Search Results - (Author, Cooperation:J. H. Song)

2011-01-29

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Adaptation, Physiological ; Anti-Bacterial Agents/pharmacology ; Antigenic Variation ; DNA Transposable Elements ; Drug Resistance, Multiple, Bacterial ; *Evolution, Molecular ; Genome, Bacterial ; Humans ; Molecular Epidemiology ; Phylogeny ; Phylogeography ; Pneumococcal Infections/drug therapy/*microbiology ; Pneumococcal Vaccines/immunology ; Polymorphism, Single Nucleotide ; Prophages/genetics ; *Recombination, Genetic ; Selection, Genetic ; Serotyping ; Streptococcus Phages/genetics ; Streptococcus pneumoniae/classification/drug effects/*genetics/immunology

2018-09-22

Institute of Physics (IOP)

1757-8981

1757-899X

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

2012-05-19

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2011-10-11

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Biocatalysis ; Catalytic Domain ; Crystallography, X-Ray ; Dihydroxyacetone Phosphate/metabolism ; Fructose-Bisphosphate Aldolase/*chemistry/*metabolism ; Fructosediphosphates/metabolism ; Gluconeogenesis ; Glyceraldehyde 3-Phosphate/metabolism ; Lysine/metabolism ; Magnesium/metabolism ; Models, Molecular ; Phosphoric Monoester Hydrolases/*chemistry/*metabolism ; Phosphorylation ; Protein Conformation ; Schiff Bases/chemistry/metabolism ; Sulfolobus/*enzymology

2018-08-07

The American Association of Immunologists (AAI)

0022-1767

1550-6606

Medicine

1089-7550

AIP Digital Archive

Physics

A simple relationship between the ratio of atomic transport induced by ion mixing and the activation energies for the impurity diffusion of constituents in a bilayer is presented to describe quantitatively the symmetric and asymmetric atomic transport in the thermal spike induced ion mixing. The model predicts fairly satisfactorily the trend of experimental observations in the bilayer systems which have near zero heats of mixing and relatively high spike activation energies. For instance, the Pd/Co bilayer system shows nearly symmetric atomic transport, since its constituents have similar activation energies for the impurity diffusion.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Photoreflectance measurements from ZnSe epilayers of different thicknesses were carried out. In photoreflectance spectra, the exciton line shape "rotation" is observed to be much slower than that in the reflectance spectra by increasing the epilayer thicknesses. To analyze the exciton line shape rotation quantitatively, the photoreflectance spectra were calculated considering the built-in electric field inhomogeneity effects near the interface as well as the interference effects. Calculated line shapes of the photoreflectance spectra show a good agreement with the observations. Our results imply that inhomogeneity effects of the interface built-in electric field plays an important role in the spectral rotation in photoreflectance. © 2000 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Heteroepitaxial Y2O3 films were grown on an Si(111) substrate by ion assisted evaporation in an ultrahigh vacuum, and their properties such as crystallinity, film stress, and morphological change were investigated using the various measurement methods. The crystallinity was assessed by x-ray diffraction (XRD) and reflection high-energy electron diffraction. Interface crystallinity was also examined by Rutherford backscattering spectroscopy (RBS) channeling and transmission electron microscopy. The strain of the films was measured by RBS channeling and XRD. Surface and interface morphological characteristics were observed by atomic force microscopy and x-ray scattering method. By comparing the interface with the surface characteristics, we can conclude that many defects at the interface region were generated by interface interaction between the yttrium metal and Si substrate. Moreover, the film quality dominantly depended on the deposition temperature. The crystallinity was greatly improved and the surface roughness was drastically decreased in the temperature range 500–600 °C. On the other hand, in the temperature range 600–700 °C, the compressive stress and film density were further increased, and the island size decreased. Also, the shape of the surface islands was transformed from elliptical to triangular. The film stress was found primarily at the interface area because of the interaction between yttrium and Si substrate. © 1999 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A Monte Carlo simulation of liquid water was carried out in order to study the influence of an external magnetic field on the internal energy and heat capacity of pure water. Analysis of the structure of water was made by calculating the radial distribution function of water molecules. A multipeak function of the magnetic effect versus magnetic flux density was found. A significant change in the internal energy and heat capacity occurred at a magnetic flux density of about 0.2 T. In particular, when the magnetic flux density increases, the second peak of the water–water radial distribution function increases markedly. This has been demonstrated by calculations for both 64- and 125-molecule systems. © 2000 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Damage and strain produced in a 370-nm-thick strained epitaxial Ge0.10Si0.90 film on Si(100) by irradiation with 320 keV 28Si+ ions at fixed temperatures ranging from 40 to 150 °C and for doses from 1 to 30×1014/cm2 have been measured by MeV 4He channeling spectrometry, transmission electron microscopy, and high-resolution x-ray diffractometry. The ion energy was chosen so that the maximum damage created by irradiation occurs very near the GeSi-Si interface. For all temperatures, the retained damage and the perpendicular strain induced by the irradiation are significantly greater in the GeSi epilayer than in the Si substrate. For all doses the retained damage and the induced perpendicular strain become small above 100 °C. Both rise nonlinearly with increasing ion dose. They are related to each other differently in GeSi than in bulk Si or Ge irradiated at room temperature. Postirradiation furnace annealing can remove a large portion of the induced damage and strain for nonamorphized samples. Amorphized samples regrow by solid-phase epitaxy after annealing at 550 °C for 30 min; the regrown GeSi is, however, highly defective and elastically relaxed. A consequence of this defectiveness is that irradiation-induced amorphization in metastable GeSi is undesirable for applications where good crystalline quality is required. Ion implantation above room temperature can prevent amorphization. © 1995 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Several 265-nm-thick metastable pseudomorphic Ge0.12Si0.88 films grown on a Si(100) substrate by molecular-beam epitaxy were implanted at room temperature with 100 keV phosphorus ions to a dose of 1.5×1015/cm2. The implantation amorphizes the top portion (∼190 nm) of the GeSi layer and leaves the rest of the film single crystalline. Implanted and nonimplanted samples were subsequently annealed simultaneously in vacuum for 30 min from 400 to 800 °C. The implanted samples undergo layer-by-layer solid-phase-epitaxial regrowth during annealing at or above 500 °C. The regrown GeSi layer is relaxed with a high density of threading dislocations (∼1010–1011/cm2). The nonamorphized portion of the layer remains fully strained when annealed between 400 and 600 °C. At or above 700 °C misfit dislocations are observed at the Si/Ge0.12Si0.88 interface. After 800 °C annealing the strain in the whole epilayer is fully relaxed. The strain relaxation is facilitated by the implantation. The presence of phosphorus in GeSi raises its regrowth velocity by about an order of magnitude over that of Ge0.12Si0.88 amorphized by irradiation of Si. The implanted phosphorus reaches ∼100% activation after the completion of solid-phase-epitaxial regrowth. The room-temperature sheet electron mobility in GeSi is ∼20% below that of a Si sample implanted and annealed under the same conditions. It is concluded that metastable Ge0.12Si0.88 on Si(100) amorphized at room temperature by P implantation and recrystallized by solid-phase epitaxy can- not recover its crystalline perfection and its pseudomorphic strain upon steady-state furnace annealing. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The pump photon energy dependence of photoreflectance (PR) of a ZnSe/GaAs heterostructure has been measured at 77 K. The phase inversion in the PR signal is observed for the pump photon energy when it decreases from above to below the excitonic absorption edge of ZnSe. The observation of the phase inversion in PR is explained in terms of the modulation of the built-in electric field at the interface of the ZnSe/GaAs heterojunction, not at the ZnSe surface. It provides evidence of a built-in triangular-well potential and of hole traps at the ZnSe/GaAs interface. This argument is confirmed by photoreflectance excitation spectroscopy. © 1998 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Metastable pseudomorphic Ge0.12Si0.88 films were grown by molecular beam epitaxy on Si(100) substrates and then implanted with 100 keV 31P at room temperature for a dose of 5×1013/cm2. Samples were subsequently annealed by rapid thermal annealing (RTA) in nitrogen and by steady-state furnace annealing in vacuum. Both damage and strain introduced by implantation can be completely removed, within instrumental sensitivity, by RTA at 700 °C for 10–40 s. Vacuum annealing for 30 min at 500–550 °C removes most of the damage and strain induced by the implantation but the activation of the P is poor. At 700 °C, the activation is nearly 100%, but the crystallinity worsens and the pseudomorphic strain begins to relax. We conclude that for a lightly implanted metastable and pseudomorphic GeSi epilayer on Si, steady-state vacuum annealing cannot achieve good dopant activation without introducing significant strain relaxation to the heterostructure, while RTA can. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

ZnSe/GaAs heteroepitaxial structures were prepared by metalorganic chemical vapor deposition with the use of thermal cleaning treatments at varying hydrogen flow rates in preparing the substrate. The photoreflectance spectra for the samples prepared revealed Franz–Keldysh oscillation (FKO) signals with the superimposition of free exciton transition features. The FKO signals changed depending on the hydrogen flow rate while the exciton transition features remained unchanged. Fitting through Aspnes' and Franz–Keldysh's model showed that the built-in electric field at the interface increased as the hydrogen flow rate decreased. These results imply that the hydrogen flow rate in the course of thermal etching plays a crucial role in the change of the energy-band profile at the interface. © 2000 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We report on the fabrication of single-crystalline thin films of RBa2Cu3O7−y (R: rare-earth element, R123) using an approach of vapor–liquid–solid tri-phase epitaxy. This method is based on application of pulsed-laser deposition under appropriate compositions and conditions predetermined from the relevant thermodynamic phase diagram. The laser-ablated gases of R, Ba, and Cu, and their oxides dissolve into a liquid Ba3Cu5Ox (3BaCuO2+2CuO) layer placed on the film/substrate surface, penetrate to reach the liquid–solid interface with a seed R123, and are condensed into the solid R123 phase under a quasiequilibrium state. The uniform single-crystalline nature of the film was verified by x-ray diffraction, atomic-force microscopy, and transmission electron microscopy by the observation of giant grain size and atomic-scale surface smoothness. © 2002 American Institute of Physics.

Electronic Resource

1089-7666

AIP Digital Archive

Physics

Beams of neutralized plasma will cross a transverse magnetic field, magnetized plasma, and neutral gas, by a combination of single particle and collective-plasma processes. At low density the beam will deflect; at higher density the beam will exhibit undeflected motion by the E×B drift or diamagnetic (high-beta) exclusion of the magnetic field. In the high-beta regime, where β〉1 (β is the ratio of plasma-beam energy density to magnetic field energy density), beam magnetization occurs on a time scale orders of magnitude faster than the classical Spitzer time scale. Recent studies of fast magnetization suggest that transport processes in large ion gyroradius beams, y/ρi〈1, are dominated by ion motion rather than electron motion as previously understood for small gyroradius beams, y/ρi〉1, where y and ρi are the beam transverse width and ion gyroradius, respectively. Although quantitative aspects of the small gyroradius propagation physics theory are still valid, most notably the E×B drift, much work remains to fully understand fast magnetic diffusion processes, beam-trapping mechanisms, and long-range propagation limits.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Dual-energy carbon implantation (1×1016/cm2 at 150 and at 220 keV) was performed on 260-nm-thick undoped metastable pseudomorphic Si(100)/ Ge0.08Si0.92 with a 450-nm-thick SiO2 capping layer, at either room temperature or at 100 °C. After removal of the SiO2 the samples were measured using backscattering/channeling spectrometry and double-crystal x-ray diffractometry. A 150-nm-thick amorphous layer was observed in the room temperature implanted samples. This layer was found to have regrown epitaxially after sequential annealing at 550 °C for 2 h plus at 700 °C for 30 min. Following this anneal, tensile strain, believed to result from a large fraction of substitutional carbon in the regrown layer, was observed. Compressive strain, that presumably arises from the damaged but nonamorphized portion of the GeSi layer, was also observed. This strain was not significantly affected by the annealing treatment. For the samples implanted at 100 °C, in which case no amorphous layer was produced, only compressive strain was observed. For samples implanted at both room temperature and 100 °C, the channelled backscattering yield from the Si substrate was the same as that of the virgin sample. © 1997 American Institute of Physics.

Electronic Resource

1460-2695

Blackwell Publishing Journal Backfiles 1879-2005

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Abstract— A two-dimensional elastic-plastic finite element analysis is performed for plane stress conditions with 4-node isoparametric elements to examine closure behaviour of fatigue cracks, giving special attention to the determination of the most appropriate mesh sizes. It is found that a smaller mesh size does not always give more accurate simulation results in the fatigue crack closure analysis, unlike a conventional structural analysis. A unique, most-appropriate mesh size exists for a given loading condition that will provide numerical results which agree well with experimental data. The most appropriate mesh size can be determined approximately in terms of the theoretical reversed plastic zone size. In particular, the ratio of the most appropriate mesh size to the theoretical reversed plastic zone size is nearly constant for a given stress ratio in the so-called crack-length-fixed method proposed in this study. By using the concept of the most appropriate mesh size, the finite element analysis can predict fatigue crack closure behaviour very well.

Electronic Resource

1460-2695

Blackwell Publishing Journal Backfiles 1879-2005

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

An elastic–plastic finite-element analysis of fatigue crack closure is performed for plane strain conditions. The stabilization behaviour of crack opening level and the effect of mesh size on the crack opening stress are investigated. It has been well reported that the crack opening level under plane stress conditions becomes stable after the crack advances beyond the initial monotonic plastic zone. In order to obtain a stabilized crack opening level for plane strain conditions, the crack must be advanced through approximately four times the initial monotonic plastic zone. The crack opening load tends to increase with the decrease of mesh size. The mesh size nearly equal to the theoretical plane strain cyclic plastic zone size may provide reasonable numerical results comparable with experimental crack opening data. The crack opening behaviour is influenced by the crack growth increment and discontinuous opening behaviour is observed.

Electronic Resource

1460-2695

Blackwell Publishing Journal Backfiles 1879-2005

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

An elastic-plastic finite element analysis with high order elements is performed to examine closure behaviour of fatigue. cracks in residua1 stress fieids and the numerical results are then compared with experimental results. The finite element analysis, performed under plane stress using 8-node isoparametric elements, can predict fatigue crack closure behaviour through residual stress fields very well. The crack opening and closing behaviour through a compressive residual stress field is found to be complicated and influenced by the applied load magnitude and the location of the crack tip. Three different types of crack opening behaviour, namely, normal, unsymmetric partial and symmetric partial crack opening behaviour are observed through a compressive residual stress field. The partial crack opening stress intensity factor including the partial crack opening effect is recommended for the prediction of fatigue crack growth through a compressive residual stress field.

Electronic Resource