26,701 research outputs found
HI-deficient galaxies in intermediate density environments
Observations show that spiral galaxies in galaxy clusters tend to have on
average less neutral hydrogen (HI) than galaxies of the same type and size in
the field. There is accumulating evidence that such HI-deficient galaxies are
also relatively frequent in galaxy groups. An important question is, which
mechanisms are responsible for the gas deficiency in galaxy groups. To gain a
better understanding of how environment affects the gas content of galaxies, we
identified a sample of six HI-deficient galaxies from the HI Parkes All Sky
Survey (HIPASS) using HI-optical scaling relations. One of the galaxies is
located in the outskirts of the Fornax cluster, four are in loose galaxy groups
and one is in a galaxy triplet. We present new high resolution HI observations
with the Australia Telescope Compact Array (ATCA) of these galaxies. We discuss
the possible cause of HI-deficiency in these galaxies based on HI observations
and various multi-wavelength data. We find that the galaxies have truncated HI
disks, lopsided gas distribution and some show asymmetries in their stellar
disks. We conclude that both ram pressure stripping and tidal interactions are
important gas removal mechanisms in low density environments.Comment: Accepted to MNRAS, 17 pages, 10 figures, 7 table
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Data Transformations for Inference with Linear Regression: Clarifications and Recommendations
Data transformations have been promoted as a popular and easy-to-implement remedy to address the assumption of normally distributed errors (in the population) in linear regression. However, the application of data transformations introduces non-ignorable complexities which should be fully appreciated before their implementation. This paper adds to existing Practical Research and Assessment Evaluation (PARE) publications on data transformations by providing a broad overview underlying the use of data transformations for the specific purpose of statistical inference and interpreting meaningful effect sizes. Data transformations not only potentially change the scale of the transformed variable; they also alter the fundamental relationships among variables while simultaneously changing the distribution of the errors. Given these repercussions, we clarify the nature of certain data transformations and strongly recommend the use of data transformations when they can enhance the interpretation of effect sizes. Accessed 5,515 times on https://pareonline.net from October 11, 2017 to December 31, 2019. For downloads from January 1, 2020 forward, please click on the PlumX Metrics link to the right
Magnetic domain walls in constrained geometries
Magnetic domain walls have been studied in micrometer-sized Fe20Ni80 elements
containing geometrical constrictions by spin-polarized scanning electron
microscopy and numerical simulations. By controlling the constriction
dimensions, the wall width can be tailored and the wall type modified. In
particular, the width of a 180 degree Neel wall can be strongly reduced or
increased by the constriction geometry compared with the wall in unconstrained
systems.Comment: 4 pages, 6 figure
The influence of the cluster environment on the star formation efficiency of 12 Virgo spiral galaxies
The influence of the environment on gas surface density and star formation
efficiency of cluster spiral galaxies is investigated. We extend previous work
on radial profiles by a pixel-to pixel analysis looking for asymmetries due to
environmental interactions. The star formation rate is derived from GALEX UV
and Spitzer total infrared data. As in field galaxies, the star formation rate
for most Virgo galaxies is approximately proportional to the molecular gas
mass. Except for NGC 4438, the cluster environment does not affect the star
formation efficiency with respect to the molecular gas. Gas truncation is not
associated with major changes in the total gas surface density distribution of
the inner disk of Virgo spiral galaxies. In three galaxies, possible increases
in the molecular fraction and the star formation efficiency with respect to the
total gas, of factors of 1.5 to 2, are observed on the windward side of the
galactic disk. A significant increase of the star formation efficiency with
respect to the molecular gas content on the windward side of ram
pressure-stripped galaxies is not observed. The ram-pressure stripped
extraplanar gas of 3 highly inclined spiral galaxies shows a depressed star
formation efficiency with respect to the total gas, and one of them (NGC 4438)
shows a depressed rate even with respect to the molecular gas. The
interpretation is that stripped gas loses the gravitational confinement and
associated pressure of the galactic disk, and the gas flow is diverging, so the
gas density decreases and the star formation rate drops. However, the stripped
extraplanar gas in one highly inclined galaxy (NGC 4569) shows a normal star
formation efficiency with respect to the total gas. We propose this galaxy is
different because it is observed long after peak pressure, and its extraplanar
gas is now in a converging flow as it resettles back into the disk.Comment: 34 pages, 24 figures, accepted for publication by A&
Heavy Quarkonia and Quark Drip Lines in Quark-Gluon Plasma
Using the potential model and thermodynamical quantities obtained in lattice
gauge calculations, we determine the spontaneous dissociation temperatures of
color-singlet quarkonia and the `quark drip lines' which separate the region of
bound states from the unbound region. The dissociation temperatures
of and in quenched QCD are found to be 1.62 and
respectively, in good agreement with spectral function analyses. The
dissociation temperature of in full QCD with 2 flavors is found to be
1.42. For possible bound quarkonium states with light quarks, the
characteristics of the quark drip lines severely limit the stable region close
to the phase transition temperature. Bound color-singlet quarkonia with light
quarks may exist very near the phase transition temperature if their effective
quark mass is of the order of 300-400 MeV and higher.Comment: 8 pages, 2 figures, in LaTex, invited talk presented at the
International Conference on Strangeness in Quark Matter, UCLA, March 26-31,
200
X-ray Observations of Parsec-Scale Tails behind Two Middle-Aged Pulsars
Chandra and XMM-Newton resolved extremely long tails behind two middle-aged
pulsars, J1509-5850 and J1740+1000. The tail of PSR J1509-5850 is discernible
up to 5.6' from the pulsar (6.5 pc at a distance of 4 kpc), with a flux of
2*10^{-13} erg s^{-1} cm^{-2} in 0.5-8 keV. The tail spectrum fits an absorbed
power-law (PL) model with the photon index of 2.3\pm0.2, corresponding to the
0.5-8 keV luminosity of 1*10^{33} ergs s^{-1}, for n_H= 2.1*10^{22} cm^{-2}.
The tail of PSR J1740+1000 is firmly detected up to 5' (2 pc at a 1.4 kpc
distance), with a flux of 6*10^{-14} ergs cm^{-2} s^{-1} in 0.4-10 keV. The PL
fit yields photon index of 1.4-1.5 and n_H=1*10^{21} cm^{-2}. The large extent
of the tails suggests that the bulk flow in the tails starts as mildly
relativistic downstream of the termination shock, and then gradually
decelerates. Within the observed extent of the J1509-5850 tail, the average
flow speed exceeds 5,000 km s^{-1}, and the equipartition magnetic field is a
few times 10^{-5} G. For the J1740+1000 tail, the equipartition field is a
factor of a few lower. The harder spectrum of the J1740+1000 tail implies
either less efficient cooling or a harder spectrum of injected electrons. For
the high-latitude PSR J1740+1000, the orientation of the tail on the sky shows
that the pulsar is moving toward the Galactic plane, which means that it was
born from a halo-star progenitor. The comparison between the J1509 and J1740
tails and the X-ray tails of other pulsars shows that the X-ray radiation
efficiency correlates poorly with the pulsar spin-down luminosity or age. The
X-ray efficiencies of the ram-pressure confined pulsar wind nebulae (PWNe) are
systematically higher than those of PWNe around slowly moving pulsars with
similar spin-down parameters.Comment: 14 pages, 16 figures and 5 table
Indistinguishability of independent single photons
The indistinguishability of independent single photons is presented by
decomposing the single photon pulse into the mixed state of different transform
limited pulses. The entanglement between single photons and outer environment
or other photons induces the distribution of the center frequencies of those
transform limited pulses and makes photons distinguishable. Only the single
photons with the same transform limited form are indistinguishable. In details,
the indistinguishability of single photons from the solid-state quantum emitter
and spontaneous parametric down conversion is examined with two-photon
Hong-Ou-Mandel interferometer. Moreover, experimental methods to enhance the
indistinguishability are discussed, where the usage of spectral filter is
highlighted.Comment: 6 pages, 3 figure
The surface accessibility of α-bungarotoxin monitored by a novel paramagnetic probe
The surface accessibility of {alpha}-bungarotoxin has been investigated by using Gd2L7, a newly designed paramagnetic NMR probe. Signal attenuations induced by Gd2L7 on {alpha}-bungarotoxin C{alpha}H peaks of 1H-13C HSQC spectra have been analyzed and compared with the ones previously obtained in the presence of GdDTPA-BMA. In spite of the different molecular size and shape, for the two probes a common pathway of approach to the {alpha}-bungarotoxin surface can be observed with an equally enhanced access of both GdDTPA-BMA and Gd2L7 towards the protein surface side where the binding site is located. Molecular dynamics simulations suggest that protein backbone flexibility and surface hydration contribute to the observed preferential approach of both gadolinium complexes specifically to the part of the {alpha}-bungarotoxin surface which is involved in the interaction with its physiological target, the nicotinic acetylcholine receptor
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