Numerical modelling of void inclusions in porous media

Numerical modelling of porous flow in a low‐permeability matrix with high‐permeability inclusions is a challenging task because the large ratio of permeabilities ill‐conditions the finite element system of equations. We propose a coupled model where Darcy flow is used for the porous matrix and potential flow is used for the inclusions. We discuss appropriate interface conditions in detail and show that the head drop in the inclusions can be prescribed in a very simple way. Algorithmic aspects are treated in full detail. Numerical examples show that this coupled approach precludes ill‐conditioning and is more efficient than heterogeneous Darcy flow. Copyright © 2003 John Wiley & Sons, Ltd.     

Efficient and accurate approach for powder compaction problems

 In this paper, a new approach for powder cold compaction simulations is presented. A density-dependent plastic model within the framework of finite strain multiplicative hyperelastoplasticity is used to describe the highly nonlinear material behaviour; the Coulomb dry friction model is used to capture friction effects at die-powder contact; and an Arbitrary Lagrangian–Eulerian (ALE) formulation is used to avoid the (usual) excessive distortion of Lagrangian meshes caused by large mass fluxes. Several representative examples, involving structured and unstructured meshes are simulated. The results obtained agree with the experimental data and other numerical results reported in the literature. It is shown that, contrary to other Lagrangian and adaptive h-remeshing approaches recently reported for this type of problems, the present approach verifies the mass conservation principle with very low relative errors (less than 1% in all ALE examples and exactly in the pure Lagrangian examples). Moreover, thanks to the use of an ALE formulation and in contrast with other simulations, the presented density distributions do not present spurious oscillations. Received: 20 March 2002 / Accepted: 15 October 2002 The partial financial support of the Ministerio de Ciencia y Tecnología (grant number DPI 2001-2204) is gratefully acknowledged.     

Immunogenicity of a Salmonella typhi CVD 908 candidate vaccine strain expressing the major surface protein gp63 of Leishmania mexicana mexicana

Attenuated Salmonella typhi are attractive for use as live vector vaccines to express protozoal antigens and deliver them to the human immune system. The gene encoding the mature form of Leishmania mexicana mexicana gp63 under control of tac promoter was integrated into the delta aroC locus of the chromosome of attenuated delta aroC, delta aroD S. typhi strain CVD 908. After oral immunization of BALB/c mice with two 1 x 10(9) colony forming unit doses given 21 days apart, CVD 908 omega (delta aroC::Ptac-gp63) elicited a broad T cell-mediated immune response against L. m. mexicana gp63 as demonstrated by: (1) lymphoproliferative response to fixed whole L. m. mexicana promastigotes; (2) activation of IL-2 (but not IL-4)-producing lymphocytes; (3) appearance of cytotoxic T cells against mouse mastocytoma cells expressing gp63. This T-cell mediated immune response was associated with significant protection in F1 (BALB/cXC57Bl/6) mice challenged in their footpads with a wild type strain of L. m. mexicana.     

Rapid characterization of four species of the Saccharomyces sensu stricto complex according to mitochondrial DNA patterns

Several strains of the four sibling species of the genus Saccharomyces (S. bayanus, S. cerevisiae, S. paradoxus, and S. pastorianus) were characterized by using a rapid and simple method of restriction analysis of mitochondrial DNA. Patterns obtained with four-cutter endonucleases (such as AluI, DdeI, HinfI, and RsaI) made it possible to differentiate each species. S. cerevisiae and S. paradoxus presented a greater number of large fragments than S. pastorianus and S. bayanus with all the assay enzymes. With AluI and DdeI, species-specific bands clearly permitted differentiation between S. pastorianus and S. bayanus. To test the resolution of this method, wild Saccharomyces strains were analyzed. The correct assignment of these strains to a known taxon by this rapid method was confirmed by means of electrophoretic karyotyping.     

Neurotechnology: expanding opportunities for funding at the National Institute of Mental Health

The National Institute of Mental Health recognizes the importance that creative development of technology and methodology play in brain and behavioral science research. This institute is making major efforts to support such development through specific initiatives, like the Human Brain Project. In addition, this Institute is actively building bridges between business and academic research communities to make optical use of funds for the research and development of commercially viable technologies relevant to all aspects of the Institute's mission through the Small Business Innovation Research and Small Business Technology Transfer Programs. Together, these efforts will culminate in a more vigorous scientific enterprise, and ultimately benefit the entire mental health community and society.     

Synchronized action of synaptically coupled chaotic model neurons

Experimental observations of the intracellular recorded electrical activity in individual neurons show that the temporal behavior is often chaotic. We discuss both our own observations on a cell from the stomatogastric central pattern generator of lobster and earlier observations in other cells. In this paper we work with models with chaotic neurons, building on models by Hindmarsh and Rose for bursting, spiking activity in neurons. The key feature of these simplified models of neurons is the presence of coupled slow and fast subsystems. We analyze the model neurons using the same tools employed in the analysis of our experimental data. We couple two model neurons both electrotonically and electrochemically in inhibitory and excitatory fashions. In each of these cases, we demonstrate that the model neurons can synchronize in phase and out of phase depending on the strength of the coupling. For normal synaptic coupling, we have a time delay between the action of one neuron and the response of the other. We also analyze how the synchronization depends on this delay. A rich spectrum of synchronized behaviors is possible for electrically coupled neurons and for inhibitory coupling between neurons. In synchronous neurons one typically sees chaotic motion of the coupled neurons. Excitatory coupling produces essentially periodic voltage trajectories, which are also synchronized. We display and discuss these synchronized behaviors using two "distance" measures of the synchronization.     

THE INVESTIGATION OF KINETICS OF HIGH-TEMPERATURE STRUCTURE TRANSFORMATION OF HOMOPHASES AND HETEROPHASES MATERIALS

1.IntroductionTheinvestigationofinternalboundaries(antiphaseandinterphaseboundaries,grainboundariesandothers)inhomophaseandheterophasematerialsistheactualproblemofphaseorder--disordertransitionkinetics.TherearesomeexpermentaldatashowingtheirimportantroleinprocessesofmaterialstructuretransformationundervariousexternalfaCtorsll--4](temperature,pressure,stressandothers).Forexample,differentstructuralfeaturesarelocalizedonantiphasedomainboundarieswithtemperaturegrowth[2,3].Antiphaseboundariesbeha…     

The Effect of Aniline Hydrochloride Hydrotrope on the Phase Behavior of SDS/Water System

The aim of this work was to determine the detailed phase behavior of the sodium dodecyl sulfate/aniline hydrochloride/water system as a function of concentration of sodium dodecyl sulfate (SDS), aniline hydrochloride (AHC) to sodium dodecyl sulfate molar ratio (R = [AHC]/[SDS]) and temperature. Phase behavior information was obtained via polarizing microscopy, differential scanning calorimetry (DSC), cryo-scanning electron microscopy (Cryo-SEM) and oscillatory linear rheological measurements with good agreement among these techniques. It is well known that SDS in water forms spherical micelles at concentrations lower than 40 wt% and temperatures above its Krafft temperature (T _k = 16–21 °C). In this region, the SDS/water system exhibits Newtonian rheological behavior, which is characteristic of spherical micellar solutions. The addition of the hydrotrope, aniline hydrochloride, to SDS aqueous solutions produces a viscosity increase in this system as R augments, and a maximum of about five orders of magnitude was found at R = 0.47 for 5 wt% SDS at 20 °C. Moreover, the system shows a transition from viscous to strong viscoelastic behavior. These changes in the rheological behavior are produced by the transitions from sphere to rodlike micelles, which are induced by the hydrophobicity of AHC causing it to be absorbed into the core and the hydrophilic interface of the micelles, which screens the repulsions between the charged head groups.