Diaqua­bis­(4,4′-bipyridine-κN)bis­(2,4,5-trifluoro-3-hy­droxy­benzoato-κO 1)manganese(II)

In the title compound, [Mn(C7H2F3O3)2(C10H8N2)2(H2O)2], the MnII ion, situated on a centre of inversion, has a distorted octa­hedral coordination geometry and is coordinated by two N atoms from two 4,4′-bipyridine ligands, two O atoms from two 2,4,5-trifluoro-3-hy­droxy­benzoate ligands and two water mol­ecules. Inter­molecular O—H⋯N hydrogen bonds link the mol­ecules into a chain along the a axis. Inter­actions between neighboring chains occur through O—H⋯O hydrogen bonds, which link the chains into a two-dimensional supra­molecular network parallel to the ac plane. In addition, O—H⋯O hydrogen bonds between the water mol­ecules and carboxyl­ate groups also exist in the the crystal structure

Meso-scale Fracture Modelling of Concrete Cover Induced by Non-uniform Corrosion of Reinforcing Bar

Corrosion-induced concrete cracking is a significant durability problem for reinforced concrete structures. In practice, critical corrosion degree to surface cracking and crack width evolution are of significance in regards to the assessment of serviceability of reinforced concrete structures. Literature review suggests that, although considerable research has been undertaken on corrosion-induced concrete cracking, little has been focused on non-uniform corrosion of reinforcing bar, especially by considering concrete as a three-phase materials. In this paper, a meso-scale fracture model, consisting of aggregates, cement paste/mortar and ITZ, is established. To simulate arbitrary cracking in concrete, cohesive elements are inserted in the fine meshes and the process is achieved through a script written in Python. It has been found that some microcracks occur before they are connected to form a dominating discrete crack approaching to the surface. The surface crack width is obtained as a function of corrosion degree and verification against experimental results from literature is conducted

A New Model for Corrosion-induced Concrete Cracking

Corrosion of reinforced concrete is one of the major deterioration mechanisms which result in premature failure of the reinforced concrete structures. Due to the actual diffusion of chloride ingress, the corrosion products distribution is seldom uniform along the reinforcing bar. Recently, some non-uniform corrosion models have been proposed to investigate the corrosion-induced cracking mechanism of concrete. In this paper, a new corrosion model based on von Mises distribution is formulated and validated against experimental data. The developed model is then compared with the existing non-uniform models and the advantages are discussed. To demonstrate the application of the developed corrosion model, a concrete cover structure, containing aggregates, cement paste/mortar and ITZ, is simulated to predict the cracking phenomena of the concrete cover under different non-uniform coefficients in the developed corrosion model. It has been found that the non-uniform corrosion model can be used to simulate the realistic corrosion rust progression around the reinforcing bar, with the best accuracy. Moreover, parametric studies are conducted to investigate the effects of the basic factors formulated in the corrosion model on the surface cracking of the reinforced concrete structures

Numerical modelling of non-uniform corrosion induced concrete crack width

Corrosion of reinforced concrete is one of the major deterioration mechanisms which result in premature failure of the reinforced concrete structures. Crack width is often used as an effective criterion to assess the serviceability of concrete structures. However, research on prediction of corrosion-induced concrete crack width, especially by considering the corrosion as a non-uniform process, has still been scarce. This paper attempts to develop a finite element model to predict the crack width for corrosion-affected concrete structures under realistic non-uniform corrosion of the reinforcement. A non-uniform corrosion model was first formulated as a function of time. To simulate arbitrary cracking in concrete, cohesive elements are inserted in the sufficiently fine mesh which is achieved through a script written in Python. The surface crack width is obtained as a function of service time and verification against experimental results from literature is conducted. Accurate prediction of crack width can allow timely maintenance which prolongs the service life of the reinforced concrete structures

Noise suppression of on-chip mechanical resonators by chaotic coherent feedback

We propose a method to decouple the nanomechanical resonator in optomechanical systems from the environmental noise by introducing a chaotic coherent feedback loop. We find that the chaotic controller in the feedback loop can modulate the dynamics of the controlled optomechanical system and induce a broadband response of the mechanical mode. This broadband response of the mechanical mode will cut off the coupling between the mechanical mode and the environment and thus suppress the environmental noise of the mechanical modes. As an application, we use the protected optomechanical system to act as a quantum memory. It's shown that the noise-decoupled optomechanical quantum memory is efficient for storing information transferred from coherent or squeezed light

Mechanisms of water infiltration into conical hydrophobic nanopores

Fluid channels with inclined solid walls (e.g. cone- and slit-shaped pores) have wide and promising applications in micro- and nano-engineering and science. In this paper, we use molecular dynamics (MD) simulations to investigate the mechanisms of water infiltration (adsorption) into cone-shaped nanopores made of a hydrophobic graphene sheet. When the apex angle is relatively small, an external pressure is required to initiate infiltration and the pressure should keep increasing in order to further advance the water front inside the nanopore. By enlarging the apex angle, the pressure required for sustaining infiltration can be effectively lowered. When the apex angle is sufficiently large, under ambient condition water can spontaneously infiltrate to a certain depth of the nanopore, after which an external pressure is still required to infiltrate more water molecules. The unusual involvement of both spontaneous and pressure-assisted infiltration mechanisms in the case of blunt nanocones, as well as other unique nanofluid characteristics, is explained by the Young’s relation enriched with the size effects of surface tension and contact angle in the nanoscale confinement

Accurate cover crack modelling of reinforced concrete structures subjected to non-uniform corrosion

Concrete cover cracking caused by reinforcement corrosion is a significant durability problem of reinforced concrete structures. Extensive research has been carried out in the last few decades while most were focused on corrosion of a single reinforcing bar. Very little research has examined the whole cover cracking of reinforced concrete structures due to multiple reinforcement corrosion. This paper develops a numerical model to predict the structural failure of the whole cover of concrete induced by corrosion of multiple reinforcing bars. Moreover, a non-uniform corrosion model is established based on experimental results, in contrast to conventional uniform assumption. Two typical cover failure modes under the non-uniform corrosion of multiple reinforcing bars are identified and discussed. The effects of cover thickness, reinforcement spacing, fracture energy of concrete, etc., on cover cracking patterns and crack width are also investigated. The derived numerical model is verified by comparing the results with those from experiments in literature. Accurate prediction of concrete cover cracking can allow timely maintenance of existing structures and rational design for new buildings which prolongs the service life of the reinforced concrete structures

A non-uniform corrosion model and meso-scale fracture modelling of concrete

Corrosion-induced concrete cracking is a significant durability problem for reinforced concrete structures. Considerable research has been carried out in the last few decades to understand and model the expansion mechanism of the corrosion products around the reinforcing bar and simulate the cracking behaviour of the concrete cover. In this paper, a new corrosion model based on non-uniform corrosion expansion is formulated and validated against experimental data. A meso-scale fracture model, consisting of aggregates, cement paste/mortar and ITZ, is established for the cases of both middle and side reinforcing bars. Under the developed corrosion and concrete fracture model, the cracking phenomena of the concrete cover are accurately simulated. It has been found that the non-uniform corrosion model can be used to express the realistic corrosion rust progression around the reinforcing bar, with the best accuracy. It has also been found that some microcracks occur before they are connected to form the dominating discrete crack which usually appears on the concrete surface. Moreover, the effects of the corrosion variables, as well as other key material and geometric parameters, on surface cracking of concrete are investigated

SENTIMENT ANALYSIS OF CHINESE MICROBLOG MESSAGE USING NEURAL NETWORK-BASED VECTOR REPRESENTATION FOR MEASURING REGIONAL PREJUDICE

Regional prejudice is prevalent in Chinese cities in which native residents and migrants lack a basic level of trust in the other group. Like Twitter, Sina Weibo is a social media platform where people actively engage in discussions on various social issues. Thus, it provides a good data source for measuring individuals’ regional prejudice on a large scale. We find that a resentful tone dominates in Weibo messages related to migrants. In this paper, we propose a novel approach, named DKV, for recognizing polarity and direction of sentiment for Weibo messages using distributed real-valued vector representation of keywords learned from neural networks. Such a representation can project rich context information (or embedding) into the vector space, and subsequently be used to infer similarity measures among words, sentences, and even documents. We provide a comprehensive performance evaluation to demonstrate that by exploiting the keyword embeddings, DKV paired with support vector machines can effectively recognize a Weibo message into the predefined sentiment and its direction. Results demonstrate that our method can achieve the best performances compared to other approaches