2,562 research outputs found
Discussion quality diffuses in the digital public square
Studies of online social influence have demonstrated that friends have
important effects on many types of behavior in a wide variety of settings.
However, we know much less about how influence works among relative strangers
in digital public squares, despite important conversations happening in such
spaces. We present the results of a study on large public Facebook pages where
we randomly used two different methods--most recent and social feedback--to
order comments on posts. We find that the social feedback condition results in
higher quality viewed comments and response comments. After measuring the
average quality of comments written by users before the study, we find that
social feedback has a positive effect on response quality for both low and high
quality commenters. We draw on a theoretical framework of social norms to
explain this empirical result. In order to examine the influence mechanism
further, we measure the similarity between comments viewed and written during
the study, finding that similarity increases for the highest quality
contributors under the social feedback condition. This suggests that, in
addition to norms, some individuals may respond with increased relevance to
high-quality comments.Comment: 10 pages, 6 figures, 2 table
Fast two-dimensional model
A two dimensional (altitude and latitude) model of the atmosphere is used to investigate problems relating to the variability of the dynamics and temperature of the atmosphere on the ozone distribution, solar cycle variations of atmospheric constituents, the sensitivity of model results to tropospheric trace gas sources, and assessment computations of changes in ozone related to manmade influences. In a comparison between two dimensional model results in which the odd nitrogen family was transported together and model results in which the odd nitrogen species was transported separately, it was found that the family approximations are adequate for perturbation scenario calculations
Spatial Heterogeneity in the Abundance and Fecundity of Arctic Mosquitoes
The abundance of mosquitoes is strongly influenced by biotic and abiotic factors that act on the immature (aquatic) and adult (terrestrial) life stages. Rapid changes in land use and climate, which impact aquatic and terrestrial mosquito habitat, necessitate studying the ecological mechanisms, and their interplay with the changing environment, that affect mosquito abundance. These data are crucial for anticipating how environmental change will impact their roles as pests, disease vectors, and in food webs. We studied a population of Arctic mosquitoes (Aedes nigripes, Diptera: Culicidae) in western Greenland, a region experiencing rapid environmental change, to quantify spatial variation in adult abundance and reproduction. Using sweep nets, we collected about sevenfold more mosquitoes within the town of Kangerlussuaq and within a lowâelevation tundra valley compared to three other tundra locations. Dissections of adult female mosquitoes revealed that only 17% were gravid overall, with a range of 7â43% among sites. If gravid, mosquitoes matured an average of 60 eggs per individualâmore in larger females. We found no indication of autogenous egg development. Analyses using our field data indicated that spatial variation in adult fecundity and survival of immatures could each account for a 10âfold range in the per capita growth of mosquito populations. The availability of vertebrate hosts and aquatic habitat is changing in many parts of the Arctic and can be expected to influence Arctic mosquito abundance. In the Arctic, and elsewhere, lifeâhistory data from natural populations of mosquitoes will significantly aid in understanding controls on the abundance of these globally ubiquitous insects
Charge Transfer Properties Through Graphene Layers in Gas Detectors
Graphene is a single layer of carbon atoms arranged in a honeycomb lattice
with remarkable mechanical, electrical and optical properties. For the first
time graphene layers suspended on copper meshes were installed into a gas
detector equipped with a gaseous electron multiplier. Measurements of low
energy electron and ion transfer through graphene were conducted. In this paper
we describe the sample preparation for suspended graphene layers, the testing
procedures and we discuss the preliminary results followed by a prospect of
further applications.Comment: 2014 IEEE Nuclear Science Symposium and Medical Imaging Conference
with the 21st Symposium on Room-Temperature Semiconductor X-Ray and Gamma-Ray
Detectors, 4 pages, 8 figure
Plasmapause formation at Saturn
Cassini observations during a rapid, highâlatitude, dawnside pass from Saturn's lobe to inner magnetosphere on 25 June 2009 provide strong evidence for the formation of a âplasmapauseâ at Saturn by Vasyliunasâtype nightside reconnection of previously massâloaded flux tubes. A population of hot, tenuous plasma that lies between the lobe and the dense inner magnetospheric plasma is consistent with a region formed by very recent injection from a reconnection region in the tail, including low density, high temperature, supercorotational flow, a significant O+ content, and the nearâsimultaneous observation of enhanced Saturn kilometric radiation emissions. The sharp boundary between that region and the cool dense inner magnetospheric plasma thus separates flux tubes that were involved in the reconnection from those that successfully traversed the nightside without mass loss. This event demonstrates that tail reconnection can strip off inner magnetospheric plasma in to at least dipole Lâ=â8.6. Clear evidence of flux tube interchange driven by the sharp boundary is found, both inward moving flux tubes of hotter plasma and, for the first time, the outward moving cool population. The outward moving cool regions have azimuthal sizes less than 1âRS, were probably created within the past 1.2âh, and have outflow speeds greater than about 5âkm/s. At the outer edge of the reconnected region, there is also a possible signature of Dungeyâtype lobe reconnection following the initial Vasyliunasâtype reconnection. Observations from this event are entirely consistent with previously described global MHD simulations of tail reconnection, plasmoid departure, and Saturnward injection of reconnected flux.Key PointsSharp boundary between hot, tenuous and cooler, denser magnetospheric plasmaHot plasma consistent with exhaust from nearâtail reconnection regionSharp boundary drives interchange instabilityPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111761/1/jgra51711.pd
Elemental boron doping behavior in silicon molecular beam epitaxy
Boron-doped Si epilayers were grown by molecular beam epitaxy (MBE) using an elemental boron source, at levels up to 2Ă1020 cmâ3, to elucidate profile control and electrical activation over the growth temperature range 450â900 °C. Precipitation and surface segregation effects were observed at doping levels of 2Ă1020 cmâ3 for growth temperatures above 600 °C. At growth temperatures below 600 °C, excellent profile control was achieved with complete electrical activation at concentrations of 2Ă1020 cmâ3, corresponding to the optimal MBE growth conditions for a range of Si/SixGe1âx heterostructures
Charge Transfer Properties Through Graphene for Applications in Gaseous Detectors
Graphene is a single layer of carbon atoms arranged in a honeycomb lattice
with remarkable mechanical and electrical properties. Regarded as the thinnest
and narrowest conductive mesh, it has drastically different transmission
behaviours when bombarded with electrons and ions in vacuum. This property, if
confirmed in gas, may be a definitive solution for the ion back-flow problem in
gaseous detectors. In order to ascertain this aspect, graphene layers of
dimensions of about 2x2cm, grown on a copper substrate, are transferred
onto a flat metal surface with holes, so that the graphene layer is freely
suspended. The graphene and the support are installed into a gaseous detector
equipped with a triple Gaseous Electron Multiplier (GEM), and the transparency
properties to electrons and ions are studied in gas as a function of the
electric fields. The techniques to produce the graphene samples are described,
and we report on preliminary tests of graphene-coated GEMs.Comment: 4pages, 3figures, 13th Pisa Meeting on Advanced Detector
Searching for Saturn's X-rays during a rare Jupiter Magnetotail Crossing using Chandra
Every 19 years, Saturn passes through Jupiter's 'flapping' magnetotail. Here,
we report Chandra X-ray observations of Saturn planned to coincide with this
rare planetary alignment and to analyse Saturn's magnetospheric response when
transitioning to this unique parameter space. We analyse three Director's
Discretionary Time (DDT) observations from the High Resolution Camera (HRC-I)
on-board Chandra, taken on November 19, 21 and 23 2020 with the aim to find
auroral and/or disk emissions. We infer the conditions in the kronian system by
looking at coincident soft X-ray solar flux data from the Geostationary
Operational Environmental Satellite (GOES) and Hubble Space Telescope (HST)
observations of Saturn's ultraviolet (UV) auroral emissions. The large
Saturn-Sun-Earth angle during this time would mean that most flares from the
Earth-facing side of the Sun would not have impacted Saturn. We find no
significant detection of Saturn's disk or auroral emissions in any of our
observations. We calculate the 3 upper band energy flux of Saturn
during this time to be 0.9 - 3.04 10 erg cm s
which agrees with fluxes found from previous modelled spectra of the disk
emissions. We conclude by discussing the implications of this non-detection and
how it is imperative that the next fleet of X-ray telescope (such as Athena and
the Lynx mission concept) continue to observe Saturn with their improved
spatial and spectral resolution and very enhanced sensitivity to help us
finally solve the mysteries behind Saturn's apparently elusive X-ray aurora.Comment: 8 pages, 3 figures, accepted for publication in MNRA
Additive CHARMM force field for naturally occurring modified ribonucleotides
International audienceMore than 100 naturally occurring modified nucleotides have been found in RNA molecules, in particular in tRNAs. We have determined molecular mechanics force field parameters compatible with the CHARMM36 all-atom additive force field for all these modifications using the CHARMM force field parametrization strategy. Emphasis was placed on fine tuning of the partial atomic charges and torsion angle parameters. Quantum mechanics calculations on model compounds provided the initial set of target data, and extensive molecular dynamics simulations of nucleotides and oligonucleotides in aqueous solutions were used for further refinement against experimental data. The presented parameters will allow for computational studies of a wide range of RNAs containing modified nucleotides, including the ribosome and transfer RNAs. (C) 2016 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc
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