1,118 research outputs found
An immersed discontinuous Galerkin method for compressible Navier-Stokes equations on unstructured meshes
We introduce an immersed high-order discontinuous Galerkin method for solving
the compressible Navier-Stokes equations on non-boundary-fitted meshes. The
flow equations are discretised with a mixed discontinuous Galerkin formulation
and are advanced in time with an explicit time marching scheme. The
discretisation meshes may contain simplicial (triangular or tetrahedral)
elements of different sizes and need not be structured. On the discretisation
mesh the fluid domain boundary is represented with an implicit signed distance
function. The cut-elements partially covered by the solid domain are integrated
after tessellation with the marching triangle or tetrahedra algorithms. Two
alternative techniques are introduced to overcome the excessive stable time
step restrictions imposed by cut-elements. In the first approach the cut-basis
functions are replaced with the extrapolated basis functions from the nearest
largest element. In the second approach the cut-basis functions are simply
scaled proportionally to the fraction of the cut-element covered by the solid.
To achieve high-order accuracy additional nodes are introduced on the element
faces abutting the solid boundary. Subsequently, the faces are curved by
projecting the introduced nodes to the boundary. The proposed approach is
verified and validated with several two- and three-dimensional subsonic and
hypersonic low Reynolds number flow applications, including the flow over a
cylinder, a space capsule and an aerospace vehicle
Entropy-satisfying scheme for a hierarchy of dispersive reduced models of free surface flow
International audienceThis work is devoted to the numerical resolution in multidimensional framework of a hierarchy of reduced models of the free surface Euler equations, also called water waves equations.The current paper, the first in a series of two, focuses on a hierarchy of monolayer dispersive models, such is the Serre-Green-Naghdi model.A particular attention is given to the dissipation of the mechanical energy at the discrete level, i.e. to design an entropy-satisfying scheme.To illustrate the accuracy and the robustness of the strategy, several numerical experiments are performed.In particular, the strategy is able to deal with dry areas without particular treatment
A unified hyperbolic formulation for viscous fluids and elastoplastic solids
We discuss a unified flow theory which in a single system of hyperbolic
partial differential equations (PDEs) can describe the two main branches of
continuum mechanics, fluid dynamics, and solid dynamics. The fundamental
difference from the classical continuum models, such as the Navier-Stokes for
example, is that the finite length scale of the continuum particles is not
ignored but kept in the model in order to semi-explicitly describe the essence
of any flows, that is the process of continuum particles rearrangements. To
allow the continuum particle rearrangements, we admit the deformability of
particle which is described by the distortion field. The ability of media to
flow is characterized by the strain dissipation time which is a characteristic
time necessary for a continuum particle to rearrange with one of its
neighboring particles. It is shown that the continuum particle length scale is
intimately connected with the dissipation time. The governing equations are
represented by a system of first order hyperbolic PDEs with source terms
modeling the dissipation due to particle rearrangements. Numerical examples
justifying the reliability of the proposed approach are demonstrated.Comment: 6 figure
Service-oriented visualization applied to medical data analysis
With the era of Grid computing, data driven experiments and simulations have become very advanced and complicated. To allow specialists from various domains to deal with large datasets, aside from developing efficient extraction techniques, it is necessary to have available computational facilities to visualize and interact with the results of an extraction process. Having this in mind, we developed an Interactive Visualization Framework, which supports a service-oriented architecture. This framework allows, on one hand visualization experts to construct visualizations to view and interact with large datasets, and on the other hand end-users (e.g., medical specialists) to explore these visualizations irrespective of their geographical location and available computing resources. The image-based analysis of vascular disorders served as a case study for this project. The paper presents main research findings and reports on the current implementation status
Combustion in thermonuclear supernova explosions
Type Ia supernovae are associated with thermonuclear explosions of white
dwarf stars. Combustion processes convert material in nuclear reactions and
release the energy required to explode the stars. At the same time, they
produce the radioactive species that power radiation and give rise to the
formation of the observables. Therefore, the physical mechanism of the
combustion processes, as reviewed here, is the key to understand these
astrophysical events. Theory establishes two distinct modes of propagation for
combustion fronts: subsonic deflagrations and supersonic detonations. Both are
assumed to play an important role in thermonuclear supernovae. The physical
nature and theoretical models of deflagrations and detonations are discussed
together with numerical implementations. A particular challenge arises due to
the wide range of spatial scales involved in these phenomena. Neither the
combustion waves nor their interaction with fluid flow and instabilities can be
directly resolved in simulations. Substantial modeling effort is required to
consistently capture such effects and the corresponding techniques are
discussed in detail. They form the basis of modern multidimensional
hydrodynamical simulations of thermonuclear supernova explosions. The problem
of deflagration-to-detonation transitions in thermonuclear supernova explosions
is briefly mentioned.Comment: Author version of chapter for 'Handbook of Supernovae,' edited by A.
Alsabti and P. Murdin, Springer. 24 pages, 4 figure
Male breast cancer
Male breast cancer (MBC) is a rare disease representing less than 1% of all breast cancers (BC) and less than 1% of cancers in men. Age at presentation is mostly in the late 60s. MBC is recognized as an estrogen-driven disease, specifically related to hyperestrogenism. About 20% of MBC patients have family history for BC. Mutations in BRCA1 and, predominantly, BRCA2, account for approximately 10% of MBC cases.
Because of its rarity, MBC is often compared with female BC (FBC). Based on age-frequency distribution, age-specific incidence rate patterns and prognostic factors profiles, MBC is considered similar to late-onset, postmenopausal estrogen/progesterone receptor positive (ER+/PR+) FBC. However, clinical and pathological characteristics of MBC do not exactly overlap FBC. Compared with FBC, MBC has been reported to occur later in life, present at a higher stage, and display lower histologic grade, with a higher proportion of ER+ and PR+ tumors.
Although rare, MBC remains a substantial cause for morbidity and mortality in men, probably because of its occurrence in advanced age and delayed diagnosis. Diagnosis and treatment of MBC generally is similar to that of FBC. Men tend to be treated with mastectomy rather than breast-conserving surgery. The backbone of adjuvant therapy or palliative treatment for advanced disease is endocrine, mostly tamoxifen.
Use of FBC-based therapy led to the observation that treatment outcomes for MBC are worse and that survival rates for MBC do not improve like FBC. These different outcomes may suggest a non-appropriate utilization of treatments and that different underlying pathogenetic mechanisms may exist between male and female BC
Efficient numerical computation and experimental study of temporally long equilibrium scour development around abutment
YesFor the abutment bed scour to reach its equilibrium state, a long flow time is needed. Hence, the
employment of usual strategy of simulating such scouring event using the 3D numerical model is
very time consuming and less practical. In order to develop an applicable model to consider
temporally long abutment scouring process, this study modifies the common approach of 2D
shallow water equations (SWEs) model to account for the sediment transport and turbulence, and
provides a realistic approach to simulate the long scouring process to reach the full scour
equilibrium. Due to the high demand of the 2D SWEs numerical scheme performance to simulate
the abutment bed scouring, a recently proposed surface gradient upwind method (SGUM) was
also used to improve the simulation of the numerical source terms. The abutment scour
experiments of this study were conducted using the facility of Hydraulics Laboratory at Nanyang
Technological University, Singapore to compare with the presented 2D SGUM-SWEs model.
Fifteen experiments were conducted over a total period of 3059.7 hours experimental time (over
4.2 months). The comparison shows that the 2D SGUM-SWEs model gives good representation
to the experimental results with the practical advantage
A compressible multiphase flow model for violent aerated wave impact problems
This paper focuses on the numerical modelling of wave impact events under air entrapment and aeration effects. The underlying flow model treats the dispersed water wave as a compressible mixture of air and water with homogeneous material properties. The corresponding mathematical equations are based on a multiphase flow model which builds on the conservation laws of mass, momentum and energy as well as the gas-phase volume fraction advection equation. A high-order finite volume scheme based on monotone upstream-centred schemes for conservation law reconstruction is used to discretize the integral form of the governing equations. The numerical flux across a mesh cell face is estimated by means of the HLLC approximate Riemann solver. A third-order total variation diminishing Runge–Kutta scheme is adopted to obtain a time-accurate solution. The present model provides an effective way to deal with the compressibility of air and water–air mixtures. Several test cases have been calculated using the present approach, including a gravity-induced liquid piston, free drop of a water column in a closed tank, water–air shock tubes, slamming of a flat plate into still pure and aerated water and a plunging wave impact at a vertical wall. The obtained results agree well with experiments, exact solutions and other numerical computations. This demonstrates the potential of the current method to tackle more general wave–air–structure interaction problems
Effect of polymorphisms in the Slc11a1 coding region on resistance to brucellosis by macrophages in vitro and after challenge in two Bos breeds (Blanco Orejinegro and Zebu)
The resistance/susceptibility of selected cattle breeds to brucellosis was evaluated in an F1 population generated by crossing animals classified as resistant (R) and susceptible (S) (R x R, R x S, S x R, S x S) based on challenges in vitro and in vivo. The association between single nucleotide polymorphisms identified in the coding region of the Slc11a1 gene and resistance/susceptibility was estimated. The trait resistance or susceptibility to brucellosis, evaluated by a challenge in vitro, showed a high heritable component in terms of additive genetic variance (h2 = 0.54 ± 0.11). In addition, there was a significant association (p < 0.05) between the control of bacterial survival and two polymorphisms (a 3'UTR and SNP4 located in exon 10). The antibody response of animals classified as resistant to infection by Brucella abortus differed significantly (p < 0.05) from that of susceptible animals. However, there was no significant association between single nucleotide polymorphisms located in the Slc11a1 gene and the antibody response stimulated by a challenge in vivo
- …