Liftoff and extinction characteristics of fuel- and air-stream-diluted methane-air flames

Partial premixing of fuel and oxidizer is of common occurrence in fires. However, most previous studies dealing with flame extinction have focused on nonpremixed flames. In this experimental-numerical study, we examine the effectiveness of fuel-stream versus air-stream dilution for extinguishing laminar methane-air partially premixed (PPFs) and nonpremixed flames (NPF) using the chemically inert fire suppressant CO₂. Experimental measurements were made in lifted methane-air coflow flames, while both counterflow and coflow flames were simulated using a time-accurate implicit algorithm that incorporates detailed chemistry and includes radiation effects. Both measurements and simulations show that with fuel-stream dilution, PPFs stabilize at a higher liftoff height and blow out at a lower CO₂ dilution than NPFs. In contrast, with air-stream dilution, NPFs move to a higher liftoff height and blow out at a lower CO₂ dilution than PPFs. Despite different configurations, there is remarkable similarity in the extinction characteristics of coflow and counterflow flames with regard to the level of partial premixing and air- and fuel-stream dilution. The critical fuel-stream CO₂ mole fraction required for the extinction of both counterflow and coflow flames increases as ? is increased, i.e., as the level of partial premixing is reduced. Conversely, the critical air-stream CO₂ mole fraction decreases as ? is increased. Results also indicate a crossover value of ?≈2.0, corresponding to the stoichiometric mixture fraction of fs=0.5, such that flames (including NPFs) with fs<0.5 are more difficult to extinguish with fuel-stream dilution, since oxygen is the deficient reactant, whereas flames with fs>0.5 are more difficult to extinguish with air-stream dilution, since fuel is the deficient reactant for these flames.     

Slip effects on boundary layer stagnation-point flow and heat transfer towards a shrinking sheet

In the present study, we analyze the effects of partial slip on steady boundary layer stagnation-point flow of an incompressible fluid and heat transfer towards a shrinking sheet. Similarity transformation technique is adopted to obtain the self-similar ordinary differential equations and then the self-similar equations are solved numerically using shooting method. This investigation explores the conditions of the non-existence, existence, uniqueness and duality of the solutions of self-similar equations numerically. Due to the increase of slip parameter (δ), the range of velocity ratio parameter (c/a) where the similarity solution exists, increases.     

Stage and Discharge Forecasting by SVM and ANN Techniques

In this study, forecasting of stage and discharge was done in a time-series framework across three time horizons using three models: (i) persistence model, (ii) feed-forward neural network (FFNN) model, and (iii) support vector machine (SVM) model. For these models, lagged values of the time series constituted the set of input variables which had been selected by principal component analysis (PCA). Parameters of FFNN and SVM models were determined by sensitivity analysis. All the three models were evaluated using data from Mahanadi River, India, and their forecasting performance was then compared. It is shown that over a shorter forecasting horizon, it is difficult to outperform the persistence model. Moreover, results show that forecasting of stage and discharge over a longer time frame by the SVM model is more accurate than that by the other two models.     

Spin-coated ZnO thin films using ZnO nano-colloid

Using ZnO nano-colloids, thin films of ZnO have been deposited and characterized. The nano-colloid has been synthesized using a top-down wet chemistry method starting from submicron ZnO particles. The steric stabilization technique is implemented using stearic acid as a capping agent to prevent agglomeration of the ZnO nanoparticles. A stable suspension is achieved, exhibiting strong optical absorbance and a band edge at 376 nm. The simple chemistry enables a uniform film on a variety of substrates using spin coating. Current-voltage (I–V) measurements of ZnO films deposited on quartz after annealing treatment show a resistivity of 1.89×10⁵ Ω · cm.     

Rapid Thermal Annealing of Oxide Electrodes for Nonvolatile Ferroelectric Memory Structures

We report on the properties of a ferroelectric stack comprising (La_0.5Sr_0.5)CoO₃ (LSCO)/Pb(Nb,Zr,Ti)O₃ (PNZT)/LSCO deposited on 4 inch diameter platinized Si wafers (Pt/Ti/SiO₂/Si). The LSCO electrodes were deposited at room temperature by pulsed laser ablation and the ferroelectric layer was deposited by the sol-gel technique. Rutherford backscattering was performed to confirm the uniformity in composition, thickness and stoichiometry of LSCO across the wafers. Conventional furnace or rapid thermal annealing was performed to crystallize the electrodes. The oxidation resistance of the conducting barrier layers, Pt/Ti, was found to be dependent on the annealing procedure adopted for the bottom electrode. In the case where the bottom LSCO was crystallized by rapid thermal annealing, Rutherford backscattering analysis and transmission electron microscopy studies revealed that there was no oxidation of the Pt/Ti conducting barrier composite. This is in contrast to the observations for in-situ deposition or conventional furnace annealing of the bottom electrode. The resistivity, coercive field and polarization of the ferroelectric stack were uniform across the 4-inch wafers. The ferroelectric capacitors showed no fatigue up to 10¹¹ cycles and no imprint at 100°C. The ferroelectric properties were independent of the annealing procedure used for crystallizing the electrodes.     

A novel non-unit protection for series compensated EHV transmissionlines based on fault generated high frequency voltage signals

A new high-speed protection technique based on fault generated high frequency (HF) voltage signals is developed and applied to the protection of EHV series compensated power transmission lines. It is a nonunit protection technique as it relies totally on locally derived information, but it has the discriminative properties normally associated with unit protection schemes. The protection scheme has been designed using CAD techniques including emulation of analogue interfaces and hardware. It is shown that the new relay scheme is able to overcome many difficult protection problems encountered on such EHV power lines using conventional methods, and discriminates clearly between internal and external faults, producing a fast trip output     

Performance of multiple access channels with asymmetric feedback

Channel state feedback at the transmitter is extensively used to increase the reliability of wireless transmissions. In multiuser systems, the downlink capacity to different users is often different due to the near-far effect. We capture this asymmetry by introducing an asymmetric feedback model where different users get a different amount of feedback from the base station. First, we derive the outage probability for the optimum maximum-likelihood receiver which forms an upper bound on the diversity-multiplexing performance. This is accompanied by the conditions under which these bounds can be achieved. Second, we analyze the performance of two popular suboptimal receivers: the spatial decorrelator and the successive interference cancellation receiver. As a special case, when there is no asymmetry, the performance matches feedback-based single-user performance in many scenarios.     

Analysis of spectrally efficient two‐way relay assisted free space optical systems in atmospheric turbulence with path loss

In this paper, we investigate the performance of two‐way relay assisted free space optical systems over atmospheric turbulence‐induced fading channels affected by molecular absorbtion‐induced path losses. A three node, dual‐hop, bi‐directional, half‐duplex relaying system with independent but not necessarily identically distributed channels is considered. Spectral efficiency is achieved by employing network coding to complete data transmission in two‐time phases. Closed form expression for system outage performance is derived considering decode‐and‐forward protocol. Additionally, the error performance in terms of average symbol error rate for M‐ary phase shift keying is evaluated. Further, the net achievable capacity of the system is also calculated. Copyright © 2014 John Wiley & Sons, Ltd.     

Low-Loss Slow Light Transmission in Photonic Crystal Waveguides Comprising of Liquid Crystal Infiltration

A low loss photonic crystal(PhC) waveguide having rectangular air holes in Si core is proposed having an average group index of 55 in the bandwidth of 1.2 THz.The possible propagation losses due to inefficient coupling are also investigated for proposed structure.It is found that high transmission is obtained for a broad bandwidth from the output of the finally designed heterogeneous waveguide consisting of a slow liquid crystal infiltrated PhC waveguide surrounded by fast PhC waveguides on both sides.     

A single-stage variable-gain amplifier with 70-dB dynamic range for CDMA2000 transmit applications

A variable-gain amplifier (VGA) circuit is presented with a gain range of more than 70 dB in a single stage. Vertical stacking of multipliers in a single-stage VGA results in a considerable saving of power, which is a prime requirement in cellular systems. The gain-in-dB is a linear function of the control voltage and has excellent stability over temperature. The amplifier is a part of a code-division multiple access cellular transmit integrated circuit, and provides good linearity and noise characteristics over a wide range of IF frequencies. The circuit is fabricated in a 30-GHz f/sub t/ BiCMOS technology and consumes 8 mA at 2.7 V.