Search PubMed⌕ Search

Biomedical subjects

E Oh

Publications and source records attributed to E Oh.

At least 19 recordsLinked to original sources
PubMed2003

Betweenness centrality correlation in social networks.

Scale-free (SF) networks exhibiting a power-law degree distribution can be grouped into the assortative, dissortative, and neutral networks according to the behavior of the degree-degree correlation coefficient. Here we investigate the betweenness centrality (BC) correlation for each type of SF networks. While the BC-BC correlation coefficients behave similarly to the degree-degree correlation coefficients for the dissortative and neutral networks, the BC correlation is nontrivial for the assortative ones found mainly in social networks. The mean BC of neighbors of a vertex with BC g(i) is almost independent of g(i), implying that each person is surrounded by almost the same influential environments of people no matter how influential the person may be.

Journal Article↗
PubMed2002

Coherent optical phonon oscillations in bulk GaN excited by far below the band gap photons.

We report on generation of coherent optical phonon oscillations in 150 microm thick bulk GaN. With photon energy far below the band gap, the generation mechanisms of coherent phonon modes of A1(LO), high- and low-frequency E2 are revealed to be the impulsive stimulated Raman scattering. We find that one among the two degenerate E2 modes is selectively detected with a proper choice of probe polarization. Dephasing times range from 1.5 to 70 ps for different modes, and phonon-three-photon absorbed carrier interactions are compared between the A1(LO) and the E2 mode.

Journal Article↗
PubMed2001

Analysis of fertilin alpha (ADAM1)-mediated sperm-egg cell adhesion during fertilization and identification of an adhesion-mediating sequence in the disintegrin-like domain.

Fertilin alpha (also known as ADAM1) is a member of the ADAM (A disintegrin and A metalloprotease domain) family of proteins. In this study, we examine the mechanism of mouse fertilin alpha's in adhesion of sperm to the egg plasma membrane during fertilization. We find that recombinant forms of fertilin alpha corresponding to either the disintegrin-like domain or the cysteine-rich domain and the EGF-like repeat can perturb sperm-egg binding, suggesting that both of these domains can participate in fertilin alpha-mediated adhesion events. In further examination of the fertilin alpha disintegrin-like domain, we find that a subdomain of disintegrin-like domain with the sequence DLEECDCG outside the putative disintegrin loop but with homology to the fertilin beta disintegrin loop can inhibit the binding of both sperm and recombinant fertilin alpha to eggs, suggesting that this is an adhesion-mediating motif of the fertilin alpha disintegrin-like domain. This sequence also inhibits the binding of recombinant fertilin beta to eggs and thus is the first peptide sequence found to block two different sperm ligands. Finally, a monoclonal antibody to the tetraspanin protein CD9, KMC.8, inhibited the binding of recombinant fertilin alpha to eggs in one type of binding assay, suggesting that, under certain conditions, fertilin alpha may interact with a KMC.8-sensitive binding site on the egg plasma membrane.

ADAM Proteins↗
PubMed2001

Preformulation studies on the S-isomer of oxybutynin hydrochloride, an Improved Chemical Entity (ICE).

(S)-Oxybutynin HCl (S-OXY) is a white crystalline solid powder with an acicular particle morphology. Differential scanning calorimetry (DSC) thermograms revealed one characteristic endotherm at 116.2 degrees C. On rescanning a sample heated to 120 degrees C, no thermal events were distinguished in the temperature range 25 degrees C to 150 degrees C. Weight loss curves determined by thermogravimetric analysis showed a continuous, gradual weight loss of about 0.15% over the temperature range 30 degrees C to 110 degrees C, followed by a change in slope and more rapid weight loss beginning at 150 degrees C. Observation by hot-stage microscopy confirmed the melting endotherm observed by DSC. Equilibrium moisture uptake studies indicated low water vapor uptake at low relative humidities (<52.8%). At relative humidities of 75.3% and 84.3%, S-OXY first deliquesced and then converted to a lower melting point crystal form. X-ray powder diffraction (XRPD) data supported the DSC findings. S-OXY underwent degradation by ester hydrolysis at alkaline pHs. The kinetics of this reaction were studied at 25 degrees C in carbonate-bicarbonate buffers. Observed rate constants of 0.008 h(-1) and 0.0552 h(-1) were determined at pH 9.69 and 10.25, respectively. The pKa of S-OXY was 7.75. The aqueous solubility of S-OXY was described as a function of pH and the free-base solubility. The mean partition coefficient log P was 3.33 using 1-octanol. The surface tensions of aqueous solutions of S-OXY decreased with increasing concentration, but no concentration-independent region was observed, indicating that S-OXY does notform micelles in aqueous solution. The dissolution rate of S-OXY from a compressed disk in 0.1 N HCl was rapid, whereas it was considerably slower at pH 7.4. Addition of 1% hexadecyltrimethylammonium bromide (CTAB) at pH 7.4 significantly improved the dissolution rate. S-OXY displayed very poor flow properties when compared to standard pharmaceutical excipients. XRPD results indicated that S-OXY exhibited a loss in crystallinity following ball milling. Hiestand tableting indices indicated that S-OXY has good bonding properties andforms strong compacts, but is likely to be susceptible to capping on ejection from the die. This indicated the needfor a plastically deformable excipient such as Avicel PH-101 in tablet formulations.

Calorimetry, Differential Scanning↗
PubMed2001

Identification of vertebral arteries on CT of the chest.

Knowledge of the superior mediastinal course of the vertebral arteries is important for radiologists who evaluate chest CT, particularly in the setting of trauma, when planning a percutaneous interventional procedure or for pre-operative planning. Our aim was to determine how often the vertebral arteries could be identified on chest CT studies. Contrast enhanced chest CT studies from 100 consecutive patients were reviewed, with specific attention to the vertebral arteries in the superior mediastinal and thoracic outlet regions. The left vertebral artery was identified in 85 patients and the right vertebral artery in 76 patients. Non-visualization of a vertebral artery was usually owing to proximal venous occlusion with extensive collateral vessels in the expected location of the vertebral arteries, local lymphadenopathy, poor contrast bolus technique or local beam hardening artefact. Radiologists need to alert surgeons planning resection of mass lesions in this region to the location of the vertebral arteries. It is also important to note that a vertebral artery was not identified on chest CT in 24% of patients.

Humans↗
PubMed1999

Surface free energy of ethylcellulose films and the influence of plasticizers.

The surface free energy parameters of ethylcellulose (EC) films were determined using the Lifshitz-van der Waals/acid-base approach and the influence of plasticizers on their surface energetics was assessed. Films were prepared by dip-coating glass slides in organic solvents containing EC and the advancing angles of drops of pure liquids on the EC films were measured with a contact angle goniometer using the captive drop technique. EC has lower surface free energy than cellulose. The acid-base (AB) term made only a slight contribution to the total surface free energy and the surfaces exhibited predominantly monopolar electron-donicity. The addition of plasticizer (dibutyl sebacate or dibutyl phthalate) resulted in a small decrease in the total surface free energy. The effects of film forming variables, including solvent system, concentration and post-formation treatment (annealing), on the surface free energy parameters of EC films were also investigated. These data were then used to analyze how the surface energetics affect the interaction of the EC films with other surfaces based on interfacial tension, work of adhesion and spreading coefficient calculations. Lifshitz-van der Waals (LW) interactions provided the major contribution to the work of adhesion for EC with all of the solid substrates analyzed. However, the AB interactions contributed significantly to the work of adhesion for EC with 'bipolar' substrates and to the spreading coefficients of EC over substrates. The consideration of work of adhesion and spreading coefficient based on surface free energy parameters may have potential use in evaluating factors affecting film adhesion and, furthermore, in optimizing pharmaceutical film coating processes.

Cellulose↗
PubMed1999

Prediction of the Hiestand bonding indices of binary powder mixtures from single-component bonding indices.

A priori predictions of the bonding indices of binary powder mixtures from the single-component indices were attempted. The binary mixtures were classified according to the mechanism of deformation of the single-components as plastic-plastic, brittle-brittle, and plastic-brittle. When the components of a binary mixture consolidated by the same mechanism (plastic-plastic and brittle-brittle mixtures), a straight line could be fit to a plot of bonding index versus composition. This linearity indicates that the bonding index can be reliably estimated by interpolation between the two single-component bonding indices. When the mixtures were such that one component was brittle while the other was plastic, a linear function did not fit the data. For these cases, a second-degree polynomial equation could be fit to a plot of bonding index versus composition. A combination of multiple linear regression and trial and error was used to generate a single generalized equation. For pairs of compounds wherein each compound has a different compaction mechanism, this new equation appears to allow satisfactory predictions of the bonding indices of mixtures with varying compositions using only the single-component bonding indices.

Drug Compounding↗
PubMed1998

Use of Fourier transform infrared (FTIR) spectroscopy to follow the adsorption of heptane and 1,4-dioxane vapors on a zinc oxide surface.

Vapor adsorption isotherms of two nonpolar model compounds, heptane and 1,4-dioxane, were determined for a very small particle size zinc oxide (ZnO) powder (median particle size approximately 23 nm) in the lower relative vapor pressure (P/Po) region. The ZnO samples for all adsorption measurements were dried at 400 degrees C for 4 h. A new method, which employed an FTIR spectrometer with a long path gas cell (IR path length of 3.0 m), was developed for the organic vapor adsorption measurements. The amount adsorbed was determined by mass balance. This method allows accurate quantification of organic vapors and is sensitive to very low P/Po values. The heptane and 1, 4-dioxane vapor adsorption isotherms appeared to exhibit the expected Type II behavior. The surface areas obtained for ZnO from BET analyses of the heptane and 1,4-dioxane vapor adsorption isotherms (36.9 and 30.3 m2/g) compared reasonably well to the surface area obtained from BET analysis of the nitrogen vapor adsorption isotherm (32.6 m2/g). The amount of vapor adsorbed by ZnO at P/Po equal to 0.1, in terms of number of moles, was observed to decrease in the order: water10 >> 1,4-dioxane > heptane. It was inferred that, while heptane was only adsorbed via a dipole-induced dipole interaction, 1,4-dioxane was physically adsorbed via an interaction dominated by the oxygen lone-pair orbital. Presumably, this interaction was more comparable to a weak dipole-dipole interaction. These results are consistent with the expected strengths of interaction.

Dioxanes↗
PubMed1997

Are rheumatoid arthritis patients more willing to accept non-steroidal anti-inflammatory drug treatment risks than osteoarthritis patients?

One hundred and thirty-four patients with either osteoarthritis or rheumatoid arthritis, and with a history of current or past non-steroidal anti-inflammatory drug (NSAID) treatment, were interviewed regarding the benefits, expectations and side-effects of NSAID therapy. Their willingness to accept risks in medical treatment was also evaluated. Both groups experienced positive effects of the NSAID treatment corresponding to their expectations. However, rheumatoid arthritis patients were significantly more willing to accept gastrointestinal side-effects when given an effective NSAID than the osteoarthritis patients, and they were also more willing to take risks in trying a hypothetical new NSAID that had been shown to be effective in clinical trials.

Adult↗
PubMed1997

Anti-rheumatic drug-prescribing behaviour of Australasian rheumatologists 1984-1994.

The prescribing behaviour of Australian and New Zealand rheumatologists was studied in 1994 using a questionnaire, and the results compared with a similar questionnaire administered in 1984. Perceived differences in efficacy and toxicity for disease-modifying anti-rheumatic drugs (DMARDs) and cytotoxics were reported. Over the decade, methotrexate and sulphasalazine have become the most commonly used anti-rheumatic agents, and methotrexate is clearly seen as the most effective drug. Wide variations in monitoring practices for DMARDs were reported, highlighting the need for cost-effectiveness studies on monitoring. There was low usage of functional outcome measurements in assessing patients.

Australia↗
PubMed1996

Rapid attenuation of AP-1 transcriptional factors associated with nitric oxide (NO)-mediated neuronal cell death.

Stimulation of glutamate receptors causes several intracellular reactions including activation of activator protein-1 (AP-1) production and nitric oxide (NO) generation. Exposing mouse cerebellar granule cells to N-methyl-D-aspartate or kainate (KA) in culture induced an increase of AP-1 DNA binding activity that was blocked by further addition of sodium nitroprusside (SNP), a typical NO donor. Immunoblotting using anti-c-Fos antiserum revealed the specific attenuation of AP-1, although total protein synthesis was not affected. Since the level of c-fos mRNA expression stimulated by KA remained constant even after exposure to SNP, the AP-1 attenuation can be post-transcriptionally induced. SNP did not affect the Ca2+ influx into the cells stimulated by KA. The involvement of NO in the AP-1 attenuation was supported by the fact that potassium ferrocyanide (K4Fe(CN)6), an analogue of SNP but devoid of NO, failed to inhibit the AP-1 DNA binding activity stimulated by KA. SNP alone induced neuronal cell death, which was blocked by the simultaneous addition of antioxidants, superoxide dismutase and catalase, and an NO scavenger, suggesting a direct role of peroxynitrite in the cell death. In good agreement with these effects, the AP-1 attenuation by SNP was also blocked by antioxidants. These results indicated that post-transcriptional attenuation of AP-1 is involved in the early processes of NO-mediated neuronal cell death.

Animals↗
PubMed1996

Psychometric functions for the discrimination of spectral variance.

An experiment was conducted to measure the shape of the psychometric function for the discrimination of spectral variance. The stimuli were simultaneous tone complexes comprised of the six octave frequencies from 250 to 8000 Hz. On each presentation the levels of components in dB were drawn independently and at random from one of two normal distributions having identical means but different variances (sigma N = 1 dB, sigma S = 2-10 dB). In the standard two-interval, forced-choice procedure, the listeners' task was to indicate which complex had the greater variance in component level. The shape of the psychometric function for all five listeners was markedly different from that of an observer limited only by additive internal noise. It was consistent with an observer that gives weight to only one or two components in the complex. However, this result was inconsistent with the weighting functions computed from the trial-by-trial data from these listeners. Both measures can be reconciled if it is assumed that listener weights vary from trial to trial, or that decisions are based on the one tone in the complex having the maximum level.

Adult↗
PubMed1996

Upper airway and soft tissue structural changes induced by CPAP in normal subjects.

Nasal continuous positive airway pressure (CPAP) is the treatment of choice for adults with obstructive sleep apnea. CPAP is known to increase upper airway size; however, the direct effects of CPAP on soft tissue structures surrounding the upper airway are less well understood. Magnetic resonance imaging was used to study the effect of incremental levels (0, 5, 10, and 15 cm H2O) of CPAP on the upper airway and surrounding soft tissue structures in 10 normal subjects. Progressive increases in CPAP resulted in the following major findings: (1) airway volume and airway area (measured at several different locations [midregion, minimal, maximal]) within the retropalatal and retroglossal regions increased; (2) lateral airway dimensional changes were greater than anterior-posterior changes; (3) lateral upper airway soft tissue structural changes were significantly greater than anterior-posterior changes; (4) lateral pharyngeal wall thickness decreased and the distance between the lateral parapharyngeal fat pads increased. An inverse relationship was demonstrated between CPAP level and pharyngeal wall thickness; (5) minimal changes were noted in the soft palate and tongue. These data suggest that the lateral pharyngeal walls are more "compliant" than the soft palate and tongue. This investigation provides further evidence that the lateral pharyngeal walls play an important role in mediating upper airway caliber.

Adult↗
PubMed1995

Determination of the mechanism for the decrease in zinc oxide surface area upon high-temperature drying.

High-temperature drying is required to remove chemisorbed water from the zinc oxide surface. High-temperature drying of a very small particle size zinc oxide powder (median particle size approximately 23 nm) resulted in a substantial decrease in the surface area. The surface areas (BET analysis of 77 K nitrogen vapor adsorption data) of ZnO samples dried at 500 degrees C decreased continually as the drying time was increased. Although the surface area decrease was fastest during the first 5 h, a 64% decrease in surface area was found after 20 h. The decrease in surface area was not due to a collapse of pore structure. Comparison of nitrogen vapor adsorption and desorption isotherms as well as geometric calculations of surface area indicated that both the original and final particles were nonporous. X-ray diffractograms of the original powder and of powders dried at two temperatures were all identical. Thus, no change in crystal structure occurred as a result of drying at 500 degrees C. Atomic force microscopy provided substantial evidence that the surface area decrease was due to a shift in the particle size distribution to a larger mean size. It was verified using two different experiments that ZnO exhibited significant sublimation at 500 degrees C. It was concluded that the increase in particle size was due to a sublimation/condensation process that obeyed the Kelvin equation. The effect of ZnO particle size on the vapor pressure ratio in the Kelvin equation was modeled at 500 degrees C for several different assumed solid surface tensions. Drying conditions for ZnO were then selected which balanced maximum removal of chemisorbed water and minimum surface area decrease. Water vapor adsorption isotherms for ZnO at 25 degrees C were subsequently obtained. Differences in the isotherms resulting from the presence or absence of a chemisorption contribution could clearly be demonstrated.

Adsorption↗
PubMed1995

Involvement of protein kinase C in Ca(2+)-signaling pathways to activation of AP-1 DNA-binding activity evoked via NMDA- and voltage-gated Ca2+ channels.

Stimulation of cultured cerebellar granule cells with N-methyl-D-aspartate (NMDA) or kainic acid (KA) leads to activation of activator protein-1 (AP-1) DNA-binding activity, which can be monitored by an increase in 12-O-tetradecanoylphorbol 13-acetate (TPA)-responsive element (TRE)-binding activity, in concert with c-fos induction. For this increase in TRE-binding activity, Ca2+ influx across the plasma membrane is essential. Treatment of cells with an intracellular Ca2+ chelator, BAPTA-AM, abolished this increase. Close correspondence between the dose-response curves of 45Ca2+ uptake and TRE-binding activity by NMDA or KA suggested that Ca2+ influx not only triggered sequential activation of Ca(2+)-signaling processes leading to the increase in TRE-binding activity, but also controlled its increased level. Stimulation of non-NMDA receptors by KA mainly caused Ca2+ influx through voltage-gated Ca2+ channels, whereas stimulation of NMDA receptors caused Ca2+ influx through NMDA-gated ion channels. The protein kinase C (PKC) inhibitors staurosporine and calphostin C inhibited the increase in TRE-binding activity caused by NMDA and KA at the same concentration at which they inhibited that caused by TPA. Furthermore, down-regulation of PKC inhibited the increase in TRE-binding activity by NMDA and KA. Thus, a common pathway that includes PKC could, at least in part, be involved in the Ca(2+)-signaling pathways for the increase in TRE-binding activity coupled with the activation of NMDA- and non-NMDA receptors.

Animals↗
PubMed1994

Modulation of AP-1 activity by nitric oxide (NO) in vitro: NO-mediated modulation of AP-1.

To understand the role of nitric oxide (NO) in controlling the specific DNA-binding activities of transcriptional factors, we investigated the in vitro effect of the NO-donor sodium nitroprusside (SNP) on the AP-1 activity of cultured mouse cerebellar granule cells. A gel-mobility assay showed that SNP inhibited AP-1 activity in the presence, but not the absence of dithiothreitol (DTT). This DTT-dependent inhibition of AP-1 activity by SNP corresponded with the activation of the chemical reactivity of SNP with DTT, which can be monitored by the production of nitrite (NO2-). In contrast, diamide, a typical sulfhydryl oxidizing agent, inhibited AP-1 activity in the absence of DTT and its inhibitory effect was reversed competitively by DTT. Studies using structurally or functionally related analogues of SNP demonstrated that S-nitrosylation of the AP-1 moiety mediated by some NO-carriers but not by free NO, which can be produced by the chemical reaction of SNP with DTT, was responsible for the inhibition of AP-1 activity, suggesting NO-mediated regulation of the AP-1 transcriptional factor.

3T3 Cells↗