Effect of pressure on the superconducting transition in Bi-Sr-Ca-Cu-O system

Abstract

The effect of pressure on T_c was studied on 110 K class Bi-Sr-Ca-Cu-O (1:1:1:2) compounds. T_c was varied with current in I^3/2 , and defined at the value extrapolated to zero current. dT_c /dP = + 0.18 K/kbar was obtained up to 10.9 kbars.     

Decay of a Linear Pendulum in a Free-Molecular Gas and in a Special Lorentz Gas

A circular disk without thickness is placed in a gas, and an external force, obeying Hooke’s law, is acting perpendicularly on the disk. If the disk is displaced perpendicularly from its equilibrium position and released, then it starts an oscillatory or non-oscillatory unsteady motion, which decays as time goes on because of the drag exerted by the gas molecules. This unsteady motion, i.e., the decay of this linear pendulum, is investigated numerically, under the diffuse reflection condition on the surface of the disk, with special interest in the manner of its decay, for two kinds of gases: one is a collisionless gas (or Knudsen gas) and the other is a special Lorentz gas interacting with a background. It is shown that the decay of the displacement of the disk is slow and is in proportion to an inverse power of time for the collisionless gas. The result complements the existing mathematical study of a similar problem (Caprino et al. in Math. Models Methods Appl. Sci. 17:1369–1403, 2007) in the case of non-oscillatory decay. It is also shown that the manner of the decay changes significantly for the special Lorentz gas.     

Chiral magnetic soliton lattice on a chiral helimagnet

Using Lorenz microscopy and small-angle electron diffraction, we directly present that the chiral magnetic soliton lattice (CSL) continuously evolves from a chiral helimagnetic structure in small magnetic fields in Cr(1/3)NbS2. An incommensurate CSL undergoes a phase transition to a commensurate ferromagnetic state at the critical field strength. The period of a CSL, which exerts an effective potential for itinerant spins, is tuned by simply changing the field strength. Chiral magnetic orders observed do not exhibit any structural dislocation, indicating their high stability and robustness in Cr(1/3)NbS2.     

Magnetic field-induced ferromagnetism in iron oxide microspheres

A magnetic field of 12 T was applied during the annealing of amorphous α-Fe₂O₃ microspheres. The authors demonstrate that magnetic field processing leads to the formation of γ-Fe₂O₃ phases in the microspheres, and the field-treated microspheres exhibit typical room-temperature ferromagnetic behavior, whereas non-field-heated sample presents paramagnetism. The improvement in magnetic properties is considered to be a result of magnetic field-induced transformation from α-Fe₂O₃ to γ-Fe₂O₃.     

Towards beyond 1 GHz NMR: Mechanism of the long-term drift of screening current-induced magnetic field in a Bi-2223 coil

The screening current-induced magnetic field in the (Bi,Pb)₂Sr₂Ca₂Cu₃O_x (Bi-2223) insert coil proposed for a beyond 1 GHz nuclear magnetic resonance (NMR) spectrometer may generate a long-term field drift, resulting in a loss of field-frequency lock operation and an inability to make high resolution NMR measurements. The measured screening current-induced magnetic field of a Bi-2223 double-pancake coil exhibits a hysteresis effect at 4.2 K that is reproduced by a numerical simulation based on a finite thickness rectangular superconductor bar model. The screening current-induced field at the coil center is of opposite polarity to that generated by the coil current, and thus the apparent field intensity shows a positive drift with time. On the contrary, the field at a coil end is of the same polarity as the coil field, and the apparent field intensity decreases with time. If we wait for ∼1000 h after coil excitation, the field drift rate approaches the field decay rate of the persistent current of 10⁻⁸ h⁻¹, suitable for a long-term NMR measurement in a beyond 1 GHz NMR spectrometer.     

Phosphate‐affinity electrophoresis on a microchip for determination of protein kinase activity

We describe microchip‐based phosphate‐affinity electrophoresis (μPAE) for separation of peptides aimed at determination of kinase activity. The μPAE exploits two recently published technologies: autonomous sample injection for PDMS microchips and a phosphate‐specific affinity ligand, Phos‐tag. We prepared a fluorescently labeled substrate peptide, specific to human c‐Src, and its phosphorylated form. We synthesized a Phos‐tag–poly(dimethylacrylamide) conjugate. The conjugate and the sample solutions were autonomously injected into a PDMS–glass hybrid microchip. The two solutions were contacted together in the microchannel. When the peptides were electrophoresed into the Phos‐tag–poly(dimethylacrylamide) region, the phosphorylated peptide was specifically trapped, and separated from the nonphosphorylated peptide in 10 s. The results were quantified by the areas of the fluorescence peaks. The calibration plot obtained with standard samples showed an excellent linearity and a LOD of 0.9% phosphorylated peptide among the total peptides. For c‐Src‐reacted samples, the results from the μPAE were in good agreement with those from matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. The μPAE was also successful in the presence of inhibitors for c‐Src. The measured 50% inhibitory concentration values for staurosporine, PP2, and SU6656 were in good agreement with the literature values.     

Theoretical study of the prion protein based on the fragment molecular orbital method

We performed fragment molecular orbital (FMO) calculations to examine the molecular interactions between the prion protein (PrP) and GN8, which is a potential curative agent for prion diseases. This study has the following novel aspects: we introduced the counterpoise method into the FMO scheme to eliminate the basis set superposition error and examined the influence of geometrical fluctuation on the interaction energies, thereby enabling rigorous analysis of the molecular interaction between PrP and GN8. This analysis could provide information on key amino acid residues of PrP as well as key units of GN8 involved in the molecular interaction between the two molecules. The present FMO calculations were performed using an original program developed in our laboratory, called “Parallelized ab initio calculation system based on FMO (PAICS)”. © 2009 Wiley Periodicals, Inc. J Comput Chem 2009     

Pd0‐Mediated Rapid Coupling between Methyl Iodide and Heteroarylstannanes: An Efficient and General Method for the Incorporation of a Positron‐Emitting 11C Radionuclide into Heteroaromatic Frameworks

The Pd⁰‐mediated rapid trapping of methyl iodide with an excess amount of a heteroaryl‐substituted tributylstannane has been investigated with the aim of incorporating a short‐lived ¹¹C‐labelled methyl group into the heteroaromatic carbon frameworks of important organic compounds, such as drugs with various heteroaromatic structures, in order to execute a positron emission tomography (PET) study of vital systems. The reaction was first performed by using our previously developed CH₃I/stannane/[Pd₂(dba)₃]/P(o‐CH₃C₆H₄)₃/CuCl/K₂CO₃ (1:40:0.5:2:2:2) system in DMF at 60 °C for 5 min (conditions A), however, the reaction gave low yields for various heteroaromatic compounds. Increasing the amount of phosphine ligand (conditions B) led to a significant improvement in the yield, but the conditions were still not suitable for a range of basic heteroaromatic structures. Use of the CuBr/CsF system (conditions C) also provided a result similar to that obtained under conditions B with an increased amount of the phosphine. Thus, pyridine and related heteroaromatic compounds remained less reactive substrates. The problem was overcome by replacing the DMF solvent with N‐methyl‐2‐pyrolidinone (NMP). The reaction in NMP at 60–100 °C for 5 min using a CH₃I/stannane/[Pd₂(dba)₃]/P(o‐CH₃C₆H₄)₃/CuBr/CsF (1:40:0.5:16:2:5) combination (conditions D) gave the methylated products in yields of more than 80 % (based on the reaction of CH₃I) for all of the heteroaromatic compounds listed in this study. Thus, the combined use of NMP and an increased amount of phosphine is important for promoting the reaction efficiently. The use of this general approach to rapid methylation has been well demonstrated by the synthesis of the PET tracers 2‐ and 3‐[¹¹C]methylpyridines by using [Pd₂(dba)₃]/P(o‐CH₃C₆H₄)₃/CuBr/CsF (1:16:2:5) in NMP at 60 °C for 5 min, which gives the desired products in HPLC analytical yields of 88 and 91 %, respectively.