Search

We introduce a model to mimic the dynamics of oscillators that are coupled by mean-field nonlinear memductance. Notably, nonlinear memductance produces dynamic nonlinearity, which causes the direction of coupling to change over time. Depending on the parameters, such a dynamic coupling drives the trajectory of oscillators to a synchronization or anti-synchronization manifold. Specifically, depending on the forcing frequency and coupling strength, we find anti-phase and intermittent synchronization. With the increase in coupling magnitude, one can observe a transition from intermittent synchronization to complete synchronization through anti-phase synchronization. The results are validated through numerical simulations. The hypothesis has a huge impact on the study of neuronal networks.

The l-glutamic acid thin films prepared using a lucrative process simplified spray pyrolysis (or) perfume atomizer technique. The absorption coefficient, refractive index, extinction coefficient, imaginary and real parts of dielectric constant, electrical and optical conductivity, optical polarization, electrical and optical susceptibility were inspected with spectrum of UV–Visible spectroscopy. The optical properties for varying molar concentration and wavelength were investigated to reveal the characteristic features of the chosen sample. In addition, the nonlinear optical constants, third-order susceptibility, nonlinear refractive index, nonlinear absorption coefficient, intensity dependent refractive coefficient and change in refractive index were also examined with Z-scan technique. The optical nonlinearities were also assayed using the Eclipse and f-scan experiments. The difference in the nonlinear optical responses relating to selected functional parameters has been considered significantly along with optical limiting behavior.

We identified the plausibility of the existence of strange nonchaotic attractors (SNAs) in a model of two sinusoidal driven LCR dissipative oscillators sharing a common piecewise nonlinearity. The detected strange nonchaos has been assayed through numerical studies encompassing phase space analysis, Poincare cross sections, Lyapunov exponents, etc., The strange nonchaotic nature of attractors was examined by recurrence quantification measure. Phase synchronization features of the attractors in the SNA regime have also been included. Experimental evidences have been furnished by means of a real-time electronic circuit to reinforce the observed results. It is expected that the outcomes of the present study could facilitate the understanding and the observation of SNAs in nonlinearly coupled networks, including small-world, scale-free networks and neuronal networks.

An organic nonlinear optical (NLO) single crystal of Pyridine 3-carboxylic acid, which has potential application in a variety of fields was grown by solution growth technique. The single crystal X-ray diffraction analysis confirms that the grown crystals possess lattice parameters of monoclinic system of space group (P 21/ c ). The Fourier transform infrared (FTIR) study provides the evidence for the presence of essential functional groups in Pyridine 3-carboxylic acid single crystal. The optical parameters such as transmittance, absorption coefficient, refractive index and optical band gap of the grown crystals were obtained using ultraviolet visible (UV-Vis-NIR) spectroscopy. The red luminescence behavior and Second Harmonic generation (SHG) efficiency were measured. The soft ferromagnetic nature of the grown sample was ascertained from vibrational sample magnetometer analyses. In addition, the mechanical property was also examined.

We examine the existence of multiple vibrational resonance (VR) and antiresonance in two coupled overdamped anharmonic oscillators where each one is individually driven by a monochromatic sinusoidal signal with widely separated frequencies ( $$\Omega \gg \omega $$ ). In contemporary VR, superposed periodic waves are adopted to infer resonance, but herein we employ non-superposed periodic waves to acquire the elevated response. We study two coupling schemes namely, unidirectional and bidirectional, to substantiate the occurrence of multiple VR and antiresonance. Such occurrences have been shown and the results were ascertained with supportive numerical and experimental outcomes. We also illustrate the effect of coupling strength on the observed phenomenon.

The present study uncovers the hyperchaotic dynamical behavior of the famous Murali-Lakshmanan-Chua (MLC) circuit, when suitably modified. In the conventional MLC oscillator, an inductor is introduced in parallel between the nonlinear element and the capacitor. Many novel and interesting dynamical behaviors such as reverse period-3 doubling, torus breakdown to chaos and hyperchaos, etc., were observed. Characterization techniques includes spectrum of Lyapunov exponents, one parameter bifurcation diagram, recurrence quantification analysis, correlation dimension, etc., were employed to analyze the different dynamical regimes. Explicit analytical solution of the model is derived and the results are corroborated with the numerical outcomes.

A biocompatible non-linear optical crystals (458 × 7 mm) of nicotinic acid-doped potassium dihydrogen phosphate (KDP) were grown by the slow evaporation technique at room temperature and their structural study was confirmed by single-crystal X-ray diffraction. Further, the presence of functional groups and elements were verified using Fourier transform infra-red and Energy dispersive X-ray studies. The optical properties of these crystals such as transmission and absorption were analysed by Ultra Violet Visible Near infra-red spectroscopy and the second harmonic generation efficiency was carried out by the Kurtz–Perry powder technique. The mechanical properties of the grown crystal were studied using Vickers’ hardness tester. The grown crystals were involved in an antibacterial activity against certain potentially threatening microbes such as Bacillus subtilis, Escherichia coli, Staphylococcus aureu and Klebsiella pneumoniae. The dopant efficiently screened the bacteria than that of the pure KDP crystal.

Titanium dioxide nanoparticles (TiNPs) were emerged as wound healing enhancer as well as an antibacterial agent against Gram-positive and Gram-negative bacteria due to its enhanced mechanical properties. Moreover, the green synthesized Titanium dioxide exhibited significant wound healing activity in Albino rats which was confirmed by measuring wound closure. Titanium dioxide nanoparticles were effectively synthesized using aqueous leaf extract of Moringa oleifera under pH and temperature dependent condition. 5 mM Titanium dioxide solution worked as a primary source for the synthesize of Titanium dioxide nanoparticles. The green synthesized TiNPs excitation was confirmed using UV–Vis spectrophotometer at 428 nm. The high-resolution Scanning Electron Microscope (SEM) results showed the spherical shape of TiNPs with a mean particle size around 100 nm. Furthermore, the wound healing activity of nano-sized particles (Control Group) when compared with micro-sized (Positive Control Group) was examined through the excision wound model by measuring wound closure and the control group revealed significant wound healing activity in Albino rats.

This paper investigates the dynamics of four-dimensional autonomous oscillator with antiparallel diodes. A rare phenomenon of volume-expanding phase space is observed from the proposed model, and the only equilibrium point at the origin is found to be a repeller. Systems of this kind pave the way for the better understanding of repellers. In addition, the oscillator possesses extremely rich dynamical behaviors, including 2-tori, 3-tori (triple tori), limit cycles, chaos and hyperchaos. These dynamical behaviors are characterized with the help of the Lyapunov spectrum, bifurcation diagram, recurrence analysis, Poincare surface of section, 0–1 test etc., Period doubling and torus breakdown to chaos are the predominant routes observed in the system for different parametric choices. The results of the real-time circuit are quite compatible with the numerical predictions.

The organic nonlinear optical (NLO) crystals of Guanidinium Carbonate (GC) were grown by the slow evaporation technique. X-ray diffraction studies reveal the tetragonal structure of the grown crystal. The characterization analysis such as powder XRD and Fourier transform infra-red (FTIR) spectral analysis were carried out to find the crystalline nature and the presence of various functional groups in the grown crystal. Further, ultra-violet (UV)–visible spectral analysis, fluorescence study, Differential Thermal Analysis (DTA), Differential Gravimetric Analysis (DGA) and Vickers’ hardness were carried out to understand the crystal's optical, thermal and mechanical properties. The nonlinear optical property was confirmed by Kurtz-powder technique and it was found that the second harmonic generation efficiency of the grown crystal is 0.3 times greater than that of the standard KDP.

In this work, we present the results of photoluminescence (PL) by the Ag doped In 2 O 3 thin films prepared by a cost-effective and much simplified perfume atomizer technique. The PL emission behavior was investigated using three distinct excitation wavelengths (350 nm, 450 nm and 550 nm) upon the deposited films coated in a temperature range of 300° C to 450° C. The stokes shift towards red color for three different excitations was analysed and it has been shown that how the PL emission plays a crucial role in indentifying a good display device material. A highly intensed red emission was found commonly in all films with the excitation wavelength of 350 nm. All films exhibit four distinct emission peaks for the excitation wavelength of 450 nm and two low intensed emissions were found for the excitation wavelength of 550 nm. Further, the X-ray diffraction studies revealed the cubic In 2 O 3 structure with preferential orientation growth along (2 2 2) direction, irrespective of the variation in substrate temperature. A negative sign of Hall coefficient was confirmed the n-type conductivity of prepared samples and the optical parameters were also estimated from transmission data measured by UV-Vis-NIR spectrometer.

We wish to report the occurrence of vibrational resonance in certain discrete systems like sine square map and sine circle map, in a unique fashion, comprising of multiple resonant peaks which pave the way for enrichment. As the systems of our choice are capable of exhibiting vibrational resonance behaviour unlike the earlier reports, they are taken for investigation and the necessary numerical and analytical results are presented. Further, we study the effect of external forcing on various attractors of these systems with appropriate bifurcation and Lyapunov exponent diagrams.

Nanocrystalline Ag-doped indium oxide (AIO) thin films, by employing a much simplified spray pyrolysis technique in different substrate temperatures (300, 350, 400 and 450°C), were fabricated for the first time. The deposited films were subjected to various characterization studies, to explore certain features like the influence of various deposition temperatures on physical and antibacterial properties. XRD results showed that all the samples exhibited preferential orientation along the (2 2 2) plane. The variation in the crystalline size with increasing substrate temperature was explained on the basis of the Zener pinning effect. The electrical sheet resistance (R sh) was found to decrease sharply with increasing substrate temperature and attained a minimum value $(62{\Omega } /\Box $ ) at 400°C and then started increasing for higher deposition temperatures. Further, PL emission spectra of the samples in the visible range ascertained the possibility of applicability of the same in nanoscale optoelectronic devices. From the studies, it was found that at 400°C deposition temperature, one could expect better antibacterial efficiency against Escherichia coli. The influence of the shape and size of AIO nanograins on the antibacterial activity was analysed using scanning electron microscopy images.

Purcell's swimmer was proposed by E. M. Purcell to explain bacterial swimming motions. It has been proved experimentally that a swimmer of this kind is possible under inertial-less and high viscous environment. But we could not investigate all the aspects of this mechanism through experiments due to practical difficulties. The computational fluid dynamics (CFD) provides complementary methods to experimental fluid dynamics. In particular, these methods offer the means of testing theoretical advances for conditions unavailable experimentally. Using such methodology, we have investigated the fluid dynamics of force production associated with the Purcell's swimmer. By employing dynamic mesh and user-defined functions, we have computed the transient flow around the swimmer for various stroke angles. Our simulations capture the bidirectional swimming property successfully and are in agreement with existing theoretical and experimental results. To our knowledge, this is the first CFD study which shows the fact that swimming direction depends on stroke angle. We also prove that for small flapping frequencies, swimming direction can also be altered by changing frequency-showing breakdown of Stokes law with inertia.

Single crystal of lithium potassium sulphate, a nonlinear optical material, was grown from aqua solution by slow evapo- ration method at room temperature. The cell parameters were estimated by single crystal X-ray diffraction analysis. The optical transmittance of the crystal was recorded using the UV-Vis-NIR spectrophotometer and the optical band gap was calculated using this method. The second harmonic generation efficiency was measured by Kurtz and Perry powder technique and the phase-matching property was confirmed. The hardness of the material was measured by Vicker’s hardness test.

The study of bacterial flagellar swimming motion remains an interesting and challenging research subject in the fields of hydrodynamics and bio-locomotion. This swimming motion is characterized by very low Reynolds numbers, which is unique and time reversible. In particular, the effect of rotation of helical flagella of bacterium on swimming motion requires detailed multi-disciplinary analysis. Clear understanding of such swimming motion will not only be beneficial for biologists but also to engineers interested in developing nanorobots mimicking bacterial swimming. In this paper, computational fluid dynamics (CFD) simulation of a three dimensional single flagellated bacteria has been developed and the fluid flow around the flagellum is investigated. CFD-based modeling studies were conducted to find the variables that affect the forward thrust experienced by the swimming bacterium. It is found that the propulsive force increases with increase in rotational velocity of flagellum and viscosity of surrounding fluid. It is also deduced from the study that the forward force depends on the geometry of helical flagella (directly proportional to square of the helical radius and inversely proportional to pitch).

We introduce a simple parametrically driven dissipative second-order chaotic circuit. In this circuit, one of the circuit parameters is varied by an external periodic control signal. Thus by tuning the parameter values of this circuit, classic period-doubling bifurcation route to chaos is found to occur. The experimentally observed phenomena is further validated through corresponding numerical simulation of the circuit equations. The periodic and chaotic dynamics of this model is further characterized by computing Lyapunov exponents.

In this paper, we report the dynamical behaviors of a four-dimensional autonomous system, that is, the modified canonical Chua's circuit. An interesting transition of three-tori–period-3 doubling–chaos is observed when the circuit parameters are varied in the range of our choice. Furthermore, the detailed numerical studies of the system behavior with supporting PSPICE simulations and hardware experiments are also presented here.

A nonlinear optical crystal of gamma glycine was grown by slow evaporation solution growth technique using deionized water and sodium acetate. The functional groups and vibrational frequencies were identified using FTIR spectral analysis. The cell parameters were determined from single crystal X-ray diffraction analysis. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study its thermal properties. The optical transmittance window and lower cutoff wavelength have been identified by UV-absorption spectrum analysis. Second harmonic generation (SHG) efficiency measurement was carried out by powder Kurtz method.

Single crystals of glycine doped potassium acid phthalate (KAP) have been grown from low temperature solution growth method by employing slow evaporation of the solvent at room temperature. The grown crystal was subjected to various studies such as X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), UV-visible and Second Harmonic Generation (SHG) studies. The thermal stability, mechanical strength and dielectric constant were also measured. The various studies revealed the influence of the glycine on KAP and the investigations indicated that glycine played an important role in the changes of the spectral, optical and mechanical properties of KAP crystals.

By making use of the developments in the fields of numerical methods, computational technology and fluid dynamics models, computational fluid dynamics (CFD) progress forward to play an active role today in various industrial, academic and research activities. In many cases, CFD simulations replace expensive and time consuming laboratory experiments successfully by allowing engineers and scientists to capture pressure, velocity and force distributions. Researchers are now able to test various theoretical conditions unavailable in the laboratory and CFD studies help them to get deeper insights on existing theories. The century-old history started just to solve some stress analysis problems numerically and today CFD methodology is being applied not only in fluid dynamics also in chemical engineering, mineral processing, fire engineering, sports, medical imaging and even in acoustics. This paper reviews the growth of CFD as a discipline and discusses its contemporary methodology.

We discuss the emergence and destruction of complex, critical and completely chaotic attractors in a nonlinear system when subjected to a small parametric perturbation in trigonometric, hyperbolic or noise function forms. For this purpose, a hybrid optical bistable system, which is a nonlinear physical system, has been chosen for investigation. We show that the emergence of new attractors is responsible for transients in many trajectories obeying power-law decay. The effect of perturbation on certain critical bifurcations such as period-2, onset of chaos, chaotic attractor with less complexity etc., has been studied and characterized using certain statistical features. Further, the effect of Gaussian noise with other types of perturbation has also been studied.

Nanocrystalline and transparent conducting SnO2- ZnO films were fabricated by employing an inexpensive, simplified spray technique using a perfume atomizer at relatively low substrate temperature (360±5 °C) compared with conventional spray method. The structural studies reveal that the SnO2-ZnO films are polycrystalline in nature with preferential orientation along the (101) plane. The dislocation density is very low (1.48×1015lines/m2), indicating the good crystallinity of the films. The crystallite size of the films was found to be in the range of 26–34 nm. The optical transmittance in the visible range and the optical band gap are 85% and 3.6 eV respectively. The sheet resistance increases from 8.74 kΩ/□ to 32.4 kΩ/□ as the zinc concentration increases from 0 to 40 at.%. The films were found to have desirable figure of merit (1.63×10–2 (Ω/□)–1), low temperature coefficient of resistance (–1.191/K) and good thermal stability. This simplified spray technique may be considered as a promising alternative to conventional spray for the massive production of economic SnO2 - ZnO films for solar cells, sensors and opto-electronic applications. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This study assesses the level of terrestrial gamma radiation and associated dose rates from the naturally occurring radionuclides (232)Th, (238)U and (40)K in 10 soil samples collected from Thanjavur (Tamil Nadu, India) using gamma-ray spectrometry. The activity profile of radionuclides has clearly showed the existence of low level activity in Thanjavur. The geometric mean activity concentrations of (232)Th, (238)U and (40)K is 42.9+/-9.4 Bq.kg(-1), 14.7+/-1.7 Bq.kg(-1) and 149.5+/-3.1 Bq.kg(-1) respectively are derived from all the soil samples studied. The activity concentration of (232)Th, (238)U and (40)K in soil is due to the presence of metamorphic rocks like shale, hornblende-biotite gneiss and quartzofeldspathic gneiss in these areas. Gamma absorbed dose rates in air outdoors were calculated to be in the range between 32 nGy.h(-1) and 59.1 nGy.h(-1) with an arithmetic mean of 43.3 +/-9 nGy.h(-1). This value is lesser than the population weighted world-averaged of 60 nGy.h(-1). Inhabitants of Thanjavur are subjected to external gamma radiation exposure (effective dose) ranging between 39.2 and 72.6 muSv.y(-1) with an arithmetic mean of 53.1+/-11 muSv.y(-1). The values of the external hazard index determined from the soil radioactivity of the study area are less than the recommended safe levels.

An organic nonlinear single crystal of Nitrilotriacetic acid (NTAA) was grown for the first time by employing a simple slow evaporation technique. Single crystal X-ray diffraction (XRD) analysis reveals that the grown crystal belongs to the monoclinic system with noncentrosymmetric space group [Formula: see text]. Fourier transform infrared (FTIR) spectral study ascertains the presence of functional groups in NTAA. The molecular structure of the grown crystal was confirmed by Nuclear Magnetic Resonance (NMR) spectral analysis. The optical parameters such as transmittance, absorption coefficient and band gap were calculated from UV–Visible and fluorescence studies. Dielectric measurements were carried out for different frequency and temperature. The mechanical strength of the grown crystal was measured using Vickers microhardness test. The high thermal stability and the melting point of the grown crystal were also estimated using thermogravimetric (TGA) and differential thermal analyses (DTA). The confirmation of the grown crystals belonging to nonlinear optical crystals was performed by Kurtz–Perry technique and found as suitable candidate for optoelectronics applications.