Scalable laws for stable network congestion control

Discusses flow control in networks, in which sources control their rates based on feedback signals received from the network links, a feature present in current TCP protocols. We develop a congestion control system which is arbitrarily scalable, in the sense that its stability is maintained for arbitrary network topologies and arbitrary amounts of delay. Such a system can be implemented in a decentralized way with information currently available in networks plus a small amount of additional signaling

Evaluating the Effectiveness of Child Safety Seats and Seat Belts in Protecting Children from Injury

Young children are required to use child safety seats, and the age threshold at which children can legally graduate to seat belts has steadily increased. This paper tests the relative effectiveness of child safety seats, lap-and-shoulder seat belts, and lap belts in preventing injuries among motor vehicle passengers aged 2-6. We analyze three large, representative samples of crashes reported to police, as well as linked hospital data. We find no apparent difference in the two most serious injury categories for children in child safety seats versus lap-and-shoulder belts. Child safety seats provide a statistically significant 25% reduction in the least serious injury category. Lap belts are somewhat less effective than the two other types of restraints, but far superior to riding unrestrained.

On Asymptotic Optimality of Dual Scheduling Algorithm In A Generalized Switch

Generalized switch is a model of a queueing system where parallel servers are interdependent and have time-varying service capabilities. This paper considers the dual scheduling algorithm that uses rate control and queue-length based scheduling to allocate resources for a generalized switch. We consider a saturated system in which each user has infinite amount of data to be served. We prove the asymptotic optimality of the dual scheduling algorithm for such a system, which says that the vector of average service rates of the scheduling algorithm maximizes some aggregate concave utility functions. As the fairness objectives can be achieved by appropriately choosing utility functions, the asymptotic optimality establishes the fairness properties of the dual scheduling algorithm. The dual scheduling algorithm motivates a new architecture for scheduling, in which an additional queue is introduced to interface the user data queue and the time-varying server and to modulate the scheduling process, so as to achieve different performance objectives. Further research would include scheduling with Quality of Service guarantees with the dual scheduler, and its application and implementation in various versions of the generalized switch model

Random Access Game and Medium Access Control Design

Motivated partially by a control-theoretic viewpoint, we propose a game-theoretic model, called random access game, for contention control. We characterize Nash equilibria of random access games, study their dynamics, and propose distributed algorithms (strategy evolutions) to achieve Nash equilibria. This provides a general analytical framework that is capable of modeling a large class of system-wide quality-of-service (QoS) models via the specification of per-node utility functions, in which system-wide fairness or service differentiation can be achieved in a distributed manner as long as each node executes a contention resolution algorithm that is designed to achieve the Nash equilibrium. We thus propose a novel medium access method derived from carrier sense multiple access/collision avoidance (CSMA/CA) according to distributed strategy update mechanism achieving the Nash equilibrium of random access game. We present a concrete medium access method that adapts to a continuous contention measure called conditional collision probability, stabilizes the network into a steady state that achieves optimal throughput with targeted fairness (or service differentiation), and can decouple contention control from handling failed transmissions. In addition to guiding medium access control design, the random access game model also provides an analytical framework to understand equilibrium and dynamic properties of different medium access protocols

System Level Synthesis

This article surveys the System Level Synthesis framework, which presents a novel perspective on constrained robust and optimal controller synthesis for linear systems. We show how SLS shifts the controller synthesis task from the design of a controller to the design of the entire closed loop system, and highlight the benefits of this approach in terms of scalability and transparency. We emphasize two particular applications of SLS, namely large-scale distributed optimal control and robust control. In the case of distributed control, we show how SLS allows for localized controllers to be computed, extending robust and optimal control methods to large-scale systems under practical and realistic assumptions. In the case of robust control, we show how SLS allows for novel design methodologies that, for the first time, quantify the degradation in performance of a robust controller due to model uncertainty -- such transparency is key in allowing robust control methods to interact, in a principled way, with modern techniques from machine learning and statistical inference. Throughout, we emphasize practical and efficient computational solutions, and demonstrate our methods on easy to understand case studies.Comment: To appear in Annual Reviews in Contro

Is Dexamethasone 4mg a More Effective Anti-Emetic than Dexamethasone 8mg for the Prevention of Early Post-Operative Nausea and Vomiting in Women Undergoing Laparoscopic Gynecological Surgery?

Postoperative nausea and vomiting (PONV) is a common problem in the surgical setting. It affects as much as 20 to 80 percent of patients undergoing surgery (D\u27souza, Swami, & Bhagwat, 2011). PONV can lead to increased patient costs and recovery time by causing the patient to stay in the healthcare facility for a longer period of time. A retrospective cohort study was completed to examine whether or not there was a significant difference between patients who received 4mg and 8mg of dexamethasone in the incidence of PONV. All patients studied received ondansetron intraoperatively as their primary anti-emetic. English speaking patients who met the following inclusion criteria were included in the retrospective chart review: those who are female, those have underwent laparoscopic gynecological surgery and received dexamethasone, those who are non-smokers, and those who are aged 18-60 with an American Society of Anesthesiologists (ASA) score of II or less. Patients that met the following exclusion criteria were not counted towards the chart review: those who are an ASA III or above, those who did not follow the recommended fasting time prior to surgery, those with a history of motion sickness, those with a history of PONV, those who are taking routine anti-emetics, those whose are deaf, those who are blind, those who are smokers, and those outside the age range for 18-60 years. Statistical analysis using a Chi-Square test was used to evaluate whether the patients receiving 4mg of dexamethasone experienced more PONV that those who received 8mg

Modeling the Tripartite Role of Cyclin C in Cellular Stress Response Coordination

For normal cellular function, exogenous signals must be interpreted and careful coordination must take place to ensure desired fates are achieved. Mitochondria are key regulatory nodes of cellular fate, undergoing fission/fusion cycles depending on the needs of the cell, and help mediate cell death fates. The CKM or Cdk8 kinase module, is composed of cyclin C (CC), Cdk8, Med12/12L, and Med13/13L. The CKM controls RNA polymerase II, acting as a regulator of stress-response and growth-control genes. Following stress, CC translocates to the mitochondria and interacts with both fission and iRCD apoptotic mediators. We hypothesize that CC represents a key mediator, linking transcription to mitochondrial fission and RCD. A more in-depth analysis of the roles of CC and the protein interactions that mediate them encompasses the focus of this dissertation. To mediate individual functions, CC uses distinct binding partners. We revealed the presence two separable/discrete cyclin box domains. To determine the residues mediating these functions, rigid body protein-protein docking simulations were performed using human cyclin C, Drp1, and Bax. These analyses revealed specific residues which support distinct functions of the CB1 and CB2 domains. Results indicate that modeled Bax-interacting residues are concentrated to the first half of the CB2 domain, while Drp1-interacting residues span the entirety of the CB2 domain. Interestingly, we determined that CC contains a unique BH2-like domain, normally only found in Bcl-2 protein family members, which appears to mediate interactions with Bax. Results from human protein modeling simulations were then applied to yeast homologous proteins. As presented here, yeast studies have confirmed residues that mediate interaction between CC and fission machinery. The results support the model that CB1 and CB2 are distinct, mediating independent functionalities. We suggest a model that CC possesses three distinct interaction domains and acts to bridge fission and apoptotic machinery, either in a mutually exclusive or trimeric manner. In conclusion, CC is shown to mediate each of its unique functions through distinct interacting residues and interfaces. With CC implicated in many human disorders, this will serve as a tool to study disease pathogeneses and treatments, taking into account unique interfaces governing the tripartite functions

Cross-layer Congestion Control, Routing and Scheduling Design in Ad Hoc Wireless Networks

This paper considers jointly optimal design of crosslayer congestion control, routing and scheduling for ad hoc wireless networks. We first formulate the rate constraint and scheduling constraint using multicommodity flow variables, and formulate resource allocation in networks with fixed wireless channels (or single-rate wireless devices that can mask channel variations) as a utility maximization problem with these constraints. By dual decomposition, the resource allocation problem naturally decomposes into three subproblems: congestion control, routing and scheduling that interact through congestion price. The global convergence property of this algorithm is proved. We next extend the dual algorithm to handle networks with timevarying channels and adaptive multi-rate devices. The stability of the resulting system is established, and its performance is characterized with respect to an ideal reference system which has the best feasible rate region at link layer. We then generalize the aforementioned results to a general model of queueing network served by a set of interdependent parallel servers with time-varying service capabilities, which models many design problems in communication networks. We show that for a general convex optimization problem where a subset of variables lie in a polytope and the rest in a convex set, the dual-based algorithm remains stable and optimal when the constraint set is modulated by an irreducible finite-state Markov chain. This paper thus presents a step toward a systematic way to carry out cross-layer design in the framework of “layering as optimization decomposition” for time-varying channel models

Cross-layer optimization in TCP/IP networks

TCP-AQM can be interpreted as distributed primal-dual algorithms to maximize aggregate utility over source rates. We show that an equilibrium of TCP/IP, if exists, maximizes aggregate utility over both source rates and routes, provided congestion prices are used as link costs. An equilibrium exists if and only if this utility maximization problem and its Lagrangian dual have no duality gap. In this case, TCP/IP incurs no penalty in not splitting traffic across multiple paths. Such an equilibrium, however, can be unstable. It can be stabilized by adding a static component to link cost, but at the expense of a reduced utility in equilibrium. If link capacities are optimally provisioned, however, pure static routing, which is necessarily stable, is sufficient to maximize utility. Moreover single-path routing again achieves the same utility as multipath routing at optimality