Sharif Digital Repository

Continuous improvement and extension of pervasive computing environments, in which objects have high mobility and limited computing power, implies service migration to be considered as one of the main issues. On the other hand, context-awareness which is the most distinguishable feature of pervasive computing helps better serving of users. Accordingly, migration in the presence of context-awareness is considered as the underlying of our motivation. This improves the performance of migration, which is not easily achievable through traditional migration techniques. In this paper we introduce a model to support context-aware migration besides its migration process phases and framework. Our... 

Forthcoming networked systems require mechanisms for on-the-fiy reconfiguration in their protocol stacks to be able to operate in different situations and networks. Since every protocol in a protocol stack has at least one peer protocol in another system, dynamic reconfiguration of a protocol raises the need for reconfiguration in the peer stack. For an assured dynamic (run-time) reconfiguration, executions of two peer protocols are stopped in a safe state, new protocols are initialized, and stacks switch to the new protocols at the same time. This paper proposes a software framework for dynamic reconfiguration of two communicating protocol stacks. A distributed algorithm is implemented in... 

This paper proposes a software framework for dynamic-reconfigurable protocol stack. The framework presents mechanisms andan algorithm/or all required phases for reconfiguration of a running protocol component that include freezing the component in a safe state, changing the component, and state transfer to a new component. Considering that every running protocol component communicates with at least one peer component in another system, we perform the reconfiguration with respect to the peer component. © 2007 IEEE  

Reconfigurability for a component of a distributed component-based system means ability to replace the component with a new one, in presence of the other components. In this context, substitutability and compatibility of components should be analyzed. In this paper, we use I/O-Constraint Automata to model behavior of components and propose enough formalism for substitutability and compatibility analysis. We show that in the context of distributed non-blocking components, there is a relation weaker than usual simulation relation in automata theory for notion of substitutability. We illustrate the relation between substitutability and compatibility to reason about the reconfigurability of a... 

A communication protocol consists of a sequence of messages used by peer entities to communicate. Each entity in a network is equipped by at least one protocol stack. Due to the need for on-the-fly reconfiguration of protocol stack in future communication and computation devices, formalizing substitutability and compatibility of protocol entities are important in correctness assessment of dynamic reconfiguration. In this paper, we extend Constraint Automata and propose I/O-Constraint Automata to model behavior of protocols and propose enough formalism for substitutability and compatibility relations between protocols. We introduce input-blocking property of communication protocols, and show... 

Semisolid casting and forming have attracted growing attention of both research and industry. A suitable semisolid microstructure consists of globular grains in a matrix of lower melting point phase and may be produced by various methods, including the cooling slope technique. The combined effect of cooling slope angle and mould vibration on the semisolid microstructures of AI7075 is reported. The results indicate that mould vibration decreases average grain size significantly and that the effect increases with increasing size of primary crystals entering the mould through the cooling slope. Mould vibration was also found to improve the shape factor of alloy grains after appropriate... 

Future communication and computation devices require mechanisms for on-the-fly reconfiguration in their protocol stack to operate in different situations and networks. This paper proposes a component-based framework for dynamic-reconfigurable protocol stack. Considering that every running protocol component communicates with at least one peer component, unlike related work our framework supports synchronous reconfiguration of two peer protocol components in two communicating protocol stacks. © Springer-Verlag Berlin Heidelberg 2007  

Growing the need for long-life and high-available programs, dynamic reconfiguration is going to be an important research issue. Dynamic reconfiguration enables the software systems to change at runtime to decrease their down-time in case of any updating, upgrading or in any changes. Any invalid reconfiguration at runtime may lead programs into invalid states. In this paper, we investigate on validity of dynamic reconfiguration for component-based programs and propose validity conditions for it. We show that the problem of validity assurance in general is undecidable and there is no general-purpose algorithm to verify dynamic reconfiguration validity. To have a computable algorithm for... 

Using multiple antennas at the transmit and receive sides of a passive radar brings both the benefits of MIMO radar and passive radar. However one of the obstacles arisen in such configuration is the receive antennas placement in proper positions so that the radar performance is improved. Here we just consider the case of positioning one receiver among multiple illuminators of opportunity. Indeed it is a start for the solution of optimizing the geometry of the multiple receivers in a passive radar  

SbCl3 supported on montmorillonite K-10 is an efficient catalyst for the ring opening of epoxides with aromatic amines under solvent-free conditions and microwave irradiation to give the corresponding b-amino alcohols in high yields with high regioselectivity  

One of the important obstacles in MIMO (Multiple Input Multiple Output) radars is the issue of designing proper transmit signals. Indeed, the capability of signal design is a significant advantage in MIMO radars, through which, the system can achieve much better performance. Many different aspects of this performance improvement have been considered yet, and the transmit signals have been designed to attain such goal, e.g., getting higher SNR or better detector's performance at the receiver. However, an important tool for evaluating the radar's performance is its ambiguity function. In this paper, we consider the problem of transmit signal design, in order to optimize the ambiguity function... 

Two gains play key roles in recently developed MIMO wireless communication systems: "spatial diversity" gain and "spatial multiplexing" gain. The diversity gain refers to the capability to decrease the error rate of the MIMO channel, while the multiplexing gain implicitly refers to the amount of increase in the capacity of the MIMO channel. It has been shown that there is a fundamental tradeoff between these two types of gains, meaning interplay between increasing reliability (via an increase in the diversity gain) and increasing data rate (via an increase in the multiplexing gain). On the other hand, recently, MIMO radars have attracted much attention for their superior ability to enhance... 

It is a well known fact that using multiple antennas at transmit and receive sides improves the detection performance. However, in such multiple-input multiple-output (MIMO) configuration, proper positioning of transmitters and receivers is a big challenge that can have significant influence on the performance of the overall system. In addition, determining the power of each transmitter under a total power constraint is a problem that should be solved in order to enhance the performance and coverage of such a system. In this paper, we design the Neyman-Pearson detector under the Rayleigh scatter model and use it to introduce a criterion for the antenna placement at both transmit and receive... 

There has been much interest, recently, towards exploiting the Multiple-Input Multiple-Output (MIMO) technique in radar. It is shown that using multiple antennas at transmit and receive sides can improve the performance of the system. However, in order to analyze the system's performance, its ambiguity function, i.e. the ambiguity function of a MIMO radar, is needed to be defined. In this paper, beginning from the information theoretic definitions, we derive such function, specifically for a MIMO radar with widely separated antennas  

By combining the two ideas of MIMO (Multiple Input Multiple Output) and PCL (Passive Coherent Location) in radar, one can achieve the advantages of both recently developed techniques simultaneously. While using multiple antennas at the receive side provides a spatial diversity of the object to be detected, using multiple illuminators of opportunity, most importantly, makes the radar covert to the interceptors. One obstacle in such MIMO configuration is choosing the positions of the receive antennas. In this paper, after analyzing the Neyman-Pearson detector for the DVB-T based PCL, we introduce the probability of missed detection as a criterion to place the receive antenna. Here, we only... 

One of the most important obstacles in passive radar applications is removing the direct signal from the target channel. Otherwise, week echoes from the targets in the target channel would be ignored due to the limited dynamic range of the system. One of the most effective techniques in this field is using adaptive filters. In this paper various adaptive filters are introduced and their performances are shown and compared  

It has been shown that using multiple antennas in a radar system improves the performance considerably, since multiple target echoes are received from different aspect angles of the target. In this way, the target detection is improved. However, when using multiple antennas, some problems, such as designing the transmit signals, synchronization, etc. emerge that should be solved. One of such problems is the receiver placement. Receiver placement deals with choosing a proper position for the receive antenna in order to optimize the whole system's performance. In this paper, a receiver placement procedure based on improving the radar ambiguity function is proposed for the case of a multisite... 

By employing the MIMO (multiple-input-multiple-output) technology in radar, some new problems emerged, that, in order to benefit the MIMO gains in radar, it was necessary to solve them suitably. One of such obstacles is determining the positions of receive antennas in a MIMO radar system with widely separated antennas (WS MIMO radar), since it is shown that the antennas' positions affect the whole system's performance considerably. In this study, a proper receivers' positioning procedure is proposed. To do this end, four criteria are developed based on the proposed MIMO detector and the MIMO ambiguity function. The simulations verify that the proposed positioning procedure improves the... 

Phenols and alcohols are silylated with hexamethyldisilazane (HMDS) under microwave irradiation in solvent-free condition in good to excellent yields