Sharif Digital Repository

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  

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  

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... 

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... 

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  

Time domain equalizers are used in the receiver of a discrete multitone (DMT) receiver to compensate the channel effects on the received signal. There are a lot of DMT equalization algorithms presented in the literature, but recently a novel Per Tone equalizer structure was proposed which offers some advantages over the previous traditional ones. The objective of this paper is to provide an overview of the important concepts of this technique and evaluate its initialization complexity. The performance of this technique is also compared with typical time-domain equalization algorithms in different simulation environments. © 2004IEEE  

Discrete multitone (DMT) modulation is used for the efficient transmission of data over nonideal channels. By nonideal channel, we mean that the channel with the frequency response is not flat. Also the noise is present in this kind of channel. In recent years, optimization of filter banks for the DMT systems is considered. Recent researches focused on the orthonormal filter banks have shown that the principal component filter bank (PCFB) is optimal for this application. We focus on one class of biorthogonal filter banks and find the optimum solution for this class. We also have shown that the performance of this structure is better than the optimum orthonormal filter bank. © 2003 IEEE  

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  

Design and operation of an opto-mechanical sensor for mass measurements is reported. This device uses a pair of optical fibers and a reflecting coated lens. The light intensity modulation is based on the relative motion of the lens due to a given mass with respect to the optical fibers. The modulated intensity because of the weighing mass has been measured by using a digital voltmeter. A full-range sensitivity of about 11.5 mV/g for a dynamic range of 80 g is obtained. A mass resolution of better than 0.25 g has been measured with this device. The measured output response is checked against the expected theoretical one and a general agreement observed. A comparison with similar experimental... 

Design and operation of an optical fiber device for temperature sensing and thermal expansion measurement are reported. The modulated intensity has been measured by using a pair of 450 μm core fiber, one acting as the source and the other one as receiving fiber. In this design, the light intensity modulation is based on the relative motion of the optical fibers and a reflective coated lens. By using displacement calibration data for this sensor, the linear thermal expansion of the aluminum rod is determined. This sensor shows an average sensitivity of about 11.3 mV/°C for temperature detection and 7 μm/°C for thermal expansion detection. Device resolution for a linear expansion measurement... 

Feasibility of a new integrated amplitude modulator/switch operating up to the visible spectrum, based on the absorption of light due to the linear interaction of the incident laser and a two-dimensional plasma layer is demonstrated. Plasma layers are generated via the Muller effect at the waveguide's interfaces. A plasma wave is excited in the two-dimensional gas when it is illuminated by electromagnetic radiation. Thus, due to the energy transfer from the electromagnetic wave to the plasma wave, the output light intensity can be controlled. The device is capable of amplitude modulation of guided beams in dielectric waveguides. Analysis based on both full-classical and semiclassical... 

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 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... 

We consider multirate time-hopping ultra-wideband (TH-UWB) communication systems where each user can have several multirate services. We investigate both constant spreading factor scheme, which uses multicode, and variable spreading factor scheme, which uses constant chip time and variable frame number. For multicode structure, we consider two methods. In the first, one kind of signature (PN) code is used to distinguish users and their diverse services alike. Whereas in the second one different users and different services of the same user are distinguished through two kinds of signature codes, namely PN code and Walsh code, respectively. For variable spreading factor scheme, one signature... 

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... 

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... 

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... 

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  

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... 

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