Fundamental solution for natural powers of the fractional Laplace and Dirac operators in the Riemann-Liouville sense

In this paper, we study the fundamental solution for natural powers of the $n$-parameter fractional Laplace and Dirac operators defined via Riemann-Liouville fractional derivatives. To do this we use iteration through the fractional Poisson equation starting from the fundamental solutions of the fractional Laplace $\Delta_{a^+}^\alpha$ and Dirac $D_{a^+}^\alpha$ operators, admitting a summable fractional derivative. The family of fundamental solutions of the corresponding natural powers of fractional Laplace and Dirac operators are expressed in operator form using the Mittag-Leffler function.publishe

Avaliação de leguminosas com potencial de uso para adubos verdes nos tabuleiros litorâneos do Piauí.

Green manure may lead to physical, chemical, and biological improvements to the soil. However, the information on its use in the Brazilian Northeast is scarce. The aim of this study was to assess the phenological cycle and phytomass productivity of seven legume species. This study was conducted in the second semester of 2015 in a completely randomized design with seven treatments and four replications

Effect of low level contamination on TiAl alloys studied by SIMS

Titanium aluminides are a valuable alternative to superalloys in applications where the ratio resistance/density is important. Since the ordinary production routes lead to high final costs, an alternative might be the use of traditional casting techniques by induction melting of the alloy in a ceramic crucible and pouring into ceramic moulds, made by the investment casting process. However, due to the high reactivity of Ti alloys, traditional ceramic materials cannot be used, as they lead to oxide formation and oxygen pick up from both the crucible and the moulding materials. In this work, the effect of low level contaminations was studied by SIMS. Special attention was given to the oxygen concentration of samples obtained with different mould materials. The comparison of SIMS in-depth profiles with hardness profiles, give insight concerning the significance of the oxygen concentration in the properties of the alloy and regarding the choice of the most suitable materials for TiAl production

Effect of the magnetic field on the operation of ionisation gauges

Funding Information: The support of the Portuguese Foundation for Science and Technology via the grants UIDB/00068/2020 and UIDP/00068/2020 is gratefully acknowledged. One of the authors (R. Silva) would like also to express his gratitude to the Portuguese Foundation for Science and Technology for his scholarship UI/BD/150626/2020. Publisher Copyright: © 2022 Elsevier LtdHot cathode ionisation gauges are the only reliable pressure measurement devices suitable for both high and ultra-high vacuum measurement. These devices are characterized by low accuracy that is hardly better than 20%. The sources of loss of accuracy are documented in the literature although their quantification and details are not fully understood. In the present work, simulations of Bayard-Alpert and extractor gauges were performed under the influence of uniform magnetic fields up to 30 Gs. Results are in qualitative agreement with measurements taken previously with the Bayard-Alpert gauge. Both gauges are sensitive to low intensity magnetic fields which may be present in vacuum chambers. However, the extractor gauge proved to be more stable in the presence of a magnetic field due to its ring-shaped cathode.publishersversionpublishe

A multispectral view of the periodic events in eta Carinae

A full description of the 5.5-yr low excitation events in Eta Carinae is presented. We show that they are not as simple and brief as previously thought, but a combination of two components. The first, the 'slow variation' component, is revealed by slow changes in the ionization level of circumstellar matter across the whole cycle and is caused by gradual changes in the wind-wind collision shock-cone orientation, angular opening and gaseous content. The second, the 'collapse' component, is restricted to around the minimum, and is due to a temporary global collapse of the wind-wind collision shock. High energy photons (E > 16 eV) from the companion star are strongly shielded, leaving the Weigelt objects at low ionization state for >6 months. High energy phenomena are sensitive only to the 'collapse', low energy only to the 'slow variation' and intermediate energies to both components. Simple eclipses and mechanisms effective only near periastron (e.g., shell ejection or accretion onto the secondary star) cannot account for the whole 5.5-yr cycle. We find anti-correlated changes in the intensity and the radial velocity of P Cygni absorption profiles in FeII 6455 and HeI 7065 lines, indicating that the former is associated to the primary and the latter to the secondary star. We present a set of light curves representative of the whole spectrum, useful for monitoring the next event (2009 January 11).Comment: 16 pages, 7 EPS figures, accepted for publication on MNRA

Evaluation of Y2O3 as front layer of ceramic crucibles for vaccum induction melting of tial based alloys

During the last decades titanium alloys were found to be valuable engineering materials for many different applications. Formerly used in critical applications like aerospace, aeronautic and military equipment, where the factor cost is not relevant, titanium alloys are finding now new and different markets. However, the development of such new markets will depend on an effective cost reduction of titanium parts, in order to achieve a selling cost suitable with its application in consumer goods. A possible solution to decrease production costs might be the use of traditional casting techniques to produce near net shape functional parts. During the last years, the authors have developed extensive research work on this field, and a new technique both for melting and moulding, using ceramic multi-layered crucibles and investment casting shells was developed. This paper presents some of the results obtained during that research work: Ti-48Al alloy were melted and cooled inside CaO, MgO and Y2O3 stabilized ZrO2 crucibles with inside layer of Y2O3. The chemical composition, hardness and microstructure at the metal-crucible interface, studied by secondary ion mass spectrometry, SEM/EDS and XRS are presented. On a second step, the same alloy was melted on the same crucibles, and poured into graphite moulds, and the crucibles wall was characterized by SEM/EDS and XRS.(undefined

Characterization of TiAl alloys by secondary Ion mass spectrometry

Titanium aluminides are arising as a valuable alternative to superalloys in applications where the ratio resistance/density is important. Together with excellent mechanical and corrosion properties at high temperatures, such characteristics are very attractive for applications in the aeronautical, aerospace and automotive industries. However, the current high selling price, due to high costs of production and raw materials and the need of very specific equipment, are limitative factors for further applications. With the end of the cold war, and the decrease of traditional markets of TiAl, the strategy to develop other applications, strongly depends on the decrease of production costs. An alternative to the present production routes might be the use of traditional casting techniques, by induction melting of the alloy in a ceramic crucible and pouring into ceramic moulds, made by the investment casting process. However, due to the high reactivity of Ti alloys, the use of traditional ceramic materials cannot be used, as they lead to oxide formation and oxygen pick up both from the crucible and the moulding materials. In this work, the relative oxygen concentration of Ti-48Al castings was measured by SIMS — Secondary Ion Mass Spectrometry. This technique provides a direct measurement of the isotopic composition with high sensitivity. The cylindrical samples were specially prepared to allow the analysis of the area close to the border. Oxygen profiles were acquired for samples obtained by with different mould materials. The comparison of such profiles with hardness profiles, give insight in the significance of the oxygen concentration in the properties of the alloy and in the choice of the most suitable materials for TiAl production(undefined

Produção de leite, gordura e proteína por lactação em cruzamentos de HVB X Guzerá.

Para caracterizar o desempenho de cruzamentos HVB X Guzerá, foram analisadas observações de primeiras lactações obtidas entre junho de 1980 e agosto de 1985 em 65 fazendas da região Sudeste, estratificadas em classes de alto e baixo nível de manejo.Resum