MOVPE growth of nonpolar a-plane GaN with low oxygen contamination and specular surface on a freestanding GaN substrate

We investigated unintentionally doped nonpolar a- and m-plane GaN layers grown by metalorganic vapor phase epitaxy under several sets of conditions on freestanding a- and m-plane GaN substrates. Oxygen contamination in a-plane GaN is greatly reduced by increasing the V/III ratio during growth. As a result, a high-resistivity GaN buffer layer for an AlGaN/GaN heterostructure field-effect transistor was realized.     

Photoluminescence of InGaN/GaN multiple quantum wells grown by mass transport

We report on studies of an In_0.12Ga_0.88N/GaN structure with three 35 Å thick quantum wells (QWs) grown by metalorganic vapor phase epitaxy with employment of mass transport. The mass-transport regions demonstrate a threading dislocation density less than 10⁷ cm⁻². The photoluminescence (PL) spectrum is dominated by a 40 meV—narrow line centered at 2.97 eV at 2 K. This emission has a typical PL decay time of about 5 ns at 2 K within the PL contour. An additional line with longer decay time (about 200 ns) is observed at an energy about 2.85 eV. The position of this line shifts towards higher energies with increasing excitation power. The data are consistent with a model, where the PL originates from at least two nonequivalent QWs, which could be realized due to a potential gradient across the layers.     

CONCEPTUAL DESIGN OF BESSEL BEAM CAVITY FOR FREE-ELECTRON LASER

The conventional cavity for a free-electron laser (FEL) oscillator usually forms an optical beam of Gaussian mode, which undergoes transverse spread along the interaction region. The transverse divergence of an optical beam will induce reduction of the FEL gain from three aspects: degenerating filling factor, causing diffraction loss and limiting the effective interaction distance. Bessel optical beam has been experimentally demonstrated diffraction-free characteristics in its propagation, which provides a possibility of improvement of FEL gain. In this paper, we present a conceptual design of a Bessel beam cavity for the free-electron laser oscillator. This cavity generates nondiffracting optical beam in the wiggler, resulting in improving the filling factor, decreasing the diffraction loss and elongating the effective interaction distance.     

Experiment on Gamma Ray Generation by Laser Compton Scattering

A gamma ray generation facility was developed through laser Compton scattering on an electron beam storage ring, for the purpose of researching nuclear transmutation. Theoretical analysis on gamma ray yield and energy spectrum was performed, as well as EGS4 simulation code was employed to simulate the interaction of gamma ray and Ge detector. The acquired experimental results are in agreement with theory.     

Mixed-valence states in TCNQ salts of monoalkylbiferrocenes and their mixed crystals with dialkyl derivative

TCNQ salts of 1-monoalkylbiferrocenes showed a temperature-independent trapped-valence state as expected for the unsymmetrical structure of cations. On the other hand, mixed crystals of 1-monobutyl- and 1.1-dibutylbiferrocenium⁺(TCNQ) ₃ ^– showed a temperature dependence of the mixed-valence states, showing that the lattice affects the mixed-valence states.     

Characteristics of a simultaneous sampling system for the speciation of atmospheric T and 14C, and its application to surface and soil air

A simultaneous sampling system for the speciation of atmospheric T and ¹⁴C has been developed. Firstly tritiated moisture together with all water vapor in air is adsorbed on Drierite after coagulation using an electric cooler. Then ¹⁴CO₂ plus stable CO₂ in the dried air is adsorbed on molecular sieve 4A. Elemental tritium gas (HT) plus hydrogen gas (H₂) in the atmosphere along with H₂ gas generated from electrolysis of groundwater which does not contain any T, are oxidized on Pd catalyst to water and adsorbed on molecular sieve 3A. Tritiated methane (CH₃T) and ¹⁴CH₄ plus stable methane in the atmosphere are oxidized on Pt catalyst to water and CO₂ under 400 °C. Then, Drierite and molecular sieve 4A adsorb the oxidized T (HTO) and C-14 (¹⁴CO₂), respectively. Tritium and C-14 in surface and soil air have been measured using this system     

Regio- and stereoselective 12-O-demethylation of schizandrin into gomisin T, an important intermediate to gomisin A, by Mortierella sp. (TM-I1104)

A strain TM-I1104 identified as Mortierella sp. was discovered from soil as the most efficient fungus, which converted schizandrin into gomisin T in 91% regioselectivity by microbial 12-O-demethylation. Under optimum conditions, the yield of gomisin T reached around 80%. The faculty of 12-O-demethylation was specific on (+)-schizandrin (natural form) and the optical purity of gomisin T converted from (±)-schizandrin was 96% ee.     

Hydrothermal routes to prepare nanocrystalline mesoporous SnO2 having high thermal stability

We report simple hydrothermal routes to prepare thermally stable SnO2 particles having high specific surface areas and mesoporosity. The preparation method includes a new combination of synthetic processes: hydrolysis of tin(IV) chloride at 95 degrees C in the absence of alkaline solutions (aqueous NH3 or NaOH), formation of nanocrystalline SnO2, and subsequent hydrothermal treatments at temperatures between 100 and 200 degrees C. After annealing treatments of the hydrothermally treated SnO2 particles at 400 or 500 degrees C, their crystallite sizes remained smaller than 7.7 nm and their specific surface areas were still higher than 110 m2/g, indicative of the high thermal stability against particle growth and sintering. Furthermore, mesoporosity evolved with a relatively narrow pore size distribution typically in the range of 3.0-4.3 nm. The effects of the hydrothermal treatment were explained by uniformization of the particle size that was beneficial to the suppression of particle growth.     

Semiempirical molecular orbital calculations on boranes

Traditional Pariser-Parr-Pople and variable electronegativity calculations have been carried out on C₆H₅B(OR)₂ and p-CH₃OC₆H₄B(OR)₂, and the results compared with calculations for C₆H₅BR₂. It is concluded that the VE-SCF method offers a real advantage over the simple PPP method for predicting percent charge transfer and transition intensity in cases where excited states possess substantial C.T. character. The restriction that empirically chosen parameters fit the observed transition energies and intensities of both triarylboranes and ArB(OR)₂ requires the choice of a boron VSIP greater than 2.0 eV in the fixed parameter procedure of the usual PPP-SCF-CI method for these molecules. Observed transitions in C₆H₅B(OR)₂ correlate with ¹ L _b, ¹ L _a, ¹ B _b, whereas the first absorption maximum of (C₆H₅)₃B is assigned to C.T. (¹ A ₁¹ A ₁) local C _2v symmetry.

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Zusammenfassung PPP- und VE SCF-Rechnungen wurden für C₆H₅B(OR)₂ und p-CH₃OC₆H₄(OR)₂ durch- geführt, und die Ergebnisse wurden mit denjenigen für C₆H₅BR₂ verglichen. Es kann der Schluß gezogen werden, daß die VE SCF-Methode einen Vorteil gegenüber der einfachen PPP-Methode bietet, um den prozentualen Charge Transfer und Übergangsintensitäten in Fällen zu bestimmen, in denen die angeregten Zustände einen wesentlichen C.T.-Charakter besitzen. Die Bedingung, daß die empirisch gewählten Parameter den beobachteten Übergangsenergien und -intensitäten von sowohl Triarylboranen als auch ArB(OR)₂ angepaßt sein sollen, erfordert die Wahl eines Bor-VSIP größer als 2,0 eV im Rahmen der üblichen Parametrisierung der PPP-SCF-CI-Methode. Beobachtete Über-gänge in C₆H₅B(OR)₂ korrelieren mit ¹ L _b, ¹ L _a, ¹ B _b, wogegen das erste Absorptionsmaximum des (C₆H₅)₃B einem C.T.-Übergang (¹ A ₁¹ A ₁) lokaler C_2v -Symmetrie zugeordnet wird.

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Résumé Des calculs traditionnels Pariser-Parr-Pople et des calculs d'électronégativité variable ont été effectués sur C₆H₅B(OR)₂ et p-CH₃OC₆H₄B(OR)₂ avec comparison aux résultats obtenus pour C₆H₅BR₂. La conclusion est que la méthode VE-SCF offre un réel avantage sur la méthode PPP simple en ce qui concerne la prédiction du transfert de charge et de l'intensité de transition pour les états excités possédant un net caractère de transfert de charge. La restriction selon laquelle les paramètres empiriques doivent permettre de reproduire les énergies de transition et les intensités des deux triarylboranes et de ArB(OR)₂, nécessite le choix d'un potential d'ionisation de l'état de valence du bore supérieur de 2 eV à celui employé dans les méthodes ordinaires. Les transitions observées dans C₆H₅B(OR)₂ sont reliées à ¹ L _b, ¹ L _a, ¹ B _b, tandis que la première absorption de (C₆H₅)₃B est attribuée à un transfert de charge (¹ A ₁¹ A ₁) de symétrie locale C_2v.

     

Detection of influenza virus: traditional approaches and development of biosensors

Influenza is an acute respiratory disease caused by the influenza virus. The disease occurs annually, causing fatality in the elderly and children and billions of dollars loss in business and productivity. Traditional viral detection methods include MDCK cell culture, complement fixation, hemagglutinin-inhibition, and recently RT-PCR. Although effective, these methods generally involve labor-intensive laboratory procedures and often require trained personnel to carry them out. The development of biosensor technologies will enable rapid and specific disease diagnosis on-site so that a clinician can quickly determine whether treatment is needed. This paper reviews traditional viral assays and progress in the biosensor development for influenza virus. Recent advances in single-step direct detection using non-labeling techniques such as surface plasmon resonance, quartz-crystal microbalance, and colorimetric functional polymers are discussed.