String Cosmology in Anisotropic Bianchi-II Space-time

The present study deals with a spatially homogeneous and anisotropic Bianchi-II cosmological model representing massive strings. The energy-momentum tensor, as formulated by Letelier (1983), has been used to construct a massive string cosmological model for which the expansion scalar is proportional to one of the components of shear tensor. The Einstein's field equations have been solved by applying a variation law for generalized Hubble's parameter that yields a constant value of deceleration parameter in Bianchi-II space-time. A comparative study of accelerating and decelerating modes of the evolution of universe has been carried out in the presence of string scenario. The study reveals that massive strings dominate the early Universe. The strings eventually disappear from the Universe for sufficiently large times, which is in agreement with the current astronomical observations.Comment: 11 pages, 6 figures (To appear in Mod. Phys. Lett. A) In this version, the cosmic string has been directed along z-direction and the resultant field equations have been solved exactl

Role of NGOs in irrigation development and management in Nepal: Proceedings of the National Workshop on the Role of NGOs in Irrigation Development and Management in Nepal, Nepal Administrative Staff College, Jawalakhel, Lalitpur, Nepal, 29-30 September 1992

Agricultural manpower / Non-governmental organizations / Rural development / Irrigation management / Nepal

Dynamics of Magnetized Bulk Viscous Strings in Brans-Dicke Gravity

We explore locally rotationally symmetric Bianchi I universe in Brans-Dicke gravity with self-interacting potential by using charged viscous cosmological string fluid. We use a relationship between the shear and expansion scalars and also take the power law for scalar field as well as self-interacting potential. It is found that the resulting universe model maintains its anisotropic nature at all times due to the proportionality relationship between expansion and shear scalars. The physical implications of this model are discussed by using different parameters and their graphs. We conclude that this model corresponds to an accelerated expanding universe for particular values of the parameters.Comment: 17 pages, 6 figure

Bianchi Type-II String Cosmological Models in Normal Gauge for Lyra's Manifold with Constant Deceleration Parameter

The present study deals with a spatially homogeneous and anisotropic Bianchi-II cosmological models representing massive strings in normal gauge for Lyra's manifold by applying the variation law for generalized Hubble's parameter that yields a constant value of deceleration parameter. The variation law for Hubble's parameter generates two types of solutions for the average scale factor, one is of power-law type and other is of the exponential form. Using these two forms, Einstein's modified field equations are solved separately that correspond to expanding singular and non-singular models of the universe respectively. The energy-momentum tensor for such string as formulated by Letelier (1983) is used to construct massive string cosmological models for which we assume that the expansion ($\theta$) in the model is proportional to the component $\sigma^{1}_{~1}$ of the shear tensor $\sigma^{j}_{i}$. This condition leads to $A = (BC)^{m}$, where A, B and C are the metric coefficients and m is proportionality constant. Our models are in accelerating phase which is consistent to the recent observations. It has been found that the displacement vector $\beta$ behaves like cosmological term $\Lambda$ in the normal gauge treatment and the solutions are consistent with recent observations of SNe Ia. It has been found that massive strings dominate in the decelerating universe whereas strings dominate in the accelerating universe. Some physical and geometric behaviour of these models are also discussed.Comment: 24 pages, 10 figure

Elektroaktivnost mangostina i njegovih kompleksa

Biomaterial has occupied a leading position in material science for its various scientific and technological applications. The present work was carried out with a natural gum extracted from raw fruit of mangosteen - an east Indian tree Gercinia mangostana. Solid specimen of the gum was developed following a sol-gel like process. AC and DC electrical analysis on the dried solid specimen of the gum was carried out. It exhibits high electrical conduction, σ ∼ 2 × 10−6 S/cm at room temperature, of which ionic and electronic contributions are 70% and 30%, respectively. The experimental investigations show that origin of high electrical conductivity is due to the presence of a substantial amount of organic acid unit in its polysaccharide background. In fact the observed σ is about 3 times that observed in gum Arabica - a plant gum. Optical absorption of this new biomaterial was also studied using UV-VIS spectro-photometry. The result shows its high absorption coefficient in UV and blue part of the spectrum. The electrical characterization of the material was also made. It has been observed that the electronic conduction can be enhanced to 70% of the total electrical conductivity by forming complex with iodine or an appropriate organic/inorganic acid, e.g. acetic acid. This high-potential material is being studied for the development in device application.Biološki materijali imaju vodeću ulogu u znanosti o materijalima zbog svojih različitih znanstvenih i tehnoloških primjena. U ovom se radu proučava prirodna smola koja je bila izlučena iz sirovog voća magnostina, ploda istočno-indijske voćke Gercinia mangostana. Pripravili smo čvrst uzorak smole sol-gel postupkom. Ispitali smo uzorak izmjeničnom i istosmjernom strujom. Na sobnoj temperaturi našli smo visoku električnu vodljivost, σ ∼ 2×10−6 S/cm, s ionskim i elektronskim doprinosima od 70% odnosno 30%. Mjerenja pokazuju da je visoka električna vodljivost posljedica poveće količine molekula organske kiseline u polisaharidnoj osnovnoj tvari. Vrijednosti σ su oko tri puta veće nego u biljnoj smoli Arabica. Proučavali smo optičku apsorpciju primjenom UV-VIS spektrofotometrije. Ishodi mjerenja pokazuju velik apsorpcijski koeficijent u plavom dijelu spektra. Također smo proučili električne značajke te tvari. Ustanovili smo kako se elektronska vodljivost može povećati na oko 70% ukupne vodljivosti tvorbom kompleksa s jodom ili pogodnom organskom ili anorganskom kiselinom, npr. octenom kiselinom. Ta se tvar velikih mogućnosti proučava radi primjena u raznim napravama