Measuring Belief Dynamics on Twitter

There is growing concern about misinformation and the role online media plays in social polarization. Analyzing belief dynamics is one way to enhance our understanding of these problems. Existing analytical tools, such as survey research or stance detection, lack the power to correlate contextual factors with population-level changes in belief dynamics. In this exploratory study, I present the Belief Landscape Framework, which uses data about people's professed beliefs in an online setting to measure belief dynamics with high resolution. I provide initial validation of the approach by comparing the method's output to a set of hypotheses drawn from the literature and by inspecting the "belief landscape" generated by the method. My analysis indicates that the method is relatively robust to different parameter settings, and results suggest that 1) there are many stable configurations of belief, or attractors, on the polarizing issue of climate change and 2) that people move in predictable ways around these attractors. The method paves the way for more powerful tools that can be used to understand how the modern digital media ecosystem impacts collective belief dynamics and what role misinformation plays in that process.Comment: 11 pages, 5 figure, to appear in the Proceedings of ICWSM '2

Enhanced spectral modeling of sparse aperture imaging systems

The remote sensing community continues to pursue advanced sensor designs and post processing techniques that improve upon the spatial quality of collected overhead imagery. Unfortunately, spaceborne applications frequently encounter launch vehicle fairing and weight constraints that limit the size of the primary aperture that can be utilized for a given application. Sparse aperture telescopes provide a potential avenue for overcoming some of the size and weight issues associated with deploying a large monolithic mirror system. These telescope systems are constructed of smaller subapertures which are phased to form a common image field and thereby synthesize a larger effective primary diameter to obtain higher spatial resolution than that achievable with a single subaperture. Much of the research conducted to date in this sparse aperture arena has focused on the panchromatic image quality performance of various optical configurations through approaches that make use of resampled, gray-scale imagery products. The research effort performed in conjunction with this dissertation focused on laying the groundwork for synthetic model-based approaches for evaluating the optical performance of sparse aperture collection systems with enhanced spectral fidelity and a polychromatic object scene. It entailed a fundamental investigation and demonstration of the first-principles physics required to model such imaging systems. This theoretical development ultimately led to the generation of a modeling concept that more rigorously addresses the spectral characteristics of classic sparse aperture optical configurations used in remote sensing applications. To demonstrate the proposed theoretical foundation, a proof-of-concept digital model was implemented that incorporates essential components of the fundamental physical processes involved with typical sparse aperture collection systems, including any potential spectral effects unique to these design configurations. In addition to modeling the detected imagery derived from the collection system, there was also an interest in exploring the quality implications of image restoration techniques typically required for sparse aperture imaging systems. Several variations of the classic Wiener-Helstrom filter were implemented and investigated in response to this research objective. The basic restoration methodologies pursued in this effort provide a foundation for research into more advanced techniques in the future. Finally, a top-level sensitivity study of the image quality performance of various sparse aperture pupil configurations subjected to varying levels of subaperture dephasing and/or aberrations was performed. This exploration of the trade space focused on a panchromatic detection scenario and attempted to bound the performance region where unique spectral quality issues are observed for the unconventional collection telescopes targeted through this research effort

Social Roles, Interactions and Community Sustainability in Social Q&A Sites: A Resource-based Perspective

Online tech support communities have become valuable channels for users to seek and provide solutions to specific problems. From the resource exchange perspective, the sustainability of a social system is contingent upon the size of its members as well as their communication activities. To further extend the resource-based model, the current research identifies a variety of social roles in a large tech support Q&A forum and examines longitudinal changes in the community’s structure based on the identification. Moreover, this study also investigates the relationship between the community’s functionality and its traffic. Results suggest that the proportion of unsolved questions negatively impacts the number of future incoming questions and the outcome of a given question is not only dependent on users’ interactions within the discussion, but also on the community activities preceding the question. These observations can help community managers to improve system design and task allocation

Melt regimes, internal stratigraphy, and flow dynamics of three glaciers in the Alaska Range

We used ground-penetrating radar (GPR), GPS and glaciochemistry to evaluate melt regimes and ice depths, important variables for mass-balance and ice-volume studies, of Upper Yentna Glacier, Upper Kahiltna Glacier and the Mount Hunter ice divide, Alaska. We show the wet, percolation and dry snow zones located below 2700 m a.s.l., at 2700 to 3900 m a.s.l. and above 3900 m a.s.l., respectively. We successfully imaged glacier ice depths upwards of 480 m using 40–100 MHz GPR frequencies. This depth is nearly double previous depth measurements reached using mid-frequency GPR systems on temperate glaciers. Few Holocene-length climate records are available in Alaska, hence we also assess stratigraphy and flow dynamics at each study site as a potential ice-core location. Ice layers in shallow firn cores and attenuated glaciochemical signals or lacking strata in GPR profiles collected on Upper Yentna Glacier suggest that regions below 2800 m a.s.l. are inappropriate for paleoclimate studies because of chemical diffusion, through melt. Flow complexities on Kahiltna Glacier preclude ice-core climate studies. Minimal signs of melt or deformation, and depth–age model estimates suggesting 4815 years of ice on the Mount Hunter ice divide (3912 m a.s.l.) make it a suitable Holocene-age ice-core location

Image Quality Analysis of a Spectra-Radiometric Sparse-Aperture Model

Sparse aperture (SA) telescopes represent a promising technology to increase the effective diameter of an optical system while reducing overall weight and stowable size. Although conceptually explored in the literature for decades, the technology has only recently matured to the point of being reasonably considered for certain applications. In general, a sparse aperture system consists of an array of sub-apertures that are phased to synthesize a larger effective aperture. The models used to date to create predictions of sparse aperture imagery typically make use of a “gray world” assumption, where the input is a resampled black and white panchromatic image. This input is then degraded and resampled with a so-called polychromatic system optical transfer function (OTF), which is a weighted average of the OTFs over the spectral bandpass. In reality, a physical OTF is spectrally dependent, exhibiting varying structure with spatial frequency (especially in the presence of optical aberrations or sub-aperture phase errors). Given this spectral variation with spatial frequency, there is some concern the traditional gray world resampling approach may not address significant features of the image quality associated with sparse aperture systems. This research investigates the subject of how the image quality of a sparse aperture system varies with respect to a conventional telescope from a spectra-radiometric perspective, with emphasis on whether the restored sparse aperture image will be beset by spectral artifacts

Using Multispectral Information to Decrease the Spectral Artifacts in Sparse-Aperture Imagery

Optical sparse-aperture telescopes represent a promising new technology to increase the effective diameter of an optical system while reducing its weight and stowable size. The sub-apertures of a sparse-aperture system are phased to synthesize a telescope system that has a larger effective aperture than any of the independentsub-apertures. Sparse-apertures have mostly been modeled to date using a gray-world approximation where the input is a grayscale image. The gray-world model makes use of a polychromatic optical transfer function (OTF) where the spectral OTFs are averaged to form a single OTF. This OTF is then convolved with the grayscale image to create the resultant sparse-aperture image. The model proposed here uses a spectral image-cube as the input to create a panchromatic or multispectral result. These outputs better approximate an actual system because there is a higher spectral fidelity present than a gray-world model. Unlike its Cassegrain counterpart that has a well behaved OTF, the majority of sparse-aperture OTFs have very oscillatory and attenuated natures. When a spectral sparse-aperture model is used, spectral artifacts become apparent when thephasing errors increase beyond a certain threshold. This threshold can be based in part on the type of phasing error (i.e. piston, tip/tilt, and the amount present in each sub-aperture), as well as the collection conditions, including configuration, signal-to-noise ratio (SNR), and fill factor.This research addresses whether integrating a restored multispectral sparse-aperture image into a panchromatic image will decrease the amount of spectral artifacts present. The restored panchromatic image created from integrating multispectral images is compared to a conventional panchromatic sparse-aperture image. Conclusionsare drawn through image quality analysis and the change in spectral artifacts

Spatial and temporal variability in the δ18Ow and salinity compositions of Gulf of Maine coastal surface waters

Hydrographic variability and dynamics in the Gulf of Maine are examined through the investigation of δ18Ow and salinity properties of coastal surface waters. Data from Gulf of Maine waters sampled over a decade, from 2003 to 2015, including a suite of samples that were collected monthly from April 2014 to March 2015, are presented. These water samples fall on a mixing line between Maine River Water (MRW) and Scotian Shelf Water (SSW). However, slope waters likely also contribute to these surface waters. The seasonal variability in water samples collected during 2014 and 2015 indicates the strong influence of river runoff on coastal Gulf of Maine surface water properties. The coastal surface Gulf of Maine mixing line presented in this paper is a needed baseline for reconstructing hydrographic variability in bicarbonates using oxygen isotopes

The Climate CoLab: Large scale model-based collaborative planning

The Climate CoLab is a system to help thousands of people around the world collectively develop plans for what humans should do about global climate change. This paper shows how the system combines three design elements (model-based planning, on-line debates, and electronic voting) in a synergistic way. The paper also reports early usage experience showing that: (a) the system is attracting a continuing stream of new and returning visitors from all over the world, and (b) the nascent community can use the platform to generate interesting and high quality plans to address climate change. These initial results indicate significant progress towards an important goal in developing a collective intelligence system - the formation of a large and diverse community collectively engaged in solving a single problem.Cisco Systems, Inc.Argosy FoundationMIT Energy InitiativeMIT Sloan Sustainability Initiativ