1,038 research outputs found
Hyperfine magnetic field in ferromagnetic graphite
Information on atomic-scale features is required for a better understanding
of the mechanisms leading to magnetism in non-metallic, carbon-based materials.
This work reports a direct evaluation of the hyperfine magnetic field produced
at 13C nuclei in ferromagnetic graphite by nuclear magnetic resonance (NMR).
The experimental investigation was made possible by the results of
first-principles calculations carried out in model systems, including graphene
sheets with atomic vacancies and graphite nanoribbons with edge sites partially
passivated by oxygen. A similar range of maximum hyperfine magnetic field
values (18-21T) was found for all systems, setting the frequency span to be
investigated in the NMR experiments; accordingly, a significant 13C NMR signal
was detected close to this range without any external applied magnetic field in
ferromagnetic graphite
Intersubband-induced spin-orbit interaction in quantum wells
Recently, we have found an additional spin-orbit (SO) interaction in quantum
wells with two subbands [Phys. Rev. Lett. 99, 076603 (2007)]. This new SO term
is non-zero even in symmetric geometries, as it arises from the intersubband
coupling between confined states of distinct parities, and its strength is
comparable to that of the ordinary Rashba. Starting from the Kane
model, here we present a detailed derivation of this new SO Hamiltonian and the
corresponding SO coupling. In addition, within the self-consistent Hartree
approximation, we calculate the strength of this new SO coupling for realistic
symmetric modulation-doped wells with two subbands. We consider gated
structures with either a constant areal electron density or a constant chemical
potential. In the parameter range studied, both models give similar results. By
considering the effects of an external applied bias, which breaks the
structural inversion symmetry of the wells, we also calculate the strength of
the resulting induced Rashba couplings within each subband. Interestingly, we
find that for double wells the Rashba couplings for the first and second
subbands interchange signs abruptly across the zero bias, while the
intersubband SO coupling exhibits a resonant behavior near this symmetric
configuration. For completeness we also determine the strength of the
Dresselhaus couplings and find them essentially constant as function of the
applied bias.Comment: 16 pages, 12 figure
Structure-property relationships in protic ionic liquids : a study of solvent-solvent and solvent-solute Interactions
The ionic nature of a functionalized protic ionic liquid cannot be rationalized simply through the differences in aqueous proton dissociation constants between the acid precursor and the conjugate acid of the base precursor. The extent of proton transfer, i.e. the equilibrium ionicity, of a tertiary ammonium acetate protic ionic liquid can be significantly increased by introducing an hydroxyl functional group on the cation, compared to the alkyl or amino-functionalized analogues. This increase in apparent ionic nature correlates well with variations in solvent-solute and solvent-solvent interaction parameters, as well as with physicochemical properties such as viscosity
Structure-property relationships in protic ionic liquids : A thermochemical study
How does cation functionality influence the strength of intermolecular interactions in protic ionic liquids (PILs)? Quantifying the energetics of PILs can be an invaluable tool to answer this fundamental question. With this in view, we have determined the standard molar enthalpy of vaporization, Delta H_vap , and the standard molar enthalpy of formation, Delta H_f, of three tertiary ammonium acetate PILs with varying cation functionality, and of their corresponding precursor amines, through a combination of Calvet-drop microcalorimetry, solution calorimetry, and ab-initio calculations. The obtained results suggest that these PILs vaporize as their neutral acid and base precursors. We also found a strong correlation between Delta H_vap of the PILs and of their corresponding amines. This suggests that, within this series of PILs, the influence of cation modification on their cohesive energies follows a group additivity rule. Finally, no correlation between the Delta H_vap of PILs and the extent of proton transfer, as estimated from the difference in aqueous pKa between the precursor acid and the conjugate acid of the precursor base, was observed
Small bowel enteroscopy - A joint clinical guideline from the spanish and portuguese small bowel study groups
The present evidence-based guidelines are focused on the
use of device-assisted enteroscopy in the management of
small-bowel diseases. A panel of experts selected by the
Spanish and Portuguese small bowel study groups reviewed
the available evidence focusing on the main indications of
this technique, its role in the management algorithm of each
indication and on its diagnostic and therapeutic yields. A set
of recommendations were issued accordingly.Estas recomendações baseadas na evidência detalham o
uso da enteroscopia assistida por dispositivo no manejo
clínico das doenças do intestino delgado. Um conjunto de
Gastrenterologistas diferenciados em patologia do intestino delgado foi selecionado pelos grupos de estudos Espanhol e Português de intestino delgado para rever a evidência disponível sobre as principais indicações desta
técnica, o seu papel nos algoritmos de manejo de cada
indicação e sobre o seu rendimento diagnóstico e terapêutico. Foi gerado um conjunto de recomendações pelos autores
Wasted cabbage (Brassica oleracea) silages treated with different levels of ground corn andsilage inoculant
Length-weight relation, condition factor and gonadosomatic index of the whitemouth croaker, Micropogonias furnieri (Desmarest, 1823) (Actinopterygii: Sciaenidae), caught in Lençóis Bay, state of Maranhão, eastern Amazon, Brazil
Growth of hydroponic lettuce with optimized mineral and organomineral nutrient solutions
- …