#### Communications in Theoretical Physics

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ISSN / EISSN : 0253-6102 / 1572-9494
Total articles ≅ 9,405
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Published: 22 October 2021
Communications in Theoretical Physics; https://doi.org/10.1088/1572-9494/ac3230

Abstract:
The research on flow and heat transfer of hybrid nanofluids has gained great significance due to their efficient heat transfer capabilities. In fact, hybrid nanofluids are a novel type of fluids designed to enhance heat transfer rate and have wide range of engineering and industrial applications. Motivated by such an evolution, a theoretical analysis is performed to explore the flow and heat transport characteristics of Cu/Al O hybrid nanofluids driven by a stretching/shrinking geometry. Further, this work will focus on physical impacts of thermal stratification as well as thermal radiation during hybrid nanofluid flow in the presence of velocity slip mechanism. The mathematical modelling incorporates the basic conservation laws and Boussinesq-approximations. This formulation gives a system of governing PDEs which are later reduced into ODEs via dimensionless variables. An efficient numerical solver, known as bvp4c in MATLAB is utilized to acquire multiple (upper and lower) numerical solutions in case of shrinking flow. The computed results are presented in the form of flow and temperature fields. The most significant findings acquired from current study suggest that multiple solutions exist only in case of shrinking surface until a critical/turning point. Moreover, the solutions are unavailable beyond this turning point, indicating flow separation. It is found that the fluid temperature has been impressively enhanced by higher nanoparticles volume fraction for both the solutions. On the other hand, the outcomes disclose that the wall shear stress reduces for higher magnetic field in the case of second solution. The simulation outcomes are in excellent agreement with earlier research, with a relative error of less than 1%.
, Ruilin Han
Published: 22 October 2021
Communications in Theoretical Physics; https://doi.org/10.1088/1572-9494/ac3231

Abstract:
Strong electromagnetic fields produced in the non-central heavy-ion collisions can indue vector meson photoproduction. In this paper, we study the photoproduction $J/\psi$ and $\phi$ mesons in the relativistic heavy-ion collision from Ultra-peripheral nuclear collisions(UPC) to peripheral Hadronic Heavy Ion Collisions(HHIC). And then include both initial hadronic production and thermal production in quark-gluon plasma(QGP). We find, for charm anti-charm bound state $J/\psi$, the photoproduced $J/\psi$s are mainly in very low momentum region and clearly exceed the hadronic production. However, considering the thermal production of strange quark anti-quark pairs in QGP produced in relativistic heavy-ion collisions, the photoproduced $\phi$ is usually smaller than the thermal production and only evident at very peripheral collisions even their photoproduction is much larger than $J/\psi$.
Ramon Becar, , Pablo Gonzalez, Bin Wang, Yerko Vasquez
Published: 18 October 2021
Communications in Theoretical Physics; https://doi.org/10.1088/1572-9494/ac3073

Abstract:
In this work we consider black hole solutions to Einstein theory coupled to a nonlinear power-law elec- tromagnetic field with a fixed exponent value. We study the extended phase space thermodynamics in canonical and grand canonical ensembles where the varying cosmological constant plays the role of an effective thermodynamic pressure. We examine thermodynamical phase transitions in such black hols and find that both first and second order phase transitions can occur in the canonical ensemble, while for the grand canonical ensemble the Hawking-Page and second order phase transitions are allowed.
Qing-Yang Fan, Nan Wu, Shuai-Ming Chen, Li Jiang, Wei Zhang, Xin-Hai Yu, Si-Ning Yun
Published: 15 October 2021
Communications in Theoretical Physics, Volume 73; https://doi.org/10.1088/1572-9494/ac20ce

Jiaxin Qi, Hongli An, Peng Jin
Published: 13 October 2021
Communications in Theoretical Physics; https://doi.org/10.1088/1572-9494/ac2f2b

Jianjun Qi, Yuyao Bai, Qianqian Guo, , Shundalau Maksim
Published: 13 October 2021
Communications in Theoretical Physics; https://doi.org/10.1088/1572-9494/ac2f38

Abstract:
Based on a high level ab initio calculation which is carried out with the multireference configuration interaction (MRCI) method under the aug-cc-pVXZ (AVXZ) basis sets, X = T, Q, 5, the accurate potential energy curves (PECs) of the ground state Χ1Σg+ and the first excited state A1Σu+ of Li2 are constructed. By fitting the ab initio potential energy points with the Murrell-Sorbie potential function, the analytic potential energy functions (APEFs) are obtained. The molecular bond length at the equilibrium (Re), the potential well depth (De), and the spectroscopic constants (Be, ωe, αe, and ωeχe) for the Χ1Σg+ state and the A1Σu+ state are deduced from the APEFs. The vibrational energy levels of the two electronic states are obtained by solving the time-independent Schrödinger equation with the Fourier grid Hamiltonian (FGH) method. All the spectroscopic constants and the vibrational levels agree well with the experimental results. The Franck-Condon factors (FCFs) corresponding to the transitions from the vibrational level (v'=0) of the ground state to the vibrational levels (v"=0-74) of the first excited state have been calculated. The FCF for the vibronic transition of A1Σu+(v"=0) ←Χ1Σg+ (v'=0) is the strongest. These PECs and corresponding spectroscopic constants provide reliable theoretical references to both the spectroscopic and the molecular dynamic studies of the Li2 dimer.
Published: 12 October 2021
Communications in Theoretical Physics; https://doi.org/10.1088/1572-9494/ac2ed6

Run Cheng, Li Wang, Hao Zhao, Cui-Bai Luo, Yong-Long Wang, Jun Wang
Published: 11 October 2021
Communications in Theoretical Physics; https://doi.org/10.1088/1572-9494/ac2e6a

, Chang-Pu Sun, Hui Dong
Published: 5 October 2021
Communications in Theoretical Physics; https://doi.org/10.1088/1572-9494/ac2cb8

Abstract:
The efficiency at the maximum power (EMP) for finite-time Carnot engines established with the low-dissipation model, relies significantly on the assumption of the inverse proportion scaling of the irreversible entropy generation $\Delta S^{(\mathrm{ir})}$ on the operation time $\tau$, i.e., $\Delta S^{(\mathrm{ir})}\propto1/\tau$. The optimal operation time of the finite-time isothermal process for EMP has to be within the valid regime of the inverse proportion scaling. Yet, such consistency was not tested due to the unknown coefficient of the $1/\tau$-scaling. In this paper, we reveal that the optimization of the finite-time two-level atomic Carnot engines with the low-dissipation model is consistent only in the regime of $\eta_{\mathrm{C}}\ll2(1-\delta)/(1+\delta)$, where $\eta_{\mathrm{C}}$ is the Carnot efficiency, and $\delta$ is the compression ratio in energy level difference of the heat engine cycle. In the large-$\eta_{\mathrm{C}}$ regime, the operation time for EMP obtained with the low-dissipation model is not within the valid regime of the $1/\tau$-scaling, and the exact EMP of the engine is found to surpass the well-known bound $\eta_{+}=\eta_{\mathrm{C}}/(2 \eta_{\mathrm{C}})$.
H Mehboob, K Maqbool, R Ellahi, Sadiq M Sait
Published: 27 September 2021
Communications in Theoretical Physics, Volume 73; https://doi.org/10.1088/1572-9494/ac2054