Management of highly-strained heterointerface in InGaAs/GaAsP strain-balanced superlattice for photovoltaic application

We report an implementation of a strain-balanced superlattice structure in a photovoltaic device. A thin-period structure is an appropriate design for a strain-balanced epitaxy allowing minimum stress accumulation in the highly strained quantum well (QW). However, a large number of interfaces cause a serious issue as critical as strain balancing. Such a structure suffers from degraded crystal quality with the increase of number of interfaces; and the atomic contents within the well or barrier also become difficult to control. With help from in situ reflectivity measurement and x-ray diffraction, it was deduced that such an interface issue could result from unpredictable interfacial strain relaxation and irregular interface morphology between strained well and barrier. According to this mechanism, we developed a smart interface management, insertion of a monolayer-thin strain-neutral GaAs, to avoid diffused interfaces and morphology degradation. The modified superlattice solar cell exhibits good performance.     

The effect of irradiation by ultraviolet light on ureido‐pyrimidinone based biomaterials

Supramolecular polymers based on ureido‐pyrimidinone (UPy) represent a promising class of biocompatible materials for medical applications. Here, the chemical modification effect of UV irradiation, used to sterilize these materials, is studied. Besides anticipated crosslinking effects, UV irradiation causes telechelic UPy‐polymers to become fluorescent. UPy‐model compounds confirm a relation between UV‐induced changes and the UPy‐moiety. UV‐induced fluorescence and IR‐spectral changes are (partially) reversible by heat and/or solvent treatment. The results indicate the presence of at least two distinct UV‐induced molecular species. UPy‐model compounds with specific tautomeric forms directly relate fluorescence to UPy‐enol tautomers. Photo‐enolization is hypothesized to occur via an excited‐state intermolecular double proton transfer. Changes in UPy‐tautomeric equilibrium and crosslinking are factors that influence the dynamics of UPy‐based materials. Identification and understanding of such factors will aid in the successful application of these materials, for example as biomaterial in tissue engineering applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 81–90     

Evaluation of peripheral vasodilative indices in skin tissue of type 1 diabetic rats by use of RGB images

Optical Review - We investigated a method to evaluate the arterial inflow and the venous capacitance in the skin tissue of streptozotocin-induced type 1 diabetic rats from RGB digital color images....     

The nucleation of faulted dipoles at intersection jogs in γ-TiAl

Single crystal samples of n-(Ti-54.7 at.% Al) deformed to a permanent strain of 2% at room temperature under multiple-slip conditions contain faulted dipoles (FDs) whose density exhibits some dependence on load orientation. Although FDs are hard to observe after compression along [210], they are profuse and congregated in places in the [1 1 8.6] load orientation. They exhibit most of the topological characteristics of FDs formed under single slip as reported by Grégori and Veyssière such as elongation in the screw direction of the primary d011] slip direction and a noticeable shape asymmetry. It is shown further that, in the [1 1 8.6] samples, bundles of FDs originate at jogs that result from intersection with forest dislocations of appropriate Burgers vectors. A mechanism for FD nucleation is proposed on the basis of asymmetrical dissociation of the parent d011] dislocation and specific impingements between the various partials on two adjacent octahedral planes. Implications of the FD nucleation at jogs on the load orientation dependence of the FD density are discussed.     

Steering performance of an inverted pendulum vehicle with pedals as a personal mobility vehicle

From the viewpoints of environmental protection, support for the aged and ensuring the right to mobility, there is a need to develop a new type of mobility vehicle that provides more effective transportation. The authors propose an inverted pendulum vehicle with pedals as one of the forms of personal mobility vehicles (PMVs). In this paper, the steering performance of the inverted pendulum vehicle with pedals is discussed based on experiments on a prototype. From the experimental results, it was confirmed that the errors from the five subjects for the target trajectory and the five-grade evaluation of the maneuverability were similar. Finally, we created an inverted pendulum vehicle with pedals to which was added a reaction actuator for the steering system. From the experimental results, it was found that setting appropriate feedback gains for the handle steering angle and its rate of rotation, which control the right and left wheel driving torques, resulted in greatly improved maneuverability.     

Reverse current reduction of Ge photodiodes on Si without post-growth annealing Invited Paper

A new approach to reduce the reverse current of Ge pin photodiodes on Si is presented, in which an i-Si layer is inserted between Ge and top Si layers to reduce the electric field in the Ge layer. Without post- growth annealing, the reverse current density is reduced to ～10 mA/cm2 at -1 V, i.e., over one order of magnitude lower than that of the reference photodiode without i-Si layer. However, the responsivity of the photodiodes is not severely compromised. This lowered-reverse-current is explained by band-pinning at the i-Si/i-Ge interface. Barrier lowering mechanism induced by E-field is also discussed. The presented "non-thermal" approach to reduce reverse current should accelerate electronics-photonics convergence by using Ge on the Si complementary metal oxide semiconductor (CMOS) platform.     

A family of quintic cyclic fields with even class number parameterized by rational points on an elliptic curve

We give a family of quintic cyclic fields with even class number parametrized by rational points on an elliptic curve associated with Emma Lehmer's quintic polynomial. Further, we use the arithmetic of elliptic curves and the Chebotarev density theorem to show that there are infinitely many such fields.     

Fluctuation of Density of States for 1d Schrödinger Operators

We consider the 1d Schrödinger operator with random decaying potential and compute the 2nd term asymptotics of the density of states, which shows substantial differences between the cases \(\alpha > \frac{1}{2}\), \(\alpha < \frac{1}{2}\) and \(\alpha = \frac{1}{2}\).     

Mechanism of microfibril contraction and anisotropic dimensional changes for cells in wood treated with aqueous NaOH solution

Anisotropic swelling of wood samples was observed upon treatment with an aqueous NaOH solution with 0–0.20 fraction concentrations. At NaOH concentrations less than 0.10, the swelling occurred only along the tangential axis (T) and not along the radial (R) or longitudinal (L) axes. At greater NaOH levels, the swelling was even more pronounced along T with shrinkage along the other axes. These anisotropic changes along R and L were closely related to the crystallinity of microfibrils in the wood cell wall and simulated with a cell structure model. This exercise revealed microfibril contraction and matrix swelling in the wood cell wall upon NaOH treatment. The observed anisotropy in cross section was caused by differences in the microfibril angles (LR and LT) with the cell wall.     

Oryzamutaic acids B-G, new alkaloids from an Oryza sativa mutant with yellow endosperm

Oryzamutaic acids B-G (1-6), structurally unique nitrogen-containing heterocyclic alkaloids, were isolated from the endosperm (polished rice) of an Oryza sativa mutant. The structures and relative stereochemistries of 1-6 were elucidated on the basis of spectroscopic and single-crystal X-ray diffraction analyses.