Aloka Sinha

A technique for image encryption using digital signature

We propose a new technique to encrypt an image for secure image transmission. The digital signature of the original image is added to the encoded version of the original image. The encoding of the image is done using an appropriate error control code, such as a Bose-Chaudhuri Hochquenghem (BCH) code. At the receiver end, after the decryption of the image, the digital signature can be used to verify the authenticity of the image. Detailed simulations have been carried out to test the encryption technique. An optical correlator, in either the JTC or the VanderLugt geometry, or a digital correlation technique, can be used to verify the authenticity of the decrypted image.

Image encryption by using fractional Fourier transform and jigsaw transform in image bit planes

We propose a new method for image encryption and decryption in which the image is broken up into bit planes. Each bit plane undergoes a jigsaw transform. The transformed bit planes are combined together and then encrypted using random phase masks and fractional Fourier transforms. The different fractional parameters, the random phase codes, and the jigsaw transform index form the key to the encrypted data. This increases the robustness of the encryption system by several orders of magnitude. Different variations of the juxtaposition of the pieces of the image are also considered. These include the rotated version of the jigsaw pieces. The computational complexity of the bit-plane-based jigsaw algorithm is further improved using the third dimension (i.e., along different bit planes) for scrambling as well. The results of computer simulation are presented to verify the proposed idea and analyze the performance of the proposed techniques.

Analog switching in the nanocolloids of ferroelectric liquid crystals

Nanoparticle (NP) dispersion in liquid crystals (LCs) results in significant changes in the physical properties of the existing LC mixtures. Two ferroelectric liquid crystals (FLCs), 5 F 6 T and 6 F 6 T , have been studied for analog switching. The 5 F 6 T sample is doped with titanium dioxide ( T i O 2 ) NPs of two different concentrations of the same average particle size and another FLC 6 F 6 T is systematically doped with barium titanate ( B a T i O 3 ) NPs of two different average particle sizes at the same concentration. The frequency and temperature dependence of the coercive voltage of FLC nanocolloids has been studied. The V-shaped switching was observed in the case of nano-doped FLCs. The value of inversion frequency for the 5 F 6 T + 1.0 wt . % TiO 2 doped sample is 30 Hz while it is 24 Hz for the 6 F 6 T + 0.5 wt . % BaTiO 3 (particle size 5–10 nm) doped sample. The conductivity measurements show that the conductivity of doped samples is higher than the conductivity of their parental FLCs and can be considered the main reason for the V-shaped switching in the FLC nanocolloids, which was initially absent in their parental FLCs.

Face and palmprint multimodal biometric systems using Gabor---Wigner transform as feature extraction

AbstractThis paper explores different multimodal biometric systems based on Gabor–Wigner transform (GWT) for subject recognition. This transform provides a simultaneous analysis of space and frequency components of a biometric image. GWT was initially proposed in the literature for signal analysis. In this technique, the GWT is utilized for extraction of feature vectors from different biometric modalities. An optimization technique, particle swarm optimization, is then used to select the dominant features from the feature vectors. This technique not only improves the performance of the system but also reduces the dimension of the obtained feature vectors. A detailed study has been carried out to investigate the fusion of face and palmprint images at different levels. The receiver operating characteristic curve and the equal error rate are used to evaluate the performance of the technique.

Effect of methoxy group instead of polar group in the nematic phase of four-ring bent-core liquid crystals

Two achiral four-ring bent-core liquid crystal possessing an alkoxy chain at one end of the molecules and methoxy group at the other end are investigated by using the optical polarizing microscope, electro-optical studies, and dielectric spectroscopy. Both the compounds exhibit enantiotropic nematic phase over a wide range of temperatures. In the dielectric spectroscopic studies of the compounds, only one sharp peak in the loss curve is observed in the entire nematic range. In addition, the dielectric permittivity of the sample is very large. The molecular structures of these two compounds are similar to the compounds studied by Ghosh et al., which are reported to exhibit the ferroelectric-like switching and electro-convection pattern. However, the differences are (a) replacement of the polar halogen substituent at one end of the molecule by a methoxy group and (b) an increased length of the alkyl chain at the other end. These studies confirm the requirement of a polar moiety for the ferro-nematic phase to exist in these four-ring bent-core compounds.

Tunable patch antenna using a liquid crystal substrate

Patch antennas are attractive in many mobile communication applications since they are light-weight and simple to manufacture. However, the traditional patch antenna suffers from narrow frequency bandwidth. In this paper, we propose the use of a liquid crystal substrate for a patch antenna whose frequency can be tuned by changing the biasing voltage across the substrate. It has been found by simulations that by varying the biasing voltage from 0 V through 11 V, the operating frequency of the circular patch antenna can be varied from 1.08 GHz through 2.35 GHz. We have also proposed two novel applications for such tunable antennas: (i) antenna based modulation (ABM) and (ii) antenna based frequency diversity (ABFD).

A Palmprint Recognition System Based on Gabor Wigner Transform as Feature Extraction Technique

In the present paper, a palmprint recognition system has been proposed in which the recently proposed Gabor-Wigner transform (GWT) has been used to extract the features from the palmprint images. The novelty of the system lies in the fact that GWT has been used for the first time for feature extraction in a biometric system. A particle swarm optimization technique has been used to select the significant features and to reduce the dimension of the obtained feature vectors while keeping the same level of performance. The receiver operating characteristic (ROC) curve and the equal error rate (EER) have been used to evaluate the performance of the technique

Solvent effects on the absorption and emission spectra of some nematic liquid crystals : Determination of dipole moment and first-order hyperpolarizability

The effect of solvent on the absorption and fluorescence spectra of two liquidcrystalline molecules LC1 and LC2 were studied. These data were used to evaluatethe values of the change in the dipole moment between the ground and excitedstate and the first-order hyperpolarizability “β” in each solvent. The values of βgives an indication of how these liquid crystalline samples can find applicationsas nonlinear materials. The β values are in the range 1–1.9 × 1029 esu for LC1and LC2. The values of β indicate that these compounds can be used as goodnonlinear materials. Here solvatochromism has been used as an effective tool toestimate the hyperpolarizability in solution.

Video encryption using chaotic masks in joint transform correlator

A real-time optical video encryption technique using a chaotic map has been reported. In the proposed technique, each frame of video is encrypted using two different chaotic random phase masks in the joint transform correlator architecture. The different chaotic random phase masks can be obtained either by using different iteration levels or by using different seed values of the chaotic map. The use of different chaotic random phase masks makes the decryption process very complex for an unauthorized person. Optical, as well as digital, methods can be used for video encryption but the decryption is possible only digitally. To further enhance the security of the system, the key parameters of the chaotic map are encoded using RSA (Rivest–Shamir–Adleman) public key encryption. Numerical simulations are carried out to validate the proposed technique.

Design, synthesis and mesomorphic behaviour of a four-ring achiral bent-core liquid crystal in the nematic phase

Bent-core nematics have attracted growing interest because of the unconventional properties and extraordinary effects exhibited by these liquid crystalline phases. In this report we design, synthesize and characterize four different four-ring achiral bent-core liquid crystals containing a methyl group in the central phenyl ring. The mesomorphic behaviour of compounds has been investigated by optical polarizing microscopy, differential scanning calorimetry, electro-optical investigation, and dielectric spectroscopy. Calculations based on density functional theory of the molecules were also carried out. The addition of a methyl group in the central phenyl ring not only induces the lowering of the clearing point but also enhances the nematic phase range. Dielectric spectroscopy reveals a low frequency relaxation peak and a very large dielectric permittivity; which is the characteristic of cybotactic clusters. In electro-optic studies, spontaneous polarization peaks are not observed. However, a periodic pattern is observed under the application of an ac electric field. Finally, the compounds show a weak tendency to crystallize; which makes it possible to supercool the cybotactic nematic phase down to room temperature.