770 research outputs found
Empirical extinction coefficients for the GALEX, SDSS, 2MASS and WISE passbands
Using the "standard pair" technique of paring stars of almost nil and high
extinction but otherwise of almost identical stellar parameters from the SDSS,
and combing the SDSS, GALEX, 2MASS and WISE photometry ranging from the far UV
to the mid-IR, we have measured dust reddening in the FUV-NUV, NUV-u, u-g, g-r,
r-i, i-z, z-J, J-H, H-Ks, Ks-W1 and W1-W2 colors for thousands of Galactic
stars. The measurements, together with the E(B-V) values given by Schlegel et
al. (1998), allow us to derive the observed, model-free reddening coefficients
for those colors. The results are compared with previous measurements and the
predictions of a variety of Galactic reddening laws. We find that 1) The dust
reddening map of Schlegel et al. (1998) over-estimates E(B-V) by about 14 per
cent, consistent with the recent work of Schlafly et al. (2010) and Schlafly &
Finkbeiner (2011); 2) All the new reddening coefficients, except those for
NUV-u and u-g, prefer the R(V) = 3.1 Fitzpatrick reddening law rather than the
R(V) = 3.1 CCM and O'Donnell (O'Donnell 1994) reddening laws. Using the Ks-band
extinction coefficient predicted by the R(V) = 3.1 Fitzpatrick law and the
observed reddening coefficients, we have deduced new extinction coefficients
for the FUV, NUV, u, g, r, i, z, J, H, W1 and W2 passbands. We recommend that
the new reddening and extinction coefficients should be used in the future and
an update of the Fitzpatrick reddening law in the UV is probably necessary. We
stress however that the FUV- and NUV-band coefficients should be used with
caution given their relatively large measurement uncertainties. Finally,
potential applications of the "standard pair" technique with the LAMOST
Galactic surveys are discussed.Comment: 13 pages, 9 figures, accepted to MNRA
Proposal of Direct Search for Strongly Bound States of ppbar, npbar Systems with High Intensity and Collective pbar beam
In this letter, we discuss the possibility to look for the direct evidence of
the existence of the ppbar and npbar bound states. Measurement of the single
\gamma ray from the ppbar and npbar systems at rest can directly confirm
whether the X(1860) and X(1835) are the resonances which are strongly coupled
to ppbar. In addition to the neutral candidate, a charged resonance is
also proposed to be searched for in npbar channel. We find that the data from
the Crystal Barrel experiment at LEAR/CERN can be used to confirm the X(1835)
observed by BES Collaboration. The possibility of measuring the
spectrum below 100 MeV at the new experiment with cold high intensity \pbar
beam at GSI is discussed. These new techniques can be used to probe the
structure of the X(1860) and X(1835) in the future.Comment: Accepted by Mod. Phys. Lett.
Empirical metallicity-dependent calibrations of effective temperature against colours for dwarfs and giants based on interferometric data
We present empirical metallicity-dependent calibrations of effective
temperature against colours for dwarfs of luminosity classes IV and V and for
giants of luminosity classes II and III, based on a collection from the
literature of about two hundred nearby stars with direct effective temperature
measurements of better than 2.5 per cent. The calibrations are valid for an
effective temperature range 3,100 - 10,000 K for dwarfs of spectral types M5 to
A0 and 3,100 - 5,700 K for giants of spectral types K5 to G5. A total of
twenty-one colours for dwarfs and eighteen colours for giants of bands of four
photometric systems, i.e. the Johnson (), the Cousins
(), the Sloan Digital Sky Survey (SDSS, ) and the Two
Micron All Sky Survey (2MASS, ), have been calibrated. Restricted
by the metallicity range of the current sample, the calibrations are mainly
applicable for disk stars ([Fe/H]). The normalized percentage
residuals of the calibrations are typically 2.0 and 1.5 per cent for dwarfs and
giants, respectively. Some systematic discrepancies at various levels are found
between the current scales and those available in the literature (e.g. those
based on the infrared flux method IRFM or spectroscopy). Based on the current
calibrations, we have re-determined the colours of the Sun. We have also
investigated the systematic errors in effective temperatures yielded by the
current on-going large scale low- to intermediate-resolution stellar
spectroscopic surveys. We show that the calibration of colour ()
presented in the current work provides an invaluable tool for the estimation of
stellar effective temperature for those on-going or upcoming surveys.Comment: 28 pages, 19 figures, 8 tables, accepted for publication in MNRA
Damage Effects of Fluid filled Submunitions by High Velocity Projectile Impact
A series of tests investigating the damage effects of fluid-filled submunitions by high velocity projectile impact were conducted. An analytical model is presented, in which the yaw angle of the projectile was taken into account. Based on the analytical model, the influence of the strike angle, hit-point offset distance and projectile length to diameter ratio on submunition damage ratio were predicted. The analytical results showed a good agreement with the experiments. The submunition damage ratio strongly depends on the hit-point offset distance, showing a significant decrease with increasing hit-point offset distance. For large hit-point offset distance, increasing the length to diameter ratio of the projectile will effectively improve the submunition damage ratio. There is an appropriate yaw angle of the projectile in which the submunition damage ratio will be maximal
Searching for doubly charmed tetraquark candidates and in decays
In this work, we propose to search for the exotic doubly charmed meson
and its analog in decays, which provide a
good environment for the formation of the exotic state containing double charm
quarks. Within the molecular scheme, the production of and
through various rescattering processes with different
intermediate states are investigated. For the moderate values of model
parameters, the branching ratios of decaying into , , and
are estimated to be of the order of ,
, and , respectively, which may be tested by future
experiments.Comment: 9 pages, 8 figure
Spatio-temporal expression of a novel neuron-derived neurotrophic factor (NDNF) in mouse brains during development
<p>Abstract</p> <p>Background</p> <p>Neuron-derived neurotrophic factor (NDNF) is evolutionarily well conserved, being present in invertebrate animals such as the nematode, <it>Caenorhabditis elegans</it>, as well as in the fruit fly, <it>Drosophila melanogaster</it>. Multiple cysteines are conserved between species and secondary structure prediction shows that NDNF is mainly composed of beta-strands. In this study, we aimed to investigate the function of NDNF.</p> <p>Results</p> <p>NDNF is a glycosylated, disulfide-bonded secretory protein that contains a fibronectin type III domain. NDNF promoted migration and growth and elicited neurite outgrowth of mouse hippocampal neurons in culture. NDNF also protected cultured hippocamal neurons against excitotoxicity and amyloid beta-peptide toxicity. Western blotting showed that NDNF was exclusively expressed in the brain and spinal cord. Immunostaining indicated that NDNF was expressed by neurons and not by astrocytes. Cajal-Retzius cells, cortex neurons, hippocampus neurons, olfactory mitral cells, cerebellar purkinje cells, cerebellar granular cells and spinal neurons were found to be NDNF-positive. NDNF expression was observed in the neurons during development.</p> <p>Conclusions</p> <p>The results of this study indicated that NDNF is a novel neurotrophic factor derived from neurons that may be useful in the treatment of neuronal degeneration diseases and nerve injuries.</p
Radio Polarization of BL Lacertae objects
In this paper, using the database of the university of Michigan Radio
Astronomy Observatory (UMRAO) at three (4.8 GHz, 8 GHZ, and 14.5 GHz) radio
frequencies, we studied the polarization properties for 47 BL Lacertae
objects(38 radio selected BL Lacertae objects, 7 X-ray selected BL Lacertae,
and two inter-middle objects (Mkn 421 and Mkn 501), and found that (1) The
polarizations at higher radio frequency is higher than those at lower
frequency, (2) The variability of polarization at higher radio frequency is
higher than those at lower frequency, (3) The polarization is correlated with
the radio spectral index, and (4) The polarization is correlated with
core-dominance parameter for those objects with known core-dominance parameters
suggesting that the relativistic beaming could explain the polarization
characteristic of BL Lacs.Comment: 5 pages, 3 figures, 1 table. PASJ, in pres
2-[1-(4-Chlorobenzoyl)pyrrolidin-2-yl]-4,4,5,5-tetramethyl-4,5-dihydroimidazole-1-oxyl-3-oxide
In the title compound, C18H23ClN3O3, the imidazole ring system has an envelope conformation, whereas the nitronyl nitroxide unit displays a half-chair or twisted conformation. In the crystal, C—H⋯O hydrogen bonds build up a three-dimensional network
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