Sharif Digital Repository

We study mix-nets with randomized partial checking (RPC) as proposed by Jakobsson, Juels, and Rivest (2002). RPC is a technique to verify the correctness of an execution both for Chaumian and homomorphic mix-nets. The idea is to relax the correctness and privacy requirements to achieve a more efficient mix-net. We identify serious issues in the original description of mix-nets with RPC and show how to exploit these to break both correctness and privacy, both for Chaumian and homomorphic mix-nets. Our attacks are practical and applicable to real world mix-net implementations, e.g., the Civitas and the Scantegrity voting systems  

The mass transfer between two immiscible liquids in butanol-succinic acid-water system was experimentally and numerically studied in axisymmetric and asymmetric jetting flow regimes. Full Navier-Stokes equations were solved for a Newtonian fluid. In all flow regimes, the rising Reynolds number caused mass transfer coefficient increment. The obtained results for mass transfer coefficient in axisymmetric jetting regime agreed with penetration theory. However, in the asymmetric regime, there was deviation from this theory due to the perturbation existing on the jet. The mass transfer coefficient of jet before breakup was twice the drops produced after breakup and raising the Reynolds number... 

An investigation was performed on the static strain aging behavior of warm-rolled low carbon steel during a nearly 1-year aging period, from the view point concerning with influence of changing the deformation speed and cooling media. Mechanical response of the examined material during aging period was evaluated through variations occurred in strength and hardness of the warm-deformed steel. It was shown that changing the rolling speed as well as cooling rate, may result in the occurrence of different metallurgical phenomena, consequently altering the aging kinetics of the material. It was also found that by increasing rolling speed, an increase in the value of hardness and UTS takes place,... 

Application of Volterra series to the modeling of static and dynamic nonlinear systems is investigated in this paper and compared to other methods. For nonlinear systems with memory, Volterra series serves as a generalization of convolution integral. To parameterize the Volterra kernels for limited dimension series, different methods are discussed. We use Laguerre functions and wavelet packets as orthonormal basis and we find the poles for the basis through a genetic algorithm search. Our test system is a hydraulic actuator with a highly nonlinear dynamics which is modeled with Volterra series. The results show that dynamic model with wavelet packets give a more accurate model with respect... 

In the present work, we used direct metal laser sintering (DMLS) process to fabricate Al-SiC composite parts directly from a three-dimensional CAD model. Al-7Si-0.3Mg powders were blended with various amounts of SiC particles (5, 10, 15, 20 vol%) at two different sizes (7 and 17 μm) and subjected to direct laser sintering using a 200 W continuous wave CO2 laser beam at various scan rates. The densification and microstructural features of the laser-sintered parts were studied. It is shown that the highest density is obtained for the Al alloy-5% SiC (7 μm) composite powder. The melt stability is also found to be improved in the presence of SiC particles. The microstructure of the... 

A gyroless deterministic attitude determination algorithm based on simulation of sun in eclipse is stated in this paper and has been compared to stochastic filters like extended Kalman filter and unscented Kalman filter. Attitude determination with low cost sensors such as magnometer and sun sensor results in usage of recursive algorithms such as Kalman filter which has the probability of divergence, but with deterministic point to point algorithm such as the one introduced in this paper we can be sure to have an attitude determination with a fixed maximum error. Proposed method has been compared with Extended Kalman Filter and Unscented Kalman filter due to its modeling error, robustness... 

Gas detectors play an important role in safety of process plants. In-time detection of flammable gas releases may prevent major fire and explosion as well as property loss in process plants. One of the challenges of the gas detection system design is determining the best layout for detectors in order to reduce the risk of gas releases as much as possible. However, current methods do not address the risk concept in placement of detectors quantitatively. A risk-based methodology is proposed for optimal placement of point type flammable gas detectors in which first the risk (defined as a combination of scenario frequency, delayed ignition probability and damage) is estimated for any release... 

A new adaptive real-coded memetic algorithm has been developed for continuous optimization problems. The proposed algorithm utilizes an adaptive variant of Continuous Ant Colony System for local search. Here new adaptive strategies are utilized for online tuning of the number of local search steps and the width of the search interval over each dimension of the search space. A new crossover scheme is also developed and utilized. The new algorithm has been examined with CEC 2005 benchmarks and compared with three other state of the art works in the field. The comparisons have showed relatively better results. © 2009 IEEE  

Amphibious single wheel robot consists of a sharp-edged wheel actuated by a spinning flywheel for steering and a drive motor for propulsion. The spinning flywheel acts as a gyroscope to stabilize the robot and also can be tilted to achieve steering. In this paper, the kinematics of a single wheel robot in water, Gyrover, is analyzed and then a simple mechanism for driving it is proposed. In previous studies, Lagrange approach is used for hydrodynamic modeling of the robot. A nonlinear position controller is designed to bring the robot to any desired position. Based on the designed controller, a tracking controller is augmented to the robot. For simplicity the added mass effect has been... 

We describe several return code schemes for secure vote submission in electronic voting systems. We consider a unified treatment where a return code is generated as a multiparty computation of a secure MAC tag applied on an encrypted message submitted by a voter. Our proposals enjoy a great level of flexibility with respect to various usability, security, and performance tradeoffs. © 2017, Springer International Publishing AG  

Transaction cost theory is largely used to investigate the formal domain of land and housing. In the informal domain, however, this perspective has been employed largely as a supplement in addressing the other fundamental notion in new institutional economics—property rights—despite the possibility that informality in land development can emerge regardless of the informality or formality of such rights. To cover this gap, this study developed a theoretical framework based on transaction cost theory to explain the formal–informal dichotomy in land development. The proposed framework maintains that land development depends on engaging in transactions that involve total or partial ownership of... 

Transaction cost theory is largely used to investigate the formal domain of land and housing. In the informal domain, however, this perspective has been employed largely as a supplement in addressing the other fundamental notion in new institutional economics—property rights—despite the possibility that informality in land development can emerge regardless of the informality or formality of such rights. To cover this gap, this study developed a theoretical framework based on transaction cost theory to explain the formal–informal dichotomy in land development. The proposed framework maintains that land development depends on engaging in transactions that involve total or partial ownership of... 

Multisensor arrays employing various sensing principles are a rapidly developing field of research as they allow simple and inexpensive quantification of various parameters in complex samples. Quantitative analysis with such systems is based on multivariate regression techniques, and deriving of traditional analytical figures of merit (e.g., sensitivity, selectivity, limit of detection, and limit of quantitation) for such systems is not obvious and straightforward. Nevertheless, it is absolutely needed for further development of the multisensor research field and for introducing these instruments into the general context of analytical chemistry. Here, we report on the protocol for... 

Enhanced Oil Recovery (EOR) methods have been widely used around the world to improve oil production from petroleum reservoirs. Recently, the injection of the low salinity/smart water has gained popularity among the EOR methods. Different mechanisms are believed to exist during low salinity/smart water injection, including dissolution, precipitation, and ion exchange at the rock surface. In this study, a coupled geochemical-transport model is presented for the detailed analysis and investigation of the interactions between brine, sandstone and carbonate rocks. The proposed model presents the coupling of a geochemical software (PHREEQC) and a species transport model. This coupled method makes... 

The direct laser sintering of Al-7Si-0.3Mg/SiC composites was studied. It is shown that the densification rate obeys first-order kinetics. The rate constant is found to increase at low SiC fractions but abruptly decreases at >∼5 vol.%. In the presence of ceramic particles, the melt track becomes more stable and a more continuous sintered surface is obtained. Meanwhile, significant reaction occurs between the aluminum melt and the reinforcement particles, leading to formation of Al4SiC4 and silicon particles. The solidification microstructure is also altered. © 2008 Acta Materialia Inc  

Pool fire modeling and risk assessment is very important and essential especially in systems with large flammable fuel inventories, e.g., refineries, offshore oil platforms, or fuel transportation systems. Results obtained from pool fire risk assessment can be used in setting up safety measure or emergency planning. Pool fire modeling is used to evaluate the heat flux at various target points around the fire source. The two major approaches in pool fire modeling are semi-empirical models and Computational Fluid Dynamics (CFD), which are called field models. Semi-empirical models are based on correlations fitted to data from large-scale Experiments and are used more frequently than CFD models... 

A major challenge for designers of competitive electricity markets is to devise market rules that limit the capability of electricity producers to exercise market power. Market power is the ability of a firm owning generation assets to raise the market price by its bidding behavior and to profit from this price increase. In addition, an important plan of market monitoring units in long term and competition policy framework is to persuade the participants to bid prices near to their marginal costs. Therefore, estimation of marginal cost function is important in way that Regulatory use it to increase competition in electricity markets. Bid price of the power plant to the power market contains... 

In this paper, the existence of periodic solutions of autonomous ordinary differential equations of a 4th and 5th order is investigated. The method used is based on the Brower's degree theorem using the homotopy invariant a property of a topological degree. © Sharif University of Technology, April 2008  

The adaptive capability of filters is known to be increased by incorporating a neural network into the filtering procedure. In this paper, an adaptive algorithm for tracking maneuvering targets based on neural networks is proposed. This algorithm is implemented with two filters based on the current statistical model and a multilayer feedforward neural network. The two filters track the same maneuvering target in parallel and the neural network automatically considers all the state information of the two filters and adaptively adjusts the process variance of one of them to achieve better performance in different target maneuver tracking. Simulations results show that the proposed adaptive...