A model of riots dynamics: shocks, diffusion and thresholds

We introduce and analyze several variants of a system of differential equations which model the dynamics of social outbursts, such as riots. The systems involve the coupling of an explicit variable representing the intensity of rioting activity and an underlying (implicit) field of social tension. Our models include the effects of exogenous and endogenous factors as well as various propagation mechanisms. From numerical and mathematical analysis of these models we show that the assumptions made on how different locations influence one another and how the tension in the system disperses play a major role on the qualitative behavior of bursts of social unrest. Furthermore, we analyze here various properties of these systems, such as the existence of traveling wave solutions, and formulate some new open mathematical problems which arise from our work

The TRIZ-CBR synergy: A knowledge based innovation process

Today innovation is recognised as the main driving force in the market. This complex process involves several intangible dimensions, such as creativity, knowledge and social interactions among others. Creativity is the starting point of the process, and knowledge is the force that transforms and materialises creativity in new products, services and processes. In this paper a synergy that aims to assists the innovation process is presented. The synergy combines several concepts and tools of the theory of inventive problem solving (TRIZ) and the case-based reasoning (CBR) process. The main objective of this synergy is to support creative engineering design and problem solving. This synergy is based on the strong link between knowledge and action. In this link, TRIZ offers several concepts and tools to facilitate concept creation and to solve problems, and the CBR process offers a framework capable of storing and reusing knowledge with the aim of accelerating the innovation process

Controlled release properties and final macroporosity of a pectin microspheres–calcium phosphate composite bone cement

The use of calcium phosphate cements (CPC) is restricted by their lack of macroporosity and poor drug release properties. To overcome these two limitations, incorporating degradable polymer microparticles into CPC is an attractive option, as polymer microparticles could help to control drug release and induce macroporosity after degradation. Although few authors have yet tested synthetic polymers, the potentiality of polysaccharides’ assuming this role has never been explored. Low-methoxy amidated pectins (LMAP) constitute valuable candidates because of their biocompatibility and ionic and pH sensitivity. In this study, the potentiality of a LMAP with a degree of esterification (DE) of 30 and a degree of amidation (DA) of 19 was explored. The aim of this study was to explore the influence of LMAP microspheres within the composite on the cement properties, drug release ability and final macroporosity after microspheres degradation. Three LMAP incorporation ratios, 2%, 4% and 6% w/w were tested, and ibuprofen was chosen as the model drug. In comparison with the CPC reference, the resulting composites presented reduced setting times and lowered the mechanical properties, which remained acceptable for an implantation in moderate-stress-bearing locations. Sustained release of ibuprofen was obtained on at least 45 days, and release rates were found to be controlled by the LMAP ratio, which modulated drug diffusion. After 4 months of degradation study, the resulting CPC appeared macroporous, with a maximum macroporosity of nearly 30% for the highest LMAP incorporation ratio, and interconnectivity between pores could be observed. In conclusion, LMAP appear as interesting candidates to generate macroporous bone cements with tailored release properties and macroporosity by adjusting the pectin content within the composites

Synergistic Cu–amine catalysis for the enantioselective synthesis of chiral cyclohexenones †

International audienceAn unprecedented utilization of 1,3-acetonedicarboxylic acid as a 1,3-bis-pro-nucleophile and a reactive acetone surrogate in enantio-selective catalysis has been reported. By synergistically activating the ketodiacid by copper catalysis and an a,b-unsaturated aldehyde by amine catalysis, an efficient domino di-decarboxylative Michael/aldol/ dehydration sequence takes place leading to valuable chiral cyclo-hexenones in one single operation in 94 to 99% ee. To fulfil the ideal of eco-compatible reactions, scientists continuously need to discover innovative activation modes able to perform unprecedented cascade transformations from simple molecules to complex architectures with a perfect control of stereoeselectivity. 1 In that regard, synergistic catalysis where different catalytic species are able to selectively activate different reaction partners has recently demonstrated its potential in the discovery of new previously inaccessible chemical transformations notably pioneered by the work from the group of Krische. 2 In this particular field, association of copper salts with organo-catalysts has proven efficient for the stereoselective activation of numerous nucleophilic and electrophilic partners. 3 Notably, copper and iminium activation could be combined synergistically, providing an improved route for the preparation of b-chiral aldehydes. 4 1,3-Acetonedicarboxylic acid (1) is an intriguing molecule possessing two pendant carboxylic acid functions that can potentially be involved in double biomimetic-like decarboxylative enolate formation rendering the corresponding acetone a,a 0-dianion easily available. 5 Prepared on a large scale from raw material namely citric acid, it can act as a potential reactive di-nucleophilic acetone surrogate. 6 This property was famously applied by Robinson in his 1917 tropinone synthesis and has since then found intensive utilization in the synthesis of tropinone like skeletons. 7 But quite surprisingly, despite its huge potential and to our knowledge there are no examples involving 1 as an acetone a,a 0-dianion equivalent in enantio-selective catalysis. 8 To fill this gap, we initiated a research program to selectively activate this unexploited 1,3-bis-pro-nucleophile in enantioselective synthesis. We first focused on its unaddressed reactivity towards a,b-unsaturated aldehydes as electrophiles in a di-decarboxylative Michael/aldol/dehydration sequence leading to synthetically useful cyclohexenone derivatives, a class of versatile molecules used in natural product synthesis. 9 Earlier reports on the preparation of these chiral cyclohexenones required multiple steps such as kinetic resolution of chiral compounds. 10 Several groups reported on the organocatalytic condensation of functionalized ketones on a,b-unsaturated aldehydes, leading after cascade cyclization by Knoevenagel or Wittig reaction to chiral cyclohexenones. 11 Unfortunately, in all these examples, additional functional groups are present on the obtained cyclohexenone backbones and require subsequent steps for their removal (tert-butyl ester for example). Given the utility of this chiral cyclohexenone motif and its numerous applications , alternative direct access to this structure remains attractive and desirable. To efficiently apply 1, we initially hypothesized that a secondary amine organocatalyst might activate the electrophile through its iminium ion while a copper salt catalyst, known to promote decarboxylative aldolizations, would activate ketodiacid 1 triggering the overall domino sequence initiated by a decarboxylative Michael addition (Scheme 1). 12 Herein we present our results on the development of such biomimetic transformation as well as supplementary successive cascade functionalization of the formed cyclohexenone. We initiated our research by condensing 1 on cinnamalde-hyde 2a in the presence of an aminocatalyst able to promote the direct Michael addition via the corresponding iminium intermediate. Selected optimizations are presented in Table 1

Acyl Transfer Strategies as Transient Activations for Enantioselective Synthesis

International audienceIn order to circumvent reactivity or selectivity issues associatedwith the addition of enolates to electrophiles, chemists have devisedinnovative methods involving transient activating groups. One ofthese powerful methods consists of the use of activated ketones, suchas -nitroketones, -dicarbonyl compounds or -ketosulfones, withelectrophiles possessing a latent hydroxy or amine function. In the presenceof a suitable catalyst, an enantioselective addition to the electrophileis facilitated triggering a subsequent Claisen-type fragmentationresulting in an acyl transfer. This subsequent step unveils the desiredmono-activated function while directly transferring the ketone, formingin situ on the other side an ester or an amide

Pressure dependence of raman modes in double wall carbon nanotubes filled with 1D tellurium

The preparation of highly anisotropic one-dimensional (1D) structures confined into carbon nanotubes (CNTs) in general is a key objective in nanoscience. In this work, capillary effect was used to fill double wall carbon nanotubes (DWCNTs) with trigonal Tellurium. The samples are characterized by high resolution transmission electronic microscopy and Raman spectroscopy. In order to investigate their structural stability and unravel the differences induced by intershell interactions, unpolarized Raman spectra of radial and tangential modes of DWCNTs filled with 1D nanocrystalline Te excited with 514 nm were studied at room temperature and high pressure. Up to 11 GPa we found a pressure coefficient of 3.7 cm−1 GPa−1 for the internal tube and 7 cm−1 GPa−1 for the external tube. In addition, the tangential band of the external and internal tubes broaden and decrease in amplitude. All findings lead to the conclusion that the outer tube acts as a protection shield for the inner tube (at least up 11 GPa). No pressure-induced structural phase transition was observed in the studied range