Building Adaptive Basis Functions with a Continuous Self-Organizing Map

This paper introduces CSOM, a continuous version of the Self-Organizing Map (SOM). The CSOM network generates maps similar to those created with the original SOM algorithm but, due to the continuous nature of the mapping, CSOM outperforms the SOM on function approximation tasks. CSOM integrates self-organization and smooth prediction into a single process. This is a departure from previous work that required two training phases, one to self-organize a map using the SOM algorithm, and another to learn a smooth approximation of a function. System performance is illustrated with three examples.Office of Naval Research (N00014-95-10409, N00014-95-0657

Vespidae (Insecta: Hymenoptera) of Puerto Rico, West Indies

The vespid fauna of Greater Puerto Rico is reviewed (Hymenoptera: Vespidae). Three new species are described, Ancistrocerus isla Carpenter, Euodynerus jeitita Carpenter and Genaro, and Omicron aridum Carpenter and Genaro. Polistes crinitus americanus (Fabricius, 1775) and P. crinitus multicolor (Olivier, 1792) are both reduced to synonyms of nominotypical P. crinitus (Felton, 1765), revised status; Zeta abdominale hispaniolae (Bequaert and Salt, 1931) and Zeta abdominale ornatum (de Saussure, 1855) are both reduced to synonyms of nominotypical Zeta abdominale (Drury, 1770), revised status; and Zethus rufinodus monensis Bohart and Stange, 1965, and Zethus rufinodus virginicus Bohart and Stange, 1965, are both reduced to synonyms of nominotypical Zethus rufinodus (Latreille, 1806), revised status. Parancistrocerus obliquus (Cresson, 1865) is newly recorded from Puerto Rico. The presence of Pachodynerus guadulpensis (de Saussure, 1853) in Puerto Rico is confirmed. An analysis of the composition of the Puerto Rican vespid fauna is presented.Se revisa la fauna de avispas de Puerto Rico e islas adyacentes (Hymenoptera: Vespidae). Se describen tres ESPECIES NUEVAS: Ancistrocerus isla Carpenter, Euodynerus jeitita Carpenter y Genaro, y Omicron aridum Carpenter y Genaro. Polistes crinitus americanus (Fabricius, 1775) y P. crinitus multicolor (Olivier, 1792) son reducidas a nombres sinónimos de la especie nominotipica P. crinitus (Felton, 1765), ESTADO REVISADO; Zeta abdominale hispaniolae (Bequaert and Salt, 1931) y Zeta abdominale ornatum (de Saussure, 1855) son reducidas a sinonimia de la especie nominotipica Zeta abdominale (Drury, 1770), ESTADO REVISADO; Zethus rufinodus monensis Bohart y Stange, 1965, y Zethus rufinodus virginicus Bohart y Stange, 1965, son reducidas a nombres sinónimos de la especie nominotipica Zethus rufinodus (Latreille, 1806), ESTADO REVISADO. Parancistrocerus obliquus (Cresson, 1865) se registra nuevamente para Puerto Rico. Se confirma la presencia de Pachodynerus guadulpensis (de Saussure, 1853) en Puerto Rico. Se analiza la composición de la fauna de véspidos de Puerto Rico

Revisiting Constraints on Fourth Generation Neutrino Masses

We revisit the current experimental bounds on fourth-generation Majorana neutrino masses, including the effects of right handed neutrinos. Current bounds from LEPII are significantly altered by a global analysis. We show that the current bounds on fourth generation neutrinos decaying to eW and mu W can be reduced to about 80 GeV (from the current bound of 90 GeV), while a neutrino decaying to tau W can be as light as 62.1 GeV. The weakened bound opens up a neutrino decay channel for intermediate mass Higgs, and interesting multi-particle final states for Higgs and fourth generation lepton decays.Comment: 7 pages 1 fi

Segmentation ART: A Neural Network for Word Recognition from Continuous Speech

The Segmentation ATIT (Adaptive Resonance Theory) network for word recognition from a continuous speech stream is introduced. An input sequeuce represents phonemes detected at a preproccesing stage. Segmentation ATIT is trained rapidly, and uses a fast-learning fuzzy ART modules, top-down expectation, and a spatial representation of temporal order. The network performs on-line identification of word boundaries, correcting an initial hypothesis if subsequent phonemes are incompatible with a previous partition. Simulations show that the system's segmentation perfonnance is comparable to that of TRACE, and the ability to segment a number of difficult phrases is also demonstrated.National Science Foundation (NSF-IRI-94-01659); Office of Naval Research (N00014-95-1-0409, N00014-95-1-0G57

Near-Infrared Photometric Variability of Stars Toward the Orion A Molecular Cloud

We present an analysis of J, H, and K time series photometry obtained with the southern 2MASS telescope over a 0.84 x 6 deg^2 region centered near the Orion Nebula Cluster. These data are used to establish the near-infrared variability properties of pre-main-sequence stars in Orion on time scales of 1-36 days, 2 months, and 2 years. A total of 1235 variable stars are identified, ~93% of which are associated with the Orion A molecular cloud. The variable stars exhibit a diversity of photometric behavior with time, including cyclic fluctuations, aperiodic day-to-day fluctuations, eclipses, slow drifts in brightness over one month, colorless variability, stars that become redder as they fade, and stars that become bluer as they fade. We examine rotational modulation of cool and hot star spots, variable obscuration from an inner circumstellar disk, and changes in the mass accretion rate and other properties in a circumstellar disk as possible origins of the variability. Cool spots can explain the variability characteristics in 56-77% of the stars, while the properties of the photometric fluctuations are more consistent with hot spots or extinction changes in at least 23% of the stars, and with variations in the disk mass accretion rate or inner disk radius in 1% of our sample. However, differences between the details of the observations and the details of variability predicted these models suggest either that another variability mechanism not considered here may be operative, or that the observed variability represents the net results of several of these phenomena. Analysis of the star count data indicates that the ONC is part of a larger area of enhanced stellar surface density which extends over a 0.4 x 2.4 deg^2 (3.4 x 20 pc^2) region containing 2700 stars brighter than K=14. (abridged version)Comment: 75 pages with 27 figures; to appear in AJ; see also http://www.astro.caltech.edu/~jmc/variables/orio

Periodic Photometric Variability in the Becklin-Neugebauer Object

The Becklin-Neugebauer (BN) object in the Orion Nebula Cluster (ONC) is a well-studied optically invisible, infrared-bright young stellar object, thought to be an intermediate-mass protostar. We report here that BN exhibited nearly-sinusoidal periodic variability at the near-infrared H- and Ks-bands during a one month observing campaign in 2000 March/April. The period was 8.28 days and the peak-to-peak amplitude ~0.2 mag. Plausible mechanisms for producing the observed variability characteristics are explored.Comment: Accepted by ApJ Letter

Does attending a charter school Reduce the likelihood of being placed into special education? Evidence from Denver, Colorado

We use administrative data to measure whether attending a charter school in Denver, Colorado, reduces the likelihood that students are newly classified as having a disability in primary grades. We employ an observational approach that takes advantage of Denver’s Common Enrollment System, which allows us to observe each school that the student listed a preference to attend. We find evidence that attending a Denver charter school reduces the likelihood that a student is classified as having a specific learning disability, which is the largest and most subjectively diagnosed disability category. We find no evidence that charter attendance reduces the probability of being classified as having a speech or language disability or autism, which are two more objectively diagnosed classifications.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Funding for this research came from The Searle Freedom Trust. (The Searle Freedom Trust)http://sites.bu.edu/marcuswinters/files/2017/09/Does-Charter-Attendence-Reduce-Likelihood-of-SPED-Placement.pdfhttp://sites.bu.edu/marcuswinters/files/2017/09/Does-Charter-Attendence-Reduce-Likelihood-of-SPED-Placement.pdfAccepted manuscrip

Are low-performing students more likely to exit charter schools? Evidence from New York City and Denver, Colorado

A common criticism of charter schools is that they systematically remove or “counsel out” their lowest performing students. However, relatively little is currently known about whether low-performing students are in fact more likely to exit charter schools than surrounding traditional public schools. We use longitudinal student-level data from two large urban school systems that prior research has found to have effective charter school sectors–New York City and Denver, Colorado–to evaluate whether there is a differential relationship between low-performance on standardized test scores and the probability that students exit their schools by sector attended. We find no evidence of a differential relationship between prior performance and the likelihood of exiting a school by sector. Low-performing students in both cities are either equally likely or less likely to exit their schools than are student in traditional public schools.We would like to thank the Denver Public School System for providing the data necessary for this paper, and we especially appreciated the assistance of Josh Drake, Yu-lu Hsiung, and Alisha Anuscencion. Funding for this project comes from the Searle Charitable Trust. We thank the Foundation for its support, but acknowledge that the findings and conclusions presented are our own and do not necessarily represent those of the Foundation. All remaining errors are our own. (Searle Charitable Trust)http://sites.bu.edu/marcuswinters/files/2017/09/Exiting-Charter-Schools.pdfAccepted manuscrip

The influence of normal stress and sliding velocity on the frictional behaviour of calcite at room temperature. Insights from laboratory experiments and microstructural observations

The presence of calcite in and near faults, as the dominant material, cement, or vein fill, indicates that the mechanical behaviour of carbonate-dominated material likely plays an important role in shallow- and mid-crustal faulting. To better understand the behaviour of calcite, under loading conditions relevant to earthquake nucleation, we sheared powdered gouge of Carrara Marble, >98 per cent CaCO3, at constant normal stresses between 1 and 100 MPa under water-saturated conditions at room temperature. We performed slide-hold-slide tests, 1–3000 s, to measure the amount of static frictional strengthening and creep relaxation, and velocity-stepping tests, 0.1–1000 µm s–1, to evaluate frictional stability. We observe that the rates of frictional strengthening and creep relaxation decrease with increasing normal stress and diverge as shear velocity is increased from 1 to 3000 µm s–1 during slide-hold-slide experiments. We also observe complex frictional stability behaviour that depends on both normal stress and shearing velocity. At normal stresses less than 20 MPa, we observe predominantly velocity-neutral friction behaviour. Above 20 MPa, we observe strong velocity-strengthening frictional behaviour at low velocities, which then evolves towards velocity-weakening friction behaviour at high velocities. Microstructural analyses of recovered samples highlight a variety of deformation mechanisms including grain size reduction and localization, folding of calcite grains and fluid-assisted diffusion mass transfer processes promoting the development of calcite nanograins in the highly deformed portions of the experimental fault. Our combined analyses indicate that calcite fault gouge transitions from brittle to semi-brittle behaviour at high normal stress and slow sliding velocities. This transition has important implications for earthquake nucleation and propagation on faults in carbonate-dominated lithologies

CARMA interferometric observations of 2MASS J044427+2512: the first spatially resolved observations of thermal emission of a brown dwarf disk

We present CARMA 1.3 mm continuum data of the disk surrounding the young brown dwarf 2MASS J044427+2512 in the Taurus molecular cloud. The high angular resolution of the CARMA observations (0.16 arcsec) allows us to spatially resolve for the first time the thermal emission from dust around a brown dwarf. We analyze the interferometric visibilities and constrain the disk outer radius adopting disk models with power-law radial profiles of the dust surface density. In the case of a power-law index equal to or lower than 1, we obtain a disk radius in the range of about 15 - 30 AU, while larger disks are inferred for steeper radial profiles. By combining this information on the disk spatial extent with the sub-mm spectral index of this source we find conclusive evidence for mm-sized grains, or larger, in this brown dwarf disk. We discuss the implications of our results on the models of dust evolution in proto-planetary disks and brown dwarf formation.Comment: 14 pages, 3 figures, Accepted for publication in ApJ Letter