Observation of a bacteriochlorophyll anion radical during the primary charge separation in a reaction center

The primary light-induced charge separation in reaction centers of Rhodobacter sphaeroides was investigated with femtosecond time resolution. The absorption changes in the time range 100 fs to 1 ns observed after direct excitation of the primary donor P at 860 nm could only be explained by a kinetic model which uses three time constants. This finding supports the following reaction scheme: (i) the electronically excited primary donor P* decays with a time constant of 3.5 ps and populates a very short-lived intermediate involving a reduced accessory bacteriochlorophyll molecule; (ii) with a time constant of 0.9 ps the electron is transferred to the neighboring bacteriopheophytin molecule; and (iii) from there within 200 ps to the quinone

Initial electron-transfer in the reaction center from Rhodobacter sphaeroides.

The initial electron transfer steps in the photosynthetic reaction center of the purple bacterium Rhodobacter sphaeroides have been investigated by femtosecond time-resolved spectroscopy. The experimental data taken at various wavelengths demonstrate the existence of at least four intermediate states within the first nanosecond. The difference spectra of the intermediates and transient photodichroism data are fully consistent with a sequential four-step model of the primary electron transfer: Light absorption by the special pair P leads to the state P*. From the excited primary donor P*, the electron is transferred within 3.5 +/- 0.4 ps to the accessory bacteriochlorophyll B. State P+B- decays with a time constant of 0.9 +/- 0.3 ps passing the electron to the bacteriopheophytin H. Finally, the electron is transferred from H- to the quinone QA within 220 +/- 40 ps

Negotiating new ICTs in the education sector in Afghanistan - participation, adoption and appropriation

The importance of a participatory component has become broadly accepted in today’s international development programs. Accordingly, most organisations dealing with technology-use strategies in the education sector in Afghanistan highlight concepts like ‘empowerment’, ‘Afghan ownership’ and ‘partnership’ in their project descriptions. Yet the definition of participation ranges from the idea that all stakeholders should actively take part to a more narrow concept of extracting local knowledge to design programs externally. This limited participation is in the case of ICTs often further reinforced by technology being seen as a black box1 (a stable ‘input-output device’) with a predefined optimal application that needs to be taught by the technology experienced West to those in need of development. This is often even motivated by particular ideas about how the technology should support certain educational practice and organisational structures. In my PhD thesis I explore the evolution and consequences of ICT project design and implementation from the perspectives of different actors involved in, or affected by, the intervention. The empirical aspects are centred on three examples all located in the Afghanistan setting: a school-laptop project, a university network infrastructure project and the broader question concerning what role ICT capacity building plays. As a consultant in the field I was able to follow the projects’ development over the course of several of years and gained profound insight. The research is informed by a broad-based review of the research literature in fields of communication and development, Science and Technology Studies and related areas. Approaches from each field contributed substantially but also each showed their individual limitations with regard to this study. The ‘Technology-in-Use’ perspective by Carroll (2004) is suggested as a suitable starting point for an interdisciplinary approach

Praxisbericht: Bildung, Digitalisierung und Nachhaltigkeit - zum Potential der Arbeitslehre für die allgemeine Lehrkräftebildung

Bildung in der digitalen Welt geht weit über den Einsatz digitaler Techno-logien zur fachdidaktischen Unterstützung des Unterrichts hinaus. Der Auftrag der Schule die Schülerschaft zu einer aktiven und verantwortlichen Teilhabe am Leben zu befähigen, bedeutet auch sie angemessen auf die zentralen gesellschaftlichen Prozesse und Veränderungen vorzube-reiten. Der Digitale Wandel spielt dabei eine ebenso einschneidende Rolle wie die Klimakrise und die Möglichkeiten einer nachhaltigen Entwicklung. In einem Online-Seminar an der Technischen Universität Berlin wurde der Frage nachgegangen, wie Bildung für Nachhaltige Entwicklung (BNE) und Digitale Bildung in projektorientierter Lehre miteinander verschränkt werden können. Dabei sollten Berührungsängste mit digitalen Technologien abgebaut, Potentiale für den didakti-schen Mehrwert aufgezeigt und Anregungen für die allgemeine Bildung identifiziert werden. Schlüsselwörter: Digitale Lehrkräftebildung, Design Thinking, Digitale Technologien, BNEEducation in the digital world goes far beyond the use of digital technologies to pro-vide didactic support for teaching. The school's mission to enable learners to actively and respon-sibly participate in their life also means to prepare them appropriately for the central social pro-cesses and changes. The digital change plays just as decisive a role as the climate crisis and the possibilities of sustainable development. In an online seminar at the Technical University Berlin, the question of how Education for Sustainable Development (ESD) and digital education can be linked in project-oriented teaching was investigated. The goals of the seminar were to reduce res-ervations concerning digital technologies, show potentials for didactic added value and provide stimuli for including digital technologies in general education. Keywords: digital teacher education, design thinking, digital technologies, ES