Binary systems are a key factor influencing the dynamical evolution of open clusters. Previous studies have shown that binary populations are closely related to the dynamical evolutionary stages of young open clusters. We employ the direct N-body code NbodyCP to investigate the dynamical evolution of open clusters with initial binary fractions of 10
Purpose: It is still open whether white dwarfs can exceed the Chandrasekhar limit and modified gravity is one way to get heavier stars. In f(R,ℒ_m,T)=R+αℒ_m T , with ℒ_m the matter Lagrangian and α the matter-geometry coupling, the static limiting mass is already above it. Here we include rotation. Methods: We take the Hartle-Thorne expansion to second order in the angular velocity and derive every closure from the modified conservation law. Because f_R=1 , the system becomes general relativity with a conserved barotropic effective fluid as source. This also makes the general-relativistic limit easy to see and decides which particle number enters the first law. Results: Across the couplings studied the static limiting mass runs from 1.34 to 1.50 M_⊙ . For α >0 the sequence ends before any turning point, where the sound speed of the effective fluid reaches the speed of light. Rotation multiplies each limit by 1.064 to 1.078, almost independently of α , reaching 1.61 M_⊙ . The two rotational mass shifts differ by three orders of magnitude, 3.3× 10^-5 at fixed particle number and 8.1% at fixed central density. The quadrupole from the relativistic exterior match agrees with a Radau volume integral to 0.3% . Conclusion: These are the first rotating white-dwarf models in this theory. They reach second order in the rotation and at α =0 reproduce published general-relativistic ones. Coupling and rotation raise the limiting mass by similar amounts, so a static bound on α assumes slow rotation. The two effects can be separated through the moment of inertia, which responds to the coupling about 2.5 times more strongly than the radius at fixed mass.
Possible mechanisms of generation of dynamical plasma structures are associated with the Schwarzschild criterion for convective instability and with excess energy (heat, magnetic): due to the superadiabatic temperature gradient, the overheated plasma starts to rise. In the framework of Navier-Stokes MHD equations, the complete system of equations for the full axisymmetric plasma model includes equations for the stream function, the azimuthal velocity component, the density change, the flow function of poloidal magnetic field, and the azimuthal component of the magnetic field. Within the framework of ideal hydrodynamics, the simplest plasma model is applicable to the initial stage of generation of plasma structures. In this case, rigorous analytical solutions are constructed from blocks. Within the framework of ideal hydrodynamics, some intermediate model – the refined model considers rotating plasma at the growth stage. In this case, some unidirectional differential rotation occurs. The full model studies the development of structures as rotating plasma from the very beginning to the highest development stage. The velocity field is adjusted to boundary conditions. Velocity components change in a coordinated manner. The stationary axisymmetric ambient magnetic field and its gradients have little effect on the plasma structure and velocity field. The movement structures for all models are similar. Radial flows converge towards the axis at the bottom, and there is an outflow to the periphery near the top of the plasma structure. The maximum vertical velocity component is reached at the center of the axis. Applications of these models to solar structures, including jets, are discussed.
Nonlinear dust-ion-acoustic waves are investigated in a collisional dusty plasma consisting of negatively charged streaming dust grains, inertial positive ions, Maxwellian electrons, and a neutral background. The model incorporates ion-neutral and dust-neutral collisions, ionization, recombination, ion-drag force, and ion viscosity. Using the reductive perturbation technique, the governing fluid equations are reduced to an extended Korteweg-de Vries-Burgers (KdV-Burgers) equation describing the nonlinear evolution of dust-ion-acoustic perturbations. The resulting equation is analyzed using the truncated Painlevé expansion method and Hirota’s bilinear method to derive exact nonlinear wave solutions. The analysis yields various nonlinear structures, including cnoidal, solitary, asymmetric periodic, and two-soliton waves. The properties of these structures are strongly governed by the dust-to-ion temperature ratio, dust charge-density ratio, dust charge number, and initial streaming velocity of the negatively charged dust grains. In particular, increasing the dust streaming velocity suppresses the wave amplitude, whereas increasing the dust charge-density ratio and dust charge number enhances the amplitude of solitary structures. These results demonstrate that dust streaming, dust-charge effects, thermal effects, and collisional dissipation play important roles in determining the nonlinear evolution and morphology of dust-ion-acoustic waves. The present findings provide useful insights into nonlinear electrostatic wave dynamics in collisional dusty-plasma environments relevant to ionospheric and space plasmas.
