Substrate Effect on the High Temperature Oxidation Behavior of a Pt-modified Aluminide Coating. Part II: Long-term Cyclic-oxidation Tests at 1,050 C

This second part of a two-part study is devoted to the effect of the substrate on the long-term, cyclic-oxidation behavior at 1,050 C of RT22 industrial coating deposited on three Ni-base superalloys (CMSX-4, SCB, and IN792). Cyclicoxidation tests at 1,050 C were performed for up to 58 cycles of 300 h (i.e., 17,400 h of heating at 1,050 C). For such test conditions, interdiffusion between the coating and its substrate plays a larger role in the damage process of the system than during isothermal tests at 900, 1,050, and 1,150 C for 100 h and cyclicoxidation tests at 900 C which were reported in part I [N. Vialas and D. Monceau, Oxidation of Metals 66, 155 (2006)]. The results reported in the present paper show that interdiffusion has an important effect on long-term, cyclic-oxidation resistance, so that clear differences can be observed between different superalloys protected with the same aluminide coating. Net-mass-change (NMC) curves show the better cyclic-oxidation behavior of the RT22/IN792 system whereas uncoated CMSX-4 has the best cyclic-oxidation resistance among the three superalloys studied. The importance of the interactions between the superalloy substrate and its coating is then demonstrated. The effect of the substrate on cyclic-oxidation behavior is related to the extent of oxide scale spalling and to the evolution of microstructural features of the coatings tested. SEM examinations of coating surfaces and cross sections show that spalling on RT22/CMSX-4 and RT22/SCB was favored by the presence of deep voids localized at the coating/oxide interface. Some of these voids can act as nucleation sites for scale spallation. The formation of such interfacial voids was always observed when the b to c0 transformation leads to the formation of a two-phase b/c0 layer in contact with the alumina scale. On the contrary, no voids were observed in RT22/IN792, since this b to c0 transformation occurs gradually by an inward transformation of b leading to the formation of a continuous layer of c0 phase, parallel to the metal/scale interface

Solvent Effects on Ionization Potentials of Guanine Runs and Chemically Modified Guanine in Duplex DNA: Effect of Electrostatic Interaction and Its Reduction due to Solvent

We examined the ionization potential (IP) corresponding to the free energy of a hole on duplex DNA by semiempirical molecular orbital theory with a continuum solvent model. As for the contiguous guanines (a guanine run), we found that the IP in the gas phase significantly decreases with the increasing number of nucleotide pairs of the guanine run, whereas the IP in water (OP, oxidation potential) only slightly does. The latter result is consistent with the experimental result for DNA oligomers in water. This decrease in the IP is mainly due to the attractive electrostatic interaction between the hole and a nucleotide pair in the duplex DNA. This interaction is reduced in water, which results in the small decrease in the IP in water. This mechanism explains the discrepancy between the experimental result and the previous computational results obtained by neglecting the solvent. As for the chemically modified guanine, the previous work showed that the removal of some solvent (water) molecules due to the attachment of a neutral functional group to a guanine in a duplex DNA stabilizes the hole on the guanine. One might naively have expected the opposite case, since a polar solvent usually stabilizes ions. This mechanism also explains this unexpected stabilization of a hole as follows. When some water molecules are removed, the attractive electrostatic interaction stabilizing the hole increases, and thus, the hole is stabilized. In order to design the hole energetics by a chemical modification of DNA, this mechanism has to be taken into account and can be used. 1

New records of Anostraca (Crustacea: Branchiopoda) in western Iberian Peninsula and considerations on their conservation status

[EN] The knowledge about geographic distribution of species and intraspecific lineages, and the populations and metapopulations dynamic is essential to stablish conservation bases in many organisms. In recent years, the insight about anostraceans local distribution in the Iberian Peninsula has been greatly increased through taxonomic surveys in temporary natural and artificial aquatic environments. In this work, we review and update the Anostraca species distribution in centre and western areas of Iberian Peninsula, incorporating 157 new records deriving from surveys performed between 2015 and 2019. There are 5 species of anostraceans, of which the Iberian endemism Tanymastigites lusitanica is the one with less known populations, limited to a few localities in the Portuguese region of Alentejo. On the other hand, the new records provided for Branchipus schaefferi, Chirocephalus diaphanus and Tanymastix stagnalis increase their currently known occurrence area in the septentrional half of the Iberian Peninsula, especially in river Duero basin. First records of Branchipus cortesi are provided for Ciudad Real and Toledo provinces, the latter being the septentrional limit recognized for this species. Derived from the last phylogeographic studies in different species of Anostraca, which revealed the occurrence of geographically structured intraspecific lineages, it is demonstrated the need of conservation efforts focused on the identification and delimitation of evolutionary independent populations to be treated as conservation units. In the same way, we highlight the interest of the group for conservation purposes, and the pressures to which it is subjected, and suggest the necessary encourage of land traditional uses development that allow ground heterogeneity and promote the formation of ephemeral and unstable ponds[ES] Conocer la distribución geográfica de especies y linajes intraespecíficos, y la dinámica de sus poblaciones o sistemas metapoblacionales, es fundamental para establecer las bases de conservación en multitud de organismos. En los últimos años, el conocimiento de la distribución local de los anostráceos en la Península Ibérica se ha visto incrementado en gran medida a través de muestreos taxonómicos en medios acuáticos temporales de carácter natural y artificial. En este trabajo revisamos y actualizamos la distribución de especies de Anostraca en las regiones del centro y del oeste de la Península Ibérica e incorporamos 157 nuevos registros derivados de muestreos llevados a cabo entre los años 2015 y 2019. La zona de estudio cuenta con 5 especies de anostráceos, de las cuales el endemismo ibérico Tanymastigites lusitanica es la de distribución más restringida, limitada a unas pocas localidades en la región portuguesa de Alentejo. Por otra parte, los nuevos registros que aportamos de Branchipus schaefferi, Chirocephalus diaphanus y Tanymastix stagnalis aumentan el área de presencia conocida en la mitad septentrional de la Península Ibérica, especialmente en la cuenca del Duero. En lo relativo a Branchipus cortesi aportamos las primeras citas para las provincias de Ciudad Real y Toledo, constituyendo esta última el límite septentrional conocido para la especie. A raíz de los últimos estudios filogeográficos en diferentes especies de Anostraca, que desvelan la presencia de linajes intraespecíficos estructurados geográficamente, se pone de manifiesto la necesidad de dirigir los esfuerzos de conservación a identificar y delimitar las poblaciones evolutivamente independientes para tratarlas como unidades de conservación. De igual forma, destacamos el potencial que tiene este grupo en términos de conservación y las presiones a las que se ve sometido, y sugerimos la necesidad de apoyar el desarrollo de los usos tradicionales del medio, que fomentan la heterogeneidad del terreno y favorecen la formación de charcos efímeros e inestables en el tiempo.El trabajo de campo y los materiales bibliográficos consultados han sido financiados por las ayudas vinculadas a los proyectos PID2019 110243GB100/AEI/10.13039/501100011033 (Ministerio de Ciencia, Innovación y Universidades) e IND2018/AMB9692 (Comunidad de Madrid) de MG-P. LS-E es beneficiaria de una beca de Doctorado Industrial (IND2018/AMB9692) de la Comunidad de Madrid (España)