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A new distributional approach to signature change
, Article General Relativity and Gravitation ; Volume 32, Issue 2 , 2000 , Pages 253-269 ; 00017701 (ISSN) ; Nozari, K ; Sharif University of Technology
Kluwer Academic/Plenum Publishers
2000
Abstract
Colombeau's generalized functions are used to adapt the distributional approach to singular hypersurfaces in general relativity with signature change. Equations governing the dynamics of a singular hypersurface are derived and a specific non-vanishing form for the energy-momentum tensor of the singular hypersurface is obtained. It is shown that matching in the case of de Sitter space in the Lorentzian sector is possible along the boundary with minimum radius but leads to the vanishing of the energy-momentum tensor of the singular hypersurface
Nonlocal Lazer–McKenna-type problem perturbed by the Hardy’s potential and its parabolic equivalence
, Article Boundary Value Problems ; Volume 2021, Issue 1 , 2021 ; 16872762 (ISSN) ; Hesaaraki, M ; Karim Hamdani, M ; Thanh Chung, N ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2021
Abstract
In this paper, we study the effect of Hardy potential on the existence or nonexistence of solutions to the following fractional problem involving a singular nonlinearity: {(−Δ)su=λu|x|2s+μuγ+fin Ω,u>0in Ω,u=0in (RN∖Ω). Here 0 < s< 1 , λ> 0 , γ> 0 , and Ω ⊂ RN (N> 2 s) is a bounded smooth domain such that 0 ∈ Ω. Moreover, 0 ≤ μ, f∈ L1(Ω). For 0 < λ≤ Λ N,s, Λ N,s being the best constant in the fractional Hardy inequality, we find a necessary and sufficient condition for the existence of a positive weak solution to the problem with respect to the data μ and f. Also, for a regular datum of f, under suitable assumptions, we obtain some existence and uniqueness results and calculate the rate of...
The spherical symmetry black hole collapse in expanding universe
, Article International Journal of Modern Physics D ; Volume 21, Issue 4 , April , 2012 ; 02182718 (ISSN) ; Sharif University of Technology
Abstract
The spherical symmetry black holes are considered in expanding background. The singularity line and the marginally trapped tube surface behavior are discussed. In particular, we address the conditions whether dynamical horizon forms for these cosmological black holes. We also discuss about the cosmological constant effect on these black hole and the redshift of the light which comes from the marginally trapped tube surface
Impedance control of a two degree-of-freedom flexible link manipulator using singular perturbation and sliding mode control theory
, Article Proceedings of the 7th Biennial Conference on Engineering Systems Design and Analysis - 2004, Manchester, 19 July 2004 through 22 July 2004 ; Volume 1 , 2004 , Pages 851-860 ; 0791841731 (ISBN); 9780791841730 (ISBN) ; Vossoughi, G. R ; Sharif University of Technology
American Society of Mechanical Engineers
2004
Abstract
In this article, impedance control of a two link flexible link manipulators is addressed. The concept of impedance control of flexible link robots is rather new and is being addressed for the first time. Impedance Control provides a universal approach to the control of flexible robots - in both constrained and unconstrained maneuvers. The initial part of the paper concerns the use Hamilton's principle to derive the mathematical equations governing the dynamics of joint angles, vibration of the flexible links and the constraining forces. The approximate elastic deformations are then derived by means of the Assumed-Mode-Method (AMM). Using the singular perturbation method, the dynamic of the...
Singularity analysis of parallel manipulators using constraint plane method
, Article Mechanism and Machine Theory ; Volume 46, Issue 1 , 2011 , Pages 33-43 ; 0094114X (ISSN) ; Mahnama, M ; Zohoor, H ; Sharif University of Technology
Abstract
One of the most challenging problems in dealing with parallel manipulators is identifying their forward singular configurations. In such configurations these mechanisms become uncontrollable and cannot tolerate any external force. In this article a geometrical method, namely Constraint Plane Method (CPM), is introduced with the use of which one can easily obtain the singular configurations in many parallel manipulators. CPM is a methodical technique based on the famous Ceva plane geometry theorem. It is interesting to note that CPM involves no calculations and yields te result quickly. In addition, some of the previous geometrical methods led to many separate singular configurations;...
Quantum vacuum effects on the final fate of a collapsing ball of dust
, Article Journal of High Energy Physics ; Volume 2017, Issue 2 , 2017 ; 11266708 (ISSN) ; Noorikuhani, M ; Sharif University of Technology
Springer Verlag
2017
Abstract
We consider the quantum vacuum effects of the massless scalar fields that are non-minimally coupled to the background geometry of a collapsing homogeneous ball of dust. It is shown that for a definite range of coupling constants, there are repulsive quantum vacuum effects, capable of stopping the collapse process inside the black hole and precluding the formation of singularity. The final fate of the collapse will be a black hole with no singularity, inside which the matter stays balanced. The density of the final static matter will be close to the Planck density. We show that the largest possible radius of the stable static ball inside a black hole with Schwarzschild mass M is given by...
Existence of a unique positive entropy solution to a singular fractional Laplacian
, Article Complex Variables and Elliptic Equations ; 2020 ; Hesaaraki, M ; Sharif University of Technology
Taylor and Francis Ltd
2020
Abstract
In this paper, we study the existence of a positive solution to the elliptic problem: (Formula presented.) Here (Formula presented.) (N>2s) is an open bounded domain with smooth boundary, (Formula presented.) and (Formula presented.). For (Formula presented.), we take advantage of the convexity of Ω. The operator (Formula presented.) indicates the restricted fractional Laplacian, and μ is a non-negative Radon measure as a source term. The assumptions on f and h will be precised later. Besides, we will discuss the notion of entropy solution and its uniqueness for some specific measures. © 2020, © 2020 Informa UK Limited, trading as Taylor & Francis Group
The singular sources method for an inverse problem with mixed boundary conditions
, Article Journal of Mathematical Analysis and Applications ; Volume 306, Issue 1 , 2005 , Pages 122-135 ; 0022247X (ISSN) ; Hesaaraki, M ; Sharif University of Technology
2005
Abstract
We use the singular sources method to detect the shape of the obstacle in a mixed boundary value problem. The basic idea of the method is based on the singular behavior of the scattered field of the incident point-sources on the boundary of the obstacle. Moreover we take advantage of the scattered field estimate by the backprojection operator. Also we give a uniqueness proof for the shape reconstruction. © 2004 Elsevier Inc. All rights reserved
On a class of singularly perturbed elliptic systems with asymptotic phase segregation
, Article Discrete and Continuous Dynamical Systems- Series A ; Volume 42, Issue 7 , 2022 , Pages 3539-3556 ; 10780947 (ISSN) ; Burger, M ; Fotouhi, M ; Sharif University of Technology
American Institute of Mathematical Sciences
2022
Abstract
This work is devoted to study a class of singular perturbed elliptic systems and their singular limit to a phase segregating system. We prove existence and uniqueness and study the asymptotic behavior of limiting problem as the interaction rate tends to infinity. The limiting problem is a free boundary problem such that at each point in the domain at least one of the components is zero, which implies that all components can not coexist simultaneously. We present a novel method, which provides an explicit solution of the limiting problem for a special choice of parameters. Moreover, we present some numerical simulations of the asymptotic problem. © 2022 American Institute of Mathematical...
Universal image steganalysis using singular values of DCT coefficients
, Article 2013 10th International ISC Conference on Information Security and Cryptology ; 2013 ; Gaemmaghami, S ; Sharif University of Technology
IEEE Computer Society
2013
Abstract
We propose a blind image steganalysis method based on the Singular Value Decomposition (SVD) of the Discrete Cosine Transform (DCT) coefficients that are revisited in this work. We compute geometric mean, mean of log values, and statistical moments (mean, variance and skewness) of the SVDs of the DCT sub-blocks that are averaged over the whole image to construct a 480-element feature vector for steganalysis. These features are fed to a Support Vector Machine (SVM) classifier to discriminate between stego and cover images. Experimental results show that the proposed method outperforms most powerful steganalyzers when applied to some well-known steganography algorithms
Investigating of Linear and Nonlinear Propagation of Plasmon Polariton Waves in Hybrid Plosmonic System
, M.Sc. Thesis Sharif University of Technology ; Sadighi Bonabi, Rasoul (Supervisor)
Abstract
In this study, how to create spectral singularity in amplitude and phase in the proposed hybrid system and controllable propagation of plasmon waves of nonlinear polaritons has been investigated. For this purpose, a nonlinear hybrid system consisting of an atomic layer and a metamaterial layer is investigated. The atomic layer can be a gaseous system like rubidium atoms that are cooled to few Kelvin by magnetic systems,or these atoms can be thought of as charged particles that are impurity doped into a clear crystal and cooled to a temperature of a few Kelvin.This quantum system is placed on a metamaterial layer in the form of Al2O3 which has a nano-fishnet structure.This frequency...
Null controllability of degenerate/singular parabolic equations
, Article Journal of Dynamical and Control Systems ; Volume 18, Issue 4 , 2012 , Pages 573-602 ; 10792724 (ISSN) ; Salimi, L ; Sharif University of Technology
Springer
2012
Abstract
The purpose of this paper is to provide a full analysis of the null controllability problem for the one dimensional degenerate/singular parabolic equation ut - (a(x)ux)x - λ/x βu = 0, (t,x) ∈ (0, T) × (0,1), where the diffusion coefficient a(·) is degenerate at x = 0. Also the boundary conditions are considered to be Dirichlet or Neumann type related to the degeneracy rate of a(·). Under some conditions on the function a(·) and parameters β, λ, we prove global Carleman estimates. The proof is based on an improved Hardy-type inequality
Optimal Control of a Stage Structured Prey-Predator Model
,
M.Sc. Thesis
Sharif University of Technology
;
Hessaraki, Mahmmod
(Supervisor)
Abstract
A prey-predator fishery model with stage structure for prey is discusing in this thises. The adult preyand predator populations are harvested in the proposed system. The dynamic behavior of the model system is discussed. It is observed that singularity induced bifurcation phenomena is appeared when variation of the economic interest of harvesting is taken into account. We have incorporated state feedback controller to stabilize the model system in the case of positive economic interest. Fishing effort used to harvest the adult prey and predator population is used as a control to develop a dynamic framework to investigate the optimal utilization of the resource. Simulation results show that the...
Controllability results for a class of one dimensional degenerate/singular parabolic equations
, Article Communications on Pure and Applied Analysis ; Volume 12, Issue 3 , 2013 , Pages 1415-1430 ; 15340392 (ISSN) ; Salimi, L ; Sharif University of Technology
2013
Abstract
We study the null controllability properties of some degenerate/singular parabolic equations in a bounded interval of ℝ. For this reason we derive a new Carleman estimate whose proof is based on Hardy inequalities
Conceptual design double feed reactive distillation columns
, Article CHISA 2012 - 20th International Congress of Chemical and Process Engineering and PRES 2012 - 15th Conference PRES ; 2012 ; Ceska Rafinerska; DEZA; Synpo; BorsodChem; Prazska Plynarenska a.s ; Sharif University of Technology
Abstract
An approach to assess feasibility and determine the feasible range of operating parameters for double-feed reactive distillation columns is put forward. It is based on the combination of analysis of the pinch point maps for the middle-section in compositional space and an efficient shortcut design method. The existence of the liming bounds on operating parameters is observed. The methodology is illustrated by the production of methyl acetate and ethyl acetate. The analysis provides an efficient method to identify the most promising candidates of double feed reactive distillation columns and to study the design flexibility in terms of operating parameters. This is an abstract of a paper...
RISM: Single-Modal Image Registration via Rank-Induced Similarity Measure
, Article IEEE Transactions on Image Processing ; Volume 24, Issue 12 , 2015 , Pages 5567-5580 ; 10577149 (ISSN) ; Fatemizadeh, E ; Sharif University of Technology
Abstract
Similarity measure is an important block in image registration. Most traditional intensity-based similarity measures (e.g., sum-of-squared-difference, correlation coefficient, and mutual information) assume a stationary image and pixel-by-pixel independence. These similarity measures ignore the correlation between pixel intensities; hence, perfect image registration cannot be achieved, especially in the presence of spatially varying intensity distortions. Here, we assume that spatially varying intensity distortion (such as bias field) is a low-rank matrix. Based on this assumption, we formulate the image registration problem as a nonlinear and low-rank matrix decomposition (NLLRMD)....
Obstruction of black hole singularity by quantum field theory effects
, Article Journal of High Energy Physics ; Volume 2016, Issue 3 , 2016 ; 11266708 (ISSN) ; Arfaei, H ; Sharif University of Technology
Springer Verlag
2016
Abstract
Abstract: We consider the back reaction of the energy due to quantum fluctuation of the background fields considering the trace anomaly for Schwarzschild black hole. It is shown that it will result in modification of the horizon and also formation of an inner horizon. We show that the process of collapse of a thin shell stops before formation of the singularity at a radius slightly smaller than the inner horizon at the order of (Formula presented.). After the collapse stops the reverse process takes place. Thus we demonstrate that without turning on quantum gravity and just through the effects the coupling of field to gravity as trace anomaly of quantum fluctuations the formation of the...
Existence of positive solution for nonlocal singular fourth order Kirchhoff equation with Hardy potential
, Article Positivity ; Volume 21, Issue 4 , 2017 , Pages 1545-1562 ; 13851292 (ISSN) ; Vaezpour, S. M ; Hesaaraki, M ; Sharif University of Technology
Abstract
This paper is concerned with the existence of positive solution to a class of singular fourth order elliptic equation of Kirchhoff type (Formula Presented.)▵2u-λM(‖∇u‖2)▵u-μ|x|4u=h(x)uγ+k(x)uα,under Navier boundary conditions, u= ▵u= 0. Here Ω⊂ RN, N≥ 1 is a bounded C4-domain, 0 ∈ Ω, h(x) and k(x) are positive continuous functions, γ∈ (0 , 1) , α∈ (0 , 1) and M: R+→ R+ is a continuous function. By using Galerkin method and sharp angle lemma, we will show that this problem has a positive solution for m0 and 0 < μ< μ∗. Here μ∗=(N(N-4)4)2 is the best constant in the Hardy inequality. Besides, if μ= 0 , λ> 0 and h, k are Lipschitz functions, we show that this problem has a positive smooth...
Adaptive singular value thresholding
, Article 2017 12th International Conference on Sampling Theory and Applications, SampTA 2017, 3 July 2017 through 7 July 2017 ; 2017 , Pages 442-445 ; 9781538615652 (ISBN) ; Marvasti, F ; Anbarjafari, G ; Kivinukk, A ; Tamberg, G ; Sharif University of Technology
Abstract
In this paper, we propose an Adaptive Singular Value Thresholding (ASVT) for low rank recovery under affine constraints. Unlike previous iterative methods that the threshold level is independent of the iteration number, in our proposed method, the threshold in adaptively decreases during iterations. The simulation results reveal that we get better performance with this thresholding strategy. © 2017 IEEE
On existence, non-existence and blow-up results for a singular semilinear laplacian problem
, Article European Journal of Mathematics ; Volume 3, Issue 1 , 2017 , Pages 150-170 ; 2199675X (ISSN) ; Hesaaraki, M ; Sharif University of Technology
Abstract
We study the optimal value of p for solvability of the problem [Equation not available: see fulltext.]Here λ, α> 0 , p> 1 , f is a non-negative measurable function and [InlineEquation not available: see fulltext.], N⩾ 3 , is an open bounded domain with smooth boundary such that 0 ∈ Ω. We find the critical threshold exponent p+(λ, α) for solvability of (1) and show that if [InlineEquation not available: see fulltext.], 1 < p< p+(λ, α) and [InlineEquation not available: see fulltext.] for some sufficiently small c0> 0 , then there exists a solution as a limit of solutions to approximating problems. Moreover, for p⩾ p+(λ, α) we show that a complete blow-up phenomenon occurs. © 2017, Springer...