Radio Link Simulator

The need for transmission of data over HF and VJUHF radio is increasing. There is a major disadvantage in testing the link in a field trial as propagation condition of the medium (especially HF) can be unpredictable and link condition may never again be the same. A simulator to create the atmospheric conditions, repeatably as required,to test the system behaviour is evident. The various propagation effects can be mathematically modelled, to get the signal affected by thechannel. Models for Gaussian, Rayleigh and Rice distributions and the implementation of the simulator using latest state-of-the-art DSP techniques are discussed

The 22 July 2009 Total Solar Eclipse: modeling D region Ionosphere using Narrowband VLF observations

We present D region ionospheric response to 22 July 2009 total solar eclipse by modeling 19.8‐kHz signal from NWC very low frequency (VLF) navigational transmitter located in the Australia. NWC VLF signal was received at five stations located in and around eclipse totality path in the Indian, East Asian, and Pacific regions. NWC signal great circle paths to five stations are unique having eclipse coverage from no eclipse to partiality to totality regions, and the signal is exclusively confined in the low and equatorial regions. Eclipse‐induced modulations in NWC signal have been modeled by using long‐wave propagation capability code to obtain D region parameters of reflection height (H′) and sharpness factor (β). Long‐wave propagation capability modeling showed an increase in H′ of about 2.3 km near central line of totality, 3.0 km in the region near to totality fringe, and 2.4 to 3.0 km in the region under partial eclipse. Using H′ and β, Wait ionosphere electron density (Ne) profile at the daytime altitude of 75 km showed a decrease in Ne by about 58% at a station near totality central line, whereas at totality fringe and in partial eclipse region decrease in the Ne was between 63% and 71% with respect to normal time values. The eclipse associated variations in the H′, β, and Ne are less in low‐latitude region as compared to midlatitude. The study contributes to explain observations of wave‐like signature in the D region during an eclipse and difference in the eclipse effect in the different latitude‐longitude sectors

VIBRATION ANALYSIS OF FLEXIBLE NARROW TUBES USING ACOUSTIC EXCITATION

Thin flexible narrow tube structures are used widely in various applications and industries such as, medical devices, mechanical structures, wire protections, marine applications, food processing and superconducting transmission lines. Vibration analysis of thin narrow flexible structures is necessary to understand the dynamic behaviour under specified boundary conditions and external load. Primarily, dynamic characteristics of a structure are expressed in terms of modal parameters such as natural frequencies, mode shapes and damping. The flexible narrow tube structures have very thin walls making measuring modal parameters a quite challenging task using contact type excitation methods such as shaker or impact hammer. Similar challenges exist for measuring vibration response on thin walls using contact type sensor such as accelerometer. So, the present study discusses considering acoustic source as vibration excitation and laser vibrometer as a vibration response measurement device. An experimental test setup is developed to measure modal parameters using an impedance tube. The impedance tube has speaker at one end while another end is exposed to thin narrow tubes. Acoustic excitation is generated using a speaker in the interested frequency range. Laser vibrometer is used to pick up response of tube wall at the same instance. The experiments are carried out under free-free boundary conditions and quiet surrounding environment was maintained to minimize effect of background noise. Modal parameters are extracted from the measured Frequency Response Function (FRF). Natural frequency obtained from experimental method for thin flexible narrow tubes are validated with Finite Element Method (FEM) results. In FEM environment, classical eigen value problem is solved using Block-Lanczos modal extraction method where sparse matrix solver is used. In order to examine the effect of geometrical properties, samples with varying diameter and length are considered for study. The results shown in this paper help in characterizing vibration response of thin structures like mechanical filters and thin acoustic metamaterials, where usage of traditional contact-type excitation, as well as contact-type sensors is not feasible to us

Effect of reactive oxygen species on cholinergic receptor function

OBJECTIVE: To investigate the role of reactive oxygen species (ROS) on cholinergic receptor function. MATERIALS AND METHODS : Rectus abdominis and isolated heart preparations of frog (Rana tigirina   ) were used to assess nicotinic and muscarinic receptor activity, respectively. Thirty percent hydrogen peroxide (H2O2) solution and Fenton mixture (Fm, 13.9 mg, 50 µM of FeSO4, 75 mg of sodium EDTA and 50 µL of 30% H2O2 were added to 10 ml of 0.1 M K2HPO4) were used to generate 1 mM H2O2 and hydroxyl free radicals. The responses were recorded with acetylcholine at different phases of exposure of tissues to ROS. Normal frog Ringer was used as a physiological solution. Responses of acetylcholine were also recorded in the presence of ROS before and after exposure of the tissue to an antioxidant (ascorbic acid). RESULTS : Free-radical-mediated receptor damage was dose (1-100 mM H2O2) and time (10-30 min) dependent when responses were taken with 30 µg and 30 ng of ACh for nicotinic and muscarinic receptors, respectively. There was no effect of ROS on prior exposure of tissue to ascorbic acid (antioxidant) at a concentration of 300 µg/ml. The antioxidant has not shown any beneficial effect on sulfhydryl groups of G-protein-coupled muscarinic receptors, which are more susceptible and sensitive to ROS than ion-channel nicotinic receptors where there is 96% protection with the antioxidant. Reactive oxygen species has shown different effects on receptor function. CONCLUSION: Free radicals continuously cause considerable damage to the receptors. G-protein-coupled muscarinic receptors are more susceptible than ion-channel-linked nicotinic receptors. Antioxidants are shown to play a major role in protecting free-radical-mediated receptor damage

Effects of St. Patrick’s Day Geomagnetic Storm of March 2015 and of June 2015 on Low-Equatorial D Region Ionosphere

D region effects of the 17–19 March 2015, a St Patrick's Day super geomagnetic storm (Dst = −223 nT), using a navigational transmitter very low frequency (VLF) signal (NWC, 19.8 kHz) recorded at a low‐latitude Indian station, Allahabad (geomag. lat., 16.45°N), have been analyzed and compared with similar strength of the 22–25 June 2015 storm (Dst = −204 nT). During the March storm, NWC signal amplitude decreased on 17 March (main phase of the storm) and recovered on 27 March, which is 1 day after the recovery of the storm, whereas for the June storm, VLF amplitude decreased for 2 days only during its recovery phase. The decrease in the amplitude was pronounced during evening terminator for both the storms. The modeling of VLF signal anomaly on 17 March and on 25 June using Long‐Wave Propagation Capability code shows an increase in the D region reference height (h′) by ~2.6 km and ~2.5 km, for March and June storms, respectively. The D region electron density (Ne) determined using storm time h′ and sharpness factor β shows a decrease in the Ne during the main phase followed by a slow recovery during the recovery phase of the March storm, whereas June 2015 storm showed a decrease in the Ne only on 25 and 26 June. Morlet Wavelet analysis of the amplitude for both the storms shows a presence of strong wave‐like signatures, suggesting propagation of atmospheric gravity waves/traveling ionosphere disturbances to the low latitude D region due to the Joule heating at high latitudes

Synthesis of new cis-fused tetrahydrochromeno[4,3-b]quinolines and their antiproliferative activity studies against MDA-MB-231 and MCF-7 breast cancer cell lines

New cis-fused tetrahydrochromeno[4,3-b]quinolines have been synthesized by intramolecular [4+2] imino-Diels-Alder reactions of 2-azadienes derived in situ from aromatic amines and 7-O-prenyl derivatives of 8-formyl-2,3-disubstituted chromenones in the presence of 20 mol % Yb(OTf)<SUB>3</SUB> in acetonitrile under reflux conditions in good to excellent yields. The structures were established by spectroscopic data and further confirmed by X-ray diffraction analysis. These compounds were evaluated for their antiproliferative activity against MDA-MB-231 and MCF-7 breast cancer cells. The results showed that compounds 3e, 3f, and 3k exhibit significant antiproliferative activity against MCF-7 breast cancer cells and low inhibitory activity against MDA-MB-231 breast cancer cell lines. Compound 3h displayed activity as comparable to tamoxifen on both the cell lines

Differentiation of diastereomeric N-aryltetrahydropyrano/tetrahydrofuranochromenylamines under electron ionization and chemical ionization conditions

A series of diastereomeric 4S,5S,6R/S-tetrahydropyrano- and 3S,4S,5R/S-tetrahydrofuranochromenylamine derivatives (a/b isomers; 1–26) has been studied under electron ionization (EI) and chemical ionization (CI) conditions. The EI mass spectra of all diastereomeric compounds show two characteristic fragment ions, of which one is formed by retro-Diels-Alder (RDA) reaction from the molecular ion, retaining the charge on the diene fragment, and the other [M–(HNAr)]<SUP>+</SUP> ion by a simple radical loss. The RDA process is more favorable in all b isomers, whereas the radical loss is dominant in all a isomers; based on these two ions it is easy to differentiate the two diastereomers. The collision-induced dissociation (CID) spectra of all the molecular ions also show the same trend, which reflects the stereoselectivity in the formation of the two characteristic fragment ions. The results of theoretical calculations performed are in accordance with the experimental observations. The CI experiments (methane and isobutane) on all the diastereomeric compounds also enabled the differentiation of the isomers