156 research outputs found
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Activity of iron pyrite towards low-temperature ammonia production
© 2016 In this work we report the characteristics of iron pyrite toward the production of ammonia at low temperatures under ultra-high vacuum conditions. We review (with additional unpublished details) our previous systematic study of nitrogen and hydrogen adsorption on single-crystal iron pyrite (FeS 2 ) and summarise our earlier findings regarding the possibility of ammonia synthesis on this material. We also present new results concerning the adsorption of nitrogen and hydrogen on two related materials, namely molybdenum-treated iron pyrite surfaces and iron pyrite nanostructures deposited on a gold single-crystal. On the bare iron pyrite samples, ammonia is produced upon hydrogenation of preadsorbed N species at 230 K, demonstrating that all hydrogenation steps are possible at low pressures and temperatures. Nitrogen adsorbs molecularly on FeS 2 {100} at low temperatures, desorbing at 130 K, but does not adsorb dissociatively even at pressures up to 1 bar. Adsorbed nitrogen species can, however, be obtained through exposure to excited nitrogen species. Hydrogen adsorbs on FeS 2 {100}, but only in the presence of an incandescent Ta filament. Recombinative desorption of H 2 occurs at 225 K and is accompanied by desorption of H 2 S at 260 K. On the molybdenum-treated iron-pyrite, no appreciable N ads species were detected under the experimental conditions studied, and the same is true for iron pyrite nanostructures on Au{111}. We also provide further details of our efficient and reproducible method for preparing well-ordered stoichiometrically pure FeS 2 {100} suitable for surface science studies
The barocaloric effect: A Spin-off of the Discovery of High-Temperature Superconductivity
Some key results obtained in joint research projects with Alex M\"uller are
summarized, concentrating on the invention of the barocaloric effect and its
application for cooling as well as on important findings in the field of
high-temperature superconductivity resulting from neutron scattering
experiments.Comment: 26 pages, 9 figure
Effects of spin-phonon interaction on the properties of in high-T superconductors
The mechanism of spin-phonon coupling in high-T copper oxides is explored
from band calculations on LaSrCuO and HgBaCuO
systems. The LMTO band calculations, based on the local density approximation,
are made for cells containing frozen phonon displacements and/or spin waves
within the CuO plane. The virtual crystal approximation is used for studies of
hole doped systems. The main result is that phonons are favorable for spin
waves and vice-versa, and that pseudogaps appear naturally in the band
structures of striped materials with strong SPC. The qualitative results are
compatible with many observations showing that the properties of high-T
superconductors depend both on lattice interactions and magnetic fluctuations.
The band results are used to model various properties, mainly of the normal
state, such as isotope effects, pseudogaps, Fermi surface broadening,
T-dependence of the pseudogap, phonon softening and some aspects of
superconductivity. The possibility of perpendicular SPC is investigated, partly
by the use of a nearly free electron model.Comment: 12 pages, 12 figure
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Epitaxial growth of few-layer MoS2(0001) on FeS2{100}.
Physical vapour deposition of Mo on an FeS2{100} surface was performed at 170 K. Near-epitaxial growth of MoS2(0001) overlayers of the order of 1 nm thickness was observed when the Mo-covered substrate was subsequently heated to 600 K.The authors thank the EPSRC (grant ref. EP/E039782/1) for
funding.This is the final published version. It first appeared at http://pubs.rsc.org/en/Content/ArticleLanding/2015/CC/c4cc06628f#!divAbstract
Pipeline for recording datasets and running neural networks on the Bela embedded hardware platform
Deploying deep learning models on embedded devices is an arduous task: oftentimes, there exist no platform-specific instructions, and compilation times can be considerably large due to the limited computational resources available on-device. Moreover, many music-making applications de- mand real-time inference. Embedded hardware platforms for audio, such as Bela, offer an entry point for beginners into physical audio computing; however, the need for cross- compilation environments and low-level software develop- ment tools for deploying embedded deep learning models imposes high entry barriers on non-expert users. We present a pipeline for deploying neural networks in the Bela embedded hardware platform. In our pipeline, we include a tool to record a multichannel dataset of sen- sor signals. Additionally, we provide a dockerised cross- compilation environment for faster compilation. With this pipeline, we aim to provide a template for programmers and makers to prototype and experiment with neural networks for real-time embedded musical applications
Liberación de la patela en las artroplastias totales de rodilla: estudio gammagráfico
Se han realizado estudios gammagráficos en 20 pacientes intervenidos de
artroplastia total cementada de rodilla. En 10 casos fue necesaria la liberación del alerón
rotuliano externo y en otros 10 no se habÃa indicado dicho gesto quirúrgico. En ningún
paciente existÃa alteración evolutiva del aparato extensor. Los estudios gammagráficos se
practicaron a los 12 meses del implante con el objeto de valorar la situación vascular de
la rótula en ese momento. Se comparó, en la proyección lateral, la captación de la rótula
en relación a la metáfisis distal del fémur homolateral. No hemos encontrado diferencias
entre ambos grupos por lo que consideramos que la liberación patelar no produce un déficit
vascular rotuliano a los 12 meses de la cirugÃa.Scintigraphic studies were performed in 20 patients with cemented total
prosthesis of the knee. The patellar release was necessary in 10 cases. None of the patients
developed knee extension deficits. Scintigraphic studies were performed 12 months after
surgery in order to know the patellar blood supply at that moment. Patellar isotopic uptake
was compared with the uptake at the distal metaphysis of the homolateral femur, at
lateral projection. We haven't found any differences between both groups, so we consider
that the patellar release doesn't make a less blood supply twelve months after surgery
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Increased thermal stability of activated N2 adsorbed on K-promoted Ni{110}
Industrial synthesis of ammonia takes place at high temperatures and pressures via the dissociative adsorption of molecular nitrogen on a transition metal catalyst. In contrast, biological ammonia synthesis occurs under ambient conditions via the hydrogenation of intact molecular nitrogen at the active site of an enzyme. We hypothesise that the latter process may be mimicked within an inorganic system if the intact nitrogen molecule can be polarised, rendering it particularly susceptible to attack by hydrogen. Furthermore, by analogy with the surface chemistry of carbon monoxide at alkali-modified nickel and cobalt surfaces, we consider whether such a polarisation may be achieved by coadsorption with potassium on the same or similar transition metals. Here, we report on reflection absorption infrared spectroscopy results, interpreted with the aid of first-principles density functional calculations, which reveal both similarities and differences between the behaviour of carbon monoxide and nitrogen. Importantly, our calculations suggest that the surface-induced dipole of molecular nitrogen can indeed be enhanced by the coadsorbed alkali metal
Spin-phonon interaction and band effects in the high-T_C superconductor HgBa_2CuO_4
Band calculations show that a stripe-like anti-ferromagnetic spin wave is
enforced by a 'half-breathing' phonon distortion within the CuO plane of
HgBa_2CuO_4. This spin-phonon coupling is increased further by shear distortion
and by increased distance between Cu and apical oxygens. The effects from
spin-phonon coupling are consistent with many observations in high-T_C
materials. Spin-phonon coupling can be important for the mechanism of spin
fluctuations and superconductivity, although the effects are quantitatively
weak when using the local density potential.Comment: 4 pages, 1 figur
Dynamical charge inhomogeneity and crystal-field fluctuations for 4f ions in high-Tc cuprates
The main relaxation mechanism of crystal-field excitations in rare-earth ions
in cuprates is believed to be provided by the fluctuations of crystalline
electric field induced by a dynamic charge inhomogeneity generic for the doped
cuprates. We address the generalized granular model as one of the model
scenario for such an ingomogeneity where the cuprate charge subsystem remind
that of Wigner crystal with the melting transition and phonon-like positional
excitation modes. Formal description of R-ion relaxation coincides with that of
recently suggested magnetoelastic mechanism.Comment: 4 page
Pseudogap behavior of nuclear spin relaxation in high Tc superconductors in terms of phase separation
We analyze anew experiments on the NMR in cuprates and find an important
information on their phase separation and its stripe character hidden in the
dependence of on degree of doping. In a broad class of materials
is the sum of two terms: the temperature independent one
attributed to ``incommensurate'' stripes that occur at external doping, and an
``universal'' temperature dependent term ascribed to moving metallic and AF
sub-phases. We argue that the frustrated first order phase transition in a
broad temperature interval bears a dynamical character.Comment: 5 pages, 3 figures; some comments and references added; accepted for
publication in JETP Letter
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