248 research outputs found
Calculations of giant magnetoresistance in Fe/Cr trilayers using layer potentials determined from {\it ab-initio} methods
The ab initio full-potential linearized augmented plane-wave method
explicitly designed for the slab geometry was employed to elucidate the
physical origin of the layer potentials for the trilayers nFe/3Cr/nFe(001),
where n is the number of Fe monolayers. The thickness of the transition-metal
ferromagnet has been ranged from up to n=8 while the spacer thickness was
fixed to 3 monolayers. The calculated potentials were inserted in the
Fuchs-Sondheimer formalism in order to calculate the giant magnetoresistance
(GMR) ratio. The predicted GMR ratio was compared with the experiment and the
oscillatory behavior of the GMR as a function of the ferromagnetic layer
thickness was discussed in the context of the layer potentials. The reported
results confirm that the interface monolayers play a dominant role in the
intrinsic GMR.Comment: 17 pages, 7 figures, 3 tables. accepted in J. Phys.: Cond. Matte
Fission modes of mercury isotopes
Background: Recent experiments on beta-delayed fission in the mercury-lead
region and the discovery of asym- metric fission in 180 Hg [1] have stimulated
theoretical interest in the mechanism of fission in heavy nuclei. Purpose: We
study fission modes and fusion valleys in 180 Hg and 198 Hg to reveal the role
of shell effects in pre-scission region and explain the experimentally observed
fragment mass asymmetry and its variation with A. Methods: We use the
self-consistent nuclear density functional theory employing Skyrme and Gogny
energy density functionals. Results: The potential energy surfaces in
multi-dimensional space of collective coordinates, including elongation,
triaxiality, reflection-asymmetry, and necking, are calculated for 180 Hg and
198 Hg. The asymmetric fission valleys - well separated from fusion valleys
associated with nearly spherical fragments - are found in in both cases. The
density distributions at scission configurations are studied and related to the
experimentally observed mass splits. Conclusions: The energy density
functionals SkM\ast and D1S give a very consistent description of the fission
process in 180 Hg and 198 Hg. We predict a transition from asymmetric fission
in 180 Hg towards more symmetric distribution of fission fragments in 198 Hg.
For 180 Hg, both models yield 100 Ru/80 Kr as the most probable split. For 198
Hg, the most likely split is 108 Ru/90 Kr in HFB-D1S and 110 Ru/88 Kr in
HFB-SkM\ast.Comment: 6 pages, 5 figures, to be published in Physical Review
Diagnostic value of MRI for predicting axillary lymph nodes metastasis in newly diagnosed breast cancer patients: Diffusion-weighted MRI
AbstractObjectiveNon-invasive preoperative detection of axillary nodal metastasis is beneficial for the outcome of breast cancer patients. We aimed to determine the value of DW MRI, ADC and their combination with MRI morphological criteria in detecting axillary metastasis.MethodsWe included recently diagnosed forty breast cancer patients. MRI morphological criteria, signal intensity on DWI, and ADC value were assessed and compared between metastatic and non-metastatic LNs using histopathological findings as reference standard. Sensitivity, specificity, PPV, NPV and accuracy for each variable and cutoff value of ADC were evaluated.ResultsNo statistically significant difference between metastatic and non-metastatic LNs in short axis diameter or L/S ratio (p value: 0.87 and 0.82 respectively); however, loss of fatty hilum, high signal intensity on DWI and low ADC value were significant with increasing sensitivity on their combination. The mean ADC was 0.96±0.9×10−3mm2/s for metastatic and 1.53±0.6×10−3mm2/s for benign LNs with cutoff value 1.09×10−3mm2/s and sensitivity (94.5%), specificity (93.6%), PPV (96%), NPV (94.7%) and accuracy (95.6%).ConclusionDW-MRI and ADC per se or in combination with loss of the fatty hila is a promising and supportive tool for detection of axillary LNs metastasis
Study of fluid displacement in 3D porous media with an improved multi-component pseudopotential lattice Boltzmann method
We generalize to three dimensions (3D) a recently developed improved
multi-component pseudopotential lattice Boltzmann method and analyze its
applicability to simulate flows through realistic porous media. The model is
validated and characterized via benchmarks, and we investigate its performance
by simulating the displacement of immiscible fluids in 3D geometries. Two
samples are considered, namely, a pack of spheres obtained numerically, and a
Bentheimer sandstone rock sample obtained experimentally. We show that, with
this model it is possible to simulate realistic viscosity ratios, to tune
surface tension independently and, most importantly, to preserve the volume of
trapped fluid. We also evaluate the computational performance of the model on
the Graphical Processing Unit (GPU) and mention the implemented optimizations
to increase the computational speed and reduce the memory requirements.Comment: arXiv admin note: text overlap with arXiv:2111.0866
Why NERICA is a successful innovation for African farmers
This paper responds to ‘Funding international agricultural research and the need to be noticed: a case study of NERICA rice’ by Stuart Orr, James Sumberg, Olaf Erenstein and Andreas Oswald, published in this issue of Outlook on Agriculture.
In summary, the article by Orr et al, based on an internal WARDA document written in November 2003 and augmented with results from Internet searches, is outdated and does not seem to be fair, objective or useful. We invite the authors to visit WARDA or any of its partners in Sub-Saharan Africa for evidence of the impact of NERICA varieties or the other improved varieties and technologies that have been developed and disseminated by WARDA in recent years
Fission half-lives of super-heavy nuclei in a microscopic approach
A systematic study of 160 heavy and super-heavy nuclei is performed in the
Hartree-Fock-Bogoliubov approach with the finite range and density dependent
Gogny force with the D1S parameter set. We show calculations in several
approximations: with axially symmetric and reflexion symmetric wave functions,
with axially symmetric and non-reflexion symmetric wave functions and finally
some representative examples with triaxial wave functions are also discussed.
Relevant properties of the ground state and along the fission path are
thoroughly analyzed. Fission barriers, Q-factors and lifetimes with
respect to fission and -decay as well as other observables are
discussed. Larger configuration spaces and more general HFB wave functions as
compared to previous studies provide a very good agreement with the
experimental data.Comment: 26 pages, 15 figure
FACT -- the First Cherenkov Telescope using a G-APD Camera for TeV Gamma-ray Astronomy (HEAD 2010)
Geiger-mode Avalanche Photodiodes (G-APD) bear the potential to significantly
improve the sensitivity of Imaging Air Cherenkov Telescopes (IACT). We are
currently building the First G-APD Cherenkov Telescope (FACT) by refurbishing
an old IACT with a mirror area of 9.5 square meters and construct a new, fine
pixelized camera using novel G-APDs. The main goal is to evaluate the
performance of a complete system by observing very high energy gamma-rays from
the Crab Nebula. This is an important field test to check the feasibility of
G-APD-based cameras to replace at some time the PMT-based cameras of planned
future IACTs like AGIS and CTA. In this article, we present the basic design of
such a camera as well as some important details to be taken into account.Comment: Poster shown at HEAD 2010, Big Island, Hawaii, March 1-4, 201
Role of the target orientation angle and orbital angular momentum in the evaporation residue production
The influence of the orientation angles of the target nucleus symmetry axis
relative to the beam direction on the production of the evaporation residues is
investigated for the Ca+Sm reaction as a function of the beam
energy. At low energies (137 MeV), the yield of evaporation
residues is observed only for collisions with small orientation angles
().
At large energies (about 140--180 MeV) all the orientation
angles can contribute to the evaporation residue cross section
in the 10--100 mb range, and at 180 MeV
ranges around 0.1--10 mb because the fission barrier for a compound nucleus
decreases by increasing its excitation energy and angular momentum.Comment: 20 pages, 10 figures, submitted to JPS
Fission Fragment Mass and Kinetic Energy Yields of Fermium Isotopes
A rapidly converging 4-dimensional Fourier shape parametrization is used to
model the fission process of heavy nuclei. Potential energy landscapes are
computed within the macroscopic-microscopic approach, on top of which the
multi-dimensional Langevin equation is solved to describe the fission dynamics.
Charge equilibration at scission and de-excitation by neutron evaporation of
the primary fragments after scission is investigated. The model describes
various observables, including fission-fragment mass, charge, and kinetic
energy yields, as well as post-scission neutron multiplicities and, most
importantly, their correlations, which are crucial to unravel the complexity of
the fission process. The parameters of the dynamical model were tuned to
reproduce experimental data obtained from thermal neutron-induced fission of
U, which allows us to discuss the transition from asymmetric to
symmetric fission along the Fm isotopic chain.Comment: Presented at the Mazurian Lakes Conference on Physics, 2023, Polan
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