Unsupervised Named-Entity Recognition: Generating Gazetteers and Resolving Ambiguity

In this paper, we propose a named-entity recognition (NER) system that addresses two major limitations frequently discussed in the field. First, the system requires no human intervention such as manually labeling training data or creating gazetteers. Second, the system can handle more than the three classical named-entity types (person, location, and organization). We describe the system’s architecture and compare its performance with a supervised system. We experimentally evaluate the system on a standard corpus, with the three classical named-entity types, and also on a new corpus, with a new named-entity type (car brands)

Differential Imaging with a Multicolor Detector Assembly: A New ExoPlanet Finder Concept

Simultaneous spectral differential imaging is a high contrast technique by which subtraction of simultaneous images reduces noise from atmospheric speckles and optical aberrations. Small non-common wave front errors between channels can seriously degrade its performance. We present a new concept, a multicolor detector assembly (MCDA), which can eliminate this problem. The device consists of an infrared detector and a microlens array onto the flat side of which a checkerboard pattern of narrow-band micro-filters is deposited, each micro-filter coinciding with a microlens. Practical considerations for successful implementation of the technique are mentioned. Numerical simulations predict a noise attenuation of 10^-3 at 0.5" for a 10^5 seconds integration on a mH=5 star of Strehl ratio 0.9 taken with an 8-m telescope. This reaches a contrast of 10^-7 at an angular distance of 0.5" from the center of the star image.Comment: 13 pages, 5 figures, accepted APJ

Angular Differential Imaging: a Powerful High-Contrast Imaging Technique

Angular differential imaging is a high-contrast imaging technique that reduces quasi-static speckle noise and facilitates the detection of nearby companions. A sequence of images is acquired with an altitude/azimuth telescope while the instrument field derotator is switched off. This keeps the instrument and telescope optics aligned and allows the field of view to rotate with respect to the instrument. For each image, a reference PSF is constructed from other appropriately-selected images of the same sequence and subtracted to remove quasi-static PSF structure. All residual images are then rotated to align the field and are combined. Observed performances are reported for Gemini North data. It is shown that quasi-static PSF noise can be reduced by a factor \~5 for each image subtraction. The combination of all residuals then provides an additional gain of the order of the square root of the total number of acquired images. A total speckle noise attenuation of 20-50 is obtained for one-hour long observing sequences compared to a single 30s exposure. A PSF noise attenuation of 100 was achieved for two-hour long sequences of images of Vega, reaching a 5-sigma contrast of 20 magnitudes for separations greater than 8". For a 30-minute long sequence, ADI achieves 30 times better signal-to-noise than a classical observation technique. The ADI technique can be used with currently available instruments to search for ~1MJup exoplanets with orbits of radii between 50 and 300 AU around nearby young stars. The possibility of combining the technique with other high-contrast imaging methods is briefly discussed.Comment: 27 pages, 7 figures, accepted for publication in Ap

Effects of Quasi-Static Aberrations in Faint Companion Searches

We present the first results obtained at CFHT with the TRIDENT infrared camera, dedicated to the detection of faint companions close to bright nearby stars. The camera's main feature is the acquisition of three simultaneous images in three wavelengths (simultaneous differential imaging) across the methane absorption bandhead at 1.6 micron, that enables a precise subtraction of the primary star PSF while keeping the companion signal. The main limitation is non-common path aberrations between the three optical paths that slightly decorrelate the PSFs. Two types of PSF calibrations are combined with the differential simultaneous imaging technique to further attenuate the PSF: reference star subtraction and instrument rotation to smooth aberrations. It is shown that a faint companion with a DeltaH of 10 magnitudes would be detected at 0.5 arcsec from the primary.Comment: 12 pages, 10 figures, to appear in Astronomy with High Contrast Imaging, EAS Publications Serie

Automatic Dream Sentiment Analysis

In this position paper, we propose a first step toward automatic analysis of sentiments in dreams. 100 dreams were sampled from a dream bank created for a normative study of dreams. Two human judges assigned a score to describe dream sentiments. We ran four baseline algorithms in an attempt to automate the rating of sentiments in dreams. Particularly, we compared the General Inquirer (GI) tool, the Linguistic Inquiry and Word Count (LIWC), a weighted version of the GI lexicon and of the HM lexicon and a standard bag-of-words. We show that machine learning allows automating the human judgment with accuracy superior to majority class choice

Deciphering the Dolomitization History of the Lower Member Winnipegosis Carbonates: Basin-Scale Gradients in Magnesium and Strontium Isotopes Identify the Deep Structural Center of the Williston Basin as a Source of Reactive Magnesium

Dolomitized carbonates in the Williston Basin are common below the Middle Devonian Prairie Evaporite Formation, highlighting the conceivable role of brine reflux as the source of magnesium (Mg) for dolomitization. However, strontium isotope ratios (87Sr/86Sr), and iron (Fe) and manganese (Mn) concentrations in a dolomite body directly below the evaporite (in the Lower Member Winnipegosis Formation near Saskatoon, SK) are inconsistent with its formation using seawater as the source of reactive Mg. It has been proposed instead that the dolomitizing fluids ascended from deep in the basin where sedimentary formation waters may develop very radiogenic 87Sr/86Sr ratios through water-rock interaction with Rb-bearing siliciclastic sediments and old crystalline rocks of the Precambrian basement (Fu et al., 2006). In this thesis, I expand the geographic range of the studied dolomite samples covering most of the northern half of the Williston Basin, and I employed novel stable Mg isotopes (26Mg) as a tracer of the dolomitizing fluids. The main finding is that the Lower Member Winnipegosis records a basin scale gradient in dolomite 26Mg values, with low values (~ –2.0‰) in the deep center of the basin in North Dakota, and higher values (~ –1.3‰) near the outcrop edge of the basin in Manitoba. The 26Mg and 87Sr/86Sr data, when plotted on a geographic map of the Williston Basin and contoured using Surfer® software, reveal a radial pattern of increasing 26Mg values and decreasing 87Sr/86Sr ratios. Using water-rock interaction modeling, I show that the gradients in 26Mg and 87Sr/86Sr formed when hot Mg-bearing and 87Sr-bearing fluids flowed upwards through the Winnipegosis from a source in the center of the basin. The gradient in 87Sr occurs from dilution of the higher 87Sr/86Sr ratio of the dolomitizing fluid by the release of seawater-derived Sr to pore fluids with a lower 87Sr/86Sr ratio along the flow path. The gradient in 26Mg reflects Mg isotope exchange between: (1) an early formed replacive proto-dolomite with a uniform 26Mg value (~ –1.55‰) reflecting its formation at ambient temperature in an open diagenetic system using seawater as a source of reactive Mg (26Mg 0.15‰), and (2) a hot (~90ºC) upwardly ascending Mg-bearing fluid with a lower 26Mg value (~ –0.80‰). The gradient arises from greater exchange occurring between proto-dolomite and fluid at higher cumulative water-rock ratios in the deep basin (closer to the source of reactive Mg) and less exchange occurring near the edges at lower cumulative water-rock ratios. The resulting ~1.0‰ gradient in dolomite 26Mg signifies cryptic mixing between primary and secondary dolomite formed at two different temperatures from Mg bearing fluids with different 26Mg values at two different stages in the basin history. The burial history of the basin is punctuated by heat flow anomalies, with fluid movement indicated by the resetting of thermal remnant magnetizations in dolomite and evaporite minerals within the basin. I speculate that ultramafic rocks supplied Mg to the bottom of the Williston Basin when they were hydrothermally altered or carbonated during an anomalous heat flow event that affected the Williston Basin in the Late Devonian/Early Carboniferous. Seismic pumping drove these fluids upwards through fracture networks in the crust, and eventually into the deep center of the Williston Basin along vertically-oriented down-to-the-basement faults, pressuring deep confined aquifers like the Winnipegosis that induced up dip migrations of fluid towards the edges of the basin. This study demonstrates that Mg isotopic mapping of large dolomite bodies is a useful tool for deciphering paleofluid-flow histories in sedimentary basins, which may help exploration geologists to find petroleum that may have migrated and become trapped along the same pathways, or Mississippi Valley Type ore deposits. Lastly, contouring mapping of Fe, Mn and 13C values in the Lower Member Winnipegosis dolomite shows that these are not tracers of dolomitizing fluid flow or signals of the dolomitization process in the studied dolomites. They see through the dolomitization and record information on carbonate depositional environments

Spectrally Similar Incommensurable 3-Manifolds

Reid has asked whether hyperbolic manifolds with the same geodesic length spectrum must be commensurable. Building toward a negative answer to this question, we construct examples of hyperbolic 3–manifolds that share an arbitrarily large portion of the length spectrum but are not commensurable. More precisely, for every n ≫ 0, we construct a pair of incommensurable hyperbolic 3–manifolds Nn and Nµn whose volume is approximately n and whose length spectra agree up to length n. Both Nn and Nµn are built by gluing two standard submanifolds along a complicated pseudo-Anosov map, ensuring that these manifolds have a very thick collar about an essential surface. The two gluing maps differ by a hyper-elliptic involution along this surface. Our proof also involves a new commensurability criterion based on pairs of pants