Sharif Digital Repository

Formation of localized magnetic states in a metallic host is a classic problem of condensed matter physics formalized by P. W. Anderson within the so called single impurity Anderson model (SIAM). The general picture in a host of a simple one-band metal is that a large Hubbard U in the impurity orbital is pre-requisite for the formation of localized magnetic states. In recent years three dimensional (3D) Dirac solids have emerged the hallmark of which is strong spin- orbit interaction. In this work we show that such a strong spin-orbit interaction allows to form localized magnetic states even with small values of Hubbard U. This opens up the fascinating possibility of forming magnetic states... 

This paper presents a technique for estimation of amplitude information from an interferometric time-domain optical coherence tomography (OCT) signal. The conventional estimation scheme is based on the in-phase and quadrate (IQ) demodulation concept. A disadvantage of this method is that the IQ components include a ripple whose frequency is the double of the interferometric signal frequency. The improved method of demodulation, presented in this paper, yields a more precise estimation of the amplitude information by fundamentally removing the ripple. Theoretical and experimental OCT signals are applied to both demodulation systems and the amplitude is computed. The detected signals from both... 

An experimental study on the onset of nucleate boiling (ONB) is performed for water annular flow to provide a systematic database for low pressure and velocity conditions. A parametric study has been conducted to investigate the effect of pressure, inlet subcooling, heat and mass flux on flow boiling. The test section includes a Pyrex tube with 21 mm inner diameter and a stainless steel (SS-304) rod with outer diameter of 6 mm. Pressure, heat and mass flux are in the range of 1.73 < P < 3.82 bar, 40 < q < 450 kW/m2 and 70 < G < 620 kg/m2 s, respectively. The results illustrate that inception heat flux is extremely dependent on pressure, inlet subcooling temperature and mass flux; for example... 

Dissolved oxygen tension and shear stress as two very important factors in fungal fermentation were studied in the batch cultures of Aspergillus niger. The intention was to maximize the total activity of glucose oxidase produced in a 5-1 bench-top bioreactor. 300 rpm found to be optimum for enzyme production, however in higher mixing rates higher growth was achieved. The maximum activity of glucose oxidase was obtained in 1.5 vvm while the best aeration rate for growth was 2 vvm. Glucose oxidase with the activity of 548 U mL-1 was produced in 1.5 vvm and 300 rpm as the optimum conditions. © 2007 Asian Network for Scientific Information  

Due to the limited resources of fossil fuels, energy supply–demand management and planning especially in the supply-side of the energy system have increasingly become very important. This article assesses Iran’s energy system in order to find the main causes of the considerably high energy intensity in the country compared with similar economies in size and production. Accordingly, fundamental policies and strategies are proposed in order to manage the recognized bottlenecks. The conclusions suggest strongly that not only the fossil-based energy system, but also incompatible patterns of production and consumption in the reference energy system as well as the use of conventional technologies... 

In this study low-grade sphalerite has been treated by the bioleaching process using native cultures of Acidithiobacillus ferrooxidans and Sulfobacillus thermosulfido-oxidans in order to determine the ability of these bacteria to the leaching of zinc. The effects of bacterial strain, pH, temperature, pulp density, iron precipitation, and initial concentration of ferric iron on the zinc leaching were evaluated. The bioleaching experiments were carried out in shake flasks at pH 1.5, 180 rpm, 33 °C and 60 °C for mesophilic and thermophilic bacteria, respectively. Compared with the use of laboratory reference strains or control conditions, zinc recovery from the respective concentrate was... 

Elemental bismuth and its compounds host strong spin-orbit interaction which is at the heart of topologically non-trivial alloys based on bismuth. These class of materials are described in terms of 4x4 matrices at each v point where spin and orbital labels of the underlying electrons are mixed. In this work we investigate the single impurity Anderson model (SIAM) within a mean field approximation to address the nature of local magnetic moment formation in a generic Dirac Hamiltonian. Despite the spin-mixing in the Hamiltonian, within the Hartree approximation it turns out that the impuritys Green function is diagonal in spin label. In the three dimensional Dirac materials defined over a... 

STUDY DESIGN. Three factors mixed-design with 1 between-subject and 2 within-subject factors. OBJECTIVE. To compare the main effects and interactions of postural and cognitive difficulty on quiet stance between subjects with and without nonspecific low back pain (LBP). SUMMARY OF BACKGROUND DATA. The interference between postural control and cognitive tasks depends on factors such as sensorimotor/cognitive integrity. Changes in peripheral sensory and muscular systems as well as cognitive processes have been observed in LBP patients. It was hypothesized that the effect of cognitive task on postural performance might be different in subjects with nonspecific LBP as compared with healthy... 

We study the rotational motion of nano-flake ferromagnetic disks suspended in a Newtonian fluid, as a potential material owing the vortex-like magnetic configuration. Using analytical expressions for hydrodynamic, magnetic and Brownian torques, the stochastic angular momentum equation is determined in the dilute limit conditions under applied magnetic field. Results are compared against experimental ones and excellent agreement is observed. We also estimate the uncertainty in the orientation of the disks due to the Brownian torque when an external magnetic field aligns them. Interestingly, this uncertainty is roughly proportional to the ratio of thermal energy of fluid to the magnetic energy... 

In this study the effects of initial concentration of Fe(II) and Fe(III) ions as well as initial pH on the bioleaching of a low-grade sphalerite ore in a leaching column over a period of 120 days with and without bacteria were investigated. Four different modifications of medium were used as column feed solutions to investigate the effects of initial concentration of Fe(II) and Fe(III) ions on zinc extraction. The experiments were carried out using a bench-scale, column leaching reactor, which was inoculated with mesophilic iron oxidizing bacteria, Acidithiobacillus ferrooxidans, initially isolated from the Sarcheshmeh chalcopyrite concentrate (Kerman, Iran). The effluent solutions were... 

In a nanoscopic thin film of a strong topological insulator (TI) the Coulomb interaction in the channel that exchanges the two electrons with the same chirality in two different planes of the slab takes advantage of the minus sign resulting from such "exchange" and gives rise to a bound state between the positive-energy states in one surface and the negative-energy states in the opposite surface. Therefore particle and hole pairs in the undoped Dirac cone of the TI thin film form an inter-surface spin-singlet state that lies below the continuum of free particle-hole pairs. This mode is similar to the excitons of semiconductors, albeit formed between the electron and hole pairs from two... 

The particle-hole continuum (PHC) for massive Dirac fermions provides an unprecedented opportunity for the formation of two collective split-off states, one in the singlet and the other in the triplet (spin-1) channel, when the short-range interactions are added to the undoped system. Both states are close in energy and are separated from the continuum of free particle-hole excitations by an energy scale of the order of the gap parameter Δ. They both disperse linearly with two different velocities, reminiscent of spin-charge separation in Luttinger liquids. When the strength of Hubbard interactions is stronger than a critical value, the velocity of singlet excitation, which we interpret as a... 

We present a formulation for the nonlinear optical response in gapped graphene, where the low-energy single-particle spectrum is modeled by massive Dirac theory. As a representative example of the formulation presented here, we obtain a closed form formula for the third harmonic generation in gapped graphene. It turns out that the covariant form of the low-energy theory gives rise to peculiar logarithmic singularities in the nonlinear optical spectra. The universal functional dependence of the response function on dimensionless quantities indicates that the optical nonlinearity can be largely enhanced by tuning the gap to smaller values  

Within the block spin renormalization group, we give a very simple derivation of the exact phase boundaries of the XYZ spin chain. First, we identify the Ising order along ◯ or ŷ as attractive renormalization group fixed points of the Kitaev chain. Then, in a global phase space composed of the anisotropy λ of the XY interaction and the coupling Δ of the Δσzσz interaction, we find that the above fixed points remain attractive in the two-dimesional parameter space. We therefore classify the gapped phases of the XYZ spin chain as: (1) either attracted to the Ising limit of the Kitaev-chain, which in turn is characterized by winding number ±1, depending on whether the Ising order parameter is... 

We show that the continuum limit of the tilted Dirac cone in materials such as 8-Pmmn borophene and layered organic conductor α-(BEDT-TTF)2I3 corresponds to deformation of the Minkowski space-time of Dirac materials. From its Killing vectors we construct an emergent tilted-Lorentz (t-Lorentz) symmetry group for such systems. As an example of the t-Lorentz transformations we obtain the exact solution of the Landau bands for a crossed configuration of electric and magnetic fields. For any given tilt parameter 0≤ζ<1, if the ratio χ=vFBz/Ey of the crossed magnetic and electric fields satisfies χ≥1+ζ, one can always find appropriate t-boosts in both valleys labeled by τ=±1 in such a way that the... 

Dirac cone can be tilted in condensed matter setting. As a result of tilt, the Lorentz symmetry is reduced to what we call tilted-Lorentz symmetry. In this paper, we derive the tilted-Lorentz transformations that leave a world with tilted Dirac cone invariant. © 2020, Isfahan University of Technology. All rights reserved