James C. Alexander

Chronic Ethanol and Triglyceride Turnover in White Adipose Tissue in Rats INHIBITION OF THE ANTI-LIPOLYTIC ACTION OF INSULIN AFTER CHRONIC ETHANOL CONTRIBUTES TO INCREASED TRIGLYCERIDE DEGRADATION

Chronic ethanol consumption disrupts whole-body lipid metabolism. Here we tested the hypothesis that regulation of triglyceride homeostasis in adipose tissue is vulnerable to long-term ethanol exposure. After chronic ethanol feeding, total body fat content as well as the quantity of epididymal adipose tissue of male Wistar rats was decreased compared with pair-fed controls. Integrated rates of in vivo triglyceride turnover in epididymal adipose tissue were measured using 2H2O as a tracer. Triglyceride turnover in adipose tissue was increased due to a 2.3-fold increase in triglyceride degradation in ethanol-fed rats compared with pair-fed controls with no effect of ethanol on triglyceride synthesis. Because increased lipolysis accompanied by the release of free fatty acids into the circulation is associated with insulin resistance and liver injury, we focused on determining the mechanisms for increased lipolysis in adipose tissue after chronic ethanol feeding. Chronic ethanol feeding suppressed β-adrenergic receptor-stimulated lipolysis in both in vivo and ex vivo assays; thus, enhanced triglyceride degradation during ethanol feeding was not due to increased β-adrenergic-mediated lipolysis. Instead, chronic ethanol feeding markedly impaired insulin-mediated suppression of lipolysis in conscious rats during a hyperinsulinemic-euglycemic clamp as well as in adipocytes isolated from epididymal and subcutaneous adipose tissue. These data demonstrate for the first time that chronic ethanol feeding increased the rate of triglyceride degradation in adipose tissue. Furthermore, this enhanced rate of lipolysis was due to a suppression of the anti-lipolytic effects of insulin in adipocytes after chronic ethanol feeding.

GENERIC HOPF BIFURCATION FROM LINES OF EQUILIBRIA WITHOUT PARAMETERS III: BINARY OSCILLATIONS

We consider discretized systems of hyperbolic balance laws. Decoupling of the flow, associated with a central difference scheme, can lead to binary oscillations — even and odd numbered grid points, separately, provide time-evolutions of two distinct, different, separate profiles. Investigating the stability of this decoupling phenomenon, we encounter Hopf-like bifurcations in the absence of parameters. With some computer-algebra assistance, we describe the qualitative behavior near these bifurcation points. In particular we observe distinct even/odd profiles which oscillate periodically in time and, for arbitrarily fine discretization, exhibit preferred, nonzero phase relationships between adjacent discretization points.

²-well-posedness of 3d div-curl boundary value problems

Criteria for the existence and uniqueness of weak solutions of div-curl boundary-value problems on bounded regions in space with C 2 -boundaries are developed. The boundary conditions are either given normal components of the field or else given tangential components of the field. Under natural integrability assumptions on the data, finite-energy (L 2 ) solutions exist if and only if certain compatibility conditions hold on the data. When compatibility holds, the dimension of the solution space of the boundary-value problem depends on the differential topology of the region. The problem is well-posed with a unique solution in L 2 (Ω; Ρ 3 ) provided, in addition, certain line or surface integrals of the field are prescribed. Such extra integrals are described. These results depend on certain weighted orthogonal decompositions of L 2 vector fields which generalize the Hodge-Weyl decomposition. They involve special scalar and vector potentials. The choices described here enable a decoupling of the equations and a weak interpretation of the boundary conditions. The existence of solutions for the equations for the potentials is obtained from variational principles. In each case, necessary conditions for solvability are described and then these conditions are shown to also be sufficient. Finally L 2 -estimates of the solutions in terms of the data are obtained. The equations and boundary conditions treated here arise in the analysis of Maxwells equations and in fluid mechanical problems.

Finite-energy solutions of mixed 3d div-curl systems

This paper describes the existence and representation of certain finite energy (L 2 -)solutions of weighted div-curl systems on bounded 3D regions with C 2 -boundaries and mixed boundary data. Necessary compatibility conditions on the data for the existence of solutions are described. Subject to natural integrability assumptions on the data, it is then shown that there exist L 2 -solutions whenever these compatibility conditions hold. The existence results are proved by using a weighted orthogonal decomposition theorem for L 2 -vector fields in terms of scalar and vector potentials. This representation theorem generalizes the classical Hodge-Weyl decomposition. With this special choice of the potentials, the mixed div-curl problem decouples into separate problems for the scalar and vector potentials. Variational principles for the solutions of these problems are described. Existence theorems, and some estimates, for the solutions of these variational principles are obtained. The unique solution of the mixed system that is orthogonal to the null space of the problem is found and the space of all solutions is described. The second part of the paper treats issues concerning the non-uniqueness of solutions of this problem. Under additional assumptions, this space is shown to be finite dimensional and a lower bound on the dimension is described. Criteria that prescribe the harmonic component of the solution are investigated. Extra conditions that determine a well-posed problem for this system on a simply connected region are given. A number of conjectures regarding the results for bounded regions with handles are stated.

Gasous Hole Closing in a Polymer Langmuir Monolayer

The hole-closing phenomenon is studied in a polymer Langmuir film with coexisting gaseous and liquid phases both as a test of hydrodynamic theories of a two-dimensional fluid embedded in a three-dimensional one and as a means to accurately determine line tension, an important parameter determining size, shape, and dynamics within these and other membrane model systems. The hole-closing curve consists of both a universal linear regime and a history-dependent nonlinear one. Improved experimental technique allows us to explore the origin of the nonlinear regime. The linear regime confirms previous theoretical work and yields a value lambda = (0.69 +/- 0.02) pN for the line tension of the boundary between the gaseous and liquid phases. The observed hole closing also demonstrates that the two-dimensional polymer gas must be taken as having a small, probably negligible elasticity, so that line-tension measurements assuming that both phases are incompressible should be re-evaluated.

Hole dynamics in polymer Langmuir films

This article develops a model for the closing of a gaseous hole in a liquid domain within a two-dimensional fluid layer coupled to a Stokesian subfluid substrate, and compares this model to experiments following hole dynamics in a polymer Langmuir monolayer. Closure of such a hole in a fluid layer is driven by the line tension at the hole boundary and the difference in surface pressure within the hole and far outside it. The observed rate of hole closing is close to that predicted by our model using estimates of the line tension obtained by other means, assuming that the surface pressure in the gas is negligible. This result both supports the model and suggests an independent means of determining the line tension. Unlike most previous hydrodynamics models of Langmuir films, the closing of a hole necessarily involves vertical motion of the underlying incompressible fluid. Fluid is dragged along with the liquid monolayer towards the center of the hole, and must plunge away from the surface. An explicit expr...

Risk Neutrality and Ordered Vector Spaces

The following result clarifies when preferences over time and under risk correspond to discounting and are not risk neutral. If a binary relation on a real vector space V satisfies four axioms, then there is a utility function U=fu from V to R where u from V to R is linear as a map of vector spaces and f from R to R is continuous and weakly monotone. Three axioms are familiar: weak ordering, continuity, and non-triviality. The fourth axiom is X-Y is weakly preferred to 0 (where 0 is the zero element in V) implies X is weakly preferred to Y (X and Y in V). The function f from R to R is linear if and only if the binary relation also satisfies the converse of the fourth axiom. When V is a real vector space of stochastic processes and 0 is the zero process, it is known that the four axioms imply the existence of discount factors and the linearity of an intra-period utility function. So preferences correspond to discounting and are not risk neutral only if the converse of the fourth axiom is not satisfied.