Self-assembly of a silica-surfactant nanocomposite in a porous alumina membrane

A mesoporous membrane composed of nanochannels with a uniform diameter has a potential use for precise size-exclusive separation of molecules. Here, we report a novel method to form a hybrid membrane composed of silica-surfactant nanocomposite and a porous alumina membrane, by which size-selective transport of molecules across the membrane becomes possible. The nanocomposite formed inside each columnar alumina pore was an assembly of surfactant-templated silica-nanochannels with a channel diameter of 3.4 nm; the channel direction being predominantly oriented along the wall of the columnar alumina pore. Molecules could be transported across the membrane including the silica-surfactant nanocomposite with a capability of nanometre-order size-exclusive separation. Our proposed membrane system has a potential use not only for separation science, but also catalysis and chip technologies.     

Observation of iron silicide formation by plan-view transmission electron microscopy

The formation and the phase transitions of iron silicide by solid-phase epitaxy have been investigated by means of plan-view transmission electron microscopy, which enables us to observe a clean interface between Fe and Si. Layers of Fe were deposited on Si (100) at room temperature in an ultrahigh vacuum chamber. The sample was annealed in the electron microscope at a temperature between 673 and 1073 K. After annealing at 673 K, FeSi crystallites were formed with various orientations. When the annealing temperature was increased to 973 K, we found that the crystallites suddenly started to coalesce into grains of several hundreds of nanometers in size and polycrystalline beta-FeSi2 was formed. These phase transitions were also confirmed with electron energy-loss spectroscopy.     

Gel permeation chromatography using controlled-porosity glass. II. Polyacrylamide aqueous solutions

In a study of polyacrylamide in solutions we have required the rapid characterization on chromatographies. The application to the aqueous solution of the GPC using controlled-porosity glass has been examined from both the viewpoint of the effect of salt addition and the GPC mechanism. An adequate addition to neutral salt, 0.005M KCI to the eluent, gave rise to the elution behaviors being in accord with the hydrodynamic volume concept of the GPC separation.     

High-power aging test on 1.3 ?m DC-PBH lasers with reflective coated mirror

High-power aging tests on 1.3 ?m double-channel planar buried-heterostructure (DC-PBH) lasers with a reflective coated mirror have been performed. Stable operation for over 6000 h has been demonstrated under constant power conditions of 20 and 30 mW from the front facet at 50°C.     

Memory encoding by theta phase precession in the hippocampal network

Recent experimental evidence on spike-timing-dependent plasticity and on phase precession (i.e., the theta rhythm dependent firing of rat hippocampal cells) associates the contribution of phase precession to episodic memory. This article aims at clarifying the role of phase precession in memory storage. Computer simulations show that the memory storage in the behavioral timescale varies in timescale of the temporal sequence from half a second to several seconds. In contrast, the memory storage caused by traditional rate coding is restricted to the temporal sequence within 40 ms. During phase precession, memory storage of a single trial experience is possible, even in the presence of noise. It is therefore concluded that encoding by phase precession is appropriate for memory storage of the temporal sequence in the behavioral timescale.     

Dependence of Superconducting Critical Temperature of A15-Type V3Ga on Composition

The composition dependence of the superconducting critical temperature T _c has been investigated for A15-type V₃Ga compounds. The T _c is determined by the specific heat and the magnetic flux transmission ratio through the sample and discussed in terms of the powder X-ray diffraction. The long-range order parameter and the lattice parameter of V₃Ga are evaluated quantitatively by the Rietveld method at each composition, which is evaluated exactly by the electron probe microanalysis (EPMA) measurements. The well-ordered homogeneous alloying structures. V _1–x Ga _x compounds are found to have nearly the same T _c as that for the stoichiometric composition between 0.23<0.25.     

Excitation and propagation of shear-horizontal-type surface and bulk acoustic waves

This paper reviews the basic properties of shear-horizontal (SH)-type surface acoustic waves (SAWs) and bulk acoustic waves (BAWs). As one of the simplest cases, the structure supporting Bleustein-Gulyaev-Shimizu waves is considered, and their excitation and propagation are discussed from various view points. First, the formalism based on the complex integral theory is presented, where the surface is assumed to be covered with an infinitesimally thin metallic film, and it is shown how the excitation and propagation of SH-type waves are affected by the surface perturbation. Then, the analysis is extended to a periodic grating structure, and the behavior of SH-type SAWs under the grating structure is discussed. Finally, the origin of the leaky nature is explained     

External doses in the environment from the Tokai-mura criticality accident

On 30 September 1999, a criticality accident occurred at a uranium processing plant operated by JCO in Tokai-mura, Japan and the criticality remained for about 20 h. Almost all doses to the neighbouring residents were brought by neutrons and gamma rays emitted from the facility rather than fission products released to the environment. External doses in the environment were evaluated using radiation monitoring data and radiation transport calculation. A pattern of the dose rate evolution was modelled based on the records of gamma ray monitors in the JCO facilities. Relations between the ambient dose equivalent rates of neutrons/gamma rays and the distance from the facility were determined from the monitoring data obtained around the accident site. Conversion from the ambient dose equivalent to the effective dose equivalent was made assuming the energy spectra calculated by the radiation transport code, ANISN. It was estimated that the people who stayed outside the 350 m zone would receive doses of less than 1 mSv.