Design optimization of highly efficient spectrum-splitting and beam-concentrating diffractive optical element for lateral multijunction solar cells

Two improved algorithms are proposed to extend a diffractive optical element （DOE） to work under the broad spec- trum of sunlight. An optimum design has been found for the DOE, with a weighted average optical efficiency of about 6.8% better than that of the previous design. The optimization of designing high optical efficiency DOEs will pave the way for future designs of high-efficiency, low-cost lateral multijunction solar cells based on such a DOE.

The optimal thickness of a transmission-mode GaN photocathode

A 150-nm-thick CaN photocathode with a Mg doping concentration of 1.6 × 1017 cm-3 is activated by Cs/O in an ultrahigh vacuum chamber, and a quantum efficiency （QE） curve of the negative electron affinity transmission-mode （t-mode） of the GaN photocathode is obtained. The maximum QE reaches 13.0% at 290 nm. According to the t-mode QE equation solved from the diffusion equation, the QE curve is fitted. From the fitting results, the electron escape probability is 0.32, the back-interface recombination velocity is 5 ×104 cm. s^-1, and the electron diffusion length is 116 nm. Based on these parameters, the influence of CaN thickness on t-mode QE is simulated. The simulation shows that the optimal thickness of GaN is 90 nm, which is better than the 150-nm GaN.

Optimal Thermal Insulation Thickness in Isolated Air-Conditioned Buildings and Economic Analysis

The removal building heat load and electrical power consumption by air conditioning system are proportional to the outside conditions and solar radiation intensity. Building construction materials has substantial effects on the transmission heat through outer walls, ceiling and glazing windows. Good thermal isolation for buildings is important to reduce the transmitted heat and consumed power. The buildings models are constructed from common materials with 0 - 16 cm of thermal insulation thickness in the outer walls and ceilings, and double-layers glazing windows. The building heat loads were calculated for two types of walls and ceiling with and without thermal insulation. The cooling load temperature difference method, CLTD, was used to estimate the building heat load during a 24-hour each day throughout spring, summer, autumn and winter seasons. The annual cooling degree-day, CDD was used to estimate the optimal thermal insulation thickness and payback period with including the solar radiation effect on the outer walls surfaces. The average saved energy percentage in summer, spring, autumn and winter are 35.5%, 32.8%, 33.2% and 30.7% respectively, and average yearly saved energy is about of 33.5%. The optimal thermal insulation thickness was obtained between 7 - 12 cm and payback period of 20 - 30 month for some Egyptian Cities according to the Latitude and annual degree-days.

A single diffractive optical element implementing spectrum-splitting and beam-concentration functions simultaneously with high diffraction efficiency

In this paper,a novel method is proposed and employed to design a single diffractive optical element（DOE） for implementing spectrum-splitting and beam-concentration（SSBC） functions simultaneously.We develop an optimization algorithm,through which the SSBC DOE can be optimized within an arbitrary thickness range according to the limitations of modern photolithography technology.Theoretical simulation results reveal that the designed SSBC DOE has a high optical focusing efficiency.It is expected that the designed SSBC DOE should have practical applications in high-efficiency solar cell systems.

One-Dimensional Study of Thermal Behavior of Typha Panel: Spectroscopy Characterization of Heat Exchange Coefficient on Front Face

Convective heat transfer coefficients, materializing exchanges between solid wall (here typha) and its environment, influence its behavior under excitation pulse. Temperature of wall and its density of flow vary with these coefficients according to its thickness (in depth). This study therefore focuses on the evaluation of convective heat transfer coefficient on front face and the optimal insulation thickness.

Optimization of a guided-mode resonance filter by varying the thickness of the buffer layer

In this Letter, we demonstrate that by adjusting the thickness of the buffer layer, the optical responses of a guided-mode resonance filter （GMRF） can be improved for sensor applications. The GMRF is fabricated using a replica molding with a plastic substrate and a UV-curable polymer. SiO2 buffer layers of different thicknesses are deposited before the waveguide-layer deposition. The sensitivity of the GMRFs decreases slightly with in- creasing SiO2 layer thickness. By contrast, the full width at half-maximum reduces substantially with increasing SiO2 layer thickness, resulting in the improvement of the overall figure of merit.

轻质层对提高陶瓷复合装甲弹道阻力影响的理论与数值分析

陶瓷复合装甲主要由陶瓷层和背板层组成,广泛应用于冲击防护.然而,目前仍缺乏背板层在提高陶瓷复合装甲系统防弹性能方面的定量认识和分析.本文以B4C/UHMWPE双层装甲体系为例,从理论上系统地研究了UHMWPE层在提高陶瓷复合装甲弹道阻力方面的增强机理和适合UHMWPE厚度的选取.开发并验证了预测双层装甲系统剩余速度的理论模型.具体而言,分别从理论上获得与塑性、断裂和摩擦相关的耗散能以及由弹性应变能和动能组成的储存能.理论结果表明,随着UHMWPE层厚度的增加,耗散能单调增加,而储存能则先增加后减少,并会出现一个转折点,这是由于储存能的主导机制由系统固有的最大储存能转变为剩余动能.此外,对于给定的弹道阻力,根据存储能的转变提出了为降低面密度的最佳UHMWPE厚度的参考值,这与陶瓷厚度、冲击速度和弹丸质量有关.本文的研究有助于指导陶瓷复合装甲的轻量化设计.

Optimum insulation thickness of external walls by integrating indoor moisture buffering effect: a case study in the hot-summer-cold-winter zone of China

In the high-humidity, hot-summer-cold-winter(HSCW) zone of China, the moisture buffering effect in the envelope is found to be significant in optimum insulation thickness. However, few studies have considered the effects of indoor moisture buffering on the optimum insulation thickness and energy consumption. In this study, we considered the energy load of an exterior wall under moisture transfer from the outdoor to the indoor environment. An optimum insulation thickness was obtained by integrating the P1-P2model. A residential building was selected for the case study to verify the proposed method. Finally, a comparison was made with two other widely used methods, namely the transient heat transfer model(TH) and the coupled heat and moisture transfer model(CHM). The results indicated that the indoor moisture buffering effect on the optimum insulation thickness is 2.54 times greater than the moisture buffering effect in the envelope, and the two moisture buffering effects make opposing contributions to the optimum insulation thickness. Therefore, when TH or CHM was used without considering the indoor moisture buffering effect, the optimum insulation thickness of the southern wall under one air change per hour(1 ACH) and 100% normal heat source may be overestimated by 2.13% to 3. 59%, and the annual energy load on a single wall may be underestimated by 10.10% to 11.44%. The decrease of airtightness and the increase of indoor heat sources may result in a slight reduction of optimum insulation thickness. This study will enable professionals to consider the effects of moisture buffering on the design of insulation thickness.