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排序方式: 共有416条查询结果,搜索用时 46 毫秒
1.
P.R.S. Gomes I. Padron E. Crema O.A. Capurro J.O. Fernández Niello G.V. Marti A. Arazi M. Trotta J. Lubian M.E. Ortega A.J. Pacheco M.D. Rodríguez J.E. Testoni R.M. Anjos L.C. Chamon M. Dasgupta D.J. Hinde K. Hagino 《Physics letters. [Part B]》2006
Complete and incomplete fusion cross sections for the 9Be + 144Sm reaction have been measured at near-barrier energies, using the delayed X-ray detection technique. At above-barrier energies these show a suppression of complete fusion for this weakly bound projectile on an intermediate mass target. The suppression factor, attributed to 9Be break-up, was deduced from a comparison of complete fusion yields with coupled-channels calculations, and appears consistent with measured incomplete fusion product yields. At ∼10%, it is considerably smaller than the value of ∼30% previously found for a 208Pb target. Simultaneous measurements of elastic and inelastic scattering permit a clearer picture of the reaction mechanisms. 相似文献
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R. Riva J. Rieger R. Jrme PH. Lecomte 《Journal of polymer science. Part A, Polymer chemistry》2006,44(20):6015-6024
This paper aims at reporting on the synthesis of a heterograft copolymer by combining the “grafting onto” process based on atom transfer radical addition (ATRA) and the “grafting from” process by atom transfer radical polymerization (ATRP). The statistical copolymerization of ε‐caprolactone (εCL) and α‐chloro‐ε‐caprolactone (αClεCL) was initiated by 2,2‐dibutyl‐2‐stanna‐1,3‐dioxepane (DSDOP), followed by ATRA of parts of the chlorinated units of poly(αClεCL‐co‐εCL) on the terminal double bond of α‐MeO,ω‐CH2?CH? CH2? CO2‐poly(ethylene oxide) (PEO). The amphiphilic poly(εCL‐g‐EO) graft copolymer collected at this stage forms micelles as supported by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The unreacted pendant chloro groups of poly(εCL‐g‐EO) were used to initiate the ATRP of styrene with formation of copolymer with two populations of randomly distributed grafts, that is PEO and polystyrene. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6015–6024, 2006 相似文献
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Ana A. C. Pacheco Arnaldo F. da Silva Filho Kristoffer Kortsen Magnus W. D. Hanson-Heine Vincenzo Taresco Jonathan D. Hirst Muriel Lansalot Franck D'Agosto Steven M. Howdle 《Chemical science》2021,12(3):1016
Reversible addition–fragmentation chain transfer (RAFT) dispersion polymerisation of methyl methacrylate (MMA) is performed in supercritical carbon dioxide (scCO2) with 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT) present as chain transfer agent (CTA) and surprisingly shows good control over PMMA molecular weight. Kinetic studies of the polymerisation in scCO2 also confirm these data. By contrast, only poor control of MMA polymerisation is obtained in toluene solution, as would be expected for this CTA which is better suited for acrylates. In this regard, we select a range of CTAs and use them to determine the parameters that must be considered for good control in dispersion polymerisation in scCO2. A thorough investigation of the nucleation stage during the dispersion polymerisation reveals an unexpected “in situ two-stage” mechanism that strongly determines how the CTA works. Finally, using a novel computational solvation model, we identify a correlation between polymerisation control and degree of solubility of the CTAs. All of this ultimately gives rise to a simple, elegant and counterintuitive guideline to select the best CTA for RAFT dispersion polymerisation in scCO2.RAFT dispersion polymerisation of methyl methacrylate is performed in scCO2 with 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT) present as chain transfer agent (CTA) and surprisingly shows good control over PMMA molecular weight. 相似文献
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Synthesis of the new l,3-dioxa-9-azaspiro[5.5]undecane ring, was realized by the scheme represented in Figure 2. Butyro-phenones 6 posses neuroleptic activity similar to that of halo-peridol. The pharmacological activity was reported in another publication (2). Conformational study of l,3-dioxa-9-azaspiro-[5.5]undecanes shows the existence of four conformations A, B, C and D, which are shown in Figure 4. The existence of these conformations depends on the nature of the substituents R and R' on the dioxane ring. Thus, in the compounds where R ≠ H, R' = H, the four conformations are possible with a preponderance of A and B. If R and R' are different from H only the conformation A is present in 99% concentration. Lastly, when R = R' = H, the four conformations are possible with equal population for the couple A, B and the couple C, D; the first couple predominating. The presence of a fluorophenylbutyric moiety on the piperidine nitrogen does not seem to stereochemically modify the heterocyclic group. 相似文献
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G. Pacheco G. Nava P. Bosch S. Bulbulian 《Journal of Radioanalytical and Nuclear Chemistry》1994,187(6):431-434
The ability of synthetic and natural Mexican zeolites and clays to remove radioactive Co from aqueous solutions is discussed. In the various samples, crystallinity was determined by X-ray diffraction. The amount of radionuclide sorbed by the aluminosilicates was determined by -spectrometry. 相似文献
8.
António Pacheco 《Queueing Systems》1994,15(1-4):289-308
The Erlang loss function, which gives the steady state loss probability in anM/M/s/s system, has been extensively studied in the literature. In this paper, we look at the similar loss probability inM/M/s/s +
c systems and an extension of it to nonintegral number of servers and queue capacity. We study its monotonicity properties. We show that the loss probability is convex in the queue capacity, and that it is convex in the traffic intensity if is below some * and concave if is greater that *, for a broad range of number of servers and queue capacities. We prove that the one-server loss system is the onlyM/M/s/s +c system for which the loss probability is concave in the traffic intensity in all its range.Research supported by Grant BD/645/90-RM from Junta Nacional de Investigação Científica e Tecnológica.On leave from: Departamento de Matemática, Instituto Superior Técnico, Av. Rovisco Pais, 1096 Lisboa Codex, Portugal. 相似文献
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