Three-dimensional instabilities in a discretely heated annular flow: onset of spatio-temporal complexity via defect dynamics

The transition to three-dimensional and unsteady flow in an annulus with a discrete heat source on the inner cylinder is studied numerically. For large applied heat flux through the heater (large Grashof number Gr), there is a strong wall plume originating at the heater that reaches the top and forms a large scale axisymmetric wavy structure along the top. For Gr approximate to 6 x 109, this wavy structure becomes unstable to three-dimensional instabilities with high azimuthal wavenumbers m similar to 30, influenced by mode competition within an Eckhaus band of wavenumbers. Coexisting with some of these steady three-dimensional states, solution branches with localized defects break parity and result in spatio-temporal dynamics. We have identified two such time dependent states. One is a limit cycle that while breaking spatial parity, retains spatio-temporal parity. The other branch corresponds to quasi-periodic states that have globally broken parity. (C) 2014 AIP Publishing LLC.Postprint (published version

Biharmonic pattern selection

A new model to describe fractal growth is discussed which includes effects due to long-range coupling between displacements $u$. The model is based on the biharmonic equation $\nabla^{4}u =0$ in two-dimensional isotropic defect-free media as follows from the Kuramoto-Sivashinsky equation for pattern formation -or, alternatively, from the theory of elasticity. As a difference with Laplacian and Poisson growth models, in the new model the Laplacian of $u$ is neither zero nor proportional to $u$. Its discretization allows to reproduce a transition from dense to multibranched growth at a point in which the growth velocity exhibits a minimum similarly to what occurs within Poisson growth in planar geometry. Furthermore, in circular geometry the transition point is estimated for the simplest case from the relation $r_{\ell}\approx L/e^{1/2}$ such that the trajectories become stable at the growing surfaces in a continuous limit. Hence, within the biharmonic growth model, this transition depends only on the system size $L$ and occurs approximately at a distance $60 \%$ far from a central seed particle. The influence of biharmonic patterns on the growth probability for each lattice site is also analysed.Comment: To appear in Phys. Rev. E. Copies upon request to [email protected]

Heterogeneous nanofluids: natural convection heat transfer enhancement

Convective heat transfer using different nanofluid types is investigated. The domain is differentially heated and nanofluids are treated as heterogeneous mixtures with weak solutal diffusivity and possible Soret separation. Owing to the pronounced Soret effect of these materials in combination with a considerable solutal expansion, the resulting solutal buoyancy forces could be significant and interact with the initial thermal convection. A modified formulation taking into account the thermal conductivity, viscosity versus nanofluids type and concentration and the spatial heterogeneous concentration induced by the Soret effect is presented. The obtained results, by solving numerically the full governing equations, are found to be in good agreement with the developed solution based on the scale analysis approach. The resulting convective flows are found to be dependent on the local particle concentration φ and the corresponding solutal to thermal buoyancy ratio N. The induced nanofluid heterogeneity showed a significant heat transfer modification. The heat transfer in natural convection increases with nanoparticle concentration but remains less than the enhancement previously underlined in forced convection case

Genomic Relationships, Novel Loci, and Pleiotropic Mechanisms across Eight Psychiatric Disorders

Genetic influences on psychiatric disorders transcend diagnostic boundaries, suggesting substantial pleiotropy of contributing loci. However, the nature and mechanisms of these pleiotropic effects remain unclear. We performed analyses of 232,964 cases and 494,162 controls from genome-wide studies of anorexia nervosa, attention-deficit/hyper-activity disorder, autism spectrum disorder, bipolar disorder, major depression, obsessive-compulsive disorder, schizophrenia, and Tourette syndrome. Genetic correlation analyses revealed a meaningful structure within the eight disorders, identifying three groups of inter-related disorders. Meta-analysis across these eight disorders detected 109 loci associated with at least two psychiatric disorders, including 23 loci with pleiotropic effects on four or more disorders and 11 loci with antagonistic effects on multiple disorders. The pleiotropic loci are located within genes that show heightened expression in the brain throughout the lifespan, beginning prenatally in the second trimester, and play prominent roles in neurodevelopmental processes. These findings have important implications for psychiatric nosology, drug development, and risk prediction.Peer reviewe

In celebration Professor D. Brian Spalding

Peer reviewed: YesNRC publication: Ye

Guest editorial

This special issue of the International Journal of Heat and Mass Transfer is dedicated to the life and work of Professor D. Brian Spalding FRS, known more familiarly to his many friends and colleagues around the world as Brian or DBS. The first paper presents a summary of some of the scientific and engineering contributions of DBS up to the present time \u2013 and, as his wife Colleen wrote to us recently, he is someone still with a lot more to do. The invited papers1 have been written by a number of those friends and colleagues, and are devoted to some of the many topics which have attracted Brian\u2019s attention over the years: combustion, computational methods, CFD/HT applied to equipment, laminar and turbulent flow modelling and two phase flow. We also include a brief biography of Brian, and a personal recollection written by Akshai Runchal.The work of preparing this issue has been a labour of love, and is presented by the authors and editors as a tribute to a man who has influenced the minds and lives of so many engineers and scientists and who has led the world in the development of computational techniques in fluid mechanics, heat and mass transfer, and many other fields.Cette \ue9dition sp\ue9ciale de l\u2019International Journal of Heat and Mass Transfer est d\ue9di\ue9e \ue0 la vie et aux travaux du professeur D. Brian Spalding (MSR), plus famili\ue8rement connu par ses amis et coll\ue8gues \ue0 travers le monde sous le nom de Brian ou de DBS. Dans le premier article, on pr\ue9sente un r\ue9sum\ue9 des contributions scientifiques et techniques de DBS \u2013 et, comme sa femme Colleen nous l\u2019a r\ue9cemment \ue9crit, c\u2019est quelqu\u2019un qui a encore beaucoup de choses \ue0 apporter. Les articles sollicit\ue9s ont \ue9t\ue9 \ue9crits par un certain nombre de ses amis et coll\ue8gues et ils portent sur bon nombre de sujets qui ont attir\ue9 l\u2019attention de Brian au fil des ans : combustion, m\ue9thodes num\ue9riques, DFN/TC appliqu\ue9 \ue0 l\u2019\ue9quipement, mod\ue9lisation de l\u2019\ue9coulement laminaire ou turbulent et \ue9coulement diphasique. Nous avons aussi inclus une br\ue8ve biographie de Brian et des souvenirs personnels r\ue9dig\ue9s par Akshai Runchal. Cette \ue9dition sp\ue9ciale se veut un vibrant t\ue9moignage qui salue un homme qui a influenc\ue9 les travaux et les vies de tant de chercheurs et ing\ue9nieurs et qui a \ue9t\ue9 \ue0 la pointe du d\ue9veloppement des techniques num\ue9riques en m\ue9canique des fluides, du transfert de chaleur et de masse et dans bien d\u2019autres domaines.Peer reviewed: YesNRC publication: Ye