InP/InGaAs double-heterojunction bipolar transistors for high-speedoptical receivers

We fabricated monolithically integrated pin/HBT photoreceivers using FPIGA (full-potential InGaAs) DHBT's with various collector thicknesses. An HBT figure-of-merit was deduced from the relationship between measured bandwidths of the preamplifiers and the f_T's and f_max's of the DHBT's. A phenomenological device model of the DHBT's is proposed to find the optimum collector thickness that gives the highest bandwidth of the photoreceivers. Finally, we discuss the feasibility of monolithically integrating a pin-PD, preamplifier, buffer amplifier, and D-type flip-flop with an operating speed of 40 Gbit/s     

Supramolecular Chiral Nanoarchitectonics

Exploration of molecular functions and material properties based on the control of chirality would be a scientifically elegant approach. Here, the fabrication and function of chiral-featured materials from both chiral and achiral components using a supramolecular nanoarchitectonics concept are discussed. The contents are classified in to three topics: i) chiral nanoarchitectonics of rather general molecular assemblies; ii) chiral nanoarchitectonics of metal–organic frameworks (MOFs); iii) chiral nanoarchitectonics in liquid crystals. MOF structures are based on nanoscopically well-defined coordinations, while mesoscopic orientations of liquid-crystalline phases are often flexibly altered. Discussion on the effects and features in these representative materials systems with totally different natures reveals the universal importance of supramolecular chiral nanoarchitectonics. Amplification of chiral molecular information from molecules to materials-level structures and the creation of chirality from achiral components upon temporal statistic fluctuations are universal, regardless of the nature of the assemblies. These features are thus surely advantageous characteristics for a wide range of applications.     

Seasonal landscape and spectral vegetation index dynamics in the Brazilian Cerrado: An analysis within the Large-Scale Biosphere-Atmosphere Experiment in Amazônia (LBA)

The Brazilian Cerrado biome comprises a vertically structured mosaic of grassland, shrubland, and woodland physiognomies with distinct phenology patterns. In this study, we investigated the utility of spectral vegetation indices in differentiating these physiognomies and in monitoring their seasonal dynamics. We obtained high spectral resolution reflectances, during the 2000 wet and dry seasons, over the major Cerrado types at Brasilia National Park (BNP) using the light aircraft-based Modland Quick Airborne Looks (MQUALS) package, consisting of a spectroradiometer and digital camera. Site-intensive biophysical and canopy structural measurements were made simultaneously at each of the Cerrado types including Cerrado grassland, shrub Cerrado, wooded Cerrado, Cerrado woodland, and gallery forest. We analyzed the spectral reflectance signatures, their first derivative analogs, and convolved spectral vegetation indices (VI) over all the Cerrado physiognomies. The high spectral resolution data were convolved to the MODIS, AVHRR, and ETM⁺ bandpasses and converted to the normalized difference vegetation index (NDVI) and the enhanced vegetation index (EVI) to simulate their respective sensors. Dry and wet season comparisons of the measured biophysical attributes were made with the reflectance and VI data for the different Cerrado physiognomies. We found that three major domains of Cerrado could be distinguished with the dry and wet season spectral signatures and vegetation indices. The EVI showed a higher sensitivity to seasonality than the NDVI; however, both indices displayed seasonal variations that were approximately one-half that found with the measured landscape green cover dynamics. Inter-sensor comparisons of seasonal dynamics, based on spectral bandpass properties, revealed the ETM⁺-simulated VIs had the best seasonal discrimination capability, followed by MODIS and AVHRR. Differences between sensor bandpass-derived VI values, however, varied with Cerrado type and between dry and wet seasons, indicating the need for inter-sensor VI translation equations for effective multi-sensor applications.     

Exponential stability of a mono-tubular heat exchanger equation with output feedback

This paper is concerned with stability analysis of a mono-tubular heat exchanger equation with static output feedback. The mono-tubular heat exchanger equation is exponentially stable when the input variable is identically zero. In this paper, it is shown that the C₀-semigroup generated by the closed-loop operator consisting of the mono-tubular heat exchanger equation and the output feedback law satisfies the spectrum determined growth assumption.     

Application of vibration milling for advanced wastewater treatment and excess sludge reduction

As a new sludge reduction technology with a phosphorus removal mechanism, a vibration milling technology that uses iron balls have been applied to the wastewater treatment process. Three anaerobic-aerobic cyclic activated sludge processes: one without sludge disintegration; one disintegrated sludge by ozonation; and the other disintegrated sludge with the vibrating ball mill were compared. Ozonation achieved the best sludge reduction performance, but milling had the best phosphorus removal. This is because iron was mixed into the wastewater treatment tank due to abrasion of the iron balls, leading to settling of iron phosphates. Thus, the simple means of using iron balls as the medium in a vibrating ball mill can achieve both a sludge reduction of half and excellent phosphorus removal. Material balances in the processes were calculated and it was found that carbon components in disintegrated sludge were more resistant to biological treatment than nitrogen.     

Reconstruction by weighted correlation for MRI with time-varying gradients

A general reconstruction algorithm for magnetic resonance imaging (MRI) with gradients having arbitrary time dependence is presented. This method estimates spin density by calculating the weighted correlation of the observed free induction decay signal and the phase modulation function at each point. A theorem which states that this method can be derived from the conditions of linearity and shift invariance is presented. Since these conditions are general, most of the MRI reconstruction algorithms proposed so far are equivalent to the weighted correlation method. An explicit representation of the point spread function (PSF) in the weighted correlation method is given. By using this representation, a method to control the PSF and the static field inhomogeneity effects is studied. A correction method for the inhomogeneity is proposed, and a limitation is clarified. Some simulation results are presented.