151 research outputs found

    On the Fundamental Limits and Symmetric Designs for Distributed Information Systems

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    Many multi-terminal communication networks, content delivery networks, cache networks, and distributed storage systems can be modeled as a broadcast network. An explicit characterization of the capacity region of the general network coding problem is one of the best known open problems in network information theory. A simple set of bounds that are often used in the literature to show that certain rate tuples are infeasible are based on the graph-theoretic notion of cut. The standard cut-set bounds, however, are known to be loose in general when there are multiple messages to be communicated in the network. This dissertation focuses on broadcast networks, for which the standard cut-set bounds are closely related to union as a specific set operation to combine different simple cuts of the network. A new set of explicit network coding bounds, which combine different simple cuts of the network via a variety of set operations (not just the union), are established via their connections to extremal inequalities for submodular functions. The tightness of these bounds are demonstrated via applications to combination networks. The tightness of generalized cut-set bounds has been further explored by studying the problem of “latency capacity region” for a broadcast channel. An implicit characterization of this region has been proved by Tian, where a rate splitting based scheme was shown to be optimal. However, the explicit characterization of this region was only available when the number of receivers are less than three. In this dissertation, a precise polyhedral description of this region for a symmetric broadcast channel with complete message set and arbitrary number of users has been established. It has been shown that a set of generalized cut-set bounds, characterizes the entire symmetrical multicast region. The achievability part is proved by showing that every maximum rate vector is feasible by using a successive encoding scheme. The framework for achievability strongly relies on polyhedral combinatorics and it can be useful in network information theory problems when a polyhedral description of a region is needed. Moreover, it is known that there is a direct relationship between network coding solution and characterization of entropy region. This dissertation, also studies the symmetric structures in network coding problems and their relation with symmetrical projections of entropy region and introduces new aspects of entropy inequalities. First, inequalities relating average joint entropies rather than entropies over individual subsets are studied. Second, the existence of non-Shannon type inequalities under partial symmetry is studied using the concepts of Shannon and non-Shannon groups. Finally, due to the relationship between linear entropic vectors and representability of integer polymatroids, construction of such vector has been discussed. Specifically, It is shown that representability of the particularly constructed matroid is a sufficient condition for integer polymatroids to be linearly representable over real numbers. Furthermore, it has been shown that any real-valued submodular function (such as Shannon entropy) can be approximated (arbitrarily close) by an integer polymatroid

    Generalized Cut-Set Bounds for Broadcast Networks

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    A broadcast network is a classical network with all source messages collocated at a single source node. For broadcast networks, the standard cut-set bounds, which are known to be loose in general, are closely related to union as a specific set operation to combine the basic cuts of the network. This paper provides a new set of network coding bounds for general broadcast networks. These bounds combine the basic cuts of the network via a variety of set operations (not just the union) and are established via only the submodularity of Shannon entropy. The tightness of these bounds are demonstrated via applications to combination networks.Comment: 30 pages, 4 figures, submitted to the IEEE Transaction on Information Theor

    On the representability of integer polymatroids: Applications in linear code construction

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    It has been shown that there is a duality between the linear network coding solution and the entropic vectors induced by collection of subspaces in a vector space over a finite field (dubbed linearly constructed entropic vectors). The region of all linearly constructed vectors, coincides with the set of all representable polymatroids. For any integer polymatroid, there is an associated matroid, which uniquely identifies the polymatroid. We conjecture that the representability of the underlying matroid is a sufficient condition for integer polymatroids to be linearly representable. We prove that the conjecture holds for representation over real numbers. Furthermore, we show that any real-valued submodular function (such as Shannon entropy) can be approximated (arbitrarily close) by an integer polymatroid

    Evaluating diagnostic accuracy of Ovarian instant frozen sections compared to delayed paraffin embedded permanent sections

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    Introduction: Frozen section is mainly performed to determine malignity, so it is of fundamental importance to evaluate the diagnostic accuracy of frozen sections performed for each group of tissues in order to reduce false diagnoses, unnecessary surgeries and following unwanted complications. This study is conducted to evaluate the diagnostic accuracy of frozen section performed on ovary tissue compared to permanent sections. Materials and Methods: In this retrospective study, we evaluate frozen sections performed at Taleghani hospital pathology department in five years and their results were compared with permanent sections’ results to calculate sensitivity, specificity, negative predictive value and positive predictive value. In cases which results were discordant, we check for probable reasons. Results: 83 species were evaluated from patients with a mean age of 42.9 years; the smallest was 19 and the oldest was 86 years old (Std. dev: 12.84). 75 cases of frozen sections were benign (90.4%) and 8 cases were malignant. 73 cases of permanent sections were benign (88%) and 10 cases were malignant (12%. Sensitivity, specificity, positive predictive value and negative predictive value rates were 66%, 100%, 100% and 96.55% respectively. Conclusions: This study shows the importance of cooperation between pathologist and surgeons that they can prevent unnecessary surgeries. In our study the only cases of discordancy were borderline tumors and the diagnostic accuracy for all other species were perfect.  &nbsp

    Modeling and Solution Procedure for a Preemptive Multi-Objective Multi-Mode Project Scheduling Model in Resource Investment Problems

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    In this paper, a preemptive multi-objective multi-mode project scheduling model for resource investment problem is proposed. The first objective function is to minimize the completion time of project (makespan);the second objective function is to minimize the cost of using renewable resources. Non-renewable resources are also considered as parameters in this model. The preemption of activities is allowed at any integer time units, and for each activity, the best execution mode is selected according to the duration and resource. Since this bi-objective problem is the extension of the resource-constrained project scheduling problem (RCPSP), it is NP-hard problem, and therefore, heuristic and metaheuristic methods are required to solve it. In this study, Non-dominated Sorting Genetic AlgorithmII (NSGA-II) and Non-dominated Ranking Genetic Algorithm (NRGA) are used based on results of Pareto solution set.We also present a heuristic method for two approaches of serial schedule generation scheme (S-SGS) and parallel schedule generation scheme (P-SGS) in the developed algorithm in order to optimize the scheduling of the activities.The input parameters of the algorithm are tuned with Response Surface Methodology (RSM). Finally, the algorithms are implemented on some numerical test problems, and their effectiveness is evaluated.  </em

    Designing a model of cultural barriers for women's participation in leisure sports activities in sports recreation centers

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    Purpose: Leisure is one of the dimensions of social life that if it contradicts the common culture of society, it can become a social problem or dilemma; Therefore, the present study was conducted with the aim of designing a model of cultural barriers to women's participation in leisure sports activities in sports recreation centers.Methodology: The research method in terms of type and data analysis was qualitative with a data theorizing approach. The statistical population of the study consisted of senior managers, officials and faculty members aware of the field of research, which in order to select the sample people, purposeful sampling method based on a theoretical approach was used. The required data were collected using in-depth interviews and analyzed in three stages of open, axial and selective coding.Results: Based on the obtained results, causal conditions include the existence of non-indigenous culture, patriarchal perspective, weakness in the capital of women's sports culture, lack of social support and motivational barriers; Underlying conditions including economic factors, facility and facility factors and managerial factors and intervening conditions including individual factors and religious tendencies were identified. Strategies were introduced in three areas of needs assessment and policy-making, localization and alignment of relevant bodies, and after presenting the consequences, a paradigm model was presented.Conclusion: Needs assessment and policy-making, alignment of organs to achieve goals and localization of leisure activities have desirable results in order to remove cultural barriers to the presence of women in sports and recreation centers and use the benefits, Will bring

    Comparison of Post Intubation Complications of Endotracheal Tube and Laryngeal Mask Airway in Pediatrics

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    Background: Postoperative sore throat, cough, nausea, apnea, and laryngospasm are common complications of intubation byendotracheal tube (ETT) in pediatrics. The laryngeal mask airway (LMA) is a supraglottic device used as an alternative equipmentfor ETT in order to decrease the complications.Objectives: To compare the incidence of postoperative sore throat after LMA with ETT in pediatrics.Methods: Seventy-six patients between the ages of 2 - 12 with ASA class I-II who underwent cochlear implant surgery were enrolledand randomly divided into 2 groups including ETT or LMA for airway management. The incidence of complications including sorethroat, apnea, vomiting, laryngospasm, post operative cough, intra, and post operative arrhythmia and the influence of these equipment’son O2 saturation, end tidal CO2, airway pressure, and hemodynamic changes during operation were compared. Wong-Bakerfacial grimace scale was used to evaluate the severity of pain.Results: The rate of postoperative sore throat and laryngospasm in the ETT group was significantly higher than the LMA group (P =0.002, 0.011; respectively). Apnea and vomiting were not significantly different. Rate of postoperative cough, incidence of intra, andpostoperative arrhythmia were not significantly different between the two groups. Mean arterial pressure, peak airway pressure,end tidal CO2, and oxygen saturation during operation, which was measured continuously, had no significant differences betweenthe two groups.Conclusions: LMA significantly decreases the rate of postoperative sore throat and laryngospasm in pediatrics. However, the ratesof apnea, oxygen saturation, and nausea were similar in both groups. Application of LMA as an alternative to ETT is appropriate inpediatric patients
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