A MODEST review

We present an account of the state of the art in the fields explored by the research community invested in 'Modeling and Observing DEnse STellar systems'. For this purpose, we take as a basis the activities of the MODEST-17 conference, which was held at Charles University, Prague, in September 2017. Reviewed topics include recent advances in fundamental stellar dynamics, numerical methods for the solution of the gravitational N-body problem, formation and evolution of young and old star clusters and galactic nuclei, their elusive stellar populations, planetary systems, and exotic compact objects, with timely attention to black holes of different classes of mass and their role as sources of gravitational waves. Such a breadth of topics reflects the growing role played by collisional stellar dynamics in numerous areas of modern astrophysics. Indeed, in the next decade, many revolutionary instruments will enable the derivation of positions and velocities of individual stars in the Milky Way and its satellites and will detect signals from a range of astrophysical sources in different portions of the electromagnetic and gravitational spectrum, with an unprecedented sensitivity. On the one hand, this wealth of data will allow us to address a number of long-standing open questions in star cluster studies; on the other hand, many unexpected properties of these systems will come to light, stimulating further progress of our understanding of their formation and evolution.Comment: 42 pages; accepted for publication in 'Computational Astrophysics and Cosmology'. We are much grateful to the organisers of the MODEST-17 conference (Charles University, Prague, September 2017). We acknowledge the input provided by all MODEST-17 participants, and, more generally, by the members of the MODEST communit

An experimental and analytical study of electrokinetic consolidation

This thesis describes settling process of clay particles in suspension and subsequent consolidation behaviour of Speswhite Kaolin clay under the influence of electrokinetics. Comprehensive experimental investigations on soil behaviour under different stress conditions (e.g. electrokinetics, self-weight, and hydraulic gradient) were performed and reported. For comparing soil behaviour under electrokinetics with self-weight consolidation, the electrode configuration of closed anode and open cathode (the anode at the base of the cathode at the top of the soil) was used. One of the problems with this electrode arrangement was the gas produced at the anode electrode entering the soil and destroying the developing structure of soils. This problem was overcome by developing a specially designed electrokinetic cell. The density measurements of soil were achieved by an accurate and non-destructive X-ray technique, and pore pressures were also measured during the process. The experimental results revealed that the electrically induced surface settlement was greater in magnitude and faster in rate than that under self-weight stresses; the dissipation rate of excess pore pressure was directly related to the applied electric field strength; the density in the anode region was increased significantly by the development of effective stress die to the effect of electroosmosis; the movement of acid and base fronts due to electrolysis was identified by the variation of pH; and the development of the denser layer at the soil surface was caused by the additional effects of electrokinetics, such as the variation of zeta potential and voltage gradient. Numerical simulations using the simple diffusion equation with constant coefficients were investigate in order to predict the soil behaviour under the influence of electrokinetics. The normal small strain assumption (equivalent to the boundary remaining fixed) made in previous solutions of the equation has been replaced by boundary movement coupled with the requirement of conservation of mass. Remarkably good agreement between the measured and simulated surface settlement, density, and excess pore pressure profiles has been achieved using the method above, with appropriate soil parameters, such as Cc, Cv, Kh, and Ke

An analytical and experimental study of large strain soil consolidation

This thesis is concerned with large strain soil consolidation and a large portion of the work is devoted to the theoretical development in modelling this phenomenon. An experimental programme based on a specially designed oedometer is also included. The governing equations are formulated in Chapter 2, where both the material and the space coordinates are considered. In space coordinate the problem is a moving boundary problem, and special numerical techniques for the idealized case of a thin soil layer are developed in Chapter 3. In Chapter 4 the consolidation of a normally consolidated stratum and a dredged fill are considered with a linear soil model, and the consolidation of a deposit undergoing continuous sedimentation is considered in Chapter 5. The material coordinate is used in the analysis which also includes the effect of self weight of soil. These problems are again considered in Chapter 6 and Chapter 7 with a nonlinear soil model. A specially designed oedometer for testing very soft soil is described in Chapter 8, and the experimental results are discussed in Chapter 9. These are compared with the theoretical solutions developed in Chapter 3, and good agreement has been obtained

An experimental investigation of sand�mud suspension settling behaviour: implications for bimodal mud contents of submarine flow deposits

The settling behaviour of particulate suspensions and their deposits has been documented using a series of settling tube experiments. Suspensions comprised saline solution and noncohesive glass-ballotini sand of particle size 35·5 ?m &lt; d &lt; 250 ?m and volume fractions, ?s, up to 0·6 and cohesive kaolinite clay of particle size d &lt; 35·5 ?m and volume fractions, ?m, up to 0·15. Five texturally distinct deposits were found, associated with different settling regimes: (I) clean, graded sand beds produced by incremental deposition under unhindered or hindered settling conditions; (II) partially graded, clean sand beds with an ungraded base and a graded top, produced by incremental deposition under hindered settling conditions; (III) graded muddy sands produced by compaction with significant particle sorting by elutriation; (IV) ungraded clean sand produced by compaction and (V) ungraded muddy sand produced by compaction. A transition from particle size segregation (regime I) to suppressed size segregation (regime II or III) to virtually no size segregation (IV or V) occurred as sediment concentration was increased. In noncohesive particulate suspensions, segregation was initially suppressed at ?s ? 0·2 and entirely inhibited at ?s ? 0·6. In noncohesive and cohesive mixtures with low sand concentrations (?s &lt; 0·2), particle segregation was initially suppressed at ?m ? 0·07 and entirely suppressed at ?m ? 0·13. The experimental results have a number of implications for the depositional dynamics of submarine sediment gravity flows and other particulate flows that carry sand and mud; because the influence of moving flow is ignored in these experiments, the results will only be applicable to flows in which settling processes, in the depositional boundary, dominate over shear-flow processes, as might be the case for rapidly decelerating currents with high suspended load fallout rates. The 'abrupt' change in settling regimes between regime I and V, over a relatively small change in mud concentration (&lt;5% by volume), favours the development of either mud-poor, graded sandy deposits or mud-rich, ungraded sandy deposits. This may explain the bimodality in sediment texture (clean 'turbidite' or muddy 'debrite' sand or sandstone) found in some turbidite systems. Furthermore, it supports the notion that distal 'linked' debrites could form because of a relatively small increase in the mud concentration of turbidity currents, perhaps associated with erosion of a muddy sea floor. Ungraded, clean sand deposits were formed by noncohesive suspensions with concentrations 0·2 ? ?s ? 0·4. Hydrodynamic sorting is interpreted as being suppressed in this case by relatively high bed aggradation rates which could also occur in association with sustained, stratified turbidity currents or noncohesive debris flows with relatively high near-bed sediment concentrations.<br/

Consolidation due to underpumping an accreting layer of sediment

Also known as soil mechanics report no. 091/89SIGLEAvailable from British Library Document Supply Centre- DSC:7623.47(OUEL--1764/89) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Nicotinylalanine increases cerebral kynurenic acid content and has anticonvulsant activity

1. Nicotinylalanine is an analogue of kynurenine which has been reported to inhibit the enzymes kynurenine hydroxylase and kynureninase. 2. In the present study rats were given a tryptophan load together with nicotinylalanine two hours before killing, and the brain, liver and kidneys analysed by HPLC for their kynurenic acid content. 3. Tryptophan alone produced a significant elevation of kynurenate but with the additional administration of nicotinylalanine, levels rose dramatically, including a 19-fold increase in brain. 4. In mice the same dose of nicotinylalanine reduced the incidence of seizures induced by leptazol or electroshock treatment. 5. Since kynurenic acid is an antagonist at excitatory amino acid receptors the results may herald a new approach to producing a pharmacological blockade of amino acid receptors in the brain

Escape of pore fluid from consolidating sediment

SIGLELD:7623.47(OUEL--1378/81). / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Measurement and modelling of the properties of cohesive sediment deposits

Research studies undertaken as part of the "Bed Dynamics" Task D of the EC funded COSINUS project are described. The studies undertaken involve the reformulation of sediment exchange equations, in situ field measurements of bed strength, laboratory settling column experiments, bed consolidation modelling, the development of a model of bed dynamics based on generalised Biot theory and the testing of an integrated erosion/entrainment model against laboratory experiments. The results of the various studies are synthesized and overall conclusions drawn