Geotagging One Hundred Million Twitter Accounts with Total Variation Minimization

Geographically annotated social media is extremely valuable for modern information retrieval. However, when researchers can only access publicly-visible data, one quickly finds that social media users rarely publish location information. In this work, we provide a method which can geolocate the overwhelming majority of active Twitter users, independent of their location sharing preferences, using only publicly-visible Twitter data. Our method infers an unknown user's location by examining their friend's locations. We frame the geotagging problem as an optimization over a social network with a total variation-based objective and provide a scalable and distributed algorithm for its solution. Furthermore, we show how a robust estimate of the geographic dispersion of each user's ego network can be used as a per-user accuracy measure which is effective at removing outlying errors. Leave-many-out evaluation shows that our method is able to infer location for 101,846,236 Twitter users at a median error of 6.38 km, allowing us to geotag over 80\% of public tweets.Comment: 9 pages, 8 figures, accepted to IEEE BigData 2014, Compton, Ryan, David Jurgens, and David Allen. "Geotagging one hundred million twitter accounts with total variation minimization." Big Data (Big Data), 2014 IEEE International Conference on. IEEE, 201

A Comparison of Sensitivity Metrics for Two-Stage Ignition Behavior in Rapid Compression Machines

A rapid compression machine (RCM) multi-zone model is used to simulate the ignition of primary reference fuel (PRF) mixtures that exhibit two-stage ignition behavior. Sensitivity coefficients for each reaction in the PRF mechanism are calculated from four different metrics: (1) first-stage energy release, (2) first-stage pressure rise, (3) first-stage ignition delay time, and (4) total ignition delay time. The sensitivity coefficients are used to provide four unique rankings, and the rankings are compared using Spearman’s rank correlation coefficient. Special emphasis is given to comparing the rankings based on first-stage energy release and total ignition delay time. The level of agreement between these two rankings is shown to depend on the reaction conditions. Simulation cases with high peak heat release rates during the first stage of ignition tend to exhibit disagreement in the rankings, indicating that new kinetic information can be obtained by studying first stage energy release in addition to total ignition delay time. Simulations show that the high peak heat release rates are associated with energy release across a broad range of temperatures (range can be in excess of 100 K even for lean conditions). This distribution leads to a discrepancy between sensitivity coefficients calculated for the total ignition delay time and the first-stage energy release. Sensitivity coefficients for the total ignition delay time are characterized by reactivity at the highest temperatures in the RCM, while sensitivity coefficients for the first-stage energy release are characterized by reactivity across the full range of temperatures in the RCM

Demonstration test catchments : the role of hydrogeological conceptual modelling

Agricultural diffuse pollution, particularly from nitrate and phosphate, is a significant problem in the UK and is the focus of the national Demonstration Test Catchments (DTC) study — a UK Government initiative. The DTC programme is providing evidence for investigating how on-farm mitigation measures can reduce the impact of agricultural diffuse water pollution on ecological function. This will involve studying how such measures affect pollutant concentrations in so-called receptors, such as the streams which drain the catchments. It is therefore important to investigate how water moves from the land surface to the receptors and in particular to quantify the amounts and timescales involved in the different water flow routes. The DTC catchments are the Eden, the Avon and the Wensum and groundwater flow is a significant component of main river flow in all of the catchments, ranging in overall terms from around 50% of river flow in the Eden to 90% in the Avon. It is therefore important that robust conceptual models of the groundwater flow systems of the catchments — and in particular of the monitored sub-catchments — are developed. BGS is contributing to the creation of DTC groundwater conceptual models in all three study catchments. The BGS work is funded principally by NERC and by DEFRA

Some comments on Monte Carlo and molecular dynamics methods

We highlight some links between molecular dynamics and Monte Carlo algorithms used to simulate condensed matter systems. Special attention is paid to the question of sampling the desired statistical ensemble

Stress-strain characteristics of rubber-like materials: Experiment and analysis

The objectives are: (1) to demonstrate tensile testing of materials and the application of the concepts of stress and strain; and (2) to yield a mathematical relationship between stress and strain for many artificial rubbers and plastics. The experiment, supplies, and procedure are presented

Preliminary empirical evidence regarding the pricing of estimation risk / 1171

Includes bibliographical references

Project Report No. 46, Loblolly Pine Plantations in East Texas Two Harvest Schedules No Thinning & Final Harvest at 25 Years Thin at 10 Years & Final Harvest at 25 Years Sawlog/Veneer Wood Flow Comparison, A Simulation

DOES A THINNING AT 10 YEARS WITH FINAL HARVEST AT 25 YEARS INCREASE SAWLOG/VENEER 1000 FLOW? DOES A THINNING AT 10 YEARS WITH FINAL HARVEST AT 25 YEARS INCREASE NET PRESENT VALUE

Project Report No. 46, Loblolly Pine Plantations in East Texas Two Harvest Schedules No Thinning & Final Harvest at 25 Years Thin at 10 Years & Final Harvest at 25 Years Sawlog/Veneer Wood Flow Comparison, A Simulation

DOES A THINNING AT 10 YEARS WITH FINAL HARVEST AT 25 YEARS INCREASE SAWLOG/VENEER 1000 FLOW? DOES A THINNING AT 10 YEARS WITH FINAL HARVEST AT 25 YEARS INCREASE NET PRESENT VALUE

Long Duration Space Materials Exposure (LDSE)

The Center on Materials for Space Structures (CMSS) at Case Western Reserve University is one of seventeen Commercial Centers for the Development of Space. It was founded to: (1) produce and evaluate materials for space structures; (2) develop passive and active facilities for materials exposure and analysis in space; and (3) develop improved material systems for space structures. A major active facility for materials exposure is proposed to be mounted on the exterior truss of the Space Station Freedom (SSF). This Long Duration Space Materials Exposure (LDSE) experiment will be an approximately 6 1/2 ft. x 4 ft. panel facing into the velocity vector (RAM) to provide long term exposure (up to 30 years) to atomic oxygen, UV, micro meteorites, and other low earth orbit effects. It can expose large or small active (instrumented) or passive samples. These samples may be mounted in a removable Materials Flight Experiment (MFLEX) carrier which may be periodically brought into the SSF for examination by CMSS's other SSF facility, the Space Materials Evaluation Facility (SMEF), which will contain a Scanning Electron Microscope, a Variable Angle & Scanning Ellipsometer, a Fourier Transform Infrared Spectrometer, and other analysis equipment. These facilities will allow commercial firms to test their materials in space and promptly obtain information on their materials survivability in the LEO environment

A dual graph construction for higher-rank graphs, and KK-theory for finite 2-graphs

Given a $k$-graph $\Lambda$ and an element $p$ of \NN^k, we define the dual $k$-graph, $p\Lambda$. We show that when $\Lambda$ is row-finite and has no sources, the $C^*$-algebras $C^*(\Lambda)$ and $C^*(p\Lambda)$ coincide. We use this isomorphism to apply Robertson and Steger's results to calculate the $K$-theory of $C^*(\Lambda)$ when $\Lambda$ is finite and strongly connected and satisfies the aperiodicity condition.Comment: 9 page