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排序方式: 共有673条查询结果,搜索用时 312 毫秒
71.
Pedroso MP Ferreira EC Hantao LW Bogusz S Augusto F 《Journal of separation science》2011,34(13):1547-1554
Combining qualitative data from the chromatographic structure of 2-D gas chromatography with flame ionization detection (GC×GC-FID) and that from gas chromatography-mass spectrometry (GC/MS) should result in a more accurate assignment of the peak identities than the simple analysis by GC/MS, where coelution of analytes is unavoidable in highly complex samples (rendering spectra unsuitable for qualitative purposes) or for compounds in very low concentrations. Using data from GC×GC-FID combined with GC/MS can reveal coelutions that were not detected by mass spectra deconvolution software. In addition, some compounds can be identified according to the structure of the GC×GC-FID chromatogram. In this article, the volatile fractions of fresh and dehydrated pineapple pulp were evaluated. The extraction of the volatiles was performed by dynamic headspace extraction coupled to solid-phase microextraction (DHS-SPME), a technique appropriate for slurries or solid matrices. Extracted analytes were then analyzed by GC×GC-FID and GC/MS. The results obtained using both techniques were combined to improve compound identifications. 相似文献
72.
Augusto Visintin 《Journal of Differential Equations》2011,250(3):1521-1552
This work deals with the homogenization of hysteresis-free processes in ferromagnetic composites. A degenerate, quasilinear, parabolic equation is derived by coupling the Maxwell-Ohm system without displacement current with a nonlinear constitutive law:
73.
Marcelo Kobelnik Douglas Lopes Cassimiro Adélia Emilia de Almeida Clóvis Augusto Ribeiro Marisa Spirandeli Crespi 《Journal of Thermal Analysis and Calorimetry》2011,105(2):415-419
The Al and In-diclofenac compounds were prepared. Thermogravimetry (TG) and X-ray diffraction powder patterns were used to
characterize these compounds. Details concerning the dehydration and thermal decomposition as well as data of kinetic parameters
have been described here. The kinetic studies of these stages were evaluated from several heating rates with mass sample of
2 and 5 mg in open crucibles under nitrogen atmosphere. The results of the present study improve the knowledge on these compounds
including their dehydration and thermal stability. The obtained data leads to a dependence on the sample mass, which results
in two kinetic behavior patterns. 相似文献
74.
Renato Vessecchi Lourenço Marcelo Kobelnik Clóvis Augusto Ribeiro Fernando L. Fernonani 《Journal of Thermal Analysis and Calorimetry》2011,106(3):735-740
The Brazilian sugarcane industry shows a great amount of generated sludge which should be utilized adequately. Two sludge
samples, aerobic and anaerobic, were collected. Both were evaluated by thermogravimetry and differential thermal analysis
(DTA) as well as X-ray power diffraction. These compounds show variations of mass between 30 and 140 °C due to the dehydration
stage. The DTA curves show that the compounds have an exothermic reaction between 450 and 550 °C, which indicates that this
can be used as an energy source. Details concerning the kinetic parameters of the dehydration and thermal decomposition have
also been described here. The kinetic study of these stages was evaluated in open crucibles under nitrogen atmosphere. The
obtained data were evaluated with the isoconversional kinetic method. The results show that different activation energies
were obtained for thermal decomposition. 相似文献
75.
Pereira AM Soares AR Hausmann A Neves MG Tomé AC Silva AM Cavaleiro JA Guldi DM Torres T 《Physical chemistry chemical physics : PCCP》2011,13(25):11858-11863
In the current work, we report on the synthesis and photophysical features of supramolecular hybrid systems that are based on newly fused porphyrin-phthalocyanine (P-Pc) conjugates and a pyridylfullerene. The ZnP-ZnPc conjugate was synthesized in three steps starting with a Diels-Alder reaction between β-vinylporphyrin and fumaronitrile. The resulting mixture of isomeric adducts was then dehydrogenated to yield the corresponding benzo[b]porphyrin-2(1),2(2)-dicarbonitrile. In the final step, cyclotetramerization with 4-tert-butylphthalonitrile, in the presence of zinc acetate, afforded the bis-metalated conjugate. Selective demetallation of ZnP led to the H(2)P-ZnPc conjugate. For both conjugates steric hindrance is the inception to a bent configuration, which does, however, not preclude enlargement of the π-conjugated system, that is, the porphyrins and the phthalocyanines. The two conjugates coordinate N-(4-pyridyl)fullero[c]pyrrolidine giving rise to the corresponding supramolecular porphyrin-phthalocyanine-fullerene systems. Photophysical measurements corroborate a sequential deactivation in the excited state, namely an initial intramolecular energy transfer from ZnP or H(2)P to ZnPc followed by an intramolecular charge transfer to yield ZnP-(ZnPc)˙(+)-(C(60))˙(-) and H(2)P-(ZnPc)˙(+)-(C(60))˙(-), respectively. 相似文献
76.
Walter Alexandre Carnielli Carlos Augusto Di Prisco 《Mathematical Logic Quarterly》1993,39(1):461-474
Several types of polarized partition relations are considered. In particular we deal with partitions defined on cartesian products of more than two factors. MSC: 03E05. 相似文献
77.
Plinio Innocenzi Tongjit Kidchob Luca Malfatti Stefano Costacurta Masahide Takahashi Massimo Piccinini Augusto Marcelli 《Journal of Sol-Gel Science and Technology》2008,48(1-2):253-259
Sol–gel processing of thin films involves time dependent phenomena which are basically driven by solvent evaporation. An example is evaporation induced self-assembly that is used to prepare mesoporous ordered films through self-organization of templating micelles. The possibility to follow in situ as a function of time the evolution of the system can give a better knowledge of the process and the physics and chemistry beneath. Time-resolved infrared techniques have been applied to different sol–gel systems to study time-dependent phenomena, in particular rapid scan time resolved infrared spectroscopy has been used to monitor in situ the process and as a tool to design the sol–gel synthesis. 相似文献
78.
79.
A family of linear copolymers, characterized by the presence along the polymer chain of variable amounts of two atomic groups of different mesogenic potentiality, has been studied by differential scanning calorimetry and X-ray diffraction methods. The range of composition that allows enantiotropic mesophasic behaviour is defined for four homologous sets of copolymers. The experimental phase diagram gives, by extrapolation, indications about the potential mesophasic properties of that extreme composition (corresponding to a homopolymer) that shows no direct mesophasic properties. 相似文献
80.
Abstract 2-Methyl-1,4-naphtoquinone (vitamin K3 ) quenches the phosphorescence from enzyme-generated triplet acetone. Concomitantly the vitamin undergoes a photochemical-like alteration as the result of transfer of the electronic energy ( k ET – 1 ± 105 M-1 ). This transfer appears to be of the long-range type. 相似文献