2,481 research outputs found
The magnetic exchange parameters and anisotropy of the quasi-two dimensional antiferromagnet NiPS
Neutron inelastic scattering has been used to measure the magnetic
excitations in powdered NiPS, a quasi-two dimensional antiferromagnet with
spin on a honeycomb lattice. The spectra show clear, dispersive magnons
with a meV gap at the Brillouin zone center. The data were fitted
using a Heisenberg Hamiltonian with a single-ion anisotropy assuming no
magnetic exchange between the honeycomb planes. Magnetic exchange interactions
up to the third intraplanar nearest-neighbour were required. The fits show
robustly that NiPS has an easy axis anisotropy with meV and
that the third nearest-neighbour has a strong antiferromagnetic exchange of
meV. The data can be fitted reasonably well with either
or , however the best quantitative agreement with high-resolution data
indicate that the nearest-neighbour interaction is ferromagnetic with meV and that the second nearest-neighbour exchange is small and
antiferromagnetic with meV. The dispersion has a minimum in the
Brillouin zone corner that is slightly larger than that at the Brillouin zone
center, indicating that the magnetic structure of NiPS is close to being
unstable.Comment: 21 pages, 7 figures, 33 reference
HEOS 1 helium observations in the solar wind
Results of alpha-particle observations performed by the European satellite HEOS 1, in the period from December 9, 1968, to April 13, 1969, and from September 6, 1969, to April 15, 1970, are presented. The average bulk velocities of protons V sub p and alpha-particles V sub alpha appear to be equal; however, due to an instrumental bias, the possibility of V sub alpha being lower than V sub p cannot be ruled out. Comparison with observations of Vela 3 and Explorer 34 satellites gives evidence of a dependence of helium abundance on the solar cycle. The problem of the stability of differences between the bulk velocities of protons and alpha-particles is investigated. The behavior of alpha-particles through interplanetary shock waves is illustrated in connection with magnetic field measurements
Thermal stability and aggregation of sulfolobus solfataricus b-glycosidase are dependent upon the N-e-methylation of specific lysyl residues: critical role of in vivo post-translational modifications.
Methylation in vivo is a post-translational modification observed in several organisms belonging to eucarya, bacteria, and archaea. Although important implications of this modification have been demonstrated in several eucaryotes, its biological role in hyperthermophilic archaea is far from being understood. The aim of this work is to clarify some effects of methylation on the properties of β-glycosidase from Sulfolobus solfataricus, by a structural comparison between the native, methylated protein and its unmethylated counterpart, recombinantly expressed in Escherichia coli. Analysis by Fourier transform infrared spectroscopy indicated similar secondary structure contents for the two forms of the protein. However, the study of temperature perturbation by Fourier transform infrared spectroscopy and turbidimetry evidenced denaturation and aggregation events more pronounced in recombinant than in native β-glycosidase. Red Nile fluorescence analysis revealed significant differences of surface hydrophobicity between the two forms of the protein. Unlike the native enzyme, which dissociated into SDS-resistant dimers upon exposure to the detergent, the recombinant enzyme partially dissociated into monomers. By electrospray mapping, the methylation sites of the native protein were identified. A computational analysis of β-glycosidase three-dimensional structure and comparisons with other proteins from S. solfataricus revealed analogies in the localization of methylation sites in terms of secondary structural elements and overall topology. These observations suggest a role for the methylation of lysyl residues, located in selected domains, in the thermal stabilization of β-glycosidase from S. solfataricu
Numerical model upgrading of a historical masonry building damaged during the 2016 Italian earthquakes: the case study of the Podestàpalace in Montelupone (Italy)
In October 2016, two major earthquakes occurred in Marche region in the Centre of Italy, causing widespread damage. The epicentre of the second one struck Norcia, Visso and Accumoli and a lot of damages to cultural heritage were done in the cities of Tolentino, San
Severino, Camerino, Matelica, Macerata and Montelupone, where are located the Podesta` Palace and the Civic Tower investigated in this paper. The main aim of this research is the determination of modal properties of these historical masonry constructions using experimental and numerical studies. The experimental analysis was based on ambient vibration survey, while numerical analysis was based on finite element analysis with solid elements. The results of the experimental study were used to tune the numerical model of the structure. As the most doubtful parameters, the modulus of elasticity of the masonry and the interaction among structural parts were adjusted to achieve the experimental results with numerical model by simple operations. Obtaining good consistency between the
experimental and numerical analyses, the study revealed the actual dynamic properties of the damaged palace
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