14,797 research outputs found
Enzymatic functionalization of carbon-hydrogen bonds
The development of new catalytic methods to functionalize carbonâhydrogen (CâH) 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 CâH 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 CâH 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 CâH 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 pĂłrtico utilizando contraventamentos (k-bracing) com perfis de aço em conjunto com elementos elastomĂ©ricos de dissipação. Os resultados das anĂĄlises nĂŁo lineares da estrutura com e sem alvenaria e com reforço sĂŁo apresentados e discutidos. Na segunda parte da comunicação apresentam-se os resultados experimentais jĂĄ disponĂveis 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
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
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 âmediaâ 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 ânarrativeâ of the simulations and highlighted the realistic and unrealistic aspects of the agentsâ interactions. Two new types of police agents â âdefensiveâ and âoffensiveâ â 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
Machinery for artificial emotions
We present a preliminary definition and theory of artificial emotion viewed as a sequential process comprising the appraisal of the agent global state, the generation of an emotion-signal, and an emotion-response. This theory distinguishes cognitive from affective appraisal on an architecture-grounded basis. Affective appraisal is performed by the affective component of the architecture; cognitive appraisal is performed by its cognitive component. A scheme for emotion classification with seven dimensions is presented. Among them, we emphasize the roles played by emotions and the way these roles are fulfilled. It is shown how emotions are generated, represented, and used in the Salt & Pepper architecture for autonomous agents (Botelho, 1997). Salt & Pepper is a specific architecture comprising an affective engine, a cognitive and behavioral engine, and an interruption manager. Most properties of the cognitive and behavioral engine rely upon a hybrid associative, schema-based long-term memory. In Salt & Pepper, emotion-signals, represented by label, object of appraisal, urgency, and valence, are generated by the affective engine through the appraisal of the agent's global state. For each emotion-signal there are several nodes stored and interconnected in long-term memory. Each of these nodes contains an emotion response that may be executed when an emotion-signal is generated. Emotion intensity relates to the activation of the node. It is shown that the Salt & Pepper architecture for autonomous agents exhibits several properties usually related to emotion: state and mood congruence, compound emotions, autonomic emotion-responses, and different emotion-responses to the same stimulus including the generation of different motives. The implementation of a concrete example is described.info:eu-repo/semantics/acceptedVersio
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, âfamilyâ and ânewsâ, 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 systemâs long term behaviour. It was found that network influences do not change either the systemâs long term behaviour or the periodicity of the rebellion peaks, but increase the size of violence bursts, particularly for the case of strong ânews impactâ. 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
Seismic strengthening of beam-column joints with multidirectional CFRP laminates
An experimental program was carried out to analyse the potentialities of a technique based on the use of multidirectional CFRP laminates (MDL-CFRP) for the seismic repair and strengthening of reinforced concrete (RC) beam-column joints. This experimental program comprises cyclic tests on three full-scale RC joints, representative of interior beam-column connections in buildings. The joints were initially submitted to a cyclic test inducing a
damage pattern representative of a seismic event. Subsequently, they were repaired and
strengthened with MDL-CFRP. The strengthened joints were then tested for the same loading
history of the original ones up to their failure. The adopted strengthening technique uses the MDL-CFRP that are simultaneously glued and anchored to the concrete surfaces. This technique is called Mechanically Fastened and Externally Bonded Reinforcement (MF-EBR).
In the present study, the effectiveness of two different strengthening configurations was investigated. The tests are described and the main results are presented and analyzed
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
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