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Spectrally selective approaches for passive cooling of solar cells: A review
摘要： Waste heat is generated in solar cells during the daytime because they operate with a limited electrical efficiency. Moreover, the generated heat increases the solar cells’ operating temperature, and this has an adverse effect on their electrical efficiency. Therefore, numerous cooling methods have been developed to cool solar cells, such as forced air/water flow, hybrid photovoltaic/thermal system, and phase change material based photovoltaic application. Recently, a novel concept of changing the solar cells’ spectral response to both sunlight and thermal radiation has been proposed and developed to provide a passive cooling method for solar cells, which has drawn much attention from materials science to engineering fields. In this paper, the recent advancements of such a spectrally selective approach to passively cool solar cells, including radiative cooling of solar cells and full-spectrum thermal management of solar cells are reviewed, analyzed, and discussed from fundamental principles to detailed demonstration. Furthermore, the technical challenges involved in developing this new cooling technology are discussed. This paper is devoted to give a systematic introduction to a new passive cooling technology for solar cells by controlling the spectral property of solar cells, aiming to open a new opportunity for solar cells’ cooling.
关键词： Radiative cooling,Thermal management,Spectrally selective filter,Solar cells,Passive cooling,Thermal radiation
更新于2025-09-19 17:13:59
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Laser-Cooled Polyatomic Molecules for Improved Electron Electric Dipole Moment Searches
摘要： Doppler and Sisyphus cooling of 174YbOH are achieved and studied. This polyatomic molecule has high sensitivity to physics beyond the Standard Model and represents a new class of species for future high-precision probes of new T-violating physics. The transverse temperature of the YbOH beam is reduced by nearly two orders of magnitude to < 600 μK and the phase-space density is increased by a factor of > 6 via Sisyphus cooling. We develop a full numerical model of the laser cooling of YbOH and ?nd excellent agreement with the data. We project that laser cooling and magneto-optical trapping of long-lived samples of YbOH molecules are within reach and these will allow a high sensitivity probe of the electric dipole moment (EDM) of the electron. The approach demonstrated here is easily generalized to other isotopologues of YbOH that have enhanced sensitivity to other symmetry-violating electromagnetic moments.
关键词： polyatomic molecules,electron electric dipole moment,laser cooling,Sisyphus cooling,YbOH
更新于2025-09-19 17:13:59
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A dominant factor of the cycloreversion reactivity of diarylethene derivatives as revealed by femtosecond time-resolved absorption spectroscopy
摘要： Dynamics of the cycloreversion reaction of a photochromic diarylethene derivative with a small ring-opening reaction yield (～1%) was investigated by using femtosecond transient absorption spectroscopy. The reaction rate constant and activation barrier on the reaction coordinate were quantitatively analyzed on the basis of the temperature and excitation wavelength dependencies of the reaction yield and excited state dynamics. From the comparison of the present results with those in a more reactive derivative, we concluded that a key factor regulating the overall reaction yield is the branching ratio at the conical intersection where the excited state population is split into the product and the initial reactant. The excitation wavelength dependence of the dynamics indicated that the geometrical relaxation and vibrational cooling proceed in a few picosecond time scale behind the cycloreversion process, and the vibrational excess energy assists the molecule to climb up the energy barrier.
关键词： vibrational cooling,diarylethene derivative,photochromic,femtosecond transient absorption spectroscopy,cycloreversion reaction
更新于2025-09-19 17:13:59
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Investigations of the possible second-stage laser cooling transitions for the holmium atom magneto-optical trap
摘要： In this work laser-spectroscopic investigations of selected electronic levels in the holmium atom are performed in the context of possible second-stage laser cooling transitions which can be considered in a magneto-optical trap. Five transitions were directly recorded by the method of laser induced fluorescence in a hollow cathode discharge. The hyperfine structure constants A and B for the upper even-parity J = 17 / 2 levels, evaluated in earlier works, were generally confirmed, and their accuracy was improved; thus the frequency differences between the hyperfine structure components, relevant for the possibility of application of the hyperfine repumping, could be determined. Investigations of the Zeeman-hyperfine structure of these spectral lines were performed in order to evaluate the Landé g J factors of the upper levels; these were reported for the first time. Semi-empirical preliminary calculations of the lifetimes of the even-parity levels in question were also carried out, allowing estimation of the expected Doppler limits for the possible narrow-band laser cooling at the respective transitions. The degree of similarity between the g J factors of the upper levels of the cooling transitions and the ground state is important for the efficiency of the sub-Doppler laser cooling in a magneto-optical trap. The results presented might facilitate the choice of the most favorable option of obtaining narrow-band laser cooling of the holmium atoms.
关键词： Landé factors,Hyperfine structure,Laser cooling,Laser spectroscopy,Holmium,Electronic levels’ lifetimes
更新于2025-09-19 17:13:59
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The effect of temperature distribution and cooling rate on microstructure and microhardness of laser re-melted and laser-borided carbon steels with various carbon concentrations
摘要： Laser heat treatment was arranged as a laser remelting and laser boriding. Materials with different carbon concentration were used. Three zones characterized the microstructure after laser treatment: re-melted zone (MZ), heat-affected zone (HAZ) and substrate material. The differences in carbon content and physical properties of used materials influenced the obtained microstructure, temperature distribution and hardness. In case of laser re-melted specimens, the limited martensite transformation proceeded only in C20, C45 and C90 steels. As a result of laser boriding the microstructure of MZ contained additionally iron borides. The specimens with higher dilution ratio value was characterized by higher hardness of re-melted zone. The aim of this study was to indicate the possibility of predicting the microstructure and depths of MZ and HAZ with the usage of Ashby and Esterling model. The influence of carbon concentration in steel on the thickness, dilution ratio and hardness of laser-borided layers was determined.
关键词： microhardness,laser remelting,temperature distribution,laser boriding,cooling rate,microstructure
更新于2025-09-19 17:13:59
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Laser-induced fluorescence and dispersed-fluorescence spectroscopy of the ?2E?X?2A1 transition of jet-cooled calcium methoxide (CaOCH <sub/>3</sub> ) radicals
摘要： Laser-induced fluorescence (LIF) and dispersed fluorescence (DF) spectra of the ?A2E ? ?X2A1 electronic transition of the calcium methoxide (CaOCH3) radical have been obtained under jet-cooled conditions. Complete active space self-consistent field and coupled-cluster calculations on the free radical were performed to aid the assignment of vibronic transitions observed in the LIF/DF spectra. In addition to dominant spectral features that are well reproduced by vibrational frequencies and Franck-Condon (FC) factors calculated ab initio, the FC matrix for the ?A2E ? ?X2A1 electronic transition contains considerable off-diagonal elements that connect (i) the CaO-stretch (ν4) mode and non-CaO stretch modes and (ii) the asymmetric CaOC stretch (ν3) and the CaOC bending (ν8) modes. The Jahn-Teller and pseudo-Jahn-Teller interactions involving the ?2E state as well as the spin-orbit interaction induce additional vibronic transitions that are not allowed under the Born-Oppenheimer approximation. Additionally, anharmonic vibrational terms in the ground state induce transitions that are forbidden in the harmonic-oscillator approximation. Spin-orbit splitting has been observed for several vibrational levels of the ?2E state, and an essentially constant value was measured at all levels accessed in the LIF experiment. Implications of the present spectroscopic investigation to the proposed schemes of laser-cooling MOCH3 (M = alkaline earth metals) molecules and detection of time-reversal-symmetry-violating interactions are discussed.
关键词： calcium methoxide,laser cooling,spin-orbit interaction,Jahn-Teller effect,Franck-Condon factors,vibronic transitions,CaOCH3,Laser-induced fluorescence,pseudo-Jahn-Teller effect,dispersed-fluorescence spectroscopy
更新于2025-09-19 17:13:59
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[IEEE 2019 International Conference on Engineering, Science, and Industrial Applications (ICESI) - Tokyo, Japan (2019.8.22-2019.8.24)] 2019 International Conference on Engineering, Science, and Industrial Applications (ICESI) - Wear Resistance Behaviour of Laser Additive Manufacture Materials: An Overview
摘要： Laser additive manufacturing technology is an exciting technology which is based on powder metallurgy and laser technologies that has come to revolutionize the way important product are designed and produced. This manufacturing technology has a number of advantages over the traditional manufacturing processes which include: ability to reduce weight of product and with improved functionality, ability to manufacture part as a composite material and with high complexity in a single manufacturing process. Some of additive manufacturing process can also be used to repair high valued part. Apart these advantages, additive manufacturing technologies have been shown to have a high impact on the resulting properties of the manufactured materials which include the wear resistance behaviour. This paper presents an overview of the wear resistance behaviour of additive manufacture materials. The various classes of additive manufacturing technology are analyzed and presented. This study revealed that the wear resistance property of materials processed using additive manufacturing technologies can be improved by adjusting the processing parameters. Also the rapid cooling that is associated with this manufacturing process has a great influence in improving the wear resistance performance of the processed materials.
关键词： wear resistance,Laser additive manufacturing,processing parameters,rapid cooling,additive manufacture materials
更新于2025-09-19 17:13:59
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Thermo-optic and spectroscopic properties of Yb:GAGG, Nd:GAGG and Nd:GGG laser materials at cryogenic temperature
摘要： The solid-state lasers provide an attractive approach to enhance the laser performance benefitting from significant improvements in both thermo-optic and spectroscopic properties of the gain mediums under cryogenic temperature. Here, thermo-optic properties of Yb:Gd3(AlxGa1-x)5O12 (Yb:GAGG) and Nd:Gd3(AlxGa1-x)5O12 (Nd:GAGG) laser crystals, including thermal conductivity (κ), thermal expansion coefficient (α) and specific heat at constant pressure (Cp) were measured from 77 to 298 K. In addition, the thermal shock resistance parameters were also calculated. The spectroscopic properties and the fluorescence lifetimes of laser gain mediums Yb:GAGG, Nd:GAGG and Nd:Gd3Ga5O12 (Nd:GGG) were characterized at 77, 150, 298 K. The stimulated emission cross sections of these laser materials were determined by use of the Füchtbauer-Ladenburg (FL) formula at each temperature.
关键词： GGG,cryogenic cooling,GAGG,spectroscopic properties,thermal properties,Neodymium,Ytterbium
更新于2025-09-19 17:13:59
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A Photovoltaic Greenhouse with Passive Variation in Shading by Fixed Horizontal PV Panels
摘要： The traditional shading systems that greenhouses use cause some of the solar radiation that is re?ected or absorbed to be lost and, therefore, not used by the plants under cultivation. An interesting solution to these problems is to position photovoltaic (PV) panels on the roofs of greenhouses. All of the photovoltaic greenhouses that have been realized in Mediterranean areas are characterized by a ?xed position of the PV panels and excessive shading, especially in autumn and winter. The purpose of this study is to describe a prototype of a photovoltaic greenhouse with both ?xed and horizontal PV panels that exploit the natural variation in the elevation angle of the sun’s rays during the year to allow for “passive” variation in shading. The considerable variation in the elevation angle of the sun’s rays (from 24.4° to 71.1°) results in a high variation in shading (from 39.4% to 72.6%), with the highest values in the summer months and the lowest values in the winter months. This trend is favorable for meeting the photosynthetically active radiation (PAR) needs of greenhouse plants. If the plants under cultivation require more solar energy, it is necessary to increase the distance between the panels. We implement a speci?c mathematical relationship to de?ne the precise distance to be assigned to the photovoltaic panels on the roof pitch.
关键词： ?xed horizontal PV panels,passive variation of shading,passive cooling system,PAR,renewable source
更新于2025-09-19 17:13:59
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Influence of Solidification Conditions on the Microstructure of Laser-Surface-Melted Ductile Cast Iron
摘要： The thermal conditions in the molten pool during the laser surface melting of ductile cast iron EN-GJS-700-2 were estimated by using infrared thermography and thermocouple measurements. The thermal data were then correlated with the microstructure of the melted zone. Additionally, the thermodynamic calculations of a Fe-C-Si alloy system were performed to predict the solidification path of the melted zone. It was found that increasing the cooling rate during solidification of the refined ledeburite eutectic but also suppressed the martensitic transformation. A continuous network of plate-like secondary cementite precipitates and nanometric spherical precipitates of tertiary cementite were observed in regions of primary and eutectic austenite. The solidification of the melted zone terminated with the Liquid → γ-Fe + Fe3C + Fe8Si2C reaction. The hardness of the melted zone was affected by both the fraction of the retained austenite and the morphology of the ledeburite eutectic.
关键词： laser surface melting,ductile cast iron,cooling rate,thermography,tertiary cementite,secondary cementite
更新于2025-09-19 17:13:59