Torque curve measurements in HCP Co in very low fields

Magnetic torque measurements have been made for a single crystal of Co of hcp structure in a very low field region where the torque intensity was not saturated. In this region it had been considered to be impossible to determine the magnetocrystalline anisotropy constants from observed torque curves. Recently, a new method of analyzing the torque curves was proposed by the present author with the help of a least mean square routine instead of the usual Fourier analysis. By using this method the first magnetocrystalline anisotropy constant Kulwas, for the first time, determined at 77 K. It was found that the Kuldetermined in the low field range between 0.3 and 0.5 T coincides with the value determined at a high field region where the torque curve was saturated enough. Below 0.2 T the value of Kuldecreased with decreasing the field. This region was found to correspond to the domain wall formation. </p

Pressure as a limiting factor for life

Facts concerning the stability and functioning of key biomolecular components suggest that cellular life should no longer be viable above a few thousand atmospheres (200–300 MPa). However, organisms are seen to survive in the laboratory to much higher pressures, extending into the GPa or even tens of GPa ranges. This is causing main questions to be posed concerning the survival mechanisms of simple to complex organisms. Understanding the ultimate pressure survival of organisms is critical for food sterilization and agricultural products conservation technologies. On Earth the deep biosphere is limited in its extent by geothermal gradients but if life forms exist in cooler habitats elsewhere then survival to greater depths must be considered. The extent of pressure resistance and survival appears to vary greatly with the timescale of the exposure. For example, shock experiments on nanosecond timescales reveal greatly enhanced survival rates extending to higher pressure. Some organisms could survive bolide impacts thus allowing successful transport between planetary bodies. We summarize some of the main questions raised by recent results and their implications for the survival of life under extreme compression conditions and its possible extent in the laboratory and throughout the universe

Critical Temperature T_c versus Charging Energy E_c in MgB2 and C60/CHBr3

The boride compounds MB_x related to the magnesium-boron stacking layered material MgB2 are discussed in terms of the B-B layers in the borides analogous to the Cu-O ones in the cuprates. We propose a possibility of superconducting materials which exhibit higher critical temperature T_c than 39 K of MgB2. We point out a role of interstitial ionic atoms M (e.g., Mg in MgB2) as capacitors, which reduce the condensation-energy loss due to the charging energy E_c between the B-B layers. In the viewpoint of the present model, the recently discovered 117-Kelvin superconductor C60/CHBr3 is also discussed in terms of the intercalation molecules CHBr3 as possible capacitors among the superconducting grains of C60 molecules.Comment: 9 pages, 1 fugure included; prepared for Proceedings of the symposium ISS2001, Kobe, Sep. 200

Effect of ultra-high pressure on small animals, tardigrades and Artemia

This research shows that small animals, tardigrades (Milnesium tardigradum) in tun (dehydrated) state and Artemia salina cists (dried eggs) can tolerate the very high hydrostatic pressure of 7.5 GPa. It was really surprising that living organisms can survive after exposure to such a high pressure. We extended these studies to the extremely high pressure of 20 GPa by using a Kawai-type octahedral anvil press. After exposure to this pressure for 30 min, the tardigrades were soaked in pure water and investigated under a microscope. Their bodies regained metabolic state and no serious injury could be seen. But they were not alive. A few of Artemia eggs went part of the way to hatching after soaked in sea water, but they never grew any further. Comparing with the case of blue-green alga, these animals are weaker under ultra-high pressure

Pressure tolerance of Artemia cysts compressed in water medium

The high pressure tolerance of cysts of Artemia salina was investigated up to several GPa in water. No survival was observed after exposure to 1.0 GPa for 15 min. After exposure to 2.0 GPa for the same time duration, the hatching rate had recovered to 33%, but decreased to 8% following compression at 7.5 GPa. This contrasts with results using Fluorinert™ as the pressure-transmitting medium where 80–88% recovery was observed. The lower survival rate in water is accompanied by swelling of the eggs, indicating that liquid H2O close to the ice-VI crystallization pressure penetrated inside the eggs. This pressure exceeds the stability limit for proteins and other key biomolecules components within the embryos that could not be resuscitated. Rehydration takes several minutes and so was not completed for all samples compressed to higher pressures, prior to ice-VI formation, resulting in renewed survival. However H2O penetration inside the shell resulted in increased mortalit

Torque curve measurements in HCP Co in very low fields TORQUE CURVE MEASUREMENTS IN HCP Co IN VERY LOW FIELDS

ABSTRACT Magnetic torque measurements have been made for a single crystal of Co of hcp structure in a very low field region where the torque intensity was not saturated. I n this region it had been considered to be impossible to determine the magnetocrystalline anisotropy constants from observed torque curves. Recently, a new method of analyzing the torque curves was proposed by the present author with the help of a least mean square routine instead of the usual Fourier analysis. By using this method the first magnetocrystalline anisotropy constant Kul was, for the first time, determined at 77 K. It was found that the Kul determined in the low field range between 0.3 and 0.5 T coincides with the value determined at a high field region where the torque curve was saturated enough. Below 0.2 T the value of Kul decreased with decreasing the field. This region was found to correspond to the domain wall formation