375 research outputs found
Investigation of microstructure defects in EUROFER97 under Heâș/FeÂłâș dual ion beam irradiation
Fusion like conditions for reduced activation ferritic/martensitic steels in the first wall are simulated with single Fe3+ and He+/Fe3+ dual ion beam irradiation of EUROFER97 at the Jannus laboratory, CEA Saclay, introducing a damage of 16 dpa and a helium content up to 260 appm. The samples are irradiated at temperatures of 330âŻÂ°C, 400âŻÂ°C and 500âŻÂ°C. The quantitative determination of size distribution and density of dislocation loops is obtained using weak-beam dark-field imaging mode. Burgers vectors of a02â©111âȘ are observed for the majority of dislocation loops at irradiation temperatures of 330âŻÂ°C and 400âŻÂ°C. At 500âŻÂ°C no dislocation loops are found. The impact of single and dual ion beam irradiation on mechanical properties is determined by means of nanoindentation. An increase in nano-hardness of up to 35% due to irradiation was measured at samples irradiated at 400âŻÂ°C. A kinetic rate model is applied for the description of nucleation and evolution of helium bubbles and compared with the experimental results. Evaluating the rate model with help of TEM-results for size and density of bubbles indicates the nucleation scheme as the main source for quantitative disagreement between the model and irradiation. Keywords: Radiation effects, Ion irradiation, Cluster dynamics, Fusion, Helium bubbles, RAFM steel
Model for the on-site matrix elements of the tight-binding hamiltonian of a strained crystal: Application to silicon, germanium and their alloys
We discuss a model for the on-site matrix elements of the sp3d5s*
tight-binding hamiltonian of a strained diamond or zinc-blende crystal or
nanostructure. This model features on-site, off-diagonal couplings between the
s, p and d orbitals, and is able to reproduce the effects of arbitrary strains
on the band energies and effective masses in the full Brillouin zone. It
introduces only a few additional parameters and is free from any ambiguities
that might arise from the definition of the macroscopic strains as a function
of the atomic positions. We apply this model to silicon, germanium and their
alloys as an illustration. In particular, we make a detailed comparison of
tight-binding and ab initio data on strained Si, Ge and SiGe.Comment: Submitted to Phys. Rev.
(13)C/(12)C composition, a novel parameter to study the downward migration of paper sludge in soilsâ
ÎŽ(13)C values of crop and forest soils were measured 8 years after disposal of paper sewage sludge. The carbon transfer from paper sludge downward to the first humic layer is evidenced by a (13)C-enrichnient of up to + 5.6â° due to the input of (13)C-enriched sludge carbonates. (13)C/(12)C composition is thus a novel, sensitive parameter to follow the downward transfer of paper sludge carbon
Loops under Strategies ... Continued
While there are many approaches for automatically proving termination of term
rewrite systems, up to now there exist only few techniques to disprove their
termination automatically. Almost all of these techniques try to find loops,
where the existence of a loop implies non-termination of the rewrite system.
However, most programming languages use specific evaluation strategies, whereas
loop detection techniques usually do not take strategies into account. So even
if a rewrite system has a loop, it may still be terminating under certain
strategies.
Therefore, our goal is to develop decision procedures which can determine
whether a given loop is also a loop under the respective evaluation strategy.
In earlier work, such procedures were presented for the strategies of
innermost, outermost, and context-sensitive evaluation. In the current paper,
we build upon this work and develop such decision procedures for important
strategies like leftmost-innermost, leftmost-outermost,
(max-)parallel-innermost, (max-)parallel-outermost, and forbidden patterns
(which generalize innermost, outermost, and context-sensitive strategies). In
this way, we obtain the first approach to disprove termination under these
strategies automatically.Comment: In Proceedings IWS 2010, arXiv:1012.533
Design of an interaction region with head-on collisions for the ILC
An interaction region (IR) with head-on collisions is considered as an
alternative to the baseline configuration of the International Linear Collider
(ILC) which includes two IRs with finite crossing-angles (2 and 20 mrad).
Although more challenging for the beam extraction, the head-on scheme is
favoured by the experiments because it allows a more convenient detector
configuration, particularly in the forward region. The optics of the head-on
extraction is revisited by separating the e+ and e- beams horizontally, first
by electrostatic separators operated at their LEP nominal field and then using
a defocusing quadrupole of the final focus beam line. In this way the septum
magnet is protected from the beamstrahlung power. Newly optimized final focus
and extraction optics are presented, including a first look at post-collision
diagnostics. The influence of parasitic collisions is shown to lead to a region
of stable collision parameters. Disrupted beam and beamstrahlung photon losses
are calculated along the extraction elements
Topical Review on "Beta-beams"
Neutrino physics is traversing an exciting period, after the important
discovery that neutrinos are massive particles, that has implications from
high-energy physics to cosmology. A new method for the production of intense
and pure neutrino beams has been proposed recently: the ``beta-beam''. It
exploits boosted radioactive ions decaying through beta-decay. This novel
concept has been the starting point for a new possible future facility. Its
main goal is to address the crucial issue of the existence of CP violation in
the lepton sector. Here we review the status and the recent developments with
beta-beams. We discuss the original, the medium and high-energy scenarios as
well as mono-chromatic neutrino beams produced through ion electron-capture.
The issue of the degeneracies is mentioned. An overview of low energy
beta-beams is also presented. These beams can be used to perform experiments of
interest for nuclear structure, for the study of fundamental interactions and
for nuclear astrophysics.Comment: Topical Review for Journal of Physics G: Nuclear and Particle
Physics, published version, minor corrections, references adde
Radio emission of extensive air shower at CODALEMA: Polarization of the radio emission along the v*B vector
Cosmic rays extensive air showers (EAS) are associated with transient radio
emission, which could provide an efficient new detection method of high energy
cosmic rays, combining a calorimetric measurement with a high duty cycle. The
CODALEMA experiment, installed at the Radio Observatory in Nancay, France, is
investigating this phenomenon in the 10^17 eV region. One challenging point is
the understanding of the radio emission mechanism. A first observation
indicating a linear relation between the electric field produced and the cross
product of the shower axis with the geomagnetic field direction has been
presented (B. Revenu, this conference). We will present here other strong
evidences for this linear relationship, and some hints on its physical origin.Comment: Contribution to the 31st International Cosmic Ray Conference, Lodz,
Poland, July 2009. 4 pages, 8 figures. v2: Typo fixed, arxiv references adde
Asteroids' physical models from combined dense and sparse photometry and scaling of the YORP effect by the observed obliquity distribution
The larger number of models of asteroid shapes and their rotational states
derived by the lightcurve inversion give us better insight into both the nature
of individual objects and the whole asteroid population. With a larger
statistical sample we can study the physical properties of asteroid
populations, such as main-belt asteroids or individual asteroid families, in
more detail. Shape models can also be used in combination with other types of
observational data (IR, adaptive optics images, stellar occultations), e.g., to
determine sizes and thermal properties. We use all available photometric data
of asteroids to derive their physical models by the lightcurve inversion method
and compare the observed pole latitude distributions of all asteroids with
known convex shape models with the simulated pole latitude distributions. We
used classical dense photometric lightcurves from several sources and
sparse-in-time photometry from the U.S. Naval Observatory in Flagstaff,
Catalina Sky Survey, and La Palma surveys (IAU codes 689, 703, 950) in the
lightcurve inversion method to determine asteroid convex models and their
rotational states. We also extended a simple dynamical model for the spin
evolution of asteroids used in our previous paper. We present 119 new asteroid
models derived from combined dense and sparse-in-time photometry. We discuss
the reliability of asteroid shape models derived only from Catalina Sky Survey
data (IAU code 703) and present 20 such models. By using different values for a
scaling parameter cYORP (corresponds to the magnitude of the YORP momentum) in
the dynamical model for the spin evolution and by comparing synthetics and
observed pole-latitude distributions, we were able to constrain the typical
values of the cYORP parameter as between 0.05 and 0.6.Comment: Accepted for publication in A&A, January 15, 201
High intensity neutrino oscillation facilities in Europe
The EUROnu project has studied three possible options for future, high intensity neutrino oscillation facilities in Europe. The first is a Super Beam, in which the neutrinos come from the decay of pions created by bombarding targets with a 4 MW proton beam from the CERN High Power Superconducting Proton Linac. The far detector for this facility is the 500 kt MEMPHYS water Cherenkov, located in the FrĂ©jus tunnel. The second facility is the Neutrino Factory, in which the neutrinos come from the decay of ÎŒ+ and ÎŒâ beams in a storage ring. The far detector in this case is a 100 kt magnetized iron neutrino detector at a baseline of 2000 km. The third option is a Beta Beam, in which the neutrinos come from the decay of beta emitting isotopes, in particular He6 and Ne18, also stored in a ring. The far detector is also the MEMPHYS detector in the FrĂ©jus tunnel. EUROnu has undertaken conceptual designs of these facilities and studied the performance of the detectors. Based on this, it has determined the physics reach of each facility, in particular for the measurement of CP violation in the lepton sector, and estimated the cost of construction. These have demonstrated that the best facility to build is the Neutrino Factory. However, if a powerful proton driver is constructed for another purpose or if the MEMPHYS detector is built for astroparticle physics, the Super Beam also becomes very attractive
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