Sharif Digital Repository

The particlehole continuum in the Dirac sea of graphene has a unique window underneath, which in principle leaves room for bound state formation in the triplet particlehole channel (Baskaran and Jafari 2002 Phys. Rev. Lett. 89 016402). In this work, we construct appropriate triplet particlehole operators and, using a repulsive Hubbard-type effective interaction, we employ equations of motion to derive approximate eigenvalue equations for such triplet operators. While the secular equation for the spin density fluctuations gives rise to an equation which is second order in the strength of the short range interaction, the explicit construction of the triplet operators obtained here shows that,... 

Using tight binding band picture for 2D graphite, and the Hubbard interaction, recently we obtained a gapless, neutral spin-1 collective mode branch in graphite [Phys. Rev. Lett. 89, 016402], In this paper we present a detailed RPA analysis of the Neutron Scattering cross section for this collective mode. Near K-point and very close to Γ-point, the intensity of neutron scattering peaks vanishes as q3. This is shown using a simple Dirac cone model for the graphite band structure, which captures the small-q behavior of the system. As we move away from the Γ- and Κ-points in the Brillouin zone of the collective mode momenta, we can identify our collective mode quanta with spin triplet excitons... 

In objective gravitational reduction of the wave function of a quantum system, the classical limit of the system is obtained in terms of the objective properties of the system. On the other hand, in Bohmian quantum mechanics the usual criterion for getting classical limit is the vanishing of the quantum potential or the quantum force of the system, which suffers from the lack of an objective description. In this regard, we investigated the usual criterion of getting the classical limit of a free particle in Bohmian quantum mechanics. Then we argued how it is possible to have an objective gravitational classical limit related to the Bohmian mechanical concepts like quantum potential or... 

There is a famous criterion for objective wave function reduction which is derived by using the Shrödinger–Newton equation [L Diosi, Phys. Lett. A105(4–5), 199 (1984)]. In this regard, a critical mass for the transition from quantum world to the classical world is determined for a particle or an object. In this paper, we shall derive that criterion by using the concept of Bohmian trajectories. This study has two consequences. The first is, it provides a geometric framework for the problem of wave function reduction. The second is, it represents the role of quantum and gravitational forces in the reduction process. © 2020, Indian Academy of Sciences  

The effect of etching time scale of glass surface on its statistical properties has been studied using atomic force microscopy technique. We have characterized the complexity of the height fluctuation of an etched surface by the stochastic parameters such as intermittency exponents, roughness, roughness exponents, drift and diffusion coefficients and found their widths in terms of the etching time. © 2006 Elsevier B.V. All rights reserved  

We have investigated the effect of bias voltage on sheet resistance, surface roughness and surface coverage of Co/NiO x magnetic bilayer. In addition, interface topography and corrosion resistance of the Ta/Co/Cu/Co/NiO x /Si(1 0 0) system have been studied for Co layers deposited at an optimum bias voltage. Atomic force microscopy (AFM) and four point probe sheet resistance (Rs) measurement have been used to determine surface and electrical properties of the sputtered Co layer at different bias voltages ranging from 0 to -80 V. The Co/NiO x bilayer exhibits a minimum surface roughness and low sheet resistance value with a maximum surface coverage at Vb=-60 V resulted in a slight increase of... 

The dynamical scattered light intensity and multiplicative cascade model was employed to characterize the anisotropic charged colloidal particles suspension during the so-called Sol-Gel transition. Generally we looked for finding a criterion to distinguish the properties of Sol and Gel states systematically. The probability density function (PDF) of the light scattering intensity shows an obvious change with proceeding of the sample aging process (during of gelation state). Our results confirmed that in the so-called Sol state, the value of non-Gaussian parameter, kW, as a function of time is larger than that of for weak-Gel or in coexistence Sol-Gel state. The number of cascades in the... 

The reactions of the bis-NHC platinum complex cis-[PtMe2(bis–NHC–1)], 1, in which bis–NHC–1 = 1,1′-methylene-3,3′-bis[(N-(tert-butyl)imidazole-2-ylidene], with strong acids and thermolysis of the reaction products were investigated. The reaction of 1 with 1 equiv B(C6F5)3 in acetone gave the borate complex cis-PtMe(bis–NHC–1)[OHB(C6F5)3], 2, that undergoes C–H bond activation of one of the tBu wingtips at 50 °C and yields the cyclometalated platinum complex Pt(bis–NHC–1′)[OHB(C6F5)3], 3, (where the prime denotes the cyclometalated ligand). However, the migration of two C6F5 groups from boron to the platinum center was observed when the thermolysis of 3 carried out in the presence of a large... 

We demonstrate that Markov processes play a fundamental role in probing rough surfaces and characterizing their topography. The surface topography obtained by a probe, as in the atomic force microscopy (AFM) technique, is based on the probe-surface interactions. When the size of the probe tip is comparable with the height of the surface fluctuation, the surface image can be aberrated from its origin. Due to the tip effect, there is a crossover in the structure function of the surface. For scales smaller than the Markov length -the minimum length scale over which a process is Markovian - the stochastic function that describes a rough surface is non-Markovian, whereas for length scales larger... 

Recently, the visibility graph has been introduced as a novel method for analyzing time series, which maps a time series to a complex network. In this paper we introduce a new algorithm of visibility, "cross-visibility", which reveals the conjugation of two coupled time series. The correspondence between the two time series is mapped to a network, "the cross-visibility graph", to demonstrate the correlation between them. We have applied the algorithm to several correlated and uncorrelated time series, generated by the linear stationary ARFIMA process, in order to better understand the results of the cross-visibility of empirical series. The comparison between the degree distribution of... 

We have constructed a collaboration network for physicists based in Iran working in different disciplines. By discussing properties like collaborators per author, shortest path, betweenness, and the concept of power in networks for this local model, and comparing with the global model, we understand how a developing country in the Middle East is contributing to the scientific growth in the world statistically. In this comparison, we found some properties of the local model which were not in accordance with the standard global society of science, which should be considered in developing the future policies. Our results show significant differences in factors like the degree and the diameter... 

This study describes an efficient method for ortho-selective halogenation of N-arylcarbamates under mild conditions for the first time. Although being weakly coordinating, N-arylcarbamates act very well as a removable directing group for activation of C-H bonds. The developed procedure results in extremely valuable halogenated N-arylcarbmates that can further be hydrolyzed to halogenated anilines. The obtained reaction conditions showed broad scope and wide functional group tolerance. All the products were formed in good yields with extremely high selectivity  

Economists and policy-makers believe that the Fiscal Decentralization is an effective strategy to promote economic growth. Thereby Economic Growth is seen as an objective of Fiscal Decentralization and efficiency in the allocation of resources in the public sector. This study analyzed the relationship between fiscal decentralization and economic growth in Iran for the period 2001-2007.We used data for 28 provinces of the country estimated the model using a panel data regression with Fixed Effect. We find that fiscal decentralization has a positive effect on Iran's economic growth  

In this paper, we investigate the statistical and scaling properties of the California earthquakes' inter-events over a period of the recent 40 years. To detect long-term correlations behavior, we apply detrended fluctuation analysis (DFA), which can systematically detect and overcome nonstationarities in the data set at all time scales. We calculate for various earthquakes with magnitudes larger than a given M. The results indicate that the Hurst exponent decreases with increasing M; characterized by a Hurst exponent, which is given by, H = 0:34 + 1:53/M, indicating that for events with very large magnitudes M, the Hurst exponent decreases to 0:50, which is for independent events. © Versita... 

Balance theory proposed by Heider for the first time modeled triplet interaction in a signed network, stating that relationships between two people, friendship or enmity, is dependent on a third person. The Hamiltonian of this model has an implicit assumption that all triads are independent, meaning that the type of each triad, being balanced or imbalanced, determined apart from the state of other triads. This independence forces the network to have completely balanced final states. However, there exists evidence indicating that real networks are partially balanced, raising the question of what is the mechanism preventing the system to be perfectly balanced. Our suggestion is to consider a... 

In this paper, we study a particular deformation of the Jackiw-Teitelboim gravity recently considered by Maxfield, Turiaci, and independently by Witten. We will compute the partition function of this model as well as its higher order correlators to all orders in genus expansion in the low temperature limit for small perturbations. In this limit, the results match with those obtained from the Airy limit of a Hermitian random matrix ensemble. Using this result, we will also study the free energy of the model. One observes that although the annealed free energy has pathological behaviors, under certain assumptions, the quenched free energy evaluated by replica trick exhibits the desired... 

In this paper, we study a particular deformation of the Jackiw-Teitelboim gravity recently considered by Maxfield, Turiaci, and independently by Witten. We will compute the partition function of this model as well as its higher order correlators to all orders in genus expansion in the low temperature limit for small perturbations. In this limit, the results match with those obtained from the Airy limit of a Hermitian random matrix ensemble. Using this result, we will also study the free energy of the model. One observes that although the annealed free energy has pathological behaviors, under certain assumptions, the quenched free energy evaluated by replica trick exhibits the desired... 

The roughness of glass surfaces after different stages of etching is investigated by reflection measurements with a spectrophotometer, light scattering, atomic force microscopy (AFM, on a small scale) and profilometry (on a large scale). The results suggest that there are three regimes during etching, according to their optical reflectivity and roughness. The first and the second regimes are studied by the Kirchhoff theory and the third one is studied by the optical geometric theory. Also, the roughness obtained by optical scattering is compared with the AFM results. Copyright © 2005 John Wiley & Sons, Ltd  

Several methods have been developed in the past for analyzing the porosity and other types of well logs for large-scale porous media, such as oil reservoirs, as well as their permeability distributions. We developed a method for analyzing the porosity logs φ(h) (where h is the depth) and similar data that are often nonstationary stochastic series. In this method one first generates a new stationary series based on the original data, and then analyzes the resulting series. It is shown that the series based on the successive increments of the log y(h)=φ(h+δh)-φ(h) is a stationary and Markov process, characterized by a Markov length scale hM. The coefficients of the Kramers-Moyal expansion for... 

An efficient, simple and regiospecific protocol for the synthesis of iodine-containing 2-imino(iminium)1,3- dithiolanes/dithianes/dithiepanes is reported via iodocyclization of corresponding S-(homo)propargyl dihtiocarbamates with molecular iodine. The reactions are regiospecific and only the exo-dig cyclization products were observed in all the cases. In addition, mild reaction conditions, high yields, easy purification, and using inexpensive reagents are the main advantages of this protocol. © 2023 Elsevier Ltd