Isosorbide‐based polysebacates as polymeric components for development of in situ forming implants

In situ forming implants (ISFIs) appear to be a convenient drug delivery system, alternative to conventional preformed implants and microparticles for parenteral drug delivery applications. It has been shown that they offer several advantages including easy and minimally invasive application, potential for local/site‐specific drug delivery that allows reduction of side effects associated with systemic administration of drug. A few ISFI formulations based on poly(α‐hydroxy acids), solidifying by solid phase separation, are currently commercially available. In this work, polyesters based on sebacic acid, isosorbide, and optionally 1,2‐propanediol were synthesized and characterized. Poly(isosorbide sebacate‐co‐1,2‐propylene sebacate) (PISEBPG) was chosen as an essential constituent of new ISFI formulations dedicated to controlled release of doxycycline hyclate (DOXY). Basic characteristics of new ISFI formulations were investigated. In particular, the influence of addition of a relatively hydrophobic cosolvent (triacetin, TA) to a more hydrophilic 1‐methyl‐2‐pyrrolidone (NMP) as well as the presence of calcium carbonate (CAC) on the morphology of resulted depots and DOXY release profile was evaluated. Scanning electron microscopy (SEM) analysis revealed that the presence of TA resulted in more porous morphology of the depots. DOXY has been releasing continuously from depots in vitro within 12 weeks depending on the composition. The release profile of the PISEBPG‐based formulation containing CAC indicates that it could be useful where short‐term (up to 14 d), rapid release of the antibiotic is required, while formulation without CAC, where after 21 days about 50% of the drug loaded may still be available for release, may be better for the long‐term delivery of DOXY.     

Large-Nc confinement and turbulence

We suggest that the transition that occurs at large N_{c} in the eigenvalue distribution of a Wilson loop may have a turbulent origin. We arrived at this conclusion by studying the complex-valued inviscid Burgers-Hopf equation that corresponds to the Makeenko-Migdal loop equation, and we demonstrate the appearance of a shock in the spectral flow of the Wilson loop eigenvalues. This picture supplements that of the Durhuus-Olesen transition with a particular realization of disorder. The critical behavior at the formation of the shock allows us to infer exponents that have been measured recently in lattice simulations by Narayanan and Neuberger in d=2 and d=3. Our analysis leads us to speculate that the universal behavior observed in these lattice simulations might be a generic feature of confinement, also in d=4 Yang-Mills theory.     

A model for “cold” laser ablation of green state ceramic materials

This paper reports calculations of predicted values of the key process parameters associated with “cold” laser ablation of ceramic materials in the green state. A model for material removal of composite organic/ceramic materials is proposed and verified experimentally by laser ablation measurements and ultrafast videography. An energy balance approach is used with the model to calculate values of threshold fluence, material removal rate and particle escape velocity, which are seen to be in good agreement with experimental results. Suggested values for optimised laser machining of LTCC are proposed. PACS 79.20.Ds; 42.62.Cf; 42.55.Lt; 81.20.Wk     

High-order Talbot fringes for atomic matter waves

We observe the interference of de Broglie waves in the diffraction near field of a microfabricated grating. The reduction of the grating period by self-imaging of second to seventh order is spatially resolved. We investigate the dependence of this effect on the de Broglie wavelength by a time-to-flight technique.     

Compact Hankel operators with conjugate analytic symbols

In 1986 S. Axler [3] proved that forf∈L _a ² the Hankel operator is compact if and only iff is in the little Bloch space {itB}{in0}. In this note we show that the same is true for , 1<p<∞. Moreover we prove that is ⋆-compact if and only if as |z|→1⁻.     

Complexation copper(II) or magnesium ions with d-glucuronic acid – potentiometric,spectral and theoretical studies

Results of potentiometric and spectral studies have shown that in d-glucuronic acid (GluA) with Cu²⁺ or Mg²⁺ systems, the complexes ML and ML(OH)_x are formed. Overall stability constants (log β) and equilibrium constants (log K_e) were calculated for all complex forms. The mode of coordination for each form was concluded on the basis of spectral values, Vis, EPR, and chemical shifts in the ¹³C NMR. According to spectral analysis, Cu(GluA) exists in two possible forms, which confirm the occurrence of the coordination dichotomy in the system. The main center of interactions in the hydroxyl complexes Cu(GluA)(OH)_x and MgGluA are oxygens from the carboxyl group. Differences in the coordination mode in the copper(II) and magnesium systems at low pH were observed.     

Globular structures of a helix-coil copolymer: self-consistent treatment

A self-consistent-field theory was developed in the grand canonical ensemble formulation to study transitions in a helix-coil multiblock globule. Helical and coil parts are treated as stiff rods and self-avoiding walks of variable lengths correspondingly. The resulting field theory takes, in addition to the conventional Zimm-Bragg, [J. Chem. Phys. 31, 526 (1959)] parameters, also three-dimensional interaction terms into account. The appropriate differential equations which determine the self-consistent fields were solved numerically with finite element method. Three different phase states are found: open chain, amorphous globule, and nematic liquid-crystalline (LC) globule. The LC-globule formation is driven by the interplay between the hydrophobic helical segment attraction and the anisotropic globule surface energy of an entropic nature. The full phase diagram of the helix-coil copolymer was calculated and thoroughly discussed. The suggested theory shows a clear interplay between secondary and tertiary structures in globular homopolypeptides.     

Universality in three dimensional random-field ground states

We investigate the critical behavior of three-dimensional random-field Ising systems with both Gauss and bimodal distribution of random fields and additional the three-dimensional diluted Ising antiferromagnet in an external field. These models are expected to be in the same universality class. We use exact ground-state calculations with an integer optimization algorithm and by a finite-size scaling analysis we calculate the critical exponents , , and . While the random-field model with Gauss distribution of random fields and the diluted antiferromagnet appear to be in same universality class, the critical exponents of the random-field model with bimodal distribution of random fields seem to be significantly different. Received: 9 July 1998 / Received in final form: 15 July 1998 / Accepted: 20 July 1998     

Sensitive equilibria for ergodic stochastic games with countable state spaces

We consider stochastic games with countable state spaces and unbounded immediate payoff functions. Our assumptions on the transition structure of the game are based on a recent work by Meyn and Tweedie [19] on computable bounds for geometric convergence rates of Markov chains. The main results in this paper concern the existence of sensitive optimal strategies in some classes of zero-sum stochastic games. By sensitive optimality we mean overtaking or 1-optimality. We also provide a new Nash equilibrium theorem for a class of ergodic nonzero-sum stochastic games with denumerable state spaces.