Sharif Digital Repository

The existing methods in attitude control of satellites are based on using the estimate of satellite attitude, which is usually generated by using multiple vector measurements. In this paper we propose an output feedback controller that directly uses a single vector measurement and does not use an attitude estimator. The output feedback gain is computed by solving a generalized Riccati differential equation (GRDE). The existence of a solution to the GRDE depends on a uniform controllability condition  

In the present study, an analytical solution is proposed to determine the interlaminar stresses in long symmetric laminated composite plates subjected to shearing loads. An improved first-order shear deformation theory (IFSDT) and a simplified IFSDT (SIFSDT) are utilized to calculate the unknown constants appearing in the reduced elasticity displacement field which actually demonstrate the global deformations of the plate. Then the numerical values of the interlaminar normal and shear stresses are established through the laminates by using Reddy's layerwise theory. Finally, several numerical examples are presented to study the interlaminar stresses in the interfaces of the layers and through... 

In this paper, employing the limit analysis theorem, critical loading on functionally graded (FG) circular plate with simply supported boundary conditions and subjected to an arbitrary rotationally symmetric loading is determined. The material behavior follows a rigid-perfectly plastic model and yielding obeys the von-Mises criterion. In the homogeneous case, the highly nonlinear ordinary differential equation governing the problem is analytically solved using a variational iteration method. In other cases, numerical results are reported. Finally, the results are compared with those of the FG plate with Tresca yield criterion and also in the homogeneous case with those of employing the... 

A large number of Wireless Sensor Network (WSN) security schemes have been proposed in the literature, relying primarily on symmetric key cryptography. To enable those, Random Key pre-Distribution (RKD) systems have been widely accepted. However, WSN nodes are vulnerable to physical compromise. Capturing one or more nodes operating with RKD would give the adversary keys to compromise communication of other benign nodes. Thus the challenge is to enhance resilience of WSN to node capture, while maintaining the flexibility and low-cost features of RKD. We address this problem, without any special-purpose hardware, proposing a new and simple idea: key splitting. Our scheme does not increase... 

We consider the problem of determining the tradeoff between the rate and the block-length of polar codes for a given block error probability when we use the successive cancellation decoder. We take the sum of the Bhattacharyya parameters as a proxy for the block error probability, and show that there exists a universal parameter μ such that for any binary memoryless symmetric channel W with capacity I(W), reliable communication requires rates that satisfy R < I(W) - αN -1/μ, where α is a positive constant and N is the block-length. We provide lower bounds on μ, namely μ ≥ 3.553, and we conjecture that indeed μ = 3.627, the parameter for the binary erasure channel  

The authors propose a new technique to model the arriving energy's knowledge (AEK) in the energy harvesting (EH) communication systems. They consider a batteryless EH transmitter with the AEK non-causally provided to it. They show that the capacity of the authors' model in general case, that is, discrete memoryless channel, can be derived through a binning scheme. This resembles a Gelfand-Pinsker type capacity formula which intuitively is the result of treating the energy as a channel state. Moreover, they investigate two especial cases of binary and Gaussian channels with the EH transmitters. In the binary symmetric channel with EH transmitter (BSCEH), their coding scheme leads to achieve... 

A large number of random key pre-distribution (RKD) schemes have been proposed in the literature to secure wireless sensor network applications, relying on symmetric key cryptography. However, sensor nodes are exposed to physical compromise by adversaries, who target the symmetric keys stored at each node. With the stolen keys in their possession, the adversaries are then able to compromise communication links between benign nodes. Here, the big challenge arises: how to increase resilience of RKD schemes for wireless sensor networks to node capture, while maintaining the flexibility and low-cost features of RKD? We propose the idea of key splitting to address this problem, without the need... 

In this study, the authors extend the concept of relay channel with orthogonal components to define a class of symmetric relay networks with orthogonal components named symmetric orthogonal relay network. In the defined network, the channels diverge from each node sender use different frequency bands whereas the channels converge to each node receiver use the same frequency band. This structure is very well understood in half-duplex transmission systems where the relays cannot send and receive at the same time or over the same frequency band. The authors show that the unicast capacity of the defined network is equal to the cut-set bound. In the achievability proof, the authors take advantage... 

An inconsistency between the circular symmetric geometry of conventional optical imagers and the geometry of long linear sensors used in today's line-scan cameras results in suboptimal separate design of optics and electronics of scanner systems. Based on the method of foveated optical imaging, a technique named foveated scanning (FS) is proposed in this paper. The FS technique is employed to enlarge the one-dimensional resolved field of view (RFOV) of conventional lenses and permits optimized performance on a line-of-interest in the image plane where the optoelectronic sensor is located. The achieved enlargement of RFOV is verified on a proof-of-concept basic telephoto lens. Both modulation... 

Let P be a set of points in the plane, each equipped with a directional antenna that covers a sector of angle α and range r. In the symmetric model of communication, two antennas u and v can communicate to each other, if and only if v lies in u's coverage area and vice versa. In this paper, we introduce the concept of fault-tolerant spanners for directional antennas, which enables us to construct communication networks that retain their connectivity and spanning ratio even if a subset of antennas are removed from the network. We show how to orient the antennas with angle α and range r to obtain a k-fault-tolerant spanner for any positive integer k. For α≥π, we show that the range 13 for the... 

Net fluid flow of soap films induced by (ac or dc) electric fields in asymmetric frames is presented. Previous experiments of controllable soap film flow required the simultaneous use of an electrical current passing through the film and an external electric field or the use of nonuniform ac electric fields. Here a single voltage difference generates both the electrical current going through the film and the electric field that actuates on the charge induced on the film. The film is set into global motion due to the broken symmetry that appears by the use of asymmetric frames. If symmetric frames are used, the film flow is not steady but time dependent and irregular. Finally, we study... 

In this study, we demonstrated a straightforward method for the easy access of chromeno[4,3-b]quinolin-6-ones via a one-pot three-component reaction of 4-hydroxycoumarin, aldehydes and aryl amines in the presence of halloysite nanoclay as an eco-friendly, inexpensive and green heterogeneous catalyst under solvent-free conditions. Moreover, symmetric and unsymmetric bis-chromeno[4,3-b]quinolin-6-ones were obtained from dialdehyde or diamines in good yields by this method. To date, this is the first report on the synthesis of symmetric and unsymmetric bis-chromeno[4,3-b]quinolin-6-ones via such a one-pot, multicomponent reaction. Some prepared chromeno[4,3-b]quinolin-6-ones displayed as... 

A new non-symmetric 5R-SPM is introduced and a geometrical approach is developed to analyze its configurations and singularities. The proposed methodology determines the type of configuration of a 5R-SPM, i.e. regular, singular, or out-of-workspace and also the type of singularity, i.e. instantaneous or finite, only based on geometric parameters and without solving verbose kinematic equations. It also provides insights into the workspace and singularities of 5R-SPMs, in the preliminary stage of design. The mechanism was analyzed by both the new geometrical approach and conventional methods for comparison. The geometrical approach could intuitively detect all the singularities observed by the... 

A specific class of differential cryptanalytic approach, named as impossible differential attack, has been successfully applied to several symmetric cryptographic primitives in particular encryption schemes such as Advanced Encryption Standard (AES). Such attacks exploit differences that are impossible at some intermediate state of the cipher algorithm. The best-known impossible differential attack against AES-128 has applied to six rounds. An attack on AES-128 up to seven rounds is proposed. The proposed attack requires 2115.5 chosen plaintexts and 2109 bytes of memory and performs 2119 seven-round AES encryptions. This is also the best-known attack on a reduced version of the AES-128 till...