Exploratory topic modeling with distributional semantics

As we continue to collect and store textual data in a multitude of domains, we are regularly confronted with material whose largely unknown thematic structure we want to uncover. With unsupervised, exploratory analysis, no prior knowledge about the content is required and highly open-ended tasks can be supported. In the past few years, probabilistic topic modeling has emerged as a popular approach to this problem. Nevertheless, the representation of the latent topics as aggregations of semi-coherent terms limits their interpretability and level of detail. This paper presents an alternative approach to topic modeling that maps topics as a network for exploration, based on distributional semantics using learned word vectors. From the granular level of terms and their semantic similarity relations global topic structures emerge as clustered regions and gradients of concepts. Moreover, the paper discusses the visual interactive representation of the topic map, which plays an important role in supporting its exploration.Comment: Conference: The Fourteenth International Symposium on Intelligent Data Analysis (IDA 2015

Perch-type Characteristics of Overwintering Red-tailed Hawks (Buteo jamaicensis) and American Kestrels (Falco sparverius)

Red-tailed Hawks (Buteo jamaicensis) and American Kestrels (Falco sparverius) are primarily sitand-wait predators that rely on perches to forage most efficiently. Overwintering Red-tailed Hawks and American Kestrels use available perches (e.g., utility poles and wires, trees, fences, gates, etc.) to hunt for prey items in agricultural fields in northeast Arkansas. Observations were made from December 2011-March 2012 and November 2012-March 2013 in three representative cover-types (short rice stubble, soybean stubble, and fallow areas including roadsides) to determine which perch-types were used by Red-tailed Hawks and American Kestrels. Utility pole crossbeams at an average height of 6.3 m were the main perchtypes used by Red-tailed Hawks, demonstrating the use of man-made structures’. These perches were generally in or near fallow areas or short rice stubble fields. Conversely, American Kestrels usually perched on wires at an average height of 4.9 m, over fallow roadsides’. Fallow areas had high prey density and vegetation cover. Niche separation via differential use of perches may be one factor that allows these raptors to avoid inter-specific competition

DNA transport by a micromachined Brownian ratchet device

We have micromachined a silicon-chip device that transports DNA with a Brownian ratchet that rectifies the Brownian motion of microscopic particles. Transport properties for a DNA 50mer agree with theoretical predictions, and the DNA diffusion constant agrees with previous experiments. This type of micromachine could provide a generic pump or separation component for DNA or other charged species as part of a microscale lab-on-a-chip. A device with reduced feature size could produce a size-based separation of DNA molecules, with applications including the detection of single nucleotide polymorphisms.Comment: Latex: 8 pages, 4 figure

High-density Mapping Guided Pulmonary Vein Isolation for Treatment of Atrial Fibrillation-Two-year clinical outcome of a single center experience

Pulmonary vein isolation (PVI) as interventional treatment for atrial fibrillation (AF) aims to eliminate arrhythmogenic triggers from the PVs. Improved signal detection facilitating a more robust electrical isolation might be associated with a better outcome. This retrospective cohort study compared PVI procedures using a novel high-density mapping system (HDM) with improved signal detection vs. age-and sex-matched PVIs using a conventional 3D mapping system (COM). Endpoints comprised freedom from AF and procedural parameters. In total, 108 patients (mean age 63.9 +/- 11.2 years, 56.5% male, 50.9% paroxysmal AF) were included (n = 54 patients/group). Our analysis revealed that HDM was not superior regarding freedom from AF (mean follow-up of 494.7 +/- 26.2 days), with one- and two-year AF recurrence rates of 38.9%/46.5% (HDM) and 38.9%/42.2% (COM), respectively. HDM was associated with reduction in fluoroscopy times (18.8 +/- 10.6 vs. 29.8 +/- 13.4 min;p < 0.01) and total radiation dose (866.0 +/- 1003.3 vs. 1731.2 +/- 1978.4 cGy;p < 0.01) compared to the COM group. HDM was equivalent but not superior to COM with respect to clinical outcome after PVI and resulted in reduced fluoroscopy time and radiation exposure. These results suggest that HDM-guided PVI is effective and safe for AF ablation. Potential benefits in comparison to conventional mapping systems, e.g. arrhythmia recurrence rates, have to be addressed in randomized trials

More salt, please:global patterns, responses, and impacts of foliar sodium in grasslands

Sodium is unique among abundant elemental nutrients, because most plant species do not require it for growth or development, whereas animals physiologically require sodium. Foliar sodium influences consumption rates by animals and can structure herbivores across landscapes. We quantified foliar sodium in 201 locally abundant, herbaceous species representing 32 families and, at 26 sites on four continents, experimentally manipulated vertebrate herbivores and elemental nutrients to determine their effect on foliar sodium. Foliar sodium varied taxonomically and geographically, spanning five orders of magnitude. Site‐level foliar sodium increased most strongly with site aridity and soil sodium; nutrient addition weakened the relationship between aridity and mean foliar sodium. Within sites, high sodium plants declined in abundance with fertilisation, whereas low sodium plants increased. Herbivory provided an explanation: herbivores selectively reduced high nutrient, high sodium plants. Thus, interactions among climate, nutrients and the resulting nutritional value for herbivores determine foliar sodium biogeography in herbaceous‐dominated systems