• BMB Reports
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• 제37권4호
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• pp.394-401
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• 2004

The purpose of this paper is to suggest that the prominence of Haldane's explanation for enzyme catalysis significantly hinders investigations in understanding enzyme structure and function. This occurs despite the existence of much evidence that the Haldane model cannot embrace. Some of the evidence, in fact, disproves the model. A brief history of the explanation of enzyme catalysis is presented. The currently accepted view of enzyme catalysis -- the Haldane model -- is examined in terms of its strengths and weaknesses. An alternate model for general enzyme catalysis (the Shifting Specificity model) is reintroduced and an assessment of why it may be superior to the Haldane model is presented. Finally, it is proposed that a re-examination of many current aspects in enzyme structure and function (specifically, protein folding, x-ray and NMR structure analyses, enzyme stability curves, enzyme mimics, catalytic antibodies, and the loose packing of enzyme folded forms) in terms of the new model may offer crucial insights.

• 한국결정학회지
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• 제11권1호
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• pp.22-27
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• 2000

The structure of cis-(malonato)[(4R,5R)-4,5-bis(aminomethyl)-2-isopropyl-1,3-dioxolane]platinum(II) with a potent anticancer activity has been determined by the X-ray crystallographic method. Crystal data are as follows: Pt(C/sub 11/H/sub 20/N₂O/sub 6/), M/sub 4/=471.38, monoclinic, P2₁, a=7.112(1), b=33.615(3), c=7.135(1)Å, β=116.80(1)°, V=1522.6(3)Å, and Z=4. The two independent molecules with very similar structures are approximately related by pseudo two-fold screw axis symmetry, which makes the monolinic cell look like the orthorhombic cell with one molecule in the asymmetric unit and space group C222₁. The crystal packing mode is similar to that of the analogue with the dimethyl substituents instead of the isopropyl group. The Pt atom is coordinate to two O and two N atoms in a square planar structure. The six-membered chelate ring in the leaving ligand assumes a conformation intermediate between the half chair and the boat forms. The seven-membered ring in the carrier ligand assumes a twist-chair conformation and the oxolane ring assumes an envelope conformation. Crystal packing consists of the extensive hydrogen-bonding network in the two-dimensional molecular layers and weak van der Waals interactions between these layers.

• Nuclear Engineering and Technology
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• 제53권7호
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• pp.2174-2183
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• 2021

Helium cooled solid breeder blanket as an important blanket candidate of the Tokamak fusion reactor uses ceramic pebble bed for tritium breeding. Considering the poor effective thermal conductivity of the ceramic breeder pebble bed, thin structure of tritium breeder pebble bed is usually adopted in the blanket design. The container wall has a great influence on the thin pebble bed packing structure, especially for the assembly of mono-sized particles, and thin pebble bed will appear anisotropic effective thermal conductivity phenomenon. In this paper, thin ceramic pebble beds composed of 1 mm diameter Li₄SiO₄ particles are generated by the EDEM 2.7. The effective thermal conductivity of different thickness pebble beds in the three-dimensional directions are analyzed by three-dimensional thermal network method. It is observed that thin Li₄SiO₄ pebble bed showing anisotropic effective thermal conductivity under the practical design size. Normally, the effective thermal conductivity along the bed vertical direction is higher than the horizontal direction due to the gravity effect. As the thickness increases from 10 mm to 40 mm, the effective thermal conductivity of the pebble bed gradually increases.

• 한국통신학회논문지
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• 제37C권11호
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• pp.1138-1147
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• 2012

본 논문에서는 차기 군 위성통신망 체계에서 서로 다른 통신 능력을 갖는 이기종 단말을 동일 중계기 대역폭내에서 효과적으로 통합하여 운용하기 위해 전력제어를 적용한 MF-TDMA 자원할당기법을 제안한다. 제안하는 알고리즘은 burst 크기 결정 단계와 burst 구조 결정단계의 2단계로 수행된다. 먼저 burst 크기 결정 단계에서는 각 단말의 채널 상태를 기반으로 링크 버짓을 분석하여 적용 가능한 ACM 레벨과 이에 따른 burst 크기를 결정한다. 다음으로 burst 구조 결정단계에서는 앞서 도출된 각 단말 별 burst 크기를 기반으로 시간-주파수 축 상에서 할당 가능한 burst 구조를 도출하고 각 구조 별 가용 Power spectral density(PSD) 구간을 계산한다. 이기종 단말을 단일 중계기로 통합하기 위해 각 burst의 가용 PSD 구간 내에서 전력제어를 수행하며, 동일 PSD 구간을 갖는 burst를 그룹화하여 MF-TDMA 프레임 내에 할당한다. 추가적으로 할당되지 못하고 남는 슬롯에 대한 자원할당 효율을 향상시키기 위해 설정된 PSD 구간 내에서 ACM 레벨을 조절하여 빈 슬롯을 활용할 수 있는 방안을 적용하였다. 제안하는 알고리즘은 주파수 사용효율, 슬롯할당 거부율 및 burst packing 효율 측면에서 기존 방식과 비교하였으며, 기존 방식에 비해 우수한 성능을 제공함을 확인하였다.

• Computers and Concrete
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• 제3권5호
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• pp.301-312
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• 2006

Experimental research revealed that the spatial dispersion of aggregate grains exerts pronounced influences on the mechanical and durability properties of concrete. Therefore, insight into this phenomenon is of paramount importance. Experimental approaches do not provide direct access to three-dimensional spacing information in concrete, however. Contrarily, simulation approaches are mostly deficient in generating packing systems of aggregate grains with sufficient density. This paper therefore employs a dynamic simulation system (with the acronym SPACE), allowing the generation of dense random packing of grains, representative for concrete aggregates. This paper studies by means of SPACE packing structures of aggregates with a Fuller type of size distribution, generally accepted as a suitable approximation for actual aggregate systems. Mean free spacing $\bar{\lambda}$, mean nearest neighbour distance (NND) between grain centres $\bar{\Delta}_3$, and the probability density function of ${\Delta}_3$ are used to characterize the spatial dispersion of aggregate grains in model concretes. Influences on these spacing parameters are studied of volume fraction and the size range of aggregate grains. The values of these descriptors are estimated by means of stereological tools, whereupon the calculation results are compared with measurements. The simulation results indicate that the size range of aggregate grains has a more pronounced influence on the spacing parameters than exerted by the volume fraction of aggregate. At relatively high volume density of aggregates, as met in the present cases, theoretical and experimental values are found quite similar. The mean free spacing is known to be independent of the actual dispersion characteristics (Underwood 1968); it is a structural parameter governed by material composition. Moreover, scatter of the mean free spacing among the serial sections of the model concrete in the simulation study is relatively small, demonstrating the sample size to be representative for composition homogeneity of aggregate grains. The distribution of ${\Delta}_3$ observed in this study is markedly skew, indicating a concentration of relatively small values of ${\Delta}_3$. The estimate of the size of the representative volume element (RVE) for configuration homogeneity based on NND exceeds by one order of magnitude the estimate for structure-insensitive properties. This is in accordance with predictions of Brown (1965) for composition and configuration homogeneity (corresponding to structure-insensitive and structure-sensitive properties) of conglomerates.

• 공업화학
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• 제28권2호
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• pp.177-185
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• 2017

본 연구에서는 스테아르산(SA), 올레산(OA), 리놀레산(LA) 등의 지방산이 지질 소포체 막과의 상호 작용에 미치는 영향에 관하여 살펴보았다. 이를 위하여 지방산 종류 및 농도 변화에 따른 리포좀 평균 입자 크기 및 제타 전위, 리포좀 막의 deformability, fluorescence anisotropy ratio 등을 측정하고 TEM 관찰을 통하여 지방산 첨가가 리포좀 막의 유동성 변화에 미치는 역할에 관하여 살펴보았다. 기본적으로 SA, OA, LA 등의 지방산 첨가는 동일한 경향을 나타내었다. 즉, 지방산을 첨가함에 따라 리포좀이 보다 치밀한 패킹을 갖게 되어서 리포좀의 크기는 감소하고 제타 전위 값은 증가하였으나, 지방산의 과도한 첨가는 리포좀에서 다형(polymorphic) 구조를 가지는 지질 입자 응집체로의 전이를 일으켰다. SA, OA 및 LA 지방산 시스템에서의 최소 리포좀 크기와 가장 치밀한 리포좀 패킹은 레시틴 대비 지방산의 몰 비율이 각각 0.70, 0.50, 0.25인 조건에서 관찰되었으며, 리포좀 막의 deformability와 fluorescence anisotropy ratio 측정에 의한 리포좀 막의 유동성 측정 결과는 TEM 및 입자 크기 측정 결과와 일치함을 알 수 있었다.

• 통합자연과학논문집
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• 제9권4호
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• pp.255-260
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• 2016

The crystal structure of the saliciline derivatives N,N'-bis(3-chloro-2-methylsalicylidene)-1,4-butanediamine ($C_{20}H_{22}Cl_2N_2O_2$) has been determined from single crystal X-ray diffraction data. In the title compound crystallizes in the triclinic space group $P{\bar{i}}$ with unit cell dimension $a=4.6085(3){\AA}$, $b=5.9747(3){\AA}$ and $c=5.9747(3){\AA}$ [${\alpha}=83.889(4)^{\circ}$, ${\beta}=86.744(5)^{\circ}$ and ${\gamma}=82.085(5)^{\circ}$]. The title compound is essentially planar conformation. The compound lies across a crystallographic inversion centre and adopts E configurations with respect to the C-N bonds. The crystal packing of the molecules of compound is stabilized through weak O-H...N intra molecular interactions

• 통합자연과학논문집
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• 제9권4호
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• pp.261-267
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• 2016

The crystal structure of the saliciline derivatives 4-chloro-2{[(2-hydroxy-5-methylphenyl)amino]methyl}5-methylphenol ($C_{15}H_{15}ClNO_2$) has been determined from single crystal X-ray diffraction data. In the title compound crystallizes in the monoclinic space group P21/c with unit cell dimension $a=11.5241(2){\AA}$, $b=8.733(2){\AA}$ and $c=13.649(2){\AA}$ [${\alpha}=90^{\circ}$, ${\beta}=130.876(2)^{\circ}$ and ${\gamma}=90^{\circ}$]. the title compound are essentially planar conformation. The compound lies across a crystallographic inversion centre and adopts E configurations with respect to the C-N bonds. The crystal packing of the molecules of compound is stabilized through weak O-H...O inter molecular interactions.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 봄 학술발표회 논문집
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• pp.217-222
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• 2000

A large Pc structure building is system that consisted of bearing wall and slab joint. It has general structure stability from unity thar each members tied at joint. The strength of mortar that packing in joint among panels is important to internal force in entire building system. Do, if we could get early strength estimation with microwave. It would bring good construction planning, reduce construction time, and judge building stability and so on. The purpose of this study is to develop early estimation method for making better quality control and constructing good PC panel structure. The results of this study were as follows :1) With sealed molds, reduced moisture volatilization to more than 60% and enlarged 30% accelerated compressive strength than before one. 2) To get more accelerated strength, we should control maximum temperature difference to $30^{\circ}C$ downward 3)Interrelation with 7-day and 28-day strength were 0.831,0.902, and it is above than before one

• 펄프종이기술
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• 제32권3호
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• pp.32-38
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• 2000

This study was carried out to determine the effect of the type of plastic pigment on the coat-ing structure and printability of coated paper. Three kinds of plastic pigments(solid-bead type binder type and hollow type) were used for hti purpose. IN this research it was observed that particle shape and structure of plastic pigment had influenced the rheology of coating color the state of packing and the properties of coated paper. Inorganic pigments used in this research were platelike kaolin clay and rhombic calcium carbonate. Three kinds of plastic pigments were blended with two inorganic pigments respec-tively. The combination of pigments were carried out(1) to determined the effect of particle structure of plastic pigment on the state of dispersion of coating color(2) to observe the effect of calendering temperature on the property of coated paper prepared with different plastic pigments. The data indicated that binder and hollow type plastic pigment gave the best results in improving the properties of coated paper such as paper gloss opacity and air pet-meability.