2,227 research outputs found
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
Naturalized truth and Plantinga's evolutionary argument against naturalism
No full textThere are three major theses in Plantinga's latest version of his evolutionary argument against naturalism. (1) Given materialism, the conditional probability of the reliability of human cognitive mechanisms produced by evolution is low; (2) the same conditional probability given reductive or non-reductive materialism is still low; (3) the most popular naturalistic theories of content and truth are not admissible for naturalism. I argue that Plantinga's argument for (1) presupposes an anti-materialistic conception of content, and it therefore begs the question against materialism. To argue for (2), Plantinga claims that the adaptiveness of a belief is indifferent to its truth. I argue that this claim is unsupported unless it again assumes an anti-materialistic conception of content and truth. I further argue that Plantinga's argument for (3) is not successful either, because an improved version of teleosemantics can meet his criticisms. Moreover, this version of teleosemantics implies that the truth of a belief is (probabilistically) positively related to its adaptiveness, at least for simple beliefs about physical objects in human environments. This directly challenges Plantinga's claim that adaptiveness is indifferent to truth.PhilosophyReligionA&HCI0ARTICLE127-467
Effect of Surface Roughness Geometry on Boundary-Layer Transition and Far-Field Noise
No full textSurface roughness elements are often used to force laminar to turbulent transition in aerodynamic and aeroacoustic wind-tunnel experiments. The statistical features and spectral content of the pressure fluctuations in the resulting turbulent boundary layer at the trailing edge can affect far-field noise. To elucidate this dependence, boundary-layer transition induced by randomly distributed roughness elements and a zigzag strip of the same height over a NACA 0012 airfoil is investigated experimentally. The effects of roughness geometry on the near-field flow topology, transition location, and far-field noise are addressed in the common experimental setting for the first time. For a fixed roughness height, distributed roughness elements are less effective in forcing transition than the zigzag strip at low freestream velocity (u∞<20 m/s). As u∞ increases, the transition front for the distributed roughness elements moves closer to the roughness location, reaching the same or even further upstream locations compared to the transition onset in the presence of the zigzag strip. The far-field noise depends on the transition location. For u∞≤20 m/s, a higher noise level is measured for the distributed roughness elements with respect to the zigzag strip. In contrast, for u∞>20 m/s, the earlier onset of transition with the distributed surface roughness leads to a lower noise level than that with the zigzag strip. The data confirm that an adequate characterization of the boundary-layer transition is necessary when measuring the far-field noise during wind-tunnel experiments.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Wind Energ
Will ortho-enriched water increase the durability of concrete?
No full textWater molecules exist as two spin isomers, differing by the relative orientation of the nuclear spins of the two hydrogen atoms: either antiparallel (para-water, S=0) or parallel (ortho-water, S=1) [1]. The transition between these nuclear spin states can be achieved through magnetic symmetry breaking via a field gradient across the spins applied by a suitably placed magnetic moment for a sufficiently long time [2]. The contradictory mechanisms of interaction between water or an aqueous solution and magnetic field were reviewed, especially the one expanded on Dynamically Ordered Liquid Like Oxyanion Polymers (DOLLOP) [3]. Then the state of art agreements that have been proved by reproductive experiments or theories were discussed. A new hypothesis for the magnetic effects on the interconversion of nuclear spin isomers of water at the interface of water-O2 was proposed, as well as its applicability in the structure modification of C-S-H.Materials and Environmen
Sachdev–Ye–Kitaev model as Liouville quantum mechanics
No full textAbstractWe show that the proper inclusion of soft reparameterization modes in the Sachdev–Ye–Kitaev model of N randomly interacting Majorana fermions reduces its long-time behavior to that of Liouville quantum mechanics. As a result, all zero temperature correlation functions decay with the universal exponent ∝τ−3/2 for times larger than the inverse single particle level spacing τ≫NlnN. In the particular case of the single particle Green function this behavior is manifestation of the zero-bias anomaly, or scaling in energy as ϵ1/2. We also present exact diagonalization study supporting our conclusions
The Chronicle of Ye Wenlan
No full text本谱记述叶文澜的主要生平事迹，通过相关资料的搜集、整理，来揭示出叶文澜在其参与的主要历史事件中所起的作用。 叶文澜早年参与镇压戴潮春起义，又帮助左宗棠参与镇压太平军李世贤部，后受左宗棠的推荐于1867年至1876年间担任福州船政局总监工，与沈葆桢共事逾十年，期间还参与了中国与暹罗的外交往来。叶文澜在任期间主要负责船政局木料的采购，为购买合适的木料，他数次远赴东南亚，为福州船政局的发展和近代新式轮船的建造作出了自己的贡献。 1876年又赴台湾基隆煤矿矿务局（后改为煤务局）担任矿务督办一职，虽然任职时间短暂，但叶文澜管理下的基隆煤矿，却是中国第一家近代化煤矿，它开了中国煤矿机器开采的先河。18...This article is a chronicle of Ye Wenlan's life, which has described the main achievement of Ye`s life. Through the collection and collation of data that relate to Ye Wenlan, the author reveals the important influence that Ye had played in the history events. In Ye Wenlan`s early days, he had involved in the suppression of the Dai Chaochun Uprising. Then, Ye turns to assist Zuo Zongtang to suppre...学位：历史学硕士院系专业：人文学院历史学系_专门史学号：1032012115218
An Improved Peak Voltage Calculation Method for Compensation Components in S-S and LCC-S Compensated Wireless Power Transfer Systems
Get PDFThe pursuit of battery charging technology for electric vehicle (EV) has led to extensive research on the inductive-based wireless power transfer (WPT) systems. In this paper, the compensation component (including coils) stresses will be studied in two commonly adopted compensation topologies, namely S-S and LCC-S compensations. Due to the peak voltage calculation inaccuracy for certain components based on conventional fundamental frequency analysis, an improved peak voltage calculation method is introduced in closed form, which is proved to be more accurate by both simulation and experiments.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & Storag
Drying shrinkage of alkali-activated slag concrete with natural/recycled aggregates
No full textEach year a large amount of construction and demolition waste (CDW) is generated in the European Union. For sustainability development the CDW is recycled and re-used. To promote the use of CDW, recycled aggregates from CDW were incorporated in alkali-activated concrete (AAC), which mainly consisted of secondary materials or industrial by-products. This study investigated the influence of recycled aggregates on workability, compressive strength and drying shrinkage of slag-based AAC. Properties of conventional concrete with natural/recycled aggregates were also tested for comparison. The results showed that the pre-saturated recycled aggregates only slightly affected the workability of conventional concrete or AAC. Recycled aggregates reduced compressive strength of both conventional concrete and AAC due to extra water for pre-saturation of the recycled aggregates. The mass loss of the concrete specimens upon drying was greater for low-strength concrete than for moderate strength concrete. The recycled aggregates increased the mass loss and drying shrinkage of AAC. For conventional concrete, low-strength concrete had a higher drying shrinkage compared with moderate strength concrete. On the contrary, for AAC in this study, low-strength concrete had a lower drying shrinkage compared with moderate strength concrete
Study of carbonation rate of synthetic C-S-H by XRD, NMR and FTIR
No full textSupplementary cementitious materials (SCMs) like fly ash (FA) and blast furnace slag (BFS) are broadly used in concrete to replace part of the Ordinary Portland Cement (OPC) because of both economic and environmental issues. In concrete blended with SCMs, C-S-H with different C/S ratios, formed from the hydration and pozzolanic reactions of blended cement, is the major calcium-bearing phases which reacts with CO2 during carbonation. Therefore, it is important to study the carbonation rate of different C-S-H phases. In this paper, the C-S-H phases (C/S ratio: 0.66 to 2.0) were synthesized and used for accelerated carbonation testing. Synthetic C-S-H phases with different C/S ratios were identified by X-ray diffraction and 29Si nuclear magnetic resonance (NMR). Carbonation rate and products of different C-S-H phases are also determined. The results show that C-S-H (I) phases with different target C/S ratio (lower than 1.40) were synthesized in the mix solution of lime and fume silica. The portlandite appears in the products when the designed C/S ratio is higher than 1.40 under this synthetic condition. C-S-H with lower C/S ratio is decomposed faster than that with a higher C/S ratio. After exposition to the accelerated carbonation condition for three days, in this research, the C-S-H phases with different C/S ratio were all fully decomposed to CaCO3 and silica gel.</p
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