Sharif Digital Repository

In the present study, it was revealed that incorporation of nanodiamond containing carboxylic group (ND-COOH) decreased considerably specific wear rate (∼30%) and COF (∼60%) of polyamide 6 (PA6) at 1 wt% loading. Compared with ND-COOH, amino functionalized ND enhanced further wear performance of PA6 which was associated with its finer dispersion as well as greater influence on the improvement of mechanical properties, toughness and crystallinity of PA6. Surface temperature increment caused by frictional heat was in close agreement with COF and wear characteristics of the samples. Optical microscopy images revealed that NDs promote the abrasive wear mechanism in PA6/ND composites. © 2017... 

Surface chemistry of as-received nanodiamond (ND) was first tailored by dry thermal oxidation to obtain carboxylated ND (ND-COOH) and by wet chemistry to obtain ethylenediamine-functionalized ND (ND-EDA). Then, the surface-functionalized ND particles were dispersed in polyamide 6 (PA6) using the melt-mixing method. Transmission optical and scanning electron microscopies indicated a fine dispersion at low nanodiamond concentrations, e.g. 0.25 wt%, particularly with ND-EDA. Differential scanning calorimetry revealed that ND-EDA favoured the α-phase crystal and enhanced the degree of crystallinity of PA6. Experimental data indicated that ND-EDA had considerably improved tensile properties at... 

So far, the need for power systems to be control automated has been approached. Moreover, the advent of smart technological infrastructures calls for a more systematic and well-designed schemes for data acquisition process. Hence, Remote Terminal Units (RTUs) are going to be considered as a crucial part of smart grid puzzle in power distribution systems. This paper aims to present a novel practical approach to have the RTU placement dilemma unraveled in power distribution systems. Practically approaching in this paper, some pragmatic factors of major importance in this respect are introduced. A framework with which the utility's experts' knowledge could be efficiently exploited is presented... 

Here, using the probabilistic evaluation based on the Monte Carlo method, back-flashover rate and shielding failure flashover rate of 230 kV overhead transmission lines in the western regions of Iran are evaluated. To such an aim, first, the number of thunderstorm days per year is collected from the reported weather information in order to determine the ground flash density. Then, using MRU-200 equipment, the tower-footing resistance of several towers is measured. Matlab® software is used in order to produce lightning surges considering its probabilistic nature and randomly distribution on the ground to evaluate striking distance based on the geometric model. Then, calculated parameters are... 

The closed neighborhood NG[e] of an edge e in a graph G is the set consisting of e and of all edges having a common endvertex with e. Let f be a function on E(G), the edge set of G, into the set {-1, 1}. If Σx∈N[e] f(x) ≥ 1 for each e ∈ E(G), then f is called a signed edge dominating function of G. The minimum of the values Σe∈E(G) f(e), taken over all signed edge dominating function f of G, is called the signed edge domination number of G and is denoted by γ′s(G). It has been conjectured that γ′s(T) ≥ 1 for every tree T. In this paper we prove that this conjecture is true and then classify all trees T with γ′s(T) = 1, 2 and 3  

A set S of vertices of a graph G = (V, E) without isolated vertex is a total dominating set if every vertex of V(G) is adjacent to some vertex in S. The total domination number γt(G) is the minimum cardinality of a total dominating set of G. The total domination subdivision number sd γt (G) is the minimum number of edges that must be subdivided (each edge in G can be subdivided at most once) in order to increase the total domination number. In this paper we first prove that sdγt(G) < n -δ + 2 for every simple connected graph G of order n ≥ 3. We also classify all simple connected graphs G with sdγt (G) = n -δ+ 2,n-δ + 1, and n-δ  

An adaptive tracker to address the problem of tracking objects which undergo abrupt and significant motion changes is introduced. Abrupt motion of objects is an issue which makes tracking a challenging task. To address this problem, a new adaptive motion model is proposed. The model is integrated into the sequential importance resampling particle filter (SIR PF), which is the most popular probabilistic tracking framework. In this model, in each time step, if necessary, the particles' configurations are updated by using feedback information from the observation likelihood. In order to overcome the local-trap problem, local search algorithm with best improvement strategy is used to update... 

The closed neighborhood N G[e] of an edge e in a graph G is the set consisting of e and of all edges having a common end-vertex with e. Let f be a function on E(G), the edge set of G, into the set {-1, 1}. If σ xεN[e] f(x) ≥ 1 for each e ε E(G), Then f is called a signed edge dominating function of G. The minimum of the values of σ xεE(G) f(x), taken over every signed edge dominating function f of G, is called the signed edge domination number of G and is denoted by γ′ s(G). It has been conjectured that γ′ s(G) ≥ n - 1 for every simple graph G of order n. In this paper we prove that this conjecture is true for Eulerian simple graphs, simple graphs with all vertices of odd degree and regular... 

It seems that the index theory for non-compact spaces has found its ultimate formulation in the realm of coarse spaces and K-theory of related operator algebras. Relative and partitioned index theorems may be mentioned as two important and interesting examples of this program. In this paper we formulate a combination of these two theorems and establish a partitioned-relative index theorem. © 2019 Elsevier Masson SAS  

In this study tracking problem of tip of a micro cantilever, actuated by electrostatic, is investigated. Dynamic model of the system is a PDE. Using electrostatic actuation.introduced significant nonlinearity in dynamic model of the system. Control goals are achieved by means of backstepping for SI and feedback linearization for MI system. Performance of control system is inspected for some assumptions and simplifications. The results are in according to numerical simulations  

In this study tracking problem of tip of a micro cantilever, actuated by electrostatic, is investigated. Dynamic model of the system is a PDE. Using electrostatic actuation introduced significant nonlinearity in dynamic model of the system. Control goals are achieved by means of backstepping for SI and feedback linearization for MI system. Performance of control system is inspected for some assumptions and simplifications. The results are in according to numerical simulations  

This paper investigates a reliability-centered approach for the placement procedure of remote terminal units (RTUs) in power distribution systems. Entire attempt is contributed to incorporate the practical aspects interrelated with the problem, e.g. the accessibility to the candidate substations, the load point criticality, as well as the load probabilistic behavior and consequently the inevitable variation in the electricity price. The placement process is done through an optimization problem wherein the common reliability indices, as the decisive factors in the placement process, are going to be minimized. The approach is successfully applied to a real power distribution feeder of Iran's... 

A new refill friction spot welding process called Threaded Hole Friction Spot Welding (THFSW) was introduced to join AA5052 aluminum to short-carbon-fiber-reinforced polypropylene (PP-SCF) composite sheets. The process was based on filling of the pre-threaded hole by melted and re-solidified polymer. The results showed that THFSW was successful to join aluminum to polymer sheets and the hole was completely filled with melted polymer. Formation of a reaction layer composed mostly of Al, C and O as well as interlocking between the threaded hole and the re-solidified polymer were recognized as main bonding mechanisms. Maximum shear-tensile strength of the joints reached to ∼80 percent of the... 

In this work the titanium dioxide powder was prepared by the optimized and simple Sol-Gel method and then characterized. The gelling pH was set to values of 3 (TiO2-A), 7 (TiO2-N) and 9 (TiO2-B) to observe the effect on the properties of the material. In these three cases nanoparticulated materials were obtained with particle sizes between 10nm and 20nm. The larger surface areas were obtained at pH 3, which is several times larger than the others. Furthermore, with the gelling condition pH 3, it was possible to synthesize pure anatase phase titania. Some preliminary results on the test of the photocatalytic activity of the synthesized materials in the reduction of nitric oxide are presented.... 

The prepared colloidal silica via ion exchange was modified by adding Mg+2 ions in the surface growth process of colloidal silica. The particle size of the modified colloidal silica was decreased by increasing the seed concentration, whereas that of colloidal silica was slightly increased as the seeds concentration exceed 15 wt%. But the trend of changes in surface area was completely reversed. Magnesium ions on surface of the modified colloidal silica were identified by the measurement of energy-dispersive X-ray spectrometry (EDS). After modifying with Mg+2 ions, the iso-electric point (IEP) of colloidal silica in pH ∼ 2 without modification, disappears over the whole pH range. © 2008... 

This work describes the preparation of magnetic and pH-sensitive beads based on κ-carrageenan and sodium alginate for use as drug-targeting carriers. Physical cross-linking using K+/Ca2+ ions was applied to obtain ionic cross-linked magnetic hydrogel beads. The produced magnetite beads were thoroughly characterized by TEM, SEM/EDS, XRD, FTIR, and VSM techniques. While the water absorbency (WA) of magnetic beads was enhanced by increasing the weight ratio of κ-carrageenan, introducing magnetic nanoparticles caused a decrease in WA capacity from 15.4 to 6.3 g/g. Investigation on the swelling of the hydrogel beads in NaCl, KCl, and CaCl2 solutions revealed the disintegration of beads depending... 

Microlensing events provide a unique capacity to study the stellar remnant population of the Galaxy. Optical microlensing suffers from a near-complete degeneracy between mass, velocity, and distance. However, a subpopulation of lensed stars, Mira variable stars, are also radio-bright, exhibiting strong SiO masers. These are sufficiently bright and compact to permit direct imaging using existing very long baseline interferometers such as the Very Long Baseline Array (VLBA). We show that these events are relatively common, occurring at a rate of ≈2 yr-1 of which 0.1 yr-1 are associated with Galactic black holes. Features in the associated images, e.g., the Einstein ring, are sufficiently well... 

In this paper, an adaptive design methodology for synthesizing a harmonic free N-path filter with reduced frequency folding is presented. System level analysis of proposed architecture shows that by adding a few extra paths with proper weights to a conventional N-path filter, several characteristics such as harmonic rejection, power reduction, foldback elimination and spectrum shaping can be achieved. The designed filter is reconfigurable to be a band-pass filter (BPF) or a band-reject filter (notch), based on the requirements. By using the nth harmonic of Local Oscillator (LO) signal, instead of the fundamental harmonic, the required input clock frequency in N-phase clock generator is... 

Recent studies showed that while code-compliant structures can generally protect the safety of the occupants, they may exhibit extensive damages during strong earthquake events. On the other hand, structures are generally designed to satisfy the seismic code requirements with the least initial cost regardless of their life cycle cost. In recent years, value-based design has been considered as an effective alternative for code-based design procedures. In this method, as well as the initial cost of the structure, a comprehensive consequence modeling is performed in the design process. In this paper, for the first time, a value-based design optimization method is developed for seismic... 

In this work, a corresponding-states correlation is presented for prediction of crude oil density in an undersaturated state. The correlation is the extension of corresponding-states liquid densities correlation. The modified corresponding states liquid densities method for predicting saturated liquid densities was coupled with the Tait equation to predict undersaturated densities. Correlations are proposed for the temperature-dependence of Tait equation parameters. Applying proper mixing and combining rules, we calculated the density of 26 crude-oil samples, mainly from Iranian reservoirs. The mixtures included a variety of compositions including N2, H 2S, CO2, and hydrocarbons. The AAD%...