Analyses Through the Metastatistical Extreme Value Distribution Identify Contributions of Tropical Cyclones to Rainfall Extremes in the Eastern United States

AbstractTropical cyclones (TCs) generate extreme precipitation with severe impacts across large coastal and inland areas, calling for accurate frequency estimation methods. Statistical approaches that take into account the physical mechanisms responsible for these extremes can help reduce the estimation uncertainty. Here we formulate a mixed‐population Metastatistical Extreme Value Distribution explicitly incorporating non‐TC and TC‐induced rainfall and evaluate its implications on long series of daily rainfall for six major U.S. urban areas impacted by these storms. We find statistically significant differences between the distributions of TC‐ and non‐TC‐related precipitation; moreover, including mixtures of distributions improves the estimation of the probability of extreme precipitation where TCs occur more frequently. These improvements are greater when rainfall aggregated over durations longer than one day are considered

Interventional programmes to improve cognition during healthy and pathological ageing: Cortical modulations and evidence for brain plasticity

Available online 06 March 2018A growing body of evidence suggests that healthy elderly individuals and patients with Alzheimer’s disease retain an important potential for neuroplasticity. This review summarizes studies investigating the modulation of neural activity and structural brain integrity in response to interventions involving cognitive training, physical exercise and non-invasive brain stimulation in healthy elderly and cognitively impaired subjects (including patients with mild cognitive impairment (MCI) and Alzheimer’s disease). Moreover, given the clinical relevance of neuroplasticity, we discuss how evidence for neuroplasticity can be inferred from the functional and structural brain changes observed after implementing these interventions. We emphasize that multimodal programmes, which combine several types of interventions, improve cognitive function to a greater extent than programmes that use a single interventional approach. We suggest specific methods for weighting the relative importance of cognitive training, physical exercise and non-invasive brain stimulation according to the functional and structural state of the brain of the targeted subject to maximize the cognitive improvements induced by multimodal programmes.This study was funded by the European Commission Marie-Skłodowska Curie Actions, Individual Fellowships; 655423-NIBSAD, Italian Ministry of HealthGR-2011-02349998, and Galician government (Postdoctoral Grants Plan I2C 2011-2015)

Transcranial electric stimulation as a neural interface to gain insight on human brain functions: current knowledge and future perspective

Abstract The use of brain stimulation approaches in social and affective science has greatly increased over the last two decades. The interest in social factors has grown along with technological advances in brain research. Transcranial electric stimulation (tES) is a research tool that allows scientists to establish contributory causality between brain functioning and social behaviour, therefore deepening our understanding of the social mind. Preliminary evidence is also starting to demonstrate that tES, either alone or in combination with pharmacological or behavioural interventions, can alleviate the symptomatology of individuals with affective or social cognition disorders. This review offers an overview of the application of tES in the field of social and affective neuroscience. We discuss the issues and challenges related to this application and suggest an avenue for future basic and translational research

Characterizing the cortical oscillatory response to TMS pulse

No abstract available

Identifying discontinuities of flood frequency curves

Discontinuities in flood frequency curves, here referred to as flood divides, hinder the estimation of rare floods. In this paper we develop an automated methodology for the detection of flood divides from observations and models, and apply it to a large set of case studies in the USA and Germany. We then assess the reliability of the PHysically-based Extreme Value (PHEV) distribution of river flows to identify catchments that might experience a flood divide, validating its results against observations. This tool is suitable for the identification of flood divides, with a high correct detection rate especially in the autumn and summer seasons. It instead tends to indicate the emergence of flood divides not visible in the observations in spring and winter. We examine possible reasons of this behavior, finding them in the typical streamflow dynamics of the concerned case studies. By means of a controlled experiment we also re-evaluate detection capabilities of observations and PHEV after discarding the highest maxima for all cases where both empirical and theoretical estimates display flood divides. PHEV mostly confirms its capability to detect a flood divide as observed in the original flood frequency curve, even if the shortened one does not show it. These findings prove its reliability for the identification of flood divides and set the premises for a deeper investigation of physiographic and hydroclimatic attributes controlling the emergence of discontinuities in flood frequency curves.publishedVersio

Behavioural and electrophysiological modulations induced by transcranial direct current stimulation in healthy elderly and Alzheimer’s disease patients: A pilot study

Available online 26 August 2019Objective To investigate whether anodal and cathodal transcranial direct current stimulation (tDCS) can modify cognitive performance and neural activity in healthy elderly and Alzheimer’s disease (AD) patients. Methods Fourteen healthy elderly and twelve AD patients performed a working memory task during an electroencephalogram recording before and after receiving anodal, cathodal, and sham tDCS over the left dorsolateral prefrontal cortex. Behavioural performance, event-related potentials (P200, P300) and evoked cortical oscillations were studied as correlates of working memory. Results Anodal tDCS increased P200 and P300 amplitudes in healthy elderly. Cathodal tDCS increased P200 amplitude and frontal theta activity between 150 and 300 ms in AD patients. Improved working memory after anodal tDCS correlated with increased P300 in healthy elderly. In AD patients, slight tendencies between enhanced working memory and increased P200 after cathodal tDCS were observed. Conclusions Functional neural modulations were promoted by anodal tDCS in healthy elderly and by cathodal tDCS in AD patients. Significance Interaction between tDCS polarity and the neural state (e.g., hyper-excitability exhibited by AD patients) suggests that appropriate tDCS parameters (in terms of tDCS polarity) to induce behavioural improvements should be chosen based on the participant’s characteristics. Future studies using higher sample sizes should confirm and extend the present findings.This study was funded by the Italian Ministry of Health GR-2011-02349998 to MCP and the European Commission Marie-Skłodowska Curie Actions, Individual Fellowships; 655423-NIBSAD to JC

Extreme flooding controlled by stream network organization and flow regime

River floods are among the most common natural disasters worldwide, with substantial economic and humanitarian costs. Despite enormous efforts, gauging the risk of extreme floods with unprecedented magnitude is an outstanding challenge. Limited observational data from very high-magnitude flood events hinders prediction efforts and the identification of discharge thresholds marking the rise of progressively larger floods, termed flood divides. Combining long hydroclimatic records and a process-based model for flood hazard assessment, here we demonstrate that the spatial organization of stream networks and the river flow regime control the appearance of flood divides and extreme floods. In contrast with their ubiquitous attribution to extreme rainfall and anomalous antecedent conditions, we show that the propensity to generate extreme floods is well predicted by intrinsic properties of river basins. Most importantly, it can be assessed prior to the occurrence of catastrophes through measurable metrics of these properties derived from commonly available discharge data, namely the hydrograph recession exponent and the coefficient of variation of daily flows. These results highlight the propensity of certain rivers for generating extreme floods and demonstrate the importance of using hazard mapping tools that, rather than solely relying on past flood records, identify regions susceptible to the occurrence of extreme floods from ordinary discharge dynamics.publishedVersio

Nanoscale properties of graphene-based interfaces

2012/2013Il tema fondamentale della mia attività di ricerca di dottorato è stato la produzione e caratterizzazione di interfacce a base di grafene. Negli ultimi dieci anni, il grafene, il singolo strato perfettamente bidimensionale di atomi di carbonio, si è imposto all'attenzione della comunità scientifica come un materiale rivoluzionario con eccezionali proprietà meccaniche, elettroniche e termiche, potenzialmente in grado di superare il silicio nella prossima generazione di dispositivi elettronici. Un problema fondamentale connesso alla produzione del grafene, tuttavia, è la sintesi di film uniformi ed estesi di carbonio, necessaria per espandere la produzione del grafene a livelli adeguati per applicazioni industriali. In questo riguardo, la crescita epitassiale del grafene mediante deposizione in fase vapore (CVD) di molecole idrocarburiche su substrati solidi è al presente uno dei procedimenti più promettenti. La mia attività di ricerca si è incentrata soprattutto sullo studio dell'interazione tra grafene e substrato in sistemi epitassiali grafene/metallo e sui suoi effetti sulla corrugazione dei sistemi con un mismatch reticolare e sulle proprietà elettroniche dello strato di carbonio. A questo scopo, la spettroscopia di fotoemissione dai livelli di core ad alta risoluzione energetica, con la sua eccezionale sensibilità alle condizioni locali degli atomi di superficie e d'interfaccia, è stata la mia tecnica preferenziale. Questa è stata affiancata da altre tecniche sperimentali, in particolare la diffrazione e microscopia a elettroni lenti e la fotoemissione risolta in angolo, così come da calcoli basati sulla teoria del funzionale densità condotti da gruppi collaboratori. L'obiettivo primario è stato conseguire un controllo fine dell'adesione grafene-metallo, fondamentale per capire come le proprietà del grafene cambiano quando l'accoppiamento con il substrato viene variato in modo continuo da interazione forte a quasi-disaccoppiamento. Questo obiettivo è stato perseguito con diverse tecniche. Questa tesi inizia presentando i risultati da noi ottenuti per un sistema grafene/metallo fortemente interagente, grafene/Re(0001), che rappresenta un caso esemplare delle diverse fasi (grafene, carburi, carbonio dissolto nel bulk) che il carbonio può formare per esposizione ad alta temperatura del substrato ad etilene. In questo riguardo, è emerso che le condizioni di temperatura e pressione svolgono un ruolo chiave nel favorire la formazione di una specie di carbonio piuttosto che un'altra. Un'altra scoperta cruciale è che l'instabilità termica ad alta temperatura del grafene/Re(0001) è direttamente correlata alla corrugazione della cella di moiré, in particolare alla presenza di 'avvallamenti', ovvero di regioni fortemente interagenti in cui la rottura del legame C-C è favorita. Oltre alla scelta della specie chimica del substrato, strategie più raffinate per ottenere un controllo accurato dell'interazione grafene-metallo sfruttano, ad esempio, alterazioni geometriche o chimiche del substrato. Utilizzare superfici cristalline con simmetria non-threefold, ad es. superfici vicinali, permette di crescere grafene con una cella di moiré anisotropica, con parametri reticolari non-equivalenti nelle direzioni parallela e ortogonale agli step. Questa opportunità è stata esplorata, durante il mio dottorato, per il caso del grafene su Rh(533). I nostri dati evidenziano un ruolo primario degli step nell'indebolire il legame del grafene con il substrato e nello stabilizzare il legame C-C ad alta temperatura, come finora predetto solo da conti teorici. Un approccio alternativo e versatile per modificare l'interazione grafene-substrato in modo continuo è variando la composizione chimica della sola superficie del substrato. Più precisamente, l'impiego di una lega superficiale di PtRu su Ru(0001), con una concentrazione variabile di atomi di Pt distribuiti omogeneamente nel primo strato, si è dimostrata un'ottima strategia per regolare finemente, in modo controllabile, il livello di accoppiamento tra adesione forte e interazione debole, senza alterare la qualità e periodicità dello strato di carbonio. Un'ulteriore strategia per disaccoppiare il grafene dal substrato è offerta dalla crescita di uno strato di ossido all'interfaccia grafene/metallo, che è di particolare interesse in vista della combinazione del grafene con materiali dielettrici ad alto k in batterie, condensatori e altri dispositivi. Come parte del mio progetto di dottorato, ho partecipato alla caratterizzazione sperimentale del grafene cresciuto epitassialmente su una superficie di Ni3Al e delle modifiche strutturali ed elettroniche indotte dalla formazione di uno spesso strato di ossido all'interfaccia. Questo metodo rappresenta una valida alternativa, a basso costo e non distruttiva, alle convenzionali tecniche di trasferimento finora sviluppate per depositare grafene su supporti dielettrici. L'ultima parte di questo lavoro di tesi è incentrata sull'impiego del grafene epitassiale come 'matrice' per la deposizione ordinata di nanocluster di metalli di transizione, resa possibile dalla corrugazione periodica a lungo raggio del reticolo di moirè. Questo aspetto è stato esplorato, in particolare, nello studio della reattività chimica di nanocluster di Rh supportati da grafene/Ir(111). L'alto grado di cristallinità esibito dai cluster a seguito del loro riscaldamento e la presenza di atomi di Rh non equivalenti con una diversa coordinazione sono stati oggetto di indagine mediante spettroscopia di fotoemissione dai livelli di core ad alta risoluzione energetica. In particolare, mi sono concentrata sull'interazione di questi sistemi con l'ossigeno e il monossido di carbonio, e sul ruolo chiave degli atomi di Rh sotto-coordinati, che sono siti preferenziali di legame nella fase iniziale dell'adsorbimento. Presenterò anche il nuovo metodo che abbiamo recentemente messo a punto per sintetizzare nanoparticelle di Rh altamente ossidate, che potrebbe essere di impatto in relazione alla superiore selettività catalitica mostrata dai film di ossidi metallici verso l'ossidazione del CO e del NO. I grandi progressi degli ultimi anni nel campo dei nanocluster metallici supportati sono molto promettenti per la futura applicazione di questi sistemi nella catalisi e nei dispositivi elettronici di prossima generazione. Oltre alla necessità di produrre reticoli di nanocluster ordinati a lungo raggio, che può essere soddisfatta facendo uso, ad es., di una matrice di grafene, un'altra sfida chiave posta dall'impiego di nanoparticelle su scala sub-nanometrica è rappresentata dal controllo accurato delle loro dimensioni, che ha effetti drammatici sulla morfologia e struttura elettronica di questi sistemi. Per questo motivo, la parte finale della mia tesi è dedicata alla descrizione di un sistema sperimentale avanzato progettato per produrre nanocluster di metalli di transizione selezionati in massa e depositarli a bassa energia su substrati solidi. Questa macchina, che è attualmente in fase di assemblaggio al Laboratorio di Scienza delle Superfici, farà uso di una sorgente di ablazione laser per generare gli ioni e di uno spettrometro di massa a quadrupolo ad alta risoluzione per assicurare una selettività superiore. Una volta operativo, questo sistema, che sarà la prima sorgente di nanocluster selezionati in massa per studi di fisica delle superfici in Italia, metterà a disposizione della comunità scientifica internazionale di utenti di Elettra uno strumento allo stato dell'arte per condurre esperimenti su nanoparticelle supportate e su materiali a base di cluster, in combinazione con tecniche basate sulla radiazione di sincrotrone.The focus of my PhD research has been on the production and characterisation of graphene-based interfaces. In the last decade, graphene, the perfectly two-dimensional single layer of carbon atoms, has risen to the attention of the scientific community as a revolutionary material with exceptional mechanical, electronic and thermal properties, which could potentially outperform silicon in the next generation of electronic devices. A key issue related to graphene synthesis, however, is the facile production of uniform and extended carbon flakes, which is required to scale up graphene synthesis for industrial applications. In this respect, the epitaxial growth of graphene by chemical vapour deposition of hydrocarbon molecules on a solid substrate is currently one of the most promising routes. My research activity has addressed, in particular, the graphene-substrate interaction in epitaxial graphene/metal systems and its effects on the corrugation of lattice-mismatched systems and on the electronic properties of the carbon sheet. For the purpose of investigating this, high-energy resolution core level photoelectron spectroscopy, with its superior sensitivity to the local environment experienced by surface and interface atoms, has been technique of choice. This has been complemented by other experimental techniques, in particular low energy electron diffraction and microscopy and angle-resolved photoemission spectroscopy, as well as by state-of-the-art density functional theory calculations performed by collaborating groups. The primary objective has been that of achieving fine control of the graphene-metal adhesion, which is key to understanding how the graphene properties evolve as the coupling to the substrate is continuously varied from strong interaction to the quasi free-standing case. This goal has been tackled with several different strategies. This thesis starts by presenting our results for a strongly interacting graphene/metal system, graphene/Re(0001), which represents an exemplary case of the different phases (graphene, carbides and bulk-dissolved carbon) carbon can form upon high temperature ethylene exposure of the substrate. In this respect, the temperature and pressure conditions are found to play a crucial role in favouring the formation of one carbon species over the others. Another key finding is that the high temperature thermal instability of graphene/Re(0001) is directly linked to the corrugation of the moiré cell, in particular to the presence of buckled, strongly interacting regions where C-C bond breaking is favoured. Besides the elemental choice of the substrate, more refined strategies to achieve accurate control of the graphene-metal interaction exploit, e.g. geometrical or chemical modifications of the substrate. Using crystalline surfaces with non-threefold symmetry, e.g. vicinal surfaces, allows growing graphene with an anisotropic moiré cell, with non-equivalent lattice parameters in the directions parallel and orthogonal to the steps. This possibility has been explored for the case of graphene on Rh(533). The obtained data point out a primary role of the steps in weakening the graphene bonding to the substrate and stabilising the carbon layer against defect--induced C-C bond breaking at high temperature, as so far predicted only by theoretical calculations. An alternative, versatile approach to modify the graphene-substrate interaction in a continuous way is by changing the elemental composition of the first layer of the substrate. More specifically, the use of a PtRu surface alloy on Ru(0001) with a variable concentration of randomly distributed Pt atoms in the first layer has proven to be an excellent strategy for tuning the degree of coupling from strong adhesion to very weak interaction in a controllable way, without affecting the quality and periodicity of the carbon layer. A further strategy for decoupling graphene from the substrate is offered by the growth of an oxide buffer layer at the graphene/metal interface, which is of special interest for the prospective combination of graphene with high-k dielectric materials in batteries, capacitors and other devices. As part of my PhD project, I participated in the experimental investigation of epitaxial graphene on a Ni3Al surface and of the structural and electronic changes induced by the formation of a thick interface oxide layer. This method represents a viable, low cost and non-destructive alternative to the conventional transfer techniques so far developed to deposit graphene on dielectric supports. The last part of this thesis work focuses on the employment of epitaxial graphene as a template for the self-assembly of transition metal nanoclusters, made possible by the long-range periodic corrugation of the moiré superlattice. This topic has been addressed, in particular, in the study of the chemical reactivity of Rh nanoclusters supported on graphene/Ir(111). The high degree of crystallinity exhibited by the clusters after annealing and the presence of non-equivalent Rh atoms with a different coordination number are addressed by means of high-energy resolution core level photoelectron spectroscopy. In particular, I have focussed on the interaction of these systems with oxygen and carbon monoxide, and on the key role played by the highly reactive, undercoordinated Rh atoms, which are preferential bonding sites in the early stage of adsorption. I will also present the new method we recently developed to synthesise highly oxidised Rh nanoparticles, which could be of impact in relation to the enhanced catalytic selectivity towards CO and NO oxidation exhibited by metal oxide films. The great progress achieved in recent years in the field of supported metal nanoclusters is very promising for the prospective application of these systems in catalysis and next-generation electronic devices. In addition to the need to producing long-range ordered superlattices of nanoclusters, which can be met by making use of, e.g a graphene template, another key challenge posed by the use of particles in the sub-nanometre scale is represented by the accurate control of their size, which has dramatic effects on the morphology and electronic structure of these systems. For this reason, the final part of my thesis is dedicated to the description of an advanced experimental setup designed to produce size-selected transition metal nanoclusters and soft-land them on solid substrates. This machine, which is currently being assembled at the Surface Science Laboratory, will make use of a laser ablation source to generate the ions and of a high resolution quadrupole mass spectrometer to ensure a superior mass selectivity. Once operational, this system, which will be the first size-selected cluster source for surface science studies in Italy, will provide the international scientific community working at Elettra with a state-of-the-art tool to conduct experiments on supported nanoparticles and cluster-based materials, in combination with synchrotron radiation-based techniques.XXVI Ciclo198

Determinación de pequeñas cantidades de talio por espectrofotometría de llama

La sensibilidad de emisión del talio en la espectrofotometría de llama es incrementada mediante el uso de solventes orgánicos. Para la determinación de talio en muestras de cualquier composición se propone un método simple: el talio es extraído con 3-octanona previo tratamiento con una mezcla de ácidos sulfúrico, nítrico y perclórico y oxidación del T1(I) a T1(III) con bromo en medio bromhídrico. No hay interferencias significativas de los elementos Au, As, Cr, Sb, Mo, Se, Te, Pt, Cu, Bi, Cd, Hg y Sn, cuando se determina 0,05 mg de T1 frente a 1 - 2 mg de los mismos. La técnica permite determinar menos de un microgramo de talio.The sensitivity of thallium emission in flaic spectrophotometry is increased by the use of organic solvents. For thallium determination on samples of any composition, a simple method is proposed. The thallium is extracted with 3-octanone, previous treatment with a mixture of sulfuric, nitric and perchloric acids, and oxidation of T1(I) to T1(III) with bromine in hidrobromic medium. There are not significatives interferences of the elements Au, As, Te, Sb, Mo, Se, Cu, Bi, Cd, Hg and Sn, when 0,05 mg of thallium is determined against 1-2 mg of these elements. With this technique less of one microgramme of thallium can be determine

Mechanochemical Synthesis of Multicomponent Crystals: One Liquid for One Polymorph? A Myth to Dispel

Identifying as many polymorphs as possible for a molecular compound is important in the design of materials with desired properties. In this paper we demonstrate, using a simple experimental procedure, how the amount of liquid present during liquid-assisted mechanochemical reactions can be used to rapidly explore polymorph diversity. Through detailed experimental evidence it is concluded that for the specific (multicomponent) crystal system investigated (caffeine−anthranilic acid) the commonly accepted rule “one liquid for one specific polymorph” is not correct. Additionally we demonstrate that through modification of the amount of added liquid it is possible to form a polymorph previously obtained only by a desolvation reaction. We believe that while the results raise many mechanistic questions the approach is advantageous as a means of rapidly screening for polymorph diversity as well as being a simple screening methodology. While we focus here on a cocrystal system, we believe a similar approach will be advantageous for single component systems.This is the final version of the article. It first appeared from the American Chemical Society via http://dx.doi.org/10.1021/acs.cgd.6b0068