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• Irradiance profiles of concentrators and their non-uniformities were obtained. • A discrete two-dimensional electrical-thermal coupled model was developed. • PV temperature distribution was obtained and its non-uniformity was evaluated. • To a certain degree, non-uniform irradiance caused obvious efficiency decline. This work concerns a type of efficient and promising solar energy utilization systems namely concentrating photovoltaic/thermal (CPV/T) systems. In CPV/T systems, uneven irradiance and PV temperature introduced by concentrators cause a rise in ohmic loss, decrease in PV fill factor and electrical efficiency, and local hot spot. Thus, the objective of this work is to develop a two-dimensional optical-thermal-electrical coupled model to predict PV temperature distribution and investigate effects of non-uniform irradiance and temperature on performance of linear concentrating CPV/T systems. Firstly, rays tracing of two kinds of truncated compound parabolic concentrators (CPCs) with different concentration ratios was simulated by TracePro to obtain their irradiance profiles. These two kinds of CPCs were designed and defined as HEMR and LEMR respectively in our previous work. Then, rays tracing results namely non-uniform irradiance distributions functioned as the inputs of a two-dimensional electrical-thermal coupled model developed by FORTRAN to obtain temperature distribution of PV array and performances of CPV/T systems. Meanwhile, a CPV/T prototype was set up to validate the theoretical results. The degrees of illumination and PV temperature non-uniformity were weighed based on the concept of standard deviation. Ultimately, the effects of non-uniform irradiance and temperature on performances of the CPV/T system were investigated with different concentration ratios. Results revealed that with a rise in concentration ratio, irradiance and PV temperature non-uniformity in the case of LEMR concentration experience a rapider increase than those in the case of HEMR concentration. Correspondingly, with increasing concentration ratios, both the fill factor and the electrical efficiency in the case of LEMR concentration experience a rapider decrease than those in the case of HEMR concentration. When the concentration ratio was 8, compared to HEMR concentration case, non-uniformity of irradiance and PV temperature in the case of LEMR concentration is increased by 63.1% and 65.7% respectively; the fill factor and the electrical efficiency in the case of LEMR concentration are decreased by 2.6% and 2.1% respectively. [ABSTRACT FROM AUTHOR]

The photovoltaic unit and the thermal unit are coupled in a concentrating photovoltaic/thermal (CPV/T) system and solar cells always operate at high temperature in order to obtain high quality thermal energy, which results in the overheating problem of solar cells. In the present study, a novel spectral splitting concentrating photovoltaic/thermal (SS-CPV/T) prototype based on direct absorption collection had been set up. The concentrator in the system is a truncated CPC by eliminating multiple reflections of solar radiation (called EMR), which was designed by our group. Water is used as both spectral splitting medium and heat transfer fluid in the spectral splitting subsystem. Distribution of the incidence angle of the irradiance illuminating on the filter at the outlet aperture of EMR was considered. The radiation transfer model was established to obtain the optical performance of the filter. And the electrical-thermal coupled model was proposed to predict the electrical and thermal performances of the SS-CPV/T system. When the total solar irradiance was about 1000 W/m 2 and the diffuse irradiance ratios were 15.0%, 17.8% and 24.0% respectively, the experimental electrical efficiencies of the SS-CPV/T system were 9.6%, 9.4% and 9.0% respectively and the thermal efficiencies were 52.0%, 50.7% and 48.5% respectively. The theoretical electrical efficiencies were 10.4%, 10.2% and 9.8% respectively and the theoretical thermal efficiencies were 52.8%, 51.5% and 49.4% respectively. Comparison experiments on the electrical and thermal performances of the CPV/T systems with and without spectral splitting were also conducted. Under the condition of the same outlet fluid temperature the maximum temperature of solar cells in the SS-CPV/T system was about 5.6 °C lower than the temperature of outlet fluid and about 12 °C lower than the maximum temperature of solar cells in the CPV/T system without spectral splitting. Finally, the theoretical model was expanded to higher concentration ratios to study the effects of the concentration ratio on the electrical and thermal performances of the CPV/T systems with and without spectral splitting. The results illustrate that compared to the CPV/T system without spectral splitting, the SS-CPV/T system has higher electrical efficiency when the concentration ratio is larger than 10 and higher exergy efficiency when the concentration ratio is larger than 14 for the outlet fluid temperature of 50 °C. And for 70 °C outlet fluid temperature, these two concentration ratios shift to 9 and 15 respectively. Thus, spectral splitting technology is more advantageous in the CPV/T systems with moderate and high outlet fluid temperature and concentration ratios. [ABSTRACT FROM AUTHOR]

The breakup of high speed liquid jets and the spray formation from a multi-hole direct-injection injector were investigated by analyzing the temporal development of spray penetration and cone angle. Planar Mie scattering was applied to generate spray images under a wide range of operating conditions with ethanol, methanol and gasoline as test fuels. Dimensionless parameters such as Reynolds number ( Re ), Weber number ( We ), and gas-to-liquid density ratio ( ρ a / ρ l ) were used to enumerate the competition and balance of forces that dominated the spray formation, including the inertia force, viscous force, surface tension force and aerodynamic force. The results show that two temporally sequential stages exist during the spray formation, namely the initial stage and developed stage. During the initial stage, the spray penetration increases linearly with time after the start of injection (ASOI). The penetrating speed during the initial stage is primarily controlled by the competition between the inertia and surface tension while the aerodynamic force shows only minor influence. The duration of the initial stage of penetration is dependent on the competing process between inertia and viscous force as well as that between inertia and aerodynamic force. During the developed stage, the effect of aerodynamic forces becomes more influential on the spray penetration. The viscous force shows weak impact on developed stage penetration under low Reynolds number ( Re < 12,500) conditions. In contrast with the strongly time-dependent penetration, the plume angle of the emerging jets stays relatively constant during the entire injection duration. Based on the above analysis, new dimensionless correlations have been established to quantitatively characterize the effects of competing forces on spray penetration and cone angle. Compared to the classical correlations, these new correlations explicitly express the relative importance of each force during different temporal stages of spray formation. Therefore, they provide more insight into the physical mechanism of high pressure spray formation process. [ABSTRACT FROM AUTHOR]

Flash boiling sprays of liquid injection under superheated conditions provide the novel solutions of fast vaporization and better air-fuel mixture formation for internal combustion engines. However, the physical mechanisms of flash boiling spray vaporization are more complicated than the droplet surface vaporization due to the unique bubble generation and boiling process inside a superheated bulk liquid, which are not well understood. In this study, the vaporization of flash boiling sprays was investigated experimentally through the quantitative measurements of vapor concentration and liquid temperature. Specifically, the laser-induced exciplex fluorescence technique was applied to distinguish the liquid and vapor distributions. Quantitative vapor concentration was obtained by correlating the intensity of vapor-phase fluorescence with vapor concentration through systematic corrections and calibrations. The intensities of two wavelengths were captured simultaneously from the liquid-phase fluorescence spectra, and their intensity ratios were correlated with liquid temperature. The results show that both liquid and vapor phase of multi-hole sprays collapse toward the centerline of the spray with different mass distributions under the flash boiling conditions. Large amount of vapor aggregates along the centerline of the spray to form a 'gas jet' structure, whereas the liquid distributes more uniformly with large vortexes formed in the vicinity of the spray tip. The vaporization process under the flash boiling condition is greatly enhanced due to the intense bubble generation and burst. The liquid temperature measurements show strong temperature variations inside the flash boiling sprays with hot zones present in the 'gas jet' structure and vortex region. In addition, high vapor concentration and closed vortex motion seem to have inhibited the heat and mass transfer in these regions. In summary, the vapor concentration and liquid temperature provide detailed information concerning the heat and mass transfer inside flash boiling sprays, which is important for the understanding of its unique vaporization process. [ABSTRACT FROM AUTHOR]

Measurements of liquid phase temperature distributions in liquid-vapor co-existing conditions (such as in evaporating sprays) are important to understand the physics of droplet evaporation. The techniques based on laser-induced fluorescence are not suitable for evaporating case since both liquid and vapor phases emit fluorescence with the same wavelength. In this study, the fluorescence from liquid and vapor phases was separated by use of laser-induced exciplex fluorescence (LIEF) technique. Two fluorescence bands from the liquid phase fluorescence spectra were detected simultaneously, and their intensity ratio was correlated to the liquid phase temperature. For the LIEF imaging system, FB-DEMA- n-hexane was selected as it was a typical LIEF system for the vapor concentration diagnostic, and thus easily to be extended to a simultaneous diagnostic on the vapor concentration and the droplet temperature. The fluorescence spectra were obtained in the temperature range from 303 to 423 K. The effects of liquid temperature, liquid pressure, dopant concentration and laser energy on the temperature measurement were investigated. The results show a good linear relationship between the fluorescence ratio and the temperature function. Increasing the dopant concentration can raise the signal-to-noise ratio but deteriorate temperature sensitivity. The optimal range of the dopant concentration was found between 0.1 % and 0.5 %. After calibration, the technique was applied to a monosized droplet stream, and the measurement results demonstrated excellent measurement accuracy with error below 1 % in the range of 303-423 K. [ABSTRACT FROM AUTHOR]

Based on the 'Code for seismic design of buildings (2010)', seismic analysis under multi-support excitation should be done to structures with large dimension. The time-history seismic analysis method is popular among the main methods used for multi-support seismic analysis. In confirming the multi-support earthquake wave, the traveling wave effect and local site effect are two critical factors. Generally, there are two methods to make multi-support excitation analysis in finite element program. One is the compulsory boundary condition method, and the other is the big-mass method. The paper suggests taking the overload element and overload proportion as the evaluation index to the influence of multi-support seismic analysis. At the same time, some common conclusions are summarized in the paper based on the analysis experience of some projects. Such conclusions include that the torsion effect will be increased under multi-support seismic analysis and then result in adverse effect on the corner and side members. The earthquake input synchronization will be reduced under multi-support seismic analysis and then decrease the structure translational displacement. Generally, the influence of multi-support seismic analysis will be increased along with the reduction of traveling wave velocity while be decreased along with the increase of the building height. [ABSTRACT FROM AUTHOR]

Purpose – The relatively short history of internet colleges in China offers a glimpse of the potential of online education in the country and also reveals many of the problems involved in institutionalizing online education in an established system. This paper aims to present the development of online higher education in China by reviewing the development of "internet colleges", examine the unique features of online higher education and the challenges it faces, and discuss the future directions of online higher education in China.Design/methodology/approach – By reviewing major policies on online education in China and the development of "internet colleges" in the past two decades, this paper reviews the development of online higher education in China.Findings – The development of online higher education in China has unique features: central control and the support from learning support centers affiliated with "internet colleges". To further develop online higher education in China, it has to address two major challenges it is facing now: perceived low quality and prestige, and limited opportunities for international collaboration. Some of the problems are universal, such as quality assurance and the perception of quality and prestige. Some are unique to China, such as the direct involvement of the Ministry of Education in setting guidelines and regulations about online educational programs (though similar problems could arise in other centralized education systems where the government, rather than the market and the public, plays a major role).Originality/value – The vast educational market in China and the potential of online education also present interesting opportunities for foreign higher education institutions. [ABSTRACT FROM AUTHOR]

Purpose – Over the past few decades China's higher education has gone through dramatic growth and multiple rounds of reforms accompanied by a remarkable amount of financial investment, all aiming at developing world-class universities to grow innovative talents. Yet the outcomes so far have been disappointing. This paper aims to investigate this issue.Design/methodology/approach – By reviewing and analyzing selected educational reforms in higher education in China, this article discusses the reasons of the gap between the massive input for innovation in higher education in China and abysmal results. This paper also reports and analyzes a case that challenges central control and the gaokao system.Findings – Central control and the gaokao, the infamous college entrance exam, are the bedrocks of China's higher education and also the culprit for China's failure to cultivate innovative talents. Unless they are fundamentally changed it is unlikely that China will have the higher education system it dreams of having.Originality/value – This article provides an overview of China's efforts to cultivate innovative talents by strategically investing in building world-class higher education institutions (HEIs) and analyzes the reasons behind the apparent gap between its massive input and the abysmal results achieved. [ABSTRACT FROM AUTHOR]

A “two-line hybrid system” was developed, previously based on thermo-sensitive cytoplasmic male sterility in Aegilops kotschyi (K-TCMS), which can be used in wheat breeding. The K-TCMS line exhibits complete male sterility and it can be used to produce hybrid wheat seeds during the normal wheat-growing season; it propagates via self-pollination at high temperatures. Isobaric tags for relative and absolute quantification-based quantitative proteome and bioinformatics analyses of the TCMS line KTM3315A were conducted under different fertility conditions to understand the mechanisms of fertility conversion in the pollen development stages. In total, 4639 proteins were identified, the differentially abundant proteins that increased/decreased in plants with differences in fertility were mainly involved with energy metabolism, starch and sucrose metabolism, phenylpropanoid biosynthesis, protein synthesis, translation, folding, and degradation. Compared with the sterile condition, many of the proteins that related to energy and phenylpropanoid metabolism increased during the anther development stage. Thus, we suggest that energy and phenylpropanoid metabolism pathways are important for fertility conversion in K-TCMS wheat. These findings provide valuable insights into the proteins involved with anther and pollen development, thereby, helping to further understand the mechanism of TCMS in wheat. [ABSTRACT FROM AUTHOR]

Low-concentration and low-profile compound parabolic concentrators (CPCs) in the quasi-stationary state were designed and investigated for potential use in rooftop and building-integrated concentrating photovoltaic–thermal applications. All the designs were investigated with a geometric concentration ratio of two. The first design was the lowest-position-truncated CPC (LEMR), and the second was the highest-position-truncated CPC (HEMR). The performances of both concentrators were compared with a full CPC (without truncation). At the outlet aperture, the optical efficiency within the half acceptance angle for the LEMR and HEMR CPCs averaged nearly 97%, whereas for the full CPC, it was 95%. At the best concentration plane (BCP), the optical efficiency within the half acceptance angle was the highest for the LEMR CPC 95%. A distributive method was used to estimate accurately the nonuniformity in the solar flux at both the outlet and the BCP. The nonuniformity analysis revealed that the LEMR and HEMR designs exhibited a uniform distribution of solar flux at the BCP. The incident-angle modifiers for all three cases were investigated, and the annual accumulated solar energy was estimated for Xi'an, China. The material consumption of the LEMR CPC was approximately 48% that of the full CPC and 78% that of the HEMR CPC. The LEMR also exhibited the highest annual-energy efficiency per unit material consumption (ηm = 1.30). Finally, the results indicate that the LEMR CPC possesses higher solar flux uniformity and represents a better trade-off between energy collection and cost reduction, and thus, the novel design can be used as a quasi-stationary concentrator. [ABSTRACT FROM AUTHOR]

Highlights • A large-scale south-north tracking hybrid CPV/T system was constructed. • The photo-voltaic and thermal performance of the system were investigated. • An unsteady-state thermal model of hybrid CPV/T system was developed. • The unsteady model can predict the instantaneous thermal performance accurately. Abstract A hybrid CPV/T unit designed in this work concentrates solar radiation by a compound parabolic concentrator (CPC) and converts solar energy into electrical and thermal energy by a PV/T module. The CPC eliminating multiple reflections of solar radiation is defined as the 'EMR-CPC' in our previous work, which improves photoelectric and thermal conversion efficiencies. Two similar CPV/T units were tested with two-axis tracking device and south-north single-axis tracking device respectively, and the average photoelectric conversion efficiencies were 13% and 12%. A large-scale south-north tracking hybrid CPV/T system with sunlight collecting area of 810 m2 was built to explore practical application of this CPV/T unit. The whole-day thermal efficiency and total thermal output of the large-scale hybrid CPV/T system were 55% and 1,730,039 kJ respectively on April 14, 2017. The steady-state and unsteady-state thermal models of the hybrid CPV/T system were established and the energy loss was analyzed. The calculated whole-day comprehensive thermal efficiencies of the unsteady-state thermal model and the steady-state thermal model were 55.3% and 55.0% respectively, which were close to the measurement 55.8%. However, the steady-state thermal model failed to accurately predict the whole-day thermal efficiency variation of the system. In comparison, the unsteady-state thermal model accurately predicts instantaneous thermal efficiency of the system varying with meteorological conditions and its total daily heat output. [ABSTRACT FROM AUTHOR]

Abstract: The spray structural changes and vaporization processes for flash-boiling multi-hole sprays over a broad range of superheated conditions were investigated using Mie-scattering and Laser-induced-exciplex-fluorescence (LIEF) optical techniques. The fuel property effects were examined by characterizing n-hexane, methanol and ethanol fluids over a wide range of conditions consistent with that found in today’s spark-ignition-direct-injection (SIDI) engines. The macroscopic spray structure was quantified using spray penetration, spray-plume width and normalized distance between spray plumes. These structural parameters were correlated to the ratio of the ambient pressure to saturation pressure (Pa/Ps) that represents the superheated degree. Three continuous regions were identified by quantifying the spray transformation with increasing superheated degree; namely the non-flash-boiling, transitional flash-boiling and flare flash-boiling regions. Two critical values of Pa/Ps were identified, where the flash-boiling and spray collapsing transitions occurred at Pa/Ps values of 1.0 and 0.3, respectively. The evaporation process was examined using the LIEF optical technique for n-hexane, providing the relative vapor quantity throughout the spray transformation process. The correlations of the spray structural change and extent of vaporization with increasing superheated degree provided good insight into the mechanisms responsible for the observed behaviors during flash-boiling conditions. [Copyright &y& Elsevier]

Abstract: We have developed a formula for studying the transmission and scattering properties of finite-sized phononic band gap (PBG) material. We will show that based on the far field approach the transmission coefficients can be obtained by treating PBG samples as scattering objects. We find that the results agree well with the band structure. [Copyright &y& Elsevier]

Abstract Polymer-derived ceramics (PDCs) which is synthesized by pyrolysis of organosilicon polymers have recently attracted an increasing attention on the electrical property with possible application in Li-ion batteries, micro electro mechanical systems (MEMS) and harsh-environmental sensors. In this paper, the chemical composition, nanostructure evolution and the electrical conductivity variation which are induced by porosity are explored systematically in polymer-derived SiCN ceramics. The SiCN ceramics with 0, 4.82%, 8.94%, 16.81% and 21.32% porosities were prepared by mixing the polymer precursors with different crosslinking degree. There are significant changes in the content of N element, free carbon, crystallization SiC and the morphology of free carbon with the increasing porosity. As the porosity increases, the electrical conductivity of the SiCN ceramics decrease gradually from 0.015 to 0.003 S cm−1. By comparing the relationship between the conductivity and the porosity from experiment and model prediction (only intrinsic porosity considered), it can be concluded that the chemical composition, nanostructure evolution dramatically decrease the conductivity of SiCN ceramics with 56.41% maximum decline, and the decrease of the free carbon content is the most significant aspect influencing the electrical conductivity of SiCN ceramics. Our findings can realize the regulation of the nanostructure and electrical conductivity in polymer-derived SiCN ceramics by the control of porosity with a new insight on the design of PDCs functional materials. Highlights • Chemical composition, nanostructure evolution induced by porosity was studied. • Electrical conductivity variation induced by porosity was studied. • Influence factor of the electrical conductivity was analyzed and summarized. [ABSTRACT FROM AUTHOR]

Abstract Decomposition and oxidation behaviors are two important characteristics in the laser ablation process of Si-C-N precursor derived ceramics. This study investigates the ablation resistance of Si-C-N ceramics in different atmospheres by laser beam. Results reveal that during the laser ablation process, Si-C-N ceramics possess superior ablation stability in air than in argon due to the improvement of thermal stability. Scanning electron microscopy and X-ray diffraction studies reveal that a dense and continuous S-O-C layer that forms on the Si-C-N ceramic surface increases the starting temperature of decomposition. An oxidation protection mechanism for at Si-C-N ceramics in the laser ablation process is proposed in this paper. [ABSTRACT FROM AUTHOR]

A computational approach to predict external spray characteristics for flashing and cavitating nozzles was presented and validated. It is developed as a fully Eulerian and compressible two-phase flow solver that simulates vaporization and condensation of the fuel using a Homogeneous Relaxation Model (HRM). The flow solver together with the interface area density model was applied to predict spray spreading angle. A method to identify spray plume boundary from the predicted flow field that offers a meaningful comparison to experimental definition was discussed in detail. Using the experimental data available in literature, a comparison between axi-symmetric and asymmetric nozzles was made to assess the nature of the influence of the nozzle geometry and the operating conditions on the ensuing spray. On the basis of this comparison, it was inferred that the spray plume angle of asymmetric nozzles is largely geometry dependent for a wide range of pressure ratios. [ABSTRACT FROM AUTHOR]

Porosity-controllable SiCN ceramics were prepared using a simple partial crosslinking method, which is promising for preparing bulk polymer-derived ceramics with different dimensions. Continuous regulation from fully dense to high porosity within polymer-derived SiCN ceramics was realized via secondary crosslinking of partially crosslinked polysilazane (PSN). A fully dense SiCN ceramic was obtained by shaping the single partially crosslinked PSN (PC-PSN) followed by pyrolysis. PC-PSN was obtained by controlling the crosslinking reaction, and it retained a strong ability to cross link further. SiCN ceramics with different porosities were prepared by mixing PC-PSN and completely crosslinked PSN (CC-PSN) at different proportions. The size and density of the pores can be controlled via the proportion of CC-PSN in a mixed powder. The resultant SiCN ceramic has a porosity that ranges from 0% to 21.32%, which is validated to ensure the component integrity of SiCN ceramics with different dimensions due to the release of residual stress during pyrolysis. [ABSTRACT FROM AUTHOR]

The height of conventional compound parabolic concentrator (CPC) increase greatly with increasing geometric concentration ratio, resulting in large reflector consumption and deteriorative optical performance. A new truncated CPC with highest truncation position called HEMR was proposed in the previous study (Xie et al., 2016), which can improve the tradeoff between cost reduction and optical performance. In order to further improve the tradeoff to make the CPC more competitive in the commercial field, the truncated CPC with lowest truncation position called LEMR is designed by eliminating multiple reflections in the present study, and the performance is researched by the material consumption assessment and Monte-Carlo simulation theoretically under the conditions of 156 mm wide best concentration plane and 4 times geometric concentration ratio. The results show that the material consumption of LEMR is about 80% of HEMR while the optical performance including uniformity and optical efficiency is almost the same as HEMR, indicating that LEMR has a better tradeoff between cost reduction and optical performance and thus has more extensive application potential. [ABSTRACT FROM AUTHOR]

In this paper, we present a stereo visual-inertial odometry algorithm assembled with three separated Kalman filters, i.e., attitude filter, orientation filter, and position filter. Our algorithm carries out the orientation and position estimation with three filters working on different fusion intervals, which can provide more robustness even when the visual odometry estimation fails. In our orientation estimation, we propose an improved indirect Kalman filter, which uses the orientation error space represented by unit quaternion as the state of the filter. The performance of the algorithm is demonstrated through extensive experimental results, including the benchmark KITTI datasets and some challenging datasets captured in a rough terrain campus. [ABSTRACT FROM PUBLISHER]