147 research outputs found
Hi-Val: Iterative Learning of Hierarchical Value Functions for Policy Generation
Task decomposition is effective in manifold applications where the global complexity of a problem makes planning and decision-making too demanding. This is true, for example, in high-dimensional robotics domains, where (1) unpredictabilities and modeling limitations typically prevent the manual specification of robust behaviors, and (2) learning an action policy is challenging due to the curse of dimensionality. In this work, we borrow the concept of Hierarchical Task Networks (HTNs) to decompose the learning procedure, and we exploit Upper Confidence Tree (UCT) search to introduce HOP, a novel iterative algorithm for hierarchical optimistic planning with learned value functions. To obtain better generalization and generate policies, HOP simultaneously learns and uses action values. These are used to formalize constraints within the search space and to reduce the dimensionality of the problem. We evaluate our algorithm both on a fetching task using a simulated 7-DOF KUKA light weight arm and, on a pick and delivery task with a Pioneer robot
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
Testing Diagnostics of Nuclear Activity and Star Formation in Galaxies at z>1
We present some of the first science data with the new Keck/MOSFIRE
instrument to test the effectiveness of different AGN/SF diagnostics at z~1.5.
MOSFIRE spectra were obtained in three H-band multi-slit masks in the GOODS-S
field, resulting in two hour exposures of 36 emission-line galaxies. We compare
X-ray data with the traditional emission-line ratio diagnostics and the
alternative mass-excitation and color-excitation diagrams, combining new
MOSFIRE infrared data with previous HST/WFC3 infrared spectra (from the 3D-HST
survey) and multiwavelength photometry. We demonstrate that a high [OIII]/Hb
ratio is insufficient as an AGN indicator at z>1. For the four X-ray detected
galaxies, the classic diagnostics ([OIII]/Hb vs. [NII]/Ha and [SII]/Ha) remain
consistent with X-ray AGN/SF classification. The X-ray data also suggest that
"composite" galaxies (with intermediate AGN/SF classification) host bona-fide
AGNs. Nearly 2/3 of the z~1.5 emission-line galaxies have nuclear activity
detected by either X-rays or the classic diagnostics. Compared to the X-ray and
line ratio classifications, the mass-excitation method remains effective at
z>1, but we show that the color-excitation method requires a new calibration to
successfully identify AGNs at these redshifts.Comment: 7 pages, 4 figures. Accepted to ApJ Letter
CHIMERA: a wide-field, multi-colour, high-speed photometer at the prime focus of the Hale telescope
The Caltech HIgh-speed Multi-colour camERA (CHIMERA) is a new instrument that has been developed for use at the prime focus of the Hale 200-inch telescope. Simultaneous optical imaging in two bands is enabled by a dichroic beam splitter centred at 567 nm, with Sloan u′ and g′ bands available on the blue arm and Sloan r′, i′ and z_s bands available on the red arm. Additional narrow-band filters will also become available as required. An electron multiplying CCD (EMCCD) detector is employed for both optical channels, each capable of simultaneously delivering sub-electron effective read noise under multiplication gain and frame rates of up to 26 fps full frame (several 1000 fps windowed), over a fully corrected 5 × 5 arcmin field of view. CHIMERA was primarily developed to enable the characterization of the size distribution of sub-km Kuiper Belt Objects via stellar occultation, a science case that motivates the frame-rate, the simultaneous multi-colour imaging and the wide field of view of the instrument. In addition, it also has unique capability in the detection of faint near-Earth asteroids and will be used for the monitoring of short-duration transient and periodic sources, particularly those discovered by the intermediate Palomar Transient Factory (iPTF), and the upcoming Zwicky Transient Facility (ZTF)
The SED Machine: a robotic spectrograph for fast transient classification
Current time domain facilities are finding several hundreds of transient
astronomical events a year. The discovery rate is expected to increase in the
future as soon as new surveys such as the Zwicky Transient Facility (ZTF) and
the Large Synoptic Sky Survey (LSST) come on line. At the present time, the
rate at which transients are classified is approximately one order or magnitude
lower than the discovery rate, leading to an increasing "follow-up drought".
Existing telescopes with moderate aperture can help address this deficit when
equipped with spectrographs optimized for spectral classification. Here, we
provide an overview of the design, operations and first results of the Spectral
Energy Distribution Machine (SEDM), operating on the Palomar 60-inch telescope
(P60). The instrument is optimized for classification and high observing
efficiency. It combines a low-resolution (R100) integral field unit (IFU)
spectrograph with "Rainbow Camera" (RC), a multi-band field acquisition camera
which also serves as multi-band (ugri) photometer. The SEDM was commissioned
during the operation of the intermediate Palomar Transient Factory (iPTF) and
has already proved lived up to its promise. The success of the SEDM
demonstrates the value of spectrographs optimized to spectral classification.
Introduction of similar spectrographs on existing telescopes will help
alleviate the follow-up drought and thereby accelerate the rate of discoveries.Comment: 21 pages, 20 figure
Supramolecular assemblies involving metal organic ring interactions: Heterometallic Cu(II)-Ln(III) two dimensional coordination polymers
Three isostructural two-dimensional coordination polymers of the general formula [Ln2(CuL)3(H2O)9]$5.5H2O, where Ln is La (1), Nd (2), and Gd (3), have been synthesized and isolated from aqueous solutions and their single-crystal structures determined by X-ray diffraction. The supramolecular interaction between the non-aromatic metallorings plays an important role in stabilizing the structure of these compounds. The thermal stability, reversible solvent uptake, electronic properties and magnetic studies of these compounds are also reported
Keck-I MOSFIRE spectroscopy of compact star-forming galaxies at z2: High velocity dispersions in progenitors of compact quiescent galaxies
We present Keck-I MOSFIRE near-infrared spectroscopy for a sample of 13
compact star-forming galaxies (SFGs) at redshift with star
formation rates of SFR100M y and masses of
log(M/M). Their high integrated gas velocity dispersions of
=230 km s, as measured from emission
lines of H and [OIII], and the resultant
M relation and MM all
match well to those of compact quiescent galaxies at , as measured from
stellar absorption lines. Since log(M/M)
dex, these compact SFGs appear to be dynamically relaxed and more evolved,
i.e., more depleted in gas and dark matter (13\%) than their
non-compact SFG counterparts at the same epoch. Without infusion of external
gas, depletion timescales are short, less than 300 Myr. This discovery
adds another link to our new dynamical chain of evidence that compact SFGs at
are already losing gas to become the immediate progenitors of
compact quiescent galaxies by .Comment: 12 pages, 7 figures, submitted to Ap
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