Phase field simulations of ferroelectrics domain structures in PbZrxTi1−xO3 bilayers

Domain stability and structures in Pb(Zr_0.3Ti_0.7)O₃/Pb(Zr_0.7Ti_0.3)O₃ bilayer films under different substrate strains are studied using the phase field method. It is demonstrated that the domain structure of the bilayer film is very different from those of the corresponding single layer films grown on the same silicon substrate with an incoherent interface. Moreover, the predicted rhombohedral domains in the Pb(Zr_0.7Ti_0.3)O₃ layer of the bilayer film have smaller sizes than those in the single layer case. These results are compared with experimental observations and previous thermodynamic analyses. The polarization distributions of the ferroelectric–paraelectric bilayer are analyzed as a function of the thickness of the bilayer film, where there is a “ferroelectric proximity effect” due to dipole–dipole interactions. The phase diagrams for both the bilayer and single layer films as a function of temperature and effective in-plane substrate strain are constructed.     

EXPERIMENTAL STUDIES ON HEAT TRANSFER AND FRICTION FACTOR CHARACTERISTICS OF TURBULENT FLOW THROUGH A CIRCULAR TUBE FITTED WITH RIGHT AND LEFT HELICAL SCREW-TAPE INSERTS

Experimental investigation on heat transfer and friction factor characteristics of a circular tube fitted with right-left helical screw inserts of equal and unequal length of different twist ratios is presented. The experimental data obtained were compared with those obtained from plain tube published data. The heat transfer enhancement for right-left helical screw inserts is higher than that for straight helical twist for a given twist ratio. The effect of right-left twist length on heat transfer augmentation is presented. The empirical relations for Nusselt number, friction factor relating Reynolds number, twist ratio, and right-left twist distance were formed and found to fit the experimental data within 10% and 20% for Nusselt number and friction factor respectively. Performance evaluation analysis was made, and the performance ratio of more than one was obtained, indicating that the proposed twist inserts can be used effectively for heat transfer augmentation without any loss in pumping power.     

Stability of SiN<Subscript>X</Subscript>/SiN<Subscript>X</Subscript> double stack antireflection coating for single crystalline silicon solar cells

Double stack antireflection coatings have significant advantages over single-layer antireflection coatings due to their broad-range coverage of the solar spectrum. A solar cell with 60-nm/20-nm SiN_X:H double stack coatings has 17.8% efficiency, while that with a 80-nm SiN_X:H single coating has 17.2% efficiency. The improvement of the efficiency is due to the effect of better passivation and better antireflection of the double stack antireflection coating. It is important that SiN_X:H films have strong resistance against stress factors since they are used as antireflective coating for solar cells. However, the tolerance of SiN_X:H films to external stresses has never been studied. In this paper, the stability of SiN_X:H films prepared by a plasma-enhanced chemical vapor deposition system is studied. The stability tests are conducted using various forms of stress, such as prolonged thermal cycle, humidity, and UV exposure. The heat and damp test was conducted for 100 h, maintaining humidity at 85% and applying thermal cycles of rapidly changing temperatures from -20°C to 85°C over 5 h. UV exposure was conducted for 50 h using a 180-W UV lamp. This confirmed that the double stack antireflection coating is stable against external stress.     

A General Method for the Synthesis of 5H‐Benzo[b]‐, Carbazolo[2,3‐b]‐ and Indolo[2,3‐b]carbazole Derivatives via Copper(II) Triflate‐Catalyzed Heteroannulation

A straightforward approach for the construction of 5H‐benzo[b]‐, carbazolo[2,3‐b]‐ and indolo[2,3‐b]carbazole derivatives has been developed by using copper(II) triflate‐catalyzed heteroannulation.     

Performance and emission characteristics of a low heat rejection spark ignited engine fuelled with E20

In internal combustion engines, the concept of low heat rejection (LHR) using thermal barrier coating on the surface of combustion chamber is gaining attention. Thermal barrier coating reduces the heat transfer to the cooling system, protects engine components from peak heat flux and fluctuating temperature produced during combustion and improves the performance of the engine. Information in the literature is plentiful for LHR diesel engine and only few studies exist on LHR spark ignited engine. The application of thermal barrier coating in spark ignited engine is limited by pre-ignition and knocking due to elevated combustion chamber temperature. A spark ignited engine with moderate insulation on the combustion chamber and higher octane fuel can overcome this difficulty. The objective of the present experimental study is to quantify the changes in performance and emission characteristics brought by partial thermal insulation on the combustion chamber of a four stroke spark ignited engine fueled with E20 blend. Partial thermal insulation was created by coating 0.3 mm thick Alumina (Al₂O₃) on the cylinder head, inlet and exhaust valves. The changes are quantified with respect to unmodified engine fueled with gasoline. The combustion parameters such as flame development and rapid burn duration are also estimated and compared. The results indicate that partially insulated SI engine when fueled with E20 improves performance and reduces emission. A maximum of 48% reduction in THC and 50% reduction in CO emission at part load was achieved.

     

Removal of spurious coherence in MEG source-space coherence analysis

Source-space coherence analysis has become a popular method to estimate functional connectivity based on MEG/EEG. Source-space analysis involves solving the inverse problem, estimating the time courses of specific brain regions, and then examining the coherence between activities at different brain regions. However, source-space coherence analysis can be confounded by spurious coherence caused due to the leakage properties of the inverse algorithm employed. Such spurious coherence is typically manifested as an artifactual large peak around the seed voxel, called seed blur, in the resulting coherence images. This seed blur often obscures important details of brain interactions. This paper proposes the use of the imaginary part of the coherence to remove the spurious coherence caused by the leakage of an imaging algorithm. We present a theoretical analysis that explains how the use of imaginary part can remove this spurious coherence. We then present results from both computer simulations and experiments using resting-state MEG data which demonstrate the validity of our analysis.     

A 2‐D surface‐potential‐based threshold voltage model for short channel asymmetric heavily doped DG MOSFETs

In recent times, transistors with heavily doped body have generated much interest because of junctionless channel. In addition, proper threshold voltage regulation requires adjustment of the channel doping, as a result of which most of the compact models become invalid as they consider an intrinsic body. In this paper, a compact surface‐potential‐based threshold voltage model is developed for short channel asymmetric double‐gate metal–oxide–semiconductor field‐effect transistors with heavily/lightly doped channel. The 2‐D surface potential is computed and compared with Technology Computer Aided Design, and a relative error of 2–4 % was obtained. The threshold voltage is solved from 2‐D Poisson's equation using ‘virtual cathode’ method, and a good agreement is observed with the numerical simulations. Also, the model is compared with a reference model and a better result is obtained for heavily doped channel. Copyright © 2014 John Wiley & Sons, Ltd.     

Combined effect of injection timing,EGR and injection pressure in reducing the NOx emission of a biodiesel blend

In this study, an attempt was made to reduce the higher oxides of nitrogen (NO_x) emission of a crude rice bran oil methyl ester (CRBME) blend through modification of combustion process by retarding fuel injection timing and exhaust gas recirculation at an increased fuel injection pressure. At modified condition, delay period and peak pressure of CRBME blend were lower than those at normal condition. The occurrence of maximum heat release rate retarded with a higher magnitude when compared with normal condition. Experimental results show that as a result of combustion modification, NO_x and carbon monoxide emissions were reduced significantly with marginal increase in smoke density. Brake thermal efficiency and unburnt hydrocarbon emissions of the engine were increased significantly as a result of this modification process. This investigation shows that the NO_x emission of a biodiesel blend can be reduced with less sacrifice on smoke density and increase in the brake thermal efficiency by modifying the combustion process.     

An analysis of subsynchronous resonance in hybrid marine current and wind farms with squirrel cage induction generator

Subsynchronous resonance (SSR) is a well-known phenomenon in series-compensated systems with synchronous generators. With the rapid growth of renewable energy systems, it is likely that with its integration to series-compensated system for the transmission of bulk power may lead to the problem of SSR. This paper conducts an analysis of SSR phenomena in the squirrel cage induction generator-based hybrid wind farm and marine current farm connected to series-compensated system with power variation due to the addition or removal of small turbine units. A dynamic model has been developed to analyse the induction generator effect and torsional interaction of SSR on the IEEE first bench mark model for SSR studies. The eigenvalue analysis was performed on the developed model with MATLAB and the time domain electro magnetic transient simulation performed on DiGSILENT Power Factory confirms the predicted results by the eigenvalue analysis.     

An experimental investigation on DI diesel engine with hydrogen fuel

The internal combustion engines have already become an indispensable and integral part of our present day life style, particularly in the transportation and agricultural sectors [Nagalingam B. Properties of hydrogen. In: Proceedings of the summer school of hydrogen energy, IIT Madras, 1984]. Unfortunately the survival of these engines has, of late, been threatened due to the problems of fuel crisis and environmental pollution. Therefore, to sustain the present growth rate of civilization, a nondepletable, clean fuel must be expeditiously sought. Hydrogen exactly caters to the specified needs. Hydrogen, even though “renewable” and “clean burning”, does give rise to some undesirable combustion problems in an engine operation, such as backfire, pre-ignition, knocking and rapid rate of pressure rise [Srinivasa Rao P. Utilization of hydrogen in a dual fueled engine. In: Proceedings of the summer school of hydrogen energy, IIT Madras, 1984; Siebers DL. Hydrogen combustion under diesel engine conditions. Hydrogen Energy 1998;23:363–71]. The present investigation compares the performance and emission characteristics of a DI diesel engine with gaseous hydrogen as a fuel inducted by means of carburation technique and timed port injection technique (TPI) along with diesel as a source of ignition [Swain N, Design and testing of dedicated hydrogen-fueled engine. SAE 961077, 1996]. In the present study the specific energy consumption, NO_x emission and the exhaust gas temperature increased by 6%, 8% and 14%, respectively, and brake thermal efficiency and smoke level reduced by 5% and 8%, respectively, using carburation technique compared to baseline diesel. But in the TPI technique, the specific energy consumption, exhaust gas temperature and smoke level reduced by 15%, 45% and 18%, respectively. The brake thermal efficiency and NO_x increased by 17% and 34%, respectively, compared to baseline diesel. The emissions such as HC, CO, and CO₂ is very low in both carburation and TPI techniques compared baseline diesel.