36,135 research outputs found
Molecular Clock on a Neutral Network
The number of fixed mutations accumulated in an evolving population often
displays a variance that is significantly larger than the mean (the
overdispersed molecular clock). By examining a generic evolutionary process on
a neutral network of high-fitness genotypes, we establish a formalism for
computing all cumulants of the full probability distribution of accumulated
mutations in terms of graph properties of the neutral network, and use the
formalism to prove overdispersion of the molecular clock. We further show that
significant overdispersion arises naturally in evolution when the neutral
network is highly sparse, exhibits large global fluctuations in neutrality, and
small local fluctuations in neutrality. The results are also relevant for
elucidating the topological structure of a neutral network from empirical
measurements of the substitution process.Comment: 10 page
Estimating packet loss rate in the access through application-level measurements
End user monitoring of quality of experience is one of the necessary steps to achieve an effective and winning control over network neutrality. The involvement of the end user, however, requires the development of light and user-friendly tools that can be easily run at the application level with limited effort and network resources usage. In this paper, we propose a simple model to estimate packet loss rate perceived by a connection, by round trip time and TCP goodput samples collected at the application level. The model is derived from the well-known Mathis equation, which predicts the bandwidth of a steady-state TCP connection under random losses and delayed ACKs and it is evaluated in a testbed environment under a wide range of different conditions. Experiments are also run on real access networks. We plan to use the model to analyze the results collected by the "network neutrality bot" (Neubot), a research tool that performs application-level network-performance measurements. However, the methodology is easily portable and can be interesting for basically any user application that performs large downloads or uploads and requires to estimate access network quality and its variation
Network Neutrality Inference using Network Tomography
Our work studies network neutrality, a property of communication networks which means that they treat all traffic the same, regardless of application, content provider or communication protocol. This is an important problem, because sometimes users suspect their ISPs of violating network neutrality, but apply inaccurate methods to check their suspicions, reaching incorrect conclusions.
Prior non-neutrality detection methods either provide only detection, but lack localization capabilities; or also perform localization, but assume perfect measurements. For the latter, we show that, in practice, the measurement process can severely impact the results.
We present a method that performs both non-neutrality detection and localization, using only end-to-end measurements, and assuming an imperfect measurement process. We identify the sources of measurement error that may affect our method, we address them, and evaluate the method extensively with simulations, emulations and experiments on the Internet. We also use our method in two studies, investigating suspicions that a set of ISPs prioritize speed-test traffic, or differentiate against BitTorrent traffic; despite circumstancial evidence that they do, we obtain reliable evidence to the contrary. Finally, we present the network emulator that we built to evaluate our method, hoping that it will be a useful tool in future research.
We conclude that it is feasible to detect and localize network neutrality violations based solely on end-to-end measurements, without assuming a perfect measurement process; and that it is important that reasoning about network neutrality is based on reliable evidence of network behavior
Evolution favors protein mutational robustness in sufficiently large populations
BACKGROUND: An important question is whether evolution favors properties such
as mutational robustness or evolvability that do not directly benefit any
individual, but can influence the course of future evolution. Functionally
similar proteins can differ substantially in their robustness to mutations and
capacity to evolve new functions, but it has remained unclear whether any of
these differences might be due to evolutionary selection for these properties.
RESULTS: Here we use laboratory experiments to demonstrate that evolution
favors protein mutational robustness if the evolving population is sufficiently
large. We neutrally evolve cytochrome P450 proteins under identical selection
pressures and mutation rates in populations of different sizes, and show that
proteins from the larger and thus more polymorphic population tend towards
higher mutational robustness. Proteins from the larger population also evolve
greater stability, a biophysical property that is known to enhance both
mutational robustness and evolvability. The excess mutational robustness and
stability is well described by existing mathematical theories, and can be
quantitatively related to the way that the proteins occupy their neutral
network.
CONCLUSIONS: Our work is the first experimental demonstration of the general
tendency of evolution to favor mutational robustness and protein stability in
highly polymorphic populations. We suggest that this phenomenon may contribute
to the mutational robustness and evolvability of viruses and bacteria that
exist in large populations
Linear magnetoresistance in compensated graphene bilayer
We report a nonsaturating linear magnetoresistance in charge-compensated
bilayer graphene in a temperature range from 1.5 to 150 K. The observed linear
magnetoresistance disappears away from charge neutrality ruling out the
traditional explanation of the effect in terms of the classical random resistor
network model. We show that experimental results qualitatively agree with a
phenomenological two-fluid model taking into account electron-hole
recombination and finite-size sample geometry
Survey of End-to-End Mobile Network Measurement Testbeds, Tools, and Services
Mobile (cellular) networks enable innovation, but can also stifle it and lead
to user frustration when network performance falls below expectations. As
mobile networks become the predominant method of Internet access, developer,
research, network operator, and regulatory communities have taken an increased
interest in measuring end-to-end mobile network performance to, among other
goals, minimize negative impact on application responsiveness. In this survey
we examine current approaches to end-to-end mobile network performance
measurement, diagnosis, and application prototyping. We compare available tools
and their shortcomings with respect to the needs of researchers, developers,
regulators, and the public. We intend for this survey to provide a
comprehensive view of currently active efforts and some auspicious directions
for future work in mobile network measurement and mobile application
performance evaluation.Comment: Submitted to IEEE Communications Surveys and Tutorials. arXiv does
not format the URL references correctly. For a correctly formatted version of
this paper go to
http://www.cs.montana.edu/mwittie/publications/Goel14Survey.pd
The State of Network Neutrality Regulation
The Network Neutrality (NN) debate refers to the battle over the design of a regulatory framework for preserving the Internet as a public network and open innovation platform. Fueled by concerns that broadband access service providers might abuse network management to discriminate against third party providers (e.g., content or application providers), policymakers have struggled with designing rules that would protect the Internet from unreasonable network management practices. In this article, we provide an overview of the history of the debate in the U.S. and the EU and highlight the challenges that will confront network engineers designing and operating networks as the debate continues to evolve.BMBF, 16DII111, Verbundprojekt: Weizenbaum-Institut für die vernetzte Gesellschaft - Das Deutsche Internet-Institut; Teilvorhaben: Wissenschaftszentrum Berlin für Sozialforschung (WZB)EC/H2020/679158/EU/Resolving the Tussle in the Internet: Mapping, Architecture, and Policy Making/ResolutioNe
Secure and Differentially Private Detection of Net Neutrality Violations by Means of Crowdsourced Measurements
Evaluating Network Neutrality requires comparing the quality of service experienced by multiple users served by different Internet Service Providers. Consequently, the issue of guaranteeing privacy-friendly network measurements has recently gained increasing interest. In this paper we propose a system which gathers throughput measurements from users of various applications and Internet services and stores it in a crowdsourced database, which can be queried by the users themselves to verify if their submitted measurements are compliant with the hypothesis of a neutral network. Since the crowdsourced data may disclose sensitive information about users and their habits, thus leading to potential privacy leakages, we adopt a privacy-preserving method based on randomized sampling and suppression of small clusters. Numerical results show that the proposed solution ensures a good trade-off between usefulness of the system, in terms of precision and recall of discriminated users, and privacy, in terms of differential privacy
Giant oscillations in a triangular network of one-dimensional states in marginally twisted graphene
The electronic properties of graphene superlattices have attracted intense
interest that was further stimulated by the recent observation of novel
many-body states at "magic" angles in twisted bilayer graphene (BLG). For very
small ("marginal") twist angles of 0.1 deg, BLG has been shown to exhibit a
strain-accompanied reconstruction that results in submicron-size triangular
domains with the Bernal stacking. If the interlayer bias is applied to open an
energy gap inside the domain regions making them insulating, marginally-twisted
BLG is predicted to remain conductive due to a triangular network of chiral
one-dimensional (1D) states hosted by domain boundaries. Here we study electron
transport through this network and report giant Aharonov-Bohm oscillations
persisting to temperatures above 100 K. At liquid helium temperatures, the
network resistivity exhibits another kind of oscillations that appear as a
function of carrier density and are accompanied by a sign-changing Hall effect.
The latter are attributed to consecutive population of the flat minibands
formed by the 2D network of 1D states inside the gap. Our work shows that
marginally twisted BLG is markedly distinct from other 2D electronic systems,
including BLG at larger twist angles, and offers a fascinating venue for
further research.Comment: 11 pages, 8 figure
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