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.

Field-effect transistor versus analog transistor (static induction transistor)

Abstract: The reason why the usual FET shows the saturated characteristics has been shown that with increasing drain voltage, the effect of the negative feedback action, increases through a marked increase of the Series channel resistance in the neighborhood of the pinch-off voltage, under which condition the apparent transfercon-ductance G_{m'}= G_{m}/(1 + r_{s}.G_{m}) becomes G_{m'} \simeq r_{s}^{-1} . It is also pointed out that a transistor in analogy to the vacuum type proposed by Watanabe and Nishizawa in 1950, exhibits the nonsaturated build-up character only When the internal negative feedback action is as little as G_{m'} \simeq G_{m} . In this case, when the channel has not yet pinched off, the characteristics are ohmic and then the transistor can operate as a good variable resistor; on the other hand, when the channel has already pinched, the transistor shows the build-up characteristics similar to those of a vacuum tube triode as a result of the static induction from the drain. The transistor similar to that of the vacuum tube triode type is named "Static Induction Transistor," because its output character is based on the static induction as well as input characteristics. The SIT has the exponential characteristics in contrast with the "Analog Transistor" which is expected by Shockley to follow the space-charge conduction law. The SIT has already been ascertained to have low noise, low distortion, and high-power capability, and its fabrication has been already realized in the form of a high-power transistor (2 kW, 8 MHz), a high-frequency transistor (a few watts, UHF), and a high-speed thyristor. Microwave transistors and very high-speed integrated circuits are being constructed, as well as variable resistors.

Contribution of carrier-mediated transport systems to the blood-brain barrier as a supporting and protecting interface for the brain; importance for CNS drug discovery and development.

Abstract: The blood-brain barrier (BBB) forms an interface between the circulating blood and the brain and possesses various carrier-mediated transport systems for small molecules to support and protect CNS function. For example, the blood-to-brain influx transport systems supply nutrients, such as glucose and amino acids. Consequently, xenobiotic drugs recognized by influx transporters are expected to have high permeability across the BBB. On the other hand, efflux transporters, including ATP-binding cassette transporters such as P-glycoprotein located at the luminal membrane of endothelial cells, function as clearance systems for metabolites and neurotoxic compounds produced in the brain. Drugs recognized by these transporters are expected to show low BBB permeability and low distribution to the brain. Despite recent progress, the transport mechanisms at the BBB have not been fully clarified yet, especially in humans. However, an understanding of the human BBB transport system is critical, because species differences mean that it can be difficult to extrapolate data obtained in experimental animals during drug development to humans. Recent progress in methodologies is allowing us to address this issue. Positron emission tomography can be used to evaluate the activity of human BBB transport systems in vivo. Proteomic studies may also provide important insights into human BBB function. Construction of a human BBB transporter atlas would be a most important advance from the viewpoint of CNS drug discovery and drug delivery to the brain.

Body wave spectra from propagating shear cracks.

Abstract: An earthquake source model studied in this paper predicts a higher value of P wave corner frequency than S wave corner frequency; the ratio of P to S wave corner frequency is about 1.3 on the average. This result owes mainly to the slip characteristics on the fault, that is, the center of the fault slips for a longer time than the edges and consequently a greater relative displacement takes place near the center. Relationships of source dimension with the corner frequencies for P and S waves are derived to estimate the source dimension of earthquakes from teleseismic body wave spectra. The far-field spectra from the present model of equidimensional rupture propagation demonstrate the spectral decay of ω-2 at high frequencies. The seismic efficiency is found to be independent of the size of source dimension and expressed as a function of initial stress, stress drop, and rupture velocity. Being interpreted in terms of this model, the ratio of frictional stress to final stress can be estimated from observations of rupture velocity.

MG53 nucleates assembly of cell membrane repair machinery

Abstract: Dynamic membrane repair and remodelling is an elemental process that maintains cell integrity and mediates efficient cellular function. Here we report that MG53, a muscle-specific tripartite motif family protein (TRIM72), is a component of the sarcolemmal membrane-repair machinery. MG53 interacts with phosphatidylserine to associate with intracellular vesicles that traffic to and fuse with sarcolemmal membranes. Mice null for MG53 show progressive myopathy and reduced exercise capability, associated with defective membrane-repair capacity. Injury of the sarcolemmal membrane leads to entry of the extracellular oxidative environment and MG53 oligomerization, resulting in recruitment of MG53-containing vesicles to the injury site. After vesicle translocation, entry of extracellular Ca(2+) facilitates vesicle fusion to reseal the membrane. Our data indicate that intracellular vesicle translocation and Ca(2+)-dependent membrane fusion are distinct steps involved in the repair of membrane damage and that MG53 may initiate the assembly of the membrane repair machinery in an oxidation-dependent manner.

Parameters controlling microstructure and hardness during friction-stir welding of precipitation-hardenable aluminum alloy 6063

Abstract: The aluminum (Al) alloys 6063-T5 and T4 were friction-stir welded at different tool rotation speeds (R), and then distributions of the microstructure and hardness were examined in these welds. The maximum temperature of the welding thermal cycle rose with increasing R values. The recrystallized grain size of the weld increased exponentially with increasing maximum temperature. The relationship between the grain size and the maximum temperature satisfied the static grain-growth equation. In the as-welded condition, 6063-T5 Al was softened around the weld center, whereas 6063-T4 Al showed homogeneous hardness profiles. Different R values did not result in significant differences in the hardness profile in these welds, except for the width of the softened region in the weld of 6063-T5 Al. Postweld aging raised the hardness in most parts of the welds, but the increase in hardness was small in the stir zone produced at the lower R values. Transmission electron microscope (TEM) observations detected a similar distribution of the strengthening precipitates in the grain interiors and the presence of a precipitation-free zone (PFZ) adjacent to the grain boundaries in all the welds. Microstructural analyses suggested that the small increase in hardness in the stir zone produced at the lower R values was caused by an increase in the volume fraction of PFZs.