3,122 research outputs found
Potentiometric determination of the gibbs energies of formation of lead aluminates
The Gibbs energies of formation of three compounds in the PbOAl2O3 systemā2PbO·Al2O3, PbOAl2O3 , and PbO· 6A1203āhave been determined from potentiometric measurements on reversible solidāstate galvanic cells
Pt, Ir I Pb,αAl2O3, PbO ·6A1203 I ZrO2CaO I NiO, Ni I Pt
Pt I NiO, Ni I ZrO2CaO I Pb, PbO·6A1203, PbO· A1203 I It, Pt
and
Pt I NiO, Ni I ZrO2CaO I Pb, PbO·A12O3, 2PbO·Al2O3 It, Pt
in the temperature range 850ā1375 K. The results are discussed in the light of reported phase diagrams for the PbOA1203 system. The partial pressures of different lead oxide species, PbnOn, n = 1−6, in the gas phase in equilibrium with the aluminates are calculated by combining the results of this study with the massāspectrometric data of Drowart et al.(1) for polymerization equilibria in the gas phase. The concentration of oxygen in lead in equilibrium with the aluminates are also derived from the results and the literature data on the Gibbs energy of solution of oxygen in liquid lead
Superconductivity Near Ferromagnetism in MgCNi3
An unusual quasi-two-dimensional heavy band mass van Hove singularity (vHs)
lies very near the Fermi energy in MgCNi3, recently reported to superconduct at
8.5 K. This compound is strongly exchange enhanced and is unstable to
ferromagnetism upon hole doping with 12% Mg --> Na or Li. The 1/4-depleted fcc
(frustrated) Ni sublattice and lack of Fermi surface nesting argues against
competing antiferromagnetic and charge density wave instabilities. We identify
an essentially infinite mass along the M-Gamma line, leading to
quasi-two-dimensionality of this vHs may promote unconventional p-wave pairing
that could coexist with superconductivity.Comment: 4 two-column pages, 4 figure
A characteristic lengthscale causes anomalous size effects and boundary programmability in mechanical metamaterials
The architecture of mechanical metamaterialsis designed to harness geometry,
non-linearity and topology to obtain advanced functionalities such as shape
morphing, programmability and one-way propagation. While a purely geometric
framework successfully captures the physics of small systems under idealized
conditions, large systems or heterogeneous driving conditions remain
essentially unexplored. Here we uncover strong anomalies in the mechanics of a
broad class of metamaterials, such as auxetics, shape-changers or topological
insulators: a non-monotonic variation of their stiffness with system size, and
the ability of textured boundaries to completely alter their properties. These
striking features stem from the competition between rotation-based
deformations---relevant for small systems---and ordinary elasticity, and are
controlled by a characteristic length scale which is entirely tunable by the
architectural details. Our study provides new vistas for designing, controlling
and programming the mechanics of metamaterials in the thermodynamic limit.Comment: Main text has 4 pages, 4 figures + Methods and Supplementary
Informatio
DESIGNING AN EXTENDED REALITY MOBILE GUIDE APPLICATION TO COMMUNICATE AND INTERPRET SERIAL WORLD HERITAGE SITES: A CASE STUDY OF KOREAāS SEOWON UNESCO WORLD HERITAGE SITE
Extended reality (XR) mobile guide applications offer unprecedented potential for immersive visitor experiences and in-depth knowledge retention to promote cultural learning at large-scale heritage sites, but, despite their significant development, the literature underexplores these applications for World Heritage sites, especially the serial properties that are spatially dispersed in various locations but configured as a single property. This paper describes a framework (blueprint) for the development of an XR mobile guide application focused on serial properties. By incorporating interactive XR and edutainment features, it explores a way to comprehensively reveal the interconnections between the heritage attributes of the subcomponent of the serial properties and their larger, cross-cultural context vis-Ć -vis the Outstanding Universal Values. To this end, at the Seowon, the UNESCO World Heritage site in Korea, we analyzed user interactions with a prototype of the XR application to identify user preferences and areas for improving the framework
The mechanical relaxation study of polycrystalline MgCNi3
The mechanical relaxation spectra of a superconducting and a
non-superconducting MgCNi3 samples were measured from liquid nitrogen
temperature to room temperature at frequency of kilohertz. There are two
internal friction peaks (at 300 K labeled as P1 and 125 K as P2) for the
superconducting sample. For the non-superconducting one, the position of P1
shifts to 250 K, while P2 is almost completely depressed. It is found that the
peak position of P2 shifts towards higher temperature under higher measuring
frequency. The calculated activation energy is 0.13eV. We propose an
explanation relating P2 to the carbon atom jumping among the off-center
positions. And further we expect that the behaviors of carbon atoms maybe
correspond to the normal state crossovers around 150 K and 50 K observed by
many other experiments.Comment: 4 figure
Core pinning by intragranular nanoprecipitates in polycrystalline MgCNi_3
The nanostructure and magnetic properties of polycrystalline MgCNi_3 were
studied by x-ray diffraction, electron microscopy, and vibrating sample
magnetometry. While the bulk flux-pinning force curve F_p(H) indicates the
expected grain-boundary pinning mechanism just below T_c = 7.2 K, a systematic
change to pinning by a nanometer-scale distribution of core pinning sites is
indicated by a shift of F_p(H) with decreasing temperature. The lack of scaling
of F_p(H) suggests the presence of 10 to 20% of nonsuperconducting regions
inside the grains, which are smaller than the diameter of fluxon cores 2xi at
high temperature and become effective with decreasing temperature when xi(T)
approaches the nanostructural scale. Transmission electron microscopy revealed
cubic and graphite nanoprecipitates with 2 to 5 nm size, consistent with the
above hypothesis since xi(0) = 6 nm. High critical current densities, more than
10^6 A/cm^2 at 1 T and 4.2 K, were obtained for grain colonies separated by
carbon. Dirty-limit behavior seen in previous studies may be tied to electron
scattering by the precipitates, indicating the possibility that strong core
pinning might be combined with a technologically useful upper critical field if
versions of MgCNi_3 with higher T_c can be found.Comment: 5 pages, 6 figures, submitted to PR
Band Calculations for Ce Compounds with AuCu-type Crystal Structure on the basis of Dynamical Mean Field Theory I. CePd and CeRh
Band calculations for Ce compounds with the AuCu-type crystal structure
were carried out on the basis of dynamical mean field theory (DMFT). The
auxiliary impurity problem was solved by a method named NCAvc
(noncrossing approximation including the state as a vertex correction).
The calculations take into account the crystal-field splitting, the spin-orbit
interaction, and the correct exchange process of the virtual excitation. These are necessary features in the
quantitative band theory for Ce compounds and in the calculation of their
excitation spectra. The results of applying the calculation to CePd and
CeRh are presented as the first in a series of papers. The experimental
results of the photoemission spectrum (PES), the inverse PES, the
angle-resolved PES, and the magnetic excitation spectra were reasonably
reproduced by the first-principles DMFT band calculation. At low temperatures,
the Fermi surface (FS) structure of CePd is similar to that of the band
obtained by the local density approximation. It gradually changes into a form
that is similar to the FS of LaPd as the temperature increases, since the
band shifts to the high-energy side and the lifetime broadening becomes
large.}Comment: 12 pasges, 13 figure
Pressure-induced magnetic transition and volume collapse in FeAs superconductors: An orbital-selective Mott scenario
Motivated by pressure experiments on FeAs-122 superconductors, we propose a
scenario based on local-moment physics to explain the simultaneous
disappearance of magnetism, reduction of the unit cell volume, and decrease in
resistivity. In this scenario, the low-pressure magnetic phase derives from Fe
moments, which become screened in the paramagnetic high-pressure phase. The
quantum phase transition can be described as an orbital-selective Mott
transition, which is rendered first order by coupling to the lattice, in
analogy to a Kondo volume collapse. Spin-fluctuation driven superconductivity
competes with antiferromagnetism and may be stabilized at low temperatures in
the high-pressure phase. The ideas are illustrated by a suitable mean-field
analysis of an Anderson lattice model.Comment: 9 pages, 3 figs; (v2) robustness of OS Mott transition vs. fragility
of superconductivity discussed, final version to be publishe
Water-Gated Charge Doping of Graphene Induced by Mica Substrates
We report on the existence of water-gated charge doping of graphene deposited
on atomically flat mica substrates. Molecular films of water in units of ~0.4
nm-thick bilayers were found to be present in regions of the interface of
graphene/mica hetero-stacks prepared by micromechanical exfoliation of kish
graphite. The spectral variation of the G and 2D bands, as visualized by Raman
mapping, shows that mica substrates induce strong p-type doping in graphene,
with hole densities of {-2}$. The ultrathin water
films, however, effectively block interfacial charge transfer, rendering
graphene significantly less hole-doped. Scanning Kelvin probe microscopy
independently confirmed a water-gated modulation of the Fermi level by 0.35 eV,
in agreement with the optically determined hole density. The manipulation of
the electronic properties of graphene demonstrated in this study should serve
as a useful tool in realizing future graphene applications.Comment: 15 pages, 4 figures; Nano Letters, accepted (2012
- ā¦