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Explicit minimum fuel intercept strategy for high-order dynamics
, Article Iranian Journal of Science and Technology, Transaction B: Engineering ; Volume 34, Issue 2 , 2010 , Pages 197-213 ; 10286284 (ISSN) ; Pourtakdoust, S. H ; Sharif University of Technology
2010
Abstract
An optimal fuel guidance strategy with acceleration limit is derived for interception of maneuvering targets. The guidance/control system is assumed as a linear time-varying arbitraryorder and is identical in each channel. An approximate model for drag acceleration is also considered in the solution. The optimal fuel strategy has some detrimental effects in most practical situations, if it is used entirely to the end. This strategy can be used at the beginning of the guidance phase for large initial heading errors in order to quickly reduce it with minimum effort. An explicit guidance law is then developed for minimum and nonminimum phase autopilots in order to modify the undesirable effects...
On the predicted errors of atmospheric guidance laws
, Article Aircraft Engineering and Aerospace Technology ; Volume 80, Issue 3 , 2008 , Pages 262-273 ; 00022667 (ISSN) ; Pourtakdoust, S. H ; Sharif University of Technology
2008
Abstract
Purpose - The purpose of this paper is to develop a novel solution for the predicted error and introduces a systematic method to develop optimal and explicit guidance strategies for different missions. Design/methodology/approach - The predicted error is derived from its basic definition through analytic]al dynamics. The relations are developed for two classes of systems. First, for systems in which the acceleration commands are truncated at a specified time. Second, for systems in which the corrective maneuvers are cut off at a specified time. The predicted error differential equation is obtained in a way that allows for derivation of several optimal and explicit guidance schemes. Findings...
Modern midcourse guidance laws in the endoatmosphere
, Article AIAA Guidance, Navigation, and Control Conference 2005, San Francisco, CA, 15 August 2005 through 18 August 2005 ; Volume 6 , 2005 , Pages 4560-4576 ; 1563477378 (ISBN); 9781563477379 (ISBN) ; Pourtakdoust, S. H ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc
2005
Abstract
In this paper, midcourse guidance strategies are derived considering approximate models for drag and thrust in the presence of gravity and autopilot dynamics. The guidance/control system is assumed as a linear time-varying and of arbitrary-order. The zero-effort miss differential equation is obtained in a way that three classes of guidance laws, namely optimal fuel, optimal energy, and closed-loop explicit strategy, can be derived by available methods for minimum and nonminimum phase autopilots. The resulting guidance laws have the structure of a guidance gain multiplied by the zero-effort miss. Several thrust/drag models arc also considered and discussed to obtain the effective navigation...
Architecting oxidized alginate methacrylate hydrogels with tunable characteristics by altering the sequence of the cross-linking steps, methacrylation reaction time, and polymer concentration
, Article Journal of Biomaterials Applications ; Volume 38, Issue 1 , 2023 , Pages 25-38 ; 08853282 (ISSN) ; Bastani, S ; Mashayekhan, S ; Sharif University of Technology
SAGE Publications Ltd
2023
Abstract
In this study, biodegradable oxidized methacrylated alginate (OMA) hydrogels with controllable mechanical properties were engineered. An ionic and photo cross-linking combination was employed to fabricate dual cross-linked hydrogels. By altering the degree of methacrylation and polymer concentration, hydrogels with an elastic modulus of 4.85 ± 0.13 to 21.02 ± 0.91 kPa, controllable swelling, and degradation kinetics, and cross-link density in the range of 1.0 × 10−5 to 6.5 × 10−5 mol/cm3 were obtained. Moreover, evaluating the effect of cross-linking sequence on the hydrogels’ mechanical properties demonstrated that in comparison to the hydrogels fabricated by ionic cross-linking followed by...
Generalized Schwarzschild's method
, Article Monthly Notices of the Royal Astronomical Society ; Volume 410, Issue 3 , 2011 , Pages 2003-2015 ; 00358711 (ISSN) ; Tremaine, S ; Sharif University of Technology
2011
Abstract
We describe a new finite element method (FEM) to construct continuous equilibrium distribution functions (DFs) of stellar systems. The method is a generalization of Schwarzschild's orbit superposition method from the space of discrete functions to continuous ones. In contrast to Schwarzschild's method, FEM produces a continuous DF and satisfies the intra-element continuity and Jeans equations. The method employs two finite element meshes, one in configuration space and one in action space. The DF is represented by its values at the nodes of the action-space mesh and by interpolating functions inside the elements. The Galerkin projection of all equations that involve the DF leads to a linear...
Density waves in debris discs and galactic nuclei
, Article Monthly Notices of the Royal Astronomical Society ; Volume 421, Issue 3 , 2012 , Pages 2368-2383 ; 00358711 (ISSN) ; Tremaine, S ; Sharif University of Technology
2012
Abstract
We study the linear perturbations of collisionless near-Keplerian discs. Such systems are models for debris discs around stars and the stellar discs surrounding supermassive black holes at the centres of galaxies. Using a finite-element method, we solve the linearized collisionless Boltzmann equation and Poisson's equation for a wide range of disc masses and rms orbital eccentricities to obtain the eigenfrequencies and shapes of normal modes. We find that these discs can support large-scale 'slow' modes, in which the frequency is proportional to the disc mass. Slow modes are present for arbitrarily small disc mass so long as the self-gravity of the disc is the dominant source of apsidal...
Statement frequency coverage: A code coverage criterion for assessing test suite effectiveness
, Article Information and Software Technology ; Volume 129 , 2021 ; 09505849 (ISSN) ; Mirian Hosseinabadi, S. H ; Jalali, S ; Sharif University of Technology
Elsevier B.V
2021
Abstract
Context: Software testing is a pivotal activity in the development of high-quality software. As software is evolving through its life cycle, the need for a fault-revealing criterion assessing the effectiveness of the test suite grows. Over the years, researchers have proposed coverage-based criteria, including statement and branch coverage, to solve this issue. In literature, the effectiveness of such criteria is attested in terms of their correlations with the mutation score. Objective: In this paper, we aim at proposing a coverage-based criterion named statement frequency coverage, which outperforms statement and branch coverage in terms of correlation with mutation score. Method: To this...
Statement frequency coverage: A code coverage criterion for assessing test suite effectiveness
, Article Information and Software Technology ; Volume 129 , 2021 ; 09505849 (ISSN) ; Mirian Hosseinabadi, S. H ; Jalali, S ; Sharif University of Technology
Elsevier B.V
2021
Abstract
Context: Software testing is a pivotal activity in the development of high-quality software. As software is evolving through its life cycle, the need for a fault-revealing criterion assessing the effectiveness of the test suite grows. Over the years, researchers have proposed coverage-based criteria, including statement and branch coverage, to solve this issue. In literature, the effectiveness of such criteria is attested in terms of their correlations with the mutation score. Objective: In this paper, we aim at proposing a coverage-based criterion named statement frequency coverage, which outperforms statement and branch coverage in terms of correlation with mutation score. Method: To this...
Cooperative hybrid ARQ in solar powered wireless sensor networks
, Article Microelectronics Reliability ; Volume 52, Issue 12 , 2012 , Pages 3043-3052 ; 00262714 (ISSN) ; Khodadoustan, S ; Ejlali, A ; Sharif University of Technology
2012
Abstract
Energy harvesters are used in today's Wireless Sensor Networks (WSNs) to harvest energy from the environment. Although an energy harvester can provide a supply source with a much greater lifetime than a battery, the amount of available energy for an energy harvesting system is a random variable. Furthermore, the proper management of energy harvesters has a considerable impact on reliability. It has been observed that cooperative error control mechanisms like Cooperative Automatic Repeat Request (C-ARQ) and Cooperative Hybrid ARQ (C-HARQ) can be used for improving the energy management and reliability in Energy Harvesting WSNs (EH-WSNs). Recently, the impact of C-ARC mechanism has been...
Error control schemes in solar energy harvesting wireless sensor networks
, Article 2012 International Symposium on Communications and Information Technologies, ISCIT 2012 ; 2012 , Pages 979-984 ; 9781467311571 (ISBN) ; Khodadoustan, S ; Ejlali, A ; Sharif University of Technology
2012
Abstract
To scavenge the energy from the environment and extend the network lifetime, some wireless sensor networks (WSNs) have been equipped with energy harvesters recently. However, the variable amount of environmental energy can affect the reliability of energy harvesting wireless sensor networks (EH-WSNs). In addition, data transmission over a wireless media is vulnerable. Hence, utilizing suitable error control schemes are necessary to improve the reliability. Regarding this point, Automatic Repeat Request (ARQ) and Cooperative ARQ (C-ARQ) schemes are applied in this generation of WSNs. Conventional ARQ as well as C-ARQ scheme are considered and examined through simulation. A comparative...
Effect of pH on aerobic granulation and treatment performance in sequencing batch reactors
, Article Chemical Engineering and Technology ; Volume 38, Issue 5 , 2015 , Pages 851-858 ; 09307516 (ISSN) ; Shayegan, J ; Jalali, S ; Sharif University of Technology
Wiley-VCH Verlag
2015
Abstract
Two sequencing batch reactors were operated to investigate the effect of influent alkalinity and reactor pH on aerobic granulation. In the first reactor R1 with high influent alkalinity the pH was adjusted in the neutral range, and in the second reactor R2 with low alkalinity the pH was held within the acidic range. The R1-dominating species were bacteria and the appearance time of granules was three weeks after reactor start-up. On the other hand, the acidic environment of R2 provided favorable conditions for fungal growth, and rapid granule formation occurred within the first week of operation. The varying microbial structure of granules resulted in different reactor performance in terms...
Rapid start-up and improvement of granulation in SBR
, Article Journal of Environmental Health Science and Engineering ; Volume 13, Issue 1 , 2015 ; 2052336X (ISSN) ; Shayegan, J ; Rezasoltani, S ; Sharif University of Technology
BioMed Central Ltd
2015
Abstract
Abstract Background: The aim of this study is to accelerate and improve aerobic granulation within a Sequencing Batch Reactor (SBR) by cationic polymer addition. Methods: To identify whether the polymer additive is capable of enhancing granule formation, two SBRs (R1 and R2, each 0.15 m in diameter and 2 m in height) are used by feeding synthetic wastewater. The cationic polymer with concentration of 30 to 2 ppm is added to R2, while no cationic polymer is added to R1. Results: Results show that the cationic polymer addition causes faster granule formation and consequently shorter reactor start-up period. The polymer-amended reactor contains higher concentration of biomass with better...
A universal image steganalysis system based on double sparse representation classification (DSRC)
, Article Multimedia Tools and Applications ; 2017 , Pages 1-20 ; 13807501 (ISSN) ; Farsi, H ; Ghaemmaghami, S ; Sharif University of Technology
Springer New York LLC
2017
Abstract
Achieving high rates of detection in low rates of embedding is still a challenging problem in many steganalysis systems. The newly proposed steganalysis system based on sparse representation classifier has shown remarkable detection rates in low embedding rate. In this paper, we propose a new steganalysis system based on double sparse representation classifier. We compare our proposed method with other steganalysis systems which use different classifier (including nearest neighbor, support vector machine, ensemble support vector machine and sparse representation). In all of our experiments, input features to the classifier are fixed and the ability of classifier is examined. Also we provide...
A universal image steganalysis system based on double sparse representation classification (DSRC)
, Article Multimedia Tools and Applications ; Volume 77, Issue 13 , 2018 , Pages 16347-16366 ; 13807501 (ISSN) ; Farsi, H ; Ghaemmaghami, S ; Sharif University of Technology
Springer New York LLC
2018
Abstract
Achieving high rates of detection in low rates of embedding is still a challenging problem in many steganalysis systems. The newly proposed steganalysis system based on sparse representation classifier has shown remarkable detection rates in low embedding rate. In this paper, we propose a new steganalysis system based on double sparse representation classifier. We compare our proposed method with other steganalysis systems which use different classifier (including nearest neighbor, support vector machine, ensemble support vector machine and sparse representation). In all of our experiments, input features to the classifier are fixed and the ability of classifier is examined. Also we provide...
Tilt-induced kink in the plasmon dispersion of two-dimensional Dirac electrons
, Article Physical Review B ; Volume 98, Issue 19 , 2018 ; 24699950 (ISSN) ; Jafari, S. A ; Sharif University of Technology
American Physical Society
2018
Abstract
The list of two-dimensional Dirac systems with a tilt in their Dirac cone spectrum is expanding, and now, in addition to the organic system α(BEDT-TTF)2I3, it includes the two-dimensional 8Pmmn-borophene sheet, which allows for controlled doping by the gate voltage. We analytically calculate the polarization function of tilted Dirac cone for an arbitrary tilt parameter, 0≤η<1, and arbitrary doping. This enables us to find two interesting plasmonic effects solely caused by the tilt. (i) In addition to the standard plasmon oscillations, a strong enough tilt induces an additional linearly dispersing overdamped branch of plasmons, which is strongly Landau damped due to overlap with a large...
Polarization tensor for tilted Dirac fermion materials: Covariance in deformed Minkowski spacetime
, Article Physical Review B ; Volume 100, Issue 7 , 2019 ; 24699950 (ISSN) ; Jafari, S. A ; Sharif University of Technology
American Physical Society
2019
Abstract
The rich structure of solid state physics provides us with Dirac materials the effective theory of which enjoys the Lorentz symmetry. In nonsymmorphic lattices, the Lorentz symmetry can be deformed in a way that the null energy-momentum vectors will correspond to the on-shell condition for tilted Dirac cone dispersion. In this sense, tilted Dirac/Weyl materials can be viewed as solid state systems where the effective spacetime is non-Minkowski. In this work, we show that the polarization tensor for tilted Dirac cone systems acquires a covariant form only when the spacetime is considered to be an appropriate deformation of the Minkowski spacetime that is compatible with the dispersion. As a...
Electromagnetic modes from Stoner enhancement: Graphene as a case study
, Article Journal of Magnetism and Magnetic Materials ; Volume 471 , 2019 , Pages 220-235 ; 03048853 (ISSN) ; Jafari, S. A ; Sharif University of Technology
Elsevier B.V
2019
Abstract
In systems with substantial spin fluctuations, dressing the polarization function by ladder diagram of Stoner (spin-flip) excitations can drastically modify the electromagnetic response. As a case study, we provide the detailed analysis of the corrections to the non-local optical conductivity of both doped and undoped graphene. While the resummation of ladder diagram of Stoner excitations does not affect the TE mode in doped graphene, it allows for a new undamped TM mode in undoped graphene. This is the sole effect of corrections arising from ladder diagrams and is dominated by Stoner excitations along the ladder rung which goes away by turning off the source of spin-flip interactions. In...
DBMSS: An event-based simulator for analyzing concurrency protocols in database systems
, Article 2006 Canadian Conference on Electrical and Computer Engineering, CCECE'06, Ottawa, ON, 7 May 2006 through 10 May 2006 ; 2006 , Pages 1874-1877 ; 08407789 (ISSN); 1424400384 (ISBN); 9781424400386 (ISBN) ; Abdollahzadeh, A ; Aliakbarian, S ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2006
Abstract
This paper explores design and implementation of an event-based simulator namely DBMSS for analyzing concurrency protocols in database systems. In the design of DBMSS we interested in event-based approach to create a real world with variety range of event possibilities. DBMSS is explored in the context of the development of a complex simulator for simulating real world conditions and provide an event-based environment to test and evaluate concurrency protocols in database systems. First we discuss the architecture of DBMSS and use it to provide arrival transactions to test and evaluate concurrency protocols in database system. We present the comparison of 4 concurrency protocols in variety...
Seismic performance of stainless-steel built-up box columns subjected to constant axial loads and cyclic lateral deformations
, Article Structures ; Volume 33 , 2021 , Pages 4080-4095 ; 23520124 (ISSN) ; Sadrara, A ; Jalali, S. R ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
The seismic behavior of stainless-steel built-up box columns subjected to constant axial loads and cyclic lateral deformation that are used in special moment frames (SMFs) has been investigated through finite element (FE) analysis. A total of 208 numerical models were conducted to cover a range of parameters affecting the seismic behavior of the columns. These include the web slenderness ratio, flange slenderness ratio, global slenderness ratio, axial load level, and lateral loading protocol. The performance indices of overstrength factor, axial shortening, out-of-plane deformation, plastic hinge length, and rotation capacity were calculated and compared. Local buckling of the columns also...
Simulation of13C nuclear magnetic resonance spectra of lignin compounds using principal component analysis and artificial neural networks
, Article Journal of Magnetic Resonance ; Volume 171, Issue 1 , 2004 , Pages 176-185 ; 10907807 (ISSN) ; Masoum, S ; Shahbazikhah, P ; Sharif University of Technology
2004
Abstract
Theoretical models relating atom-based structural descriptors to 13C NMR chemical shifts were used to accurately simulate 13C NMR spectra of lignin model compounds (poly-substituted phenols). The structure-activity relationship (SAR) studies for 15 lignins using pattern recognition methods of principal component analysis (PCA) and artificial neural networks (ANNs) were performed in this work. The most important parameters affecting the 13C chemical shifts of different carbons were descriptors consisting of the charge density of the atoms at different distances from the center carbon. Among the large number of parameters, these descriptors were selected using PCA and were used as ANN input....