Physicochemical properties of high-molecular-weight poly(α,β-malic acid) synthesized by direct polycondensation

Summary We studied high-molecular-weight α,β-PMA synthesized by polycondensation in order to find possible applications for biomaterials. Its solubility in different solvents, its hydrolysis and its acidity were also examined. The α,β-PMA molecular weight increased markedly up to 20 h and then decreased showing that the molecular weights for synthesized α,β-PMA depends on the reaction time. We prepared high-yield α,β-PMA with a molecular weight of 3600 by direct polycondensation using tin(II) chloride as a catalyst at 130°C for 20 hours and concluded that our method is suitable to synthesize higher molecular weight compounds of α,β-PMA. Received: 20 December 2002/Revised version: 18 February 2003/ Accepted: 22 February 2003 Correspondence to Tetsuto Kajiyama     

An approximation to the steady state probabilities of a multi-echelon repair model for a series system

A multi-echelon repair system is often employed for the repair of a complex device. There have been many papers on a multi-echelon repair system. Most of them, however, treat the case that i) the repair system has one central repair station(two-echelon repair model), ii)the device is a single item system. The purpose of this paper is to extend a two-echelon repair model with single item systems to a multi-echelon repair model with multi-item systems. This extension makes the repair model more realistic. Then an approximation method to obtain the steady state probabilities of the repair model is presented. This method obtains the probabilities rapidly and accurately. The reliability measure considered in this model is the system availability. It is obtained as a byproduct of the steady state probabilities.     

Transmission limitations due to self-phase modulation in opticalPSK heterodyne detection systems employing chromatic dispersionequalization

Even if the amplitude of a phase-modulated optical signal is constant before transmission, amplitude modulation is caused by fiber chromatic dispersion. As a result, self-phase modulation (SPM) is induced. In optical heterodyne detection, SPM cannot be compensated for by the delay equalizer (electrical domain) used to compensate fiber chromatic dispersion. However, the transmission distance limitation of multi-repeatered coherent transmission systems has not been investigated in the presence of SPM. This paper theoretically and experimentally investigates the transmission distance achievable with a phase-shift-keying (PSK) heterodyne detection system employing in-line optical amplifiers and delay equalization. The calculated results show that equalization is effective when γP₀/2B²|β₂|<10 in the normal dispersion regime, and γP₀/2B²|β ₂|<15 in the anomalous dispersion regime. Furthermore, the increase in transmission distance achieved by using equalization is experimentally shown in an 8 Gb/s PSK heterodyne transmission experiment using a conventional single-mode (SM) fiber and in-line fiber amplifiers     

Influence of intensity modulation produced by LD direct modulationon transmission characteristics of CPFSK differential detection system

Transmission characteristics of a CPFSK differential detection system with LD direct modulation are studied by computer simulation. Simulation results show that the optimum wavelength for LD direct modulation CPFSK transmission shifts to a wavelength longer than zero dispersion wavelength because of the phase difference between the intensity and frequency modulation components. A precise investigation of the dependence of optimum total dispersion on several parameters reveals the essential role of the phase difference between intensity and frequency modulation induced by LD direct modulation. The transmission distance allowing a 1-dB power penalty at 10 Gb/s is 117 km for a wavelength 30 nm shorter than the zero dispersion wavelength, while the distance is 183 km for a wavelength 30 nm longer. This indicates that the zero dispersion wavelength shift is 11 nm for 100-km transmission     

Leaching characteristics of boron and selenium for various coal fly ashes

The leaching characteristics of B and Se for coal fly ash (CFA) were examined. Twenty-one CFA samples were subjected to a leaching test, in which CFA was shaken with pure water in a liquid to solid ratio (L/S) of 100 for 24 h at room temperature. The correlation between the leaching amount and the concentration of element in CFA was investigated. The leaching amounts of B, Ca, S, and Se were essentially dependent upon their concentrations in CFA. As the degree of % leaching was higher, the leaching amount was more dependent upon the concentration. Also, the leaching test was performed under constant pH conditions. The leaching of Se tended to increase as the pH in the aqueous phase was raised. For CFA samples, which gave large degree of Ca leaching amount, the leaching of B and Se was decreased especially under high alkaline conditions. The effects of pH and the presence of leached Ca ion in the aqueous phase upon the leaching behavior were discussed.     

Removal of mercury from coal by mild pyrolysis and leaching behavior of mercury

Various types of coals were subjected to the pyrolysis at 300 and 400 °C (mild pyrolysis), and the removal of Hg from coal was determined. The removal efficiency of Hg greatly varied with coal type from 20 to 80%. The removal efficiency was dependent neither on the specific surface area of coal nor on the particle size of coal. The leaching of Hg from coal was tested using sulfur-containing chelating agents such as 3-mercaptopropionic acid (MPA). The Hg leaching efficiency also varied greatly with coal type. There was a good correlation between the degree of %Hg leaching in the MPA leaching and that of %Hg removal in the mild pyrolysis.     

Titanium powder production by TiCl4 gas injection into magnesium through molten salts

A process to produce titanium powder continuously is proposed and its applicability is examined experimentally. The method is based on the chemical reaction in the conventional Kroll reduction process; however, TiCl₄ gas is injected into molten salt on which a molten magnesium layer is floated as the reductant. Bubbles of gaseous TiCl₄ can be reacted at the lower surface of the liquid Mg layer, while TiCl₄ gas reacts on the upper surface in the Kroll process. The fine Ti particles produced in this study were well separated from magnesium and could be recovered from the bottom of the molten salts. The particles were small and fine enough for use in powder metallurgy, while congregated lumps of about 20 μm in size are obtained by the Kroll process. The composition of molten salts and an operation temperature above 1073 K did not affect the morphology of the Ti particles, if suitable material for the reaction vessel was chosen.     

Range image smoothing and completion utilizing laser intensity

In this paper, we propose new denoising techniques for a deteriorated range image taken by a laser scanner. Laser scanner acquires a range value from the scanner to the target by measuring the round-trip time of the emitted laser pulse. At the same time, they can obtain the strength of the reflected light as a side product of the range value. Focusing on the laser intensity, we propose two denoising techniques for a deteriorated range image utilizing the intensity image: smoothing by extended bilateral filter, and completion by belief propagation. The extended bilateral filter makes use of laser intensity in addition to the spatial and range information in order that we can smooth a range image corrupted by noises while the geometric features such as jump and roof edges are preserved. The range image completion technique with belief propagation restores a deteriorated range image using the adjacent range values and the corresponding intensity values simultaneously. We conduct simulations and experiments using synthesized images and actual range images taken by a laser scanner and verify that the proposed techniques suppress noise while preserving jump and roof edges and repair deteriorated range images.