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571.
Unknown and controversial aspects related to the mechanisms of hydrolysis of borane complexes and to the mechanisms of chemical vapor generation for trace element determination in strongly acidic media (0.01-10 M HCl) have been investigated and clarified. The overall hydrolysis rates of borane complexes (BH(4)(-), H(3)N-BH(3)) in the acidity range of 0.2-10 M HCl were several orders of magnitude lower than those predicted by kinetics laws and obtained in the pH range of 3.8-14. The decomposition of the borane complexes takes place stepwise and proceeds through the formation of hydroboron intermediates, L(x)()BH(4)(-)(x)()(n)() (x = 1, 2, 3), where L could be one or more species among the donor groups H(2)O, NH(3), OH(-), and Cl(-) and n is the charge of the hydroboron species (n = 0, +1, -1, depending on L). Some intermediates present surprisingly long lifetimes at elevated acidities and play a key role in determining both the overall hydrolysis rates of borane complexes and the reactivity of Hg(II), As(III), Sb(III), Bi(III), Se(IV), Te(IV), and Sn(IV) in chemical vapor generation for trace element determination. Atomic absorption experiments demonstrated that almost all trihydroboron species (LBH(3)(n)()), dihydroboron species (L(2)BH(2)(n)()), and monohydroboron species (L(3)BH(n)()) play an active role in the generation of elemental mercury and stibine. Some of these intermediates are inactive or play a marginal role in the generation of arsine, bismuthine, and hydrogen selenide. Hydrogen telluride is preferentially formed by those hydroboron species, which are stable in strongly acidic conditions, while the same species are unreactive in the generation of stannane. The collected experimental evidence is in agreement with the general reactivity of the elements in chemical vapor generation techniques and, together with other literature data, definitely rule out the hypothesis of "nascent hydrogen" as a possible mechanism of chemical vapor generation by borane complex derivatization. 相似文献
572.
A method for performing a reliability analysis of structural systems within a standard finite element code is presented. This numerical procedure can be implemented in any finite element (f.e.) code having an internal optimization routine. The design points of structural problems are determined by calculating the minimum distance from the origin to the failure surface in a set of normalized variables, by using the minimization routine of the f.e. code. In order to test the procedure, simple structural systems are solved and the results are compared with those obtained by using different approaches. Some examples of application of the procedure for the reliability analysis of real structures are presented. 相似文献
573.
Alessandro Passardi Emanuela Scarpi Paola Ulivi 《International journal of molecular sciences》2021,22(14)
The present editorial aims to summarise the six scientific papers that have contributed to this Special Issue, focusing on different aspects of molecular and translational research on colorectal cancer. We believe that the present Special Issue might contribute to the expansion of the current knowledge concerning potential molecular predictive and/or prognostic biomarkers in CRC, as well as new targets for anticancer treatment. This may help in identifying new strategies to improve diagnostic and therapeutic approaches. 相似文献
574.
Gabriella Garbarino Paola Riani Mattia Alberto Lucchini Fabio Canepa Shrikant Kawale Guido Busca 《International Journal of Hydrogen Energy》2013
Results obtained in the synthesis, characterization and application as catalyst of cobalt nanoparticles are reported. Cobalt nanoparticles were prepared via reduction method in aqueous solution. Structural characterization was carried out using X-ray diffraction (XRD), morphological studies were performed with a scanning electron microscope equipped with a field emission gun (FE-SEM). A DC-superconducting quantum interference device “SQUID” magnetometer was used to measure the room temperature (RT) magnetic hysteresis cycle in the −5 ÷ 5 Tesla (T) μ0H magnetic field range as well as magnetization as a function of temperature. This material is constituted by very small primary particles (∼2.8 nm radius) which appear amorphous to XRD and have a superparamagnetic behaviour. However, annealing at 773 K and also utilization in the catalytic reactor at the same temperature result in XRD detectable cubic Co nanocrystals. These unsupported cobalt nanoparticles were found catalytically active in the ethanol steam reforming reaction, producing hydrogen with 90% yield at 773 K. These nanoparticles show a better catalytic behaviour compared to those of more conventional Co and Ni based catalysts, due to very low CO and methane production, and with moderate formation of carbonaceous materials. 相似文献
575.
Joachim Schmid Michael Klippel Alar Just Andrea Frangi Mattia Tiso 《Fire Technology》2018,54(5):1113-1148
Cross-laminated timber, typical abbreviations CLT or XLAM, is currently one of the most innovative product in building with wood. This solid engineered timber product provides advantages compared to other solid timber slabs as the dimension stability, i.e. swelling and shrinkage, is controlled by the crosswise laminations. As for other components, the fire resistance has to be verified for this type of product. While fire testing is time consuming and costly, simulations provide flexibility to optimize the product or to develop simplified design models for structural engineers. In this paper, a simulation technique is presented which can be used to determine the fire resistance of CLT. The technique was then used to develop simplified design equations to be used by engineers to predict the behavior of CLT in fire resistance tests and verify its fire resistance. Following existing models, the simplified design model aims for a two-step process whereby in a (i) first step the residual cross section and in (ii) a second step the load bearing capacity of the partly heated residual cross section is determined. The presented simulations consider the effective thermal–mechanical characteristics of wood exposed to standard fire and perform an advanced section analysis using a temperature profile corresponding to the actual protection and the location of the centroid together with the possibility of plasticity on the side of compression. It was shown that simulation results agree well with test results and that they can be used to determine layup specific modification factors used by the reduced properties method or zero-strength layers used by the effective cross section method. It was shown that the use of the zero-strength layers is favorable compared to the modification factors to calculate the resistance of the residual cross section. This is due to the large range of modification factors answering the typical layup of CLT comprising layers with their fiber direction cross the span direction. Subsequently, the methodology was used to determine design equations for initially unprotected and protected three-, five- and seven-layer CLT in bending and buckling. While the zero-strength layer for glulam beams in bending is assumed to be 7 mm (0.3 in), for CLT the corresponding value is in most of the cases between 5 mm and 12 mm but is different for other loading modes such as buckling (wall elements) and depending on the applied protection. 相似文献
576.
577.
Vitale F Fratoddi I Battocchio C Piscopiello E Tapfer L Russo MV Polzonetti G Giannini C 《Nanoscale research letters》2011,6(1):103
Stable gold nanoparticles stabilized by different mono and bi-functional arenethiols, namely, benzylthiol and 1,4-benzenedimethanethiol,
have been prepared by using a modified Brust's two-phase synthesis. The size, shape, and crystalline structure of the gold
nanoparticles have been determined by high-resolution electron microscopy and full-pattern X-ray powder diffraction analyses.
Nanocrystals diameters have been tuned in the range 2 ÷ 9 nm by a proper variation of Au/S molar ratio. The chemical composition
of gold nanoparticles and their interaction with thiols have been investigated by X-ray photoelectron spectroscopy. In particular,
the formation of networks has been observed with interconnected gold nanoparticles containing 1,4-benzenedimethanethiol as
ligand. 相似文献
578.
D'Agostino A Errico ME Malinconico M De Rosa M Avella M Schiraldi C 《Journal of materials science. Materials in medicine》2011,22(3):481-490
In this research work organic/inorganic nano composites were synthesized from poly-2-hydroxyethylmethacrylate and properly
modified silica nanoparticles by in situ polymerization. In particular, fumed nanosilica was functionalized with methacryloylpropyltrimetoxy
silane (MPTMS) in order to obtain a more homogeneous, reliable and mechanically performing nano composite. For comparison,
nano composites with non functionalised silica were also prepared. Scanning electron microscopy was performed in order to
visualize the effects of functionalization on the mode and state of dispersion. This analysis demonstrated that MPTMS grafted
onto silica surface acts as an effective coupling agent and assures a good dispersion and distribution of nanoparticles as
well as a strong nano particle/matrix interfacial adhesion. As a result of strong interactions occurring between phases, a
pronounced increase of the glass transition temperature and mechanical parameters were recorded. Finally, these novel nano
composites were seeded with murine fibroblast and human mesenchymal stem cells, and observed in time-lapse experiments proving
an effective biological response. 相似文献
579.
580.
Felice Crupi Raffaele De Rose Maksym Paliy Marco Lanuzza Mattia Perna Giuseppe Iannaccone 《International Journal of Circuit Theory and Applications》2018,46(4):779-795
This work proposes a new class of current references based on only 3 transistors that allows sub‐0.5 V operation. The circuit consists of a 2‐transistor block that generates a proportional‐to‐absolute‐temperature or a complementary‐to‐absolute‐temperature voltage and a load transistor. The idea of a 3T current reference is validated by circuit simulations for different complementary metal‐oxide‐semiconductor technologies and by experimental measurements on a large set of test chips fabricated with a commercial 0.18 μm complementary metal‐oxide‐semiconductor process. As compared to the state‐of‐art competitors, the 3T current reference exhibits competitive performance in terms of temperature coefficient (578 ppm/°C), line sensitivity (3.9%/V), and power consumption (213 nW) and presents a reduction by a factor of 2 to 3 in terms of minimum operating voltage (0.45 V) and an improvement of 1 to 2 orders of magnitude in terms of area occupation (750 μm2). In spite of the extremely reduced silicon area, the fabricated chips exhibit low‐process sensitivity (2.7%). A digital trimming solution to significantly reduce the process sensitivity is also presented and validated by simulations. 相似文献