A New Chebyshev-like Low-pass Filter Approximation

A new Chebyshev-like low-pass filter approximation is proposed for which the order is always odd and hence there is no problem for doubly terminated LC ladder realization. Flexibility of shaping the response and lower Q values of complex poles appear to be the major advantages of the new approximation as compared to the normal Chebyshev filter.     

Enhanced performance of direct methanol fuel cells: a study on the combined effect of various supporting electrolytes,flow channel designs and operating temperatures

Establishing a better coordination between operating parameters and flow channel design is one of the most critical factors in achieving an optimum final performance of a fuel cell, since even a marginal change in any of the parameters can sharply affect the cell's performance. In this study, we report the use of three different acids, viz. sulphuric acid (H₂SO₄), formic acid (HCOOH) and phosphoric acid (H₃PO₄) as supporting electrolytes in combination with 2 M methanol fuel, wherein we demonstrated the effects of different combinations of acidic fuels and channel designs on the final cell performance. For this purpose, we made use of four different types of serpentine flow design. In the process, it was observed that an addition of 2 M concentrations of H₂SO₄ and H₃PO₄ enhanced the cell performance sharply in terms of current density, reaching values of 210 mAcm^?2 and 180 mAcm^?2, respectively, when analyzed at 0.2 V potential. This result was a considerable improvement over the current density value of 90 mAcm^?2 achieved while using only 2 M methanol analyzed at the same potential. Moreover, the open‐circuit voltage showed a value of greater than 0.6 V for both fuel samples. With a flow channel length of 650 mm (A5SF2) and at an open ratio of 52%, we obtained maximum power values of 42 mWcm^?2 and 36 mWcm^?2 for fuels containing 2 M H₂SO₄ (M2S2) and 2 M H₃PO₄ (M2P2), respectively, when analyzed at 70°C. Copyright © 2013 John Wiley & Sons, Ltd.     

Development and study of an automatic AC bridge for impedancemeasurement

An automatic ac bridge method employing the principle of balancing by means of a stochastic gradient search algorithm is presented. Among the various gradient search techniques, the Widrow-Hoff least mean square (LMS) technique has been chosen as it involves a low computational burden. The LMS algorithm has been used by the authors for the operation of an ac bridge operating with continuous variables. The relevant operation has been verified by simulation; it can also measure negative impedance. A relation has been established between parameters to be used in the LMS algorithm for discrete and continuous versions of the bridge. The balance convergence time for a relatively simple form of the LMS bridge, namely, the R-R type bridge, has been theoretically established and experimentally verified both by simulation and real-time implementation. The frequency response of the LMS algorithm has also been determined     

Developing norms for manual carrying tasks using mechanical efficiency as the optimization criterion

The primary objective of this investigation was to determine optimum activity levels when carrying symmetrical loads in front of the body. Efficiency of mechanical work was used as the response variable for optimization purposes. This was defined as the ratio between the rate of energy transfer between and within body segments (Wwb) and the rate of net metabolic energy expenditure during the task (RNME). Response surface methodology was used to develop a model describing the relationship between the efficiency of mechanical work and three task related variables, i.e., load handled, frequency of handling and carrying distance. It was determined that a maximum efficiency of 31.74% is achieved under a combination of task conditions as follows: load = 16.72 kg; frequency = 3.64 handlings/min and carrying distance = 10.61 m. The implications of these findings are discussed in the paper.     

Influence of molecular rigidity on interfacial ordering in diphenyl-based polysiloxane films

Synchrotron X-ray reflectivity (XRR) shows significant differences between the ordering in thin films of diphenyl-based siloxane oligomers with single versus double backbones of -Si-O- repeating groups. We show that the more restricted conformational arrangement of twofold-skeleton molecules results in a higher degree of molecular ordering indicated by 2-2.5 times higher value of intensity of the corresponding Bragg peak in thin solid films of poly(phenylsilsesquioxane) than in films of poly(diphenylsiloxane), regardless of the solvent used for film casting. In both cases, the ordered molecules are located within 40-50 Å of the substrate surface. The results indicate unambiguously that the chain stiffness of siloxanes governs the degree of ordering in the restricted geometry of the interfacial region.     

Comparative study of electron conduction in azulene and naphthalene

We have studied the feasibility of electron conduction in azulene molecule and compared with that in its isomer naphthalene. We have used non-equilibrium Green’s function formalism to measure the current in our systems as a response of the external electric field. Parallely we have performed the Gaussian calculations with electric field in the same bias window to observe the impact of external bias on the wave functions of the systems. We have found that the conduction of azulene is higher than that of naphthalene inspite of its intrinsic donor-acceptor property, which leads a system to more insulating state. Due to stabilization through charge transfer the azulene system can be fabricated as a very effective molecular wire. Our calculations show the possibility of huge device application of azulene in nano-scale instruments.     

Thermal and electronic properties of Bi1 − xSbx alloys

Polycrystalline Bi_1 ? xSb_x (x = 0.10, 0.12 and 0.15) semiconducting alloys were synthesized by mechanical alloying in order to achieve homogeneous thermoelectric materials with improved mechanical strength. The homogeneity of the powder samples were repeatedly checked by X-ray diffraction and scanning electron microscopy to standardize the milling conditions. The best possible homogenized material was developed with the milling conditions of BPR 30:1, ball diameter 30 mm, 400 rpm and milling time of 15 h. The electrical resistivity, thermoelectric power and thermal conductivity were measured in the temperature range 300–500 K. It was found through these experiments that the composition with x = 0.12 behaved in a normal semiconducting way, whereas the other two compositions (x = 0.10 and 0.15) showed degenerate semiconductor behaviour. These features have been qualitatively explained from the band structure and interband scattering mechanisms.     

Single-parameter controlled-variable amplitude change function for digital filtering

A single-parameter controlled-variable amplitude change function has been constructed for digital filtering using multiple units of a prototype filter. The limits of variation are discussed. The technique is shown to be useful not only for the reduction of errors in either the pass band or the stop band of the overall filter, but also for varying the cutoff frequency of the overall filter over a wide range. Hardware implementation problems resulting from a wide variation are shown to be overcome by a modular approach.     

Locking range and stability of injection locked 1.54 µm InGaAsp semiconductor lasers

Measurements of the intensity of an injection locked 1.54 μm InGaAsP laser are reported. The change in intensity of the locked laser across the locking range is quite asymmetric, with a shape that agrees well with the theory of Lang. A linewidth parameter ofalpha = 6 pm 1was determined from the magnitude of the locking range. The injection locked laser was found to be unstable on the high frequency end of the locking range. The physical origin of this instability is explained in terms of a laser intensity change altering the phase of the laser field relative to that of the injected field.     

High-speed target tracking by fuzzy hostility-induced segmentation of optical flow field

A time efficient technique for real-time tracking of high-speed objects in a video sequence is presented in this article. The technique is primarily based on the segmentation of the optical flow field computed between the successive image frames of a video sequence, followed by the tracking of a detected point of interest (POI) within the segmented flow field. In the initial phase of the technique, the optical flow field between the first two successive image frames acquired from a video sequence, is computed. A fuzzy hostility index indicative of the degree of coherence of the moving objects in the image frames, is used to segment the optical flow field. This yields different coherent regions of interest (ROIs) in the segmented flow field. A POI is then detected in the different ROIs obtained. Tracking of the moving object is then carried out by computing the flow fields between predefined ROIs in the neighborhood of the detected POI in the subsequent image frames.Since the selected ROIs are smaller than the image frames, a fair amount of reduction in the time required for the computation of the optical flow field is achieved, thereby facilitating real-time operation. An application of the proposed technique is demonstrated on three video sequences of high-speed flying fighter aircrafts.