1,720,973 research outputs found
Congestion Control and Sizing Router Buffers in the Internet
No full textThe Internet is made of communication links and packet switching nodes named routers. Routers are equipped with buffers that hold packets during congestion and feed output links with packets during underutilization. A rule largely known in literature is the "bandwidth-delay rule", which states that, in order to guarantee full link utilization, it is necessary to provide each link with a buffer B = RTT.C, where RTT is the round trip time and C is the link capacity. The bandwidth delay rule requires buffer size that increases linearly with link capacity. With the recent introduction of 10 Gbps Routers and Ethernet cards, buffer requirements as dictated by the bandwidth-delay rule become extremely large. For instance, a 10Gbps router link with a RTT of 200ms would require a 2Gbits buffer size, which is a challenging requirement for manufacturers. Moreover, such a large buffers would introduce large and time-varying queuing delays that are harmful for time sensitivity traffic such as audio and video. In this paper we investigate the relation between the TCP congestion control and the buffer size required to guarantee full link utilization. We consider two TCP congestion control algorithms: the standard TCP NewReno and the recently proposed TCP Westwood+. Analytical results show that while classic TCP Reno/NewReno requires buffer of order size ~ 1 n, where n is the number of coexisting flows, Westwood+ TCP, in principle, can provide full link utilization for any buffer size
The effect of reverse traffic on the performance of new TCP congestion control algorithms for gigabit networks
No full textAn analytical approach to characterize the service process and the tradeoff between throughput and service time burstiness in IEEE 802.11 DCF
Get PDFWe derive a complete characterization (marginal distribution, autocovariance) of the service time process in a saturated IEEE 802.11 wireless LAN, both from the point of view of a single station and of the system as a whole.
Our service time distribution model is then exploited to highlight the burstiness of service times and its dependence on the maximum value of the IEEE 802.11 contention window. We discuss a trade-off between throughput efficiency and service time variance, showing that a minor throughput loss can bring about a major benefit in service time smoothness, at least for practical values of the number of simultaneously competing stations (e.g.\ less than 15)
An unusual case of a cardiocutaneous fistula presenting 30 years after a breast carcinoma
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Bleeding duodenal varices urgently treated with TIPS and coil embolization in a patient with cirrhosis: A rare case
No full textDuodenal varices are ectopic varices that can cause severe and life-threatening gastrointestinal bleeding. Diagnosis and treatment of ectopic varices is challenging, because endoscopy is often unproductive in detecting and treating ectopic varices. Interventional radiology appears as an alternative in this setting, thanks to its important role in treating the bleeding caused by ectopic varices and in preventing rebleedings. We present an interesting case of bleeding ectopic varices in a male 62-years-old cirrhotic patient (Child-Pugh B8). The patient presented with hemorrhagic shock caused by massive melena. CT angiography showed intraluminal blood and identified the source of bleeding as an ectopic varicose vein draining into the superior mesenteric vein. Interventional radiology approach was the only applicable one to reach and effectively treat the source and cause of bleeding by TIPS placement and embolization of the collateral feeding at the same sessio
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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