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排序方式: 共有435条查询结果,搜索用时 31 毫秒
31.
Tolédano P Figueiredo Neto AM Boulbitch AA Roy A 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,59(6):6785-6797
The stable antiferroelectric and ferrielectric smectic phases which may arise below a chiral SmA* phase are investigated theoretically. The symmetry and physical properties of the bilayer and multilayer configurations are worked out. Antiferroelectric and ferrielectric bilayer and multilayer configurations, possessing an induced spontaneous ferroelectric polarization component perpendicular to the smectic layers, are shown to take place, as the result of a nonlinear piezoelectric effect. These states of low polar symmetries occur when the angle between the inlayer projections of the dipoles and the director of the molecules is different from 90 degrees. 相似文献
32.
Cuppo FL Gómez SL Figueiredo Neto AM 《The European physical journal. E, Soft matter》2004,13(4):327-333
In this paper is reported a systematic experimental study of the linear-optical-absorption coefficient of ferrofluid-doped isotropic lyotropic mixtures as a function of the magnetic-grains concentration. The linear optical absorption of ferrolyomesophases increases in a nonlinear manner with the concentration of magnetic grains, deviating from the usual Beer-Lambert law. This behavior is associated to the presence of correlated micelles in the mixture which favors the formation of small-scale aggregates of magnetic grains (dimers), which have a higher absorption coefficient with respect to that of isolated grains. We propose that the indirect heating of the micelles via the ferrofluid grains (hyperthermia) could account for this nonlinear increase of the linear-optical-absorption coefficient as a function of the grains concentration.Received: 16 December 2003, Published online: 27 April 2004PACS:
61.30.-v Liquid crystals - 83.80.Qr Surfactant and micellar systems, associated polymers - 78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity) 相似文献
33.
J.R. Fernández I.N. Figueiredo 《Journal of Mathematical Analysis and Applications》2008,343(2):951-964
We consider the approximation of a bone remodeling model with the Signorini contact conditions by a contact problem with normal compliant obstacle, when the obstacle's deformability coefficient converges to zero (that is, the obstacle's stiffness tends to infinity). The variational problem is a coupled system composed of a nonlinear variational equation (in the case of normal compliance contact conditions) or a variational inequality (for the case of Signorini's contact conditions), for the mechanical displacement field, and a first-order ordinary differential equation for the bone remodeling function. A theoretical result, which states the convergence of the contact problem with normal compliance contact law to the Signorini problem, is then proved. Finally, some numerical simulations, involving examples in one and two dimensions, are reported to show this convergence behaviour. 相似文献
34.
35.
Ricardo Figueiredo Checoni 《Journal of Thermal Analysis and Calorimetry》2010,101(1):349-357
Experimental data of excess molar enthalpy (H
mE) of binary liquid mixtures containing (methanol or ethanol or 1-propanol, or 1-butanol) + n-butylamine mixtures have been determined as a function of composition at temperatures 288.15 and 308.15 K, at atmospheric
pressure, using a modified 1455 PARR mixture calorimeter. The H
mE values are negative for both systems over the whole composition range. The applicability of the ERAS Model to correlate H
mE of mixtures studied is tested, and the agreement between experimental and theoretical results is satisfactory. The model
results are discussed in terms of the cross-association interactions with temperature variation as well as in terms of the
variation of the carbon chain in the alcohols presents in the mixtures. 相似文献
36.
Clara Grosso Ana Cristina Figueiredo Jesus Burillo Ana M. Mainar José S. Urieta José G. Barroso José A. Coelho António M. F. Palavra 《Journal of separation science》2010,33(14):2211-2218
Supercritical fluid extraction (SFE) of the volatile oil from Thymus vulgaris L. aerial flowering parts was performed under different conditions of pressure, temperature, mean particle size and CO2 flow rate and the correspondent yield and composition were compared with those of the essential oil isolated by hydrodistillation (HD). Both the oils were analyzed by GC and GC‐MS and 52 components were identified. The main volatile components obtained were p‐cymene (10.0–42.6% for SFE and 28.9–34.8% for HD), γ‐terpinene (0.8–6.9% for SFE and 5.1–7.0% for HD), linalool (2.3–5.3% for SFE and 2.8–3.1% for HD), thymol (19.5–40.8% for SFE and 35.4–41.6% for HD), and carvacrol (1.4–3.1% for SFE and 2.6–3.1% for HD). The main difference was found to be the relative percentage of thymoquinone (not found in the essential oil) and carvacryl methyl ether (1.0–1.2% for HD versus t?0.4 for SFE) which can explain the higher antioxidant activity, assessed by Rancimat test, of the SFE volatiles when compared with HD. Thymoquinone is considered a strong antioxidant compound. 相似文献
37.
Thyme is the common name of many taxa belonging to the Thymbra and Thymus genera. Given the economic importance of thyme oils, many thyme species have been studied and their essential oils and other volatile-containing extracts chemically characterized. Thymbra and Thymus species are frequent in the west Mediterranean region, considered to be the centre of origin of the genus Thymus, and extend further westwards in the Iberian Peninsula and northwest Africa, to the Macaronesian region in the Atlantic Ocean. The present work gives an overview of the chemical composition of the volatiles from the taxa of these two genera occurring in the above geographic area. 相似文献
38.
Ricardo Figueiredo Checoni 《The Journal of chemical thermodynamics》2010,42(5):612-620
39.
Rosa IL Filho PC Neri CR Serra OA de Figueiredo AT Varela JA Longo E 《Journal of fluorescence》2011,21(4):1575-1583
This work reports on the synthesis and characterization of a new complex of Eu3+ with the 3-hydroxypicolinamide ligand (Hhpa). Here we present an approach for obtaining bis[2-carbamoyl(κO)pyridin-3-olato(κO’)]
lanthanide complexes, which were characterized through elemental analysis, thermal analysis, infrared and photoluminescence
spectroscopies (emission, excitation, luminescence lifetimes, quantum efficiencies, Judd-Ofelt parameters and quantum yields).
Although hpa can act as a bidentate ligand in different conformations, the results attest for the occurrence of a unique coordination
site of low symmetry for the Eu3+ ions, in which two anionic hpa ligands coordinate the cations through an O/O chelating system. The phosphorescence of the
synthesized gadolinium complex provides the energy of the triplet state, which is determined to be at 20,830 cm-1 over the ground state. This makes the Hhpa ligand very adequate for sensitizing the Eu3+ luminescence, which leads to a very efficient antenna effect and opens a wide range of applications for the complex in light
emitting organic-inorganic devices. 相似文献
40.
Batalioto F Martins OG Duarte AR Figueiredo Neto AM 《The European physical journal. E, Soft matter》2011,34(1):10
In this work we investigate the influence of the adsorption of ions on the impedance spectroscopy of an electrolytic cell.
We consider that the positive and negative ions present in a dielectric liquid are adsorbed in the electrode surfaces with
different adsorption energies. This difference in adsorption energies causes an additional plateaux in the limit of the low-frequency
range of the real part of the impedance Z . In the same frequency range, a second minimum in the imaginary part of Z is predicted. The theory is illustrated with measurements of the impedance of an electrolytic solution in the frequency range
from 10-2Hz to 1KHz. A comparison between the present model and others from the literature to describe the experimental results is
also made. 相似文献