons point in the same direction. In this new high-density photoexcited state, the s, p-d exchange interaction between photoexcited electrons (holes) and magnetic ions plays an important role.     

Enantioselective total synthesis of (-)-flustramines A, B and (-)-flustramides A, B via domino olefination/isomerization/Claisen rearrangement sequence

The concise total synthesis of marine alkaloids, (-)-flustramines A and B, and (-)-flustramides A and B has been achieved through the domino olefination/isomerization/Claisen rearrangement (OIC) for highly enantioselective construction of the asymmetric quaternary carbon center and the chemoselective reduction-cyclization (RC) for pyrrolidine formation as key steps.     

Synthesis of Heterocyclic Compounds Using Amidines as Their Ene-1,1-diamine Tautomers,IV: Synthesis of N-Bridged Heterocycles 1,2,3,4-Tetrahydropyrido[1,2-a]pyrimidin-6-ones and Methyl 1,2,3,4-Tetrahydropyrrolo[1,2-a]pyrimidin-7-ylideneacetates

2-Benzyl-1,4,5,6-tetrahydropyrimidines 1 (as ene-1,1-diamine N,C-tautomers) in diglyme reacted with ethyl benzoylacetate at 160 °C in an oil bath to give 1,2,3,4-tetrahydropyrido[1,2-a]pyrimidin-6-ones 3 and with dimethyl acetylenedicarboxylate in methanol at room temperature, leading to methyl 1,2,3,4-tetrahydropyrrolo[1,2-a]pyrimidin-7-ylideneacetates 5, respectively.      

Improvement of a free piston driver for a high-enthalpy shock tunnel

In order to improve the operation of a high-enthalpy free piston shock tunnel its tuned operation was studied analytically and experimentally. First, the piston motion in the free piston driver tube was analytically solved by proposing a simple piston/gasdynamic model, and the tuned operation condition was formulated as an eigenvalue with which the piston has sufficiently high speed at the moment of diaphragm rupture, so as to maintain a constant driver gas pressure, and reduces its speed to come to rest when very closely approaching the end of the driver tube. Second, the result of this analysis was validated by its comparison with experiments which were conducted in the medium-sized free piston shock tunnel HEK installed at the NAL Kakuda Research Center. By observing the detail of piston landing at the end of the driver tube the present tuned operation was found to be successfully achieved with the operating condition given here. Its advantages in improving the pressure recovery factor and in enhancing the stagnation enthalpy were successfully demonstrated. Received 8 June 1997 / Accepted 1 October 1997     

Biosensor for L-phenylalanine based on the optical detection of NADH using a UV light emitting diode

A biosensor was developed for the detection of L-phenylalanine (Phe) and demonstrated for use in the diagnosis of phenylketonuria (PKU). It consists of L-phenylalanine dehydrogenase (L-PheDH) immobilized on a membrane, an ultraviolet light-emitting diode excitation system, and a photomultiplier tube. The L-PheDH was immobilized on a teflon membrane modified with 2-methacryloyloxyethyl phosphorylcholine and placed at the distal and of an optical fiber. The concentration of Phe was determined by immersing the sensor into a sample solution that also contained NAD⁺ and measurement of the fluorescence of the NADH produced by enzymatic reaction. Two L-PheDHs (from Thermoactinomyces intermedius and Sporosarcina sp.) were studied and compared. The fluorescence intensities of the biosensor are linearly related to the L-Phe concentrations in the range from 10 μmol L^?1 to 10 mmol L^?1. The sensor also was operated in the kinetic mode by differential determination of the slope of the signal within 2 min. The analytical range of the sensor is adequate for application in the genotypic diagnosis of PKU (diagnostic value >600 μmol L^?1). High sensitivity, good cost-benefit ratio, and low power consumption are typical features of this biosensing system that can can be applied to routine screening of newborn.

Change in electrical resistivity of commercial purity aluminium severely plastic deformed

Commercial purity aluminium sheets were severely plastic deformed by accumulative roll bonding (ARB). Changes in electrical resistivity at 77 K and microstructure during the ARB process were traced up to 12 cycles, which corresponded to an equivalent strain of 10. The resistivity at 77 K increased with increasing number of ARB cycles, then saturated after about the sixth ARB cycle with a maximum increment of resistivity from starting material of about 1.1 nΩ m. Since lattice defects affect the resistivity of metals, the internal dislocation density and the density of grain boundaries were evaluated from scanning transmission electron microscopy images using Ham's method and grain boundary maps obtained from electron back-scattering diffraction, respectively. The relationship between the change in resistivity and the lattice defects is discussed.     

Defects in CaF2 caused by long-time irradiation and their response to annealing

Samples of CaF₂ irradiated for millions of years in nature were studied by several methods, including X-Ray diffraction, positron annihilation spectroscopy (PAS), photoluminescence spectroscopy (PLS) and transmission electron microscopy (TEM). It was found that the unexpectedly high density of radiation-induced defects present in the fluorite structure (documented by TEM) causes significant micro-strains. Even annealing up to 450°C cannot completely remove these micro-strains, which are stabilised by impurities. PAS and subsequent theoretical calculations revealed the behaviour of the defects during heating. The PL spectra of irradiated fluorite were also interpreted.     

Interaction of polyoxyethylene cholesteryl ethers with liposomal membranes

In order to deduce the mechanisms of hemolysis induced with the nonionic surfactants, polyoxyethylene cholesteryl ethers, C₂₇H₄₅(OCH₂CH₂) _n OH (n=8, 25, 30, 50) and polyoxyethylene dihydrocholesteryl ethers, C₂₇H₄₇(OCH₂CH₂) _n OH (n=15, 30, 50), the interaction of these surfactants with the liposomal membrane as a simple model membrane was investigated in terms of a leakage of the entrapped marker, and a change of the membrane fluidity. The time-courses of the marker leakage were characterized with two kinetic parameters, the initial induction period and the apparent first-order rate constant. The polyoxyethylene chain length was an important factor in the membrane-lytic activities, and the maximal rate as well as the maximal amount of the marker leakage was observed with n=25–30 in these surfactants series. However, the apparent activation energies derived from the two kinetic parameters increased almost linearly with the hydrophilic chain length. The used surfactants tended to fluidize the liposomal membrane in the concentration ranges of surfactants where the marker leakage is not at all or only slightly induced — but with the higher concentration of the cholesteryl derivatives, the apparent fluidity was significantly reduced. From these observations, the mechanisms of the membrane-lysis are discussed.