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The influence of morphological distribution of melanin on parameter selection in laser thermotherapy for vascular skin diseases
摘要： Port wine stains (PWSs) are congenital vascular malformations that progressively darken and thicken with age. Currently, laser therapy is the most effective way in clinical management of PWS. It is known that skin pigmentation (melanin content) affects the radiant exposure that can be safely applied to treat PWS. However, the effect of melanin distribution in the epidermis on the maximum safe radiant exposure has not been studied previously. In this study, 10 different morphological distributions of melanin were proposed according to the formation and migration characteristics of melanin, and the two-scale heat transfer model was employed to investigate the influence of melanin distribution on the threshold radiant exposure of epidermis and blood vessels. The results show that melanin distributions do have a strong effect on laser parameter selection. When uniform melanin distribution is assumed, the threshold radiant exposure to damage a typical PWS blood vessel (50 μm diameter) is 8.62 J/cm2 lower than that to injure epidermis. The optimal pulse duration is 1–5 ms for a typical PWS blood vessel of 50 μm when melanin distribution is taken into consideration. PWS blood vessels covered by non-uniformly distributed melanin are more likely to have poor response to laser treatment.
关键词： Port wine stains,Melanin distribution,Two-scale model,Cryogen spray cooling,Laser treatment
更新于2025-09-12 10:27:22
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Laser refrigeration of gas filled hollow-core fibres
摘要： We evaluate prospects, performance and temperature limits of a new approach to macroscopic scale laser refrigeration. The considered refrigeration device is based on exciplex-mediated frequency up-conversion inside hollow-core fibers pressurized with a dopant - buffer gas mixture. Exciplexes are excited molecular states formed by two atoms (dopant and buffer) which do not form a molecule in the ground state but exhibit bound states for electronically excited states. The cooling cycle consists of absorption of laser photons during atomic collisions inducing light assisted exciplex formation followed by blue-shifted spontaneous emission on the atomic line of the bare dopant atoms after molecular separation. This process, closely related to reversing the gain mechanism in excimer lasers, allows for a large fraction of collision energy to be extracted in each cycle. The hollow-core fiber plays a crucial role as it allows for strong light-matter interactions over a long distance, which maximizes the cooling rate per unit volume and the cooling efficiency per injected photon while limiting re-absorption of spontaneously emitted photons channeled into unguided radiation modes. Using quantum optical rate equations and refined dynamical simulations we derive general conditions for efficient cooling of both the gas and subsequently of the surrounding solid state environment. Our analytical approach is applicable to any specific exciplex system considered and reveals the shape of the exciplex potential landscapes as well as the density of the dopant as crucial tuning knobs. The derived scaling laws allow for the identification of optimal exciplex characteristics that help to choose suitable gas mixtures that maximize the refrigeration efficiency for specific applications.
关键词： quantum optical rate equations,exciplex-mediated frequency up-conversion,laser refrigeration,hollow-core fibers,cooling efficiency
更新于2025-09-12 10:27:22
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Candidate for Laser Cooling of a Negative Ion: High-Resolution Photoelectron Imaging of
摘要： Laser cooling is a well-established technique for the creation of ensembles of ultracold neutral atoms or positive ions. This ability has opened many exciting new research fields over the past 40 years. However, no negatively charged ions have been directly laser cooled because a cycling transition is very rare in atomic anions. Efforts of more than a decade currently have La? as the most promising candidate. We report on experimental and theoretical studies supporting Th? as a new promising candidate for laser cooling. The measured and calculated electron affinities of Th are, respectively, 4901.35e48T cm?1 and 4832 cm?1, or 0.607 690(60) and 0.599 eV, almost a factor of 2 larger than the previous theoretical value of 0.368 eV. The ground state of Th? is determined to be 6d37s2 4Fe 5=2. The consequence of this there are several strong electric dipole transitions between the bound levels arising from configurations 6d37s2 and 6d27s27p in Th?. The potential laser-cooling transition is 2So 3=2 with a wavelength of 2.6 μm. The zero nuclear spin and hence lack of hyperfine structure in Th? reduces the potential complications in laser cooling as encountered in La?, making Th? a new and exciting candidate for laser cooling.
关键词： Laser cooling,photoelectron imaging,electron affinity,Th?,negative ion
更新于2025-09-12 10:27:22
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A new production cost effectiveness factor for assessing photovoltaic module cooling techniques
摘要： Numerous cooling techniques are available to reduce photovoltaic module (PV) temperature and thus improve PV efficiency. Sometimes, the manufacturing cost of some PV cooling techniques is higher as compared with their power productivity, and thus the cost parameter is needed to be taken into consideration to justify producing certain PV cooling techniques. This paper is intended to link the manufacturing cost of the PV cooler with its output power by providing an economic analysis as there is a research gap in previous studies related to the economic aspect of these products. It proposes a new method by defining and deriving a new parameter called the PV cooling technique production cost effectiveness factor whose value is affected by the PV efficiency gained of a PV with and without a cooler, the manufacturing cost of the PV cooling technique, and the cost of one watt of PV power. Based on the value of this new factor, three possible classifications are suggested. They are production/not production cost effective or neutral. To determine the optimum PV cooler, the minimum value of the PV cooling technique production cost effectiveness factor is defined. The applicability conditions and limitations of the proposed method are illustrated. It is shown that the PV cooling technique production cost effectiveness factor and its minimum value are helpful in classifying the PV cooling techniques based on their power productivity and manufacturing cost. This parameter may have a potential to be used by PV cooling technique designers and manufacturers on making their design decisions.
关键词： manufacturing cost,photovoltaic module,photovoltaic efficiency,PV cooling technique,PV cooling technique production cost effectiveness evaluation
更新于2025-09-11 14:15:04
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High-performance subambient radiative cooling enabled by optically selective and thermally insulating polyethylene aerogel
摘要： Recent progress in passive radiative cooling technologies has substantially improved cooling performance under direct sunlight. Yet, experimental demonstrations of daytime radiative cooling still severely underperform in comparison with the theoretical potential due to considerable solar absorption and poor thermal insulation at the emitter. In this work, we developed polyethylene aerogel (PEA)—a solar-reflecting (92.2% solar weighted reflectance at 6 mm thick), infrared-transparent (79.9% transmittance between 8 and 13 mm at 6 mm thick), and low-thermal-conductivity (kPEA = 28 mW/mK) material that can be integrated with existing emitters to address these challenges. Using an experimental setup that includes the custom-fabricated PEA, we demonstrate a daytime ambient temperature cooling power of 96 W/m2 and passive cooling up to 13°C below ambient temperature around solar noon. This work could greatly improve the performance of existing passive radiative coolers for air conditioning and portable refrigeration applications.
关键词： subambient cooling,solar reflectance,thermal insulation,polyethylene aerogel,radiative cooling
更新于2025-09-11 14:15:04
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Ideal Laser Cooling Efficiency Utilizing Anti-Stokes Luminescence in Yb-Doped Yttrium Aluminum Garnet Powder Crystals; Yb添加イットリウムアルミニウムガーネット結晶粉末におけるアンチストークス発光を利用した理想レーザー冷却効率;
摘要： Laser cooling in rare-earth doped material using anti-Stokes photoluminescence (PL) caused by phonon annihilation realizes novel cooling devices without generating heat and vibration. Yb-doped yttrium aluminum garnet powder crystals, (Y:Yb)AG with the Yb concentration from 2 to 13 mol%, were fabricated by a solid state reaction method. PL of (Y:Yb)AG excited at 659 nm shows the maximum intensity at the Yb concentration of 6 mol% because of concentration quenching of the PL. When we resonantly excite at 1030 nm corresponding to the energy distance between the E5 and E3 levels of the f-f transition of Yb3+, obvious anti-Stoke PL signal has been observed at 968 nm. This result indicates that phonons are absorbed, and, then, an up-converted photon with the energy between the E5 and E1 levels is emitted. The relative cooling efficiency, defined by a product of the ideal cooling efficiency and the integrated PL intensity, becomes maximum at the 1030-nm excitation. The ideal cooling efficiency was estimated to be 1.9% at the Yb concentration of 6 mol% and the 1030-nm excitation at room temperature.
关键词： Self-absorption,Solid state reaction,Phonon absorption,(Y:Yb)AG,Rare-earth,Laser cooling in solids
更新于2025-09-11 14:15:04
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AIP Conference Proceedings [AIP Publishing 15th International Conference on Concentrator Photovoltaic Systems (CPV-15) - Fes, Morocco (25–27 March 2019)] 15th International Conference on Concentrator Photovoltaic Systems (CPV-15) - Finite element analysis of cooling mechanism by flat heat-sinks in ultra-high CPV systems
摘要： The potential cost reduction of Concentrator photovoltaic (CPV) systems is closely related to the concentration factor because higher light concentrations imply lower amount of semiconductor material required for the solar cells. However, the thermal management at such ultra-high light fluxes is difficult. The use of small-sized solar cells is beneficial for improving the thermal management. Among the possible cooling strategies, the use of flat-plate heat-sinks for passive cooling, if feasible, would be the simplest way to dissipate heat and would accelerate the development of ultra-high CPV prototypes. In this work, a thermal 3D finite-element model is used to investigate the possibilities of flat-plate heat-sinks for passive cooling at concentration ratios within 2,000-10,000 suns. Results show that a micro solar cells of 1mm x 1mm area can be thermally handled with conventional Aluminium flat plate heat-sinks up to 10,000 suns.
关键词： ultra-high concentration,passive cooling,Concentrator photovoltaic (CPV),thermal management,flat-plate heat-sinks
更新于2025-09-11 14:15:04
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Improving Performance of a Photovoltaic Panel by Pin Fins: A Theoretical Analysis
摘要： As efficiency of PV modules decreases with temperature rise, cooling methods can increase the power output and efficiency. One of the strategies for this purpose is passive cooling by implementing fins to the backside of a module. In the present study, annual energy output of a 50 W panel is analytically calculated in two unfinned and pin-finned cases based on hourly meteorological data for Shiraz, Iran. The results show that with the installation of 2-cm, 4-cm and 6-cm aluminum pin fins with finned-to-total-backside-area ratios of 0.17, 0.27 and 0.55, the power output increases by 1.24–4.16%, compared to the unfinned case. This increase is equivalent to 1.04–3.50 kWh more electrical energy production during a year.
关键词： Fin,Photovoltaic panels,Passive cooling,Solar energy
更新于2025-09-11 14:15:04
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Advanced Cooling Technologies and Applications || Development of Modular Cooling for Water-Cooled Photovoltaic Plant in Real Scale
摘要： This chapter evaluates module architectures and units of photovoltaic cooling systems, aiming to determine, select and design a modular system that can be applied in a real-scale photovoltaic power plant (PVPP) in order to enhance the yields of electricity production (entitled cooled photovoltaic plant). An analysis of the local climatic, geographic and solar conditions as well as construction, operational and maintenance aspects was carried out. Worldwide, there are three main types of cooled photovoltaic systems: PVT liquid and air collectors, PV ventilated with heat recovery and non-PVT systems. Based on the local weather conditions (tropical warm and dry) with both temperature and solar irradiation index being high, it results the PVT-liquid system to be more suitable in a scenario with available cooling fluid. We conclude that the best design and arrangement of the cooling system are of the type coil and multiple channel because they permit better rates of heat exchange between the cooling fluid and the PV module.
关键词： solar energy,cooling photovoltaic system,photovoltaic/thermal,PVPP,SFV
更新于2025-09-11 14:15:04
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An ultrastable laser system at 689 nm for cooling and trapping of strontium
摘要： We present a 689-nm cavity-based laser system for cooling and trapping strontium atoms. The laser is stabilized to a high-finesse cavity by the Pound–Drever–Hall technique, exhibiting a frequency stability in the 10?14 range for averaging times up to 100 s. A cavity drift of 8 kHz per day is mapped out and compensated. At short times, the laser exhibits a linewidth of a few kilohertz. With this laser system, we realize a magneto-optical trap of strontium operated on the narrow inter-combination transition yielding sub-microkelvin temperatures, and demonstrate absorption spectroscopy on the strontium inter-combination line.
关键词： cooling and trapping,magneto-optical trap,strontium,Pound–Drever–Hall technique,ultrastable laser
更新于2025-09-11 14:15:04