3,117 research outputs found
Nitric oxide synthase:non-canonical expression patterns
Science can move ahead by questioning established or canonical views and, so it may be with the enzymes, nitric oxide synthases (NOS). Nitric oxide (NO) is generated by NOS isoforms that are often described by their tissue-specific expression patterns. NOS1 (nNOS) is abundant in neural tissue, NOS2 is upregulated in activated macrophages and known as inducible NOS (iNOS), and NOS3 (eNOS) is abundant in endothelium where it regulates vascular tone. These isoforms are described as constitutive or inducible, but in this perspective we question the broad application of these labels. Are there instances where âconstitutiveâ NOS (NOS1 and NOS3) are inducibly expressed; conversely, are there instances where NOS2 is constitutively expressed? NOS1 and NOS3 inducibility may be linked to post-translational regulation, making their actual patterns activity much more difficult to detect. Constitutive NOS2 expression has been observed in several tissues, especially the human pulmonary epithelium where it may regulate airway tone. These data suggest that expression of the three NOS enzymes may include non-established patterns. Such information should be useful in designing strategies to modulate these important enzymes in different disease states
Porosities and dimensions of measures
We introduce a concept of porosity for measures and study relations between
dimensions and porosities for two classes of measures: measures on which
satisfy the doubling condition and strongly porous measures on .Comment: Jarvenpaa = J\"arvenp\"a\"
Infrared Photometry of Starless Dense Cores
Deep JHKs photometry was obtained towards eight dense molecular cores and J-H
vs. H-Ks color-color plots are presented. Our photometry, sensitive to the
detection of a 1 solar mass, 1 X 10^6 year old star through approx. 35 - 50
magnitudes of visual extinction, shows no indication of the presence of
star/disk systems based on J-H vs. H-Ks colors of detected objects. The stars
detected towards the cores are generally spatially anti-correlated with core
centers suggesting a background origin, although we cannot preclude the
possibility that some stars detected at H and Ks alone, or Ks alone, are not
low mass stars or brown dwarfs (< 0.3 Solar Masses) behind substantial amounts
of visual extinction (e.g. 53 magnitudes for L183B). Lower limits to optical
extinctions are estimated for the detected background stars, with high
extinctions being encountered, in the extreme case ranging up to at least Av =
46, and probably higher. The extinction data are used to estimate cloud masses
and densities which are comparable to those determined from molecular line
studies. Variations in cloud extinctions are consistent with a systematic
nature to cloud density distributions and column density variations and
extinctions are found to be consistent with submillimeter wave continuum
studies of similar regions. The results suggest that some cores have achieved
significant column density contrasts (approx. 30) on sub-core scales (approx.
0.05 pc) without having formed known stars.Comment: 44 pages including tables and figures, accepted ApJ, March 24, 200
The Core-Collapse Supernova Rate in Arp299 Revisited
We present a study of the CCSN rate in nuclei A and B1 of the luminous
infrared galaxy Arp299, based on 11 years of Very Large Array monitoring of
their radio emission at 8.4 GHz. Significant variations in the nuclear radio
flux density can be used to identify the CCSN activity in the absence of
high-resolution very long baseline interferometry observations. In the case of
the B1-nucleus, the small variations in its measured diffuse radio emission are
below the fluxes expected from radio supernovae, thus making it well-suited to
detect RSNe through flux density variability. In fact, we find strong evidence
for at least three RSNe this way, which results in a lower limit for the CCSN
rate of 0.28 +/- 0.16 per year. In the A-nucleus, we did not detect any
significant variability and found a SN detection threshold luminosity which
allows only the detection of the most luminous RSNe known. Our method is
basically blind to normal CCSN explosions occurring within the A-nucleus, which
result in too small variations in the nuclear flux density, remaining diluted
by the strong diffuse emission of the nucleus itself. Additionally, we have
attempted to find near-infrared counterparts for the earlier reported RSNe in
the Arp299 nucleus A, by comparing NIR adaptive optics images from the Gemini-N
telescope with contemporaneous observations from the European VLBI Network.
However, we were not able to detect NIR counterparts for the reported radio SNe
within the innermost regions of nucleus A. While our NIR observations were
sensitive to typical CCSNe at 300 mas from the centre of the nucleus A,
suffering from extinction up to A_v~15 mag, they were not sensitive to such
highly obscured SNe within the innermost nuclear regions where most of the EVN
sources were detected. (abridged)Comment: 12 pages, 4 figures and 7 tables. Accepted for publication in MNRA
Differentiability of fractal curves
While self-similar sets have no tangents at any single point, self-affine
curves can be smooth. We consider plane self-affine curves without double
points and with two pieces. There is an open subset of parameter space for
which the curve is differentiable at all points except for a countable set. For
a parameter set of codimension one, the curve is continuously differentiable.
However, there are no twice differentiable self-affine curves in the plane,
except for parabolic arcs
Supernovae and radio transients in M 82
We present optical and near-infrared (IR) photometry and near-IR spectroscopy
of SN 2004am, the only optically detected supernova (SN) in M 82. These
demonstrate that SN 2004am was a highly reddened type II-P SN similar to the
low luminosity type II-P events such as SNe 1997D and 2005cs. We show that SN
2004am was located coincident with the obscured super star cluster M 82-L, and
from the cluster age infer a progenitor mass of 12 +7/-3 Msun. In addition to
this, we present a high spatial resolution Gemini-N K-band adaptive optics
image of the site of SN 2008iz and a second transient of uncertain nature, both
detected so far only at radio wavelengths. Using image subtraction techniques
together with archival data from the Hubble Space Telescope, we are able to
recover a near-IR transient source co-incident with both objects. We find the
likely extinction towards SN 2008iz to be not more than Av ~ 10. The nature of
the second transient remains elusive and we regard an extremely bright
microquasar in M 82 as the most plausible scenario.Comment: 14 pages, 8 figures, accepted for publication in MNRA
Infrared Spectroscopy of the Diffuse Ionized Halo of NGC 891
We present infrared spectroscopy from the Spitzer Space Telescope at one disk
position and two positions at a height of 1 kpc from the disk in the edge-on
spiral NGC 891, with the primary goal of studying halo ionization. Our main
result is that the [Ne III]/[Ne II] ratio, which provides a measure of the
hardness of the ionizing spectrum free from the major problems plaguing optical
line ratios, is enhanced in the extraplanar pointings relative to the disk
pointing. Using a 2D Monte Carlo-based photo-ionization code which accounts for
the effects of radiation field hardening, we find that this trend cannot be
reproduced by any plausible photo-ionization model, and that a secondary source
of ionization must therefore operate in gaseous halos. We also present the
first spectroscopic detections of extraplanar PAH features in an external
normal galaxy. If they are in an exponential layer, very rough emission
scale-heights of 330-530 pc are implied for the various features. Extinction
may be non-negligible in the midplane and reduce these scale-heights
significantly. There is little significant variation in the relative emission
from the various features between disk and extraplanar environment. Only the
17.4 micron feature is significantly enhanced in the extraplanar gas compared
to the other features, possibly indicating a preference for larger PAHs in the
halo.Comment: 35 pages in ApJ preprint format, 8 figures, accepted for publication
in ApJ. Minor change to Introduction to give appropriate credit to earlier,
related wor
Detection efficiency and photometry in supernova surveys - the Stockholm VIMOS Supernova Survey I
The aim of the work presented in this paper is to test and optimise supernova
detection methods based on the optimal image subtraction technique. The main
focus is on applying the detection methods to wide field supernova imaging
surveys and in particular to the Stockholm VIMOS Supernova Survey (SVISS). We
have constructed a supernova detection pipeline for imaging surveys. The core
of the pipeline is image subtraction using the ISIS 2.2 package. Using real
data from the SVISS we simulate supernovae in the images, both inside and
outside galaxies. The detection pipeline is then run on the simulated frames
and the effects of image quality and subtraction parameters on the detection
efficiency and photometric accuracy are studied. The pipeline allows efficient
detection of faint supernovae in the deep imaging data. It also allows
controlling and correcting for possible systematic effects in the SN detection
and photometry. We find such a systematic effect in the form of a small
systematic flux offset remaining at the positions of galaxies in the subtracted
frames. This offset will not only affect the photometric accuracy of the
survey, but also the detection efficiencies. Our study has shown that ISIS 2.2
works well for the SVISS data. We have found that the detection efficiency and
photometric accuracy of the survey are affected by the stamp selection for the
image subtraction and by host galaxy brightness. With our tools the subtraction
results can be further optimised, any systematic effects can be controlled and
photometric errors estimated, which is very important for the SVISS, as well as
for future SN searches based on large imaging surveys such as Pan-STARRS and
LSST.Comment: 17 pages, 10 figure, accepted for publication in A&
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