In recent years, haze pollution has become one of the most critical environmental issues in Xi'an, China, with particular matter (PM) being one of the top pollutants. As an important fraction of PM, ...bioaerosols may have adverse effects on air quality and human health. In this study, to better understand the characteristics of such biological aerosols, airborne microbial samples were collected by using an Andersen six-stage sampler in Xi'an from October 8th to 22nd, 2014. The concentration, size distribution and genera of airborne viable bacteria and fungi were comparably investigated during the haze days and non-haze days. Correlations of bioaerosol levels with meteorological parameters and PM concentrations were also examined. The results showed that the daily average concentrations of airborne viable bacteria and fungi during the haze days, 1102.4–1736.5 and 1466.2–1703.9 CFU/m3, respectively, were not only much higher than those during the non-haze days, but also exceeded the recommended permissible limit values. Comparing to size distributions during the non-haze days, slightly different patterns for bacterial aerosols and similar single-peak distribution pattern for fungal aerosols were observed during the haze days. Moreover, more allergic and infectious genera (e.g. Neisseria, Aspergillus, and Paecilomyces) in bioaerosols were identified during the haze days than during non-haze days. The present results reveal that bioaerosols may have more significant effects on public health and urban air quality during the haze days than during non-haze days.
•On haze days, concentrations of viable bacteria and fungi were much higher than on non-haze days.•There was different size distribution for airborne bacteria between the haze and non-haze days.•For fungal aerosols, similar size distribution can be found between the haze and non-haze days.•Compared to the non-haze days, some more allergic and infectious genera can be found during the haze days.•More attention should be paid to the potential health risk related to bioaerosols during the haze days.
The traditional method for assessing the quality and maturity of loquats has disadvantages such as destructive sampling and being time-consuming. In this study, hyperspectral imaging technology was ...used to nondestructively predict and visualise the colour, firmness, and soluble solids content (SSC) of loquats and discriminate maturity. On comparison of the performance of different feature variables selection methods and the calibration models, the results indicated that the multiple linear regression (MLR) models combined with the competitive adaptive reweighting algorithm (CARS) yielded the best prediction performance for loquat quality. Particularly, CARS-MLR models with optimal prediction performance were obtained for the colour (R
= 0.96, RMSEP = 0.45, RPD = 5.38), firmness (R
= 0.87, RMSEP = 0.23, RPD = 2.81), and SSC (R
= 0.84, RMSEP = 0.51, RPD = 2.54). Subsequently, distribution maps of the colour, firmness, and SSC of loquats were obtained based on the optimal CARS-MLR models combined with pseudo-colour technology. Finally, on comparison of different classification models for loquat maturity, the partial least square discrimination analysis model demonstrated the best performance, with classification accuracies of 98.19% and 97.99% for calibration and prediction sets, respectively. This study demonstrated that the hyperspectral imaging technique is promising for loquat quality assessment and maturity classification.
•An artificial environment simulation laboratory was built.•An indoor scale solar chimney setup was constructed in the AESL.•The upper limitations of collector radius and chimney height were ...discussed.•Collector efficiency increases non-linearly with solar radiation intensity.
An artificial environment simulation laboratory (AESL) was built and successfully applied to the experimental study of a solar chimney setup for the first time. A solar simulator and a temperature control system are included in the laboratory to achieve active control of environmental parameters. An indoor scale solar chimney setup with a collector diameter of 1.22m and chimney height of 1m was constructed in the testing area of the AESL. The airflow temperature and updraft velocity were measured for the solar chimney setup with varying radiation intensities and chimney heights. The measured data were used to validate a thermal model for the collector. The thermal characteristics of the solar collector were investigated through the temperature field in the collector. The upper limitations on the collector radius and chimney height were discussed based on experimental results. The experimental work on the basic solar chimney setup performance helped in understanding the thermodynamic characteristics of the solar chimney power plant (SCPP), thereby serving as the basis for the design of large-scale commercial SCPPs.
Monolayer molybdenum disulfide （MoS2） has attracted much attention because of the variety of potential applications. However, its controlled growth is still a great challenge. Here, we report a ...modified chemical vapor deposition method to grow monolayer MoS2. We observed that the quality of the MoS2 crystals could be greatly improved by tuning the carrier gas flow rate during the heating stage. This subtle modification prevents the uncontrollable reaction between the precursors, a critical factor for the growth of high-quality monolayer MoS2. Based on an optimized gas flow rate, the MoS2 coverage and flake size can be controlled by adjusting the growth time.
► A new economical large-scale solar simulator was designed. ► The average irradiance can be adjusted between 150 and 1100
W/m
2. ► Diurnal irradiance variation trends could also be simulated through ...suitable control. ► The irradiation characteristics were investigated using an optical simulation model. ► The radiation characteristics are improved and the optimized effectively irradiation surface is expanded up to 81.6%.
A new economical large-scale multiple-lamp solar simulator was designed and constructed to provide a test platform for the simulation of solar radiation at the earth’s surface. The light source and fabrication of the simulator is described. Measurement of the irradiance indicates that the multiple-lamp simulator conforms to Class B of the ASTM (American Society for Testing and Materials) and IEC (International Electrotechnical Commission) standard in regard to spectrum match, irradiance uniformity and stability. Without altering the spectral distribution, the average irradiance on the target area can be adjusted between 150 and 1100
W/m
2 by varying the number of lamps and/or the lamp-to-area distance. Diurnal irradiance variation trends could also be simulated through suitable control. The irradiation characteristics of the solar simulator under a variety of operating conditions were investigated using an optical simulation model, which was experimentally validated and provided physical experiments with reference data with savings in both time and cost. To enlarge the effective irradiated area, two large mirror-like stainless steel plates was mounted on both of the long sides of the solar simulator. The optimal reflection angle was determined by means of optical simulation. The radiation characteristics of simulator are improved and the optimized effectively irradiation surface is expanded up to 81.6%.
The optically tunable properties of the hybrid three-dimensional (3D) metamaterials with dual- and broadband response frequencies are theoretically investigated in the terahertz spectrum. The planar ...double-split-ring resonators (DSRRs) and the standup double-split-ring resonators are fabricated on a sapphire substrate, forming a 3D array structures. The bi-anisotropy of the hybrid 3D metamaterials is considered because the stand-up DSRRs are not symmetrical with respect to the electric field vector. Due to the electric and magnetic response realized by the planar and the standup double-split-ring resonators respectively, the dual-band resonance response and the negative refractive index can be achieved. The potential of the phase modulation under photoexcitation is also demonstrated. Further analysis indicates that, photoexcitation of free carriers in the silicon within the capacitive region of the standup DSRRs results in a broad resonance response bandwidth (about 0.47 THz), and also functions as a broadband negative refractive index that roughly lies between 0.80 and 2.01 THz. This tunable metamaterials is proposed for the potential application of electromagnetic wave propagation in terahertz area.
The damage threshold of lithium niobate crystal under single and multiple femtosecond laser pulses has been studied theoretically and experimentally. Firstly, the model for the damage threshold ...prediction of crystal materials based on the improved rate equation has been proposed. Then, the experimental measure method of the damage threshold of crystal materials has been given in detail. On the basis, the variation of the damage threshold of lithium niobate crystal with the pulse duration has also been analyzed quantitatively. Finally, the damage threshold of lithium niobate crystal under multiple laser pulses has been measured and compared to the theoretical results. The results show that the transmittance of lithium niobate crystal is almost a constant when the laser pulse fluence is relative low, whereas it decreases linearly with the increase in the laser pulse fluence below the damage threshold. The damage threshold of lithium niobate crystal increases with the increase in the duration of the femtosecond laser pulse. And the damage threshold of lithium niobate crystal under multiple laser pulses is obviously lower than that irradiated by a single laser pulse. The theoretical data fall in good agreement with the experimental results.
Detection of the moisture content (MC) and freshness for loquats is crucial for achieving optimal taste and economic efficiency. Traditional methods for evaluating the MC and freshness of loquats ...have disadvantages such as destructive sampling and time‐consuming. To investigate the feasibility of rapid and non‐destructive detection of the MC and freshness for loquats, optical fiber spectroscopy in the range of 200–1000 nm was used in this study. The full spectra were pre‐processed using standard normal variate method, and then, the effective wavelengths were selected using competitive adaptive weighting sampling (CARS) and random frog algorithms. Based on the selected effective wavelengths, prediction models for MC were developed using partial least squares regression (PLSR), multiple linear regression, extreme learning machine, and back‐propagation neural network. Furthermore, freshness level discrimination models were established using simplified k nearest neighbor, support vector machine (SVM), and partial least squares discriminant analysis. Regarding the prediction models, the CARS‐PLSR model performed relatively better than the other models for predicting the MC, with R2P and RPD values of 0.84 and 2.51, respectively. Additionally, the CARS‐SVM model obtained superior discrimination performance, with 100% accuracy for both calibration and prediction sets. The results demonstrated that optical fiber spectroscopy technology is an effective tool to fast detect the MC and freshness for loquats.
The developed CARS‐PLSR prediction model performed relatively better than the other models for predicting the moisture content of loquats, with RPD values of 2.51. The CARS‐SVM discrimination model for determining the freshness of loquats obtained superior discrimination performance, with 100% accuracy for both calibration and prediction sets. This study demonstrated that optical fiber spectroscopy technology is an effective tool to fast detect the moisture content and freshness for loquats.
With the increasing popularity of renewable energy sources and the globally increasing electricity demand, the task of balancing the intermittent energy supply with varying demand becomes ...increasingly difficult. Instead of adjusting the supply, improving the demand response (DR) can be a more efficient way to optimize power balance. HVAC (heating, ventilation, and air-conditioning) systems, which operate on the demand side of power-grids, have a huge potential to improve the power balance. To assess their potential in a variable air volume (VAV) air-conditioning system with energy storage tank we introduce a demand response method that combines active cool-energy storage (ACES) with global temperature adjustment (GTA). To confirm the effectiveness of this combined ACES+GTA approach, we conduct measurements with the help of a full-scale VAV air-conditioning test setup. The experimental results are compared with a TRNSYS simulation. The measurements indicate that an energy-storing water-tank can effectively reduce the number of starts and stops for the heat pump. The simulation confirms that the ACES+GTA method can also effectively reduce the peak load of the power grid with little impact on the thermal comfort of the energy consumers. The cost-saving rate, compared to the conventional operating mode (no energy-storage during other periods), reaches 7.02% for an entire cooling season if the GTA method (with DR) is used.
To improve the prediction accuracy of heating demand, an appropriate base temperature should be estimated before using the heating degree-days (HDD) approach. This study collected the measured data ...for gas consumption at half-hourly resolution and the building physical characteristics from 89 educational buildings over four years. To determine the base temperature, in addition to the ambient temperature, more detailed independent variables, i.e. solar insolation, relative humidity, wind speed, and one-day ahead residual temperature, were incorporated into a three-parameter change-point multi-variable regression (3PH-MVR) for heating. The mean base temperature using the 3PH-MVR approach was about 0.4°C lower than the results from the 3PH method only. The relationships between base temperature and annual HDD (based on 15.5°C), building location, and mean daily solar insolation were evaluated. It is found that the annual HDD and the daily insolation had clear impacts on base temperature, while there was a plausible relationship between base temperature and building location. Compared with traditional approach, the proposed 3PH-MVR method considers multiple weather parameters and determines a more robust base temperature, thus improving the prediction accuracy of HDD with higher average
R
2
value at 0.86 than that of univariate regression (0.82).
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