825 research outputs found
Extensive population synthesis of isolated neutron stars with field decay
We perform population synthesis studies of different types of neutron stars
taking into account the magnetic field decay. For the first time, we confront
our results with observations using {\it simultaneously} the Log N -- Log S
distribution for nearby isolated neutron stars, the Log N -- Log L distribution
for magnetars, and the distribution of radio pulsars in the --
diagram. We find that our theoretical model is consistent with all sets of data
if the initial magnetic field distribution function follows a log-normal law
with and . The
typical scenario includes about 10% of neutron stars born as magnetars,
significant magnetic field decay during the first million years of a NS life.
Evolutionary links between different subclasses may exist, although robust
conclusions are not yet possible.
We apply the obtained field distribution and the model of decay to study
long-term evolution of neuton stars till the stage of accretion from the
interstellar medium. It is shown that though the subsonic propeller stage can
be relatively long, initially highly magnetized neutron stars ( G) reach the accretion regime within the Galactic lifetime if their
kick velocities are not too large. The fact that in previous studies made 10
years ago, such objects were not considered results in a slight increase of the
Accretor fraction in comparison with earlier conclusions. Most of the neutron
stars similar to the Magnificent seven are expected to become accreting from
the interstellar medium after few billion years of their evolution. They are
the main predecestors of accreting isolated neutron stars.Comment: 4 pages, conference "Astrophysics of Neutron Stars - 2010" in honor
of M. Ali Alpar, Izmir, Turke
Long, Bellows-Free Vertical Helium Transfer Lines for the LHC Cryogenic System
The cryogenic system for the Large Hadron Collider (LHC) under construction at CERN will include four new vertical helium transfer lines connecting the new helium refrigerators to the underground areas. These four transfer lines will be installed between a refrigerator on the surface and an interconnection box located 80 m to 145 m underground. They consist of a vacuum jacket, a thermal screen and four internal helium pipes. Due to space and accessibility limitations, the lines have been specified without bellows or bends of any kind in the long vertical part; the thermal contractions must be compensated at the surface only. The displacement due to these contractions amounts to more than 35 cm in one case, and all four internal pipes, as well as the thermal screen, must be able to contract and expand independently. The lines will be built and installed by a consortium of Linde AG and Babcock Noell Nuclear GmbH. Their technical design choices are presented together with expected performance
X-ray and near-infrared observations of the middle-aged pulsar B1055-52, its multiwavelength spectrum, and proper motion
Previous observations of the middle-aged -ray, X-ray, and radio
pulsar B1055-52 indicated some peculiarities, such as a suspected changing of
the X-ray flux and spectral parameters, a large excess of the alleged thermal
component of the ultraviolet (UV) spectrum over the Rayleigh-Jeans extension of
the X-ray thermal spectrum, and a possible double break in the nonthermal
spectral component between the optical and X-ray bands. We observed PSR
B1055-52 with the XMM-Newton observatory in X-rays and the Hubble Space
Telescope in near-infrared (NIR). The analysis of the XMM-Newton observations
does not support the notion of long-term changes in the X-ray flux and
broad-band X-ray spectrum of the pulsar. Using an observing mode less affected
by background noise than the previous XMM-Newton observations, we constrain the
power-law (PL) spectral index as () in the energy band 3-10 keV. From the NIR-optical data
we obtain a PL slope for the color index
mag. The slopes and fluxes of the NIR-optical and X-ray
nonthermal spectra suggest that the NIR through X-ray emission can be described
by the same PL and is generated by the same mechanism, unlike the pulsar's
-ray emission. The excess of the UV thermal component over the
extension of the X-ray thermal component became smaller but did not disappear,
indicating a non-uniformity of the bulk surface temperature. The NIR data also
enable us to accurately measure the proper motion with values and .Comment: ApJ accepted; 19 pages, 10 Figures, 5 Table
Space cowboys odyssey: beyond the Gould Belt
We present our new advanced model for population synthesis of close-by
cooling NSs. Detailed treatment of the initial spatial distribution of NS
progenitors and a detailed ISM structure up to 3 kpc give us an opportunity to
discuss the strategy to look for new isolated cooling NSs. Our main results in
this respect are the following: new candidates are expected to be identified
behind the Gould Belt, in directions to rich OB associations, in particular in
the Cygnus-Cepheus region; new candidates, on average, are expected to be
hotter than the known population of cooling NS. Besides the usual approach
(looking for soft X-ray sources), the search in 'empty' -ray error
boxes or among run-away OB stars may yield new X-ray thermally emitting NS
candidates.Comment: 3 pages, 2 figures, proceedings of the conference "40 Years of
Pulsars ", 12-17 August 2007, Montreal, Canad
The Magnificent Seven in the dusty prairie -- The role of interstellar absorption on the observed neutron star population
The Magnificent Seven have all been discovered by their exceptional soft X-ray spectra and high ratios of X-ray to optical flux. They all are considered to be nearby sources. Searching for similar neutron stars with larger distances, one expects larger interstellar absorption resulting in harder X-ray counterparts. Current interstellar absorption treatment depends on chosen abundances and scattering cross-sections of the elements as well as on the 3D distribution of the interstellar medium. After a discussion of these factors we use the comprehensive 3D measurements of the Local Bubble by Lallement et al. 2003 to construct two simple models of the 3D distribution of the hydrogen column density. We test these models by using a set of soft X-ray sources with known distances. Finally, we discuss possible applications for distance estimations and population synthesis studies
Observational Analysis of Cloud and Precipitation in Midlatitude Cyclones: Northern Versus Southern Hemisphere Warm Fronts
Extratropical cyclones are responsible for most of the precipitation and wind damage in the midlatitudes during the cold season, but there are still uncertainties on how they will change in a warming climate. An ubiquitous problem amongst General Circulation Models (GCMs) is a lack of cloudiness over the southern oceans that may be in part caused by a lack of clouds in cyclones. We analyze CloudSat, CALIPSO and AMSR-E observations for 3 austral and boreal cold seasons and composite cloud frequency of occurrence and precipitation at the warm fronts for northern and southern hemisphere oceanic cyclones. We find that cloud frequency of occurrence and precipitation rate are similar in the early stage of the cyclone life cycle in both northern and southern hemispheres. As cyclones evolve and reach their mature stage, cloudiness and precipitation at the warm front increase in the northern hemisphere but decrease in the southern hemisphere. This is partly caused by lower amounts of precipitable water being available to southern hemisphere cyclones, and smaller increases in wind speed as the cyclones evolve. Southern hemisphere cloud occurrence at the warm front is found to be more sensitive to the amount of moisture in the warm sector than to wind speeds. This suggests that cloudiness in southern hemisphere storms may be more susceptible to changes in atmospheric water vapor content, and thus to changes in surface temperature than their northern hemisphere counterparts. These differences between northern and southern hemisphere cyclones are statistically robust, indicating A-Train-based analyses as useful tools for evaluation of GCMs in the next IPCC report
Nothing to hide: An X-ray survey for young stellar objects in the Pipe Nebula
We have previously analyzed sensitive mid-infrared observations to establish
that the Pipe Nebula has a very low star-formation efficiency. That study
focused on YSOs with excess infrared emission (i.e, protostars and pre-main
sequence stars with disks), however, and could have missed a population of more
evolved pre-main sequence stars or Class III objects (i.e., young stars with
dissipated disks that no longer show excess infrared emission). Evolved
pre-main sequence stars are X-ray bright, so we have used ROSAT All-Sky Survey
data to search for diskless pre-main sequence stars throughout the Pipe Nebula.
We have also analyzed archival XMM-Newton observations of three prominent areas
within the Pipe: Barnard 59, containing a known cluster of young stellar
objects; Barnard 68, a dense core that has yet to form stars; and the Pipe
molecular ring, a high-extinction region in the bowl of the Pipe. We
additionally characterize the X-ray properties of YSOs in Barnard 59. The ROSAT
and XMM-Newton data provide no indication of a significant population of more
evolved pre-main sequence stars within the Pipe, reinforcing our previous
measurement of the Pipe's very low star formation efficiency.Comment: Accepted for publication in Ap
Multiple Satellite Observations of Cloud Cover in Extratropical Cyclones
Using cloud observations from NASA Moderate Resolution Imaging Spectroradiometer, Multiangle Imaging Spectroradiometer, and CloudSat-CALIPSO, composites of cloud fraction in southern and northern hemisphere extratropical cyclones are obtained for cold and warm seasons between 2006 and 2010, to assess differences between these three data sets, and between summer and winter cyclones. In both hemispheres and seasons, over the open ocean, the cyclone-centered cloud fraction composites agree within 5% across the three data sets, but behind the cold fronts, or over sea ice and land, the differences are much larger. To supplement the data set comparison and learn more about the cyclones, we also examine the differences in cloud fraction between cold and warm season for each data set. The difference in cloud fraction between cold and warm season southern hemisphere cyclones is small for all three data sets, but of the same order of magnitude as the differences between the data sets. The cold-warm season contrast in northern hemisphere cyclone cloud fractions is similar for all three data sets: in the warm sector, the cold season cloud fractions are lower close to the low, but larger on the equator edge than their warm season counterparts. This seasonal contrast in cloud fraction within the cyclones warm sector seems to be related to the seasonal differences in moisture flux within the cyclones. Our analysis suggests that the three different data sets can all be used confidently when studying the warm sector and warm frontal zone of extratropical cyclones but caution should be exerted when studying clouds in the cold sector
Technical Performance and Energy Intensity of the Electrode-Separator Composite Manufacturing Process
AbstractEnergy storage is one of the key technological factors that determine the success of a sustainable future. Especially green mobility concepts for electric or hybrid electric vehicles highly depend upon storage technologies with high energy density and light-weight materials. At the same time, innovative production processes should be conceived that ensure energy and resource efficient manufacturing of these energy storage devices. This paper focuses on the technical as well as dynamic energetic performance analysis and evaluation of an innovative electrode-separator composite manufacturing process of lithium-ion batteries for automotive applications. The technical performance indicators such as battery capacity and the energy intensity of the manufacturing process are highly dependent upon process parameters, machine and product design. Hence, in-depth process knowledge must be acquired to understand interdependencies between all system components. Thus, the manufacturing process is analysed in terms of its dynamics, and correlations between process parameters, process energy demand and final product properties are assessed. The resulting knowledge is important for the subsequent design of large-scale products and processes involved design, as well as for characterisation of the manufacturing process for life cycle inventory databases or life cycle costing calculations
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