16,174 research outputs found
Influences of chloride immersion on zeta potential and chloride in concentration of cement-based materials
In this paper, the zeta potential of freshly mixed cement paste and hardened cement pastes, as well as the concentration index, was measured. The influences of chloride concentration in mixing water and slag content on zeta potential of freshly mixed pastes were studied. A proposed model was expressed to explain the relationship of zeta potential and concentration index of hardened cement pastes immersed in chloride solution. The results showed that the increase of chloride concentration in mixing water and slag replacement improved the zeta potential of freshly mixed cement, the hydration rate and concentration of ions in mixed water affects the zeta potential. With the increase of chloride concentration in soaking solution, the chloride concentration index and zeta potential of hardened cement paste all gradually decreased. The addition of slag gave some changes on chloride in concentration and zeta potential. The relationship among chloride concentration index, chloride concentration in soaking solution and slag replacement revealed by Gouy-Chapman model was in good agreement with the measured results
Investigation on influential factors on chloride concentration index of cement-based materials by pore solution expression method
In this study, the effects of different factors on chloride concentration index (N-c) of cement paste were studied. The factors including chloride concentration in soaking solution, slag replacement, external applied voltage and cation ions of soaking solution were all studied from the electrical double layer (EDL) properties point of view. Zeta potential and proton Nuclear Magnetic Resonance (H-1 NMR) measurements were conducted to investigate the properties of electrical double layer for cement paste specimens and their effects on the value of chloride concentration index. The results showed that these factors all impacted effects on chloride concentration in electrical double layer and chloride concentration index. The properties of electrical double layer including chloride distribution and thickness of electrical double layer mainly controlled the phenomenon of "chloride concentrate" and value of chloride concentration index. As the increase of zeta potential and electrical double layer thickness, the content of chloride ions in electrical double layer and the value of chloride concentration index gradually increased. (C) 2019 Elsevier Ltd. All rights reserved
Effects of chloride concentration on microstructure of cement pastes by AC impedance spectroscopy HU
Alternating current (AC) impedance spectroscopy has been applied in characterizing
microstructural evolution and electrochemical properties of cement-based systems. In the present
paper, an equivalent circuit model was proposed to study the influences of chloride binding on
microstructure and solid-liquid interfacial properties of cement paste. Chloride concentration index of
pore solution was measured to correlate to the parameters in equivalent circuit model corresponding
to electrical double layer at solid-liquid interface. The results showed that the parameters of
equivalent circuit model can properly indicate the microstructure and interfacial properties of cement
paste. Resistance of continuous pores was gradually decreased with chloride concentration in soaking
solution due to the higher conductivity of pore solution. The capacitance of electrical double layer was
increased with chloride concentration in pore solution due to more content of chloride ions in
electrical double layer. While the thickness of electrical double layer was decreased as chloride
concentration increased, which is in agreement with mathematical calculation
AC impedance spectroscopy characteristics of chloride-exposed cement pastes
In this paper, the characteristics of AC impedance spectroscopy of cement paste immersed in chloride solution were measured and analyzed with a proposed equivalent circuit model. The elements in the proposed equivalent circuit, including the resistance of interface between electrode and specimens, resistance of continuous and discontinuous pore, capacitance of solid phase and electrical double layer (EDL) were discussed. The results showed that the resistance of interface between electrode and testing specimen was much lower than that of cement paste. With the increase of chloride concentration in the soaking solution, the resistance of continuous gradually decreased due to the higher conductivity of chloride solution. Stripped out the impacts of concentration of pore solution on resistance of pores, the resistance of continuous pore increased firstly due to the decrease of continuous pore volume from the formation of Friedel's salt. However, the resistance of discontinuous pores gradually decreased with the increase of soaking solution concentration due to the transformation of continuous pores to discontinuous pores. The reaction between chloride ions and hydration products and formation of Friedel's salt decreased the porosity of cement pastes and led to higher capacitance of solid phase. Based on an idealized two-plate capacitor model for EDL, the thickness of EDL was calculated from the measured capacitance. The decrease of EDL thickness with chloride concentration in soaking solution was in agreement with the results of chloride contents in EDL obtained from pore solution expression test. (C) 2019 Elsevier Ltd. All rights reserved
Endophytic Fungi of Bitter Melon \u3ci\u3e(Momordica Charantia)\u3c/i\u3e in Guangdong Province, China
Endophytic fungi can mutualistically interact with their host plants by deterring herbivores. Overall 1172 endophytic fungal isolates were recovered from roots, stems, leaves, flowers and fruits of bitter melon, Momordica charantia, at five sites in Guangdong Province. These isolates were identified to 25 genera using morphological and molecular characteristics. The endophyte communities at the five sites were similar. Alternaria alternata, Aspergillus spp., Cladosporium spp., Colletotrichum spp., Nigrospora spp., Penicillium spp., Arthrinium spp., Chaetimium spp., Curvularia spp., Fusarium spp., Phoma spp., and Phomopsis spp. were isolated from at least three of the five sites. The coefficient of similarity for endophytes ranged from 60.6% to 83.3% between any two sites. There were significant differences in the species composition of endophytes recovered from different tissues of bitter melon. Fusarium spp. was the most frequent in root and stem samples, Colletotrichum spp. in leaf samples, A. alternata in flower samples, and Cladosporium spp. in fruit samples. The coefficients of similarity for endophytes were between 42.9% and 80.0% from any two tissues. We found that the composition of endophytes of bitter melon was relatively stable across sites, but differed greatly among tissues. We also found that there were fewer insects such as aphids (Homoptera: Aphididae), leafminers (Lepidoptera, Gracillariidae), and cotton leafworms Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) collected from the leaves of bitter melon at the Huadu site compared to those collected at the Yunfu site. Whether this is related to the endophyte communities isolated from different sites requires further research
Structure, spectra and variability of some GPS radio sources
We report the results of multifrequency-VLBI observations of
GHz-Peaked-Spectrum (GPS) radio sources. The VLBI structure and component
spectra of some GPS sources are presented. Our VLBI results show that about 80%
of the GPS galaxies exhibit a compact double or CSO-like structure, while the
GPS quasars tend to show a core-jet. The component spectra of the GPS galaxies
are often steep/convex, and the core has a flat spectrum but it is usually
hidden or weak. In addition, we studied the variability of GPS sources by
comparing new flux density measures, acquired with the Urumqi 25m telescope at
4.85 GHz, with previous 87GB data. The results show that 44% of the GPS quasars
varied higher than 10% in passed 20 years, while the fraction is only 12% for
the GPS galaxies meaning that the GPS quasars are much more variable than GPS
galaxies. In total, 25% of GPS sources show >10% variability at 4.85 GHz in our
sample.Comment: 4 pages, 7 figure
Knowledge-Aided STAP Using Low Rank and Geometry Properties
This paper presents knowledge-aided space-time adaptive processing (KA-STAP)
algorithms that exploit the low-rank dominant clutter and the array geometry
properties (LRGP) for airborne radar applications. The core idea is to exploit
the fact that the clutter subspace is only determined by the space-time
steering vectors,
{red}{where the Gram-Schmidt orthogonalization approach is employed to
compute the clutter subspace. Specifically, for a side-looking uniformly spaced
linear array, the} algorithm firstly selects a group of linearly independent
space-time steering vectors using LRGP that can represent the clutter subspace.
By performing the Gram-Schmidt orthogonalization procedure, the orthogonal
bases of the clutter subspace are obtained, followed by two approaches to
compute the STAP filter weights. To overcome the performance degradation caused
by the non-ideal effects, a KA-STAP algorithm that combines the covariance
matrix taper (CMT) is proposed. For practical applications, a reduced-dimension
version of the proposed KA-STAP algorithm is also developed. The simulation
results illustrate the effectiveness of our proposed algorithms, and show that
the proposed algorithms converge rapidly and provide a SINR improvement over
existing methods when using a very small number of snapshots.Comment: 16 figures, 12 pages. IEEE Transactions on Aerospace and Electronic
Systems, 201
Changes of pore structure and chloride content in cement pastes after pore solution expression
Pore solution expression is a widely accepted approach to extract pore solution of cement-based materials by appllying high pressure. In this study, the variations of pore solution distribution and chloride content in cement pastes before and after pore solution expression were examined. The results showed that the value of chloride concentration index N-c were mostly higher than 1.0 for cement pastes immersed in NaCl solution, and decreased with the chloride concentration of soaking solution and water-to-binder (w/b) ratio. During the pore solution expression, the pores larger than 40 nm were totally removed and the porosity of smaller pore was decreased. Based on a proposed physical model on structure of cement paste, the value of N-c was calculated according to the variations of pore structure and chloride content during pore solution expression. The calculated results showed similar trend as the experimental results obtained by pore solution expression method
Attention Clusters: Purely Attention Based Local Feature Integration for Video Classification
Recently, substantial research effort has focused on how to apply CNNs or
RNNs to better extract temporal patterns from videos, so as to improve the
accuracy of video classification. In this paper, however, we show that temporal
information, especially longer-term patterns, may not be necessary to achieve
competitive results on common video classification datasets. We investigate the
potential of a purely attention based local feature integration. Accounting for
the characteristics of such features in video classification, we propose a
local feature integration framework based on attention clusters, and introduce
a shifting operation to capture more diverse signals. We carefully analyze and
compare the effect of different attention mechanisms, cluster sizes, and the
use of the shifting operation, and also investigate the combination of
attention clusters for multimodal integration. We demonstrate the effectiveness
of our framework on three real-world video classification datasets. Our model
achieves competitive results across all of these. In particular, on the
large-scale Kinetics dataset, our framework obtains an excellent single model
accuracy of 79.4% in terms of the top-1 and 94.0% in terms of the top-5
accuracy on the validation set. The attention clusters are the backbone of our
winner solution at ActivityNet Kinetics Challenge 2017. Code and models will be
released soon.Comment: The backbone of the winner solution at ActivityNet Kinetics Challenge
201
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