Influence of sintering temperature on secondary phases formation and microwave dielectric properties of Ca2Ce2Ti5O16 ceramics

Ca₂Ce₂Ti₅O₁₆ dielectric ceramics prepared by conventional solid-state ceramic route was investigated. Phase composition and microwave dielectric properties were measured using XRD and Vector network analyzer, respectively. XRD analysis of the calcined and sintered samples revealed the formation of CeO₂ and another unidentified phase (that vanished at ? 1400 °C) as secondary phases along with the parent Ca₂Ce₂Ti₅O₁₆ phase. The amount of the parent Ca₂Ce₂Ti₅O₁₆ phase increased with increasing sintering temperature from 1350 °C to 1450 °C accompanied by a decrease in the apparent density. The density decreased but ? _r and Q _u f _o increased with sintering temperature. An ? _r ～ 81.5, Q _u f _o ～ 5915 GHz and τ _f ～ 219 GHz were achieved for the sample sintered at 1450 °C.     

A process-tolerant out-of-band blocker rejection technique for SAW-less receivers

In this paper, an active filtering technique is presented which is capable of filtering the out-of-band blockers in wireless receivers. The concept is based on the feedforward cancellation technique where a blocker replica is subtracted at the output of the low-noise amplifier (LNA). In contrast to the previously reported feedforward cancellation methods, exact gain and phase matching are easily obtained in the proposed architecture to produce a highly selective narrowband frequency response at the output of the LNA with wide rejection bandwidth. For the proof of concept, the system is implemented in a 65 nm CMOS technology. It occupies a total area of 0.8 mm² and the current consumption is 24 mA from a 1.2 V supply. The system post-layout simulations showed a blocker rejection of more than 33 dB for blocker signals 100 MHz away from the desired signal when the feedforward path is activated. The noise figure (NF) of the entire system is 3.8 dB that degrades to 5.8 dB when the feedforward path is activated.     

Hierarchical TiO2/ZnO Nanostructure as Novel Non-precious Electrocatalyst for Ethanol Electrooxidation

Metal oxides have a higher chemical stability in comparison to metals,so they can be utilized as electrocatalysts if the activity could be enhanced.Besides the composition,the morphology of the nanostructures has a considerable impact on the electrocatalytic activity.In this work,zinc oxide nano branches-attached titanium dioxide nanofibers were investigated as an economic and stable catalyst for ethanol electrooxidation in the alkaline media.The introduced material has been synthesized by electrospinning process followed by hydrothermal technique.Briefly,electrospinning of colloidal solution consisting of titanium isopropoxide,poly(vinyl acetate) and zinc nanoparticles was performed to produce nanofibers embedding solid nanoparticles.In order to produce TiO_2 nanofibers containing ZnO nanoparticles,the obtained electrospun nanofiber mats were calcined in air at 600 °C.The formed ZnO nanoparticles were exploited as seeds to outgrow ZnO branches around the TiO_2 nanofibers using the hydrothermal technique at sub-critical water conditions in the presence of zinc nitrate and bis-hexamethylene triamine.The morphology of the final product,as well as the electrochemical measurements indicated that zinc nanoparticles content in the original electrospun nanofibers has a significant influence on the electrocatalytic activity as the best performance was observed with the nanofibers synthesized from electrospun solution containing 0.1 g Zn,and the corresponding current density was 37 mA/cm~2.Overall,this study paves a way to titanium dioxide to be exploited to synthesize effective and stable metal oxide-based electrocatalysts.     

Harvesting Lost Photons: Plasmon and Upconversion Enhanced Broadband Photocatalytic Activity in Core@Shell Microspheres Based on Lanthanide‐Doped NaYF4, TiO2, and Au

Efficiently harvesting solar energy for photocatalysis remains very challenging. Rational design of architectures by combining nanocomponents of radically different properties, for example, plasmonic, upconversion, and photocatalytic properties, offers a promising route to improve solar energy utilization. Herein, the synthesis of novel, plasmonic Au nanoparticle decorated NaYF₄:Yb³⁺, Er³⁺, Tm³⁺‐core@porous‐TiO₂‐shell microspheres is reported. They exhibit high surface area, good stability, broadband absorption from ultraviolet to near infrared, and excellent photocatalytic activity, significantly better than the benchmark P25 TiO₂. The enhanced activity is attributed to synergistic effects from nanocomponents arranged into the nanostructured architecture in such a way that favors the efficient charge/energy transfer among nanocomponents and largely reduced charge recombination. Optical and energy‐transfer properties are modeled theoretically to support our interpretations of catalytic mechanisms. In addition to yielding novel materials and interesting properties, the current work provides physical insights that can contribute to the future development of plasmon‐enhanced broadband catalysts.     

Fabricating a Homogeneously Alloyed AuAg Shell on Au Nanorods to Achieve Strong,Stable, and Tunable Surface Plasmon Resonances

Colloidal metal nanocrystals with strong, stable, and tunable localized surface plasmon resonances (SPRs) can be useful in a corrosive environment for many applications including field‐enhanced spectroscopies, plasmon‐mediated catalysis, etc. Here, a new synthetic strategy is reported that enables the epitaxial growth of a homogeneously alloyed AuAg shell on Au nanorod seeds, circumventing the phase segregation of Au and Ag encountered in conventional synthesis. The resulting core–shell structured bimetallic nanorods (AuNR@AuAg) have well‐mixed Au and Ag atoms in their shell without discernible domains. This degree of mixing allows AuNR@AuAg to combine the high stability of Au with the superior plasmonic activity of Ag, thus outperforming seemingly similar nanostructures with monometallic shells (e.g., Ag‐coated Au NRs (AuNR@Ag) and Au‐coated Au NRs (AuNR@Au)). AuNR@AuAg is comparable to AuNR@Ag in plasmonic activity, but that it is markedly more stable toward oxidative treatment. Specifically, AuNR@AuAg and AuNR@Ag exhibit similarly strong signals in surface‐enhanced Raman spectroscopy that are some 30‐fold higher than that of AuNR@Au. When incubated with a H₂O₂ solution (0.5 m ), the plasmonic activity of AuNR@Ag immediately and severely decayed, whereas AuNR@AuAg retained its activity intact. Moreover, the longitudinal SPR frequency of AuNR@AuAg can be tuned throughout the red wavelengths (≈620–690 nm) by controlling the thickness of the AuAg alloy shell. The synthetic strategy is versatile to fabricate AuAg alloyed shells on different shaped Au, with prospects for new possibilities in the synthesis and application of plasmonic nanocrystals.     

Dynamic behavior of a two-stage gear train used in a fixed-speed wind turbine

The dynamic behavior of a two stage spur gear system used in a typical wind turbine is investigated in this paper. With the purpose of having an accurate simulation, for a given excitations, of the dynamic response of bearings, shafts and teeth in contact.In this study, we developed a lamped mass dynamic model with 12 DOFs. This model is excited by external and internal issues sources. The main factors of these excitations are the variability in the wind resource and the time varying mesh stiffness fluctuation.The aerodynamic torque is calculated from an empirical approach of the power coefficient. The incoming flow is modeled by an analytic equation test varies with time. The differential equations governing the system motion are solved by an implicit Newmark algorithm.     

Quadric segmentation and fitting of data captured by a laser profile scanner mounted on an industrial robot

Applications like geometric reverse engineering, robot vision and automatic inspection require sets of points to be measured from the surfaces of objects and then processed by segmentation and fitting algorithms to establish shape parameters of interest. In industrial applications where speed, reliability and automatic operation is of interest a measuring system based on a laser profile scanner mounted on an industrial robot can be of interest. In earlier publications we have presented such a system and also a segmentation algorithm for planar surfaces using 2D profile data in combination with robot poses. Due to the data reduction offered by this approach the segmentation algorithm computes faster than algorithms based on 3D point sets alone. Encouraged by the results we have now developed a segmentation algorithm for two different quadric surfaces also based on 2D profiles in combination with robot poses. This paper presents the new algorithm together with test results and also an interesting observation that points to future work.     

Economical evaluation of electricity generation considering externalities

The economics of renewable energy are the largest barrier to renewable penetration. Nevertheless, the strong desire to reduce environmental emissions is considered a great support for renewable energy sources. In this paper, a full analysis for the cost of the kWh of electricity generated from different systems actually used in Egypt is presented. Also renewable energy systems are proposed and their costs are analyzed. The analysis considers the external cost of emissions from different generating systems. A proposed large scale PV plant of 3.3 MW, and a wind farm 11.25 MW grid connected at different sites are investigated. A life cycle cost analysis for each system was performed using the present value criterion. The comparison results showed that wind energy generation has the lowest cost, followed by a combined cycle–natural gas fired system. A photovoltaic system still uses comparatively expensive technology for electricity generation; even when external costs are considered the capital cost of photovoltaic needs to be reduced by about 60% in order to be economically competitive.