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991.
M. H. Godinho J. P. Borges J. C. Bordado M. T. Cidade A. F. Martins 《Liquid crystals》1993,14(3):653-659
A novel liquid-crystalline polymer, the toluene-4-sulphonyl urethane of hydroxypropylcellulose (TSUHPC), was prepared through chemical modification of hydroxypropylcellulose (HPC) of Mw = 60000 g mol-1. The resulting polymer was characterized by infrared spectroscopy, differential scanning calorimetry (DSC) and polarizing microscopy. It was found that thermotropic liquid crystal phases are formed between about 60°C and 110°C. Concentrated solutions of TSUHPC in acetone and N,N-dimethylacetamide exhibit cholesteric behaviour, at room temperature. When approaching the lyotropic mesophase to solid transition, either by cooling or by solvent evaporation, very interesting arborescent structures of a seemingly fractal nature may be observed, depending on the kinetics of the transition. A banded texture can be observed when the polymer is sheared near the transition to the isotropic phase. 相似文献
992.
993.
Data on the ratio of photodisintegration to electrodisintegration of several nuclei (12C, 63Cu, 64Zn, 109Ag, 181Ta and 197Au) are compared with the theoretical ratios predicted by plane-wave and distorted-wave calculations. The analysis with distorted waves shows that all data are compatible with photoabsorption through dominant E1 transitions, as can be explained by the electric dipole sum rule. This outcome does not agree with published conclusions for high Z using the plane-wave approximation. 相似文献
994.
M.J.M. Pires A.A.C. CottaM.D. Martins A.M.A. SilvaW.A.A. Macedo 《Journal of magnetism and magnetic materials》2011,323(6):789-793
The development of devices based on magnetic tunnel junctions has raised new interests on the structural and magnetic properties of the interface Co/MgO. In this context, we have grown ultrathin Co films (≤30 Å) by molecular-beam epitaxy on MgO(0 0 1) substrates kept at different temperatures (TS). Their structural and magnetic properties were correlated and discussed in the context of distinct magnetic anisotropies for Co phases reported in the literature. The sample characterization has been done by reflection high energy electron diffraction, magneto-optical Kerr effect and ferromagnetic resonance. The main focus of the work is on a sample deposited at TS=25 °C, as its particular way of growth has enabled a bct Co structure to settle on the substrate, where it is not normally obtained without specific seed layers. This sample presented the best crystallinity, softer magnetic properties and a four-fold in-plane magnetic anisotropy with Co〈1 1 0〉 easy directions. Concerning the samples prepared at TS=200 and 500° C, they show fcc and polycrystalline structures, respectively and more intricate magnetic anisotropy patterns. 相似文献
995.
Martins P. Costa C. M. Lanceros-Mendez S. 《Applied Physics A: Materials Science & Processing》2011,103(1):233-237
Multiferroic and magnetoelectric materials show enormous potential for technological developments. Multiferroic composites
are more attractive for applications due to their enhanced properties with respect to single-phase multiferroic materials.
In this paper we report on the nucleation of the electroactive β-phase of poly(vinylidene fluoride), PVDF, by the addition of CoFe2O4 and NiFe2O4 nanoparticles in order to prepare poly(vinylidene fluoride)/ferrite nanocomposite for multiferroic and magnetoelectric applications,.
The dispersed ferrite nanofiller particles strongly enhance the nucleation of the β-phase of the polymer matrix. In this way, magnetoelectric polymer nanocomposites can be processed avoiding the usual α- to β-phase transformation by stretching of the polymer matrix. 相似文献
996.
Pedro Martins Girão 《Nonlinear Analysis: Theory, Methods & Applications》2011,74(1):94-113
We construct the global bifurcation curves, solutions versus level of harvesting, for the steady states of a diffusive logistic equation on a bounded domain, under Dirichlet boundary conditions and other appropriate hypotheses, when a, the linear growth rate of the population, is below λ2+δ. Here λ2 is the second eigenvalue of the Dirichlet Laplacian on the domain and δ>0. Such curves have been obtained before, but only for a in a right neighborhood of the first eigenvalue. Our analysis provides the exact number of solutions of the equation for a≤λ2 and new information on the number of solutions for a>λ2. 相似文献
997.
Freunberger SA Chen Y Peng Z Griffin JM Hardwick LJ Bardé F Novák P Bruce PG 《Journal of the American Chemical Society》2011,133(20):8040-8047
The nonaqueous rechargeable lithium-O(2) battery containing an alkyl carbonate electrolyte discharges by formation of C(3)H(6)(OCO(2)Li)(2), Li(2)CO(3), HCO(2)Li, CH(3)CO(2)Li, CO(2), and H(2)O at the cathode, due to electrolyte decomposition. Charging involves oxidation of C(3)H(6)(OCO(2)Li)(2), Li(2)CO(3), HCO(2)Li, CH(3)CO(2)Li accompanied by CO(2) and H(2)O evolution. Mechanisms are proposed for the reactions on discharge and charge. The different pathways for discharge and charge are consistent with the widely observed voltage gap in Li-O(2) cells. Oxidation of C(3)H(6)(OCO(2)Li)(2) involves terminal carbonate groups leaving behind the OC(3)H(6)O moiety that reacts to form a thick gel on the Li anode. Li(2)CO(3), HCO(2)Li, CH(3)CO(2)Li, and C(3)H(6)(OCO(2)Li)(2) accumulate in the cathode on cycling correlating with capacity fading and cell failure. The latter is compounded by continuous consumption of the electrolyte on each discharge. 相似文献
998.
Helio G. Bonacorso Cleber A. Cechinel Gisele R. Paim Marcos A. P. Martins Nilo Zanatta Alex F. C. Flores 《Journal of heterocyclic chemistry》2011,48(1):113-117
The facile and convenient access by a conventional procedure in ethanol as solvent to a new series of succinyl‐spaced pyrazoles including 1,4‐bis[5‐(trichloromethyl)‐5‐hydroxy‐4,5‐dihydro‐1H‐pyrazol‐1‐yl]butane‐1,4‐diones (64–82%) and the respective dehydrated derivatives as 1,4‐bis[5‐(trichloromethyl)‐1H‐pyrazol‐1‐yl]butane‐1,4‐diones in 57–82% yields, from the regioselective cyclocondensation reactions of 4‐substituted 4‐methoxy‐1,1,1‐trichloroalk‐3‐en‐2‐ones with succinic acid dihydrazide, where the 4‐substituents are Me, Ph, 4‐FC6H4, 4‐ClC6H4, 4‐NO2C6H4, 2‐furyl, and 2‐thienyl, is reported. J. Heterocyclic Chem., 2011. 相似文献
999.
Nilo Zanatta Simone S. Amaral Josiane M. dos Santos Liana da S. Fernandes Helio G. Bonacorso Marcos A. P. Martins 《Journal of heterocyclic chemistry》2011,48(5):1085-1090
The regioselective synthesis and characterization of a new series of 3‐aryl‐7‐trifluoromethyl[1,2,4]triazolo[4,3–a]pyrimidines from the oxidative heterocyclization of 2‐(N′‐benzylidenehydrazino)‐4‐trifluoromethylpyrimidines with copper dichloride is described. J. Heterocyclic Chem., (2011). 相似文献
1000.
Helio G. Bonacorso Michele S. CorreaLiliane M.F. Porte Everton P. PittalugaNilo Zanatta Marcos A.P. Martins 《Tetrahedron letters》2012,53(41):5488-5491
An efficient and regioselective procedure for the synthesis of a series of alkyl(aryl/heteroaryl) substituted 3-trifluoromethyl-1H-1-phenylpyrazoles and alkyl 3-carboxylate analogs, from the cyclocondensation reactions of 4-alkoxy-1,1,1-trihaloalk-3-en-2-ones [CX3C(O)CR2=CR1(OMe/OEt), where R1 = H, Me, Ph, 2-Furyl; R2 = H; R1-R2 = -C4H8- and X = F, Cl] and 1-phenylsemicarbazide in an acidified alcoholic medium (R3OH/H2SO4), where R3 = Me, Et, Pri was successfully applied and is described here in detail. 相似文献