Analysis of the number of hydrogen bond groups of a multiwalled carbon nanotube probe tip for chemical force microscopy

In this paper, we describe a statistical method of quantification of the number of functional groups at the contact area of a probe tip for atomic force microscopy from the result of repetitive pull-off force measurements. We have investigated laboratory-made carbon nanotube (CNT) probe tips to apply them for chemical force microscopy because limited number of functional groups at the tip-end is expected. Using a CNT tip, we conducted repetitive pull-off force measurements against a self-assembled monolayer terminated with carboxyl group and analyzed them in terms of the number of hydrogen bond groups at the CNT tip. The elementary hydrogen bond rupture force quantum in n-decane medium was estimated to be 84.2 ± 0.5 pN in the present system. Thus it was revealed that only a couple of hydrogen bond groups of the CNT tip were participating in hydrogen bonding with the sample on an average in this experimental system.     

Spin-density-wave and superconducting states in thermally quenched (TMTSF)2ClO4

Successive transitions from metal to the spin-density-wave (SDW) state and the three-dimensional superconducting (3D-SC) state were found in thermally quenched bis-tetramethyltetraselenafulvalenium perchlorate, (TMTSF)₂ClO₄. The SDW state was suppressed after the sample was warmed above ～25 K and cooled slowly. The appearance of the SDW state in addition to the 3D-SC state in the quenched sample is interpreted by the decrease in interchain coupling which could result from the thermal quenching of a high temperature configuration with disordered (ClO₄)-anions. The effect of thermal quenching on quantum oscillations in transverse magnetoresistance was also studied.     

Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.     

Antiferromagnetic d-electron exchange via a spin-singlet pi-electron ground state in an organic conductor

Electron spin resonance reveals the spin behavior of conduction (pi) and localized (d) electrons in beta-(BDA-TTP)2MCl4 (M=Fe, Ga). Both the Ga3+(S=0) and Fe3+(S=5/2) compounds exhibit a metal-insulator transition at 113 K with the simultaneous formation of a spin-singlet ground state in the pi electron system of the donor molecules. The behavior is consistent with charge ordering in beta-(BDA-TTP)2MCl4 at the metal-insulator transition. At 5 K, the Fe3+ compound orders antiferromagnetically, even though the pi electrons, which normally would facilitate magnetic exchange, are localized nonmagnetic singlets.     

Temperature rising elution fractionation, infra red and rheology study on gamma irradiated HMSPP

It is well known that polypropylene undergoes simultaneous crosslinking and degradation under irradiation. However, there are speculations regarding the formation of branching under special conditions. It is also well known that the melt-strength property of a polymer increases with molecular weight and with long-chain branching due to the increase in the entanglement level. This study was a contribution to the understanding of the following points: the role of molecular weight, the role of structural modifications on nucleation properties; the structural changes on polypropylene.

The results showed that degradation was the major reaction in the initial step of irradiation, however, the largely modified molecules concentrated in the high molecular weight fraction. The results also confirm that the branching formation is likely to occur.     

PRESSURE-VELOCITY EQUILIBRIUM HYDRODYNAMIC MODELS

This article describes mathematical models for phase separated mixtures of materials that are in pressure and velocity equilibrium but not necessarily temperature equilibrium. General conditions for constitutive models for such mixtures that exhibit a single mixture sound speed are discussed and specific examples are described.     

Identification of α-type subunits of the Xenopus 20S proteasome and analysis of their changes during the meiotic cell cycle

Background  

The 26S proteasome is the proteolytic machinery of the ubiquitin-dependent proteolytic system responsible for most of the regulated intracellular protein degradation in eukaryotic cells. Previously, we demonstrated meiotic cell cycle dependent phosphorylation of α4 subunit of the 26S proteasome. In this study, we analyzed the changes in the spotting pattern separated by 2-D gel electrophoresis of α subunits during Xenopus oocyte maturation.     

Preparation of ZnO Nanoparticles: Structural Study of the Molecular Precursor

The structure of zinc acetate derived precursor currently used in the sol-gel synthesis of ZnO nanoparticles is described. The reaction products obtained before and after reflux of ethanolic zinc acetate solution have been studied by UV-Vis, photoluminescence, FTIR and EXAFS at the Zn K edge. EXAFS results evidence for both precursor solutions a change from the octahedral coordination sphere of oxygen atoms characteristic of the solid zinc acetate dihydrate compound into a four-fold environment. The EXAFS spectra of precursor solutions can be satisfactorily reproduced using the molecular structure reported for Zn₄O(Ac)₆ (Ac = COOCH₃). UV-Vis and FTIR measurements are also in agreement with the formation of this oligomeric precursor. The structural modification is more pronounced after reflux at 80°C, because the increase of the Zn₄O(Ac)₆ amount and the formation of nearly 3.0 nm sized ZnO nanoparticle.     

Large-scale separation of metallic and semiconducting single-walled carbon nanotubes

In the applications of single-walled carbon nanotubes (SWNTs), it is extremely important to separate semiconducting and metallic SWNTs. Although several methods have been reported for the separation, only low yields have been achieved at great expense. We show a separation method involving a dispersion-centrifugation process in a tetrahydrofuran solution of amine, which makes metallic SWNTs highly concentrated to 87% in a simple way.