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A direct method for acoustic impedance measurement based on the measurement of electrical impedance of acoustic transmitter
, Article Applied Acoustics ; Vol. 77, Issue. 1 , 2014 , pp. 76-81 ; ISSN: 0003-682X ; Bakhtiar, M. S ; Sharif University of Technology
2014
Abstract
A simple and straight forward method for acoustic impedance measurement is presented and evaluated. In this method a speaker is used as the signal source. The relationship between the electrical impedance of the speaker and its acoustical load is developed and studied. It is shown that the electrical current and voltage of the speaker relate to the acoustical pressure and volume velocity. The mechanical and acoustical impedances are therefore easily derived by measuring the electrical current and voltage of the circuit. The proposed method yield itself to the automatic computer measurement and can be used for the field and in situ measurements. Comparison of the measurement data with those...
Leak detection in water-filled plastic pipes through the application of tuned wavelet transforms to Acoustic Emission signals
, Article Applied Acoustics ; Volume 71, Issue 7 , 2010 , Pages 634-639 ; 0003682X (ISSN) ; Sharif Bakhtiar, M ; Sharif University of Technology
2010
Abstract
A new method to detect leakage in a water-filled plastic pipe is proposed. In this method, a leakage signal-signature in time domain is first captured by monitoring the Short Time Fourier Transforms (STFT) of AE (Acoustic Emission) signals over a relatively long time-interval. The captured signal is then used to find a mother wavelet (tuned wavelet) for the best signal localization in time and frequency domains. The technique for AE signal detection using tuned wavelet is then described. Practical application of the method proposed herein is then presented using a water-filled plastic pipe as a case study. Signals generated from this experimental setup are collected to identify leakage...
Is there any polynomial upper bound for the universal labeling of graphs?
, Article Journal of Combinatorial Optimization ; 2016 , Pages 1-11 ; 13826905 (ISSN) ; Dehghan, A ; Saghafian, M ; Sharif University of Technology
Springer New York LLC
2016
Abstract
A universal labeling of a graph G is a labeling of the edge set in G such that in every orientation (Formula presented.) of G for every two adjacent vertices v and u, the sum of incoming edges of v and u in the oriented graph are different from each other. The universal labeling number of a graph G is the minimum number k such that G has universal labeling from (Formula presented.) denoted it by (Formula presented.). We have (Formula presented.), where (Formula presented.) denotes the maximum degree of G. In this work, we offer a provocative question that is: “Is there any polynomial function f such that for every graph G, (Formula presented.)?”. Towards this question, we introduce some...
Algorithmic complexity of weakly semiregular partitioning and the representation number
, Article Theoretical Computer Science ; 2017 ; 03043975 (ISSN) ; Dehghan, A ; Mollahajiaghaei, M ; Sharif University of Technology
Elsevier B.V
2017
Abstract
A graph G is weakly semiregular if there are two numbers a,b, such that the degree of every vertex is a or b. The weakly semiregular number of a graph G, denoted by wr(G), is the minimum number of subsets into which the edge set of G can be partitioned so that the subgraph induced by each subset is a weakly semiregular graph. We present a polynomial time algorithm to determine whether the weakly semiregular number of a given tree is two. On the other hand, we show that determining whether wr(G)=2 for a given bipartite graph G with at most three numbers in its degree set is NP-complete. Among other results, for every tree T, we show that wr(T)≤2log2 δ(T)+O(1), where δ(T) denotes the maximum...
Algorithmic complexity of weakly semiregular partitioning and the representation number
, Article Theoretical Computer Science ; Volume 674 , 2017 , Pages 60-72 ; 03043975 (ISSN) ; Dehghan, A ; Mollahajiaghaei, M ; Sharif University of Technology
Elsevier B.V
2017
Abstract
A graph G is weakly semiregular if there are two numbers a,b, such that the degree of every vertex is a or b. The weakly semiregular number of a graph G, denoted by wr(G), is the minimum number of subsets into which the edge set of G can be partitioned so that the subgraph induced by each subset is a weakly semiregular graph. We present a polynomial time algorithm to determine whether the weakly semiregular number of a given tree is two. On the other hand, we show that determining whether wr(G)=2 for a given bipartite graph G with at most three numbers in its degree set is NP-complete. Among other results, for every tree T, we show that wr(T)≤2log2Δ(T)+O(1), where Δ(T) denotes the maximum...
Is there any polynomial upper bound for the universal labeling of graphs?
, Article Journal of Combinatorial Optimization ; Volume 34, Issue 3 , 2017 , Pages 760-770 ; 13826905 (ISSN) ; Dehghan, A ; Saghafian, M ; Sharif University of Technology
2017
Abstract
A universal labeling of a graph G is a labeling of the edge set in G such that in every orientation ℓ of G for every two adjacent vertices v and u, the sum of incoming edges of v and u in the oriented graph are different from each other. The universal labeling number of a graph G is the minimum number k such that G has universal labeling from { 1 , 2 , … , k} denoted it by χu→ (G). We have 2 Δ (G) - 2 ≤ χu→ (G) ≤ 2 Δ ( G ), where Δ (G) denotes the maximum degree of G. In this work, we offer a provocative question that is: “Is there any polynomial function f such that for every graph G, χu→ (G) ≤ f(Δ (G)) ?”. Towards this question, we introduce some lower and upper bounds on their parameter...
On the Complexity of Deciding Whether the Regular Number is at Most Two
, Article Graphs and Combinatorics ; Volume 31, Issue 5 , September , 2014 , pp 1359-1365 ; ISSN: 09110119 ; Sadeghi, M. R ; Ahadi, A ; Sharif University of Technology
2014
Abstract
The regular number of a graph (Formula presented.) denoted by (Formula presented.) is the minimum number of subsets into which the edge set of (Formula presented.) can be partitioned so that the subgraph induced by each subset is regular. In this work we answer to the problem posed as an open problem in Ganesan et al. (J Discrete Math Sci Cryptogr 15(2-3):49-157, 2012) about the complexity of determining the regular number of graphs. We show that computation of the regular number for connected bipartite graphs is NP-hard. Furthermore, we show that, determining whether (Formula presented.) for a given connected (Formula presented.)-colorable graph (Formula presented.) is NP-complete. Also, we...
Conductor-insulator transition and electronic structure of Ca-doped BiFeO 3 films
, Article Materials Letters ; Volume 83 , 2012 , Pages 124-126 ; 0167577X (ISSN) ; Nemati, A ; Mahdavi, S. M ; Sharif University of Technology
Elsevier
2012
Abstract
The electronic conductor-insulator transition in Ca-doped BiFeO 3 films grown by pulsed-laser deposition technique has been investigated. Nature of the transition is resolved to be Mott type through the control of band-filling. Calcium resolved to have colossal effect on enhancing the electrical conductivity of BiFeO 3, but it did not affect band gap of the mother phase perceptibly. UV-visible study yielded band gap of 2.72-2.81 eV (at 300 K) for different concentrations of calcium. Both UV-visible and photoluminescence spectra revealed sub-band gap transitions at 2.17 and 2.38 eV, of which the latter might be ascribed to the oxygen vacancies
Effect of chemical substitution on the morphology and optical properties of Bi1-xCaxFeO3 films grown by pulsed-laser deposition
, Article Journal of Materials Science: Materials in Electronics ; Volume 24, Issue 1 , 2013 , Pages 248-252 ; 09574522 (ISSN) ; Mahdavi, S. M ; Nemati, A ; Sharif University of Technology
2013
Abstract
The morphological characteristics as well the optical properties of Ca-doped BiFeO3 films grown by pulsed-laser deposition technique have been investigated. AFM images revealed that calcium has a radical effect on the surface features of BiFeO3 films. By utilizing spectrophotometer, transmission behaviour of the films was investigated. Local IV characteristics of the films disclosed about three orders of magnitude enhancement concerning electrical conductivity through Ca doping. X-ray photoelectron spectroscopy results revealed that Ca can reduce the valence state of iron in the compound
Algorithmic complexity of proper labeling problems
, Article Theoretical Computer Science ; Volume 495 , 2013 , Pages 25-36 ; 03043975 (ISSN) ; Sadeghi, M. R ; Ahadi, A ; Sharif University of Technology
2013
Abstract
A proper labeling of a graph is an assignment of integers to some elements of a graph, which may be the vertices, the edges, or both of them, such that we obtain a proper vertex coloring via the labeling subject to some conditions. The problem of proper labeling offers many variants and received a great interest during recent years. We consider the algorithmic complexity of some variants of the proper labeling problems, we present some polynomial time algorithms and NP-completeness results for them
Not-all-equal and 1-in-degree decompositions: Algorithmic complexity and applications
, Article Algorithmica ; Volume 80, Issue 12 , 2018 , Pages 3704-3727 ; 01784617 (ISSN) ; Sadeghi, M. R ; Ahadi, A ; Sharif University of Technology
Springer New York LLC
2018
Abstract
A Not-All-Equal decomposition of a graph G is a decomposition of the vertices of G into two parts such that each vertex in G has at least one neighbor in each part. Also, a 1-in-Degree decomposition of a graph G is a decomposition of the vertices of G into two parts A and B such that each vertex in the graph G has exactly one neighbor in part A. Among our results, we show that for a given graph G, if G does not have any cycle of length congruent to 2 mod 4, then there is a polynomial time algorithm to decide whether G has a 1-in-Degree decomposition. In sharp contrast, we prove that for every r, r≥ 3 , for a given r-regular bipartite graph G determining whether G has a 1-in-Degree...
Photoconductivity and diode effect in Bi rich multiferroic BiFeO 3 thin films grown by pulsed-laser deposition
, Article Journal of Materials Science: Materials in Electronics ; Volume 22, Issue 7 , 2011 , Pages 815-820 ; 09574522 (ISSN) ; Mahdavi, S. M ; Nemati, A ; Kianinia, M ; Sharif University of Technology
2011
Abstract
Bismuth ferrite, BiFeO 3, is almost the only material that is simultaneously magnetic and a strong ferroelectric at room temperature. As a result it is the most investigated multiferroic material. In this study, bismuth ferrite thin films were deposited on silicon wafer (100) and glass by pulsed-laser deposition and their structural, optical, and electrical properties were measured. Our study indicates that Bi richness in these films can stimulate formation of oxygen vacancy in the system which in its turn leads to delocalization of carriers and a more intensified photoconductivity response. X-ray diffraction analysis revealed formation of BiFeO 3 (BFO), but it also showed formation of Bi 2O...
Electronic structure and morphological study of BaTiO 3 film grown by pulsed-laser deposition
, Article Materials Letters ; Volume 72 , April , 2012 , Pages 107-109 ; 0167577X (ISSN) ; Mahdavi, S. M ; Nemati, A ; Tabesh, M ; Ranjbar, M ; Sharif University of Technology
2012
Abstract
The morphological characteristics and electronic structure of the BaTiO 3 films grown by pulsed-laser deposition technique have been investigated. AFM and FE-SEM images reveal columnar growth characteristic of these films. Utilizing spectrophotometer, optical band gap of the films were reckoned to be about 3.76 eV. Both dα/dE and PL vs. E plots reveal numerous luminance states in the gap. Despite the presence of many luminance faults in the gap, cations manage to preserve their electronic states
Robust multiplicative patchwork method for audio watermarking
, Article IEEE Transactions on Audio, Speech and Language Processing ; Volume 17, Issue 6 , 2009 , Pages 1133-1141 ; 15587916 (ISSN) ; Akhaee, M. A ; Ahadi, M ; Amindavar, H ; Sharif University of Technology
2009
Abstract
This paper presents a Multiplicative Patchwork Method (MPM) for audio watermarking. The watermark signal is embedded by selecting two subsets of the host signal features and modifying one subset multiplicatively regarding the watermark data, whereas another subset is left unchanged. The method is implemented in wavelet domain and approximation coefficients are used to embed data. In order to have an error-free detection, the watermark data is inserted only in the frames where the ratio of the energy of subsets is between two predefined values. Also in order to control the inaudibility of watermark insertion, we use an iterative algorithm to reach a desired quality for the watermarked audio...
Computation of lucky number of planar graphs is NP-hard
, Article Information Processing Letters ; Volume 112, Issue 4 , February , 2012 , Pages 109-112 ; 00200190 (ISSN) ; Dehghan, A ; Kazemi, M ; Mollaahmadi, E ; Sharif University of Technology
2012
Abstract
A lucky labeling of a graph G is a function l:V(G)→N, such that for every two adjacent vertices v and u of G, σ w∼vl(w)≠ σ w∼ul(w) (x∼y means that x is joined to y). A lucky number of G, denoted by η(G), is the minimum number k such that G has a lucky labeling l:V(G)→{1,⋯,k}. We prove that for a given planar 3-colorable graph G determining whether η(G)=2 is NP-complete. Also for every k≥2, it is NP-complete to decide whether η(G)=k for a given graph G
On the difference between chromatic number and dynamic chromatic number of graphs
, Article Discrete Mathematics ; Volume 312, Issue 17 , September , 2012 , Pages 2579-2583 ; 0012365X (ISSN) ; Akbari, S ; Dehghan, A ; Ghanbari, M ; Sharif University of Technology
Elsevier
2012
Abstract
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
Audio watermarking based on quantization index modulation in the frequency domain
, Article 2007 IEEE International Conference on Signal Processing and Communications, ICSPC 2007, Dubai, 14 November 2007 through 27 November 2007 ; 2007 , Pages 1127-1130 ; 9781424412365 (ISBN) ; Akhaee, M. A ; Ahadi, S. M ; Moradi, M ; Kashi, A ; Sharif University of Technology
2007
Abstract
In this paper, our main purpose is to embed data in the frequency domain of audio signals. Data was embedded by means of Quantization Index Modulation (QIM) in the frequency domain. With this aim, the spectrum of the audio signal was divided into two parts. The first part consisted of the first 19 Barks and the second included the remaining 6 Barks. Each of these parts had a different quantization step size. In order to have large quantization step sizes which yield more robustness, Human Auditory System (HAS) has been used. Decoder detects the watermark signal, without using the original audio signal. Simulation results have shown that this watermarking scheme has better robustness against...
Robust multiplicative patchwork method for audio watermarking
, Article DSP 2009:16th International Conference on Digital Signal Processing, Santorini, 5 July 2009 through 7 July 2009 ; 2009 ; 9781424432981 (ISBN) ; Akhaee, M. A ; Ahadi, M ; Amindavar, H. R ; Sharif University of Technology
2009
Abstract
A Multiplicative Patchwork Method (MPM) for audio watermarking is proposed in this paper. In order to embed watermark data within the host signal, two subsets of the host signal features are selected using two secret keys. Then, watermark data is inserted simply by multiplying one subset and leaving the other one unchanged. In order to have an error free detection in attack-free case, embedding is performed in the selected frames of the host signal which satisfies a certain condition. This method is implemented in the wavelet domain and approximation coefficients are used for data embedding. Furthermore, the inaudibility of watermark insertion is controlled using iterative approach aided by...
Silver Block Intersection Graphs of Steiner 2-Designs
, Article Graphs and Combinatorics ; Volume 29, Issue 4 , 2013 , Pages 735-746 ; 09110119 (ISSN) ; Besharati, N ; Mahmoodian, E. S ; Mortezaeefar, M ; Sharif University of Technology
2013
Abstract
For a block design D, a series of block intersection graphs G i, or i-BIG(D), i = 0,..., k is defined in which the vertices are the blocks of D, with two vertices adjacent if and only if the corresponding blocks intersect in exactly i elements. A silver graph G is defined with respect to a maximum independent set of G, called an α-set. Let G be an r-regular graph and c be a proper (r + 1)-coloring of G. A vertex x in G is said to be rainbow with respect to c if every color appears in the closed neighborhood N[x] = N(x) ∪ {x}. Given an α-set I of G, a coloring c is said to be silver with respect to I if every x ∈ I is rainbow with respect to c. We say G is silver if it admits a silver...
Effect of iron oxide and silica doping on microstructure, bandgap and photocatalytic properties of titania by water-in-oil microemulsion technique
, Article Transactions of the Indian Ceramic Society ; Volume 70, Issue 4 , Jan , 2011 , Pages 227-232 ; 0371750X (ISSN) ; Nemati, A ; Zari, M. H ; Ahadi, K ; Sharif University of Technology
2011
Abstract
The microemulsion method was successfully used to prepare a series of TiO2, Fe oxide and SiO2 doped TiO2 nanoparticles at Fe/Ti atomic ratio of 10% and Si/Ti atomic ratio of 15%. The molar ratio of water to surfactant (W0) was 2. The samples were calcinated at 350°C. The structural features of TiO2, Fe oxide and SiO 2-TiO2 were investigated by XRD, UV-Visible spectroscopy, SEM and TEM. XRD data verified the formation of typical characteristic anatase form in all the prepared Fe and SiO2-doped TiO2 samples. In comparison with the pure TiO2, Fe oxide and SiO 2-TiO2 samples were relatively large in particle size, indicating that doping with Fe oxide and SiO2 can help in increasing the particle...