Larval fish dispersal in a coral-reef seascape

Free to read at publisher's site. Larval dispersal is a critical yet enigmatic process in the persistence and productivity of marine metapopulations. Empirical data on larval dispersal remain scarce, hindering the use of spatial management tools in efforts to sustain ocean biodiversity and fisheries. Here we document dispersal among subpopulations of clownfish (Amphiprion percula) and butterflyfish (Chaetodon vagabundus) from eight sites across a large seascape (10,000 km(2)) in Papua New Guinea across 2 years. Dispersal of clownfish was consistent between years, with mean observed dispersal distances of 15 km and 10 km in 2009 and 2011, respectively. A Laplacian statistical distribution (the dispersal kernel) predicted a mean dispersal distance of 13-19 km, with 90% of settlement occurring within 31-43 km. Mean dispersal distances were considerably greater (43-64 km) for butterfly-fish, with kernels declining only gradually from spawning locations. We demonstrate that dispersal can be measured on spatial scales sufficient to inform the design of and test the performance of marine reserve networks

Massive binary black holes in galactic nuclei and their path to coalescence

Massive binary black holes form at the centre of galaxies that experience a merger episode. They are expected to coalesce into a larger black hole, following the emission of gravitational waves. Coalescing massive binary black holes are among the loudest sources of gravitational waves in the Universe, and the detection of these events is at the frontier of contemporary astrophysics. Understanding the black hole binary formation path and dynamics in galaxy mergers is therefore mandatory. A key question poses: during a merger, will the black holes descend over time on closer orbits, form a Keplerian binary and coalesce shortly after? Here we review progress on the fate of black holes in both major and minor mergers of galaxies, either gas-free or gas-rich, in smooth and clumpy circum-nuclear discs after a galactic merger, and in circum-binary discs present on the smallest scales inside the relic nucleus.Comment: Accepted for publication in Space Science Reviews. To appear in hard cover in the Space Sciences Series of ISSI "The Physics of Accretion onto Black Holes" (Springer Publisher

N-body simulations of gravitational dynamics

We describe the astrophysical and numerical basis of N-body simulations, both of collisional stellar systems (dense star clusters and galactic centres) and collisionless stellar dynamics (galaxies and large-scale structure). We explain and discuss the state-of-the-art algorithms used for these quite different regimes, attempt to give a fair critique, and point out possible directions of future improvement and development. We briefly touch upon the history of N-body simulations and their most important results.Comment: invited review (28 pages), to appear in European Physics Journal Plu

Evaluation of the rapid chloride migration (rcm) test

No abstract

On the early age behavior of earth-moist concrete

No abstract

Multi-scale hydration modeling of calcium sulphates

Computer models for cement hydration has been proven to be a useful tool for understanding the chemistry of cement hydration, simulating the microstructure development of hydrating paste and predicting the properties of the hydration process /1/. One of these advanced models is CEMHYD3D, which is used and extended within the University of Twente for the last 12 years with pore water chemistry /2/, slag cement /3/ and multi-time modeling /4/. Chen and Brouwers /5/ pointed out that the smallest size handled in CEMHYD3D, called the ‘system resolution’ is important for a digitized model. Features smaller than the voxel sizes cannot be represented since the model works based on the movement and phase change of each discrete voxel. Furthermore, the system resolution determines the amount of computing time needed for a specific task, a higher system resolution will lead to longer computational time. Due to better computational possibilities, the use of higher resolutions is possible nowadays. This article shows the effects of using different resolutions with CEMHYD3D. This is done for the ‘fresh’ mixtures as well as during hydration modeling of the binder. The model has been modified to cope with several different resolutions from 0.20-2 μm (or 500-50 voxels in the system in a box of 100 μm x 100 μm x 100 μm). This paper shows two methods for the multi-scale modeling. The first method consists of a system, which use a modified PSD-line for each resolution. The second method uses the same digitized initial microstructure, but in stead of 1 voxel of 1 x 1 x 1 μm3 for 200 μm-system 8 voxels of 0.5 x 0.5 x 0.5 μm3 are used and for the 300-μm system 27 voxels of 0.33 x 0.33 x 0.33 μm3

Gypsum hydration: a theoretical and experimental study

Calcium sulphate dihydrate (CaSO4·2H2O or gypsum) is used widely as building material because of its excellent fire resistance, aesthetics, and low price. Hemihydrate occurs in two formations of α- and β-type. Among them β-hemihydrate is mainly used to produce gypsum plasterboard since the hydration product of the α-hemihydrate is too brittle to be used as building material /10/. This article addresses the hydration of hemihydrate since it determines the properties of gypsum and it is influenced strongly by water and the properties of hemihydrate. The microstructure development of gypsum during hydration is investigated. The influence of water is studied from its effect on fresh behavior and void fraction of the gypsum

Xentrivalpeptides A-Q: depsipeptide diversification in Xenorhabdus

Item does not contain fulltextSeventeen depsipeptides, xentrivalpeptides A-Q (1-17), have been identified from an entomopathogenic Xenorhabdus sp. Whereas the structure of xentrivalpeptide A (1) was determined after its isolation by NMR spectroscopy and the advanced Marfey's method, the structures of all other derivatives were determined using a combination of stable isotope labeling and detailed MS analysis