A 0.5-2.0 GHz injection locked oscillator cascade for parallel wideband RF spectrum sensing

An area-efficient, wideband RF frequency synthesizer, which simultaneously generates multiple local oscillator (LO) signals, is designed. It is suitable for parallel wideband RF spectrum sensing in cognitive radios. The frequency synthesizer consists of an injection locked oscillator cascade (ILOC) where all the LO signals are derived from a single reference oscillator. The ILOC is implemented in a 130-nm technology with an active area of . It generates 4 uniformly spaced LO carrier frequencies from 500 MHz to 2 GHz. This design is the first known implementation of a CMOS based ILOC for wide-band RF spectrum sensing applications.

Zero-Crossings Based Spectrum Sensing Under Noise Uncertainties

In this work, the hypothesis testing problem of spectrum sensing in a cognitive radio is formulated as a Goodness-of-fit test against the general class of noise distributions used in most communications-related applications. A simple, general, and powerful spectrum sensing technique based on the number of weighted zero-crossings in the observations is proposed. For the cases of uniform and exponential weights, an expression for computing the near-optimal detection threshold that meets a given false alarm probability constraint is obtained. The proposed detector is shown to be robust to two commonly encountered types of noise uncertainties, namely, the noise model uncertainty, where the PDF of the noise process is not completely known, and the noise parameter uncertainty, where the parameters associated with the noise PDF are either partially or completely unknown. Simulation results validate our analysis, and illustrate the performance benefits of the proposed technique relative to existing methods, especially in the low SNR regime and in the presence of noise uncertainties.

RNA nucleosides as chiral sensing agents in NMR spectroscopy

The study reports chiral sensing properties of RNA nucleosides. Adenosine, guanosine, uridine and cytidine are used as chiral derivatizing agents to differentiate chiral 1 degrees-amines. A three component protocol has been adopted for complexation of nucleosides and amines. The chiral differentiating ability of nucleosides is examined for different amines based on the H-1 NMR chemical shift differences of diastereomers (Delta delta(R,S)). Enantiomeric differentiation has been observed at multiple chemically distinct proton sites. Adenosine and guanosine exhibit large chiral differentiation (Delta delta(R,S)) due to the presence of a purine ring. The diastereomeric excess (de) measured by using adenosine is in good agreement with the gravimetric values.

EXPERIMENTAL STUDIES ON AIR-ASSISTED ATOMIZATION OF JATROPHA PURE PLANT OIL

The present study focuses on exploring air-assisted atomization strategies for effective atomization of high-viscosity biofuels, such as pure plant oils (PPOs). The first part of the study concerns application of a novel air-assisted impinging jet atomization for continuous spray applications, and the second part concerns transient spray applications. The particle/droplet imaging analysis (PDIA) technique along with direct imaging methods are used for the purpose of spray characterization. In the first part, effective atomization of Jatropha PPO is demonstrated at gas-to-liquid ratios (GLRs) on the order 0.1. The effect of liquid and gas flow rates on the spray characteristics is evaluated, and results indicate a Sauter mean diameter (SMD) of 50 mu m is achieved with GLRs as low as 0.05. In the second part of the study, a commercially available air-assisted transient atomizer is evaluated using Jatropha PPO. The effect of the pressure difference across the air injector and ambient gas pressure on liquid spray characteristics is studied. The results indicate that it is possible to achieve the same level of atomization of Jatropha as diesel fuel by operating the atomizer at a higher pressure difference. Specifically, a SMD of 44 mu m is obtained for the Jatropha oil using injection pressures of <1 MPa. A further interesting observation associated with this injector is the near constancy of a nondimensional spray penetration rate for the Jatropha oil spray.

Developing acetylcholinesterase-based inhibition assay by modulated synthesis of silver nanoparticles: applications for sensing of organophosphorus pesticides

A novel and highly sensitive sensing strategy for the detection of organophosphorus compounds (OPs) based on the catalytic reaction of acetylcholinesterase (AChE) and acetylcholine (ATCh) during the modulated synthesis of silver nanoparticles (AgNPs) has been developed. The enzymatic hydrolysis of ATCh by AChE yields thiocholine (TCh), which induces the aggregation of AgNPs during synthesis, and the absorption peak at 382 nm corresponding to AgNPs decreases. The enzymatic reaction can be regulated by OPs, which can covalently bind to the active site of AChE and decrease the TCh formation, thereby decreasing the aggregation and significantly enhancing the absorption peak at 382 nm. The proposed system achieved good linearity and limits of detection of 0.078 nM and 2.402 nM for trichlorfon and malathion, respectively, by UV-visible spectroscopy. Further, the sensitivity of the proposed system was demonstrated through the determination of OPs in different spiked real samples. The described work shows the potential application for further development of a colorimetric sensor for other OP pesticide detection during the synthesis of AgNPs using enzyme-based assays.

Application of principal component analysis to gas sensing characteristics of Cr0.8Fe0.2NbO4 thick film array

The transient changes in resistances of Cr0.8Fe0.2NbO4 thick film sensors towards specified concentrations of H-2, NH3, acetonitrile, acetone, alcohol, cyclohexane and petroleum gas at different operating temperatures were recorded. The analyte-specific characteristics such as slopes of the response and retrace curves, area under the curve and sensitivity deduced from the transient curve of the respective analyte gas have been used to construct a data matrix. Principal component analysis (PCA) was applied to this data and the score plot was obtained. Distinguishing one reducing gas from the other is demonstrated based on this approach, which otherwise is not possible by measuring relative changes in conductivity. This methodology is extended for three Cr0.8Fe0.2NbO4 thick film sensor array operated at different temperatures. (C) 2015 Elsevier B.V. All rights reserved.

Enantio sensing property of helicin, the derivative of a natural product: Discrimination of amines and amino alcohols

The chiral sensing property of helicin (the derivative of natural product obtained by partial oxidation of salicin, extracted from willow tree (Salix helix)) is reported. The use of helicin as a chiral derivatizing agent for the discrimination of amines and amino alcohols is convincingly established using H-1 NMR spectroscopy. The large chemical shift separation achieved between the discriminated peaks facilitated the accurate quantification of enantiomeric composition. The consistent trend observed in the shifting of imine proton peak (Delta delta) of helicin in all the derivatized molecules might aid the determination of spatial configuration. (C) 2015 Elsevier B.V. All rights reserved.

Enantio sensing property of helicin, the derivative of a natural product: Discrimination of amines and amino alcohols

The chiral sensing property of helicin (the derivative of natural product obtained by partial oxidation of salicin, extracted from willow tree (Salix helix)) is reported. The use of helicin as a chiral derivatizing agent for the discrimination of amines and amino alcohols is convincingly established using H-1 NMR spectroscopy. The large chemical shift separation achieved between the discriminated peaks facilitated the accurate quantification of enantiomeric composition. The consistent trend observed in the shifting of imine proton peak (Delta delta) of helicin in all the derivatized molecules might aid the determination of spatial configuration. (C) 2015 Elsevier B.V. All rights reserved.

Enantio sensing property of helicin, the derivative of a natural product: Discrimination of amines and amino alcohols

The chiral sensing property of helicin (the derivative of natural product obtained by partial oxidation of salicin, extracted from willow tree (Salix helix)) is reported. The use of helicin as a chiral derivatizing agent for the discrimination of amines and amino alcohols is convincingly established using H-1 NMR spectroscopy. The large chemical shift separation achieved between the discriminated peaks facilitated the accurate quantification of enantiomeric composition. The consistent trend observed in the shifting of imine proton peak (Delta delta) of helicin in all the derivatized molecules might aid the determination of spatial configuration. (C) 2015 Elsevier B.V. All rights reserved.

Nickel substitution induced effects on gas sensing properties of cobalt ferrite nanoparticles

Ni2+ ion induced unusual conductivity reversal and an enhancement in the gas sensing properties of ferrites based gas sensors, is reported. The Co1-xNixFe2O4 (for x = 0, 0.5 and 1) nanoparticles were synthesized by wet chemical co-precipitation method and gas sensing properties were studied as a function of composition and temperature. The structural, morphological and microstructural characterization revealed crystallite size of in the range 10-20 nm with porous morphology consisting of nano-sized grains. The Energy Dispersive X-ray (EDX) mapping confirms homogeneous distribution of Co, Ni, Fe and O elements in the ferrites. The non-stoichiometry of the inverse spinel type ferrites and the relative concentration of Ni3+/Co3+ defects were studied using X-ray photoelectron spectroscopy. It is found that the addition of Ni2+ ions into cobalt ferrite shows preferred selectivity towards CO gas at high temperature (325 degrees C) and ethanol gas at low temperature (250 degrees C), unlike undoped cobalt ferrite or undoped nickel ferrite, which show similar response for both these gases. Moreover, an unusual conductivity reversal is observed, except cobalt ferrite due to the difference in reactivity of the gases as well as characteristic non-stoichiometry of ferrites. This behavior is highly gas ambient dependent and hence can be well-exploited for selective detection of gases. (C) 2015 Elsevier B.V. All rights reserved.

Tailored nitrogen dioxide sensing response of three-dimensional graphene foam

Ultralight and macroporous three-dimensional reduced graphene oxide (rGO) foams are prepared by lyophilization (freeze-drying) technique to avoid a conventional template method. This method allows tailoring the porosity of the foams by varying the weight percentages of graphene oxide dispersions in water. Three different rGO foams of 0.2, 0.5 and 1.0 wt% are used for NO2 sensing. Sensing response from the tailored structure of rGO is found to be directly related to the density. A maximum of 20% sensing response is observed for a higher porosity of the structure, better than the known results so far on graphene foams in the literature. (C) 2015 Elsevier B.V. All rights reserved.

Diffractive Optical Analysis for Refractive Index Sensing using Transparent Phase Gratings

We report the implementation of a micro-patterned, glass-based photonic sensing element that is capable of label-free biosensing. The diffractive optical analyzer is based on the differential response of diffracted orders to bulk as well as surface refractive index changes. The differential read-out suppresses signal drifts and enables time-resolved determination of refractive index changes in the sample cell. A remarkable feature of this device is that under appropriate conditions, the measurement sensitivity of the sensor can be enhanced by more than two orders of magnitude due to interference between multiply reflected diffracted orders. A noise-equivalent limit of detection (LoD) of 6 x 10(-7) was achieved with this technique with scope for further improvement.

Near-Optimal Detection Thresholds for Bayesian Spectrum Sensing Under Fading

This paper considers the problem of energy-based, Bayesian spectrum sensing in cognitive radios under various fading environments. Under the well-known central limit theorem based model for energy detection, we derive analytically tractable expressions for near-optimal detection thresholds that minimize the probability of error under lognormal, Nakagami-m, and Weibull fading. For the Suzuki fading case, a generalized gamma approximation is provided, which saves on the computation of an integral. In each case, the accuracy of the theoretical expressions as compared to the optimal thresholds are illustrated through simulations.

Multi-dimensional Goodness-of-Fit Tests for Spectrum Sensing Based on Stochastic Distances

In this paper, we study two multi-dimensional Goodness-of-Fit tests for spectrum sensing in cognitive radios. The multi-dimensional scenario refers to multiple CR nodes, each with multiple antennas, that record multiple observations from multiple primary users for spectrum sensing. These tests, viz., the Interpoint Distance (ID) based test and the h, f distance based tests are constructed based on the properties of stochastic distances. The ID test is studied in detail for a single CR node case, and a possible extension to handle multiple nodes is discussed. On the other hand, the h, f test is applicable in a multi-node setup. A robustness feature of the KL distance based test is discussed, which has connections with Middleton's class A model. Through Monte-Carlo simulations, the proposed tests are shown to outperform the existing techniques such as the eigenvalue ratio based test, John's test, and the sphericity test, in several scenarios.

Conductometric Sensing of H-2 by Chromium Niobate

Investigations on chromium niobate (CrNbO4) have shown that the material responds to a wide hydrogen concentration range of 0.01%-0.40% at 613 K. The conductivity of CrNbO4 is independent of oxygen partial pressure and offers to be a promising candidate for monitoring H-2 in radioactive spent fuel storage facilities. Reduction of metal ions to lower valence states during hydrogen sensing was evidenced by X-ray photoelectron spectroscopic studies.