Anizotropni svemiri Bianchijeve III vrste s oblakom struna u Lyrinoj geometriji

Bianchi type-III string cosmological models are investigated in the presence of string fluid as a source of matter in the framework of Lyra’s geometry. It is observed that the models start with singular state and evolve continuously as t → ∞. It is found that, in all cases, the displacement vector β(t) is a decreasing function of time analogous to the behaviour of the cosmological constant Λ. The physical and geometrical aspects of the models are also discussed.Istražujemo Bianchijeve kozmološke modele III vrste u prisustvu tekućine struna kao izvora tvari u okviru Lyrine geometrije. Nalazimo da prema modelima svemir počinje sa singularnim stanjem i razvija se postepeno kako t → ∞. U svim slučajevima smo našli da je vektor posmika β(t) opadajuća funkcija vremena, poput svojstva kozmološke stalnice Λ. Raspravljamo fizičke i geometrijske značajke modela

Investigating high redshift short GRBs: signatures of collapsars?

The conventional classification of Gamma-Ray Bursts (GRBs) as short or long bursts based on their duration is widely accepted as arising from different progenitor sources identified as compact object mergers and collapsars, respectively. However, recent observational shreds of evidence challenged this view, with signatures of collapsars in short GRBs and mergers in long GRBs. We conduct a comparative analysis of the characteristics of short and long GRBs, both at low and high redshifts, taking into account the locations and environments of their host galaxies. Our analysis suggests that some short GRBs at higher redshifts exhibit features similar to long GRBs, indicating a possible collapsar origin. Further investigation, utilizing multi-messenger observations, could provide a resolution to this issue.Comment: Accepted for publication in the Bulletin de la Soci\'et\'e Royale des Sciences de Li\`ege as proceeding of the 3rd Belgo-Indian Network for Astronomy and Astrophysics (BINA) workshop, held in Bhimtal, Uttarakhand (India) on 22-24 March 202

Cilindrično-simetrični nehomogeni kozmološki modeli s magnetskim poljem, strunama, perfektnom raspodjelom fluida i promjenljivom permeabilnošću

A new class of cylindrically-symmetric magnetized inhomogeneous perfect-fluid string cosmological models with variable magnetic permeability is investigated. We assume that F12 is the only non-vanishing component of the electromagnetic field tensor Fij . The Maxwell’s equations show that F12 is the function of x alone, whereas the magnetic permeability ¯µ may be the function of both x and t. To get the deterministic solution, it has been assumed that the metric coefficients are separable in the form as A = f(x)ℓ(t), B = g(x)k(t), C = g(x)ν(t). Also, the Einstein field equations have been solved with string source in which magnetic field is absent. Some physical and geometric aspects of the models in the presence and absence of magnetic field are discussed.Istražujemo novu vrstu cilindrično-simetričnih nehomogenih kozmoloških modela s magnetskim poljem, perfektnim fluidom, strunama i promjenljivom permeabilnošću. Pretpostavljamo da je F12 jedina neiščezavajuća sastavnica tenzora elektromagnetskog polja Fij . Maxwellove jednadžbe daju da je F12 funkcija samo x, dok magnetska permeabilnost može ovisiti o x i o t. Radi postizanja određenosti rješenja, pretpostavili smo separabilne metričke koeficijente u obliku A = f(x)ℓ(t), B = g(x)k(t), C = g(x)ν(t). Također smo riješili Einsteinove jednadžbe polja sa strunskim izvorom bez prisustva magnetskog polja. Raspravljamo neka fizička i geometrijska svojstva modela u prisustvu i bez magnetskog polja

Cylindrically Symmetric Inhomogeneous Universes with a Cloud of Strings

Cylindrically symmetric inhomogeneous string cosmological models are investigated in presence of string fluid as a source of matter. To get the three types of exact solutions of Einstein's field equations we assume $A = f(x)k(t)$, $B = g(x)\ell(t)$ and $C = h(x)\ell(t)$. Some physical and geometric aspects of the models are discussed.Comment: 9 page

Generation of Bianchi type V cosmological models with varying Λ\Lambda-term

Bianchi type V perfect fluid cosmological models are investigated with cosmological term $\Lambda$ varying with time. Using a generation technique (Camci {\it et al.}, 2001), it is shown that the Einstein's field equations are solvable for any arbitrary cosmic scale function. Solutions for particular forms of cosmic scale functions are also obtained. The cosmological constant is found to be decreasing function of time, which is supported by results from recent type Ia supernovae observations. Some physical aspects of the models are also discussed.Comment: 16 pages, 3 figures, submitted to CJ

Bianchi Type III Anisotropic Dark Energy Models with Constant Deceleration Parameter

The Bianchi type III dark energy models with constant deceleration parameter are investigated. The equation of state parameter $\omega$ is found to be time dependent and its existing range for this model is consistent with the recent observations of SN Ia data, SN Ia data (with CMBR anisotropy) and galaxy clustering statistics. The physical aspect of the dark energy models are discussed.Comment: 12 pages, 2 figures, Accepted version of IJT

Reactivity of tricine in the presence of Cu(ClO₄)₂.6H₂O and 2,2'-bipyridine: Synthesis, characterization and magnetic property of the complexes

1035-1042Three complexes, [Cu(bpy)(μ-OH)]2·2ClO4 (1) [Cu(H4TRI)(bpy)]ClO4 (2) and [Cu3(bpy)5(μ-O)(NO3)]2·6ClO4 (3) {H4TRI= tricine, bpy= 2,2'-bipyridine} have been synthesized and characterized using their IR, UV-vis and ESR spectroscopic data , elemental analysis and single crystal X-ray diffraction studies. The π-π interaction along the a-axis in complex (1) provides a channel- type structure while similar interaction in complex (2) generates a channel with floating ClO4- anions. Complex (3) comprises a pair of Cu(II) centers connected via (μ2-O) oxo bridges. These are further linked to Cu3 and Cu3#1 centers via oxygen atoms of the nitrate anion. The assembled structure of this complex along the c- axis displays a zig-zag chain formation. The variable temperature magnetic measurement of a representative complex (3), [Cu3(bpy)5(μ-O)(NO3)]2·6ClO4, shows that two of the Cu(II) centers couple ferromagnetically