Sharif Digital Repository

In this paper, we consider a special version of the well-known line-simplification problem for simplifying the boundary of a region illuminated by a point light source q, or its visibility polygon VP(q). In this simplification approach, we should take the position of q as an essential factor into account to determine the quality of the resulting simplification. For this purpose, we redefine the known distance- and area-distortion error criteria as the main simplification criteria to take into account the distance between the observer q and the boundary of VP(q). Based on this, we propose algorithms for simplifying VP(q). More precisely, we propose simplification algorithms of O(n2) and... 

We consider a planar gravitating thick domain wall of the λφ4 theory as a space-time with finite thickness glued to two vacuum space-times on each side of it. Darmois junction conditions written on the boundaries of the thick wall with the embedding space-times reproduce the Israel junction condition across the wall in the limit of infinitesimal thickness. The thick planar domain wall located at a fixed position is then transformed to a new coordinate system in which its dynamics can be formulated. It is shown that the wall's core expands as if it were a thin wall. The thickness in the new coordinates is not constant anymore and its time dependence is given. © World Scientific Publishing... 

In this paper, a comparison between several array geometries, including planar arrays and volume arrays, for two-dimensional Direction of Arrival (DOA) estimation using Multiple Signal Classification (MUSIC) is presented. For each geometry, various criteria is taken into consideration and a comparative study of the performance of geometries is carried out. The geometries together with their ultimate direction finding performance are compared based on Root Mean Square Error (RMSE), the ambiguity functions, and Cramer-Rao Bounds (CRB). Furthermore, the effects of phase and amplitude variations of the array element radiation pattern, namely Vivaldi and Monopole antenna, on DOA estimation... 

Let R be a ring with nonzero identity. The unit graph of R, denoted by G(R), has its set of vertices equal to the set of all elements of R; distinct vertices x and y are adjacent if and only if x + y is a unit of R. In this article, the basic properties of G(R) are investigated and some characterization results regarding connectedness, chromatic index, diameter, girth, and planarity of G(R)are given. (These terms are defined in Definitions and Remarks 4.1, 5.1, 5.3, 5.9, and 5.13.)  

A graph G is called uniquelyk-list colorable (UkLC) if there exists a list of colors on its vertices, say L= { Sv∣ v∈ V(G) } , each of size k, such that there is a unique proper list coloring of G from this list of colors. A graph G is said to have propertyM(k) if it is not uniquely k-list colorable. Mahmoodian and Mahdian (Ars Comb 51:295–305, 1999) characterized all graphs with property M(2). For k≥ 3 property M(k) has been studied only for multipartite graphs. Here we find bounds on M(k) for graphs embedded on surfaces, and obtain new results on planar graphs. We begin a general study of bounds on M(k) for regular graphs, as well as for graphs with varying list sizes. © 2018, Springer... 

Let Γ(R) be the zero-divisor graph of a commutative ring R. An interesting question was proposed by Anderson, Frazier, Lauve, and Livingston: For which finite commutative rings R is Γ (R) planar? We give an answer to this question. More precisely, we prove that if R is a local ring with at least 33 elements, and Γ(R) ≠ 0, then Γ(R) is not planar. We use the set of the associated primes to find the minimal length of a cycle in Γ(R). Also, we determine the rings whose zero-divisor graphs are complete r-partite graphs and show that for any ring R and prime number p, p ≥ 3, if Γ(R) is a finite complete p-partite graph, then Z(R) = p2, R = p3, and R is isomorphic to exactly one of the rings ℤp3,... 

Using Hamilton's principle, exact equations of motion for non-linear planar and spatial Euler-Bernoulli beams are derived. In the existing non-linear Euler-Bernoulli beam formulations, some elastic terms are dropped by differentiation from the incomplete Green-Lagrange strain tensor followed by negligible elastic deformations of cross-sectional frame. On the other hand, in this article, the exact strain field concerning considerable elastic deformations of cross-sectional frame is used as a source in differentiations. As a result, the achieved closed-form equations are exact and more accurate than formerly reported equations in the literature. Moreover, the applicable dynamic model of... 

In this work, we study a kind of manipulation process during which we deal with active objects. An active object is a concept covering a variety of objects that are not rigid and need to be controlled during the manipulation process. Here, we use a multi-link mechanism with active motors (actuator) as the object and a series of simple planar manipulators to perform the manipulation process. Dynamic, control, motion planning, and stability at the presence of impact are the most important challenges in this work  

In this paper, we propose a method for maintaining the region visible from a moving point observer inside a planar scene. In this method, we check the observer position in discrete time-stamps to detect and apply changes to the visible or illuminated region of a moving point observer q, or VP(q). We efficiently maintain a list C(q) of edges in VP(q) which are subject to change during the motion. In each time-stamp that VP(q) is to be updated, we only refine and redraw the view against the edges of C(q) that indicate the positions of the visibility changes. We build an enriched representation of the visibility graph in a preprocessing step to apply the required updates on C(q) efficiently and... 

Here in this research, a modified interface between the electron transport layer (ETL) and the perovskite layer in a perovskite solar cell (PSC) is provided by adding the ammonium chloride (NH4Cl) to the tin oxide (SnO2) as the modified ETL of a planar structure as follows: fluorine-doped tin oxide (FTO)/NH4Cl-SnO2/Mixed cation perovskite/Copper indium disulfide (CIS)/Gold (Au). The effects of NH4Cl on ETL are investigated in different amounts from 0.003 to 0.02 M and the best results were obtained in the amount of 0.013 M. The best NH4Cl-SnO2 ETL could increase the power conversion efficiency (PCE) of fabricated planar PSC by 16.79% with open-circuit voltage (Voc) of 1.15 V and negligible... 

We introduce the concept of local spanners for planar point sets with respect to a family of regions, and prove the existence of local spanners of small size for some families. For a geometric graph G on a point set P and a region R belonging to a family R, we define G∩ R to be the part of the graph G that is inside R (or is induced by R). A local t-spanner w.r.t R is a geometric graph G on P such that for any region R∈ R, the graph G∩ R is a t-spanner for K(P) ∩ R, where K(P) is the complete geometric graph on P. For any set P of n points and any constant ε> 0 , we prove that P admits local (1 + ε) -spanners of sizes O(nlog 6n) and O(nlog n) w.r.t axis-parallel squares and vertical slabs,... 

We introduce the concept of local spanners for planar point sets with respect to a family of regions, and prove the existence of local spanners of small size for some families. For a geometric graph G on a point set P and a region R belonging to a family R, we define G∩ R to be the part of the graph G that is inside R (or is induced by R). A local t-spanner w.r.t R is a geometric graph G on P such that for any region R∈ R, the graph G∩ R is a t-spanner for K(P) ∩ R, where K(P) is the complete geometric graph on P. For any set P of n points and any constant ε> 0 , we prove that P admits local (1 + ε) -spanners of sizes O(nlog 6n) and O(nlog n) w.r.t axis-parallel squares and vertical slabs,... 

This method introduces the structural error of regression deviation, which is an effective method for the path generation of a vast type of planar and spatial mechanism. The proposed method avoids point-by-point comparison and requirement of timing and reflects the difference between the two curves very effectively in the objective function. By decreasing the number of the design variables, this method would help considerably in decreasing CPU time. The objective function that is based on regression error would converge to a global minimum by a genetic algorithm. At the end, the effectiveness of the method is shown by two numerical examples. © Sharif University of Technology  

Here in this research, a modified interface between the electron transport layer (ETL) and the perovskite layer in a perovskite solar cell (PSC) is provided by adding the ammonium chloride (NH4Cl) to the tin oxide (SnO2) as the modified ETL of a planar structure as follows: fluorine-doped tin oxide (FTO)/NH4Cl-SnO2/Mixed cation perovskite/Copper indium disulfide (CIS)/Gold (Au). The effects of NH4Cl on ETL are investigated in different amounts from 0.003 to 0.02 M and the best results were obtained in the amount of 0.013 M. The best NH4Cl-SnO2 ETL could increase the power conversion efficiency (PCE) of fabricated planar PSC by 16.79% with open-circuit voltage (Voc) of 1.15 V and negligible... 

A multiple input multiple output (MIMO) radar system is an emerging research field which has attracted many studies in recent years. This type of radar, unlike conventional phased array radar, can transmit different probing signals via its antennas, that may be correlated or uncorrelated with each other. This waveform diversity offered by MIMO radar systems enable superior capabilities compared to conventional phased array radar. Many papers have introduced different ways for beamforming of MIMO radar. In this paper it is desirable to analysis some methods for beamforming of MIMO radars with planar arrays constellation and examine their 3D result beam-pattern of such constellations for... 

In this paper an approach was described for determination of direction of sliding block in rock slopes containing planar non-persistent open joints. For this study, several gypsum blocks containing planar non-persistent open joints with dimensions of 15?15?15 cm were build. The rock bridges occupy 45, 90 and 135 cm2 of total shear surface (225cm2 ), and their configuration in shear plane were different. From each model, two similar blocks were prepared and were subjected to shearing under normal stresses of 3.33 and 7.77 kg/cm-2 . Based on the change in the configuration of rock-bridges, a factor called the Effective Joint Coefficient (EJC) was formulated, that is the ratio of the effective... 

Hoffmann–Ostenhof's conjecture states that the edge set of every connected cubic graph can be decomposed into a spanning tree, a matching and a 2-regular subgraph. In this paper, we show that the conjecture holds for claw-free subcubic graphs and 4-chordal subcubic graphs. © 2020  

In this paper, we present a randomized LOCAL constant approximation factor algorithm for minimum dominating set (MDS) problem and minimum total dominating set (MTDS) problem in graphs. The approximation factor of this algorithm for planar graphs with no 4-cycles is 18 and 9 for MDS and MTDS problems, respectively. © 2020 Owner/Author  

In the Partial Vertex Cover (PVC) problem, we are given an n-vertex graph G and a positive integer k, and the objective is to find a vertex subset S of size k maximizing the number of edges with at least one end-point in S. This problem is W[1]-hard on general graphs, but admits a parameterized subexponential time algorithm with running time 2O(k)nO(1) on planar and apex-minor free graphs [Fomin et al. (FSTTCS 2009, IPL 2011)], and a kO(k)nO(1) time algorithm on bounded degeneracy graphs [Amini et al. (FSTTCS 2009, JCSS 2011)]. Graphs of bounded degeneracy contain many sparse graph classes like planar graphs, H-minor free graphs, and bounded tree-width graphs (see Fig. 1). In this work, we...