Non-Adiabatic Vibrational Damping of Molecular Adsorbates: Insights into Electronic Friction and the Role of Electronic Coherence

We present a perturbation approach rooted in time-dependent density-functional theory to calculate electron hole (eh)-pair excitation spectra during the non-adiabatic vibrational damping of adsorbates on metal surfaces. Our analysis for the benchmark systems CO on Cu(100) and Pt(111) elucidates the surprisingly strong influence of rather short electronic coherence times. We demonstrate how in the limit of short electronic coherence times, as implicitly assumed in prevalent quantum nuclear theories for the vibrational lifetimes as well as electronic friction, band structure effects are washed out. Our results suggest that more accurate lifetime or chemicurrent-like experimental measurements could characterize the electronic coherence.Comment: Article as accepted for publication in Physical Review Letter

Electronic friction-based vibrational lifetimes of molecular adsorbates: Beyond the independent atom approximation

We assess the accuracy of vibrational damping rates of diatomic adsorbates on metal surfaces as calculated within the local-density friction approximation (LDFA). An atoms-in-molecules (AIM) type charge partitioning scheme accounts for intra-molecular contributions and overcomes the systematic underestimation of the non-adiabatic losses obtained within the prevalent independent atom approximation. The quantitative agreement obtained with theoretical and experimental benchmark data suggests the LDFA-AIM as an efficient and reliable approach to account for electronic dissipation in ab initio molecular dynamics simulations of surface chemical reactions.Comment: 5 pages including 2 figure

Systematics and Species Delimitation in New Guinea Skink Species Complexes (Squamata: Scincidae)

Though among the most controversial topics in systematic and evolutionary biology, species are a fundamental unit in biology, and are utilized by and critical to a wide variety of studies in the life sciences. Despite this importance, little work has focused on developing and examining objective methods for species delimitation until recently. Further, New Guinea and the surrounding regions are among the most diverse and geologically complex regions globally, yet the region remains poorly explored biologically, and little work has examined the evolutionary history of the fauna in the region. To investigate the influence of factors such as sampling intensity, species richness, and phylogenetic structure on discovery methods for species delimitation, I combine simulated and empirical data. In Chapter 1, I use simulated data to examine the accuracy of three discovery methods for species delimitation under a variety of different sampling strategies. I find that genetic clustering algorithms, such as Structurama, can be highly accurate in identifying even recent divergences with limited sampling of individuals and of loci, and that Gaussian clustering can be similarly accurate, though somewhat less sensitive to detecting recent divergences. However, my results show that nonparametric delimitation is highly sensitive to errors in gene genealogy estimation, and generally fails to delimit species accurately when true coalescent gene genealogies are unknown, as in empirical applications. In Chapters 3 and 4, I apply these methods empirically to examine the species boundaries, as well as the phylogeny and other aspects of the evolutionary history of, scincid lizards of the C. bicarinata and C. fusca groups, respectively. My results in Chapter 3 indicate that species delimitation analyses may be prone to underestimating the number of species by identifying only higher levels of clustering in systems with deep phylogenetic structure. I additionally find evidence for several cryptic species in the group, including deep, species-level divergence among the populations of C. storri from Australia, the Aru Islands, and New Guinea, despite their recent connectivity via Sahul Shelf emergence during Pleistocene glaciations. Through also examining niche evolution in the group, I find evidence for niche conservatism among most species in the group, but two species, C. bicarinata and C. sp. Amau from eastern Papua New Guinea, show evidence for environmental niche divergence. Analyses of the C. fusca group in Chapter 4 provide further evidence for a tendency of discovery methods for species delimitation to under-detect species in groups with high diversity or deep phylogenetic structure. Genetic clustering algorithms based on the complete dataset only identify a small number of clusters that correspond largely to deep phylogenetic clades, but when restricted to within these clades, this method identifies clusters that correspond well to finer, putative species-level structure. I also find evidence for extensive cryptic diversity in this group, identifying 28 distinct species among my sampling of 16 currently recognized species, as well as other incongruence with current taxonomy, including synonymous species and mis-assigned populations, supporting previous evidence of the need for extensive taxonomic revision in the C. fusca group. My biogeographic analyses also providence evidence that the C. fusca group likely evolved in Australia or Australia and New Guinea before diversifying in New Guinea, dispersing at least twice across Lydekker’s line into Wallacea, and possibly also recolonizing Australia. Finally, in Chapter 5, I take a more comprehensive approach, and combine genomic and morphological data to test the validity of and examine the demographic history of two putative species of Tribolonotus from the islands of Buka and Bougainville in the northwestern Solomon Archipelogo. I use next-generation sequencing to collect a genomic dataset of several thousand loci, and apply species discovery (genetic clustering algorithms) and species validation (Bayes factor delimitations) to test for speciation between these populations. My results support this speciation event, despite the recent connectivity between these islands. I also collect a suite of morphological characters for this group and provide evidence for morphological divergence and diagnosibility. Demographic analyses applied using approximate Bayesian computation and diffusion analysis further provide evidence for a complex demographic scenario in which migration between these populations continued for some time following their initial divergence, but subsequently decreased in rate or ceased entirely. Combined, these results yield extensive insight into the utility of several methods for species delimitation, the taxonomy and systematics of Carlia and Tribolonotus in New Guinea and the surrounding regions, and the complex processes responsible for driving the generation and maintenance of the phenomenal diversity in the Sahul shelf region

Energy dissipation at metal surfaces

Conversion of energy at the gas–solid interface lies at the heart of many industrial applications such as heterogeneous catalysis. Dissipation of parts of this energy into the substrate bulk drives the thermalization of surface species, but also constitutes a potentially unwanted loss channel. At present, little is known about the underlying microscopic dissipation mechanisms and their (relative) efficiency. At metal surfaces, prominent such mechanisms are the generation of substrate phonons and the electronically non-adiabatic excitation of electron–hole pairs. In recent years, dedicated surface science experiments at defined single-crystal surfaces and predictive-quality first-principles simulations have increasingly been used to analyze these dissipation mechanisms in prototypical surface dynamical processes such as gas-phase scattering and adsorption, diffusion, vibration, and surface reactions. In this topical review we provide an overview of modeling approaches to incorporate dissipation into corresponding dynamical simulations starting from coarse-grained effective theories to increasingly sophisticated methods. We illustrate these at the level of individual elementary processes through applications found in the literature, while specifically highlighting the persisting difficulty of gauging their performance based on experimentally accessible observables

Age-related cellular copper dynamics in the fungal ageing model Podospora anserina and in ageing human fibroblasts

In previous investigations an impact of cellular copper homeostasis on ageing of the ascomycete Podospora anserina has been demonstrated. Here we provide new data indicating that mitochondria play a major role in this process. Determination of copper in the cytosolic fraction using total reflection X-ray fluorescence spectroscopy analysis and eGfp reporter gene studies indicate an age-related increase of cytosolic copper levels. We show that components of the mitochondrial matrix (i.e. eGFP targeted to mitochondria) become released from the organelle during ageing. Decreasing the accessibility of mitochondrial copper in P. anserina via targeting a copper metallothionein to the mitochondrial matrix was found to result in a switch from a copper-dependent cytochrome-c oxidase to a copper-independent alternative oxidase type of respiration and results in lifespan extension. In addition, we demonstrate that increased copper concentrations in the culture medium lead to the appearance of senescence biomarkers in human diploid fibroblasts (HDFs). Significantly, expression of copper-regulated genes is induced during in vitro ageing in medium devoid of excess copper suggesting that cytosolic copper levels also increase during senescence of HDFs. These data suggest that the identified molecular pathway of age-dependent copper dynamics may not be restricted to P. anserina but may be conserved from lower eukaryotes to humans

Oxidação eletrocatalítica de metanol utilizando eletrodos modificados com Hidróxido de Níquel

Estudos eletrocatalíticos se referem ao efeito da natureza do material, do qual o eletrodo é feito, e sobre a cinética de uma reação eletroquímica, podendo ser usado em diferentes finalidades, como em células a combustível de metanol direto (DMFC). Neste trabalho, estudou-se o comportamento eletrocatalítico de eletrodos quimicamente modificados usando como eletrodos base, Platina e Níquel, na oxidação de metanol. Como mediador eletroquímico, foi eletrodepositado um filme de hidróxido de níquel, que possui características eletroquímicas interessantes em estudos de oxidação de álcoois. A modificação no eletrodo de Platina foi realizada com a prensagem de Ni(OH)2 suportado com dois materiais diferentes, nujol e acetato de polivinila. Já no eletrodo de Níquel, o filme de Ni(OH)2 foi feito eletroquimicamente com uma corrente catódica de -0,1 mA. Essa deposição foi aplicada durante quatro diferentes tempos: 15, 30, 60 e 120 minutos. Para a quantificação de metanol, a partir da reação de oxidação, foi utilizada a cronoamperometria aplicando-se um potencial de 0,435 VAg/AgCl e os dados foram tomados pela técnica do “ponto final”. O eletrodo de Platina modificado suportado com nujol não apresentou a região do Ni3+, quando caracterizado por voltametria cíclica, não podendo ser utilizado na quantificação do analito, pois a oxidação do Ni(OH)2 está relacionada com a do metanol. O eletrodo modificado suportado com acetato de polivinila apresentou uma resistência elétrica maior do que o eletrodo de platina pura, detectando assim correntes mais altas, porém quantificando uma concentração menor de metanol. Dentre os eletrodos de Níquel modificados, o que teve tempo de eletrodeposição de 120 minutos apresentou um filme de baixa aderência e que não pode ser utilizado enquanto que os eletrodos depositados nos demais tempos foram os mais sensíveis à reação de oxidação do metanol quando comparados ao eletrodo base metálico. O conjunto dos dados obtidos confirma que se pode considerar como promissor o uso de hidróxido de níquel eletrodepositado em Níquel como uma forma alternativa e de baixo custo à eletrocatálise da reação de oxidação de metanol na utilização como material anódico em DMFC em meio alcalino

SAC 2.0 na TAM: o atendimento nas redes sociais e o relacionamento entre clientes e marcas

Analisa uma das consequências do movimento de convergência das mídias e da inversão de papeis na comunicação midiática: a entrada em massa das empresas e suas marcas no mundo das redes sociais com o intuito de monitorarem o que os consumidores pensam sobre elas. Busca-se compreender a relevância, para as empresas, da comunicação direta com seus clientes, transformando as redes sociais em Serviços de Atendimento ao Cliente (SAC) 2.0, onde tudo é muito mais rápido, mais transparente e mais arriscado. A fim de se obter uma mensuração mais precisa em relação ao processo de atendimento, será estudado o case da TAM Linhas Aéreas, através de entrevistas com funcionários, análise das páginas da marca nas redes sociais, pesquisas quantitativas e entrevistas com usuários atendidos via mídias sociais. O objetivo da monografia é verificar a importância desse atendimento no relacionamento com as marcas atuais

J-500, En route vers la Bibliothèque du Rolex Learning Center

L'EPFL construit actuellement le Rolex Learning Center, dont l'inauguration est prévue en 2010. Le RLC est un lieu de vie et de travail pour la communauté EPFL, notamment pour ses étudiants, pour qui il doit constituer un port d'attache. Le RLC est un centre d'activités construit autour d'une grande bibliothèque multifonctionnelle, équipée en RFID et proposant des services avancés en matière d'accès et de gestion de l'information, sous forme papier et numérique. Le contexte de l'EPFL, le concept du "RLC" et les étapes de sa réalisation sont présentés du point de vue du responsable de la bibliothèque