Considering the flat rotation curves as input and treating the matter content in the galactic halo region as quark matter, we have found out a background spacetime metric for the region of the galactic halo. We obtain fairly general conditions that ensure that gravity in the halo region is attractive. We also investigate the stability of circular orbits, along with a different role for quark matter. Bag-model quark matter meeting these conditions therefore provides a suitable model for dark matter.Comment: 5 Latex pages, Accpted in Phys. Lett. B (available in Online

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The nonlinear propagation of dust-acoustic (DA) waves in an unmagnetized dusty plasma consisting of nonthermal electrons, vortex-like (trapped) distributed ions and mobile negative dust have been investigated by employing the reductive perturbation technique. The effects of nonthermal electrons and trapped ions are found to modify the properties of the DA solitary waves.

The nonlinear propagation and interaction of dust acoustic multi-solitons in a four component dusty plasma consisting of negatively and positively charged cold dust fluids, non-thermal electrons, and ions were investigated. By employing reductive perturbation technique (RPT), we obtained Korteweged–de Vries (KdV) equation for our system. With the help of Hirota’s bilinear method, we derived two-soliton and three-soliton solutions of the KdV equation. Phase shifts of two solitons and three solitons after collision are discussed. It was observed that the parameters α, β, β1, μe, μi, and σ play a significant role in the formation of two-soliton and three-soliton solutions. The effect of the parameter β1 on the profiles of two soliton and three soliton is shown in detail.

Using digital games in language learning is beneficial, but their effectiveness in the Bangladeshi EFL context has been overlooked. Therefore, the purpose of this research was to evaluate the impact of playing digital games on Bangladeshi EFL learners’ ability to remember and retain the language. The Oxford Quick Placement Test was given to 78 Bangladeshi English as foreign language students. Based on the findings, 50 primary school pupils were selected based on the convenient sampling method as the study’s target group for further investigation. Afterward, they were separated into two groups: one for the experiment and another for the CG. After that, all subjects were subjected to pretesting, and then, the therapy was administered. The EG was educated by the researcher via the use of digital games. The participants in the EG were taught English vocabulary via the use of a computerized game, which they found entertaining. On the other hand, the students of the CG received a traditional vocabulary teaching. After teaching 90 vocabulary in nine sessions, an immediate vocabulary posttest was conducted on both groups to determine the treatment’s possible effects on their vocabulary recall. Three weeks later, a delayed posttest was given to the participants to examine the effect of digital games on their vocabulary retention. The results of paired samples and independent sample t -tests showed that there was a significant difference between the immediate and delayed posttests of the EG and CGs in favor of the EG. The EG outperformed the CG both on the immediate and delayed posttests. This study has some implications for teaching and learning vocabulary.