The structure of liquid As2Se3 and GeSe2 by neutron diffraction

The liquid structures of As₂Se₃ and GeSe₂ have been investigated using the neutron diffraction patterns. In both cases the structure factor showed a low first peak maximum which follows a weak but apparent pre-peak at very low momentum transfer. It was also observed that the radial distribution function of both materials are characterized by the well-defined first neighbor shell because of the deep minimum on its right-hand side although in the liquid state. These results indicate that strong covalent bondings between unlike atoms in the solid state still remain when melting. Both the structure factor and the distribution curves of these alloys are, on the whole, similar to those in the amorphous phase which have already been examined. A slight difference in the coordination number, however, is found between amorphous and liquid phases of these materials.     

Synthesis and properties of oxygen‐, methylene‐, and alkylene‐bridged poly(dithiafulvene)s

Polymerization by cycloaddition between aldothioketene and its alkynethiol tautomer (derived in situ from a diyne) leading to the formation of dithiafulvene unit‐linked polymers has been studied. Two aromatic diynes [bis(4‐ethynyldiphenyl)methane ( 1a ) and 4,4′‐diethynyldiphenyl ether) ( 1b )] were used as starting materials with the aim of obtaining non‐π‐conjugated methylene‐ and oxygen‐bridged aromatic poly(dithiafulvene)s. The poly(dithiafulvene) derived from bis(4‐ethynyldiphenyl)methane can be considered as an interesting precursor to a small band‐gap polymer having alternating aromatic and quinonoid moieties. Further, two aliphatic diynes [1,7‐octadiyne ( 3a ) and 1,9‐decadiyne ( 3b )] were subjected to cycloaddition polymerization to obtain aliphatic poly(dithiafulvene)s containing localized electron‐rich dithiafulvene units. The polymers obtained were characterized by IR, ¹H NMR, gel permeation chromatography, and cyclic voltammetry. The electron‐donating property of the polymers was evident from the charge‐transfer (CT) complex formation with an electron acceptor 7,7,8,8‐teracyanoquinodimethane. The CT complexes were characterized by IR, ¹H NMR, and ultraviolet–visible spectroscopies. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3593–3603, 2001     

Robust particle image velocimetry using gradient method with upstream difference and downstream difference

In the first part of this paper, sub-pixel displacement detection methods in particle image velocimetry (PIV) measurements were discussed. Some schemes for calculating the spatial gradient in a gradient method, which is one of sub-pixel displacement detection methods, were evaluated. It was found that the second order central finite difference scheme tends to underestimate the gradient of the tracer-particle’s intensity. Consequently it leads to an overestimation of sub-pixel displacements. A first-frame upstream and second-frame downstream finite difference scheme was then proposed and evaluated for one-dimensional flow measurements. Furthermore, the proposed difference scheme was extended to apply to two-dimensional flows. It was shown that taking the direction of the sub-pixel correction into account and using fewer adjacent pixels are important for PIV images consisting of small tracer particle images. Finally, a robust procedure for the execution of the gradient method was proposed, which can eliminate the effect of noises. It was found that the proposed scheme is not only highly accurate but is highly robust to noise.     

Novel flexible frameworks of porous cobalt(II) coordination polymers that show selective guest adsorption based on the switching of hydrogen-bond pairs of amide groups

Four porous crystalline coordination polymers with two-dimensional frameworks of a double-edged axe-shaped motif, [[Co(NCS)(2)(3-pia)(2)] x 2 EtOH.11 H(2)O](n) (1 a), [[Co(NCS)(2)(3-pia)(2)] x 4 Me(2)CO](n) (3 a), [[Co(NCS)(2)(3-pia)(2)] x 4T HF](n) (3 b) and [[Co(NCS)(2)(3-pna)(2)](n)] (5), have been synthesized by the reaction of cobalt(II) thiocyanate with N-(3-pyridyl)isonicotinamide (3-pia) or N-(3-pyridyl)nicotinamide (3-pna). X-ray crystallographic characterization reveals that adjacent layers are stacked such that channels are created, except in 5. The channels form a hydrogen-bonded interior for guest molecules; in practice, 1 a contains ethanol and water molecules as guests in the channels with hydrogen bonds, whereas 3 b (3 a) contains tetrahydrofuran (acetone) molecules. In 1 a, the "double-edged axe-shaped" motifs in adjacent sheets are not located over the top of each other, while the motifs in 3 b stack so perfectly as to overlap each other in an edge-to-edge fashion. This subtle change in the three-dimensional framework is associated with the template effect of the guests. Compound 5 has no guest molecules and, therefore, the amide groups in one sheet are used for hydrogen-bonding links with adjacent sheets. Removal of the guest molecules from 1 a and 3 b (3 a) causes a structural conversion accompanied by a color change. Pink 1 a cannot retain its original framework and changes into a blue amorphous compound. On the other hand, the framework of pink 3 b (3 a) is transformed to a new crystalline framework of violet 4. Interestingly, 4 reverts to the original pink crystals of 3 b (3 a) when it is exposed to THF (or acetone) vapor. Spectroscopic measurements (visible, EPR, and IR) provide a clue to the crystal-to-crystal transformation; on removal of the guests, the amide groups are used to form the beta sheet-type hydrogen bonding between the sheets, and thus the framework withstands significant stress on removal of guest molecules. This mechanism is attributed to the arrangement of the adjacent sheets so suited in regularity that the beta sheet-type structure forms efficiently. The apohost 4 does not adsorb cyclopentane, showing a guest selectivity that, in addition to size, hydrogen-bonding capability is required for the guest molecules. The obtained compound is categorized as a member of a new generation of compounds tending towards functional porous coordination polymers.     

On Symmetric Stable-Like Processes: Some Path Properties and Generators

We derive some path properties of symmetric stable-like processes constructed via Dirichlet form theory and then sufficient conditions in order that the generators of the forms contain a nice functions space, are given.     

Copper NQR study of the La 214 system from an aspect of microscopic environment of copper

The nuclear quadrupole resonance (NQR) has been investigated for Cu in La_2–x A _x CuO _y (A=Sr and Ba). Three Cu NQR lines, A, B and C, have been observed, which correspond to three different Cu sites. From the analysis of these NQR intensities, site assignments are possibly as follows. These lines A, B and C are attributed to CuO₆ octahedral, CuO₅ pyramidal and CuO₄ planar sites, respectively. The apical oxygen O(2) is induced to transfer to the interstitial O(3) site between LaO planes when two or more Sr²⁺ ions are located in its neighboring La sites. The excess holes doped into the CuO₂ plane are provided mainly by O(3) as well as the unpaired Sr²⁺ ion.     

Cryopreservation of shoot apices of in-vitro grown gentian plants: comparison of vitrification and encapsulation-vitrification protocols

Using vitrification and encapsulation-vitrification protocols, we successfully cryopreserved shoot apices from in-vitro plants of different Gentiana cultivars (lines). Although both protocols gave high survival percentages after storage in liquid nitrogen, the encapsulation-vitrification protocol had several distinct advantages over the vitrification protocol: (i) survival was higher under optimal conditions, (ii) the range of optimal exposure periods to the plant vitrification solution 2 (PVS2) was broader, and (iii) regrowth of cryopreserved shoot apices was apparently more vigorous and faster. Shoot apices from ten cultivars/lines of three Gentiana species (G. scabra, G. triflora, and G. pneumonanthe) were successfully cryopreserved using the two protocols with average survival of 49.0 percent and 73.7 percent for vitrification and encapsulation-vitrification, respectively. These results indicate that the two protocols optimized in the present study are promising for cryopreservation of a wide range of Gentiana genetic resources.     

Search for magnetic order in undoped and doped spin‐gap systems by μSR

We introduce our μSR investigations of spin‐gap systems, such as, (1) a 2‐leg spin‐ladder material SrCu₂O₃, (2) a Haldane material (S=1 spin‐chain) Y₂BaNiO₅, (3) a spin‐Peierls material CuGeO₃, (4) a spin‐chain# material Sr₆Ca₈Cu₂₄O₄₁. All of these antiferromagnetic spin systems are characterized by a spin‐gap between the singlet ground‐state and the triplet first excited states. In the above‐mentioned materials, we confirmed the absence of magnetic order down to milli‐Kelvin regime, supporting the non‐magnetic feature of the ground‐state. If a spin‐gap system is doped with charges and/or vacancies at the spin site, unpaired spins are induced out of the singlet ground‐state. In some materials, doping completely destroys the singlet ground‐state and induces a bulk magnetic order. We report μSR investigations of doped materials as well, which clarifies the existence/absence of a magnetic order upon doping. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structures of two oxidation products obtained from palytoxin

The structures of two oxidation products of N-(p-bromobenzoyl)palytoxin were unambiguously determined by means of X-ray crystallographic analysis.     

Muon spin relaxation in a spin glass CuMn observed in finite longitudinal magnetic fields

Muon spin depolarization in a spin glass CuMn (1.1 at.%, T_g = 10.8 K) has been observed in longitudinal external magnetic fields H_L = 0–640 Oe. The depolarization rate did not depend on H_L at T > T_g, reflecting a fast dynamical fluctuation of Mn moments. In contrast, a remarkable field dependence was observed below T_g. Static and dynamical local fields on μ⁺ from Mn moments were found to coexist at T ～ 0.9 T_g. The results suggested a rapid change of spin dynamics around T_g.