Biomedical subjects

HJ Kim

Publications and source records attributed to HJ Kim.

At least 19 recordsLinked to original sources

PubMed2000

A Hyperbranched Poly(ethyleneimine) Grown on Surfaces.

Aminosilylated substrate was treated with aziridines in order to prepare hyperbranched polymers on solid supports such as silicon wafer and fused silica. It is observed that the primary amine on the substrate is good enough to initiate the ring-opening polymerization of aziridine. Measuring the thickness of the film and the absolute density of the primary amine functionality shows that a very highly branched poly(ethyleneimine) is formed upon the reaction. The surface density of the primary amine functional group (-NH(2)) on the very top surface increased dramatically (from 3.5 amines/nm(2) to 66 amines/nm(2)). A protected aziridine, benzyl 1-aziridinecarboxylate, was employed for the stepwise growth of the film. Two step-processes, chain growth and deprotection, were successful in growing the molecular layer, and a linear chain was formed without branching. Copyright 2000 Academic Press.

Journal Article↗

PubMed2000

Synchronization in a system of globally coupled oscillators with time delay

We study the synchronization phenomena in a system of globally coupled oscillators with time delay in the coupling. The self-consistency equations for the order parameter are derived, which depend explicitly on the amount of delay. Analysis of these equations reveals that the system in general exhibits discontinuous transitions in addition to the usual continuous transition, between the incoherent state and a multitude of coherent states with different synchronization frequencies. In particular, the phase diagram is obtained on the plane of the coupling strength and the delay time, and ubiquity of multistability as well as suppression of the synchronization frequency is manifested. Numerical simulations are also performed to give consistent results.

Journal Article↗

PubMed2000

Renormalization group analysis of the anisotropic nonlocal kardar-parisi-zhang equation with spatially correlated noise

We study an anisotropic nonlocal Kardar-Parisi-Zhang (KPZ) equation with spatially correlated noise by using the dynamic renormalization group method. When the signs of nonlinear terms in parallel and perpendicular directions are opposite, the correlated noise coupled with the long ranged nature of interaction produces a stable non-KPZ fixed point for d<d(c). For the uncorrelated noise, the roughness and dynamic exponents associated with the stable fixed point are different from those of the isotropic nonlocal KPZ equation, while for the correlated noise the exponents are the same as those of the isotropic case.

Journal Article↗

PubMed2000

River networks on the slope-correlated landscape

We study the morphologies of river networks on various landscapes. In general, the probability density distribution of drainage area a of the river network scales as P(a) approximately a(-tau). We consider a slope-slope correlation function G(r) and define the persistent length R where G(r=R) becomes zero. In our restricted solid on solid network model, R is independent of the system size L and tau is close to 4/3, which is the value of the Scheidegger's river network model with random walk process. We also consider an avalanche model, where R is proportional to L. There is a large slope-slope correlation length and the river network does not follow the directed random walk process with tau approximately 1.42.

Journal Article↗

PubMed2000

Measurement method for electric fields based on stark spectroscopy of argon atoms

We report the development of a method for the measurement of electric fields in glow discharge plasmas, based on Stark spectroscopy of argon atoms. The method is based on laser excitation of transitions in atomic argon. The key feature of the method is that the electric field is determined by matching experimentally obtained absorption spectra to theoretically calculated spectra. The dependence of the positions of energy levels of argon atoms on the strength of the electric field was calculated by solving the Schrodinger equation for the argon atom. Measurements of Stark spectra were made in the sheath region of a glow discharge using laser optogalvanic spectroscopy. The wavelength of the laser radiation was tuned to the transitions 4s-->nf (n=7,8,ellipsis,14) of the argon atom. For n=11, the lower limit for electric field measurements was estimated to be 14 V/mm.

Journal Article↗

PubMed2000

Growth of a driven interface in isotropic and anisotropic random media

We introduce a simple stochastic model for a driven interface in a random medium, in which we can control the degree of the anisotropy of a random medium. When there is no anisotropy of a random medium, the motion of a growing interface in our model can be well described by the quenched Edwards-Wilkinson equation. When there is anisotropy of a random medium, however, the motion of a growing interface can be described by the quenched Kardar-Parisi-Zhang (KPZ) equation. In the two interfaces, apart from one growing in an isotropic medium and the other growing in an anisotropic medium, the growth rule of our model is the same. Our results support the fact that the anisotropy of a random medium is a source of the KPZ nonlinearity.

Journal Article↗

PubMed1998

Morphological change and enhanced pigment production of monascus when cocultured with saccharomyces cerevisiae or aspergillus oryzae

When a Monascus isolate, a producer of Monascus pigments, was cocultured with either Saccharomyces cerevisiae or Aspergillus oryzae in a solid sucrose medium, there were significant morphological changes in Monascus culture. Cocultures exhibited cell mass increases of 2 times and pigment yield increases of 30 to 40 times compared to monocultures of Monascus. However, enhanced cell growth, an increase in pigment production, and morphological change did not occur in coculture with Bacillus cereus. Saccharomyces cerevisiae was more effective at enhancing pigment production than Asp. oryzae. Enhanced cell growth and increased pigment production occurred only in conjunction with morphological changes. Culture filtrates of S. cerevisiae were also effective in inducing morphology change in Monascus, similar to culture broths of S. cerevisiae. The hydrolytic enzymes produced by S. cerevisiae, such as amylase, and chitinase, are thought to be the effectors. The commercial enzymes alpha-amylase and protease from Asp. oryzae both caused a morphological change in Monascus and were effective in enhancing pigment production. However, lysozyme, alpha-amylase and protease from Bacillus species, protease from Staphylococcus, and chitinase from Streptomyces were not effective. The hydrolytic enzymes which cause a morphological change of Monascus culture and enhancement of pigment production are thought to be capable of degrading Monascus cell walls. An approximate 10-fold increase in pigment production was observed in liquid cocultures with S. cerevisiae. Copyright 1998 John Wiley & Sons, Inc.

Journal Article↗

PubMed1996