369 research outputs found
Unveiling the photophysics of thiourea from CASPT2/CASSCF potential energy surfaces and singlet/triplet excited state molecular dynamics simulations
This work describes the decay mechanism of photoexcited thiourea, both in gas
phase and in solution, from the information inferred from the topography of the
excited and ground state potential energy surfaces and mixed singlet/triplet
quantum classical molecular dynamics simulations. Our gas phase results reveal
T1/S0 intersystem crossing as the dominant (49%) intrinsic decay channel to the
ground state, which reaches a population of 0.28 at the final time of our
simulations (10 ps). Population of the T1, would occur after internal
conversion to the S1 from the spectroscopic S2 electronic state, followed by
S1->T2 intersystem crossing and T2->T1 internal conversion processes. Minor
decay channels occurring exclusively along the singlet manifold, i.e. S2->S0
(33%) and S1->S0 (18%), were also observed to play a role in the relaxation of
photoexcited thiourea in the gas phase. The explicit incorporation of
water-thiourea interactions in our simulations was found to provoke a very
significant delay in the decay to the ground state of the system, with no
transitions to the S0 being registered during the first 10 ps of our
simulations. Intermolecular vibrational energy redistribution and explicit
hydrogen bond interaction established between water molecules and the NH2 group
of thiourea were found to structurally or energetically hamper the access to
the intersystem crossing or internal conversion funnels with the ground state
Excited state dynamics of some nonsteroidal anti-inflammatory drugs: a surface-hopping investigation
Here we present a computational investigation of the excited state dynamics
of 5 different active medical substances (aspirin, ibuprofen, carprofen,
suprofen, indomethacin) which belong to the family of nonsteroidal
anti-inflammatory drugs (NSAIDs). The nonadiabatic dynamics simulations were
performed using the surface hopping method, with electronic energies and
couplings evaluated on the fly in a semiempirical framework. For aspirin, the
solvent decay dynamics was also considered by inserting it in a cluster of
water molecules, following a QM/MM scheme. A quite diverse behavior was
observed for the systems considered, going from fast deactivation to the ground
state (aspirin and ibuprofen), to ultrafast intersystem crossing to the triplet
manifold (carprofen and suprofen), or to the generation of long lived S1 states
(indomethacin). To our knowledge, this is the first computational study of the
photodynamics of these NSAIDs
Multi-Scale Modelling of Aggregation of TiO2 Nanoparticle Suspensions in Water
Titanium dioxide nanoparticles have risen concerns about their possible toxicity and the European Food Safety Authority recently banned the use of TiO2 nano-additive in food products. Following the intent of relating nanomaterials atomic structure with their toxicity without having to conduct large-scale experiments on living organisms, we investigate the aggregation of titanium dioxide nanoparticles using a multi-scale technique: starting from ab initio Density Functional Theory to get an accurate determination of the energetics and electronic structure, we switch to classical Molecular Dynamics simulations to calculate the Potential of Mean Force for the connection of two identical nanoparticles in water; the fitting of the latter by a set of mathematical equations is the key for the upscale. Lastly, we perform Brownian Dynamics simulations where each nanoparticle is a spherical bead. This coarsening strategy allows studying the aggregation of a few thousand nanoparticles. Applying this novel procedure, we find three new molecular descriptors, namely, the aggregation free energy and two numerical parameters used to correct the observed deviation from the aggregation kinetics described by the Smoluchowski theory. Ultimately, molecular descriptors can be fed into QSAR models to predict the toxicity of a material knowing its physicochemical properties, enabling safe design strategies
Multi-Scale Modelling of Aggregation of TiO2 Nanoparticle Suspensions in Water
Titanium dioxide nanoparticles have risen concerns about their possible toxicity and the European Food Safety Authority recently banned the use of TiO2 nano-additive in food products. Following the intent of relating nanomaterials atomic structure with their toxicity without having to conduct large-scale experiments on living organisms, we investigate the aggregation of titanium dioxide nanoparticles using a multi-scale technique: starting from ab initio Density Functional Theory to get an accurate determination of the energetics and electronic structure, we switch to classical Molecular Dynamics simulations to calculate the Potential of Mean Force for the connection of two identical nanoparticles in water; the fitting of the latter by a set of mathematical equations is the key for the upscale. Lastly, we perform Brownian Dynamics simulations where each nanoparticle is a spherical bead. This coarsening strategy allows studying the aggregation of a few thousand nanoparticles. Applying this novel procedure, we find three new molecular descriptors, namely, the aggregation free energy and two numerical parameters used to correct the observed deviation from the aggregation kinetics described by the Smoluchowski theory. Ultimately, molecular descriptors can be fed into QSAR models to predict the toxicity of a material knowing its physicochemical properties, enabling safe design strategies
Legal determinants of external finance revisited : the inverse relationship between investor protection and societal well-being
This paper investigates relationships between corporate governance traditions and quality of life as measured by a number of widely reported indicators. It provides an empirical analysis of indicators of societal health in developed economies using a classification based on legal traditions. Arguably the most widely cited work in the corporate governance literature has been the collection of papers by La Porta et al. which has shown, inter alia, statistically significant relationships between legal traditions and various proxies for investor protection. We show statistically significant relationships between legal traditions and various proxies for societal health. Our comparative evidence suggests that the interests of investors may not be congruent with the interests of wider society, and that the criteria for judging the effectiveness of approaches to corporate governance should not be restricted to financial metrics
Corporate boards, ownership structure and firm performance in an environment of severe political and economic crisis
This study examines the relationship between board and ownership structures and firm performance in an environment of severe political and economic crisis. Using panel data from the Zimbabwe Stock Exchange (ZSE) for the period 2000-2005, we split the period into prepresidential election period (2000-2002) (a relatively stable political and economic period) and post-presidential election period (2003-2005) (a hostile political and economic period) to capture the differences in the political and economic landscape. We find that board size, ownership concentration and executive directorsâ share ownership increased whilst the proportion of nonexecutive directors reduced in the post-presidential election period. Employing a system Generalized Method of Moments (GMM) approach, we find that performance is positively related to board size and ownership concentration in the post- (but not in the pre-) presidential election period. The results also show that performance is negatively related to executive directorsâ share ownership in the post-presidential election period, but positively related in the pre-presidential election period. The proportion of non-executive directors is negative and significant in both periods. These findings support the notion that the effects of board and ownership structures depend on the nature of the firmâs environment, and therefore have important implications for policy-makers
Microbiology, our trajectory in ICT : Computer workshop. Teaching experience, use of ICT as resources teaching
Fil: Castro, Nora Mirta.
Universidad Nacional de Cuyo. Facultad de OdontologĂaFil: Porta, MarĂa Cecilia.
Universidad Nacional de Cuyo. Facultad de OdontologĂaFil: Ciccarelli, MarĂa Albertina .
Universidad Nacional de Cuyo. Facultad de OdontologĂaFil: Ulloa, Andrea Alejandra .
Universidad Nacional de Cuyo. Facultad de OdontologĂaFil: Aguilera, Milton.
Universidad Nacional de Cuyo. Facultad de OdontologĂ
Shareholder protection, income inequality and social health:a proposed research agenda
This paper develops a proposed research agenda in order to highlight how corporate governance, accounting and company law are relevant to the consideration of income inequality and wider social health. To illustrate this proposed research agenda, this paper draws on corporate governance research in the law and finance tradition, as well as macro-level studies in accounting concerned with the wider corporate governance context, in order to consider the association between shareholder protection, income inequality and child mortality. Under 5 child mortality is an objective indication of a countryâs ability to nurture its children. In an influential body of work, La Porta et al. (1997a, 1997b, 1998, 2008) concluded that a common law legal system which protected the interests of shareholders gave rise to better economic and social outcomes. However, drawing on corporate governance and accounting literature we contend that such a conclusion is flawed. The findings of this paper suggest that common law countries (i.e. those with the greater legal protection for investors) have worse social outcomes in terms of under-5 child mortality.PostprintPeer reviewe
The institutional determinants of private equity involvement in business groups â the case of Africa
This study examines the governance attributes of post-IPO (initial public offering) retained ownership of private equity in business group constituent firms in contrast to their unaffiliated counterparts, in 202 newly listed firms in 22 emerging African economies. We adopt an actor centered institutional-theoretic perspective in rationalizing institutional voids and the advantages of maintained governance by both business angels (BA) and venture capital (VC) private equity. Our findings reveal private equity retain higher post-IPO ownership in business group constituents compared to unaffiliated firms and that this is inversely moderated in the context of improving institutional quality â where this is particularly strong in case of foreign VC as opposed to domestic VC or BA. Our result adds to the literature on multifocal corporate governance mechanisms and the institutional determinants of private equity investment
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