Unconfined fluid electrospun into high quality nanofibers from a plate edge

We demonstrate an easily-implemented, edge-plate geometry for electrospinning and produce high quality nanofibers from unconfined polymer fluids. We show that for electrospinning in general, the electric field gradient, not just the electric field amplitude, is a critical parameter for successful self-initiated jetting. Considering a single spinning site, the edge-plate configuration resulted in the same or a higher fabrication rate as traditional needle electrospinning, while producing nanofibers similar in quality (diameter, diameter distribution, and collected mat porosity); moreover, this novel configuration operates without the possibility of clogging and has high potential for scale-up. We analyze the fundamental physical processes which underlie edge-plate electrospinning, including electric field, working distance, and feed rate dependence and the resultant changes to the linear and whipping regions, and thus to the fiber diameter. We conclude that the edge-plate configuration functions in a remarkably similar manner to traditional needle electrospinning.     

Automatic transcription of continuous speech into syllable-like units for Indian languages

The focus of this paper is to automatically segment and label continuous speech signal into syllable-like units for Indian languages. In this approach, the continuous speech signal is first automatically segmented into syllable-like units using group delay based algorithm. Similar syllable segments are then grouped together using an unsupervised and incremental training (UIT) technique. Isolated style HMM models are generated for each of the clusters during training. During testing, the speech signal is segmented into syllable-like units which are then tested against the HMMs obtained during training. This results in a syllable recognition performance of 42·6% and 39·94% for Tamil and Telugu. A new feature extraction technique that uses features extracted from multiple frame sizes and frame rates during both training and testing is explored for the syllable recognition task. This results in a recognition performance of 48·7% and 45·36%, for Tamil and Telugu respectively. The performance of segmentation followed by labelling is superior to that of a flat start syllable recogniser (27·8%and 28·8%for Tamil and Telugu respectively).     

Uniform shell patterning using rubber‐assisted hot embossing process. II. Process analysis

This two‐article sequence on rubber‐assisted embossing was aimed to understand the basic mechanisms affecting the pattern uniformity and replicability and to determine a process window for achieving uniform patterning and faithful replication. In Part I, the effects of major process and material parameters were identified and studied, and strategies for successful hot embossing with rubber as a pressure medium were proposed. In Part II, the rubber‐assisted embossing process was analyzed considering the unique rheological behavior of the materials involved to develop useful predictive capabilities for this new process. Specifically, a finite‐strain hyperelastic formulation was used for simulating the isothermal embossing stage, and a generalized Maxwell model was used to study the stress relaxation during the holding stage and to predict the elastic recovery after demolding. The rheological properties obtained in Part I were fitted to the constitutive models and implemented in the simulation procedures. The simulation results agreed with the major findings in the experimental work and provided a more quantitative insight into the process. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Effect of ultrasound on bubble breakup within the mixing chamber of an effervescent atomizer

Gas bubbles introduced into a liquid in the mixing chamber help to break up the liquid into fine droplets on being expanded to the ambient pressure. The passage of gas bubbles through the orifice of the nozzle requires that the size of the bubbles be much smaller than the diameter of the orifice. In the present work, the effectiveness of 20 kHz ultrasound to increase number density of fine bubbles within the mixing chamber of an effervescent atomizer by breaking up bubbles introduced in it by an aerator was investigated. Bubbles of initial size in the range of 5-10 mm were shown to get disintegrated into clusters of micron and sub-micron sized bubbles. A fine spray was produced in the presence of ultrasound at a gas-to-liquid mass flowrate ratio (GLR) of 0.063%. The half-cone angle of spray was in the range of 6-10°, which compares favorably with conventional atomizers. The experimental findings of bubble breakup were theoretically modeled by the Rayleigh-Plesset equation. The results of the model indicate that bubbles having initial radius less than 3 mm undergo growth and subsequent disintegration at 20 kHz for the given acoustic pressure of 0.3 MPa.     

Time-frequency MEG-MUSIC algorithm

We propose a method that incorporates the time-frequency characteristics of neural sources into magnetoencephalographic (MEG) source estimation. The method is based on the multiple-signal-classification (MUSIC) algorithm and it calculates a time--frequency matrix in which diagonal and off-diagonal terms are the auto and crosstime--frequency distributions of multichannel MEG recordings, respectively. The method averages this time-frequency matrix over the time--frequency region of interest. The locations of neural sources are then estimated by checking the orthogonality between the noise subspace of this averaged matrix and the sensor lead field. Accordingly, the method allows us to estimate the locations of neural sources from each time--frequency component. A computer simulation was performed to test the validity of the proposed method, and the results demonstrate its effectiveness.     

Performance and emission study in manifold hydrogen injection with diesel as an ignition source for different start of injection

Over the past two decades there has been a considerable effort to develop and introduce alternative transportation fuels to replace conventional fuels, gasoline and diesel. Environmental issues are the principal driving forces behind this effort. To date the bulk of research has focused on the carbon-based fuels such as reformulated gasoline, methanol and natural gas. One alternative fuel to carbon-based fuels is hydrogen which is considered to be low polluting fuel. In the present experimental investigation hydrogen was injected into the intake manifold by using an injector. Using an electronic control unit (ECU) the injection timing and the duration were controlled. From the results it is observed that the optimum injection timing is at gas exchange top dead center (GTDC). The efficiency improved by about 15% with an increase in NO_X emission by 3% compared to diesel. The smoke emission decreased by almost 100%. A net reduction in carbon emissions was also noticed due to the use of hydrogen. By adopting manifold injection technique the hydrogen–diesel dual fuel engine operates smoothly with a significant improvement in performance and reduction in emissions.     

Effect of injection pressure on performance,emission and combustion characteristics of high linolenic linseed oil methyl ester in a DI diesel engine

Due to the increasing demand for fossil fuels and environmental threat, a number of renewable sources of energy have been studied worldwide. In the present investigation a high linolenic linseed oil methyl ester has been investigated in a constant speed, DI diesel engine with varied fuel injection pressures (200, 220 and 240 bar). The main objective of this study is to investigate the effect of injection pressures on performance, emissions and combustion characteristics of the engine. The test results show that the optimum fuel injection pressure is 240 bar with linseed methyl ester. At this optimized pressure the thermal efficiency is similar to diesel and a reduction in carbon monoxide, unburned hydrocarbon and smoke emissions with an increase in the oxides of nitrogen was noticed compared to diesel. The combustion analysis shows that, the ignition delay is lower at higher injection pressures compared to diesel and the peak pressure is also higher at full load. The combustion duration was almost same at all the injection pressures. It is concluded that linseed methyl ester at 240 bar injection pressure is more efficient than 200 and 220 bar, except for nitrogen oxides emission.     

Experimental investigation on a DI dual fuel engine with hydrogen injection

Over the past two decades considerable efforts have been undertaken to develop and introduce new alternative fuels for the conventional gasoline and diesel. Many alternative fuels, both liquid and gaseous, have been experimented and some have even been commercialized such as ethanol, natural gas, etc. Hydrogen has been considered as an excellent fuel to replace the petroleum‐based fuels due to its clean burning characteristics. In the present experimental investigation, hydrogen was injected in the intake manifold and diesel fuel was injected inside the engine cylinder in the conventional manner. Hydrogen injection parameters such as injection timing, injection duration and quantity of hydrogen injected were optimized based on the performance and emission characteristics. Exhaust gas recirculation (EGR) technique was adopted to reduce the oxides of nitrogen emission. From the results it was observed that for hydrogen diesel dual fuel (DF) engine, the optimal operating parameters for hydrogen injection were start of injection at gas exchange top dead centre with injection duration of 30° crank angle with the hydrogen flow rate of 7.5 litres per minute (lpm). With EGR the optimized condition was found to be 20% for the entire load. The brake thermal efficiency with 20% EGR increases by 16% at 75% load as compared with diesel, while at full load it reduces by 8% due to the recirculation of exhaust gases that results in a reduction of intake oxygen concentration compared with part load. NO_X emission decreases by five and half times, while other emissions increase by 1.4 times as compared with DF engine. Copyright © 2008 John Wiley & Sons, Ltd.     

Evidence for compliance controlled oxygen vacancy and metal filament based resistive switching mechanisms in RRAM

We present electrical evidence on asymmetric metal-insulator-semiconductor (MIS) based test structures in support of the presence of two different independent switching mechanisms in a resistive random access memory (RRAM) device. The valid mechanism for switching depends on the compliance capping (I_gl) for forming/SET transition. Our results convincingly show that low compliance based switching only involves reversible oxygen ion drift to and from oxygen gettering gate electrodes, while high compliance switching involves formation and rupture of conductive metallic nanofilaments, as verified further by our physical analysis investigations. We have observed this unique dual mode switching mechanism only in NiSi-based gate electrodes, which have a moderate oxygen solubility as well as relatively low melting point.