Kurzzeitspektroskopische Untersuchungen der Fotoschutzmechanismen an Lichtsammelkomplexen

In der vorliegenden Arbeit wurden die Photoschutzmechanismen in Pflanzen und Purpurbakterien auf molekularer Ebene experimentell untersucht. Zu diesem Zweck kamen verschiedene spektroskopische Methoden zur Aufklärung der Funktion der dabei vor allem beteiligten Carotinoide zur Anwendung. Die Experimente konzentrierten sich auf die Quenching-Mechanismen von Singulett- und Triplett-Zuständen der elektronisch angeregten (Bacterio-) Chlorophylle. Diese photosynthetischen Reaktionen treten auf ultraschnellen Zeitskalen im Bereich vom Femtosekunden bis Nanosekunden auf, sodass sich Femtosekunden zeitaufgeloeste Absorptionsspektroskopie als geeignetes Methode erweist die molekulare Dynamik in Echtzeit zu verfolgen. Sowohl mittels herkoemmlicher Anreg-Abtast-Spektrokopie als auch mit im Rahmen dieser Arbeit weiter entwickelter resonanter Zwei-Photonen Zwei-Farben Ionisation (R2P2CI), wurden eine Reihe von photosynthetischen Antennensystemen untersucht: Aus photosynthetischen Purpurbakerien wurden der Lichtsammelkomplex 1 (LH1) sowie der Lichtsammelkomplex II (LHC II) und die chlorophyllgebunden Proteine CP24, CP26 und CP29 höherer Pflanzen charakterisiert. Darüber hinaus wurden eine Reihe von Carotinoiden und ihre Radikalkationen als wesentlicher Bestandteil der photoindizierten Reaktionskanaele in Lösung untersucht. Diese Experimente erlauben die Auswirkung der Lösungsmittelpolarität auf die Eigenschaften der Carotinoide (energetische Lage und die Dynamik der angeregten Zustände, Wechselwirkung mit benachbarten photosynthetischen Pigmenten) zu untersuchen.In the present work, the photo-protection mechanisms in plants and purple bacteria were investigated experimentally at the molecular level. For this purpose, several spectroscopic methods were combined and applied to elucidate the function of carotenoids, pigments of the photosynthetic apparatus, in photo-protection. The experiments were focused on the mechanisms involved in quenching of singlet and triplet states of the electronically excited (bacterio)chlorophylls. This photosynthetic reaction events occur on an ultrafast time-scale. Measuring such short-lived events, and understanding the underlying principles, demand some of the most precise experiments and exact measurement technologies currently available. This implies certain requirements for the light source used: a suitable wavelength within the absorption band of the sample, sufficient power, and, most importantly, a pulse duration short compared to the studied reaction. Nowadays, we can achieve all this requirements using femtosecond-spectroscopic systems, which produce laser pulses shorter than 100 femtoseconds (fs). Transient absorption spectroscopy provides important information on molecular dynamics interrogating electronic transitions. The technique is based on photochemical generation of transient species with femtoseconds pump pulses and measuring transient absorption changes of the sample using a second, time delayed probe pulse which in this case is a spectrally broad white-light pulse

Sub-micron surface plasmon resonance sensor systems

A sensor for detecting the presence of a target analyte, ligand or molecule in a test fluid, comprising a light transmissive substrate on which an array of surface plasmon resonant (SPR) elements is mounted is described. A multi-channel sensor for detecting the presence of several targets with a single micro-chip sensor is described. A multi-channel sensor including collections of SPR elements which are commonly functionalized to one of several targets is also described. The detectors sense changes in the resonant response of the SPR elements indicative of binding with the targets

Investigating students seriousness during selected conceptual inventory surveys

Conceptual inventory surveys are routinely used in education research to identify student learning needs and assess instructional practices. Students might not fully engage with these instruments because of the low stakes attached to them. This paper explores tests that can be used to estimate the percentage of students in a population who might not have taken such surveys seriously. These three seriousness tests are the pattern recognition test, the easy questions test, and the uncommon answers test. These three tests are applied to sets of students who were assessed either by the Force Concept Inventory, the Conceptual Survey of Electricity and Magnetism, or the Brief Electricity and Magnetism Assessment. The results of our investigation are compared to computer simulated populations of random answers.Comment: 8 pages; submitted to Phys Rev PE

Sub-micron surface plasmon resonance sensor systems

A sensor for detecting the presence of a target analyte, ligand or molecule in a test fluid, comprising a light transmissive substrate on which an array of surface plasmon resonant (SPR) elements is mounted is described. A multi-channel sensor for detecting the presence of several targets with a single micro-chip sensor is described. A multi-channel sensor including collections of SPR elements which are commonly functionalized to one of several targets is also described. The detectors sense changes in the resonant response of the SPR elements indicative of binding with the targets

Praxis et formations littéraires : ce que nous apprend le creative writing américain

Pour rendre compte du déplacement exercé sur l’appréhension du littéraire par les formations privilégiant la pratique créative, l’examen se porte sur des séances d’ateliers d’écriture dans les cursus américains en creative writing. L’étude prend d’abord acte d’un investissement différent dans les traditions française et américaine des termes praxis et poièsis. L’analyse est ensuite conduite en tenant compte d’objections présentes dans Condition de l’homme moderne d’Hannah Arendt. Le recueil d’observations, comportant également des témoignages de professeurs, d’étudiants et de directeurs de programmes, est donc examiné en envisageant que l’assignation de fins pratiques, en phase avec une certaine modernité, puisse contrevenir à la nature de l’acte littéraire. Les échanges engendrés par l’examen des textes d’étudiants invitent pourtant à reconnaître la qualité de l’enquête littéraire engagée ; ils invitent également à distinguer la posture de l’écrivain, fût-il débutant, de celle du commentateur. Ce sont finalement des pistes de théorisation de l’écriture créative comme champ de recherche qui sont envisagées, en tirant profit de la comparaison internationale.In order to appreciate how writing programs favoring practical approach move the literary approach, the present paper aims at studying writing workshops at different US universities. The research study begins with the difference between French and American traditions in the use of the words praxis and poièsis. It then focuses on the objections reported by Hannah Arendt in The Human Condition. The data, that encompass testimonies from professors, students and program directors, are analyzed in the scope of the practical aims in harmony with a certain modernity. This scope might be in contradiction with the literary process. However, the workshop discussions based upon the students’ texts entail the acknowledgement of the literary quality of their production ; it leads as well to the distinction between the attitude of the writer, even the beginner, and the position of the commentator. Finally, the study considers the clues to theorization of creative writing as a field of research, by means of international comparison

An Algorithm for File Transfer Scheduling in Grid Environments

This paper addresses the data transfer scheduling problem for Grid environments, presenting a centralized scheduler developed with dynamic and adaptive features. The algorithm offers a reservation system for user transfer requests that allocates them transfer times and bandwidth, according to the network topology and the constraints the user specified for the requests. This paper presents the projects related to the data transfer field, the design of the framework for which the scheduler was built, the main features of the scheduler, the steps for transfer requests rescheduling and two tests that illustrate the system's behavior for different types of transfer requests.Comment: Proceedings of the International Workshop on High Performance Grid Middleware (HiPerGrid), pp. 33-40, Bucharest, Romania, 21-22 November, 2008. (ISSN: 2065-0701