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Search Results: 1 - 10 of 457572 matches for " S-K. Hong "
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Imaging Mechanism of Piezoresponse Force Microscopy in Capacitor Structures
Sergei V. Kalinin,Brian J. Rodriguez,Seung-Hyun Kim,S-K. Hong,Alexei Gruverman,Eugene A. Eliseev
Physics , 2008, DOI: 10.1063/1.2905266
Abstract: The image formation mechanism in Piezoresponse Force Microscopy (PFM) of capacitor structures is analyzed. We demonstrate that the spatial resolution is a bilinear function of film and top electrode thicknesses, and derive the corresponding analytical expressions. For many perovskites, the opposite contributions of d31 and d33 components can result in anomalous domain wall profiles. This analysis establishes the applicability limits of PFM for polarization dynamics studies in capacitors, and applies to other structural probes, including focused X-ray studies of capacitor structures.
Cytotoxic Activity of Hexane Extracts of Psidium guajava L (Myrtaceae) and Cassia alata L (Caesalpineaceae) in Kasumi-1 and OV2008 Cancer Cell Lines
AS Levy, S-K Carley
Tropical Journal of Pharmaceutical Research , 2012,
Abstract: Purpose: The cytotoxic effects of hexane extracts of Cassia alata and Psidium guajava leaves were evaluated in OV2008 ovarian and Kasumi-1 leukemia cancer cell lines, respectively. Methods: The cancer cells were exposed to various concentrations of either C. alata (100 – 180 μg/ml) or P. guajava (100 – 500 μg/ml) leaf extract for 24 h. Following treatment, the cells were evaluated using the 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay to determine the cytotoxic effect of the extracts. C. alata extract was also analyzed using high performance liquid chromatography (HPLC). Results: C. alata and P. guajava extracts produced significant (p < 0.05) cytotoxicity in OV2008 and Kasumi-1 cell lines, respectively. The IC50 values were 160 μg/ml for C. alata and 200 μg/ml for P guajava. Further, the cytotoxicity exhibited by C. alata might be attributable to the flavonoid, kaempferol, which was identified as a constituent of the extract. Conclusion: The results suggest that further chemical analysis and mechanistic investigations should be conducted on P. guajava and C. alata extracts to validate their potential uses for anticancer therapy.
Finite size effects as the explanation of ``freezing'' in vortex liquids
S-K. Chin,M. A. Moore
Physics , 1997,
Abstract: We investigate the effect of thermal fluctuations on the (mean-field) Abrikosov phase. The lower critical dimension of the superconducting phase is three, indicating the absence of the Abrikosov phase for dimensions d<3. Within the d=3 vortex liquid, the phase correlation length along the magnetic field direction grows exponentially rapidly as the temperature is lowered. For a finite bulk system, there is a 3D-2D crossover effect when the phase correlation length becomes comparable to the sample thickness. Such a crossover effect takes place over a very narrow temperature interval and mimics the ``first order transition'' seen in experiments on clean YBCO and BSCCO crystals. We calculate the jumps in the entropy, magnetization and specific heat due to the crossover and find reasonably good agreement with experiments on both YBCO and BSCCO.
Phase-transitions in isotropic extreme type-II superconductors
S-K. Chin,A. K. Nguyen,A. Sudboe
Physics , 1998, DOI: 10.1103/PhysRevB.59.14017
Abstract: Using large scale Monte Carlo simulations on a uniformly frustrated 3DXY model, we report a first order vortex lattice melting transition in clean, isotropic extreme type-II $\kappa \to \infty$ superconductors. This work clarifies an important issue: the unpinned vortex liquid is always incoherent with no phase coherence in any directions for all anisotropies. Previous claims of a disentangled vortex liquid for isotropic superconductors based on simulations, are due to finite size effects. We explicitly show that the effective vortex-line tension vanishes precisely at the superconducting phase transition in zero magnetic field. This loss of line tension is accompanied by an abrupt change in the connectivity of the vortex tangle across the superconductor. We also obtain results indicating that the connectivity of the vortex tangle changes in a similar way even in finite magnetic field, and suggest that this could also be associated with a genuine phase-transition.
The distribution and frequency of endocrine cells in the splenic lobe of grass lizard (Takydromus wolteri): An immunohistochemical study
S-K Ku,H-S Lee
European Journal of Histochemistry , 2004, DOI: 10.4081/917
Abstract: The regional distribution and frequency of the pancreatic endocrine cells in the splenic lobe of grass lizard, Takydromus wolteri, were studied by immunohistochemical (PAP) method using six types of specific mammalian antisera against bovine Sp-1/chromogranin (bCG), serotonin, insulin, glucagon, somatostatin and human pancreatic polypeptide (hPP). The pancreas was subdivided into two regions – islet kike and exocrine regions. The frequency of each immunoreactive (IR) endocrine cells was calculated as mean number/total 100 islet cells and as mean number/total 1000 cells (including exocrine and endocrine cells) using automated image analysis process. In addition, the percentage of each IR cell was also calculated. All of six endocrine cells were demonstrated. They were dispersed in the whole pancreatic parenchyma between exocrine acinar cells, or they were also observed as islet like clusters. In islet-like regions, bCG-, insulin- and glucagon-IR cells were detected as one or two cell layer cords and they were located between this cell-cords with 14.30±5.62, 61.50±9.76 and 26.50±9.31/100 cells frequencies, respectively. However, somatostatin-IR cells were mainly located in the peripheral parts not in cell-cords with 12.40±4.86/100 cells, and no serotonin- and hPP-IR cells were demonstrated. In exocrine regions, all of bCG-, serotonin-, insulin-, glucagon-, somatostatin- and hPP-IR cells were detected and they occurred mainly among the exocrine parenchyma as solitary cells with 10.30±2.54, 0.80±0.63, 15.50±5.30, 5.80±2.66, 3.10±1.29 and 11.00±3.33/1000 cells frequencies, respectively. In addition, serotonin-IR cells were mainly located between epithelia and connective tissue of pancreatic duct. Overall, there were 0.58±0.49% serotonin–, 56.44±9.35% insulin–, 23.73±8.22% glucagon–, 11.28±3.03% somatostatin– and 7.97±2.02% hPP-IR cells
Zeroth Sound Modes of Dilute Fermi Gas with Arbitrary Spin
S-K. Yip,Tin-Lun,Ho
Physics , 1998,
Abstract: Motivated by the recent success of optical trapping of alkali bosons, we have studied the zeroth sound modes of dilute Fermi gases with arbitrary spin-f, which are spin-S excitations ($0\leq S\leq 2f$). The dispersion of the mode (S) depends on a single Landau parameter $F^{(S)}$, which is related to the scattering lengths of the system through a simple formula. Measurement of (even a subset of) these modes in finite magnetic fields will enable one to determine all the interaction parameters of the system.
Mixed phases in U(N) superconductivity
M. A. Moore,T. J. Newman,A. J. Bray,S-K. Chin
Physics , 1997, DOI: 10.1103/PhysRevB.58.936
Abstract: We consider a general class of type-II superconductors which are described by N complex order parameters (OP), with an overall U(N) symmetry for the energy functional. In the lowest energy state, each OP adopts its own particular lattice structure, making the spatial variation of the overall condensate very complex. We present detailed results for the case N=2. We also treat the limit N -> infinity, which allows us to resolve a recent controversy, by showing that all previous studies are fundamentally flawed.
Structural awareness, variation theory and ICT support.
Ki, W-W.,Lam, H-C.,Chung, A. L-S.,Tse, S-K.
L1 Educational Studies in Language and Literature , 2003,
Abstract: To be literate in Chinese, one needs to learn over a thousand Chinese characters. This is obviously a challenging task for young learners. Psychological and developmental studies have provided evidence that awareness of structural regularities among the characters is important for its learning. Yet how this structural awareness can be enhanced in instruction is still not clear. Some worry that any explicit instruction about structures might actually increase the cognitive burden of the young learners, as they might be asked to think analytically about the characters, or to learn a meta-language that describes the structural principles underlying Chinese character composition. This paper discusses the nature of structural awareness in light of Gurtwitsch’s general theory of awareness [Gurwitsch, A. (1964). The Field of consciousness. Pittsburgh: Duguesne University Press] and the theory of variation by Marton and S. Booth [(1997) Learning and awareness. Mahwah, New Jersey: Lawrence Erlbaum] and F. Marton and A. Tsui [(in press) Classroom discourse and the spacing of learning. Mahwah, New Jersey: Lawrence Erlbaum], and proposes how the awareness of Chinese character structures can be developed through experiencing systemic variations among related instances. It discusses how information and communication technologies can be used to provide useful support for this purpose. These ideas are implemented in a school–university collaboration project in Hong Kong and anecdotal evidence supports the conjecture of the authors. The structural awareness instruction can also be embedded naturally into meaningful language learning contexts to form an integrative model of teaching that is well received by teachers and students. The instruction does not appear to impose any additional cognitive load on the students. On the contrary, learners’ interest and sensitivity in picking up the structural features of Chinese characters increases.
Seperation, identification and analysis of pigment (melanin) production in Streptomyces
SG Dastager, WJ Li, A Dayanand, S-K Tang, X-P Tian, X-Y Zhi, L-H Xu, C-L Jiang
African Journal of Biotechnology , 2006,
Abstract: Nine strains among 180 Streptomyces isolates produce a diffusible dark brown pigment on both peptone-yeast extract agar and synthetic tyrosine-agar. They also show the positive reaction to Ltyrosine or L-dopa substrates. The pigment has been referred to be as merely as dark brown watersoluble pigment, as melanoid or melanin. The different carbon and nitrogen sources which influence the pigment production in the Streptomyces isolates were also investigated, and the carotenoid content in the pigment was analyzed. The melanin formation in the Streptomyces species is the key feature for the classification of the Stretomyces group
Self-trapping of a Fermi super-fluid in a double-well potential in the BEC-unitarity crossover
S. K. Adhikari,Hong Lu,Han Pu
Physics , 2009, DOI: 10.1103/PhysRevA.80.063607
Abstract: We derive a generalized Gross-Pitaevskii density-functional equation appropriate to study the Bose-Einstein condensate (BEC) of dimers formed of singlet spin-half Fermi pairs in the BEC-unitarity crossover while the dimer-dimer scattering length $a$ changes from 0 to $\infty$. Using an effective one-dimensional form of this equation, we study the phenomenon of dynamical self-trapping of a cigar-shaped Fermi super-fluid in the entire BEC-unitarity crossover in a double-well potential. A simple two-mode model is constructed to provide analytical insights. We also discuss the consequence of our study on the self-trapping of an atomic BEC in a double-well potential.
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