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61.
J. C. Gaburo A. S. Todo M. H. T. Taddei N. C. Silva 《Journal of Radioanalytical and Nuclear Chemistry》2006,269(2):499-503
Summary The measurement of radioactivity concentrations in excreta is an important tool for the monitoring of possible radionuclide
intakes by occupationally exposed workers. For this purpose, a radiochemical procedure for the determination of alpha-emitting
isotopes of uranium in excreta has been optimized. The main steps involved in this procedure are pre-concentration, dissolution
of sample, separation by ion-exchange resin, electrodeposition and alpha-spectroscopy. 232U tracer is used to monitor chemical recoveries and correct the results to improve precision and accuracy. The quality control
of radiochemical analysis in urine and faecal samples has been performed with participation in intercomparison exercises.
The results obtained from these samples, with chemical recoveries (80-95%), are shown to be highly consistent. The method
offers good prospects to be applied in routine monitoring programme of workers. 相似文献
62.
A new PS-DVB supported phthalic anhydride and UHP (urea-hydrogen peroxide complex) have been used for metal-free alkene epoxidation reactions. The resin was prepared by MW mediated ‘PEGylation’ of Merrifield resin followed by esterification with trimellitic anhydride chloride. Epoxidation of several alkenes was carried out with this resin and UHP. 相似文献
63.
64.
Guido Perboli Ferdinando Pezzella Roberto Tadei 《Mathematical Methods of Operations Research》2008,68(2):361-382
This paper presents EVE-OPT, a Hybrid Algorithm based on Genetic Algorithms and Taboo Search for solving the Capacitated Vehicle
Routing Problem. Several hybrid algorithms have been proposed in recent years for solving this problem. Despite good results,
they usually make use of highly problem-dependent neighbourhoods and complex genetic operators. This makes their application
to real instances difficult, as a number of additional constraints need to be considered. The algorithm described here hybridizes
two very simple heuristics and introduces a new genetic operator, the Chain Mutation, as well as a new mutation scheme. We
also apply a procedure, the k-chain-moves, able to increase the neighbourhood size, thereby improving the quality of the solution with negligible computational
effort. Despite its simplicity, EVE-OPT is able to achieve the same results as very complex state-of-the art algorithms. 相似文献
65.
Michael R. Martinez Sylwia Dworakowska Adam Gorczyński Grzegorz Szczepaniak Ferdinando De Luca Bossa Krzysztof Matyjaszewski 《Journal of polymer science. Part A, Polymer chemistry》2022,60(12):1887-1898
The photoinduced energy/electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerizations of oligo(ethylene oxide) monomethyl ether methacrylate (OEOMA, also known as poly[ethylene glycol] methyl ether methacrylate, PEGMA) and isomeric methyl 2-(oligo(ethylene oxide) methyl ether)acrylate (2OEOAM) macromonomers with OEO average degree of polymerization of 22 or 45 were conducted in aqueous media to provide insight into the effect of monomer structure on grafting-through RAFT of 1,1-disubstituted acrylic macromonomers. The polymerizations of all four monomers reached nearly quantitative conversion. The longer macromonomers polymerized faster than the shorter ones within the same monomer class. The OEO side chain at the α (i.e., 2-) position of isomeric acrylates significantly slowed RAFT polymerization in comparison with OEO ester side chain of methacrylates. 相似文献
66.
Paola Taddei Eleonora Pavoni Masuhiro Tsukada 《Journal of Raman spectroscopy : JRS》2016,47(6):731-739
Bombyx mori silk fibroin fibers were grafted with methacrylamide (MAA) and characterized by Raman and infrared (IR) vibrational spectroscopy before and after hydrolysis in NaOH 5% to elucidate the possible interactions between the two components and the stability of the fibers toward alkaline hydrolysis. Upon grafting, the fibers underwent conformational rearrangements toward a more unordered state and lost orientation at weight gains higher than 60%. Vibrational spectroscopy disclosed the occurrence of intermolecular interactions (mainly hydrogen bonds) between B. mori silk fibroin and polyMAA in the grafted fibers, and the formation of covalent bonds has been explored. These strong interactions made the grafted fibers as a whole more stable toward alkaline hydrolysis because they prevented the solubilization of the polymer upon hydrolysis and made slower the transformation of its CONH2 groups into COOH and COO− groups. Upon hydrolysis, silk fibroin underwent an enrichment in the β‐sheet crystalline domains, because of the preferential removal of the unordered domains, which were more prone to the OH− attack. IR and Raman spectroscopy proved valid techniques to investigate the degradation mechanism and kinetics of grafted silk fibroin fibers and so for designing high‐performing silk‐based materials. The A731/A1004 Raman intensity ratio was proposed to spectroscopically evaluate the composition of the grafted samples; its value was found to linearly increase with weight gain (R2 = 0.998), envisaging the possibility of using Raman spectroscopy as a routine analytical technique for qualitative and quantitative characterization of grafted industrial samples. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
67.
Summary This paper discusses the dynamic loading of rigid-perfectly plastic structures by adopting a structural model discretized with constant stress finite elements. This assumption together with the hypothesis of small displacements and of a piecewise linear yield surface leads to the formulation of a problem in linear inequalities, which is, implicitly, time discretized. It is shown how the non linearity of the associated plastic flow laws leads to an equivalent extremal formulation. A numerical algorithm for solving the problem is directly derived from the mechanical statements. Numerical examples illustrate this approach. In the appendix an approximate technique is developed, which takes into account the influence of the strain-hardening and the strain rate sensitivity of material.
Research supported by the National Research Council (C.N.R. - P.A.d.I.S.) of Italy. 相似文献
Sommario Il problema del caricamento dinamico delle strutture rigido-plastiche viene affrontato attraverso un modello discretizzato per elementi finiti a stato di sollecitazione costante. Tale assunzione insieme alle ipotesi di superficie di plasticizzazione lineare a tratti e di piccoli spostamenti, conduce alla formulazione di un problema retto da diseguaglianze lineari che si presenta discretizzato, implicitamente, nel tempo. Si mostra che la non linearità delle leggi del flusso plastico associato conduce ad una equivalente formulazione di estremo.È esposto un algoritmo risolvente affatto aderente alla formulazione meccanica. Alcuni esempi illustrano il procedimento. Una proposta di adattamento al caso di materiali incrudenti e sensibili alle velocità di deformazione è presentata in appendice.
Research supported by the National Research Council (C.N.R. - P.A.d.I.S.) of Italy. 相似文献
68.
Different anilides derived from carboxylic acids and substituted anilines have been submitted to the photochemically induced Fries rearrangement giving the corresponding o-amino phenones under conditions that are compatible with the presence of acid-labile groups (such as N-Boc or TBDMSO) on R1 and R3. These compounds, not easily obtained in other ways, are useful building blocks for the preparation of benzocondensated heterocycles. After coupling with N-Boc amino acids and TFA-mediated deprotection, the products cyclized to the corresponding 3,5-disubstituted 1,4-benzodiazepin-2-ones, privileged structures predominantly active in the central nervous system. The same results were obtained by coupling with N-Cbz-protected alpha-amino acids followed by microwave assisted hydrogenolysis. When the Fries rearrangement was carried out on the anilide derived from N-Boc-Ala-OH and the further coupling done with N-Cbz-(OMe)Asp-OH, the formed benzodiazepines could be inserted in a peptide chain for the preparation of conformationally constrained peptidomimetics. 相似文献
69.
An innovative route to prepare a number of variously substituted new biphenyl derivatives is presented here. The protocol avoids the use of a catalyst, an organic solvent, and dry conditions. [reaction: see text] 相似文献
70.
Airiau E Girard N Pizzeti M Salvadori J Taddei M Mann A 《The Journal of organic chemistry》2010,75(24):8670-8673
Linear hydroformylation of N-protected allyl- or homoallylamines (cyclohydrocarbonylation: CHC), followed by a reductive amination constitute the two key steps toward convenient routes to aza-heterocycles. 相似文献