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排序方式: 共有215条查询结果,搜索用时 468 毫秒
31.
In this paper we consider the numerical integration on a polygonal domain Ω in ?2 of a function F(x,y) which is integrable except at a point \(P_{0}=(x_{0},y_{0})\in{\stackrel{\circ}{\Omega}}\), where F becomes infinite of order two. We approximate either the finite-part or the two-dimensional Cauchy principal value of the integral by using a spline finite element method combined with a subdivision technique also of adaptive type. We prove the convergence of the obtained sequence of cubatures. Finally, to illustrate the behaviour of the proposed method, we present some numerical examples. 相似文献
32.
V. Vittoria A. Ruvolo Filho F. De Candia 《Journal of Macromolecular Science: Physics》2013,52(2):133-148
Syndiotactic polystyrene (sPS) films were obtained either by casting or by melt crystallization in the β form. Different thermal treatments of the melt led to mixed α and β forms. The structural organization was investigated by x-rays, transport properties, and Fourier transform infrared analysis. The β form is characterized by chains in zigzag planar conformation. For samples prevalently in β form, the fraction of impermeable phase, derived from sorption measurements, was found coincident with the fraction of crystalline phase derived from x-rays. In samples with mixed α and β forms, however, a fraction of mesophase is also present. The β form of sPS is stable to dichloromethane, whereas the α form is transformed into a crystalline form with the chains in helical conformation. Nevertheless, when the relative fraction of β form is lower than a critical value, it also dissolves in liquid dichloromethane, undergoing the conformational transition into the helical form. 相似文献
33.
Syndiotactic polystyrene films were prepared from the melt with different thermal treatments. Amorphous or crystalline films were obtained; x-ray analysis shows that in the crystalline samples two crystalline forms can be present and that the phase composition depends on the thermal conditions. The two forms show a different stability to liquid methylene chloride, one being stable while the other can be dissolved or transformed to a completely different crystalline structure. In all the analyzed samples the study of transport properties of CH2 Cl2 at low activity indicates that the amorphous component behaves as atactic polystyrene. This allows the determination of the crystallinity in the different samples. 相似文献
34.
Geiler AL Yang A Zuo X Yoon SD Chen Y Harris VG Vittoria C 《Physical review letters》2008,101(6):067201
Using a novel alternating target laser ablation deposition technique, Mn cations were placed in specific interstitial sites of BaFe12O19 thin films as opposed to being distributed throughout the unit cell as in conventional bulk materials. The distribution of Mn cations has been confirmed experimentally and predicted theoretically. As a result of site selection, the saturation magnetization increased 12%-22%, and the Néel temperature increased by 40-60 K compared to bulk materials. This technique implies a new methodology to design and process a new generation of ferrite, oxide, and alloy materials. 相似文献
35.
Luca Giacomo Bettini Maria Vittoria Diamanti Maurizio Sansotera Maria Pia Pedeferri Walter Navarrini Paolo Milani 《Journal of nanoparticle research》2016,18(8):238
Anatase/rutile mixed-phase titanium dioxide (TiO2) photocatalysts in the form of nanostructured powders with different primary particle size, specific surface area, and rutile content were produced from the gas-phase by flame spray pyrolysis (FSP) starting from an organic solution containing titanium (IV) isopropoxide as Ti precursor. Flame spray-produced TiO2 powders were characterized by means of X-ray diffraction, Raman spectroscopy, and BET measurements. As-prepared powders were mainly composed of anatase crystallites with size ranging from 7 to 15 nm according to the synthesis conditions. TiO2 powders were embedded in a multilayered fluoropolymeric matrix to immobilize the nanoparticles into freestanding photocatalytic membranes. The photocatalytic activity of the TiO2-embedded membranes toward the abatement of hydrosoluble organic pollutants was evaluated employing the photodegradation of rhodamine B in aqueous solution as test reaction. The photoabatement rate of best performing membranes significantly overcomes that of membranes produced by the same method and incorporating commercial P25-TiO2. 相似文献
36.
Fabio Ferrini Daniele Fraternale Sabrina Donati Zeppa Giancarlo Verardo Andrea Gorassini Vittoria Carrabs Maria Cristina Albertini Piero Sestili 《Molecules (Basel, Switzerland)》2021,26(16)
Cannabis sativa L. has been used for a long time to obtain food, fiber, and as a medicinal and psychoactive plant. Today, the nutraceutical potential of C. sativa is being increasingly reappraised; however, C. sativa roots remain poorly studied, despite citations in the scientific literature. In this direction, we identified and quantified the presence of valuable bioactives (namely, β-sitosterol, stigmasterol, campesterol, friedelin, and epi-friedelanol) in the root extracts of C. sativa, a finding which might pave the way to the exploitation of the therapeutic potential of all parts of the C. sativa plant. To facilitate root harvesting and processing, aeroponic (AP) and aeroponic-elicited cultures (AEP) were established and compared to soil-cultivated plants (SP). Interestingly, considerably increased plant growth—particularly of the roots—and a significant increase (up to 20-fold in the case of β-sitosterol) in the total content of the aforementioned roots’ bioactive molecules were observed in AP and AEP. In conclusion, aeroponics, an easy, standardized, contaminant-free cultivation technique, facilitates the harvesting/processing of roots along with a greater production of their secondary bioactive metabolites, which could be utilized in the formulation of health-promoting and health-care products. 相似文献
37.
Vittoria de Nitto Personè 《Annals of Operations Research》2009,170(1):95-112
The aim of this paper is to improve the machine interference model with vacation to deal with more recent problems of the
communication area. To this scope the model is extended to include parallelism in the vacation station. The underlying Markov
process is analyzed and a state arrangement is found that yields an efficient matrix-analytic technique that substantially
lowers down the time- and space-complexity of standard methods. A numerical example of the method effectiveness is presented,
and an example of resource allocation is introduced that finds applications in the QoS management of wireless networks.
The author is thankful to the anonymous referees for the improvements their comments have earned to the quality of the presentation
and to the completeness of the paper. The author is thankful to Giuseppe Iazeolla, whose careful reading of the original draft
of this paper led to significant improvements in its overall quality. This work was partially supported by funds from the
FIRB project “Performance Evaluation of Complex Systems: Techniques Methodologies and Tools” and by the University of Roma
TorVergata project on High Performance ICT Platforms. 相似文献
38.
Nicoletta Panziera Ilaria Fratoddi Maria Vittoria Russo 《Journal of organometallic chemistry》2006,691(12):2648-2656
The new dialkynylated complexes Ru(η6-DEB-Si)(η4-COD), 4a, Ru(η6-DEBP-Si)(η4-COD), 4b1, Ru2(η6,η6-DEBP)(η4-COD)2, 4b2 [COD = 1,5-cyclooctadiene; DEB-Si = 1,4-bis(trimethylsilylethynyl)benzene; DEBP-Si = 4,4′-bis(trimethylsilylethynyl)biphenyl] have been synthesized by the arene exchange reaction with the complex Ru(η6-naphthalene)(η4-COD). The complexes Ru(η6-DEB)(η4-COD), 5a, and Ru(η6-DEBP)(η4-COD), 5b1, have been prepared by desilylation of the corresponding compounds 4a and 4b1. All the complexes have been fully characterized by means of spectroscopic techniques. 相似文献
39.
Moving from the observation that drainage network configurations minimizing total energy dissipation are stationary solutions of the general equation describing landscape evolution, we review theoretical and observational evidence on river patterns and their scale-invariant structure. Exact results complemented by numerical annealing of the basic equation in the presence of additive noise suggest that configurations at (or very close to) the global minimum of energy dissipation differ from dynamically accessible states, which have rather different scaling properties and conform much better to natural forms. Thus we argue that, at least in the fluvial landscape, Nature works through imperfect searches for dynamically accessible optimal configurations. We also show that optimal networks are spanning loopless configurations only under precise physical requirements. This is stated in a form applicable to generic networks, suggesting that other branching structures occurring in Nature (e.g. scale-free and looping) may possibly arise through optimality to selective pressures. Indeed, we show that this is the case. 相似文献
40.
Hierarchical structures in fibrillar collagens 总被引:6,自引:0,他引:6
Ottani V Martini D Franchi M Ruggeri A Raspanti M 《Micron (Oxford, England : 1993)》2002,33(7-8):587-596