Nonlinear transient engagement characteristics of planetary gear train

Based on the engagement principle of the gear drive, the nonlinear transient dynamic characteristics of the planetary gearing are researched and the corresponding dynamic equilibrium equations for sun gear, planet gear and internal gear are respectively derived. Then transient engagement simulation analysis of the planetary gear train is performed in ANSYS. The corresponding stress-time curves of sun gear, planet gear and internal gear are obtained, and the worst engaging location and the ultimate stress in every gear are calculated accurately. The simulation experiment shows that the engagement characteristics of the planetary gearing at any time and in any location can be accurately analyzed by transient engagement analysis. It provides a reliable guaranty for the subsequent fatigue analysis and structural optimization of the planetary gear train

Chloride induced mechanical degradation of ultra-high performance fiber-reinforced concrete:Insights from corrosion evolution paths

Chloride-induced corrosion of ultra-high-performance fiber-reinforced concrete (UHPFRC) inevitably affects structural durability. However, the process of multi-fiber corrosion and mechanical deterioration still lacks sufficient understanding. This work aims to reveal the fiber corrosion degradation mechanism from a microscopic to macroscopic view, applying multiple analytical analyses of atomic absorption spectrometry, SEM-EDS, nano-indentation, polarization, and macroscopic mechanical testing. Results show that the flexural strength of specimens decreases significantly with the increase of corrosion degree, and a clear reduction of up to 47% is found at a high corrosion degree. Elastic modulus and nano-hardness of corroded samples vary in a wide range of 30–189 GPa and 0.16–6.41 GPa. With the increase in fiber content, two distinctive corrosion mechanisms are proposed. The corrosion path deteriorates from fiber edge to inner by the invasion of erosive solution through the matrix at low contents (<2 vol%). Considering impurities, greater interfacial defects and macro-cell potential differences at high contents (≥2 vol%), another corrosion path originates from the fiber inner outward to the matrix. Fiber corrosion damages the fiber’s structural integrity and induces matrix deterioration, the micromechanics of the matrix along the fiber edge 20 μm decreases at least 10% more than the concrete matrix. This work firstly sheds light on the mechanical deterioration of UHPFRC from the perspective of fiber corrosion paths considering different initiation scenarios

Video-based evidence analysis and extraction in digital forensic investigation

As a result of the popularity of smart mobile devices and the low cost of surveillance systems, visual data are increasingly being used in digital forensic investigation. Digital videos have been widely used as key evidence sources in evidence identification, analysis, presentation, and report. The main goal of this paper is to develop advanced forensic video analysis techniques to assist the forensic investigation. We first propose a forensic video analysis framework that employs an efficient video/image enhancing algorithm for the low quality of footage analysis. An adaptive video enhancement algorithm based on contrast limited adaptive histogram equalization (CLAHE) is introduced to improve the closed-circuit television (CCTV) footage quality for the use of digital forensic investigation. To assist the video-based forensic analysis, a deep-learning-based object detection and tracking algorithm are proposed that can detect and identify potential suspects and tools from footages

Impacts of emissions trading scheme initiatives on corporate carbon proactivity and financial performance

This study introduces the concept of carbon proactivity and considers not only the quantity of emissions but also corporate carbon-reduction efforts and actions to explore the relationship between carbon proactivity, the emissions trading scheme (ETS) mechanism, and corporate financial performance. A matched-pair approach was adopted to explore the difference in carbon proactivity between ETS and non-ETS firms. The study aims to investigate the impacts of an ETS on corporate carbon proactivity and whether participating in an ETS can help a firm achieve a desired outcome in which it can improve both environmental and economic performance. Using manually collected data on carbon disclosure, it was found that carbon proactivity is higher among firms that participate in an ETS than among those that do not, and carbon proactivity is trending upward for the participating firms. In addition, evidence suggests that while investing more resources in carbon proactivity decreases current financial performance, it will boost future financial performance. This relationship is observed among firms that participate in an ETS. This study extends the understanding of the relationship between ETSs, corporate carbon proactivity, and corporate financial performance. It also provides evidence on how to improve the ETS mechanism

Corrosion-induced deterioration and fracture mechanisms in ultra-high-performance fiber-reinforced concretet

Ultra-high-performance fiber-reinforced concrete (UHPFRC) is an excellent material for harsh environments, but corrosion will change its internal microstructure and complicate the fracture evolution, bringing great difficulties in evaluating the long-term service life. Limited attention has been paid to the fracture mechanism of the UHPFRC upon corrosion. In the present study, integrating acoustic emission (AE) and digital image correlation (DIC) techniques are used to assess the micro/macrocracking characteristics of the specimens upon various corrosion degrees. Results show that the 56-day corroded UHPFRC with 2 vol% presents a remarkable decrease rate of 32%, 29% and 30% in the flexural stiffness, flexural strength and compressive strength. During the loading process, compaction of the original defects induced by fiber corrosion is concentrated in the elastic stage, the newborn cracks triggered by loading mainly occur in the strain-hardening stage, and the expansion of cracks mainly lies in the strain-softening stage. Corroded UHPFRC specimens with higher corrosion damage have a greater maximum strain value at the crack. In addition, the failure mode changes from shear crack failure to a brittle failure of tensile crack as corrosion damage increases. The macroscopic destruction of the corroded UHPFRC is a manifestation of internal microdamage evolution in fiber corrosion and matrix deterioration.</p

Corrosion risk and corrosion-induced deterioration of ultra-high performance fiber-reinforced concrete containing initial micro-defects

Micro-defects in UHPFRC, inevitably generated from the manufacturing to engineering service stage, impact its durability under extreme service environments. However, relevant understanding is still insufficient. This work assesses the corrosion risk and corrosion-induced deterioration in UHPFRC containing initial micro-defects, simulated by a combination of mechanical pre-loading and thermal treatment. Analytical analyses include electrochemical tests (OCP, Tafel, EIS), SEM, MIP, compressive strength measurements, etc. Results show that initial defect degree and steel fiber contents have significant effects on the corrosion resistance and mechanical performance of UHPFRC. Micro-cracks and pores are the major channels to deepen fiber corrosion risk, degrading mechanical performance up to 52%-56% in the most severely damaged UHPFRC. The porosity is increased by the corrosion/increased defects and fiber contents up to a growth rate of 35%, 56% and 78%, respectively, as corrosion triggers the occurrence of new defects (e.g., fiber splitting, newborn micro-cracks, pores). The present results provide a reference for predicting the corrosion potential of the defective UHPFRC.</p

Effects of amorphous silica on mechanical contribution of coarse aggregates in UHPC:From micromechanics to mesoscale fracture and macroscopic strength

Despite the enhancement of amorphous silica on Ultra-High Performance Concrete (UHPC), the influence of amorphous silicas on the mechanical contribution of coarse aggregates (CA) in UHPC from the perspective of multiscale is still unclear. Herein, the mechanical contribution of CA owing to the incorporation of silica with different morphology (i.e. nano-silica and silica fume) is studied from micromechanics to mesoscale fracture and macroscopic strength. The results show that, on the premise of guarantee flowability, silica fume generates more C–S–H but more microcracks owing to the higher content, while nano-silica results in a higher percentage of high-density C–S–H. The fracture across CA in pure tensile cracking is controlled by the competition between high-density C–S–H content and microcracks, whereas, the fracture across CA in pure shear cracking is governed by microstructure compactness. That is, the high-density C–S–H benefits more the fracture of CA in the case of tensile condition, while the microstructure compactness benefits more the fracture of CA in the case of shear condition. Consequently, in terms of the macroscopic strength, silica fume benefits more the mechanical contribution of CA in compressive loading because of the denser microstructure, while nano-silica is more beneficial to that in flexural loading owing to the higher content of high-density C–S–H.</p

Deep Metric Learning Assisted by Intra-variance in A Semi-supervised View of Learning

Deep metric learning aims to construct an embedding space where samples of the same class are close to each other, while samples of different classes are far away from each other. Most existing deep metric learning methods attempt to maximize the difference of inter-class features. And semantic related information is obtained by increasing the distance between samples of different classes in the embedding space. However, compressing all positive samples together while creating large margins between different classes unconsciously destroys the local structure between similar samples. Ignoring the intra-class variance contained in the local structure between similar samples, the embedding space obtained from training receives lower generalizability over unseen classes, which would lead to the network overfitting the training set and crashing on the test set. To address these considerations, this paper designs a self-supervised generative assisted ranking framework that provides a semi-supervised view of intra-class variance learning scheme for typical supervised deep metric learning. Specifically, this paper performs sample synthesis with different intensities and diversity for samples satisfying certain conditions to simulate the complex transformation of intra-class samples. And an intra-class ranking loss function is designed using the idea of self-supervised learning to constrain the network to maintain the intra-class distribution during the training process to capture the subtle intra-class variance. With this approach, a more realistic embedding space can be obtained in which global and local structures of samples are well preserved, thus enhancing the effectiveness of downstream tasks. Extensive experiments on four benchmarks have shown that this approach surpasses state-of-the-art method

Understanding the generation and evolution of hydrophobicity of silane modified fly ash/slag based geopolymers

Silanes are widely used to enhance the corrosion resistance of cement-based materials by endowing the substrate with hydrophobicity. However, their applications in fly ash/slag based geopolymer (FSBG) are still rare. This study comprehensively investigates the hydrophobicity properties and reaction products of FSBG modified by isooctyltriethoxysilane admixture to reveal the mechanisms involved in the generation and evolution of hydrophobization effect. In spite of the verified compromise in compressive strength of modified FSBG for longer ages, the early strength at 1 day is amazingly found to slightly increase, ascribed to the heat release along with the hydrolysis of silane. The reduction of porosity is caused by the siloxane products of silane after condensation reactions and thus does not show consistencies to the decreasing compressive strength as well as the formation of hydration products. The amount of N-A-S-H gel is found to reduce more intensively compared to the C-A-S-H gel when silane is used. The evolution of contact angle on the surface of modified FSBG is dependent on the mutual effect of superficial density of silane and porosity, with the former controlled by the amount of coupling sites. The formula of contact angle evolution is proposed and can be potentially used to regulate and govern the hydrophobicity properties of FSBG, with the feasibility to be applied in other geopolymers and cement-based materials.</p

Techno-Economic Analysis of Biodiesel Production from Microalgae: A Review

The development of the microalgae-based biodiesel technology has become a hot research topic in the bioenergy field in recent years. Presently, the technical possibility of the conversion of microalgae to biodiesel has been confirmed at the laboratory scale. The fundamental issues impeding the industrialization of microalgae-based biodiesel include the high cost of production and the lack of research on the scaling-up technology. In this paper, the technical challenges and economic aspects of biodiesel production from microalgae were analyzed. It was found that the production cost of microalgae-based biodiesel mainly come from three processes: microalgae cultivation, harvest, and lipid extraction, among which microalgae cultivation represented the highest cost. Finally, the prospect of the industrialization of the microalgae-based biodiesel was proposed. Citation: Junying Chen, Qingliang Li, Chun Chang, Jing Bai, Liping Liu, Shuqi Fang ,Hongliang Li, Techno-Economic Analysis of Biodiesel Production from Microalgae: A Review, Trends in Renewable Energy, 2017, 3(2): 141-52. DOI: 10.17737/tre.2017.3.2.003