1,721,274 research outputs found
Removal of organic acid salts from simulated fermentation broth containing succinate by nanofiltration
No full textIn microbial cultures for the production of sodium succinate, often monovalent salts of sodium formate, sodium acetate and/or sodium lactate are produced as major by-products. In this study, nanofiltration (NF) was employed for the recovery of sodium succinate and the removal of by-products from simulated fermentation broth. In a series of preliminary experiments with synthetic single-salt solutions, five nanofiltration membranes were evaluated, and NF45 and ESNA1 membranes with a relatively low rejection to monovalent anions were selected for the subsequent experiments. The rejection of each salt at various fluxes was measured for single, binary, ternary and quaternary organic acid salts solutions containing succinate, formate, acetate, and/or lactate, simulating a real fermentation broth. Succinate rejection in multi-salt solutions was observed much higher than that in its single-salt solution, which was quite opposite to the cases of the monovalent acid salts involved. This could be well described by the facilitated transport of the monovalent anions due to Donnan effect in the presence of succinate, a divalent anion. Finally, nanofitration of a quaternary salts solution in a diafiltration mode was carried out for 36 h. With time, the rejection of succinate increased and the rejection of the by-products drastically decreased as the concentration ratio of succinate to by-products increased. From the extrapolation using a diafiltration model developed in this study, it was expected that almost complete removal of by-products was possible with no significant loss of succinate. (C) 2004 Elsevier B.V. All rights reserved
Effect of pH and lattice distortion on the luminescence of (Y, Gd) BO3 : Eu3+ phosphor prepared by the coprecipitation method
No full text(Y, Gd) BO3: Eu3+ phosphor was produced by a coprecipitation method. The morphology of the particles could be controlled by adjustment of the pH value and the heat-treatment method used. The pH value of the coprecipitation solution was a critical parameter for the luminescent properties of the phosphor. The improved chromaticity in smaller or disk-like particles was attributed to higher lattice distortion, which gives rise to the loss of the inversion symmetry at the site of the Eu3+ ion, thus enhancing the D-5(0) -> F-7(2) transition. (c) 2006 The Electrochemical Society.N
Scheduling algorithm for partially parallel architecture of ldpc decoder by matrix permutation
No full textA CAC scheme based on real-time cell loss estimation for ATM multiplexers
No full textFor the superposition of ON/OFF sources, we propose a real-time computable two-state Markov modulated Poisson process [MMPP(2)] modeling method characterizing the aggregate cell arrival rate and the variance-time curve for cell counts. Numerical examples show that the proposed method yields a good estimation of cell loss ratio (CLR) in asynchronous transfer mode (ATM) multiplexers, Then, we propose an approximation method for calculating the workload for the MMPP(2)/D/1 system. By considering the workload as an upper bound of CLR of ATM multiplexers, He propose a connection admission control (CAC) algorithm utilizing peak cell rate, sustainable cell rate, and maximum burst size as user traffic descriptors. Using the proposed CAC algorithm, an acceptance decision is made with computational complexities of less than 3000 floating point operations. It is also observed from numerical evaluations that the proposed CAC algorithm yields a high multiplexing gain, compared with other methods in the literature
Characterization and Modeling of Variable Bit Rate Video Traffic Sources as Autoregressive Markov Vector Processes
No full textLoosely coupled memory-based decoding architecture for low density parity check codes
No full textParallel decoding is required for low density parity check (LDPC) codes to achieve high decoding throughput, but it suffers from a large set of registers and complex interconnections due to randomly located 1's in the sparse parity check matrix. This paper proposes a new LDPC decoding architecture to reduce registers and alleviate complex interconnections. To reduce the number of messages to be exchanged among processing units (PUs), two data flows that can be loosely coupled are developed by allowing duplicated operations. In addition, intermediate values are grouped and stored into local storages each of which is accessed by only one PU. In order to save area, local storages are implemented using memories instead of registers. A partially parallel architecture is proposed to promote the memory usage and an efficient algorithm that schedules the processing order of the partially parallel architecture is also proposed to reduce the overall processing time by overlapping operations. To verify the proposed architecture, a 1024 bit rate-1/2 LDPC decoder is implemented using a 0.18-mu m CMOS process. The decoder runs correctly at the frequency of 200 MHz, which enables almost 1 Gbps decoding throughput. Since the proposed decoder occupies an area of 10.08 mm(2), it is less than one fifth of area compared to the previous architecture.This work
was supported in part by the Institute of Information Technology Assessment
through the ITRC, by the Korea Science and Engineering Foundation through
MICROS center and by IC Design Education Center
Two-State MMPP Modeling of the ATM Multiplexed Traffic Streams Based on the Interarrival Time Processes
No full textThermo-elasto-plastic finite element analysis of quenching process of carbon steel
No full textQuenching is one of manufacturing processes used for improving mechanical properties such as strength, hardness, and wear/fatigue resistances of the mechanical components for automobiles, aircrafts and machines subjected to high load and impact. Due to temperature variation and phase transformation during the quenching process, dimensional change of the steel specimen takes place. Thus, a three-dimensional thermo-elastic-plastic finite element (FE) program was developed and used for predicting the dimensional change and stress distribution according to carbon content and variations of the temperature and volume fraction of each phase generated within the steel specimen. In order to validate the simulation pro-ram developed in this study, FE analyses of quenching of the cylindrical eutectoid and hypoeutectoid steels were carried out. It was found out that the numerically obtained values of temperature and stress distributions were in good agreement with experimental results available in the literature. It was found out from this study that the three-dimensional thermo-elastic-plastic FE program developed can be useful in investigating the processing parameters for the quenching process. (c) 2007 Elsevier B.V. All rights reserved.The authors wish to thank for the grant of National Research
Laboratory program of the Ministry of Science and Technology
through the Korea Science and Engineering Foundation
Natural convection effect on the droplet ignition in high pressure condition
No full textA simulation of the droplet combustion in the high-pressure environment is very important in understanding the fundamental phenomena of liquid rocket, gas turbine and diesel engine combustion. Therefore, a more reliable ignition model of a droplet under high pressure condition is highly desirable in developing a useful tool for design. In this paper, the ignition model of the n-heptane droplet is suggested for high pressure environment and solved for the ignition delay. Its variations with the change in the ambient pressure and temperature are discussed for the cases with/without gravity so that the natural convection effects on the droplet ignition delay time are also examined. The Redlich-Kwong equation of state is used for calculating the phase equilibrium at the droplet surface under high pressure. The natural convection effects are considered by introducing so-called the time scale correction method. The results show that the logarithmic ignition delay time linearly decreases with the inverse of the ambient temperature, and its decreasing slope is independent of the ambient pressure. Thereby, the overall activation energy is found not to be affected by the pressure variation. As the pressure increases, the ignition delay time gets shorter since the droplet vaporization rate is enhanced. But, at a higher ambient pressure, the reduction rate in the ignition delay time becomes smaller. The natural convection effect is also found to make the ignition delay time shorter due to the improved heat feedback to the droplet.This work was supported by a grant from the Ministry of Science and Technology of Korea through KAIST research fund
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