Band-structure-dependent demagnetization in the Heusler alloy Co₂Mn(1-x)FexSi

We investigate the ultrafast demagnetization for two Heusler alloys (Co?Mn(1-x)FexSi) with a different lineup of the minority band gap and the Fermi level. Even though electronic spin-flip transitions are partially blocked by the band gap in one compound, the respective magnetization dynamics, as measured by the time-resolved Kerr effect, are remarkably similar. Based on a dynamical model that includes momentum and spin-dependent carrier scattering, we show that the magnetization dynamics are dominated by hole spin-flip processes, which are not influenced by the gap.     

A standard method to calibrate sonochemical efficiency of an individual reaction system

Fricke reaction, KI oxidation and decomposition of porphyrin derivatives by use of seven types of sonochemical apparatus in four different laboratories were examined in the range of frequency of 19.5 kHz to 1.2 MHz. The ultrasonic energy dissipated into an apparatus was determined also by calorimetry. Sonochemical efficiency of Fricke reaction and KI oxidation was defined as the number of reacted molecule per unit ultrasonic energy. The sonochemical efficiency is independent of experimental conditions such as the shape of sample cell and irradiation instruments, but depends on the ultrasonic frequency. We propose the KI oxidation dosimetry using 0.1 moldm(-3) KI solution as a standard method to calibrate the sonochemical efficiency of an individual reaction system.     

A single-electron circuit as a discrete dynamical system

A single-electron circuit can be operated as a discrete dynamical system because it changes its internal state discontinuously because of electron tunneling. To confirm this idea, we designed a sample circuit for discrete dynamical operation and confirmed by computer simulation that the circuit successfully generated a sequence of discrete-time outputs by following a return map. The concept of discrete dynamical systems will be useful in developing new functional systems that consist of quantum devices and nanostructures.     

Spectral analysis for intrinsic time processes

This paper discusses an estimation procedure for the spectral density of intrinsic time processes because there has been no argument of the spectral analysis for subordinated processes. Such processes have been proposed in a variety of contexts to describe asset price behavior. They are used when the movement of prices is tied to the number of market transactions, trading volume or the more illusive concept of information arrival. We develop the asymptotic theory for an estimated spectral density of intrinsic time processes and elucidate the asymptotics, which show some interesting structures. Also, numerical studies are given to confirm the results.     

A new “switched-on” crown ether which exhibits a reversible all-or-none ion-binding ability

A new photoresponsive crown ether (2) in which the poly)oxyethylene) chain is linked to 4? and 4′-position of azobenzene was synthesized. Trans-(2) completely lacked the affinity to alkali metal cations, while photoisomerized cis-(2) was capable of binding K⁺, Rb⁺, and Cs⁺.     

Generation of ketone dilithio α,β-dianions and their reactions with electrophiles

Ketone dilithio α,β- and α,β′-dianions can be generated by a tin-lithium exchange reaction of the lithium enolate of β-tributyltin substituted ketones. A chelation-aided approach, which employs β-dichlorobutyltin substituted ketones and n-BuLi, is also useful for the generation of ketone α,β-dianions having the Z-geometry at the alkene. The generated dianions can be transformed into substituted ketones by reaction with various carbon electrophiles.     

Comparison of radioactive and stable cesium uptake in aquatic macrophytes affected by the Fukushima Dai-ichi Nuclear Power Plant accident

Concentrations of ^134+137Cs and ¹³³Cs in aquatic macrophytes, water, and sediment were measured in samples collected from Fukushima Prefecture, Japan. The concentrations of ¹³⁷Cs in submerged and floating-leaved plants were higher than the values for emergent plants according to their main Cs uptake mode. The geometric mean water-to-plant concentration ratio for ¹³⁷Cs and ¹³³Cs was comparable observed in submerged and floating-leaved plants, while the geometric mean sediment-to-plant concentration ratio for ¹³⁷Cs in emergent plants was higher than that of ¹³³Cs, which suggest that the mobility of Fukushima accident-derived ¹³⁷Cs is not in steady state 4–5 years after the accident.

     

Constructing self-organized structures on silicon and sapphire surfaces

We investigated methods to fabricate distinctive structures on silicon and sapphire substrates to grow a carbon nanotube (CNT) network using a solution from the Belousov-Zhabotinsky (BZ) reaction. The BZ reaction is a chemical system where chemical reactions and material diffusion coexist in a nonequilibrium state and generate spatiotemporal patterns in a petri dish. Precipitates from the reaction should also produce distinctive structures after being piled on the substrates. The structures have metal particles that act as catalysts for growing CNTs or quantum dots of nanodot devices. Therefore, such structures should be suitable to fabricate three-dimensional CNT networks or nanodot devices. To confirm this, we investigated the fabrication of distinctive structure using a BZ reaction solution. Results indicated that the BZ reaction solution produced interesting structures on the substrates. Moreover, we confirmed that the shape of the structure changed when the substrate used was changed. We believe that the developed methods are suitable to fabricate nanodevices, especially CNT network devices.