GO VII Meeting, Ovronnaz (CH), June 13?17, 2010

Editorial of the Special Issue of Discrete Applied Math

Regulating pesticide risk reduction: : the practice and dynamics of legal pluralism

Schrijver, N.J. [Promotor]Verbruggen, H. [Promotor

Three essays on the role of proximity in science and innovation

This thesis proposes three studies that provide novel empirical evidence on how different types of proximity can affect innovation and science activities through various mechanisms and in different contexts. In the first study (second chapter of this thesis), in collaboration with Julio Raffo, we analyze the relationship between geography and the likelihood of duplication in inventive activities. We argue that the uneven diffusion of knowledge means that the duplication of inventions will not be randomly distributed geographically and over time. First, as knowledge diffuses over time and competitive incentives decrease, the probability of a claimed invention duplicating an existing one will decrease in the time distance between the two. Second, for recent and upcoming inventions, competitive incentives are high, and localized knowledge flows increase the probability of duplication. Therefore, over a brief time period, the probability of duplication decreases with geographic distance. Conversely, the duplication of less recent inventions is more likely to occur at long distances as a consequence of less awareness of a technology existing due to missing knowledge flows. We test our hypotheses on European Patent Office (EPO) patent bibliographical data on patent citation categories. Geographic distance matters significantly less in sectors in which patents are known to be more effective as a source of information such as discrete technologies. In the second study (third chapter), in collaboration with Annamaria Conti and Fabiana Visentin, we investigate the effects of professorsâ social proximity with external universities on the level of productivity of PhD students hired from these universities. Researchers hired from external environments tend to have high scientific productivity compared to those who completed their studies in the same institution where they are employed. In a population of 4,666 PhD students, we further study the scientific productivity of external students from professorsâ networks, defined as students with a master's degree from a different university from that of their PhD, and also from a university with which their supervisors' co-authors are affiliated. We find that these students are significantly more productive, both compared to other students with a master's degree from a different university, and to students with a master's degree from the same university as that of their PhD. In our analyses, we control for the heterogeneity of supervisors and the heterogeneity of institutions where the students obtained their master's degrees, including proxies for the specific relevance of these universities for a given supervisor. Thus, we conclude that professors hire students with higher scientific productivity from universities where their co-authors are affiliated. Additional analyses further suggest that the reduction of information asymmetries is the main mechanism to explain this finding. In the third study (fourth chapter), in collaboration with Guillaume Burghouwt, we investigate the role of interregional knowledge integration as a driver of firm innovative performance. We adopt an unbalanced panel of 3,871 innovative companies in Germany between 1992 and 2010, for a total of 15,819 observations, and we study their innovative productivity. [...

Ultrafast Visible and Ultraviolet Fluorescence Studies of Molecular and Biological Sytems in Solution

A wide variety of physical and chemical processes at the molecular level, as charge or energy transfer, solvation, electronic as well as vibrational relaxation, is at the origin of the biological functionality of proteins. The work reported in this thesis is devoted to the study of these molecular dynamics in different chromophore systems. More specifically, this study is focused on the role of these dynamics in the ultrafast photophysics and photochemistry of haemoproteins. This important class of proteins has been widely studied through various spectroscopic techniques, in order to understand their functionality. These proteins contain several chromophore moieties, among which one aminoacid residue, Tryptophan, and the haem prosthetic group, which are of particular interest in this work. While Tryptophan is used as a probe of the local environment via intermolecular relaxation dynamics, we investigated the role of haem intramolecular dynamics on the protein functionality. While different kind of ultrafast spectroscopic techniques are indicated to tackle these issues, like pump probe or photon-echo peak shift experiments, we choose a different approach to probe directly the energetic relaxation, which consists in following the ultrafast changes in the photoluminescence spectrum. The dynamics are then extracted from the spectral evolution of the emission. With this purpose, we implemented a fluorescence up-conversion set-up, which allows us resolving temporally and spectrally the photoluminescence of the sample under investigation, excited with an ultrashort light pulse, and with a temporal resolution on the femtosecond timescale. The thesis is structured in 9 chapters. Chapter 1 resumes the theoretical background required for the interpretation of the experimental results. Chapter 2 describes the photophysical properties of the different systems investigated. Chapter 3 presents the experimental technique of fluorescence up-conversion, used to achieve broadband femtosecond detection of photoluminescence. In Chapter 4, we present a study on the role of ultrafast vibrational and structural dynamics on the time-resolved fluorescence spectra from two UV dyes. The measurements allow us exploring the capabilities of the set-up in revealing subtle relaxation dynamics with an unequaled accuracy. In Chapter 5, we move on to the study of the relaxation dynamics of Tryptophan (Trp) in water. This aminoacid served as an in vivo probe of solvation dynamics, owing to its high dipolar moment in its excited state. Our study focuses on water reorganization around the chromophore and on the distinction of this important process from the electronic internal conversion occurring on a similar timescale. In the framework of the study of protein dynamics, Chapter 6 reports the investigation of a family of molecules extensively found in nature, namely porphyrins. In these molecular systems, a quite complex pattern of intramolecular relaxation mechanisms occurs, which needed to be clarified. A systematic study on the free base and on a wide series of metallo-porphyrins definitely clarified the picture of their electronic relaxation pathways. We finally elaborate a comprehensive scheme of this relaxation, including substituent's influence. The mechanisms observed are intrinsically related to the photophysical properties used by nature, as will be illustrated in the next Chapter. Trp and metallo-porphyrin constitute the key natural chromophore molecules for the non-invasive spectroscopic investigation of complex biological systems as haemoproteins. In Chapter 7, we follow relaxation dynamics of photo-excited Tryptophan and Haem (Fe-porphyrin) in ferro- and ferricytochrome c and in Myoglobin in its met form. In the former protein, an ultrafast energy transfer from Tryptophan to Heme is evidenced, the efficiency of which is found to depend on the oxidation state. The energetic relaxation pathway of the haem, also dependent on the oxidation state, is characterized by a porphyrin to metal charge transfer that triggers the ligand dissociation. In metMyoglobin, the fluorescence contribution of the two Tryptophans (W14 and W7), also quenched by resonant energy transfer to the haem, are temporally and spectrally separated, and the solvation dynamics of W7, located in the water-protein interface, is followed. The haem of metMb, which is in the ferric form, shows an electronic relaxation similar to that of ferricytochrome c. In parallel to the biology oriented investigations presented above, we extended our study to the metal-polypiridine complexes. Due to their specific photophysics, mainly characterized by a photo-induced Metal-to-Ligand Charge Transfer (MLCT), they are extensively used in photochemical applications involving charge transfer dynamics. In particular, they are used as sensitizer in the Dye-Sensitized-Solar-Cells (DSSCs). In Chapter 8, we present studies of these dyes, both in solution and adsorbed on a substrate, in order to understand the role of intra- and intermolecular dynamics on the electron injection process occurring upon absorption of light. Finally, Chapter 9 summarizes the conclusions of the investigations of the various systems studied