Dynamics of Learning with Restricted Training Sets I: General Theory

We study the dynamics of supervised learning in layered neural networks, in the regime where the size $p$ of the training set is proportional to the number $N$ of inputs. Here the local fields are no longer described by Gaussian probability distributions and the learning dynamics is of a spin-glass nature, with the composition of the training set playing the role of quenched disorder. We show how dynamical replica theory can be used to predict the evolution of macroscopic observables, including the two relevant performance measures (training error and generalization error), incorporating the old formalism developed for complete training sets in the limit $\alpha=p/N\to\infty$ as a special case. For simplicity we restrict ourselves in this paper to single-layer networks and realizable tasks.Comment: 39 pages, LaTe

Detection of Coulomb Charging around an Antidot in the Quantum Hall Regime

We have detected oscillations of the charge around a potential hill (antidot) in a two-dimensional electron gas as a function of a large magnetic field B. The field confines electrons around the antidot in closed orbits, the areas of which are quantised through the Aharonov-Bohm effect. Increasing B reduces each state's area, pushing electrons closer to the centre, until enough charge builds up for an electron to tunnel out. This is a new form of the Coulomb blockade seen in electrostatically confined dots. Addition and excitation spectra in DC bias confirm the Coulomb blockade of tunnelling.Comment: 4 pages, 4 Postscript figure

Chemical Abundances Of Open Clusters From High-Resolution Infrared Spectra. I. NGC 6940

We present near-infrared spectroscopic analysis of 12 red giant members of the Galactic open cluster NGC 6940. High-resolution (R$\simeq$45000) and high signal-to-noise ratio (S/N > 100) near-infrared H and K band spectra were gathered with the Immersion Grating Infrared Spectrograph (IGRINS) on the 2.7m Smith Telescope at McDonald Observatory. We obtained abundances of H-burning (C, N, O), ${\alpha}$ (Mg, Si, S, Ca), light odd-Z (Na, Al, P, K), Fe-group (Sc, Ti, Cr, Fe, Co, Ni) and neutron-capture (Ce, Nd, Yb) elements. We report the abundances of S, P, K, Ce, and Yb in NGC 6940 for the first time. Many OH and CN features in the H band were used to obtain O and N abundances. C abundances were measured from four different features: CO molecular lines in the K band, high excitation C I lines present in both near-infrared and optical, CH and $C_2$ bands in the optical region. We have also determined $^{12}C/^{13}C$ ratios from the R-branch band heads of first overtone (2-0) and (3-1) $^{12}CO$ (2-0) $^{13}CO$ lines near 23440 \overset{\lower.5em\circ}{\mathrm{A}} and (3-1) $^{13}CO$ lines at about 23730 \overset{\lower.5em\circ}{\mathrm{A}}. We have also investigated the HF feature at 23358.3 \overset{\lower.5em\circ}{\mathrm{A}}, finding solar fluorine abundances without ruling out a slight enhancement. For some elements (such as the ${\alpha}$ group), IGRINS data yield more internally self-consistent abundances. We also revisited the CMD of NGC 6940 by determining the most probable cluster members using Gaia DR2. Finally, we applied Victoria isochrones and MESA models in order to refine our estimates of the evolutionary stages of our targets.Comment: 16 pages, 10 figure

Strong Nebular Line Ratios in the Spectra of z~2-3 Star-forming Galaxies: First Results from KBSS-MOSFIRE

We present initial results of a deep near-IR spectroscopic survey covering the 15 fields of the Keck Baryonic Structure Survey (KBSS) using MOSFIRE on the Keck 1 telescope, focusing on a sample of 251 galaxies with redshifts 2.0< z < 2.6, star-formation rates 2 < SFR < 200 M_sun/yr, and stellar masses 8.6 < log(M*/M_sun) < 11.4, with high-quality spectra in both H- and K-band atmospheric windows. We show unambiguously that the locus of z~2.3 galaxies in the "BPT" nebular diagnostic diagram exhibits a disjoint, yet similarly tight, relationship between the ratios [NII]6585/Halpha and [OIII]/Hbeta as compared to local galaxies. Using photoionization models, we argue that the offset of the z~2.3 locus relative to z~ 0 is explained by a combination of harder ionizing radiation field, higher ionization parameter, and higher N/O at a given O/H than applies to most local galaxies, and that the position of a galaxy along the z~2.3 star-forming BPT locus is surprisingly insensitive to gas-phase oxygen abundance. The observed nebular emission line ratios are most easily reproduced by models in which the net ionizing radiation field resembles a blackbody with effective temperature T_eff = 50000-60000 K and N/O close to the solar value at all O/H. We critically assess the applicability of commonly-used strong line indices for estimating gas-phase metallicities, and consider the implications of the small intrinsic scatter in the empirical relationship between excitation-sensitive line indices and stellar mass (i.e., the "mass-metallicity" relation), at z~2.3.Comment: 41 pages, 25 figures, accepted for publication in the Astrophysical Journal. Version with full-resolution figures available at http://www.astro.caltech.edu/~ccs/mos_bpt_submit.pd

Ancient Egypt 1922 Part 3

Part 3 of the 1922 Ancient Egypt books. Contents include Hittite letters on Egypt, heddle-jacks of looms, loom weights in Egypt, and a discussion of Nebti Sma.https://knowledge.e.southern.edu/kweeks_coll/1020/thumbnail.jp

Constraining Nucleosynthesis in Two CEMP Progenitors Using Fluorine

© 2020 The Author(s). The version of record [Aldo Mura-Guzmán, D Yong, C Abate, A Karakas, C Kobayashi, H Oh, S-H Chun, G Mace, Constraining nucleosynthesis in two CEMP progenitors using fluorine, Monthly Notices of the Royal Astronomical Society, Volume 498, Issue 3, November 2020, Pages 3549–3559] is available online at: https://doi.org/10.1093/mnras/staa2610.We present new fluorine abundance estimations in two carbon enhanced metal-poor (CEMP) stars, HE 1429-0551 and HE 1305+0007. HE 1429-0551 is also enriched in slow neutron-capture process (s-process) elements, a CEMP-s, and HE 1305+0007 is enhanced in both, slow and rapid neutron-capture process elements, a CEMP-s/r. The F abundances estimates are derived from the vibration-rotation transition of the HF molecule at 23358.6 Š using high-resolution infrared spectra obtained with the Immersion Grating Infrared Spectrometer (IGRINS) at the 4-m class Lowell Discovery Telescope. Our results include an F abundance measurement in HE 1429-0551 of A(F) = +3.93 ([F/Fe] = +1.90) at [Fe/H] = -2.53, and an F upper limit in HE 1305+0007 of A(F) < +3.28 ([F/Fe] < +1.00) at [Fe/H] = -2.28. Our new derived F abundance in HE 1429-0551 makes this object the most metal-poor star where F has been detected. We carefully compare these results with literature values and state-of-the-art CEMP-s model predictions including detailed asymptotic giant branch (AGB) nucleosynthesis and binary evolution. The modelled fluorine abundance for HE 1429-0551 is within reasonable agreement with our observed abundance, although is slightly higher than our observed value. For HE 1429-0551, our findings support the scenario via mass transfer by a primary companion during its thermally pulsing phase. Our estimated upper limit in HE 1305+0007, along with data from the literature, shows large discrepancies compared with AGB models. The discrepancy is principally due to the simultaneous s- and r-process element enhancements which the model struggles to reproduce.Peer reviewedFinal Published versio

Report on Second Activations with the Lead Slowing Down Spectrometer

Summary On August 18 and 19 2011, five items were irradiated with neutrons using the Lead Slowing Down Spectrometer (LSDS). After irradiation, dose measurements and gamma-spectrometry measurements were completed on all of the samples. No contamination was found on the samples, and all but one provided no dose. Gamma-spectroscopy measurements qualitatively agreed with expectations based on the materials. As during the first activation run, we observed activation in the room in general, mostly due to 56Mn and 24Na. Most of the activation of the samples was short lived, with half-lives on the scale of hours to days, except for 60Co which has a half-life of 5.3 y

Hubble Space Telescope Spectroscopy of Brown Dwarfs Discovered with the Wide-field Infrared Survey Explorer

We present a sample of brown dwarfs identified with the {\it Wide-field Infrared Survey Explorer} (WISE) for which we have obtained {\it Hubble Space Telescope} ({\it HST}) Wide Field Camera 3 (WFC3) near-infrared grism spectroscopy. The sample (twenty-two in total) was observed with the G141 grism covering 1.10$-$1.70 $\mu$m, while fifteen were also observed with the G102 grism, which covers 0.90$-$1.10 $\mu$m. The additional wavelength coverage provided by the G102 grism allows us to 1) search for spectroscopic features predicted to emerge at low effective temperatures (e.g.\ ammonia bands) and 2) construct a smooth spectral sequence across the T/Y boundary. We find no evidence of absorption due to ammonia in the G102 spectra. Six of these brown dwarfs are new discoveries, three of which are found to have spectral types of T8 or T9. The remaining three, WISE J082507.35$+$280548.5 (Y0.5), WISE J120604.38$+$840110.6 (Y0), and WISE J235402.77$+$024015.0 (Y1) are the nineteenth, twentieth, and twenty-first spectroscopically confirmed Y dwarfs to date. We also present {\it HST} grism spectroscopy and reevaluate the spectral types of five brown dwarfs for which spectral types have been determined previously using other instruments.Comment: Accepted for publication in the Astrophysical Journal. 20 pages, 18 figures, 7 table