407 research outputs found
An unconditional maximum likelihood test for a unit root
We investigate a test for unit roots in autoregressive time series based on maximization of the unconditional likelihood. This is the likelihood function appropriate for stationary time series. While this function is the true likelihood only under the stationary alternative, it can nevertheless be maximized for any data including data from a unit root process. It thus gives a way to test for unit roots, provided percentill~s can be calculated. For models with estimated means, the power of the new test is better than that of some currently popular tests
HRTEM study of a new non-stoichiometric BaTiO(3-δ) structure
BaTiO3-based multilayer ceramic capacitors (MLCCs) with Ni internal electrodes are co-fired in
reducing atmospheres to avoid oxidation of the electrode. Although dielectric materials are doped by
acceptor, donor and amphoteric dopants to minimize the oxygen vacancy content, there is still a
large concentration of oxygen vacancies that are accommodated in the BaTiO3 active layers. In
general, ABO3 perovskites demonstrates a strong ability to accommodate the oxygen vacancies and
maintain a regular pseudo-cubic structure. Oxygen deficient barium titanate can be transformed to a
hexagonal polymorph (h-BT) at high temperatures1,2. In this paper, we report the new modulated and
long range ordered structures of non-stoichiometric BaTiO3-δ that are observed in the electrically
degraded Ni-BaTiO3 MLCCs at low temperature
G88-876 Ridge Plant Systems: Equipment
Ridge plant systems, ridge cleaning equipment, planter stabilizing attachments, cultivation and ridge management are discussed here. Ridge plant systems are methods of planting crops into a ridge formed during cultivation of the previous crop. Such systems combine tillage and herbicides to control weeds. Weed seed and residue lying on the soil surface are pushed from the ridge to the area between the rows by row-cleaning devices on the planter. Crop seed is planted into the old row in a cleanly tilled strip at an elevation slightly higher than the row middles. A band application of herbicide behind the planter typically is used in the row for weed control. Crop cultivation controls weeds between the rows and rebuilds ridges for the following year
The large-scale shock in the cluster of galaxies Hydra A
We analyzed a deep XMM-Newton observation of the cluster of galaxies Hydra A,
focusing on the large-scale shock discovered as a surface brightness
discontinuity in Chandra images. The shock front can be seen both in the
pressure map and in temperature profiles in several sectors. The Mach numbers
determined from the temperature jumps are in good agreement with the Mach
numbers derived from EPIC/pn surface brightness profiles and previously from
Chandra data and are consistent with M~1.3. The estimated shock age in the
different sectors using a spherically symmetric point explosion model ranges
between 130 and 230 Myr and the outburst energy between 1.5 and 3e61 ergs. The
shape of the shock seen in the pressure map can be approximated with an ellipse
centered 70 kpc towards the NE from the cluster center. We aimed to develop a
better model that can explain the offset between the shock center and the AGN
and give a consistent result on the shock age and energy. To this end, we
performed 3D hydrodynamical simulations in which the shock is produced by a
symmetrical pair of AGN jets launched in a spherical galaxy cluster. As an
explanation of the observed offset of the shock center, we consider large-scale
bulk flows in the intracluster medium. The simulation successfully reproduces
the size, ellipticity, and average Mach number of the observed shock front. The
predicted age of the shock is 160 Myr and the total input energy 3e61 erg. Both
values are within the range determined by the spherically symmetric model.
Matching the observed 70 kpc offset of the shock ellipse from the cluster
center requires large-scale coherent motions with a high velocity of 670 km/s.
We discuss the feasibility of this scenario and offer alternative ways to
produce the offset and to further improve the simulation.Comment: 14 pages, accepted for publication in A&A, minor revision compared to
previous versio
The elemental abundances in the intracluster medium as observed with XMM-Newton
XMM-Newton observations of 19 galaxy clusters are used to measure the
elemental abundances and their spatial distributions in the intracluster
medium. The sample mainly consists of X-ray bright and relaxed clusters with a
cD galaxy. Along with detailed Si, S and Fe radial abundance distributions
within 300-700 kpc in radius, the O abundances are accurately derived in the
central region of the clusters. The Fe abundance maxima towards the cluster
center, possibly due to the metals from the cD galaxy,are spatially resolved.
The Si and S abundances also exhibit central increases in general, resulting in
uniform Fe-Si-S ratios within the cluster. In contrast, the O abundances are in
general uniform over the cluster. The mean O to Fe ratio within the cluster
core is sub-solar, while that of the cluster scale is larger than the solar
ratio. These measurements indicate that most of the Fe-Si-S and O in the
intracluster medium have different origins, presumably in supernovae Ia and II,
respectively. The obtained Fe and O mass are also used to discuss the past star
formation history in clusters.Comment: Accepted for publication in Astronomy and Astrophysic
A sample of X-ray emitting normal galaxies from the BMW -- HRI Catalogue
We have obtained a sample of 143 normal galaxies with X-ray luminosity in the
range erg s from the cross-correlation of the ROSAT
HRI Brera Multi-scale Wavelet (BMW -- HRI) Catalogue with the Lyon-Meudon
Extragalactic Database (LEDA). We find that the average X-ray properties of
this sample are in good agreement with those of other samples of galaxies in
the literature. We have selected a complete flux limited serendipitous sample
of 32 galaxies from which we have derived the logN-logS distribution of normal
galaxies in the flux range erg cm s.
The resulting distribution is consistent with the euclidean -1.5 slope.
Comparisons with other samples, such as the Extended Medium Sensitivity Survey,
the ROSAT All Sky Survey, the XMM - Newton/2dF survey and the Chandra Deep
Field Survey indicate that the logN-logS distribution of normal galaxies is
consistent with an euclidean slope over a flux range of about 6 decades.Comment: Accepted for publication in A&A. 19 pages, 7 figures. Full resolution
version of Figure 2 is available at http://www.brera.mi.astro.it/~tajer
Measuring the non-thermal pressure in early type galaxy atmospheres: A comparison of X-ray and optical potential profiles in M87 and NGC1399
We compare the gravitational potential profiles of the elliptical galaxies
NGC 4486 (M87) and NGC 1399 (the central galaxy in the Fornax cluster) derived
from X-ray and optical data. This comparison suggests that the combined
contribution of cosmic rays, magnetic fields and micro-turbulence to the
pressure is ~10% of the gas thermal pressure in the cores of NGC 1399 and M87,
although the uncertainties in our model assumptions (e.g., spherical symmetry)
are sufficiently large that the contribution could be consistent with zero. In
the absence of any other form of non-thermal pressure support, these upper
bounds translate into upper limits on the magnetic field of ~10-20 muG at a
distance of 1'-2' from the centers of NGC1399 and M87. We show that these
results are consistent with the current paradigm of cool cluster cores, based
on the assumption that AGN activity regulates the thermal state of the gas by
injecting energy into the intra-cluster medium. The limit of ~10-20% on the
energy density in the form of relativistic protons applies not only to the
current state of the gas, but essentially to the entire history of the
intra-cluster medium, provided that cosmic ray protons evolve adiabatically and
that their spatial diffusion is suppressed.Comment: Accepted for MNRAS. 19 pages; 14 figures; expanded version in
response to comments from the refere
High-content siRNA screening of the kinome identifies kinases involved in Alzheimer's disease-related tau hyperphosphorylation
<p>Abstract</p> <p>Background</p> <p>Neurofibrillary tangles (NFT), a cardinal neuropathological feature of Alzheimer's disease (AD) that is highly correlated with synaptic loss and dementia severity, appear to be partly attributable to increased phosphorylation of the microtubule stabilizing protein tau at certain AD-related residues. Identifying the kinases involved in the pathologic phosphorylation of tau may provide targets at which to aim new AD-modifying treatments.</p> <p>Results</p> <p>We report results from a screen of 572 kinases in the human genome for effects on tau hyperphosphorylation using a loss of function, high-throughput RNAi approach. We confirm effects of three kinases from this screen, the eukaryotic translation initiation factor 2 α kinase 2 (EIF2AK2), the dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 1A (DYRK1A), and the A-kinase anchor protein 13 (AKAP13) on tau phosphorylation at the 12E8 epitope (serine 262/serine 356). We provide evidence that EIF2AK2 effects may result from effects on tau protein expression, whereas DYRK1A and AKAP13 are likely more specifically involved in tau phosphorylation pathways.</p> <p>Conclusions</p> <p>These findings identify novel kinases that phosphorylate tau protein and provide a valuable reference data set describing the kinases involved in phosphorylating tau at an AD-relevant epitope.</p
NoSOCS in SDSS. I. Sample Definition and Comparison of Mass Estimates
We use Sloan Digital Sky Survey (SDSS) data to investigate galaxy cluster
properties of systems first detected within DPOSS. With the high quality
photometry of SDSS we derived new photometric redshifts and estimated richness
and optical luminosity. For a subset of low redshift () clusters, we
have used SDSS spectroscopic data to identify groups in redshift space in the
region of each cluster, complemented with massive systems from the literature
to assure the continuous mass sampling. A method to remove interlopers is
applied, and a virial analysis is performed resulting in estimates of velocity
dispersion, mass, and a physical radius for each low- system. We discuss the
choice of maximum radius and luminosity range in the dynamical analysis,
showing that a spectroscopic survey must be complete to at least M if one
wishes to obtain accurate and unbiased estimates of velocity dispersion and
mass. We have measured X-ray luminosity for all clusters using archival data
from RASS. For a smaller subset (twenty-one clusters) we selected temperature
measures from the literature and estimated mass from the M-T relation,
finding that they show good agreement with the virial estimate. However, these
two mass estimates tend to disagree with the caustic results. We measured the
presence of substructure in all clusters of the sample and found that clusters
with substructure have virial masses higher than those derived from T. This
trend is not seen when comparing the caustic and X-ray masses. That happens
because the caustic mass is estimated directly from the mass profile, so it is
less affected by substructure.Comment: 21 pages, 17 figures, 5 tables, Accepted to MNRA
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