Transport Protocol Throughput Fairness

Interest continues to grow in alternative transport protocols to the Transmission Control Protocol (TCP). These alternatives include protocols designed to give greater efficiency in high-speed, high-delay environments (so-called high-speed TCP variants), and protocols that provide congestion control without reliability. For the former category, along with the deployed base of ‘vanilla’ TCP – TCP NewReno – the TCP variants BIC and CUBIC are widely used within Linux: for the latter category, the Datagram Congestion Control Protocol (DCCP) is currently on the IETF Standards Track. It is clear that future traffic patterns will consist of a mix of flows from these protocols (and others). So, it is important for users and network operators to be aware of the impact that these protocols may have on users. We show the measurement of fairness in throughput performance of DCCP Congestion Control ID 2 (CCID2) relative to TCP NewReno, and variants Binary Increase Congestion control (BIC), CUBIC and Compound, all in “out-of-the box” configurations. We use a testbed and endto- end measurements to assess overall throughput, and also to assess fairness – how well these protocols might respond to each other when operating over the same end-to-end network path. We find that, in our testbed, DCCP CCID2 shows good fairness with NewReno, while BIC, CUBIC and Compound show unfairness above round-trip times of 25ms

Using the Java Media Framework to build Adaptive Groupware Applications

Realtime audio and video conferencing has not yet been satisfactorily integrated into web-based groupware environments. Conferencing tools are at best only loosely linked to other parts of a shared working environment, and this is in part due to their implications for resource allocation and management. The Java Media Framework offers a promising means of redressing this situation. This paper describes an architecture for integrating the management of video and audio conferences into the resource allocation mechanism of an existing web-based groupware framework. The issue of adaptation is discussed and a means of initialising multimedia session parameters based on predicted QoS is described

The effect of hot and cold drinks on thermoregulation, perception and performance: the role of the gut in thermoreception

Purpose. Hot compared to cold drinks alter sweating responses during very low intensity exercise in temperate conditions. The thermoregulatory, perceptual and performance effects of hot compared to cold drinks in hot, dry conditions during high-intensity exercise have not been examined. Method. Ten participants (mean ± SD characteristics age 25 ± 5 years, height 1.81 ± 0.07 m, body mass 73.5 ± 10.6 kg, maximal power output (PMax) 350 ± 41 W). completed two conditions where they drank four boluses (ingested at -9, 15, 30 & 45 minutes respectively) of 3.2 mL.kg-1 (~960 mL total) of either a COLD (5.3°C) or a HOT drink (49.0°C), which were contrasted to a no drink CONTROL. They cycled for 60-minutes (55% PMax in hot (34.4°C) dry (34% RH) ambient conditions followed by a test to exhaustion (TTE; 80% PMax). The thermoregulatory, performance and perceptual implications of drink temperature were measured. Results. TTE was worse in the CONTROL (170 ± 132 s) than the COLD drink (371 ± 272 s; p = .021) and HOT drink conditions (367 ± 301 s; p = .038) which were not different (p = .965). Sweat responses (i.e. reflex changes in mean skin temperature (Tmsk) and galvanic skin conductance) indicated transient reductions in sweating response after COLD drink ingestion. The COLD drink improved thermal comfort beyond the transient changes in sweating. Conclusion. Only COLD drink ingestion changed thermoregulation but improved perceptual response. Accordingly, we conclude a role for gut thermoreception in thermal perception during exercise in hot, dry conditions

Aeolianite and barrier dune construction spanning the last two glacial-interglacial cycles from the southern Cape coast, South Africa

The southern Cape region of South Africa has extensive coastal aeolianites and barrier dunes. Whilst previously reported, limited knowledge of their age has precluded an understanding of their relationship with the climatic and sea-level fluctuations that have taken place during the Late Quaternary. Sedimentological and geomorphological studies combined with an optical dating programme reveal aeolianite development and barrier dune construction spanning at least the last two glacial–interglacial cycles. Aeolianite deposition has occurred on the southern Cape coast at ca 67–80, 88–90, 104–128, 160–189 and >200 ka before the present. Using this and other published data coupled with a better understanding of Late Quaternary sea-level fluctuations and palaeocoastline configurations, it is concluded that these depositional phases appear to be controlled by interglacial and subsequent interstadial sea-level high stands. These marine transgressions and regressions allowed onshore carbonate-rich sediment movement and subsequent aeolian reworking to occur at similar points in the landscape on a number of occasions. The lack of carbonates in more recent dunes (Oxygen Isotope Stages 1/2 and 4/5) is attributed not to leaching but to changes to carbonate production in the sediment source area caused by increased terrigenous material and/or changes in the balance between the warm Agulhas and nutrient-rich Benguela ocean current

Generational spreading speed and the dynamics of population range expansion

Author Posting. © University of Chicago Press, 2015. This article is posted here by permission of University of Chicago Press for personal use, not for redistribution. The definitive version was published in American Naturalist 186 (2015): 362-375, doi:10.1086/682276.Some of the most fundamental quantities in population ecology describe the growth and spread of populations. Population dynamics are often characterized by the annual rate of increase, λ, or the generational rate of increase, R0. Analyses involving R0 have deepened our understanding of disease dynamics and life-history complexities beyond that afforded by analysis of annual growth alone. While range expansion is quantified by the annual spreading speed, a spatial analog of λ, an R0-like expression for the rate of spread is missing. Using integrodifference models, we derive the appropriate generational spreading speed for populations with complex (stage-structured) life histories. The resulting measure, relevant to locations near the expanding edge of a (re)colonizing population, incorporates both local population growth and explicit spatial dispersal rather than solely growth across a population, as is the case for R0. The calculations for generational spreading speed are often simpler than those for annual spreading speed, and analytic or partial analytic solutions can yield insight into the processes that facilitate or slow a population’s spatial spread. We analyze the spatial dynamics of green crabs, sea otters, and teasel as examples to demonstrate the flexibility of our methods and the intuitive insights that they afford.Support for this work was provided, in part, by a postdoctoral fellowship (A.W.B.), Discovery Grants (M.K., M.A.L.), and an Accelerator Grant (M.A.L.) from the Natural Sciences and Engineering Research Council of Canada. The material is based on work supported by the US National Science Foundation under grants DEB-1145017 and DEB-1257545 to M.G.N. M.A.L. also received support from the Canada Research Chair program and a Killam Research Fellowship.2016-08-0

What makes a target: politicians and abuse on social media [Note: The chapter “What makes a target: politicians and abuse on social media” from the edited collection “Anti Social Media?” was reprinted in the British Journalism Review under the title “And they thought papers were rude.”]

Politicians are known to be targets for some of the worst abuse on social media, including rape and death threats. But exactly how bad is it? Who gets it worst? And where is this onslaught of negativity taking us? This article is based on the analysis of all tweets sent as single @messages to British MPs between December 2016 and the general election in June 2017. This dataset of roughly 80,000 tweets was categorised using sentiment analysis software into hostile, disagree and other. The results show little difference in levels of hostility by gender, race or political party. The major drivers of long-term hostility were high profile jobs and criticising Corbyn. Incautious public appearances or tweets resulted in major spikes. Scottish politics also proved more aggressive. The effect of publicity due to high profile jobs on hostility may partly explain the relatively flat relationship between hostility and gender/race, as front bench jobs are more likely to be filled by white men

Parameter estimation in a spatial unit root autoregressive model

Spatial unilateral autoregressive model $X_{k,\ell}=\alpha X_{k-1,\ell}+\beta X_{k,\ell-1}+\gamma X_{k-1,\ell-1}+\epsilon_{k,\ell}$ is investigated in the unit root case, that is when the parameters are on the boundary of the domain of stability that forms a tetrahedron with vertices $(1,1,-1), \ (1,-1,1),\ (-1,1,1)$and$(-1,-1,-1)$. It is shown that the limiting distribution of the least squares estimator of the parameters is normal and the rate of convergence is$n$when the parameters are in the faces or on the edges of the tetrahedron, while on the vertices the rate is$n^{3/2}$.Comment: 47 pages, 1 figur

Persistent currents in ballistic normal-metal rings

Recent experiments renewed interest in persistent currents in mesoscopic normal-metal rings. We show that in ballistic rings in high magnetic fields the Zeeman splitting leads to periodic current quenching with period much larger than the period of the persistent current. Simple arguments show that this effect might be relevant for diffusive rings as well. Another aim of this paper is to discuss fluctuations of the persistent current due to thermal excitation of high energy levels. Being observed such fluctuations would witness a coherent state of an electron system at high temperatures when the persistent current is exponentially suppressed.Comment: Submitted to Special Issue of the international journal Low Temperature Physics : "Quantum coherent effects in superconductors and normal metals" devoted to 75-years anniversary of Prof. Igor Kuli