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101.
We report an experimental study on the shape of the 1.9 eV emission associated with non-bridging oxygen hole centers in silica and its temperature dependence, from 4 up to 300 K, under visible and ultraviolet excitation. Our analysis points out that these defects are coupled with their environment by phonons whose contribution can be described by the single mode of mean frequency between 300–400 cm−1 and Huang–Rhys factor of 3. On increasing the temperature, the luminescence intensity undergoes a thermal quenching caused by non-radiative processes, its deviation from a pure Arrhenius law can be accounted for by an uniform distribution of activation energy, from 0.002 to 0.05 eV. Meanwhile the emission band gets narrower, this contrasts with the broadening with temperature observed in other silica defects and suggests that the vibrational levels associated with the excited state are not thermally populated according to Boltzmann's law. 相似文献
102.
Paolo Ciambelli Maria Grazia Meo Paola Russo & Salvatore Vaccaro 《advances in applied mathematics and mechanics.》2011,3(3):327-353
Modelling based on Computational Fluid Dynamics (CFD) is by now
effectively used in fire research and hazard analysis. Depending
on the scenario, radiative heat transfer can play a very important
role in enclosure combustion events such as tunnel fires. In this work,
the importance of radiation and the effect of the use of different approaches
to account for it were assessed. Firstly, small-scale tunnel fire simulations
were performed and the results compared with experimental data, then realistic
full-scale scenarios were simulated. The results show up the capability of CFD
modelling to reproduce with good approximation tunnel fires. Radiation proved to
be noteworthy mainly when the scale of the fire is relatively large. Among the
various approaches employed to simulate radiation, the use of the Discrete Transfer
model gave the most accurate results, mainly when the absorption-emission characteristics
of the combustion products were taken into account. Finally, the suitability of the
use of CFD in quantitative Fire Hazard Analysis is discussed. 相似文献
103.
Edoardo Luca Vigan Erika Colombo Giuseppa Raitano Alberto Manganaro Alessio Sommovigo Jean Lou CM Dorne Emilio Benfenati 《Molecules (Basel, Switzerland)》2022,27(19)
Read-across applies the principle of similarity to identify the most similar substances to represent a given target substance in data-poor situations. However, differences between the target and the source substances exist. The present study aims to screen and assess the effect of the key components in a molecule which may escape the evaluation for read-across based only on the most similar substance(s) using a new open-access software: Virtual Extensive Read-Across (VERA). VERA provides a means to assess similarity between chemicals using structural alerts specific to the property, pre-defined molecular groups and structural similarity. The software finds the most similar compounds with a certain feature, e.g., structural alerts and molecular groups, and provides clusters of similar substances while comparing these similar substances within different clusters. Carcinogenicity is a complex endpoint with several mechanisms, requiring resource intensive experimental bioassays and a large number of animals; as such, the use of read-across as part of new approach methodologies would support carcinogenicity assessment. To test the VERA software, carcinogenicity was selected as the endpoint of interest for a range of botanicals. VERA correctly labelled 70% of the botanicals, indicating the most similar substances and the main features associated with carcinogenicity. 相似文献
104.
Aiming for more sustainable chemical production requires an urgent shift towards synthetic approaches designed for waste minimization. In this context the use of azeotropes can be an effective tool for “recycling” and minimizing the large volumes of solvents, especially in aqueous mixtures, used. This review discusses the implementation of different kinds of azeotropic mixtures in relation to the environmental and economic benefits linked to their recovery and re-use. Examples of the use of azeotropes playing a role in the process performance and in the purification steps maximizing yields while minimizing waste. Where possible, the advantages reported have been highlighted by using E-factor calculations. Lastly azeotrope potentiality in waste valorization to afford value-added materials is given. 相似文献
105.
Barretta Raffaele Marotti de Sciarra Francesco Pinnola Francesco P. Vaccaro Marzia S. 《Meccanica》2022,57(4):807-820
Meccanica - Nonlocal hereditariness in Bernoulli–Euler beam is investigated in this paper. An approach to solve that problem is proposed and some analytical solutions are provided. To this... 相似文献
106.
Marijke WA de Backer Maike AD Brans Mieneke CM Luijendijk Keith M Garner Dianne MA van den Heuvel R Jeroen Pasterkamp Roger AH Adan 《BMC neuroscience》2010,11(1):94
Background
Multiple neuropeptides, sometimes with opposing functions, can be produced from one precursor gene. To study the roles of the different neuropeptides encoded by one large precursor we developed a method to overexpress minigenes and establish local secretion. 相似文献107.
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110.
J.W. Vanderhoff M.S. El-Aasser F.J. Micale E.D. Sudol CM. Tseng A. Silwanowicz 《Journal of Dispersion Science and Technology》2013,34(3-4):231-246
Monodisperse polystyrene latexes are prepared by seeded emulsion polymerization; however, sizes larger than 2μm are difficult to prepare because of the creaming and settling of the particles, and their sensitivity to mechanical shear. Preparation in space would obviate the creaming and settling, and allow agitation just sufficient for good heat transfer and mixing. Three polymerizations yielding 3-5μm size particles were carried out successfully on the third flight of the “Columbia” launched March 22, 1982; however, four polymerizations yielding sizes up to 10μm on the fourth flight launched June 27, 1982, were incomplete owing to apparatus malfunction. The results of these polymerizations and the prospects of developing a preparative space process are reviewed 相似文献