Light scattering by a medium with a spatially modulated optical conductivity: the case of graphene

We describe light scattering from a graphene sheet having a modulated optical conductivity. We show that such modulation enables the excitation of surface plasmon-polaritons by an electromagnetic wave impinging at normal incidence. The resulting surface plasmon-polaritons are responsible for a substantial increase of electromagnetic radiation absorption by the graphene sheet. The origin of the modulation can be due either to a periodic strain field or to adatoms (or absorbed molecules) with a modulated adsorption profile.Comment: http://iopscience.iop.org/0953-8984/24/24/24530

Effect of charged line defects on conductivity in graphene: Numerical Kubo and analytical Boltzmann approaches

Charge carrier transport in single-layer graphene with one-dimensional charged defects is studied theoretically. Extended charged defects, considered an important factor for mobility degradation in chemically-vapor-deposited graphene, are described by a self-consistent Thomas-Fermi potential. A numerical study of electronic transport is performed by means of a time-dependent real-space Kubo approach in honeycomb lattices containing millions of carbon atoms, capturing the linear response of realistic size systems in the highly disordered regime. Our numerical calculations are complemented with a kinetic transport theory describing charge transport in the weak scattering limit. The semiclassical transport lifetimes are obtained by computing scattered amplitudes within the second Born approximation. The transport electron-hole asymmetry found in the semiclassical approach is consistent with the Kubo calculations. In the strong scattering regime, the conductivity is found to be a sublinear function of electronic density and weakly dependent on the Thomas-Fermi screening wavelength. We attribute this atypical behavior to the extended nature of one-dimensional charged defects. Our results are consistent with recent experimental reports.Comment: 15 pages, 9 figure

Voltage-dependent anion-selective channels VDAC2 and VDAC3 are abundant proteins in bovine outer dense fibers, a cytoskeletal component of the sperm flagellum

Outer dense fibers (ODF) are specific subcellular components of the sperm flagellum. The functions of ODF have not yet been clearly elucidated. We have investigated the protein composition of purified ODF from bovine spermatozoa and found that one of the most abundant proteins is a 30-32-kDa polypeptide. This protein was analyzed by sequencing peptides derived following limited proteolysis. Peptide sequences were found to match VDAC2 and VDAC3. VDACs (voltage-dependent, anion-selective channels) or eukaryotic porins are a group of proteins first identified in the mitochondrial outer membrane that are able to form hydrophilic pore structures in membranes. In mammals, three VDAC isoforms (VDAC1, -2, -3) have been identified by cDNA cloning and sequencing. Antibodies against synthetic peptides specific for the three mammal VDAC isoforms were generated in rabbits. Their specificity was demonstrated by immunoblotting using recombinant VDAC1, -2, and -3. In protein extracts of bovine spermatozoa, VDAC1, -2, and -3 were detected by specific antibodies, while only VDAC2 and -3 were found as solubilized proteins derived from purified bovine ODFs. Immunofluorescence microscopy of spermatozoa revealed that anti-VDAC2 and anti-VDAC3 antibodies clearly bound to the sperm flagellum, in particular to the ODF. Transmission electron immunomicroscopy supported the finding that VDAC2 protein is abundant in the ODF. Since the ODF does not have any known membranous structure, it is tempting to speculate that VDAC2 and VDAC3 might have an alternative structural organization and different functions in ODF than in mitochondria

Integrating multiple satellite observations into a coherent dataset to monitor the full water cycle – application to the Mediterranean region

The Mediterranean region is one of the climate hotspots where the climate change impacts are both pronounced and documented. The HyMeX (Hydrometeorological Mediterranean eXperiment) aims to improve our understanding of the water cycle from the meteorological to climate scales. However, monitoring the water cycle with Earth observations (EO) is still a challenge: EO products are multiple, and their utility is degraded by large uncertainties and incoherences among the products. Over the Mediterranean region, these difficulties are exacerbated by the coastal/mountainous regions and the small size of the hydrological basins. Therefore, merging/integration techniques have been developed to reduce these issues. We introduce here an improved methodology that closes not only the terrestrial but also the atmospheric and ocean budgets. The new scheme allows us to impose a spatial and temporal multi-scale budget closure constraint. A new approach is also proposed to downscale the results from the basin to pixel scales (at the resolution of 0.25∘). The provided Mediterranean WC budget is, for the first time, based mostly on observations such as the GRACE water storage or the netflow at the Gibraltar Strait. The integrated dataset is in better agreement with in situ measurements, and we are now able to estimate the Bosporus Strait annual mean netflow.</p

Grassroots Agency: Participation and Conflict in Buenos Aires Shantytowns seen through the Pilot Plan for Villa 7 (1971–1975)

open access articleIn 1971, after more than a decade of national and municipal policies aimed at the top-down removal of shantytowns, the Buenos Aires City Council approved the Plan Piloto para la Relocalización de Villa 7 (Pilot Plan for the Relocation of Shantytown 7; 1971–1975, referred to as the Pilot Plan hereinafter). This particular plan, which resulted in the construction of the housing complex, Barrio Justo Suárez, endures in the collective memory of Argentines as a landmark project regarding grassroots participation in state housing initiatives addressed at shantytowns. Emerging from a context of a housing shortage for the growing urban poor and intense popular mobilizations during the transition to democracy, the authors of the Pilot Plan sought to empower shantytown residents in novel ways by: 1) maintaining the shantytown’s location as opposed to eradication schemes that relocated the residents elsewhere, 2) formally employing some of the residents for the stage of construction, as opposed to “self-help” housing projects in which the residents contributed with unpaid labor, and 3) including them in the urban and architectural design of the of the new housing. This paper will examine the context in which the Pilot Plan was conceived of as a way of re-assessing the roles of the state, the user, and housing-related professionals, often seen as antagonistic. The paper argues that residents’ fair participation and state intervention in housing schemes are not necessarily incompatible, and can function in specific social and political contexts through multiactor proposals backed by a political will that prioritizes grassroots agency

Effects of drought ? altered seasonality and low rainfall ? in net ecosystem carbon exchange of three contrasting Mediterranean ecosystems

International audienceDroughts cause reductions in gross primary production (GPP) and also in net ecosystem exchange (NEE), contributing to most of the inter-annual variability in terrestrial carbon sequestration. In seasonally dry climates (Mediterranean) droughts result from reductions in annual rainfall and from changes in rain seasonality. In western Iberia, the hydrological-year (i.e., from October to September) of 2004?2005 was extremely dry, with precipitation 50% below the long-term mean (691 mm in 1961?1990), but 2005?2006 was normal. We compared the carbon fluxes measured by the eddy covariance technique from three contrasting ecosystems in southern Portugal: an evergreen oak woodland (savannah-like) with ca. 21% tree cover; a Mediterranean C3/C4 grassland; and a coppiced eucalyptus plantation. During the dry hydrological-year of 2004?2005, NEE was lowest, the highest sink strength was in the eucalypt plantation (NEE = ?399 g C m ?2 year?1) as compared to the oak woodland (NEE = ?88 g C m ?2 year?1), and the grassland (NEE = +49 g C m ?2 year ?1). The latter was a source of carbon dioxide. The NEE values of the dry year were, however, much lower than those for wetter years, e.g. NEE = ?861 g C m?2 year ?1 in 2002?2003 in the eucalypt plantation. The NEE of the grassland and the oak savannah in the 2005?2006 hydrological-year, with annual precipitation above the long term mean, were ?190 and ?120 g C m ?2 year?1, respectively. All ecosystems studied increased their rain-use efficiency (GPP per unit of rain volume) increased in dry years. In the case of annual vegetation ? grassland and low tree density woodland, however &ndash, rain-use efficiency decreased with severe drought. However, this was more pronounced in the eucalypt plantation due to greater GPP and the use of deep soil water resources. Although both calendar years of 2004 and 2005 had equally low rainfall, the effect of drought on the eucalypt plantation was delayed until the second dry year. This suggests that the effects of water deficits on Mediterranean forests are exacerbated by prolonged droughts when long-term soil water reserves are depleted. The grassland, however, was more vulnerable and responded faster to water deficits. This effect of drought was less pronounced in the oak woodland due to the sparse tree cover

Bimetallic PdAg nanoparticle arrays from monolayer films of diblock copolymer micelles

International audienceThe self-assembly technique provides a highly efficient route to generate well-ordered structures on a nanometer scale. In this paper, well-ordered arrays of PdAg alloy nanoparticles on flat substrates with narrow distributions of particle size (6-7 nm) and interparticle spacing (about 60 nm) were synthesized by the block copolymer micelle approach. A home-made PS-b-P4VP diblock copolymer was prepared to obtain a micellar structure in toluene. Pd and Ag salts were then successfully loaded in the micellar core of the PS-b-P4VP copolymer. A self-assembled monolayer of the loaded micelles was obtained by dipping the flat substrate in the solution. At this stage, the core of the micelles was still loaded with the metal precursor rather than with a metal. Physical and chemical reducing methods were used to reduce the metal salts embedded in the P4VP core into PdAg nanoparticles. HRTEM and EDX indicated that Pd-rich PdAg alloy nanoparticles were synthesized by chemical or physical reduction; UV-visible spectroscopy observations confirmed that metallic PdAg nanoparticles were quickly formed after chemical reduction; XPS measurements revealed that the PdAg alloy nanoparticles were in a metallic state after a short time of exposure to O-2 plasma and after hydrazine reduction

Net ecosystem carbon exchange in three contrasting Mediterranean ecosystems ? the effect of drought

International audienceDroughts reduce gross primary production (GPP) and ecosystem respiration (Reco), contributing to most of the inter-annual variability in terrestrial carbon sequestration. In seasonally dry climates (Mediterranean), droughts result from reductions in annual rainfall and changes in rain seasonality. We compared carbon fluxes measured by the eddy covariance technique in three contrasting ecosystems in southern Portugal: an evergreen oak woodland (savannah-like) with ca.~21% tree crown cover, a grassland dominated by herbaceous annuals and a coppiced short-rotation eucalyptus plantation. During the experimental period (2003?2006) the eucalyptus plantation was always the strongest sink for carbon: net ecosystem exchange rate (NEE) between ?861 and ?399 g C m?2 year?1. The oak woodland and the grassland were much weaker sinks for carbon: NEE varied in the oak woodland between ?140 and ?28 g C m?2 year?1 and in the grassland between ?190 and +49 g C m?2 year?1. The eucalyptus stand had higher GPP and a lower proportion of GPP spent in respiration than the other systems. The higher GPP resulted from high leaf area duration (LAD), as a surrogate for the photosynthetic photon flux density absorbed by the canopy. The eucalyptus had also higher rain use efficiency (GPP per unit of rain volume) and light use efficiency (the daily GPP per unit incident photosynthetic photon flux density) than the other two ecosystems. The effects of a severe drought could be evaluated during the hydrological-year (i.e., from October to September) of 2004?2005. Between October 2004 and June 2005 the precipitation was only 40% of the long-term average. In 2004?2005 all ecosystems had GPP lower than in wetter years and carbon sequestration was strongly restricted (less negative NEE). The grassland was a net source of carbon dioxide (+49 g C m?2 year?1). In the oak woodland a large proportion of GPP resulted from carbon assimilated by its annual vegetation component, which was strongly affected by the shortage of rain in winter. Overall, severe drought affected more GPP than Reco leading to the deterioration of NEE. Although the rain-use efficiency of the eucalyptus plantation increased in the dry year, this was not the case of evergreen oak woodland, which rain-use efficiency was not influenced by drought. Recovery after drought alleviation, i.e., beginning with heavy rain in October 2005, was fully accomplished in 2006 in the oak woodland and grassland, but slow in the eucalyptus plantation

Using three-phase partitioning for the purification and recovery of antibodies from biological media

Antibodies, in particular immunoglobulin G (IgG), are one of the biopharmaceutical industry highflyers, with relevance for the treatment of several diseases. However, the recovery of antibodies from complex biological media with high quality and purity is difficult and requires multi-step and expensive approaches. Herein, we propose a cost-effective approach using three-phase partitioning (TPP) systems based on polyethylene glycol (PEG)-salt aqueous biphasic systems (ABS) with ionic liquids (ILs) as adjuvants for the purification and recovery of IgG antibodies from three biological media, i.e., human serum, and serum-containing and serum-free Chinese hamster ovary (CHO) cell culture supernatants. The economic analysis of the developed process was carried out. The results obtained using PEG-salt ABS without ILs and human serum show that IgG could be recovered either at the interphase of the TPP or in the top phase, depending on the molecular weight of the PEG. The system composed of PEG with a molecular weight of 1000 g/mol is the PEG-salt system enabling the highest purity of human polyclonal IgG at the interphase (80.7 %, with a recovery yield of 65.8 %). Still, by adding 1 wt% of the ILs tetra(n-butyl)ammonium bromide ([N4444]Br) and 1-butyl-3-methylimidazolium chloride ([C4mim]Cl), it is possible to compete or even outperform the PEG 1000-salt system with no IL regarding purity/recovery performance and production costs under given operation conditions. The best systems were then applied for the purification and recovery of monoclonal antibodies from serum-containing and serum-free culture supernatants. Improved recovery of monoclonal antibodies from serum-free Chinese hamster ovary (CHO) cell culture supernatants with a reduction of the host cell proteins (HCPs) content are obtained by introducing ILs as adjuvants in PEG-salt systems, with [N4444]Br providing the lowest production costs. Overall, TPP systems were shown to be not only cost-effective, but also robust and flexible routes to purify and recover IgG from complex biological matrices as shown here with human serum, serum-containing and serum-free cell culture supernatants.publishe