Nanoscale amorphous “band-like” structure induced by friction stir processing in Zr55Cu30Al10Ni5 bulk metallic glass

Friction stir processing (FSP) is successfully applied in Zr-based bulk metallic glass in this study. In the FSP specimen obtained, large defects and cracks are not present in the FSP region. The microstructure in the friction zone (FZ) exhibited an amorphous “band-like” structure with widths of 10-45 nm and a small number of nanoscale crystalline particles were observed along the “band-like” structure. We concluded that the nanoscale amorphous “band-like” structure obtained in this study is nanoscale shear bands. From this result, FSP is expected to be a useful method of processing bulk metallic glass with nanoscale shear bands to investigate the influence of shear bands on the deformation behavior of bulk metallic glass.     

High breakdown Voltage undoped AlGaN-GaN power HEMT on sapphire substrate and its demonstration for DC-DC converter application

Undoped AlGaN-GaN power high electron mobility transistors (HEMTs) on sapphire substrate with 470-V breakdown voltage were fabricated and demonstrated as a main switching device for a high-voltage dc-dc converter. The fabricated power HEMT realized a high breakdown voltage with a field plate structure and a low on-state resistance of 3.9 m/spl Omega//spl middot/cm/sup 2/, which is 10 /spl times/ lower than that of conventional Si MOSFETs. The dc-dc converter operation of a down chopper circuit was demonstrated using the fabricated device at the input voltage of 300 V. These results show the promising possibilities of the AlGaN-GaN power HEMTs on sapphire substrate for future switching power devices.     

Unstable fracture criterion in a power-law hardening material

A fracture criterion for a pre-cracked plate subjected to large deformation is presented in a power-law hardening material based on the energy conservation law. First Hencky equations are applied to a non-linear elastic model in a small strain to derive the criterion and the theory is extended to a large strain case with the aid of numerical analysis. The criterion is expressed as a relation between a crack length and a remote fracture strain, and it is identical with Griffith's criterion when the power exponent is unity.Large strain and stress fields near a crack tip are also assessed. Experiments with pre-cracked steel plates well verify the theory, that is, the criterion based on elastic analysis appears to apply to an actual plastic material. The transition from the brittle fracture to the present unstable ductile fracture and a physical implication of the reduction of area in tension test are discussed.

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Résumé On présente un critère de rupture pour une tôle préfissurée soumise à une grande déformation dans une matériau durcissant suivant une loi parabolique et en se basant sur une loi de propagation de l'énergie. Les premières équations de Hencky sont appliquées à un modèle élastique non linéaire pour des déformations de faible amplitude en vue de dériver un critère, et la théorie est étendue au cas des grandes déformations à l'aide d'analyse numérique. Le critère est exprimé comme une relation entre la longueur de la fissure et une déformation à la rupture lointaine, et il est identique au critère de Griffith lorsque l'exposant de la loi de durcissement du matériau est l'unité.Les déformations en amplitude et les champs de contrainte au voisinage de l'extrémité de la fissure sont également prises en considération. Des expériences réalisées avec des tôles d'acier préfissurées vérifient la théorie de manière satisfaisante, c'est-à-dire que le critère basé sur l'analyse élastique apparait applicable à un matériau se comportant de façon plastique. La transition de la rupture fragile à une rupture ductile instable et les implications physiques de la striction lors de l'essai de traction sont discutées.

     

Digital TDM-FDM Translator with Multistage Structure

In this paper, a new digital signal processing algorithm for the digital TDM-FDM translator is proposed. The digital TDM-FDM translator, which performs a direct translation between two multiplex formats in the telephone network (time-division-multiplexing (TDM) and frequency-division-multiplexing (FDM)) by using digital techniques, has advantages in accuracy and stability of characteristics over equivalent analog equipments. However from the economical point of view, it largely depends on the cost reduction of semiconductor devices and LSI technologies. The proposed algorthm can be realized using only two digital filters and does not require product modulators or Fast Fourier Transform (FFT) processors. The required number of multiplications, which is closely related to the quantity of hardware, is considerably reduced by the multistage structure of this algorithm. The reduction in the kind of required digital hardware and the required number of multiplications makes it possible to efficiently utilize the new hardware realization techniques of digital filters or multipliers using read-only memories and simple logic devices. Since it is foreseen that cost reduction of memory devices will be more rapid than that of logic devices, the proposed algorithm is expected to be advantageous with regard to cost over existing algorithms where complex multiplier logic is required. The estimation of the computation rate is carried out with reference to a practical case. The computer simulation results are also shown.     

The Photonic Technologies Impact on the Next Generation Network

This paper describes the possible impact of photonic technologies on the next-generation network. With the explosion of the Internet (IP), the capacity demand is increasing exponentially, which exceeds Moor's law. The next-generation IP network should sustain this increase. This paper shows the possible node processing bottleneck even the transmission capacity can be supported by the use of WDM technology. Based on this analysis, the paper proposes a virtual router network as a solution, which applies a logical full-mesh connection based on salient features of photonic network technology. Development of the WDM technology sets the target at 1000 wavelengths on a fiber so that a dynamic wavelength routing function is becoming available. The increase in wavelengths, transparency among wavelengths, and the wavelength routing function can provide an optical path, which forms the base of a logical full-mesh structure and also provides an easy migration scenario from the current network to the next-generation IP network. The possibility is examined by calculation using a bi-directionalloop network as an example. As the foundation of the proposal, the current statusof photonic network technologies is described with future projection.     

Performance analysis of a dispersion compensator usingarrayed-waveguide gratings

We have developed a dispersion compensator that uses arrayed-waveguide gratings (AWGs) and a spatial filter. The compensator using AWGs with 380 waveguides in each array and the diffraction order of 53, can compensate a total second-order dispersion of 260 ps/nm with an eye-closure penalty of 1 dB for a 40-Gb/s nonreturn-to-zero (NRZ) signal. It is shown that the required spatial resolution of the spatial phase filter for compensation is 2.55 μm for silica AWGs of usual design. The acceptable fluctuation in the refractive index of the waveguides in the AWGs is as large as 5×10^-5     

Synthesis and properties of green sustainable carbonate-type nonionics containing polyoxyethylene chains

A series of polyoxyethylene surfactants containing carbonate linkages as biodegradable and chemically recyclable segments was designed and synthesized by a green process. A two-step carbonate exchange reaction was used: dimethyl or diphenyl carbonate was reacted with 1-alkanol, and the product was reacted with poly (ethylene) glycol in the presence of a lipase or chemical catalyst. The obtained carbonate-type nonionics exhibited good surface-active properties such as a low critical micelle concentration value and a surface tension lowering action. They were readily biodegraded by activated sludge, furthermore, could be chemical recycled using a lipase.     

Convergent-beam electron diffraction

This paper reviews the convergent-beam electron diffraction (CBED) technique. Point- and space-group determination methods of ordinary crystals are described, along with an example of the determination method for Sr?Ru?O?. The symmetry determination of one-dimensionally incommensurate crystals and quasicrystals is explained. The large-angle CBED technique, which is indispensable for lattice defect and lattice strain analysis, is also described. A real procedure for lattice strain analysis is provided, using an example of a multilayer Si?-xGe(x)/Si material. A nanometer-scale crystal structure refinement method and charge density and crystal potential determination method by CBED are briefly described.