56,238 research outputs found
Carbon-silicon composite anode electrodes modified with MWCNT for high energy battery applications
No full textIn this study, we comparatively study the electrochemical characteristics of Si, Si-C and vacuum-assisted filtration fabrication of a novel free-standing Si@C/Mutli Wall Carbon Nanotubes (MWCNT) nanocomposite. The surfaces of the as-received Si nanaoparticles were coated with an amorphous carbon layer and homogenously anchored onto the surfaces of as-received MWCNTs by a simple vacuum filtration method. The samples were then analyzed with field emission scanning electron microscopy and X-ray diffraction (XRD) methods. Si@C/MWCNT samples have shown a stable capacity of 1290 mA h g(-1) after 200 cycles. The results have proven that MWCNT's large surface area, highly conductive network which can provide good contact between Si@C nanoparticles, tolerating large volume change sand suppressing aggregation of Si@C nanoparticles during charge/discharge processes. Such a comparison between the performances of carbon-MWCNT-metal materials is reasonably envisaged not only to be useful for understanding the individual contribution from MWCNT and metal but also to form a fundamental basis for energy storage applications. Free-standing Si-C/MWCNT nano paper has been successfully obtained by a facile vacuum filtration method. (C) 2018 Elsevier B.V. All rights reserved
Experimental investigation of plasma impedance in Linac4 source
No full textCERN ’s new particle accelerator Linac4 is part of the upgrade of the LHC accelerator chain. Linac4 is required to deliver 160 MeV H− beam to improve the beam brightness and luminosity in the Large Hadron Collider (LHC). The Linac4 H− source must deliver 40-50 mA, 45 keV H− beam in the RFQ acceptance. Since the RF power coupled to the H− source plasma is one of the important parameters that determines the quality of the H− beam, the experimental investigation of the dependence of the load impedance on the operational parameters is mandatory. In this study, we have measured the impedance of the H− source plasma varying the RF power coupled to the plasma and the condition of the hydrogen gas. Also, optical emission spectroscopy (OES) measurements have been carried out simultaneously with the impedance measurement in order to determine the plasma parameters. The determination of the plasma parameters allows us to compare the experimental results with the analytic model of the plasma parameters, which is useful to discuss the results from a physical point of view
Track degradation analysis in the scope of railway infrastructure maintenance management systems
No full textStanje elemenata željezničke infrastrukture ključni je faktor koji utječe na sigurnost prometa, raspoloživost infrastrukture, ukupne troškove radova na održavanju i remontu, kao i prihode. Mjerenje i analiza stanja elemenata željezničke infrastrukture je jedini ispravan pristup kako bi se na učinkovit način pratilo njihovo ponašanje te planirali radovi na održavanju. U radu se opisuje optimalna struktura sustava za upravljanje održavanjem željezničke infrastrukture (Railway Maintenance Management System - RMMS) s posebnim osvrtom na primjenu modela degradacije kao jednog od ključnih dijelova RMMS-a.The condition of railway infrastructure elements is the key factor influencing the traffic safety, infrastructure availability, total maintenance and renewal costs, and revenues. The measurement and analysis of the condition of railway infrastructure elements is the only correct approach enabling an efficient monitoring of their behaviour and proper planning of maintenance activities. An optimum structure of the railway Maintenance Management System - RMMS is presented in the paper, with a special emphasis on the utilization of deterioration models, as one of the RMMS’s key components
Influence of the cusp field on the plasma parameters of the Linac4 H− ion source
No full textWhen the H ion source of CERN’s Linac4 is operated in volume mode, a maximum of the extracted current is obtained at varying RF power. The power required for this maximum and its absolute value is strongly influenced by the cusp magnets installed at the source for electron confinement: without magnets, 15−20 mA are typically obtained at 20 kW whereas with magnets a factor of two more power is needed and 25−30 mA are achieved. In order to access the reasons behind the peaked performance with varying RF power and for determining the influence of the cusp field on the discharge, optical emission spectroscopy (OES) measurements of the atomic Balmer series and of the molecular Fulcher transition have been carried out. In all investigated cases, the gas temperature of the discharge has been virtually equal to the ambient temperature as the short discharge pulse length of 500 s is not long enough for considerable heavy particle heating. When no cusp magnets are installed, the plasma parameters evaluated with the collisional radiative models Yacora H and Yacora H show a minimum in the electron temperature of 3.25 eV and a maximum in the electron density of and also in the vibrational excitation of the hydrogen molecule at 20 kW. Assessing the relevant production and destruction processes demonstrates that the H yield is maximal at this point thereby explaining the optimum ion source performance. When the cusp magnets are applied, the same general trends are observed but the required RF power is a factor of two higher. The OES results indicate an optimum performance around 30 kW whereas the highest H current is actually achieved around 40 kW. Furthermore, a higher H yield is indicated without cusp magnets but a better ion source performance is observed with magnets. These differences can most likely be attributed to changing gradients in the plasma parameters which are not accessible by OES. Nevertheless, the obtained plasma parameters can be used as benchmark for RF coupling codes simulating the Linac4 ion source
A molecular dynamics study of N-A-S-H gel with various Si/Al ratios
No full textThe understanding of sodium aluminosilicate hydrate (N-A-S-H) gel is still limited due to its complex and amorphous structure. Recently, molecular dynamics simulation has provided a unique opportunity to better understand the structure of N-A-S-H gel from nanoscale. In this work, the N-A-S-H gel structure was obtained by simulating the polymerization of Si and Al monomers by molecular dynamics. The simulated polymerization process is in good agreement with the experimental results especially in terms of the reaction rate of Si and Al species. The atomic structural features of the N-A-S-H gel were analyzed in terms of bond length and bond angle information, simulated X-ray diffraction (XRD) and Qn distribution. A significant finding is the existence of pentacoordinate Al in all simulated N-A-S-H structures, indicating that pentacoordinate Al in geopolymer does not only come from raw material. Besides, the results show that a smaller Si/Al ratio led to a more crosslinked and compacted structure of N-A-S-H gel
The construction of Karen Karnak: The multi-author-function
No full textThis thesis is situated within the comparatively recent developments of Web 2.0 and the emergence of interactive WikiMedia, and explores the mode of authorship within a Read/Write culture compared to that of a Read/Only tradition. The hypothesis of this study is that the role of the audience has become merged with the author, and as such, represents new functions and attributes, distinct from a more conventional concept of authorship, in which the roles of audience and author are more separate. Read/Write and participatory culture, as defined by this study, is focused on collaboration, and includes the influences of D.I.Y. culture, Open-Source practices and the production of text by multiple authors. Multi-authorship presents a re-thinking of several concepts which support the notion of the individual author, since the focus of multi-authorship is not on attribution and ownership of a finished text, but on the continued malleability of a text. Modes of multi-authorship, demonstrated in the use of the pseudonyms Alan Smithee and Karen Eliot, represent declarative authors whose names signify multiple origins, whilst concurrently indicating a distinct body of work. The function of these names form an important context to this study, since primary research involves the construction of an experimental mode of multi-authorship utilising WikiMedia technology and the interaction of thirty nine participants, who are invited to create a body of work under the collective pseudonym Karen Karnak. The data generated by this experiment is analysed using aspects of Michel Foucault's author-function to identify and determine power structures inherent in the WikiMedia context. The interplay of power structures, including concepts such as identity, ownership and the body of work, affect the resulting mode of authorship and contribute to the construction of Karen Karnak, suggesting further areas of research into the emerging multi-author
Effects of the extraction voltage applied by the puller-electrode on the H extraction in the Linac4 negative ion source
No full textIn order to understand the H extraction mechanism and investigate the effect of the extraction voltage applied by the puller-electrode on the H extraction in the Linac4 negative ion source, we are developing a 2D3V-PIC (two dimensions in the real space and three dimensions in the velocity space, Particle in Cell) model with volume produced H ions. It is shown that how to take the magnetic filter field direction is important for the 2D modeling to take into account the important 3D effect of electron drift. It is also shown that the meniscus formation is not symmetric due to the electron drift in the extraction region and the divergence of the H beam is asymmetric. In order to make more quantitative comparison of the extracted H and electron currents with the experiments and 3D modeling, further improvements, especially the electron loss along the magnetic filter field line will be needed
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Measuring industry-science links through inventor-author relations: A profiling method
No full textIn this pilot study we examine the performance of text-based profiling in recovering a set of validated inventor-author links. In a first step we match patents and publications solely based on their similarity in content. Next, we compare inventor and author names on the highest ranked matches for the occurrence of name matches. Finally, we compare these candidate matches with the names listed in a validated set of inventor-author names. Our text-based profile methodology performs significantly better than a random matching of patents and publications, suggesting that text-based profiling is a valuable complementary tool to the name searches used in previous studies.innovation; industry-science links; text-based profiling;
Electrostatic properties of C-S-H and C-A-S-H for predicting calcium and chloride adsorption
No full textThe adsorption capacity of cement hydrates considerably affects the ionic ingress into cementitious materials. In this study, the surface electrostatic properties of calcium silicate hydrate (C-S-H) and calcium aluminosilicate hydrate (C-A-S-H) were determined to understand the effects of the properties on calcium and chloride adsorption. The density of the surface functional groups was determined by analysing the structure of C-S-H and CASH through Al-27 and Si-29 MAS NMR. The surface sites of SiOH and AlOH are available in CASH whereas C-S-H has SiOH groups for ionic adsorption. We found that the incorporation of aluminium decreases the number of total adsorption sites in C-A-S-H. Furthermore, the site density increased with Ca/(Si + Al). To understand the C-A-S-H/solution interface, a triple-layer surface complexation model was developed and the associated equilibrium constants for depmtonation, calcium, and chloride adsorption were determined by fitting the experimental data of potentiometric titration and zeta potential measurement results. The estimated surface complexation modelling parameters were verified by predicting the experimental data of calcium and chloride adsorption on C-S-H and C-A-S-H
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