JOURNAL OF THEORETICAL AND APPLIED PHYSICS (IRANIAN PHYSICAL JOURNAL)
Year:2013 | Volume:7 | Issue:-|Papers Count:8

We have demonstrated the structural and magnetic properties of small carbon clusters (Cn, n=2−12) in the framework of collinear approximation using density functional theory. The calculations were performed for amorphous, linear, and ring carbon clusters using full-potential local-orbital (FPLO) method. We have obtained stable structures, total energies, total magnetic moments, and HOMOLUMO energy gap of these clusters. We have found that the amorphous carbon clusters with minimum energy are not magnetic clusters whereas their less-stable isomers with special configurations are ferromagnetic objects. Two robust magnetic moments were found for C5 carbon ring (6mB) and for pentagonal pyramid C6 structure (4mB).

Efficient and cheap dye-sensitized solar cells (DSSCs) were fabricated using natural dyes from Pastinaca sativa and Beta vulgaris. Natural dyes are environmentally and economically superior to ruthenium-based dyes because they are nontoxic and cheap. However, the conversion efficiency of dye-sensitized solar cells based on natural dyes is low. One way to improve the DSSC performance is to enhance the absorptivity of extracted dyes. We investigated the influence of various factors in the extraction process, such as utilization of different extraction approaches, the acidity of extraction solvent, and different compounds of solvents on the optical absorption spectra. It was found that we could considerably enhance the optical absorptivity of dye and consequently the performance of DSSC by choosing a proper mixture of ethanol and water for extracting solvent and also the acidity of dye solution.

We have studied quark matter coupled with string cloud and domain walls in the context of general relativity. For this purpose, we solved Einstein's field equations for quark matter coupled to the string cloud and domain walls in spherical symmetric kink space-time. It is found that cosmic strings and domain walls do not survive in this space-time. Hence, the space-time in both the cases reduces to Minkowskian and the space-time is flat.

In this paper, we construct a methodology for separating divergencies due to different topological manifolds dual to Feynman graphs in a colored group field theory. After having introduced the amplitude bounds using propagator cuts, we show how Graph-Encoded Manifold (GEM) techniques can be used in order to factorize divergencies related to different parts of the dual topologies of the Feynman graphs in the general case. We show the potential of the formalism in the case of three-dimensional solid torii in the colored Boulatov model.

We show that many independent scenarios as the ‘accelerated expansion of the universe’, ‘eternal inflation’, ‘eternally oscillating universe’, ‘nonsingular oscillating universe’, and ‘collapse of an oscillating universe’ may occur without modifying the gravity theory or introducing scalar fields of any type. This is achieved by replacing the standard Lagrangian in the Friedmann-Robertson-Walker spacetime model by an exponentially nonstandard Lagrangian which modify the Euler-Lagrange equation although the standard variational approach is used.

Traveling wave resolution of Korteweg-de Vries (K-dV) solitary and numerical estimation of analytic solutions have been studied in this paper for imaginary concept. Pretend model of traveling wave deals with giant waves or series of waves created by an undersea earthquake, volcanic eruption or landslide. The concept of traveling wave is frequently used by mariners and in coastal, ocean and naval engineering. We have found some exact traveling wave solutions with relevant physical parameters using new auxiliary equation method introduced by Pang et al. (Appl. Math. Mech-Engl. Ed 31 (7): 929–936, 2010). We have solved the imaginary part of exact traveling wave equations analytically, and numerical results of time-dependent wave solutions have been presented graphically. This procedure has a potential to be used in more complex system for other types of K-dV equations.

Using orbital-free framework, a simple numerical optimization of the density functional for ground state electronic energy is described for any type of functional approximation, demonstrated via the example of linear combinations of homogeneous functionals of the density. The numerical recipe is given and analyzed for solution: Originating from the linear dependence of nuclear-electron attraction functional on one-electron density (Vne [ρ0 (r1)] =−SA=1, …, M ZAòρ0 (r1) rA1-1dr1), and a quadratic LCAO approximation for ρ0, the optimization can be done with iterative use of lin solver. This quadratic approximation, as simplest educated choice for ρ0, is compared and analyzed algebraically to the HF-SCF one in the Appendices. We call the attention that the introduction of a self-consistent field optimization of non-linear density functional is a new element in this part of the related, general theory.

Nonstandard Lagrangians entitled ‘nonnaturals’ by Arnold have recently gained increasing importance both in applied mathematics and in physical theories. These types of Lagrangians appear in some group of dissipative dynamical systems, and they play an important role in a number of field theories. However, the role of nonstandard Lagrangians in geometric theories like general relativity is still absent. In this communication, we would like to discuss the relevance of nonstandard Lagrangians in general relativity using the principles of calculus of variations. In fact, nonstandard Lagrangians came in different forms, features, and characteristics, depending on the nature of the dynamical problem under study. In this work, we will be concerned with time-dependent Lagrangians of the form L1+g (t). After deriving the modified geodesic equation using the basic techniques of Riemannian differential geometry which will be used to axiomatize a large part of our work, we show that many interesting consequences will be raised accordingly when applied to FRW cosmology.