A measurement-based approach to service modeling and bandwidth estimation in IEEE 802.11 wireless networks

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Understanding Fairness and its Impact on Quality of Service in IEEE 802.11

The Distributed Coordination Function (DCF) aims at fair and efficient medium access in IEEE 802.11. In face of its success, it is remarkable that there is little consensus on the actual degree of fairness achieved, particularly bearing its impact on quality of service in mind. In this paper we provide an accurate model for the fairness of the DCF. Given M greedy stations we assume fairness if a tagged station contributes a share of 1/M to the overall number of packets transmitted. We derive the probability distribution of fairness deviations and support our analytical results by an extensive set of measurements. We find a closed-form expression for the improvement of long-term over short-term fairness. Regarding the random countdown values we quantify the significance of their distribution whereas we discover that fairness is largely insensitive to the distribution parameters. Based on our findings we view the DCF as emulating an ideal fair queuing system to quantify the deviations from a fair rate allocation. We deduce a stochastic service curve model for the DCF to predict packet delays in IEEE 802.11. We show how a station can estimate its fair bandwidth share from passive measurements of its traffic arrivals and departures

Einfluss der operativen Reposition auf die Entstehung einer posttraumatischen Koxarthrose

Einleitung Die operative Versorgung von Azetabulumfrakturen stellt eine große Herausforderung an den Chirurgen insbesondere im Hinblick auf Langzeitfolgen wie die Koxarthrose dar. Ein adäquates Werkzeug zur Erfassung der Güte der operativen Reposition ist somit vonnöten. Bisher wurden hierfür im Großteil der Literatur die Matta-Kriterien zu Rate gezogen, welche auf konventionellen Röntgenaufnahmen beruhen und traditionell nicht zwischen verschiedenen Arten der residualen Gelenkflächendislokation unterscheiden. Das Ziel dieser Arbeit ist die Relevanz der Matta- Kriterien zur Vorhersage von Koxarthrose im Anblick der allgegenwärtigen CT-Technologie zu evaluieren. Methoden Es wurde eine retrospektive Datenauswertung von 2001 bis 2016 am Centrum für Muskuloskeletale Chirurgie der Charité – Universitätsmedizin Berlin operativ versorgter Azetabulumfrakturen durchgeführt. Postoperative CT-Bilder wurden untersucht auf residuale Stufen („Steps“) oder Spalten („Gaps“) in der Gelenkfläche. Das Ausmaß dieser residualen Dislokationen wurde korreliert mit der Höhe des Kellgren-Lawrence-Scores im Röntgenbild im Follow-Up. Die Studienpopulation wurde zudem zweigeteilt in niedrige (0-2) und hohe (3-4) Kellgren-Lawrence-Scores und eine ROC-Kurve zur Untersuchung von Sensitivitäts- und Spezifitätsniveaus der Größe von Steps und Gaps in Relation zu einem niedrigen oder hohen Kellgren-Lawrence-Score angefertigt. Ergebnisse Insgesamt wurden 58 Fälle in die Studie eingeschlossen. Sowohl postoperative Steps als auch postoperative Gaps korrelierten positiv mit der Höhe des Kellgren-Lawrence-Scores im Follow- Up. Der Frakturtyp nach Judet-Letournel hatte scheinbar keinen Einfluss auf die Güte der operativen Reposition. Die ROC-Kurve zeigt, dass Steps > 2 mm mit einer Spezifität von mehr als 90% mit einem Kellgren-Lawrence-Score von ≥ 3 im Follow-up assoziiert waren, während ein weitaus größerer Gap > 5 mm für ein ähnliches Ergebnis nötig war. Schlussfolgerung Sowohl Steps als auch Gaps lassen sich als Gütekriterien der operativen Reposition von Azetabulumfrakturen heranziehen. Jedoch müssen Gaps wesentlich größer als Steps sein, um mit einem ähnlichen oder gar schlechteren radiologischen Langzeitergebnis assoziiert zu sein. Eine Neubewertung der Matta-Kriterien insbesondere im Hinblick auf die Unterscheidung zwischen Steps und Gaps kann somit in Erwägung gezogen werden.Introduction The operative treatment of acetabular fractures poses a significant challenge to the surgeon, especially concerning the long-term outcome with the goal of avoiding postoperative osteoarthritis of the hip in mind. An adequate tool for assessing the quality of the operative reduction is therefore necessary. So far, the vast majority of publications asses the operative reduction using Matta’s criteria which are based on plain X-rays of the hip and traditionally do not differentiate between different kinds of residual joint dislocation. The goal of this work is to evaluate whether Matta’s criteria are still accurate enough in predicting the development in osteoarthritis of the hip, especially in the light of advancements in CT-imaging. Methods A retrospective analysis of operatively treated acetabular fractures from 2001 to 2016 was conducted at the department of musculoskeletal surgery of the Charité – University of Medicine Berlin. Postoperative CT-images were screened for residual steps and/or gaps in the joint surface and the height of these steps and/or gaps was correlated with a Kellgren-Lawrence-Score after medium to long-term radiological follow-up. The study population was furthermore divided into two groups with Kellgren-Lawrence-Scores of 0-2 and 3-4, respectively, and an ROC-Curve was plotted to examine the sensitivity and specificity for differently sized steps and gaps in a relationship to a low (0-2) or high (3-4) Kellgren-Lawrence-Score. Results In total, 58 cases were included in the study. Both postoperative steps and postoperative gaps correlated positively in their height with the Kellgren-Lawrence-Score in follow-up. The type of fracture classified after Judet-Letournel appeared to have no influence on the height of a step or a gap. The ROC-curve showed that steps of more than 2 mm were associated with a specificity of more than 90% for a Kellgren-Score of ≥3 during follow-up, while a much higher gap of more than 5 mm was necessary to be associated with a similar outcome. Conclusion Both steps and gaps are associated with the quality of the operative reduction and predict the radiological outcome of an operatively treated acetabular fracture. However, gaps need to be much larger than steps to be associated with the same or a worse outcome. Thus, revising Matta’s criteria to differentiate between steps and gaps can be considered

Emotional and emotive language: modal particles and tags in unified Berlin

This paper endeavours to show the relationship between emotion and language, in particular with respect to the use of modal particles in German. Modal particles have long been considered insignificant fillers without a specific function and as such, not worthy of linguistic investigation. This is clearly a view which cannot be sustained. Modal particles have been found to illustrate the speaker’s opinion of what is being said; in addition, they may add emphasis. Certain German modal particles (especially halt and eben) are examined as they occur in a corpus of utterances containing accounts of highly emotional events, related to East and West Berliners’ experiences after the fall of the Berlin Wall and German unification. By reviewing spoken accounts of events which were life-changing for one side, but only nominal for the other, thereby producing different emotions, the article demonstrates the use of these modal particles. The analysis suggests that there is a direct link between emotion and the way these speakers of German use their language

Interoperability Between GRDC\u27s Data Holding And The GEOSS Infrastructure

The Global Runoff Data Centre (GRDC) operates under the auspices of the World Meteorological Organization as an international data centre for hydrological data and information on a global scale. Its primary objective is to support the water and climate related programmes and projects of the United Nations, its specialised agencies, and the scientific research community on global and climate change and integrated water resources management. The Global Runoff Database maintained by the GRDC is a valuable data resource and a subset of its data is contributed to the Global Earth Observation System of Systems’ (GEOSS) freely accessible Data Core. As a partner in the project GEOSS Interoperability for Weather, Ocean and Water (GEOWOW) the GRDC supports the evolving GEOSS in terms of interoperability, standardization and functionality. In the framework of GEOWOW a profile of the OGC Sensor Observation Service Interface Standard 2.0 (SOS) is being developed. This SOS Profile for the Hydrology Domain specifies extensions to the service interface and uses the OGC WaterML 2.0 standard for encoding hydrological time series data. Moreover, technical partners of the GEOWOW project facilitate software implementations of the standardization advancements. Deploying and incorporating these into GRDC’s data holding infrastructure allows for a seamless integration of GRDC’s data provision capabilities into GEOSS. Furthermore, client web applications to visualize time series data provided via an OGC Web Service infrastructure makes it possible to offer additional benefit and allows for accessing and assessing data more easily

Proton and sodium MRI assessment of emerging tumor chemotherapeutic resistance

The ultimate goal of any cancer therapy is to target the elimination of neoplastic cells. Although newer therapeutic strategies are in constant development, therapeutic assessment has been hampered by the inability to assess, rapidly and quantitatively, efficacy in vivo . Diffusion imaging and, more recently, sodium MRI have demonstrated their distinct abilities to detect therapy-induced alterations in tumor cellularity, which has been demonstrated to be indicative of therapeutic efficacy. More importantly, both imaging modalities detect tumor response much earlier than traditional methodologies that rely on macroscopic volumetric changes. In this study, the correlation between tumor sodium and diffusion was further tested to demonstrate the sensitivity of sodium imaging to gauge tumor response to therapy by using a 9L rat gliosarcoma treated with varying doses of BCNU [1,3-bis(2-chloroethyl)-1-nitrosourea]. This orthotopic model has been demonstrated to display variability in response to BCNU therapy where initial insult has been shown to lead to drug-resistance. In brief, a single 26.6 mg/kg BCNU dose yielded dramatic responses in both diffusion and sodium MRI. However, a second equivalent BCNU dose yielded a much smaller change in diffusion and sodium, suggesting a drop in tumor sensitivity to BCNU. The MRI responses of animals treated with 13.3 mg/kg BCNU were much lower and similar responses were observed after the initial and secondary applications of BCNU. Furthermore, these results were further validated using volumetric measurements of the tumor and also ex vivo determination of tumor sensitivity to BCNU. Overall, these experiments demonstrate the sensitivity and applicability of sodium and diffusion MRI as tools for dynamic assessment of tumor response to therapy. Copyright © 2006 John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/55899/1/1074_ftp.pd