Biomedical subjects

P E Wagner

Publications and source records attributed to P E Wagner.

6 recordsLinked to original sources

PubMed2005

Homogeneous nucleation of n-nonane and n-propanol mixtures: a comparison of classical nucleation theory and experiments.

The homogeneous nucleation rates for n-nonane-n-propanol vapor mixtures have been calculated as a function of vapor-phase activities at 230 K using the classical nucleation theory (CNT) with both rigorous and approximate kinetic prefactors and compared to previously reported experimental data. The predicted nucleation rates resemble qualitatively the experimental results for low n-nonane gas phase activity. On the high nonane activity side the theoretical nucleation rates are about three orders of magnitude lower than the experimental data when using the CNT with the approximate kinetics. The accurate kinetics improves the situation by reducing the difference between theory and experiments to two orders of magnitude. Besides the nucleation rate comparison and the experimental and predicted onset activities, the critical cluster composition is presented. The total number of molecules is approximated by CNT with reasonable accuracy. Overall, the classical nucleation theory with rigorous kinetic prefactor seems to perform better. The thermodynamic parameters needed to calculate the nucleation rates are revised extensively. Up-to-date estimates of liquid phase activities using universal functional activity coefficient Dortmund method are presented together with the experimental values of surface tensions obtained in the present study.

Journal Article↗

PubMed2003

Nucleation probability in binary heterogeneous nucleation of water-n-propanol vapor mixtures on insoluble and soluble nanoparticles.

Nucleation probabilities for binary heterogeneous nucleation have been measured quantitatively. Heterogeneous nucleation of binary n-propanol-water vapor mixtures on partially soluble 6.9-nm NaCl particles and on nonsoluble oxidized and nonoxidized 8-nm Ag particles at a constant nucleation temperature of 288 K (NaCl) or 285 K (Ag) has been investigated experimentally and theoretically. An expansion chamber was applied to generate supersaturated vapor mixtures. Number concentrations of particles activated to condensational growth were determined optically for various vapor phase activities at constant temperature. Nucleation probabilities have been measured as functions of the vapor phase activities for several n-propanol-water vapor mixing ratios. Beyond certain vapor phase activities a sharp onset of heterogeneous nucleation was observed both for NaCl and for Ag particles. For insoluble particle surfaces the theoretical slopes of the nucleation probability versus vapor phase activity curves were found to be somewhat steeper as compared to the experiment. On the other hand, for soluble particles the experimental slopes were found to be in satisfactory agreement with theory. The onset of the nucleation process is defined at an activity value where 50% of the particles were activated to condensational growth. Onset activities were obtained for various mixing ratios of the binary vapor mixtures. In the case of NaCl nuclei for n-propanol rich mixtures, the heterogeneous nucleation calculations based on a thermodynamically consistent version of Fletcher theory and an experimentally determined contact angle provide a reasonable approximation of the experimental data. However, it appears that the Fletcher theory is not applicable in the region of transition from n-propanol rich to water rich mixtures. Based on the Köhler theory of activation of soluble particles, a theory was formulated accounting for the presence of two condensable vapors and limited solubility of NaCl in water-propanol liquid mixtures. This approach provides a satisfactory description of the transition from activation of soluble particles to nucleation of vapors on insoluble particles. In the case of silver particles Fletcher theory with macroscopic experimental contact angles as well as with contact angle zero results in strong deviations from experimental data. A significant improvement was achieved by introducing fit contact angles, which are substantially lower than the macroscopic experimental values and may be considered as approximate values of the microscopic contact angles.

Journal Article↗

PubMed2001

Soluble-insoluble transition in binary heterogeneous nucleation.

In this Letter, we report the first experimental study of binary heterogeneous gas-liquid nucleation. Onset activities were obtained for nucleation of various n-propanol-water vapor mixtures on 6.9 nm NaCl particles soluble in water and practically insoluble in n-propanol. The Fletcher theory of vapor nucleation on insoluble particles provided a reasonable approximation for n-propanol rich mixtures only, whereas the Köhler theory of activation of soluble particles worked only for water rich mixtures. A new theory was formulated providing a satisfactory description of the transition from activation of soluble particles to vapor nucleation on insoluble particles.

Journal Article↗

PubMed1996

Assessing individual differences in constructive versus destructive responses to anger across the lifespan.

Scenario-based, self-report measures were developed to assess how people characteristically experience and manage anger from middle childhood through adulthood. The Anger Response Inventories (ARIs) for children, adolescents, and adults each assess (a) anger arousal, (b) intentions, (c) cognitive and behavioral responses, and (d) Long-term consequences. Several independent studies provide support for the reliability and validity of the ARIs. Theoretically consistent patterns of correlations were observed with (a) global self-report measures of hostility, aggression, and anger-management strategies (adult version); (b) teacher reports of behavioral and emotional adjustment (child and adolescent versions); and (c) self- and family-member reports of behaviors on specific anger episodes (adolescent and adult versions). Findings from additional personality and developmental studies are summarized, further supporting construct validity.

Adaptation, Psychological↗

PubMed1996

Relation of shame and guilt to constructive versus destructive responses to anger across the lifespan.

This study explored the relation of shame proneness and guilt proneness to constructive versus destructive responses to anger among 302 children (Grades 4-6), adolescents (Grades 7-11), 176 college students, and 194 adults. Across all ages, shame proneness was clearly related to maladaptive response to anger, including malevolent intentions; direct, indirect, and displaced aggression; self-directed hostility; and negative long-term consequences. In contrast, guilt proneness was associated with constructive means of handling anger, including constructive intentions, corrective action and non-hostile discussion with the target of the anger, cognitive reappraisals of the target's role, and positive long-term consequences. Escapist-diffusing responses showed some interesting developmental trends. Among children, these dimensions were positively correlated with guilt and largely unrelated to shame; among older participants, the results were mixed.

Adaptation, Psychological↗

PubMed1982

Metabolic profiles in Virginia dairy herds of different milk yields.

This study examined metabolic profiles of commercial dairy herds differing in milk production. Thirty herds were selected with 10 herds averaging more than 7258 kg milk, 10 herds between 6350 and 7258 kg, and 10 herds averaged below 6350 kg. In each herd, 28 cows were selected for blood sampling, which was collected every 3 mo during 12 mo. Cows varied in estimated relative producing ability. Metabolic profiles were established for 19 blood components. Differences among treatment means were significant between high and low producing herds and little between profiles for milking and pregnant nonlactating cows. Metabolic profiles of problem herds remained within normal ranges for all herds except one. Profiles of herds with breeding or mastitis problems remained in the normal range. Metabolic profile testing was of limited value in screening a dairy herd for potential problems or deficiencies.

Animals↗