Pramana最新文献

The resonance of a plasma column with an elliptical cross-section surrounded by a dielectric layer is investigated. It is assumed that the incident electromagnetic wave has a wavelength much larger than the dimensions of the assumed cross-section of the column. Using boundary conditions, the electric potentials and resonant frequencies of an elliptical plasma column covered by a dielectric for two polarisations of incident electric field are calculated. The incident electric field is considered in directions of the minor and major axes of the boundary ellipse. The limit cases are examined. The dependence of the resonant frequency on the dielectric constant and the plasma and dielectric dimensions are investigated. The obtained results are drawn and analysed. Then an elliptical plasma column with a coaxial dielectric core and a dielectric layer in scattering process by long wavelength waves is considered and the resonant frequencies of this object for two polarisations of incident electric field are calculated. The obtained results are plotted and analysed. This configuration can be presented as a plasma antenna.

Using a quantum hydrodynamic model, quantum effects (via Bohm potential) on modulational amplification in ion-implanted semiconductor magnetoplasmas are investigated. Expressions are obtained for the threshold pump amplitude and the growth rate of modulated beam for both the electrons and implanted colloids. Numerical analysis is performed for n-InSb/CO₂ laser system. The dependence of the threshold pump amplitude and the growth rate of modulated beam for electrons on wave number, applied magnetic field (via electron cyclotron frequency) and electron concentration (via electron-plasma frequency) and the dependence of the threshold pump amplitude and the growth rate of modulated beam for implanted colloids on wave number and colloid concentration (via colloid-plasma frequency) are explored. The lowering in threshold pump amplitude and enhancement of the growth rate of modulated beam for both the electrons and implanted colloids are observed by incorporating the quantum effects. The analysis provides detailed information of quantum effects on modulational amplification in ion-implanted semiconductor magnetoplasmas composed of electrons and negatively charged implanted colloids and establishes the technological potentiality of chosen samples as the hosts for the fabrication of efficient optical modulators.

MAX-phase compounds have recently gained increased technical interest owing to their distinctive characteristics that combine the inherent properties of metals and ceramics, making them suitable for various high-level industrial applications. Based on this vision, we report a detailed theoretical study of a new quaternary ferromagnetic MAX-phase compound Mn₂VSnC₂. We found that Mn₂VSnC₂ is mechanically and thermodynamically stable in α-polymorph ferromagnetic ordering. The macroscopic mechanical properties showed that Mn₂VSnC₂ was ductile (i.e., tolerant to damage). The obtained high melting and Debye temperatures validated the possible application of Mn₂VSnC₂ in harsh environmental applications. The electronic structures revealed that this compound exhibited metallic behaviour. Furthermore, we analysed the effects of pressure and temperature on different properties. Finally, the findings established that the title compound has good thermomechanical efficiency.

The nucleon–nucleus optical potential calculated in the Brueckner–Hartree–Fock (BHF) approach is non-local due to exchange and thus requires the solution of an integro-differential equation. We use an alternative approach to show that the exchange part of the central potential can be written as the sum of an infinite series. By using a local approximation, the first term of the series is the Brieva–Rook equivalent local approximation. We consider the first three terms of the series and show that each term of the series can be evaluated without solving the integral equation. We then show, for proton scattering from (^{40}hbox {Ca}) in the energy region (30 le E le 500) MeV, that the second term contributes less than (6% ) to the exchange part of the potential and that the third term is an order of magnitude smaller than the second term. We also show that the addition of the contribution from the second term in the total central potential makes a negligible contribution to the differential cross-section for the scattering of protons from (^{40}hbox {Ca}). Our results thus show that the Brieva–Rook (BR) localisation approximation is accurate to within (6%) in a wide energy region. Our method also provides a qualitative explanation of why the terms beyond the first are so remarkably small and justifies the use of a local approximation. We have also shown that only the direct part of the calculated potential is responsible for the development of the wine-bottle-bottom shape of the real central potential for intermediate energy nucleon scattering.

We present all the partial wave descriptions of the nucleon–nucleus system by proposing a new additive phenomenological potential with emphasis on off-energy-shell scattering. For most of the general treatment of the physical processes, the off-shell transition matrices are most expedient quantities because they carry as much information as the potential. As the off-shell Jost solution is an indispensable ingredient for deriving transition matrices, we initially construct this function by taking into account the ordinary differential equation method. Finally, we execute certain tests on our expressions with respect to various limiting conditions and present numerical results using the MATLAB programme. Numerical results are in sensible conformity with the previous works.

Elastic synapses in realistic neurons receive external stimuli for inducing appropriate firing modes, and fast creation of synapse to neurons can regulate neural activities. The energy diversity is decreased to keep energy balance between neurons. In this work, thermistor and photocell are used to rebuild a neural circuit, and it becomes sensitive to external temperature and illumination. A magnetic flux-controlled memristor is used to bridge connection to neural circuits and its coupling channel is controlled adaptively by energy diversity. The coupling intensity is controlled exponentially when energy difference is beyond a threshold. The involvement of memristive synapse in the coupling channel activates the ability for energy pumping and storage via magnetic field. The energy propagation along the memristive channel is controlled and its value is estimated when the memristive synapse is created to connect the functional neurons. It is found that neurons can reach complete synchronisation adaptively and finally reach energy balance when magnetic field coupling via memristor is further enhanced. It explains the potential mechanism for activating memristive synaptic regulation on neurons, and the gradient energy diversity enables the creation of synapse connections to neuron and thus neurons can reach possible energy balance in the physical field.

The purpose of this article is to derive a class of multi-soliton solutions of the Burgers equation employing Darboux transformation with the help of the Lax pair. By means of an effective transformation, the Burgers equation is reduced to a suitable form, and accordingly, the Lax pair of the said equation is derived utilising the Ablowitz–Kaup–Newell–Segur (AKNS) approach. Thus, the integrability of the Burgers equation is confirmed. To find an effective solution for the Burgers equation, for the first time, we apply the Darboux transformation through the Lax pair and explore new types of one-soliton solutions and two-soliton solutions of the Burgers equation. These solutions provide some new features of the Burgers equation. To the best of our knowledge, this is the first study in which a parabolic type of structure is found in the Burgers system. Moreover, taking these solutions as the seed solution, higher-order multi-soliton solution can also be generated. Finally, some important three-dimensional plots of the wave solutions are presented to visualise the dynamics of the model.

A system of baryons is studied where the system consists of the nucleon (N) and its first excited delta ((Delta )). The present study investigates the double magic nucleus (^{56})Ni under compression. To achieve the aim of this study, a technique called constrained spherical Hartree–Fock (CSHF) is employed. The effective potential of N–N, N–(Delta ) and (Delta )–(Delta ) is used. Examination of the sensitivity for results on the model space is studied. For a large model space, the compressibility of the nuclear system increases. By increasing the model space, the radial density distribution and the formation of (Delta )s decrease. Then the nucleus becomes more bounded under compression by increasing the model space when delta resonances have occurred. The formation of (Delta )s is an increment to 8.93% of all components of (^{56})Ni nucleus. Under compression, a part of the increment in binding energy creates (Delta ) particles.

In this research article, we report the various functional properties of [Pb(Fe_0.5Nb_0.5)O₃]_0.2- [(Ca_0.2Sr_0.8)TiO₃]_0.8 perovskite ceramic compound prepared by the solid-state process. Rietveld refinement proved that the compound crystallises in a pseudocubic structure as the primary phase. The dual oxidation states of Fe, Nb, Ti and the presence of oxygen vacancies were analysed by X-ray photoelectron spectroscopy. Ti–O and Ti–O–Ti prominent perovskite vibrations were examined by Fourier transform infrared (FTIR) analysis. Raman spectroscopy technique was employed to study the asymmetric TiO₆ octahedral stretching and A_1g phonon mode of PbFe_0.5Nb_0.5O₃ (PFN). Field emission scanning electron microscopy (FESEM) predicted better grain growth with an average grain size of 2.445 µm. Energy-dispersive X-ray spectroscopy (EDS) analysis was done for elemental confirmation and purity of the sample. A detailed optical analysis was done by incorporating both absorbance and diffuse reflectance spectroscopy. A narrow band gap was revealed from the optical studies and Urbach energy was analysed. The conduction band minimum (CBM) level was estimated to be − 1.14 eV exploring the photocatalytic response. Electrical properties were investigated in terms of dielectric constant, conductivity, complex impedance and modulus analyses. A weak ferroelectric response was noticed with the remnant polarisation of 0.181 µC(/)cm² from P–E loop analysis. Mössbauer spectroscopy revealed a strong paramagnetic doublet indicating the high-spin Fe³⁺ species in the octahedral environment.

The knowledge of the neutron-induced reaction cross-section is important, especially, for the fusion and fission reactor technologies. In the absence of experimental data or for cases where measurements are difficult, theoretical predictions of nuclear cross-sections are needed to be improved upon using refined model calculations or effective semi-empirical formulas. Accurate, physics-based modelling of neutron-induced reactions is key to all nuclear science and technology applications. In the present work, the excitation functions for (n, p), (n, (alpha )) and (n, 2n) reactions up to 20 MeV for stable isotopes of Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. are calculated using the EMPIRE-3.2 nuclear reaction model code using optimised values of input parameters. The experimental data available in EXFOR database for these stable isotopes are reproduced to determine the optimum parameters. The optimised parameters, so obtained, are then used to calculate the reaction cross-sections for a series of unstable nuclides for the incident neutron energy of 1–20 MeV. The calculated cross-sections are compared with the evaluated data available in literature (ENDF). We have also compared our results with the estimated cross-sections using available empirical formulas. Based on the calculations, we recommend a reliable set of parameters to estimate the (n, p), (n, (alpha )) and (n, 2n) cross-sections for unstable nuclides in the mass region (A sim ) 40–70.