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91.
92.
Annibal Figueiredo Marcio T. de Castro Regina C.B. da Fonseca Iram Gleria 《Physics letters. A》2013,377(25-27):1571-1581
We investigate which type of diffusion equation is most appropriate to describe the time evolution of foreign exchange rates. We modify the geometric diffusion model assuming a non-exponential time evolution and the stochastic term is the sum of a Wiener noise and a jump process. We find the resulting diffusion equation to obey the Kramers–Moyal equation. Analytical solutions are obtained using the characteristic function formalism and compared with empirical data. The analysis focus on the first four central moments considering the returns of foreign exchange rate. It is shown that the proposed model offers a good improvement over the classical geometric diffusion model. 相似文献
93.
Abstract The direct near‐infrared spectroscopic reflectance measurements of prevulcanized natural rubber (brown crepe) was employed for determination of its Mooney viscosity. NIR reflectance spectra were obtained for a total of 100 samples whose Mooney viscosity (VM in the range 68–95 units) have been determined by the standard reference procedure using a commercial computerized Mooney viscometer. These samples were employed as the raw material or were treated to achieve better homogenization. A Fourier transform near infrared (FT‐NIR) spectrophotometer was employed, and the reflectance spectra were obtained with resolution of 4 cm?1 in the range 4000–10,000 cm?1 as an average of 75 scans. The samples were split in a calibration set containing 70 samples and in an external validation set consisting of the remaining 30 samples. The calibration and validation spectra sets were treated to correct for baseline shift, further transformed by first derivative and finally modeled by partial least squares (PLS) employing four latent variables. The model was evaluated with the external sample test set, and a RMSEP of 3.6 and 3.9 units of Mooney viscosity were obtained for homogenized and nonhomogenized samples, respectively. The NIR method is capable of determining the Mooney viscosity in few minutes in the non‐pretreated sample with an error that is satisfactory for quality control of natural rubber destined for automobile tire manufacturing. 相似文献
94.
In this paper, we show that the strict mononicity of the eigen-values of an uniformly elliptic operator of second order is equivalent to a unique continuation property. 相似文献
95.
Let ${\mathcal P}$ be a partial order and ${\mathcal A}$ an arboreal extension of it (i.e. the Hasse diagram of ${\mathcal A}$ is a rooted tree with a unique minimal element). A jump of ${\mathcal A}$ is a relation contained in the Hasse diagram of ${\mathcal A}$ , but not in the order ${\mathcal P}$ . The arboreal jump number of ${\mathcal A}$ is the number of jumps contained in it. We study the problem of finding the arboreal extension of ${\mathcal P}$ having minimum arboreal jump number—a problem related to the well-known (linear) jump number problem. We describe several results for this problem, including NP-completeness, polynomial time solvable cases and bounds. We also discuss the concept of a minimal arboreal extension, namely an arboreal extension whose removal of one jump makes it no longer arboreal. 相似文献
96.
Bañuelos J López Arbeloa F Arbeloa T Salleres S Vilas JL Amat-Guerri F Liras M López Arbeloa I 《Journal of fluorescence》2008,18(5):899-907
The structural, electronic and photophysical properties of three new asymmetric, highly fluorescent difluoroborondipyrromethene
(BODIPY) dyes, bearing an amino or an acetamido group at position 3 of the chromophoric core, have been studied in different
apolar, polar and polar/protic solvents. The presence of the 3-amido group extents the delocalization of the π-system, leading to bathochromic shifts in the absorption and fluorescence bands, as predicted by quantum mechanic calculations.
The 3-amino dye shows photophysical properties highly dependent on the solvent polarity and acidity, and is characterized
by a hypsochromic shift of its absorption band, with regard to the corresponding acetylated dye, as well as a low fluorescence
quantum yield in acid media with proton concentration lower than 4 × 10−4 M. In media with higher proton concentration, the BF2 bridge group of the 3-amino dye is removed, yielding the corresponding non-fluorescent dipyrromethene precursor. These results
suggest that the 3-amino dye could be used as a fluorescence probe for the study of the acidity of different environments. 相似文献
97.
Kumar Niraj Rodriguez Jassiel R. Pol Vilas G. Sen Arijit 《Journal of Solid State Electrochemistry》2019,23(5):1443-1454
Journal of Solid State Electrochemistry - Here, we present a unique morphology comprising a blend of ultrafine 1D MnO2 and graphene oxide as an efficient anode material to overcome the issue of... 相似文献
98.
M.O. Figueiredo T.P. Silva J.P. Veiga 《Applied Physics A: Materials Science & Processing》2008,92(1):151-154
A review is presented on constructive techniques plus materials and the processes involved in degradation phenomena observed
in two historical monuments: the Zambujeiro dolmen (Portugal) and the Roman Aqueduct of Carthage (Tunisia).
Dolmens are particularly impressive megalithic constructions for the dimensions of granite blocks. At Zambujeiro, the upright
stones have undergone a catastrophic evolution after the archaeological exploitation due to accelerated weathering through
a process apparently distinct from natural granite decay in nearby outcrops. The biological attack of granite minerals by
lichen exudates has emphasized the hazardous character of bromine and more has been learnt about construction techniques,
namely, the insertion in the mound of an impermeable clay stratum that hinders water penetration into the dolmen chamber.
The characterization of original Roman ashlar blocks, including masonry and the diagnosis of Byzantine and medieval reconstruction
testimonies in the Aqueduct of Carthage were the object of a detailed study by X-ray diffraction and synchrotron radiation
X-ray fluorescence. Traditional constructive techniques and local construction materials were studied and successive historical,
modern and recent rehabilitations were reappraised.
PACS 83.80.Nb; 64.70.Kb; 78.70.En; 41.60.Ap 相似文献
99.
100.
Connecting free volume with shape memory properties in noncytotoxic gamma‐irradiated polycyclooctene 下载免费PDF全文
José María Cuevas Clarisse Ribeiro David Mérida José Manuel Laza José Ángel García José Luis Vilas Senentxu Lanceros‐Méndez Fernando Plazaola Luis Manuel León 《Journal of Polymer Science.Polymer Physics》2015,53(15):1080-1088
The free volume holes of a shape memory polymer have been analyzed considering that the empty space between molecules is necessary for the molecular motion, and the shape memory response is based on polymer segments acting as molecular switches through variable flexibility with temperature or other stimuli. Therefore, thermomechanical analysis (TMA) and positron annihilation lifetime spectroscopy (PALS) have been applied to analyze shape recovery and free volume hole sizes in gamma‐irradiated polycyclooctene (PCO) samples, as a noncytotoxic alternative to more conventional PCO crosslinked via peroxide for future applications in medicine. Thus, a first approach relating structure, free volume holes and shape memory properties in gamma‐irradiated PCO is presented. The results suggest that free volume holes caused by gamma irradiation in PCO samples facilitate the recovery process by improving movement of polymer chains and open possibilities for the design and control of the macroscopic response. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1080–1088 相似文献