Search results for "NODAL"

Formation of Ordered Structures in Quenching Experiments: Scaling Theory and Simulations

1987

In this note we want to address the particular problem of the formation of ordered structures resulting from “quenching experiments”. The generic experimental situation is depicted in Figure 1. Initially the system is in an unordered random state in the one-phase region. Then the temperature is lowered (for some systems like polymers the coexistence curve is inverted so that the temperature must be raised) until the system is in the two phase region. The system is now in a non-equilibrium situation and evolves toward equilibrium. It is during the evolution toward equilibrium that the system develops ordered structures /1,2/.

Mesoscopic gels at low agarose concentration: perturbation effects of ethanol

1997

Aqueous agarose solutions at low concentrations (0.5 g/liter) were temperature quenched below the spinodal line to form mutually disconnected mesoscopic gels. In the presence of 6% ethanol, these solutions, obtained by quenching at the same temperature depth as in pure water, appear much more fluid, as determined by probe diffusion experiments. We show by static and dynamic light scattering that this can be explained by the solvent-mediated effects of ethanol, leading to a globular shape of mesoscopic agarose gels, rather than to an extended rodlike structure observed in pure water. Our findings show the significant effects of solvent perturbations on particle condensation and, therefore, m…

Microgel regions in dilute agarose solutions: the notion of non-gelling concentration, and the role of spinodal demixing

1991

Abstract Freely drifting microgel regions are found in aqueous solutions of agarose, a representative biostructural polysaccharide, at concentrations between 0.01% and 0.05% w/v when quenched from 100°C to lower temperature. The size of these domains depends on the quench temperature and agarose concentration. The results agree with recent findings on the role that fluctuations within or close to the instability region of solution have as the initial step towards the self-assembly of supramolecular structures, and throw a new light on the notion of the lowest solute concentration needed for gelation.

Kinetics of phase separation in polymer blends for deep quenches

1986

Electro microscopy was used to study the phase separation kinetics of a polystyrene/polyvinylmethylether system subjected to a critical deep quench. The size of the phase-separated domains was found to increase linearly with time, implying that hydrodynamic effects control the rate of growth of the domains in the time scale and temperature range under consideration. From these measurements the growth velocity and approximate diffusion constants can be determined for three different temperatures. Comparison of these results with those obtained by light scattering on other systems and with theoretical predictions is possible by replotting in dimensionless units.

Multiple nodal solutions for semilinear robin problems with indefinite linear part and concave terms

2017

We consider a semilinear Robin problem driven by Laplacian plus an indefinite and unbounded potential. The reaction function contains a concave term and a perturbation of arbitrary growth. Using a variant of the symmetric mountain pass theorem, we show the existence of smooth nodal solutions which converge to zero in $C^1(\overline{\Omega})$. If the coefficient of the concave term is sign changing, then again we produce a sequence of smooth solutions converging to zero in $C^1(\overline{\Omega})$, but we cannot claim that they are nodal.

Suppression of nodal expression in prospective dorsal cells of the early sea urchin embryo by the hbox12 homeodomain regulator

2014

Dorsal/Ventral (DV) axis formation in the sea urchin embryo depends upon the expression of nodal on the ventral side, which behaves as a DV organizing centre. However, only fuzzy clues are known as to the early symmetry-breaking steps that lead to the positioning of such an organizer. An extremely interesting candidate for this role is the hbox12 homeobox-containing gene. In Paracentrotus lividus, hbox12 expression is antecedent and complementary with respect to that of nodal, being confined in prospective dorsal cells. We show that ectopic expression of Hbox12 provokes DV abnormalities and attenuates nodal as well as nodal-dependent gene transcription. By blastomere transplantation, we als…

Discussion on "Protein crystallization: universal thermodynamic vs. specific effects of PEG"

2008

Multiple solutions with sign information for a (p,2)-equation with combined nonlinearities

2020

We consider a parametric nonlinear Dirichlet problem driven by the sum of a p-Laplacian and of a Laplacian (a (p,2)-equation) and with a reaction which has the competing effects of two distinct nonlinearities. A parametric term which is (p−1)-superlinear (convex term) and a perturbation which is (p−1)-sublinear (concave term). First we show that for all small values of the parameter the problem has at least five nontrivial smooth solutions, all with sign information. Then by strengthening the regularity of the two nonlinearities we produce two more nodal solutions, for a total of seven nontrivial smooth solutions all with sign informations. Our proofs use critical point theory, critical gro…

Positive and nodal solutions for nonlinear nonhomogeneous parametric neumann problems

2020

We consider a parametric Neumann problem driven by a nonlinear nonhomogeneous differential operator plus an indefinite potential term. The reaction term is superlinear but does not satisfy the Ambrosetti-Rabinowitz condition. First we prove a bifurcation-type result describing in a precise way the dependence of the set of positive solutions on the parameter λ > 0. We also show the existence of a smallest positive solution. Similar results hold for the negative solutions and in this case we have a biggest negative solution. Finally using the extremal constant sign solutions we produce a smooth nodal solution.

Lysozyme crystallization rates controlled by anomalous fluctuations

2005

Abstract Nucleation of protein aggregates and crystals is a process activated by statistical fluctuations of concentration. Nucleation rates may change by several orders of magnitude upon apparently minor changes in the multidimensional space of parameters (temperature, pH, protein concentration, salt type and concentrations, additives). We use available data on hen egg lysozyme crystal induction times in different solution conditions. We measure by static and dynamic light scattering the amplitudes and lifetimes of anomalously ample and long-lived fluctuations occurring in proximity of the liquid–liquid demixing region of the given lysozyme solutions. This allows determining the related sp…