Online Forum Thread Retrieval using Pseudo Cluster Selection and Voting Techniques

Online forums facilitate knowledge seeking and sharing on the Web. However, the shared knowledge is not fully utilized due to information overload. Thread retrieval is one method to overcome information overload. In this paper, we propose a model that combines two existing approaches: the Pseudo Cluster Selection and the Voting Techniques. In both, a retrieval system first scores a list of messages and then ranks threads by aggregating their scored messages. They differ on what and how to aggregate. The pseudo cluster selection focuses on input, while voting techniques focus on the aggregation method. Our combined models focus on the input and the aggregation methods. The result shows that some combined models are statistically superior to baseline methods.Comment: The original publication is available at http://www.springerlink.com/. arXiv admin note: substantial text overlap with arXiv:1212.533

Cosmic distance-duality as probe of exotic physics and acceleration

In cosmology, distances based on standard candles (e.g. supernovae) and standard rulers (e.g. baryon oscillations) agree as long as three conditions are met: (1) photon number is conserved, (2) gravity is described by a metric theory with (3) photons travelling on unique null geodesics. This is the content of distance-duality (the reciprocity relation) which can be violated by exotic physics. Here we analyse the implications of the latest cosmological data sets for distance-duality. While broadly in agreement and confirming acceleration we find a 2-sigma violation caused by excess brightening of SN-Ia at z > 0.5, perhaps due to lensing magnification bias. This brightening has been interpreted as evidence for a late-time transition in the dark energy but because it is not seen in the d_A data we argue against such an interpretation. Our results do, however, rule out significant SN-Ia evolution and extinction: the "replenishing" grey-dust model with no cosmic acceleration is excluded at more than 4-sigma despite this being the best-fit to SN-Ia data alone, thereby illustrating the power of distance-duality even with current data sets.Comment: 6 pages, 4 colour figures. Version accepted as a Rapid Communication in PR

Strong Gravitational Lensing and Dark Energy Complementarity

In the search for the nature of dark energy most cosmological probes measure simple functions of the expansion rate. While powerful, these all involve roughly the same dependence on the dark energy equation of state parameters, with anticorrelation between its present value w_0 and time variation w_a. Quantities that have instead positive correlation and so a sensitivity direction largely orthogonal to, e.g., distance probes offer the hope of achieving tight constraints through complementarity. Such quantities are found in strong gravitational lensing observations of image separations and time delays. While degeneracy between cosmological parameters prevents full complementarity, strong lensing measurements to 1% accuracy can improve equation of state characterization by 15-50%. Next generation surveys should provide data on roughly 10^5 lens systems, though systematic errors will remain challenging.Comment: 7 pages, 5 figure

Geographical origin of dabbling ducks wintering in Iberia: Sex differences and implications for pair formation

Los humedales ibéricos naturales y antropógenos del sur de Europa son bien conocidos por sustentar a un gran número de aves migratorias acuáticas del Palaearctico en cada invierno. Sin embargo, la información sobre el origen geográfico de los patos de humedal que pasan el invierno en estos espacios es escasa y se limita principalmente a datos de sonar. Aquí, hemos utilizado marcadores isotópicos para determinar el origen geográfico de machos y hembras de Pintails septentrional, Anas acuta y Anas crecca euroasiática en Extremadura, en el interior de la península Ibérica, sitio clave para invernar los patos de humedal. Además, hemos instalado seis etiquetas GPSGSM en Pintails septentrional para complementar los datos derivados del análisis de isótopos estables. La mayoría (> 70%) de los Pintails septentrional, dentro del primer año calendario, fueron asignados a regiones situadas por encima de los 55° N, volando 2600-5600 km desde sus regiones de procedencia a Extremadura. Los valores promedio de δ2Hf variaron significativamente entre macho y hembra de Pintails septentrional, sugiriendo que los sexos tienen diferentes orígenes geográficos. Los datos de los adultos etiquetados Pintails septentrional apoyan los datos isotópicos, un macho volando más de 5000 km de la costa de la mar Pechora (Rusia). La mayoría (> 70%) de los Teal euroasiáticos, dentro del primer año calendario, fueron asignados a la región situada entre 48° y 60° N y viajaron 1500-4500 km para llegar en Extremadura. Los machos y hembras de Cerceta euroasiáticos mostraron diferencias marginales en valores promedio de δ2Hf. En patos de humedal migratorios, el emparejamiento se produce normalmente en las zonas de invernada, y los patos en su primer invierno pueden reproducirse en la primavera siguiente. Para Pintails septentrional, la formación de parejas en Extremadura podría suceder entre individuos con diferentes orígenes geográficos, lo que podría contribuir a la variabilidad genética de su descendencia.Natural and anthropogenic Iberian wetlands in southern Europe are well known for supporting large numbers of migratory Palaearctic waterbirds each winter. However, information on the geographical origin of dabbling ducks overwintering in these wetlands is scarce and mostly limited to data from ringing recoveries. Here, we used intrinsic isotopic markers to determine the geographical origin of male and female Northern Pintails Anas acuta and Eurasian Teal Anas crecca in Extremadura, inland Iberia, a key site for overwintering dabbling ducks. Additionally, we fitted six Northern Pintails with GPSGSM tags to complement the data derived from stable isotope analysis. Most (> 70%) first calendar-year Northern Pintails were assigned to regions above 55°N, flying 2600–5600 km from their main natal regions to Extremadura. Mean values of δ2Hf varied significantly between male and female Northern Pintails, suggesting that the sexes had different geographical origins. Data from tagged adult Northern Pintails supported the isotopic data, one male flying more than 5000 km to the coast of the Pechora Sea (Russia). Most (> 70%) first calendar-year Eurasian Teal were assigned to the region between 48° and 60°N, travelling 1500–4500 km to arrive in Extremadura. Male and female Eurasian Teal showed marginal differences in mean values of δ2Hf. In migratory dabbling ducks, pairing typically occurs on the wintering grounds, and ducks in their first winter can breed the following spring. For Northern Pintails, pair formation in Extremadura could occur between individuals with different geographical origins, which could contribute to the genetic variability of their offspring.Trabajo patrocinado por: Junta de Extremadura. Proyecto PRI 09C128 Gobierno de Extremadura y Fondos FEDER. Ayuda GR10174 Confederación Hidrográfica del Guadiana (Ministerio de Medio Ambiente). Ayuda financierapeerReviewe

Making things happen : a model of proactive motivation

Being proactive is about making things happen, anticipating and preventing problems, and seizing opportunities. It involves self-initiated efforts to bring about change in the work environment and/or oneself to achieve a different future. The authors develop existing perspectives on this topic by identifying proactivity as a goal-driven process involving both the setting of a proactive goal (proactive goal generation) and striving to achieve that proactive goal (proactive goal striving). The authors identify a range of proactive goals that individuals can pursue in organizations. These vary on two dimensions: the future they aim to bring about (achieving a better personal fit within one’s work environment, improving the organization’s internal functioning, or enhancing the organization’s strategic fit with its environment) and whether the self or situation is being changed. The authors then identify “can do,” “reason to,” and “energized to” motivational states that prompt proactive goal generation and sustain goal striving. Can do motivation arises from perceptions of self-efficacy, control, and (low) cost. Reason to motivation relates to why someone is proactive, including reasons flowing from intrinsic, integrated, and identified motivation. Energized to motivation refers to activated positive affective states that prompt proactive goal processes. The authors suggest more distal antecedents, including individual differences (e.g., personality, values, knowledge and ability) as well as contextual variations in leadership, work design, and interpersonal climate, that influence the proactive motivational states and thereby boost or inhibit proactive goal processes. Finally, the authors summarize priorities for future researc

Metal-insulator transition and charge ordering in the extended Hubbard model at one-quarter filling

We study with exact diagonalization the zero temperature properties of the quarter-filled extended Hubbard model on a square lattice. We find that increasing the ratio of the intersite Coulomb repulsion, $V$, to the band width drives the system from a metal to a charge ordered insulator. The evolution of the optical conductivity spectrum with increasing $V$ is compared to the observed optical conductivity of several layered molecular crystals with the theta and beta'' crystal structures.Comment: 5 pages, 3 figure

Constraining the expansion rate of the Universe using low-redshift ellipticals as cosmic chronometers

We present a new methodology to determine the expansion history of the Universe analyzing the spectral properties of early type galaxies (ETG). We found that for these galaxies the 4000\AA break is a spectral feature that correlates with the relative ages of ETGs. In this paper we describe the method, explore its robustness using theoretical synthetic stellar population models, and apply it using a SDSS sample of $\sim$14 000 ETGs. Our motivation to look for a new technique has been to minimise the dependence of the cosmic chronometer method on systematic errors. In particular, as a test of our method, we derive the value of the Hubble constant $H_0 = 72.6 \pm 2.8$ (stat) $\pm2.3$ (syst) (68% confidence), which is not only fully compatible with the value derived from the Hubble key project, but also with a comparable error budget. Using the SDSS, we also derive, assuming w=constant, a value for the dark energy equation of state parameter $w = -1 \pm 0.2$ (stat) $\pm0.3$ (syst). Given the fact that the SDSS ETG sample only reaches $z \sim 0.3$, this result shows the potential of the method. In future papers we will present results using the high-redshift universe, to yield a determination of H(z) up to $z \sim 1$.Comment: 25 pages, 17 figures, JCAP accepte

Charge kinks as Raman scatterers in quarter-filled ladders

Charge kinks are considered as fundamental excitations in quarter-filled charge-ordered ladders. The strength of the coupling of the kinks to the three-dimensional lattice depends on their energy. The integrated intensity of Raman scattering by kink-antikink pairs is proportional to $\phi ^{5}$ or $\phi ^{4},$ where $\phi$ is the order parameter. The exponent is determined by the system parameters and by the strength of the electron-phonon coupling.Comment: To be published in Phys. Rev.B (june 2001

Cosmic Chronometers: Constraining the Equation of State of Dark Energy. I: H(z) Measurements

We present new determinations of the cosmic expansion history from red-envelope galaxies. We have obtained for this purpose high-quality spectra with the Keck-LRIS spectrograph of red-envelope galaxies in 24 galaxy clusters in the redshift range 0.2 < z < 1.0. We complement these Keck spectra with high-quality, publicly available archival spectra from the SPICES and VVDS surveys. We improve over our previous expansion history measurements in Simon et al. (2005) by providing two new determinations of the expansion history: H(z) = 97 +- 62 km/sec/Mpc at z = 0.5 and H(z) = 90 +- 40 km/sec/Mpc at z = 0.8. We discuss the uncertainty in the expansion history determination that arises from uncertainties in the synthetic stellar-population models. We then use these new measurements in concert with cosmic-microwave-background (CMB) measurements to constrain cosmological parameters, with a special emphasis on dark-energy parameters and constraints to the curvature. In particular, we demonstrate the usefulness of direct H(z) measurements by constraining the dark- energy equation of state parameterized by w0 and wa and allowing for arbitrary curvature. Further, we also constrain, using only CMB and H(z) data, the number of relativistic degrees of freedom to be 4 +- 0.5 and their total mass to be < 0.2 eV, both at 1-sigma.Comment: Submitted to JCA

Stripes and holes in a two-dimensional model of spinless fermions and hardcore bosons

We consider a Hubbard-like model of strongly-interacting spinless fermions and hardcore bosons on a square lattice, such that nearest neighbor occupation is forbidden. Stripes (lines of holes across the lattice forming antiphase walls between ordered domains) are a favorable way to dope this system below half-filling. The problem of a single stripe can be mapped to a spin-1/2 chain, which allows understanding of its elementary excitations and calculation of the stripe's effective mass for transverse vibrations. Using Lanczos exact diagonalization, we investigate the excitation gap and dispersion of a hole on a stripe, and the interaction of two holes. We also study the interaction of two, three, and four stripes, finding that they repel, and the interaction energy decays with stripe separation as if they are hardcore particles moving in one (transverse) direction. To determine the stability of an array of stripes against phase separation into particle-rich phase and hole-rich liquid, we evaluate the liquid's equation of state, finding the stripe-array is not stable for bosons but is possibly stable for fermions.Comment: 24 pages, 18 figure