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Search Results: 1 - 10 of 148 matches for " Milad Siami "
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Fundamental Limits and Tradeoffs on Disturbance Propagation in Large-Scale Dynamical Networks
Milad Siami,Nader Motee
Mathematics , 2014,
Abstract: We consider performance deterioration of interconnected linear dynamical networks subject to exogenous stochastic disturbances. The focus of this paper is on first-order and second-order linear consensus networks. We employ the expected value of the steady state dispersion of the state of the entire network as a performance measure and develop a graph-theoretic methodology to relate structural specifications of the underlying graphs of the network to the performance measure. We explicitly quantify several inherent fundamental limits on the best achievable levels of performance in linear consensus networks and show that these limits of performance are merely imposed by the specific structure of the underlying graphs. Furthermore, we discover new connections between notions of sparsity and the performance measure. Particularly, we characterize several fundamental tradeoffs that reveal interplay between the performance measure and various sparsity measures of a linear consensus network. At the end, we apply our results to two real-world dynamical networks and provide energy interpretations for the proposed performance measures. It is shown that the total power loss in synchronous power networks and total kinetic energy of a network of autonomous vehicles in a formation are viable performance measure for these networks and fundamental limits on these measures quantify the best achievable levels of energy-efficiency in these dynamical networks.
Systemic Measures for Performance and Robustness of Large-Scale Interconnected Dynamical Networks
Milad Siami,Nader Motee
Mathematics , 2014,
Abstract: In this paper, we develop a novel unified methodology for performance and robustness analysis of linear dynamical networks. We introduce the notion of systemic measures for the class of first--order linear consensus networks. We classify two important types of performance and robustness measures according to their functional properties: convex systemic measures and Schur--convex systemic measures. It is shown that a viable systemic measure should satisfy several fundamental properties such as homogeneity, monotonicity, convexity, and orthogonal invariance. In order to support our proposed unified framework, we verify functional properties of several existing performance and robustness measures from the literature and show that they all belong to the class of systemic measures. Moreover, we introduce new classes of systemic measures based on (a version of) the well--known Riemann zeta function, input--output system norms, and etc. Then, it is shown that for a given linear dynamical network one can take several different strategies to optimize a given performance and robustness systemic measure via convex optimization. Finally, we characterized an interesting fundamental limit on the best achievable value of a given systemic measure after adding some certain number of new weighted edges to the underlying graph of the network.
Scaling Laws for Disturbance Propagation in Cyclic Dynamical Networks
Milad Siami,Nader Motee
Mathematics , 2015,
Abstract: Our goal is to analyze performance of stable linear dynamical networks subject to external stochastic disturbances. The square of the $\mathcal H_2$-norm of the network is used as a performance measure to quantify the expected steady-state dispersion of the outputs of the network. We show that this performance measure can be tightly bounded from below and above by some spectral functions of the state-space matrices of the network. This result is applied to a class of cyclic linear networks and shown that their performance measure scale quadratically with the network size.
Eminence Grise Coalitions: On the Shaping of Public Opinion
Sadegh Bolouki,Roland P. Malhame,Milad Siami,Nader Motee
Mathematics , 2014,
Abstract: We consider a network of evolving opinions. It includes multiple individuals with first-order opinion dynamics defined in continuous time and evolving based on a general exogenously defined time-varying underlying graph. In such a network, for an arbitrary fixed initial time, a subset of individuals forms an eminence grise coalition, abbreviated as EGC, if the individuals in that subset are capable of leading the entire network to agreeing on any desired opinion, through a cooperative choice of their own initial opinions. In this endeavor, the coalition members are assumed to have access to full profile of the underlying graph of the network as well as the initial opinions of all other individuals. While the complete coalition of individuals always qualifies as an EGC, we establish the existence of a minimum size EGC for an arbitrary time-varying network; also, we develop a non-trivial set of upper and lower bounds on that size. As a result, we show that, even when the underlying graph does not guarantee convergence to a global or multiple consensus, a generally restricted coalition of agents can steer public opinion towards a desired global consensus without affecting any of the predefined graph interactions, provided they can cooperatively adjust their own initial opinions. Geometric insights into the structure of EGC's are given. The results are also extended to the discrete time case where the relation with Decomposition-Separation Theorem is also made explicit.
On The Signed Edge Domination Number of Graphs
Saeed Akbari,Sadegh Bolouki,Pooya Hatami,Milad Siami
Computer Science , 2010,
Abstract: Let $\gamma'_s(G)$ be the signed edge domination number of G. In 2006, Xu conjectured that: for any $2$-connected graph G of order $ n (n \geq 2),$ $\gamma'_s(G)\geq 1$. In this article we show that this conjecture is not true. More precisely, we show that for any positive integer $m$, there exists an $m$-connected graph $G$ such that $ \gamma'_s(G)\leq -\frac{m}{6}|V(G)|.$ Also for every two natural numbers $m$ and $n$, we determine $\gamma'_s(K_{m,n})$, where $K_{m,n}$ is the complete bipartite graph with part sizes $m$ and $n$.
Generation of Non-Gaussian Wide-Sense Stationary Random Processes with Desired PSDs and PDFs  [PDF]
Milad Johnny
Journal of Signal and Information Processing (JSIP) , 2012, DOI: 10.4236/jsip.2012.34056
Abstract: This paper describes a new method to generate discrete signals with arbitrary power spectral density (PSD) and first order probability density function (PDF) without any limitation on PDFs and PSDs. The first approximation has been achieved by using a nonlinear transform function. At the second stage the desired PDF was approximated by a number of symmetric PDFs with defined variance. Each one provides a part of energy from total signal with different ratios of remained desired PSD. These symmetric PDFs defined by sinusoidal components with random amplitude, frequency and phase variables. Both analytic results and examples are included. The proposed scheme has been proved to be useful in simulations involving non-Gaussian processes with specific PSDs and PDFs.
Control and Implementation of Single-Inverter Microgrid  [PDF]
Mehdi Moradian, Milad Moradian
Smart Grid and Renewable Energy (SGRE) , 2019, DOI: 10.4236/sgre.2019.102003
Abstract: In this paper, simulation and implementation way for practical control of Single Inverter Microgrid (SIMG) is presented. This system is equipped by solar system, wind energy conversion system (WECS), and microturbine system. Each DG’s has controlled independently. This is a kind of decentralize control because each DG’s has difference controller. Control of Microgrid (MG) during both grid tie and islanding modes is presented. Solar system and WECS are modeled based on santerno products. This system is compared with three inverter MGs with Centralize control strategy. Controlled signals show that SIMG is more reliable and economical. THD is improved and strategy is simplified for SIMG.
Mohammadbagher Gorji,Sahar Siami
Business and Management Review , 2011,
Abstract: The main purpose of the present study is to assess a hospital's Performance assessment with regard to EFQM model and then determining the relationship between nine criteria and Organizational model of excellence with hospital's Performance. The research method was Survey –Correlation and the selected sample included all managers and 203 employees were selected. To collect data a standard questionnaire of Performance assessment, and two questionnaires of relationship assessment one for Enablers criteria and another for results` criteria with Organizational Performance. For self- assessment performance, Radar logic and for hypothesis testing, Pearson correlation coefficient, factor analysis, and T-test was employed. Research Findings show that the received points regarding self- assessment of the hospital's performance(from 1000 points) was 562.2(Enablers criteria= 319.2 and results` criteria= 243) respectively, from among them, people criterion received the highest(%69.1) and Society's criterion received the lowest(%36). So the results showed that all research hypotheses were accepted and there was a significant relationship between hospital's Performance and nine criteria EFQM model. The priority of effectiveness of Enablers criteria on hospital's performance are as follows: processes criteria, partners and resources, leadership, People, policies and strategies and results` criteria includes: people results, Key performance results, customers and society results.
Sahar Siami,Mohammadbagher Gorji
Business and Management Review , 2011,
Abstract: The main purpose of this paper is to determining the effect of Empowerment implementation by considering the three factors of delegation, implementation of participating management, encouragement and giving reward and also determination of classification of priority and importance of effect of each factor with employee’s performance improvement in Golestan Telecommunication Company in Iran. The research method has been descriptive and causal comparative and statistical sample under study was 226 people in order to collecteddata, two questionnaires and existing documents about rate of employee performance were used in two periods of time before and after Empowerment implementation. The tools validity with Content method and their Reliability by Cornbach method coefficients 0.98, 0.95 has been confirmed. In order to analyze the data, Spearman correlation method, Wilcoxon tests method, and multiple regressions, were used. Findings showedthat there is significant difference between rate of employee’s performance before and after Empowerment implementing, by the way Empowerment implementing emphasizing the factors, delegation, participating management and encouragement and giving reward cause employee’s performance to improve.
The Evaluation of the Effect of TENS Therapy on Reducing Acute and Chronic Pain Following Varicocelectomy  [PDF]
Dawood Agamohammadi, Haleh Farzin, Solmaz Fakhari, Roshide Siami
Open Journal of Internal Medicine (OJIM) , 2017, DOI: 10.4236/ojim.2017.73005
Abstract: Introduction: Post-varicocelectomy pain is a considerable pain with probability of promotion toward chronicity. Some reasons, including surgical technique or nerve injury and inappropriate attention to treatment of acute pain play role in the emergence of acute pain. The pain could lead to limitation in movement and working, patient dissatisfaction and waste of medical resources. Transcutaneous electrical nerve stimulation (TENS) therapy as the patient control analgesia (PCA) is associated with reduction of pain intensity and analgesic consumptions. This study aimed to evaluate the effect of TENS therapy on reducing the acute and chronic pain following varicocelectomy. Methods and Materials: The study was conducted after obtaining the approval of the local Institute Ethics Committee and written informed consent from all of the patients. Eighty patients scheduled for undergoing varicocelectomy, were randomly classified according to a randomization list prepared using online software at a 1:1 ratio to Groups A (intervention group) and B (placebo group). In postoperative and recovery period, Group A received TENS therapy for 30 minutes in parallel to surgical scar with high frequency by sensory level. Group B was treated with off-device. The treatment course was replicated for the two groups at 2, 6, 12 and 24 hours after operation. Then, postoperative pain was measured by VAS (visual analogue scale) at the same time and after 1 week and 1, 2 and 3 months. The amount of used analgesics was recorded. Results: The results showed that based on the VAS, pain significantly decreased after intervention in 2 hours (25% with VAS = 5 versus 32.5% with VAS = 8 in control group). The differences among, amount of used analgesics at 2, 6 and 12 hours were significant with p-value = 0.001, <0.0001 and =0.02, respectively. Conclusion: TENS therapy could efficiently decrease pain degree for hours, weeks and months after varicocelectomy; this was associated with decreased post-operation analgesic requirements.
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