Tohoku University

About: Tohoku University is a education organization based out in Sendai, Japan. It is known for research contribution in the topics: Magnetization & Alloy. The organization has 72116 authors who have published 170791 publications receiving 3941714 citations. The organization is also known as: Tōhoku daigaku.

A class of almost contact riemannian manifolds

Abstract: Recently S. Tanno has classified connected almostcontact Riemannian manifolds whose automorphism groups have themaximum dimension [9]. In his classification table the almost contactRiemannian manifolds are divided into three classes: (1) homogeneousnormal contact Riemannian manifolds with constant 0-holomorphic sec-tional curvature if the sectional curvature for 2-planes which contain

Device-to-Device Communication in LTE-Advanced Networks: A Survey

Abstract: Among the LTE-A communication techniques, Device-to-Device (D2D) communication which is defined to directly route data traffic between spatially closely located mobile user equipments (UEs), holds great promise in improving energy efficiency, throughput, delay, as well as spectrum efficiency As a combination of ad-hoc and centralized communication mechanisms, D2D communication enables researchers to merge together the long-term development achievements in previously disjoint domains of ad-hoc networking and centralized networking To help researchers to have a systematic understanding of the emerging D2D communication, we provide in this paper a comprehensive survey of available D2D related research works ranging from technical papers to experimental prototypes to standard activities, and outline some open research problems which deserve further studies

Microflow devices and systems

Abstract: Microflow devices including microvalves, micropumps and microflow sensors fabricated by micromachining are reviewed from the point of view of the actuating principle and structures. Integration of microflow control devices and microflow sensors allowed very precise control of small flow. High performance liquid dosing microsystems and sophisticated chemical analysing microsystems were demonstrated by the combination of microflow devices and microsensors. Applications of microflow devices and systems are also introduced.

Strengthening Mechanisms of Creep Resistant Tempered Martensitic Steel

Abstract: The creep deformation resistance and rupture life of high Cr ferritic steel with a tempered martensitic lath structure are critically reviewed on the basis of experimental data. Special attention is directed to the following three subjects: creep mechanism of the ferritic steel, its alloy design for further strengthening, and loss of its creep rupture strength after long-term use. The high Cr ferritic steel is characterized by its fine subgrain structure with a high density of free dislocations within the subgrains. The dislocation substructure is the most densely distributed obstacle to dislocation motion in the steel. Its recovery controls creep rate and rupture life at elevated temperatures. Improvement of creep strength of the steel requires a fine subgrain structure with a high density of free dislocations. A sufficient number of pinning particles (MX particles in subgrain interior and M 23 C 6 particles on sub-boundaries) are necessary to cancel a large driving force for recovery due to the high dislocation density. Coarsening and agglomeration of the pinning particles have to be delayed by an appropriate alloy design of the steel. Creep rupture strength of the high Cr ferritic steel decreases quickly after long-term use. A significant improvement of creep rupture strength can be achieved if we can prevent the loss of rupture strength. In the steel tempered at high temperature, enhanced recovery of the subgrain structure along grain boundaries is the cause of the premature failure and the consequent loss of rupture strength. However, the scenario is not always applicable. Further studies are needed to solve this important problem of high Cr ferritic steel. MX particles are necessary to retain a fine subgrain structure and to achieve the excellent creep strength of the high Cr ferritic steel. Strengthening mechanism of the MX particles is another important problem left unsolved.

Enhanced deformation mechanisms by anisotropic plasticity in polycrystalline Mg alloys at room temperature

Abstract: This article presents room-temperature deformation mechanisms in polycrystalline Mg alloys. Dislocation slip of basal 〈a〉 and prismatic 〈a〉 types are shown to occur nearly at the same ease when the basal planes are tilted in such a way that the Schmid-factor ratio (equivalent to the critically resolved shear stress (CRSS) ratio) of prismatic 〈a〉 to basal 〈a〉 slip is larger than a value ranging from 1.5 to 2.0, depending on the initial texture distribution and grain size. Grain-boundary sliding (GBS) also occurs at room temperature up to 8 pct of total strain, enhanced by plastic anisotropy as well as by the increasing number of grain-boundary dislocations. Twinning plays an important role in both flow and fracture behaviors. Twins are induced mostly by stress concentrations caused by the anisotropic nature of dislocation slip. Twins can be classified into two types based on their shape: a wide lenticular type and a narrow banded type. The wide twins are $$\{ 10\bar 12\} $$ twins appearing in the early stage of deformation and accompany little change of surface height. The narrow twins are $$\{ 10\bar 11\} $$ or $$\{ 30\bar 32\} $$ appearing in the late stage of deformation and accompany a substantial change in surface height. The formation of the narrow twins seems to give rise to highly localized shear deformation within the twin, leading to strain incompatibility and to final failure.