Sharif Digital Repository

It is a great challenge for the universities to present undergraduate students the fundamental knowledge needed to develop intelligent unstable robots. Due to the inherent instability and nonholonomic constraints, the problem of two-wheeled inverted pendulum (TWIP) mobile robot is appealing and challenging case in control and dynamic systems. In this paper, an approach is presented to introduce undergraduate students of the control engineering, the principle of developing a. TWIP mobile robot. For this purpose, a. conceptual design algorithm for TWIP robots is contributed and based on the algorithm and the design criteria, a. prototype of the robot is constructed. In the construction... 

The stability issue of mobile manipulators, particularly when the end-effector and the vehicle have to follow a predefined trajectory (for some special duties like painting a plane or carrying a light load), is a crucial subject and needs special attention. In this paper, by utilizing the manipulator compensation motions, the instantaneous proper configuration for a redundant mobile robot is determined. A fast methodology taking into account the dynamic interaction between the manipulator and the vehicle is proposed for enhancing the tipover stability (i.e. stability against overturning) of the mobile manipulator by employing the soft computing approach including a genetic algorithm, neural... 

Nowadays the size and dimension of mobile manipulators have been decreased for being usable in various regions. This leads several problems such as danger of instability. Therefore, many researches have been done to overcome the problem of overturning of a mobile manipulator. In this paper, an algorithm for increasing the stability of a mobile manipulator is presented based on the optimization of a performance index. The path of vehicle and the desired task of the end-effector are predefined. In order to apply the optimal stability criterion, it is more convenient that the manipulator be of a redundant. Considering the interaction between the vehicle and the manipulator and using the genetic... 

Mobile manipulators are developed in order to execute separately in various regions where there is not possibility for human to appear there. Recently, the size of mobile manipulators has been decreased according to their given tasks. For such systems, the stability issue is very important. The robot system should be able to keep itself in an optimal situation. For reaching to this goal, one can use a redundant degree of freedom for the mobile manipulator such that this redundancy makes it possible to recover the system's stability by dynamic compensatory motion of manipulator when the system is unstable. In this paper, we present an algorithm which is fast enough to stabilize the mobile... 

There was a mistake in the author mane. The right fifth author is “K. Motaghed A.” There was a mistake in the first keyword. The keyword is “Two-wheeled inverted pendulum(TWIP).” The original article can be found online at https://doi.org/10.3103/S0025654419040162. © 2019, Allerton Press, Inc  

Inferior temporal (IT) cortex is the most important part of the brain and plays an important role in response to visual stimuli. In this study, object decoding has been performed using neuron spikes in IT cortex region. Single Unit Activity (SUA) was recorded from 123 neurons in IT cortex. Pseudo-population firing rate vectors were created, then dimension reduction was done and an Artificial Neural Network (ANN) was used for object decoding. Object decoding accuracy was calculated for various window lengths from 50 ms to 200 ms and various window steps from 25 ms to 100 ms. The results show that 150 ms length and 50 ms window step size gives an optimum performance in average accuracy  

Inferior temporal (IT) cortex is the most important part of the brain and plays an important role in response to visual stimuli. In this study, object decoding has been performed using neuron spikes in IT cortex region. Single Unit Activity (SUA) was recorded from 123 neurons in IT cortex. Pseudo-population firing rate vectors were created, then dimension reduction was done and an Artificial Neural Network (ANN) was used for object decoding. Object decoding accuracy was calculated for various window lengths from 50 ms to 200 ms and various window steps from 25 ms to 100 ms. The results show that 150 ms length and 50 ms window step size gives an optimum performance in average accuracy  

In this paper we introduce and propose novel signaling methods and receiver structures based on advanced binary optical logic gates for fiber-optic code division multiple access (FO-CDMA) systems using all-optical signal processing. In the proposed system the users of the network are categorized into multiple classes. Users of each class transmit at the same power level but different from the levels of the other classes' users. Using a combination of optical OR, AND and XNOR logic gates for the receiver structure we show that such a network not only takes the full advantages of all-optical signal processing but also demonstrates a considerable throughput efficiency when compared to ordinary... 

This paper presents a new inference algorithm for Active Learning Method (ALM). ALM is a pattern-based algorithm for soft computing which uses the Ink Drop Spread (IDS) algorithm as its main engine for feature extraction. In this paper a fuzzy number is extracted from each IDS plane rather than the narrow path and spread as in previous approaches. In order to compare performance of the proposed algorithm with the original one, two functions which are widely used in literature are modeled as the benchmark. Simulation results show that the proposed algorithm is as effective as previous one in the modeling task  

Ta0.8Hf0.2C ceramic has the highest melting point among the known materials (4000 °C). However, this high melting point makes the ceramic difficult to be sintered at temperatures lower than 2300 °C, pressurelessly. The purpose of this study is to consolidate Ta 0.8Hf0.2C UHTC by pressureless sintering at 2000 °C using MoSi2 as sintering aid. In this regard, effect of different amounts of MoSi2 on sintering behavior of Ta0.8Hf 0.2 UHTC was investigated. It was observed that condensation of the UHTC after sintering at 2000 °C was enhanced by increasing MoSi2 content and the highest relative density of 95% was obtained in the presence of 24 vol.% MoSi2. XRD pattern of the sintered UHTC... 

We present a constant-time randomized distributed algorithms in the congested clique model that computes an O(α)-vertex-coloring, with high probability. Here, α denotes the arboricity of the graph, which is, roughly speaking, the edge-density of the densest subgraph. Congested clique is a well-studied model of synchronous message passing for distributed computing with all-to-all communication: per round each node can send one O(log n)-bit message algorithm to each other node. Our O(1)-round algorithm settles the randomized round complexity of the O(α)-coloring problem. We also explain that a similar method can provide a constant-time randomized algorithm for decomposing the graph into O(α)... 

In this article we present an all passive optical iterative interference cancellation method for optical CDMA. We propose the receiver structure based on advanced binary optical logic gates (ABOLGs). Since the performance bottleneck in optical communication systems is the conversion from optical to electronic domains for optical detectors, the interference cancellation has been performed in the optical domain. In incoherent optical communication systems, we have only the positive values for the optical signals. In the proposed system, we bypass the negative values using logic arrays. In the simulations we consider multiple access interference and neglect other sources of noise. Simulation... 

Large scale decentralized communication systems have motivated a new trend towards online routing where routing decisions are performed based on a limited and localized knowledge of the network. Geometrical greedy routing has been among the simplest and most common online routing schemes. While a geometrical online routing scheme is expected to deliver each packet to the point in the network that is closest to the destination, geometrical greedy routing, when applied over generalized substrate graphs, does not guarantee such delivery as its forwarding decision might deliver packets to a localized minimum instead. This letter investigates the necessary and sufficient conditions of greedy... 

The A5/1 algorithm is one of the most applicable and famous stream cipher algorithms. However, the period of A5/1 keystream sequence and the exact structure of its internal state transition were not investigated thoroughly, until now. This paper deals with the transition of the internal state of A5/1 algorithm and tries to present a model for such a transition. Additionally, the internal states are divided into two groups, initially periodic and ultimately periodic. The presented model is verified using a variety of simulations and it is consistent with theoretical results as well  

In this work, phase evolution, solid solution formation and diffusion behavior of three binary systems, including TaC-HfC, TaC-ZrC and HfC-ZrC, were investigated. In this regard, pure carbide powders of TaC, HfC, and ZrC were selected as starting raw materials. The prepared samples were heat treated at 2000 C for 1 hour in Ar atmosphere. For each system, three compositions were chosen for phase evolution investigation by X-ray diffractometer. Moreover, three couple samples were prepared for diffusion behavior survey through SEM/EDX analyses. It was found that ZrC diffuses faster in TaC structure rather than HfC and a single phase solid solution phase with hosting TaC is formed in TaC-HfC and... 

Ta0.8Hf0.2C ceramic has the highest melting point among the known materials (4000°C). Spark plasma sintering is a new route for consolidation of materials, specially ultra high temperature ceramics (UHTCs), which are difficult to be sintered at temperatures lower than 2000°C.The purpose of this study is to consolidate Ta0.8Hf0.2C by spark plasma sintering at low temperature using MoSi2 and TaSi2 as sintering aid. In this regard, effect of different amounts of sintering aids and carbides ratio on densification behavior and mechanical properties of Ta1-xHfxC were investigated.Fully consolidation of Ta0.8Hf0.2C was achieved in presence of 12vol.% sintering aid after sintering at 1650°C for 5min... 

Echo and sound resonance in a conference room cause obscure speech and make listeners tired. Thus, the acoustical properties of a conference room are vitally important. The conference room 412 at Sharif University Physics Department failed to meet basic acoustical standards. The aim of this research is to improve reverberation time (RT) of the conference room using Helmholtz resonators with defined dimensions, diffusers, and sound absorbers. Helmholtz resonators are widely used to absorb sound noise especially at low frequencies. They are particularly useful when noise has a narrow-frequency band. One of the advantages of using Helmholtz resonators is their capacity to be tuned on different... 

With the aid of nanotechnology and understanding of visual and retinal neuroscience, tremendous advances have been achieved in the treatment of people who have lost their vision. Among vision restoration techniques, stem cells or gene therapy remain in their early phases of development, while visual prosthesis (bionic eye) attains some approaches in vision restoration. There are several ongoing projects around the world on visual prosthesis, including Argus II (received FDA approval), Boston Retinal Implant Project, Epi-Ret 3, Intelligent Medical Implants and Alpha-IMS (Retina Implant AG). One of the most crucial traits of implants is vision resolution that theoretically correlates with... 

In this study, a new method for the simulation of the time-dependent behavior of actin cytoskeleton during cell shape change is proposed. For this purpose, a three-dimensional model of endothelial cell consisting of cell membrane, nucleus membrane, and main components of cytoskeleton, namely actin filaments, microtubules, and intermediate filaments is utilized. Actin binding proteins, which play a key role in regulating actin cytoskeleton behavior, are also simulated by using a novel technique. The actin cytoskeleton in this model is more dynamic and adoptable during cell deformation in comparison to previous models. The proposed model is subjected to compressive force between parallel micro... 

In this paper, we present and analyze a novel all-optical multilevel multiclass optical code division multiple access (OCDMA) system, using optical analog-to-digital converter (ADC) and advanced optical logic gate elements. In such OCDMA network, users are distributed in Mdifferent classes. Furthermore, power level with which users in class j,j = 2⋯M, transmit optical pulses, is twice the power level at which users of class j - 1transmit their optical pulses. We achieve optical transmitter structure that satisfies these conditions using power control schemes. Also, we suggest two receiver structures for the aforementioned multiclass multilevel system. The first and simple receiver structure...