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排序方式: 共有263条查询结果,搜索用时 31 毫秒
21.
22.
Carolina Lourencetti Pilar Fernández Celia Prado Joan O. Grimalt 《Analytica chimica acta》2010,662(1):23-30
A method for the estimation of the human intake of trihalomethanes (THMs), namely chloroform, bromodichloromethane, dibromochloromethane and bromoform, during showering and bathing is reported. The method is based on the determination of these compounds in exhaled breath that is collected by solid adsorption on Tenax using a device specifically designed for this purpose. Instrumental measurements were performed by automatic thermal desorption coupled to gas chromatography with electron capture detection. THMs in exhaled breath samples were determined during showering and swimming pool attendance. The levels of these compounds in indoor air and water were also determined as reference for interpretation of the exhaled breath results. The THM concentrations in exhaled breath of the volunteers measured before the exposure experiments showed a close correspondence with the THMs levels in indoor air where the sampler was located. Limits of detection in exhaled breath were dependent on THM analytes and experimental sites. They ranged between 170 and 710 ng m−3 in the swimming pool studies and between 97 and 460 ng m−3 in the showering studies. Application of this method to THMs determination during showering and swimming pool activities revealed statistically significant increases in THMs concentrations when comparing exhaled breath before and after exposure. 相似文献
23.
Fernando Pigeard de Almeida Prado Gunter M. Schütz 《Journal of statistical physics》2011,142(5):984-999
We consider a kinetic Ising model which represents a generic agent-based model for various types of socio-economic systems.
We study the case of a finite (and not necessarily large) number of agents N as well as the asymptotic case when the number of agents tends to infinity. The main ingredient are individual decision thresholds
which are either fixed over time (corresponding to quenched disorder in the Ising model, leading to nonlinear deterministic
dynamics which are generically non-ergodic) or which may change randomly over time (corresponding to annealed disorder, leading
to ergodic dynamics). We address the question how increasing the strength of annealed disorder relative to quenched disorder
drives the system from non-ergodic behavior to ergodicity. Mathematically rigorous analysis provides an explicit and detailed
picture for arbitrary realizations of the quenched initial thresholds, revealing an intriguing “jumpy” transition from non-ergodicity
with many absorbing sets to ergodicity. For large N we find a critical strength of annealed randomness, above which the system becomes asymptotically ergodic. Our theoretical
results suggests how to drive a system from an undesired socio-economic equilibrium (e.g. high level of corruption) to a desirable
one (low level of corruption). 相似文献
24.
Carlos Gomez Humberto Prado Sergei Trofimchuk 《Journal of Mathematical Analysis and Applications》2014
This paper is concerned with a scalar nonlinear convolution equation, which appears naturally in the theory of traveling waves for monostable evolution models. First, we prove that, at each end of the real line, every bounded positive solution of the convolution equation should either be separated from zero or be exponentially converging to zero. This dichotomy principle is then used to establish a general theorem guaranteeing the uniform persistence and existence of semi-wavefront solutions to the convolution equation. Finally, we apply our theoretical results to several well-studied classes of evolution equations with asymmetric non-local and non-monotone response. We show that, contrary to the symmetric case, these equations can possess simultaneously stationary, expansion and extinction waves. 相似文献
25.
Hernane T. Barcelos Luclecia D. Nunes Guilherme W. Tavares Edesio F. C. Alcantara Alexandre G. S. Prado 《Journal of Thermal Analysis and Calorimetry》2011,106(2):421-425
Silica gel was modified by silanization reaction followed by functionalization of histamine in a heterogeneous route. These
materials were characterized by elementary nitrogen and chloride analyses, porosity, thermogravimetry, and infrared. The functionalized
surface adsorbed Cu(II), Co(II), Ni(II), and Zn(II) ions in an aqueous solution at 25 °C. The isotherms of adsorption are
in accordance with Langmuir model and the surface presented a great potential to form complexes metal-surface in the chemical
reason of 1:1. 相似文献
26.
Polyanna Silveira Hornung Layse do Prado Cordoba Simone Rosa da Silveira Lazzarotto Egon Schnitzler Marcelo Lazzarotto Rosemary Hoffmann Ribani 《Journal of Thermal Analysis and Calorimetry》2017,127(3):1869-1877
Determination of the characteristics of native starches is crucial in order to select their best application in various industrial fields. Thus, two different types of non-traditional native starches from the Dioscoreaceas species (Dioscorea sp. and Dioscorea piperifolia Humb. var. Wild) were studied regarding their thermal, structural and rheological properties. The results were contrasted with traditional commercial starch sources (potato, cassava and corn). From the thermogravimetric results (TG/DTG), D. piperifolia starch obtained the highest thermal stability of the samples, except for potato starch. Furthermore, using differential scanning calorimetry and viscoamylograph profiles (RVA), it was found that the Dioscoreaceas starches presented a higher onset (T o) temperature and susceptibility to retrogradation. They also showed lower values in relation to relative crystallinity, which was calculated from their X-ray patterns and tendency to white (L*) colour. The shapes of the Discoreaceas starch granules were determined using electron microscopy; it was found that as the potato starch the Dioscoreaceas starches showed a wide range of particle size. 相似文献
27.
Paulo B. Gonçalves Frederico M. A. Silva Zenón J. G. N. Del Prado 《Nonlinear dynamics》2007,50(1-2):121-145
In the present study, the large-amplitude vibrations and stability of a perfect circular cylindrical shell subjected to axial
harmonic excitation in the neighborhood of the lowest natural frequencies are investigated. Donnell's shallow shell theory
is used and the shell spatial discretization is obtained by the Ritz method. An efficient low-dimensional model presented
in previous publications is used to discretize the continuous system. The main purpose of this work is to discuss the use
of basins of attraction as a measure of the reliability and safety of the structure. First, the nonlinear behavior of the
conservative system is discussed and the basin structure and volume is understood from the topologic structure of the total
energy and its evolution as a function of the system parameters. Then, the behavior of the forced oscillations of the harmonically
excited shell is analyzed. First the stability boundaries in force control space are obtained and the bifurcation events connected
with these boundaries are identified. Based on the bifurcation diagrams, the probability of parametric instability and escape
are analyzed through the evolution and erosion of basin boundaries within a prescribed control volume defined by the manifolds.
Usually, basin boundaries become fractal. This together with the presence of catastrophic subcritical bifurcations makes the
shell very sensitive to initial conditions, uncertainties in system parameters, and initial imperfections. Results show that
the analysis of the evolution of safe basins and the derivation of appropriate measures of their robustness is an essential
step in the derivation of safe design procedures for multiwell systems. 相似文献
28.
Prado AG Pescara IC Evangelista SM Holanda MS Andrade RD Suarez PA Zara LF 《Talanta》2011,84(3):759-765
Biodiesel and diesel-like have been obtained from soybean oil by transesterification and thermal cracking process, respectively. These biofuels were characterized as according to ANP standards by using specific ASTM methods. Ethanol, gasoline, and diesel were purchased from a gas station. Deacetylation degree of chitosan was determined by three distinct methods (conductimetry, FTIR and NMR), and the average degree was 78.95%. The chitosan microspheres were prepared from chitosan by split-coating and these spheres were crosslinked using glutaraldehyde. The surface area of microspheres was determined by BET method, and the surface area of crosslinked microspheres was 9.2 m2 g−1. The adsorption isotherms of cooper, nickel and zinc on microspheres of chitosan were determined in petroleum derivatives (gasoline and diesel oil), as well as in biofuels (alcohol, biodiesel and diesel-like). The adsorption order in all fuels was: Cu > Ni > Zn. The elution tests presented the following preconcentration degrees: >4.5 to ethanol, >4.4 to gasoline, >4.0 to diesel, >3.8 to biodiesel and >3.6 to diesel-like. The application of chitosan microspheres in the metal ions preconcentration showed the potential of this biopolymer to enrich fuel sample in order to be analyzed by flame atomic absorption spectrometry. 相似文献
29.
Izumi E Ueda-Nakamura T Dias Filho BP Veiga Júnior VF Nakamura CV 《Natural product reports》2011,28(4):809-823
Here, we review studies that have investigated the activity of plant-derived compounds against Trypanosoma cruzi, the etiologic agent of Chagas’ disease. In the last decade, more than 300 species belonging to almost 100 families have been evaluated for activity, and here we describe the compounds isolated; 85 references are cited. 相似文献
30.
Alécio R. Nunes Aline O. Moura Alexandre G. S. Prado 《Journal of Thermal Analysis and Calorimetry》2011,106(2):445-452
H-magadiite was applied to remove the pesticides 2,4-d, diuron, and atrazine from water. The H-magadiite containing herbicides adsorbed were investigated by FTIR, DRX, N2 adsorption and desorption isotherms, and surface area. Calorimetric studies were carried out to determine the heat of interaction
between pesticides and magadiite. It was possible to ride the cycle of interaction of magadiite–pesticide for a better understanding
of the process involved. From the results of the thermal effect of the interaction of magadiite–pesticide, the thermochemical
parameters can be determined by using the relationship between the data obtained from adsorption and calorimetry results.
The interaction of pesticide–magadiite follows the sequence of adsorption: diuron > atrazine > 2,4-d. The ΔH values for the interactions were determined to be −20.62 ± 1.08, −24.04 ± 0.86–26.34 ± 0.93 kJ mol−1 for 2,4-d, diuron and atrazine, respectively. All the interactions were spontaneous, enthalpically and entropically favored demonstrating
the effectiveness and efficiency of the method. 相似文献