Ultrafast pump-probe spectroscopy of electronic excitation transfer in random molecular systems and in photosynthetic antennae

Optical pump-probe (transient absorption) spectroscopy was used to study excitation energy transfer (EET) in random molecular systems and in antenna complexes of photosynthetic organisms. Energy transfer was first studied for Rhodamine 640 adsorbed on ZnO and fused silica surfaces at submonolayer coverage. Ground state recovery on fused silica was coverage-dependent due to excitation trapping by dye aggregates; on ZnO recovery was fast and independent of coverage. This can be explained by energy transfer into semiconductor surface states. Also, EET experiments were performed on solutions of Rhodamine 640 in glycerol using both absorption depolarization and the well-known technique of fluorescence depolarization using time-correlated single photon counting. Data from both techniques match within experimental error theoretical predictions, showing the validity of pump-probe techniques in studying EET;The absorption depolarization of the Q[subscript] x electronic transition in BChl a-protein from P. aestuarii was monitored, and the anisotropy was found to decay to a constant, nonzero value due to nonrandom chromophore orientations. The timescale of depolarization was found to be consistent with transfer between delocalized exciton states. Results of experiments on the core antenna complex of photosystem I were remarkably similar, showing that local ordering exists in PS I. This also suggests that EET occurs between groups of chromophores in PS I similar to those in the BChl a-protein. ftn[superscript]1DOE Report IS-T-1383. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy

Is Recess an Achievement Context? An Application of Expectancy-Value Theory to Playground Choices

This study investigated the application of an expectancy-value model to children’s activity choices on the playground at recess. The purpose was to test the prediction that expectancies for success and subjective task values are related to decisions to engage in specific recess activities such as climbing, playing soccer, or skipping rope. Participants included 242 children in grades 1-4 from five schools. Participation in playground activities was assessed using the Activities for Daily Living in Physical Play (ADL-PP) (Watkinson et al., 2001). Task-specific expectancies and values were measured on the playground activities contained in the ADL-PP. The results indicated that children’s perceptions of competence were significantly higher on playground skills that they had identified as most important compared with least important (pCe projet de recherche porte sur l’application d’un modèle de la perception de la valeur sur le choix d’activités que font les enfants dans le parc de jeux à la récréation. L’objectif de la recherche était de tester la prédiction selon laquelle les perceptions relativement à la réussite et les valeurs subjectives sont liées aux décisions de participer à des activités spécifiques pendant la récréation telles que grimper, jouer au soccer, ou sauter à la corde. À l’étude ont participé 242 élèves de la 1re à la 4e année provenant de cinq écoles. La participation aux activités du terrain de jeux a été évaluée selon le Activities for Daily Living in Physical Play (ADLPP) de Watkinson et al., 2001 (Activités pour le quotidien dans les jeux actifs). On a mesuré les perceptions de la valeur qu’attribuaient les enfants aux activités nommées dans la liste de Watkinson et al. Les résultats indiquent que les enfants percevaient que leur compétence quant aux habiletés sur le terrain de jeux étaient bien plus élevée pour celles qu’ils avaient identifiées comme étant plus importantes par rapport à celles auxquelles ils attribuaient moins d’importance (

Protein response to ligation reactions in myoglobin

The protein response to the photodissociation, escape and subsequent rebinding of carbon monoxide in myoglobin is studied using time-resolved infrared (TRIR) spectroscopy. All phases of these reactions areinvestigated, from ultrafast phenomena (picoseconds) to relatively slow processes (milliseconds). Conformational changes in myoglobin (Mb) are detected by time-resolved absorption changes in the amide I band. On the hundreds of nanoseconds to milliseconds timescale, a ``real-time`` apparatus is used. This apparatus is based on a tunable diode laser operating in the region of 1650 cm{sup {minus}1} . The time course ofchanges in the amide I band are shown to follow the recombination of CO with photolyzed Mb. On the basis of the rise times of the amide I and FE-CO signals, it is concluded that protein motion is complete within 100 n. A time-resolved difference spectrum in the amide I region is generated from single wavelength transients taken throughout the amide I envelope. A static difference spectrum is also generated by subtracting FTIR spectra of carbonmonoxy and deoxy myoglobin. The two difference spectra are compared and are interpreted in terms of the three-dimensional structures of deoxy and carbonmonoxy Mb. Preliminary picosecond TRIR data are also given for the ultrafast response of the protein immediately following photodissociation of CO

A Descriptive Profile of Physical Education Teachers and Related Program Characteristics in Alberta

A survey of teachers and principals in Alberta was conducted to gain a descriptive profile of who is leaching physical education (PE) and to assess the relationship between PE specialists and variables associated with program delivery. A probability-sampling procedure was used to obtain a representative sample of schools. In these schools nonprobability procedures were used to recruit teachers. A total of'480 teachers' and 162 principals' questionnaires were returned. Although 50% (n=236) of PE teachers in the sample were classified as PE specialists (i.e., had either a degree, major or minor, in PE or a closely related area), there was a significant gap in the number of PE classes being taught by division. Of the 1,219 PE classes surveyed in this study, PE specialists taught 49% and 55% of classes at the elementary levels (Divisions I & 11) compared with 91% of junior high (Division III) and 90% of secondary (Division TV) PE classes. Significant differences were found between PE specialists and non-PE specialists on a number of items including perceptions of preparedness, teaching enjoyment and competence to teach PE, the number of PE specialists across grade levels, and the percentage of time devoted to PE in the timetable. Implications with respect to implementing PE specialists across all grades and the need for future pedagogical research to investigate the effect of PE specialists are also discussed.Une enquête a été entreprise auprès d'enseignants et de directeurs d'école en Alberta dans le but d'établir un profil descriptif des enseignants d'éducation physique (EP) et d'évaluer le rapport entre les spécialistes en EP et les variables associées à l'exécution de programmes. On a eu recours aune méthode d'échantillonnage au hasard pour obtenir un échantillon représentatif des écoles. Par la suite, on y a employé des procédures non probabilistes pour recruter des enseignants. En tout, 642 questionnaires (480 provenant d'enseignants et 162 de directeurs) nous ont été renvoyés. Alors que 50% (n=236) des enseignants de EP de l'échantillon se classaient comme spécialistes en EP (c'est-à-dire qu'ils avaient soit un diplôme, une majeure ou une mineure en EP ou dans un domaine connexe), un écart notable existait dans le nombre de cours de EP enseignés par division. Des 1 219 cours de EP inclus dans l'enquête, à l'élémentaire, 49% (Division I) et 55% (Division II) d'entre eux étaient enseignés par des spécialistes en EP. Au secondaire premier cycle (Division III), 91% des cours étaient enseignés par des spécialistes en EP; au secondaire (Division IV), 90% des cours l'étaient. Des différences importantes distinguaient les spécialistes en EP des non spécialistes, y compris leurs perceptions quant à leur état de préparation, le plaisir qu'il retirait de l'enseignement de l'EP, leur compétence à le faire, le nombre de spécialistes en EP à tous les niveaux scolaires et le nombre d'heures consacrées aux cours de EP. Une discussion portant sur les implications de la mise en place de spécialistes en EP à tous les niveaux scolaires et sur la nécessité d'étudier l'effet qu'exercent ceux-ci, termine l'article

Reliable protein folding on non-funneled energy landscapes: the free energy reaction path

A theoretical framework is developed to study the dynamics of protein folding. The key insight is that the search for the native protein conformation is influenced by the rate r at which external parameters, such as temperature, chemical denaturant or pH, are adjusted to induce folding. A theory based on this insight predicts that (1) proteins with non-funneled energy landscapes can fold reliably to their native state, (2) reliable folding can occur as an equilibrium or out-of-equilibrium process, and (3) reliable folding only occurs when the rate r is below a limiting value, which can be calculated from measurements of the free energy. We test these predictions against numerical simulations of model proteins with a single energy scale.Comment: 13 pages, 9 figure

Perfectionism and Grit in Competitive Sport

Perfectionism and grit have both been linked to the achievement-striving process in sport, yet very little is known about the relationships between the two constructs. The present study explored the degree to which perfectionistic strivings and perfectionistic concerns predicted two dimensions of grit—consistency of interest and perseverance of effort—in a sample of 251 intercollegiate varsity athletes (Mage = 20.34 years; SD = 2.0). Both perfectionism and grit were conceptualized and measured as multidimensional domain-specific constructs. Results of structural equation modeling analyses indicated that perfectionistic strivings was positively associated with consistency of interest (β = .49, p < .001) and perseverance of effort (β = .92, p < .001). In contrast, perfectionistic concerns was negatively associated with both consistency of interest (β = -.47, p < .001) and perseverance of effort (β = -.66, p < .001). Results indicate that higher-order dimensions of perfectionism (i.e., perfectionistic strivings and perfectionistic concerns) are associated with domain-specific aspects of grit in sport. Results highlight the importance of (a) differentiating between athletes’ perfectionistic strivings and perfectionistic concerns in sport, and (b) treating consistency of interest and perseverance of effort as separate components of grit. Future research that examines the combined effects of perfectionism and grit on the achievement-striving process in competitive sport is recommended