Enzymatic functionalization of carbon-hydrogen bonds

The development of new catalytic methods to functionalize carbon–hydrogen (C–H) bonds continues to progress at a rapid pace due to the significant economic and environmental benefits of these transformations over traditional synthetic methods. In nature, enzymes catalyze regio- and stereoselective C–H bond functionalization using transformations ranging from hydroxylation to hydroalkylation under ambient reaction conditions. The efficiency of these enzymes relative to analogous chemical processes has led to their increased use as biocatalysts in preparative and industrial applications. Furthermore, unlike small molecule catalysts, enzymes can be systematically optimized via directed evolution for a particular application and can be expressed in vivo to augment the biosynthetic capability of living organisms. While a variety of technical challenges must still be overcome for practical application of many enzymes for C–H bond functionalization, continued research on natural enzymes and on novel artificial metalloenzymes will lead to improved synthetic processes for efficient synthesis of complex molecules. In this critical review, we discuss the most prevalent mechanistic strategies used by enzymes to functionalize non-acidic C–H bonds, the application and evolution of these enzymes for chemical synthesis, and a number of potential biosynthetic capabilities uniquely enabled by these powerful catalysts (110 references)

Dynamic nonlinear analyses for the 4-storey infilled R/C frame: study of a retrofitting solution

A research project on assessment and retrofitting of R/C frame structures is currently being developed under the research programme of the ICONS TMR-research network. This paper presents and discusses the preliminary experimental results from a 4-storey bare frame representative of the common practice of 40~50 years ago in most south European countries and devotes special attention to the study of a retrofitting solution based on bracing and rubber dissipaters, which intends to increase stiffness and damping reducing consequently the earthquake deformation demands.O estudo aqui apresentado concentra-se numa solução de reforço de um pórtico utilizando contraventamentos (k-bracing) com perfis de aço em conjunto com elementos elastoméricos de dissipação. Os resultados das análises não lineares da estrutura com e sem alvenaria e com reforço são apresentados e discutidos. Na segunda parte da comunicação apresentam-se os resultados experimentais já disponíveis e discute-se o problema da modelação recorrendo aos resultados experimentais e comparando os resultados obtidos com diferentes tipos de modelos

Seismic analyses of a R/C building: study of a retrofitting solution

The preliminary experimental results from the tests on a 4-storey R/C frame structure are presented and discussed. The full-scale model is representative of the common practice of 40~50 years ago in most south European countries. Special attention is devoted to the study of a retrofitting solution based on bracing and rubber dissipaters, which intends to increase stiffness and damping reducing consequently the earthquake deformation demands

Quantitative measures of crowd patterns in agent-based models of street protests

In this work we describe the introduction of quantitative measures of emergent crowd patterns in an existing Agent-Based model (ABM) of street protests with multiple actors (police, protester and ‘media’ agents). The model was applied to a scenario of a police force defending a government building which protesters seek to invade. The improved model provided a coherent ‘narrative’ of the simulations and highlighted the realistic and unrealistic aspects of the agents’ interactions. Two new types of police agents – ‘defensive’ and ‘offensive’ – were introduced, leading to a realistic model representation of police cordons defending a site or charging to disperse clusters of violent protesters. The new quantitative measures provided information on cluster size and orientation of clusters of violent protesters, as well as police coverage and protester breaching of the defensive perimeter, together with the time history of the bursts of localized fights and arrests. It was shown how the quantitative measures of the emergent properties can be used for both parameterization and validation of the model.info:eu-repo/semantics/acceptedVersio

Investigation of the existence of hybrid stars using Nambu-Jona-Lasinio models

We investigate the hadron-quark phase transition inside neutron stars and obtain mass-radius relations for hybrid stars. The equation of state for the quark phase using the standard NJL model is too soft leading to an unstable star and suggesting a modification of the NJL model by introducing a momentum cutoff dependent on the chemical potential. However, even in this approach, the instability remains. In order to remedy the instability we suggest the introduction of a vector coupling in the NJL model, which makes the EoS stiffer, reducing the instability. We conclude that the possible existence of quark matter inside the stars require high densities, leading to very compact stars.Comment: 4 pages, 2 figures; prepared for IV International Workshop on Astronomy and Relativistic Astrophysics (IWARA 2009), Maresias, 4-8 Oct 200

Network influence effects in agent-based modelling of civil violence

In this paper we describe an agent-based model of civil violence with network influence effects. We considered two different networks, ‘family’ and ‘news’, as a simplified representation of multiple-context influences, to study their individual and joint impact on the size and timing of violence bursts, the perceived legitimacy, and the system’s long term behaviour. It was found that network influences do not change either the system’s long term behaviour or the periodicity of the rebellion peaks, but increase the size of violence bursts, particularly for the case of strong ‘news impact’. For certain combinations of network influences, initial legitimacy, and legitimacy feedback formulation, the solutions showed a very complicated behaviour with unpredictable alternations between long periods of calm and turmoil.info:eu-repo/semantics/acceptedVersio

An agent-based model of civil violence with imprisonment delay and legitimacy feedback

Epstein's Agent-Based model of civil violence has been very successful due to its simplicity and explanatory power, but does not represent important phenomena, such as processes operating at multiple scales and feedback mechanisms. In this work, we present an extension of Epstein's model that includes the effects of imprisonment delay, media coverage and feedback of rebellion bursts of the government's legitimacy. These innovations are relevant for a more realistic modeling of the complex and path-dependent effect of protests and violent confrontations on the evolution of the social context. The resulting simulations showed punctuated equilibrium as in Epstein's model, but the violence bursts lasted longer and displayed more complicated structure and interdependence on previous events. The rebellion peaks lead to drops and lowering of the time-averaged value of the government's legitimacy.info:eu-repo/semantics/acceptedVersio

Ensuring successful introduction of Wolbachia in natural populations of Aedes aegypti by means of feedback control

The control of the spread of dengue fever by introduction of the intracellular parasitic bacterium Wolbachia in populations of the vector Aedes aegypti, is presently one of the most promising tools for eliminating dengue, in the absence of an efficient vaccine. The success of this operation requires locally careful planning to determine the adequate number of individuals carrying the Wolbachia parasite that need to be introduced into the natural population. The introduced mosquitoes are expected to eventually replace the Wolbachia-free population and guarantee permanent protection against the transmission of dengue to human. In this study, we propose and analyze a model describing the fundamental aspects of the competition between mosquitoes carrying Wolbachia and mosquitoes free of the parasite. We then use feedback control techniques to devise an introduction protocol which is proved to guarantee that the population converges to a stable equilibrium where the totality of mosquitoes carry Wolbachia.Comment: 24 pages, 5 figure

Agent-based modeling of social conflict, civil violence and revolution: State-of-the-art-review and further prospects

In this paper, we present a state-of-the-art review of Agent-based models (ABM) for simulation of social conflict phenomena, such as peaceful or violent street protests, civil violence and revolution. First, a simplified characterization of social conflict phenomena as emergent properties of a complex system is presented, together with a description of their macro and micro levels and the scales of the emergent properties. Then, existing ABM for simulation of crowd dynamics, civil violence and revolution are analyzed and compared, using a framework that considers their purpose/scope, environment representation, agent types and their architecture, the scales of the emergent properties, the qualitative and quantitative understanding of the phenomena provided by the results obtained from the models. We discuss the strengths and limitations of the existing models, as well as the promising lines of research for filling the gaps between the state-of-the-art models and real phenomena. This review is part of a work in progress on the assembling and dynamics of protests and civil violence, involving both simulation of the assembling process and the protest dynamics, as well as data collection in real protest events, and provides hints and guidelines for future developments.info:eu-repo/semantics/publishedVersio