Packet reordering, high speed networks and transport protocol performance

We performed end-to-end measurements of UDP/IP flows across an Internet backbone network. Using this data, we characterized the packet reordering processes seen in the network. Our results demonstrate the high prevalence of packet reordering relative to packet loss, and show a strong correlation between packet rate and reordering on the network we studied. We conclude that, given the increased parallelism in modern networks and the demands of high performance applications, new application and protocol designs should treat packet reordering on an equal footing to packet loss, and must be robust and resilient to both in order to achieve high performance

After the games are over: life-history trade-offs drive dispersal attenuation following range expansion.

Increased dispersal propensity often evolves on expanding range edges due to the Olympic Village effect, which involves the fastest and fittest finding themselves together in the same place at the same time, mating, and giving rise to like individuals. But what happens after the ranges leading edge has passed and the games are over? Although empirical studies indicate that dispersal propensity attenuates following range expansion, hypotheses about the mechanisms driving this attenuation have not been clearly articulated or tested. Here, we used a simple model of the spatiotemporal dynamics of two phenotypes, one fast and the other slow, to propose that dispersal attenuation beyond preexpansion levels is only possible in the presence of trade-offs between dispersal and life-history traits. The Olympic Village effect ensures that fast dispersers preempt locations far from the ranges previous limits. When trade-offs are absent, this preemptive spatial advantage has a lasting impact, with highly dispersive individuals attaining equilibrium frequencies that are strictly higher than their introduction frequencies. When trade-offs are present, dispersal propensity decays rapidly at all locations. Our models results about the postcolonization trajectory of dispersal evolution are clear and, in principle, should be observable in field studies. We conclude that empirical observations of postcolonization dispersal attenuation offer a novel way to detect the existence of otherwise elusive trade-offs between dispersal and life-history traits

Scaling Properties of Paths on Graphs

Let $G$ be a directed graph on finitely many vertices and edges, and assign a positive weight to each edge on $G$. Fix vertices $u$ and $v$ and consider the set of paths that start at $u$ and end at $v$, self-intersecting in any number of places along the way. For each path, sum the weights of its edges, and then list the path weights in increasing order. The asymptotic behaviour of this sequence is described, in terms of the structure and type of strongly connected components on the graph. As a special case, for a Markov chain the asymptotic probability of paths obeys either a power law scaling or a weaker type of scaling, depending on the structure of the transition matrix. This generalizes previous work by Mandelbrot and others, who established asymptotic power law scaling for special classes of Markov chains.Comment: 23 pages, 2 figure

Experiences with high definition interactive video conferencing

We review the design and implementation of UltraGrid, a new high definition video conferencing system, and present some experimental results. UltraGrid was the first system to support gigabit rate high definition interactive video conferencing on commodity systems and networks, and we present measurements to illustrate behavior of production networks subject to such real time traffic. We illustrate the benefits of hybrid IP/provisioned optical networks over best effort IP networks for this class of traffic, and motivate the development of congestion control algorithms for interactive conferencing on best effort IP networks

Strength of the DTM RapidSteel 1.0 Material

This paper reports the results of a study into the strength of the DTM RapidSteel 1.0 material. Elastic modulus and strength of the metal/copper composite material was investigated as a function of the distance from the point of copper infiltration, the furnace cycle duration, and the furnace type. The microstructure of the RapidSteel material was also examined in an attempt to understand the science behind the infiltration process. The results have implications for the design of tools to be made using the RapidTool process in situations where the tool will be used as a production tool, rather than a prototype tool.Mechanical Engineerin

Cartan Normal Conformal Connections from Pairs of 2nd Order PDE's

We explore the different geometric structures that can be constructed from the class of pairs of 2nd order PDE's that satisfy the condition of a vanishing generalized W\"{u}nschmann invariant. This condition arises naturally from the requirement of a vanishing torsion tensor. In particular, we find that from this class of PDE's we can obtain all four-dimensional conformal Lorentzian metrics as well as all Cartan normal conformal O(4,2) connections. To conclude, we briefly discuss how the conformal Einstein equations can be imposed by further restricting our class of PDE's to those satisfying additional differential conditions.Comment: 39 page

Temperature-controlled resistor

Electrical resistance of a carbon-pile resistor is controlled by the compression or relaxation of a pile of carbon disks by a thermally actuated bimetallic spring. The concept is advantageous in that it is direct-acting, can cover a wide range of controllable characteristics, and can handle considerable power directly

Cross Sectional Analysis of Patients with Alpha-1 Antitrypsin Deficiency Enrolled in a Disease Management and Prevention Program

Background: Alpha-1 antitrypsin deficiency is a heritable genetic condition that is largely underdiagnosed and has been estimated to affect 1 out of every 5,000-7,000 people in North America. The condition is characterized by a decrease in the production or activity of the alpha-1 antitrypsin protein, increasing risk for chronic lung or liver inflammation, that may lead to disease. Currently, there is no cure for the condition and augmentation therapy, which replaces the lost protein, has shown mixed results, meaning preventive measures taken by the patient are a large component of the prescribed treatment. Thus, patients with the condition are strongly encouraged to quit smoking, reduce drinking, avoid occupations or areas that have high levels of particulate matter or toxic air pollutants as well as maintain active vaccinations against lung and liver infections like pneumonia, hepatitis A and B, and the flu to prevent complications from the condition. Objectives: This study aims to 1) Access the associations between adherence to the AlphaNet disease management and prevention program and the prophylactic measures that are encouraged by the program and; 2) determine if any of these associations are a result of demographic and health differences between individuals who are adherent ADMAPP and those who are not. Methods: This is a cross-sectional study of 3,526 individuals with alpha-1 antitrypsin deficiency who answered a questionnaire administered by AlphaNet from May 29th 2008 to February 14th 2015 as part of the Alpha-1 Antitrypsin Management and Prevention Program. This study focused on questions related to adherence to the program and prophylactic measures taken by the individual that are encouraged by the literature given out by the program. Only individuals who 3 answered questions about their adherence to the program were included in this current study. Demographic differences between the two stratified populations and an index for comorbidities were used for logistic regression analysis. Results: After adjustment for sex, age, income, and comorbidies, compared with individuals who self-reported as being non-adherent to the disease management and prevention program, adherent individuals were more likely to be comfortable with their knowledge of the disease (ORadj=4.95, 95% CI: 3.24-7.57), have read any part of the literature provided by the program (ORadj=6.44, 95% CI: 5.45-7.62), and use augmentation therapy (ORadj=2.08, 95% CI: 1.53-2.82). These individuals were also more likely to be vaccinated for the flu (ORadj=1.34, 95% CI: 1.08-1.68), Hepatitis A (ORadj=1.41, 95% CI: 1.20-1.66), and Hepatitis B (ORadj=1.62, 95% CI: 1.37-1.91), as well as exercise (ORadj=2.07, 95% CI: 1.74-2.47), while being less likely to be active smokers (ORadj=0.47, CI: 0.31-0.70). Conclusions: This study suggests that AlphaNet program may be a useful tool for informing and improving preventive measures taken by individuals with alpha-1 antitrypsin deficiency. Individuals who self-reported their percent adherence to the program as being nonzero were more likely to be informed about their condition and taking preventive measures, such as smoking cessation, getting vaccinated for conditions that could magnify the effects of AATD, and increases in self-reported exercise. Future studies are needed to show causality and improvement in participant outcomes such as mortality and quality of life