SPH

Distribution by Scientific Domains


Selected Abstracts


Hybrid Simulation of Miscible Mixing with Viscous Fingering

COMPUTER GRAPHICS FORUM, Issue 2 2010
Seung-Ho Shiny
Abstract By modeling mass transfer phenomena, we simulate solids and liquids dissolving or changing to other substances. We also deal with the very small-scale phenomena that occur when a fluid spreads out at the interface of another fluid. We model the pressure at the interfaces between fluids with Darcy's Law and represent the viscous fingering phenomenon in which a fluid interface spreads out with a fractal-like shape. We use hybrid grid-based simulation and smoothed particle hydrodynamics (SPH) to simulate intermolecular diffusion and attraction using particles at a computable scale. We have produced animations showing fluids mixing and objects dissolving. [source]


Coupling of mesh-free methods with finite elements: basic concepts and test results

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 10 2006
T. Rabczuk
Abstract This paper reviews several novel and older methods for coupling mesh-free particle methods, particularly the element-free Galerkin (EFG) method and the smooth particle hydrodynamics (SPH), with finite elements (FEs). We study master,slave couplings where particles are fixed across the FE boundary, coupling via interface shape functions such that consistency conditions are satisfied, bridging domain coupling, compatibility coupling with Lagrange multipliers and hybrid coupling methods where forces from the particles are applied via their shape functions on the FE nodes and vice versa. The hybrid coupling methods are well suited for large deformations and adaptivity and the coupling procedure is independent of the particle distance and nodal arrangement. We will study the methods for several static and dynamic applications, compare the results to analytical and experimental data and show advantages and drawbacks of the methods. Copyright © 2006 John Wiley & Sons, Ltd. [source]


An SPH shell formulation for plasticity and fracture analysis in explicit dynamics

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 7 2008
B. Maurel
Abstract This paper introduces a new modeling method suitable for the simulation of shell fracture under impact. This method relies on an entirely meshless approach based on the smoothed particle hydrodynamics (SPH) method. The paper also presents the SPH shell formulation being used as well as the different test cases used for its validation. A plasticity model of the global type throughout the thickness is also proposed and validated. Finally, in order to illustrate the capabilities of the method, fracture simulations using a simplified fracture criterion are presented. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Stabilized updated Lagrangian corrected SPH for explicit dynamic problems

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 13 2007
Y. Vidal
Abstract Smooth particle hydrodynamics with a total Lagrangian formulation are, in general, more robust than finite elements for large distortion problems. Nevertheless, updating the reference configuration may still be necessary in some problems involving extremely large distortions. However, as discussed here, a standard updated formulation suffers the presence of zero-energy modes that are activated and may completely spoil the solution. It is important to note that, unlike an Eulerian formulation, the updated Lagrangian does not present tension instability but only zero-energy modes. Here a stabilization technique is incorporated to the updated formulation to obtain an improved method without any mechanisms and which is capable to solve problems with extremely large distortions. Copyright © 2006 John Wiley & Sons, Ltd. [source]


Simulation of high velocity concrete fragmentation using SPH/MLSPH

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 10 2003
T. Rabczuk
Abstract The simulation of concrete fragmentation under explosive loading by a meshfree Lagrangian method, the smooth particle hydrodynamics method (SPH) is described. Two improvements regarding the completeness of the SPH-method are examined, first a normalization developed by Johnson and Beissel (NSPH) and second a moving least square (MLS) approach as modified by Scheffer (MLSPH). The SPH-Code is implemented in FORTRAN 90 and parallelized with MPI. A macroscopic constitutive law with isotropic damage for fracture and fragmentation for concrete is implemented in the SPH-Code. It is shown that the SPH-method is able to simulate the fracture and fragmentation of concrete slabs under contact detonation. The numerical results from the different SPH-methods are compared with the data from tests. The good agreement between calculation and experiment suggests that the SPH-program can predict the correct maximum pressure as well as the damage of the concrete slabs. Finally the fragment distributions of the tests and the numerical calculations are compared. Copyright © 2003 John Wiley & Sons, Ltd. [source]


Remarks on tension instability of Eulerian and Lagrangian corrected smooth particle hydrodynamics (CSPH) methods

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2001
Javier Bonet
Abstract The paper discusses the problem of tension instability of particle-based methods such as smooth particle hydrodynamics (SPH) or corrected SPH (CSPH). It is shown that tension instability is a property of a continuum where the stress tensor is isotropic and the value of the pressure is a function of the density or volume ratio. The paper will show that, for this material model, the non-linear continuum equations fail to satisfy the stability condition in the presence of tension. Consequently, any discretization of this continuum will result in negative eigenvalues in the tangent stiffness matrix that will lead to instabilities in the time integration process. An important exception is the 1-D case where the continuum becomes stable but SPH or CSPH can still exhibit negative eigenvalues. The paper will show that these negative eigenvalues can be eliminated if a Lagrangian formulation is used whereby all derivatives are referred to a fixed reference configuration. The resulting formulation maintains the momentum preservation properties of its Eulerian equivalent. Finally a simple 1-D wave propagation example will be used to demonstrate that a stable solution can be obtained using Lagrangian CSPH without the need for any artificial viscosity. Copyright © 2001 John Wiley & Sons, Ltd. [source]


Permeable and non-reflecting boundary conditions in SPH

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2009
Martin Lastiwka
Abstract Inflow and outflow boundary conditions are essential for the application of computational fluid dynamics to many engineering scenarios. In this paper we present a new boundary condition implementation that enables the simulation of flow through permeable boundaries in the Lagrangian mesh-free method, smoothed particle hydrodynamics (SPH). Each permeable boundary is associated with an inflow or outflow zone outside the domain, in which particles are created or removed as required. The analytic boundary condition is applied by prescribing the appropriate variables for particles in an inflow or outflow zone, and extrapolating other variables from within the domain. Characteristic-based non-reflecting boundary conditions, described in the literature for mesh-based methods, can be implemented within this framework. Results are presented for simple one-dimensional flows, quasi-one-dimensional compressible nozzle flow, and two-dimensional flow around a cylinder at Reynolds numbers of 40 and 100 and a Mach number of 0.1. These results establish the capability of SPH to model flows through open domains, opening a broad new class of applications. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Defining and optimizing algorithms for neighbouring particle identification in SPH fluid simulations

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2008
G. Viccione
Abstract Lagrangian particle methods such as smoothed particle hydrodynamics (SPH) are very demanding in terms of computing time for large domains. Since the numerical integration of the governing equations is only carried out for each particle on a restricted number of neighbouring ones located inside a cut-off radius rc, a substantial part of the computational burden depends on the actual search procedure; it is therefore vital that efficient methods are adopted for such a search. The cut-off radius is indeed much lower than the typical domain's size; hence, the number of neighbouring particles is only a little fraction of the total number. Straightforward determination of which particles are inside the interaction range requires the computation of all pair-wise distances, a procedure whose computational time would be unpractical or totally impossible for large problems. Two main strategies have been developed in the past in order to reduce the unnecessary computation of distances: the first based on dynamically storing each particle's neighbourhood list (Verlet list) and the second based on a framework of fixed cells. The paper presents the results of a numerical sensitivity study on the efficiency of the two procedures as a function of such parameters as the Verlet size and the cell dimensions. An insight is given into the relative computational burden; a discussion of the relative merits of the different approaches is also given and some suggestions are provided on the computational and data structure of the neighbourhood search part of SPH codes. Copyright © 2008 John Wiley & Sons, Ltd. [source]


A stabilized SPH method for inviscid shallow water flows,

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 2 2005
Riadh Ata
Abstract In this paper, the smoothed particle hydrodynamics (SPH) method is applied to the solution of shallow water equations. A brief review of the method in its standard form is first described then a variational formulation using SPH interpolation is discussed. A new technique based on the Riemann solver is introduced to improve the stability of the method. This technique leads to better results. The treatment of solid boundary conditions is discussed but remains an open problem for general geometries. The dam-break problem with a flat bed is used as a benchmark test. Copyright © 2004 John Wiley & Sons, Ltd. [source]


The evolutionary species pool hypothesis and patterns of freshwater diatom diversity along a pH gradient

JOURNAL OF BIOGEOGRAPHY, Issue 3 2005
Jason Pither
Abstract Aim, To interpret the unimodal relationship between diatom species richness and lake pH within the context of the evolutionary species pool hypothesis (SPH). We test the following primary prediction arising from the SPH: the size of the potential species pool (PSP) will increase along a gradient representing the historical commonness of different pH environments (pH commonness). To do this we assume that the present-day spatial dominance of near-neutral pH conditions compared with acidic and alkaline conditions reliably mimics the relative spatial availabilities of historical pH conditions among freshwater lakes. We also determine whether local richness represents a constant proportion of PSP size along the pH commonness gradient. Location, Two hundred and thirty-four lakes distributed over a 405,000 km2 region of the north-eastern United States of America. Methods, Sediment diatom morphospecies lists and pH data were acquired from the US Environmental Protection Agency's Environmental Monitoring and Assessment Program (EMAP) website. Using 248 morphospecies that occurred in at least 10 of the 234 lakes, four different measures of PSPs were calculated along the pH gradient. Local species richness was equated with the number of species occurring within the lake. Alpha diversity was equated with the average species richness of lakes with similar pH values. A combination of statistical methods were employed, including correlations, quadratic regression and piecewise regression. Results, PSP size increased significantly with pH commonness for all four measures of PSP size, thus supporting the primary prediction of the evolutionary SPH. Local richness comprised a larger proportion of the PSP within acidic lakes than within circumneutral lakes. Alpha diversity and lake species richness both increased significantly with pH commonness, but the former did so in a two-step fashion. We test and reject several alternative contemporary time-scale explanations for our findings. Main Conclusions, Our findings are consistent with the hypothesis that diatom taxonomic richness is presently lower within acidic and highly alkaline lakes than in circumneutral lakes owing to the limited opportunity in space and/or time for the evolution of suitably adapted species. Whereas ecological processes can explain why certain species are excluded from particular habitats, e.g. acidic lakes, they cannot account for why so few species are adapted to those habitats in the first place. [source]


A Role for G Protein-Coupled Lysophospholipid Receptors in Sphingolipid-Induced Ca2+ Signaling in MC3T3-E1 Osteoblastic Cells

JOURNAL OF BONE AND MINERAL RESEARCH, Issue 11 2001
Jeremy M. Lyons
Abstract Sphingolipids have been proposed to modulate cell function by acting as intracellular second messengers and through binding to plasma membrane receptors. Exposure of MC3T3-E1 osteoblastic cells to sphingosine (SPH), sphingosine-1-phosphate (SPP), or sphingosylphosphorylcholine (SPC) led to the release of Ca2+ from the endoplasmic reticulum (ER) and acute elevations in cytosolic-free Ca2+ ([Ca2+]i). Desensitization studies suggest that SPP and SPC bind plasma membrane endothelial differentiation gene (Edg) receptors for lysophosphatidic acid (LPA). Consistent with the coupling of Edg receptors to G proteins, SPP- and SPC-induced Ca2+ signaling was inhibited by pretreatment of the cells with pertussis toxin (PTx). Of the Edg receptors known to bind SPH derivatives in other cell types, MC3T3-E1 cells were found to express transcripts encoding Edg -1 and Edg -5 but not Edg -3, Edg -6, or Edg -8. In contrast to SPP and SPC, the ability of SPH to elicit [Ca2+]i elevations was affected neither by prior exposure of cells to LPA nor by PTx treatment. However, LPA-induced Ca2+ signaling was blocked in MC3T3-E1 cells previously exposed to SPH. Elevations in [Ca2+]i were not evoked by SPP or SPC in cells treated with 2-aminoethoxydiphenylborate (2-APB), an inhibitor of inositol 1,4,5-trisphosphate (IP3)-gated Ca2+ channels in the ER. No effect of 2-APB was observed on SPH- or LPA-induced [Ca2+]i elevations. The data support a model in which SPP and SPC bind Edg -1 and/or Edg -5 receptors in osteoblasts leading to the release of Ca2+ from the ER through IP3 -gated channels. [source]


Application of poly(acrylic acid) superporous hydrogel microparticles as a super-disintegrant in fast-disintegrating tablets

JOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 4 2004
Shicheng Yang
ABSTRACT Poly(acrylic acid) superporous hydrogel (SPH) microparticles possessing a unique porous structure were used as a wicking agent to decrease disintegration time of fast-disintegrating tablets (FDTs). The compression behaviour of poly(acrylic acid) SPH microparticles was evaluated using the Kawakita equation. Effects of various SPH microparticle sizes and a 19-run fractional factorial design were evaluated. The factorial design was based on four factors consisting of ketoprofen, SPH microparticle, filler, and tableting pressure, and each factor contained three levels on the disintegration time and tensile strength of the prepared FDTs. The poly(acrylic acid) SPH microparticles existed in an amorphous state and swelled approximately 80-times in distilled water and 50-times in pH 6.8 0.2 m phosphate buffer. The compressibility of SPH microparticles increased significantly as the microparticle size increased. The FDTs made of SPH microparticles in the range of 75,106 ,m showed the fastest disintegration time and higher tensile strength. SPH microparticle, tableting pressure and ketoprofen had significant effects on disintegration time and tensile strength of ketoprofen FDTs. The FDTs that were prepared with 2.5% w/w SPH microparticles of 75,106 ,m at 63 MPa pressure possessed a tensile strength of 84.4+4.1 N cm,2 and disintegrated in 15.0+2.0 s. It was concluded that the poly(acrylic acid) SPH microparticles could serve as a good super-disintegrant decreasing the disintegration time of FDTs. [source]


MYELINATION DEFICIT IN NERVE OF SUCKLING RATS DUE TO CYCLOLEUCINE -INDUCED DEFICIENCY OF METHYL DONORS

JOURNAL OF THE PERIPHERAL NERVOUS SYSTEM, Issue 1 2000
R. Bianchi
We used cycloleucine (CL) , which prevents methionine conversion to S-adenosyl-methionine (SAMe) by inhibiting ATP-L-methionine-adenosyl-transferase (MAT) , to characterize the lipid and protein changes induced by methyl donors deficit in peripheral nerve and brain myelin in rats during development. We have previously shown that CL (400 mg/kg ip) given to suckling rats at days 7, 8, 12, and 13 after birth reduced brain and sciatic nerve weight gain, brain myelin content, protein, phospholipid (PL), and galactolipid concentration in comparison to control. Among PLs, only sphingomyelin (SPH) significantly increased by 35,50%. SAMe p-toluensulphonate (SAMe-SD4) (100 mg/kg, ip) given daily from day 7, as with exogenous SAMe, partially prevented some lipid alterations induced by CL, particularly galactolipid and SPH. To test the ability of CL to affect PL metabolism we have measured de novo PL biosynthesis, ex vivo in nerve homogenates (in comparison with brain homogenates) from control and CL-treated animals killed at day 18 after birth, starting from labelled substrates ([3H]-choline, specific activity 20 mCi/mmol) in a Tris/HCl buffer, containing 5 mM MgCl2, 0.2 mM EDTA, 0.1 mM ATP, and 0.5 mM of the labelled substrates. After 60 min incubation, lipids were extracted, PL separated by TLC, and corresponding silica gel fractions scraped and counted in a liquid scintillator. Phosphatidylcholine enrichment in labelled choline resulted in slight increases in brain and sciatic nerve of CL-treated rats, suggesting an increased synthesis rate via the Kennedy pathway, possibly due to the reduced availability of methyl donors. Interestingly, choline incorporation into SPH in brain and nerve myelin resulted in significant increases of 30,40%. In agreement with the observed decrease of galactolipid content and the relative increase in SPH, these data suggest an alteration in sphingolipid metabolism after CL. Among proteins, in sciatic nerves of CL-treated pups the relative content of a number of polypeptides, namely the 116, 90, 66, 58, and 56 kDa bands, decreased, whereas others increased; the most abundant PNS protein, protein zero, remained unchanged. The analyses of myelin basic protein isoforms revealed a dramatic increase in the 14.0 and 18.5 forms, indicating early active myelination. SAMe-SD4 treatment counteracted, and in some cases normalized, these changes. In summary, methyl donor deficiency induced by MAT inhibition produces myelin lipid and protein alterations, partly counteracted by SAMe-SD4 administration. The financial support of Telethon-Italy (grant No. D 51) is gratefully acknowledged. [source]


Validation of numerical codes for impact and explosion cratering: Impacts on strengthless and metal targets

METEORITICS & PLANETARY SCIENCE, Issue 12 2008
E. PIERAZZO
When properly benchmarked and validated against observation, computer models offer a powerful tool for understanding the mechanics of impact crater formation. This work presents results from the first phase of a project to benchmark and validate shock codes. A variety of 2D and 3D codes were used in this study, from commercial products like AUTODYN, to codes developed within the scientific community like SOVA, SPH, ZEUS-MP, iSALE, and codes developed at U.S. National Laboratories like CTH, SAGE/RAGE, and ALE3D. Benchmark calculations of shock wave propagation in aluminum-on-aluminum impacts were performed to examine the agreement between codes for simple idealized problems. The benchmark simulations show that variability in code results is to be expected due to differences in the underlying solution algorithm of each code, artificial stability parameters, spatial and temporal resolution, and material models. Overall, the inter-code variability in peak shock pressure as a function of distance is around 10 to 20%. In general, if the impactor is resolved by at least 20 cells across its radius, the underestimation of peak shock pressure due to spatial resolution is less than 10%. In addition to the benchmark tests, three validation tests were performed to examine the ability of the codes to reproduce the time evolution of crater radius and depth observed in vertical laboratory impacts in water and two well-characterized aluminum alloys. Results from these calculations are in good agreement with experiments. There appears to be a general tendency of shock physics codes to underestimate the radius of the forming crater. Overall, the discrepancy between the model and experiment results is between 10 and 20%, similar to the inter-code variability. [source]


Protein hydrolysates from ,-conglycinin enriched soybean genotypes inhibit lipid accumulation and inflammation in vitro

MOLECULAR NUTRITION & FOOD RESEARCH (FORMERLY NAHRUNG/FOOD), Issue 8 2009
Cristina Martinez-Villaluenga
Abstract Obesity is a worldwide health concern and a well recognized predictor of premature mortality associated with a state of chronic inflammation. The objective was to evaluate the effect of soy protein hydrolysates (SPH) produced from different soybean genotypes by alcalase (SAH) or simulated gastrointestinal digestion (SGIH) on lipid accumulation in 3T3-L1 adipocytes. The anti-inflammatory effect of SPH produced by alcalase on LPS-induced macrophage RAW 264.7 cell line was also investigated. SAH (100 ,M) derived from soybean enriched in ,-conglycinin (BC) (up to 47% total protein) decreased lipid accumulation (33,37% inhibition) through downregulation of gene expression of lipoprotein lipase (LPL) and fatty acid synthase (FAS). SGIH (100 ,M) inhibited lipid accumulation to a lesser extent (8,14% inhibition) through inhibition of LPL gene expression. SAH (5 ,M) decreased the production of nitric oxide (NO) (18,35%) and prostaglandin E2 (PGE2) (47,71%) and the expression of inducible nitric oxide synthase (iNOS) (31,53%) and cycloxygenase-2 (COX-2) (30,52%). This is the first investigation showing that soy hydrolysates inhibit LPS-induced iNOS/NO and COX-2/PGE2 pathways in macrophages. Soybeans enriched in BCs can provide hydrolysates that limit fat accumulation in fat cells and inflammatory pathways in vitro and therefore warrant further studies as a healthful food. [source]


The outburst duration and duty cycle of GRS 1915+105

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2009
Patrick Deegan
ABSTRACT The extraordinarily long outburst of GRS 1915+105 makes it one of the most remarkable low-mass X-ray binaries (LMXBs). It has been in a state of constant outburst since its discovery in 1992, an eruption which has persisted ,100 times longer than those of more typical LXMBs. The long orbital period of GRS 1915+105 implies that it contains large and massive accretion disc which is able to fuel its extreme outburst. In this paper, we address the longevity of the outburst and quiescence phases of GRS 1915+105 using smooth particle hydrodynamics (SPH) simulations of its accretion disc through many outburst cycles. Our model is set in the two-, framework and includes the effects of the thermoviscous instability, tidal torques, irradiation by central X-rays and wind mass loss. We explore the model parameter space and examine the impact of the various ingredients. We predict that the outburst of GRS 1915+105 should last a minimum of 20 yr and possibly up to ,100 yr if X-ray irradiation is very significant. The predicted recurrence times are of the order of 104 yr, making the X-ray duty cycle a few 0.1 per cent. Such a low duty cycle may mean that GRS 1915+105 is not an anomaly among the more standard LMXBs and that many similar, but quiescent, systems could be present in the Galaxy. [source]


An implementation of radiative transfer in the cosmological simulation code gadget

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2009
Margarita Petkova
ABSTRACT We present a novel numerical implementation of radiative transfer in the cosmological smoothed particle hydrodynamics (SPH) simulation code gadget. It is based on a fast, robust and photon-conserving integration scheme where the radiation transport problem is approximated in terms of moments of the transfer equation and by using a variable Eddington tensor as a closure relation, following the Optically Thin Variable Eddington Tensor suggestion of Gnedin & Abel. We derive a suitable anisotropic diffusion operator for use in the SPH discretization of the local photon transport, and we combine this with an implicit solver that guarantees robustness and photon conservation. This entails a matrix inversion problem of a huge, sparsely populated matrix that is distributed in memory in our parallel code. We solve this task iteratively with a conjugate gradient scheme. Finally, to model photon sink processes we consider ionization and recombination processes of hydrogen, which is represented with a chemical network that is evolved with an implicit time integration scheme. We present several tests of our implementation, including single and multiple sources in static uniform density fields with and without temperature evolution, shadowing by a dense clump and multiple sources in a static cosmological density field. All tests agree quite well with analytical computations or with predictions from other radiative transfer codes, except for shadowing. However, unlike most other radiative transfer codes presently in use for studying re-ionization, our new method can be used on-the-fly during dynamical cosmological simulation, allowing simultaneous treatments of galaxy formation and the re-ionization process of the Universe. [source]


Is AGN feedback necessary to form red elliptical galaxies?

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
A. Khalatyan
ABSTRACT We have used the smoothed particle hydrodynamics (SPH) code gadget-2 to simulate the formation of an elliptical galaxy in a group-size cosmological dark matter halo with mass Mhalo, 3 × 1012 h,1 M, at z= 0. The use of a stellar population synthesis model has allowed us to compute magnitudes, colours and surface brightness profiles. We have included a model to follow the growth of a central black hole and we have compared the results of simulations with and without feedback from active galactic nuclei (AGN). We have studied the interplay between cold gas accretion and merging in the development of galactic morphologies, the link between colour and morphology evolution, the effect of AGN feedback on the photometry of early-type galaxies, the redshift evolution in the properties of quasar hosts, and the impact of AGN winds on the chemical enrichment of the intergalactic medium (IGM). We have found that the early phases of galaxy formation are driven by the accretion of cold filamentary flows, which form a disc galaxy at the centre of the dark matter halo. Disc star formation rates in this mode of galaxy growth are about as high as the peak star formation rates attained at a later epoch in galaxy mergers. When the dark matter halo is sufficiently massive to support the propagation of a stable shock, the gas in the filaments is heated to the virial temperature, cold accretion is shut down, and the star formation rate begins to decline. Mergers transform the spiral galaxy into an elliptical one, but they also reactivate star formation by bringing gas into the galaxy. Without a mechanism that removes gas from the merger remnants, the galaxy ends up with blue colours, which are atypical for its elliptical morphology. We have demonstrated that AGN feedback can solve this problem even with a fairly low heating efficiency. Our simulations support a picture where AGN feedback is important for quenching star formation in the remnant of wet mergers and for moving them to the red sequence. This picture is consistent with recent observational results, which suggest that AGN hosts are galaxies in migration from the blue cloud to the red sequence on the colour,magnitude diagram. However, we have also seen a transition in the properties of AGN hosts from blue and star forming at z, 2 to mainly red and dead at z, 0. Ongoing merging is the primary but not the only triggering mechanism for luminous AGN activity. Quenching by AGN is only effective after the cold filaments have dried out, since otherwise the galaxy is constantly replenished with gas. AGN feedback also contributes to raising the entropy of the hot IGM by removing low-entropy tails vulnerable to developing cooling flows. We have also demonstrated that AGN winds are potentially important for the metal enrichment of the IGM a high redshift. [source]


Clumpy shocks and the clump mass function

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006
Paul C. Clark
ABSTRACT One possible mechanism for the formation of molecular clouds is large-scale colliding flows. In this paper, we examine whether clumpy, colliding, flows could be responsible for the clump mass functions that have been observed in several regions of embedded star formation, which have been shown to be described by a Salpeter-type slope. The flows presented here, which comprise a population of initially identical clumps, are modelled using smoothed particle hydrodynamics (SPH) and calculations are performed with and without the inclusion of self-gravity. When the shock region is at its densest, we find that the clump mass spectrum is always well modelled by a Salpeter-type slope. This is true regardless of whether the self-gravity is included in the simulations or not, and for our choice of filling factors for the clumpy flows (10, 20 and 40 per cent), and Mach number (5, 10 and 20). In the non-self-gravitating simulations, this slope is retained at lower Mach numbers as the simulations progress past the densest phase. In the simulations which include self-gravity, we find that low Mach number runs yield a flatter mass function after the densest phase. This is simply a result of increased coagulation due to gravitational collapse of the flows. In the high Mach number runs the Salpeter slope is always lost. The self-gravitating calculations also show that the subgroup of gravitationally bound clumps in which star formation occurs, always contain the most massive clumps in the population. Typically these clumps have a mass of order of the Jeans mass of the initial clumps. The mass function of these bound star-forming clumps is not at all similar to the Salpeter-type mass function observed for stars in the field. We conclude that the clump mass function may not only have nothing to do with gravity, but also nothing to do with the star formation process and the resulting mass distribution of stars. This raises doubt over the claims that the clump mass function is the origin of the stellar initial mass function (IMF), for regions such as , Oph, Serpens and the Orion B cloud. [source]


Gas and stellar dynamics in NGC 1068: probing the galactic gravitational potential

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2006
Eric Emsellem
ABSTRACT We present SAURON integral field spectrography of the central 1.5 kpc of the nearby Seyfert 2 galaxy NGC 1068, encompassing the well-known near-infrared (NIR) inner bar observed in the K band. We have successively disentangled the respective contributions of the ionized gas and stars, thus deriving their two-dimensional distribution and kinematics. The [O iii] and H, emission lines exhibit a very different spatial distribution and kinematics, the latter following inner spiral arms with clumps associated with star formation. Strong inward streaming motions are observed in both the H, and [O iii] kinematics. The stellar kinematics also exhibit clear signatures of a non-axisymmetric tumbling potential, with a twist in both the velocity and Gauss,Hermite h3 fields. We re-examined the long-slit data of Shapiro, Gerssen & van der Marel using a pPXF: a strong decoupling of the Gauss,Hermite term h3 is revealed, and the central decrease of Gauss,Hermite term h4 hinted in the SAURON data is confirmed. These data also suggest that NGC 1068 is a good candidate for a so-called , drop. We confirm the possible presence of two separate pattern speeds applying the Tremaine,Weinberg method to the Fabry,Perot H, map. We also examine the stellar kinematics of bars formed in N -body + smoothed particle hydrodynamics (SPH) simulations built from axisymmetric initial conditions approximating the luminosity distribution of NGC 1068. The resulting velocity, dispersion and higher order Gauss,Hermite moments successfully reproduce a number of properties observed in the two-dimensional kinematics of NGC 1068 and the long-slit data, showing that the kinematic signature of the NIR bar is imprinted in the stellar kinematics. The remaining differences between the models and the observed properties are likely mostly due to the exclusion of star formation and the lack of the primary large-scale oval/bar in the simulations. These models nevertheless suggest that the inner bar could drive a significant amount of gas down to a scale of , 300 pc. This would be consistent with the interpretation of the , drop in NGC 1068 being the result of central gas accretion followed by an episode of star formation. [source]


Turbulent gas motions in galaxy cluster simulations: the role of smoothed particle hydrodynamics viscosity

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2005
K. Dolag
ABSTRACT Smoothed particle hydrodynamics (SPH) employs an artificial viscosity to properly capture hydrodynamic shock waves. In its original formulation, the resulting numerical viscosity is large enough to suppress structure in the velocity field on scales well above the nominal resolution limit, and to damp the generation of turbulence by fluid instabilities. This could artificially suppress random gas motions in the intracluster medium (ICM), which are driven by infalling structures during the hierarchical structure formation process. We show that this is indeed the case by analysing results obtained with an SPH formulation where an individual, time-variable viscosity is used for each particle, following a suggestion by Morris & Monaghan. Using test calculations involving strong shocks, we demonstrate that this scheme captures shocks as well as the original formulation of SPH, but, in regions away from shocks, the numerical viscosity is much smaller. In a set of nine high-resolution simulations of cosmological galaxy cluster formation, we find that this low-viscosity formulation of SPH produces substantially higher levels of turbulent gas motions in the ICM, reaching a kinetic energy content in random gas motions (measured within a 1-Mpc cube) of up to 5,30 per cent of the thermal energy content, depending on cluster mass. This also has significant effects on radial gas profiles and bulk cluster properties. We find a central flattening of the entropy profile and a reduction of the central gas density in the low-viscosity scheme. As a consequence, the bolometric X-ray luminosity is decreased by about a factor of 2. However, the cluster temperature profile remains essentially unchanged. Interestingly, this tends to reduce the differences seen in SPH and adaptive mesh refinement simulations of cluster formation. Finally, invoking a model for particle acceleration by magnetohydrodynamics waves driven by turbulence, we find that efficient electron acceleration and thus diffuse radio emission can be powered in the clusters simulated with the low-viscosity scheme provided that more than 5,10 per cent of the turbulent energy density is associated with fast magneto-sonic modes. [source]


Smoothed Particle Magnetohydrodynamics , III.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2005
Multidimensional tests, ·B= 0 constraint
ABSTRACT In two previous papers (Papers I and II), we have described an algorithm for solving the equations of Magnetohydrodynamics (MHD) using the Smoothed Particle Hydrodynamics (SPH) method. The algorithm uses dissipative terms in order to capture shocks and has been tested on a wide range of one-dimensional problems in both adiabatic and isothermal MHD. In this paper, we investigate multidimensional aspects of the algorithm, refining many of the aspects considered in Papers I and II and paying particular attention to the code's ability to maintain the ,·B= 0 constraint associated with the magnetic field. In particular, we implement a hyperbolic divergence cleaning method recently proposed by Dedner et al. in combination with the consistent formulation of the MHD equations in the presence of non-zero magnetic divergence derived in Papers I and II. Various projection methods for maintaining the divergence-free condition are also examined. Finally, the algorithm is tested against a wide range of multidimensional problems used to test recent grid-based MHD codes. A particular finding of these tests is that in Smoothed Particle Magnetohydrodynamics (SPMHD), the magnitude of the divergence error is dependent on the number of neighbours used to calculate a particle's properties and only weakly dependent on the total number of particles. Whilst many improvements could still be made to the algorithm, our results suggest that the method is ripe for application to problems of current theoretical interest, such as that of star formation. [source]


On the properties of young multiple stars

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2004
E. J. Delgado-Donate
ABSTRACT We present numerical results on the properties of young binary and multiple stellar systems. Our analysis is based on a series of smoothed particle hydrodynamics (SPH) +N -body simulations of the fragmentation of small molecular clouds, which fully resolve the opacity limit for fragmentation. These simulations demonstrate that multiple star formation is a major channel for star formation in turbulent flows. We have produced a statistically significant number of stable multiple systems, with component separations in the range ,1,103 au. At the end of the hydrodynamic stage (0.5 Myr), we find that ,60 per cent of stars and brown dwarfs are members of multiples systems, with about a third of these being low-mass, weakly bound outliers in wide eccentric orbits. Our results imply that in the stellar regime most stars are in multiples (,80 per cent) and that this fraction is an increasing function of primary mass. After N -body integration to 10.5 Myr, the percentage of bound objects has dropped to about 40 per cent, this decrease arising mostly from very low-mass stars and brown dwarfs that have been released into the field. Brown dwarfs are never found to be very close companions to stars (the brown dwarf desert at very small separations), but one case exists of a brown dwarf companion at intermediate separations (10 au). Our simulations can accommodate the existence of brown dwarf companions at large separations, but only if the primaries of these systems are themselves multiples. We have compared the outcome of our simulations with the properties of real stellar systems as deduced from the infrared colour,magnitude diagram of the Praesepe cluster and from spectroscopic and high-resolution imaging surveys of young clusters and the field. We find that the spread of the observed main sequence of Praesepe in the 0.4,1 M, range appears to require that stars are indeed commonly assembled into high-order multiple systems. Similarly, observational results from Taurus and , Ophiuchus, or moving groups such as TW Hydrae and MBM 12, suggest that companion frequencies in young systems can indeed be as high as we predict. The comparison with observational data also illustrates two problems with the simulation results. First, low mass ratio (q < 0.2) binaries are not produced by our models, in conflict with both the Praesepe colour,magnitude diagram and independent evidence from field binary surveys. Secondly, very low-mass stars and brown dwarf binaries appear to be considerably underproduced by our simulations. [source]


A smoothed particle hydrodynamics simulation of the collapse of the interstellar medium

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2001
Y. Golanski
A smoothed particle hydrodynamic (SPH) code is used to model a collapsing region of the interstellar medium (ISM). A region of the ISM is seeded with coolant material ejected from a supernova. The resulting pressure imbalance between the cooling region and the surrounding ISM induces collapse. The collapse first forms dense low-temperature regions (protoclouds) each containing several tens of solar masses of material and in quasi-equilibrium with the surrounding ISM. Turbulence is generated within the collapsing regions as they form. Collisions between protoclouds leads to regions of further increased mass and density, the final outcome being a dense cold cloud with mean density 10,18 kg m,3, mean temperature about 20 K and total mass a few hundred solar masses. The final cloud is sufficiently turbulent for star formation to occur within it. A new form of boundary condition was used in the SPH simulation to solve the problem inherent in modelling a continuum. [source]


Synthesis, characterization, mechanical properties and biocompatibility of interpenetrating polymer network,super-porous hydrogel containing sodium alginate

POLYMER INTERNATIONAL, Issue 12 2007
Lichen Yin
Abstract In this investigation an interpenetrating polymer network,superporous hydrogel containing sodium alginate (IPN-SPHAlg) was synthesized. The morphology of the polymer was characterized using scanning electron microscopy, light images and porosity, and the polymer was further examined by swelling ratio, mechanical strength and biocompatibility. The results indicated that the IPN-SPHAlg possessed both large numbers of interconnected pores and an interpenetrating network. The swelling ratio of IPN-SPHAlg was lower than that of the superporous hydrogel (SPH) and it decreased as the sodium alginate/monomer ratio increased. The IPN-SPHAlg exhibited pH responsiveness and salt-sensitive properties. Compared to SPH and SPH composites, the mechanical strength of IPN-SPHAlg was significantly enhanced. Thiazolyl blue assay on AD293 cells, in situ lactate dehydrogenase assay and morphological study of rat intestine showed that the polymer induced no significant cell or mucosal damage. The fast swelling, good mechanical properties, pH sensitivity and biocompatibility of the IPN-SPHAlg suggested it as a potential candidate in the field of drug-delivery systems. Copyright © 2007 Society of Chemical Industry [source]


Characterization of "Cd10S4(SPh)12", the Thermal Decomposition Product of (NMe4)4[Cd10S4(SPh)16]: Synthesis of a Neutral Cd54 Sulfide Cluster and of a Polymeric Chain of Thiolate-Bridged Cd17 Sulfide Clusters

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2010
Maria Bendova
Abstract Contrary to claims in the literature that a cluster of the composition of "Cd10S4(SPh)12" was formed by thermal treatment of (NMe4)4[Cd10S4(SPh)16], experimental evidence was gathered that the core structure of the cluster is not exclusively retained and other CdS species are also formed. When "Cd10S4(SPh)12" was treated with PhSH/NEt3 only a part of the material was converted into (NHEt3)4[Cd10S4(SPh)16]. From solutions of "Cd10S4(SPh)12" in strongly coordinating solvents the new neutral CdS clusters Cd54S28(SPh)52Lx (L = pyridine, DMSO or DMF) and [Cd17S4(SPh)26py], were crystallized. The latter forms polymeric chains of phenylthiolate-bridged Cd17 units. [source]


Studies on the Formation of CdS Nanoparticles from Solutions of (NMe4)4[Cd10S4(SPh)16]

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2010
Maria Bendova
Abstract The stepwise cluster growth, and formation of CdS nanoparticles from solutions of (NMe4)4[Cd10S4(SPh)16] in dimethyl sulfoxide (DMSO), dimethylformamide (DMF) and acetonitrile was investigated. Cluster growth is fast in DMSO and DMF at room temperature, and slow in acetonitrile at elevated temperatures. Larger sulfide clusters (initially Cd32, then Cd54) are initially formed, which upon further growth eventually give rise to CdS nanoparticles. Strong evidence was found that the byproduct formed during the reaction in DMSO is mononuclear [Cd(SPh)x(DMSO)y](2,x) (x , 3). [source]


MS-TOF Study of the Formation of Thiolato-Bridged Rhodium Oligomers

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2010
Josée Boudreau
Abstract The complex [Cp*Rh(,-SPh)3RhCp*]Cl was used as a starting material to synthesize various oligomeric materials of the general formula [Cp*Rh(,-SPh)x(,-Cl)3,x{Rh(,-SPh)3}nRhCp*] (x = 1 to 3; n = 1 to 4), which are formally formed by insertion of nRh(SPh)3 units into one ,-Rh,SPh bond. The insertion of Ir(SPh)3 was also observed to generate theheterotrimetallic species. All complexes were observed by using HRMS-TOF and [Cp*Rh(,-SPh)3Rh(,-SPh)3RhCp*]Cl, [3+]Cl, was characterized by using X-ray crystallography. [source]


1-D-Tin(II) Phenylchalcogenolato Complexes ,1[Sn(EPh)2] (E = S, Se, Te) , Synthesis, Structures, Quantum Chemical Studies and Thermal Behaviour

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2010
Andreas Eichhöfer
Abstract A series of three 1-D-tin(II) phenylchalcogenolato complexes ,1[Sn(EPh)2] (E = S, Se, Te) were synthesized in yields > 80,% by reaction of SnCl2 with two equivalents of PhESiMe3 in organic solvents. In the crystal the molecules form two different types of one-dimensional chains. In ,1[Sn(SPh)2] the tin atoms are distorted trigonal pyramidal coordinated by sulfur atoms (two bonds within a monomer and one longer bond between neighbored monomers), while in ,1[Sn(EPh)2] (E = Se, Te) the tin atoms show contacts to two neighbored monomers leading to a fourfold coordination of the tin atoms by either selenium or tellurium atoms. The bond situation is discussed on the basis of density functional calculations. Thermal treatment mostly leads to the formation of the corresponding phase pure tin(II) chalcogenides however sublimation plays an increasing role ongoing from the tellurolato to the thiolato complex especially for the use of vacuum conditions. The investigation of the volatile cleavage products reveals the occurence of more complex reactions in the gas phase than the formal stoichiometric cleavage of EPh2 (E = S, Se, Te) with formation of SnE. [source]


Syntheses, Structures and Theoretical Investigations of [Li(thf)4]2[Ti2Cu8S4(SPh)10] and [Ti2Ag6S6Cl2(PPhiPr2)6]

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 28 2009
Heino Sommer
Abstract The reaction of CuOAc (OAc = acetate) with TiCl4·2thf and LiSPh in thf leads to the formation of tiny deep-red crystals of [Li(thf)4]2[Ti2Cu8S4(SPh)10]. The silver/titanium cluster complex [Ti2Ag6S6Cl2(PPhiPr2)6] was synthesized by the reaction of TiCl4·2thf with AgPhCO2 and S(SiMe3)2 in the presence of PPhiPr2. The crystal structures of the compounds were determined by X-ray analysis of single crystals. Additionally, theoretical investigations were performed to assign the proper chlorine/sulfur atomic positions and to rationalize the bonding situation in 1 and 2. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]