Association Schemes with Multiple Q-polynomial Structures

It is well known that an association scheme with has at most two P-polynomial structures. The parametrical condition for an association scheme to have two P-polynomial structures is also known. In this paper, we give a similar result for Q-polynomial association schemes. In fact, if , then we obtain exactly the same parametrical conditions for the dual intersection numbers or Krein parameters.     

Two dimensional elliptic equation with critical nonlinear growth

We study the asymptotic behavior of solutions to a semilinear elliptic equation associated with the critical nonlinear growth in two dimensions.

where is a unit disk in and denotes a positive parameter. We show that for a radially symmetric solution of (1.1) satisfies

Moreover, by using the Pohozaev identity to the rescaled equation, we show that for any finite energy radially symmetric solutions to (1.1), there is a rescaled asymptotics such as

locally uniformly in . We also show some extensions of the above results for general two dimensional domains.

     

A Low-Noise 230 GHz SIS Receiver for Radio Astronomy Employing Untuned Nb/AlOx/Nb Tunnel Junctions

A heterodyne receiver based on a 1/3 reduced height rectangular waveguide SIS mixer with two mechanical tuners has been built for astronomical observations of molecular transitions in the 230 GHz frequency band. The mixer used an untuned array (R_nC_j3, R_n70 ) of four Nb/AIOx/Nb tunnel junctions in series as a nonlinear mixing element. A reasonable balance between the input and output coupling efficiencies has been obtained by choosing the junction number N=4. The receiver exhibits DSB (Double Side Band) noise temperature around 50 K over a frequency range of more than 10 GHz centered at 230 GHz. The lowest system noise temperature of 38 K has been recorded at 232.5 GHz. Mainly by adjusting the subwaveguide backshort, the SSB (Single Side Band) operation with image rejection of 15 dB is obtained with the noise temperature as low as 50 K. In addition, the noise contribution from each receiver component has been studied further. The minimum SIS mixer noise temperature is estimated as 15 K, pretty close to the quantum limit v/k11 K at 230 GHz. It is believed that the receiver noise temperatures presented are the lowest yet reported for a 230 GHz receiver using untuned junctions.     

Bestimmung des Nitrations und des Nitritions

Ohne Zusammenfassung     

The structure of liquid Sb---Se alloys

The structure of liquid Sb_1-xSe_x alloys with x = 0.5, 0.6 and 0.7 was investigated in the temperature range of 600–800°C. The neutron diffraction measurements were carried out by using the high intensity total (HIT) scattering spectrometer of the booster synchrotron utilization facility (BSF) at the National Laboratory for High Energy Physics. A prepeak is observed in the structure factor for these three alloys. It suggests that the medium-range order stillo remains melting for liquid Sb_1-xSe_x alloys, with x = 0.5, 0.6 and 0.7. The structure factor liquid Sb₂Se₃ alloys shows no appreciable temperature variation. For liquid Sb_0.5Se_0.5 alloy, the intensity of the prepeak exhibits an apparent decrease in the temperature range in which the non-metal-metal transition occurs. The non-metal-metal transition in liquid Sb---Se alloys is due to the change in the medium range structure.     

The polycarbosilane-to-SixC1−x conversion studied by inelastic neutron scattering and infrared absorption

Polycarbosilane (PC) is a precursor which is converted to Si_xC_1−x fibers by pyrolysis in an inert gas atmosphere. The changes in the atomic vibrational spectrum during the conversion process from PC to Si_xC_1−x have been examined by means of inelastic neutron scattering (INS) and infrared absorption (IR). The existence of transverse-optical(TO)- and longitudinal-optical(LO)-like phonon modes due to amorphous SiC clusters was established in the original and pyrolyzed PC by INS measurements. After pyrolyzing at 700–800°C, these modes appear distinctly around 730 and 930 cm⁻¹, respectively, in the INS spectra. Pyrolysis at 1000°C makes these TO- and LO-like phonon modes sharper.     

Positron annihilation lifetime study of organic-inorganic hybrid materials prepared by irradiation

Silica based hybrid materials, some containing zirconia, prepared by gamma-irradiation, were studied by positron annihilation lifetime (PAL) spectroscopy, in the temperature range of 30-370 K. One long-lived component was observed in group of samples without zirconia. The behavior of this component as a function of temperature resembles that for polymers. This is explained by the elastomer like structure of the samples and the excellent linking between the inorganic and organic networks. The average radius, R, of the free-volume holes was in the range 0.26-0.42 nm depending on the temperature. In the group of samples containing zirconia two long-lived components were observed. A model with three different free-volume holes was suggested to explain the PAL results. Small closed holes (R ∼ 0.26 nm) and large closed holes introduced by Zr (R ∼ 0.5 nm), the sizes of both holes not changing with the temperature, together with intermediate polymer-like free-volume holes - the same behavior as those present in samples not containing zirconia.     

Dynamic process of crystallization of Sb2Se3 from Sb50Se50 amorphous film

Dynamics of crystallization of amorphous antimony-selenium film deposited on carbon substrate have been studied by the high-resolution transmission electron microscopy. The amorphous film was suddenly crystallized at 200°C by heating in vacuum. By the electron beam irradiation crystallization occurred at the focused electron beam region in the amorphous film. The growth process of crystallization by electron beam irradiation was recorded on a video image at the atomic resolution mode. The growth front of crystallization showed nano-concave and -convex shapes. The recrystallization with the different orientation at the first grown crystal have been found, and discussed as the influence of remaining antimony crystallites at the first crystallized film region.     

A SAXS study of V2O5·nH2O sols and gels

Small-angle X-ray scattering (SAXS) measurements on V₂O₅·nH₂O sols and gels, prepared by dissolving V₂O₅ glass into water at room temperature, show that there are V₂O₅ polymeric fibers entangled like random coils in the sol of n 5000, while the deviation from the random coil behavior occurs in the dilute sol of n 6000.

A Bragg peak appears at the scattering vector h 0.02 Å⁻¹ to be superimposed on an asymptotic h⁻²-course in the SAXS curve of the concentrated sol of n 680. This means that the spatial correlation between V₂O₅ polymeric fibers takes place even in the fluid state.

V₂O₅·nH₂O sols completely lose fluidity at n 250 to transfer to the gel state, where V₂O₅ polymeric fibers begin to pile up in the parallel with a substrate surface. Such a layer structure is preserved up to the gel of n 4. However, V₂O₅ polymeric fibers are randomly oriented within each layer.     

Second-generation total synthesis of haterumalide NA using B-alkyl Suzuki-Miyaura coupling

Second-generation total synthesis of haterumalide NA, a potent cytotoxic marine macrolide, was achieved by using B-alkyl Suzuki-Miyaura coupling and Nozaki-Hiyama-Kishi coupling as key steps (1.2% in 33 steps). Compared to our first-generation approach, the second-generation synthesis is much improved in the yield of key intermediate.