290 research outputs found
Sources of short-lived bromocarbons in the Iberian upwelling system
Seawater concentrations of the four brominated trace gases dibromomethane (CH2Br2), bromodichloromethane (CHBrCl2), dibromochloromethane (CHBr2Cl) and bromoform (CHBr3) were measured at different depths of the water column in the Iberian upwelling off Portugal during summer 2007. Bromocarbon concentrations showed elevated values in recently upwelled and aged upwelled waters (mean values of 30 pmol Lâ1 for CHBr3), while values in the open ocean were significantly lower (7.4 pmol Lâ1 for CHBr3). Correlations with biological variables and marker pigments indicated that phytoplankton could be identified as a weak bromocarbon source in the open ocean. In upwelled water masses along the coast, halocarbons were not correlated to Chl-a, indicating an external source, overlapping the possible internal production by phytoplankton. We showed that the tidal frequency had a significant influence on halocarbon concentrations in the upwelling and we linked those findings to a strong intertidal coastal source, as well as to a transport of those halocarbon enriched coastal waters by westward surface upwelling currents. Coastal sources and transport can be accounted for maximum values of up to 185.1 pmol Lâ1 CHBr3 in the upwelling.
Comparison with other productive marine areas revealed that the Iberian upwelling had stronger halocarbon sources than the phytoplankton dominated sources in the Mauritanian upwelling. However, the concentrations off the Iberian Peninsula were still much lower than those of coastal macroalgal influenced waters or those of polar regions dominated by cold water adapted diatom
Enhanced ocean carbon storage from anaerobic alkalinity generation in coastal sediments
The coastal ocean is a crucial link between land, the open ocean and the atmosphere. The shallowness of the water column permits close interactions between the sedimentary, aquatic and atmospheric compartments, which otherwise are decoupled at long time scales (â
1000 yr) in the open oceans. Despite the prominent role of the coastal oceans in absorbing atmospheric CO2 and transferring it into the deep oceans via the continental shelf pump, the underlying mechanisms remain only partly understood. Evaluating observations from the North Sea, a NW European shelf sea, we provide evidence that anaerobic degradation of organic matter, fuelled from land and ocean, generates total alkalinity (AT) and increases the CO2 buffer capacity of seawater. At both the basin wide and annual scales anaerobic AT generation in the North Sea's tidal mud flat area irreversibly facilitates 7â10%, or taking into consideration benthic denitrification in the North Sea, 20â25% of the North Sea's overall CO2 uptake. At the global scale, anaerobic AT generation could be accountable for as much as 60% of the uptake of CO2 in shelf and marginal seas, making this process, the anaerobic pump, a key player in the biological carbon pump. Under future high CO2 conditions oceanic CO2 storage via the anaerobic pump may even gain further relevance because of stimulated ocean productivity
Spin-Diffusion Lengths in Metals and Alloys, and Spin-Flipping at Metal/Metal Interfaces: an Experimentalist's Critical Review
In magnetoresistive (MR) studies of magnetic multilayers composed of
combinations of ferromagnetic (F) and non-magnetic (N) metals, the magnetic
moment (or related 'spin') of each conduction electron plays a crucial role,
supplementary to that of its charge. While initial analyses of MR in such
multilayers assumed that the direction of the spin of each electron stayed
fixed as the electron transited the multilayer, we now know that this is true
only in a certain limit. Generally, the spins 'flip' in a distance
characteristic of the metal, its purity, and the temperature. They can also
flip at F/N or N1/N2 interfaces. In this review we describe how to measure the
lengths over which electron moments flip in pure metals and alloys, and the
probability of spin-flipping at metallic interfaces. Spin-flipping within
metals is described by a spin-diffusion length,l^M(sf), where the metal M = F
or N. Spin-diffusion lengths are the characteristic lengths in the
current-perpendicular-to-plane (CPP) and lateral non-local (LNL) geometries
that we focus upon in this review. In certain simple cases, l^N(sf) sets the
distance over which the CPP-MR and LNL-MR decrease as the N-layer thickness
(CPP-MR) or N-film length (LNL) increases, and l^F(sf) does the same for
increase of the CPP-MR with increasing F-layer thickness. Spin-flipping at
M1/M2 interfaces can be described by a parameter, delta(M1/M2), which
determines the spin-flipping probability, P = 1 - exp(-delta). Increasing
delta(M1/M2) usually decreases the MR. We list measured values of these
parameters and discuss the limitations on their determinations.Comment: Invited Review, to appear in J. Phys. Cond. Matter. 50 pages, 18
figures. The new version contains additional material and revisions to
improve clarit
A review of selected indicators of particle, nutrient and metal inputs in coral reef lagoon systems
This review presents environmental and biological indicators of the impact of three major categories of inputs in coral reef lagoons i.e. particles, nutrients and metals. Information was synthesized to extract well established indicators together with some interesting new concepts currently under development, and to provide the reader with an assessment of their respective advantages and drawbacks. The paper has been organized according to the capacity of three categories of indicators to respond either in a specific or a non specific way to a given source of input. The first section focuses on abiotic indicators which main interest is to respond instantaneously and in a truly specific way to a given source of input. The second and third sections present informations on bioindicators either at the sub-individual level or at the individual to community level, indicator specificity generally decreasing as a direct function of biological or ecological complexity. This review showed that even though significant work has already been done on coral reef ecosystems, much more scientific studies are still needed to answer the growing local demands for simple and truly validated tools to be used in environmental surveys. It is further stressed that, due to the biological and environmental diversity of coral reef lagoons, a preliminary step of on-site validation must be considered as an absolute prerequisite when indicators are planned to be used in the frame of a local environmental monitoring programme
Dynamics of airâsea CO2 fluxes in the northwestern European shelf based on voluntary observing ship and satellite observations
From January 2011 to December 2013, we constructed a comprehensive pCO2 data set based on voluntary observing ship (VOS) measurements in the western English Channel (WEC). We subsequently estimated surface pCO2 and airâsea CO2 fluxes in northwestern European continental shelf waters using multiple linear regressions (MLRs) from remotely sensed sea surface temperature (SST), chlorophyll a concentration (Chl a), wind speed (WND), photosynthetically active radiation (PAR) and modeled mixed layer depth (MLD). We developed specific MLRs for the seasonally stratified northern WEC (nWEC) and the permanently well-mixed southern WEC (sWEC) and calculated surface pCO2 with uncertainties of 17 and 16 ÎŒatm, respectively. We extrapolated the relationships obtained for the WEC based on the 2011â2013 data set (1) temporally over a decade and (2) spatially in the adjacent Celtic and Irish seas (CS and IS), two regions which exhibit hydrographical and biogeochemical characteristics similar to those of WEC waters. We validated these extrapolations with pCO2 data from the SOCAT and LDEO databases and obtained good agreement between modeled and observed data. On an annual scale, seasonally stratified systems acted as a sink of CO2 from the atmosphere of â0.6 ± 0.3, â0.9 ± 0.3 and â0.5 ± 0.3 mol C mâ2 yrâ1 in the northern Celtic Sea, southern Celtic sea and nWEC, respectively, whereas permanently well-mixed systems acted as source of CO2 to the atmosphere of 0.2 ± 0.2 and 0.3 ± 0.2 mol C mâ2 yrâ1 in the sWEC and IS, respectively. Airâsea CO2 fluxes showed important inter-annual variability resulting in significant differences in the intensity and/or direction of annual fluxes. We scaled the mean annual fluxes over these provinces for the last decade and obtained the first annual average uptake of â1.11 ± 0.32 Tg C yrâ1 for this part of the northwestern European continental shelf. Our study showed that combining VOS data with satellite observations can be a powerful tool to estimate and extrapolate airâsea CO2 fluxes in sparsely sampled area
The GRA Beam-Splitter Experiments and Particle-Wave Duality of Light
Grangier, Roger and Aspect (GRA) performed a beam-splitter experiment to
demonstrate the particle behaviour of light and a Mach-Zehnder interferometer
experiment to demonstrate the wave behaviour of light. The distinguishing
feature of these experiments is the use of a gating system to produce near
ideal single photon states. With the demonstration of both wave and particle
behaviour (in two mutually exclusive experiments) they claim to have
demonstrated the dual particle-wave behaviour of light and hence to have
confirmed Bohr's principle of complementarity. The demonstration of the wave
behaviour of light is not in dispute. But we want to demonstrate, contrary to
the claims of GRA, that their beam-splitter experiment does not conclusively
confirm the particle behaviour of light, and hence does not confirm
particle-wave duality, nor, more generally, does it confirm complementarity.
Our demonstration consists of providing a detailed model based on the Causal
Interpretation of Quantum Fields (CIEM), which does not involve the particle
concept, of GRA's which-path experiment. We will also give a brief outline of a
CIEM model for the second, interference, GRA experiment.Comment: 24 pages, 4 figure
Evolution of Linear Absorption and Nonlinear Optical Properties in V-Shaped Ruthenium(II)-Based Chromophores
In this article, we describe a series of complexes with electron-rich cis-{Ru^(II)(NH_3)_4}^(2+) centers coordinated to two pyridyl ligands bearing N-methyl/arylpyridinium electron-acceptor groups. These V-shaped dipolar species are new, extended members of a class of chromophores first reported by us (Coe, B. J. et al. J. Am. Chem. Soc. 2005, 127, 4845â4859). They have been isolated as their PF_6â salts and characterized by using various techniques including ^1H NMR and electronic absorption spectroscopies and cyclic voltammetry. Reversible Ru^(III/II) waves show that the new complexes are potentially redox-switchable chromophores. Single crystal X-ray structures have been obtained for four complex salts; three of these crystallize noncentrosymmetrically, but with the individual molecular dipoles aligned largely antiparallel. Very large molecular first hyperpolarizabilities ÎČ have been determined by using hyper-Rayleigh scattering (HRS) with an 800 nm laser and also via Stark (electroabsorption) spectroscopic studies on the intense, visible d â Ï^* metal-to-ligand charge-transfer (MLCT) and Ï â Ï^* intraligand charge-transfer (ILCT) bands. The latter measurements afford total nonresonant ÎČ_0 responses as high as ca. 600 Ă 10^(â30) esu. These pseudo-C_(2v) chromophores show two substantial components of the ÎČ tensor, ÎČ_(zzz) and ÎČ_(zyy), although the relative significance of these varies with the physical method applied. According to HRS, ÎČ_(zzz) dominates in all cases, whereas the Stark analyses indicate that ÎČ_(zyy) is dominant in the shorter chromophores, but ÎČ_(zzz) and ÎČ_(zyy) are similar for the extended species. In contrast, finite field calculations predict that ÎČ_(zyy) is always the major component. Time-dependent density functional theory calculations predict increasing ILCT character for the nominally MLCT transitions and accompanying blue-shifts of the visible absorptions, as the ligand Ï-systems are extended. Such unusual behavior has also been observed with related 1D complexes (Coe, B. J. et al. J. Am. Chem. Soc. 2004, 126, 3880â3891)
Nanomaterials for the cleaning and pH adjustment of vegetable tanned leather
Leather artifacts in historical collections and archives are often contaminated by physical changes such as soiling, which alter their appearance and readability, and by chemical changes which occur on ageing and give rise to excessive proportion of acids that promote hydrolysis of collagen, eventually leading to gelatinization and loss of mechanical properties. However, both cleaning and pH adjustment of vegetable tanned leather pose a great challenge for conservators, owing to the sensitivity of these materials to the action of solvents, especially water-based formulations and alkaline chemicals. In this study the cleaning of historical leather samples was optimized by confining an oil-in-water (o/w) nanostructured fluid in a highly retentive chemical hydrogel, which allows the controlled release of the cleaning fluid on sensitive surfaces. The chemical gel exhibits optimal viscoelasticity, which facilitates its removal after the application without leaving residues on the object. Nanoparticles of calcium hydroxide and lactate, dispersed in 2-propanol, were used to adjust the pH up to the natural value of leather, preventing too high alkalinity which causes swelling of fibers and denaturation of the collagen. The treated samples were characterized using Scanning Electron Microscopy (FE SEM), controlled environment dynamic mechanical analysis (DMA-RH), and infrared spectroscopy (ATR-FTIR). The analytical assessment validated the use of tools derived from colloid and materials science for the preservation of collagen-based artifacts
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