Multi-temporal Landsat data are used for this study over the period of 1989 to 2016 with imageries of 1989, 2001, 2009 and 2016. Band rationing method and threshold technique are applied for the coastline extraction. The Digital Shoreline Analysis System ENVI 5.1, eCognition and ArcGIS 10.3 are used to calculate shoreline rate-of-change statistics from multiple historical shoreline positions. The results show that shoreline change in the Hau river mouth area has a trend of deposition between 1989 and 2016 (27 years) with the accretion area ranging from 162.68 ha to 1,210.83 ha. Meanwhile, the erosion area only ranges from 0.002 ha to 183.53 ha. The results obtained from this study set a stage for new studies to understand the morphological changes of the river mouths in the Mekong Delta and coastal areas of Hau river.
In this paper we study graded ideals I in a polynomial ring S such that the numerical function k → depth(S/I k ) is constant. We show that, if (i) the Rees algebra of I is Cohen-Macaulay, (ii) the cohomological dimension of I is not larger than the projective dimension of S/I and (iii) the K-algebra generated by some homogeneous generators of I is a direct summand of S, then depth(S/I k ) is constant. All the ideals with constant depth-function discovered by Herzog and Vladoiu in [HV] satisfy the criterion given above. In the contest of square-free monomial ideals, there is a chance that a converse of the previous fact holds true.
In this article, we try to understand which generically complete intersection monomial ideals with fixed radical are Cohen-Macaulay. We are able to give a complete characterization for a special class of simplicial complexes, namely the Cohen-Macaulay complexes without cycles in codimension 1. Moreover, we give sufficient conditions when the square-free monomial ideal has minimal multiplicity.
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