Walking across Wikipedia: a scale-free network model of semantic memory retrieval.

Semantic knowledge has been investigated using both online and offline methods. One common online method is category recall, in which members of a semantic category like "animals" are retrieved in a given period of time. The order, timing, and number of retrievals are used as assays of semantic memory processes. One common offline method is corpus analysis, in which the structure of semantic knowledge is extracted from texts using co-occurrence or encyclopedic methods. Online measures of semantic processing, as well as offline measures of semantic structure, have yielded data resembling inverse power law distributions. The aim of the present study is to investigate whether these patterns in data might be related. A semantic network model of animal knowledge is formulated on the basis of Wikipedia pages and their overlap in word probability distributions. The network is scale-free, in that node degree is related to node frequency as an inverse power law. A random walk over this network is shown to simulate a number of results from a category recall experiment, including power law-like distributions of inter-response intervals. Results are discussed in terms of theories of semantic structure and processing

Hard Burst Emission from the Soft Gamma Repeater SGR 1900+14

We present evidence for burst emission from SGR 1900+14 with a power-law high energy spectrum extending beyond 500 keV. Unlike previous detections of high energy photons during bursts from SGRs, these emissions are not associated with high-luminosity burst intervals. Not only is the emission hard, but the spectra are better fit by Band's GRB function rather than by the traditional optically-thin thermal bremsstrahlung model. We find that the spectral evolution within these hard events obeys a hardness/intensity anti-correlation. Temporally, these events are distinct from typical SGR burst emissions in that they are longer (~ 1 s) and have relatively smooth profiles. Despite a difference in peak luminosity of > 1E+11 between these bursts from SGR 1900+14 and cosmological GRBs, there are striking temporal and spectral similarities between the two kinds of bursts, aside from spectral evolution. We outline an interpretation of these events in the context of the magnetar model.Comment: 11 pages (text and figures), submitted to ApJ Letters, corrected erroneous hardness ratio

A Search for Stars of Very Low Metal Abundance. VI. Detailed Abundances of 313 Metal-Poor Stars

We present radial velocities, equivalent widths, model atmosphere parameters, and abundances or upper limits for 53 species of 48 elements derived from high resolution optical spectroscopy of 313 metal-poor stars. A majority of these stars were selected from the metal-poor candidates of the HK Survey of Beers, Preston, and Shectman. We derive detailed abundances for 61% of these stars for the first time. Spectra were obtained during a 10-year observing campaign using the Magellan Inamori Kyocera Echelle spectrograph on the Magellan Telescopes at Las Campanas Observatory, the Robert G. Tull Coude Spectrograph on the Harlan J. Smith Telescope at McDonald Observatory, and the High Resolution Spectrograph on the Hobby-Eberly Telescope at McDonald Observatory. We perform a standard LTE abundance analysis using MARCS model atmospheres, and we apply line-by-line statistical corrections to minimize systematic abundance differences arising when different sets of lines are available for analysis. We identify several abundance correlations with effective temperature. A comparison with previous abundance analyses reveals significant differences in stellar parameters, which we investigate in detail. Our metallicities are, on average, lower by approx. 0.25 dex for red giants and approx. 0.04 dex for subgiants. Our sample contains 19 stars with [Fe/H] < -3.5, 84 stars with [Fe/H] < -3.0, and 210 stars with [Fe/H] < -2.5. Detailed abundances are presented here or elsewhere for 91% of the 209 stars with [Fe/H] < -2.5 as estimated from medium resolution spectroscopy by Beers, Preston, and Shectman. We will discuss the interpretation of these abundances in subsequent papers.Comment: Accepted for publication in the Astronomical Journal. 60 pages, 59 figures, 18 tables. Machine-readable versions of the long tables can be found in the ancillary data file

A Cytochrome-b Perspective on Passerina Bunting Relationships

We sequenced the complete mitochondrial cytochrome-b gene (1,143 nucleotides) for representatives of each species in the cardinalid genera Passerina (6 species), Guiraca (1 species), and Cyanocompsa (3 species), and used a variety of phylogenetic methods to address relationships within and among genera. We determined that Passerina, as presently recognized, is paraphyletic. Lazuli Bunting (P. amoena) is sister to the much larger Blue Grosbeak (Guiraca caerulea). Indigo Bunting (P. cyanea) and Lazuli Bunting are not sister taxa as generally thought. In all weighted parsimony trees and for the gamma-corrected HKY tree, Indigo Bunting is the sister of two sister groups, a “blue” (Lazuli Bunting and Blue Grosbeak) and a “painted” (Rosita\u27s Bunting [P. rositae], Orange-breasted Bunting [P. leclancherii], Varied Bunting [P. versicolor], and Painted Bunting [P. ciris]) clade. The latter two species form a highly supported sister pair of relatively more recent origin. Uncorrected (p) distances for ingroup (Passerina and Guiraca) taxa range from 3.0% (P. versicolor–P. ciris) to 7.6% (P. cyanea–P. leclancherii) and average 6.5% overall. Assuming a molecular clock, a bunting “radiation” between 4.1 and 7.3 Mya yielded four lineages. This timing is consistent with fossil evidence and coincides with a late-Miocene cooling during which a variety of western grassland habitats evolved. A reduction in size at that time may have allowed buntings to exploit that new food resource (grass seeds). We speculate that the Blue Grosbeak subsequently gained large size and widespread distribution as a result of ecological character displacement

The Abundances Of Neutron-Capture Species In The Very Metal-Poor Globular Cluster M15: A Uniform Analysis Of Red Giant Branch And Red Horizontal Branch Stars

The globular cluster M15 is unique in its display of star-to-star variations in the neutron-capture elements. Comprehensive abundance surveys have been previously conducted for handfuls of M15 red giant branch (RGB) and red horizontal branch (RHB) stars. No attempt has been made to perform a single, self-consistent analysis of these stars, which exhibit a wide range in atmospheric parameters. In the current effort, a new comparative abundance derivation is presented for three RGB and six RHB members of the cluster. The analysis employs an updated version of the line transfer code MOOG, which now appropriately treats coherent, isotropic scattering. The apparent discrepancy in the previously reported values for the metallicity of M15 RGB and RHB stars is addressed and a resolute disparity of Delta(RHB-RGB) approximate to 0.1 dex in the iron abundance was found. The anti-correlative behavior of the light neutron-capture elements (Sr, Y, Zr) is clearly demonstrated with both Ba and Eu, standard markers of the s- and r-process, respectively. No conclusive detection of Pb was made in the RGB targets. Consequently for the M15 cluster, this suggests that the main component of the s-process has made a negligible contribution to those elements normally dominated by this process in solar system material. Additionally for the M15 sample, a large Eu abundance spread is confirmed, which is comparable to that of the halo field at the same metallicity. These abundance results are considered in the discussion of the chemical inhomogeneity and nucleosynthetic history of M15.National Science Foundation AST 07-07447, AST 09-08978Astronom

Everolimus Exposure as a Predictor of Toxicity in Renal Cell Cancer Patients in the Adjuvant Setting: Results of a Pharmacokinetic Analysis for SWOG S0931 (EVEREST), a Phase III Study (NCT01120249).

BackgroundS0931 is assessing recurrence-free survival in renal cell carcinoma (RCC) patients randomized to receive everolimus (EVE) versus placebo for one year following nephrectomy. Due to a higher than expected dropout rate, we assessed EVE trough levels in the adjuvant setting to evaluate the relationship between EVE exposure and probability of toxicity.MethodsPatients received 10 mg daily EVE for nine 6-week cycles. Pre-dose whole blood samples were collected pre-cycle 2 and pre-cycle 3 and analyzed for EVE. Patients with pre-cycle 2 and/or pre-cycle 3 EVE results were used in the analysis. Patients were segregated into quartiles (Q) based on EVE levels and logistic regression was used to model the most common adverse event outcomes using EVE trough as a predictor. Hazard and odds ratios were adjusted for age, BMI and performance status.ResultsA total of 467 patients were included in this analysis. Quartiles normalized to an EVE dose of 10 mg/day were &lt; 9.0, 9.0-12.9, 12.9-22.8, and &gt; 22.8 ng/mL, respectively. EVE trough levels increased with increasing age (p &lt; 0.001). Furthermore, EVE trough levels were higher in men than women (19.4 versus 15.4 ng/mL, p = 0.01). Risk of grade 2 + triglycerides was increased in Q2 and Q3 vs Q1 (OR = 2.08; p = 0.02 and OR = 2.63; p = 0.002). Risk of grade 2 + rash was increased in Q2 and Q4 vs Q1 (OR = 2.99; p = 0.01 and OR = 2.90; p = 0.02). There was also an increased risk of any grade 3 + tox in Q2 vs Q1 (OR = 1.71; p = 0.05).ConclusionsWe identified significant gender and age-related differences in EVE trough levels in patients receiving adjuvant treatment for RCC. Furthermore, our analysis identified significant associations between EVE exposure and probability of toxicity

Statistical properties of SGR 1900+14 bursts

We study the statistics of soft gamma repeater (SGR) bursts, using a data base of 187 events detected with BATSE and 837 events detected with RXTE PCA, all from SGR 1900+14 during its 1998-1999 active phase. We find that the fluence or energy distribution of bursts is consistent with a power law of index 1.66, over 4 orders of magnitude. This scale-free distribution resembles the Gutenberg-Richter Law for earthquakes, and gives evidence for self-organized criticality in SGRs. The distribution of time intervals between successive bursts from SGR 1900+14 is consistent with a log-normal distribution. There is no correlation between burst intensity and the waiting times till the next burst, but there is some evidence for a correlation between burst intensity and the time elapsed since the previous burst. We also find a correlation between the duration and the energy of the bursts, but with significant scatter. In all these statistical properties, SGR bursts resemble earthquakes and solar flares more closely than they resemble any known accretion-powered or nuclear-powered phenomena. Thus our analysis lends support to the hypothesis that the energy source for SGR bursts is internal to the neutron star, and plausibly magnetic.Comment: 11 pages, 4 figures, accepted for publication in ApJ