Sharif Digital Repository

We have studied the thermally activated flux creep in the newly fabricated superconductors Y3Ba5Cu8O18+δ and Gd3Ba5Cu8O18+δ with transition temperature above 100 K. The thermally activated flux creep model explains the electron share in the magnetoresistivity of the samples in the vicinity of transition temperature T c . The activation energy U in a magnetic field below 15 kOe has been calculated by the corrected thermally activated flux creep model; and the pinning energy is exponentially related to the magnetic field  

Let G and H be two graphs. A proper vertex coloring of G is called a dynamic coloring, if for every vertex v with degree at least 2, the neighbors of v receive at least two different colors. The smallest integer k such that G has a dynamic coloring with k colors denoted by χ2(G). We denote the cartesian product of G and H by G□H. In this paper, we prove that if G and H are two graphs and δ(G) ≥ 2, then χ2(G□H) ≤ max(χ2(G),x(H)). We show that for every two natural numbers m and n, m,n ≥ 2, χ2(Pm□Pn) = 4. Also, among other results it is shown that if 3|mn, then χ2(C m□Cn) = 3 and otherwise χ2(C m□Cn) = 4  

Predictions of soil behavior in response to dynamic loads require an understanding of dynamic properties of soil. Studies on dynamic properties of unsaturated soils at large-strains are quite limited, while some dynamic loadings, like earthquakes, are in the medium to large-strain ranges. A cyclic simple shear apparatus was developed to measure large-strain shear modulus and damping ratio under different matric suction or degree of saturation. Six cyclic tests, with referring to the soil-water retention curve, were conducted on clean medium sand. Results indicated that shear modulus slightly increases when suction varies from zero up to the air entry value. Approaching the residual value, a... 

A proper vertex k-coloring of a graph G is called dynamic, if there is no vertex v∈V(G) with d(v)<2 and all of its neighbors have the same color. The smallest integer k such that G has a k-dynamic coloring is called the dynamic chromatic number of G and denoted by χ2(G). We say that v∈V(G) in a proper vertex coloring of G is a bad vertex if d(v)<2 and only one color appears in the neighbors of v. In this paper, we show that if G is a graph with the chromatic number at least 6, then there exists a proper vertex χ(G)-coloring of G such that the set of bad vertices of G is an independent set. Also, we provide some upper bounds for χ2(G)- χ(G) in terms of some parameters of the graph G  

Analysis of flow in fluidized beds, a common chemical reactor, is of much current interest due to its fundamental as well as industrial importance. Experimental data for the successive increments of the pressure fluctuations time series in a fluidized bed are analyzed by computing a multiscale probability density function (PDF) of the increments. The results demonstrate the evolution of the shape of the PDF from the short to long time scales. The deformation of the PDF across time scales may be modeled by the log-normal cascade model. The results are also in contrast to the previously proposed PDFs for the pressure fluctuations that include a Gaussian distribution and a PDF with a power-law... 

We present an analytical model to analyze the influence of carrier dynamics on the static and dynamic responses of transistor laser (TL). Our analysis is based on solving the continuity equation and the rate equations which incorporate the virtual states as a conversion mechanism. We show that the details of the dc and small signal behavior of transistor lasers are strongly affected by the escape and capture times of carriers in quantum well (QW). Also, the effects of carrier recombination lifetime in the quantum well and base regions on the TL static and dynamic performances are investigated  

A familiarity with denaturation process is highly significant in understanding the DNA replication, manipulation, and interactions involving DNA double helix stability. We have performed molecular dynamics simulation on B-DNA duplex (CGCGAATTGCGC) at different temperatures. At each temperature, configurational entropy was estimated using the covariance matrix of atom-positional fluctuations. By plotting the configuration entropy versus temperature, we calculated the melting temperature which was found to be 329.7 K. We also calculated the hydrogen bonding energy and heat capacity for the atoms participating in the hydrogen bonding between two strands of DNA. Moreover, their temperature... 

We have investigated the size dependence of a nano-cavity properties produced in a Xe fluid using molecular dynamics simulations. We have created a nano-cavity of different sizes at 170 and 200 K (cavities diameters are within 1-10 nm). Liquid pressure, vapor pressure and surface tension of the nano-cavity for some given values of diameter are calculated. Within 1-10 nm cavity diameter, we have observed two opposite behavior for dependency of surface tension on the cavity diameter: for the range of 1-5 nm, it increases with the diameter, while, for the range of 5-10 nm remains constant. Also, the value of liquid pressure becomes less negative, when the size of cavity increases. Vapor... 

In this study, a new antibacklash gear mechanism design comprising three pinions and a rack is introduced. This mechanism offers several advantages compared to conventional antibacklash mechanisms, such as lower transmission error as well as lower required preload. Nonlinear dynamic modeling of this mechanism is developed to acquire insight into its dynamic behavior. It is observed that the amount of preload required to diminish the backlash depends on the applied input torque and nature of periodic mesh stiffness. Then, an attempt is made to obtain an approximate relation to find the minimum requiring preload to preserve the system's antibacklash property and reduce friction and wear on the... 

DNA supercoiling is a widespread phenomenon in biology. Here we introduce a coarse-grained DNA model and study supercoiled DNA rings via a rigid body molecular dynamics simulation. Our model allows us to investigate these structures in more detail than previously. The simulations are performed on rings of one to six kilobase pairs length and are compared to available experimental data and former simulation studies. The current study provides new additional information about some of the geometrical parameters of the supercoiled DNA rings. It also shows how enforcing a supercoiled DNA ring to two-dimensional space changes its geometrical parameters. Finally, our molecular dynamics method... 

The paper investigates the effects of application of nonlocal elasticity theory on electromechanical behaviors of single-walled carbon nanotubes under electrostatic actuation. The influences of different dimensions and boundary conditions on the vibration and dynamic instability of the carbon nanotubes are studied, in detail, using this theory. The results reveal that application of the non-local elasticity theory leads to the higher pull-in voltages for the nonlocal model applied for carbon nanotubes. Thus, in order to have more accurate results, one should apply nonclassical theorems such as the nonlocal elasticity theory to scrutinize the mechanical and electromechanical behaviors of the... 

A model has been proposed to capture the complex strain rate effect on dynamic precipitation of GP zones in an age-hardenable aluminum alloy. The contributions of vacancies and dislocations to dynamically formed GP zones have been specified in the model. It has been demonstrated that the proposed model is capable for predicting the contribution of each dynamic precipitation mechanisms, accurately, which are acting during deformation. Furthermore, the vacancy and dislocation evolutions during deformation have been considered in this modeling. The effect of strain rate by considering different mechanisms of dynamic precipitation of GP zones has been studied and confirmed by experimental data... 

In the aftermath of earthquakes, hospitals serve the critical role of treating casualties. In many cases, the key components of a hospital (i.e., the building, staff, medicine inventory, technical systems, and medical equipment) are affected by an earthquake. To handle the demand surge, affected hospitals should recover in an effective manner. Hospital recovery is a complex and dynamic process because each component requires specific types and amount of resources to recover. Furthermore, the recovery of each component not only affects its performance but also plays a role in the overall hospital recovery. Hospital administrators need to model the complex recovery process after a future... 

Molecular dynamics (MD) simulation was used to study of mechanical properties of NiTiCu with different content of copper. It was shown that the percent composition of copper are significantly affects the stress-strain curves curve. The results showed that as the Cu content increased, the Yield Strength and Young's modulus decreased. © 2017 Elsevier Ltd  

In this chapter we present the steps of reconstruction procedure for writing down the Langevin and jump diffusion stochastic dynamical equations for uni- and bivariate time series, sampled with time intervals τ. © 2019, Springer Nature Switzerland AG  

In this chapter we present the steps of reconstruction procedure for writing down the Langevin and jump diffusion stochastic dynamical equations for uni- and bivariate time series, sampled with time intervals τ. © 2019, Springer Nature Switzerland AG  

Key performance indicators (KPIs) are the fundamental building blocks in measuring and monitoring processes of safety management. This chapter describes a classification of safety KPIs and a review of literature leads to a new framework. It aims to develop a logical selection and aggregation methodology for generating a single number that reflects safety performance. Determining a mechanism for performance measurement and monitoring is a key part of any management system, and this has a higher importance for total safety management. Personal safety deals with the prevention of occupational accidents that usually have low severities and high frequencies. The measurement of safety has been... 

A set of bi-orthogonal potential-density basis functions is introduced to model the density and its associated gravitational field of three dimensional stellar systems. Radial components of our basis functions are weighted integral forms of spherical Bessel functions. We discuss on the properties of our basis functions and demonstrate their shapes for the latitudinal Fourier number l = 2. © 2008 Copyright International Astronomical Union 2008  

In this paper the dynamic properties of Babolsar dry sand was investigated through one dimensional shaking table tests. 8 models of Babolsar loose dry sand under low confining pressures, were subjected to different harmonic and irregular dynamic loadings. The container was a laminar shear box having 24 layers each moving on the lower one. The dynamic properties including shear wave velocity, maximum shear modulus and damping ratio of the samples were addressed in this project. © 2006 Taylor & Francis Group, London  

Owing to the local/heterogeneous structures in supercooled liquids, after several decades of research, it is now clear that supercooled liquids are structurally different from their conventional liquid counterparts. Accordingly, an approach based on a local probe should provide a better understanding about the local mechanical properties as well as heterogeneous structures. Recently, the superiority of active microrheology over global rheology has been demonstrated [Yu et al., Sci. Adv., 2020, 6, 8766]. Here, we elaborate this new avenue of research and provide more evidence for such superiority. We report on the results of an extensive molecular dynamics simulation of active microrheology...