[Show abstract][Hide abstract] ABSTRACT: Using a 'Cut and Paste' technique, we develop a thin-shell wormhole in the heterotic string theory. We determine the surface stresses, which are localized in the shell, by using Darmois–Israel formalism. The linearized stability of this thin wormhole is also analyzed.
International Journal of Modern Physics D 01/2012; 16(10). · 1.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Exact solutions are obtained for an inhomogeneous cosmological model in normal gauge for Lyra's geometry. Some properties of the model have also been discussed.
International Journal of Modern Physics D 01/2012; 11(09). · 1.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper reports a fully monolithic subthreshold CMOS receiver with integrated subthreshold quadrature LO chain for 2.4 GHz WPAN applications. Subthreshold operation, passive voltage boosting, and various low-power circuit techniques such as current reuse, stacking, and differential cross coupling have been combined to lower the total power consumption. The subthreshold receiver, consisting of the switched-gain low noise amplifier, the quadrature mixers, and the variable gain amplifiers, consumes only 1.4 mW of power and has a gain of 43 dB and a noise figure of 5 dB. The entire quadrature LO chain, including a stacked quadrature VCO and differential cross-coupled buffers, also operates in the subthreshold region and consumes a total power of 1.2 mW. The subthreshold receiver with integrated LO generation is implemented in a 0.18 mum CMOS process. The receiver has a 3-dB IF bandwidth of 95 MHz.
IEEE Journal of Solid-State Circuits 11/2008; · 3.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this article, a special static spherically symmetric perfect fluid solution of Einstein's equations is provided. Though pressure and density both diverge at the origin, their ratio remains constant. The solution presented here fails to give positive pressure but nevertheless, it satisfies all energy conditions. In this new spacetime geometry, the metric becomes singular at some finite value of radial coordinate although, by using isotropic coordinates, this singularity could be avoided, as has been shown here. Some characteristics of this solution are also discussed.
[Show abstract][Hide abstract] ABSTRACT: Considering the short-term exposure limit of SO2 to be 5 ppm, we first time report that semiconductor sensors based on vanadium doped SnO2 can be used for SO2 leak detection because of their good sensitivity towards SO2 at concentrations down to 5 ppm. Such sensors are quite selective in presence of other gases like carbon monoxide, methane and butane. The high sensitivity of vanadium doped tin dioxide towards SO2 may be understood by considering the oxidation of sulfur dioxide to sulfur trioxide on SnO2 surface through redox cycles of vanadium-sulfur-oxygen adsorbed species.
[Show abstract][Hide abstract] ABSTRACT: According to the KEMI report, products with polycyclic aromatic compounds, PCA, levels exceeding 3% by weight must be labelled. The report pointed out that worn tyre tread material was being spread on the roadsides, introducing high amounts of PCA into the environment. PCA is having toxic effects on aquatic organisms. Polyaromatic-hydrocarbon-rich extender oils are to be banned by December 2009, which gives rise to challenges for the oil and rubber industries. In the present work, 10 types of naturally occurring oils and six types of petroleum-based oils were characterised in natural-rubber-based truck tyre tread cap compound. Compounds made with some of the naturally occurring oils showed better mechanical and dynamic mechanical properties.
[Show abstract][Hide abstract] ABSTRACT: Nanocrystalline gamma iron oxide (γ-Fe2O3) has been synthesized at room temperature through sonication-assisted precipitation technique. The key in obtaining γ-Fe2O3 at room temperature lies in exploiting high-power ultrasound (600W). The gas-sensing properties to n-butane of pure γ-Fe2O3 were investigated by studying the electrical properties of the sensor elements fabricated from the synthesized powder. The maximum response (∼90%) of the sensor to 1000ppm n-butane at 300°C can be explained on the basis of catalytic activity of the nanocrystallites. The response and recovery time of the sensor to 1000ppm n-butane were less than 12s and 120s, respectively.
Sensors and Actuators B Chemical 03/2008; 130(2):882-888. · 3.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Along with high sensitivity towards detecting gases, the response and recovery times of semiconductor gas sensors are of paramount importance for practical applications. In most of the cases, the recovery time is larger than the response time. Incidentally, water vapour present in the ambience is chemisorbed on the semiconductor oxide surface and the water molecules dissociate into hydroxyl species, which act as electron donors. In the present study on tin dioxide-based methane sensor, we find that if the interference of adsorbed moisture can be reduced by surface treatment with a dilute thiourea solution, the recovery time and stability of the sensor improve, which make them suitable for practical applications.
Sensors and Actuators B Chemical 11/2007; 127(2):554-558. · 3.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A SiGe sub-harmonic down-conversion mixer using a novel active anti-parallel diode pair is presented for millimeter-wave applications. The proposed architecture can help reduce conversion loss and also lower the required local oscillator power. With an LO power of 0 dBm, the measured 2times conversion gain varies from -5 to -7.8 dB in the 50 to 65 GHz range. Compared to earlier reports of millimeter-wave SiGe and GaAs sub-harmonic mixers requiring 5 to 10 dBm of LO power, this circuit achieves similar conversion loss with an LO power as low as -7.5 dBm, while consuming only 0.5 mW of DC power.
[Show abstract][Hide abstract] ABSTRACT: In this article, we have found a series solution of 3D Einstein equations describing a wormhole for an inhomogeneous distribution of phantom energy. Here, we assume equation of state is linear but highly anistropic.
[Show abstract][Hide abstract] ABSTRACT: It has been recently shown that Hoyle-Narlikar's C-field theory admits wormhole geometry. We derive the deflection angle of light rays caused by C-field wormhole in the strong field limit approach of gravitational lensing theory. The linearized stability of C-field wormhole under spherically symmetric perturbations about static equilibrium is also explored.
Chinese Journal of Physics- Taipei- 06/2007; · 0.43 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Polyaromatic hydrocarbon-rich extender oils are to be banned by December 2009 which gives rise to challenges for the oil and rubber industries. In the present work, 10 types of naturally occurring oils and six types of petroleum-based oils were characterized for chemical and physical properties. The effect of these process oils in natural rubber-based truck-tyre tread cap compound was also studied. Some of the naturally occurring oils showed better processing properties, polymer–filler interaction and dispersion properties.
[Show abstract][Hide abstract] ABSTRACT: We propose wormholes solutions by assuming space dependent equation of state parameter. Our models show that the existence of wormholes is supported by arbitrary small quantities of averaged null energy condition (ANEC) violating phantom energy characterized by variable equation state parameter.
Acta Physica Polonica Series B 02/2007; · 1.00 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Infrared spectroscopy can be used efficiently by polymer and rubber technologists for identification of polymer, polymer–blend ratio calculation, raw material evaluation, study of reaction mechanism, microstructure determination, etc. The present article represents a method to characterize nitrile rubber by Fourier-transformed infrared spectrophotometry (FTIR). The absorbance ratio of specific peaks of different grades of nitrile rubber was correlated with the acrylonitrile content measured by the Kjeldhal method. The acrylonitrile content of unknown acrylonitrile butadiene rubber (nitrile rubber, NBR) was calculated from a calibration graph.
[Show abstract][Hide abstract] ABSTRACT: Thick film methane sensors have been fabricated from nanosized tin dioxide powder containing antimony oxide and palladium. The powder has been prepared by sonication-assisted simultaneous precipitation and the sensors made with this powder showed optimum resistance for device applications and good sensitivity towards methane. This contrasts with the thick film sensors prepared with the powder synthesized without sonication, which showed very high resistance at the operating temperature. The complex plane impedance spectroscopy of the sensors (both in air and in the presence of gas) can be a good indicator of the sensor quality. It has been observed that the nature of the complex plane impedance plot of the sensors fabricated by using powders synthesized through sonication-assisted simultaneous precipitation matches well with that of high-quality imported Figaro (Japan) sensors.
Sensors and Actuators B Chemical 12/2006; 119(2):431-434. · 3.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Every time a user conducts an electronic transaction over the Internet a wealth of personal information is revealed, either voluntarily or involuntarily. This causes serious breach of privacy for the user, in particular, if the personally identifying information is misused by the other users present in the network. Ideally, therefore, the user would like to have a considerable degree of control over what personal information to reveal and to whom. Researchers have proposed models to allow a user to determine what personal information to reveal while doing a transaction over the Internet. However, these models do not help the user in determining who to trust, how much to trust and why to trust them with the personal information. The models fail to address loss of privacy through the misuse of information. In this paper we propose a privacy enhancing trust model to measure the degree of confidence that a user can have in the context of preservation of her privacy during a transaction. The model considers several factor while computing trust which include a user's own experience and knowledge about the target user and feedback obtained from groups of peer users called 'trusted neighbors' and 'friends'. The proposed scheme provides a flexible and powerful approach for the secure handling of private data and offers a user considerable control over how she wishes to disseminate her personal data
Information Assurance Workshop, 2006 IEEE; 07/2006
[Show abstract][Hide abstract] ABSTRACT: In the present study we find that it is possible to develop sensors based on iron doped tin dioxide, which can detect both methane and butane (present in CNG and LPG, respectively) at a temperature of 350 °C. However, the same sensors can selectively detect butane at a temperature of 425 °C. Such differential behaviour can be explained by considering the decrease in the number and/or strength of Lewis acid sites on SnO2 due to Fe-doping and the role of chain length on the adsorption–desorption characteristics of alkanes. However, the incorporation of palladium as a catalyst in Fe-doped SnO2 sensors removes the typical selectivity, and the temperatures of the maximum response coincide for methane and butane.
Sensors and Actuators B Chemical 06/2006; · 3.84 Impact Factor