Phonon softening and double-well potential formation due to electron-phonon interaction in heavy-fermion systems

We investigate the periodic Anderson-Holstein model by using the dynamical mean-field theory combined with the exact diagonalization method. For the strong electron-phonon coupling g\simg g_c, the system shows an anomalous heavy-fermion behaviour which is accompanied by a large lattice fluctuation and an extreme phonon softening. We also calculate an effective potential for the ions and find that a simple harmonic potential for g\siml g_c changes into a double-well potential for g\simg g_c. The effective pairing interaction between the conduction electrons shows a maximum at $g \approx g_c$ where the superconducting transition temperature is expected to be maximum.Comment: 5 pages, 4 figures, accepted for publication in Physica

On the Interaction between Dislocations and Decomposition Products in an Al-4% Cu Alloy

The temperature dependence of critical shear stress and the behavior of work-hardening in stress-strain curves were investigated in single crystals of an aluminium-4 wt. % copper alloy, which were hardened by G-P (1) zones, G-P (2) zones or θ\u27 precipitates. Also dislocation structures after deformation were observed by a transmission electron microscope in specimens with θ\u27 precipitates. From the results of these experiments, the interaction of dislocations with each of decomposition products was discussed as follows. (i) The condition that determines whether or not a dislocation can pass through a decomposition product can be described in terms of the strength of the decomposition product ; it is concluded that a dislocation passes through G-P (1) zones and G-P (2) zones under critical shear stress. (ii) The temperature dependence of critical shear stress in specimens with G-P (1) zones and G-P (2) zones can be explained by an effect that the force required for a dislocation to cut into a zone is larger than that required to move the dislocation within the zone. (iii) A mechanism that a dislocation can pass through a θ\u27 precipitate under suitable conditions is proposed. On this model, the features of stress-strain curves of specimens with θ\u27 precipitates, and the dislocation structures in deformed specimens are explained

Interface Dislocations and Glide Dislocations on θ\u27 Precipitates in an Al-4% Cu Alloy

Thin foils of Al-4 per cent Cu alloy containing platelets of θ\u27 precipitate were prepared by electrolytic thinning technique and appearances of θ\u27 precipitates parallel to the surface of foils were examined under different diffraction conditions with a transmission electron microscope. Examining the contrast of interface of θ\u27 precipitates in undeformed specimens, it was confirmed that some interface dislocations with a Burgers vector of [001]_ direction were present at the periphery of the coherent interface of θ\u27 precipitates. Also, a grid of interface dislocations was observed in the whole interface in some lens-shaped precipitates. In deformed specimens, numerous dislocations were observed to adhere to θ\u27 precipitates perpendicular to the foil surface and striations appeared on precipitates parallel to the foil surface. These striations were attributed either to dislocation images or to moire pattern. In either case it was concluded that they were related to the distribution of dislocations on the interface of θ\u27 precipitates, and that the characteristic of most of the dislocations was not of pure screw but of mixed type, as expected from the slip model of θ\u27 precipitates proposed by the present authors. A relation between dislocation array and moire pattern was discussed and it was suggested that the striations might appear only as moire pattern if the spacing between neigh-bouring dislocations was smaller than the width of dislocation images

Hydrophobic Silicone Elastomer Chamber for Recording Trajectories of Motile Porcine Sperms without Adsorption

Motile porcine sperms adhere to hydrophilic materials such as glass and plastics. The adsorption of sperms to a hydrophobic poly(dimethylsiloxane) (PDMS) membrane is less compared with that to glass. We investigated the linear velocity (LV) and amplitude of lateral head displacement (ALHD) of motile porcine sperm on glass and PDMS preparations using computer-assisted sperm analysis (CASA). Significant decreases were observed in the 15-min LV (P<0.05) and ALHD (P<0.05) in motile porcine sperm on glass preparations compared with those on PDMS preparations. These differences were due to adsorption of the head and/or neck to hydrophilic substrates. Because of the elasticity of PDMS, we propose that a PDMS membrane should be used for CASA. To investigate the dynamics of motile porcine sperms with microfluidics, we do not recommend plasma treatment to bond PDMS and glass in the microchannel preparation; instead, we suggest that a PDMS molding process without plasma treatment be used for preparation of microfluidic channels

軌道縮退を有する磁性絶縁体における動的構造

学位の種別: 課程博士審査委員会委員 : （主査）東京大学教授 有馬 孝尚, 東京大学教授 芝内 孝禎, 東京大学教授 吉澤 英樹, 東京大学教授 求 幸年, 東京大学准教授 山下 穣University of Tokyo(東京大学

Direct Observation of the Interaction of Dislocations with θ\u27 Precipitates in an Aluminium-3.8 wt.-% Copper Alloy

The distribution of dislocations in an aluminium-3.8 wt.-% copper alloy, aged for 4 days at 240℃ to develop θ\u27 precipitates and deformed by various amounts before thinning, has been examined by transmission electron microscopy. During observation, frequent movement of dislocations occurred, as a result of the stress caused by local heating from the electron beam, and various interactions were observed between dislocations and precipitates under different conditions. Thus, on arriving at a precipitate particle, a dislocation may : (i) be held up ; (ii) avoid the precipitate by cross-slip ; (iii) shear through the precipitate. Cases (ii) and (iii) were frequently observed as dislocation motion increased. In the specimen deformed by 1-2%, most of the dislocations were arrested by precipitates, on which striations were observed parallel to directions. In another specimen deformed 5%, numerous tangled dislocations and dislocation loops were seen around the precipitates and in the matrix. In the light of these results, the slip processes occurring in this alloy are discussed in relation to strain-hardening

Interaction between Dislocations and θ\u27 Precipitates in an Aluminium-Copper Alloy

In the specimens containing θ\u27 precipitates, the interaction between moving dislocations and precipitates was observed, using an electron microscope with a special 16mm movie camera. The following interactions could be seen : (1) cross-slip of a dislocation between precipitates ; (2) cross-slip of a dislocation at the interface of a precipitate ; (3) bending of a dislocation at a precipitate ; (4) piled-up dislocations is front of a precipitate ; (5) the passing of a dislocation through a precipitate. These results were discussed