ALEJANDRO PARRA GUTIERREZ - Academia.edu (original) (raw)

Papers by ALEJANDRO PARRA GUTIERREZ

Research paper thumbnail of Potential of genomic selection for improvement of resistance to Ostreid Herpes virus in Pacific oyster (Crassostrea gigas)

In genomic selection (GS), genome-wide SNP markers are used to generate genomic estimated breedin... more In genomic selection (GS), genome-wide SNP markers are used to generate genomic estimated breeding values (gEBVs) for selection candidates. The application of GS in shellfish looks promising and has the potential to help in dealing with one of the main issues currently affecting Pacific oyster production worldwide, which is the “summer mortality syndrome”. This causes periodic mass mortality in farms worldwide and has mainly been attributed to a specific variant of the Ostreid herpesvirus (OsHV-1-μvar). In the current study, we evaluated the potential of genomic selection for host resistance OsHV in Pacific oysters, and compared it to pedigree-based approaches. An OsHV-1 disease challenge was performed using an immersion-based virus exposure treatment for oysters for seven days. 768 samples were genotyped using the medium density SNP array for oysters. GWAS was performed for the survival trait using a GBLUP approach in BLUPF90 software. Heritability ranged from 0.25±0.05 to 0.37±0.0...

Research paper thumbnail of Gene Expression Response to Sea Lice in Atlantic Salmon Skin: RNA Sequencing Comparison Between Resistant and Susceptible Animals

Frontiers in Genetics, 2018

Sea lice are parasitic copepods that cause large economic losses to salmon aquaculture worldwide.... more Sea lice are parasitic copepods that cause large economic losses to salmon aquaculture worldwide. Frequent chemotherapeutic treatments are typically required to control this parasite, and alternative measures such as breeding for improved host resistance are desirable. Insight into the host-parasite interaction and mechanisms of host resistance can lead to improvements in selective breeding, and potentially novel treatment targets. In this study, RNA sequencing was used to study the skin transcriptome of Atlantic salmon (Salmo salar) parasitized with sea lice (Caligus rogercresseyi). The overall aims were to compare the transcriptomic profile of skin at louse attachment sites and "healthy" skin, and to assess differences in gene expression response between animals with varying levels of resistance to the parasite. Atlantic salmon pre-smolts were challenged with C. rogercresseyi, growth and lice count measurements were taken for each fish. 21 animals were selected and RNA-Seq was performed on skin from a louse attachment site, and skin distal to attachment sites for each animal. These animals were classified into family-balanced groups according to the traits of resistance (high vs. low lice count), and growth during infestation. Overall comparison of skin from louse attachment sites vs. healthy skin showed that 4,355 genes were differentially expressed, indicating local up-regulation of several immune pathways and activation of tissue repair mechanisms. Comparison between resistant and susceptible animals highlighted expression differences in several immune response and pattern recognition genes, and also myogenic and iron availability factors. Components of the pathways involved in differential response to sea lice may be targets for studies aimed at improved or novel treatment strategies, or to prioritize candidate functional polymorphisms to enhance genomic selection for host resistance in commercial salmon breeding programs.

Research paper thumbnail of Detailed insights into pan‐European population structure and inbreeding in wild and hatchery Pacific oysters (Crassostrea gigas) revealed by genome‐wide SNP data

Evolutionary Applications, 2018

This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Research paper thumbnail of Characterization Of Amylase And Protease Activities In The Digestive System Of Concholepas concholepas (Gastropoda, muricidae)

Concholepas concholepas (loco) is a carnivorous gastropod that inhabits the coast of Chile and Pe... more Concholepas concholepas (loco) is a carnivorous gastropod that inhabits the coast of Chile and Peru. Its fisheries showed a great importance in the past decades, however, now mainly relies on artisanal management of wild stocks. Feeding is one of the important factors that have restrained the establishment of large scale field rearing of loco. C. concholepas food preferences consist of mytilids and cirripeds, however its digestive physiology has not been studied and its digestive enzymes have not been yet characterized. The purification of amylase and protease from the digestive gland and the gland of Leiblein of C. concholepas were performed by ionic exchange chromatography (DEAE-cellulose), and substrate-PAGE indicated the presence of the amylase and protease in the fractions collected from the column. Amylase enzymatic assays showed its maximum activity at pH 7.0 and 50°C in the digestive gland. Protease on the other hand showed a great acidic activity, specifically at pH 3.0 in ...

Research paper thumbnail of TEAD3, implicated by association to grilsing in Atlantic salmon

Aquaculture, 2017

With the recent finding that the vestigial-like family member 3 (Vgll3) gene is associated with e... more With the recent finding that the vestigial-like family member 3 (Vgll3) gene is associated with early maturation, we decided to reexamine previously reported quantitative trait loci (QTL) and genome wide association (GWA) studies, involved with early maturation, to see if Vgll3 was the source of any of these associations. Using a TaqMan assay for Vgll3, we were able to verify that a prominent QTL for early maturation was indeed associated with Vgll3. Next, we used Vgll3 genotypes as a cofactor to reexamine for any additional QTLs or GWAs. Several were found at the chromosome-wide significance level. By examining interacting partners of Vgll3 from other organisms, we identified several candidate genes that may interact with Vgll3 in Atlantic salmon and effect early maturation. The location of these genes were determined from the genome sequence, while markers near QTL were examined to see if they were near any Vgll3 interacting genes. In this way, we identified TEAD3 as a putative gene also influencing early maturation in Atlantic salmon. A TaqMan assay was used to genotype TEAD3. These genotypes appear to be associated with early maturation.

Research paper thumbnail of Development of a Medium Density Combined-Species SNP Array for Pacific and European Oysters (Crassostrea gigas and Ostrea edulis)

G3 (Bethesda, Md.), Jul 22, 2017

SNP arrays are enabling tools for high-resolution studies of the genetic basis of complex traits ... more SNP arrays are enabling tools for high-resolution studies of the genetic basis of complex traits in farmed and wild animals. Oysters are of critical importance in many regions from both an ecological and economic perspective, and oyster aquaculture forms a key component of global food security. The aim of our study was to design a combined-species medium density SNP array for Pacific oyster (C. gigas) and European flat oyster (O. edulis), and to test the performance of this array on farmed and wild populations from multiple locations, with a focus on European populations. SNP discovery was carried out by whole genome sequencing of pooled genomic DNA samples from eight C. gigas populations, and RAD Sequencing of 11 geographically diverse O. edulis populations. Nearly 12 million candidate SNPs were discovered and filtered based on several criteria including preference for SNPs segregating in multiple populations and SNPs with monomorphic flanking regions. An Affymetrix Axiom® Custom A...

Research paper thumbnail of Genome-Wide Association Study (GWAS) for Growth Rate and Age at Sexual Maturation in Atlantic Salmon (Salmo salar)

PloS one, 2015

Early sexual maturation is considered a serious drawback for Atlantic salmon aquaculture as it re... more Early sexual maturation is considered a serious drawback for Atlantic salmon aquaculture as it retards growth, increases production times and affects flesh quality. Although both growth and sexual maturation are thought to be complex processes controlled by several genetic and environmental factors, selection for these traits has been continuously accomplished since the beginning of Atlantic salmon selective breeding programs. In this genome-wide association study (GWAS) we used a 6.5K single-nucleotide polymorphism (SNP) array to genotype ∼480 individuals from the Cermaq Canada broodstock program and search for SNPs associated with growth and age at sexual maturation. Using a mixed model approach we identified markers showing a significant association with growth, grilsing (early sexual maturation) and late sexual maturation. The most significant associations were found for grilsing, with markers located in Ssa10, Ssa02, Ssa13, Ssa25 and Ssa12, and for late maturation with markers ...

Research paper thumbnail of X-ray absorption spectroscopy study at the SiK-edge of tungsten carbide-silicon carbide thin films

Scripta Materialia, 2007

ABSTRACT X-ray absorption spectroscopy (XAS) has been used to determine the compositional and str... more ABSTRACT X-ray absorption spectroscopy (XAS) has been used to determine the compositional and structural nature of the phases formed in sputter-deposited W-Si-C films. The Si K-edge was examined to determine the presence and crystallinity of the SiC phase. For a film composition of 22% SiC, the XAS results show that there is at best only a minor amount of crystallization of SiC when deposited ;at 350 degrees C, but crystallization becomes more definitive at 600 degrees C. For a film with 29% SiC deposited at 350 degrees C, no crystalline SiC was detected. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Research paper thumbnail of Cyclin C is a haploinsufficient tumour suppressor

Nature Cell Biology, 2014

S. and W.W. contributed molecular mechanistic analyses of cyclin C→Fbw7→ICN1 link, X.L. and H. v.... more S. and W.W. contributed molecular mechanistic analyses of cyclin C→Fbw7→ICN1 link, X.L. and H. v. B. contributed bone marrow transduction with ICN1 experiments, T.K. and H. v. B. performed analyses of thymocyte populations and studies of bone marrow chimeras. M.R.M. S.J., R.E.G. and D.C.L. discovered mutations in human patients which render cyclin C-CDK unable to phosphorylate Notch1, L.L. contributed to molecular studies and phosphorylation analyses, H.W. performed all analyses of ICN1 phosphorylation by cyclin C-CDK8, C-CDK19 and C-CDK3, B.K. and I.A. contributed in vivo mouse tumorigenesis studies, A.G. and A.T.L. contributed analyses of human TALL samples, A.O and J.W.H. performed analyses of endogenous ICN1 polyubiquitination, T.O. contributed shRNA analyses of mouse cells and analyses of pRB phosphorylation, Lu.B. and J.J.Z. helped with molecular in vivo analyses, C.A.M. analyzed gene expression data, M.J.K and J.C.A. performed immunostaining for ICN1, M.R. and J.C.A contributed analyses of anti-phospho ICN1 antibody, S.K. helped with analyses of human TALL , X.Z. and J.C.A. developed anti-phospho-ICN1 antibody, C.G.M. contributed DNA sequencing and copy number analyses of the cyclin C, CDK8, CDK19 and CDK3 genes in human T

Research paper thumbnail of Methods for Applied Mobile Digital Library Research: A Framework for Extensible Wayfinding Systems

The Reference Librarian, 2010

Research paper thumbnail of 3p→3d resonant photoemission spectroscopy of a TiO2 sub-monolayer grown on Al2O3

Surface Science, 2004

The valence band resonant photoemission spectra of a TiO 2 sub-monolayer grown on an Al 2 O 3 sub... more The valence band resonant photoemission spectra of a TiO 2 sub-monolayer grown on an Al 2 O 3 substrate have been measured throughout the Ti 3p absorption edge, i.e. at photon energies between 40 and 60 eV. The resonance process has been analysed in terms of constant initial state (CIS) curves, showing a peak at 49.5 eV photon energy, corresponding to a Fano-like resonant process. The Ti 3d contribution to the valence band shows a significant energy shift with respect to bulk TiO 2. These results are compared to cluster model calculations for a TiO 6 cluster.

Research paper thumbnail of Surface microstructure of the oxide protective layers grown on vanadium-free Ti alloys for use in biomedical applications

Surface Science, 2006

El artículo seleccionado no se encuentra disponible por ahora a texto completo por no haber sido ... more El artículo seleccionado no se encuentra disponible por ahora a texto completo por no haber sido facilitado todavía por el investigador a cargo del archivo del mismo.

Research paper thumbnail of Surface and optical characterization of yttrium hydride films deposited on regular glass to be used as switchable mirrors

Surface and Interface Analysis, 2002

Yttrium and palladium thin films deposited on glass have been characterized by means of XPS depth... more Yttrium and palladium thin films deposited on glass have been characterized by means of XPS depth profiling, SEM, energy-dispersive x-ray spectroscopy and ultraviolet-visible spectroscopy. These films allow optical windows of variable transparency to be obtained based on the formation of yttrium hydride by hydrogenation, with the palladium film working as a barrier against yttrium oxidation but being permeable to hydrogen. The transformation of yttrium into its hydride is concomitant with a metal-semiconducting transition that changes the physical properties of the material, especially its optical behaviour: the transmittance in the visible range goes from 0% for the metallic state to 30-70% for the hydrogenated state. In this work, the preparation conditions of optical windows using low-cost regular glass as substrate have been optimized, both regarding the deposition and the hydrogenation. Uniform films free of impurities, such as oxygen and carbon, have been obtained under ultrahigh vacuum conditions of ∼10 −7 Pa. Deposition has been performed by electron bombardment of the material, using palladium and yttrium of high purity.

Research paper thumbnail of Surface characterization of the oxide layer grown on TiNbZr and TiNbAl alloys

Surface and Interface Analysis, 2004

Research paper thumbnail of Soft x-ray absorption spectroscopy study of oxide layers on titanium alloys

Surface and Interface Analysis, 2002

Soft x-ray absorption spectroscopy (XAS) has been used to perform chemical analysis of oxide film... more Soft x-ray absorption spectroscopy (XAS) has been used to perform chemical analysis of oxide films formed after contact with air, both at room temperature and at 750 • C, on three titanium alloys. The alloys investigated were Ti-13Nb-13Zr, Ti-15Zr-4Nb and Ti-7Nb-6Al. Soft x-ray absorption spectra were taken at the Ti 2p and O 1s edges. The spectra corresponding to the room-temperature-oxidized samples are similar for the three alloys and show the presence of native oxide with a small metallic contribution. For the heat-treated samples, the alloying elements as well as element diffusion play a significant role in the formation of the oxide layer. In this case, the spectra exhibit clear differences between the TiNbZr alloys and Ti-7Nb-6Al. The oxide layer of the two TiNbZr alloys for the different heat treatment times is composed of TiO 2 in the form of rutile. However, for Ti-7Nb-6Al short heat treatments give rise to the formation of Al 2 TiO 5. By increasing the oxidation time, an Al 2 O 3 layer grows on the initial oxide film, becoming thicker as the exposure time is enhanced.

Research paper thumbnail of Surface effects in the Ni2px-ray photoemission spectra of NiO

Physical Review B, 2007

We report experimental and theoretical evidence of surface effects in the Ni 2p x-ray photoemissi... more We report experimental and theoretical evidence of surface effects in the Ni 2p x-ray photoemission spectra ͑XPS͒ of NiO. The Ni 2p 3/2 surface-enhanced XPS of a NiO sample show a relative enhancement of the intensity of the known satellite at 1.5 eV higher binding energy from the main line, indicating a considerable surface contribution of this satellite. The results are discussed in terms of bulk-octahedral and surfacepyramidal Ni symmetries. Other contributions, like nonlocal screening effects, cannot be neglected.

Research paper thumbnail of Splitting ofNi3dstates at the surface ofNiOnanostructures

Physical Review B, 2006

The electronic structure of NiO nanometric planar islands on highly oriented pyrolitic graphite h... more The electronic structure of NiO nanometric planar islands on highly oriented pyrolitic graphite has been studied by means of the Ni 2p and O 1s x-ray absorption spectra. The O 1s spectrum of the early stages of growth shows a double peak at threshold which is attributed to a splitting of the unoccupied Ni e g states. This spectrum is compared to previous results for 3 nm NiO nanoparticles which also show a rather similar splitting of the Ni e g states. This splitting observed in the O 1s spectra of the NiO nanostructures is caused by the reduced symmetry of the Ni ions at the surface. Cluster model calculations for a high-spin Ni 2+ ion performed in both octahedral ͑bulk͒ and pyramidal ͑surface͒ symmetries confirm this interpretation. This new interpretation of the surface electronic structure of NiO suggests a revision of the accepted concepts concerning this system.

Research paper thumbnail of Interface effects in theNi2px-ray photoelectron spectra of NiO thin films grown on oxide substrates

Physical Review B, 2008

We report the Ni 2p x-ray photoelectron spectra of NiO thin films grown on different oxide substr... more We report the Ni 2p x-ray photoelectron spectra of NiO thin films grown on different oxide substrates, namely, SiO 2 , Al 2 O 3 , and MgO. The main line of the Ni 2p spectra is attributed to the bulk component, and the shoulder at 1.5 eV higher binding energies to the surface component. The spectra of the NiO thin films show strong differences with respect to that of bulk NiO. The energy separation between the main peak and the shoulder increases with the substrate covalence. This indicates the strong covalent interactions between the NiO thin films and the oxide substrates, and reflects changes in the bonding at the interface from a more ionic to a more covalent interaction. These conclusions are supported by cluster model calculations with a reduced O 2p-Ni 3d hybridization.

Research paper thumbnail of Low and increased solubility of silicon in metal nitrides: evidence by X-ray absorption near edge structure

Journal of Materials Science, 2007

Research paper thumbnail of Study of the growth of NiO on highly oriented pyrolytic graphite by X-ray absorption spectroscopy

Journal of Electron Spectroscopy and Related Phenomena, 2007

In this work, we present a X-ray absorption spectroscopy (XAS) study of the growth of NiO on high... more In this work, we present a X-ray absorption spectroscopy (XAS) study of the growth of NiO on highly oriented pyrolytic graphite (HOPG). NiO has been grown by reactive evaporation of metallic Ni in an oxygen atmosphere (2×10−5Torr) at room temperature. We paid special attention to the study of the early stages of growth. Both, Ni 2p and O 1s core-level

Research paper thumbnail of Potential of genomic selection for improvement of resistance to Ostreid Herpes virus in Pacific oyster (Crassostrea gigas)

In genomic selection (GS), genome-wide SNP markers are used to generate genomic estimated breedin... more In genomic selection (GS), genome-wide SNP markers are used to generate genomic estimated breeding values (gEBVs) for selection candidates. The application of GS in shellfish looks promising and has the potential to help in dealing with one of the main issues currently affecting Pacific oyster production worldwide, which is the “summer mortality syndrome”. This causes periodic mass mortality in farms worldwide and has mainly been attributed to a specific variant of the Ostreid herpesvirus (OsHV-1-μvar). In the current study, we evaluated the potential of genomic selection for host resistance OsHV in Pacific oysters, and compared it to pedigree-based approaches. An OsHV-1 disease challenge was performed using an immersion-based virus exposure treatment for oysters for seven days. 768 samples were genotyped using the medium density SNP array for oysters. GWAS was performed for the survival trait using a GBLUP approach in BLUPF90 software. Heritability ranged from 0.25±0.05 to 0.37±0.0...

Research paper thumbnail of Gene Expression Response to Sea Lice in Atlantic Salmon Skin: RNA Sequencing Comparison Between Resistant and Susceptible Animals

Frontiers in Genetics, 2018

Sea lice are parasitic copepods that cause large economic losses to salmon aquaculture worldwide.... more Sea lice are parasitic copepods that cause large economic losses to salmon aquaculture worldwide. Frequent chemotherapeutic treatments are typically required to control this parasite, and alternative measures such as breeding for improved host resistance are desirable. Insight into the host-parasite interaction and mechanisms of host resistance can lead to improvements in selective breeding, and potentially novel treatment targets. In this study, RNA sequencing was used to study the skin transcriptome of Atlantic salmon (Salmo salar) parasitized with sea lice (Caligus rogercresseyi). The overall aims were to compare the transcriptomic profile of skin at louse attachment sites and "healthy" skin, and to assess differences in gene expression response between animals with varying levels of resistance to the parasite. Atlantic salmon pre-smolts were challenged with C. rogercresseyi, growth and lice count measurements were taken for each fish. 21 animals were selected and RNA-Seq was performed on skin from a louse attachment site, and skin distal to attachment sites for each animal. These animals were classified into family-balanced groups according to the traits of resistance (high vs. low lice count), and growth during infestation. Overall comparison of skin from louse attachment sites vs. healthy skin showed that 4,355 genes were differentially expressed, indicating local up-regulation of several immune pathways and activation of tissue repair mechanisms. Comparison between resistant and susceptible animals highlighted expression differences in several immune response and pattern recognition genes, and also myogenic and iron availability factors. Components of the pathways involved in differential response to sea lice may be targets for studies aimed at improved or novel treatment strategies, or to prioritize candidate functional polymorphisms to enhance genomic selection for host resistance in commercial salmon breeding programs.

Research paper thumbnail of Detailed insights into pan‐European population structure and inbreeding in wild and hatchery Pacific oysters (Crassostrea gigas) revealed by genome‐wide SNP data

Evolutionary Applications, 2018

This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Research paper thumbnail of Characterization Of Amylase And Protease Activities In The Digestive System Of Concholepas concholepas (Gastropoda, muricidae)

Concholepas concholepas (loco) is a carnivorous gastropod that inhabits the coast of Chile and Pe... more Concholepas concholepas (loco) is a carnivorous gastropod that inhabits the coast of Chile and Peru. Its fisheries showed a great importance in the past decades, however, now mainly relies on artisanal management of wild stocks. Feeding is one of the important factors that have restrained the establishment of large scale field rearing of loco. C. concholepas food preferences consist of mytilids and cirripeds, however its digestive physiology has not been studied and its digestive enzymes have not been yet characterized. The purification of amylase and protease from the digestive gland and the gland of Leiblein of C. concholepas were performed by ionic exchange chromatography (DEAE-cellulose), and substrate-PAGE indicated the presence of the amylase and protease in the fractions collected from the column. Amylase enzymatic assays showed its maximum activity at pH 7.0 and 50°C in the digestive gland. Protease on the other hand showed a great acidic activity, specifically at pH 3.0 in ...

Research paper thumbnail of TEAD3, implicated by association to grilsing in Atlantic salmon

Aquaculture, 2017

With the recent finding that the vestigial-like family member 3 (Vgll3) gene is associated with e... more With the recent finding that the vestigial-like family member 3 (Vgll3) gene is associated with early maturation, we decided to reexamine previously reported quantitative trait loci (QTL) and genome wide association (GWA) studies, involved with early maturation, to see if Vgll3 was the source of any of these associations. Using a TaqMan assay for Vgll3, we were able to verify that a prominent QTL for early maturation was indeed associated with Vgll3. Next, we used Vgll3 genotypes as a cofactor to reexamine for any additional QTLs or GWAs. Several were found at the chromosome-wide significance level. By examining interacting partners of Vgll3 from other organisms, we identified several candidate genes that may interact with Vgll3 in Atlantic salmon and effect early maturation. The location of these genes were determined from the genome sequence, while markers near QTL were examined to see if they were near any Vgll3 interacting genes. In this way, we identified TEAD3 as a putative gene also influencing early maturation in Atlantic salmon. A TaqMan assay was used to genotype TEAD3. These genotypes appear to be associated with early maturation.

Research paper thumbnail of Development of a Medium Density Combined-Species SNP Array for Pacific and European Oysters (Crassostrea gigas and Ostrea edulis)

G3 (Bethesda, Md.), Jul 22, 2017

SNP arrays are enabling tools for high-resolution studies of the genetic basis of complex traits ... more SNP arrays are enabling tools for high-resolution studies of the genetic basis of complex traits in farmed and wild animals. Oysters are of critical importance in many regions from both an ecological and economic perspective, and oyster aquaculture forms a key component of global food security. The aim of our study was to design a combined-species medium density SNP array for Pacific oyster (C. gigas) and European flat oyster (O. edulis), and to test the performance of this array on farmed and wild populations from multiple locations, with a focus on European populations. SNP discovery was carried out by whole genome sequencing of pooled genomic DNA samples from eight C. gigas populations, and RAD Sequencing of 11 geographically diverse O. edulis populations. Nearly 12 million candidate SNPs were discovered and filtered based on several criteria including preference for SNPs segregating in multiple populations and SNPs with monomorphic flanking regions. An Affymetrix Axiom® Custom A...

Research paper thumbnail of Genome-Wide Association Study (GWAS) for Growth Rate and Age at Sexual Maturation in Atlantic Salmon (Salmo salar)

PloS one, 2015

Early sexual maturation is considered a serious drawback for Atlantic salmon aquaculture as it re... more Early sexual maturation is considered a serious drawback for Atlantic salmon aquaculture as it retards growth, increases production times and affects flesh quality. Although both growth and sexual maturation are thought to be complex processes controlled by several genetic and environmental factors, selection for these traits has been continuously accomplished since the beginning of Atlantic salmon selective breeding programs. In this genome-wide association study (GWAS) we used a 6.5K single-nucleotide polymorphism (SNP) array to genotype ∼480 individuals from the Cermaq Canada broodstock program and search for SNPs associated with growth and age at sexual maturation. Using a mixed model approach we identified markers showing a significant association with growth, grilsing (early sexual maturation) and late sexual maturation. The most significant associations were found for grilsing, with markers located in Ssa10, Ssa02, Ssa13, Ssa25 and Ssa12, and for late maturation with markers ...

Research paper thumbnail of X-ray absorption spectroscopy study at the SiK-edge of tungsten carbide-silicon carbide thin films

Scripta Materialia, 2007

ABSTRACT X-ray absorption spectroscopy (XAS) has been used to determine the compositional and str... more ABSTRACT X-ray absorption spectroscopy (XAS) has been used to determine the compositional and structural nature of the phases formed in sputter-deposited W-Si-C films. The Si K-edge was examined to determine the presence and crystallinity of the SiC phase. For a film composition of 22% SiC, the XAS results show that there is at best only a minor amount of crystallization of SiC when deposited ;at 350 degrees C, but crystallization becomes more definitive at 600 degrees C. For a film with 29% SiC deposited at 350 degrees C, no crystalline SiC was detected. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Research paper thumbnail of Cyclin C is a haploinsufficient tumour suppressor

Nature Cell Biology, 2014

S. and W.W. contributed molecular mechanistic analyses of cyclin C→Fbw7→ICN1 link, X.L. and H. v.... more S. and W.W. contributed molecular mechanistic analyses of cyclin C→Fbw7→ICN1 link, X.L. and H. v. B. contributed bone marrow transduction with ICN1 experiments, T.K. and H. v. B. performed analyses of thymocyte populations and studies of bone marrow chimeras. M.R.M. S.J., R.E.G. and D.C.L. discovered mutations in human patients which render cyclin C-CDK unable to phosphorylate Notch1, L.L. contributed to molecular studies and phosphorylation analyses, H.W. performed all analyses of ICN1 phosphorylation by cyclin C-CDK8, C-CDK19 and C-CDK3, B.K. and I.A. contributed in vivo mouse tumorigenesis studies, A.G. and A.T.L. contributed analyses of human TALL samples, A.O and J.W.H. performed analyses of endogenous ICN1 polyubiquitination, T.O. contributed shRNA analyses of mouse cells and analyses of pRB phosphorylation, Lu.B. and J.J.Z. helped with molecular in vivo analyses, C.A.M. analyzed gene expression data, M.J.K and J.C.A. performed immunostaining for ICN1, M.R. and J.C.A contributed analyses of anti-phospho ICN1 antibody, S.K. helped with analyses of human TALL , X.Z. and J.C.A. developed anti-phospho-ICN1 antibody, C.G.M. contributed DNA sequencing and copy number analyses of the cyclin C, CDK8, CDK19 and CDK3 genes in human T

Research paper thumbnail of Methods for Applied Mobile Digital Library Research: A Framework for Extensible Wayfinding Systems

The Reference Librarian, 2010

Research paper thumbnail of 3p→3d resonant photoemission spectroscopy of a TiO2 sub-monolayer grown on Al2O3

Surface Science, 2004

The valence band resonant photoemission spectra of a TiO 2 sub-monolayer grown on an Al 2 O 3 sub... more The valence band resonant photoemission spectra of a TiO 2 sub-monolayer grown on an Al 2 O 3 substrate have been measured throughout the Ti 3p absorption edge, i.e. at photon energies between 40 and 60 eV. The resonance process has been analysed in terms of constant initial state (CIS) curves, showing a peak at 49.5 eV photon energy, corresponding to a Fano-like resonant process. The Ti 3d contribution to the valence band shows a significant energy shift with respect to bulk TiO 2. These results are compared to cluster model calculations for a TiO 6 cluster.

Research paper thumbnail of Surface microstructure of the oxide protective layers grown on vanadium-free Ti alloys for use in biomedical applications

Surface Science, 2006

El artículo seleccionado no se encuentra disponible por ahora a texto completo por no haber sido ... more El artículo seleccionado no se encuentra disponible por ahora a texto completo por no haber sido facilitado todavía por el investigador a cargo del archivo del mismo.

Research paper thumbnail of Surface and optical characterization of yttrium hydride films deposited on regular glass to be used as switchable mirrors

Surface and Interface Analysis, 2002

Yttrium and palladium thin films deposited on glass have been characterized by means of XPS depth... more Yttrium and palladium thin films deposited on glass have been characterized by means of XPS depth profiling, SEM, energy-dispersive x-ray spectroscopy and ultraviolet-visible spectroscopy. These films allow optical windows of variable transparency to be obtained based on the formation of yttrium hydride by hydrogenation, with the palladium film working as a barrier against yttrium oxidation but being permeable to hydrogen. The transformation of yttrium into its hydride is concomitant with a metal-semiconducting transition that changes the physical properties of the material, especially its optical behaviour: the transmittance in the visible range goes from 0% for the metallic state to 30-70% for the hydrogenated state. In this work, the preparation conditions of optical windows using low-cost regular glass as substrate have been optimized, both regarding the deposition and the hydrogenation. Uniform films free of impurities, such as oxygen and carbon, have been obtained under ultrahigh vacuum conditions of ∼10 −7 Pa. Deposition has been performed by electron bombardment of the material, using palladium and yttrium of high purity.

Research paper thumbnail of Surface characterization of the oxide layer grown on TiNbZr and TiNbAl alloys

Surface and Interface Analysis, 2004

Research paper thumbnail of Soft x-ray absorption spectroscopy study of oxide layers on titanium alloys

Surface and Interface Analysis, 2002

Soft x-ray absorption spectroscopy (XAS) has been used to perform chemical analysis of oxide film... more Soft x-ray absorption spectroscopy (XAS) has been used to perform chemical analysis of oxide films formed after contact with air, both at room temperature and at 750 • C, on three titanium alloys. The alloys investigated were Ti-13Nb-13Zr, Ti-15Zr-4Nb and Ti-7Nb-6Al. Soft x-ray absorption spectra were taken at the Ti 2p and O 1s edges. The spectra corresponding to the room-temperature-oxidized samples are similar for the three alloys and show the presence of native oxide with a small metallic contribution. For the heat-treated samples, the alloying elements as well as element diffusion play a significant role in the formation of the oxide layer. In this case, the spectra exhibit clear differences between the TiNbZr alloys and Ti-7Nb-6Al. The oxide layer of the two TiNbZr alloys for the different heat treatment times is composed of TiO 2 in the form of rutile. However, for Ti-7Nb-6Al short heat treatments give rise to the formation of Al 2 TiO 5. By increasing the oxidation time, an Al 2 O 3 layer grows on the initial oxide film, becoming thicker as the exposure time is enhanced.

Research paper thumbnail of Surface effects in the Ni2px-ray photoemission spectra of NiO

Physical Review B, 2007

We report experimental and theoretical evidence of surface effects in the Ni 2p x-ray photoemissi... more We report experimental and theoretical evidence of surface effects in the Ni 2p x-ray photoemission spectra ͑XPS͒ of NiO. The Ni 2p 3/2 surface-enhanced XPS of a NiO sample show a relative enhancement of the intensity of the known satellite at 1.5 eV higher binding energy from the main line, indicating a considerable surface contribution of this satellite. The results are discussed in terms of bulk-octahedral and surfacepyramidal Ni symmetries. Other contributions, like nonlocal screening effects, cannot be neglected.

Research paper thumbnail of Splitting ofNi3dstates at the surface ofNiOnanostructures

Physical Review B, 2006

The electronic structure of NiO nanometric planar islands on highly oriented pyrolitic graphite h... more The electronic structure of NiO nanometric planar islands on highly oriented pyrolitic graphite has been studied by means of the Ni 2p and O 1s x-ray absorption spectra. The O 1s spectrum of the early stages of growth shows a double peak at threshold which is attributed to a splitting of the unoccupied Ni e g states. This spectrum is compared to previous results for 3 nm NiO nanoparticles which also show a rather similar splitting of the Ni e g states. This splitting observed in the O 1s spectra of the NiO nanostructures is caused by the reduced symmetry of the Ni ions at the surface. Cluster model calculations for a high-spin Ni 2+ ion performed in both octahedral ͑bulk͒ and pyramidal ͑surface͒ symmetries confirm this interpretation. This new interpretation of the surface electronic structure of NiO suggests a revision of the accepted concepts concerning this system.

Research paper thumbnail of Interface effects in theNi2px-ray photoelectron spectra of NiO thin films grown on oxide substrates

Physical Review B, 2008

We report the Ni 2p x-ray photoelectron spectra of NiO thin films grown on different oxide substr... more We report the Ni 2p x-ray photoelectron spectra of NiO thin films grown on different oxide substrates, namely, SiO 2 , Al 2 O 3 , and MgO. The main line of the Ni 2p spectra is attributed to the bulk component, and the shoulder at 1.5 eV higher binding energies to the surface component. The spectra of the NiO thin films show strong differences with respect to that of bulk NiO. The energy separation between the main peak and the shoulder increases with the substrate covalence. This indicates the strong covalent interactions between the NiO thin films and the oxide substrates, and reflects changes in the bonding at the interface from a more ionic to a more covalent interaction. These conclusions are supported by cluster model calculations with a reduced O 2p-Ni 3d hybridization.

Research paper thumbnail of Low and increased solubility of silicon in metal nitrides: evidence by X-ray absorption near edge structure

Journal of Materials Science, 2007

Research paper thumbnail of Study of the growth of NiO on highly oriented pyrolytic graphite by X-ray absorption spectroscopy

Journal of Electron Spectroscopy and Related Phenomena, 2007

In this work, we present a X-ray absorption spectroscopy (XAS) study of the growth of NiO on high... more In this work, we present a X-ray absorption spectroscopy (XAS) study of the growth of NiO on highly oriented pyrolytic graphite (HOPG). NiO has been grown by reactive evaporation of metallic Ni in an oxygen atmosphere (2×10−5Torr) at room temperature. We paid special attention to the study of the early stages of growth. Both, Ni 2p and O 1s core-level