809 research outputs found
Possible singlet to triplet pairing transition in NaxCoO2 H2O
We present precise measurements of the upper critical field (Hc2) in the
recently discovered cobalt oxide superconductor. We have found that the
critical field has an unusual temperature dependence; namely, there is an
abrupt change of the slope of Hc2(T) in a weak field regime. In order to
explain this result we have derived and solved Gor'kov equations on a
triangular lattice. Our experimental results may be interpreted in terms of the
field-induced transition from singlet to triplet superconductivity.Comment: 6 pages, 5 figures, revte
Superconductivity and electronic structure of the W7Re13B compound
The superconductor W7Re13B has been studied by the magnetic measurements and microwave absorption. The crystal structure of W7Re13B is cubic (¯-Mn type). This compound exhibits a sharp superconducting transition at a temperature of Tc = 7:2 K. The electronic structure of W7Re13B has been studied by X-ray photoelectron spectroscopy and the band structure has been calculated by the full-potential local-orbital minimum-basis method using the scalar-relativistic mode. The main contribution to the density of states at the Fermi level is from 5d electrons of W and Re. The W and Re bands are similar and substituting W by Re does not change the total density of states
Manufacturing and characterization of sustainable and recyclable wood-polypropylene biocomposites:Multiprocessing-properties-structure relationships
In this study, sustainable polymeric materials with a polypropylene matrix reinforced with wood waste were developed for structural applications. The new polymer biocomposites (WPCs) were evaluated for their mechanical and structural properties regarding their susceptibility to multiple processing. As thermo-mechanical degradation processes are associated with the repeated processing of plastics, which causes changes in the properties and structure of these materials. Therefore, to determine the extent to which the composites can be used under operating conditions, the composites were examined by DMA. As a result of the study observed some effects caused by the repeated effects of shear stress and temperature on the rheological and mechanical properties of polymer composites. The first of these is related to a decrease in viscosity of WPC composites subjected to the six times processing and changes in flow conditions during extrusion and injection moulding due to the degradation of the polypropylene matrix. As the viscosity of the composites decreased, a reduction in tensile strength and other mechanical properties of the polypropylene matrix was noted. On the other hand, the second effect observed leads to the conclusion that, as the composites' processing cycles increase, the WPC composite's mechanical properties increase due to an increase in the degree of homogenization of the individual components of the WPC composition. This study aims to describe the relationship between these two primary processes and to determine the relationship between the properties and the structure of the new WPCs.</p
Transcranial Stimulation of Alpha Oscillations Up-Regulates the Default Mode Network
The default mode network (DMN) is the most-prominent intrinsic connectivity network, serving as a key architecture of the brain\u27s functional organization. Conversely, dysregulated DMN is characteristic of major neuropsychiatric disorders. However, the field still lacks mechanistic insights into the regulation of the DMN and effective interventions for DMN dysregulation. The current study approached this problem by manipulating neural synchrony, particularly alpha (8 to 12 Hz) oscillations, a dominant intrinsic oscillatory activity that has been increasingly associated with the DMN in both function and physiology. Using high-definition alpha-frequency transcranial alternating current stimulation (α-tACS) to stimulate the cortical source of alpha oscillations, in combination with simultaneous electroencephalography and functional MRI (EEG-fMRI), we demonstrated that α-tACS (versus Sham control) not only augmented EEG alpha oscillations but also strengthened fMRI and (source-level) alpha connectivity within the core of the DMN. Importantly, increase in alpha oscillations mediated the DMN connectivity enhancement. These findings thus identify a mechanistic link between alpha oscillations and DMN functioning. That transcranial alpha modulation can up-regulate the DMN further highlights an effective noninvasive intervention to normalize DMN functioning in various disorders
Evidence of Josephson-coupled superconducting regions at the interfaces of Highly Oriented Pyrolytic Graphite
Transport properties of a few hundreds of nanometers thick (in the graphene
plane direction) lamellae of highly oriented pyrolytic graphite (HOPG) have
been investigated. Current-Voltage characteristics as well as the temperature
dependence of the voltage at different fixed input currents provide evidence
for Josephson-coupled superconducting regions embedded in the internal
two-dimensional interfaces, reaching zero resistance at low enough
temperatures. The overall behavior indicates the existence of superconducting
regions with critical temperatures above 100 K at the internal interfaces of
oriented pyrolytic graphite.Comment: 6 Figures, 5 page
Experimental neutron capture data of 58 Ni from the CERN n_TOF facility
The
58
Ni(
n
,
γ
) cross section has been measured at the neutron time of flight facility n_TOF at CERN, in the energy range from 27 meV up to 400 keV. In total, 51 resonances have been analyzed up to 122 keV. Maxwellian averaged cross sections (MACS) have been calculated for stellar temperatures of
k
T
=
5
–
100
keV with uncertainties of less than 6%, showing fair agreement with recent experimental and evaluated data up to
k
T
= 50 keV. The MACS extracted in the present work at 30 keV is
34.2
±
0
.
6
stat
±
1
.
8
sys
mb, in agreement with latest results and evaluations, but 12% lower relative to the recent KADoNIS compilation of astrophysical cross sections. When included in models of the
s
-process nucleosynthesis in massive stars, this change results in a 60% increase of the abundance of
58
Ni, with a negligible propagation on heavier isotopes. The reason is that, using both the old or the new MACS,
58
Ni is efficiently depleted by neutron captures.National Science Foundation (NSF) de los Estados Unidos. PHY 02-16783 y PHY 09-22648Joint Institute for Nuclear Astrophysics (JINA) de los Estados Unidos. EU MIRG-CT-2006-04652
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Methods and codes for neutronic calculations of the MARIA research reactor.
The core of the MARIA high flux multipurpose research reactor is highly heterogeneous. It consists of beryllium blocks arranged in 6 x 8 matrix, tubular fuel assemblies, control rods and irradiation channels. The reflector is also heterogeneous and consists of graphite blocks clad with aluminum. Its structure is perturbed by the experimental beam tubes. This paper presents methods and codes used to calculate the MARIA reactor neutronics characteristics and experience gained thus far at IAE and ANL. At ANL the methods of MARIA calculations were developed in connection with the RERTR program. At IAE the package of programs was developed to help its operator in optimization of fuel utilization
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