Development of Bismuth Ferrite as a Piezoelectric and Multiferroic Material by Cobalt Substitution

Bismuth ferrite (BiFeO₃) is the most widely studied multiferroic material with robust ferroelectricity and antiferromagnetic ordering at room temperature. One of the possible device applications of this material is one that utilizes the ferroelectric/piezoelectric property itself such as ferroelectric memory components, actuators, and so on. Other applications are more challenging and make full use of its multiferroic property to realize novel spintronics and magnetic memory devices, which can be addressed electrically as well as magnetically. This progress report summarizes the recent attempt to control the piezoelectric and magnetic properties of BiFeO₃ by cobalt substitution.     

Nanostructural changes in bamboo cell walls with aging and their possible effects on mechanical properties

In Asian countries, only bamboo culms that are 3–5 years old are used especially as materials because of their toughness, pliability, and/or workability. In this study, we evaluated the mechanical properties of bamboo in correlation with age-dependent changes in the nanostructures of cell walls, such as microfibril angles (MFAs), crystallite sizes, and crystallinity. Current year and 1.5-, 3.5-, 4.5-, 6.5-, and 8.5-year-old Phyllostachys pubescens samples were used. Three-point bending tests and wide-angle X-ray scattering experiments were conducted. The specific bending of Young’s modulus and the specific bending strength of 3.5- and 4.5-year-old bamboo samples were greater than those of other ages. The MFAs decreased in 1.5-year-old bamboo, were constant until samples were 6.5-years old, and then increased slightly in 8.5-year-old bamboo. The widths of crystallites appeared to be constant for all ages, while the lengths of crystallites and crystallinity showed age-dependent differences only on the inner side. In this study, the MFA was negatively correlated with the toughness of bamboo culms. This result should be considered with other structural features at the tissue level; however, the age-related changes in MFA values appear to be important factors related to the mechanical properties of bamboo.     

Proton transfer reactions and hydrogen-bond networks in protein environments

In protein environments, proton transfer reactions occur along polar or charged residues and isolated water molecules. These species consist of H-bond networks that serve as proton transfer pathways; therefore, thorough understanding of H-bond energetics is essential when investigating proton transfer reactions in protein environments. When the pK_a values (or proton affinity) of the H-bond donor and acceptor moieties are equal, significantly short, symmetric H-bonds can be formed between the two, and proton transfer reactions can occur in an efficient manner. However, such short, symmetric H-bonds are not necessarily stable when they are situated near the protein bulk surface, because the condition of matching pK_a values is opposite to that required for the formation of strong salt bridges, which play a key role in protein–protein interactions. To satisfy the pK_a matching condition and allow for proton transfer reactions, proteins often adjust the pK_a via electron transfer reactions or H-bond pattern changes. In particular, when a symmetric H-bond is formed near the protein bulk surface as a result of one of these phenomena, its instability often results in breakage, leading to large changes in protein conformation.     

Influence of oxidized layer on operating voltage and luminance of nanocrystalline silicon electroluminescent device

A direct current (DC) operating voltage and luminescence property of red electroluminescent (EL) devices with and/or without a silicon dioxide (SiO2) layer at interface between nanocrystalline Si (nc-Si) region and Si substrate has investigated. The removal of SiO2 layer in the EL device led to the lowering of DC operating voltage from 4.0 up to 2.0 V and the increase of luminescence intensity more than one order of magnitude. The external quantum efficiency of red luminescence from the EL device without the SiO2 layer at the DC operating voltage of 3.0 V was 0.5%. These were realized by the efficient and easy injection of carriers to the radiative recombination centers in the nc-Si region due to the removal of SiO2 layer. These results indicate that the removal of SiO2 layer is drastically improved the DC operating voltage and luminescence intensity for the nc-Si based EL device.     

Generic Guiding Law Between Irreversibility Field and Anisotropy—Chemical Control of Critical Current of High Temperature Superconductors

Systematic studies on the irreversibility field H _irr, and anisotropy factor ² of high temperature superconductors (HTSC) were performed using single crystals with high quality. The generic scaling law have been found to hold for all the HTSC systems examined, i.e., H _irr[Oe]=4×10^7–2 (1–T/T _c)1.5 at T0.7T _c. In addition, of each HTSC material is roughly expressed as 2=2 exp(0.78d[Å]) at the carrier optimally-doped state. Based on the generic scaling law, the behaviors of the variously doped superconductors, such as Bi(Pb)2212 and Hg(Re)1223, are discussed in terms of the critical current.     

Static linearity error analysis of subranging A/D converters

An 8- to 10-bit CMOS A/D converter with a conversion rate of more than 16 megasample/second is required in consumer video systems. Subranging architecture is widely used to realize such A/D converters. This architecture, however, exhibits a reference voltage error caused by resistor ladder loadings. The error has been discussed with respect to a flash A/D converter by Dingwall. However, it can not be applied for a subranging A/D converter as it is. The analysis of this error is very important in realizing the desired accuracy of a subranging A/D converter. This paper describes a static analysis to improve the linearity, and reports the results of this analysis for two typical types, one with individual comparator arrays for coarse and fine A/D conversions, and the other with the same comparator array for both conversions. This analysis makes it clear that a subranging A/D converter has unique saw-tooth characteristic in fine linearity errors. Furthermore, this analysis clarifies what conditions are necessary to achieve the desired accuracy. It is necessary, for example, that the product of the total input capacitance of the comparators C, the conversion rate f _sand the total ladder resistance R is less than 0.03 in A/D converters with individual comparator arrays and 0.016 in A/D converters with the same comparator array in order to achieve 10-bit accuracy.     

Unicast probing techniques for estimation of shared loss rate

The paper introduces two new unicast active end‐to‐end measurement techniques, called the single–double unicast probing (SDUP) and the delay‐based unicast probing (DUP), to estimate the rate of losses which occurs on the shared network path of two flows. A comprehensive performance evaluation and a comparison between these two techniques and an existing one having the same objective, the striped unicast probing (SUP) (Proceedings of the INFOCOM 2001—The IEEE Conference on Computer Communications, No. 2, Anchorage, Alaska, U.S.A., 2001; 915–923), were carried out. We demonstrate that our proposed SDUP technique provides even better estimation accuracy compared to that of the SUP while it requires only one piece of measurement equipment at only one receiver instead of deploying units to both receivers. Furthermore, with only one sender and receiver pair we can measure not only one shared path, but any partial path that begins at the sender and is located on the sender–receiver path. We also show that while the DUP have the same accuracy as the SUP in the case of Drop‐Tail buffer management, the DUP is capable of measuring loss rates of RED buffers, which the other techniques do not work with. The SDUP and the DUP are less intrusive and cause less bursty traffic compared to the SUP. Finally, the adaptation of these techniques into passive measurements is also considered. Copyright © 2006 John Wiley & Sons, Ltd.     

Continuous Control and Enhancement of Excitonic Valley Polarization in Monolayer WSe2 by Electrostatic Doping

Enhancement and continuous control of the excitonic valley polarization in electrostatically doped monolayer WSe₂ are demonstrated. Under excitation with circularly polarized light, 20% valley polarization of excitons around the charge neutrality condition at 70 K is increased to 40% by modulating the electron/hole density up to 2 × 10¹² cm^?2. This increase originates from slow valley relaxation for neutral exciton between the K and ?K valleys owing to screening of long‐range e–h exchange interactions by doped carriers. The gate‐dependences of the exciton valley polarization at various temperatures are reproduced by theoretical calculations, which holds potential for next‐generation valleytronic devices continuously controlled by an applied bias voltage.     

Analysis of crack propagation due to rebar corrosion using RBSM

Cracking behavior due to rebar corrosion in concrete specimens having a single rebar is evaluated experimentally and analytically. In the experiments, in which corrosion was induced electronically, the propagation of cracks (including internal crack patterns and surface crack widths) was monitored. In addition, deformation of the specimen surface was measured using a laser displacement meter. In the analysis, a three-dimensional Rigid-Body-Spring Method (RBSM), combined with a three-phase material corrosion–expansion model, is proposed to simulate crack propagation due to rebar corrosion. The effects of the properties of corrosion products such as elastic modulus, penetration of corrosion products into cracks, and local corrosion after cracking of the concrete are investigated. Cracking behavior due to rebar corrosion is simulated reasonably well. The simulations using RBSM provide insight into the mechanisms of crack initiation and propagation due to rebar corrosion.