Trace element partitioning in HP-LT metamorphic assemblages during subduction-related metamorphism, Ile de Groix, France: a detailed LA-ICPMS study

Devolatilization reactions and subsequent transfer of fluid from subducted oceanic crust into the overlying mantle wedge are important processes, which are responsible for the specific geochemical characteristics of subduction-related metamorphic rocks, as well as those of arc magmatism. To better understand the geochemical fingerprint induced by fluid mobilization during dehydration and rehydration processes related to subduction zone metamorphism, the trace element and rare earth element (REE) distribution patterns in HP-LT metamorphic assemblages in eclogite-, blueschist- and greenschist-facies rocks of the Ile de Groix were obtained by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) analysis. This study focuses on 10 massive basic rocks representing former hydrothermally altered mid-ocean ridge basalts (MORB), four banded basic rocks of volcano-sedimentary origin and one micaschist. The main hosts for incompatible trace elements are epidote (REE, Th, U, Pb, Sr), garnet [Y, heavy REE (HREE)], phengite (Cs, Rb, Ba, B), titanite [Ti, Nb, Ta, REE; HREE > LREE (light REE)], rutile (Ti, Nb, Ta) and apatite (REE, Sr). The trace element contents of omphacite, amphibole, albite and chlorite are low. The incompatible trace element contents of minerals are controlled by the stable metamorphic mineral assemblage and directly related to the appearance, disappearance and reappearance of minerals, especially epidote, garnet, titanite, rutile and phengite, during subduction zone metamorphism. Epidote is a key mineral in the trace element exchange process because of its large stability field, ranging from lower greenschist- to blueschist- and eclogite-facies conditions. Different generations of epidote are generally observed and related to the coexisting phases at different stages of the metamorphic cycle (e.g. lawsonite, garnet, titanite). Epidote thus controls most of the REE budget during the changing P-T conditions along the prograde and retrograde path. Phengite also plays an important role in determining the large ion lithophile element (LILE) budget, as it is stable to high P-T conditions. The breakdown of phengite causes the release of LILE during retrogression. A comparison of trace element abundances in whole-rocks and minerals shows that the HP-LT metamorphic rocks largely retain the geochemical characteristics of their basic, volcano-sedimentary and pelitic protoliths, including a hydrothermal alteration overprint before the subduction process. A large part of the incompatible trace elements remained trapped in the rocks and was recycled within the various metamorphic assemblages stable under changing metamorphic conditions during the subduction process, indicating that devolatilization reactions in massive basic rocks do not necessarily imply significant simultaneous trace element and REE release.

Were Spanish migrants attracted by industrial agglomerations?: an analysis for the interwar years in the light of the new economic geography

In this paper we examine whether access to markets had a significant influence onmigration choices of Spanish internal migrants in the inter-war years. We perform astructural contrast of a New Economic Geography model that focus on the forwardlinkage that links workers location choice with the geography of industrial production,one of the centripetal forces that drive agglomeration in the NEG models. The resultshighlight the presence of this forward linkage in the Spanish economy of the inter-warperiod. That is, we prove the existence of a direct relation between workers¿ localizationdecisions and the market potential of the host regions. In addition, the direct estimationof the values associated with key parameters in the NEG model allows us to simulatethe migratory flows derived from different scenarios of the relative size of regions andthe distances between them. We show that in Spain the power of attraction of theagglomerations grew as they increased in size, but the high elasticity estimated for themigration costs reduced the intensity of the migratory flows. This could help to explainthe apparently low intensity of internal migrations in Spain until its upsurge during the1920s. This also explains the geography of migrations in Spain during this period,which hardly affected the regions furthest from the large industrial agglomerations (i.e.,regions such as Andalusia, Estremadura and Castile-La Mancha) but had an intenseeffect on the provinces nearest to the principal centres of industrial development.

The role of the vacuolar H+ - ATPase in membrane fusion

RésuméLa H+-ATPase vacuolaire (V-ATPase) est un complexe enzymatique composé de deux secteurs multimériques (VQ et Vi) dont l'association dans la cellule est réversible. Le secteur intramembranaire de la V-ATPase (V0) interagit physiquement avec des protéines SNARE et stimule la fusion homotypique des vacuoles de la levure (lysosomes), la sécrétion de neurotransmetteurs et d'insuline, la fusion entre phagosome et lysosome ainsi que la sécrétion des corps multivésiculaires par un mécanisme inconnu. Dans cette étude j'ai identifié des résidues d'acides amines situés dans des sous-unités de V0 impliqués dans le mécanisme de fusion des vacuoles mais non essentiels pour l'acidification vacuolaire par la V-ATPase. j'ai utilisé un protocole de mutagenèse aléatoire pour produire des libraries de mutants des sous unités de V0. Ces libraries ont été analysées in vivo afin d'identifier des alleles qui permettent la translocation des protons mais produisent une vacuole fragmentée, phénotype indiquant un défaut dans la fusion membranaire. Les vacuoles des mutants ont été isolées et caractéisées en utilisant une grande variété d'outils biochimiques pour déterminer précisément l'impact des différentes mutations sur l'accomplissement d'événements clés du processus de fusion.J'ai identifié des mutations associées à des défauts spécifiques de la fusion dans plusieurs sous-unités de V0. Dans les protéolipides c, c' et c" ces mutations se concentrent dans la partie cytosolique des domaines transmembranaires. Elles renforcent les associations entre les secteurs de la V-ATPase et entre V0 et les SNAREs. Dans la fusion vacuolaire ces mutations permettent la formation de complexes SNAREs en trans mais inhibent l'induction de la fusion. Par contre, la deletion de la sous- unité d influence les étapes de la fusion qui précèdent la formation des complexes trans-SNAREs. Mes résultats démontrent que V0 joue des rôles différents dans plusieurs étapes de la fusion et que ces fonctions sont liées au système des SNAREs. Ils différencient génétiquement les activités de V0 dans la translocation des protons et dans la fusion et identifient de nombreux résidus importants pour la fusion vacuolaire. De plus, compte tenu de la grande conservation de sequence des protéolipides chez les eukaryotes les mutations identifiées dans cette l'étude apportent de nouvelles informations pour analyser la fonction de V0 dans des organismes multicellulaires pour lesquels la function catalytique de la V-ATPase est essentielle à la survie.Résumé pour le large publicLe transport de protéines et de membranes est important pour maintenir la fonction des organelles dans la cellule. Il s'excerce au niveau des vesicules. La fusion membranaire est un processus élémentaire de ce transport. Pour fusionner deux membranes, il faut la coordination de deux activités: le rapprochement et la déstabiiization des deux membranes. La collaboration d'un ensemble de proteins conservés chez les eukaryotes, est nécessaire pour catalyser ces activités. Les proteins SNAREs sont les protagonistes principaux dans la fusion membranaire. Néanmoins, d'autres protéines, comme des Rab-GTPases et des chaperonnes, sont nécessaires pour permettre ce phénomène de fusion. Toutes ces protéines sont temporairement associées avec les SNAREs et leur fonction dans la fusion membranaire est souvent directement liée à leur activité dans cette association. Le secteur transmembranaire V0 de la V-ATPase rnteragit avec des SNAREs et est essentiel pour la fusion dans une variété de systèmes modèles comme la mouche, la souris et la levure. Le secteur V0 est composé de six protéines différentes. Avec te secteur Va, qui réside dans le cytosol, il forme la V-ATPase dont la fonction principale est l'acidification des organelles par translocation des protons à travers la membrane par un mécanisme ressemblant à celui d'une pompe. V0joue un role dans la fusion membranaire, indépendamment de son activité catalytique liée au pompage des protons, et ce rôle est encore largement méconnu à ce jour. Le but de ma thèse était de mieux comprendre l'implication de V0 dans ce contexte.Pour étudier des activités liées à la V-ATPase, la levure est un excellent modèle d'étude car elle survie à une inactivation de l'enzyme alors que le meme traitement serait léthal pour des organismes multicellulaires. Dans ma thèse j'ai utilisé la fusion homotypique de la vacuole de levure comme système modèle pour étudier le rôle de V0 dans la fusion. J'ai muté des gènes qui encodent des sous- unités de V0 et les ai introduit dans des souches privées des gènes respectifs. Dans les librairies de souches portant différentes versions de ces gènes j'ai cherché des clones exprimant une V-ATPase intacte et fonctionnelle mais qui possèdent une vacuole fragmentée. Le plus souvent, une vacuole fragmentée indique un défaut dans la fusion vacuolaire. Dans les trois types de protéolipides qui composent un cylindre dans le secteur V0, j'ai trouvé des clones avec une vacuole fragmentée. Après avoir isolé les mutations responsable de ce type de morphologie vacuolaire, j'ai isolé les vacuoles de ces clones pour étudier leur activités dans différentes étapes de la fusion vacuolaire. Les résultats de ces analyses mettent en évidence une implication de V0 dans plusieurs étapes de la fusion vacuolaire. Certaines mutations sélectionnées dans mon étude inhibent une étape précoce de la fusion qui inclue la dissociation des complexes SNARE, tandis que d'autres mutations inhibent une étape tardive du processus de fusion qui inclue la transmission d'une force disruptive dans la membrane.AbstractThe membrane-integral V0 sector of the vacuolar H+-ATPase (V-ATPase) interacts with SNARE proteins. V0 stimulates fusion between yeast vacuoles (lysosomes) (Peters et al., 2001b), secretion of neurotransmitters and insulin (Hiesinger et al., 2005a, Sun-Wada et al., 2006a), phagosome-lysosome fusion (Peri and Nusslein-Volhard, 2008) and secretion of multivesicular bodies (Liegeois et al., 2006b) by a yet unknown mechanism. In my thesis, I identified sites in V0 subunits that are involved in yeast vacuole fusion but dispensable for the proton pumping by the V-ATPase. I randomly mutagenized V0 subunits and screened in vivo for mutant alleles that support proton pumping but cause fragmented vacuoles, a phenotype indicative of a fusion defect. Mutant vacuoles were isolated and analyzed in a cell-free system, allowing assay of key events in fusion, such as trans-SNARE pairing, lipid transition and fusion pore opening (Reese et al., 2005b).Mutants with selective fusion defects were found in several V0 subunits. In the proteolipids c, c' and c", critical mutations are concentated in the cytosolic half of the transmembrane domains. These mutations rendered the V-ATPase holoenzyme more stable and modulated V0-SNARE associations. In vacuole fusion critical proteolipid mutations permitted trans-SNARE pairing but impeded the induction of lipid flow between the membranes. Deletion of subunit d, by contrast, influenced early stages of fusion that precede trans-SNARE pairing. My results show that V0 acts in several steps of the fusion process and that its function is intimately connected to the SNARE system. They genetically separate the proton pump and fusion activities of V0 and identify numerous critical residues. Given the high sequence conservation of proteolipids in eukaryotic life, the identified mutations may be helpful in analyzing the fusion function of V0 also in mammalian cells, where V- ATPase pump function is essential for survival.

Evidence for segregated and integrative connectivity patterns in the human Basal Ganglia.

Detailed knowledge of the anatomy and connectivity pattern of cortico-basal ganglia circuits is essential to an understanding of abnormal cortical function and pathophysiology associated with a wide range of neurological and neuropsychiatric diseases. We aim to study the spatial extent and topography of human basal ganglia connectivity in vivo. Additionally, we explore at an anatomical level the hypothesis of coexistent segregated and integrative cortico-basal ganglia loops. We use probabilistic tractography on magnetic resonance diffusion weighted imaging data to segment basal ganglia and thalamus in 30 healthy subjects based on their cortical and subcortical projections. We introduce a novel method to define voxel-based connectivity profiles that allow representation of projections from a source to more than one target region. Using this method, we localize specific relay nuclei within predefined functional circuits. We find strong correlation between tractography-based basal ganglia parcellation and anatomical data from previously reported invasive tracing studies in nonhuman primates. Additionally, we show in vivo the anatomical basis of segregated loops and the extent of their overlap in prefrontal, premotor, and motor networks. Our findings in healthy humans support the notion that probabilistic diffusion tractography can be used to parcellate subcortical gray matter structures on the basis of their connectivity patterns. The coexistence of clearly segregated and also overlapping connections from cortical sites to basal ganglia subregions is a neuroanatomical correlate of both parallel and integrative networks within them. We believe that this method can be used to examine pathophysiological concepts in a number of basal ganglia-related disorders.

Contribution of microbial and invertebrate communities to leaf litter colonization in a Mediterranean stream

Leaf litter inputs and retention play an important role in ecosystem functioning in forested streams. We examined colonization of leaves by microbes (bacteria, fungi, and protozoa) and fauna in Fuirosos, an intermittent forested Mediterranean stream. Black poplar (Populus nigra) and plane (Platanus acerifolia) leaf packs were placed in the stream for 4 mo. We measured the biomasses and calculated the densities of bacteria, fungi, protozoa, meiofauna, and macroinvertebrates to determine their dynamics and potential interactions throughout the colonization process. Colonization was strongly correlated with hydrological variability (defined mainly by water temperature and discharge). The 1st week of colonization was characterized by hydrological stability and warm water temperatures, and allocation of C from microbial to invertebrate compartments on the leaf packs was rapid. Clumps of fine particulate organic matter (FPOM) were retained by the leaf packs, and enhanced rapid colonization by microfauna and meiofaunal collector-gatherers (ostracods and copepods). After 2 wk, an autumnal flood caused a 20-fold increase in water flow. Higher discharge and lower water temperature caused FPOM-related fauna to drift away from the packs and modified the subsequent colonization sequence. Fungi showed the highest biomass, with similar values to those recorded at the beginning of the experiment. After 70 d of postflood colonization, fungi decreased to nearly 40% of the total C in the leaf packs, whereas invertebrates became more abundant and accounted for 60% of the C. Natural flood occurrence in Mediterranean streams could be a key factor in the colonization and processing of organic matter.

Geomorphological method in the elaboration of hazard maps for flash-floods in the municipality of Jucuarán (El Salvador)

This work deals with the elaboration of flood hazard maps. These maps reflect the areas prone to floods based on the effects of Hurricane Mitch in the Municipality of Jucuarán of El Salvador. Stream channels located in the coastal range in the SE of El Salvador flow into the Pacific Ocean and generate alluvial fans. Communities often inhabit these fans can be affected by floods. The geomorphology of these stream basins is associated with small areas, steep slopes, well developed regolite and extensive deforestation. These features play a key role in the generation of flash-floods. This zone lacks comprehensive rainfall data and gauging stations. The most detailed topographic maps are on a scale of 1:25 000. Given that the scale was not sufficiently detailed, we used aerial photographs enlarged to the scale of 1:8000. The effects of Hurricane Mitch mapped on these photographs were regarded as the reference event. Flood maps have a dual purpose (1) community emergency plans, (2) regional land use planning carried out by local authorities. The geomorphological method is based on mapping the geomorphological evidence (alluvial fans, preferential stream channels, erosion and sedimentation, man-made terraces). Following the interpretation of the photographs this information was validated on the field and complemented by eyewitness reports such as the height of water and flow typology. In addition, community workshops were organized to obtain information about the evolution and the impact of the phenomena. The superimposition of this information enables us to obtain a comprehensive geomorphological map. Another aim of the study was the calculation of the peak discharge using the Manning and the paleohydraulic methods and estimates based on geomorphologic criterion. The results were compared with those obtained using the rational method. Significant differences in the order of magnitude of the calculated discharges were noted. The rational method underestimated the results owing to short and discontinuous periods of rainfall data with the result that probabilistic equations cannot be applied. The Manning method yields a wide range of results because of its dependence on the roughness coefficient. The paleohydraulic method yielded higher values than the rational and Manning methods. However, it should be pointed out that it is possible that bigger boulders could have been moved had they existed. These discharge values are lower than those obtained by the geomorphological estimates, i.e. much closer to reality. The flood hazard maps were derived from the comprehensive geomorphological map. Three categories of hazard were established (very high, high and moderate) using flood energy, water height and velocity flow deduced from geomorphological and eyewitness reports.

EORTC topics in neurooncology: The long path from a focus on neurological complications of cancer towards molecularly defined trials and therapies in neurooncology

Over the past decade a series of trials of the EORTC Brain Tumor Group (BTG) has substantially influenced and shaped the standard-of-care of primary brain tumors. All these trials were coupled with biological research that has allowed for better understanding of the biology of these tumors. In glioblastoma, EORTC trial 26981/22981 conducted jointly with the National Cancer Institute of Canada Clinical Trials Group showed superiority of concomitant radiochemotherapy with temozolomide over radiotherapy alone. It also identified the first predictive marker for benefit from alkylating agent chemotherapy in glioblastoma, the methylation of the O6-methyl-guanyl-methly-transferase (MGMT) gene promoter. In another large randomized trial, EORTC 26951, adjuvant chemotherapy in anaplastic oligodendroglial tumors was investigated. Despite an improvement in progression-free survival this did not translate into a survival benefit. The third example of a landmark trial is the EORTC 22845 trial. This trial led by the EORTC Radiation Oncology Group forms the basis for an expectative approach to patients with low-grade glioma, as early radiotherapy indeed prolongs time to tumor progression but with no benefit in overall survival. This trial is the key reference in deciding at what time in their disease adult patients with low-grade glioma should be irradiated. Future initiatives will continue to focus on the conduct of controlled trials, rational academic drug development as well as systematic evaluation of tumor tissue including biomarker development for personalized therapy. Important lessons learned in neurooncology are to dare to ask real questions rather than merely rapidly testing new compounds, and the value of well designed trials, including the presence of controls, central pathology review, strict radiology protocols and biobanking. Structurally, the EORTC BTG has evolved into a multidisciplinary group with strong transatlantic alliances. It has contributed to the maturation of neurooncology within the oncological sciences.

R6le de l'urotlogue dans le dépistage des maladies osseuses [Role of the urologist in the screening of bone diseases].

During their lifetime, 20% of men will suffer from a fracture secondary to osteoporosis, and morbidity and mortality of a hip fracture in men are more severe than in women. Despite these facts, there are only few studies on osteoporosis in men. Hyopgonadism is a known risk factor for bone mineral density decrease. Hypogonadism can be found in patients diagnosed with prostate cancer who are receiving androgen deprivation therapy, but can also be discovered in patients with male infertility or erectile dysfunction. Urologists have central role in men's health aftercare, and therefore have key role in the screening and in the multidisciplinary treatment of osteoporosis and osteopenia.

Biomarkers of oxidative stress and its association with the urinary reducing capacity in bus maintenance workers.

BACKGROUND: Exposure to particles (PM) induces adverse health effects (cancer, cardiovascular and pulmonary diseases). A key-role in these adverse effects seems to be played by oxidative stress, which is an excess of reactive oxygen species relative to the amount of reducing species (including antioxidants), the first line of defense against reactive oxygen species. The aim of this study was to document the oxidative stress caused by exposure to respirable particles in vivo, and to test whether exposed workers presented changes in their urinary levels for reducing species.METHODS: Bus depot workers (n = 32) exposed to particles and pollutants (respirable PM4, organic and elemental carbon, particulate metal content, polycyclic aromatic hydrocarbons, NOx, O3) were surveyed over two consecutive days. We collected urine samples before and after each shift, and quantified an oxidative stress biomarker (8-hydroxy-2'-deoxyguanosine), the reducing capacity and a biomarker of PAH exposure (1-hydroxypyrene). We used a linear mixed model to test for associations between the oxidative stress status of the workers and their particle exposure as well as with their urinary level of reducing species.RESULTS: Workers were exposed to low levels of respirable PM4 (range 25-71 μg/m3). However, urinary levels of 8-hydroxy-2'-deoxyguanosine increased significantly within each shift and between both days for non-smokers. The between-day increase was significantly correlated (p < 0.001) with the concentrations of organic carbon, NOx, and the particulate copper content. The within-shift increase in 8OHdG was highly correlated to an increase of the urinary reducing capacity (Spearman ρ = 0.59, p < 0.0001).CONCLUSIONS: These findings confirm that exposure to components associated to respirable particulate matter causes a systemic oxidative stress, as measured with the urinary 8OHdG. The strong association observed between urinary 8OHdG with the reducing capacity is suggestive of protective or other mechanisms, including circadian effects. Additional investigations should be performed to understand these observations.

Farnesol-induced apoptosis in Candida albicans is mediated by Cdr1-p extrusion and depletion of intracellular glutathione.

Farnesol is a key derivative in the sterol biosynthesis pathway in eukaryotic cells previously identified as a quorum sensing molecule in the human fungal pathogen Candida albicans. Recently, we demonstrated that above threshold concentrations, farnesol is capable of triggering apoptosis in C. albicans. However, the exact mechanism of farnesol cytotoxicity is not fully elucidated. Lipophilic compounds such as farnesol are known to conjugate with glutathione, an antioxidant crucial for cellular detoxification against damaging compounds. Glutathione conjugates act as substrates for ATP-dependent ABC transporters and are extruded from the cell. To that end, this current study was undertaken to validate the hypothesis that farnesol conjugation with intracellular glutathione coupled with Cdr1p-mediated extrusion of glutathione conjugates, results in total glutathione depletion, oxidative stress and ultimately fungal cell death. The combined findings demonstrated a significant decrease in intracellular glutathione levels concomitant with up-regulation of CDR1 and decreased cell viability. However, addition of exogenous reduced glutathione maintained intracellular glutathione levels and enhanced viability. In contrast, farnesol toxicity was decreased in a mutant lacking CDR1, whereas it was increased in a CDR1-overexpressing strain. Further, gene expression studies demonstrated significant up-regulation of the SOD genes, primary enzymes responsible for defense against oxidative stress, with no changes in expression in CDR1. This is the first study describing the involvement of Cdr1p-mediated glutathione efflux as a mechanism preceding the farnesol-induced apoptotic process in C. albicans. Understanding of the mechanisms underlying farnesol-cytotoxicity in C. albicans may lead to the development of this redox-cycling agent as an alternative antifungal agent.

Reproducibility and relative validity of a food-frequency questionnaire for French-speaking Swiss adults.

BACKGROUND: Due to the distinct cultural and language differences that exist in Switzerland, there is little information on the dietary intake among the general Swiss population. Adequately assessing dietary intake is thus paramount if nutritional epidemiological studies are to be conducted. OBJECTIVE: To assess the reproducibility and validity of a food-frequency questionnaire (FFQ) developed for French-speaking Swiss adults. DESIGN: A total of 23 men and 17 women (43.1+/-2.0 years) filled out one FFQ and completed one 24-hour dietary recall at baseline and 1 month afterward. RESULTS: Crude Pearson's correlation coefficients between the first and the second FFQ ranged from 0.58 to 0.90, intraclass correlation coefficient (ICC) ranged between 0.53 and 0.92. Lin's concordance coefficients ranged between 0.55 and 0.87. Over 80% of participants were classified in the same or adjacent tertile using each FFQ. Macronutrient intakes estimated by both FFQs were significantly higher than those estimated from the 24-hour recall for protein and water, while no significant differences were found for energy, carbohydrate, fats (five groups), and alcohol. De-attenuated Pearson's correlation coefficients between the 24-hour recall and the first FFQ ranged between 0.31 and 0.49, while for the second FFQ the values ranged between 0.38 and 0.59. Over 40 and 95% of participants fell into the same or the adjacent energy and nutrient tertiles, respectively, using the FFQs and the 24-hour recall. CONCLUSIONS: This FFQ shows good reproducibility and can be used determining macronutrient intake in a French-speaking Swiss population in an epidemiological setting.

bHLH class transcription factors take centre stage in phytochrome signalling.

The phytochrome family of photoreceptors (there are five phytochromes in Arabidopsis, named phyA to phyE) maximally absorbs red and far-red light and plays important functions throughout the life cycle of plants. Several recent studies have shown that multiple related bHLH (basic helix-loop-helix) class transcription factors play key roles in phytochrome signal transduction. Somewhat surprisingly these transcription factors primarily act as negative regulators of phytochrome signalling. Moreover, in some cases, the phytochromes inhibit those negative regulators.

Comparison between a linear ion trap and a triple quadruple MS in the sensitive detection of large peptides at femtomole amounts on column.

In addition to the importance of sample preparation and extract separation, MS detection is a key factor in the sensitive quantification of large undigested peptides. In this article, a linear ion trap MS (LIT-MS) and a triple quadrupole MS (TQ-MS) have been compared in the detection of large peptides at subnanomolar concentrations. Natural brain natriuretic peptide, C-peptide, substance P and D-Junk-inhibitor peptide, a full D-amino acid therapeutic peptide, were chosen. They were detected by ESI and simultaneous MS(1) and MS(2) acquisitions. With direct peptide infusion, MS(2) spectra revealed that fragmentation was peptide dependent, milder on the LIT-MS and required high collision energies on the TQ-MS to obtain high-intensity product ions. Peptide adsorption on surfaces was overcome and peptide dilutions ranging from 0.1 to 25 nM were injected onto an ultra high-pressure LC system with a 1 mm id analytical column and coupled with the MS instruments. No difference was observed between the two instruments when recording in LC-MS(1) acquisitions. However, in LC-MS(2) acquisitions, a better sensitivity in the detection of large peptides was observed with the LIT-MS. Indeed, with the three longer peptides, the typical fragmentation in the TQ-MS resulted in a dramatic loss of sensitivity (> or = 10x).

"Suddenly I get into the zone": Examining discontinuities and nonlinear changes in flow experiences at work

Work-related flow is defined as a sudden and enjoyable merging of action and awareness that represents a peak experience in the daily lives of workers. Employees" perceptions of challenge and skill and their subjective experiences in terms of enjoyment, interest and absorption were measured using the experience sampling method, yielding a total of 6981 observations from a sample of 60 employees. Linear and nonlinear approaches were applied in order to model both continuous and sudden changes. According to the R2, AICc and BIC indexes, the nonlinear dynamical systems model (i.e. cusp catastrophe model) fit the data better than the linear and logistic regression models. Likewise, the cusp catastrophe model appears to be especially powerful for modelling those cases of high levels of flow. Overall, flow represents a nonequilibrium condition that combines continuous and abrupt changes across time. Research and intervention efforts concerned with this process should focus on the variable of challenge, which, according to our study, appears to play a key role in the abrupt changes observed in work-related flow.

Modelling hydrodynamics in the Rio Parana, Argentina : an evaluation and inter-comparison of reduced-complexity and physics based models applied to a large sand-bed river

Depth-averaged velocities and unit discharges within a 30 km reach of one of the world's largest rivers, the Rio Parana, Argentina, were simulated using three hydrodynamic models with different process representations: a reduced complexity (RC) model that neglects most of the physics governing fluid flow, a two-dimensional model based on the shallow water equations, and a three-dimensional model based on the Reynolds-averaged Navier-Stokes equations. Row characteristics simulated using all three models were compared with data obtained by acoustic Doppler current profiler surveys at four cross sections within the study reach. This analysis demonstrates that, surprisingly, the performance of the RC model is generally equal to, and in some instances better than, that of the physics based models in terms of the statistical agreement between simulated and measured flow properties. In addition, in contrast to previous applications of RC models, the present study demonstrates that the RC model can successfully predict measured flow velocities. The strong performance of the RC model reflects, in part, the simplicity of the depth-averaged mean flow patterns within the study reach and the dominant role of channel-scale topographic features in controlling the flow dynamics. Moreover, the very low water surface slopes that typify large sand-bed rivers enable flow depths to be estimated reliably in the RC model using a simple fixed-lid planar water surface approximation. This approach overcomes a major problem encountered in the application of RC models in environments characterised by shallow flows and steep bed gradients. The RC model is four orders of magnitude faster than the physics based models when performing steady-state hydrodynamic calculations. However, the iterative nature of the RC model calculations implies a reduction in computational efficiency relative to some other RC models. A further implication of this is that, if used to simulate channel morphodynamics, the present RC model may offer only a marginal advantage in terms of computational efficiency over approaches based on the shallow water equations. These observations illustrate the trade off between model realism and efficiency that is a key consideration in RC modelling. Moreover, this outcome highlights a need to rethink the use of RC morphodynamic models in fluvial geomorphology and to move away from existing grid-based approaches, such as the popular cellular automata (CA) models, that remain essentially reductionist in nature. In the case of the world's largest sand-bed rivers, this might be achieved by implementing the RC model outlined here as one element within a hierarchical modelling framework that would enable computationally efficient simulation of the morphodynamics of large rivers over millennial time scales. (C) 2012 Elsevier B.V. All rights reserved.