4,899 research outputs found
Cross sections of proton-induced reactions on 152Gd, 155Gd and 159Tb with emphasis on the production of selected Tb radionuclides
Cross sections are presented for various Dy, Tb and Gd radionuclides produced in the proton bombardment
of 159Tb as well as for the reactions 152Gd(p,4n)149Tb and 155Gd(p,4n)152Tb up to 66 MeV. The
experimental excitation functions are compared with theoretical predictions by means of the geometrydependent
hybrid (GDH) model as implemented in the code ALICE/ASH, as well as with values from the
TENDL-2012 library and previous literature experimental data, where available. Physical yields have been
derived for the production of some of the medically important radioterbiums, namely 149Tb (radionuclide
therapy), 152Tb (PET) and 155Tb (SPECT). The indirect production of high-purity 155Tb via the decay of
its precursor 155Dy is reported. The possibility of a large-scale production facility based on a commercial
70 MeV cyclotron is also discussed
The inner radio jet region and the complex environment of SS433
We present multi-frequency VLBA+VLA observations of SS433 at 1.6, 5 and 15
GHz. These observations provide the highest angular resolution radio spectral
index maps ever made for this object. Motion of the components of SS433 during
the observation is detected. In addition to the usual VLBI jet structure, we
detect two radio components in the system at an anomalous position angle. These
newly discovered radio emitting regions might be related to a wind-like
equatorial outflow or to an extension of the accretion disk. We show that the
radio core component is bifurcated with a clear gap between the eastern and
western wings of emission. Modelfitting of the precessing jets and the moving
knots of SS433 shows that the kinematic centre -- i.e. the binary -- is in the
gap between the western and eastern radio core components. Spectral properties
and observed core position shifts suggest that we see a combined effect of
synchrotron self-absorption and external free-free absorption in the innermost
AU-scale region of the source. The spatial distribution of the ionized matter
is probably not spherically symmetric around the binary, but could be
disk-like.Comment: Accepted for publication by Astronomy and Astrophysic
ISWI chromatin remodeling complexes in the DNA damage response
Regulation of chromatin structure is an essential component of the DNA damage response (DDR), which effectively preserves the integrity of DNA by a network of multiple DNA repair and associated signaling pathways. Within the DDR, chromatin is modified and remodeled to facilitate efficient DNA access, to control the activity of repair proteins and to mediate signaling. The mammalian ISWI family has recently emerged as one of the major ATP-dependent chromatin remodeling complex families that function in the DDR, as it is implicated in at least 3 major DNA repair pathways: homologous recombination, non-homologous end-joining and nucleotide excision repair. In this review, we discuss the various manners through which different ISWI complexes regulate DNA repair and how they are targeted to chromatin containing damaged DNA.</p
ISWI chromatin remodeling complexes in the DNA damage response
Regulation of chromatin structure is an essential component of the DNA damage response (DDR), which effectively preserves the integrity of DNA by a network of multiple DNA repair and associated signaling pathways. Within the DDR, chromatin is modified and remodeled to facilitate efficient DNA access, to control the activity of repair proteins and to mediate signaling. The mammalian ISWI family has recently emerged as one of the major ATP-dependent chromatin remodeling complex families that function in the DDR, as it is implicated in at least 3 major DNA repair pathways: homologous recombination, non-homologous end-joining and nucleotide excision repair. In this review, we discuss the various manners through which different ISWI complexes regulate DNA repair and how they are targeted to chromatin containing damaged DNA.</p
Modelling Catchment-Scale Evapotranspiration and Net Primary Production in Sub-Humid African Grasslands: Towards Understanding Carbon and Water Trade-Offs in Communal Rangelands
Being able to confidently predict net primary production within intensively used rangeland systems has become the goal of many rangeland scientists. The communally-managed rangelands of Africa, with their very high livestock numbers, represent such a challenge, as above-ground biomass is most often depleted before it has had chance to accumulate. In order to provide more accurate estimates of NPP for these rangelands, we explored the use of direct measurements of canopy cover, standing biomass and leaf area index, against standard vegetation indices from the Sentinel 2 sensors. Following intensive field surveys, we developed regression models of the relationships between Sentinel 2 NDVI and these three bio-physical attributes. Repeated measurements along an NDVI gradient revealed a good relationship between NDVI and LAI, which was used to predict the ET across landscapes under communal tenure arrangements. Although un-improved grasslands and abandoned cultivated lands are the dominant land cover classes in the study area, woody invasive alien plants (IAPs) along seep-lines have increased in spatial extent since their introduction in the middle of the last century. These IAPs are now responsible for most of the catchment ET in these highly modified ecosystems. Grass biomass production for the upper reaches of the Umzimvubu catchment was calculated using the relationship between Sentinel 2 NDVI and grass canopy cover
Physical parameters of a relativistic jet at very high redshift: the case of the blazar J1430+4204
Context. The high-redshift (z = 4.72) blazar J1430+4204 produced a major
radio outburst in 2005. Such outbursts are usually associated with the
emergence of a new component in the inner radio jet. Aims. We searched for
possible changes in the radio structure on milli-arcsecond angular scales, to
determine physical parameters that characterise the relativistic jet ejected
from the centre of this source. Methods. We analysed 15-GHz radio
interferometric images obtained with the Very Long Baseline Array (VLBA) before
and after the peak of the outburst. Results. We did not identify any
significant new jet component over a period of 569 days. We estimated the
Doppler factor, the Lorentz factor, and the apparent transverse speed of a
putative jet component using three different methods. The likely small jet
angle to the line of sight and our values of the apparent transverse speed are
consistent with not detecting a new jet feature.Comment: (6 pages, 4 figures) accepted for publication in Astronomy and
Astrophysic
Integrating large-scale stationary and local mobile measurements to estimate hyperlocal long-term air pollution using transfer learning methods
Mobile air quality measurements are collected typically for several seconds per road segment and in specific timeslots (e.g., working hours). These short-term and on-road characteristics of mobile measurements become the ubiquitous shortcomings of applying land use regression (LUR) models to estimate long-term concentrations at residential addresses. This issue was previously found to be mitigated by transferring LUR models to the long-term residential domain using routine long-term measurements in the studied region as the transfer target (local scale). However, long-term measurements are generally sparse in individual cities. For this scenario, we propose an alternative by taking long-term measurements collected over a larger geographical area (global scale) as the transfer target and local mobile measurements as the source (Global2Local model). We empirically tested national, airshed countries (i.e., national plus neighboring countries) and Europe as the global scale in developing Global2Local models to map nitrogen dioxide (NO(2)) concentrations in Amsterdam. The airshed countries scale provided the lowest absolute errors, and the Europe-wide scale had the highest R(2). Compared to a "global" LUR model (trained exclusively with European-wide long-term measurements), and a local mobile LUR model (using mobile data from Amsterdam only), the Global2Local model significantly reduced the absolute error of the local mobile LUR model (root-mean-square error, 6.9 vs 12.6 mug/m(3)) and improved the percentage explained variances compared to the global model (R(2), 0.43 vs 0.28, assessed by independent long-term NO(2) measurements in Amsterdam, n = 90). The Global2Local method improves the generalizability of mobile measurements in mapping long-term residential concentrations with a fine spatial resolution, which is preferred in environmental epidemiological studies
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