24,255 research outputs found
Maximum thickness of amorphous NiZr interlayers formed by a solid-state reaction technique
Formation of the equilibrium intermetallic compound NiZr in sputter deposited Ni/Zr diffusion couples is suppressed by the formation of a metastable amorphous NiZr alloy until a critical thickness of the amorphous NiZr interlayer is reached. The temperature dependence of this critical thickness is studied experimentally. A phenomenological model based on the premise of interfacial heterogeneous nucleation is proposed to understand the evolution of Ni/Zr diffusion couples
Solid-state interdiffusion reactions in Ni/Ti and Ni/Zr multilayered thin films
We have performed a comparative transmission electron microscopy study of solid-state interdiffusion reactions in multilayered Ni/Zr and Ni/Ti thin films. The Ni-Zr reaction product was amorphous while the Ni-Ti reaction product was a simple intermetallic compound. Because thermodynamic and chemical properties of these two alloy systems are similar, we suggest kinetic origins for this difference in reaction product
Simultaneous planar growth of amorphous and crystalline Ni silicides
We report a solid-state interdiffusion reaction induced by rapid thermal annealing and vacuum furnace annealing in evaporated Ni/Si bilayers. Upon heat treatment of a Ni film overlaid on a film of amorphous Si evaporated from a graphite crucible, amorphous and crystalline silicide layers grow uniformly side by side as revealed by cross-sectional transmission electron microscopy and backscattering spectrometry. This phenomenon contrasts with the silicide formation behavior previously observed in the Ni-Si system, and constitutes an interesting counterpart of the solid-state interdiffusion-induced amorphization in Ni/Zr thin-film diffusion couples. Carbon impurity contained in the amorphous Si film stabilizes the amorphous phase. Kinetic and thermodynamic factors that account for the experimental findings are discussed
Automatic Classification of Text Databases through Query Probing
Many text databases on the web are "hidden" behind search interfaces, and
their documents are only accessible through querying. Search engines typically
ignore the contents of such search-only databases. Recently, Yahoo-like
directories have started to manually organize these databases into categories
that users can browse to find these valuable resources. We propose a novel
strategy to automate the classification of search-only text databases. Our
technique starts by training a rule-based document classifier, and then uses
the classifier's rules to generate probing queries. The queries are sent to the
text databases, which are then classified based on the number of matches that
they produce for each query. We report some initial exploratory experiments
that show that our approach is promising to automatically characterize the
contents of text databases accessible on the web.Comment: 7 pages, 1 figur
Superconductivity in pure and electron doped MgB2: Transport properties and pressure effects
The normal state and superconducting properties of MgB2 and Mg1-xAlxB2 are
discussed based on structural, transport, and high pressure experiments. The
positive Seebeck coefficient and its linear temperature dependence for Tc<T<160
K provide evidence that the low-temperature transport in MgB2 is due to
hole-like metallic carriers. Structural and transport data show the important
role of defects as indicated by the correlation of Tc, the residual resistance
ratio, and the microstrain extracted from x-ray spectra. The decrease of Tc
with hydrostatic pressure is well explained by the strong-coupling BCS theory.
The large scatter of the pressure coefficients of Tc for different MgB2
samples, however, cannot be explained within this theory. We speculate that
pressure may increase the defect density, particularly in samples with large
initial defect concentration.Comment: Presented at NATO Advanced Research Workshop "New Trends in
Superconductivity", Yalta (Ukraine) 16-20 September, 200
Increase in soil organic carbon by agricultural intensification in northern China
Acknowledgements. This research was supported by National Natural Science Foundation of China (no. 31370527 and 31261140367) and the National Science and Technology Support Program of China (no. 2012BAD14B01-2). The authors gratefully thank the Huantai Agricultural Station for providing of the Soil Fertility Survey data. We also thank Zheng Liang from China Agricultural University for the soil sampling and analysis in 2011. Thanks are extended to Jessica Bellarby for helpful discussion and suggestions.Peer reviewedPublisher PD
Self-gravitating Yang Monopoles in all Dimensions
The (2k+2)-dimensional Einstein-Yang-Mills equations for gauge group SO(2k)
(or SU(2) for k=2 and SU(3) for k=3) are shown to admit a family of
spherically-symmetric magnetic monopole solutions, for both zero and non-zero
cosmological constant Lambda, characterized by a mass m and a magnetic-type
charge. The k=1 case is the Reissner-Nordstrom black hole. The k=2 case yields
a family of self-gravitating Yang monopoles. The asymptotic spacetime is
Minkowski for Lambda=0 and anti-de Sitter for Lambda<0, but the total energy is
infinite for k>1. In all cases, there is an event horizon when m>m_c, for some
critical mass , which is negative for k>1. The horizon is degenerate when
m=m_c, and the near-horizon solution is then an adS_2 x S^{2k} vacuum.Comment: 16 pp. Extensive revision to include case of non-zero cosmological
constant and implications for adS/CFT. Numerous additional reference
Pseudospin symmetry and its approximation in real nuclei
The origin of pseudospin symmetry and its broken in real nuclei are discussed
in the relativistic mean field theory. In the exact pseudospin symmetry, even
the usual intruder orbits have degenerate partners. In real nuclei, pseudospin
symmetry is approximate, and the partners of the usual intruder orbits will
disappear. The difference is mainly due to the pseudo spin-orbit potential and
the transition between them is discussed in details. The contribution of
pseudospin-orbit potential for intruder orbits is quite large, compared with
that for pseudospin doublets. The disappearance of the pseudospin partner for
the intruder orbit can be understood from the properties of its wave function.Comment: 10 pages, 3 figure
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