Statistical properties of mechanically generated surface gravity waves: a laboratory experiment in a three-dimensional wave basin

A wave basin experiment has been performed in the MARINTEK laboratories, in one of the largest existing three-dimensional wave tanks in the world. The aim of the experiment is to investigate the effects of directional energy distribution on the statistical properties of surface gravity waves. Different degrees of directionality have been considered, starting from long-crested waves up to directional distributions with a spread of ±30 • at the spectral peak. Particular attention is given to the tails of the distribution function of the surface elevation, wave heights and wave crests. Comparison with a simplified model based on second-order theory is reported. The results show that for long-crested, steep and narrow-banded waves, the second-order theory underestimates the probability of occurrence of large waves. As directional effects are included, the departure from second-order theory becomes less accentuated and the surface elevation is characterized by weak deviations from Gaussian statistics

In-Situ Evidence for Uranium Immobilization and Remobilization

The in-situ microbial reduction and immobilization of uranium was assessed as a means of preventing the migration of this element in the terrestrial subsurface. Uranium immobilization (putatively identified as reduction) and microbial respiratory activities were evaluated in the presence of exogenous electron donors and acceptors with field push-pull tests using wells installed in an anoxic aquifer contaminated with landfill leachate. Uranium-(VI) amended at 1.5 µM was reduced to less than 1 nM in groundwater in less than 8 d during all field experiments. Amendments of 0.5 mM sulfate or 5 mM nitrate slowed U(VI) immobilization and allowed for the recovery of 10% and 54% of the injected element, respectively, as compared to 4% in the unamended treatment. Laboratory incubations confirmed the field tests and showed that the majority of the U(VI) immobilized was due to microbial reduction. In these tests, nitrate treatment (7.5 mM) inhibited U(VI) reduction, and nitrite was transiently produced. Further push-pull tests were performed in which either 1 or 5 mM nitrate was added with 1.0 µM U(VI) to sediments that already contained immobilized uranium. After an initial loss of the amendments, the concentration of soluble U(VI) increased and eventually exceeded the injected concentration, indicating that previously immobilized uranium was remobilized as nitrate was reduced. Laboratory experiments using heat-inactivated sediment slurries suggested that the intermediates of dissimilatory nitrate reduction (denitrification or dissimilatory nitrate reduction to ammonia), nitrite, nitrous oxide, and nitric oxide were all capable of oxidizing and mobilizing U(IV). These findings indicate that insitu subsurface U(VI) immobilization can be expected to take place under anaerobic conditions, but the permanence of the approach can be impaired by disimilatory nitrate reduction intermediates that can mobilize previously reduced uranium

Initiation of ensemble data assimilation

A B S T R A C T The specification of the initial ensemble for ensemble data assimilation is addressed. The presented work examines the impact of ensemble initiation in the Maximum Likelihood Ensemble Filter (MLEF) framework, but is also applicable to other ensemble data assimilation algorithms. Two methods are considered: the first is based on the use of the KardarParisi-Zhang (KPZ) equation to form sparse random perturbations, followed by spatial smoothing to enforce desired correlation structure, while the second is based on the spatial smoothing of initially uncorrelated random perturbations. Data assimilation experiments are conducted using a global shallow-water model and simulated observations. The two proposed methods are compared to the commonly used method of uncorrelated random perturbations. The results indicate that the impact of the initial correlations in ensemble data assimilation is beneficial. The root-mean-square error rate of convergence of the data assimilation is improved, and the positive impact of initial correlations is notable throughout the data assimilation cycles. The sensitivity to the choice of the correlation length scale exists, although it is not very high. The implied computational savings and improvement of the results may be important in future realistic applications of ensemble data assimilation

Ocean warming enhances respiration and carbon demand of coastal microbial plankton

Abstract The increase of anthropogenic CO 2 during this century is expected to cause warming of large regions of the ocean. Microbes lead the biological role in the CO 2 balance of marine ecosystems, their activity is known to be influenced by temperature, and it is important to constrain and quantify these effects on bacterial carbon use. Furthermore, if warming were to enhance the carbon demand (production 1 respiration) of planktonic microbes but would maintain their efficiency low (as it generally is), then most carbon consumed would end up respired. We designed a strategy in which we measured bacterial production and respiration throughout a seasonal cycle in a coastal Mediterranean site, and determined experimentally the effects of ca. 2.5 1C on these processes. We show that warming will increase nearly 20% the total carbon demand of coastal microbial plankton without any effect on their (commonly low) growth efficiency, which could generate a positive feedback between coastal warming and CO 2 production

Genome-wide linkage scan in affected sibling pairs identifies novel susceptibility region for venous thromboembolism: Genetics In Familial Thrombosis study

To cite this article: de Visser MCH, van Minkelen R, van Marion V, den Heijer M, Eikenboom J, Vos HL, Slagboom PE, Houwing-Duistermaat JJ, Rosendaal FR, Bertina RM. Genome-wide linkage scan in affected sibling pairs identifies novel susceptibility region for venous thromboembolism: Genetics in Familial Thrombosis study. J Thromb Haemost 2013; 11: 1474-84. Summary. Background: Venous thromboembolism (VTE) is a multicausal disorder involving environmental and genetic risk factors. In many thrombophilic families the clustering of thrombotic events cannot be explained by known genetic risk factors, indicating that some remain to be discovered. Objectives: We aimed to identify novel thrombosis susceptibility alleles in a large panel of small thrombophilic families: the Genetics In Familial Thrombosis (GIFT) study. Patients/Methods: In the GIFT study, 201 families were recruited consisting of 438 siblings with an objectively confirmed VTE at a young age. Multipoint linkage analysis (402 SSR markers) and fine mapping were performed, followed by genotyping of tagging SNPs in positional candidate genes. Results: Established genetic risk factors such as factor V Leiden, ABO blood group non-O, prothrombin 20210A, fibrinogen gamma 10034T and deficiencies of antithrombin, protein C and protein S were more frequent in GIFT patients than in unselected VTE patients. Linkage supported the presence of novel thrombosis susceptibility loci on 7p21.3-22.2 (LOD score = 3.23) and Xq24-27.3 (LOD score = 1.95). Simulation analysis showed that the chr7 signal was genome-wide statistically significant (P = 0.022). Tagging SNPs (n = 157) in eight positional candidate genes (LOD drop 1.5 regions) were genotyped in GIFT patients and 332 healthy controls. Five chr7 SNPs associated with VTE. SNP THSD7A rs2074597 was responsible for part of the chr7 signal. Conclusions: The GIFT panel is rich in established genetic risk factors for VTE, but genetic factors remain unidentified in many families. Genome-wide linkage failed to identify the previously established genetic risk factors for VTE, but identified a novel VTE susceptibility locus on chr7

Relationship between photosynthetic metabolism and cell cycle in a synchronized culture of the marine alga Cylindrotheca fusiformis (Bacillariophyceae)

The aim of this study was to characterize the variation and regulation of photosynthetic carbon metabolism in Cylindrotheca fusiformis during the cell cycle. The cells were synchronized using two cell cycle inhibitors: one for cells grown under light:dark cycles and one for growth in continuous light. We observed that the maximal photosynthetic capacity, P B m and ETR m were lowest just before cell division, when the percentage of cells in G2+M was maximal, and were highest after division, when the percentage of cells in G1 was maximal. These results clearly show that photosynthetic activity is related to the cell cycle. In addition, the role of different oxygen uptake processes was determined using 18 O 2 . We showed that light stimulated oxygen uptake, which increased with irradiance between 0 and 250 mmol photons m 7 2 s 7 1 . This variation was partly due to an increase of mitochondrial respiration, but mostly to a high Mehler activity. It seems that this increase was due to the Mehler reaction rather than photorespiration, because no increase of oxygen uptake was observed at low DIC (0.1 mM) concentration, which should have stimulated Rubisco oxygenase if there was diffusive CO 2 entry. The activity of the Mehler reaction was independent of the cell cycle and explained 50 -60% of the light stimulated oxygen uptake at irradiances equal to or exceeding the growth irradiance

Deforestation and CO 2 emissions in coastal Tanzania from 1990 to 2007

SUMMARY Conversion of forest to other land uses is a major Regional forest clearance in Tanzania is highly dynamic; while rates have slowed since 2000, forest habitat conversion has continued and there is no guarantee that future rates will remain low. A rigorous policy on reducing emissions from deforestation and degradation (REDD) should be implemented to avoid future increases in deforestation rates

Effect of acid treatment on the structure of sepiolite

ABSTRACT: An ab initio determination of the structure of sepiolite after acid treatment (HCl 0.5 N for 24 h) was carried out using X-ray powder diffraction data. After acid treatment, the sections normal to the a and c axes presented discontinuities,~2.25 Å wide, parallel to the (010) plane, with no electronic density maxima, thus suggesting that adjacent planes are joined by van der Waals-like residual links. Partial dissolution was detected on both octahedral and tetrahedral sheets, beginning by breaking the ribbons not along the edges, but in the centre, thus creating a 5.2066.79 Å tunnel along the a axis. By interrupting the tetrahedral sheet, this mechanism changes the phyllosilicate-like nature of the sepiolite to an inosilicate-like structure

Fewer invited talks by women in evolutionary biology symposia

Abstract Lower visibility of female scientists, compared to male scientists, is a potential reason for the under-representation of women among senior academic ranks. Visibility in the scientific community stems partly from presenting research as an invited speaker at organized meetings. We analysed the sex ratio of presenters at the European Society for Evolutionary Biology (ESEB) Congress 2011, where all abstract submissions were accepted for presentation. Women were under-represented among invited speakers at symposia (15% women) compared to all presenters (46%), regular oral presenters (41%) and plenary speakers (25%). At the ESEB congresses in 2001-2011, 9-23% of invited speakers were women. This under-representation of women is partly attributable to a larger proportion of women, than men, declining invitations: in 2011, 50% of women declined an invitation to speak compared to 26% of men. We expect invited speakers to be scientists from top ranked institutions or authors of recent papers in high-impact journals. Considering all invited speakers (including declined invitations), 23% were women. This was lower than the baseline sex ratios of early-mid career stage scientists, but was similar to senior scientists and authors that have published in high-impact journals. High-quality science by women therefore has low exposure at international meetings, which will constrain Evolutionary Biology from reaching its full potential. We wish to highlight the wider implications of turning down invitations to speak, and encourage conference organizers to implement steps to increase acceptance rates of invited talks

Fewer invited talks by women in evolutionary biology symposia

Abstract Lower visibility of female scientists, compared to male scientists, is a potential reason for the under-representation of women among senior academic ranks. Visibility in the scientific community stems partly from presenting research as an invited speaker at organized meetings. We analysed the sex ratio of presenters at the European Society for Evolutionary Biology (ESEB) Congress 2011, where all abstract submissions were accepted for presentation. Women were under-represented among invited speakers at symposia (15% women) compared to all presenters (46%), regular oral presenters (41%) and plenary speakers (25%). At the ESEB congresses in 2001-2011, 9-23% of invited speakers were women. This under-representation of women is partly attributable to a larger proportion of women, than men, declining invitations: in 2011, 50% of women declined an invitation to speak compared to 26% of men. We expect invited speakers to be scientists from top ranked institutions or authors of recent papers in high-impact journals. Considering all invited speakers (including declined invitations), 23% were women. This was lower than the baseline sex ratios of early-mid career stage scientists, but was similar to senior scientists and authors that have published in high-impact journals. High-quality science by women therefore has low exposure at international meetings, which will constrain Evolutionary Biology from reaching its full potential. We wish to highlight the wider implications of turning down invitations to speak, and encourage conference organizers to implement steps to increase acceptance rates of invited talks