Rapid analysis of 2,4-D in soil samples by modified Soxhlet apparatus using HPLC with UV detection

The 2,4-dichlorophenoxy acetic acid (2,4-D) is used as a systemic herbicide to control broadleaf weeds in wheat, corn, range land/pasture land, sorghum, and barley. In this study, a fast and efficient method is developed by selection of modified extraction apparatus and high-performance liquid chromatography (HPLC)-UV conditions for the determination of 2,4-D in soil samples. The method is applied to the study of soil samples collected from the agricultural field. The herbicide is extracted from soil samples by acetonitrile in a modified Soxhlet apparatus. The advantages of the apparatus are that it uses small volume of organic solvent, reduced time of extraction, and better recovery of the analyte. The extract is filtered using a very fine microfiber paper. The total extract is concentrated in a rotatory evaporator, dried under ultrahigh pure N2, and finally reconstituted in 1 mL of acetonitrile. HPLC-UV at 228 nm is used for analysis. The herbicide is identified and quantitated using the HPLC system. The method is validated by the analysis of spiked soil samples. Recoveries obtained varied from 85% to 100% for spiked soil samples. The limit of quantitation (LOQ) and the limit of detection (LOD) are 0.010 and 0.005 parts per million (ppm), respectively, for spiked soil samples. The LOQ and LOD are 0.006 and 0.003 ppm for unspiked soil samples. The measured concentrations of 2,4-D in spiked soil samples are between 0.010 and 0.020 ppm with an average of 0.016 +/- 0.003 ppm. For unspiked soil samples it is between 0.006 ppm and 0.012 ppm with an average of 0.009 +/- 0.002 ppm. The measured concentrations of 2,4-D in soil samples are generally low and do not exceed the regulatory agencies guidelines.     

Time domain measurement of dispersion in optical fibres

A time domain dispersion measurement apparatus was successfully built and tested at the Indian Institute of Technology, Madras. This instrument can measure directly the pulse broadening in a multimode optical fibre. The basic dispersion mechanisms in optical fibres and the design details of the system are discussed.     

Effect of distortion on optical-fiber waveguides

We analyze the modes and coupling efficiency of asymmetric optical-fiber waveguides. We treated the step index-asymmetric optical-fiber waveguide as a boundary-value problem and obtain the expressions for the modes under logical assumptions. Using these expressions, we describe the propagation constants, mode delay, and power distribution of two asymmetric optical-fiber waveguides under consideration. Based on the perturbation theory, we also present the coupling coefficients of these asymmetric optical-fiber waveguides. We show that the waveguide parameters are considerably changed in the presence of distortion, and one can tune these parameters at the desired level by choosing suitable distortions.     

Dislocation unpinning model of acoustic emission from alkali halide crystals

The present paper reports the dislocation unpinning model of acoustic emission (AE) from alkali halide crystals. Equations are derived for the strain dependence of the transient AE pulse rate, peak value of the AE pulse rate and the total number of AE pulse emitted. It is found that the AE pulse rate should be maximum for a particular strain of the crystals. The peak value of the AE pulse rate should depend on the volume and strain rate of the crystals, and also on the pinning time of dislocations. Since the pinning time of dislocations decreases with increasing strain rate, the AE pulse rate should be weakly dependent on the strain rate of the crystals. The total number of AE should increase linearly with deformation and then it should attain a saturation value for the large deformation. By measuring the strain dependence of the AE pulse rate at a fixed strain rate, the time constantτ _s for surface annihilation of dislocations and the pinning timeτ _p of the dislocations can be determined. A good agreement is found between the theoretical and experimental results related to the AE from alkali halide crystals.     

PageRank model of opinion formation on social networks

We propose the PageRank model of opinion formation and investigate its rich properties on real directed networks of the Universities of Cambridge and Oxford, LiveJournal, and Twitter. In this model, the opinion formation of linked electors is weighted with their PageRank probability. Such a probability is used by the Google search engine for ranking of web pages. We find that the society elite, corresponding to the top PageRank nodes, can impose its opinion on a significant fraction of the society. However, for a homogeneous distribution of two opinions, there exists a bistability range of opinions which depends on a conformist parameter characterizing the opinion formation. We find that the LiveJournal and Twitter networks have a stronger tendency to a totalitarian opinion formation than the university networks. We also analyze the Sznajd model generalized for scale-free networks with the weighted PageRank vote of electors.     

Investigations on Pd:SnO2/porous silicon structures for sensing LPG and NO2 gas

P-type porous silicon (PS) structure has been prepared by anodic electrochemical etching process under optimized conditions. Photoluminescence studies of the PS structure show emission at longer wavelengths (red) for the excitation at 365 nm. Scanning electron microscope investigations of the PS surface confirm the formation of uniform porous structure, and the pore diameter have been estimated as 25 μm. Pd:SnO₂/PS/p-Si heterojunction with top gold ohmic contact developed by conventional methods has been used as the sensor device. Sensing properties of the device towards liquefied petroleum gas (LPG) and NO₂ gas have been investigated in an indigenously developed sensor test rig. The response and recovery characteristics of the sensor device at different operating temperatures show short response time for LPG. From the studies, maximum sensitivity and optimum operating temperature of the device towards LPG and NO₂ gas sensing has been estimated as 69% at 180 °C and 52% at 220 °C, respectively. The developed sensor device shows a short response time of 25 and 57 s for sensing LPG and NO₂ gases, respectively. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

Analysis of fiber optic SPR sensor utilizing platinum based nanocomposites

SPR based fiber optic sensor using nanocomposite is presented. Nanocomposites comprising of Pt nanoparticles with various volume fractions embedded in dielectric matrices of TiO₂ and SnO₂ are considered. Sensitivity enhances with increase in thickness of nanocomposite and volume fraction of nanoparticles for both nanocomposites. Optimized thicknesses are obtained to be 40 and 50 nm for Pt–TiO₂ and Pt–SnO₂ nanocomposites respectively while optimized volume fraction is found to be 0.85 for both nanocomposites. 40 nm thick Pt–TiO₂ nanocomposite based sensor with 0.85 volume fraction possesses utmost sensitivity.     

Dispersion behavior of electromagnetic wave near the resonance in 1D magnetized ferrite photonic crystals

In the present article, we have analyzed the dispersion of electromagnetic wave in the one dimensional magnetized ferrite photonic crystals near the resonance in the permeability of the constituent materials for transverse magnetization in the transverse electric mode. The dispersion relation is obtained by transfer matrix method. It is observed that in the vicinity of resonant frequency, large numbers of oscillations occur in the normalized Bloch wave number. These oscillations in the Bloch wave number are strongly dependent on external magnetic fields, filling factor, and damping constant. The frequency regime of these oscillations is found to be shifted in higher frequency range with increase in the magnitude of the magnetic fields. With increase in the filling factor keeping length of periods fixed, number of oscillations is found to be increased. Near the resonance, effect of incident angle is negligible. It is demonstrated that these nearly equidistant oscillations occurring in the vicinity of resonance may be used for making filter in micro wave frequency range.     

Design of Hamming Code Checker Using Titanium-Diffused Lithium Niobate-Based Waveguide

ABSTRACT

This work presents an electro-optic effect-based design for the widely used Hamming code for checking single bit errors in the received data. The structure is based on Mach-Zehnder Interferometer, designed using Titanium-diffused Lithium Niobate-based waveguides. The proposed device has been successfully tested using the beam propagation method. For a received 7-bit code, the three simultaneously generated check bits are combined to check the error position. Critical performance parameters like extinction ratio (24.39dB), contrast ratio (25.711dB), insertion loss (0.041dB), and amplitude modulation (0.079dB) calculated for the overall device are within acceptable limits for the feasibility of the device.     

Selective O-deallylation of dihydropyrazoles by molecular iodine in the presence of active N-allyl and formyl groups

Selective O-deallylation of dihydropyrazoles has been achieved by use of iodine (10 mol%) in PEG-400 as ecofriendly solvent. Iodine (10 mol%) in dimethyl sulfoxide at 100 °C also afforded O-deallylation with aromatization compatible with highly reactive N-allyl and formyl groups. The function of iodine in the synthesis of substituted pyrazoles under different conditions is described.