BP (entreprise) | EPFL Graph Search

La société BP est une compagnie britannique de recherche, d'extraction, de raffinage et de vente de pétrole fondée en 1909. Anciennement nommée Anglo-Persian Oil Company (APOC-1909), puis Anglo-Iranian Oil Company (AIOC-1935), puis British Petroleum Company (BP-1954), puis BPAmoco (2001), avant d'être renommée BP. Après sa fusion avec Amoco, Atlantic Richfield (Arco) et Burmah Castrol, elle est devenue la plus grande société du Royaume-Uni et la troisième compagnie pétrolière mondiale. La division BP de Londres est évaluée à environ cinquante milliards de dollars (environ trente-neuf milliards d'euros). Internationalement, BP est présente dans plus de cent pays et emploie environ en 2010. Depuis 2010, l'image de l'entreprise a souffert de la mauvaise publicité due à l'explosion de l'une de ses plates-formes pétrolières, Deepwater Horizon qui coûta la vie à 11 personnes le 20 avril 2010. Elle est considérée comme l'une des plus importantes catastrophes écologiques liées à l'exploit

Electronic transport properties of vertical and lateral graphene-based heterostructures

Roberto Urcuyo Solorzano

Graphene has some drawbacks, like the absence of an electronic band gap which leads to only small gate switching ratios, and its fast carrier recombination that limits its use in optoelectronics. In order to overcome these issues, the aim of this thesis was to tune the properties of graphene by two different modification approaches. The first approach involved chemical functionalization to create lateral graphene heterostructures, whereas the second approach was directed toward vertical heterostructures that combine graphene with another 2D material. For the former case, two novel chemical functionalization methods were investigated. The first method relied upon hyperthermal molecular ion collisions with 4,4¿-azobis(pyridine). This enabled the covalent functionalization of graphene with a functionalization degree of up to 3%, as demonstrated by Raman in combination with XPS. AFM studies revealed that the functionalized sheets retain their topographic integrity. Thus obtained stripe-like patterns of covalently graphene within extended graphene sheets enabled enhanced on/off ratios upon gate switching. In the second functionalization, OsO4 was used to selectively introduce hydroxyl groups to graphene. Best results were obtained using UV light activation, which yielded graphene of high covalent functionalization degree, as concluded from its optical transparency and gate-induced on/off switching ratios of up to 500. Temperature dependent electrical measurements revealed 2D hopping as the dominant transport mechanism. The first type of vertical heterostructure, gr-TiOx-Ti diodes were fabricated and their electrical properties in the dark and under visible light illumination studied. In contrast to conventional MIM diodes, the performance of the graphene-based diodes was found to increase with decreasing thickness of the oxide insulator. Bias-induced modulation of the work function of graphene was identified as the key to the operation mechanism of the graphene diodes, enabling them to reach a very high asymmetry and nonlinearity (9000 and 8). The diodes compete well with state-of-the-art MIM diodes. Furthermore, the graphene-TiOx-Ti diodes could be operated as photovoltaic cell, with a maximum open-circuit voltage of 0.3 V and a short-circuit photocurrent of 14 nA under global illuminationt. This finding constitutes the first proof-of-principle of hot carrier extraction from graphene, based on the photovoltaic effect. The second type of vertical heterostructures was based on black phosphorus (BP). As a first step, thin BP sheets were combined with n-GaAs into novel pn devices. They displayed pronounced rectification behavior that, in the low bias regime, approaches that of ideal diodes. Moreover, when operated as photodiodes they reached external quantum efficiencies (EQE) above 30% under higher reverse bias. On this basis, the bP was then combined with gr into a p+/p heterojunction. Thus obtained devices achieved a maximum internal quantum efficiency (IQE) and responsivity of 13% and 10.7 mA/W, respectively. This IQE is the highest thus far reported for diodes comprising BP and another 2D material. Moreover, with the aid of a top gate it was possible to modulate both, the photo-conversion efficiency and photocurrent generation mechanism of the black phosphorous-graphene diodes. Together with the possibility to tune the photocurrent response by the thickness of the black phosphorous, these diodes emerge as promising photodetectors.

EPFL2016

Palmitoylation mediates membrane association of hepatitis E virus ORF3 protein and is required for infectious particle secretion

Laurence Gouzi Abrami, Maxime Matter, Johann Mauron, Noémie Oechslin, Joël Oppliger, Françoise Gisou van der Goot Grunberg

Hepatitis E virus (HEV) is a positive-strand RNA virus encoding 3 open reading frames (ORF). HEV ORF3 protein is a small, hitherto poorly characterized protein involved in viral particle secretion and possibly other functions. Here, we show that HEV ORF3 protein forms membrane-associated oligomers. Immunoblot analyses of ORF3 protein expressed in cell-free vs. cellular systems suggested a posttranslational modification. Further analyses revealed that HEV ORF3 protein is palmitoylated at cysteine residues in its N-terminal region, as corroborated by H-3-palmitate labeling, the investigation of cysteine-to-alanine substitution mutants and treatment with the palmitoylation inhibitor 2-bromopalmitate (2-BP). Abrogation of palmitoylation by site-directed mutagenesis or 2-BP treatment altered the subcellular localization of ORF3 protein, reduced the stability of the protein and strongly impaired the secretion of infectious particles. Moreover, selective membrane permeabilization coupled with immunofluorescence microscopy revealed that HEV ORF3 protein is entirely exposed to the cytosolic side of the membrane, allowing to propose a model for its membrane topology and interactions required in the viral life cycle. In conclusion, palmitoylation determines the subcellular localization, membrane topology and function of HEV ORF3 protein in the HEV life cycle.

PUBLIC LIBRARY SCIENCE2018

Brainstem Correlates of a Cold Pressor Test Measured by Ultra-High Field fMRI

Sandra Elisabete Borges da Costa, Domenica Bueti, Fatma Megdiche, Olivier Benoit Thomas Reynaud, Dimitri Nestor Alice Van De Ville

Introduction Modern imaging techniques such as blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) allow the non-invasive and indirect measurement of brain activity. Whether changes in signal intensity can be detected in small brainstem regions during a cold pressor test (CPT) has not been explored thoroughly. The aim of this study was to measure whole brain and brainstem BOLD signal intensity changes in response to a modified CPT. Methods BOLD fMRI was measured in healthy normotensive participants during a randomized crossover study (modified CPT vs. control test) using ultra-high field 7 Tesla MRI scanner. Data were analyzed using Statistical Parametric Mapping (SPM) in a whole-brain approach, and with a brainstem-specific analysis using the spatially unbiased infra-tentorial template (SUIT) toolbox. Blood pressure (BP) and hormonal responses (norepinephrine and epinephrine levels) were also measured. Paired t-test statistics were used to compare conditions. Results Eleven participants (six women, mean age 28 +/- 8.9 years) were analyzed. Mean arterial BP increased from 83 +/- 12 mm Hg to 87 +/- 12 mm Hg (p = 0.0009) during the CPT. Whole-brain analysis revealed significant activations linked to the CPT in the right supplementary motor cortex, midcingulate (bilateral) and the right anterior insular cortex. The brainstem-specific analysis showed significant activations in the dorsal medulla. Conclusion Changes in BOLD fMRI signal intensity in brainstem regions during a CPT can be detected, and show an increased response during a cold stress in healthy volunteers. Consequently, BOLD fMRI at 7T is a promising tool to explore and acquire new insights in the comprehension of neurogenic hypertension.

2020

Electronic transport properties of vertical and lateral graphene-based heterostructures

Roberto Urcuyo Solorzano

EPFL2016