Conventional multi-antenna receiver front-ends require multiple RF/baseband chains and analog-to-digital converters (ADC). This increases power consumption and chip area substantially. In this letter, we introduce a new Code-Modulated Path-Sharing Multi-Antenna (CPMA) receiver architecture suitable for any multi-antenna scheme including spatial multiplexing, spatial diversity, and beamforming. The receiver uses code modulation to distinguish the antenna signals before combining them in the analog domain. The combined signal propagates through shared-path blocks and all the original signals are later recovered in the digital domain for further processing. Due to the spread spectrum nature of code modulation, a larger bandwidth is needed for the blocks in the shared path. To alleviate this effect, the use of non-orthogonal coding is examined. An effective channel matrix is derived and the system capacity is evaluated in terms of the cross-correlation between signature codes. Implementation and code selection issues are discussed. Analysis and simulation results indicate that by properly selecting non-orthogonal code sets, the spreading factor, and therefore, the overall analog signal bandwidth is reduced while incurring minimal performance degradation. 相似文献
In this paper, the ultra-short pulsed laser treatment is numerically simulated for a focused laser beam applied to a cylindrical domain. To do so, the general form of the variable-order fractional-order, dual-phase lag bioheat transfer equation is implemented. To determine the major affecting parameters, the dimensionless form of the heat equation is derived and solved numerically. An efficient method based on the 2D Legendre wavelets is developed to provide a numerical solution for this variable-order time fractional model. The man advantage of the proposed algorithm is that it converts the solution of the problem into solution of a system of algebraic equations. The validity of the formulated method is investigated through one numerical example. The effect of several operational and thermo-physical properties including the phase lag time, fractional order, and the duration of active laser beam in each on/off cycle on the thermal field and heat penetration depth is examined. According to the results, it is concluded that by increasing the fractional order from 0.1 to 0.9, 65.1% increase in the penetration length occurs.
In this study, large band gap zinc oxide nanoparticles (ZnO-NPs) were prepared by a facile, cost-effective, and eco-friendly co-precipitation method in aqueous solutions. Trisodium citrate was employed as a green and bio-safe complexing agent for zinc ions without using ammonia and/or any organic solution. The annealing effect on crystal structure, morphology, particle size, composition, UV absorption, and fluorescence (FL) properties of the synthesized ZnO-NPs was evaluated using various techniques. The UV–Visible absorption spectra of the ZnO-NPs showed a strong absorption peak in the UV-C region with a wide band gap energy of 4.2–4.4 eV. Field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) images demonstrated fine spherical particles with approximate diameters of 20–50 nm. The average hydrodynamic diameter and zeta potential values of the as-prepared and the annealed ZnO-NPs in deionized water were 28.2 nm, ? 32.4 mV, 38.9 nm, and ? 16.1 mV, respectively. The FL and UV–Visible results illustrated that the annealing could considerably influence the emission and absorption spectra of the samples in the UV region. The FL and EDX results revealed that the annealing affects the composition, defect points, and states population in the crystal structure of the ZnO-NPs. Practical experiments of exposing the samples to UV radiation and the FL measurements indicated that the ZnO-NPs were sensitive to the excitation wavelengths, therefore, they have potential application in fabricating various types of UV sensors and filters (blockers), as well as photocatalytic activities.
In this paper, a new class of two‐dimensional nonlinear variable‐order fractional optimal control problems (V‐OFOCPs) is introduced where the variable‐order fractional derivative is defined in the Caputo type. The general procedure for solving theses systems is expanding the state variable and the control variable based on the Legendre cardinal functions in the matrix form. Hence, we derive their operational matrix of derivative (OMD) and operational matrix of variable‐order fractional derivative (OMV‐OFD). More significantly, some properties of these basis functions are proved to be exploited in our approach. Using these achieved results, we simply expand the matrix form of the nonlinear performance index in terms of the Legendre cardinal functions and subsequently convert it to an algebraic equation. We emphasize that it is a valuable advantage of applying cardinal functions in approximation theory. Then, we implement the OMD and the OMV‐OFD of the Legendre cardinal functions to transform the variable‐order fractional dynamical system to a system of algebraic equations. Next, the method of constrained extremum is applied to adjoin the constraint equations including the given dynamical system and the initial‐boundary conditions to the performance index by a set of undetermined Lagrange multipliers. Finally, the necessary conditions of the optimality are derived as a system of nonlinear algebraic equations including the unknown coefficients of the state variable, the control variable and the Lagrange multipliers. The applicability and efficiency of the proposed approach are investigated through the various types of test problems. 相似文献
A spacecraft in orbit undergoes extreme temperature cycling, space radiations, and other extreme conditions that can potentially raise the temperature of spacecraft to harmful levels. Hardware and sensitive detectors utilized in spacecrafts require that temperatures be maintained within specified ranges. Thermal control coatings (TCCs) help to maintain the thermal equilibrium of the spacecraft at a level acceptable for vital components. This is done by employing the diffused reflection of all effective ultraviolet (UV), visible (VIS), and near-IR (NIR) wavelengths of solar radiation and emitting the infrared (IR) energy. The most commonly used TCCs have utilized potassium silicate as the binder and ZnO as the pigment (Z-93), but absorption of UV light by ZnO pigment affects the ideal scheme of these TCCs. In the present study, silica-supported zinc oxide particles with different ZnO contents were synthesized as pigments for white thermal control coatings and the optimized one was selected based on the experimental determination of the optical properties of the prepared coatings. The results revealed that the optimized TCCs containing pigment with the zinc to silicon ratio of 1.91 had better reflection and emission properties in comparison with Z-93, due to the improvement in the refractive index and the dispersion quality of pigment. Then, the scattering properties (S) of the synthesized pigments and ZnO in TCC were investigated based on the reflectance data, according to the Kubelka–Munk analysis. The general trend in scattering coefficients for each formulation showed the same shape, such that with the increase in S values, the zinc to silicon ratio of pigments was raised too. Also, this trend revealed that scattering was more efficient at longer rather than shorter wavelengths. For Z-93, this trend was completely opposite. Also, S values for Z-93 in the wavelength range of 200–400 nm were around zero, while for the prepared coatings, this was not the case. Finally, the statistical nonlinear regression method was utilized to prepare a model for reflectance as a function of the zinc to silicon ratio of pigments and the wavelength of light. 相似文献
Industrialized countries have provided heavy funding for nanotechnology and made its development a priority. Some applications are entering the market and prominent scientists have assessed nanotechnology as a potentially wonderful phenomenon [1]. The worldwide investment in nanotechnology research and development (R&D) by government organizations has increased from $432 million in 1997 to about $4.1 billion in 2005 [2]. Several developing countries also have launched nanotechnology initiatives in order to exploit its benefits and sustain economic growth [3]. But the national issues and problems of developing countries are totally different from those of industrialized countries. Poverty, unemployment, inequality, and inability to fulfill basic needs are common problems in developing countries [4]. On the other hand, industrialized countries are faced with problems like aging populations, collapsing birth rates, unemployment, security issues, and cultural chaos [5]. There are also problems that are shared, such as environmental degradation, air and water pollution, exhaustion of natural resources, and incurable illnesses [3], [5]. From the beginning, nanotechnology pioneers have suggested they will solve these problems and that they will achieve social goals through nanotechnology's development [6]. In 2001, Iran also established a council for the development of nanotechnology and started formulating a nanotechnology development plan. The country faces both opportunities and threats with respect to nanotechnology. This article presents four possible scenarios for nanotechnology in Iran, and evaluates the effectiveness of these different strategies for nanotechnology development in the country. 相似文献
This paper addresses coordination and competition problem in two reverse supply chains each having its own exclusive retailer and manufacturer. The chains have various collecting channel structures so that one of them uses the advantages of dual channels, where the consumer can return their e-waste through direct or traditional channels, while its competitor collects obsolete products only through its traditional channel. The willingness to return in each channel is a function of self- and cross-discounts of the competitors. Four decision scenarios are investigated; the first and second chain respectively select, Decentralised-Decentralised, Centralised-Centralised, Centralised-Decentralised or Decentralised-Centralised scenario. The closed-form optimal solution of each channel is derived based on the Stackelberg game when the second chain acts as a leader. The most economical scenario is determined by using a Non-Zero-Sum game when each chain plays as a single player in the game. To coordinate the members’ decisions and to convince unsatisfied members, two coordination contracts are offered. Numerical investigations reveal that direct channel suggests more discount and obtains more share of market. The results show that Centralised-Centralised scenario is the best decision from the SCs’ perspective which proposing contracts are able to persuade members to change their strategy to a global decision. 相似文献
In this work, for the first time, zein nanofiber mats loaded with ethanol extracts propolis (EEP) were successfully produced. Raw propolis was extracted by ethanol 70% and total flavonoid content was estimated by aluminum chloride colorimetric method. The anti-microbial activity of the EEP was investigated and compared with amoxicillin via zone of inhibition test against various microorganisms included gram-positive: Staphylococcus aureus, Staphylococcus epidermidis, gram-negative: Escherichia coli, Salmonella enterica, Pseudomonas aeruginosa and fungus: Candida albicans. The EEP showed activity only against gram-positive types and fungus, whereas no activity was observed against gram-negative types. Electrospun zein nanofiber was obtained from 70% ethanolic solutions included different content of zein, 15–40?wt.%. The SEM images revealed a smooth ribbon-like morphology for zein nanofibers without any beads in zein content more than 25?wt.%. As well, the SEM images of electrospun zein nanofibers containing different content of propolis (0–40?wt.% based on the zein content) disclosed the increase in the average size of fibers with propolis content from 264 to 419?nm. This increasing was more probably due to the reduction in ionic conductivity of zein solutions with propolis content. The proteinic nature of zein along with the antimicrobial activity and the herbal nature of the propolis make the obtained mats promising candidate for more evaluation in wound healing study.
