Sharif Digital Repository

For a simple polygon P of size n, we define weak visibility counting problem (WVCP) as finding the number of visible segments of P from a query line segment pq. We present different algorithms to compute WVCP in sub-linear time. In our first algorithm, we spend O(n7) time to preprocess the polygon and build a data structure of size O(n6), so that we can optimally answer WVCP in O(logn) time. Then, we reduce the preprocessing costs to O(n4+ε) time and space at the expense of more query time of O(log5n). We also obtain a trade-off between preprocessing and query time costs. Finally, we propose an approximation method to reduce the preprocessing costs to O(n2) time and space and O(n1/2+ε) query... 

In estimating an unknown parameter of a quantum state the quantum Fisher information (QFI) is a pivotal quantity, which depends on the state and its derivate with respect to the unknown parameter. We prove the continuity property for the QFI in the sense that two close states with close first derivatives have close QFIs. This property is completely general and irrespective of dynamics or how states acquire their parameter dependence and also the form of parameter dependence-indeed this continuity is basically a feature of the classical Fisher information that in the case of the QFI naturally carries over from the manifold of probability distributions onto the manifold of density matrices. We... 

In this paper, the design and optimization of a wideband THz metamaterial absorber (MMA) are proposed. By simulation, we reached four structures with absorptions higher than 50%, 70%, 80%, and 90%, with relative absorption bandwidths (RABWs) of 1.43, 1.29, 0.93, and 0.72, respectively. Terahertz absorbers can be used in many potential applications, such as in imaging, energy harvesting, scattering reduction, and thermal sensing. Our intended application was to use the optimal absorber on a thermal detector for detectivity over a wide THz range. Since broadband absorption in the range of 0.3 to 2 terahertz is considered for use in medical imaging, the MMA with more than 50% absorption in the... 

In the present study, hardness and tribological properties of nanostructured copper reinforced with SiC nanoparticles of various volume fractions (0, 2, 4, and 6 vol%) were investigated. The nanocomposites were fabricated by high-energy mechanical milling and hot pressing method. The Cu-SiC nanocomposites showed enhanced hardness and wear resistance against WC counterface. The hardness and wear resistance of the nanocomposite increased with increasing the amount of SiC nanoparticles up to 2 vol% in the matrix, but they decreased at higher percentages of SiC (4 and 6 vol%). Flake formation-spalling and abrasion were identified as the predominant wear mechanisms. It was found that reducing the... 

Hybrid Cu-SiC composites have been highly considered in order to achieve a combination of electrical and thermal properties along with high strength and wear resistance. However, limited investigations have ever been conducted over the effects of using hybrid (combination of nano and micro size) particles on the wear resistance behavior of these composites. Hence, in the present study, Cu-SiC nanocomposite with 4 vol% nanosize and 4 vol% microsize SiC, and Cu-SiC microcomposite with 8 vol% micro- SiC were fabricated through mechanical milling and hot pressing process. Results revealed the homogeneous dispersion of SiC particles in the matrix, high densification, and ultrafine-grain matrix... 

Hybrid Cu-SiC composites have been highly considered in order to achieve a combination of electrical and thermal properties along with high strength and wear resistance. However, limited investigations have ever been conducted over the effects of using hybrid (combination of nano and micro size) particles on the wear resistance behavior of these composites. Hence, in the present study, Cu-SiC nanocomposite with 4 vol% nanosize and 4 vol% microsize SiC, and Cu-SiC microcomposite with 8 vol% micro- SiC were fabricated through mechanical milling and hot pressing process. Results revealed the homogeneous dispersion of SiC particles in the matrix, high densification, and ultrafine-grain matrix... 

Using flake powder metallurgy (FPM) technique, combined with high pressure torsion, super high strength-ductile Cu-CNT nanocomposite with high electrical conductivity is developed. The nanocomposite with 4 vol% CNT showed high tensile strength of ~474 MPa, high electrical conductivity of ~82.5% IACS as well as appreciable ductility of ~11%. According to microstructural studies, the excellent properties of the nanocomposite are attributed to the formation of trimodal grains, high density of twin and low angle grain boundaries, improvement in CNT and Cu interfacial bonding, and appropriate distribution and maintaining the microstructure of the nanotubes in the production process. The results... 

We show how a recent experiment of quantum imaging with undetected photons can basically be described as an (a partial) ancilla-assisted process tomography in which the object is described by an amplitude-damping quantum channel. We propose a simplified quantum circuit version of this scenario, which also enables one to recast quantum imaging in quantum computation language. Our analogy and analysis may help us to better understand the role of classical and/or quantum correlations in imaging experiments. © 2016 American Physical Society  

The application of agricultural fibers for making particleboards has been studied in two types of composites: (i) type I particleboards were composites of wheat straw and rice husk fibers with polymeric methylene di-phenyl diisocyanate resin (pMDI) as a binder made by compression moulding; (ii) type II particleboards were composites of rice husk and polypropylene made by extrusion and injection moulding. In type I particleboards, the effects of varying the resin content and various combinations of wheat straw/rice husk fibers were investigated and characterised in terms of physical and mechanical properties of particle boards such as modulus of rupture, modulus of elasticity, compression... 

Various challenging pollutants are produced in the environment by organic materials of diverse industries including leather, paint, and textile. Nowadays, it is vital to develop efficient manners regarding the fundamental issues and removing pollutants. Such pollutants can be effectively removed from the environment through heterogeneous catalysts. Recently, a huge deal of interest has been attracted by hydrogel-based metal catalysts as heterogeneous and efficient catalysts. In this regard, silver with its unique features is suitable for environmental remediation. Hence, the present review deals with summarizing the present advances in the synthesis of silver-based hydrogel catalysts, as... 

Kresling is one of the most well-known and widely-used origami patterns. Its outstanding features, such as deployability, bistability, and coupled extensional-rotational motion, have attracted considerable attention from many engineering applications, including aerospace structures. In this research, three approaches for the geometrical design of Kresling modules are investigated and their capabilities are compared. The first two approaches are based on the quasi-static analysis. The third one is an analytical approach focusing on the frequently-used type of Kresling module with two zero-energy stable states. Moreover, based on the number of stable configurations, the amount of potential... 

Fused Deposition Modeling with Polypropylene filament was employed to make a lap joint between Polypropylene and pre-punched Al-Mg alloy sheets, in the form of bonds between the polymeric substrate and the additive part and mechanical lock between the additive part and aluminum base sheet. Effects of the joint interface area (hole diameter of 5–13 mm) and preheating of the substrates (room temperature, 50 and 90℃) were investigated on the mechanical properties of the joints. Peak load in the tensile-shear and cross-tension tests increased with enhancement of the joint interface area (up to ˜280 N and ˜160 N, respectively). Higher joint strength in the tensile-shear test compared to the... 

Using the matrix product formalism, we find exact ground states for two new spin-(1/2) and spin-(3/2) quantum chains. On a lattice of 3N sites, these ground states have a total spin of N/2, and hence have ferrimagnetic character. The novel point of this construction is that we construct a matrix product representation, not for a state which is invariant under rotation as has been hitherto considered, but for a state which transforms to other states under this symmetry operation. The method can be directly generalized to other symmetry groups. © Europhysics Letters Association  

In this research, full density, single phase microstructure (in the XRD and SEM detection limits), and fine-grained SnO2 varistors with an average grain size of 0.65 μm was acquired at low temperature by the two-step sintering technique. The sintering temperature was successfully decreased from 1300 °C in the normal sintering to 1150 °C and 1100 °C of respectively the first and the second stage in the two-step sintering. The mechanism of grain growth suppression of the two-step sintered samples was discussed and it was suggested that in addition to triple point junction, solute drag and/or nano-secondary phases contribute to cease the grain growth. These SnO2 varistors exhibited ultra-high... 

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  

The problem of finding necessary and sufficient conditions to decompose a complete tripartite graph K(r, s, t) into 5-cycles was first considered by Mahmoodian and Mirzakhani (1995). They stated some necessary conditions and conjectured that these conditions are also sufficient. Since then, many cases of the problem have been solved by various authors; however the case when the partite sets r ≤ s ≤ t have odd and distinct sizes remains open. A necessary condition is t ≤ 3r. Billington and Cavenagh (2011) have shown that when r, s, and t are all odd and r ≤ s ≤ t ≤ κr, where κ ≈ 1.0806, then the conjectured necessary conditions for decomposing are also sufficient. We extend this result... 

Shape memory hydrogels attract increasing attention as flexible strain sensors due to their shape recovery property that can improve the lifetime of the sensor. Herein, we have designed a magnetic shape memory hydrogel based on Fe3O4 nanoparticles, carrageenan, and poly (acrylamide-co-acrylic acid) with self-adhesive and conductive properties. The resulting double network hydrogel showed promising actuator and strain sensor applications. Electrical conductivity was observed in this hydrogel without using additional ions. The presence of magnetite nanoparticles increased the tensile strength and temporary shape fixity ratio to around 6.5 MPa and 94.3 %, respectively. The excellent cantilever... 

In this paper we investigated the structural properties of the ultra high voltage power transmission network of Iran. We modeled the power grid as a network with 105 nodes and 142 connection links. We found that the Iranian power grid displays a relatively moderate clustering coefficient-much larger than that of corresponding random networks-and small characteristics path length comparable to that of corresponding random networks; i.e. the power grid is a small-world network with exponential degree distribution. Global efficiency was considered as an indicator of grid's performance and the influence of random and intentional nodal failures on the efficiency was investigated. We also studied... 

Given a terrain and a query point p on or above it, we want to count the number of triangles of terrain that are visible from p. We present an approximation algorithm to solve this problem. We implement the algorithm and then we run it on the real data sets. The experimental results show that our approximation solution is very close to the real solution and compare to the other similar works, the running time of our algorithm is better than their algorithm. The analysis of time complexity of algorithm is also presented. Also, we consider visibility testing problem, where the goal is to test whether p and a given triangle of train are visible or not. We propose an algorithm for this problem... 

For a set of n disjoint line segments S in R2, the visibility testing problem (VTP) is to test whether the query point p sees a query segment s∈S. For this configuration, the visibility counting problem (VCP) is to preprocess S such that the number of visible segments in S from any query point p can be computed quickly. In this paper, we solve VTP in expected logarithmic query time using quadratic preprocessing time and space. Moreover, we propose a (1+δ)-approximation algorithm for VCP using at most quadratic preprocessing time and space. The query time of this method is Oε (1/δ 2√n) where Oε (f(n))=O(f(n)nε) and ε>0 is an arbitrary constant number