4,408 research outputs found
Disorder induced brittle to quasi-brittle transition in fiber bundles
We investigate the fracture process of a bundle of fibers with random Young
modulus and a constant breaking strength. For two component systems we show
that the strength of the mixture is always lower than the strength of the
individual components. For continuously distributed Young modulus the tail of
the distribution proved to play a decisive role since fibers break in the
decreasing order of their stiffness. Using power law distributed stiffness
values we demonstrate that the system exhibits a disorder induced brittle to
quasi-brittle transition which occurs analogously to continuous phase
transitions. Based on computer simulations we determine the critical exponents
of the transition and construct the phase diagram of the system.Comment: 6 pages, 6 figure
The Quasar-frame Velocity Distribution of Narrow CIV Absorbers
We report on a survey for narrow (FWHM < 600 km/s) CIV absorption lines in a
sample of bright quasars at redshifts in the Sloan Digital
Sky Survey. Our main goal is to understand the relationship of narrow CIV
absorbers to quasar outflows and, more generally, to quasar environments. We
determine velocity zero-points using the broad MgII emission line, and then
measure the absorbers' quasar-frame velocity distribution. We examine the
distribution of lines arising in quasar outflows by subtracting model fits to
the contributions from cosmologically intervening absorbers and absorption due
to the quasar host galaxy or cluster environment. We find a substantial number
( per cent) of absorbers with REW \AA in the velocity range
+750 km/s \la v \la +12000 km/s are intrinsic to the AGN outflow. This
`outflow fraction' peaks near km/s with a value of . At velocities below km/s the incidence
of outflowing systems drops, possibly due to geometric effects or to the
over-ionization of gas that is nearer the accretion disk. Furthermore, we find
that outflow-absorbers are on average broader and stronger than
cosmologically-intervening systems. Finally, we find that per cent of
the quasars in our sample exhibit narrow, outflowing CIV absorption with REW \AA, slightly larger than that for broad absorption line systems.Comment: 11 pages, 9 figures, accepted for publication in MNRA
Landslide Risk: Economic Valuation in the North-Eastern Zone of Medellin City
Natural disasters of a geodynamic nature can cause enormous economic and human losses. The economic costs of a landslide disaster include relocation of communities and physical repair of urban infrastructure. However, when performing a quantitative risk analysis, generally, the indirect economic consequences of such an event are not taken into account. A probabilistic approach methodology that considers several scenarios of hazard and vulnerability to measure the magnitude of the landslide and to quantify the economic costs is proposed. With this approach, it is possible to carry out a quantitative evaluation of the risk by landslides, allowing the calculation of the economic losses before a potential disaster in an objective, standardized and reproducible way, taking into account the uncertainty of the building costs in the study zone. The possibility of comparing different scenarios facilitates the urban planning process, the optimization of interventions to reduce risk to acceptable levels and an assessment of economic losses according to the magnitude of the damage. For the development and explanation of the proposed methodology, a simple case study is presented, located in north-eastern zone of the city of MedellÃn. This area has particular geomorphological characteristics, and it is also characterized by the presence of several buildings in bad structural conditions. The proposed methodology permits to obtain an estimative of the probable economic losses by earthquake-induced landslides, taking into account the uncertainty of the building costs in the study zone. The obtained estimative shows that the structural intervention of the buildings produces a reduction the order of 21 % in the total landslide risk. © Published under licence by IOP Publishing Ltd
Magnon valley Hall effect in CrI3-based vdW heterostructures
Magnonic excitations in the two-dimensional (2D) van der Waals (vdW)
ferromagnet CrI3 are studied. We find that bulk magnons exhibit a non-trivial
topological band structure without the need for Dzyaloshinskii-Moriya (DM)
interaction. This is shown in vdW heterostructures, consisting of single-layer
CrI3 on top of different 2D materials as MoTe2, HfS2 and WSe2. We find
numerically that the proposed substrates modify substantially the out-of-plane
magnetic anisotropy on each sublattice of the CrI3 subsystem. The induced
staggered anisotropy, combined with a proper band inversion, leads to the
opening of a topological gap of the magnon spectrum. Since the gap is opened
non-symmetrically at the K+ and K- points of the Brillouin zone, an imbalance
in the magnon population between these two valleys can be created under a
driving force. This phenomenon is in close analogy to the so-called valley Hall
effect (VHE), and thus termed as magnon valley Hall effect (MVHE). In linear
response to a temperature gradient we quantify this effect by the evaluation of
the temperature-dependence of the magnon thermal Hall effect. These findings
open a different avenue by adding the valley degrees of freedom besides the
spin, in the study of magnons
Mapping the stellar age of the Milky Way bulge with the VVV : II. Deep JK s catalog release based on PSF photometry
Context. The bulge represents the best compromise between old and massive Galactic components, and as such its study is a valuable opportunity to understand how the bulk of the Milky Way formed and evolved. In addition, being the only bulge in which we can individually resolve stars in all evolutionary sequences, the properties of its stellar content provide crucial insights into the formation of bulges. Aims. We are providing a detailed and comprehensive census of the Milky Way bulge stellar populations by producing deep and accurate photometric catalogs of the inner ∼300 deg 2 of the Galaxy. Methods. We performed DAOPHOT/ALLFRAME point spread function (PSF) fitting photometry of multi-epochs J and K s images provided by the VISTA Variables in the VÃa Láctea (VVV) survey to obtain deep photometric catalogs. Artificial star experiments have been conducted on all images to properly assess the completeness and the accuracy of the photometric measurements. Results. We present a photometric database containing nearly 600 million stars across the bulge area surveyed by the VVV. Through the comparison of derived color-magnitude diagrams of selected fields representative of different levels of extinction and crowding, we show the quality, completeness and depth of the new catalogs. With the exception of the fields located along the plane, this new photometry samples stars down to ∼1-2 mag below the old main sequence turnoff with unprecedented accuracy. To demonstrate the tremendous potential inherent to this new dataset, we give a few examples of possible applications, including (i) star count studies through the dataset completeness map; (ii) surface brightness map; and (iii) cross-correlation with Gaia DR2. Conclusions. The database presented here represents an invaluable collection for the whole community, and we encourage its exploitation. The photometric catalogs including completeness information are publicly available through the ESO Science Archive as part of the MW-BULGE-PSPHOT release.Peer reviewedFinal Accepted Versio
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Technical note: how accurate can stalagmite formation temperatures be determined using vapour bubble radius measurements in fluid inclusions?
Stalagmites are natural archives containing detailed information on continental climate variability of the past. Microthermometric measurements of fluid inclusion homogenisation temperatures allow determination of stalagmite formation temperatures by measuring the radius of stable laser-induced vapour bubbles inside the inclusions. A reliable method for precisely measuring the radius of vapour bubbles is presented. The method is applied to stalagmite samples for which the formation temperature is known. An assessment of the bubble radius measurement accuracy and how this error influences the uncertainty in determining the formation temperature is provided. We demonstrate that the nominal homogenisation temperature of a single inclusion can be determined with an accuracy of ±0.25 °C, if the volume of the inclusion is larger than 105 μm3. With this method, we could measure in a proof-of-principle investigation that the formation temperature of 10–20 yr old inclusions in a stalagmite taken from the Milandre cave is 9.87 ± 0.80 °C, while the mean annual surface temperature, that in the case of the Milandre cave correlates well with the cave temperature, was 9.6 ± 0.15 °C, calculated from actual measurements at that time, showing a very good agreement. Formation temperatures of inclusions formed during the last 450 yr are found in a temperature range between 8.4 and 9.6 °C, which corresponds to the calculated average surface temperature. Paleotemperatures can thus be determined within ±1.0 °C
Management Model of Ecological Tourism for the City of Francisco de Orellana
The purpose of the present study is to design a management model of ecological tourism for the city of Francisco de Orellana. Through the compilation of information and tourist offers, and the analysis of biophysical, sociocultural and economic areas, and plants, superstructures and attractions that appeal to tourists, 4 natural and 5 cultural places were identified. With the application of the environmental impact matrix, it was determined that tourist attractions present a high level of contamination due to the presence of the industrial sector and the inadequate handling of dirty water and solid waste. The most affected tourist attractions are: Napo and Payamino rivers, the Yacu eco-park and the boardwalk; throughout the environmental impact matrix they establish obstacles to environmental remediation. With the results obtained, a sustainable tourism management model was designed based on the objectives of Plan Nacional del Buen Vivir and PLANDETUR 2020. The study concludes that the management model will provide a starting point for the development of sustainable tourism activity in the city.
Keywords: sustainable tourism, management model, environmental sustainability, government policies, environmental impact, strategic plan.
Resumen
El objetivo de la presente investigación es diseñar un modelo de gestión del turismo ecológico para la ciudad de Francisco de Orellana. A través de la recopilación de información, oferta turÃstica y el análisis de áreas biofÃsicas, socioculturales, económicas, planta turÃstica, superestructura turÃstica y el atractivo turÃstico donde se identificaron 4 lugares naturales y 5 culturales. Con la aplicación de la matriz de impacto ambiental se determinó que los atractivos turÃsticos presentan un alto nivel de contaminación debido a la presencia del sector industrial y al manejo inadecuado del agua sucia y los residuos sólidos. Los atractivos turÃsticos más afectados son: RÃos Napo y Payamino, Payamino El eco parque Yacu y el malecón, a lo largo de la matriz de soluciones, establecen alternativas de remediación ambiental. Con los resultados obtenidos, se diseña un modelo de gestión del turismo sostenible basado en los objetivos del Plan Nacional del Buen Vivir y PLANDETUR 2020. Se concluye que el modelo de gestión proporcionará el comienzo para desarrollar una actividad turÃstica sostenible en la ciudad.
Palabras clave: turismo sostenible, modelo de gestión, sostenibilidad ambiental, polÃticas gubernamentales, impacto ambiental, plan estratégico
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