Inferring Population Preferences via Mixtures of Spatial Voting Models

Understanding political phenomena requires measuring the political preferences of society. We introduce a model based on mixtures of spatial voting models that infers the underlying distribution of political preferences of voters with only voting records of the population and political positions of candidates in an election. Beyond offering a cost-effective alternative to surveys, this method projects the political preferences of voters and candidates into a shared latent preference space. This projection allows us to directly compare the preferences of the two groups, which is desirable for political science but difficult with traditional survey methods. After validating the aggregated-level inferences of this model against results of related work and on simple prediction tasks, we apply the model to better understand the phenomenon of political polarization in the Texas, New York, and Ohio electorates. Taken at face value, inferences drawn from our model indicate that the electorates in these states may be less bimodal than the distribution of candidates, but that the electorates are comparatively more extreme in their variance. We conclude with a discussion of limitations of our method and potential future directions for research.Comment: To be published in the 8th International Conference on Social Informatics (SocInfo) 201

On the need for multi-dimensional models for the safety analysis of (fast-spectrum) Molten Salt Reactors

This paper aims at characterizing the impact of adopting numerical models with different dimensionalities on the predicted behavior of fast-spectrum Molten Salt Reactors (MSRs). The study encompasses 1-D, 2-D, and 3-D representations of thermal-hydraulics and precursor transport/diffusion, along with spatial and point kinetics models for neutronics. We evaluate the accuracy of each model based on steady-state results and on the reactor response to 2 different transient initiators. The findings emphasize the significance of utilizing a 3-D representation with accurate thermal-hydraulics modeling, and with either spatial kinetics or carefully calibrated point kinetics incorporating a spatial description of precursors transport. 2-D and 1-D models can reproduce main trends and remain valuable tools for e.g. reactor design, control-oriented studies or uncertainty quantification. However, proper calibration of these models is needed and the user should be aware that alterations in flow patterns could jeopardize model calibration and hide first-order local effects

How Polarized Have We Become? A Multimodal Classification of Trump Followers and Clinton Followers

Polarization in American politics has been extensively documented and analyzed for decades, and the phenomenon became all the more apparent during the 2016 presidential election, where Trump and Clinton depicted two radically different pictures of America. Inspired by this gaping polarization and the extensive utilization of Twitter during the 2016 presidential campaign, in this paper we take the first step in measuring polarization in social media and we attempt to predict individuals' Twitter following behavior through analyzing ones' everyday tweets, profile images and posted pictures. As such, we treat polarization as a classification problem and study to what extent Trump followers and Clinton followers on Twitter can be distinguished, which in turn serves as a metric of polarization in general. We apply LSTM to processing tweet features and we extract visual features using the VGG neural network. Integrating these two sets of features boosts the overall performance. We are able to achieve an accuracy of 69%, suggesting that the high degree of polarization recorded in the literature has started to manifest itself in social media as well.Comment: 16 pages, SocInfo 2017, 9th International Conference on Social Informatic

The effectiveness of full actinide recycle as a nuclear waste management strategy when implemented over a limited timeframe - Part I: Uranium fuel cycle

Disposal of spent nuclear fuel is a major political and public-perception problem for nuclear energy. From a radiological standpoint, the long-lived component of spent nuclear fuel primarily consists of transuranic (TRU) isotopes. Full recycling of TRU isotopes can, in theory, lead to a reduction in repository radiotoxicity to reference levels corresponds to the radiotoxicity of the unburned natural U required to fuel a conventional LWR in as little as ∼500 years provided reprocessing and fuel fabrication losses are limited. This strategy forms part of many envisaged ‘sustainable’ nuclear fuel cycles. However, over a limited timeframe, the radiotoxicity of the ‘final’ core can dominate over reprocessing losses, leading to a much lower reduction in radiotoxicity compared to that achievable at equilibrium. The importance of low reprocessing losses and minor actinide (MA) recycling is also dependent on the timeframe during which actinides are recycled. In this paper, the fuel cycle code ORION is used to model the recycle of light water reactor (LWR)-produced TRUs in LWRs and sodium-cooled fast reactors (SFRs) over 1–5 generations of reactors, which is sufficient to infer general conclusions for higher numbers of generations. Here, a generation is defined as a fleet of reactors operating for 60 years, before being retired and potentially replaced. Over up to ∼5 generations of full actinide recycle in SFR burners, the final core inventory tends to dominate over reprocessing losses, beyond which the radiotoxicity rapidly becomes sensitive to reprocessing losses. For a single generation of SFRs, there is little or no advantage to recycling MAs. However, for multiple generations, the reduction in repository radiotoxicity is severely limited without MA recycling, and repository radiotoxicity converges on equilibrium after around 3 generations of SFRs. With full actinide recycling, at least 6 generations of SFRs are required in a gradual phase-out of nuclear power to achieve transmutation performance approaching the theoretical equilibrium performance – which appears challenging from an economic and energy security standpoint. TRU recycle in pressurized water reactors (PWRs) with zero net actinide production provides similar performance to low-enriched-uranium (LEU)-fueled LWRs in equilibrium with a fleet of burner SFRs. However, it is not possible to reduce the TRU inventory over multiple generations of PWRs. TRU recycle in break-even SFRs is much less effective from a point of view of reducing spent nuclear fuel radiotoxicity.The first author would like to acknowledge the UK Engineering and Physical Sciences Research Council (EPSRC) and the Institution of Mechanical Engineers for providing funding towards this work.This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.pnucene.2015.07.02

The effectiveness of full actinide recycle as a nuclear waste management strategy when implemented over a limited timeframe - Part II: Thorium fuel cycle

Full recycling of transuranic (TRU) isotopes can in theory lead to a reduction in repository radiotoxicity to reference levels in as little as ∼500 years provided reprocessing and fuel fabrication losses are limited. However, over a limited timeframe, the radiotoxicity of the ‘final’ core can dominate over reprocessing losses, leading to a much lower reduction in radiotoxicity compared to that achievable at equilibrium. In Part I of this paper, TRU recycle over up to 5 generations of light water reactors (LWRs) or sodium-cooled fast reactors (SFRs) is considered for uranium (U) fuel cycles. With full actinide recycling, at least 6 generations of SFRs are required in a gradual phase-out of nuclear power to achieve transmutation performance approaching the theoretical equilibrium performance. U-fuelled SFRs operating a break-even fuel cycle are not particularly effective at reducing repository radiotoxicity as the final core load dominates over a very long timeframe. In this paper, the analysis is extended to the thorium (Th) fuel cycle. Closed Th-based fuel cycles are well known to have lower equilibrium radiotoxicity than U-based fuel cycles but the time taken to reach equilibrium is generally very long. Th burner fuel cycles with SFRs are found to result in very similar radiotoxicity to U burner fuel cycles with SFRs for one less generation of reactors, provided that protactinium (Pa) is recycled. Th-fuelled reduced-moderation boiling water reactors (RBWRs) are also considered, but for burner fuel cycles their performance is substantially worse, with the waste taking ∼3–5 times longer to decay to the reference level than for Th-fuelled SFRs with the same number of generations. Th break-even fuel cycles require ∼3 generations of operation before their waste radiotoxicity benefits result in decay to the reference level in ∼1000 years. While this is a very long timeframe, it is roughly half that required for waste from the Th or U burner fuel cycle to decay to the reference level, and less than a tenth that required for the U break-even fuel cycle. The improved performance over burner fuel cycles is due to a more substantial contribution of energy generated by 233U leading to lower radiotoxicity per unit energy generation. To some extent this an argument based on how the radiotoxicity is normalised: operating a break-even fuel cycle rather than phasing out nuclear power using a burner fuel cycle results in higher repository radiotoxicity in absolute terms. The advantage of Th break-even fuel cycles is also contingent on recycling Pa, and reprocessing losses are significant also for a small number of generations due to the need to effectively burn down the TRU. The integrated decay heat over the scenario timeframe is almost twice as high for a break-even Th fuel cycle than a break-even U fuel cycle when using SFRs, as a result of much higher 90Sr production, which subsequently decays into 90Y. The peak decay heat is comparable. As decay heat at vitrification and repository decay heat affect repository sizing, this may weaken the argument for the Th cycle.The first author would like to acknowledge the UK Engineering and Physical Sciences Research Council (EPSRC) and the Institution of Mechanical Engineers for providing funding towards this work.This is the final version of the article. It first appeared from Elsevier at http://dx.doi.org/10.1016/j.pnucene.2014.11.01

A term-by-term direct numerical simulation validation study of the multi-environment conditional probability-density-function model for turbulent reacting flows

The multi-environment conditional probability-density-function (MECPDF) approach for modeling extinction and re-ignition in turbulent nonpremixed reacting flows in analyzed. A unique derivation of the model is given, which makes use of numerical Gaussian quadrature in addition to physical assumptions. The new derivation offers insight into the physical meaning of model terms and offers a more rigorous method for model validation. The assumptions required to close the dissipation terms are validated term by term using data from direct numerical simulations of an inert and a reacting scalar in decaying isotropic turbulence. Results show convergence of the numerical quadrature with an increasing number of quadrature points. Also, good agreement is shown for the physical model assumptions required to close the mixed dissipation and the progress-variable dissipation terms. The MECPDF methods is also demonstrated to offer the flexibility to incorporate either micromixing or otherwise more sophisticated models for the mixing between regions of the flow that exhibit differing degrees of extinction

Downs, Stokes and the Dynamics of Electoral Choice

A six-wave 2005–09 national panel survey conducted in conjunction with the British Election Study provided data for an investigation of sources of stability and change in voters’ party preferences. The authors test competing spatial and valence theories of party choice and investigate the hypothesis that spatial calculations provide cues for making valence judgements. Analyses reveal that valence mechanisms – heuristics based on party leader images, party performance evaluations and mutable partisan attachments – outperform a spatial model in terms of strength of direct effects on party choice. However, spatial effects still have sizeable indirect effects on the vote via their influence on valence judgements. The results of exogeneity tests bolster claims about the flow of influence from spatial calculations to valence judgments to electoral choice.</jats:p

Channeler Ant Model: 3D segmentation of medical images through ant colonies

In this paper the Channeler Ant Model (CAM) and some results of its applications to the analysis of medical images are described. The CAM is an algorithm able to segment 3D structures with different shapes, intensity and background. It makes use of virtual ant colonies and exploits their natural capabilities to modify the environment and communicate with each other by pheromone deposition. Its performance has been validated with the segmentation of 3D artificial objects and it has been already used successfully in lung nodules detection on Computer Tomography images. This work tries to evaluate the CAM as a candidate to solve the quantitative segmentation problem in Magnetic Resonance brain images: to evaluate the percentage of white matter, gray matter and cerebrospinal fluid in each voxel

The mobilising effect of political choice

Political choice is central to citizens’ participation in elections. Nonetheless, little is known about the individual-level mechanisms that link political choice and turnout. It is argued in this article that turnout decisions are shaped not only by the differences between the parties (party polarisation), but also by the closeness of parties to citizens’ own ideological position (congruence), and that congruence matters more in polarised systems where more is at stake. Analysing cross-national survey data from 80 elections, it is found that both polarisation and congruence have a mobilising effect, but that polarisation moderates the effect of congruence on turnout. To further explore the causal effect of political choice, the arrival of a new radical right-wing party in Germany, the Alternative for Germany (AfD), is leveraged and the findings show that the presence of the AfD had a mobilising effect, especially for citizens with congruent views