DBS电视接收机低中频与直接转换调谐器的比较

CMOS技术是把L波段卫星调谐器、解调器和其它功能整合至低成本、高效能单芯片的关键。本文将探讨新型低中频和传统零中频DBS调谐器架构在单芯片DBS射频前端设计中的优缺点。     

Photocatalytic degradation of methyl tert‐butyl ether (MTBE) in contaminated water by ZnO nanoparticles

BACKGROUND: Over the past several decades methyl tert‐butyl ether (MTBE) as additive to gasoline, intended to either boost ratings of fuel or to reduce air pollution, has been accepted worldwide. Since MTBE has high water solubility, the occurrence of fuel spills or leaks from underground storage tanks or transferring pipeline has led to the contamination of natural waters. In this study the degradation of aqueous MTBE at relatively high concentrations was investigated by a UV‐visible/ZnO/H₂O₂ photocatalytic process. The effects of important operational parameters such as pH, amount of H₂O₂, catalyst loading and irradiation time were also investigated. Concentration of MTBE and intermediates such as tert‐butyl formate and tert‐butyl alcohol were measured. RESULTS: Time required for complete degradation increased from 20 to 150 min when the initial concentration was increased from 10 to 500 mg L^?1. The first‐order rate constants for degradation of MTBE were estimated to be 0.183–0.022 min^?1 as the concentration increased from 10 to 500 mg L^?1. Study of the overall mineralization monitored by total organic carbon analysis showed that at an initial concentration of 100 mg L^?1 MTBE complete mineralization was obtained after 100 min under UV‐visible/ZnO/H₂O₂ photocatalysis. CONCLUSION: The data presented in this paper clearly indicated that UV‐visible/ZnO/O₂ as an advanced oxidation process provides an efficient treatment alternative for the remediation of MTBE‐contaminated waters. Copyright © 2008 Society of Chemical Industry     

Chidamber and Kemerer's metrics suite: a measurement theoryperspective

The metrics suite for object-oriented design put forward by Chidamber and Kemerer (1994) is partly evaluated by applying principles of measurement theory. Using the object coupling measure (CBO) as an example, it is shown that failing to establish a sound empirical relation system can lead to deficiencies of software metrics. Similarly, for the object-oriented cohesion measure (LCOM) it is pointed out that the issue of empirically testing the representation condition must not be ignored, even if other validation principles are carefully obeyed. As a by-product, an alternative formulation for LCOM is proposed     

An incentive scheduling mechanism for peer-to-peer video streaming

P2P video streaming networks are found as a scalable solution and an alternative for traditional client–server based video streaming over the Internet. One of the significant issues affecting the success of any P2P streaming network is cooperation between peers. Practical observations have proved the prevalence of free riders in P2P networks that degrade their performance. To solve this problem, using incentive mechanisms, which encourage peers to contribute more in the network, is necessary. In this paper, we designed and proposed a distributed and scalable incentive mechanism for mesh based P2P video streaming networks. In the proposed approach the contribution of the peers is measured and maintained in a distributed fashion. Furthermore, we proposed an incentive sending side scheduler in which peers are served based on their contribution in the network. Our simulation evaluations show the efficiency of the proposed approach in improving the overall perceived video quality by the non-free rider nodes and consequently in the whole network.     

Development of an RVE using a DEM–FEM scheme under modified approximate periodic boundary condition to estimate the elastic mechanical properties of open foams

Engineering with Computers - In this article, a methodology based on Discrete Element Method (DEM) and Finite Elements Method (FEM) combined with modified Approximate Periodic Boundary Condition...     

Thermal cure monitoring of phenolic resole resins based on in situ fluorescence technique

The thermal curing reaction of two phenolic resole resins is monitored using the fluorescence technique. The intrinsic fluorescence can be used as an indicator for cure monitoring for the first resole. As the thermal curing proceeds, the intrinsic fluorescence intensity of the resole resin decreases and exhibits a few nanometers of redshift. The fluorescence intensity of the emission maxima is correlated with the conversion measured by differential scanning spectroscopy. A linear correlation is found at three different temperatures. The intrinsic fluorescence cannot always be used for monitoring the curing process of phenolic resole resins. Thus, three intramolecular charge transfer compounds and two organic donor–π‐acceptor salts are selected and applied for the cure monitoring of the second phenolic resole resin. As the curing reaction proceeds, the fluorescence emission spectra of the probes exhibit a blue spectral shift and the intensity changes because of environmental changes. An intensity ratio method is applied in which the ratios of the low‐ to high‐intensity changes in the emission bands are used to determine the degree of the curing process. There is a smooth correlation between the intensity ratio method and the degree of cure. The method enables one to follow the changes in the polymer structure at low and intermediate degrees of the curing process (below 70%) and obtain comparable results from different types of probes during the same curing process. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1773–1780, 2002     

Thermo economic evaluation of oxy fuel combustion cycle in Kazeroon power plant considering enhanced oil recovery revenues简

Oxy fuel combustion and conventional cycle （currently working cycle） in Kazeroon plant are modeled using commercial thermodynamic modeling software. Economic evaluation of the two models regarding the resources of transport and injection of carbon dioxide into oil fields at Gachsaran for enhanced oil recovery in the various oil price indices is conducted and indices net present value （NPV） and internal rate of return on investment （IRR） are calculated. The results of the two models reveal that gross efficiency of the oxy fuel cycle is more than reference cycle （62% compared to 49.03%）, but the net efficiency is less （41.85% compared to 47.92%） because of the high-energy consumption of the components, particularly air separation unit （ASU） in the oxy fuel cycle. In this model, pure carbon dioxide with pressure of 20~ 105 Pa and purity of 96.84% was captured. NOx emissions also decrease by 4289.7 tons per year due to separation of nitrogen in ASU. In this model, none of the components of oxy fuel cycle is a major engineering challenge. With increasing oil price, economic justification of oxy fuel combustion model increases. With the price of oil at $ 80 per barrel in mind and $ 31 per ton fines for emissions of carbon dioxide in the atmosphere, IRR is the same for both models.     

Surface characterization and biological properties of regular dentin,demineralized dentin,and deproteinized dentin

Bone autografts are often used for reconstruction of bone defects; however, due to the limitations of autografts, researchers have been in search of bone substitutes. Dentin is of particular interest for this purpose due to high similarity to bone. This in vitro study sought to assess the surface characteristics and biological properties of dentin samples prepared with different treatments. This study was conducted on regular (RD), demineralized (DemD), and deproteinized (DepD) dentin samples. X-ray diffraction and Fourier transform infrared spectroscopy were used for surface characterization. Samples were immersed in simulated body fluid, and their bioactivity was evaluated under a scanning electron microscope. The methyl thiazol tetrazolium assay, scanning electron microscope analysis and quantitative real-time polymerase chain reaction were performed, respectively to assess viability/proliferation, adhesion/morphology and osteoblast differentiation of cultured human dental pulp stem cells on dentin powders. Of the three dentin samples, DepD showed the highest and RD showed the lowest rate of formation and deposition of hydroxyapatite crystals. Although, the difference in superficial apatite was not significant among samples, functional groups on the surface, however, were more distinct on DepD. At four weeks, hydroxyapatite deposits were noted as needle-shaped accumulations on DemD sample and numerous hexagonal HA deposit masses were seen, covering the surface of DepD. The methyl thiazol tetrazolium, scanning electron microscope, and quantitative real-time polymerase chain reaction analyses during the 10-day cell culture on dentin powders showed the highest cell adhesion and viability and rapid differentiation in DepD. Based on the parameters evaluated in this in vitro study, DepD showed high rate of formation/deposition of hydroxyapatite crystals and adhesion/viability/osteogenic differentiation of human dental pulp stem cells, which may support its osteoinductive/osteoconductive potential for bone regeneration.     

Spray-Coating of Superhydrophobic Coatings for Advanced Applications

Superhydrophobic coatings are widely applicable, e.g., as self-cleaning surfaces or water–oil separation membranes, yet their wider usage is impeded due to costs of fabrication, size, or substrate limitation. Spray-coating is a versatile coating procedures and might offer a good solution for the fabrication of these superhydrophobic coatings, due to the fact that coatings can be fabricated on various materials in a simple, fast, and inexpensive manner. Most procedures rely on hybrid coatings of hydrophobized nanoparticles and a polymeric matrix, which have several drawbacks including the easy loss of nanoparticles and difficult waste handling. Here, the fabrication of the superhydrophobic material, called Fluoropor, for the first time, by spray-coating on various substrates including metals, tissues, concrete, and glass is presented. It is fabricated by spray-coating a mixture of a highly fluorinated monomer blended with porogens followed by photopolymerization. The superhydrophobicity of the material relies on the porous structure on the micro-/nanoscale across the bulk material and does not require any nanoparticles. Excellent self-cleaning ability of these coatings, resistance against thermal and abrasive impact, and their application as oil–water separation membranes are shown. This versatile applicability is highly promising for real-world application as self-cleaning coatings or oil–water separating membranes.     

The Modeling of Magnetorheological Elastomers: A State-of-the-Art Review

The magnetorheological elastomers (MREs) are novel multifunctional materials wherein their viscoelastic properties can be varied instantly under an application of applied magnetic field. Due to their field-dependent stiffness and damping properties, MREs are widely used in the development and design of MRE-based adaptive vibration isolators and absorbers and also biomedical engineering. Moreover, MREs due to their inherent magnetostriction effect have enormous potential for the development of soft actuators. The dynamic behavior of MREs is affected by various material parameters (e.g., matrix and particle types, particle concentration, additives) as well as mechanical and magnetic loading parameters (e.g., frequency, amplitude, temperature, magnetic flux density). Understanding and predicting the effect of materials and loading parameters on the response behavior of MREs are of paramount importance for the design of MRE-based adaptive structures and systems. This review paper mainly aims to provide a comprehensive study of material constitutive models to predict the nonlinear magnetomechanical behavior of MREs. Particular emphasis is paid to physics-based models including continuum- and microstructure-based models. Moreover, phenomenological models describing the dynamic magnetoviscoelastic behavior of MREs as well as the effect of temperature on the magnetomechanical behavior of such materials are properly addressed.