556 research outputs found
Five supernova survey galaxies in the southern hemisphere. I. Optical and near-infrared database
The determination of the supernova (SN) rate is based not only on the number
of detected events, but also on the properties of the parent galaxy population.
This is the first paper of a series aimed at obtaining new, refined, SN rates
from a set of five SN surveys, by making use of a joint analysis of
near-infrared (NIR) data. We describe the properties of the 3838 galaxies that
were monitored for SNe events, including newly determined morphologies and
their DENIS and POSS-II/UKST I, 2MASS and DENIS J and Ks and 2MASS H
magnitudes. We have compared 2MASS, DENIS and POSS-II/UKST IJK magnitudes in
order to find possible systematic photometric shifts in the measurements. The
DENIS and POSS-II/UKST I band magnitudes show large discrepancies (mean
absolute difference of 0.4 mag), mostly due to different spectral responses of
the two instruments, with an important contribution (0.33 mag rms) from the
large uncertainties in the photometric calibration of the POSS-II and UKST
photographic plates. In the other wavebands, the limiting near infrared
magnitude, morphology and inclination of the galaxies are the most influential
factors which affect the determination of photometry of the galaxies.
Nevertheless, no significant systematic differences have been found between of
any pair of NIR magnitude measurements, except for a few percent of galaxies
showing large discrepancies. This allows us to combine DENIS and 2MASS data for
the J and Ks filters.Comment: 17 pages, 3 figures, 5 tables, published in Astrophysics, Vol. 52,
No. 1, 2009 (English translation of Astrofizika
Energy- and flux-budget (EFB) turbulence closure model for the stably stratified flows. Part I: Steady-state, homogeneous regimes
We propose a new turbulence closure model based on the budget equations for
the key second moments: turbulent kinetic and potential energies: TKE and TPE
(comprising the turbulent total energy: TTE = TKE + TPE) and vertical turbulent
fluxes of momentum and buoyancy (proportional to potential temperature).
Besides the concept of TTE, we take into account the non-gradient correction to
the traditional buoyancy flux formulation. The proposed model grants the
existence of turbulence at any gradient Richardson number, Ri. Instead of its
critical value separating - as usually assumed - the turbulent and the laminar
regimes, it reveals a transition interval, 0.1< Ri <1, which separates two
regimes of essentially different nature but both turbulent: strong turbulence
at Ri<<1; and weak turbulence, capable of transporting momentum but much less
efficient in transporting heat, at Ri>1. Predictions from this model are
consistent with available data from atmospheric and lab experiments, direct
numerical simulation (DNS) and large-eddy simulation (LES).Comment: 40 pages, 6 figures, Boundary-layer Meteorology, resubmitted, revised
versio
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
Turbulence and galactic structure
Interstellar turbulence is driven over a wide range of scales by processes
including spiral arm instabilities and supernovae, and it affects the rate and
morphology of star formation, energy dissipation, and angular momentum transfer
in galaxy disks. Star formation is initiated on large scales by gravitational
instabilities which control the overall rate through the long dynamical time
corresponding to the average ISM density. Stars form at much higher densities
than average, however, and at much faster rates locally, so the slow average
rate arises because the fraction of the gas mass that forms stars at any one
time is low, ~10^{-4}. This low fraction is determined by turbulence
compression, and is apparently independent of specific cloud formation
processes which all operate at lower densities. Turbulence compression also
accounts for the formation of most stars in clusters, along with the cluster
mass spectrum, and it gives a hierarchical distribution to the positions of
these clusters and to star-forming regions in general. Turbulent motions appear
to be very fast in irregular galaxies at high redshift, possibly having speeds
equal to several tenths of the rotation speed in view of the morphology of
chain galaxies and their face-on counterparts. The origin of this turbulence is
not evident, but some of it could come from accretion onto the disk. Such high
turbulence could help drive an early epoch of gas inflow through viscous
torques in galaxies where spiral arms and bars are weak. Such evolution may
lead to bulge or bar formation, or to bar re-formation if a previous bar
dissolved. We show evidence that the bar fraction is about constant with
redshift out to z~1, and model the formation and destruction rates of bars
required to achieve this constancy.Comment: in: Penetrating Bars through Masks of Cosmic Dust: The Hubble Tuning
Fork strikes a New Note, Eds., K. Freeman, D. Block, I. Puerari, R. Groess,
Dordrecht: Kluwer, in press (presented at a conference in South Africa, June
7-12, 2004). 19 pgs, 5 figure
Display of probability densities for data from a continuous distribution
Based on cumulative distribution functions, Fourier series expansion and
Kolmogorov tests, we present a simple method to display probability densities
for data drawn from a continuous distribution. It is often more efficient than
using histograms.Comment: 5 pages, 4 figures, presented at Computer Simulation Studies XXIV,
Athens, GA, 201
Energy- and flux-budget turbulence closure model for stably stratified flows. Part II: the role of internal gravity waves
We advance our prior energy- and flux-budget turbulence closure model
(Zilitinkevich et al., 2007, 2008) for the stably stratified atmospheric flows
and extend it accounting for additional vertical flux of momentum and
additional productions of turbulent kinetic energy, turbulent potential energy
(TPE) and turbulent flux of potential temperature due to large-scale internal
gravity waves (IGW). Main effects of IGW are following: the maximal value of
the flux Richardson number (universal constant 0.2-0.25 in the no-IGW regime)
becomes strongly variable. In the vertically homogeneous stratification, it
increases with increasing wave energy and can even exceed 1. In the
heterogeneous stratification, when IGW propagate towards stronger
stratification, the maximal flux Richardson number decreases with increasing
wave energy, reaches zero and then becomes negative. In other words, the
vertical flux of potential temperature becomes counter-gradient. IGW also
reduce anisotropy of turbulence and increase the share of TPE in the turbulent
total energy. Depending on the direction (downward or upward), IGW either
strengthen or weaken the total vertical flux of momentum. Predictions from the
proposed model are consistent with available data from atmospheric and
laboratory experiments, direct numerical simulations and large-eddy
simulations.Comment: 37 pages, 5 figures, revised versio
The impact of egg incubation temperature on the personality of oviparous reptiles
Personality traits, defined as differences in the behavior of individual animals of the same species that are consistent over time and context, such as βboldness,β have been shown to be both heritable and be influenced by external factors, such as predation pressure. Currently, we know very little about the role that early environmental factors have upon personality. Thus, we investigated the impact of incubation temperature upon the boldness on an oviparous reptile, the bearded dragon (Pogona vitticeps). Eggs, from one clutch, were incubated at two different average temperatures within the normal range. After hatching the lizards were raised under the same environmental conditions. Novel object and novel environment tests were used to assess personality. Each test was repeated in both the short term and the long term. The results revealed that incubation temperature did impact upon βboldnessβ but only in the short term and suggests that, rather than influencing personality, incubation temperature may have an effect on the development of behavioral of oviparous reptiles at different stages across ontogeny
Inclusive Production Cross Sections from 920 GeV Fixed Target Proton-Nucleus Collisions
Inclusive differential cross sections and
for the production of \kzeros, \lambdazero, and
\antilambda particles are measured at HERA in proton-induced reactions on C,
Al, Ti, and W targets. The incident beam energy is 920 GeV, corresponding to
GeV in the proton-nucleon system. The ratios of differential
cross sections \rklpa and \rllpa are measured to be and , respectively, for \xf . No significant dependence upon the
target material is observed. Within errors, the slopes of the transverse
momentum distributions also show no significant
dependence upon the target material. The dependence of the extrapolated total
cross sections on the atomic mass of the target material is
discussed, and the deduced cross sections per nucleon are
compared with results obtained at other energies.Comment: 17 pages, 7 figures, 5 table
Jet energy measurement with the ATLAS detector in proton-proton collisions at root s=7 TeV
The jet energy scale and its systematic uncertainty are determined for jets measured with the ATLAS detector at the LHC in proton-proton collision data at a centre-of-mass energy of βs = 7TeV corresponding to an integrated luminosity of 38 pb-1. Jets are reconstructed with the anti-kt algorithm with distance parameters R=0. 4 or R=0. 6. Jet energy and angle corrections are determined from Monte Carlo simulations to calibrate jets with transverse momenta pTβ₯20 GeV and pseudorapidities {pipe}Ξ·{pipe}<4. 5. The jet energy systematic uncertainty is estimated using the single isolated hadron response measured in situ and in test-beams, exploiting the transverse momentum balance between central and forward jets in events with dijet topologies and studying systematic variations in Monte Carlo simulations. The jet energy uncertainty is less than 2. 5 % in the central calorimeter region ({pipe}Ξ·{pipe}<0. 8) for jets with 60β€pT<800 GeV, and is maximally 14 % for pT<30 GeV in the most forward region 3. 2β€{pipe}Ξ·{pipe}<4. 5. The jet energy is validated for jet transverse momenta up to 1 TeV to the level of a few percent using several in situ techniques by comparing a well-known reference such as the recoiling photon pT, the sum of the transverse momenta of tracks associated to the jet, or a system of low-pT jets recoiling against a high-pT jet. More sophisticated jet calibration schemes are presented based on calorimeter cell energy density weighting or hadronic properties of jets, aiming for an improved jet energy resolution and a reduced flavour dependence of the jet response. The systematic uncertainty of the jet energy determined from a combination of in situ techniques is consistent with the one derived from single hadron response measurements over a wide kinematic range. The nominal corrections and uncertainties are derived for isolated jets in an inclusive sample of high-pT jets. Special cases such as event topologies with close-by jets, or selections of samples with an enhanced content of jets originating from light quarks, heavy quarks or gluons are also discussed and the corresponding uncertainties are determined. Β© 2013 CERN for the benefit of the ATLAS collaboration
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