Development of a Novel HVDC System Model for Control Design

The operation of HVDC converters is discrete in nature. It is, therefore, proper to take into account the discrete behavior of converter operation while developing the system model for small signal stability analysis. This paper presents the development of such a system model, which also explicitly includes the effect of phase angle of respective AC bus voltages. A modular approach has been adopted for the formulation of complete state space system model. Utilizing the system model, the stability is examined in the controller parameter plane using eigenvalue analysis. The stability domains thus obtained are validated through detailed dynamic digital simulation.     

A design approach for myoelectric arm with hand and wrist motions using single actuator

This paper relates to the development of prosthetic myoelectric hand that performs many functions of real human hand like opening and closing of fingers and wrist rotation. This dual movement of prosthetic hand is controlled by a single DC motor. Below-elbow amputee persons with missing limbs can append this prosthetic hand with the available stump and can do some of the hand operations with multiple degrees of freedom by voluntary activation of muscles using electromyogram (EMG) electrodes. To rehabilitate such a person, facilities like opening, closing, grasping, and lifting objects of different weight with variable grip force are available like natural hand. The main design consideration includes degrees of freedom, number of actuators, power of actuators, reliability, electronic control, light weight, economic viability, wrist rotation, variable grip force pattern, and ease of attachment with limb. Use of electromagnetic clutches along with the coupling logic of DC motor and microcontroller based on grip force generation and wrist rotation based on EMG signals imparts a new function to the device. It will be useful for both robotic and prosthetic industry.     

Performance of Roof Tiles under Simulated Hurricane Impact

Widespread damage to tile roofs over the last few years, even for weaker hurricanes, has raised concerns regarding construction practices and codes. An experimental study was carried out for clay and concrete roof tiles with adhesive- and mortar-set attachments using a “Wall of Wind” apparatus. The estimated peak 3-s gust wind speeds achieved in the simulations were 31.5 and 57.9?m/s (70.5 and 129.5?mi/h), as defined by the ASCE 7 Standard. Tests were conducted for winds from the 0° direction and subsequently, unless the roofs suffered significant damage, from the 50° direction. The research objectives were to assess roof-tile performance and observe failure modes in simulated hurricane conditions, and obtain wind pressure data allowing comparisons of measured pressures with pressures for components and cladding specified in the ASCE 7-05 Standard. Comparisons of pressure time histories for different tile systems showed that the external pressure on a tile is strongly influenced by the surface geometry of the tile. The concrete tile roof with mortar set showed the best performance among all tested roofs. Workmanship was found to be a major factor to roof-tile performance. Test results also suggested that the ASCE 7-05 pressure coefficient values are conservative for assessing wind loads acting on individual tiles.     

Nonisothermal Crystallization Modeling and Simulation for Polypropylene/Nano CaSO4 Composites with Variations in Nanosizes and Wt.% of Loading

Avrami and Ozawa's combined analysis was employed to study the nonisothermal crystallization kinetics of Polypropylene (PP): CaSO₄ (of 12 and 22 nm) composites using a Differential Scanning Calorimeter (DSC). The parameters, such as Avrami's exponent (n) and growth rate constant (Z_t), that characterized the system of different nanosize composites and virgin PP, were determined. The relative degree of crystallinity as a function of temperature for PP/nano CaSO₄ composites at the same cooling rate and the Sigmoidal shape of curves indicate a strong interaction between PP molecules and the nanolayer, which leads to greater nucleation with a reduction in nanosizes. The theoretical combination of kinetic equations was found to be suitable to describe the physical phenomena of real system. The values of parameters n, Z_t and predicted time t for crystallization at a single cooling rate were obtained from the mathematical model.     

Behavior of alginate–gelatin blended gel with embedded macrovoids: Stress-induced changes and the solute release characteristics

Blending of gelatin to alginate promote cell–material interaction. However, the changes in diffusive and mechanical properties need to be ascertained. This study shows that the presence of two superposed polymer networks, where gelatin is not additionally crosslinked resulted in higher uptake and slower release of vitamin B₁₂. In the presence of gelatin, the stress is found higher for the same level of compressive deformation, and the permeability of the pore fluid during expulsion under compressive stress is found significantly lower. Also, a large residual strain at the end of each cycle in case of cyclic compression is observed, when gelatin is present. A microfluidic device is used to introduce voids uniformly across the blended gel with an objective to increase compressibility, permeability (for faster equilibration of pore pressure), and uptake of bioactive species. The results showing lower permeability and higher uptake in the presence of gelatin are discussed.     

Non-linear weight adjustment in adaptive gamma correction for image contrast enhancement

Multimedia Tools and Applications - Image enhancement remains an intricate problem, crucial for image analysis. Several algorithms exist for the same. A few among these algorithms categorize images...     

In vitro assessment of antimicrobial efficacy of the D-tagatose and lactobacilli-based synbiotic preparations against the pathogenic Escherichia coli and Salmonella typhimurium

The study aimed to investigate the utilisation of prebiotic D-tagatose by probiotic lactobacilli (L. rhamnosus GG, L. casei, L. acidophilus and L. fermentum) and enteric pathogens (E. coli and S. typhimurium) to determine synbiotic potential of D-tagatose and lactobacilli combination. The antimicrobial efficacy of the synbiotic preparations (D-tagatose with lactobacillus) was assessed against selected pathogens in co-culture assays. Evidently, D-tagatose supported growth of selected lactobacilli, especially the L. rhamnosus GG and L. casei, but not the enteric pathogens. The tested synbiotic preparations completely inhibited growth of both the pathogens, even in the presence of D-glucose in co-cultures. The well-diffusion assay demonstrated the presence of antimicrobial activity as recorded by drop of culture pH. The study substantiated that D-tagatose could be an effective prebiotic component for formulation of potential synbiotic combinations with L. rhamnosus GG or L. casei that can be used as an alternative to antibiotics against enteric pathogens.     

Applications of RF aperture-array spatially-bandpass 2-D IIR filters in sub-Nyquist spectrum sensing,wideband doppler radar and radio astronomy beamforming

The application of two-dimensional (2-D) infinite impulse response (IIR) spatially-bandpass (SBP) filters as a digital beamformer for a wide spectrum of practical applications spanning wireless cognitive radio communications, doppler radar, and radio astronomy instrumentation is discussed. The paper starts with an introduction of the recently proposed 2-D SBP filter. The first application is a spectrum sensing scheme for dynamic spectrum access based cognitive radios. A 2-D IIR SBP filter is used in conjunction with a sub-Nyquist wideband signal reconstruction technique to achieve aperture-array directional spectrum sensing using sub-Nyquist sparse sampling based on the recently reported Eldar algorithm. The second application is related to wideband pulse and continuous-wave frequency modulated Doppler radar sensing. The SBP filter is integrated with a wideband radar back-end connected to an electronically-steerable aperture antenna. A a low-complexity directional localization algorithm is presented, which estimates the range and angle of a target scatterer with a signal to interference ratio improvement of 10 dB. We also present applications of 2-D IIR SBP in the fields of classification and remote sensing of unmanned aerial vehicles. Finally, a digital aperture-array wideband beamforming model using the 2-D IIR SBP filters is presented for radio telescope systems based on dense aperture arrays and time-domain beamforming. A well-known example is the study of pulsar astrophysics using a highly-directional aperture antenna system. The 2-D IIR SBP beamformer is simulated as the digital backend of the time-domain beamforming system with array signals synthesized using measured time-domain signatures from the Crab pulsar obtained from the GAVRT. The SBP filter shows a gain of 12.3 dB with an order of magnitude lower circuit complexity compared to traditional phased-array digital beamformers. To obtain comparable levels of SINR improvement, the wideband phased-array beamformers require 48-point FFTs per antenna. Assuming the optimum three real-multiplications per complex multiplication for the Gauss algorithm, it is discovered that the proposed 2-D IIR SBP beamformers are more than 97 % lower in digital multiplier complexity compared to traditional FIR phased-array FFT-beamformers.