Sharif Digital Repository

In this work, the production and properties of Al 6061/SiC composites, made using a squeeze casting method, were investigated. SiC preforms were manufactured by mixing SiC powder, having a 16 and 22 pm particle size, with colloidal silica as a binder. 6061 Al melt was squeeze cast into the pores of the SiC preform to manufacture a DRA composite containing 30v/o reinforcement. The aging behavior, tensile properties and fracture mechanism of the cast material were studied. The results show that higher hardness, yield strength, tensile strength and Young's modulus can be obtained by the addition of SiC particles to 6061 Al alloy, whereas tensile elongation decreases. This is mainly caused by a... 

Vivid banding pattern of the chromosome image is a crucial part for diagnosis in karyotype medical test. Furthermore, thriving computer aided segmentation and classification depend on the initial image quality. In this paper, we propose an adaptive and iterative histogram matching algorithm for chromosome contrast enhancement especially in banding patterns which is one of the most important information laid in chromosome image. Objective histogram, with which the initial image needs to be matched, is created based on processes on the initial image histogram. Calculation of statistical moments of image histogram and determination of parameters in each step of iteration based on these moments... 

Vivid banding patterns in medical images of chromosomes are a vital feature for karyotyping and chromosome classification. The chromosome image quality may be degraded by many phenomenon such as staining, sample defectness and imaging conditions. Thus, an image enhancement processing algorithm is needed before classification of chromosomes. In this paper, we propose an adaptive and iterative histogram matching (AIHM) algorithm for chromosome contrast enhancement especially in banding patterns. The reference histogram, with which the initial image needs to be matched, is created based on some processes on the initial image histogram. Usage of raw information in the histogram of initial image... 

In this paper, we study a variant of the well-known line-simplification problem. For this problem, we are given a polygonal path P=p1, p2,...,pn and a set S of m point obstacles in the plane, with the goal being to determine an optimal homotopic simplification of P. This means finding a minimum subsequence Q=q1,q2,..., qk (q1=p1 and qk=pn) of P that approximates P within a given error ε that is also homotopic to P. In this context, the error is defined under a distance function that can be a Hausdorff or Fréchet distance function, sometimes referred to as the error measure. In this paper, we present the first polynomial-time algorithm that computes an optimal homotopic simplification of P in... 

We consider a network creation game in which, each player (vertex) has a limited budget to establish links to other players. In our model, each link has a unit cost and each agent tries to minimize its cost which is its local diameter or its total distance to other players in the (undirected) underlying graph of the created network. Two variants of the game are studied: in the MAX version, the cost incurred to a vertex is the maximum distance between that vertex and other vertices, and in the SUM version, the cost incurred to a vertex is the sum of distances between that vertex and other vertices. We prove that in both versions pure Nash equilibria exist, but the problem of finding the best... 

We introduce a network creation game in which each player (vertex) has a fixed budget to establish links to other players. In this model, each link has a unit price, and each agent tries to minimize its cost, which is either its eccentricity or its total distance to other players in the underlying (undirected) graph of the created network. Two versions of the game are studied: In the MAX version, the cost incurred to a vertex is the maximum distance between the vertex and other vertices, and, in the SUM version, the cost incurred to a vertex is the sum of distances between the vertex and other vertices. We prove that in both versions pure Nash equilibria exist, but the problem of finding the... 

Contact modeling plays a central role in motion planning, simulation and control of legged robots, as legged locomotion is realized through contact. The two prevailing approaches to model the contact consider rigid and compliant premise at interaction ports. Contrary to the dynamics model of legged systems with rigid contact (without impact) which is straightforward to develop, there is no consensus among researchers to employ a standard compliant contact model. Our main goal in this paper is to study the dynamics model structure of bipedal walking systems with rigid contact and a novel compliant contact model, and to present experimental validation of both models. For the model with rigid... 

Electric power systems are typically operated at least cost subject to technical and reliability constraints. This paper presents a probabilistic approach for risk evaluation in competitive electricity market scheduling. A competitive structure is proposed which includes a purchasing agency with centrally optimized scheduling (MaxISO structure). Spinning and non-spinning reserves are considered in the proposed approach. The value of unit commitment risk is deduced from the generation model. The required generation model is constructed using the outage replacement rate (ORR) of units. The load forecast uncertainty is included in operational risk evaluation. This is due to the increased... 

Since the discovery of inertial focusing in 1961, numerous theories have been put forward to explain the migration of particles in inertial flows, but a complete understanding is still lacking. Recently, computational approaches have been utilized to obtain better insights into the underlying physics. In particular, fundamental aspects of particle focusing inside straight and curved microchannels have been explored in detail to determine the dependence of focusing behavior on particle size, channel shape, and flow Reynolds number. In this review, we differentiate between the models developed for inertial particle motion on the basis of whether they are semi-analytical, Navier-Stokes-based,... 

In this research, the effect of different amounts of Cr2O3 (2.5, 5, 7.5, and 10 wt.%) and sintering temperature (1850, 1900, and 1950 °C) on the sinterability and mechanical properties of liquid-phase sintered SiC-matrix composites was studied. First, raw materials were ground for 3 h using a planetary mill whose rotational speed was 180 rpm. The process of pressing the samples was completed using uniaxial pressing with the applied pressure of 90 MPa. Finally, the samples were sintered under an argon atmosphere at various temperatures for 1.5 h. In the end, the best sintered sample was annealed at 2000°C for 2 h. The phases, microstructure, and chemical composition of the samples were... 

Assume that we are given a set of points some of which are black and the rest are white. The goal is to find a set of convex polygons with maximum total area that cover all white points and exclude all black points. We study the problem on three different settings (based on overlapping between different convex polygons): (1) In case convex polygons are permitted to have common area, we present a polynomial algorithm. (2) In case convex polygons are not allowed to have common area but are allowed to have common vertices, we prove the NP-hardness of the problem and propose an algorithm whose output is at least (Formula presented.). (3) Finally, in case convex polygons are not allowed to have... 

Let G be a graph of order n. For every v ∈ V (G), let EG(v) denote the set of all edges incident with v. A signed k-matching of G is a function f : E(G) −→ {−1, 1}, satisfying f(EG(v)) ≤ 1 for at least k vertices, where f(S) = ∑e∈S f(e), for each S ⊆ E(G). The maximum of the values of f(E(G)), taken over all signed k-matchings f of G, is called the signed k-matching number and is denoted by βk S (G). In this paper, we prove that for every graph G of order n and for any positive integer k ≤ n, βk S (G) ≥ n −k −ω(G), where w(G) is the number of components of G. This settles a conjecture proposed by Wang. Also, we present a formula for the computation of βn S(G)  

As elastic optical networks (EONs) are expected to convey high bitrate connections, a failure in these networks causes vast data losses. Thus, addressing the problem of survivability in EONs is of great importance. In this paper, survivability of an EON with multiclass traffic is investigated, where each traffic type needs specific protection mechanism and scheduling strategy. In particular, a connection request may demand for dedicated path protection, shared backup path protection, or restoration mechanism. Besides, it can tolerate a pre-determined delay and be scheduled at future time slots, referred to as advance reservation, or must be served immediately without any delay, referred to...