2,795 research outputs found
Computing with and without arbitrary large numbers
In the study of random access machines (RAMs) it has been shown that the
availability of an extra input integer, having no special properties other than
being sufficiently large, is enough to reduce the computational complexity of
some problems. However, this has only been shown so far for specific problems.
We provide a characterization of the power of such extra inputs for general
problems. To do so, we first correct a classical result by Simon and Szegedy
(1992) as well as one by Simon (1981). In the former we show mistakes in the
proof and correct these by an entirely new construction, with no great change
to the results. In the latter, the original proof direction stands with only
minor modifications, but the new results are far stronger than those of Simon
(1981). In both cases, the new constructions provide the theoretical tools
required to characterize the power of arbitrary large numbers.Comment: 12 pages (main text) + 30 pages (appendices), 1 figure. Extended
abstract. The full paper was presented at TAMC 2013. (Reference given is for
the paper version, as it appears in the proceedings.
The Cosmic Ray Hodoscopes for Testing Thin Gap Chambers at the Technion and Tel Aviv University
Thin gap chambers (TGCs) are built for the muon trigger chambers in the
endcap region of the LHC experiment ATLAS. More than 2500 ATLAS TGCs are being
produced at the Weizmann institute in Israel, and in Shandong University in
China. Detailed testing of these chambers is performed at the Technion and at
the Tel-Aviv University. Two cosmic ray hodoscopes for testing the operation of
these detectors were built in Israel. In these hodoscopes the response of the
chambers to energetic cosmic ray muons is recorded and analyzed. The hodoscopes
measure the exact time and space location of the cosmic ray hit and read out
the chambers which are being tested to verify that they produce a corresponding
signal within the required time interval. The cosmic ray hodoscopes built at
the Technion and at the Tel Aviv University for the test of ATLAS TGCs are
described. The mechanical structure, readout electronics, data acquisition and
operating scheme are presented. Typical TGC test results are presented and
discussed
IMAGES II. A surprisingly low fraction of undisturbed rotating spiral disks at z~0.6: The morpho-kinematical relation 6 Gyrs ago
We present a first combined analysis of the morphological and dynamical
properties for the Intermediate MAss Galaxy Evolution Sequence (IMAGES) sample.
It is a representative sample of 52 z~0.6 galaxies with Mstell from 1.5 to 15
10^10Msun and possessing 3D resolved kinematics and HST deep imaging in at
least two broad band filters. We aim at evaluate robustly the evolution of
rotating spirals since z~0.6, as well as to test the different schemes for
classifying galaxies morphologically. We used all the information provided by
multi-band images, color maps and 2 dimensional light fitting to assign to each
object a morphological class. We divided our sample between spiral disks,
peculiar objects, compact objects and mergers. Using our morphological
classification scheme, 4/5 of identified spirals are rotating disks and more
than 4/5 of identified peculiar galaxies show complex kinematics, while
automatic classification methods such as Concentration-Asymmetry and GINI-M20
severely overestimate the fraction of relaxed disk galaxies. Using this
methodology, we find that the fraction of rotating spirals has increased by a
factor ~ 2 during the last 6 Gyrs, a much higher fraction that found previously
based on morphologies alone. These rotating spiral disks are forming stars very
rapidly, doubling their stellar masses over the last 6 Gyrs, while most of
their stars have been formed few Gyrs earlier, which reveals the presence of a
large gas supply. Because they are likely the progenitors of local spirals, we
can conjecture how their properties are evolving. Their disks show some
evidence for an inside-out growth and the gas supply/accretion is not made
randomly as the disk need to be stable in order to match the local disk
properties.Comment: Typos corrected, reference adde
Rotation Curves of Spiral Galaxies
Rotation curves of spiral galaxies are the major tool for determining the
distribution of mass in spiral galaxies. They provide fundamental information
for understanding the dynamics, evolution and formation of spiral galaxies. We
describe various methods to derive rotation curves, and review the results
obtained. We discuss the basic characteristics of observed rotation curves in
relation to various galaxy properties, such as Hubble type, structure,
activity, and environment.Comment: 40 pages, 6 gif figures; Ann. Rev. Astron. Astrophys. Vol. 39, p.137,
200
Molecular Gas and the Modest Star Formation Efficiency in the ``Antennae'' Galaxies: Arp~244=NGC 4038/39
(abridged) We report here a factor of 5.7 higher total CO flux in Arp~244
(the ``Antennae'' galaxies) than that previously accepted in the literature
(thus a total molecular gas mass of 1.5x10 Msun), based on our fully
sampled CO(1-0) observations at the NRAO 12m telescope. Our observations show
that the molecular gas peaks predominately in the disk-disk overlap region
between the nuclei, similar to the far-infrared (FIR) and mid-infrared (MIR)
emission. The bulk of the molecular gas is forming into stars with a normal
star formation efficiency (SFE) L_{IR}/M(H_2) \approx 4.2 Lsun/Msun, same as
that of giant molecular clouds in the Galactic disk. Additional supportive
evidence is the extremely low fraction of the dense molecular gas in Arp~244,
revealed by our detections of the HCN(1-0) emission.
We estimate the local SFE indicated by the ratio map of the radio continuum
to CO(1-0) emission. Remarkably, the local SFE stays roughly same over the bulk
of the molecular gas distribution. Only some localized regions show the highest
radio-to-CO ratios that we have identified as the sites of the most intense
starbursts with SFE >~ 20 Lsun/Msun. These starburst regions are confined
exclusively in the dusty patches seen in the HST images near the CO and FIR
peaks where presumably the violent starbursts are heavily obscured.
Nevertheless, recent large-scale star formation is going on throughout the
system, yet the measured level is more suggestive of a moderate starburst (SFE
>~ 10 Lsun/Msun) or a weak to normal star formation (SFE ~ 4 Lsun/Msun). The
overall starburst from the bulk of the molecular gas is yet to be initiated as
most of the gas further condenses into kpc scale in the final coalescence.Comment: 31 pages including 3 postscript & 10 gif figures, final version to
appear in ApJ, 2001 Feb. 10. A single .ps.gz file can be down-loaded from:
http://spider.ipac.caltech.edu/staff/gao/Papers
IMAGES-III: The evolution of the Near-Infrared Tully-Fisher relation over the last 6 Gyr
Using the multi-integral field spectrograph GIRAFFE at VLT, we have derived
the K-band Tully-Fisher relation (TFR) at z~0.6 for a representative sample of
65 galaxies with emission lines. We confirm that the scatter in the z~0.6 TFR
is caused by galaxies with anomalous kinematics, and find a positive and strong
correlation between the complexity of the kinematics and the scatter that they
contribute to the TFR. Considering only relaxed-rotating disks, the scatter,
and possibly also the slope of the TFR, do not appear to evolve with z. We
detect an evolution of the K-band TFR zero point between z~0.6 and z=0, which,
if interpreted as an evolution of the K-band luminosity of rotating disks,
would imply that a brightening of 0.66+/-0.14 mag occurs between z~0.6 and z=0.
Any disagreement with the results of Flores et al. (2006) are attributed to
both an improvement of the local TFR and the more detailed accurate measurement
of the rotation velocities in the distant sample. Most of the uncertainty can
be explained by the relatively coarse spatial-resolution of the kinematical
data. Because most rotating disks at z~0.6 are unlikely to experience further
merging events, one may assume that their rotational velocity does not evolve
dramatically. If true, our result implies that rotating disks observed at z~0.6
are rapidly transforming their gas into stars, to be able to double their
stellar masses and be observed on the TFR at z=0. The rotating disks observed
are indeed emission-line galaxies that are either starbursts or LIRGs, which
implies that they are forming stars at a high rate. Thus, a significant
fraction of the rotating disks are forming the bulk of their stars within 6 to
8 Gyr, in good agreement with former studies of the evolution of the M-Z
relation.Comment: 17 pages, 11 figures, accepted for publication in A&A. v2 taking into
account comments from language edito
Background Light in Potential Sites for the ANTARES Undersea Neutrino Telescope
The ANTARES collaboration has performed a series of {\em in situ}
measurements to study the background light for a planned undersea neutrino
telescope. Such background can be caused by K decays or by biological
activity. We report on measurements at two sites in the Mediterranean Sea at
depths of 2400~m and 2700~m, respectively. Three photomultiplier tubes were
used to measure single counting rates and coincidence rates for pairs of tubes
at various distances. The background rate is seen to consist of three
components: a constant rate due to K decays, a continuum rate that
varies on a time scale of several hours simultaneously over distances up to at
least 40~m, and random bursts a few seconds long that are only correlated in
time over distances of the order of a meter. A trigger requiring coincidences
between nearby photomultiplier tubes should reduce the trigger rate for a
neutrino telescope to a manageable level with only a small loss in efficiency.Comment: 18 pages, 8 figures, accepted for publication in Astroparticle
Physic
IMAGES I. Strong evolution of galaxy kinematics since z=1
(abbreviated) We present the first results of the ESO large program,
``IMAGES'' which aims at obtaining robust measurements of the kinematics of
distant galaxies using the multi-IFU mode of GIRAFFE on the VLT. 3D
spectroscopy is essential to robustly measure the often distorted kinematics of
distant galaxies (e.g., Flores et al. 2006). We derive the velocity fields and
-maps of 36 galaxies at 0.4<z<0.75 from the kinematics of the [OII]
emission line doublet, and generate a robust technique to identify the nature
of the velocity fields based on the pixels of the highest signal-to-noise
ratios (S/N). We have gathered a unique sample of 63 velocity fields of
emission line galaxies (W0([OII]) > 15 A) at z=0.4-0.75, which are a
representative subsample of the population of M_stellar>1.5x10^{10} M_sun
emission line galaxies in this redshift range, and are largely unaffected by
cosmic variance. Taking into account all galaxies -with or without emission
lines- in that redshift range, we find that at least 41+/-7% of them have
anomalous kinematics, i.e., they are not dynamically relaxed. This includes
26+/-7% of distant galaxies with complex kinematics, i.e., they are not simply
pressure or rotationally supported. Our result implies that galaxy kinematics
are among the most rapidly evolving properties, because locally, only a few
percent of the galaxies in this mass range have complex kinematics.Comment: 17 pages, 6 figures, Accepted by A&
Streamlined Calibrations of the ATLAS Precision Muon Chambers for Initial LHC Running
The ATLAS Muon Spectrometer is designed to measure the momentum of muons with
a resolution of dp/p = 3% and 10% at 100 GeV and 1 TeV momentum respectively.
For this task, the spectrometer employs 355,000 Monitored Drift Tubes (MDTs)
arrayed in 1200 Chambers. Calibration (RT) functions convert drift time
measurements into tube-centered impact parameters for track segment
reconstruction. RT functions depend on MDT environmental parameters and so must
be appropriately calibrated for local chamber conditions. We report on the
creation and application of a gas monitor system based calibration program for
muon track reconstruction in the LHC startup phase.Comment: 25 pages, 21 figure
Images IV: Strong evolution of the oxygen abundance in gaseous phases of intermediate mass galaxies since z=0.8
Intermediate mass galaxies (logM(Msun)>10) at z~0.6 are the likeliest
progenitors of the present-day numerous population of spirals. There is growing
evidence that they have evolved rapidly since the last 6 to 8 Gyr ago, and
likely have formed a significant fraction of their stellar mass, often showing
perturbed morphologies and kinematics. We have gathered a representative sample
of 88 such galaxies and have provided robust estimates of their gas phase
metallicity. For doing so, we have used moderate spectral resolution
spectroscopy at VLT/FORS2 with unprecedented high S/N allowing to remove biases
coming from interstellar absorption lines and extinction to establish robust
values of R23=([OII]3727 + [OIII]4959,5007)/Hbeta. We definitively confirm that
the predominant population of z~0.6 starbursts and luminous IR galaxies (LIRGs)
are on average, two times less metal rich than the local galaxies at a given
stellar mass. We do find that the metal abundance of the gaseous phase of
galaxies is evolving linearly with time, from z=1 to z=0 and after comparing
with other studies, from z=3 to z=0. Combining our results with the reported
evolution of the Tully Fisher relation, we do find that such an evolution
requires that ~30% of the stellar mass of local galaxies have been formed
through an external supply of gas, thus excluding the close box model. Distant
starbursts & LIRGs have properties (metal abundance, star formation efficiency
& morphologies) similar to those of local LIRGs. Their underlying physics is
likely dominated by gas infall probably through merging or interactions. Our
study further supports the rapid evolution of z~0.4-1 galaxies. Gas exchanges
between galaxies is likely the main cause of this evolution.Comment: 21 pages, 12 figures, A&A, In pres
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