A Cyclic Universe With Varying Cosmological Constant in f(R,T)f(R,T) gravity

A new kind of evolution for cyclic models in which the Hubble parameter oscillates and keeps positive has been explored in a specific $f(R,T)$ gravity reconstruction. A singularity-free cyclic universe with negative varying cosmological constant has been obtained which supports the role suggested for negative $\Lambda$ in stopping the eternal acceleration. The cosmological solutions have been obtained for the case of a flat universe, supported by observations. The cosmic pressure grows without singular values, it is positive during the early-time decelerated expansion and negative during the late-time accelerating epoch. The time varying EoS parameter $\omega(t)$ shows a quintom behavior and is restricted to the range $-2.25 \leq \omega(t) \lesssim \frac{1}{3}$. The validity of the classical linear energy conditions and the sound speed causality condition has been studied. The non-conventional mechanism of negative cosmological constant that are expected to address the late-time acceleration has been discussed.Comment: 15 pages, 10 figure

Kinetic energy of vortex knots and unknots

New results on the kinetic energy of ideal vortex filaments in the shape of torus knots and unknots are presented. These knots are given by small-amplitude torus knot solutions (Ricca, 1993) to the Localized Induction Approximation (LIA) law. The kinetic energy of different knot and unknot types is calculated and presented for comparison. These results provide new information on relationships between geometry, topology and dynamics of complex vortex systems and help to establish possible connections between aspects of structural complexity of dynamical systems and vortical flows.Comment: 14 pages, 5 figure

Reconnection of superfluid vortex bundles

Using the vortex filament model and the Gross Pitaevskii nonlinear Schroedinger equation, we show that bundles of quantised vortex lines in helium II are structurally robust and can reconnect with each other maintaining their identity. We discuss vortex stretching in superfluid turbulence and show that, during the bundle reconnection process, Kelvin waves of large amplitude are generated, in agreement with the finding that helicity is produced by nearly singular vortex interactions in classical Euler flows.Comment: 10 pages, 7 figure

Effects of Radiation sterilization Dose on the Molecular Weight and Gelling Properties of Commercial Alginate Samples

From Frontiers via Jisc Publications RouterHistory: collection 2021, received 2021-08-20, accepted 2021-11-12, epub 2021-12-20Publication status: PublishedTo estimate the molecular weight (Mw) and gelling properties, a total of 26 alginate samples consisting of control (n = 13) and 15 kGy γ-irradiated (n = 13) samples were characterized through viscometric and gel permeation chromatography (GPC-MALLS) methods. Based on the observations, a remarkable decrease in the intrinsic viscosity of all samples of alginates was evident due to the effects of radiation, with a linear relationship between viscosity and concentration in 0.01 M NaCl solution. The correlation among the Mw, percentage mass recovery, radii of gyration (Rz/Rg), and percentage reduction of Mw assessed by GPC was significant. The Mw decreased dramatically (from 3.1 × 105 to 0.49 × 105 mole/g in sample no. 12) by the effect of radiation with momentous relation to the % reduction of the molecular weight. The highest molecular weight reduction (84%), which is the most sensitive to γ-radiation, and the average reduction rate was ≥50%. The mass recovery was 100% obtained from samples no. 1,3,4,5,7,12, and 13, while the rest of the samples’ recovery rate was significantly higher. The reduction rate of mass molecular weight (Mw) is higher than the average molecular weight (Mv), but they showed a sensitivity towards radiation, consequently their performance are different from each other. The stability test was performed as a critical behaviour in the control, recurrently same as in the irradiated samples. Thus, the sterilization dose of 15 kGy for the Mw distribution, and subsequently for the characterization, was significantly effective

Study the Behavior of Vortex-Antivortex Bundles in He II

Abstract: We present a numerical simulation to compute the evolution of vortex filaments bundle in superfluid helium. We show that the vortex-antivortex bundles with sinusoidally have stable structures and each bundle rotates about its common center. Because of they have circulation in opposing directions, the two vortex bundles move down together parallel to each other. A three dimensional periodic cube is used. Thus, the vortex filament points move through one side of the periodic volume and re-entering on the other side. The two bundles move for long time without reconnection. We found that our results are in agreement with the finding of Koplik and Levine [Phys. Rev. Lett. 71, 137

Study the Behavior of Vortex-Antivortex Bundles in He II

We present a numerical simulation to compute the evolution of vortex filaments bundle in superfluid helium. We show that the vortex-antivortex bundles with sinusoidally have stable structures and each bundle rotates about its common center. Because of they have circulation in opposing directions, the two vortex bundles move down together parallel to each other. A three dimensional periodic cube is used. Thus, the vortex filament points move through one side of the periodic volume and re-entering on the other side. The two bundles move for long time without reconnection. We found that our results are in agreement with the finding of Koplik and Levine [Phys. Rev. Lett. 71, 1375 (1993)], who used the nonlinear Schr¨odinger equation (NLSE) model to study the cases of single vortices. This movement leads to stretching and flexure of vortex lines which cause changes in velocities, radius, number of points and total length

Vortex Tangle Dynamics under the Effect of Mutual Friction in Superfluid HeII

We have studied numerically the vortex tangle under both counterflow and attending of mutual friction by using localinduction approximation model (LIA). We find that the vortex lines are grown by the effect of normal fluid velocity in the existence of mutual friction. Many numerical experiments are performed to calculate the vortex filaments development in superfluid helium II. We explained how the total length density, the number of vortex points, the velocity, reconnection events and average inverse radius of curvature are affected by both counterflow and temperature. We find that the vortex rings extend fast and the helical disturbances of vortex tangle increases as long as the temperature increases. The cubic box with periodic boundary conditions is employed for all our numerical simulations

Mathematical methods via the nonlinear two-dimensional water waves of Olver dynamical equation and its exact solitary wave solutions

The problem formulations of the nonlinear for the small-long amplitude two-dimensional water waves propagation with free surface are studied. The water wave problem leads to the nonlinear Olver dynamical equation. By applying the extended mapping method, We derive the solitary wave solutions of the nonlinear Olver dynamical equation. These solutions for the nonlinear Olver dynamical equation are obtained efficiency and precisely of the method can be demonstrated. The movement role of the waves by making the graphs of the exact solutions and the stability of these solutions are analyzed and discussed. All solutions are stable and exact. Keywords: Shallow water waves, Solitary waves solutions, Extended mapping method, Mathematical physics method