Pramana最新文献

Periodically kicked Floquet systems, such as the kicked rotor, are a paradigmatic and illustrative simple model of chaos. For non-integrable quantum dynamics, there are several diagnostic measures, such as Loschmidt echo, autocorrelation function and out of time order correlator (OTOC) to study the presence of (or the transition to) chaotic behaviour. We analytically compute these measures in terms of the eigensystem of the unitary Floquet operator of the driven quantum systems. We use these expressions to determine the time variation of the measures for the quantum-kicked rotor (QKR) on the torus, for the integrable as well as the chaotic case. For a simpler integrable variant of the kicked rotor, we also give a representation theoretic derivation of its dynamics.

Positron emission tomography (PET) scans are vital in diagnosing cancer and neurological disorders but raise concerns due to exposure to ionising radiation. This research is focussed on the development of an intelligent regression model to investigate the effective radiation dose received by a patient during the whole-body PET scan. Our newly developed intelligent model refers to the application of artificial intelligence (AI) and machine learning (ML) techniques. Since underfitting and overfitting are basic issues of any ML model, data fitting methodology for developing intelligent regression is taken care of by implementing the least absolute shrinkage and selection operator (Lasso) and ridge regression. In order to have the comparative performance of our model, we have also applied support vector and decision tree-based ML techniques as regressors to predict radiation doses in whole-body PET scans, keeping patient safety in mind. By incorporating patient-specific data and imaging parameters, these models aim to accurately estimate radiation doses, thereby optimising imaging protocols and reducing unnecessary exposure risks. The study uses PET({/})CT data from 2009 to 2012. The linearly-independent covariates applied in this model are age, weight, height, residence time and injected activity and the dependence variable is taken as the effective dose. Model performance is evaluated using root mean square error (RMSE). A systematic exploratory data analysis has been carried out to investigate data cleaning, missing information, scaling and normalisation. The top five organs such as the brain, stomach, kidney, adrenal and spleen are focussed to produce the traditional descriptive statistics of data summary. Least absolute shrinkage and selection operator (lasso) regression exhibit stable RMSE values for organ equivalent doses across genders, while substantial RMSE variations exist among different models and organs, suggesting sensitivity to specific organs and patient gender. Accurate dose estimation is pivotal for risk assessment and protocol optimisation. This study evidenced the need to improve radiation dosimetry for specific organs aiming at patient care and radiology practices by considering individualised factors in dose estimation methodologies to refine PET scan dose estimation methods.

This article uses a finite-element approximation approach for solving a three-dimensional flow problem of a nanofluid influenced by heat transfer due to nanoparticles over a non-linearly stretching sheet within an unbounded domain. Utilising similarity transformations, a well-posed coupled system of nonlinear ordinary differential equations is derived from the governing partial differential equations describing the flow and heat transfer processes. The resulting system is then solved by using quadratic Lagrange polynomials as basic functions over a mesh of different finite elements through the Galerkin finite element (GFE) technique. This implementation is based on a regular grid utilising Lagrange polynomials for solving the converted equations. The effects of various parameters of interest are efficiently discussed with the help of graphs and numeric tables. Both numerical and exact solutions are compared favourably, demonstrating a high level of accuracy. It is noteworthy that the GFE method emerges as a much more stable numerical technique than the other existing analytic and semi-analytical methods. Furthermore, the adopted finite-element method reduces the dimensionality of Sobolev's space's finite-dimensional subspace and also improves the solution's convergence rate. Moreover, the velocity is negative, and its magnitude increases as the stretching rates ratio increases due to the downward flow in the vertical direction. The temperature and heat transmission from the sheet are barely impacted by Brownian motion due to the dominance of other forces and length scales involved in the heat transfer process.

A new generalised non-local nonlinear Schrödinger (NLS) equation is introduced which possesses a Lax pair and is parity–time (PT)-symmetric. Thus, it is confirmed that the generalised non-local NLS equation is integrable. The inverse scattering transform for the generalised non-local NLS equation is developed using a Riemann–Hilbert problem for rapidly decaying initial data and an approach for finding pure soliton solutions is described. The analytical characteristics of the eigenfunctions, scattering data and their symmetries are discussed. Finally, using Mathematica some important two-dimensional plots of the wave solutions are shown to illustrate the dynamics of the model.

In this study, we employ molecular dynamics simulations to develop a large model (19,998 atoms) of liquid SiO₂ at 3500 K. We construct models at different pressures in the 0–100 GPa range using the Beest–Kramer–Santen (BKS) potential and periodic boundary conditions. The goal is to detail the structural transition from the polyamorphic liquid state of SiO₂ to the crystalline stishovite form, which occurs between 45 and 60 GPa. We analyse the polyamorphic state of liquid SiO₂ by examining the formation of SiO_x clusters from 2 to 60 GPa. Beyond 60 GPa, the pair radial distribution functions (PRDFs) for Si–O, O–O and Si–Si display multiple peaks, indicating the crystalline phase. This observation is further supported by examining the bond angle distribution, the fraction of SiO_x units and OSi_x linkages, Si–O bond lengths within SiO_x units, structural visualisations and the analysis of ring statistics in the liquid SiO₂ system, all of which underscore the comprehensive changes in the structure of the system.

The performance of multilayer organic light emitting diode (OLED) is studied by stacking poly(3,4-ethylenedioxythiophene) polystyrene sulphonate (PEDOT:PSS) as the hole transport layer (HTL), tris(4-carbazoyl-9-ylphenyl) amine (TCTA) as the hole injection layer (HIL) and bathophenanthroline (BPhen) as the electron transport layer (ETL). Modification is done in the emissive layer (EML) by the introduction of host–guest material which is bis[2-(4,6-difluorophenyl) pyridinato-C2,N](picolinato)iridium(III) (FlrPic) and bis[2-(diphenylphosphino) phenyl] ether oxide (DPEPO). Multiple devices are fabricated and the performance is compared in terms of turn-on voltage, current density, brightness and luminous efficiency. The device with co-deposition of guest and host materials has improved the luminous efficiency by 6.17% when compared to the other fabricated devices.

It is obvious that due to its higher viscosity, non-Newtonian fluid show better heat transport than the Newtonian fluid. Moreover, shear flow helps us to make our surrounding environment friendly. With this view point, an attempt has been taken in this paper to explore the two-dimensional flow of low electrically conducting Eyring–Prandtl fluid and heat transfer over a moving porous plate subject to suction/blowing with externally applied magnetic field. The flow is maintained due to the incoming shear away from the plate so that boundary layer type of flow is formed over the plate. This makes the problem new, not yet been addressed by any researcher. Similarity transformations are applied to obtain self-similar structure of the leading equations. However, similar solutions of the problem are attained for a specific power-law velocity (index, (n=1/3)) of the moving plate. The equations are solved numerically and compared with different flow quantities having different grid sizes. The data are plotted graphically to represent velocity, velocity gradient and temperature for different parametric values. The influences of suction/blowing parameter, fluid material parameters, Prandtl number and magnetic parameter on velocity, temperature and velocity gradient are shown and explained at length with physical explanations as far as practicable. The velocity decreases with increasing values of magnetic parameter due to the appearance of Lorenz force. However, temperature increases. So, the boundary layer flow can be controlled using a suitable magnetic field. It is found that fluid velocity rises with the growing suction/blowing parameter and fluid material parameter (alpha ) but the temperature is found to diminish resulting in the reduction of heat transfer in fluid. The analysis reveals that blowing destabilises the flow, while the suction stabilises the boundary layer flow. This study explores the boundary layer flow structure of a fluid with low electrical conductivity along with heat transfer in the presence of suction/blowing, externally applied magnetic field and shear flow.

Most physical systems, whether classical or quantum mechanical, exhibit spherical symmetry. Angular momentum, denoted as (ell ), is a conserved quantity that appears in the centrifugal potential when a particle moves under the influence of a central force. This study introduces a formalism in which (ell ) plays a unifying role, consolidating solvable central potentials into a superpotential. This framework illustrates that the Coulomb potential emerges as a direct consequence of a homogeneous (r-independent) isotropic superpotential. Conversely, an (ell )-independent central superpotential results in a 3-dimensional harmonic oscillator (3-DHO) potential. Moreover, a local (ell )-dependent central superpotential generates potentials applicable to finite-range interactions such as molecular or nucleonic systems. Additionally, we discuss generalisations to arbitrary D dimensions and investigate the properties of the superpotential to determine when supersymmetry is broken or unbroken. This scheme also shows that the free-particle wave function in three dimensions is obtained from the spontaneous breakdown of supersymmetry and clarifies how a positive 3-DHO potential, as an upside-down potential, can have a negative energy spectrum. We also present complex isospectral deformations of the central superpotential and superpartners, which can have interesting applications for open systems in dynamic equilibrium. Finally, as a practical application, we apply this formalism to specify a new effective potential for the deuteron.

In this work, we have obtained new phantom fluid-type traversable wormhole (WH) solutions in the context of (f(mathcal {R}, T)) modified gravity. We investigate the potential that some equations of state (EoS), specifically phantom energy, which describes the accelerated expansion of the universe, could support the existence of traversable wormholes. This cosmic fluid thus offers us a plausible explanation for the occurrence of WH geometries. We construct two WH models with matter Lagrangian density (mathcal {L}_{m}=-(-rho +mathcal {P}_{r}+2mathcal {P}_{t})) and inspect numerous characteristics of these models under the WH geometry. The first WH solution (WH-I) is discovered by utilising a linear barotropic equation of state (EoS) connected with phantom energy (omega <-1) indicating the presence of the phantom fluid and pointing to the Universe’s expansion, while in the second WH (WH-II) solution, we take into account an interesting EoS (rho =eta (mathcal {P}_{t}-mathcal {P}_{r})) to generate a WH model. Additionally, it showed that the phantom fluid WH-I solution violates the radial null energy condition (NEC) while tangential NEC is satisfied. On the other hand, for the WH-II solution, NEC is violated. Extensive detailed discussions of the matter components have been done via graphical analysis. The obtained WH geometries satisfy a stable WH’s physically acceptable criteria.

The dynamical probing and linear offset boosting of constants in Josephson junction (JJ) instigated by the Wien bridge oscillator (JJIWBO) are investigated in this paper. Via numerical simulations, the JJIWBO unveiled bistable periodic oscillations, bistable periodic doubling with an evolving path to bistable chaotic characteristics, monostable chaotic behaviours and monostable periodic characteristics. The numerical dynamics are realised by the microcontroller validation (MCV) scheme. Two constant parameters are introduced in the rate equations of JJIWBO to implement the linear offset boosting of constants based on the two voltage variables. It is demonstrated that the polarity of the chaotic voltage and phase difference signals can be flexibly changed by varying one of the two constant parameters which is different from zero and the other constant parameter is zero. When two constant parameters have the same value, the chaotic voltages and phase difference signals can switch between bipolar and unipolar signals flexibly by changing the unique constant parameter.