823 research outputs found
More on unicoherence at subcontinua
Studies are continued of unicoherence of a continuum X at
its subcontinuum Y. Relations are analyzed between unicoherence of X at Y, unicoherence of either X or Y, and structure of components of the complement X Y. The obtained results generalize certain teorems
proved in cite [OP]. Further, it is shown that terminality of Y implies
unicoherence of X at Y. Applications are shown of this result to
compactifications of a ray
City of dreams
Higher ability workers benefit more from bigger cities while housing costs there are higher for everyone, and yet there is little sorting on ability. A possible explanation is that young individuals have an imperfect assessment of their ability, and, when they learn about it, early decisions have had a lasting impact and reduce their incentives to move. We formalize this idea through an overlapping generations model of urban sorting by workers with heterogenous ability and self-confidence, with the latter defined as individuals’ assessment of their own ability. We then test the location patterns predicted by the model over the life cycle on panel data from the National Longitudinal Survey of Youth 1979. We find that the city-size choices of individuals at different stages vary with ability and self-confidence in a way that closely matches our theoretical predictions
Casting A356+SiCp with ultrasonically treated melts: effect reinforcement and processing in the microstructure
Low mass fractions (0.05 wt%) of SiC micro sized particles have been added to an A356 melt and dispersed by ultrasonic vibration to study their impact on the microstructural morphology of cast samples. It is shown that the ultrasonic melt treatment at 680°C can promote a homogenizeddistribution of the reinforcement while also degassing the melt and induces a moderate grain refinement. Even though SiC may act as a nucleant, its use did not induce a significant grain refinement relatively to ultrasonically treated unreinforced melts. Adding SiC microparticles, however, seems to enhance Eutectic Si modification, although it contributes to its slight coarsening at the expense of Mg2Si.publishe
On assessment of processing variables on vertical centrifugal casting technique
The aim of the present study is to investigate the influence of the vertical centrifugal casting
technique over mechanical and metallurgical properties of a hypereutectic Al–18Si alloy. Due to
the inherent vibration of the centrifugal casting technique, and in order to study and understand
the individual effects of the equipment vibration and the centrifugal force itself (pressure or fluid
dynamics), as well as the combined effect of both, three different tests were performed: gravity
casting, gravity casting with vibration and centrifugal casting. It was concluded that the
metallurgical and mechanical properties of castings obtained by the centrifugal casting process
depend on the combined effect of the centrifugal pressure and/or fluid dynamics and on the
inherent vibration of the technique itself. Correlations between the different casting techniques
and obtained mechanical and metallurgical properties are presentedFCT - Fundação para a Ciência e Tecnologi
Chemical composition of corn and sorghum grains cultivated in Oxisol with different application methods and doses of zinc.
In general, tropical soils present low concentrations of zinc (Zn), and the deficiency of Zn is recognized as a world nutritional problem for cereal production and human beings. Therefore, the main goal of this study was to assess the effects of different methods of Zn application on the quality of corn and sorghum grains grown in Oxisol. Two experiments were set up in the experimental area of UNESP (campus of Jaboticabal, Brazil). The following nine treatments were applied:three doses of Zn by banded application (seed furrows), three doses of Zn by incorporation into soil (0-20 cm depth), foliar application, seed application, and control (no Zn applied). The treatments were arranged in randomized blocks with four replicates. The contents of Zn, carbohydrates and proteins were determined for corn and sorghum grains. Regardless of the method, Zn application promoted higher contents of this micronutrient in corn and sorghum grains. The banded application method of Zn in soil promoted greater contents of total carbohydrates, starch and protein in both cultures. The incorporation of Zn into the soil method provided higher contents of soluble carbohydrates in both corn and sorghum grains
Ceramic sonotrodes for light alloy melt treatment
Alloy melt treatment by ultrasonic vibration is a physical processing technique that has been gathering the support of the scientific community. The use of metallic sonotrodes for this purpose has been proven very efficient; however, it promotes melt inclusion by sonotrode erosion. Such an issue is being addressed by the use of ceramic sonotrodes in low-amplitude resonance. Given that these novel sonotrodes generally have complex shapes and low displacements, this study shows an innovative approach for their characterization. Based on scanning laser Doppler vibrometry, the signal processing Python-based script was used to map the overall resonant behavior of a tubular SiAlON sonotrode, and this route is able to characterize the complex shapes in low-amplitude and high-frequency radial resonance in resonant ceramic sonotrodes. Velocity time-domain profiles are shown to be dependent on the position, and even though the radial natural frequencies of ceramic sonotrodes have low amplitudes, they are proposed as an efficient tool for melt treatment. While characterizing the radial natural mode in ceramic sonotrodes, this study proves that their low-amplitude Lamb waves are responsible for the refinement of a-grains and secondary phases in light alloys.This work was supported by PTDC/EMEEME/30967/
2017 and NORTE-0145-FEDER-030967, co-financed
by the European Regional Development Fund (ERDF),
through the Operational Programme for Competitive ness and Internationalization (COMPETE 2020), under
Portugal 2020, and by the Fundação para a Cência e a
Tecnologia – FCT I.P. national funds. Also, this work
was supported by Portuguese FCT, under the reference
project UIDB/04436/2020, and Stimulus of Scientific
Employment Application CEECIND/03991/2017
Ionisation-induced star formation III: Effects of external triggering on the IMF in clusters
We report on Smoothed Particle Hydrodynamics (SPH) simulations of the impact
on a turbulent M star--forming molecular cloud of
irradiation by an external source of ionizing photons. We find that the
ionizing radiation has a significant effect on the gas morphology, but a less
important role in triggering stars. The rate and morphology of star formation
are largely governed by the structure in the gas generated by the turbulent
velocity field, and feedback has no discernible effect on the stellar initial
mass function. Although many young stars are to be found in dense gas located
near an ionization front, most of these objects also form when feedback is
absent. Ionization has a stronger effect in diffuse regions of the cloud by
sweeping up low--density gas that would not otherwise form stars into
gravitationally--unstable clumps. However, even in these regions, dynamical
interactions between the stars rapidly erase the correlations between their
positions and velocities and that of the ionization front.Comment: 12 pages, 16 figures (some downgraded to fit on astro-ph), accepted
for publication in MNRA
Systematic characterisation of the Herschel SPIRE Fourier Transform Spectrometer
A systematic programme of calibration observations was carried out to monitor
the performance of the SPIRE FTS instrument on board the Herschel Space
Observatory. Observations of planets (including the prime point-source
calibrator, Uranus), asteroids, line sources, dark sky, and cross-calibration
sources were made in order to monitor repeatability and sensitivity, and to
improve FTS calibration. We present a complete analysis of the full set of
calibration observations and use them to assess the performance of the FTS.
Particular care is taken to understand and separate out the effect of pointing
uncertainties, including the position of the internal beam steering mirror for
sparse observations in the early part of the mission. The repeatability of
spectral line centre positions is <5km/s, for lines with signal-to-noise ratios
>40, corresponding to <0.5-2.0% of a resolution element. For spectral line
flux, the repeatability is better than 6%, which improves to 1-2% for spectra
corrected for pointing offsets. The continuum repeatability is 4.4% for the SLW
band and 13.6% for the SSW band, which reduces to ~1% once the data have been
corrected for pointing offsets. Observations of dark sky were used to assess
the sensitivity and the systematic offset in the continuum, both of which were
found to be consistent across the FTS detector arrays. The average point-source
calibrated sensitivity for the centre detectors is 0.20 and 0.21 Jy [1 sigma; 1
hour], for SLW and SSW. The average continuum offset is 0.40 Jy for the SLW
band and 0.28 Jy for the SSW band.Comment: 41 pages, 37 figures, 32 tables. Accepted for publication in MNRA
Padrões nutricionais para lavouras arrozeiras irrigadas por inundação pelos métodos da CND e Chance Matemática.
Para o arroz irrigado, poucos trabalhos utilizam métodos de diagnose foliar desenvolvidos para as condições locais de clima, solo ou cultivares. O objetivo deste trabalho foi avaliar os métodos da Diagnose da Composição Nutricional e da Chance Matemática na definição dos padrões nutricionais de lavouras arrozeiras do Estado do Rio Grande do Sul. Resultados de produtividade de grãos e teores foliares de N, P, K, Ca, Mg, S, B, Cu, Fe, Mn, Zn e Mo de 356 lavouras arrozeiras cultivadas sob sistema de irrigação por inundação foram utilizados para a determinação das faixas de suficiência calculadas pelo método da Chance Matemática. As faixas de suficiência foram comparadas com valores críticos propostos pela literatura e com o intervalo de confiança do teor médio dos nutrientes em lavouras consideradas nutricionalmente equilibradas, identificadas pelo método Diagnose da Composição Nutricional. Observou-se pouca concordância entre os valores das faixas de suficiência indicados pelos métodos da Chance Matemática e da Diagnose da Composição Nutricional e os respectivos valores indicados na literatura. A faixa de teores foliares adequados, consistentes com maior produtividade média das lavouras arrozeiras, foi indicada ser de 23 a 28 g kg-1 para N; 11 a 14 g kg-1 para K; 1,4 a 2,0 g kg-1 para S; 6 a 12 mg kg-1 para B; e 70 a 200 mg kg-1 para Fe. Para os teores foliares de P, Ca, Mg, B, Cu, Mn e Zn e Mo nenhuma das faixas adequadas testadas indicou capacidade para distinguir as lavouras arrozeiras quanto à produtividade média
Effect of grain and secondary phase morphologies in the mechanical and damping behavior of Al7075 alloys
The present study evaluates the role of the microstructure in the static and dynamic mechanical behavior of as-cast Al7075 alloy promoted by ultrasonic treatment (US) during solidification. The characterization of samples revealed that US treatment promoted grain and intermetallics refinement, changed the shape of the intermetallic phases (equilibrium phases of soluble M and/or T (Al, Cu, Mg, Zn) and their insoluble Al-Cu-Fe compounds) and lead to their uniform distribution along the grain boundaries. Consequently, the mechanical properties and damping capacity above critical strain values were enhanced by comparison with values obtained for castings produced without US vibration. This results suggest that the grain and secondary phases refinement by US can be a promising solution to process materials to obtain high damping and high strength characteristics.This research was supported by FEDER/COMPETE funds and by national funds through FCT - Portuguese Foundation for Science and Technology and was developed on the aim of the research Post-Doctoral grant SFRH/BPD/76680/2011. Also, this work has been supported by the FCT in the scope of the project: UID/EEA/04436/2013.info:eu-repo/semantics/publishedVersio
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