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51.
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
52.
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
53.
Ricardo Figueiredo Checoni 《The Journal of chemical thermodynamics》2010,42(5):612-620
54.
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
55.
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
56.
Sena C Godinho MH Sebastião PJ Sousa D Neto FA 《The European physical journal. E, Soft matter》2011,34(1):8-11
We report on an experimental study of the structures presented by urethane/urea elastomeric films without and with ferromagnetic
nanoparticles incorporated. The study is made by using the X-ray diffraction, nuclear magnetic resonance (NMR), optical, atomic
and magnetic force (MFM) microscopy techniques, and mechanical assays. The structure of the elastomeric matrix is characterized
by a distance of 0.46nm between neighboring molecular segments, almost independent on the stretching applied. The shear casting
performed in order to obtain the elastomeric films tends to orient the molecules parallel to the flow direction thus introducing
anisotropy in the molecular network which is reflected on the values obtained for the orientational order parameter and its
increase for the stretched films. In the case of nanoparticles-doped samples, the structure remains nearly unchanged although
the local order parameter is clearly larger for the undoped films. NMR experiments evidence modifications in the molecular
network local ordering. Micrometer size clusters were observed by MFM for even small concentration of magnetic particles. 相似文献
57.
The Maximum Balanced Subgraph Problem (MBSP) is the problem of finding a subgraph of a signed graph that is balanced and maximizes the cardinality of its vertex set. This paper is the first one to discuss applications of the MBSP arising in three different research areas: the detection of embedded structures, portfolio analysis in risk management and community structure. The efficient solution of the MBSP is also in the focus of this paper. We discuss pre-processing routines and heuristic solution approaches to the problem. a GRASP metaheuristic is developed and improved versions of a greedy heuristic are discussed. Extensive computational experiments are carried out on a set of instances from the applications previously mentioned as well as on a set of random instances. 相似文献
58.
In this paper we will be concerned with questions of existence and multiplicity of radial nonnegative solutions of the quasilinear elliptic equation We will use variational methods in order to prove the existence of multiple solutions in case f is a sign-changing nonlinearity. 相似文献
59.
The basic relationships required to analyse permeability data of fluorite-based solid electrolytes are rewritten in order
to account for an overpotential term related to slow surface exchange. Results of a gadolinia doped ceria solid electrolyte
suggest that surface exchange might limit the permeability especially at low Po2 and temperature. However, the analysis of the data with different relationships leads to somewhat different estimates of
the electron and hole conductivity and overpotential values.
Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998 相似文献
60.
Stability Constants of Complexes of Divalent and Rare Earth Metals with Substituted Salicynals 总被引:1,自引:0,他引:1
Summary. 5-Chloro-4-6-dimethyl-salicylaldehyde was synthesized from 4-chloro-3,5-dimethyl-phenol. A series of substituted salicynals
were obtained by condensation of 5-chloro-4,6-dimethyl-salicylaldehyde with several amines. The amines were chosen such as
to vary the basicity of salicynals by changing the substituents at one of the coordination sites. The stability constants
of complexes of bivalent (Mg2+, Ca2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+) and trivalent (Y3+, La3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+, Er3+, Yb3+) metal ions with these salicynals and the pK values corresponding to the dissociation of the phenolic proton and the association of a proton to the azomethine nitrogen
were determined potentiometrically using the Calvin-Bjerrum technique as adopted by Irving and Rossotti at 303 K and a constant ionic strength of 0.1 M in a 75:25 (v/v) dioxan-water mixture in an inert atmosphere. The influence of substituents on the proton affinity of the
ligands was examined on the basis of inductive and mesomeric effects. It is also shown that some of the complexes possess
antibacterial, antitubercular, antifungal, and anticoagulant activity.
Received August 5, 1999./Accepted November 11, 1999 相似文献