Topological lower bounds for the chromatic number: A hierarchy

This paper is a study of ``topological'' lower bounds for the chromatic number of a graph. Such a lower bound was first introduced by Lov\'asz in 1978, in his famous proof of the \emph{Kneser conjecture} via Algebraic Topology. This conjecture stated that the \emph{Kneser graph} \KG_{m,n}, the graph with all $k$-element subsets of $\{1,2,...,n\}$ as vertices and all pairs of disjoint sets as edges, has chromatic number $n-2k+2$. Several other proofs have since been published (by B\'ar\'any, Schrijver, Dolnikov, Sarkaria, Kriz, Greene, and others), all of them based on some version of the Borsuk--Ulam theorem, but otherwise quite different. Each can be extended to yield some lower bound on the chromatic number of an arbitrary graph. (Indeed, we observe that \emph{every} finite graph may be represented as a generalized Kneser graph, to which the above bounds apply.) We show that these bounds are almost linearly ordered by strength, the strongest one being essentially Lov\'asz' original bound in terms of a neighborhood complex. We also present and compare various definitions of a \emph{box complex} of a graph (developing ideas of Alon, Frankl, and Lov\'asz and of \kriz). A suitable box complex is equivalent to Lov\'asz' complex, but the construction is simpler and functorial, mapping graphs with homomorphisms to $\Z_2$-spaces with $\Z_2$-maps.Comment: 16 pages, 1 figure. Jahresbericht der DMV, to appea

Optimization Algorithms for Large-Scale Real-World Instances of the Frequency Assignment Problem

Nowadays, mobile communications are experiencing a strong growth, being more and more indispensable. One of the key issues in the design of mobile networks is the Frequency Assignment Problem (FAP). This problem is crucial at present and will remain important in the foreseeable future. Real world instances of FAP typically involve very large networks, which can only be handled by heuristic methods. In the present work, we are interested in optimizing frequency assignments for problems described in a mathematical formalism that incorporates actual interference information, measured directly on the field, as is done in current GSM networks. To achieve this goal, a range of metaheuristics have been designed, adapted, and rigourously compared on two actual GSM networks modeled according to the latter formalism. In order to generate quickly and reliably high quality solutions, all metaheuristics combine their global search capabilities with a local-search method specially tailored for this domain. The experiments and statistical tests show that in general, all metaheuristics are able to improve upon results published in previous studies, but two of the metaheuristics emerge as the best performers: a population-based algorithm (Scatter Search) and a trajectory based (1+1) Evolutionary Algorithm. Finally, the analysis of the frequency plans obtained offers insight about how the interference cost is reduced in the optimal plans.Publicad

Performance Optimization in Wireless Local Area Networks

Wireless Local Area Networks (WLAN) are becoming more and more important for providing wireless broadband access. Applications and networking scenarios evolve continuously and in an unpredictable way, attracting the attention of academic institutions, research centers and industry. For designing an e cient WLAN is necessary to carefully plan coverage and to optimize the network design parameters, such as AP locations, channel assignment, power allocation, MAC protocol, routing algorithm, etc... In this thesis we approach performance optimization in WLAN at di erent layer of the OSI model. Our rst approach is at Network layer. Starting from a Hybrid System modeling the ow of tra c in the network, we propose a Hybrid Linear Varying Parameter algorithm for identifying the link quality that could be used as metric in routing algorithms. Go down to Data Link, it is well known that CSMA (Carrier Sense Multiple Access) protocols exhibit very poor performance in case of multi-hop transmissions, because of inter-link interference due to imperfect carrier sensing. We propose two novel algorithms, that are combining Time Division Multiple Access for grouping contending nodes in non-interfering sets with Carrier Sense Multiple Access for managing the channel access behind a set. In the rst solution, a game theoretical study of intra slot contention is introduced, in the second solution we apply an optimization algorithm to nd the optimal degree between contention and scheduling. Both the presented solutions improve the network performance with respect to CSMA and TDMA algorithms. Finally we analyze the network performance at Physical Layer. In case of WLAN, we can only use three orthogonal channels in an unlicensed spectrum, so the frequency assignments should be subject to frequent adjustments, according to the time-varying amount of interference which is not under the control of the provider. This problem make necessary the introduction of an automatic network planning solution, since a network administrator cannot continuously monitor and correct the interference conditions su ered in the network. We propose a novel protocol based on a distributed machine learning mechanism in which the nodes choose, automatically and autonomously in each time slot, the optimal channel for transmitting through a weighted combination of protocols

Scarcity, self-interest and maximization from Islamic angle

This paper clarifies some misinterpretations of three foundational concepts in mainstream economics from Islamic viewpoint. These are scarcity of resources, pursuit of self-interest and maximizing behavior of economic agents. It argues that stocks of resources that God has provided are inexhaustible. But important is the availability of resources out of stocks to mankind. Availability is a function of human effort and the state of knowledge about resources over time and space. In that sense resources are scarce in relation to multiplicity of human wants for Islamic economics as well. Self-interest must be distinguished from selfishness. The motive operates on both ends of human existence: mundane and spiritual. Its pursuit does not preclude altruism from human life. Counter interests keep balance in society and promote civility. Islam recognizes the motive as valid. Maximization relates to quantifiable ex ante variables. Uncertainty of future outcomes of actions makes maximization a heuristic but useful analytical tool. The concept is value neutral. What is maximized, how and to what end alone give rise to moral issues. Modified in the light of Shari’ah requirements the three concepts can provide a firmer definition for Islamic economics centered on the notion of falah.Scarcity; self-interest, maximization, Islamic Economics, israf; Shri'ah, heuristics

On The Effects of The Variations In Network Characteristics In Cyber Physical Systems

The popular robotic simulator, Gazebo, lacks the feature of simulating the effects of control latency that would make it a fully-fledged cyber-physical system (CPS) simulator. The CPS that we address to measure is a robotic arm (UR5) controlled remotely with velocity commands. The main goal is to measure Quality of Control (QoC) related KPIs during various network conditions in a simulated environment. We propose a Gazebo plugin to make the above measurement feasible by making Gazebo capable to delay internal control and status messages and also to interface with external network simulators to derive even more advanced network effects. Our preliminary evaluation shows that there is certainly an effect on the behavior of the robotic arm with the introduced network latency in line with our expectations, but a more detailed further study is needed.Comment: In Proc., 31st European Simulation and Modelling Conference, Oct 25-27, 201

Exploring family recreation activities in families that include children with developmental disabilities

Based on a larger exploratory investigation that employed a mixed method research design, this paper reports the recreation activities of families that included children with developmental disabilities (N = 65). The most popular and frequent forms of family recreation reflected five general categories of activities: passive (e.g., watching television), play (e.g., board or video games), physical (e.g., swimming), social (e.g., visiting family and friends), and entertainment/special events (e.g., going to the movies). Variations in popularity and frequency of these activities were explored in relation to patterns of family involvement and selected socio-demographic characteristics (e.g., employment status, nature of disability). Although variations were evident, family recreation most often included physical recreation activities-commonly swimming, walking, and bicycling. Methodological considerations and practical applications associated with this research are discussed

Clinical social work and the medical model : use of art and play therapy interventions

This study aims to determine the self-identified role of clinicians working within the medical model. Secondly, the study intends to determine if art and play therapy interventions were regularly implemented by clinical social workers practicing with hospitalized children within a pediatric medical facility. The study hopes to gauge both the clinicians\u27 understanding of possible barriers to these interventions within the medical model, and also the clinicians\u27 beliefs about the importance of play within pediatric hospital settings as a determining factor to patients\u27 psychological needs during their illnesses. A mixed-methods online survey was sent to over 300 medical social workers within the United States. All 137 participating clinicians held at least an MSW and worked within a pediatric medical facility. Clinicians were asked to self-identify their primary time commitments within their current setting, their primary theoretical orientation, and their beliefs on the benefits of play, any barriers they felt existed within their current medical setting, and any examples of play techniques they utilize within the medical model. The conclusion of the study indicates that art and play therapy interventions are not commonly utilized within pediatric medical settings due to structural barriers such as time constraints, a lack of space or appropriate materials, and the lack of exiting policies that refer patients to child life specialists or volunteers for such interventions. Further, this study\u27s results indicate that most medical social workers find that their primary role is to conduct psychosocial assessments, conduct patient and family counseling and psycho-education around illness and hospitalization, plan patient discharge, and serve as a case manager, which includes resource referrals for patients and familie

The Future of Connection : Serendipity and Control in Interpersonal Communication Tools

This foresight project explored the contemporary trends and tensions inherent in people's experiences with and using interpersonal communication tools. A standard foresight process was overlaid with an experiential lens in order to provide technology designers with useful insights. The outcomes of this project include four tools intended for designers of interpersonal communication applications. These tools include a map of experiential tensions, a landscape of contemporary behaviour, a set of four future scenarios and implications of each, and finally a set of ten reflection questions intended to provoke critical thought about the choices designers make about the balance between serendipity and control in interpersonal communication tools