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排序方式: 共有296条查询结果,搜索用时 62 毫秒
1.
Optimal synthesis of tunable elastic wave-guides 总被引:1,自引:0,他引:1
Anton Evgrafov Cory J. Rupp 《Computer Methods in Applied Mechanics and Engineering》2008,198(2):292-301
Topology optimization, or control in the coefficients of partial differential equations, has been successfully utilized for designing wave-guides with precisely tailored functionalities. For many applications it would be desirable to have the possibility of drastically altering the wave-guiding properties of a device “on the fly,” in a controllable manner as an influence of some external input. This would enable wave-guides with highly non-linear input-output mappings, such as for example controllable wave switches.In this paper, we propose using finite elastic pre-straining for the purpose of tuning a wave-guide. In order to systematically formulate and solve the wave-guide synthesis problems we utilize mathematical programming methods in conjunction with topology optimization for parametrizing the design space. The resulting extremal problem is, from a practical point, equivalent to finding an optimal subdivision of a given control volume into two disjoint subsets occupied by two different materials, normally resulting in a highly heterogeneous elastic body with desired wave-guiding functionalities in the original and finitely deformed configurations.The proposed methodology is illustrated with numerical examples. 相似文献
2.
基于HOP的可调光编码/解码器的研究 总被引:1,自引:0,他引:1
提出了一种基于全息光处理器的可调光编码/解码器的实现方案。全息光处理器可以在空间进行编/解码,每个通信网络单元可以采用任意速率的数字或模拟的调制信号,它非常适合于多媒体的通信网络环境,通过对全息光处理器的折射率大小和位置的控制,当一个输入光脉冲经过光处理器中具有特定折射率的空间位置后,便可在处理器的输出端口得到合适的输出信号。本文给出了这种基于全息光处理器的可调光编码/解码器的仿真实验,结果是可行的,与以前文献中提出的结构相比,减小了硬件实现的复杂性,降低了成本和功耗,便于集成。 相似文献
3.
Facile synthesis of ordered nanocrystalline alumina thin films with tunable mesopore structures 总被引:1,自引:0,他引:1
Lijuan Wan Honggang Fu Keying Shi Xiqiang Tian 《Microporous and mesoporous materials》2008,115(3):301-307
Mesoporous alumina layers have attracted attention for their potential use in ultrafiltration of salts, as a heterogeneous catalyst support, an adsorbent in environmental cleanup, and in petroleum refinement. The ability to control the fast hydrolysis rate of the inorganic precursors using simple and inexpensive routes is important for that potential to be realized. Herein, we introduce a novel and facile route to synthesize mesoporous alumina thin films from the combination of inexpensive and commercially available copolymer with aluminum chloride or nitrate (salts) in an EtOH–surfactant–NH3 · H2O–salts (EsNs) system through the evaporation-induced self-assembly (EISA) method. Mesoporous alumina layers obtained utilizing the EsNs system have ordered and tunable pore structures. The ability to easily control the mesophases of the alumina layers within a short time provides distinct advantages over previously reported synthesis procedures. Most importantly, we demonstrate that the binding of surfactant and NH3 · H2O for the formation of hydrogen bond between them in the EsNs system controls the fast hydrolysis rate of the inorganic species. This allows for the synthesis of nanocrystalline alumina layers via the aluminum oxo-clusters’ assembly with the surfactant. Such simple route may be applied in the synthesis of other non-silica mesostructured oxides. 相似文献
4.
《Expert systems with applications》2014,41(14):6123-6130
Steganography is knowledge and art of hiding secret data into information which is largely used in information security systems. Various methods have been proposed in the literature which most of them are not capable of both preventing visual degradation and providing a large embedding capacity. In this paper, we propose a tunable visual image quality and data lossless method in spatial domain based on a genetic algorithm (GA). The main idea of the proposed technique is modeling the steganography problem as a search and optimization problem. Experimental results, in comparison with other currently popular steganography techniques, demonstrate that the proposed algorithm not only achieves high embedding capacity but also enhances the PSNR of the stego image. 相似文献
5.
Using social media in business, referred to as social business, is exploding. In reviewing past research according to brand-driving efforts for products, customers, employees, and business partners, we find a focus on benefits, with little attention to risks. Seemingly disregarded in the IS literature is the risk of electronic discovery resulting from legal actions. We categorize and exemplify risks, while analyzing the legal risk. We conclude by providing recommendations for practice and directions for future research. 相似文献
6.
7.
《Mechatronics》2022
Dynamic vibration absorber (DVA) is an effective device for suppressing resonant vibration of noisy machineries and structures. However, the optimum design of DVA requires precise tuning of the damping force in the DVA, which unfortunately is often not practical and prone to changes of working conditions. In this paper, a tunable electromagnetic shunt damper (EMSD) with different opposing magnet pairs configurations is tested for the optimum design of DVA. The optimum magnet pairs configuration is derived to provide the maximum damping force in the DVA. Both simulations and experiments are conducted to verify the damping coefficient variation with the number of magnet pairs in the EMSD. The experimental optimization procedure of the DVA is designed according to the fixed-points theory. The damping force generated by the EMSD can be readily adjusted by varying the external resistance of the EMSD. This is the first experimental implementation report of the optimization procedure described in the fixed-points theory. The proposed tunable EMSD can conveniently allow for onsite optimal tuning of DVA. The proposed design methodology provides fine tuning of the damping coefficient of EMSD to achieve robust optimal DVA performance, even when subject to changes of external parasitic damping. 相似文献
8.
In this paper, all-optical tunable filters based on two-dimensional photonic crystals with very small dimensions for optical telecommunication of WDM technology are designed and simulated. The structure is made of air holes in a dielectric background. The tuning is done by changing resonant defect angle. The channels obtained for this structure will be set in wavelength range of 1550 nm. Created channels are at wavelengths of 1550, 1551, 1552, and 1565 (16 channels); the distance between adjacent channels is 1 nm. Design and simulation of this filter is done by RSOFT software. Quality factor, transmission efficiency, and band gap shows that filter performance is very good. 相似文献
9.
《Ceramics International》2019,45(12):15048-15056
A series of europium (Eu)-activated silicon oxynitride samples with various atomic ratios x of Eu/Si from 0.001 to 0.057 was prepared by employing the polymer-derived method with polycarbosilane and Eu acetylacetonate as starting materials. Chemical compositions, phase structures, morphologies, and luminescence properties of the samples were investigated. It was found that all samples contained a dominated β-Si3N4-like phase, and had emission spectra with two peaks. The emission colors of the samples under near-UV excitation were tunable from blue to white, and then to yellow as x in the samples increased from 0.009 to 0.030, and then to 0.057. The white emitting sample with x = 0.030 was in the β-Si3N4-like single phase with its particles being single-crystallized in two space groups P63 and P63/m. Eu2+ ions located at interstitial sites of lattices and were coordinated by nine N/O atoms with different average bond lengths for the two space groups. A discussion was given to attribute the difference in the lattice environments for Eu2+ ions in two space groups P63 and P63/m to the appearance of two emission peaks at the lower (597 nm) and higher (454 nm) energy levels for the sample with x = 0.030. 相似文献
10.
《Optical Fiber Technology》2014,20(5):487-490
A dual-wavelength erbium-doped ring fiber laser is proposed and experimentally demonstrated though a detailed theoretical analysis and experimental verification. The proposed dual-wavelength erbium-doped fiber (EDF) laser, which is based on a ring fiber laser structure, is fabricated using two fiber Bragg gratings. By adjusting the gains and losses of the fiber laser structure, the laser can be switched between single- and double-wavelength modes. A saturable absorber (SA) is used to improve the output laser stability, which is further enhanced by splicing a thin core passive fiber (TCPF) into the laser cavity to produce a Mach–Zehnder filter effect. Optimizing the lengths of the SA and TCPF results in the adoption of a 1-m EDF and a 4-m passive fiber. On the basis of these enhancements and optimizations, a fiber laser with stable output is constructed that incurs single- or dual-wavelength laser shifts of less than 3 pm at room temperature over a period of 250 s. 相似文献