Narrow Results

The materials with a perovskite phase have been in the limelight due to their power conversion efficiency (PSC) in solar cells. New perovskite materials are essential to predict the abundant availability of efficient materials for technological applications. Mechanical properties can predict the mechanical stability of crystals. Therefore, it is very important to know their mechanical parameters. So, in this work, the elastic constants $C_{11}$, $C_{12}$ and $C_{44}$ of the cubic chloride perovskites (ABCl${}_3)$ have been determined through first principles study using density functional theory by using the Chirpan method integrated with WIEN2k. After calculating the elastic constants, we have also calculated different moduli like Shear, Bulk and Young moduli, different parameters like Kleinman’s constant, Lame constants, Chung–Buessem anisotropy index, universal anisotropic index, acoustic behavior and its anisotropy, hardness, melting temperature, Poisson ratios by using different formulas in connection with the elastic constants. It has been found that the studied compounds possess low resistance to the plastic deformations. It has also been found that the majority of the materials possess a central type of force because Poisson’s ratio is greater than 0.25. It has been studied that six out of eighteen new perovskites were brittle and the rest were ductile. The anisotropy of the materials was checked and found that all the materials are anisotropic elastically. This work is useful for the synthesis of these new perovskites.

This research paper is two-fold. In the first part, we study Noether and Killing symmetries in Bianchi Type-III spacetimes, along with the associated conservation laws. The study uses the Maple RIFSIMP package to transform a set of nonlinear differential equations into a simpler form called the reduced involutive form (RIF). This method generates a RIF tree, where each branch is solved to find the explicit forms of Noether symmetries. We also examine the Noether symmetry related to homothety and analyze this symmetry separately within each group. In the second part, we investigate the behavior of an anisotropic fluid under the influence of a magnetic field, which is assumed to be aligned along the z-axis. The anisotropic fluid model is consistent with the inherent anisotropy of Bianchi Type-III, which may be amplified by the presence of the magnetic field. We also study how this magnetic field affects the fluid’s physical properties and explore the conditions under which the fluid may approach isotropy.

In this study, we explore topologically spherical relativistic objects and analyze the factors that are involved in maintaining the smooth composition of anisotropic content. The corresponding field equations resulting from this extension show a different behavior due to the higher-order correction terms. We study the role of structure scalar in the possible modeling of complex objects in a well-known way, discussed by [L. Herrera, A. Di Prisco and J. Ospino, Phys. Rev. D98 (2018) 104059]. After orthogonally splitting the curvature tensor, the associated dynamical equations are evaluated. We examine the complexity of the pattern of evolution by considering the homologous constraint. Furthermore, in the presence and absence of dissipation, the behavior, characteristics, and stability of the self-gravitating structures are analyzed. It is inferred that correction terms are trying to disturb the usual scenario of the homologous evolution of the relativistic dynamical system.

This paper is the continuation of the groundwork laid in [A. Iram, A. A. Siddiqui and T. Feroze, Int. J. Mod. Phys. D31(11) (2022) 2240006], where the Segre classification scheme was applied to categorize spherically symmetric static spacetime metrics into four possible Segre types $[(1,111)],$$[1,(111)],$$[(1,1)(11)],$ or $[1,1(11)]$. The solution for type $[(1,111)]$ leads to the Schwarzschild de-Sitter/anti de-Sitter metrics. The eigenvalue degeneracy in Segre types identifies the kind of matter distribution in space and aid in the consideration of novel solutions for the corresponding energy momentum tensor. We deal with an anisotropic distribution of matter correlated with electric field intensity for types $[(1,1)(11)]$ and $[1,1(11)]$. The type $[1,(111)]$ refers to ideal fluid characterized by uniformly distributed pressure. A comprehensive examination is conducted in scenarios where all physical and stability criteria are satisfied. Nevertheless, for type $[(1,1)(11)]$, the strong energy and causality prerequisites are breached due to negative pressure, suggesting the existence of dark energy where the attributes of standard matter cannot be met. Furthermore, the numerical test for models is conducted for the compact objects $4\text{U}1538-52$, $\text{PSR}\text{J}1614-2230$, $4\text{U}1608-52$, and $\text{EXO}1785-248$. Each star’s density, pressure, and compactness factor are observed, showing the regularity at the origin. These observations impart that the discover models are plausible since they accurately represent the observable system.

This research paper aims to redefine the complexity factor in $f(R,G)$ gravity and the appearance of electric charge, where $R$ is the Ricci scalar and $G$ is the Gauss–Bonnet term. In this context, we intend to analyze the splitting of the Riemann tensor after considering the anisotropic distribution of the charged fluid related to the spherically symmetric spacetime. We interpret $Y_{\mathrm{\text{TF}}}$ as the complexity factor among all the determined structural scalars that encompasses the characteristics of anisotropic pressure and the effective representation of the energy density. The correction terms associated with modified theory are considered to calculate some significant results related to the Weyl scalar, Tolman mass, and the complexity factor (CF). Moreover, the expression for CF is established by using the structure scalars determined in our paper, and the diminishing complexity restraint is utilized to determine the solutions for the various models. The celestial object having non-uniform energy density and anisotropic pressure asserts the maximum intricacy. But, if the effects of non-uniform energy density and anisotropic distribution of pressure are eradicated due to the presence of dark source terms associated with modified gravity then these fluids may not exhibit any complexity. Consequently, it is revealed that the constituents of effective and electromagnetic parts directly influence the structure scalars and CF.

This paper explores a comprehensive approach to modeling compact stars that incorporates both normal matter and dark energy. We employ the Durgapal–Fuloria ansatz within the context of Rastall gravity to derive a relativistic analytical solution. The model is thoroughly analyzed both analytically and graphically, to assess its physical properties and facilitates a comparison with the results of classical general relativity. Our findings demonstrate that the model we have put forward is in substantial agreement with observational data for three different compact star representatives like Her X-1, PSR J0348+0432, and RX J1856.3-37.2. We evaluate the model’s viability by examining its energy conditions, stability, and adherence to the Buchdahl limit, all of which are found to be satisfactory. The analysis confirms the stable solution for Rastall parameter spanning −0.005 to 0.11, and it converges to standard general relativity when the coupling parameter approaches to zero.

The terahertz frequency absorption spectra of DNA molecules reflect low-frequency internal helical vibrations involving rigidly bound subgroups that are connected by the weakest bonds, including the hydrogen bonds of the DNA base pairs, and/or non-bonded interactions. Although numerous difficulties make the direct identification of terahertz phonon modes in biological materials very challenging, recent studies have shown that such measurements are both possible and useful. Spectra of different DNA samples reveal a large number of modes and a reasonable level of sequence-specific uniqueness. This chapter utilizes computational methods for normal mode analysis and theoretical spectroscopy to predict the low-frequency vibrational absorption spectra of short artificial DNA and RNA. Here the experimental technique is described in detail, including the procedure for sample preparation. Careful attention was paid to the possibility of interference or etalon effects in the samples, and phenomena were clearly differentiated from the actual phonon modes. The results from Fourier-transform infrared spectroscopy of DNA macromolecules and related biological materials in the terahertz frequency range are presented. In addition, a strong anisotropy of terahertz characteristics is demonstrated. Detailed tests of the ability of normal mode analysis to reproduce RNA vibrational spectra are also conducted. A direct comparison demonstrates a correlation between calculated and experimentally observed spectra of the RNA polymers, thus confirming that the fundamental physical nature of the observed resonance structure is caused by the internal vibration modes in the macromolecules. Application of artificial neural network analysis for recognition and discrimination between different DNA molecules is discussed.

In this work, we investigate the influence of substrate temperature on the surface morphology for substrate coverage below one monolayer. The model of film growth is based on random deposition enriched by limited surface diffusion. Also, anisotropy in the growth is involved. We found from computer simulations for the simple cubic lattice and solid-on-solid model that the surface morphology changes with increasing temperature from isotropically distributed isolated small islands through anisotropic 1D stripes to larger 2D anisotropic islands and again randomly distributed single atoms. The transition is also marked in height–height correlation function dependence on temperature as directly seen by snapshots from simulations. The results are in good qualitative agreement with already published results of kinetic Monte Carlo simulations as well as with some experimental data.

The Grüneisen parameter for covalent crystals is calculated by employing an angular force model with eight parameters and using a 6–12 potential [Lennard–Jones potential (L–J)] whereas for ionic crystals, it is calculated by employing the Daniel's method, which uses anisotropy factor tables f(s,t) of de Launay.

Directed spiral percolation (DSP) is a new percolation model with crossed external bias fields. Since percolation is a model of disorder, the effect of external bias fields on the properties of disordered systems can be studied numerically using DSP. In DSP, the bias fields are an in-plane directional field (E) and a field of rotational nature (B) applied perpendicular to the plane of the lattice. The critical properties of DSP clusters are studied here varying the direction of E field and intensities of both E and B fields in two-dimensions. The system shows interesting and unusual critical behavior at the percolation threshold. Not only the DSP model is found to belong in a new universality class compared to that of other percolation models but also the universality class remains invariant under the variation of E field direction. Varying the intensities of the E and B fields, a crossover from DSP to other percolation models has been studied. A phase diagram of the percolation models is obtained as a function of intensities of the bias fields E and B.

Two extended cooperative driving lattice hydrodynamic models are proposed by incorporating the intelligent transportation system and the backward-looking effect in traffic flow under certain conditions. They are the lattice versions of the hydrodynamic model of traffic: one (model A) is described by the differential-difference equation where time is a continuous variable and space is a discrete variable, and the other (model B) is the difference-difference equation in which both time and space variables are discrete. In light of the real traffic situations, the appropriate forward and backward optimal velocity functions are selected, respectively. Then the stability conditions for the two models are investigated with the linear stability theory and it is found that the new consideration leads to the improvement of the stability of traffic flow. The modified Korteweg-de Vries equations (the mKdV equation, for short) near the critical point are derived by using the nonlinear perturbation method to show that the traffic jam could be described by the kink-antikink soliton solutions for the mKdV equations. Moreover, the anisotropy of traffic flow is further discussed through examining the negative propagation velocity as the effect of following vehicle is involved.

Site invasion percolation (IP) processes are combined with bond percolation model, to study the effects of size restriction on low capillary number immiscible displacement in heterogeneous nanoporous media. Both cases of compressible (NTIP) and incompressible defender fluid (TIP) are considered. It is found that in site IP the value of mass uptake increases with the size of invader particles, if the latter is not greater than a critical value. This occurs when the accessible porosity of the medium decreases as the size of fluid particles increases. We also investigate the effect of nanopore's concentration on the mass and the anisotropy of sample spanning cluster as well as the critical exponent of trap numbers.

In this paper, we have tried to point out the features of the correlation between the lanes of a two-lane road, created by the entry of this facility. For this purpose, we have adopted a quasi-one-dimensional system composed of a diverging node connecting two roads and where no lanes’ changing is allowed. Our study has highlighted the strong effect of a node. We have found that if we create a disturbance in one lane, a spontaneous symmetry breaking occurs in the whole system. In fact, a self-anisotropy is produced at the node, to which the system responds via a self-organization mechanism. Those results have urged us to investigate the anisotropy as an extrinsic parameter. By privileging one lane over the other at the node, we have been able to confirm that the system can always get self-organized and that three phases can be established: the symmetric high density phase, the asymmetric low density phase and the asymmetric phase of transition low density/high density. Finally, we have found that the system is strongly correlated when it is in a symmetric phase, and is not when in an asymmetric phase. This finding brought us to the assumption that the cross-correlation of the observables of a quasi-one-dimensional system can be considered as an order parameter that defines the phases’ transitions.

The equilibrium behaviors of the anisotropic XY ferromagnet, with nonmagnetic impurity, have been investigated in three dimensions by Monte Carlo simulation using Metropolis algorithm. Two different types of anisotropy, namely, the bilinear exchange type and single-site anisotropy are considered here. The thermodynamic behaviors of the components of the magnetizations (M), susceptibility ($\chi$) and the specific heat (C) have been studied systematically through extensive Monte Carlo simulations. The ferro–para phase transition has been observed to take place at a lower temperature for impure anisotropic XY ferromagnet. The pseudocritical temperature ($T_c^{\ast }$) has been found to decrease as the system gets more and more impure (impurity concentration p increases). In the case of bilinear exchange type of anisotropy ($\lambda$), the pseudocritical temperature ($T_c^{\ast }$) increases linearly with $\lambda$ for any given concentration of nonmagnetic impurity (p). The slope of this linear function has been found to depend on the impurity concentration (p). The slope decreases linearly with the impurity concentration (p). In the case of the single-site anisotropy (D), the pseudocritical temperature ($T_c^{\ast }$) has been found to decrease linearly with p for fixed D. The critical temperature (for a fixed set of parameter values) has been estimated from the temperature variation of fourth-order Binder cumulants ($U_L$) for different system sizes (L). The critical magnetization ($M(T_c)$) and the maximum value of the susceptibility (${\chi }_p$) are calculated for different system sizes (L). The critical exponents for the assumed scaling laws, $M(T_c)\sim L^{-\frac{\beta }{\nu }}$ and ${\chi }_p\sim L^{\frac{\gamma }{\nu }}$, are estimated through the finite size analysis. We have estimated, $\frac{\beta }{\nu }$, equals $0.48\pm 0.05$ and $0.37\pm 0.04$ for bilinear exchange and single-site anisotropy, respectively. We have also estimated, $\frac{\gamma }{\nu }$ equals $1.78\pm 0.05$ and $1.81\pm 0.05$ for bilinear exchange and single-site anisotropy, respectively.

The IceCube Observatory at the South Pole is composed of a cubic kilometer scale neutrino telescope buried beneath the icecap and a square-kilometer surface water Cherenkov tank detector array known as IceTop. The combination of the surface array with the in-ice detector allows the dominantly electromagnetic signal of air showers at the surface and their high-energy muon signal in the ice to be measured in coincidence. This ratio is known to carry information about the nuclear composition of the primary cosmic rays. This paper reviews the recent results from cosmic-ray measurements performed with IceTop/IceCube: energy spectrum, mass composition, anisotropy, search for PeV γ sources, detection of high energy muons to probe the initial stages of the air shower development, and study of transient events using IceTop in scaler mode.

Recently, an anisotropic cosmological model was proposed. An arbitrary one-form, which picks out a privileged axis in the universe, was added to the Friedmann–Robertson–Walker (FRW) line element. The distance-redshift relation was modified such that it is direction-dependent. In this paper, we use the Union2 dataset and 59 high-redshift gamma-ray bursts (GRBs) to give constraints on the anisotropy of the universe. The results show that the magnitude of anisotropy is about D = -0.044±0.018, and the privileged axis points toward the direction (l₀, b₀) = (306.1°±18.7°, -18.2°±11.2°) in the galactic coordinate system. The anisotropy is small and the isotropic cosmological model is an excellent approximation.

This paper is devoted to identify some physical causes of energy density inhomogeneity and stability of self-gravitating relativistic fluids in plane symmetry such as Weyl tensor, local anisotropy, dissipative terms and their specific combination. We first develop a relationship between matter variables and the Weyl tensor and then formulate dynamical equations using Bianchi identities. For the non-dissipative dust fluid, we conclude that the system will remain homogeneous if and only if it is conformally flat which implies the shear-free condition. However, the converse is not true for the non-dissipative isotropic fluid. For non-dissipative anisotropic fluid, the inhomogeneity factor is identified to be one of the structure scalars. A particular case of geodesic with dissipation is also discussed.

A new conformally non-flat interior spacetime embedded in five-dimensional (5D) pseudo Euclidean space is explored in this paper. We proceed our calculation with the assumption of spherically symmetric anisotropic matter distribution and Karmarkar condition (necessary condition for class one). This solution is free from geometrical singularity and well-behaved in all respects. We ansatz a new type of metric potential $g_{11}$ and solve for the metric potential $g_{00}$ via Karmarkar condition. Further, all the physical parameters are determined from Einstein’s field equations using the two metric potentials. All the constants of integration are determined using boundary conditions. Due to its conformally non-flat character, it can represent bounded configurations. Therefore, we have used it to model two compact stars Vela X-1 and Cyg X-2. Indeed, the obtained masses and radii of these two objects from our solution are well matched with those observed values given in [T. Gangopadhyay et al., Mon. Not. R. Astron. Soc.431, 3216 (2013)] and [J. Casares et al., Mon. Not. R. Astron. Soc.401, 2517 (2010)]. The equilibrium of the models is investigated from generalized TOV-equation. We have adopted [L. Herrera’s, Phys. Lett. A165, 206 (1992)] method and static stability criterion of Harisson–Zeldovich–Novikov [B. K. Harrison et al., Gravitational Theory and Gravitational Collapse (University of Chicago Press, 1965); Ya. B. Zeldovich and I. D. Novikov, Relativistic Astrophysics, Vol. 1, Stars and Relativity (University of Chicago Press, 1971)] to analyze the stability of the models.

This paper studies the gravitational collapse of charged anisotropic spherical stellar objects in $f({𝒢})$ gravity. For this purpose, we derive dynamical equations by considering Misner–Sharp mechanism and explore physical impact of charge, anisotropy and effective pressure on the rate of collapse. We establish the relationship between matter variables, Weyl tensor and the Gauss–Bonnet (GB) terms. For constant value of $f({𝒢})$, it turns out that conformal flatness condition is no longer valid due to the effect of anisotropic factor in the present scenario. To obtain conformally flat metric, we impose the condition of isotropic matter distribution which provides energy density homogeneity and conformal flatness of the metric. We conclude that GB terms lead to decrease in the collapse rate due to their anti-gravitational effects.

This paper is devoted to examine the cracking of spherically symmetric anisotropic fluid configuration for polytropic equation of state. For this purpose, we formulate the corresponding field equations as well as generalized Tolman–Oppenheimer–Volkoff equation. We introduce density perturbations in matter variables and then construct the force distribution function. In order to examine the occurrence of cracking/overturning, we consider two models corresponding to two values of the polytropic index. It is found that the first model exhibits overturning for the considered values of polytropic constant while the second model neither exhibits cracking nor overturning for larger values of polytropic constant.