Collapse and dispersal of a homogeneous spin fluid in Einstein-Cartan theory

In the present work, we revisit the process of gravitational collapse of a spherically symmetric homogeneous dust fluid which is known as the Oppenheimer-Snyder (OS) model [1]. We show that such a scenario would not end in a spacetime singularity when the spin degrees of freedom of fermionic particles within the collapsing cloud are taken into account. To this purpose, we take the matter content of the stellar object as a homogeneous Weyssenhoff fluid which is a generalization of perfect fluid in general relativity (GR) to include the spin of matter. Employing the homogeneous and isotropic FLRW metric for the interior spacetime setup, it is shown that the spin of matter, in the context of a negative pressure, acts against the pull of gravity and decelerates the dynamical evolution of the collapse in its later stages. Our results bode a picture of gravitational collapse in which the collapse process halts at a finite radius whose value depends on the initial configuration. We thus show that the spacetime singularity that occurs in the OS model is replaced by a non-singular bounce beyond which the collapsing cloud re-expands to infinity. Depending on the model parameters, one can find a minimum value for the boundary of the collapsing cloud or correspondingly a threshold value for the mass content below which the horizon formation can be avoided. Our results are supported by a thorough numerical analysis.Comment: 16 pages, 5 figures, revised versio

Emergent Cosmos in Einstein-Cartan Theory

Based on the Padmanabhan's proposal, the accelerated expansion of the universe can be driven by the difference between the surface and bulk degrees of freedom in a region of space, described by the relation $dV/dt=N_{sur}-N_{bulk}$ where $N_{sur}$ and $N_{bulk}=-N_{em}+N_{de}$ are the degrees of freedom assigned to the surface area and the matter-energy content inside the bulk such that the indexes $"em"$ and $"de"$ represent energy-momentum and dark energy, respectively. In the present work, the dynamical effect of the Weyssenhoff perfect fluid with intrinsic spin and its corresponding spin degrees of freedom in the framework of Einstein-Cartan (EC) theory are investigated. Based on the modification of Friedmann equations due to the spin-spin interactions, a correction term for the Padmanabhan's original relation $dV/dt=N_{sur}+N_{em}-N_{de}$ including the number of degrees of freedom related to this spin interactions is obtained through the modification in $N_{bulk}$ term as $N_{bulk}=-N_{em}+N_{spin}+N_{de}$ leading to $dV /d t=N_{sur}+N_{em}-N_{spin} -N_{de}$ in which $N_{spin}$ is the corresponding degrees of freedom related to the intrinsic spin of the matter content of the universe. Moreover, the validity of the unified first law and the generalized second law of thermodynamics for the Einstein-Cartan cosmos are investigated. Finally, by considering the covariant entropy conjecture and the bound resulting from the emergent scenario, a total entropy bound is obtained. Using this bound, it is shown that the for the universe as an expanding thermodynamical system, the total effective Komar energy never exceeds the square of the expansion rate with a factor of $\frac{3}{4\pi}$.Comment: 12 Pages, Accepted for Publication in Eur. Phys. J.

Study on hydrophobic modification of basil seed gum-based (BSG) films by octenyl succinate anhydride (OSA)

The main objective of this study was to evaluate the changes in the characteristics of basil (Ocimum bacilicum L.) seed gum (BSG) films after modification with octenyl succinate anhydride (OSA) at different OSA:BSG weight ratios (WRs) of 0, 0.01 and 0.03. HPLC analysis revealed that the amount of added OS groups was 0%, 0.28%, and 1.01%, respectively. The introduction of OS groups along the BSG backbone was also confirmed by FT-IR and NMR analysis. XRD results revealed no significant change of physical state after modification. The contact angle (i.e., hydrophobicity) of modified BSG films was higher than that of control film. A decrease in the film solubility in water (29%) and water vapor permeability (50%), but an increase in density (14.28%) and opacity (21.37%) was observed after modification at the WR of 0.03. Also, the results showed that modification with OSA had no significant influence on the film thickness, moisture content and color properties. BSG modification with OSA at the WR of 0.03 significantly increased the flexibility and ultimate strength of respective films. The results of this study showed that OSA-modified BSG is a good candidate for developing edible films and coating with relatively high resistance to water

The Effect of Sand and Dust Storms (SDSs) and Rain on the Performance of Cellular Networks in the Millimeter Wave Band

Future cellular systems are expected to use millimeter-wave (mm-Wave) frequency bands in addition to the existing microwave bands under 6 GHz. Severe weather conditions, including sand and dust storms (SDSs) and heavy rainfalls, challenge reliable communications over wireless links at those higher frequencies. In such conditions, besides frequency-dependent path-loss, radio signals experience additional attenuation. The SDS attenuation is related to visibility, receiver distance to the storm origin point, soil type, frequency, temperature and humidity. On the other hand, the rainfall attenuation is affected by rainfall rate, polarization, carrier frequency, temperature and raindrop size distribution. Leveraging on experimental measurements carried out in previous works, a novel unified mathematical framework is introduced in this paper to include SDS/rainfall-dependent attenuation in the performance evaluation of terrestrial wireless cellular networks in terms of coverage probability, bit error rate (BER) and achievable rate in the mm-Wave band. Extensive numerical results are presented to show the effects of the different SDS/rainfall parameters on performance, showing that the degradation due to SDS is generally higher than that due to rain and may cause a reduction of even six orders of magnitude in the average achievable bit rate when the frequency increases from 28 to 38 GHz

Is there any difference in executive function and social adequacy between the children with dyslexia or dyscalculia disorder?

BACKGROUND: Review of literature indicates that there is difference between various types of learning disorder based on functional skills. This study aims to compare the executive function and social adequacy of children with dyslexia and dyscalculia.METHODS: This descriptive fundamental research was a comparative causative type study. The statistical population included all children with dyslexia and dyscalculia in Tehran Province, Iran, in 2018. Using available sampling method, 43 children (24 with dyslexia and 19 with dyscalculia) were selected from learning disorder centers. Fellner questionnaire was used to assess the social adequacy of the children, and to evaluate the executive functions, Parental Reflective Functioning Questionnaire (PRFQ) was used. The data were analyzed using multivariate analysis of variance (MANOVA).RESULTS: There was no significant difference between the various components of executive functions and social adequacy of children with dyslexia and dyscalculia (P > 0.050).CONCLUSION: Based on the research findings, function of children with dyslexia and dyscalculia is equivalent in executive function and social adequacy