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Imprints of local lightcone projection effects on the galaxy bispectrum IV: Second-order vector and tensor contributions
, Article Journal of Cosmology and Astroparticle Physics ; Volume 2019, Issue 3 , 2019 ; 14757516 (ISSN) ; Allahyari, A ; Clarkson, C ; Larena, J ; Umeh, O ; Maartens, R ; Sharif University of Technology
Institute of Physics Publishing
2019
Abstract
The galaxy bispectrum on scales around and above the equality scale receives contributions from relativistic effects. Some of these arise from lightcone deformation effects, which come from local and line-of-sight integrated contributions. Here we calculate the local contributions from the generated vector and tensor background which is formed as scalar modes couple and enter the horizon. We show that these modes are sub-dominant when compared with other relativistic contributions
Simultaneous effect of modified gravity and primordial non-Gaussianity in large scale structure observations
, Article Journal of Cosmology and Astroparticle Physics ; Vol. 2014, issue. 1 , January , 2014 ; Khosravi, S ; Baghram, S ; Moshafi, H ; Sharif University of Technology
Abstract
In this work we study the simultaneous effect of primordial non-Gaussianity and the modification of the gravity in f(R) framework on large scale structure observations. We show that non-Gaussianity and modified gravity introduce a scale dependent bias and growth rate functions. The deviation from ΛCDM in the case of primordial non-Gaussian models is in large scales, while the growth rate deviates from ΛCDM in small scales for modified gravity theories. We show that the redshift space distortion can be used to distinguish positive and negative fNL in standard background, while in f(R) theories they are not easily distinguishable. The galaxy power spectrum is generally enhanced in presence of...
Canard-wing interactions in subsonic flow
, Article Iranian Journal of Science and Technology - Transactions of Mechanical Engineering ; Volume 37, Issue M2 , 2013 , Pages 133-147 ; 22286187 (ISSN) ; Davari, A. R ; Soltani, M. R ; Sharif University of Technology
Shiraz University
2013
Abstract
Extensive subsonic wind tunnel tests were conducted on a coplanar wing-canard configuration at various angles of attack. In these experiments, a 60° swept canard was placed upstream of a 60° swept main delta wing. This paper deals with the distribution of mean and fluctuating pressure coefficients on the upper surfaces of both the canard and the wing immersed in a variety of angles of attack. According to the results, presence of canard postpones the vortex formation and growth on the wing to higher angles of attack compared to the canard-off case. Due to the canard downwash field, the wing operates at lower effective angles of attack and therefore, its vortex breakdown is delayed. The...
Late time sky as a probe of steps and oscillations in primordial Universe
, Article Journal of Cosmology and Astroparticle Physics ; Volume 2018, Issue 1 , 2018 ; 14757516 (ISSN) ; Baghram, S ; Sharif University of Technology
Abstract
The standard model of cosmology with nearly Gaussian, isotropic, scale invariant and adiabatic initial conditions describes the cosmological observations well. However, the study of any deviation from the mentioned conditions will open up a new horizon to the physics of early universe. In this work, we study the effect of the oscillatory and step-like features in potentials of inflationary models in late time large scale structure observations. Mainly we study the matter power spectrum, number density of the structures, dark matter halo bias and specifically CMB lensing. We show that the oscillatory models can introduce some degeneracy with late time effects on BAO scale. We also conclude...
Structure formation in f(R) gravity: A distinguishing probe between the dark energy and modified gravity
, Article Journal of Cosmology and Astroparticle Physics ; Volume 2010, Issue 12 , 2010 ; 14757516 (ISSN) ; Rahvar, S ; Sharif University of Technology
2010
Abstract
In this work, we study the large scale structure formation in the modified gravity in the framework of Palatini formalism and compare the results with the equivalent smooth dark energy models as a tool to distinguish between these models. Through the inverse method, we reconstruct the dynamics of universe, modified gravity action and the structure formation indicators like the screened mass function and gravitational slip parameter. Consequently, we extract the matter density power spectrum for these two models in the linear regime and show that the modified gravity and dark energy models predictions are slightly different from each other at large scales. It is also shown that the growth...
ISW-galaxy cross correlation: A probe of dark energy clustering and distribution of dark matter tracers
, Article Journal of Cosmology and Astroparticle Physics ; Volume 2016, Issue 9 , 2016 ; 14757516 (ISSN) ; Mollazadeh, A ; Baghram, S ; Sharif University of Technology
Institute of Physics Publishing
Abstract
Cross correlation of the Integrated Sachs-Wolfe signal (ISW) with the galaxy distribution in late time is a promising tool for constraining the dark energy properties. Here, we study the effect of dark energy clustering on the ISW-galaxy cross correlation and demonstrate the fact that the bias parameter between the distribution of the galaxies and the underlying dark matter introduces a degeneracy and complications. We argue that as the galaxy's host halo formation time is different from the observation time, we have to consider the evolution of the halo bias parameter. It will be shown that any deviation from ΛCDM model will change the evolution of the bias as well. Therefore, it is deduced...
Detecting Primordial Black Holes with the Help of 21-cm Cosmology
, M.Sc. Thesis Sharif University of Technology ; Baghram, Shant (Supervisor)
Abstract
The existence of primordial black holes has been proposed for about half a century, but so far we have not been able to have convincing observations to prove the existence of such black holes. With the discovery of gravitational waves, hopes for finding primordial black holes have increased again; So that in recent years, different ways have been proposed to reveal them. This matter becomes even more important when we know that these black holes can explain all or at least part of the missing matter of the universe known as dark matter. One of the proposed ways is to investigate the 21 cm line of hydrogen in the intergalactic medium. Over time, the temperature of the intergalactic medium is...
Blur identification in noisy images using radon transform and power spectrum modeling
, Article IWSSIP 2005 - 12th International Workshop on Systems, Signals and Image Processing(SSIP-SPI, 2005), Chalkida, 22 September 2005 through 24 September 2005 ; 2005 , Pages 347-352 ; 0907776205 (ISBN); 9780907776208 (ISBN) ; Jamzad, M ; Sharif University of Technology
2005
Abstract
Motion blur is one of the most common blurs that degrades images. Restoration of such images are highly dependent to estimation of motion blur parameters. Many researchers since 1976 have developed algorithms to estimate linear motion blur parameters. These algorithms are different in their performance, time complexity, precision and their robustness in noisy environments. In this paper we have presented a novel algorithm to estimate linear motion blur parameters such as direction and extend by using Radon transform to find direction and power spectrum modeling to find its extend. The most benefit of this algorithm is its robustness and precision in noisy images. This algorithm is a...
Large Scale Structures as a Probe of Physics of Early Universe
, M.Sc. Thesis Sharif University of Technology ; Baghram, Shant (Supervisor) ; Firouzjahi, Hassan (Co-Advisor)
Abstract
The standard model of cosmology with nearly Gaussian, isotropic, scale invariant and adiabatic initial conditions describes the cosmological observations. However, the study of any deviation from the mentioned conditions will open up a new window to the physics of early universe. In this work we study the effect of the oscillatory and step in potential inflationary models in late time large scale structure observations. Almost we study the matter power spectrum, number density of the structures, the halo bias an the bulk flow in mentioned models. We assert that inflationary models with step functions which deviates from the standard model in small scales l ≤ 1Mpc can be confirmed by Large...
A survey on talamocortical activity of ADHD patients based on mean-field bursting model
, Article 10th IEEE International Workshop on Biomedical Engineering, BioEng 2011, Kos Island, 5 October 2011 through 7 October 2011 ; 2011 ; 9781457705526 (ISBN) ; Janghorbani, A ; Vahdat, B. V ; University of Patras; University of Ioannina; National Technical University of Athens; University of Thessaly; Univ. Ioannina, Unit Med. Technol. Intelligent Inf. Syst ; Sharif University of Technology
2011
Abstract
Modeling is one of assessing tools for better understanding of human body organs and study of diseases. One of the brain diseases is ADHD, which has been studied before, mostly by means of EEG signals. In this paper, the mean-field model, which is a model of neuron-population spiking, and the Power Spectrum of the resulting spikes have been studied by changing parameters of model. The results show that there is a meaningful relationship between firing activity of ADHD patients neuron population and the parameters of mean-field model and Power Spectrum of spikes. In addition, the effects of stimulant medications for ADHD patients on firing activity and power spectrum of firing activity of...
Linear motion blur parameter estimation in noisy images using fuzzy sets and power spectrum
, Article Eurasip Journal on Advances in Signal Processing ; Volume 2007 , 2007 ; 11108657 (ISSN) ; Jamzad, M ; Sharif University of Technology
2007
Abstract
Motion blur is one of the most common causes of image degradation. Restoration of such images is highly dependent on accurate estimation of motion blur parameters. To estimate these parameters, many algorithms have been proposed. These algorithms are different in their performance, time complexity, precision,and robustness in noisy environments. In this paper, we present a novel algorithm to estimate direction and length of motion blur,using Radon transform and fuzzy set concepts. The most important advantage of this algorithm is its robustness and precision in noisy images. This method was tested on a wide range of different types of standard images that were degraded with different...
Power spectrum and FFT-based signal analysis in turbulence measurements
, Article World Academy of Science, Engineering and Technology ; Volume 40 , 2009 , Pages 275-278 ; 2010376X (ISSN) ; Tamadonfar, P ; Soltani, M. R ; Ghorbanian, K ; Masdari, M ; Sharif University of Technology
2009
Abstract
In this research, the employment of an innovative but simple and cost effective method for turbulent reduction in a low speed wind tunnel is investigated and the effect of this turbulence reduction on the Power Spectrum and FFT-Based signals that obtained from Hot-wire Anemometry is studied. These terms represents the amount of power contained in the signals. Several situations are studied in this paper. One of these situations is when there are four screens in the settling chamber of the wind tunnel and after that by adding the trip strip in the contraction region of the wind tunnel the tests were repeated. In the next stage, three screens were removed from the settling chamber of the wind...
Reduction of doppler estimation error by multi-frequency transmission
, Article IET International Radar Conference 2009, Guilin, 20 April 2009 through 22 April 2009 ; Issue 551 CP , 2009 ; 9781849190107 (ISBN) ; Sheikhi, A ; Nayebi, M. M ; Sharif University of Technology
2009
Abstract
In this paper, after introduction of symmetric multi- frequency signal, it will be presented how to estimate Doppler frequency from estimated frequency tones of returned echo. After that, three methods of Pisarenko, Prony and MUSIC for frequency estimation will be introduced, and then these methods are applied to estimate tone frequencies of a multi-carrier signal. It will be shown that estimation of Doppler frequency by multi-frequency signal transmission leads to less rms error than single-frequency signal, in the condition of equal SNR. Infact it will be suggested that distribution of the power of signal in spectrum instead of adding up all the power in one point, leads to less Doppler...
Detection of sustained auditory attention in students with visual impairment
, Article 27th Iranian Conference on Electrical Engineering, ICEE 2019, 30 April 2019 through 2 May 2019 ; 2019 , Pages 1798-1801 ; 9781728115085 (ISBN) ; Detection of sustained auditory attention in students with visual impairment ; Momtazpour, M ; Hajipour Sardouie, S ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2019
Abstract
The efficiency of a learning process directly depends on how well the students are attentive. Detecting the level of attention can help to improve the learning quality. In recent years, there have been several attempts to leverage EEG signal processing as a tool to detect whether a student is attentive or not. In such work, the level of attention is determined by analyzing the EEG power spectrum, which is mostly followed by machine learning approaches. However, the efficiency of such methods for detecting auditory attention of blind or visually-impaired students has not been analyzed. This study aims to investigate such a scenario. To this end, we propose an EEG recording protocol to...
On the intelligent eavesdropping of differential frequency hopping
, Article IEEE Wireless and Microwave Technology Conference, WAMICON 2006, Clearwater Beach, FL, 4 December 2006 through 5 December 2006 ; 2006 ; 1424408482 (ISBN); 9781424408481 (ISBN) ; Aref, M. R ; Sharif University of Technology
2006
Abstract
Dirential frequency hopping (DFH) was introduced as a new technology for reliable high data rate transmission. Since the system utilizes lower transmitting power relative to the other spread spectrum techniques and also principle part of the technique, frequency transition function (FTF), is designed privately and uniformly, the scheme is said to be safe and secure. In spite of previous researches, this paper shows that an intelligent eavesdropper may threat the security of the system by finding FTF and sending jamming signal toward authorized receivers. As a result, regular DFH can not provide consumers with security in wireless networks and hence we propose that FTF should be designed with...
AFM spectral analysis of self-agglomerated metallic nanoparticles on silica thin films
, Article Current Nanoscience ; Volume 6, Issue 1 , 2010 , Pages 116-123 ; 15734137 (ISSN) ; Sharif University of Technology
2010
Abstract
Stochastic parameters of self-agglomerated metallic nanoparticles on a dielectric film surface were studied using atomic force microscopy (AFM) analysis. In this regard, the rough surfaces including the nanoparticles were analyzed and characterized using structure function, roughness exponent and power spectrum density of the AFM profiles and their gradients, for different metal concentrations and heat treatment temperatures. The diffusion parameters, such as activation energy, of the nanoparticles initially accumulated on the surface into a porous and aqueous silica thin film were obtained using the AFM spectral analysis of the profiles and their gradients. It was found that the tip...
AFM stochastic analysis of surface twisted nanograin chains of iron oxide: a kinetic study
, Article Journal of Physics D: Applied Physics ; Volume 42, Issue 6 , 2009 ; 00223727 (ISSN) ; Azimirad, R ; Sharif University of Technology
2009
Abstract
We have studied the stochastic parameters of surface iron oxide nanograin chains, 97 nm in diameter and 2.4 νm in length, prepared at different annealing temperatures, using atomic force microscopy (AFM) spectral analysis. In this regard, the roughness of the thin films including self-assembled twisted nanograin chains has been analysed and characterized using the height-height correlation function, the roughness exponent as well as the power spectrum density of the AFM profiles and their gradient, for the different annealing temperatures. The tip convolution effect on the stochastic parameters under study has also been investigated. The kinetics of the formation of nanograins on the film...
A new simple method for analysing of thermal noise in switched-capacitor filters
, Article International Journal of Electronics ; Volume 99, Issue 12 , Feb , 2012 , Pages 1729-1737 ; 00207217 (ISSN) ; Hemmatyar, A. M. A ; Hashemipour, O ; Sharif University of Technology
2012
Abstract
Thermal noise is one of the most important challenges in analogue integrated circuits design. This problem is more crucial in switched-capacitor (SC) filters due to the aliasing effect of wide-band thermal noise. In this article, a new simple method is proposed for estimating the power spectrum density of output thermal noise in SC filters, which have acceptable accuracy and short running time. In the proposed method, first using HSPICE simulator, accurate value of accumulated sampled noise on sampler capacitors in each clock state is achieved. Next, using difference equations of the SC filter, frequency response of the SC filter is shaped by time domain analysis. Based on the proposed...
Effect of a standing baffle on the flow structure in a rectangular open channel
, Article Journal of Hydraulic Research ; Volume 48, Issue 3 , Jun , 2010 , Pages 400-404 ; 00221686 (ISSN) ; Takeda, Y ; Firoozabadi, B ; Sharif University of Technology
2010
Abstract
The effect of an intermediate standing baffle on the flow structure in a rectangular open channel has been investigated by a three-dimensional acoustic Doppler velocimeter. Investigation of time-averaged velocity profiles at different streamwise positions reveals that the approach flow is fully developed upstream of the baffle. By analysing the space-averaged power spectra of streamwise velocity, a peak structure was observed in the upstream baffle region. Downstream of the baffle this peak structure has been alleviated by the baffle. The same analysis for the vertical component indicates the existence of a peak structure both up- and downstream of the baffle. Consequently, a baffle affects...
A superconductor THz modulator based on vortex flux flow
, Article IEEE Transactions on Applied Superconductivity ; Volume 19, Issue 4 , 2009 , Pages 3653-3657 ; 10518223 (ISSN) ; Hosseini, M ; Chalabi, H. R ; Moftakharzadeh, A ; Zandi, H ; Khorasani, S ; Fardmanesh, M ; Sharif University of Technology
2009
Abstract
A terahertz modulator based on the Type-II superconductor flux flow oscillator has been proposed. Analytical calculations are presented and the effects of intrinsic and extrinsic parameters such as disorder strength of crystal, penetration depth, frequency, and amplitude of the modulated current on the radiation power spectrum have been studied. The proposed structure also exhibits a mixer-like behavior, in the sense that its output harmonics range from the washboard frequency up to the superconductor gap frequency, so the input signal is practically mixed with the washboard frequency and its harmonics. The modulation index for each harmonic of this modulator has also been investigated. This...