Large signal analysis of mixers with difference frequency injection

Large signal analysis of mixers excited by three tone signals is presented. The special case of two equal-amplitude sinusoids plus a difference-frequency injection is considered in detail and the results are compared, whenever possible, with previously published results. Contrary to previously published results, it is shown that even under large signal conditions and strong nonlinearity it is possible, at least in theory, to totally eliminate the third-order intermodulation when the amplitudes of the equal-amplitudes input sinusoids and the difference-frequency injection are equal.     

Effects of Surfactants on the Properties of Styrene/Methacrylate–Type Superplasticizer in Cement Paste

Copolymer emulsion lattices based on styrene (St) with methacrylate monomers, were synthesized with composition ratio (5/5) in the presence of a co-surfactants that consists of dodecyl benzene sodium sulfonate with polyvinyl alcohol (DBSS/PVA) and DBBS with polyoxyethylene glycol monomethyl ether (DBBS/POE). The obtained latices were characterized by ¹H NMR, rheological and morphological techniques. The effect of latices on the physicomechanical properties of ordinary Portland cement (OPC) pastes was investigated. The results showed that the addition of water mixed to the cement with copolymer improves most of the specific characteristics of OPC.     

HYDROMAGNETIC UNSTEADY RIVLIN-ERICKSEN THIRD-GRADE FLOW FOR STOKES' SECOND PROBLEM

In this article, the flow of an unsteady third-grade Rivlin-Ericksen fluid on an oscillating plate is discussed. The magnetic lines of force act perpendicular to the flow field. Several interesting features of the flow are obtained. The physical interpretation of the second-grade parameters, third-grade parameters, oscillating frequency, and magnetohydrodynamic parameters are examined graphically and then are deduced to already known results in the literature.     

Repetitive acceptance sampling plans for burr type XII percentiles

Under truncated life tests, two types of repetitive acceptance sampling plans are proposed to ensure the quality of products in terms of percentile lifetime when the lifetime follows the Burr type XII distribution. The proposed acceptance sampling plans, including the ordinary repetitive acceptance sampling plan and the repetitive version of a group acceptance sampling plan, are developed to meet producer’s and consumer’s risks at two specified lifetime percentiles, simultaneously. Useful tables have been established for a wide range of Burr type XII distributions which include the log–logistic distribution for practical utilization. Finally, some examples are provided for illustration.     

Influence of absorber doping in a-SiC：H/a-Si：H/a-SiGe：H solar cells

This work deals with the design evaluation and influence of absorber doping for a-Si:H/a-SiC:H/a-SiGe:H based thin-film solar cells using a two-dimensional computer aided design (TCAD) tool. Various physical parameters of the layered structure, such as doping and thickness of the absorber layer, have been studied. For reliable device simulation with realistic predictability, the device performance is evaluated by implementing necessary models (e.g., surface recombinations, thermionic field emission tunneling model for carrier transport at the heterojunction, Schokley-Read Hall recombination model, Auger recombination model, bandgap narrowing effects, doping and temperature dependent mobility model and using Fermi-Dirac statistics). A single absorber with a graded design gives an efficiency of 10.1% for 800 nm thick multiband absorption. Similarly, a tandem design shows an efficiency of 10.4% with a total absorber of thickness of 800 nm at a bandgap of 1.75 eV and 1.0 eV for the top a-Si and bottom a-SiGe component cells. A moderate n-doping in the absorber helps to improve the efficiency while p doping in the absorber degrades efficiency due to a decrease in the V_OC (and fill factor) of the device.     

A Filter Bank Based Approach for Rotation Invariant Fingerprint Recognition

This paper presents a systematic approach for image-based fingerprint recognition. The proposed method first enhances an input fingerprint image using a contextual filtering based method in the frequency domain. Complex filters are used for the detection of the core point, and a region of interest (ROI) of a predefined size centered at the detected core point is extracted. The resulting ROI is rotated based on the angle of the detected core point to ensure rotation invariance. Subsequently, the proposed system extracts the average absolute deviation (AAD) from the outputs of a Gabor filter bank. To reduce the dimensionality of the extracted features whilst generating more discriminatory representation, this paper compares the unsupervised Principal Component Analysis (PCA) and the supervised Linear Discriminant Analysis (LDA) methods for dimensionality reduction. User-specific thresholding schemes are investigated to improve the verification performance. The effectiveness of the proposed method is demonstrated through extensive experimentation on the FVC2002 set_a public database, in both identification and verification scenarios.     

Heat transfer from a spinning disk during semi-confined axial impingement from a rotating nozzle

Conjugate heat transfer from a uniformly heated spinning solid disk of finite thickness and radius during a semi-confined liquid jet impingement from a rotating nozzle is studied. The model covers the entire fluid region including the impinging jet on a flat circular disk and flow spreading out downstream under the spinning confinement plate and free surface flow after exposure to the ambient gaseous medium. The model examines how the heat transfer is affected by adding a secondary rotational flow under semi-confined jet impingement. The solution is made under steady state and laminar conditions. The study considered various plate materials such as aluminum, copper, silver, constantan and silicon. Ammonia, water, flouroinert FC-77 and MIL-7808 oil were used as working fluids. The range of parameters covered included Reynolds number (220–900), Ekman number (7.08 × 10^?5–∞), nozzle-to-target spacing (β = 0.25–1.0), disk thicknesses to nozzle diameter ratio (b/d_n = 0.25–1.67), Prandtl number (1.29–124.44) and solid to fluid thermal conductivity ratio (36.91–2222). It was found that a higher Reynolds number increased local heat transfer coefficient reducing the interface temperature difference over the entire disk surface. The rotational rate also increased local heat transfer coefficient under most conditions. An engineering correlation relating the Nusselt number with other dimensionless parameters was developed for the prediction of the system performance.     

Impacts of low-pressure (LP) compressors’ fouling of a turbofan upon operational-effectiveness of a military aircraft

Some in-service deterioration in any mechanical device, such as an aircraft’s gas-turbine engine, is inevitable. However, its extent and rate depend upon the qualities of design and manufacture, as well as on the maintenance/repair practices followed by the users. As a result of experiencing deterioration (of the engine as a whole or any of its components individually), an engine will seek a different steady operating point relative to that for an engine with no deterioration. This results in changes in the available thrust from the engine(s) at the same TETs and/or rotational-speeds. Any reduction in the available thrust at specified engine settings, especially maximum available thrust from the engines, will have a significant adverse effect upon the aircraft’s operational-performance. These adverse effects can be reduced by having a better knowledge of the effects of each such deterioration on the aircraft’s operational-performance. Subsequently improvements can be made in the design and manufacture of adversely-affected components as well as in maintenance and repair practices.     

Microstructural and Hardness Studies of Cu-10wt.%Sn Alloy Under Different Aging Conditions

Microstructure of Cu-10wt.%Sn alloy, prepared by powder metallurgy technique and sintered at 900 °C for 120 min in hydrogen atmosphere, was studied by optical microscopy and XRD technique as a function of aging time. Isothermal aging of the alloy specimens was performed at 250 °C for a period of 30, 60, 120, 300, and 1440 min after solution treatment at 500 °C for 60 min. Rockwell hardness of aged specimens was also measured at room temperature as a function of aging time. It was observed that microstructure of the as-sintered specimens consists of the grains of alpha Cu-Sn solid solution. Moreover, solution treatment of the alloy specimens followed by quenching in water increased the hardness of the as-sintered alloy specimens from 35.5 to 59.8 HRF due to the residual stresses generated by fast cooling. Aging at 250 °C for 30, 60, and 120 min was found to cause a decrease in hardness from 59.8 to 45.1 HRF, whereas the specimens aged for 300 and 1440 min show an increase in hardness from 45.1 to 75.7 HRF. The values of porosity calculated from XRD patterns of the alloy specimens referred to show that porosity varies with aging time in a manner opposite to that of hardness, e.g., porosity is maximum for 120 min aging time where hardness is minimum.