• Title/Summary/Keyword: Size and Number Concentration

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Evaluation on Flotation Efficiency of Bubble-floc Agglomerates and Operation Characteristics of Hydraulic Loading Rate Using Population Balance in DAF Process (DAF공정에서 개체군 수지를 이용한 기포-플록 응집체의 부상효율과 수리학적 부하율의 운전특성 평가)

  • Kwak, Dong-Heui
    • Journal of Korean Society of Water and Wastewater
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    • v.22 no.5
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    • pp.531-540
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    • 2008
  • The main advantage of dissolved air flotation (DAF) in water treatment process is the small dimension compared with conventional gravity sedimentation and it can be basically reduced by the separation zone performed with the short solid-liquid separation time. Fine bubbles make such a short time possible to carry out solid from liquid separation as a collector on the course of water treatment. Therefore, the dimension of separation zone in DAF process is practically determined by the rise velocity of the bubble-floc agglomerates, which is a floc attached with several bubbles. To improve flotation velocity and particle removal efficiency in DAF process, many researchers have tried to attach bubbles as much as possible to flocs. Therefore, the maximum number of attached bubble on a floc and the rise velocity of bubble-floc agglomerates considered as the most important factor to design the separation zone of flotation tank in DAF process was simulated based on the population balance theory. According to the simulation results of this study, the size and volume concentration of bubble influenced on the possible number of attached bubble on a floc. The agglomerates attached with smaller bubble was more sensitive to hydraulic loading rate in the separation zone of DAF process. For the design of a high rate DAF process applied over surface loading 40 m/hr. it is required a precise further study on the variation of bubble property and behavior including in terms of bubble size distribution.

The Concentration of Economic Power in Korea (경제력집중(經濟力集中) : 기본시각(基本視角)과 정책방향(政策方向))

  • Lee, Kyu-uck
    • KDI Journal of Economic Policy
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    • v.12 no.1
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    • pp.31-68
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    • 1990
  • The concentration of economic power takes the form of one or a few firms controlling a substantial portion of the economic resources and means in a certain economic area. At the same time, to the extent that these firms are owned by a few individuals, resource allocation can be manipulated by them rather than by the impersonal market mechanism. This will impair allocative efficiency, run counter to a decentralized market system and hamper the equitable distribution of wealth. Viewed from the historical evolution of Western capitalism in general, the concentration of economic power is a paradox in that it is a product of the free market system itself. The economic principle of natural discrimination works so that a few big firms preempt scarce resources and market opportunities. Prominent historical examples include trusts in America, Konzern in Germany and Zaibatsu in Japan in the early twentieth century. In other words, the concentration of economic power is the outcome as well as the antithesis of free competition. As long as judgment of the economic system at large depends upon the value systems of individuals, therefore, the issue of how to evaluate the concentration of economic power will inevitably be tinged with ideology. We have witnessed several different approaches to this problem such as communism, fascism and revised capitalism, and the last one seems to be the only surviving alternative. The concentration of economic power in Korea can be summarily represented by the "jaebol," namely, the conglomerate business group, the majority of whose member firms are monopolistic or oligopolistic in their respective markets and are owned by particular individuals. The jaebol has many dimensions in its size, but to sketch its magnitude, the share of the jaebol in the manufacturing sector reached 37.3% in shipment and 17.6% in employment as of 1989. The concentration of economic power can be ascribed to a number of causes. In the early stages of economic development, when the market system is immature, entrepreneurship must fill the gap inherent in the market in addition to performing its customary managerial function. Entrepreneurship of this sort is a scarce resource and becomes even more valuable as the target rate of economic growth gets higher. Entrepreneurship can neither be readily obtained in the market nor exhausted despite repeated use. Because of these peculiarities, economic power is bound to be concentrated in the hands of a few entrepreneurs and their business groups. It goes without saying, however, that the issue of whether the full exercise of money-making entrepreneurship is compatible with social mores is a different matter entirely. The rapidity of the concentration of economic power can also be traced to the diversification of business groups. The transplantation of advanced technology oriented toward mass production tends to saturate the small domestic market quite early and allows a firm to expand into new markets by making use of excess capacity and of monopoly profits. One of the reasons why the jaebol issue has become so acute in Korea lies in the nature of the government-business relationship. The Korean government has set economic development as its foremost national goal and, since then, has intervened profoundly in the private sector. Since most strategic industries promoted by the government required a huge capacity in technology, capital and manpower, big firms were favored over smaller firms, and the benefits of industrial policy naturally accrued to large business groups. The concentration of economic power which occured along the way was, therefore, not necessarily a product of the market system. At the same time, the concentration of ownership in business groups has been left largely intact as they have customarily met capital requirements by means of debt. The real advantage enjoyed by large business groups lies in synergy due to multiplant and multiproduct production. Even these effects, however, cannot always be considered socially optimal, as they offer disadvantages to other independent firms-for example, by foreclosing their markets. Moreover their fictitious or artificial advantages only aggravate the popular perception that most business groups have accumulated their wealth at the expense of the general public and under the behest of the government. Since Korea stands now at the threshold of establishing a full-fledged market economy along with political democracy, the phenomenon called the concentration of economic power must be correctly understood and the roles of business groups must be accordingly redefined. In doing so, we would do better to take a closer look at Japan which has experienced a demise of family-controlled Zaibatsu and a success with business groups(Kigyoshudan) whose ownership is dispersed among many firms and ultimately among the general public. The Japanese case cannot be an ideal model, but at least it gives us a good point of departure in that the issue of ownership is at the heart of the matter. In setting the basic direction of public policy aimed at controlling the concentration of economic power, one must harmonize efficiency and equity. Firm size in itself is not a problem, if it is dictated by efficiency considerations and if the firm behaves competitively in the market. As long as entrepreneurship is required for continuous economic growth and there is a discrepancy in entrepreneurial capacity among individuals, a concentration of economic power is bound to take place to some degree. Hence, the most effective way of reducing the inefficiency of business groups may be to impose competitive pressure on their activities. Concurrently, unless the concentration of ownership in business groups is scaled down, the seed of social discontent will still remain. Nevertheless, the dispersion of ownership requires a number of preconditions and, consequently, we must make consistent, long-term efforts on many fronts. We can suggest a long list of policy measures specifically designed to control the concentration of economic power. Whatever the policy may be, however, its intended effects will not be fully realized unless business groups abide by the moral code expected of socially responsible entrepreneurs. This is especially true, since the root of the problem of the excessive concentration of economic power lies outside the issue of efficiency, in problems concerning distribution, equity, and social justice.

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The effects of cutting parameters on the characteristics of mist generation in turning (선삭시 미스트 발생특성에 미치는 절삭변수의 영향)

  • Oh, Myung-Seok
    • Journal of the Korean Society of Industry Convergence
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    • v.7 no.1
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    • pp.55-62
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    • 2004
  • The presence of cutting fluid for cutting tool and workpiece leads a temperature decrease, and reduces tool wear and residual stress. Moreover, it disposes chips from cutting area, and reduces thermal distortion. However, in manufacturing, cutting fluid used in cutting process is undesirable for both human and environmental aspect. Also, it's not economic for cutting cost. This paper studied experimentally the effects of cutting parameters on the characteristics of mist generation in turning. The results of experiment are as follows: 1) The more severe cutting conditions the more mist generate, 2) The ratio of weight concentrations of cutting fluid nearly have no an effect on the amounts of mist generation 3) The size of SMD is not affected by cutting parameters.

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pH-Sensitivity Control of PEG-Poly(${\beta}$-amino ester) Block Copolymer Micelle

  • Hwang, Su-Jong;Kim, Min-Sang;Han, Jong-Kwon;Lee, Doo-Sung;Kim, Bong-Sup;Choi, Eun-Kyung;Park, Heon-Joo;Kim, Jin-Seok
    • Macromolecular Research
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    • v.15 no.5
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    • pp.437-442
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    • 2007
  • Poly(ethylene glycol) methyl ether (PEG)-poly(${\beta}$-amino ester) (PAE) block copolymers were synthesized using a Michael-type step polymerization, and the construction of pH-sensitive polymeric micelles (PM) investigated. The ${\beta}$-amino ester block of the block copolymers functioned as a pH-sensitive moiety as well as a hydrophobic block in relation to the ionization of PAE, while PEG acted as a hydrophilic block, regardless of ionization. The synthesized polymers were characterized using $^1H-NMR$, with their molecular weights measured using gel permeation chromatography. The $pK_b$ values of the pH-sensitive polymers were measured using a titration method. The pH-sensitivity and critical micelle concentration (CMC) of the block copolymers in PBS solution were estimated using fluorescence spectroscopy. The pH dependent micellization behaviors with various bisacrylate esters varied within a narrow pH range. The critical micelle concentration at pH 7.4 decreased from 0.032 to 0.004 mg/mL on increasing the number of methyl group in the bisacrylate from 4 to 10. Also, the particle size of the block copolymer micelles was determined using dynamic light scattering (DLS). The DLS results revealed the micelles had an average size below 100 nm. These pH-sensitive polymeric micelles may be good carriers for the delivery of an anticancer drug.

Surimi Preparation from mechanically Deboned Chicken Meat (기계발골 계육으로부터 닭고기 수리미의 제조)

  • 이성기
    • Korean Journal of Poultry Science
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    • v.26 no.2
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    • pp.85-95
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    • 1999
  • The mechanically deboned chicken meat(MDCM) has several limits in using for in using for in processed meat products as a main material because of poor color and textural properties, chance of microbial contamination and lipid oxidation. There has been a growing interest all over world in the application of MDCM to the surimi process. The surimi made from MDCM contains a high concentration of myofibrillar protein since this processing involves repeated washing processes with an aqueous solution in order to remove heme pigments, fat and other undesirable substances. The quality of the surimi made from MDCM is affected by various processing factors, such as kinds of wash solution, ion strength, washing cycle, temperature, pH changes, composition, part of muscle, particle size, and rigor state etc. A number of researchers havee investigated the effect of the various washing conditions on the properties of surimi gels. A fuller information of all the factors affecting surimi processing and gel formation by heat-induced gelation has not been known yet.

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A Numerical Analysis for Optimum Design of Multi-Stage Amplifier System of High Power Dye Laser (고출력 색소 레이저의 다단 증폭 시스템의 최적설계에 관한 수치해석)

  • 고도경
    • Korean Journal of Optics and Photonics
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    • v.4 no.3
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    • pp.281-288
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    • 1993
  • We have investigated the output characteristics and optimal conditions of a multi-stage amplifier system of Rhodamine 6G dye laser. The parameters in this simulation work were the beam diameter of the dye laser oscillator, the size of dye cell, the dye concentration, the number of stages in the amplifier system, and the pumping energy ratio of each amplifier at given pump energy. As a result, the output energy 10 mJ and the conversion efficiency of 40% in the two stage amplifier system were obtained with the pumping energy of 25mJ and the oscillator energy of 0.01 mJ.

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A Study on the Style Factors of Office Investment -An Analysis using Appraisal-based Returns- (오피스 투자의 스타일인자에 관한 연구 -평가기반 수익률을 기준으로-)

  • Min, Seonghun;Lee, Young Ho
    • Korea Real Estate Review
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    • v.24 no.1
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    • pp.53-62
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    • 2014
  • A test on the significance of style factors which were revealed to be significant in U.S. and U.K. literature is conducted in this study using appraisal-based returns of offices in Korea. Region, size (appraisal value), value-growth propensity (yield gain gap) and leasing conditions (the number of tenants, the length of average leased period and the proportion of key tenant) are included in the analysis model as style factors. The empirical result suggests that firstly core region and large size are significant but they increase risk as well as return contrary to general belief, secondly value propensity significantly decreases risk as well as return as it does in U.S. and U.K., finally the number of tenants among leasing conditions decreases risk as well as return but the length of average leased period and the proportion of key tenant are not significant.

A Theoretical Approach on the Turbulence Intensity of the Carrier Fluid in Two-phase Particle-laden Flows (고체입자가 부상된 이상유동에서 운반유체의 난류강도에 대한 해석적 접근)

  • Kim, Se-Yun;Lee, Chung-Gu;Lee, Kye-Bock
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.2037-2042
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    • 2003
  • The purpose of this research is to develop the model of turbulence modulation due to the presence of particles in various types of particle-laden flows. Available experimental data were surveyed and the dependence of turbulence modulation of carrier-phase on particle size, concentration and particle Reynolds number were examined. This study takes into account the effect of wake produced by particle, the drag between phases and the velocity gradient in the wake to estimate the production of turbulence. The model of turbulence modulation using the mixing length theory under the assumption of equilibrium flow is proposed. Numerical results show that the model is successful in predicting the characteristics of the particle-laden flow in various conditions both qualitatively and quantitatively.

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A Theoretical Approach on the Turbulence Intensity of the Carrier Fluid in Two-phase Particle-laden Flows (고체입자가 부상된 이상유동에서 운반유체의 난류강도에 대한 해석적 접근)

  • Kim, Se-Yun;Lee, Chung-Gu;Lee, Kye-Bock
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.27 no.6
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    • pp.813-820
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    • 2003
  • The purpose of this research is to develop the model of turbulence modulation due to the presence of particles in various types of particle-laden flows Available experimental data are surveyed and the dependence of turbulence modulation of carrier-phase on particle size, concentration and. particle Reynolds number are examined. This study takes into account the effect of wake produced by particle, the drag between phases and the velocity gradient in the wake to estimate the production of turbulence. The model of turbulence modulation using the mixing length theory under the assumption of equilibrium flow is proposed. Numerical results show that the model is successful in predicting the characteristics of the particle-laden in various flow conditions both qualitatively and quantitatively.

An Experiment on Particle Collection Characteristics of a Duct-type Wet Scrubber (덕트형 세정집진기의 입자포집 특성실험)

  • Yoo, Kyung-Hoon;Yeo, Kuk-Hyun;Son, Seung-Woo;Hwang, Kwang-Ho;Jung, Jin-Won;Kim, Yoon-Shin
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.1795-1800
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    • 2004
  • DOS and NaCl aerosol particles with geometric mean diameter of $0.1{\sim}3.0{\mu}m$ geometric standard deviation of $1.1{\sim}1.8$ and total number concentration of $450{\sim}400$ $particles/cm^3$ were used to determine collection efficiencies of a duct-type wet scrubber with respect to particle size. The tested operating variables included air velocity and water injection rate. It was shown from the experimental results that the collection efficiencies increased with increasing water injection rate and decreasing air velocity. It was also seen that the collection efficiency of the Duct-type wet scrubber is mainly governed by the mechanism of inertial impaction.

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