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Biomedical subjects

Y Kwon

Publications and source records attributed to Y Kwon.

At least 19 recordsLinked to original sources
PubMed2006

Serum HER-2 concentration in patients with primary breast cancer.

OBJECTIVE: To evaluate whether serum HER-2/neu (HER-2) concentration is a valid index of HER-2 status in women with primary breast cancer, and to establish a normal reference range for serum HER-2 concentration in Korean women. METHODS: Serum HER-2 concentration was measured and immunohistochemistry (IHC) and fluorescence in situ hybridisation (FISH) carried out on tissue samples from 86 consecutive female patients. The results of the three datasets were compared. The cut off value of HER-2 concentration was determined from the mean +2SD values derived from the serum of 93 healthy volunteers. RESULTS: The IHC and FISH data were significantly correlated (p<0.01), but neither showed significant correlation with the serum HER-2 data. The cut off value of serum HER-2 was 10.2 microg/l, and the serum HER-2 concentration of patients with primary breast cancer ranged from 5.0 to 17.5 microg/l. Only five patients had a serum HER-2 value above the cut off value. CONCLUSIONS: Serum HER-2 concentration cannot be substituted for IHC or FISH to evaluate HER-2 status, nor can it be used as a diagnostic tumour marker in primary breast cancer, considering the low prevalence of serum HER-2 elevation.

Adult↗
PubMed2005

Path integral methods for rotating molecules in superfluids.

We present a path integral Monte Carlo (PIMC) methodology for quantum simulation of molecular rotations in superfluid environments such as helium and para-hydrogen that combines the sampling of rotational degrees of freedom for a molecular impurity with multilevel Metropolis sampling of Bose permutation exchanges for the solvating species. We show how the present methodology can be applied to the evaluation of imaginary time rotational correlation functions of the molecular impurity, from which the effective rotational constants can be extracted. The combined rotation/permutation sampling approach allows for the first time explicit assessment of the effect of Bose permutations on molecular rotation dynamics, and the converse, i.e., the effect of molecular rotations on permutation exchanges and local superfluidity. We present detailed studies showing that the effect of Bose permutations in the solvating environment is more significant for the dynamics of heavy than light molecules in helium, and that Bose permutation exchanges are slightly enhanced locally by molecular rotation. Finally, the examples studied here reveal a size dependence of rotational excitations for molecules possessing a strongly anisotropic interaction with helium in 4HeN clusters between N approximately 20 and N approximately 10(3).

Journal Article↗
PubMed2005

OCS in para-hydrogen clusters: rotational dynamics and superfluidity.

We present a detailed analysis of the rotational excitations of the linear OCS molecule solvated by a variable number of para-hydrogen molecules (9 < or = N < or = 17). The effective rotational constant extracted from the fit of the rotational energy levels decreases up to N = 13, indicating near-rigid coupling between OCS rotations and para-hydrogen motion. Departure from rigidity is instead seen for larger clusters with 14 < or = N < or = 17. Path-integral Monte Carlo calculations show that the N dependence of the effective rotational constant can be explained in terms of a partial superfluid response of para-hydrogen to rotations about an axis perpendicular to the OCS axis. Complete para-hydrogen superfluid response to rotations about the OCS axis is found for N > or = 10.

Journal Article↗
PubMed2005

Onset of superfluidity in small CO2(4He)N clusters.

We provide definitive theoretical evidence for the onset of superfluidity in small helium clusters doped with molecules at less than one solvation shell, with quantitative analysis of spectroscopic constants for CO2 in (4)He(N) in terms of nonclassical rotational inertia and helium superfluidity calculated by path integral methods. We find a significant superfluid response for N>/=5, with essentially unit response to rotations around the CO2 axis and partial response to rotations about an axis perpendicular to the CO2 axis for N>/=6. This anisotropic superfluid response is shown to be responsible for the N dependence of measured CO2 rotational spectra in (4)He(N).

Journal Article↗
PubMed2005

A theoretical study of the effects of RF fields in the vicinity of membranes.

In this article the forces associated with the gradients of a radio frequency (RF) field at the boundary between fluids and cell membranes are calculated, and it is shown that they can be large enough to affect the particle motion by amounts that are on the same order of magnitude as the random diffusion motion when the energy imparted to the particles is a reasonable fraction of the thermal energy. The induced dipole moment is assumed to track the alternating RF so that the force exerted by the gradient is in a constant direction; and this in turn leads to a modification of the particle distribution, even when the energy added to the particle is very small. For RF fields of 45 V/m the energy acquired by an induced dipole moment is expected to be on the order of a micro electron volt and small compared to the average thermal energy.

Animals↗
PubMed2004

Roton-rotation coupling of acetylene in 4He.

Rotational absorption spectra of acetylene in superfluid 4He calculated using a path-integral correlation function approach are seen to result in an anomalously large distortion constant in addition to a reduced rotational constant, with values in excellent agreement with recent experiments. Semianalytic treatment of the dynamics with a combined correlated basis function-diffusion Monte Carlo method reveals that this anomalous behavior is due to strong coupling of the higher rotational states of the molecule with the roton and maxon excitations of 4He, and the associated divergence of the 4He density of states in this region.

Journal Article↗
PubMed2004

Development of SH-SAW sensors for underwater measurement.

We developed SH (shear horizontal) surface acoustic wave (SAW) sensors to detect protein molecules in liquid solutions applying a particular antibody thin film on the delay line of transverse SAW devices. The antibody investigated was human-immuno-globulin G (HigG) to hold the antigens (anti-HigG) in the protein solution to be measured. The sensor showed stable response to the mass loading effects of the anti-HigG molecules with the sensitivity up to 10.8 ng/ml/Hz.

Acoustics↗
PubMed2003

Mesenchymal tumours of the thorax: CT findings and pathological features.

Mesenchymal tumours of the thorax are uncommon and may originate from the muscle, bone, cartilage, vessel, nerves, fat and fibrous tissue. These tumours occur at different sites including the lung, pleura, mediastinum or chest wall. Mesenchymal tumours tend to show protean and non-specific imaging characteristics. However, in some instances, the imaging characteristics of the tumour may allow a specific diagnosis to be made, such as with lipoid or vascular tumours.

Adolescent↗
PubMed2001

Antilambda production in Au+Au collisions at 11.7A GeV/c.

We present results for antilambda and antiproton production in Au+Au collisions at 11.7 A GeV/c including spectra and extracted invariant yields for both species in central and peripheral collisions in the rapidity range 1.0<y<1.4. The antilambda yield increases from dN(Lambda;)/dy = 1.2(+0.7+0.2)(-0.6-0.2)x10(-3) in peripheral collisions to 19(+4+3)(-5-2)x10(-3) in central collisions. The direct antiproton yield is deduced from the measured total antiproton spectra to extract the ratio of antilambda-to-direct-antiproton production. The Lambda/p ratio near midrapidity increases from 0.26(+0.19+0.5)(-0.15-0.4) in peripheral collisions to 3.6(+4.7+2.7)(-1.8-1.1) in central collisions, a value larger than current theoretical estimates.

Journal Article↗
PubMed2001

Baryon rapidity loss in relativistic Au + Au collisions.

An excitation function of proton rapidity distributions for different centralities is reported from AGS Experiment E917 for Au+Au collisions at 6, 8, and 10.8 GeV/nucleon. The rapidity distributions from peripheral collisions have a valley at midrapidity which smoothly change to distributions that display a broad peak at midrapidity for central collisions. The mean rapidity loss increases with increasing beam energy, whereas the fraction of protons consistent with isotropic emission from a stationary source at midrapidity decreases with increasing beam energy. The data suggest that the stopping is substantially less than complete at these energies.

Journal Article↗
PubMed2001

DNA sequencing and genotyping by transcriptional synthesis of chain-terminated RNA ladders and MALDI-TOF mass spectrometry.

Sets of RNA ladders can be synthesized by transcription of a bacteriophage-encoded RNA polymerase using 3'-deoxynucleotides as chain terminators. These ladders can be used for sequencing of DNA. Using a nicked form of phage SP6 RNA polymerase in this study substantially enhanced yields of transcriptional sequencing ladders. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) of chain-terminated RNA ladders allowed DNA sequence determination of up to 56 nt. It is also demonstrated that A-->G and C-->T variations in heterozygous and homozygous samples can be unambiguously identified by the mass spectrometric analysis. As a step towards single-tube sequencing reactions, alpha-thiotriphosphate nucleotide analogs were used to overcome problems caused by chain terminator-independent, premature termination and by the small mass difference between natural pyrimidine nucleotides.

Base Sequence↗
PubMed2001

Water-soluble and low molecular weight chitosan-based plasmid DNA delivery.

PURPOSE: Chitosan, a natural cationic polysaccharide, is a candidate non-viral vector for gene delivery because of its high positive charges and low cytotoxicity. In this study, low molecular weight chitosan (LMWC, molecular weight of 22 kDa) was characterized and evaluated as a gene carrier. METHODS: Plasmid/LMWC complex was analyzed in 1% agarose gel electrophoresis. To confirm that the LMWC protected plasmids from nuclease. DNase I protection assays were performed. pSV-beta-galactosidase plasmid/LMWC complex was transfected into 293T cells and transfection efficiency was evaluated by beta-galactosidase assay. Cytotoxicity of LMWC was determined by MTT assay. RESULTS: Unlike high molecular weight chitosan (HMWC), LMWC is highly water soluble, and can form complex with plasmids in physiological buffer. The plasmid DNA was completely retarded at a weight ratio of 1:2 (plasmid:LMWC) in 1% agarose gel. DNase I protection assay showed that plasmids were protected from DNase-I over 60 min. The most efficient transfection was obtained at a weight ratio of 1:3 (plasmid:LMWC). The transfection efficiency of LMWC was significantly higher than naked DNA and higher than poly-L-lysine (PLL). MTT assay showed that LMWC was less cytotoxic than PLL. CONCLUSIONS: LMWC is non-toxic and has higher transfection efficiency than PLL. Therefore, LMWC will be useful in the development of safe gene carriers.

Antineoplastic Agents↗
PubMed2000

Annealing of the Co/Hf bilayer on single Si, polycrystalline Si and SiO(2).

Silicidation of the Co/refractory metal/Si system in which the refractory metal is used as an epitaxy promoter for CoSi(2) has recently received much attention. Hf is one of the candidates for the epitaxy promoter of cobalt silicide like Ti. In this paper, we investigated the layer structures of the Co/Hf bilayer on various substrates like single (100)Si, polycrystalline Si and SiO(2) after rapid thermal annealing. Epitaxy of CoSi(2) was obtained on (100)Si by annealing Co/Hf/(100)Si. Co-Hf compounds seem to play an important role of barriers against the reaction between Co and Si during silicidation of Co/Hf/(100)Si. The existence of Co-Hf compounds is helpful in the formation of epitaxial CoSi(2) since they retard the diffusion of cobalt and silicon atoms. The transition temperatures of cobalt silicides in the Co/Hf/poly-Si system were found to be lower than those in the Co/Hf/(100)Si system. The reaction between the metal and the spacer SiO(2) during silicidation is a matter of concern since any conducting residue of this reaction could degrade oxide integrity or produce bridging. In the Co/Hf/SiO(2) system Hf oxides formed as a result of the reaction between Hf and SiO(2) but a conducting material like HfSi(2) was not found to form after annealing. Considering the temperature at which epitaxial CoSi(2) forms along with the one from which the SiO(2) substrate starts collapsing we may conclude that the optimum silicidation annealing temperature for Co/Hf/Si is 600 degrees C.

Cobalt↗
PubMed2000

Observation of B --> K(+/-) pi(0) and B --> (K)0 pi(0), and evidence for B --> pi(+)pi(-).

We have studied charmless hadronic decays of B mesons into two-body final states with kaons and pions and observe three new processes with the following branching fractions: beta(B-->pi(+)pi(-)) = (4.3(+1. 6)(-1.4)+/-0.5)x10(-6), beta(B-->K(0)pi(0)) = (14.6(+5.9+2.4)(-5.1-3. 3))x10(-6), and beta(B-->K(+)/-pi(0)) = (11.6(+3.0+1.4)(-2.7-1.3))x10(-6). We also update our previous measurements for the decays B-->K(+)/-pi(-/+) and B+/--->K(0)pi(+/-).

Journal Article↗
PubMed2000

Two-body B meson decays to eta and eta('): observation of B --> eta K*.

In a sample of 19 x 10(6) produced B mesons, we have observed the decays B-->eta K(*) and improved our previous measurements of B-->eta'K. The branching fractions we measure for these decay modes are B(B+-->eta K(*+)) = (26.4(+9.6)(-8.2)+/-3.3)x10(-6), B(B(0)-->eta K(*0)) = (13.8(+5.5)(-4.6)+/-1.6)x10(-6), B(B(+)-->eta'K(+) = (80(+10)(-9)+/-7)x10(-6), and B(B(0)-->eta'K0) = (89(+18)(-16)+/-9)x10(-6). We have searched with comparable sensitivity for related decays and report upper limits for these branching fractions.

Journal Article↗
PubMed2000

Measurement of charge asymmetries in charmless hadronic B meson decays.

We search for CP-violating charge asymmetries (alpha(CP)) in the B meson decays to K(+/-)pi(-/+), K(+/-)pi(0), K(0)(S)pi(+/-), K(+/-)eta('), and omega pi(+/-). Using 9.66 million upsilon(4S) decays collected with the CLEO detector, the statistical precision on alpha(CP) is in the range of +/-0.12 to +/-0.25 depending on decay mode. While CP-violating asymmetries of up to +/-0.5 are possible within the standard model, the measured asymmetries are consistent with zero in all five decay modes studied.

Journal Article↗
PubMed2000

The p53 tumor suppressor stimulates the catalytic activity of human topoisomerase IIalpha by enhancing the rate of ATP hydrolysis.

DNA topoisomerase II is an essential nuclear enzyme for proliferation of eukaryotic cells and plays important roles in many aspects of DNA processes. In this report, we have demonstrated that the catalytic activity of topoisomerase IIalpha, as measured by decatenation of kinetoplast DNA and by relaxation of negatively supercoiled DNA, was stimulated approximately 2-3-fold by the tumor suppressor p53 protein. In order to determine the mechanism by which p53 activates the enzyme, the effects of p53 on the topoisomerase IIalpha-mediated DNA cleavage/religation equilibrium were assessed using the prototypical topoisomerase II poison, etoposide. p53 had no effect on the ability of the enzyme to make double-stranded DNA break and religate linear DNA, indicating that the stimulation of the enzyme catalytic activity by p53 was not due to alteration in the formation of covalent cleavable complexes formed between topoisomerase IIalpha and DNA. The effects of p53 on the catalytic inhibition of topoisomerase IIalpha were examined using a specific catalytic inhibitor, ICRF-193, which blocks the ATP hydrolysis step of the enzyme catalytic cycle. Clearly manifested in decatenation and relaxation assays, p53 reduced the catalytic inhibition of topoisomerase IIalpha by ICRF-193. ATP hydrolysis assays revealed that the ATPase activity of topoisomerase IIalpha was specifically enhanced by p53. Immunoprecipitation experiments revealed that p53 physically interacts with topoisomerase IIalpha to form molecular complexes without a double-stranded DNA intermediary in vitro. To investigate whether p53 stimulates the catalytic activity of topoisomerase II in vivo, we expressed wild-type and mutant p53 in Saos-2 osteosarcoma cells lacking functional p53. Wild-type, but not mutant, p53 stimulated topoisomerase II activity in nuclear extract from these transfected cells. Our data propose a new role for p53 to modulate the catalytic activity of topoisomerase IIalpha. Taken together, we suggest that the p53-mediated response of the cell cycle to DNA damage may involve activation of topoisomerase IIalpha.

Adenosine Triphosphate↗