Changes of Yield Stress of Sand During Undrained Cyclic Loading

In this study, the yield locus of sand being subjected to several cycles of undrained loading was investigated by using the triaxial testing device capable of measuring the acoustic emission, AE, of soil. The AE measurement indicates that the undrained shear on isotropically consolidated sand changes the shape of yield locus so as to have more kinematic hardening type of yield locus. More importantly, a change occurred in the size of yield locus, and the undrained loading has reduced the size of yield locus. Subsequent undrained cyclic loadings further reduced the size of yield locus so that there were some additional yielding during the cyclic loadings which accompanied gradual accumulations of pore water pressures

Nonquasiparticle states in the half-metallic ferromagnet simulated by the two-band Hubbard model

The density-matrix renormalization group method is used to study the three-band zigzag ladder model that simulates the electronic state of the t 2g-orbital system of the double string of the edge-shared CrO 6 octahedra in the half-metallic ferromagnet K2Cr 8O16. The saturated ferromagnetism caused by the double-exchange mechanism is thereby demonstrated. We also use the Lanczos exact-diagonalization technique on small clusters to study the two Hubbard chains coupled with the ferromagnetic exchange interaction, whereby we consider the nonquasiparticle states in the half-metallic ferromagnet that appear in the single-particle spectral function.Ministry of Education, Culture, Sports, Science and Technology of Japa

Rock-salt SnS and SnSe: Native Topological Crystalline Insulators

Unlike time-reversal topological insulators, surface metallic states with Dirac cone dispersion in the recently discovered topological crystalline insulators (TCIs) are protected by crystal symmetry. To date, TCI behaviors have been observed in SnTe and the related alloys Pb$_{1-x}$Sn$_{x}$Se/Te, which incorporate heavy elements with large spin-orbit coupling (SOC). Here, by combining first-principles and {\it ab initio} tight-binding calculations, we report the formation of a TCI in the relatively lighter rock-salt SnS and SnSe. This TCI is characterized by an even number of Dirac cones at the high-symmetry (001), (110) and (111) surfaces, which are protected by the reflection symmetry with respect to the ($\bar{1}$10) mirror plane. We find that both SnS and SnSe have an intrinsically inverted band structure and the SOC is necessary only to open the bulk band gap. The bulk band gap evolution upon volume expansion reveals a topological transition from an ambient pressure TCI to a topologically trivial insulator. Our results indicate that the SOC alone is not sufficient to drive the topological transition.Comment: 5 pages, 5 figure

DETERMINING AN EFFECTIVE STRETCHING TIME FOR ACHILLES TENDON EXTENSION

Stretching exercises are commonly undertaken for sports and rehabilitation. However, it is unknown how an in vivo muscle-tendon unit responds to added stretching stimulation. The purpose of this study was to determine an effective stretching time for Achilles tendon extension. The human medial head of the gastrocnemius muscle was stretched and ultrasonography was used to determine and then compare the length of the Achilles tendon between before and after stretching. Achilles tendon extension for one minute of stretching was 3.4±2.5mm, two 6.8±2.1mm, three 6.9±1.0mm, five 7.2±0.7mm, and ten 7.4±0.8mm. Achilles tendon length was significantly increased for up to two minutes of stretching (

Disorder and superconductivity in doped semiconductor nanotubes

Finite-size systems of the one-dimensional attractive Hubbard model with random potential are studied as an effective model for doped semiconductor nanotubes. We calculate the binding energy of Cooper pairs and pair correlation function by the density-matrix renormalization group method. We show that, when the scattering potential is strong, there appears the ground state where Cooper pairs are formed but are localized spatially, with a decay length of pair correlation smaller than the system size. Experimental relevance is discussed. © 2009 IOP Publishing Ltd.JSPS Research Fellowship for Young ScientistsMinistry of Education, Science, Sports and Culture of Japa

A new half-metallic ferromagnet K2Cr8O16 predicted by an ab-initio electronic structure calculation

The first-principles electronic structure calculation is carried out to predict that a chromium oxide K2Cr8O16 with the hollandite-type crystal structure should be a new half-metallic ferromagnet. We compare our results with recent experimental data which indicate the ferromagnetic-metal to ferromagnetic-insulator transition at T ∼ 90 K, as well as the paramagnetic-metal to ferromagnetic-metal transition at T ∼ 180 K. Based on the calculated electronic structures, we argue that the double-exchange mechanism is responsible for the observed saturated ferromagnetism and the formation of the incommensurate, long-wavelength density wave of spinless fermions caused by the Fermi-surface nesting may be the origin of the opening of the charge gap.Ministry of Education, Culture, Sports, Science and Technology of Japa