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Abstract: Abstract In this paper, guiding of Gaussian laser pulse in plasma channel in the presence of Kerr effect is studied numerically. We assume that the plasma channel has radial variation. We obtain matched condition to guide intense laser pulse through plasma channel in presence of Kerr effect. Using the SDE method, four coupled equations for the pulse amplitude, phase, spot size and wave front curvature will be derived. We apply two numerical methods for solving these equations, Runge–Kutta and extrapolation methods. We give the functional form of the nonlinear initial value problem and obtain some properties about the convergence of the methods. Since these are pure mathematical considerations, they are mentioned in Appendix section. The solutions obtained by the methods are compared together and we see that the solutions are the same. Hence, the proposed methods are applicable and have the sufficient accuracy for the current system of equations. PubDate: 2022-05-22

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Abstract: Abstract Different bursting patterns and the generation principles are investigated in a generalized parametrically forced van der Pol-Duffing system. Six bursting patterns induced by the bifurcation delay, namely bursting of “delayed pitchfork/pitchfork” form, bursting of symmetric “delayed pitchfork/pitchfork” form, bursting of “delayed pitchfork/delayed sup-Hopf” form via “delayed pitchfork/pitchfork” hysteresis loop, bursting of symmetric “delayed pitchfork/delayed sup-Hopf” form via “delayed pitchfork/pitchfork” hysteresis loop, bursting of “delayed pitchfork/delayed sup-Hopf/Homoclinic” form via “delayed pitchfork/pitchfork” hysteresis loop and bursting of symmetric “delayed pitchfork/delayed sup-Hopf/Homoclinic” form via “delayed pitchfork/pitchfork” hysteresis loop, are analyzed. First, considering the parametrically forced term as a slow-changing state variable, a time invariant continuous smooth system is exhibited. Then, with the help of the calculation of the characteristic equation and bifurcation map, the critical conditions of pitchfork bifurcation, Hopf bifurcation and Homoclinic bifurcation are presented. In addition, two bifurcation delay behaviors named supercritical Hopf bifurcation delay and pitchfork bifurcation delay are proposed. Based on that, the generation mechanisms of the bursting dynamics triggered by the bifurcation delay phenomenon are revealed. The present study shows that the delayed dynamical behaviors act a crucial part in the generation of different bursting oscillations, since the delay dynamics occurs in distinct parameter intervals, which results in distinct repetitive excited state forms. Finally, the numerical simulations are provided to support the correctness of the results proposed in the paper. PubDate: 2022-05-22

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Abstract: Abstract The Indo-Gangetic basin is one of the biggest, most populated and polluted regions in the world. Satellite- and ground-based data show strong seasonal variability of aerosol loading with a maximum during pre-monsoon (summer) season. In this study, decadal (2003–2012) variability of aerosol optical depth (AOD) derived from AERONET measurements over Kanpur is presented which indicates maximum AOD during 2003 and minimum during 2012. The aerosol size distribution (ASD) exhibits an increase in the radius and a decrease in the width of distribution. It shows an enhancement during 2003 and 2010 and diminished values during 2004, 2007, 2009 and 2011. The ASD is found to show a peak during summer season (pre-monsoon) throughout 2003–2012 only except the years 2008 and 2011. Moreover, for years 2008 and 2011 ASD showed a peak value during a monsoon month (July). Changes in the spectrum of ASD are explained in terms of surface temperature and precipitation. Seasonal variation of aerosol radiative forcing and its climatic impacts have also been discussed. PubDate: 2022-05-22

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Abstract: Abstract In the present study, a new model of the universe, based on using a generalized form of the linearly varying deceleration parameter, is presented. This model is an oscillating expansion form and simultaneously a contraction form at different stages. It behaves normally as a conventional Big Bang model till the first half-age i.e. at a Big Rip (It represents the maximum value of the expansion of the universe). Then, it reverses its behavior up to the Big Crunch. Such a model has the same physical behavior at its beginning and ending stages. During its first half-age and second half-age, it begins with a singular stage and ends with a non-singular one. Yet, in the first half-age, the model covers a linearly varying deceleration parameter model. Furthermore, it covers the law of Berman and corresponds to the periodic universe of the varying deceleration parameter of the second degree in the Riemannian geometry. The effect of the constant terms in the proposed deceleration parameter is examined and discussed. Also, this article introduces a new model to explain the evolution of the universe by using the Riemannian geometry, together with a constant boundary connecting the two scaling parameters which have some quantum properties. The proposed model predicts the future of the universe after the Big Rip. The results obtained match the recent cosmological observations at the present moment. Finally, the relationship between the spin tensor and the redshift is obtained and discussed. PubDate: 2022-05-21

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Abstract: Abstract In this paper, we propose a vacuum ultraviolet (VUV) torch with the help of copper-based plasmonic photonic crystal fibre. The principle of operational mechanism relies on the distribution of electric field in the photonic fibre. The working principle of the torch relies on the generation of vacuum ultraviolet signal with respect to the red signal (input signal). Here, plane wave expansion technique is employed to acquire the electric field distribution in the fibre. Moreover, the output result indicates that suitable combinations of different structure parameters of the plasmonic fibre structure are right candidate to realise VUV torch. Furthermore, the said torch could be used for solving environmental issue because the output (VUV) signal scan breaks CO2 molecules and converts them into the oxygen. PubDate: 2022-05-01

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Abstract: Abstract We perform a first-principles calculation to understand the effect of the additional valence electron of the transition atom in Wyckoff position 4 a, on the electronic structure, magnetic and structural stability of the full Heusler \({\mathrm{Mn}}_{2}\mathrm{PtZ}(\mathrm{Z}=\mathrm{V and Co})\) compound. L21, Xa and tetragonal structures are considered to verify the most stable phase. Within the framework of the plan \({\mathrm{Mn}}_{2}\mathrm{PtZ}(\mathrm{Z}=\mathrm{V and Co})\) favored the ferromagnetic configuration in the L21 structure. The results show that the 63% and 91% spin polarization at the Fermi level for \({\mathrm{Mn}}_{2}\mathrm{PtV}\) and \({\mathrm{Mn}}_{2}\mathrm{PtCo}\) , respectively. The most contribution of the magnetic moment is due to the Mn atom, the total magnetic moments equal to \({4.87\upmu }_{\mathrm{B}}\) and \({9.012\upmu }_{\mathrm{B}}\) have been reported. To prove the half metallicity of our compound, we used the GGA + U approach. Within the framework of this approach, the value gap in the minority spin band is 0.755 eV, more, the magnetic moment satisfying the Slater-Pauling rule for the \({\mathrm{Mn}}_{2}\mathrm{PtV}\) compound. In addition, we give the two values of the curie temperatures for the two cubic structural phases. Finally, both full Heusler \({\mathrm{Mn}}_{2}\mathrm{PtV}\) and \({\mathrm{Mn}}_{2}\mathrm{PtCo}\) are a promising candidate for the use of future devices as spin-FETs and nonvolatile magnetic memory. PubDate: 2022-05-01

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Abstract: Abstract In this paper, we have investigated the exact solutions of a perfect fluid Bianchi type \(-I\) cosmological model in the context of \(f(R, T) = R + \lambda T\) gravity, where R is Ricci scalar, and T is a trace of the energy-momentum tensor. We show that the generalized Friedman equation’s exact solution for the average scale factor a involves the hypergeometric function. This approach is novel, and it has not been previously carried out by other authors. Consequently, a set of three cosmological models, namely dust, radiation and dark energy, have been investigated. The physical and kinematical parameters in each model are discussed. It is shown that the modeled universe asymptotically becomes isotropic at late times. PubDate: 2022-05-01

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Abstract: Abstract Nanofluids flow and heat transfer in micro-channels have a wide range of attributes in industrial process as well as engineering and biomedical applications. Therefore, the aim of this study is to analyze the hydrodynamic and thermal behaviors of unsteady mixed convection flow of nanofluid in a micro-channel filed with a saturated porous medium. The highly nonlinear governing partial differential equations corresponding to the momentum, energy and concentration profiles were formulated and solved numerically by utilizing the semi-discretization finite difference method. The effects of each governing thermophysical parameters on the micro-channel hydrodynamic and thermal behaviors are discussed with the usage of graphs. The numerical results indicate that the velocity and temperature profiles show an increasing behavior with pressure gradient parameter, variable viscosity parameter, Eckert number, thermal Grashof number, solutal Grashof number and thermophoresis parameter, whereas the concentration profile increases with increasing values of suction/injection Reynolds number, porous medium shape parameter, Forchheimer number, Prandtl number, Schmidt number and thermophoresis parameter. Moreover, the result reveals that the skin friction coefficient, the Nusselt number and the Sherwood number are higher for large values of pressure gradient parameter, thermal Grashof number, Prandtl number and Schmidt number. PubDate: 2022-05-01

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Abstract: Abstract In situ Raman spectroscopy is an important tool for describing the actual phase transfer conditions in metal oxides and provides important insights into the phase transition mechanism. The particle size, non-stoichiometry, and surface stress are well-known factors in the shifting and broadening of Raman modes for the TiO2 anatase phase with increasing the temperature. Also, anharmonic effects in the form of phonon–phonon coupling and optical-phonon coupling are other factors in the shifting and broadening of Raman modes at high temperatures. In this paper, TiO2 nanocrystals in the anatase phase are synthesized by the sol–gel method. Then the structure and size of the particles are investigated using XRD diffraction and SEM. Meanwhile, the contribution of phonon–phonon coupling for the third- and fourth-order has been studied for the active modes Eg, A1g, and B1g, with increasing temperature (from room temperature to 943 K). The results of the back-scattering of in situ Raman spectroscopy show that the contribution of phonon–phonon coupling for the third-order has a significant effect on the shifting and broadening of Raman active modes. Also, the 412 cm−1 mode behavior differs from the other two modes in the contrast between anharmonic couplings contribution and pure-volume contribution. PubDate: 2022-05-01

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Abstract: Abstract Ternary zinc–sodium–phosphate glasses doped with transition metal of the composition Na2MxZn1−xP2O7(x = 0, 1, 2 and 5 mol %) (where M = Ni, Cu and Co) were prepared by the traditional quenching method. The ac conductivity measurements at different temperatures for the prepared glasses have been investigated, and the activation energy for dc conduction has been determined in each transition metal doped sample. The results showed that the evolution of the activation energy of the conductivity depends on the nature of the dopant ions. A model based on formal density functional theory concept in which the electrical charge exchanged between the transition-metal cations and the surrounding material surface is proposed. The outcome is a “simplified” formula which allows us to explain the evolution of the ionic dc conductivity activation energy as a function of the doped ion in interaction with the cation and the surface. PubDate: 2022-05-01

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Abstract: Oscillation is ubiquitous and important in both bio-engineering and biosystems. We here analyze the features of oscillation in a well-studied biochemical model of glycolysis with autocatalytic kinetic step. This Selkov model is followed deterministically using mass action kinetics. We explore the sensitivity analysis technique to assess degree of susceptibility of the system with respect to different input parameters for a thorough understanding of the merit of individual parameters controlling the core dynamics. Emphasis is concentrated on the system’s biological response via oscillation, bracketing the range of perturbation allowed to the kinetic parameters. An interesting observation is the switchover of the dynamics from non-oscillating to damping followed by stable sustained undulation with one or two controlling kinetic parameters which are quite appealing. The result may be illuminating in understanding the dynamics behind oscillations in biochemical systems in general. A key outcome of the study is the prioritization of most sensitive parameter for the network model controlling the dynamical features via scatterplot analysis. Graphical abstract PubDate: 2022-05-01

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Abstract: Abstract In this paper, we examine the spatially homogeneous and anisotropic Kantowski–Sachs (KS) space–time with viscous Ricci dark energy in the framework of Saez and Ballester (Phys Lett A 113:467, 1986) scalar tensor theory of gravitation. To solve the field equations, we use (i) the relationship between metric potentials which is obtained from the condition that shear scalar of the model is proportional to the expansion scalar and (ii) the relationship between average scale factor (a(t)) and bulk viscous coefficient \((\xi )\) as \(\xi =\xi _0+\xi _1\big (\frac{\dot{a}}{a}\big )+\xi _2\big (\frac{\ddot{a}}{\dot{a}}\big )\) , where \(\xi _0\) , \(\xi _1\) and \(\xi _2\) are constants. Some well-known cosmological implications such as deceleration parameter, equation of state parameter, statefinder and Om diagnostic parameters of the model are constructed and analyzed through graphical representation. It is also observed that the KS viscous Ricci dark energy model presented here is compatible with the current cosmological observations. PubDate: 2022-05-01

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Abstract: Abstract The first-principles calculations have been applied to investigate the impact of Fe impurity on the electronic, magnetic, and optical properties of graphene-like InAs and compare the results. The calculations have been accomplished through the full-potential augmented plane wave technique in the density functional theory framework using WIEN2k computational software. The band structures, density of states, and magnetic moment have been calculated. Since the presence of Fe causes magnetic effects such as spin–orbit interaction and electronic treatment variations, substituting In by Fe changes the non-magnetic InAs nanosheets semiconductor to a metalloid with the magnetic moment of about 5 Bohr magneton. Moreover, both real and imaginary diagrams of the dielectric function, loss function, optical conductivity, refraction index, and extinction coefficients have been discussed in the pure and impure cases. PubDate: 2022-05-01

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Abstract: Abstract The dielectric and percolation behavior of polymer nanocomposites (PNC) comprising of polyvinylidene fluoride (PVDF)/nanocrystalline nickel (n-Ni) [conducting filler] and PVDF/n-BaTiO3 [ferroelectric insulating filler], prepared under the novel cold press method are compared. Higher effective dielectric constants (ɛeff) of 2400 and 400 at 40 Hz with volume fractions of filler fcon = 0.28 and \(f_{{{\text{BaTiO}}_{3} }} = 0.60\) were observed, respectively. PVDF/n-Ni composites show percolation behavior associated with insulator to metal transition (IMT) at the percolation threshold (fc), while PVDF/n-BaTiO3 shows an effective electrical behavior due to the sum effect without showing any IMT. The drastic modulation in their dielectric, electrical and percolation behavior are attributed to the nature of filler present in them and has been explained by Percolation theory, Yamada model and VRH models. The universality and non-universality of exponents have been understood within the framework of the above models, the geometry of the fillers and the process conditions. Cold-pressed PNC based on ferroelectric filler are of superior quality for dielectric applications. PubDate: 2022-05-01

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Abstract: Abstract Here, we investigate an enzymatic reaction system subjected to additive and multiplicative noises and a weak periodic signal. By means of numerical simulations, we find that structure of stationary probability distribution function changes from one peak to two peaks by regulating not only the noise intensities (i.e., noise-induced transition), but also system parameters. The mean first passage time as a function of the multiplicative noise intensity exhibits a maximum, showing that the noise can enhance stability of the system. Moreover, by using the two-states theory, analytically expression of signal-to-noise ratio (SNR) of the system in the adiabatic limit is derived. The results indicate that: (1) The SNR as a function of noise intensity exhibits a maximal value, i.e., a stochastic resonance (SR) phenomenon; (2) as the noise intensities remain unchanged, the curve of the SNR with respect to the parameters of the system displays a peak, i.e., a SR-like phenomenon. Because the noise and the parameters reflect, respectively, temperature and rates of the enzymatic reactions, choosing optimal temperature and rates can enhance response of the system. This findings will be beneficial for controlling enzymatic reaction systems. PubDate: 2022-05-01

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Abstract: Abstract In this study, the effects of the piezoelectric polarization field have been investigated on the spectral and power characteristics of In0.2Ga0.8N/GaN superluminescent light-emitting diodes. The Schrödinger and Poisson equations, the rate equations in the multiple quantum well active region and separate confinement heterostructure layers, and the optical propagating equations have been solved in the presence of the piezoelectric field. The results have been compared with results of the case of without piezoelectric field. According to the results, in the presence of piezoelectric field, the red-shift occurs in the spectra, and the width of spectrum increases. Also, the piezoelectric field decreases the peak intensity of spectrum and modal gain of the device. PubDate: 2022-05-01

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Abstract: Abstract Nonlinear propagation of magnetoacoustic waves in magnetized, collisionless, warm bi-ion plasmas with positive and negative ions of different masses and charge states are investigated. The two-fluid model is used here. Using reductive perturbation technique, the Korteweg-de Vries equation is derived as nonlinear dispersion relation, and its solution for the magnetoacoustic solitons propagating in the direction perpendicular to the external magnetic field is obtained. Using experimental values for the plasma parameters, magnetoacoustic soliton structures for K-fullerene plasma are illustrated along with some other useful alkali-fullerene plasmas. PubDate: 2022-05-01

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Abstract: Abstract In the present study, various solar and atmospheric parameters, namely solar radiation, surface ozone, relative humidity, air temperature, and wind speed, have been studied first time for the annular solar eclipse of June 21, 2020, at seven Indian stations simultaneously. All the seven different stations are selected along the solar eclipse path having the maximum eclipse magnitude of 92% and above. The various atmospheric parameters have shown the change in behavior during the solar eclipse duration. The incoming solar radiation has a maximum 95.97% decrease at Ludhiana at the time of maximum obscuration compared to the previous day. The surface ozone concentration has shown a decrease for all the seven stations during the maximum obscuration period. A maximum of 9.25% decrease in surface temperature has been observed nearly after 30 min of the time of maximum obscuration of the eclipse. Relative humidity started increasing at all the stations and showed an inverse trend from temperature. The wind speed was found to suppress during the maximum solar eclipse which may be attributed to stabilization of atmospheric boundary layer due to cooling. PubDate: 2022-05-01

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Abstract: Abstract We propose a five-level quasi-tripod type atomic system for realizing two-channel cross-phase modulation (XPM) based on the light-storage. Due to the existence of the double dark-state polaritons, both probe fields can be coherently mapped into and out of the cold atoms by switching off and on the coupling field adiabatically. The analytic results and the numerical simulations show that the application of an additional weak microwave field during the storage time can efficiently modify the atomic spin coherence, and a continuous and controllable phase shift can be imposed on the retrieved probe fields with negligible attenuation in the amplitude. The phase shift and the energy retrieving rate of the probe fields are neither influenced by the coupling field nor by the atomic optical density. Such a novel scheme can be easily extended to realize the XPM of multiple-probe fields and may find potential applications in multiple-channel classical and quantum information processing. PubDate: 2022-05-01

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Abstract: Abstract Present Paper describes analysis of GPS-data recorded at low latitude station Hyderabad (Geographic latitude 17 \(^\circ \) , 25′ N, longitude 78 \(^\circ \) , 33′ E), India to study the effect of magnetic activity on ionospheric TEC. The total electron content (TEC) data were considered for the ionosphere during five most quiet and most disturbed days for each month of the solar minimum year 2009 and the high solar activity year 2013. The results show that GPS-TEC is found to be more during disturbed days than that during quiet days with a maximum difference during the equinox season. In addition, the difference in TEC during quiet and disturbed days is found to be higher for solar maximum than that for solar minimum year. Moreover the GPS-TEC variations depend on the season with the maximum in equinox season and minimum in summer and winter season. Generally daytime TEC is found to be larger than that in the nighttime which is maximized around the local noontime hour but the peak formation delayed for the solar minimum year. The EIA development process during the solar minimum is quite slow and occurs in late afternoon as compared to that during the high solar activity year. In addition, this delay is larger for summer and winter season than that for equinox months. The formation of post sunset anomaly in the post-sunset sector (1900–2300 LT) is prominent during high solar activity year 2013 whereas same is insignificant for solar minimum year 2009. The post-sunset anomaly could be attributed to pre-reversal enhancement (PRE) of zonal electric field. PubDate: 2022-05-01