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1

Effect of cooling rate on microstructure and microhardness of hypereutectic Al–Ni alloy

Carrara A. P., Kakitani R., Garcia A., Cheung N.

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 1

230--238

EN

High solidification cooling rates during unsteady-state conditions of solidification of Al-based alloys can induce different microstructural length scales or metastable phases, leading to improved properties. The present study aims to characterize the microstructural arrangement of the hypereutectic Al–8 wt%Ni alloy, unidirectionally solidified in unsteady-state heat flow conditions, examining the influence of the cooling rate in the development of the Al–Al3Ni eutectic and the primary phase. A columnar-to-equiaxed macrostructural transition is shown to occur at a solidification cooling rate [...] of about 4.8 °C/s, with different microstructures associated with each morphological zone. The observation of microstructures of hypoeutectic, eutectic and hypereutectic Al–Ni alloys, has permitted an asymmetric coupled zone diagram to be proposed. The microstructural interphase spacings of the Al–8 wt%Ni alloy are experimentally determined and correlated to [...], and the Vickers microhardness (HV) is shown to decrease with the increase in such spacings. The higher experimental HV profile of the examined hypereutectic alloy as compared to that of the eutectic Al–Ni alloy is attributed to the formation of a supersaturated solid solution of Ni in α-Al.

2

On algebras of bounded continuous functions valued in a topological algebra

Arizmendi-Peimbert H., Chō M., Garcia A.

Commentationes Mathematicae

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2017

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Vol 57, No. 2

123--129

EN

Let X be a completely regular space. We denote by C(X,A) the locally convex algebra of all continuous functions on X valued in a locally convex algebra A with a unit e. Let Cb(X,A) be its subalgebra consisting of all bounded continuous functions and endowed with the topology given by the uniform seminorms of A on X. It is clear that A can be seen as the subalgebra of the constant functions of Cb(X,A). We prove that if A is a Q-algebra, that is, if the set G(A) of the invertible elements of A is open, or a Q-álgebra with a stronger topology, then the same is true for Cb(X,A).

3

Dynamical parameter analysis of continuous seismic signals of Popocatépetl volcano (Central Mexico): A case of tectonic earthquakes influencing volcanic activity

Tarraga M., De la Cruz-Reyna S., Mendoza-Rosas A., Carniel R., Martinez-Bringas A., Garcia A., Ortiz R.

Acta Geophysica

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2012

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Vol. 60, no. 3

664-681

EN

The continuous background seismic activity contains information on the internal state of a volcanic system. Here, we report the influence of major regional tectonic earthquakes (M > 5 in most cases) on such state, reflected as changes in the spectral and dynamical parameters of the volcano continuous seismic data. Although changes do not always occur, analysis of five cases of earthquake-induced variations in the signals recorded at Popocatepetl volcano in central Mexico reveal significant fluctuations following the tectonic earthquakes. External visible volcanic activity, such as small to moderate explosions and ash emissions, were related to those fluctuations. We briefly discuss possible causes of the variations. We conclude that recognition of fluctuations in the dynamical parameters in volcano monitoring seismic signals after tectonic earthquakes, even those located in the far field, hundreds of kilometers away, may provide an additional criterion for eruption forecasting, and for decision making in the definition of volcanic alert levels.

4

A spectral synthesis property for C_b (X, β)

Arizmendi-Peimbert H., Carrillo-Hoyo A., Garcia A.

Commentationes Mathematicae

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2008

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Vol. 48, [Z] 2

121-127

EN

Let (Cb (X) , ) be the algebra of all continuous bounded real or complex valued functions defined on a completely regular Hausdorff space X with the usual algebraic operations and with the strict topology . It is proved that (Cb (X) , β) has a spectral synthesis, i.e. every of its closed ideals is an intersection of closed maximal ideals of codimension 1. We give one necessary and two sufficient conditions over X in order that (Cb (X) , β) has no proper non-zero closed principal ideals. Moreover if X satisfy any of these two conditions and is also a k-space, then any non zero element of Cb (X) is invertible or a topological divisor of zero.