303 research outputs found
Networking Support For Bidirectional Cross-Technology Communication
No full textRecent research on physical layer cross technology communication (PHY-CTC) brings a timely answer for escalated wireless coexistence and open spectrum movement. PHY-CTC achieves direct communication among heterogeneous wireless technologies (e.g.,WiFi, Bluetooth, and ZigBee) in physical layer and thus brings communication support for coexistence service such as spectrum management and IoT device control. To put PHY-CTC into service, however, there still exists a gap due to its transmission failure and asymmetric link (i.e., one-way PHY-CTC) issues. In this paper, we propose NetCTC the first networking support design for PHY-CTC to establish feedbacks (e.g., ACKs) and thus meet the upper layer networking requirements in heterogeneous unicast, multicast and broadcast. The core design of NetCTC is a real-time interaction mechanism which achieves reliable, transmission efficient and concurrent interactive communication among heterogeneous devices. We implement and evaluate NetCTC on commodity devices and the USRP-N210 platform. Our extensive evaluation demonstrates that NetCTC achieves reliable bidirectional cross technology communication under a full range of wireless configurations including stationary, mobile and duty-cycled settings.
9 W average power, 150 kHz repetition rate diamond Raman laser at 1519 nm, pumped by a Yb fibre amplifier
Full text linkCommercially available pulsed fibre lasers at ~1.5 μm have many uses in imaging, defense, communications and light radar (LIDAR) [1]. For 3D scanning LIDAR, higher signal-to-noise ratio requires lasers with high average power and high pulse repetition rate (ideally several MHz) for faster scanning rate, whereas to improve distance resolution requires pulse durations <10 ns [2,3]. One limitation of the pulsed fibre lasers at ~1.5 μm is scaling to high average powers [4]. Raman frequency conversion of high average power fibre master oscillator power amplifier (MOPA) systems at ~1 μm is a potential alternative. The large Raman shift and Raman gain of diamond allows two-stage Raman conversion to ~1.5 μm for ~1 μm pumping [5]. Excellent thermal properties make diamond suitable for high average powers [6]. Much work has been done on conversion of 1.064 μm lasers to 1.485 μm using diamond [7]; however, the “eye-safety” requirements for LIDAR typically call for wavelengths above 1.5 μm, due to the order of magnitude higher Maximum Permissible Exposure limit [8]. Developing such a diamond Raman laser (DRL) was the major motivation for this research
Thermomechanical Stress in Solar Cells and Modules: A Finite Element Modelling and Experimental Investigation
No full textWith the swift progress in Si Photovoltaic (PV) cell and module technologies, significant changes in geometry, materials, and technological processes are taking place. The adoption of emerging technologies raises concerns about potential durability issues like solder joint failure and cell cracking, which can be attributed to thermomechanical stress induced during the fabrication process. This thesis aims to deepen the understanding of the evolution of thermomechanical stress in Si cells and modules by utilising finite element modelling (FEM) complemented by experimental validations.
Models were developed to analyse the stress evolution in Multi-Busbar (MBB) tiled modules after soldering and lamination. The impact of cell overlapping in modules and the selection of solders on maximum stress and stress distribution of MBB modules was investigated. Simulation results predicted that a maximum 1st principal stress of up to ~230 MPa occurred in the Si wafer at the edge of outmost Ag pads. In addition, highly localised stress areas occurred at the overlapped area when tiled which was verified by Raman spectroscopy. The application of SnBi solder can effectively reduce the maximum 1st principal stress in the tiled module to ~160 MPa, although its material properties tend to result in higher stress in the interconnection with a cell gap than SnPb solder.
The evolution of thermomechanical stress in screen printed Ag and Cu plated Silicon Heterojunction (SHJ) cells throughout annealing and soldering was explored. It was found that Ag electrodes induced only negligible stress after annealing, with a comparatively low stress of ~160 MPa in Si cells. In contrast, Cu pads underwent both elastic and plastic deformation, with an average stress of ~90 MPa observed along the edges of the Cu pads post-soldering, and a significant stress concentration of ~220 MPa at the edges of the outermost Cu pads. Raman mapping confirmed the FEM's prediction of stress distribution. The FEM also suggested that increasing the width of Cu pads in the direction of the Cu wires effectively reduces soldering induced stress.
Finally, a detailed methodology was presented for determining the constitutive model of plated Cu on SHJ cells by integrating nanoindentation and reverse FEM. SHJ cells with Cu pads were mounted in epoxy resin and mechanically polished for nanoindentation. The power law constitutive model of the plated Cu was obtained by aligning the FEM and experimental load-displacement curves. This model enables the precise prediction of thermomechanical stress evolution in Cu plated SHJ cells and deepens the understanding of how cell metallisation can potentially affect the durability of modules
Effect of Rock Film Mulching on Preferential Flow at Rock–Soil Interfaces in Rocky Karst Areas
No full textPreferential flow is the most common form of water loss occurring at the interface between rock and soil (hereinafter referred to as “rock–soil interface”) in karst areas, and it is also one of the important factors causing soil water leakage into the underground. Therefore, it is of great significance to cut off the pathway of soil water loss through control of preferential flow. In this experiment, rock film mulching (RFM) was used to control the preferential flow at the rock–soil interface, and its influence on the soil water infiltration pattern and soil water content was analyzed by simulating rainfall, dye tracer tests, and digging soil profiles. The results show that: (1) the RFM can significantly control the soil water loss at the rock–soil interface, (2) so that the water intercepted by the above-ground rocks changed from longitudinal infiltration to transverse diffusion, more water moved into the surrounding soil patches, and (3) the soil water content was significantly increased. These results indicate that the RFM has an important blocking effect on preferential flow at the rock–soil interface, which has important guiding significance for reducing soil water erosion in karst areas
Las antologías de la poesía de Gabriela Mistral traducidas al chino
Full text linkThe Cultural Revolution ended in 1976. After that, the Chinese people’s interest in Latin American poetry was greatly awakened and a large number of poetry anthologies were published. Gabriela Mistral, as a world-renowned poet and the first Latin American woman who won the Nobel Prize in Literature, came into the eyes of Chinese readers by the translation and compilation of her poetic works into anthologies. This article analyzes a series of issues in the fourteen Chinese translation of Mistral\u27s poems: the author, the period of publication, the selected poems, and the publishers. In addition, it is accompanied by a descriptive and contrastive analysis of the different versions of «Los sonetos de la muerte».Después de la Gran Revolución Cultural, terminada en 1976, en China se despertó un gran interés por la poesía latinoamericana y se publicaron numerosas antologías poéticas. Gabriela Mistral, como una poeta de notoriedad mundial y la primera mujer latinoamericana en conseguir el Premio Nobel de Literatura, llegó a los lectores chinos mediante la traducción y recopilación de sus obras poéticas en antologías. El presente artículo analiza una serie de cuestiones en torno a las catorce antologías de la obra poética de Mistral traducidas al chino: la autora, los poemas seleccionados, el período de publicación y las editoriales. Además, se acompaña con un análisis descriptivo y contrastivo de las diferentes versiones de «Los sonetos de la muerte»
Revealing the degradation pathways of layered Li-rich oxide cathodes
No full textLayered lithium-rich transition metal oxides are promising cathode candidates for high-energy-density lithium batteries due to the redox contributions from transition metal cations and oxygen anions. However, their practical application is hindered by gradual capacity fading and voltage decay. Although oxygen loss and phase transformation are recognized as primary factors, the structural deterioration, chemical rearrangement, kinetic and thermodynamic effects remain unclear. Here we integrate analysis of morphological, structural and oxidation state evolution from individual atoms to secondary particles. By performing nanoscale to microscale characterizations, distinct structural change pathways associated with intraparticle heterogeneous reactions are identified. The high level of oxygen defects formed throughout the particle by slow electrochemical activation triggers progressive phase transformation and the formation of nanovoids. Ultrafast lithium (de)intercalation leads to oxygen-distortion-dominated lattice displacement, transition metal ion dissolution and lithium site variation. These inhomogeneous and irreversible structural changes are responsible for the low initial Coulombic efficiency, and ongoing particle cracking and expansion in the subsequent cycles
Force Sensor Based Tool Condition Monitoring Using a Heterogeneous Ensemble Learning Model
No full textTool condition monitoring (TCM) plays an important role in improving machining efficiency and guaranteeing workpiece quality. In order to realize reliable recognition of the tool condition, a robust classifier needs to be constructed to depict the relationship between tool wear states and sensory information. However, because of the complexity of the machining process and the uncertainty of the tool wear evolution, it is hard for a single classifier to fit all the collected samples without sacrificing generalization ability. In this paper, heterogeneous ensemble learning is proposed to realize tool condition monitoring in which the support vector machine (SVM), hidden Markov model (HMM) and radius basis function (RBF) are selected as base classifiers and a stacking ensemble strategy is further used to reflect the relationship between the outputs of these base classifiers and tool wear states. Based on the heterogeneous ensemble learning classifier, an online monitoring system is constructed in which the harmonic features are extracted from force signals and a minimal redundancy and maximal relevance (mRMR) algorithm is utilized to select the most prominent features. To verify the effectiveness of the proposed method, a titanium alloy milling experiment was carried out and samples with different tool wear states were collected to build the proposed heterogeneous ensemble learning classifier. Moreover, the homogeneous ensemble learning model and majority voting strategy are also adopted to make a comparison. The analysis and comparison results show that the proposed heterogeneous ensemble learning classifier performs better in both classification accuracy and stability
Effects of Soil–Rock Geomorphic Units on the Yield of Surface Runoff: A Case Study on Uncultivated Land of a Karst Area
No full textSurface runoff on karst is a multifactorial hydrological process. There are a great number of studies focusing on rainfall–runoff from karst slopes on a large scale, but microscale studies related to soil–rock geomorphic units have been rarely reported. This study used rock–soil runoff plots on uncultivated land as a new form of natural rainfall catchment, and the yield of surface runoff was measured during four different rainfall events. Through monitoring rainfall runoff by soil–rock runoff plots under different rainfall events, it has been proven that the coefficient of surface runoff measured on uncultivated land of a karst area is very small compared to that of non-karst areas, only ranging from 0.0145 to 0.0408 in the measurement period. And multiple regression analysis showed that the rocks contributed less to the yield of surface runoff than the soils, and with the increase in rainfall, the contributions of both showed an increasing trend. The calculated surface runoff yield produced by soils showed a positive relationship with soil bulk density and a negative relationship with soil porosity, soil hydraulic conductivity, and root biomass, and the significance increased with rainfall, which was consistent with previous findings and demonstrated the accuracy and efficiency of the proposed method in our study. These study results contribute to a deeper understanding of the rainfall–runoff process in rocky desertification areas, and the proposed method of soil–rock runoff plots provides a new way to estimate the yield of rainfall runoff on the complicated geomorphic units of karst slopes
Simple Preparation of Flower⁃Like BiOI and Its Visible Photocatalytic Properties
No full textWith the development of industrialization and modernization, water pollution has become increasingly serious, and the use of sunlight for water pollution degradation has become a future development trend. In this paper, flower⁃like BiOI photocatalyst was prepared via a solution route at room temperature without any template, and characterized by X⁃ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV⁃Vis diffuse reflectance spectra (UV⁃Vis DRS). As⁃synthesized flower⁃like BiOI showed better visible light photocatalytic activity for degrading Rhodamine B (RhB) than TiO2. The experimental results of active species and electron spin resonance (ESR) measurement showed that ·O
was the main active species in the photocatalytic degraded process of organic pollutant over flower⁃like BiOI, and the possible degradation mechanism was speculated. This study provides a simple and convenient synthesis method for high activity photocatalysts
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