Search PubMed⌕ Search

Biomedical subjects

Y H Yoon

Publications and source records attributed to Y H Yoon.

At least 37 records · Page 2Linked to original sources
PubMed1996

Respirator cartridge service-life: exposure to mixtures.

Expressions associated with a previously developed procedure to assess respirator cartridge service-life were modified to address the cartridge breakthrough properties of each of individual compounds comprising systems with more than two components. These were applied to specific ternary and quaternary test mixtures. Experimental breakthrough data were collected for (1) acetone/cyclohexane/toluene, (2) ethyl acetate/cyclohexane/toluene, (3) cyclohexane/toluene/ m-xylene, (4) ethyl acetate/cyclohexane/toluene/m-xylene, and (5) acetone/ cyclohexane/toluene/ m-xylene. Data indicate that as an exposure experiment proceeds, a compound that is adsorbed relatively weakly by the carbon bed may be displaced by a more strongly adsorbed component, which may result in a breakthrough concentration for displaced compounds that exceeds the challenge concentration in the mixture. The approach described accounts for the displacement phenomenon and can predict the ratio of the number of displaced molecules to the corresponding number of displacing molecules. Experimental data for each multicomponent system were used to determine values of three parameters (k', tau, and A(m)) for each compound in each challenge system. The value of k' characterizes the rate of adsorption of a compound under applicable experimental conditions, tau indicates the capacity of the charcoal, and A(m) describes the effectiveness of a compound in displacing a previously adsorbed compound. Parameter values were applied to calculate complete breakthrough curves for each compound of each mixture. Calculated curves were compared with corresponding experimental data; reasonable agreement justifies simplifying assumptions incorporated into the application of the approach to mixtures of more than two compounds. The time-dependence of the weight of each compound adsorbed by the carbon was calculated. The service-life of respirator cartridges exposed to multicomponent mixtures depends on the challenge concentration of each component of the system and is significantly influenced by the displacement effect. The adsorption capacity of the carbon and the breakthrough time for weakly adsorbed compounds are decreased significantly by exposure to mixtures.

Acetates↗
PubMed1996

Pollen of a male-sterile mutant of Arabidopsis thaliana isolated from a T-DNA insertion pool is not effectively released from the anther locule.

We have isolated a male-sterile mutant from a pool of T-DNA insertional lines of Arabidopsis thaliana generated by an in planta transformation procedure [Chang et al. (1994) Plant J. 5: 551]. Pollen in this mutant is not effectively released from anther locules after cleavage of the stomium. Most mutant pollen grains are round, in contrast to the tricolpate wild-type pollen, and some pollen grains show an abnormal surface structure. Manually released mutant pollen grains are not fertile and show defects in pollen tube germination in vitro. Genetic analysis disclosed that this lesion is due to a single recessive nuclear mutation located on chromosome 3 closely linked to the gll locus. The mutation locus is tightly linked to the inserted T-DNA.

Arabidopsis↗
PubMed1996

Preservation of retinal sensitivity in central visual field after panretinal photocoagulation in diabetics.

Changes in retinal sensitivity within central 30 degrees following panretinal photocoagulation (PRP) for more severe diabetic retinopathy were investigated. Twenty-five eyes with visual acuity of 0.4 or better and minimal maculopathy were studied prospectively. All underwent PRP in two sittings, and Humphrey field analyzer 30-2 threshold test was done before and 1 week, 1 and 3 months after the treatment. The mean retinal sensitivity threshold was obtained from each hemifield between 15 and 30 degrees and from the central 15 degree area, and the changes in the values were analyzed. Mean sensitivity threshold in the upper visual field at pre-PRP, post-PRP 1 week, 1, 3 months were 15.62, 13.81, 14.31, 14.85, respectively. Values in the lower field were 18.71, 17.25, 17.10, 18.17. Difference between pre-PRP and post-PRP was statistically significant at 1 week but no longer thereafter. Retinal sensitivity within the central 15 degrees remained stable. The data show that retinal sensitivity decreases significantly 1 week after PRP but recovers upto 95% of pre-PRP level over the following 3 months.

Adult↗
PubMed1993

Retinal pigment epithelium adhesion to Bruch's membrane is weakened by hemicholinium-3 and sodium iodate.

We have studied the effects of hemicholinium-3 (HC-3), an outer segment and retinal pigment epithelium (RPE) toxin and sodium iodate, an RPE toxin, on retinal and RPE adhesion in rabbits. During the first 3 days after intravitreal HC-3, the force required to peel retina from RPE fell to 50% of normal, and large patches of RPE separated from Bruch's membrane and adhered to the peeled retina. The same phenomena were observed during the first 100 min after intravenous sodium iodate. Beyond 3 days after HC-3, and 100 min after sodium iodate, the peeling force became even weaker, but separation occurred at the subretinal space or by fragmentation of RPE cells. Acute RPE toxicity probably accounts for the initial weakening of the bond between RPE and Bruch's membrane.

Animals↗
PubMed1992

Breakthrough time and adsorption capacity of respirator cartridges.

A model developed in previous studies was applied to investigate the respirator cartridge contaminant breakthrough of 121 different chemical compounds. Included in this set of 121 contaminants are representative examples of various types of organic compounds, (e.g., acetates, ketones, aromatics, alcohols, amines, alkanes, chlorinated hydrocarbons). Intrinsic to the model are two important parameters, k' (a rate constant) and tau (50% breakthrough time). Values of the two parameters pertinent to an assault concentration of 1000 ppm were determined for each of the 121 organic compounds. These values were used to calculate the breakthrough time at specified fractional breakthrough as well as the respirator cartridge loading capacity under various conditions. An approach was presented that permits the determination of contaminant loading capacity (on carbon) as a function of breakthrough time at a specified assault concentration. The effect of contaminant assault concentration on the saturation capacity was investigated for various combinations of nine different compounds and three different types of respirator cartridges. Calculated saturation capacity data derived from application of the model compare favorably (+/- 5%) with corresponding experimental data. Saturation capacities calculated by using the model addressed in this study were compared with corresponding results previously calculated by others using the Dubinin adsorption isotherm.

Acetates↗
PubMed1992

A theoretical model for respirator cartridge service life for binary systems: application to acetone/styrene mixtures.

A theoretical model, developed previously to assess respirator cartridge service life, was applied to various acetone/styrene binary assault systems. Experimental data, collected for several binary mixtures differing only with respect to the concentration of each of the two compounds, were interpreted in terms of the model. Styrene concentrations varied from 228 to 1578 ppm; the range of acetone concentrations was 92-985 ppm. The specific influence of the compound assault concentrations on respirator cartridge service life was carefully characterized, as break-through curves were generated for both acetone and styrene for each of several different binary systems. Specifically, experimental data for each system were used to determine values of the following theoretical parameters: k'1, tau 1, k'2, tau 2, and Am. These parameters were employed with the theory to generate complete theoretical breakthrough curves and to determine the time-dependence of the weight of each compound adsorbed by the respirator cartridge carbon bed. An interesting phenomenon observed for the acetone/styrene systems was the displacement (from the carbon) of previously adsorbed acetone molecules by styrene molecules. Acetone breakthrough was observed first in each of the systems studied. Following the onset of this breakthrough, the acetone breakthrough concentration was enhanced by the displacement of acetone from the carbon bed by the adsorption of styrene. The theoretical model accurately predicts both this enhancement and the associated breakthrough characteristics of styrene. In addition, the theory is capable of predicting the ratio of the number of displaced acetone molecules to the corresponding number of displacing styrene molecules. For these studies, this ratio ranged from 0.3 to 0.7. The service life of respirator cartridges exposed to acetone/styrene mixtures depends on the assault concentration of each compound and is significantly influenced (shortened) by the displacement phenomenon.

Acetone↗
PubMed1990

Effects of humidity and contaminant concentration on respirator cartridge breakthrough.

A model described previously was developed further to examine the effect of both test humidity and contaminant assault concentration on respirator cartridge service life. The model emphasized the characterization of cartridge performance in the range of 0% to 50% breakthrough. This study specifically addressed a contaminant concentration range of 250-2000 ppm and test humidities ranging from 0% to 80%. The preconditioning humidity was fixed at 50%. The compounds studied were benzene and methyl chloroform. Two parameters, k' and tau, were described and values of these parameters were determined for each of several different sets of experimental conditions. The determined values of k' and tau were applied using derived expressions to generate each of several complete breakthrough curves for benzene and for methyl chloroform at specified contaminant assault concentrations and test humidities. The effect of humidity on the value of an additional theoretical parameter, a, was investigated. Values of this parameter and the parameters, k and K", were determined for specific test conditions. These values were substituted into pertinent expressions to produce a complete set of breakthrough curves (each curve corresponding to a particular contaminant assault concentration) for a given compound at a fixed test humidity. Several examples of breakthrough curves were generated for methyl chloroform. The results derived from the study agreed with corresponding experimental data.

Equipment Failure↗
PubMed1990

Contaminant breakthrough: a theoretical study of charcoal sampling tubes.

A previously developed theoretical model was applied to investigate contaminant breakthrough on charcoal sampling tubes. Associated with the model are two important theoretical parameters. These parameters are k' (a rate constant) and tau (the time required for 50% contaminant breakthrough). In this study, values of K' and tau were determined for n-heptane at five different concentration levels in air: 98, 117, 234, 330, and 988 ppm. These values were used along with pertinent theoretical considerations to calculate the entire (0-100%) breakthrough curve (plot of percent breakthrough versus time) regarding the adsorbance of n-heptane on charcoal sampling tubes. In addition, available experimental data for perchloroethylene, isobutyl acetate, ethyl acetate, and dichloromethane were used in conjunction with the theory to generate theoretical breakthrough curves over the entire range of 0 to 100%. In each case, calculated theoretical breakthrough curves are in remarkable agreement with corresponding experimental data. With the use of an additional theoretical parameter, a, the theory was extended to calculate the weight of contaminant collected on a single element (section) of a charcoal sampling tube at 10% breakthrough and at each of several different contaminant assault concentrations.

Acetates↗
PubMed1989

Dextromethorphan protects retina against ischemic injury in vivo.

Retinal ischemia was induced in rabbits by increasing intraocular pressure above systolic blood pressure for 60 or 75 minutes, and retinal function was monitored by electroretinography. Pretreatment with intravenous dextromethorphan, a nonprescription antitussive and selective antagonist of N-methyl-D-aspartate receptors, enhanced greatly the post-ischemic recovery of b-wave amplitude. Dextromethorphan may prove to be useful clinically in the management of retinal ischemic disease.

Animals↗
PubMed1989

Antiulcerogenic compounds isolated from Chinese cinnamon.

Two active compounds that prevent serotonin-induced ulcerogenesis in rats were isolated from Chinese cinnamon (the stem bark of Cinnamomum cassia) and identified as 3-(2-hydroxyphenyl)-propanoic acid and its O-glucoside. The former compound, administered orally or parenterally to rats at a remarkably low dose (40 micrograms/kg body weight), also inhibited gastric ulcers induced by the other ulcerogens such as phenylbutazone, ethanol, and water immersion stress, although it failed to prevent indomethacin-induced ulcers. Pharmacological studies have shown that 3-(2-hydroxyphenyl)-propanoic acid hardly inhibited the secretion of gastric acid, but promoted the gastric blood flow. These results suggest that the antiulcerogenic effect of this compound is probably attributable to the potentiation of defensive factors through the improvement of the circulatory disorder and gastric cytoprotection.

Animals↗
PubMed1988

Rapid enhancement of retinal adhesion by laser photocoagulation.

To determine how quickly laser photocoagulation produces a bond between retina and pigment epithelium, the authors measured the strength of retinal adhesion after making laser burns through intact and recently reattached rabbit retina. After photocoagulation of intact retina, the adhesive force was reduced 50% at 8 hours but increased beyond normal (to approximately 140%) by 24 hours and remained twice normal between 3 days and 4 weeks. Photocoagulation of retina that had just settled after experimental detachment produced similar results, except that the maximum strength of adhesion (reached at 2 weeks) was three times normal. In contrast, retina that reattached spontaneously, without photocoagulation, showed only 10% of normal adhesiveness at 24 hours, and still was only 75% of normal after 4 weeks. These data suggest that laser photocoagulation may be acutely beneficial in the prevention or management of retinal tears and detachments.

Adhesiveness↗
PubMed1988

Effects of retinal adhesion of temperature, cyclic AMP, cytochalasin, and enzymes.

We have studied factors that contribute to retinal adhesion, by measuring directly the force required to peel rabbit retina from the retinal pigment epithelium (RPE). Exposing the tissue to either testicular hyaluronidase or neuraminidase, or acidifying the medium to pH 6.0, reduced the peeling force within 2 min. Cooling the tissue to 25 degrees C or 4 degrees C increased the peeling force to such a degree that retinal separation occurred by rupture of the RPE cells rather than widening of the subretinal space. Inhibition of the cytoplasmic contractile system with cytochalasin had no significant effect on peeling force, but dibutyryl cAMP (which decreases fluid absorption by the RPE) weakened adhesion. These results suggest that retinal adhesion involves a number of interrelated physical and metabolic factors.

Adhesiveness↗
PubMed1984

Preclinical safety evaluation of the nadolol/bendroflumethiazide combination in mice, rats, and dogs.

Nadolol, a beta-adrenergic antagonist, and bendroflumethiazide, a thiazide diuretic, were administered orally alone and in combination to animals in acute and 6-month toxicity studies and in a rat teratology study. The two drugs in combination showed no evidence of potentiation of acute toxicity in mice. Nadolol and/or bendroflumethiazide were administered orally to rats at daily doses of 1000 or 160 mg/kg of nadolol and 125 or 20 mg/kg of bendroflumethiazide and to dogs at daily doses of 160 or 40 mg/kg of nadolol and 20 or 5 mg/kg of bendroflumethiazide for 6 months. The two drugs, alone and in combination, caused only minor changes in clinical-laboratory tests and no major gross or histopathologic changes. Many of the changes noted were expected pharmacologic effects of the individual agents. The drugs, alone or in combination, produced no evidence of embryotoxicity, fetotoxicity, or teratogenicity in rats. The results of these studies indicate that nadolol and bendroflumethiazide have a low order of toxicity individually, and when given in combination show no additional or potentiated toxicity.

Animals↗
PubMed1984

Application of gas adsorption kinetics. I. A theoretical model for respirator cartridge service life.

Using the principles of gas adsorption kinetics, we have developed a new theoretical model addressing the adsorption and breakthrough of contaminant vapors or gases with respect to solid sorbents. Specifically, we have applied the theory to predict respirator cartridge service life in connection with individual contaminant exposure to toluene, vinyl chloride, ethyl acetate, and each of several different trichlorinated hydrocarbons at several levels of concentration. Theoretical expressions and contaminant breakthrough curves derived from our new approach are compared with those published previously by Mecklenburg and by Wheeler. The breakthrough curves derived by Mecklenburg and by Wheeler have approximately the same shape as the corresponding experimental curves for 0% to 40% breakthrough. However, these curves deviate in varying degrees from the experimental data at breakthrough values exceeding 40%. By contrast, our new theory agrees with published experimental results over the entire range of 0% to 100% breakthrough. The new model not only agrees with experimental observation, it is also less complicated and easier to apply to practical industrial hygiene problems than theories developed previously.

Adsorption↗
PubMed1984

Application of gas adsorption kinetics--II. A theoretical model for respirator cartridge service life and its practical applications.

A previously introduced theoretical model addressing respirator cartridge contaminant breakthrough was further developed in this study. This development involved the introduction of a new theoretical parameter, a, to complement the parameters k' and tau employed in the initial theoretical approach. The extension of the theory permits the theoretical investigation of the following: (1) the effect of contaminant concentration on breakthrough time; (2) the effect of flow rate on breakthrough time; (3) the influence of contaminant concentration on percentage of breakthrough; and (4) the effect of contaminant concentration on the weight of adsorbed contaminant at a given time. We also compared new theoretical expressions with previously published empirical equations. Utilizing the parameter a, we derived a set of equations of significant practical value. These equations relate the ratio of two contaminant concentrations (one experimental reference concentration and any other concentration of interest) to either the ratio of the corresponding breakthrough times or the corresponding weights of adsorbed contaminant. Three practical examples are provided demonstrating that the new theoretical model reduces experimental work required to predict respirator cartridge service life.

Adsorption↗
PubMed1977

Single partition function for three phases.

The significant structures theory of liquids has been extended to take into account (i) translational degrees of freedom in the degeneracy term and (ii) the perturbation term which becomes important near the critical region. With these improvements, the calculated thermodynamic properties of argon agree very well with experimental results from the melting point through the critical point, along the coexistence curve as well as along the critical isochore and for the solid and the vapor.

Journal Article↗