Efficient synthesis and magnetic properties of triphenylamine bearing three nitronylnitroxide radicals

Improved synthesis and reinvestigation of the magnetic properties of triphenylamine bearing three nitronylnitroxide radicals (1) were carried out. Single crystal X-ray crystallographic analysis of 1 established that its molecular shape had a C₃-symmetry. Our newly prepared 1 showed different physical properties from those of reported. SQUID measurements of 1 showed that each of the three spins of 1 behaved independently at room temperature. In contrast, the three spins coupled antiferromagnetically at lower temperature as low as ca. 1.8 K. These spin behaviors can be explained by a regular triangular antiferromagnetic model (J/k_B = ?3.3 K) and interpreted as a spin frustration system.     

Transient Behavior of Gas Entrainment Caused by Surface Vortex

A compact sodium-cooled reactor is an important candidate as a fast breeder reactor (FBR) and has been investigated in the feasibility study of FBR cycle. Due to the compact sizing of the reactor vessel, gas entrainment at the free surface of sodium coolant becomes one of the significant issues for reactor design, and it is required to clarify the criterion of gas entrainment at free surface and the tolerance. In the present study, some visualization experiments were performed in a water-air system focusing on the gas entrainment due to surface vortex and its transient phenomena. Influences of horizontal velocity were clarified by the visualization. The gas entrainment due to the surface vortex occurs intermittently. Time trends of circulation and length of gas core for the intermittent surface vortices were measured by the particle image velocimetry and visualization. It was found that the gas core length extends with time delay to the increase of circulation around the vortex.     

Fast and slow electrons in liquid Ar and N2 mixtures

Fast and slow electron current signals in N₂/Ar liquid mixtures have been observed. From the fast signal, the drift velocity and life time of delocalized electrons in the liquid with N₂ molar fractions X=N₂/(N₂+Ar) below 20 mol% were obtained for field strengths E between 5 and 45 kV/cm. The mobility for delocalized electrons in the liquids was shown to decrease exponentially with X as indicated in a previous paper. However, the mobility for localized electrons was shown to increase with increasing X, but only slightly around the N₂ liquid value     

Dependence of ion selectivity on ordered orientation of neutral carriers in ion-sensing membranes based on thermotropic liquid crystals

Thermotropic liquid-crystalline compounds were applied as membrane materials (membrane solvent and neutral carrier) for neutral carrier-type ion sensors to investigate how the ordered arrangement of neutral carriers affects the property of the resulting ion sensors. Nematic, smectic, and cholesteric liquid-crystalline compounds were used as the membrane solvents and crown ether derivatives with a molecular structure similar to the liquid-crystalline solvent as the K+ neutral carriers. Polarized IR spectroscopy and X-ray diffraction experiments confirmed that the highly ordered arrangement of membrane components was retained in the liquid-crystal-based ion-sensing membranes containing a neutral carrier and a lipophilic salt. The ordered arrangement of neutral carriers in the liquid-crystalline membranes enhanced the ion selectivity significantly, probably due to the efficient cooperation of two adjacent crown ether moieties in the highly ordered and aggregated state.     

Mid-Gap State Formed Inside Mott Gap of 1T-TaS2 Single Crystals and Metal-Insulator Transition

We have measured electrical resistivity, Hall coefficient, thermoelectric power, and magnetization for charge-density wave (CDW) material 1T-TaS₂ single crystals grown by varying the excess sulfur content x _es. We have revealed that a small mid-gap state is formed inside the Mott gap and that anomalous low temperature transport is not governed by the Mott gap state itself but by the mid-gap state. The electric properties of the mid-gap state are modified by increasing x _es (or hole doping), and we have found the insulator-metal transition occurs by hole doping below 60K.     

On unique representations of certain dynamical systems produced by continuous-time recurrent neural networks

This article extends previous mathematical studies on elucidating the redundancy for describing functions by feedforward neural networks (FNNs) to the elucidation of redundancy for describing dynamical systems (DSs) by continuous-time recurrent neural networks (RNNs). In order to approximate a DS on R(n) using an RNN with n visible units, an n-dimensional affine neural dynamical system (A-NDS) can be used as the DS actually produced by the above RNN under an affine map from its visible state-space R(n) to its hidden state-space. Therefore, we consider the problem of clarifying the redundancy for describing A-NDSs by RNNs and affine maps. We clarify to what extent a pair of an RNN and an affine map is uniquely determined by its corresponding A-NDS and also give a nonredundant sufficient search set for the DS approximation problem based on A-NDS.     

Molecular imprinting of biotin derivatives and its application to competitive binding assay using nonisotopic labeled ligands

Synthetic biotin-binding polymers were prepared by molecular imprinting. Methacrylic acid (MAA) was copolymerized with ethylene glycol dimethacrylate in the presence of biotin methyl ester (B-Me) in chloroform. Hydrogen-bonding-based complexation of B-Me with MAA generates the binding sites complementary to B-Me after extracting B-Me from the resulting copolymers. Data from NMR titration suggest a one-to-one prepolymerization complex formation of B-Me with MAA in chloroform. A possible complex structure was estimated by docking of the most stable conformers by intermolecular Monte Carlo conformational search under the assumption of a one-to-one association. The selectivity of the imprinted polymers was investigated and an imprinted polymer-based competitive binding assay for B-Me was demonstrated using biotin p-nitrophenyl ester as a nonisotopic-labeled ligand.     

Trehalose embedding technique for high-resolution electron crystallography: application to structural study on bacteriorhodopsin

Trehalose was compared with glucose in its use as an embedding medium for the preparation of two-dimensional crystals for electron crystallographic structure analysis. Purple membranes (two-dimensional crystals of bacteriorhodopsin) embedded in either sugar were studied in a 'partially hydrated' state as well as after 'drying' of the specimen. Diffraction patterns of the four conditions, all showing spots to a resolution better than 3.0 A, were analysed and merged. In the case of glucose embedded specimens, the merging R-factor obtained from the diffraction patterns of dried specimens was significantly better than the one obtained from partially hydrated specimens. In the case of trehalose embedding, the merging R-factor for partially hydrated specimens was significantly better than the dried one. The trehalose embedded, partially hydrated specimens gave the best merging R-factor in all four cases.     

Regulation of selectin binding activity by cyclization of sialic acid moiety of carbohydrate ligands on human leukocytes

We provide here evidence that supports the occurrence of a biologically dormant form of selectin ligand carbohydrate, the sialyl 6-sulfo Lewis X containing modified sialic acid, in human leukocytes. The modification of sialic acid involves first de-N-acetylation of sialic acid moiety through ubiquitous de-N-acetylation/re-N-acetylation cycle, followed by the dehydrative cyclization of de-N-acetyl sialic acid to form "cyclic sialic acid." The enzyme involved in the dehydration of de-N-acetyl sialic acid is a calcium-dependent enzyme having neutral-alkaline pH optimum. De-N-acetyl sialyl 6-sulfo Lewis X retained selectin binding activity as well as parental sialyl 6-sulfo Lewis X, but cyclic sialyl 6-sulfo Lewis X was devoid of selectin binding activity. Sialyl 6-sulfo Lewis X carrying the cyclic sialic acid is specifically recognized by the newly generated mAb, G159. The determinant was distributed widely among normal human leukocytes, especially on monocytes and subsets of lymphocytes including NK cells, helper memory T cells, Tcr-gammadelta T cells, and a part of B cells. The determinant was detected also on several cultured lymphocytic leukemia cell lines and O-tetradecanoylphorbol 13-acetate-activated lymphoid cells. Cyclic sialyl 6-sulfo Lewis X is efficiently formed by the action of the partly membrane-bound calcium-dependent enzyme, tentatively called "sialic acid cyclase," and a possible physiological significance of this reaction could be a rapid inactivation of selectin binding activity at the cell surface. Conversely, the accumulated intracellular cyclic sialyl 6-sulfo Lewis X determinant may function as a dormant pool of selectin ligands, which, on appropriate stimulation, is hydrolyzed and becomes active in selectin-dependent cell adhesion.