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181.
We use multispeckle diffusive wave spectroscopy to probe the micron-scale dynamics of a water-saturated granular pile submitted to discrete gentle taps. The typical time scale between plastic events is found to increase dramatically with the number of applied taps. Furthermore, this microscopic dynamics weakly depends on the solid fraction of the sample. This process is largely analogous to the aging phenomenon observed in thermal glassy systems. We propose a heuristic model where this slowing-down mechanism is associated with a slow evolution of the distribution of the contact forces between particles. This model accounts for the main features of the observed dynamics. 相似文献
182.
Two distinct humic acids, one extracted from Brazilian peat soil, HAPS, and another one obtained from commercial source, HAFL, were attachment onto silica gel modified with aminopropyltrimethoxysilane, producing two material named SiHAPS and SiHAFL, respectively. The ability of these materials in removing indigo carmine dye from aqueous solution was followed through series of adsorption isotherms adjusted to modified Langmuir equation. The maximum number of moles adsorbed gave 6.82 ± 0.12 × 10−4 and 2.15 ± 0.17 × 10−4 mol g−1 for SiHAPS and SiHAFL, respectively. Same interactions were calorimetrically followed and the thermodynamic data showed endothermic enthalpic values: 12.31 ± 0.55 and 24.69 ± 1.05 kJ mol−1 for SiHAPS and SiHAFL surfaces, respectively. Gibbs free energies for two adsorption processes of indigo carmine dye presented negative values, reflecting dye/surface interactions must be accompanied by an increased in entropy values, which are 65 ± 3 and 98 ± 5 J mol−1 K−1 for SiHAPS and SiHAFL materials, respectively. The adsorption processes for both materials were spontaneous in nature although they presented an endothermic enthalpy for the interaction, resulting in an entropically favored process. 相似文献
183.
Ewan Couic Alicia Tribondeau Vanessa Alphonse Alexandre Livet Noureddine Bousserrhine 《Molecules (Basel, Switzerland)》2022,27(6)
Understanding ecological trajectories after mine site rehabilitation is essential to develop relevant protocols adapted for gold mining sites. This study describes the influence of a range of mine site rehabilitation and revegetation protocols on soil physicochemical parameters and microbial activities related to carbon, nitrogen and phosphorus cycles. We sampled soil from six rehabilitated mining sites in French Guiana with different plant cover (herbaceous, Cyperaceous, monoculture of Clitoria racemosa and Acacia mangium and association of C. racemosa and A. mangium). We measured the mineralization potential of organic matter by estimating the mineralization of carbon, nitrogen and phosphorus and the microbial catabolic diversity balance. The results showed an improvement in the quality of organic matter on revegetated sites with tree cover. On restored sites with fabaceous species, the microbial biomass is three times higher than non-restored sites, improving the rates of organic matter mineralization and restoring the catabolic diversity to the level of natural Guyanese soils. These results confirm that the establishment of fabaceous species under controlled conditions significantly improves the restoration of microbial communities in mining soils. 相似文献
184.
The synthesis of enantiopure bis-THF is described, starting from d-mannitol. Bis-THF is used as chiral ligand for organolithium reagents in four different reactions. The enantioselectivity provided by this ligand is moderate, and the asymmetric induction is in line with the expected model. 相似文献
185.
Insights into the Complexity of Weak Intermolecular Interactions Interfering in Host–Guest Systems 下载免费PDF全文
Dawei Zhang Dr. Bastien Chatelet Eloisa Serrano Dr. Olivier Perraud Dr. Jean‐Pierre Dutasta Prof. Dr. Vincent Robert Prof. Dr. Alexandre Martinez 《Chemphyschem》2015,16(14):2931-2935
The recognition properties of heteroditopic hemicryptophane hosts towards anions, cations, and neutral pairs, combining both cation–π and anion–π interaction sites, were investigated to probe the complexity of interfering weak intermolecular interactions. It is suggested from NMR experiments, and supported by CASSCF/CASPT2 calculations, that the binding constants of anions can be modulated by a factor of up to 100 by varying the fluorination sites on the electron‐poor aromatic rings. Interestingly, this subtle chemical modification can also reverse the sign of cooperativity in ion‐pair recognition. Wavefunction calculations highlight how short‐ and long‐range interactions interfere in this recognition process, suggesting that a disruption of anion–π interactions can occur in the presence of a co‐bound cation. Such molecules can be viewed as prototypes for examining complex processes controlled by the competition of weak interactions. 相似文献
186.
Sheyla Santa Isabel Marques Iracema Andrade Nascimento Paulo Fernando de Almeida Fábio Alexandre Chinalia 《Applied biochemistry and biotechnology》2013,171(8):1933-1943
Microalgae farming has been identified as the most eco-sustainable solution for producing biodiesel. However, the operation of full-scale plants is still limited by costs and the utilization of industrial and/or domestic wastes can significantly improve economic profits. Several waste effluents are valuable sources of nutrients for the cultivation of microalgae. Ethanol production from sugarcane, for instance, generates significant amounts of organically rich effluent, the vinasse. After anaerobic digestion treatment, nutrient remaining in such an effluent can be used to grow microalgae. This research aimed to testing the potential of the anaerobic treated vinasse as an alternative source of nutrients for culturing microalgae with the goal of supplying the biodiesel industrial chain with algal biomass and oil. The anaerobic process treating vinasse reached a steady state at about 17 batch cycles of 24 h producing about 0.116 m3CH4 kgCODvinasse ?1. The highest productivity of Chlorella vulgaris biomass (70 mg l?1 day?1) was observed when using medium prepared with the anaerobic digester effluent. Lipid productivity varied from 0.5 to 17 mg l?1 day?1. Thus, the results show that it is possible to integrate the culturing of microalgae with the sugarcane industry by means of anaerobic digestion of the vinasse. There is also the advantageous possibility of using by-products of the anaerobic digestion such as methane and CO2 for sustaining the system with energy and carbon source, respectively. 相似文献
187.
Driowya M Puissant A Robert G Auberger P Benhida R Bougrin K 《Ultrasonics sonochemistry》2012,19(6):1132-1138
A simple and efficient synthesis of modified 1,2,3-triazole nucleosides was developed. The strategy involved sequential one-pot acetylation-azidation-cycloaddition procedure and was found to be highly effective under a cooperative effect of ultrasound activation and iron/copper catalysis. The reactions were carried out under both conventional and ultrasonic irradiation conditions. In general, improvement in rates and yields were observed when reactions were carried out under sonication compared with conventional conditions. This one-pot procedure provides several advantages such as operational simplicity, high yield, safety and environment friendly protocol. The resulting substituted nucleosides were evaluated for their anticancer activity against K562 chronic myelogenous leukemia (CML) cell line. 相似文献
188.
Sarah Sulzer‐Mossé Alexandre Alexakis Prof. Jiri Mareda Dr. Guillaume Bollot Gerald Bernardinelli Dr. Yaroslav Filinchuk Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(13):3204-3220
Chiral framework : Chiral amines with pyrrolidine frameworks catalyze the enantioselective conjugate addition of a wide range of aldehydes to various vinyl sulfones and vinyl phosphonates in high yields and with enantioselectivities up to >99 % ee (see scheme). The high versatility of the Michael adducts is exemplified by various functionalizations with conservation of the optical purity.
189.
Alexandre Freire Stefan Müller Michael Struwe 《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》1998,15(6):725
We show that a weak limit of a sequence of wave maps in (1 + 2) dimensions with uniformly bounded energy is again a wave map. Essential ingredients in the proof are Hodge structures related to harmonic maps,
1 estimates for Jacobians,
1-BMO duality, a “monotonicity” formula in the hyperbolic context and the concentration compactness method. Application of similar ideas in the elliptic context yields a drastically shortened proof of recent results by Bethuel on Palais-Smale sequences for the harmonic map functional on two dimensional domains and on limits of almost H-surfaces. 相似文献
190.
Copper‐Catalyzed Propargylic Substitution of Dichloro Substrates: Enantioselective Synthesis of Trisubstituted Allenes and Formation of Propargylic Quaternary Stereogenic Centers 下载免费PDF全文
Dr. Hailing Li Dr. David Grassi Dr. Laure Guénée Prof. Dr. Thomas Bürgi Prof. Dr. Alexandre Alexakis 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(50):16694-16706
An easy and versatile Cu‐catalyzed propargylic substitution process is presented. Using easily prepared prochiral dichloro substrates, readily available Grignard reagents together with catalytic amount of copper salt and chiral ligand, we accessed a range of synthetically interesting trisubstituted chloroallenes. Substrate scope and nucleophile scope are broad, providing generally high enantioselectivity for the desired 1,3‐substitution products. The enantioenriched chloroallenes could be further transformed into the corresponding trisubstituted allenes or terminal alkynes bearing all‐carbon quaternary stereogenic centers, through the copper‐catalyzed enantiospecific 1,1/1,3‐substitutions. The two successive copper‐catalyzed reactions could be eventually combined into a one‐pot procedure and different desired allenes or alkynes were obtained respectively with high enantiomeric excesses. 相似文献