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    A graphene-based THz ring resonator for label-free sensing

    , Article IEEE Sensors Journal ; Volume 16, Issue 11 , 2016 , Pages 4338-4344 ; 1530437X (ISSN) Zangeneh Nejad, F ; Safian, R ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc 
    In this paper, we report on a novel resonant THz sensor for label-free analysis. The structure consists of a silicon nitride dielectric ring resonator vertically coupled to a thin layer of graphene strip ring resonator on top. The cladding is assumed to be porous alumina on the top of the graphene strip, which enhances the interaction of the surface plasmon wave and the target molecules. Finite difference time domain analysis is used to systematically design the structure and to investigate the performance of the sensor. Our simulations show that the proposed structure has larger refractive index sensitivity and lower intrinsic quality factor with respect to the similar optical structure. It... 

    A high-performance and low-cost ethanol vapor sensor based on a TiS2/PVP composite

    , Article ChemistrySelect ; Volume 4, Issue 21 , 2019 , Pages 6662-6666 ; 23656549 (ISSN) Hosseini Shokouh, S. H ; Fardindoost, S ; Iraji Zad, A ; Sharif University of Technology
    Wiley-Blackwell  2019
    Low-cost ethanol vapor sensors are fabricated by electrospinning of TiS2/PVP fibers on pre-patterned metal electrodes. TiS2 ribbons have been synthesized through sulfuration of titanium (Ti) foil using chemical vapor transport (CVT). We found selective and stable responses at a low concentration of ethanol vapor (2 ppm) at room temperature with the transient response and recovery times experimentally around 60 s and 2 s respectively. The relatively high responses of sensors (6800% at 18 ppm) are attributable to the synergy effect of TiS2/PVP composite structure. The mechanism of sensing is discussed based on proton hopping while the sensors exposed to ethanol vapor. © 2019 Wiley-VCH Verlag... 

    Successive concave sparsity approximation for compressed sensing

    , Article IEEE Transactions on Signal Processing ; Volume 64, Issue 21 , 2016 , Pages 5657-5671 ; 1053587X (ISSN) Malek Mohammadi, M ; Koochakzadeh, A ; Babaie Zadeh, M ; Jansson, M ; Rojas, C. R ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2016
    In this paper, based on a successively accuracy-increasing approximation of the ℓ0 norm, we propose a new algorithm for recovery of sparse vectors from underdetermined measurements. The approximations are realized with a certain class of concave functions that aggressively induce sparsity and their closeness to the ℓ0 norm can be controlled. We prove that the series of the approximations asymptotically coincides with the ℓ1 and ℓ0 norms when the approximation accuracy changes from the worst fitting to the best fitting. When measurements are noise-free, an optimization scheme is proposed that leads to a number of weighted ℓ1 minimization programs, whereas, in the presence of noise, we propose... 

    Block adaptive compressive sensing for distributed MIMO radars in clutter environment

    , Article Proceedings International Radar Symposium, 10 May 2016 through 12 May 2016 ; Volume 2016-June , 2016 ; 21555753 (ISSN) ; 9781509025183 (ISBN) Abtahi, A ; Mohajer Hamidi, S ; Marvasti, F ; Sharif University of Technology
    IEEE Computer Society  2016
    For the target parameter estimation in MIMO radars in the presence of strong clutter, non-adaptive compressive sensing methods have a poor performance. On the other hand, the adaptive ones usually need higher data acquisition time. In this paper, we propose an adaptive compressive sensing method called L-BGT that has tolerable data acquisition time. furthermore, we have presented the essential changes in a distributed MIMO radar to exploit an adaptive group testing compressive sensing method  

    A new approach to flexible humidity sensors using graphene quantum dots

    , Article Journal of Materials Chemistry C ; Volume 5, Issue 35 , 2017 , Pages 8966-8973 ; 20507534 (ISSN) Hosseini, Z. S ; Iraji Zad, A ; Ghiass, M. A ; Fardindoost, S ; Hatamie, S ; Sharif University of Technology
    Highly sensitive flexible humidity sensors based on graphene quantum dots (GQDs) were developed. The GQDs were prepared using a facile hydrothermal method and characterized considering morphological, structural, and compositional experiments. Then, their humidity sensing properties in correlation with flexibility characteristics were investigated. Good selectivity and response (∼390 for a RH change of 99%), broad detection range (1-100% RH), rather short response and recovery times (12 and 43 s, respectively) as well as flexibility were obtained, demonstrating that the GQD sensors have potential for application in wearable electronics and RH monitoring. Detection of hydrogen (H2) gas by the... 

    Walking in streets with minimal sensing

    , Article Journal of Combinatorial Optimization ; Volume 30, Issue 2 , 2014 , Pages 387-401 ; ISSN: 13826905 Tabatabaei, A ; Ghodsi, M ; Sharif University of Technology
    We consider the problem of walking a robot in an unknown polygon called “street”, starting from a point (Formula presented.) to reach a target (Formula presented.). The robot is assumed to have minimal sensing capability in a way that cannot infer any geometric properties of the environment, such as its coordinates, angles or distances; but it is equipped with a sensor that can only detect the discontinuities in the depth information (or gaps). Our robot can also locate the target point (Formula presented.) as soon as it enters in robot’s visibility region. In addition, one pebble is assumed to be available to the robot to be used as an identifiable point and to mark any position of the... 

    Re-extraction of the second order terms of high frequency radio wave backscattering in the presence of uniform surface current

    , Article Iranian Journal of Science and Technology - Transactions of Electrical Engineering ; Volume 40, Issue 1 , 2016 , Pages 45-49 ; 22286179 (ISSN) Shams, S. H ; Bastani, M. H ; Moniri, M. R ; Sharif University of Technology
    Shiraz University  2016
    HF radar systems are widely used for the measurement of ocean surface currents and wave parameters. Theoretical analysis of high frequency radio wave backscattering from the sea has been derived in the past. Also, the relationship between Bragg frequencies and surface currents is determined and has been proved by HF radars. It is known that when surface currents are present, the Bragg frequencies move to new frequencies. Their movement is proportional to the surface current in the direction toward radar. In addition, it is observed that sea surface current changes the second order part of the spectrum of radar reflection from the sea surface. In this paper, a theoretical analysis of... 

    Distributed algorithms for power saving optimization in sensor network

    , Article Proceedings of the 8th WSEAS International Conference on Data Networks, Communications, Computers, DNCOCO '09, 7 November 2009 through 9 November 2009 ; 2009 , Pages 109-115 ; 9789604741342 (ISBN) Ghani, S ; Mousavi, M ; Movaghar, A ; Sharif University of Technology
    Sensor networks have a wide range of potential and practical application. A sensor network consists of a large number of tiny, low power and short-living sensors. Some sensor network applications require k-coverage to ensure the quality of surveillance. Meanwhile, energy is another primary concern for sensor networks. In this dissertation, an algorithm proposed which groups sensors in to disjoint subsets. Every subset cans k-cover the whole area. The subsets are scheduled to work successively. Therefore, the network lifetime is prolonged. Furthermore, sensing range is fixed. Also another algorithm, proposed which constructs some non-disjoint subsets, and in each active subset, each sensor... 

    Scanning tunneling spectroscopy of MoS2 monolayer in presence of ethanol gas

    , Article Materials Research Express ; Volume 5, Issue 4 , April , 2018 ; 20531591 (ISSN) Hosseini, S. A ; Iraji Zad, A ; Berahman, M ; Aghakhani Mahyari, F ; Hosseini Shokouh, S. H ; Sharif University of Technology
    Institute of Physics Publishing  2018
    Due to high surface to volume ratio and tunable band gap, two dimensional (2D) layered materials such as MoS2, is good candidate for gas sensing applications. This research mainly focuses on variation of Density of States (DOS) of MoS2 monolayes caused by ethanol adsorption. The nanosheets are synthesized by liquid exfoliation, and then using Scanning Tunneling Spectroscopy (STS) and Density Functional Theory (DFT), local electronic characteristic such as DOS and band gap in non-vacuum condition are analyzed. The results show that ethanol adsorption enhances DOS and deform orbitals near the valence and conduction bands that increase transport of carriers on the sheet. © 2018 IOP Publishing... 

    A turn-on graphene quantum dot and graphene oxide based fluorometric aptasensor for the determination of telomerase activity

    , Article Microchimica Acta ; Volume 186, Issue 12 , 2019 ; 00263672 (ISSN) Kazemi, E ; Bagheri, H ; Norouzian, D ; Sharif University of Technology
    Springer-Verlag Wien  2019
    A turn-on fluorometric assay is described for determination of the activity of enzyme telomerase. For this purpose, graphene quantum dots (GQDs) were first modified with the telomeric sequence (5′-amino-AATCCGTCGAGCAGAGTT-3′) via a condensation reaction. Injection of graphene oxide causes instant quenching of the blue fluorescence of the GQDs. Addition of cell extract containing telomerase, triggers the extension of telomer via addition of specific sequence (TTAGGG)n to its 3′ end. Fluorescence, best measured at excitation/emission wavelengths of 390/446 nm, is subsequently restored due to folding of the extended telomeric sequence into G-quadruplex structure. The method was applied to the... 

    Distributed Compressed Sensing (DCS) and its Application in Wireless Sensor Network (WSN)

    , M.Sc. Thesis Sharif University of Technology Ghasimi, Mohsen (Author) ; Babaei Zadeh, Masoud (Supervisor)
    Recent advances in Micro-Electro-Mechanical Systems (MEMS) technology, wireless communications,and digital electronics have enabled the development of low-cost, low-power,multifunctional sensor nodes that are small in size and communicate untethered in short distances.Wireless Sensor Network (WSN) including these sensors has been utilized in many applications, namely military and environmental applications. Due to unchangeable battery in most WSNs, Power consumption is an important challenge in such systems. A sensor node expends maximum energy in data communication. Control environmental parameter is among the most important applications of WSN. The actual physical environmental information... 

    Spectrum Sensing in Cognitive Radios Using Compressive Sensing and Random Sampling

    , M.Sc. Thesis Sharif University of Technology Dezfouli, Milad (Author) ; Marvasti, Farrokh (Supervisor)
    Cognitive radio (CR) can successfully deal with the growing demand and scarcity of the wireless spectrum. To exploit limited spectrum efficiently, CR technology allows unlicensed users to access licensed spectrum bands. Since licensed users have priorities to use the bands, the unlicensed users need to continuously monitor the licensed users activities to avoid interference and collisions. How to obtain reliable results of the licensed users activities is the main task for spectrum sensing. Based on the sensing results, the unlicensed users should adapt their transmit powers and access strategies to protect the licensed communications. The requirement naturally presents challenges to the... 

    Distributed multiuser sequential channel sensing schemes in multichannel cognitive radio networks

    , Article IEEE Transactions on Wireless Communications ; Volume 12, Issue 5 , 2013 , Pages 2055-2067 ; 15361276 (ISSN) Shokri Ghadikolaei, H ; Sheikholeslami, F ; Nasiri Kenari, M ; Sharif University of Technology
    Effective spectrum sensing strategies enable cognitive radios (CRs) to identify and opportunistically transmit on under-utilized spectral resources. In this paper, sequential channel sensing problems for single and multiple secondary users (SUs) networks are effectively modeled through finite state Markovian processes. More specifically, a model for single user case is introduced and its performance is validated through analytical analysis. Then, in order to address multiple SUs case, this model is extended to include the modified p-persistent access (MPPA) protocol. Since the scheme utilized experiences a high level of collision among the SUs, to mitigate the problem appropriately,... 

    Learning-based spectrum sensing time optimization in cognitive radio systems

    , Article 2012 6th International Symposium on Telecommunications, IST 2012, 6 November 2012 through 8 November 2012 ; November , 2012 , Pages 249-254 ; 9781467320733 (ISBN) Shokri Ghadikolaei, H ; Abdi, Y ; Nasiri-Kenari, M ; Sharif University of Technology
    Powerful spectrum sensing schemes enable cognitive radios (CRs) to find transmission opportunities in spectral resources allocated exclusively to primary users. In this paper, the problem of maximizing the average throughput of a cognitive radio system through optimizing its spectrum sensing time is investigated, and a systematic neural network-based optimization approach is proposed which avoids challenges associated with the conventional analytical solutions. The proposed method exploits a novel learning and optimization cycle to enable an effective cooperation between two kinds of well-known artificial neural networks and finds the optimum value of the channel sensing time without any... 

    A new spectrum sensing circuit for cognitive radio applications

    , Article Proceedings - CIMSim 2011: 3rd International Conference on Computational Intelligence, Modelling and Simulation, 20 September 2011 through 22 September 2011, Langkawi ; 2011 , Pages 404-407 ; 9780769545622 (ISBN) Vahidpoor, Z ; Forooraghi, K ; Atlasbaf, Z ; Ahmadi, A. F ; Sharif University of Technology
    Fast, accurate and efficient sensing is of important aspects in cognitive radio technology. A new sensing circuit is proposed using a phase frequency detector for cognitive radio applications. Using this method, spectral sensing can be done in a very short time by a low cost, low power circuit, compared with available implemented methods. The PFD circuit resolves different frequencies without the need of variable filter bandwidth or the banks of filters. Also it accelerates sensing procedure because of short time needed to detect the signal. Simulations show the accurate operation of this method and comparison with other methods shows faster sweep rates  

    A compact hybrid current/voltage sense amplifier with offset cancellation for high-speed SRAMs

    , Article IEEE Transactions on Very Large Scale Integration (VLSI) Systems ; Volume 19, Issue 5 , 2011 , Pages 883-894 ; 10638210 (ISSN) Sharifkhani, M ; Rahiminejad, E ; Jahinuzzaman, S. M ; Sachdev, M ; Sharif University of Technology
    A hybrid current/voltage sense amplification scheme is proposed for high speed SRAMs. The scheme includes an offset cancellation technique which makes it robust against the current sense amplifier (CSA) mismatch. The offset cancellation allows for fast open loop operation of the differential CSA. A fourfold reduction of the cell access time is achieved compared to the conventional scheme under similar cell current and bitline capacitance. Thanks to its automatic turn off nature, the proposed CSA incurs zero static power without an auxiliary turn off circuit. The reduction of the charge redistribution on the bitlines offers a low bitline dynamic power consumption as well. In this work, the... 

    CS-ComDet: A compressive sensing approach for inter-community detection in social networks

    , Article Proceedings of the 2015 IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining, ASONAM 2015, 25 August 2015 through 28 August 2015 ; 2015 , Pages 89-96 ; 9781450338547 (ISBN) Mahyar, H ; Rabiee, H. R ; Movaghar, A ; Ghalebi, E ; Nazemian, A ; Pei, J ; Tang, J ; Silvestri, F ; Sharif University of Technology
    Association for Computing Machinery, Inc  2015
    One of the most relevant characteristics of social networks is community structure, in which network nodes are joined together in densely connected groups between which there are only sparser links. Uncovering these sparse links (i.e. intercommunity links) has a significant role in community detection problem which has been of great importance in sociology, biology, and computer science. In this paper, we propose a novel approach, called CS-ComDet, to efficiently detect the inter-community links based on a newly emerged paradigm in sparse signal recovery, called compressive sensing. We test our method on real-world networks of various kinds whose community structures are already known, and... 

    An adaptive iterative thresholding algorithm for distributed MIMO radars

    , Article IEEE Transactions on Aerospace and Electronic Systems ; 16 July , 2018 , Page(s): 523 - 533 ; 00189251 (ISSN) Abtahi, A ; Azghani, M ; Marvasti, F ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2018
    In this paper, a Block Iterative Method with Adaptive Thresholding for Sparse Recovery (BIMATSR) is proposed to recover the received signal in an under-sampled distributed MIMO radar. The BIMATSR scheme induces block sparsity with the aid of a signal-dependent thresholding operator which increases the accuracy of the target parameter estimation task. We have proved that under some sufficient conditions, the suggested scheme converges to a stable solution. Moreover, different simulation scenarios confirm that the BIMATSR algorithm outperforms its counterparts in terms of the target parameter estimation. This superiority is achieved at the expense of slightly more computational complexity. It... 

    Secure communication and archiving of low altitude remote sensing data using high capacity fragile data hiding

    , Article Multimedia Tools and Applications ; 2018 ; 13807501 (ISSN) Akhtarkavan, E ; Majidi, B ; Manzuri, M. T ; Sharif University of Technology
    Springer New York LLC  2018
    Fragile data hiding has been extensively used for secure transmission of the sensitive data using cover images, audios and videos. In the past decade, increasingly the remote sensing applications require transmission and archiving of large number of aerial images and videos. Storage and processing of remote sensing data in the public cloud computing and storage platforms, with servers outside the control of the data owners, requires sufficient attention to persevering the privacy of the data. Furthermore, in the past few years the applications of drones and unmanned aerial vehicles demand algorithms designed especially for low altitude remote sensing data. In this paper, a novel fragile data... 

    Simultaneous Block Iterative Method with Adaptive Thresholding for Cooperative Spectrum Sensing

    , Article IEEE Transactions on Vehicular Technology ; Volume 68, Issue 6 , 2019 , Pages 5598-5605 ; 00189545 (ISSN) Azghani, M ; Abtahi, A ; Marvasti, F ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    The effective utilization of the spectrum has become an essential goal in the communications field, which is addressed by the Cognitive Radio (CR) systems. The primary task in a CR system is to sense the spectrum to identify its holes to be exploited by the secondary users. In this paper, we tackle the compressed spectrum sensing problem in a cooperative manner. The CRs distributed in an area take the samples of the signal that has been reached to them through a wireless fading channel. The spectrum has the block-sparse structure. Moreover, the spectrum observed by different CRs in an area share the same block-sparse support. Therefore, we suggest to exploit the joint block-sparsity...