• Vacuum Magazine
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• v.5 no.1
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• pp.13-17
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• 2018

Phase transition is not unique to solid state systems or homogeneous molecular systems but it is also observed in highly heterogeneous biological systems. Phase transition and phase separation in cells are recently being found to be central to many biological functions by temporarily and locally controlling the storage and exchange of certain proteins and RNAs. There are also clues suggesting them to be playing pivotal roles in the spatial organization of chromosomes into topological domains and its time-dependent control. Here we introduce early efforts to explain at the molecular level how the spatiotemporal organization of chromosomes are programmed and modulated by the sequence and chemical modifications of the DNA. Continuing works may provide a physical framework to understand the molecular level control of chromosome structure and dynamics that determine the epigenetic state and the fate of the cells.

• Proceedings of the Membrane Society of Korea Conference
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• 1997.10a
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• pp.27-30
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• 1997

1. Introduction : Molecular diffusion of small molecules in polymers plays an important role in many areas where polymers are acting as barriers, and in separation processes, such as selective diffusion. Different applications of polymers have different requirements on their transport properties. Therefore, reliable predictions of diffusion coefficients for small molecules in polymeric materials could be a useful tool to design appropriate materials. For many years, the theories based on free-volume concepts have been widely used to correlate and predict diffusion behavior in polymer/solvent systems. In the theory derived by Vrentas and Duda, the empty space between molecules that is available for molecular transport, referred to as hole free-volume, is being redistributed. Molecular transport will occur only when a free-volume of sufficient size appears adjacent to a molecule and the molecule has enough energy to jump into this void. The diffusive jump is considered complete when the void left behind is closed before the molecule returns to its original position. In this paper, the Vrentas-Duda free-volume theory is presented and the methods to estimate free-volume parameters for predicting polymer/ solvent diffusion coefficients are described in detail.

• The Plant Pathology Journal
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• v.26 no.3
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• pp.260-263
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• 2010

Scald, caused by Rhynchosporium secalis has been the major yield-reducing factor for barley production during the last decade. In this study, pathogenic groups of R. secalis were identified to obtain a global picture of the assembly of isolates involved in Syrian populations which is essential for the development of scald-resistant barley cultivars. To identify a number of pathogenic groups, 49 isolates collected over ten years from major barley growing areas in Syria were evaluated on five differential barley genotypes. Genotypes presented a continuous range of response from highly susceptible to moderately resistant, but none were immune to the disease. A cluster analysis placed isolates in six distinct differential pathogenic groups. Mean disease rating of 39.24% was the separation point between avirulent and virulent reactions. Isolate Rs46 exhibited distinct differential virulence patterns associated with high frequency across all genotypes. Hence, the data presented here provides crucial information for future selection of isolates to develop durable barley scald resistance.

• Korean Membrane Journal
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• v.6 no.1
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• pp.30-36
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• 2004

The gas permeation performance of commercially available polyetherimide (Ultem$\^$/) is simulated by means of molecular dynamics methods. By the observation of trajectory, long distance hopping of gas molecules is needed to transverse from top to bottom of membrane. Two possibilities mechanism of diffusion phenomena through glassy polymers can be issued. Diffusion coefficients were calculated by Einstein relation equation. In solubility simulation, the value of the constants C'$\_$H/ and b for O$_2$ at 300 K were calculated. The diffusion and solubility coefficient of He for PEI were simulated in this simulation work. the permeability coefficient is 9.88 Barrer. This value is closed to experimental value of 9.4 Barrer.

• Macromolecular Research
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• v.16 no.7
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• pp.590-595
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• 2008

The pressure driven membrane process has been a breakthrough in the removal of pollutants from drinking water. These experiments examined the removal of chlorophenol compounds from water using low pressure membranes. The removal performance of the membranes was based primarily on size exclusion. Apart from size exclusion, the polarity and pKa of the compounds also influences the membrane performance. The molecular size and dipole moments of the respective molecules were calculated using a quantum chemical method. The rejection of pollutants also followed the same trend as salt rejection by the membranes.

• Macromolecular Research
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• v.11 no.1
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• pp.53-61
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• 2003

A molecular-thermodynamic model is developed for the salt-induced protein precipitation. The protein molecules interact through four intermolecular potentials. An equation of state is derived based on the statistical mechanical perturbation theory with the modified Chiew's equation for the fluid phase, Young's equation for the solid phase as the reference system and a perturbation based on the protein-protein effective two body potential. The equation of state provides an expression for the chemical potential of the protein. In a single protein system, the phase separation is represented by fluid-fluid equilibria. The precipitation behaviors are simulated with the partition coefficient at various salt concentrations and degree of pre-aggregation effect for the protein particles. In a binary protein system, we regard the system as a fluid-solid phase equilibrium. At equilibrium, we compute the reduced osmotic pressure-composition diagram in the diverse protein size difference and salt concentrations.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.5
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• pp.111-116
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• 2018

Thermal fusion bonding is a method to enclose open microchannels fabricated on polymer chips for use in lab-on-a-chip (LOC) devices. Polymethyl methacrylate (PMMA) is utilized in various biomedical-microelectromechanical systems (bio-MEMS) applications, such as medical diagnostic kits, biosensors, and drug delivery systems. These applications utilize PMMAs biochemical compatibility, optical transparency, and mold characteristics. In this paper, we elucidate both the conformational entanglement of PMMA molecules at the contact interfacial regime, and the qualitative nature of the thermal fusion bonding phenomena through systematic molecular dynamics simulations.

• Analytical Science and Technology
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• v.20 no.3
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• pp.255-260
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• 2007

A new method for the simultaneous determination of low molecular weight amines and quaternary ammonium ions based on the separation by IC with a suppressor and the detection by MS with ESI has been developed. The method has been applied to the analysis of a mixture containing tetramethylammonium ion, tetraethylammonium ion, tetrapropylammonium ion, triethanolamine, trimethylamine and triethylamine. The constituents were separated by isocratic elution using an IonPac CS17 column, a cation-exchange column, and detected by conductivity and mass spectrometry. The newly developed method for the six components demonstrated that the repeatability in terms of relative standard deviation for three measurements was in the range of 0.1-0.5 %. The detection limits were between 0.2 and $0.9{\mu}g/mL$ by the IC/ESI-MS.

• Polymer(Korea)
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• v.25 no.1
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• pp.78-89
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• 2001

Morphological changes of unsaturated polyester/polyvinylacetate semi-IPN were studied while the phase separation and the cure reaction occurred in a competing fashion. The light scattering and thermal analysis techniques were used to investigate the phase separation rates and mechanical properties resultantly induced by molecular diffusion of thermoplastic polymer during the curing process of thermosetting polymer. The reaction activation energy was calculated by using Flynn-Wall method and the semi-IPN structure exhibited various phase-separation morphological characteristics. When PVAc composition was 10 wt%, the phase separation was not observed during the curing reaction, but the phase separation occurred in a similar fashion to nucleation and growth(NG) mechanism at room temperature. On the other hand, when PVAc composition was over 11.65 wt%, the phase separation was generated in the middle of the curing process. Consequently, the phase separation seemed to influence the curing reaction rate, which was also supported by the changing activation energy with conversion and PVAc composition. Finally, the total scattered intensity was measured at various temperature, and subsequently the diffusion rates of phase separation R(${\beta}m$) were evaluated.

• Korean Journal of Food Science and Technology
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• v.14 no.2
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• pp.174-178
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• 1982

Various separation methods such as solvent extraction, chemical treatment and molecular distillation were tested for the separation of tocopherols and sterols from soy oil scum. The end products of these methods were tocopherol concentrates and sterol crystals. In the solvent extraction, purity and yield of tocopherols were 21.2% and 28.3%, and those of sterols were 69.2% and 2.6%. In the chemical treatment, purity and yield of tocopherols were 11.8% and 76.4% and those of sterols were 85.1% and 34.3% respectively. In the molecular distillation, purity and yield of tocopherols were 45.0% and 68.0%, and those of sterols were 49.3% and 57.0% respectively. The end products from the methods were characterized by HPLC. Based on the results of this study, the molecular distillation method was found to be more efficient than any other method tested.