Exciton Dephasing and Thermal Line Broadening in Molecular Aggregates

Using a model of Frenkel excitons coupled to a bath of acoustic phonons in the host medium, we study the temperature dependence of the dephasing rates and homogeneous line width in linear molecular aggregates. The model includes localization by disorder and predicts a power-law thermal scaling of the effective homogeneous line width. The theory gives excellent agreement with temperature dependent absorption and hole-burning experiments on aggregates of the dye pseudoisocyanine.Comment: 11 pages, 3 PostScript figure

Decoherence of Excitons in Multichromophore Systems: Thermal Line Broadening and Destruction of Superradiant Emission

We study the temperature-dependent dephasing rate of excitons in chains of chromophores, accounting for scattering on static disorder as well as acoustic phonons in the host matrix. From this we find a powerlaw temperature dependence of the absorption line width, in excellent quantitative agreement with experiments on dye aggregates. We also propose a relation between the line width and the exciton coherence length imposed by the phonons. The results indicate that the much debated steep rise of the fluorescence lifetime of pseudo-isocyanine aggregates above 40 K results from the fact that this coherence length drops below the localization length imposed by static disorder.Comment: 4 pages, 2 figure

Matching methods for impact evaluation of public subsidies to business R&D: Measuring heterogeneous effects

The objective of this paper is to offer a broad profile of firms with publicly supported R&D projects, which allows us to explain their different degrees of additionality. With this objective, in a first step we use standard Propensity Score Matching techniques to estimate treatment effects at the firm level, and then we explore the determinants of the heterogeneity in these individual effects through the estimation of an equation for their determinants. For our analysis, we use information from a sample of 8,168 Spanish firms for the period 2007-2014. We report three main results. First, firms with multiple program participation show higher additionality. However, individual treatment effects, which are positive for firms with low support intensities, go sharply below the average for firms with very high support intensities. Second, the degree of additionality is positively related to firm characteristics denoting a more innovative nature, while it is negatively associated with features present in firms involved in more market-oriented R&D projects. Third, firm size has a positive relation to the probability of full additionality, but a negative association with the degree of additionality in terms of net R&D intensity. These results can provide public agencies with some tools for adjusting their selection procedures

Thermal broadening of the J-band in disordered linear molecular aggregates: A theoretical study

We theoretically study the temperature dependence of the J-band width in disordered linear molecular aggregates, caused by dephasing of the exciton states due to scattering on vibrations of the host matrix. In particular, we consider inelastic one- and two-phonon scattering between different exciton states (energy-relaxation-induced dephasing), as well as elastic two-phonon scattering of the excitons (pure dephasing). The exciton states follow from numerical diagonalization of a Frenkel Hamiltonian with diagonal disorder; the scattering rates between them are obtained using the Fermi Golden Rule. A Debye-like model for the one- and two-phonon spectral densities is used in the calculations. We find that, owing to the disorder, the dephasing rates of the individual exciton states are distributed over a wide range of values. We also demonstrate that the dominant channel of two-phonon scattering is not the elastic one, as is often tacitly assumed, but rather comes from a similar two-phonon inelastic scattering process. In order to study the temperature dependence of the J-band width, we simulate the absorption spectrum, accounting for the dephasing induced broadening of the exciton states. We find a power-law (T^p) temperature scaling of the effective homogeneous width, with an exponent p that depends on the shape of the spectral density of host vibrations. In particular, for a Debye model of vibrations, we find p ~ 4, which is in good agreement with experimental data on J-aggregates of pseudoisocyanine [J. Phys. Chem. A 101, 7977 (1997)].Comment: 14 pages, 7 figure

Selection of dominant multi-exciton transitions in disordered linear J-aggregates

We show that the third-order optical response of disordered linear J-aggregates can be calculated by considering only a limited number of transitions between (multi-) exciton states. We calculate the pump-probe absorption spectrum resulting from the truncated set of transitions and show that, apart from the blue wing of the induced absorption peak, it agrees well with the exact spectrum.Comment: 8 pages, 2 figures, accepted to Journal of Luminescenc

The J- and H-bands of dye aggregate spectra: Analysis of the coherent exciton scattering (CES) approximation

The validity of the CES approximation is investigated by comparison with direct diagonalisation of a model vibronic Hamiltonian of $N$ identical monomers interacting electronically. Even for quite short aggregates (N\gtrsim 6) the CES approximation is shown to give results in agreement with direct diagonalisation, for all coupling strengths, except that of intermediate positive coupling (the H-band region). However, previously excellent agreement of CES calculations and measured spectra in the H-band region was obtained [A. Eisfeld, J. S. Briggs, Chem. Phys. 324, 376]. This is shown to arise from use of the measured monomer spectrum which includes implicitly dissipative effects not present in the model calculation

The effect of technological relatedness on firm sales evolution through external knowledge sourcing

This paper analyzes the impact of knowledge spillovers on firm performance measured through total sales, the percentage of innovative sales and a categorical variable that classifies firms into three different groups depending on the stage of their sales growth evolution: upturn, downturn, or transition. We specifically focus on whether there are asymmetric spillover effects depending on the intermediary role of firms’ technological relatedness, which we proxy by the use of external sources of knowledge. Using data on 5900 Spanish firms for the period 2004–2016, we find that spillover effects from intra-sector and upstream knowledge pools are—in general—positive, although with some differences depending on the measure of firm performance and on the moderating role of technological networking. Our results also suggest the presence of a “business stealing effect” in environments with a high proportion of knowledge-based gross added value. Furthermore, we find that spillover effects are asymmetric depending on the firm’s size and intensity of R&D employment. Knowledge spillovers seem to play a more significant role in the case of SMEs than in large companies, and firms with high intensities of R&D employment benefit more from upstream spillovers and less from horizontal spillovers than firms with low intensities

Technology policy evaluation: The interaction between the financial constraint of firms and level of financial additionality

This study analyses the differentiated effects of the public support for private R&D and innovation considering the financial situation of the firm. Two main questions are analyzed. Firstly, do the firms that have less access to funds for RDI –and therefore could depend more on the public support- get more frequently support? And, secondly, do such firms show a higher level of financial additionality than the firms with less financial restrictions? Despite of the fact that market failures imply basically that firms underinvest in R&D and often lack access to financial markets, only a few papers were detected that analyze the above-mentioned questions and present contradictory non-conclusive results. All of them used only one or two –often dummy- variables as indicator to measure the financial restrictions. Moreover, only four studies analyzed the intermediating role of the financial restriction on the policy impact in terms of the financial additionality and five measures its effect on the degree of participation. The main novelty of this paper is the simultaneous use of a broad set 17 different indicators (reflecting quantitative data on the firm’s liabilities or indebtedness, assets, and liquidity) directly derived from the firms’ balance sheet. These were clustered by a factor analysis in 7 synthetic indicators, which are used in an innovation policy evaluation framework based on the Propensity Score Matching Method. The main findings show that in Spain financial constraints negatively affect the access to public funds. There are significant differences between the level and cost of debt for both probability and financial additionality. Solvency indicators report that solvent firms are negatively discriminated for the likelihood of participation, however we find different effects for the impact depending on the public support that firms receive and their size

The labyrinth of life-styles

Abstract The increasing complexity of multi-cultural society has given rise to the thought that traditional (demographic and socio-economic) variables are no longer sufficient to substantiate policy development and planning in the housing sector. The concept of life-style is presumed to add to the description and prediction of the demand side, thus enabling housing strategies that are consistent with more dynamic and differentiated preferences. The usefulness of life-styles for policy development was studied in a literature review, in particular of research in the Netherlands. The study shows that the current significance of the concept is doubtful for various reasons: the indefiniteness of life-styles; the static and simplified view of society that is often presented, which is partly caused by the methods used; the uncertain relation to types of residential environment; and the unproven necessity of using life-styles alongside or as a substitute for more traditional variables. Recommendations are offered for future research on this subject

Notitie Denktank Overlijdensschade. Nieuwe richting benadering en berekening overlijdensschade

In 2009 is een werkgroep onder de naam Denktank Overlijdensschade gestart met het bestuderen van een ander, aan de huidige tijd aangepast model voor de berekening van overlijdensschade. Doelstelling was te komen tot een, ook voor nabestaanden, transparantie systematiek welke recht doet aan de vorderingsgerechtigdheid van de nabestaanden. In 2014 heeft de Denktank Overlijdensschade haar werkzaamheden voltooid met het opleveren van een nieuwe rekenmethodiek. In deze Notitie wordt beschreven hoe de Denktank tot deze nieuwe benadering van het berekenen van overlijdensschade is gekomen, welke onderzoeken daaraan ten grondslag liggen en wat de uiteindelijke rekenregel is, die nu voorgesteld wordt. Kern van de nieuwe methodiek is het uitgangspunt dat het gezin als economische eenheid wordt beschouwd, voor én na het overlijden