Fossil fuel consumption for heating and cooling represents a considerable portion, approximately half, of the world’s total energy use, thereby presenting a substantial challenge in diminishing dependence on these energy sources. Our study presents the design and fabrication of a zero-energy switchable radiative cooler (ZESRC) to address the global climate crisis by reducing energy consumption within buildings. ZESRC utilizes a simple morphology-driven method that exploits materials’ differing thermal expansion coefficients, enabling a seamless switch between cooling and heating modes at any preset temperature point, enabling superior adaptive thermal management. Field experiments demonstrate that, relative to ambient temperature, ZESRC usage results in a maximum temperature decrease of 7.1°C during summer and a maximum increase of 7.5°C in winter. Furthermore, we developed an energy-efficiency map for different climate zones, showing the ZESRC’s superiority over devices with only solar heating or radiative cooling, cutting building energy use by 14.3%. The results underscore the ZESRC’s capability for net-zero energy consumption, significantly advancing global energy conservation and the 2050 net-zero carbon goal.
13.5nm femtosecond laser induced damage behaviors of Mo/Si multilayer were investigated. In this repo rt, we designed and prepared the Mo/Si mirrors for high reflectivity at 20 degrees. The laser damage test for EUV femtosecond pulses was executed at domestic soft x-ray free-electron laser facility in Shanghai. The EUV central wavelength is 13.5 nm and pulse duration is 300 fs. To understand the influence of absorption distribution in the Mo/Si multilayers, the sample was irradiated at normal incident angle for no reflection status. The damage morphologies were characterized by SEM and TEM. It is found that the most severe absorption area appears bubble-like damage, in which the first ten pairs of Mo/Si bilayer merged thoroughly and the bubble under the multilayers is located at the interface close to the substrate. The absorption distribution in the multilayers was simulated by Monto Carlo method, and that was compared with the electric field distribution simulation. We can conclude from the simulation that the damage locations are consistent with the high absorption layers in the coating stacks.
Passive radiative cooling is an environmentally friendly and energy-free cooling method, but the practical application of radiative cooling materials is still limited by high costs and cumbersome preparation processes. Here, low-cost and chemically stable polyvinylidene fluoride (PVDF) was selected as the raw material and porous P-PVDF films for daytime radiative cooling were prepared by a simple phase separation method. A solar reflectivity of 95.6% and an atmospheric window emissivity of 99.1% were obtained, resulting in high-performance radiative cooling without a metal reflective layer. A cooling power of 69.43 W · m − 2 was achieved in direct sunlight, achieving sub-ambient cooling of 4.2°C. This work provides a unique solution for radiative cooling materials, which is expected to be implemented in practical applications of passive radiative cooling.
The principle of radiative cooling is to radiate the extra heat energy of Earth into outer space, and a lot of progress has been made in recent years. Radiative cooling is significantly affected by the air quality, and coolers reported at present only work well under a clear sky. Moreover, most of the world’s industrial cities are facing serious haze problems; thus improving the cooling performance under haze conditions needs to be addressed. We propose a water evaporation assisted radiative cooling technique, and the experimental results showed a remarkable subambient cooling of 6.4°C in daytime haze.
Currently, unidirectional energy flow films mainly rely on surface plasma polarization and photonic crystals, their working bands are narrow and they are mainly used in the field of optical communication. This paper simulates and optimizes an optical array film attached with a large number of micro hemispheres. When the parallel incident light is incident from the inner side of the film (A side) to the outer side (B side), most of the incident light can pass through the film to the outer side at different angles; when the parallel incident light is incident from the outer side to the inner side, a considerable portion of the incident light returns to the outer side when the incident angles are larger than 60°. Therefore, the film will generate energy flow difference. Although the energy flow difference cannot reach 100%, the working band of the film is relatively broad. In this paper, the height and refractive index of the micro hemisphere are continuously optimized, and the maximum energy flow difference reaches up to 97.5% at the angle of 80° eventually.
Thin films have been widely used, and their preparation methods are varied. In this paper, a new type of hot pressing process is introduced to fabricate silicon dioxide thin films based on PET. The thickness of the prepared silica film is up to 40 microns, and the film is transparent. The SiO2 thin films were deposited uniformly on Polyethylene terephthalate (PET) without obvious cracks, and the films could also be crimped. The prepared silicon dioxide films have the ability of passive radiative cooling, that is, the temperature of the films can reduce to lower than that of the ambient air. It can be expected that this method is also suitable for the preparation of other thin films.
Diffraction efficiency and its uniformity are both the important performance indicators of a large-aperture pulse compression grating (PCG), and their accurate measurement is of great importance for evaluating the performance of a PCG and improving the manufacturing technique of a PCG. In this paper, based on the traditional double beam photometric measuring framework, and in combination with synchronously scanning in two-dimension the optical fiber and the detector (small size, light weight), fast measurement for the diffraction efficiency and its uniformity of a largeaperture PCG was realized. Experimental result shows that for a PCG in the size of 1400×430 mm, when the sampling intervals in both the horizontal and the vertical directions are 10 mm, the whole measurement takes about 3 hours, and a repeatability error of about 0.1% is obtained with the corresponding experiment. Compared with the currently popular measuring strategy by scanning the large-aperture PCG (large size, heavy weight), our proposed measurement system has the advantages of significantly increasing the data acquisition speed, and reducing the cost of system construction, meanwhile the safety loophole is greatly eliminated.
In optical testing, such as the fringe reflection technology and Shack-Hartman wavefront sensor technology, slope of a surface is measured instead, from which the faithful surface of the test optic is obtained. Therefore, a gradient data-based wavefront reconstruction is needed. This paper shows the use of the Gram-Schmidt process for orthonormalizing the gradients of the two-dimensional Legendre polynomials. After a set of orthonormalized vector polynomials is generated in a square region, these polynomials can be used to fit the gradient data in the region. By a simple linear transformation, the fitting coefficients can be derived and transformed to the wavefront description of the two-dimension Legendre polynomials, and the wavefront and primary aberration are then obtained. Based on the zonal method, this can effectively reconstruct the high-frequency component by fitting the difference of the high-frequency error, which cannot be done by polynomial fitting. According to the computer simulation, this algorithm can primely realize the reconstruction of wavefront.
Adrenaline (AD) plays a vital role in the functioning of the central nervous system and the cardiovascular systems. We proposed a fluorescence probe for adrenaline detection based on the modified carbon quantum dots (CQDs). Carbon quantum dots were synthesized by the hydrothermal method, in which citric acid was used as a carbon source, and then modified with ammonia solution. Fluorescence spectrophotometer, transmission electron microscope and Fourier infrared spectroscopy were used to characterize the modified CQDs, respectively. CQDs modified with ammonia have strong fluorescence intensity and emit blue light under ultraviolet light. The adrenaline was related to the quenching fluorescence of CQDs, which was caused by the electron transfer between CQDs and adrenaline quinone under alkaline conditions. The optimum pH value and reaction time of the adrenaline detection used by CQDs were determined to be 10.14 and 300 seconds, respectively. A good linear dependence between the fluorescence intensity ratio of the CQDs and adrenaline concentration(10~100uM) was found after the introduction of a modified Stern-Volmer equation.
We propose a novel absorber with over 90% absorption and is not sensitive to polarization at mid-infrared frequencies (from 31.37 THz to 34.14 THz, 2.77 THz broadwith). The structure of the graphene absorber is special in that it has MgF2 and SiO2 multilayer stacking unit cells and arrayed on an Au film plane, which can be easy to fabricate under current manufacturing technology. We can adjust the position of the absorption bands by tuning the Fermi energy without changing the geometric parameters of the complex three-dimensional structure. The tunability of this metamaterial absorber can be achieved via changing the external gate voltage to modify the Fermi energy of graphene. Simulation results demonstrate that the absorption efficiency of the proposed structure can be as high as more than 90% from 28.7THz to 34.14 THz with variation of the Fermi energy from 1.6 eV to 2.0 eV. At the same time, we can also change the Fermi energy to achieve high absorption or high reflection of the absorber.
Graphene has been reported to show polarization-dependent optical absorption in the visible spectral range, that it shows more absorption for s-polarized light than p-polarized light. We study further on it and demonstrate that this unique property can be utilized to design a fiber optic sensor, which works in a similar way of surface plasmon resonance (SPR) fiber optic sensor. However, they are based on different mechanisms. Numerical simulation reveals that graphene layer of 5 nm is appropriate for the fiber optic sensor to achieve its best sensing performance, with a high sensitivity from 1700 to 6900 nm/RIU (refractive index unit).
Aiming at the problem that the damage threshold of gold coated grating is relatively low, a dielectric film is considered on the gold coated gratings as a protective layer. The thickness range of the protective layer is determined under the prerequisite that the diffraction efficiency of the gold coated grating is reduced to an acceptable degree. In this paper, the electromagnetic field, the temperature field and the stress field distribution in the grating are calculated when the silica and hafnium oxide are used as protective layers, under the preconditions of the electromagnetic field distribution of the gratings known. The results show that the addition of the protective layer changes the distribution of the electromagnetic field, temperature field and stress field in the grating, and the protective layer with an appropriate thickness can improve the laser damage resistance of the grating.
Particle stacking structured SiO2 porous films were prepared by sol-gel method. A model has been established to analyze
the heat conductivity of these films. It is assumed that the heat energy mainly transfers through particles and their contact
points. In particle stacking structured materials, a particle contacts with twelve contiguous particles, and forms twelve
heat conduction branches. This model is suit to the conditions that: the size of particles in the porous material is uniform;
heat conductivity of particle skeleton is much greater than particle clearance; and all contact area between particles
approximately equal. The results show that: heat conductivity of particles stacking porous material is anisotropic,
material heat conductivity depends on that of the particle skeleton and the ratio between radiuses of particle contact area
and particle itself.
KEYWORDS: Etching, Electron beams, Coating, Tablets, Thin films, Atmospheric particles, Optical spheres, Particles, High power lasers, System on a chip
Coating material has been considered as being made up of a lot of small tablets. These tablets have plane surface during the whole film
preparation process. Based on the assumption that a column etching pit will form in coating material when electron beam is used for heating,
influences of the etching pit's dimension and the internal structure of the vacuum chamber on films thickness uniformity have been
investigated. Results reflect that the appearance of etching pit does not always cause negative influence on films thickness uniformity. The
negative impact of etching on films thickness uniformity can be reduced by optimizing the internal structure of the vacuum chamber and
preparation technical parameters. But, it is difficult to achieve the beneficial action. This investigation is useful to help us understand physical
meaning of the emission characteristics of the evaporation particle and design experimental scheme.
The conditions that the droplet's thermodynamic parameters change with time have been calculated, and the contrast between them when
different laser pulse patterns are selected have been analyzed accordingly. The results show that: Two atomization processes are formed, and
the second one is not evident for the case of gaussian distribution laser pulse. The change trend of the time-related expansion velocity is first
increased, then decreased for the case of flat top distribution laser pulse, and is first increased, then maintained for the case of gaussian
distribution laser pulse. The expansion process displays a stable stage in which the expansion velocity fluctuates slightly after atomization for
the case of gaussian distribution laser pulse. In the terminal phase of the laser pulse, negative expansion acceleration appears for the case of flat
top distribution laser pulse. The time-related temperature variations are more complicated for the case of flat top distribution laser pulse.
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