390 research outputs found
Outer Regions of the Milky Way
With the start of the Gaia era, the time has come to address the major
challenge of deriving the star formation history and evolution of the disk of
our MilkyWay. Here we review our present knowledge of the outer regions of the
Milky Way disk population. Its stellar content, its structure and its dynamical
and chemical evolution are summarized, focussing on our lack of understanding
both from an observational and a theoretical viewpoint. We describe the
unprecedented data that Gaia and the upcoming ground-based spectroscopic
surveys will provide in the next decade. More in detail, we quantify the expect
accuracy in position, velocity and astrophysical parameters of some of the key
tracers of the stellar populations in the outer Galactic disk. Some insights on
the future capability of these surveys to answer crucial and fundamental issues
are discussed, such as the mechanisms driving the spiral arms and the warp
formation. Our Galaxy, theMilkyWay, is our cosmological laboratory for
understanding the process of formation and evolution of disk galaxies. What we
learn in the next decades will be naturally transferred to the extragalactic
domain.Comment: 22 pages, 10 figures, Invited review, Book chapter in "Outskirts of
Galaxies", Eds. J. H. Knapen, J. C. Lee and A. Gil de Paz, Astrophysics and
Space Science Library, Springer, in pres
Valence electronic structure of Mn in undoped and doped lanthanum manganites from relative K x-ray intensity studies
Relative x-ray intensities of in , , and
( = , , and ) systems have been
measured following excitation by 59.54 keV -rays from a 200 mCi
Am point-source. The measured results for the compounds deviate
significantly from the results of pure . Comparison of the experimental
data with the multiconfiguration Dirac-Fock (MCDF) effective atomic model
calculations indicates reasonable agreement with the predictions of ionic model
for the doped {manganites except} that the electron doped
and hole doped compounds
show some small deviations. The results of and deviate
considerably from the predictions of the ionic model. Our measured
ratio of in cannot be explained
as a linear superposition of ratios of for the end
members which is in contrast to the recent proposal by Tyson et al. from their
spectra.Comment: 14 pages, 4 figures. to appear in NIM-B.Please send an e-mail for
figure
Microstructure and mechanical behavior of similar butt-joints of ZK60 and ZK60â1.5RE magnesium alloys produced by linear friction stir welding
The microstructure and mechanical properties of butt-joints produced by linear friction stir welding of similar plates of as-cast ZK60 and
modified ZK60 with 1.5 wt.% RE (ZK60â1.5RE) are investigated. The thermomechanical affected zone is investigated in both advancing and
retrieving sides, and the microstructure is compared to the base metal and the stirred zone. Electron backscattered diffraction measurements
provide the average microstructural features of the transformed microstructure. The mechanical properties are assessed using hardness, tensile
testing, and surface residual stress measured using X-ray diffraction. Higher torque and heat input are obtained for the ZK60â1.5RE compared
to the ZK60. The thermomechanical affected zone is notably larger for the ZK60 compared to the ZK60â1.5RE. A gradient microstructure
is formed in thermomechanical affected zones where deformed grains are progressively more recrystallised towards the stirred zone. There
is no visible interface between the thermomechanical affected zone and the stirred zone. A fine and partially recrystallised microstructure
is formed in the stirred zone. The retrieving side of the ZK60â1.5RE has a slightly more refined microstructure compared to the other
investigated zones. Anisotropy measured with increment in the maximum intensity of the (0001) increases towards to stirred zone. The
formed microstructure is correlated with the role of twinning, recovery, static, and dynamic recrystallisation that can occur during friction
stir welding. Twinning and grains with large misorientation spread are more pronounced in the thermomechanical affected zone and regions
towards the base metal. Sharp low angle grain boundaries are observed towards the stirred zone. From refined recrystallised grains decorating
the grain in the thermomechanical affected zone, a mosaic-like of low and high angle grain boundaries are observed in the stirred zone. The
joints have comparable surface residual stresses. The friction stir welding improved the ductility and strength of the as-cast ZK60â1.5RE
alloy since the tensile samples fractured in the BM
Effect of Ce-base mischmetal addition on the microstructure and mechanical properties of hot-rolled ZK60 alloy
Mg-Zn-Zr (ZK) alloys exhibit notably high mechanical strength amongst all magnesium alloy grades. However, due to the formation of low
melting point Mg3Zn7-precipitates, these alloys are susceptible to hot cracking, thus compromising their metallurgical processing. The addition
of rare earths to ZK alloys is an alternative to form higher melting point intermetallic compounds, speed up dynamic recrystallization, refine
grain size, enhance corrosion resistance and extend the service temperature due to improved creep resistance. This work deals with the effect
of Ce-base mischmetal addition on the hot rolling behaviour of as-cast ZK60 alloy. The microstructure investigation conducted using electron
microscopy and X-Ray diffraction shows that precipitation of Mg7Zn3 intermetallics occur during hot rolling, whereas no further precipitation
is observed for the ZK60-Mm alloys. The fragmentation of the intermetallic compounds occur during hot rolling and finer particles of Mg7Zn3
are observed for the ZK60, whereas Mg7Zn3 and MgZn2Ce intermetallics are formed in the alloy modified with mischmetal addition. A higher fraction of dynamically recrystallized grains is observed for the ZK60-Mm in comparison to the ZK60. Continuous recrystallization takes place in ZK60 with the formation of sub-grains near to the intermetallics and the addition of mischmetal promotes the occurrence of discontinuous recrystallization with the nucleation of new grains close to the precipitates. The mechanical strength and, in particular, the ductility of the hot-rolled alloys are notably improved when compared to the same alloys in the as-cast condition. The mechanical strength is, however, higher for the ZK60 alloy. Less solid solution strengthening, softer MgZn2Ce intermetallics and more extensive recrystallization contribute to reduce the mechanical strength of ZK60-Mm. Failure in both alloys are initiated at coarse intermetallics and propagate through intermetallic-rich regions
USP30 sets a trigger threshold for PINK1âPARKIN amplification of mitochondrial ubiquitylation
The mitochondrial deubiquitylase USP30 negatively regulates the selective autophagy of damaged mitochondria. We present the characterisation of an N-cyano pyrrolidine compound, FT3967385, with high selectivity for USP30. We demonstrate that ubiquitylation of TOM20, a component of the outer mitochondrial membrane import machinery, represents a robust biomarker for both USP30 loss and inhibition. A proteomics analysis, on a SHSY5Y neuroblastoma cell line model, directly compares the effects of genetic loss of USP30 with chemical inhibition. We have thereby identified a subset of ubiquitylation events consequent to mitochondrial depolarisation that are USP30 sensitive. Within responsive elements of the ubiquitylome, several components of the outer mitochondrial membrane transport (TOM) complex are prominent. Thus, our data support a model whereby USP30 can regulate the availability of ubiquitin at the specific site of mitochondrial PINK1 accumulation following membrane depolarisation. USP30 deubiquitylation of TOM complex components dampens the trigger for the Parkin-dependent amplification of mitochondrial ubiquitylation leading to mitophagy. Accordingly, PINK1 generation of phospho-Ser65 ubiquitin proceeds more rapidly in cells either lacking USP30 or subject to USP30 inhibition
Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter
Data collected by the Pierre Auger Observatory through 31 August 2007 showed
evidence for anisotropy in the arrival directions of cosmic rays above the
Greisen-Zatsepin-Kuz'min energy threshold, \nobreak{eV}. The
anisotropy was measured by the fraction of arrival directions that are less
than from the position of an active galactic nucleus within 75 Mpc
(using the V\'eron-Cetty and V\'eron catalog). An updated
measurement of this fraction is reported here using the arrival directions of
cosmic rays recorded above the same energy threshold through 31 December 2009.
The number of arrival directions has increased from 27 to 69, allowing a more
precise measurement. The correlating fraction is , compared
with expected for isotropic cosmic rays. This is down from the early
estimate of . The enlarged set of arrival directions is
examined also in relation to other populations of nearby extragalactic objects:
galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in
hard X-rays by the Swift Burst Alert Telescope. A celestial region around the
position of the radiogalaxy Cen A has the largest excess of arrival directions
relative to isotropic expectations. The 2-point autocorrelation function is
shown for the enlarged set of arrival directions and compared to the isotropic
expectation.Comment: Accepted for publication in Astroparticle Physics on 31 August 201
The Fluorescence Detector of the Pierre Auger Observatory
The Pierre Auger Observatory is a hybrid detector for ultra-high energy
cosmic rays. It combines a surface array to measure secondary particles at
ground level together with a fluorescence detector to measure the development
of air showers in the atmosphere above the array. The fluorescence detector
comprises 24 large telescopes specialized for measuring the nitrogen
fluorescence caused by charged particles of cosmic ray air showers. In this
paper we describe the components of the fluorescence detector including its
optical system, the design of the camera, the electronics, and the systems for
relative and absolute calibration. We also discuss the operation and the
monitoring of the detector. Finally, we evaluate the detector performance and
precision of shower reconstructions.Comment: 53 pages. Submitted to Nuclear Instruments and Methods in Physics
Research Section
Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
We review HB stars in a broad astrophysical context, including both variable
and non-variable stars. A reassessment of the Oosterhoff dichotomy is
presented, which provides unprecedented detail regarding its origin and
systematics. We show that the Oosterhoff dichotomy and the distribution of
globular clusters (GCs) in the HB morphology-metallicity plane both exclude,
with high statistical significance, the possibility that the Galactic halo may
have formed from the accretion of dwarf galaxies resembling present-day Milky
Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the
second-parameter problem is presented. A technique is proposed to estimate the
HB types of extragalactic GCs on the basis of integrated far-UV photometry. The
relationship between the absolute V magnitude of the HB at the RR Lyrae level
and metallicity, as obtained on the basis of trigonometric parallax
measurements for the star RR Lyrae, is also revisited, giving a distance
modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are
studied. Finally, the conductive opacities used in evolutionary calculations of
low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and
Space Scienc
Advanced functionality for radio analysis in the Offline software framework of the Pierre Auger Observatory
The advent of the Auger Engineering Radio Array (AERA) necessitates the
development of a powerful framework for the analysis of radio measurements of
cosmic ray air showers. As AERA performs "radio-hybrid" measurements of air
shower radio emission in coincidence with the surface particle detectors and
fluorescence telescopes of the Pierre Auger Observatory, the radio analysis
functionality had to be incorporated in the existing hybrid analysis solutions
for fluoresence and surface detector data. This goal has been achieved in a
natural way by extending the existing Auger Offline software framework with
radio functionality. In this article, we lay out the design, highlights and
features of the radio extension implemented in the Auger Offline framework. Its
functionality has achieved a high degree of sophistication and offers advanced
features such as vectorial reconstruction of the electric field, advanced
signal processing algorithms, a transparent and efficient handling of FFTs, a
very detailed simulation of detector effects, and the read-in of multiple data
formats including data from various radio simulation codes. The source code of
this radio functionality can be made available to interested parties on
request.Comment: accepted for publication in NIM A, 13 pages, minor corrections to
author list and references in v
Anisotropy studies around the galactic centre at EeV energies with the Auger Observatory
Data from the Pierre Auger Observatory are analyzed to search for
anisotropies near the direction of the Galactic Centre at EeV energies. The
exposure of the surface array in this part of the sky is already significantly
larger than that of the fore-runner experiments. Our results do not support
previous findings of localized excesses in the AGASA and SUGAR data. We set an
upper bound on a point-like flux of cosmic rays arriving from the Galactic
Centre which excludes several scenarios predicting sources of EeV neutrons from
Sagittarius . Also the events detected simultaneously by the surface and
fluorescence detectors (the `hybrid' data set), which have better pointing
accuracy but are less numerous than those of the surface array alone, do not
show any significant localized excess from this direction.Comment: Matches published versio
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