14,639 research outputs found
Enseñanza de la Topología y Geometría en los niveles elementales
Tanto las nociones topológicas como las geométricas son un componente particularmente esencial en el desarrollo de la conciencia de los niños. Muchos autores están de acuerdo en la importancia de este conocimiento, pero están en disputa sobre cómo debe estructurarse. Estamos dividiendo el trabajo en dos partes: en la primera tratamos el contenido y ofrecemos un esquema de aprendizaje; En el segundo, ofrecemos orientación didáctica
Some doubts on the validity of the foreground Galactic contribution subtraction from microwave anisotropies
The Galactic foreground contamination in CMBR anisotropies, especially from
the dust component, is not easily separable from the cosmological or
extragalactic component. In this paper, some doubts will be raised concerning
the validity of the methods used to date to remove Galactic dust emission in
order to show that none of them achieves its goal.
First, I review the recent bibliography on the topic and discuss critically
the methods of foreground subtraction: the cross-correlation with templates,
analysis assuming the spectral shape of the Galactic components, the "maximum
entropy method", "internal linear combination", and "wavelet-based high
resolution fitting of internal templates". Second, I analyse the galactic
latitude dependence from WMAP data. The frequency dependence is discussed with
the data in the available literature. The result is that all methods of
subtracting the Galactic contamination are inaccurate. The galactic latitude
dependence analysis or the frequency dependence of the anisotropies in the
range 50-250 GHz put a constraint on the maximum Galactic contribution in the
power spectrum to be less than a ~10% (68% C. L.) for a ~1 degree scale, and
possibly higher for larger scales.
The origin of most of the signal in the CMBR anisotropies is not Galactic. In
any case, the subtraction of the Galaxy is not accurate enough to allow a
"precision Cosmology"; other sources of contamination (extragalactic, solar
system) are also present.Comment: 24 pages, 1 figure, accepted to be published in J. Astrophys. Ast
The Bartonian-Priabonian marine record of the eastern South Pyrenean Foreland Basin (NE Spain) : a new calibration of the larger foraminifers and calcareous nannofossil biozonation
This study presents a combined biostratigraphic (calcareous nannofossils, larger foraminifers) and magnetostratigraphic study of the Middle and Late Eocene marine units of the Igualada area, eastern Ebro Basin. The studied sections of Santa Maria de Miralles and La Tossa encompass the complete marine succession of the Santa Maria Group, where assemblages rich in larger foraminifers have been studied since the early 1950's. A total of 224 paleomagnetic sites and 62 biostratigraphic samples were collected along a 1350m-thick section that ranges from chron C20n to chron C16n (~43Ma to ~36Ma). The resulting magnetostratigraphy-based chronology challenges existing chronostratigraphic interpretations of these units and results in a new calibration of the biostratigraphic zonations. The base of calcareous nannofossil Zone NP19-20 is pinned down to an older age than its presently accepted attribution, whereas the time span assigned to Zone NP18 is significantly reduced. A revised calibration of larger foraminifers indicates that Zone SBZ18, formerly assigned exclusively to the late Bartonian, extends its range to the earlymost Priabonian, the Bartonian stage being almost entirely represented by Zone SBZ17. A division of Zone SBZ18 into two subzones is proposed
Holy Water: Photo-Brightening in Quasi-2D Perovskite Films under Ambient Enables Highly Performing Light-Emitting Diodes
Quasi-2D perovskites provide new opportunities for lighting and display applications due to their high radiative recombination and excellent stability. However, seldom attention has been placed on their self-stability/working operation under ambient storage. Herein, quasi-2D perovskites/Polyethylene oxide (PEO) films are studied, showing an unforeseen photo-brightening effect under ambient storage (i.e., an increase of the photoluminescence quantum yield from 55% to 74% after 100 days). In stark contrast, those stored under a dark/inert atmosphere show a significant decrease down to 38%. This counterintuitive phenomenon responds to the increasing radiative recombination rate caused by the passivation of the surface Br vacancies in the presence of physically adsorbed water molecules, as corroborated by in situ/ex situ X-ray photoelectron spectroscopy and density functional theory calculations. Capitalizing on this surprising effect, stable light-emitting diodes (LEDs) using quasi-2D perovskites/PEO color filters are fabricated, realizing high stabilities of ≈400 h@10 mA under operating ambient conditions, representing a 20-fold enhancement compared to LEDs with 3D counter partners. Hence, this study reveals a unique insight into the impact of water passivation on the optical/structural properties of quasi-2D perovskite films, broadening their applications under operating ambient conditions.Y.D. thanks the financial support from the China Scholarship Council (CSC, no. 201808440326). Financial support has been received from AEI-MINECO/FEDER, UE through the Nympha Project (PID2019-106315RB-I00), the regional government of "Comunidad de Madrid" and the European Structural Funds through FotoArt-CM Project (S2018/NMT-4367). F.O. acknowledges funding from the Marie Skłodowska-Curie grant agreement no 754382. M.U.K. and G.N. thank ELI-ALPS, which is supported by the European Union and co-financed by the European Regional Development Fund (GI-NOP-2.3.6-15-2015-00001). This publication has also received funding from PANOSC, the European Union's Horizon 2020 research and innovation programme under grant agreement no 823852. M.U.K. and G.N. also acknowledge Project no. 2019-2.1.13-TÉT-IN-2020-00059 which has been implemented with the support provided from the National Research, Development and Innovation Fund of Hungary, financed under the 2019-2.1.13-TÉT-IN funding scheme. O.A.R. has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 899987. R.D.C. and L.M.C. acknowledge the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 956923
Memoria del Taller
Se aborda sobre América Latina y el Caribe y sus esfuerzos regionales y nacionales que intentan mejorar el flujo de información tecnológica agropecuaria a través de las tecnologías de información y comunicación (TICs) basadas en Interne
Sources of experimental errors in the observation of nanoscale magnetism
It has been recently reported that some non-magnetic materials in bulk state,
exhibit magnetic behavior at the nanscale due to surface and size effects. The
experimental observation of these effects is based on the measurement of very
small magnetic signals. Thus, some spurious effects that are not critical for
bulk materials with large magnetic signals may become important when measuring
small signals (typically below 0.0001 emu). Here, we summarize some sources of
these small magnetic signals that should be considered when studying this new
nanomagnetismComment: 16 pages, 10 figure
The a-theorem and conformal symmetry breaking in holographic RG flows
We study holographic models describing an RG flow between two fixed points
driven by a relevant scalar operator. We show how to introduce a spurion field
to restore Weyl invariance and compute the anomalous contribution to the
generating functional in even dimensional theories. We find that the
coefficient of the anomalous term is proportional to the difference of the
conformal anomalies of the UV and IR fixed points, as expected from anomaly
matching arguments in field theory. For any even dimensions the coefficient is
positive as implied by the holographic a-theorem. For flows corresponding to
spontaneous breaking of conformal invariance, we also compute the two-point
functions of the energy-momentum tensor and the scalar operator and identify
the dilaton mode. Surprisingly we find that in the simplest models with just
one scalar field there is no dilaton pole in the two-point function of the
scalar operator but a stronger singularity. We discuss the possible
implications.Comment: 50 pages. v2: minor changes, added references, extended discussion.
v3: we have clarified some of the calculations and assumptions, results
unchanged. v4: published version in JHE
Buenas prácticas de extensión para capacitar, organizar y transferir tecnologías a los productores de café
Este manual surge en momentos en que la caficultura de
Centroamérica y el Caribe enfrenta una crisis causada por la disminución de los precios del café en los mercados internacionales, la reaparición de la enfermedad de la roya (Hemileia vastatrix) y la presencia de otras enfermedades y plagas como el ojo de gallo (Mycena citricolor) y la broca del café (Hypothenemus hampei ferrari), entre otras. El manual ha sido organizado en cinco módulos. El primero aborda la importancia de determinar los problemas y las necesidades de los productores por medio de diagnósticos, mientras el segundo resalta la relevancia de la planificación para responder a las necesidades o problemas detectados mediante esos diagnósticos. En el tercero se describen los procesos de extensión requeridos para mejorar las condiciones de producción y de vida de los productores, en tanto en el cuarto se ofrece una serie de metodologías, técnicas y actividades para desarrollar esos procesos. En el quinto módulo se presentan instrumentos para evaluar los resultados del programa de extensión
Overview of Plasma Lens Experiments and Recent Results at SPARC_LAB
Beam injection and extraction from a plasma module is still one of the
crucial aspects to solve in order to produce high quality electron beams with a
plasma accelerator. Proper matching conditions require to focus the incoming
high brightness beam down to few microns size and to capture a high divergent
beam at the exit without loss of beam quality. Plasma-based lenses have proven
to provide focusing gradients of the order of kT/m with radially symmetric
focusing thus promising compact and affordable alternative to permanent magnets
in the design of transport lines. In this paper an overview of recent
experiments and future perspectives of plasma lenses is reported
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