121 research outputs found
Numerical Modelling of Surface Quality in EDM Processes
AbstractElectro-discharge machining (EDM) is a non-conventional cutting technology widely applied to generate mechanical parts with a complex geometry. In order to describe the thermo-physical phenomena involved in this process and estimate the expected results for different cutting conditions, not only the experimental observation but also the numerical modelling is convenient. In the present work, a simplified numerical model is proposed to analyse the surface finish in penetration EDM with a minimized time for numerical computation. This model is focused on prediction of the material removal and surface irregularities on the workpiece material, from the heat transfer and cutting temperatures provoked by the successive sparks. The changes originated on the topography of machined surface can be properly predicted as a function of cutting time by the proposed model. The numerical predictions are compared with experimental results for the same cutting conditions, and a good agreement is found between both results
Fermi surface and electronic structure of Pb/Ge(111)
The electronic structure of Pb/Ge(111) has been probed along the temperature-induced phase transition ct -root 3X root 3R30 degrees double right arrow 3 X 3 using angle-resolved photoemission. The alpha-root 3X root 3R30 degrees phase is metallic due to the existence of a half-filled, dispersing surface band. The 3 X 3 phase is characterized by the appearance of an additional surface band with 3 X 3 periodicity, whose role in the phase transition is discussed. The Fermi-surface topology of the alpha-root 3X root 3R30 degrees phase has been probed using angle-resolved photoemission. Its shape is undulated, and it resembles strongly the theoretical prediction, with a Fermi momentum of 0.31 Angstrom(-1) along directions and 0.40 Angstrom(-1) along directions. These values were determined from different experimental methods, and agree with the values needed for a perfect 3 X 3 nesting. However, the Fermi surface exhibits no large flat areas suitable for electronic nesting
Heterogeneity and bipotency of astroglial-like cerebellar progenitors along the interneuron and glial lineages
Cerebellar GABAergic interneurons in mouse comprise multiple subsets of morphologically and neurochemically distinct phenotypes located at strategic nodes of cerebellar local circuits. These cells are produced by common progenitors deriving from the ventricular epithelium during embryogenesis and from the prospective white matter (PWM) during postnatal development. However, it is not clear whether these progenitors are also shared by other cerebellar lineages and whether germinative sites different from the PWM originate inhibitory interneurons. Indeed, the postnatal cerebellum hosts another germinal site along the Purkinje cell layer (PCL), in which Bergmann glia are generated up to first the postnatal weeks, which was proposed to be neurogenic. Both PCL and PWM comprise precursors displaying traits of juvenile astroglia and neural stem cell markers. First, we examine the proliferative and fate potential of these niches, showing that different proliferative dynamics regulate progenitor amplification at these sites. In addition, PCL and PWM differ in the generated progeny. GABAergic interneurons are produced exclusively by PWM astroglial-like progenitors, whereas PCL precursors produce only astrocytes. Finally, through in vitro, ex vivo, and in vivo clonal analyses we provide evidence that the postnatal PWM hosts a bipotent progenitor that gives rise to both interneurons and white matter astrocytes
Study of protein kinase c signalling in saccharomyces cerevisiae by silac-based phosphoproteomics
Comunicaciones a congreso
Magnetic domains on magnetite islands: from XMCD-PEEM to micromagnetism
Oral presentation given at the 13th European Conference on Surface Crystallography and Dynamics, held in Donostia-San Sebastián, Spain, on June 19-21th, 2017.Magnetite nanostructures and thin films have been grown in spintronic devices such as spin valves in order to take advantage of the high Curie temperature, stability, and predicted half-metal character. However, thin films present magnetic properties which are rather different from the properties of bulk magnetite: high coercive fields, high saturation fields, out-of-plane magnetization, superparamagnetism in ultrathin films, or unexpected easy-axes. An explanation for these effects are growth defects, among which antiphase domain boundaries (APBs) are the best example. In the present work, we study the magnetic domains on flat single-crystal magnetite and other mixed spinels grown on Ru(0001) by molecular beam epitaxy [1,2]. As each island grows from a single nucleus, there are expected to be free of APBs. We have measured with nanometer-resolution the 3D magnetization of the islands by combining x-ray magnetic circular dichroism images acquired in a photoemission electron microscope at different azimuthal angles. The 3D magnetization maps have been used as the initial magnetization configuration for micromagnetic simulations of islands with the same lateral and vertical dimensions as the experimental ones. The Mumax3 software has been used to perform the micromagnetic simulations. By comparing the evolution of the micromagnetic simulations with the experimental behavior of the islands after annealing, we seek to validate the material parameters that define their magnetic behavior and to identify cases where defects or other effects play a role
Charge density waves and surface Mott insulators for adlayer structures on semiconductors: extended Hubbard modeling
Motivated by the recent experimental evidence of commensurate surface charge
density waves (CDW) in Pb/Ge(111) and Sn/Ge(111) sqrt{3}-adlayer structures, as
well as by the insulating states found on K/Si(111):B and SiC(0001), we have
investigated the role of electron-electron interactions, and also of
electron-phonon coupling, on the narrow surface state band originating from the
outer dangling bond orbitals of the surface. We model the sqrt{3} dangling bond
lattice by an extended two-dimensional Hubbard model at half-filling on a
triangular lattice. We include an on-site Hubbard repulsion U and a
nearest-neighbor Coulomb interaction V, plus a long-ranged Coulomb tail. The
electron-phonon interaction is treated in the deformation potential
approximation. We have explored the phase diagram of this model including the
possibility of commensurate 3x3 phases, using mainly the Hartree-Fock
approximation. For U larger than the bandwidth we find a non-collinear
antiferromagnetic SDW insulator, possibly corresponding to the situation on the
SiC and K/Si surfaces. For U comparable or smaller, a rich phase diagram
arises, with several phases involving combinations of charge and
spin-density-waves (SDW), with or without a net magnetization. We find that
insulating, or partly metallic 3x3 CDW phases can be stabilized by two
different physical mechanisms. One is the inter-site repulsion V, that together
with electron-phonon coupling can lower the energy of a charge modulation. The
other is a novel magnetically-induced Fermi surface nesting, stabilizing a net
cell magnetization of 1/3, plus a collinear SDW, plus an associated weak CDW.
Comparison with available experimental evidence, and also with first-principle
calculations is made.Comment: 11 pages, 9 figure
Two-domains bulklike Fermi surface of Ag films deposited onto Si(111)-(7x7)
Thick metallic silver films have been deposited onto Si(111)-(7x7) substrates
at room temperature. Their electronic properties have been studied by using
angle resolved photoelectron spectroscopy (ARPES). In addition to the
electronic band dispersion along the high-symmetry directions, the Fermi
surface topology of the grown films has been investigated. Using ARPES, the
spectral weight distribution at the Fermi level throughout large portions of
the reciprocal space has been determined at particular perpendicular
electron-momentum values. Systematically, the contours of the Fermi surface of
these films reflected a sixfold symmetry instead of the threefold symmetry of
Ag single crystal. This loss of symmetry has been attributed to the fact that
these films appear to be composed by two sets of domains rotated 60 from
each other. Extra, photoemission features at the Fermi level were also
detected, which have been attributed to the presence of surface states and
\textit{sp}-quantum states. The dimensionality of the Fermi surface of these
films has been analyzed studying the dependence of the Fermi surface contours
with the incident photon energy. The behavior of these contours measured at
particular points along the Ag L high-symmetry direction puts forward
the three-dimensional character of the electronic structure of the films
investigated.Comment: 10 pages, 12 figures, submitted to Physical Review
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