4,532 research outputs found
Atomic Hydrogen Cleaning of Polarized GaAs Photocathodes
Atomic hydrogen cleaning followed by heat cleaning at 450C was used
to prepare negative-electron-affinity GaAs photocathodes. When hydrogen ions
were eliminated, quantum efficiencies of 15% were obtained for bulk GaAs
cathodes, higher than the results obtained using conventional 600C heat
cleaning. The low-temperature cleaning technique was successfully applied to
thin, strained GaAs cathodes used for producing highly polarized electrons. No
depolarization was observed even when the optimum cleaning time of about 30
seconds was extended by a factor of 100
Impact of robot responsiveness and adult involvement on children's social behaviours in human-robot interaction
A key challenge in developing engaging social robots is creating convincing, autonomous and responsive agents, which users perceive, and treat, as social beings. As a part of the collaborative project: Expressive Agents for Symbiotic Education and Learning (EASEL), this study examines the impact of autonomous response to children's speech, by the humanoid robot Zeno, on their interactions with it as a social entity. Results indicate that robot autonomy and adult assistance during HRI can substantially influence children's behaviour during interaction and their affect after. Children working with a fully-autonomous, responsive robot demonstrated greater physical activity following robot instruction than those working with a less responsive robot, which required adult assistance to interact with. During dialogue with the robot, children working with the fully-autonomous robot also looked towards the robot in anticipation of its vocalisations on more occasions. In contrast, a less responsive robot, requiring adult assistance to interact with, led to greater self-report positive affect and more occasions of children looking to the robot in response to its vocalisations. We discuss the broader implications of these findings in terms of anthropomorphism of social robots and in relation to the overall project strategy to further the understanding of how interactions with social robots could lead to task-appropriate symbiotic relationships
The Subaru Ly-alpha blob survey: A sample of 100 kpc Ly-alpha blobs at z=3
We present results of a survey for giant Ly-alpha nebulae (LABs) at z=3 with
Subaru/Suprime-Cam. We obtained Ly-alpha imaging at z=3.09+-0.03 around the
SSA22 protocluster and in several blank fields. The total survey area is 2.1
square degrees, corresponding to a comoving volume of 1.6 x 10^6 Mpc^3. Using a
uniform detection threshold of 1.4 x 10^{-18} erg s^{-1} cm^{-2} arcsec^{-2}
for the Ly-alpha images, we construct a sample of 14 LAB candidates with
major-axis diameters larger than 100 kpc, including five previously known blobs
and two known quasars. This survey triples the number of known LABs over 100
kpc. The giant LAB sample shows a possible "morphology-density relation":
filamentary LABs reside in average density environments as derived from compact
Ly-alpha emitters, while circular LABs reside in both average density and
overdense environments. Although it is hard to examine the formation mechanisms
of LABs only from the Ly-alpha morphologies, more filamentary LABs may relate
to cold gas accretion from the surrounding inter-galactic medium (IGM) and more
circular LABs may relate to large-scale gas outflows, which are driven by
intense starbursts and/or by AGN activities. Our survey highlights the
potential usefulness of giant LABs to investigate the interactions between
galaxies and the surrounding IGM from the field to overdense environments at
high-redshift.Comment: MNRAS Letters accepted (6 pages, 4 figures, 2 tables
Spitzer observations of extended Lyman-alpha Clouds in the SSA22 field
We present the results of a Spitzer IRAC and MIPS 24 micron study of extended
Lyman-alpha clouds (or Lyman-alpha Blobs, LABs) within the SSA22 filamentary
structure at z = 3.09. We detect 6/26 LABs in all IRAC filters, four of which
are also detected at 24 micron, and find good correspondence with the 850
micron measurements of Geach et al. 2005. An analysis of the rest-frame
ultraviolet, optical, near- and mid-infrared colors reveals that these six
systems exhibit signs of nuclear activity (AGN)and/or extreme star formation.
Notably, they have properties that bridge galaxies dominated by star formation
(Lyman-break galaxies; LBGs) and those with AGNs (LBGs classified as QSOs). The
LAB systems not detected in all four IRAC bands, on the other hand, are, as a
group, consistent with pure star forming systems, similar to the majority of
the LBGs within the filament. These results indicate that the galaxies within
LABs do not comprise a homogeneous population, though they are also consistent
with scenarios in which the gas halos are ionized through a common mechanism
such as galaxy-scale winds driven by the galaxies within them, or gravitational
heating of the collapsing cloud itself.Comment: 11 pages, 6 figures, accepted for publication in the Astrophysical
Journa
Electroweak Radiative Corrections To Polarized M{\o}ller Scattering Asymmetries
One loop electroweak radiative corrections to left-right parity violating
M{\o}ller scattering () asymmetries are presented. They
reduce the standard model (tree level) prediction by 40 \% where the
main shift and uncertainty stem from hadronic vacuum polarization loops. A
similar reduction also occurs for the electron-electron atomic parity violating
interaction. That effect can be attributed to an increase of
by in running from to 0. The
sensitivity of the asymmetry to ``new physics'' is also discussed.Comment: 14 pages, Revtex, postscript file including figures is available at
ftp://ttpux2.physik.uni-karlsruhe.de/ttp95-14/ttp95-14.ps or via WWW at
http://ttpux2.physik.uni-karlsruhe.de/cgi-bin/preprints/ (129.13.102.139
The Calibration of Mid-Infrared Star Formation Rate Indicators
With the goal of investigating the degree to which the mid-infrared emission
traces the star formation rate (SFR), we analyze Spitzer 8 um and 24 um data of
star-forming regions in a sample of 33 nearby galaxies with available
HST/NICMOS images in the Paschen-alpha (1.8756 um) emission line. The galaxies
are drawn from the Spitzer Infrared Nearby Galaxies Survey (SINGS) sample, and
cover a range of morphologies and a factor ~10 in oxygen abundance. Published
data on local low-metallicity starburst galaxies and Luminous Infrared Galaxies
are also included in the analysis. Both the stellar-continuum-subtracted 8 um
emission and the 24 um emission correlate with the extinction-corrected
Pa-alpha line emission, although neither relationship is linear. Simple models
of stellar populations and dust extinction and emission are able to reproduce
the observed non-linear trend of the 24 um emission versus number of ionizing
photons, including the modest deficiency of 24 um emission in the low
metallicity regions, which results from a combination of decreasing dust
opacity and dust temperature at low luminosities. Conversely, the trend of the
8 um emission as a function of the number of ionizing photons is not well
reproduced by the same models. The 8 um emission is contributed, in larger
measure than the 24 um emission, by dust heated by non-ionizing stellar
populations, in agreement with previous findings. Two SFR calibrations, one
using the 24 um emission and the other using a combination of the 24 um and
H-alpha luminosities (Kennicutt et al. 2007), are presented. No calibration is
presented for the 8 um emission, because of its significant dependence on both
metallicity and environment. The calibrations presented here should be directly
applicable to systems dominated by on-going star formation.Comment: 67 pages, 15 figures, accepted for publication on the Astrophysical
Journal; replacement contains: correction to equation 8; important tweaks to
equation 9; various typos correcte
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