26,284 research outputs found
Shear-melting of a hexagonal columnar crystal by proliferation of dislocations
A hexagonal columnar crystal undergoes a shear-melting transition above a
critical shear rate or stress. We combine the analysis of the shear-thinning
regime below the melting with that of synchrotron X-ray scattering data under
shear and propose the melting to be due to a proliferation of dislocations,
whose density is determined by both techniques to vary as a power law of the
shear rate with a 2/3 exponent, as expected for a creep model of crystalline
solids. Moreover, our data suggest the existence under shear of a line hexatic
phase, between the columnar crystal and the liquid phase
The atomic orbitals of the topological atom
The effective atomic orbitals have been realized in the framework of Bader’s atoms in molecules theory for a general wavefunction. This formalism can be used to retrieve from any type of calculation a
proper set of orthonormalized numerical atomic orbitals, with occupation numbers that sum up to the
respective Quantum Theory of Atoms in Molecules (QTAIM) atomic populations. Experience shows
that only a limited number of effective atomic orbitals exhibit significant occupation numbers. These
correspond to atomic hybrids that closely resemble the core and valence shells of the atom. The
occupation numbers of the remaining effective orbitals are almost negligible, except for atoms with
hypervalent character. In addition, the molecular orbitals of a calculation can be exactly expressed
as a linear combination of this orthonormalized set of numerical atomic orbitals, and the Mulliken
population analysis carried out on this basis set exactly reproduces the original QTAIM atomic populations of the atoms. Approximate expansion of the molecular orbitals over a much reduced set of
orthogonal atomic basis functions can also be accomplished to a very good accuracy with a singular
value decomposition procedure
Is emamectin benzoate effective against the different stages of Spodoptera exigua (Hübner) (Lepidoptera, Noctuidae)?
peer-reviewedThis work was partially supported by the Spanish Ministry of Science and Innovation (project AGL 2007-66130-C03-02 to P. Medina). F. Amor and P. Bengochea acknowledge the ministry of Education
and Culture and the Technical University of Madrid (UPM) for the doctoral fellowships. Special thanks to Syngenta Agro S.A. for their support.The beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera, Noctuidae), is a major
polyphagous pest in greenhouses and open fields worldwide and also a main problem
in sweet pepper greenhouses. The effectiveness of the pesticide emamectin benzoate was tested in the laboratory on different stages of S. exigua using different concentrations and uptake routes. After dipping young (48-h-old) S. exigua eggs in emamectin benzoate at 0.5, 1 and 1.5 mg/L a.i. the chemical did not exhibit any ovicidal activity. There was, however, progressive neonate mortality at all concentrations,
culminating at 72 hours after hatching, when 100% of the larvae from the treated young
eggs died. Second and fourth instar S. exigua larvae did not exhibit significant mortality when exposed to the inert surfaces which were treated. In contrast, ingesting a diet contaminated with 0.5 mg/L a.i. of emamectin benzoate caused 100% mortality in L2 and L4 larvae 24 and 72 hours after ingestion, respectively. The LC50 value of the compound against L4 larvae that fed on sprayed sweet pepper leaves for 24 hours was 0.81 mg/L a.i..
When adults were fed on a solution of 0.5 mg/L a.i., there was a reduction in the female and male lifespan of 29.3% and 55.3%, respectively. Fecundity was reduced by more than 99%. These data suggest that emamectin benzoate is not only a useful insecticide when ingested by beet armyworm larvae but it also has ovolarvicidal and adult activity.Spanish Ministry of Science and Innovatio
Riding the kinematic waves in the Milky Way disk with Gaia
Gaia DR2 has delivered full-sky 6-D measurements for millions of stars, and
the quest to understand the dynamics of our Galaxy has entered a new phase. Our
aim is to reveal and characterize the kinematic sub-structure of the different
Galactic neighbourhoods, to form a picture of their spatial evolution that can
be used to infer the Galactic potential, its evolution and its components. We
take ~5 million stars in the Galactic disk from the Gaia DR2 catalogue and
build the velocity distribution of many different Galactic Neighbourhoods
distributed along 5 kpc in Galactic radius and azimuth. We decompose their
distribution of stars in the V_R-V_phi plane with the wavelet transformation
and asses the statistical significance of the structures found. We detect many
kinematic sub-structures (arches and more rounded groups) that diminish their
azimuthal velocity as a function of Galactic radius in a continuous way,
connecting volumes up to 3 kpc apart in some cases. The decrease rate is, on
average, of ~23 km/s/kpc. In azimuth, the kinematic sub-structures present much
smaller variations. We also observe a duality in their behaviour: some conserve
their vertical angular momentum with radius (e.g., Hercules), while some seem
to have nearly constant kinetic energy (e.g., Sirius). These two trends are
consistent with the approximate predictions of resonances and of phase mixing,
respectively. Besides, the overall spatial evolution of Hercules is consistent
with being related to the Outer Lindblad Resonance of the Bar. We also detect
structures without apparent counterpart in the vicinity of the Sun. The various
trends observed and their continuity with radius and azimuth allows for future
work to deeply explore the parameter space of the models. Also, the
characterization of extrasolar moving groups opens the opportunity to expand
our understanding of the Galaxy beyond the Solar Neighbourhood.Comment: 16 pages. Submitted to Astronomy and Astrophysics on 24th of May,
2018. Related on-line material available (see Appendix B
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