مجله پژوهش فیزیک ایران
سال پنجم شماره 4 (زمستان 1384)

Classical thermodynamic laws and relations have been developed for macroscopic systems that satisfy the thermodynamic limit. These relations are challenged as the system size decreases to the scale of nano-systems, in which thermodynamic properties are overshadowed by system size, and the usual classical concepts of extensivity and intensivity are no longer valid. The challenges to the classical thermodynamics in relation to small systems are demonstrated, and via the approach introduced by Hill, the concept of sub-division potential is clarified in details. The fundamental thermodynamic relations are obtained using a rational-based method.

We study duality of field theories in (d+1) dimensional flat Euclidean space and (d+1) dimensional Euclidean AdS space for both scalar the and vector fields. In the case of the scalar theory, the injective map between conformally coupled massless scalars in two spaces is reviewed. It is shown that for vector fields the injective map exists only in four dimensions. Since Euclidean AdS space is equivalent to half flat Euclidean space up to a conformal map, using the injective maps, we interpret AdS/CFT duality as a correspondence between solutions of equation of motion and the corresponding Cauchy data.

In this paper we study the integer quantum Hall effect (IQHE) on the systems with different types of impurities in delta and gaussian forms. The Landau energy levels in the presence of impurity split in two different levels,the extended and localized levels, emerging then the Hall step. Finally, we add a specified form of a quantum dot potential to a system with impurity, and observed that increasing the width and height of quantum dot result in removing the Hall step and disappearing the Hall effect. The numerical calculations are in a good agreement with Laughlin’s argument and Prange’s calculation of quantum hall effect.

Fusion energy due to inertial confinement has progressed in the last few decades. In order to increase energy efficiency in this method various designs have been presented. The standard scheme for direct ignition and fast ignition fuel targets are considered. Neutrons, electrons and photons transport in targets containing different combinations of Li and Be are calculated in both direct and fast ignition schemes. To compress spherical multilayer targets having fuel in the central part, they are irradiated by laser or heavy ion beams. Neutrons energy deposition in the target is considered using Monte Carlo method code MCNP. A significant amount of neutrons energy is deposited in the target which resulted in growing fusion reactions rates. It is found that Beryllium compared to Lithium is more important. In an introductory consideration of relativistic electron beam transport into central part of a fast ignition target, we have calculated electron energy deposition in highly dense D-T fuel and Beryllium layer of the target. It has been concluded that a fast ignition scheme is preferred to direct ignition because of the absence of hydrodynamic instability.

Layered structures in the oceans have always attracted the attention of oceanographers. The formation of these structures have been attributed to phenomena such as double – diffusive convection, internal waves and turbulent modulated mixing. In this paper, the vertical structures of temperature, salinity, density and the layered structure in the middle parts of Caspian Sea have been studied. Counters of iso-quantities of these physical properties, show the existence of regular structures, which indicate that internal waves which are produced by exchanging flow between two basins, as a result of horizontal density gradients (usually from north basin to south basin) may generate these layers. Froude number of this flow is about one. The length of wave of the internal waves is found to be about 200 km and the flow velocity associated with this gravity drive flow is about 0.2 m/s, the frequency of these waves is of order of inertial frequency. The normal modes of these waves have a near steady structure and can fold the inflow front from the North Caspian sea to South Caspian Sea basins, then the layered structure are formed. The thickness of these layers so formed is found to be about 10-20 m. These are in agreement with the values predicted by the model of Wong et al, (2001). In these waters density ratio is negative. Thus, double – diffusive convection does not often happen and cannot produce these layered structures.

In this paper, we first study the conditions for the existence of the solitonic solutions in ion-electron-positron plasma. Then we investigate the effect of increasing positron on the solitonic wave properties, We also consider the time evolution of these waves in passing through the boundaries of two plasma with different positron densities and different positron-electron temperature ratios.

Manganites are considered as subbranches of condensed matter physics with a great wealth of physical mechanisms. In this investigation we have studied the structural, electrical and magnetic properties of a series of La1-xCaxMnO3 manganite with x=0.1, 0.2, …,0.5. We observed that the crystal structure of this manganite, with small dopping, at room temperature is orthorhombic and by increasing the amount of dopping, its structure changes towards tetragonal. Also, by increasing calcium dopping a metallic phase induction occurs at low temperature and also a metal-insulator transition occurs at the samples Curie temperature. By increasing the amount of dopping to 0.5 the metalic-insulator transition temperature and the Curie temperature of the samples both increase first and then decrease. We suggest a theoretical model with which we can interpret qualitatively many properties of manganites, such as their metal-insulator phase transition and their colossal magnetoresistance.

In this article, we investigate the redistribution of implanted As+ ion and effect of it on the rate of oxide growth during steam oxidation of Si wafers at 900oC. Our results show that a highly enriched, thin layer of Arsenic forms at the interface between the oxide and the underlying Si. Also, the oxidation rate was found to increase depending on the depth distribution and dose of the implanted impurity As. The thin As layer collected at the interface can be used in the design of shallow junctions. Rutherford Backscattering Spectroscopy(RBS) was used to investigate the oxide characteristics.

In this study polycrystaline samples of Y1-2xCaxThxBa2Cu3O7-δ with x=0, 0.025, 0.05, 0.075 were made by standard solid state methods. The transport and superconducting properties have been studied by the thermoelectric power S(x,T) measurements as a function of temperature and doping concentration. The critical temperature decreased linearly by increasing the doping concentration. S(x,T) was analysed and well described by a phenomenalogical narrow band model. The critical temperature, room temperature thermoelectric power S(290 K) and phenomenological narrow band model results were suggested in wich charge carrier (hole) localization was the main reason of the suppression of superconductivity in this alloys.