6,755 research outputs found
Tetragonal zirconia: Wet chemical preparation, mechanical and electrical properties
Yttria-stabilized zirconia powders were prepared in the composition range of 3 to 13 at% yttria. The hydrolysis-gel precipitation technique was used, starting from metal alkoxides or chlorides. In the composition range between 5 and 10 at% yttria, the materials sintered at 1250°C have a fully tetragonal structure. The density was higher than 95% and the grain sizes can be varied between 0.1 and 0.5μm depending on the preparation conditions. The fracture toughness KIC amounts 6 to 11 MPam but is not dependent on the composition. The transformation toughening mechanism and the properties of the tetragonal phase itself play an important role in the increase of KIC compared with cubic materials. The magnitude of the oxygen-ion conductivity value is comparable with that for cubic materials
Dense Regular Packings of Irregular Non-Convex Particles
We present a new numerical scheme to study systems of non-convex, irregular,
and punctured particles in an efficient manner. We employ this method to
analyze regular packings of odd-shaped bodies, not only from a nanoparticle but
also both from a computational geometry perspective. Besides determining
close-packed structures for many shapes, we also discover a new denser
configuration for Truncated Tetrahedra. Moreover, we consider recently
synthesized nanoparticles and colloids, where we focus on the excluded volume
interactions, to show the applicability of our method in the investigation of
their crystal structures and phase behavior. Extensions to the presented scheme
include the incorporation of soft particle-particle interactions, the study of
quasicrystalline systems, and random packings.Comment: 4 pages, 3 figure
Ab initio correlation approach to a ferric wheel-like molecular cluster
We present an ab initio study of electronic correlation effects in a
molecular cluster derived from the hexanuclear ferric wheel
[LiFe6(OCH3)12-(dbm)6]PF6. The electronic and magnetic properties of this
cluster have been studied with all-electron Hartree-Fock, full-potential
density functional calculations and multi-reference second-order perturbation
theory. For different levels of correlation, a detailed study of the impact of
the electronic correlation on the exchange parameter was feasible. As the main
result, we found that the influence of the bridge oxygen atoms on the exchange
parameter is less intense than the influence of the apical ligand groups, which
is due to the geometry of the cluster. With respect to the cluster model
approach, the experimental value of the exchange parameter was affirmed.Comment: to be published in EPJ
Quasimodes of a chaotic elastic cavity with increasing local losses
We report non-invasive measurements of the complex field of elastic
quasimodes of a silicon wafer with chaotic shape. The amplitude and phase
spatial distribution of the flexural modes are directly obtained by Fourier
transform of time measurements. We investigate the crossover from real mode to
complex-valued quasimode, when absorption is progressively increased on one
edge of the wafer. The complexness parameter, which characterizes the degree to
which a resonance state is complex-valued, is measured for non-overlapping
resonances and is found to be proportional to the non-homogeneous contribution
to the line broadening of the resonance. A simple two-level model based on the
effective Hamiltonian formalism supports our experimental results
A Triangular Tessellation Scheme for the Adsorption Free Energy at the Liquid-Liquid Interface: Towards Non-Convex Patterned Colloids
We introduce a new numerical technique, namely triangular tessellation, to
calculate the free energy associated with the adsorption of a colloidal
particle at a flat interface. The theory and numerical scheme presented here
are sufficiently general to handle non-convex patchy colloids with arbitrary
surface patterns characterized by a wetting angle, e.g., amphiphilicity. We
ignore interfacial deformation due to capillary, electrostatic, or
gravitational forces, but the method can be extended to take such effects into
account. It is verified that the numerical method presented is accurate and
sufficiently stable to be applied to more general situations than presented in
this paper. The merits of the tessellation method prove to outweigh those of
traditionally used semi-analytic approaches, especially when it comes to
generality and applicability.Comment: 21 pages, 11 figures, 0 table
Caudal cervical vertebral morphological variation is not associated with clinical signs in Warmblood horses
Background Variation in equine caudal cervical spine morphology at C6 and C7 has high prevalence in Warmblood horses and is suspected to be associated with pain in a large mixed-breed group of horses. At present no data exist on the relationship between radiographic phenotype and clinical presentation in Warmblood horses in a case-control study. Objectives To establish the frequency of radiographically visible morphologic variation in a large group of Warmblood horses with clinical signs and compare this with a group without clinical signs. We hypothesised that occurrence of morphologic variation in the case group would not differ from the control group, indicating there is no association between clinical signs and morphologic variation. Study design Retrospective case-control. Methods Radiographic presence or absence of morphologic variation of cervical vertebrae C6 and C7 was recorded in case (n = 245) and control horses (n = 132). Case and control groups were compared by univariable Pearson's Chi-square and multivariable logistic regression for measurement variables age, sex, breed, degenerative joint disease and morphologic variation at C6 and C7. Odds ratio and confidence intervals were obtained. A P <= 0.05 was considered statistically significant. Results Morphologic variation at C6 and C7 (n = 108/377 = 28.6%; Cases 58/245 = 23.7%; Control 50/132 = 38%) was less frequent in horses with clinical signs in univariable testing (OR 0.48, 95% CI 0.3-0.8, P = 0.001). Age, sex, breed and degenerative joint disease were not retained in the final multivariable logistic regression step whereas morphologic variation remained significantly less present in horses with clinical signs. Main limitations Possible demographic differences between equine clinics. Conclusions Morphologic variation in the caudal cervical spine was detected more frequently in horses without clinical signs. Therefore, radiographic presence of such variation does not necessarily implicate the presence of clinical signs
Een historische uitspraak over gaswinning?
Afdeling bestuursrechtspraak van de Raad van State 15 november 2017, ECLI: NL: RVS: 2017: 315
Building or stumbling blocks? Assessing the performance of polycentric energy and climate governance networks
Polycentric governance networks are on the rise in global energy and climate governance, but we know surprisingly little about their effectiveness. This paper analyzes the performance of four such transnational energy and climate governance networks. In the realm of sustainable energy, our cases are the Renewable Energy and Energy Efficiency Partnership (REEEP) and the Global Alliance for Clean Cookstoves (GACC). In the climate sphere, we examine the effectiveness of the Green Climate Fund (GCF) and the Clinton Climate Initiative (CCI). Using principles from governance and public administration about the effectiveness of institutions, we examine the extent to which four networks have contributed to improving governance outcomes in the spheres of climate and sustainable energy. Our evaluation focuses on the clarity of purpose, funding, institutional formality, efficacy, and level of resilience of these networks. Some differences between the networks notwithstanding, we find that the transnational governance networks generally fail to meet the criteria about what constitutes an effective institution. The paper concludes with a reflection on what could be done to enhance the performance of these governance networks
- …