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At least 937 records · Page 52Linked to original sources
PubMed2004

Fluctuations of the initial conditions and the continuous emission in the hydrodynamical description of two-pion interferometry.

Within the hydrodynamical approach, we study the Bose-Einstein correlation of identical pions by taking into account both event-by-event fluctuating initial conditions and continuous pion emission during the whole development of the hot and dense matter formed in high-energy collisions. Important deviations occur, compared to the usual hydrocalculations with smooth initial conditions and a sudden freeze-out on a well defined hypersurface. Comparison with data at the BNL Relativistic Heavy Ion Collider (RHIC) shows that, despite the rather rough approximation we used here, this description can account for the m(T) dependence of R(L) and R(s), and produces a significant improvement for R(o) with respect to the usual version.

Journal Article↗
PubMed2004

Self-consistent finite-mode approximations for the hydrodynamics of an incompressible fluid on nonrotating and rotating spheres.

Self-consistent finite-mode approximations for both Euler and Navier-Stokes equations for vorticity on a sphere are constructed and extended to the case of a rotating sphere, aiming at application to ocean and atmosphere modeling. In the absence of dissipation they preserve the specific Hamiltonian structure of hydrodynamics and have, at each level of approximation, an appropriate number of integrals of motion, which is not the case for standard schemes.

Journal Article↗
PubMed2005

Symmetry breaking via global bifurcations of modulated rotating waves in hydrodynamics.

The combined experimental and numerical study finds a complex mechanism of Z(2) symmetry breaking involving global bifurcations for the first time in hydrodynamics. In addition to symmetry breaking via pitchfork bifurcation, the Z(2) symmetry of a rotating wave that occurs in Taylor-Couette flow is broken by a global saddle-node-infinite-period (SNIP) bifurcation after it has undergone a Neimark-Sacker bifurcation to a Z(2)-symmetric modulated rotating wave. Unexpected complexity in the bifurcation structure arises as the curves of cyclic pitchfork, Neimark-Sacker, and SNIP bifurcations are traced towards their apparent merging point. Instead of symmetry breaking due to a SNIP bifurcation, we find a more complex mechanism of Z(2) symmetry breaking involving nonsymmetric two-tori undergoing saddle-loop homoclinic bifurcations and complex dynamics in the vicinity of this global bifurcation.

Journal Article↗
PubMed2005

Hydrodynamic singularities and clustering in a freely cooling inelastic gas.

We employ hydrodynamic equations to follow the clustering instability of a freely cooling dilute gas of inelastically colliding spheres into a well-developed nonlinear regime. We simplify the problem by dealing with a one-dimensional coarse-grained flow. We observe that at a late stage of the instability the shear stress becomes negligibly small, and the gas flows solely by inertia. As a result the flow formally develops a finite-time singularity, as the velocity gradient and the gas density diverge at some location. We argue that flow by inertia represents a generic intermediate asymptotic of unstable free cooling of dilute inelastic gases.

Journal Article↗
PubMed2005

Experimental investigation of high-mach-number 3D hydrodynamic jets at the national ignition facility.

The first hydrodynamic experiments were performed on the National Ignition Facility. A supersonic jet was formed via the interaction of a laser driven shock ( approximately 40 Mbar) with 2D and 3D density perturbations. The temporal evolution of the jet's spatial scales and ejected mass were measured with point-projection x-ray radiography. Measurements of the large-scale features and mass are in good agreement with 2D and 3D numerical simulations. These experiments provide quantitative data on the evolution of 3D supersonic jets and provide insight into their 3D behavior.

Journal Article↗
PubMed2005

Transition to spatiotemporal chaos in a two-dimensional hydrodynamic system.

We study the transition to spatiotemporal chaos in a two-dimensional hydrodynamic experiment where liquid columns take place in the gravity induced instability of a liquid film. The film is formed below a plane grid which is used as a porous media and is continuously supplied with a controlled flow rate. This system can be either ordered (on a hexagonal structure) or disordered depending on the flow rate. We observe, for the first time in an initially structured state, a subcritical transition to spatiotemporal disorder which arises through spatiotemporal intermittency. Statistics of numbers, creations, and fusions of columns are investigated. We exhibit a critical behavior close to the directed percolation one.

Journal Article↗
PubMed2005

Hydrodynamic induced deformation and orientation of a microscopic elastic filament.

We describe simulations of an elastic filament immersed in a fluid and subjected to a body force. The coupling between the fluid flow and the friction that the filament experiences induces bending and alignment perpendicular to the force. With increasing force there are four shape regimes, ranging from slight distortion to an unsteady tumbling motion. We also find marginally stable structures. The instability of these shapes and the alignment are explained by induced bending and nonlocal hydrodynamic interactions. These effects are experimentally relevant for stiff microfilaments.

Actin Cytoskeleton↗
PubMed2005

Influence of hydrodynamic coupling on pair diffusion in a quasi-one-dimensional colloid system.

The effect of hydrodynamic interaction on the separation dependence of the center of mass and relative pair diffusion coefficients of colloid particles in a quasi-one-dimensional system, including the influence of proximate walls, is calculated using the method of reflections. There is excellent agreement between the theoretical predictions and the experimental data. We show that the separation dependence of the relative pair diffusion coefficient has an oscillatory structure on the scale length of the correlation length in the system, and we directly relate that oscillatory structure to the pair correlation function of the system.

Biopolymers↗
PubMed2005

Hydrodynamics of droplet coalescence.

We study droplet coalescence in a molecular system with a variable viscosity and a colloid-polymer mixture with an ultralow surface tension. When either the viscosity is large or the surface tension is small enough, we observe that the opening of the liquid bridge initially proceeds at a constant speed set by the capillary velocity. In the first system we show that inertial effects become dominant at a Reynolds number of about 1.5+/- 0.5 and the neck then grows as the square root of time. In the second system we show that decreasing the surface tension by a factor of 10(5) opens the way to a more complete understanding of the hydrodynamics involved.

Journal Article↗
PubMed2006

Universal features of hydrodynamic Lyapunov modes in extended systems with continuous symmetries.

Numerical and analytical evidence is presented to show that hydrodynamic Lyapunov modes (HLMs) do exist in lattices of coupled Hamiltonian and dissipative maps. More importantly, we find that HLMs in these two classes of systems are different with respect to their spatial structure and their dynamical behavior. To be concrete, the corresponding dispersion relations of Lyapunov exponent versus wave number are characterized by lambda approximately k and lambda approximately k2, respectively. The HLMs in Hamiltonian systems are propagating, whereas those of dissipative systems show only diffusive motion. Extensive numerical simulations of various systems confirm that the existence of HLMs is a very general feature of extended dynamical systems with continuous symmetries and that the above-mentioned differences between the two classes of systems are universal in large extent.

Journal Article↗
PubMed1977

Hydrodynamic properties of 2-mercaptoethanol-modified glycogen.

Treatment of glycogen with 2-mercaptoethanol and iodoacetamide gives rise to a modified glycogen which resembles the original glycogen in its hydrodynamic behaviour but has a pronounced tendency to aggregate. The modified glycogen can be distinguished easily, by its diffusion coefficient, from glycogen degraded by more traditional methods of extraction. The 'fundamental' glycogen particle appears to be composed of two or three glycogen beta-particles linked by a single protein chain.

Animals↗
PubMed1986

Structure of initiation factor eIF-3 from rat liver. Hydrodynamic and electron microscopic investigations.

On the basis of hydrodynamic, electron microscopic and biochemical investigations a new model of the structure of initiation factor eIF-3 is proposed. From sedimentation and diffusion coefficients of 16.35 S and 2.13 X 10(-7) cm2/s, respectively, as well as from sedimentation equilibrium measurements, a molecular mass of about 650 kDa was determined for isolated eIF-3. This is in agreement with molecular mass estimations by sodium dodecyl sulphate gel electrophoresis. A partial specific volume of 0.723 cm3/g was determined by means of the amino acid composition and the specific volume increments of the amino acids. From this value and from the molecular mass, a volume of 780 nm3 was calculated for eIF-3. In electron micrographs of isolated eIF-3, images with triangular profiles and side lengths of 14 nm, 16 nm, and 17 nm have been observed. Taking into account the calculated volume and considering the triangular image as one face of the particle, it is suggested that eIF-3 has the shape of a flat triangular prism with a height of about 7 nm and the above-mentioned side-lengths. This model is in agreement with results of electron microscopic investigations of eIF-3 in native small ribosomal subunits [Lutsch, G., Benndorf, R., Westermann, P., Bommer, U.-A. & Bielka, H. (1986) Eur. J. Cell Biol. 40/2, in press]. The high frictional ratio of about 1.7 also supports eIF-3 to be rather of a flat than of a globular shape.

Amino Acids↗
PubMed1989

Hydrodynamic, structural and magnetic properties of Megasphaera elsdenii Fe hydrogenase reinvestigated.

Megasphaera elsdenii hydrogenase has been purified to homogeneity using an FPLC procedure as the final step. The protein gives a single band in SDS/PAGE with an apparent molecular mass of 57-59 kDa. There is no second hydrogenase activity in the soluble fraction of M. elsdenii. The hydrodynamics of the enzyme have been compared to those of the two-subunit Fe hydrogenase from Desulfovibrio vulgaris (Hildenborough) in the analytical ultracentrifuge using the absorption of the intrinsic iron-sulfur clusters as the monitor. Sedimentation-velocity experiments indicate the M. elsdenii enzyme (s20,w = 4.95 S) to be essentially globular, while the D. vulgaris enzyme (s20,w = 4.1 S) has a less symmetric shape. From the sedimentation equilibrium measurements under a variety of conditions an average molecular mass is calculated of 58 kDa (M. elsdenii) and 54 kDa (D. vulgaris), respectively. Pure, maximally active M. elsdenii hydrogenase has A405/A280 = 0.36 and has a specific H2-production activity of 400 mumol H2.min-1.(mg protein)-1 at 30 degrees C and pH 8.0. The enzyme contains some 13-18 iron and acid-labile sulfur ions/58-kDa monomer. Eight of these Fe-S are present as two electron-transferring ferredoxin-like cubanes with Em approximately greater than -0.3 V, as indicated by pH-dependent EPR spectroscopy on the H2-reduced enzyme. In the (re)oxidized state the remainder iron gives rise to a single S = 1/2 rhombic EPR signal. Hydrogen-production activity, content of remainder iron and rhombic EPR signal intensity are mutually correlated. Purified hydrogenase appears to exist as a mixture of fully active holoenzyme and inactive protein still carrying the two cubanes but deficient in active-site iron.

Bacteria, Anaerobic↗
PubMed1989

Folding of thermolysin fragments. Hydrodynamic properties of isolated domains and subdomains.

Sedimentation analysis in the analytical ultracentrifuge has been used to characterize the size and shape of thermolysin and a number of its fragments obtained by chemical or enzymatic cleavage of the protein. Four fragments (121-316, 206-316, 225/226-316 and 255-316) originate from the C-terminal domain, and two (1-155 and 1-205) from the N-terminal domain of the intact molecule. In aqueous solution at neutral pH the hydrodynamic properties of the C-terminal fragments, except 255-316, are consistent with compact homogeneous monomers. Fragment 255-316 is a monomeric species below 0.08 mg/ml concentration and forms a dimer above this concentration. Dimerization does not lead to changes in fragment conformation, as determined by far-ultraviolet circular dichroic measurements, but to an increase of 5.6 degrees C (to 68.2 degrees C at 1.0 mg/ml) in the temperature for thermal unfolding and a corresponding increase of 4.6 kJ/mol in the free energy of unfolding. Fragments derived from the N-terminal domain show a strong tendency to form high-molecular-mass aggregates. Previous experiments utilizing circular dichroic measurements and antibody binding data suggested that the C-terminal fragments listed above are able to refold in aqueous solution at neutral pH into a stable conformation of native-like characteristics [Dalzoppo, D., Vita, C. & Fontana, A. (1985) J. Mol. Biol. 182, 331-340] (and references cited therein). Present data establish that all these C-terminal fragments are globular monomeric species in solution (at concentrations approximately 0.1 mg/ml) and thus represent 'isolated' domains (or subdomains) with intrinsic conformational stability typical of small globular proteins.

Bacillus↗
PubMed1990

[Detection of hydrodynamically operative tissue in the substantia spongiosa of the femoral head in Bos taurus and Ovis aries].

The authors show the presence of CC-Tensulae in Bos taurus and Ovis aries. They define CC-Tensulae as tense membranes in openings between the trabeculae of spongy bone. These structures were interpreted in man as a hydrodynamic subsystem which serves the flow and the impulses of mechanical forces. The authors point especially to the similarity that exists between their findings and what has been seen in man.

Animals↗
PubMed1984

Hydrodynamic properties of muscarinic acetylcholine receptors solubilized from rat forebrain.

Muscarinic receptors from rat forebrain have been solubilized by Lubrol PX, lysophosphatidylcholine (LPC), digitonin and cholate/1 M sodium chloride. The overall level of solubilization was characterized using receptors prelabelled with an irreversible antagonist. The recovery of nondenatured soluble binding activity was estimated using reversible tritiated antagonists. All these detergents solubilized 60-85% of the total binding sites. In Lubrol PX most of the receptors were recovered in a denatured form. In the other detergents 30-90% of the solubilized receptors were stable and capable of binding reversible [3H]-antagonists with high affinity. The hydrodynamic properties of the soluble receptors have been examined by gel filtration and sucrose gradient centrifugation in H2O and D2O. The soluble receptors in Lubrol PX, lysophosphatidylcholine and cholate were, in general, heterogeneous as regards their molecular size. Estimates of the molecular weight after correction for bound detergent, varied from 82,000 to 134,000. Conditions were identified under which the receptor was largely monodisperse, and the estimates of molecular weight agreed with values (ca. 83,000) from sodium dodecylsulphate (SDS) polyacrylamide gel electrophoresis. The amount of bound detergent could not be calculated for the digitonin-muscarinic receptor complex which had an estimated overall median molecular weight of about 290,000. It is concluded that a subpopulation of muscarinic receptors from the rat forebrain is capable of existing in a monomeric soluble form and binding ligands. There is also evidence that complexes with other proteins can exist, but their specificity and functional relevance are not known.

Animals↗
PubMed1988

Hydrodynamic investigation of mechanical bileaflet valves.

For hydrodynamic comparison, 11 mechanical bileaflet valves have been perfused in a mock circulation system under pulsatile flow conditions. Six St. Jude Medical valves with different sizes from No. 21 to No. 31 and five Duromedics prostheses with corresponding sizes from No. 21 to No. 29 have been investigated. Flow, pressure, and orifice area were measured, while cardiac output was varied between 2 and 6 L/min. Insufficiency (I), maximal orifice area (Amax), mean orifice area (A), discharge coefficient (CD), performance index (PI), and efficiency index (EI) were determined. The St. Jude Medical valves show higher values of orifice area when compared with the Duromedics valves. For smaller valve sizes up to No. 25, the values of the orifice area are similar. The Duromedics valves show much lower values of insufficiency; thus, for small valve sizes, the Duromedics prosthesis seems to be superior. For larger valve sizes (No. 27, No. 29, and No. 31), a decision has to be made whether higher insufficiency and higher orifice area of the St. Jude Medical valve or lower insufficiency with lower orifice area is more acceptable.

Heart Valve Prosthesis↗
PubMed1992

Improvement of the hydrodynamic response of a ventricular assist device: a false auricle solution.

We propose a new design of the auricular cannula in ventricular assist devices (VADs), consisting of a collapsible large cannula with a capacity approximately equal to the ejection volume of the VAD. The device works as a false auricle and filters the negative pressure that occurs during diastole. We show that the use of this type of cannula improves the hydrodynamic efficiency and the stability of the working conditions. Moreover, during chronic implantation in sheep, hemolysis stays well below pathological levels. These improvements result in much better controllability of the whole VAD.

Animals↗