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Total 464 records

    Modules with finitely many submodules

    , Article Algebra Colloquium ; Volume 23, Issue 3 , 2016 , Pages 463-468 ; 10053867 (ISSN) Akbari, S ; Khalashi Ghezelahmad, S ; Yaraneri, E ; Sharif University of Technology
    World Scientific Publishing Co. Pte Ltd  2016
    Abstract
    In this paper, we study modules having only finitely many submodules over any ring which is not necessarily commutative. We try to understand how such a module decomposes as a direct sum. We justify that any module V having only finitely many submodules over any ring A is an extension of a cyclic A-module by a finite A-module. Under some assumptions on A, such as commutativity of A, we prove that an A-module V has finitely many submodules if and only if V can be written as a direct sum of a cyclic A-module having only finitely many A-submodules and a finite A-module  

    Pure-injectivity of tensor products of modules

    , Article Algebra Colloquium ; Vol. 21, issue. 1 , 2014 , pp. 151-156 ; ISSN: 10053867 Pournaki, M. R ; Torrecillas, B ; Tousi, M ; Yassemi, S ; Sharif University of Technology
    Abstract
    A classical question of Yoneda asks when the tensor product of two injective modules is injective. A complete answer to this question was given by Enochs and Jenda in 1991. In this paper the analogue question for pure-injective modules is studied  

    On the complement of the intersection graph of submodules of a module

    , Article Journal of Algebra and its Applications ; Volume 14, Issue 8 , October , 2015 ; 02194988 (ISSN) Akbari, S ; Tavallaee, H. A ; Khalashi Ghezelahmad, S ; Sharif University of Technology
    World Scientific Publishing Co. Pte Ltd  2015
    Abstract
    Let R be a ring with identity and M be a unitary left R-module. The complement of the intersection graph of submodules of M, denoted by Γ(M), is defined to be a graph whose vertices are in one-to-one correspondence with all nontrivial submodules of M and two distinct vertices are adjacent if and only if the corresponding submodules of M have zero intersection. In this paper, we consider the complement of the intersection graph of submodules of a module. We prove that, if Γ(M) is connected and Δ(Γ(M)) < ∞, then M is semisimple, where Δ(Γ(M)) is the maximum degree of Γ(M). We show that, if Γ(M) is a forest, then each component of Γ(M) is a star graph. Moreover, it is proved that, if Γ(M) is a... 

    Some results on the intersection graph of submodules of a module

    , Article Mathematica Slovaca ; Volume 67, Issue 2 , 2017 , Pages 297-304 ; 01399918 (ISSN) Akbari, S ; Tavallaee, H ; Khalashi Ghezelahmad, S ; Sharif University of Technology
    De Gruyter Open Ltd  2017
    Abstract
    Let R be a ring with identity and M be a unitary left R-module. The intersection graph of submodules of M, denoted by G(M), is defined to be a graph whose vertices are in one to one correspondence with all non-trivial submodules of M and two distinct vertices are adjacent if and only if the corresponding submodules of M have non-zero intersection. In this paper, we consider the intersection graph of submodules of a module. We determine the structure of modules whose clique numbers are finite. We show that if 1 < ω(G(M)) < ∞, then M is a direct sum of a finite module and a cyclic module, where ω(G(M)) denotes the clique number of G(M). We prove that if ω(G(M)) is not finite, then M contains... 

    Type based sign modulation for molecular communication

    , Article IWCIT 2016 - Iran Workshop on Communication and Information Theory, 3 May 2016 through 4 May 2016 ; 2016 ; 9781509019229 (ISBN) Mosayebi, R ; Gohari, A ; Mirmohseni, M ; Nasiri Kenari, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2016
    Abstract
    One of the foremost challenges in modulation scheme for molecular communication is positivity of the transmission signal (only a positive concentration of molecules can be released in the environment). This restriction makes handling of the InterSymbol Interference (ISI) a challenge for molecular communication. In this paper, a novel modulation is proposed which introduces use of negative signals to ameliorate the transmission link performance. A precoder scheme based on the diffusion channel model is proposed and shown to have a significant improvement compared to previous modulation schemes such as CSK and MCSK  

    Deformation of outer representations of Galois group

    , Article Iranian Journal of Mathematical Sciences and Informatics ; Volume 6, Issue 1 , 2011 , Pages 35-52 ; 17354463 (ISSN) Rastegar, A ; Sharif University of Technology
    2011
    Abstract
    To a hyperbolic smooth curve defined over a number-field one naturally associates "ananabelian" representation of the absolute Galois group of the base field landing in outer automorphism group of the algebraic fundamental group. In this paper, we introduce several deformation problems for Lie-algebra versions of the above representation and show that, this way we get a richer structure than those coming from deformations of "abelian" Galois representations induced by the Tate module of associated Jacobian variety. We develop an arithmetic deformation theory of graded Lie algebras with finite dimensional graded components to serve our purpose  

    Cohen-Macaulayness and Limit Behavior of Depth for Powers of Cover Ideals

    , Article Communications in Algebra ; Volume 43, Issue 1 , Aug , 2015 , Pages 143-157 ; 00927872 (ISSN) Constantinescu, A ; Pournaki, M. R ; Seyed Fakhari, S. A ; Terai, N ; Yassemi, S ; Sharif University of Technology
    Taylor and Francis Inc  2015
    Abstract
    Let K{double-struck} be a field, and let R = K{double-struck}[x1,.., xn] be the polynomial ring over K{double-struck} in n indeterminates x1,.., xn. Let G be a graph with vertex-set {x1,.., xn}, and let J be the cover ideal of G in R. For a given positive integer k, we denote the kth symbolic power and the kth bracket power of J by J(k) and J[k], respectively. In this paper, we give necessary and sufficient conditions for R/Jk, R/J (k), and R/J [k] to be Cohen-Macaulay. We also study the limit behavior of the depths of these rings  

    Design and performance of an optical fiber sensor based on light leakage

    , Article Review of Scientific Instruments ; Volume 77, Issue 6 , 2006 ; 00346748 (ISSN) Golnabi, H ; Jafari, R ; Sharif University of Technology
    2006
    Abstract
    Design and operation of an optical fiber sensor based on the light leakage from one fiber to another one causing intensity modulation are reported. Performance of this sensor is tested as a liquid level sensor for different liquids and the experimental results are reported. The dry and wet signals for this probe are measured for a series of measurements and important factors concerning sensor operation are described. The precision of measured values, reproducibility of the results (1.3%), and the stability of sensing operation as a function of time at different launching powers are also reported (0.8%). The reported results are promising and verify the successful operation of such a device... 

    Ion Channel Based Bio-Synthetic Modulator for Diffusive Molecular Communication

    , Article IEEE Transactions on Nanobioscience ; Volume 15, Issue 5 , 2016 , Pages 418-432 ; 15361241 (ISSN) Arjmandi, H ; Ahmadzadeh, A ; Schober, R ; Nasiri Kenari, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2016
    Abstract
    In diffusion-based molecular communication (DMC), a transmitter nanomachine is responsible for signal modulation. Thereby, the transmitter has to be able to control the release of the signaling molecules employed for representing the transmitted information. In nature, an important class of control mechanisms for releasing molecules from cells utilizes ion channels which are pore-forming proteins across the cell membrane. The opening and closing of the ion channels is controlled by a gating parameter. In this paper, an ion channel based modulator for DMC is proposed which controls the rate of molecule release from the transmitter by modulating a gating parameter signal. Exploiting the... 

    Nonlinear FM waveform design to reduction of sidelobe level in autocorrelation function

    , Article 2017 25th Iranian Conference on Electrical Engineering, ICEE 2017, 2 May 2017 through 4 May 2017 ; 2017 , Pages 1973-1977 ; 9781509059638 (ISBN) Ghavamirad, R ; Babashah, H ; Sebt, M. A ; Sharif University of Technology
    Abstract
    This paper will design non-linear frequency modulation (NLFM) signal for Chebyshev, Kaiser, Taylor, and raised-cosine power spectral densities (PSDs). Then, the variation of peak sidelobe level with regard to mainlobe width for these four different window functions are analyzed. It has been demonstrated that reduction of sidelobe level in NLFM signal can lead to increase in mainlobe width of autocorrelation function. Furthermore, the results of power spectral density obtained from the simulation and the desired PSD are compared. Finally, error percentage between simulated PSD and desired PSD for different peak sidelobe level are illustrated. The stationary phase concept is the possible... 

    A 10MHz CTDSM with differential VCO-based quantizer in 90nm

    , Article Proceedings of the 2013 8th International Conference on Design and Technology of Integrated Systems in Nanoscale Era, DTIS 2013 ; 2013 , Pages 128-133 ; 9781467360388 (ISBN) Yousefzadeh, B ; Hajian, A ; Sharifkhani, M ; Sharif University of Technology
    2013
    Abstract
    This paper presents a new architecture for VCO-based Continuous Time Delta Sigma Modulators. This approach is based on the differential configuration for the quantizer while maintains its inherent dynamic element matching property. Consuming no additional power and area compared to the conventional scheme, this architecture can eliminate the even orders of harmonic distortion and achieve higher linearity. Theoretical analysis for signal to quantization noise, power and area consumption and mismatch effect is provided. To illustrate the effectiveness of the new architecture in continuous time modulators, a modulator with 640 MHz sampling rate utilizing the mentioned quantizer is simulated in... 

    Performance improvement of an optimal family of exponentially accurate sigma delta modulator

    , Article International Conference on Signal Processing Proceedings, ICSP, 24 October 2010 through 28 October 2010, Beijing ; 2010 , Pages 1-4 ; 9781424458981 (ISBN) Kafashan, M ; Beygiharchegani, S ; Marvasti, F ; Sharif University of Technology
    2010
    Abstract
    In this paper a new iterative method is used to convert analog signals to digital (A/D) using sigma delta modulator (SDM). If intelligent reconstruction technique is used for decoding, either signals with higher bandwidth can be digitized or simpler circuitry can be utilized. An optimal family of SDM has recently been devised in order to improve performance of A/D converters. In this work, we improve performance of A/D converters even more, by combining this optimal family of SDM with iterative methods  

    A solution to gain attack on watermarking systems: logarithmic homogeneous rational dither modulation

    , Article ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings, 142010 through 19 March 2010 ; March , 2010 , Pages 1746-1749 ; 15206149 (ISSN) ; 9781424442966 (ISBN) Akhaee, M. A ; Amini, A ; Ghorbani, G ; Marvasti, F ; Sharif University of Technology
    2010
    Abstract
    Among the many attacks against watermarked data, the gain attack is less supported with countermeasures. The effectiveness of this attack becomes more evident in quantization-based embedding algorithms such as Dither Modulation (DM). In this paper, the general solution for both block and sample type DM schemes that are robust against gain attacks is considered. Among the solutions, we concentrate on a subclass of the algorithms which are insensitive to additive noise attacks; i.e., we introduce watermarking schemes which are both robust against gain and additive noise attacks. The simulation results confirm the desired performance of the final algorithm against these attacks while outperform... 

    A low-power, second-order Δ/∑ modulator using a single class-AB op-amp for voice-band applications

    , Article Analog Integrated Circuits and Signal Processing ; Volume 49, Issue 2 , 2006 , Pages 199-211 ; 09251030 (ISSN) Safarian, A ; Sahandiesfanjani, F ; Heydari, P ; Atarodi, S. M ; Sharif University of Technology
    2006
    Abstract
    The design of a power-efficient second-order Δ/∑ modulator for voice-band is presented. At system level, a new single-loop, single-stage modulator is proposed. The modulator employs only one class-AB op-amp to realize a second-order noise shaping for voice-band applications. The modulator is designed in a 0.25μm standard CMOS process, and exhibits 86 dB dynamic range (DR) for a 4 kHz voice-bandwidth. The proposed modulator consumes 125μW from a 2.5 V supply. © Springer Science + Business Media, LLC 2006  

    Label swapping in all-optical networks using tunable fiber Bragg grating arrays

    , Article 8th International Conference Advanced Communication Technology, ICACT 2006, Phoenix Park, 20 February 2006 through 22 February 2006 ; Volume 2 , 2006 , Pages 1429-1431 ; 8955191294 (ISBN); 9788955191295 (ISBN) Rajabvand, M ; Behnia, F ; Fatehi, M. T ; Sharif University of Technology
    IEEE Computer Society  2006
    Abstract
    In this paper we use tunability of FBG to introduce a novel device for optically reading, writing or modifying the low-speed label(s). We utilize tunable FBG arrays as concurrent label modulating (multiplexing) elements. This second-level intensity modulation is used to send signaling messages between nodes of WDM networks. The fiber optic small-signal modulator is formulated, and its behavior is compared with the published reports  

    Efficient modulation technique for optical code division multiple access networks: Differential pulse position modulation

    , Article IET Optoelectronics ; Vol. 8, issue. 5 , 2014 , p. 181-190 Khazraei, S ; Shoaie, M. A ; Pakravan, M. R ; Sharif University of Technology
    Abstract
    In this study, the authors study a fibre-optic local area network deploying optical code division multiple access technique with differential M-ary pulse position modulation (DPPM). The authors present the performance analysis of DPPM signalling using a double optical hardlimiter receiver structure considering the impairment caused by interference of other users. The analysis assumes a set of bit asynchronous transmitters employing generalised optical orthogonal codes for their DPPM signalling (GOOC-DPPM). Using mathematical analysis and simulations, the authors have demonstrated that GOOCDPPM improves both frame error probability and the maximum achievable network throughput compared with... 

    Non-linear effects of intensity-modulated and directly detected optical links on receiving a linear frequency-modulated waveform

    , Article IET Optoelectronics ; Volume 5, Issue 6 , 2011 , Pages 255-260 ; 17518768 (ISSN) Shabani, M ; Akbari, M ; Sharif University of Technology
    Abstract
    Limitations imposed by the non-linearity of optical links, in the front end of a receiving array antenna, on the performance of a pulse compression radar are studied. Particularly linear frequency-modulated waveforms backscattered from a pair of targets are inspected. Inter-modulation and gain compression by noise are presented as two remarkable phenomena. For an interconnection of two dual-drive Mach-Zehnder modulators, the sensitivity of the compressed echo at the output of a matched filter receiver to certain tunable parameters is studied numerically. Finally, certain values of DC bias and phase shift between the modulators' electrodes are recommended  

    Improved unity-STF sturdy MASH ΣΔ modulator for low-power wideband applications

    , Article Electronics Letters ; Volume 51, Issue 23 , November , 2015 , Pages 1941-1942 ; 00135194 (ISSN) Taghizadeh, M ; Sadughi, S ; Sharif University of Technology
    Institution of Engineering and Technology  2015
    Abstract
    A novel sturdy multi-stage noise-shaping sigma-delta modulator that cancels the first-stage quantisation error at the output of the modulator is presented. Since any stage of the modulator has unity signal transfer function, the modulator would be very robust to circuit non-idealities such as finite op-amp gain. Furthermore, the signal processing timing issue in the critical paths of the proposed topology has been relaxed due to shifting the delay of the last integrator to the feedback path of the modulator. Moreover, this topology can be implemented in the circuit level by a fewer active blocks. Therefore, it practically would be suitable for low-voltage and low-oversampling applications.... 

    Different optical fiber sensor designs for liquid flow monitoring

    , Article Australian Journal of Basic and Applied Sciences ; Volume 4, Issue 8 , 2010 , Pages 3315-3323 ; 19918178 (ISSN) Bahar, M ; Kargaran, L ; Golnabi, H ; Sharif University of Technology
    2010
    Abstract
    Design and operation of three different optical sensors based on the intensity modulation are reported in this article. These sensors are measuring absence or presence of any liquid and the measurement variable is refractive index and optical absorption. Reported devices can also check the presence of air bubbles in the liquid flow line. Performance of these sensors is tested as a liquid flow monitoring device while using different light sources. Sensor #1 uses a simple cell with the long transmitter and receiver optical fibers. Sensor #2 utilizes a small cell assembly that includes the short transmitter and receiver fibers. Sensor #3 employs a quartz flow cell with the direct light... 

    Performance analysis of carrier-less modulation schemes for wireless nanosensor networks

    , Article 15th IEEE International Conference on Nanotechnology, 27 July 2015 through 30 July 2015 ; 2015 , Pages 45-50 ; 9781467381550 (ISBN) Zarepour, E ; Hassan, M ; Chou, C. T ; Bayat, S ; Nanotechnology Council ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc 
    Abstract
    Wireless Nano-scale Sensor Networks (WNSNs) are very simple and energy restricted networks that operate over terahertz band ranging from 0.1-10 THz, which faces significant molecular absorption noise and attenuation. Given these challenges, reliability, energy efficiency, and simplicity constitute the main criteria in designing communication protocols for WNSNs. Due to its simplicity and energy efficiency, carrier-less pulse based modulation is considered the best candidate for WNSNs. In this paper, we compare the performance of four different carrier-less modulations, PAM, OOK, PPM, and BPSK, in the context of WNSNs operating within the terahertz band. Our study shows that although BPSK is...