Pramana最新文献

{"title":"Traversable wormhole solutions with phantom fluid in modified f(R, T) gravity","authors":"Sourav Chaudhary,&nbsp;S K Maurya,&nbsp;Jitendra Kumar,&nbsp;Sweeti Kiroriwal","doi":"10.1007/s12043-024-02811-5","DOIUrl":"10.1007/s12043-024-02811-5","url":null,"abstract":"<div><p>In this work, we have obtained new phantom fluid-type traversable wormhole (WH) solutions in the context of <span>(f(mathcal {R}, T))</span> 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 <span>(mathcal {L}_{m}=-(-rho +mathcal {P}_{r}+2mathcal {P}_{t}))</span> 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 <span>(omega &lt;-1)</span> 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 <span>(rho =eta (mathcal {P}_{t}-mathcal {P}_{r}))</span> 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.</p></div>","PeriodicalId":743,"journal":{"name":"Pramana","volume":"98 4","pages":""},"PeriodicalIF":1.9,"publicationDate":"2024-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142414739","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Dynamical probing and multiple actions of linear offset boosting of constants in Josephson junction instigated by Wien bridge oscillator embedded in the microcontroller","authors":"Balakrishnan Sriram,&nbsp;Daniel Maoussi Godonou,&nbsp;Cyrille Ainamon,&nbsp;Isidore Komofor Ngongiah,&nbsp;Karthikeyan Rajagopal","doi":"10.1007/s12043-024-02816-0","DOIUrl":"10.1007/s12043-024-02816-0","url":null,"abstract":"<div><p>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.</p></div>","PeriodicalId":743,"journal":{"name":"Pramana","volume":"98 4","pages":""},"PeriodicalIF":1.9,"publicationDate":"2024-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142414802","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Numerical study of unsteady reactive third-grade fluid flow in a microchannel through a porous medium subject to exothermic reaction","authors":"Idrees Khan,&nbsp;TIRI Chinyoka,&nbsp;Rozli Zulkifli,&nbsp;Emad A A Ismail,&nbsp;Fuad A Awwad,&nbsp;Ahmed M Hassan,&nbsp;Oluwole D Makinde,&nbsp;Zubair Ahmad","doi":"10.1007/s12043-024-02820-4","DOIUrl":"10.1007/s12043-024-02820-4","url":null,"abstract":"<div><p>The purpose of this study is to investigate the transient dynamics of a third-grade fluid, which can undergo exothermic reactions in a saturated porous microchannel. The adverse pressure gradient force constitutes the primary flow driver. In addition to exothermic reactions, the system is also subjected convective cooling at the microchannel boundaries. Newton’s law of cooling and Arrhenius kinetics are employed to model the boundary cooling and exothermic reactions, respectively. The temperature-dependent fluid viscosity is modelled via a Nahme-type law and the porous material between the parallel microchannels is assumed to have constant permeability. To account for this, the unsteady modified Darcy’s law is applied, effectively capturing the impact of porosity. Computational solutions are employed to solve the non-homogeneous partial differential equations (PDEs) for the flow temperature and velocity. These computational solutions are developed from efficient, convergent and unconditionally stable, semi-implicit finite difference (SIFD) methods. Examining the thermodynamic and fluid-dynamical consequences of variations in the numerical exponent <span>(aleph )</span> and exothermic reaction parameter <span>(delta _2)</span> are the principal motives of the study. A comparative evaluation of the thermal runaway susceptibility of the numerical exponent parameter for two distinct types of fluids is outlined, indicating that the ranking of susceptibility ranges from most to least susceptible in the bimolecular case, the Arrhenius case and the sensitised case. Newtonian fluids are the most prone to non-Newtonian fluids. Additionally, the study systematically explores the sensitivity of field variables to changes in different flow parameters through graphical representations and shows that the fluid variables increase with the increase in Reynolds number, viscosity parameter and Brinkman number, while decrease for the third-order parameter and porous medium parameter. The obtained results are qualitatively discussed and compared with the published data.\u0000</p></div>","PeriodicalId":743,"journal":{"name":"Pramana","volume":"98 4","pages":""},"PeriodicalIF":1.9,"publicationDate":"2024-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142413307","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Impinging flow of a special third-grade nanofluid streaming over a porous receding sheet using the tri-temperature model","authors":"Palanisamy Gayathri,&nbsp;Nagarajan Nithyadevi,&nbsp;Krishnan Sathyasri,&nbsp;Naramgari Sandeep","doi":"10.1007/s12043-024-02802-6","DOIUrl":"10.1007/s12043-024-02802-6","url":null,"abstract":"<div><p>The heat transfer characterisation of the three-phase local thermal non-equilibrium analysis due to the nanofluid (solid particle phase and the base fluid phase) and the absorbing phase (due to the porous surface) is performed for a third-grade nanofluid impinging over a receding surface. The mathematical formulation of the physical model includes the Rivlin–Ericksen tensor for fluids of grade three with appropriate restriction to viscous flows and also incorporates the Buongiorno nanofluid model for studying the impact of thermophoresis and Brownian motion. The resultant governing time-dependent partial differential equations has been converted to ordinary differential equations by applying similarity transformation. The computational results are obtained using the finite-difference approach in the Matlab software. The non-Newtonian and the time-dependent flow phenomena demands an additional boundary condition to ensure the uniqueness of the solution. With a general third-grade assumption with the wall shrinking and unsteadiness, the resultant equations govern the occurrence of dual solution in the obtained numerical results. The stability investigation reports the existence of multiple (dual) solutions due to the unsteadiness imparted in the flow and the flow behaviour of both the stable and unstable solutions are revealed. The boundary layer characteristics are explored for various vital physical parameters, such as material parameter, porous permeability parameter, Brownian motion parameter, thermophoresis parameter, inter-phase heat transfer coefficient, modified thermal capacity ratio, modified thermal diffusivity ratio and buoyancy ratio parameter. The temperature distribution across different phases is analysed for the stable solutions.</p></div>","PeriodicalId":743,"journal":{"name":"Pramana","volume":"98 4","pages":""},"PeriodicalIF":1.9,"publicationDate":"2024-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142413318","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Performance evaluation of frequency-modulated NR–DCSK using compound chaotic sequence under alpha–mu fading channel","authors":"Namrata Biswas,&nbsp;I Raja Mohamed,&nbsp;M Sangeetha","doi":"10.1007/s12043-024-02808-0","DOIUrl":"10.1007/s12043-024-02808-0","url":null,"abstract":"<div><p>This work evaluates the performance of frequency-modulated noise reduction-differential chaos shift keying (FM-NR–DCSK) when using a compound chaotic sequence (CCS) under a multipath fading channel. To construct a more complex and random CCS, the outputs of chaotic maps like the logistic map, tent map, Chebyshev map and Henon map are incorporated. In this scheme, the CCS is first frequency-modulated (FM) to generate a signal with constant energy per bit. This improves the bit error rate (BER) performance of noise reduction-differential chaos shift keying (NR–DCSK). The functionality of the CCS-based FM-NR–DCSK system is being assessed in the presence of both additive white Gaussian noise (AWGN) and alpha–mu (<i>α</i>–<i>µ</i>) fading to determine its efficacy. In conclusion, we analyse the effectiveness of the CCS compared to other existing chaotic maps.</p></div>","PeriodicalId":743,"journal":{"name":"Pramana","volume":"98 4","pages":""},"PeriodicalIF":1.9,"publicationDate":"2024-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142413290","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Cryogenic magnetocaloric properties in Xenotime-type HoPO4","authors":"Assaad Elouafi,&nbsp;Sara Ezairi,&nbsp;Fatima Lmai,&nbsp;Abdeslam Tizliouine","doi":"10.1007/s12043-024-02831-1","DOIUrl":"10.1007/s12043-024-02831-1","url":null,"abstract":"<div><p>Holmium orthophosphate (HoPO₄) was prepared using the solid-state method. The XRD pattern analyses have proved that HoPO₄ crystallises in the tetragonal structure (I4₁<span>(/)</span>amd). The maximum magnetic entropy change (−<span>(Delta {S}_{text{M}}^{text{max}}))</span> and the relative cooling power (RCP) reach 34.5 J<span>(/)</span>kg·K and 414.84 J kg⁻¹ at 2.4 K under a magnetic field of 50 kOe, respectively. The lowest transition temperature and the large magnetocaloric effect (MCE) showed that HoPO₄ is a potential candidate for superfluid helium magnetic refrigeration applications.\u0000</p></div>","PeriodicalId":743,"journal":{"name":"Pramana","volume":"98 4","pages":""},"PeriodicalIF":1.9,"publicationDate":"2024-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142413337","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Magnon tunnelling between two magnon Bose–Einstein condensates","authors":"A D Belanovsky,&nbsp;P M Vetoshko,&nbsp;Yu M Bunkov","doi":"10.1007/s12043-024-02828-w","DOIUrl":"10.1007/s12043-024-02828-w","url":null,"abstract":"<div><p>The rapid development of quantum magnonics can be attributed to its potential applications in quantum computing, information processing and the creation of hybrid quantum systems. Quantum quasiparticles, known as magnons, undergo Bose condensation at high densities, a phenomenon observed during radiofrequency excitation. This phenomenon was initially discovered in the antiferromagnetic superfluid <span>(^3)</span>He. Magnonic superfluidity effects, Josephson effect and magnon tunnelling were also observed in this system. Similar effects have been identified in yttrium iron garnet at room temperature, suggesting the possibility of utilising these effects in a manner akin to superconductivity. In this article, we conduct simulations of magnon tunnelling processes across the energy gap, aiming to compare these simulations with experimental findings.</p></div>","PeriodicalId":743,"journal":{"name":"Pramana","volume":"98 4","pages":""},"PeriodicalIF":1.9,"publicationDate":"2024-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142413316","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Nanoscale resistive switching behaviour and photoabsorption response from NiO nanoflakes","authors":"Vanaraj Solanki,&nbsp;Shikha Varma","doi":"10.1007/s12043-024-02830-2","DOIUrl":"10.1007/s12043-024-02830-2","url":null,"abstract":"<div><p>Hydrothermally grown NiO nanoflakes have been investigated here for their resistive switching (RS) and photoabsorption characteristics. The formation and disruption of the conducting filament (CF) under an applied external electric field leads to bistable resistive switching in the grown NiO nanoflakes. Comprehensive investigations of the <i>I–V</i> behaviour show that the formation and rupturing of the CF depend on the concentration of the metallic Ni. Interestingly, photoabsorption response demonstrates a nearly similar behaviour in UV and visible regions for nanoflakes grown at low reaction time, but an enhanced UV response for the flakes obtained at larger reaction times. These nanoflakes displaying multifunctional properties of photoabsorption and RS behaviour, that can be modulated with reaction time, are attractive for optoelectronic, electrochromic and RS-based memory applications.</p></div>","PeriodicalId":743,"journal":{"name":"Pramana","volume":"98 4","pages":""},"PeriodicalIF":1.9,"publicationDate":"2024-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142413311","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Two-proton emission within a deformed Yukawa-plus-exponential model","authors":"P Mehana,&nbsp;N S Rajeswari","doi":"10.1007/s12043-024-02817-z","DOIUrl":"10.1007/s12043-024-02817-z","url":null,"abstract":"<div><p>The Yukawa-plus-exponential model (YEM) is the modified form of liquid drop model incorporating parameter to include short-range interaction and surface diffuseness. We have studied two-proton (2p) radioactivity within the YEM for spherical nuclei in our previous work [Mehana and Rajeswari in <i>Eur. Phys. J.</i> A <b>59</b>, 104 (2023)]. The present study is the extension of the previous work to apply the model to deformed 2p emitters. Deformation is incorporated in YEM through Coulomb potential and Yukawa interaction potential. The calculated half-lives are found to have less deviation than experimental half-lives, when compared to spherical ones. Further, half-lives are also predicted for 2p emitters which are not yet studied experimentally. The calculated half-lives show good match with half-lives predicted by other theoretical models. It is seen that the half-lives of the prolate-shaped daughter nuclei are lower than spherical nuclei of the same parent, whereas the half-lives of oblate daughters are higher than that of the spherical ones.\u0000</p></div>","PeriodicalId":743,"journal":{"name":"Pramana","volume":"98 4","pages":""},"PeriodicalIF":1.9,"publicationDate":"2024-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142413317","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Computing intelligence for the magnetised chemically reactive bidirectional radiative nanofluid flow through the Bayesian regularisation back-propagated neural network","authors":"Zahoor Shah,&nbsp;Muhammad Asif Zahoor Raja,&nbsp;Muhammad Shoaib,&nbsp;Shumaila Javeed,&nbsp;Taseer Muhammad,&nbsp;Mehboob Ali,&nbsp;Waqar Azeem Khan,&nbsp;Raja Zaki Haider","doi":"10.1007/s12043-024-02794-3","DOIUrl":"10.1007/s12043-024-02794-3","url":null,"abstract":"<div><p>This research work aims to explain the model and assessment of a differential mathematical system of the magneto-bioconvection of the Williamson nanofluid model (MBWNFM) by capitalising on the strength of the stochastic technique through computational intelligence of Bayesian regularisation back-propagated neural networks (CIBRB-NNs). This facilitates a more accurate, reliable and proficient computation of the dynamics. A reference dataset is built using the Adams technique in the Mathematica software to depict multiple situations and account for numerous influential parameters of the MBWNFM. The reference data results are split into 70% for training and 30% for validation and testing methods. This approach aims to enhance the accuracy of the approximated results and enable them to be compared with established solutions. The demonstration of the accuracy and efficiency of the created CIBRB-NNs involves a comparison of the results obtained from the dataset using the Adams approach, by adjusting several influential parameters which include magnetic parameter (<span>(M)</span>), bioconvection Lewis Number (<span>(L_{b})</span>), thermal diffusivity (<span>(alpha)</span>) and thermal Biot number (<span>(gamma)</span>). The stability and accuracy of CIBRB-NNs are validated using various methodologies, including the analysis of fitness curves depicting mean square error, regression studies, evaluation of error using histogram plots and measurement of absolute errors. The excellent measures of performance in terms of MSE are achieved at levels 4.50e-12, 6.73e-13, 1.07e-13, 7.08e-13, 4.77e-13 and 1.70e-13 against 82, 150, 98, 83, 170 and 189 epochs. The error analysis of the proposed and reference datasets shows that CIBRB-NNS is authentic and precise, ranging from e-09 to e-04 for all scenarios.</p></div>","PeriodicalId":743,"journal":{"name":"Pramana","volume":"98 4","pages":""},"PeriodicalIF":1.9,"publicationDate":"2024-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142413310","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}