Improved microwave absorption and electrostatic charge dissipation efficiencies of conducting polymer grafted fabrics prepared via in situ polymerization

Polyaniline (PANI) and polypyrrole (PPY) were grafted over cotton fabrics by in situ polymerization. FTIR spectra show systematic shifting of bands corroborating surface grafting of conducting polymers on cotton fabric. SEM images revealed that the surface coating of PANI was smoother than PPY. However, better control over coating thickness and uniformity was achieved in PPY fabric. The probable formation mechanism of grated fabrics has also been proposed. The good thermal stability and acceptable electronic conductivity values indicate that these fabrics could be used for electrostatic charge dissipation and microwave absorption. The antistatic studies have shown complete charge dissipation (decay time <0.01 sec). The microwave absorption studies of the conducting fabrics in X‐band (8.2–12.4 GHz) show absorption dominated total shielding effectiveness in the range ?11.3 to ?11.7 dB (>92% attenuation) and ?9.2 to ?9.6 dB (>88% attenuation) for fabrics grafted with PPY and PANI, respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

Polyelectrolyte‐Assisted Noncovalent Functionalization of Carbon Nanotubes with Ordered Self‐Assemblies of a Water‐Soluble Porphyrin

The self‐assembly and induced supramolecular chirality of meso‐tetrakis(4‐sulfonatophenyl)porphyrin (TSPP) on both single‐wall (SWCNT) and multiwall carbon nanotubes (MWCNT) are investigated. Under mild pH conditions (pH 3), TSPP forms aggregates when CNTs are dispersed in an aqueous solution containing positively charged polyelectrolytes such as poly‐L ‐lysine (PLL) or poly(allylamine hydrochloride) (PAH). Evidence for the geometry of the porphyrin aggregates is obtained from absorption spectra, whereby the fingerprints of J‐ and H‐aggregates are clearly seen only in the presence of smaller‐diameter nanotubes. J‐aggregates are better stabilized with PLL, whereas in the presence of PAH mainly H‐aggregates prevail. Excited‐state interactions within these nanohybrids are studied by steady‐state and time‐resolved fluorescence. The porphyrin emission intensity in the nanohybrid solution is significantly quenched compared to that of TSPP alone, and this implies strong electronic interaction between CNTs and porphyrin molecules. Fluorescence lifetime imaging microscopy (FLIM) further supports that porphyrin arrays are associated with the MWCNT sidewalls wrapped in PLL. In the case of the SWCNT hybrid, spherical structures associated with longer fluorescence lifetime appeared after one week, indicative of H‐aggregates of TSPP. The latter are the result of π–π stacking of porphyrin units on neighboring nanotubes facilitated by the strong tendency of these nanotubes to interact with each other. These results highlight the importance of optimum dimensions and surface‐area architectures of CNTs in the control/stability of the porphyrin aggregates with promising properties for light harvesting.     

Hypervalent iodine oxidation of benzil-α-arylimino oximes: an efficient synthesis of 2,3-diphenylquinoxaline-1-oxides

A mild and efficient synthetic protocol for the oxidation of benzil-α-arylimino oximes 3 utilizing iodobenzene diacetate (IBD) as an oxidizing agent has been developed. Oximes 3, obtained by the condensation of (E)-benzil monoxime 2 with various appropriately substituted anilines 1, on treatment with iodobenzene diacetate in dichloromethane at room temperature underwent oxidative cyclization to afford 2,3-diphenylquinoxaline-1-oxide 4 in excellent yields.     

Antiferromagnetic stripe ordering at the tetragonal-orthorhombic transition in LnOFeAs probed by X-ray absorption spectroscopy

Measurements of the Fe K-edge X-ray absorption near edge (XANES) spectra of LnOFeAs high T_c superconductors exhibit small but measurable changes across the tetragonal to orthorhombic phase structural phase transition. Calculations, based on the local structure centered at the Fe site obtained by crystallographic investigations, reproduce the observed changes in the spectra under the change of the crystal structure, indicating variations in the Fe local unoccupied electronic states. Calculated Fe density of states including stripe spin ordering in the orthorhombic phase show significant modifications with respect to Fe 3d density of states in the tetragonal phase or the density of states in the orthorhombic phase calculated ignoring spin ordering. This implies that the striped spin ordering in the orthorhombic phase is necessary to describe its electronic properties not only in the ground state but also for excited states above the Fermi energy.     

Optics based biometric encryption using log polar transform

We propose an optics based biometric encryption technique using log polar transform. In this method, the key of the encryption process has been linked to the fingerprint of the enrolled person. The order of fractional Fourier transform and the seed values of the chaotic random phase masks in combination act as the key for the encryption process. In order to link the combined key to the fingerprint, a lookup table has been formed by the key and the log polar transform of the fingerprint. The linking algorithm not only encrypts the image of the enrolled person but also authenticates the input image. The main advantage of this method is its capability to retrieve the same key in the decryption process by using the live fingerprint. The key is not required to be communicated to the receiver side. The retrieval of the image is possible only when the live fingerprint of the enrolled person is presented at the decryption side. The real life fingerprints have been used to demonstrate the proposed technique. Simulations have been performed on the Matlab platform to validate the proposed technique. The signal to noise ratio and mean square error has been calculated in order to support the proposed technique. The effect of the rotation and the scaling of the fingerprints have been studied to check the key retrieval from the live fingerprint of the enrolled person. The study of the different whorl types of fingerprint of different persons has also been done to check the efficacy of the key retrieval from the whorl types of the live fingerprints of different person.     

Optics based biohashing using joint transform correlator

Most authentication process uses password and personal identification numbers (PIN) for security purposes. In order to remove the problem of hacking or stealing of the password and PIN numbers, there has been an increased interest in the utilization of specific biometric feature of the user. Recently, biohashing systems have been introduced for automatic biometric recognition. In a biohashing system, biohash codes are generated using the feature of the biometric. A basic biohashing system involves two steps. First is the extraction of the feature from the input biometric image and second is the discretisation of the obtained feature vector by using ortho-normalized random numbers. In this paper, a new biohashing system has been proposed in which joint transform correlator (JTC) has been used for extraction of the specific feature of the biometric. In the enrolment process, a biohash code has been generated by using a single face image and then stored. In the verification process, this biohash code is matched with the verification codes for recognition purpose. The main advantage of the proposed biohashing method is the possibility of the optical implementation of the feature extraction of the face image. Experimental as well as simulation results have been given to validate the proposed technique. Normalized Hamming distance has been calculated to discriminate the genuine and impostor face images. By varying the dimension of the feature matrix, the study of the variation of the normalized Hamming distance with the density of the population has been undertaken. For the performance evaluation of the proposed technique the false rejection ratio (FRR) and false acceptance ratio (FAR) have also been calculated.     

Ion-acoustic solitons in multispecies spatially inhomogeneous plasmas

Ion-acoustic solitons are investigated in the spatially inhomogeneous plasma having electrons-positrons and ions. The soliton characteristics are described by Korteweg-de Vries equation which has an additional term. The density and temperature of different species play an important role for the amplitude and width of the solitons. Numerical calculations show only the possibility of compressive solitons. Further, analytical results predict that the peak amplitude of soliton decreases with the decrease of density gradient. Soliton characteristics like peak amplitude and width are substantially different from those based on KdV theory for homogeneous plasmas     

Dynamics of self-focusing and self-phase modulation of elliptic Gaussian laser beam in a Kerr-medium

Using a direct variational technique involving elliptic Gaussian laser beam trial function, the combined effect of non-linearity and diffraction on wave propagation of optical beam in a homogeneous bulk Kerr-medium is presented. Particular emphasis is put on the variation of beam width and longitudinal phase delay with the distance of propagation. It is observed that no stationary self-trapping is possible. The regularized phase is also seen to be always negative.     

Effect of ionized plasma medium on the radiation from a RITMA structure on ferrite substrate

This paper presents theoretical investigations on the radiation properties of a right isosceles triangular microstrip antenna (RITMA) printed on a magnetized ferrite substrate Ni_0.62Co_0.02Fe_1.948O₄ in the presence of ionized plasma medium. The theoretical study on RITMA structure in free space is carried out in TM₁₁ mode of excitation by applying cavity model-based modal expansion technique while hydrodynamic theory is used for its analysis in plasma medium. By varying the bias magnetic field, far-field radiation patterns in free space and plasma medium are obtained which in turn are applied in computing radiated power, directivity, quality factor and bandwidth of antenna. It is found that the presence of plasma medium affects the performance of RITMA structure significantly Article presented at the International Conference on the Frontiers of Plasma Physics and Technology, 9–14 December 2002, Bangalore, India.