Clear Days Research Articles

Understanding and assessing demographic (in)equity resulting from extreme heat and direct sunlight exposure due to lack of tree canopies in Norfolk, VA using agent-based modeling

Prolonged exposure to extreme heat and direct sunlight can result in illness and death. In urban areas of dense concentrations of pavement, buildings, and other surfaces that absorb and retain heat, harmful environmental exposures to extreme heat and direct sunlight for residents can occur on a daily basis during certain parts of the year. Tree canopies provide shade and help to cool the environment, making mature trees with large canopies a simple and effective way to reduce urban heat and avoid direct sunlight. We develop a demographically representative agent-based model to understand the extent to which different demographics of residents in Norfolk, VA are (in)equitably shaded from direct sunlight and extreme heat conditions during a walk on a clear summer day. In the model each agent represents a different resident of Norfolk, VA. We use the model to assess the extent to which the city’s tree planting plan will be effective in remediating any existing inequities. Our results show that inequitable conditions exist for residents at (1) different education levels, (2) different income levels, and (3) living in different census tracts. Norfolk’s Tree Planting Program effectively reduces the distance residents of all demographics walk in extreme heat and are exposed to direct sunlight. However, residents of the city at lower income levels still experience statistically significantly more extreme heat and direct sunlight exposure due to a lack of tree canopies in summer months than those at higher income levels.

A Novel Adaptive Power Smoothing Approach for PV Power Plant with Hybrid Energy Storage System

Clouds passing over solar photovoltaic (PV) power system causes power fluctuations, which contributes to power quality issues. Power fluctuations are usually compensated by an energy storage system (ESS) integrated with a filtering or smoothing controller. However, there is a great burden to tune and determine the filtering time constant (TF) that leads to better alleviation of PV power fluctuations because the irradiance variability varies from day to day. Lack of cloud information leads to incorrect selection of TF values which leads to poor smoothing performance when setting low values on cloudy days, or to unnecessary ESS operation when setting high values on clear days. This paper introduces a novel power smoothing framework to avoid the arbitrary selection of TF values and reduce the stress on ESS based on predictive and adaptive smoothing mechanisms. The proposed controller contains two layers, the first layer predicts the next day's irradiance profile and uses a clear sky model to identify the cloud class. Next, the controller sets the initial values of the filter time constants for cloudy, moderate, and mild days, and disables smoothing on clear and overcast days. The second layer adaptively adjusts the initial filter time constant based on the current power ramp rate and shares power for a hybrid energy storage system (HESS). The performance of the proposed controller is tested against the forecasting errors and compared to fixed time constant-based smoothing techniques and ramp rate control in a range of scenarios, including smoothing, ramp rate reduction, and battery degradation assessment.

Daytime radiative cooling aerogel with favorable amphiphobic surface properties

Passive daytime radiative cooling technology without any electricity input offers great promise to mitigate carbon emissions and greenhouse effects. As a type of daytime radiative cooling emitters (DRCEs), daytime radiative cooling aerogel attracts a lot of attention and has great advantages in minimizing parasitic solar absorption and reducing environmental heat gain. However, designing daytime radiative cooling aerogel with amphiphobic surface properties is still challenging. Herein, a novel daytime radiative cooling aerogel based on eco-friendly bacterial cellulose (BC) as the skeleton, modified barium sulfate (BaSO4) as functional particles and fluoride coating as amphiphobic surface modifier was developed by simple freeze-drying and spraying. The optimal daytime radiative cooling aerogel, designated as M-BC/BaSO4-14 (M-BC/BaSO4-14 refers to the modified BC/BaSO4 aerogel), exhibited a high average reflectivity (95.6%) and excellent average emissivity (98.1%). The M-BC/BaSO4-14 achieved a mean temperature drop of 6.64°C and maximum temperature drop of 13.30°C on a cloudy day, and a mean temperature drop of 8.49°C and maximum temperature drop of 12.34°C on a clear day. It should be noted that the temperature drop referred to the temperature inside the measurement box (called the inner ambient temperature throughout this article) not the true ambient temperature. Meanwhile, the M-BC/BaSO4-14 aerogel exhibited favorable amphiphobic surface properties (water contact angle of about 151°, ethylene glycol contact angle of 141° and N-Hexadecane contact angle of 139°) and daytime radiative cooling performance before and after self-cleaning changed insignificantly. This work provides a viable strategy for the simultaneous improvement of the spectral properties and amphiphobic surface properties of the DRCEs.

Energetic, Exergetic, and Heat Transfer Assessment of PCM-Integrated Heat-Pipe-Based ETSC for Clear and Cloudy Weather Conditions

Solar energy’s most promising application is in water heating, followed by other solar thermal applications. In this investigation, a novel method of incorporating a phase-change material (PCM) between the annulus space of an evacuated tube and an aluminum finned heat pipe is employed. During day time, the PCM stores the excess amount of heat and releases it in order to heat the flowing water during high-demand/insufficient solar radiation. This study aims to evaluate the detailed heat transfer assessment and energetic and exergetic efficiencies of the developed PCM-integrated solar water heater in both clear and cloudy weather conditions at 20 LPH. The outcomes of the study found that the maximum useful amounts of energy collected daily for the clear and cloudy days were 10.65 MJ and 8.52 MJ, respectively, whereas temperatures of the stored water were found to be 45.2 °C and 41.4 °C on the next day at 6:00 a.m. for the corresponding days. The daily energetic and exergetic outputs of the designed system were 76.57% and 79.64%, and 2.37% and 1.38%, respectively, at fixed mass flow rate for the clear and cloudy day conditions. The overall heat transfer coefficients (UL) for both days were 0.75 and 0.72 W/m2 K, respectively. The findings show that the proposed system overcomes the issue of overheated heat pipes and can provide hot water even in cloudy/low-sunshine conditions.

Outdoor Thermal Environment Regulation of Urban Green and Blue Infrastructure on Various Types of Pedestrian Walkways

Urban green and blue infrastructure (GBI) is effective in urban heat mitigation. However, the diurnal variations in the thermal regulation of GBI on different types of urban pedestrian walkways in the subtropical humid climate zone are unclear. Based on traverse measurements in January 2022, this study investigates how outdoor air temperature (Ta) and wet-bulb temperature (Tw) at the pedestrian level are affected by various urban morphology and GBI characteristics in the central urbanized area of Guangzhou (China). Six building-related, three vegetation-related, and three water-related parameters were applied in the analyses. Results show that green infrastructure (GI) has the strongest cooling effect (Pearson’s coefficient r = −0.33~−0.54) on Ta on cloudy evenings and the weakest cooling effect (r = −0.22~−0.32) on clear evenings. Blue infrastructure (BI) exhibits the highest correlations with the cooling effect for Ta on clear afternoons (r = −0.35~−0.51) and weaker, but more consistent, correlations throughout cloudy days (r = −0.23~−0.43). Strong correlations between GI and Tw cooling are observed in the morning and evening on clear days (r = −0.13~−0.48), while BI exhibits the strongest correlation with Tw cooling on clear afternoons (r = −0.13~−0.37). In addition, both GI and BI show a greater cooling effect on both Ta and Tw in low-rise areas compared to high-rise areas. Compared to the individual GI or BI, the integrated GBI has a higher cooling intensity for both Ta and Tw in high-rise areas. However, the cooling potential of integrated GBI is slightly lower for both Ta and Tw during noon and afternoon in low-rise areas. The findings of this study give insights into urban GBI planning and design of specific urban microclimate regulation strategies.

Satellite parking: a new method for measuring parking occupancy

Abstract. Parking management plays a critical role in keeping urban spaces accessible and urban managers strive for an optimal balance between not enough and too much parking. Deciding which parking space can be liberated or needs to be extended requires detailed data on parking occupancy trends. In person inspection and in-situ sensors can provide such data but are too costly for city wide deployment. High-resolution satellite imagery is becoming more affordable, has the advantage of instantaneously collecting information from the whole city, is continuously being updated, and available for several years now to allow building a time series. Yet, identifying cars in satellite imagery is not a trivial task. We propose a method for classifying parking spot occupancy based on thresholding the reflectance range. The method requires individual parking spot data to be available and analyses each parking zone individually. We tested the method on a 0.5 metre resolution image (Pleiades satellite) that was specifically ordered for this purpose during a clear spring day in a medium-size city. The method has the advantage of not requiring extensive training data and is non-parametric. To assess accuracy, we collected ground truth data for the exact same moment as the image was ordered. The colour bands (blue, green, and red) performed equally well, while NIR seriously underperformed. We achieved a F1 score of 0.82 for all parking spots in the ground truth. The method is sensitive to tree canopy. When removing the tree obscured spots, the F1 score increased to 0.85. Tree canopy spots were automatically determined and filtered using NDVI.

Have You Seen My Invisible Dinosaur? by Helen Yoon

Reviewed by: Have You Seen My Invisible Dinosaur? by Helen Yoon Ally Byerly Yoon, Helen Have You Seen My Invisible Dinosaur?; written and illus. by Helen Yoon. Candlewick, 2023 [32p] Trade ed. ISBN 9781536226256 $18.99 Reviewed from digital galleys R 3-6 yrs A little girl conducts a tireless search for her invisible dinosaur, who seems to have gone missing in the wake of a bath that washed away all evidence of his existence. Though she prepares platters of her dinosaur’s favorite jam sandwiches and plasters the streets with missing posters, her prehistoric friend fails to materialize. Or does he? The trick of keeping an invisible dinosaur is that you can never quite tell where he’s wandered, especially on a clear day. Without any tracks to follow, the little girl flounders but finds unexpected hope while traversing the natural world around her. Yoon’s minimalist mixed media illustrations and generous use of white space activate the imagination, inviting readers into a hidden world of wonder, with the disappeared dino’s contours revealed by rain sluicing off his back or jam staining his cheeks. The juxtaposition of an endearingly diminutive, spikey-haired protagonist traversing sprawling landscapes recalls spreads from Watterson’s Calvin and Hobbes. This picture book’s concise word count and conceit of directly addressing the reader make this an excellent interactive pick for a storytime for younger audiences, just make sure there’s enough room for every child’s invisible dinosaur to find a seat. Copyright © 2023 The Board of Trustees of the University of Illinois

Weather influence on the performance of solar collector

A laboratory-scale evacuated tube solar collector (ETSCs) has been developed and tested for unloading conditions in Lanzhou, China. clear sky and cloudy conditions have been tested. Heat is generally considered instantaneous because it is a function of multiple instantaneous factors, like ambient temperature and solar radiation. The results show a clear sky day with a maximum and average value of ambient temperature, outlet, inlet, and solar radiation of 12 and -60C, 56 and 310C, 69 and 340C, 931 and 576W/m2, respectively, while a cloudy day was eight and -30C and 861.2 and 449W/m2 respectively. Clear sky day maximum and the average mass flow rate was 0.25 and 0.21 Kg/sec, while the cloudy flow rate was 0.27 and 0.03 Kg/sec, respectively. A clear sky has a heat loss of -0.307 and -0.05kW for a cloudy day. R square were 0.76 and 0.4 for clear sky and cloudy day, respectively. For the heat and radiation correlation relationship, a clear sky has a slope of 0.0029 and 0.0539 for a cloudy day. In other conditions, the solar radiation per unit area increases by 1 W/m2, and the daily heat is collected. Increasing A W/m2, the temperature difference between the average temperature of the hot water storage tank and the average temperature of the environment increases by one °C, and the daily heat collection decreases A W/m2. It concludes that a clear sky has much better efficiency than a cloudy day.

A note on the release and tracking of a rehabilitated pygmy sperm whale (Kogia breviceps)

A stranded, rehabilitated 220cm female pygmy sperm whale was radiotracked from 31 May-4 June 1994 after its release in the Gulf Stream off Cape Canaveral, Florida. The whale moved directly off the continental shelf and headed northward within a corridor bounded by the shelf break and the eastern edge of the Gulf Stream. It moved offshore up to 32 n.miles from the shelf break during the late afternoons and nights and headed back toward the shelf break during the day. The average travelling speed was 3.0kts, and ranged from 0-6kts. Speeds were greatest offshore of the shelf break (4.7kts), where the speed of the Gulf Stream was the greatest, and both travelling speeds and Gulf Stream speeds decreased with distance offshore. The whale did not appear, however, to be drifting passively with the current. Diving duration varied significantly with light levels. The whale made long dives ( > 8min) at night and on overcast days when squid are known to be closer to the surface. During clear days, the whale’s dives were significantly shorter, typically less than five minutes (n = 841). Although these results come from only a single, rehabilitated animal, the four days of data provided the first information on pygmy sperm whale movements and diving behaviour at sea: how its behaviour was influenced by time of day, oceanographic features, and environmental conditions, and how the whale’s surfacing behaviour could allow survey estimates to be adjusted for diving whales missed along the trackline.

Multiple source apportionments, secondary transformation potential and human exposure of VOCs: A case study in a megacity of China

The Central Plain City Cluster represented by Zhengzhou is one of the most haze-polluted regions, especially for the heating period. As critical precursors of Secondary Organic Aerosol (SOA) and Ozone, the ambient Volatile Organic Compounds (VOCs) emitted from anthropogenic activities have aroused widespread concern. This study provided a revealing insight on the concentration level, chemical composition, multiple source apportionments (SAs), SOA formation potential (SOAp) and exposed health risk of VOCs before and during heating periods at a megacity site. The average concentrations of TVOCs during clear days before heating, pollution days before heating, clear days during heating, and pollution days during heating were 37.81 ± 17.21, 54.48 ± 17.83, 39.27 ± 16.38 and 63.98 ± 22.42 ppbv, respectively. Compared with the before heating period, the concentration of TVOCs increased by 3.9% and 17.4% on clear days and polluted days during the heating period, respectively. Among them, alkanes were the most abundant species of VOCs, followed by halocarbons and alkenes. The multiply SAs methods were applied to identify potential sources, and the contributions of source structures were reasonable and credible by comparing PMF and emission inventory. Vehicular exhaust was the largest contributor during the non-heating period (33.2%), while for the heating period, combustion source contributed the most to VOCs emission (24.2%). In terms of the contribution to SOAp formation, aromatics were the most abundant VOCs species, and combustion (29.4%) was the major source, followed by solvent usage (26.5%) and vehicular exhaust (24.6%). The non-carcinogenic risks of VOCs sources were significantly lower than the acceptable safety threshold, while all the specific VOCs sources posed carcinogenic risks except for biogenic emission. The ways of analysis and assessment in this study can highlight the need for more effective control strategies related to VOCs anthropogenic activities during the heating period in megacities of Central China.

Field Study of Novel Storage Tank of Solar Water Heating System

In this paper thermo-hydrodynamic characteristics were investigated experimentally for a new type shell-helical coiled tube heat exchanger used as a storage tank of closed loop solar water heater system. Triple concentric helical coils were made of copper tubes of (12.5mm OD and 10mm ID) with coils diameter of (207, 152.2, 97mm) for outer, middle and inner coils respectively. The experiments were carried out during a clear sky days of (March and April 2012). The parameters studied in this work are: history of average temperature of shell side of the storage tank, collector heat gain, heat rejected from coils to shell side of the storage tank, collector efficiency, thermal effectiveness of the heat exchanger (storage tank), and pressure drop. These parameters were studied at four different circulating mass flow rates of (1.8, 3, 6, 9 l/min) and for two consuming modes of supply water namely no withdrawal, and continuous withdrawal of (1 l/min). The results show that stratification temperature in the storage tank is increased for no withdrawal compared with water withdrawal, also the shell side average temperature increases with increased solar time. Collector efficiency is increased with increasing circulation flow rates, also increases with water withdrawn from storage tank. The pressure drop decreases with the increase of solar radiation .

A novel dual feedwater circuit for a parabolic trough solar power plant

The validated dynamic model of a parabolic trough power plant (PTPP) is improved by the combination of a new feedwater circuit (feedwater/HTF circuit) and a reference feedwater circuit (feedwater/steam circuit) as well as the development of the steam turbine model. Such design represents the first effort of research to utilize a dual feedwater circuit inside the PTPP to increase the power output in the daylight from 50 to 68 MWel and raise night operating hours at a lower cost. The purpose of increasing the operating night hours at a power (48 MWel) as in the reference PTPP is to get rid of the fossil fuel backup system and rely only on the absorbed solar energy and the stored energy in the molten salt. During daylight hours, the feedwater circuit is operated using Feedwater/HTF. In the transient period, the feedwater/HTF circuit will gradually be closed due to a decrease in solar radiation. Furthermore, the rest of the nominal feedwater mass flow rate (49 kg/s) is gradually replenished from the feedwater/steam circuit. After sunset, the entirety of the feedwater is heated based on the steam extracted from the turbine. The purpose of this improvement is to raise the number of nightly operational hours by reducing the nominal load from 61.93 to 48 MWel as a result of low energy demand during the evening hours. Therefore, a comparison study between the reference model and this optimization (optimization 2) is conducted for clear days (26th–27th/June and 13th–14th/July 2010) in order to understand the influence of dual feedwater circuit. The comparison indicates that the operational hours of the power block (PB) will be obviously increased. Moreover, this improvement reduces based on the fossil fuel system at night. As the last step, an economic analysis was performed on the costs of the referenced and the optimized PTPP as a function of the levelized energy cost (LEC). The results illustrate that the specific energy cost of a PTPP with 7.5 h of storage capacity is lowered by about 14.5% by increasing the output of the PTPP from 50 to 68 MWel.

Prediction of Daily Maximum Air Temperature for Transitional Seasons by Statistical Methods in Baghdad

Predicting the maximum temperature is of great importance because it is related to various aspects of life, starting from people’s lives and their comfort, passing through the medical, industrial, agricultural and commercial fields, as well as concerning global warming and what can result from it. Thus, the historical observations of maximum and minimum air temperature, wind speed and relative humidity were analyzed in this work. In Baghdad, the climatic variables were recorded on clear sky days dawn at 0300 GMT for the period between (2005-2020). Using weather station's variables multiple linear regression equation, their correlation coefficients were calculated to predict the daily maximum air temperature for any day during the transitional seasons (autumn, spring). By analyzing the results, a comparison was made between the expected and recorded maximum air temperature to improve the equation. The bias was tracked by analyzing the number of relative frequencies of the occurrence of these errors. (0.2 ) for the autumn season and (0.15 ) for the spring season was added to the multiple linear regression equation as a correction value.

Air quality impacts on rooftop photovoltaic energy production during the 2019–2020 Australian bushfires season

The ”Black Summer” 2019–2020 bushfires covered large areas of eastern Australia, causing substantial health impacts, animal deaths and damage to infrastructure. The smoke-related aerosols produced from these fires can also impact solar energy production by attenuating useable radiation. This study assesses the impacts of high particulate matter (PM) concentrations in photovoltaic (PV) energy production in New South Wales (NSW), from November 2019 to January 2020, during the bushfire season. We use in-situ measurements of commercial rooftop PV systems, pollution data from NSW Air Quality Monitoring Network and the Schools Weather and Air Quality, and satellite information from Himawari-8. We focus the study on clear days to eliminate the effects of clouds and concentrate on the impact of PM alone. We compare the energy generated by rooftop PV systems during clean/polluted conditions with a statistical conditional analysis approach. Results show that most locations exhibit similar behaviour, with PV generation reductions in polluted environments compared to clean conditions. The air quality impacts are stronger in locations near bushfire burning areas. For instance, in Katoomba, mean reductions up to 20% in the generated PV energy are found during high PM episodes. High-speed westerly winds transported the smoke several hundreds of kilometres, influencing the air quality and PV energy generation in most stations across Sydney. On a particular day of high bushfire activity (10 December 2019), we use satellite information to show how smoke caused increases in aerosol levels, increased PM concentrations, attenuated radiation and produced up to 65% reductions in hourly PV energy.

Spatial Variability of Albedo and Net Radiation at Local Scale Using UAV Equipped with Radiation Sensors

Energy balance closure is an important feature in studies of ecosystem exchanges of energy and greenhouse gases using the eddy covariance method. Previous analyses show that this is still a problem with imbalances in the order of 0.6–0.7 to full closure (for only a few sites). It has been suggested that mesoscale transport processes that are not captured by the eddy covariance measurements are the main reason behind the closure problem. So far, very little action has been taken to investigate another potential cause of the problem, namely, the role of spatial variation in net radiation at the scale of typical flux footprints. The reason for this knowledge gap is mainly due to the lack of suitable methods to perform such investigations. Here, we show that such measurements can be performed with an unmanned aerial vehicle equipped with radiation sensors. A comparison using a reference radiometer on a fixed mast with a hovering UAV equipped with pyranometers for incoming and outgoing shortwave radiation and an infrared thermometer for surface temperature measurements shows that incoming and outgoing shortwave radiation can be measured with a standard error of 7.4 Wm−2 and 1.8 Wm−2, respectively. An application of the system was made over a five-year-old forest flux site in Sweden. Here, the net longwave radiation was estimated from the measured surface temperature and the calculated incoming longwave radiation. The results show that during the mission around noon on a clear day, distinct ‘hotspots’ existed over the plantation with the albedo varying between 15.5 and 17.9%, the surface temperature varying between 22.2 and 25.5 °C and the net radiation varying between 330 and 380 Wm−2. These variations are large enough to have a significant impact on the energy balance closure problem. Our conclusion is that we now have the tools to investigate the spatial variability of the radiation regime over flux sites and that this should be given more attention in the future.

Effects of fruit load on growth, photosynthesis, biochemical characteristics, and fruit quality of Camellia oleifera

Camellia oleifera Abel is one of the four major woody oil species that produce edible oil from seeds. Nevertheless, its oil yield is comparably low, due to an imbalance in its source–sink relationship caused by its alternate bearing cycle. In this study, we conducted a pot experiment using 5-year-old C. oleifera ‘Huaxin’ young plants to examine the source–sink relationship and determine the optimal fruit load for oil production that ensures maximum economic value for C. oleifera. From April to October, the C. oleifera young plants were subjected to different leaf:fruit ratios: no fruit (control, CK), low fruit load (FL1, leaf:fruit ratio of 36:1), medium fruit load (FL2, leaf:fruit ratio of 18:1), and high fruit load (FL3, leaf:fruit ratio of 9:1). The results showed that the FL2 and FL3 treatments significantly reduced plant height, stem diameter, and flower bud differentiation from August to October, compared with the control. The net photosynthetic rate (Pn) and stomatal conductivity (Gs) of new leaves on clear days from June to August were decreased in the FL2 and FL3 treatments, compared with the control. Medium and high fruit loads (FL2 and FL3 treatments) and prolonged growth duration led to greater reductions in fruit size, weight, seed kernel oil content, oil production per plant, oil body volume, and distribution area, compared with the FL1 treatment. However, stearic acid and oleic acid contents were significantly higher in camellia oil obtained from the FL1 treatment than in camellia oil obtained from the FL2 and FL3 treatments. Thus, a leaf:fruit ratio of 36:1 is recommended to ensure proper C. oleifera ‘Huaxin’ growth and yield, and higher fruit loads should be avoided.

On Saharan Air Layer Stability and Suppression of Convection over the Northern Tropical Atlantic: Case Study Analysis of a 2007 Dust Outflow Event

A prominent Saharan Air Layer (SAL) was detected over the Northern Atlantic from the West African Coast to the Caribbean Sea in 2007. Data was collected from the Aerosols and Ocean Science Expedition (AEROSE), which encountered a major dust outflow on 13 and 14 May 2007. These observational measurements came from onboard instrumentation and radiosondes that captured the dust-front event from 13 to 14 May 2007. Aerosol backscatter was confined within the Marine Boundary Layer (MBL), with layers detected up to 3 km. Aerosol Optical Depth (AOD) increased by one order of magnitude during the dust front, from 0.1 to 1. Downward solar radiation was also attenuated by 200 W/m2 and 100 W/m2 on the first and second days, respectively. A weaker gradient at and above 500 m from potential temperature profiles indicates a less-defined MBL, and an ambient air temperature of 26 °C on 14 May and 28 °C on 15 May were observed above 500 m, reinforcing the temperature inversion and static stability of the SAL. Subsequent days, clear and boundary-layer cloudy days were observed after the dust front. From 14 to 18 May, a Convective Inhibition (CIN) layer started to form at the top of the MBL, developing into a negative buoyancy from 17 to 23 May, and reinforcing the large-scale anticyclonic atmospheric conditions. These results show that the SAL acts as positive feedback on suppressing deep convection over the tropical Atlantic during this dust outflow and several days after its passage.

Experimental investigation of an asymmetric compound parabolic concentrator–based direct absorption solar collector using plasmonic nanofluids

Plasmonic nanofluid-based direct absorption solar collector (DASC) systems have shown a better perspective over surface-based solar thermalcollectors. These nanofluids demonstrated high thermal performance in photo-thermal conversion efficiency even at minute concentration compared to other testednanofluids. However, very few studies have been reported so farwith real-time outdoor experiments to show the opportunities and challenges in the practical applications of concentrating DASC systems. For the work presented here, an asymmetric compound parabolic concentrator (ACPC)-based DASC system has been designed, fabricated, and tested using mono-spherical gold and silver nanoparticle-based plasmonicnanofluids over several clear sky days at Jalandhar city (31.32° N, 75.57° E), India. The optical and morphological properties of synthesized nanoparticles were studied using UV-Vis spectrophotometry and High-resolution transmission electron microscopy (HR-TEM). Photo-thermal conversion tests were conducted using different working fluids and compared with a flat DASC system under similar operating conditions. The experimental results revealed that ACPC-based DASC system reached a maximum thermal efficiency of around 70% using plasmonic nanofluids which was approximately 28% higher than a flat DASC system with water as the working fluid. The stability analysis showed that plasmonic nanofluids are capable of retaining their optical properties even after several hours of sun exposure. The present study highlights the use of plasmonic nanostructures for achieving high photo-thermal conversion efficiency in concentrating DASC systems.

Ka-band cryogenic low-noise receiver of the Misasa 54 m antenna for deep-space communications and radio astronomy

Abstract We built a Ka-band dual-circular-polarization low-noise receiver for the Misasa 54 m parabola antenna in Misasa, Japan. The antenna is designed to be combined with a transmitter and receiver system at the X band (around 8 GHz) and simultaneously with a receiver system at the Ka band. The Ka band is the frequency band around 30 GHz, which is important for deep-space communications and radio astronomy. The receiver comprises some waveguide components including a feed horn, a circular polarizer, and low-noise amplifiers. The components are installed in a vacuum vessel and are cooled to 4 K with a Gifford–McMahon refrigerator, providing low-noise performance. The receiver is capable of simultaneously handling the left- and right-hand circular-polarization (LHCP and RHCP) channels. The receiver-noise temperature was measured to be TRX ≃ 14 K in both the LHCP and RHCP channels. The system-noise temperature, including the antenna loss and atmospheric attenuation at the zenith, was measured to be Tsys = 36–37 K in both the LHCP and RHCP channels on a clear day in September at Misasa. When the receiver is used with the X-band transmitter, the system-noise temperature is maintained at Tsys ≃ 42 K in the RHCP channel. The degradation in the system-noise temperature is attributed to a frequency-selective reflector, which divides the signals in the X and Ka bands. There is no contamination from the transmitter to damage the receiver. The receiver has already been in use for deep-space communications and radio-astronomy observations. Our team in the radio-astronomy laboratory of ISAS/JAXA is responsible for the development of the receiver and the measurements of its performance.

Lowest-threshold solar laser operation under cloudy sky condition

Classical solar-pumped lasers often demand a significant amount of concentrated solar power for laser emission, which is only attainable under clear sky condition, limiting their applicability. In this research, we report the first solar laser emission at very low threshold solar power under cloudy sky condition by end-side-pumping a 2.5 mm diameter, 25 mm length Ce:Nd:YAG rod at the focus of a parabolic mirror concentrator. The Ce:Nd:YAG solar laser performance was also evaluated under clear sky condition for comparison. Low threshold pump power of 32.4 W for continuous-wave solar-pumped laser was obtained under clear sky condition, being two times lower than the previous record. However, the cloud-filtered infrared sunlight enabled notable improvements in the solar laser performance by lessening the thermal lensing effects in the laser medium. The threshold pump power was further reduced to 29.2 W and maximum solar laser output of 14 W was successfully measured. This nearly doubled the focal slope efficiency from 4.03% during clear weather to 7.71% under a cloudy sky. The solar-to-laser conversion efficiency of 6.32% was nearly tripled compared to the 2.32% on a clear sky, while the solar laser conversion efficiency of 21.47 W/m2 was nearly twice the value of 12.62 W/m2 obtained on a clear day. This demonstrates that a cloudy environment could be an asset for solar laser research.