Synthesis of Fibrin-Type I Collagen Biomaterials via an Acidic Gel

Fibrin-Type I collagen composite gels have been widely studied as biomaterials, in which both networks are usually formed simultaneously at a neutral pH. Here, we describe a new protocol in which mixed concentrated solutions of collagen and fibrinogen were first incubated at acidic pH to induce fibrinogen gel formation, followed by a pH change to neutral inducing collagen fiber formation. Thrombin was then added to form fibrin-collagen networks. Using this protocol, mixed gels containing 20 mg.mL⁻¹ fibrin and up to 10 mg.mL⁻¹ collagen could be prepared. Macroscopic observations evidenced that increasing the content of collagen increases the turbidity of the gels and decreases their shrinkage during the fibrinogen-to-fibrin conversion. The presence of collagen had a minor influence on the rheological properties of the gels. Electron microscopy allowed for observation of collagen fibers within the fibrin network. 2D cultures of C2C12 myoblasts on mixed gels revealed that the presence of collagen favors proliferation and local alignment of the cells. However, it interferes with cell differentiation and myotube formation, suggesting that further control of in-gel collagen self-assembly is required to elaborate fully functional biomaterials.     

Two parabolic generator kleinian groups

This paper is concerned with torsion-free Kleinian groups that are generated by two parabolic transformations. Our main result is that every such group of the second kind is geometrically finite; this is in response to a question raised by Riley. We also show that in the natural one (complex) dimensional setting, the space of torsion-free Kleinian groups of the second kind is path-connected. The first author was supported in part by NSF Grant #8701774.     

Spin asymmetry in γe ↑→e+2 jets: A laboratory for final state interactions

We isolate final state interactions not parametrized by fragmentation functions and yet present in QCDO(α _s ) corrections to two-jet production in photon-longitudinally polarized electron scattering. Our calculation focuses on dynamical imaginary (absorptive) corrections that are absent in any tree diagrams. We explicitly demonstrate cancellation of imaginary infinities in the sum over graphs. The resulting asymmetry is predicted to be small. Such a quantity should be soon measured in experiments exploiting the naturally large electron polarization occurring in standard high energy storage rings.     

Functions of bounded boundary rotation

Classes of functionsU _k, which generalize starlike functions in the same manner that the classV _k of functions with boundary rotation bounded bykπ generalizes convex functions, are defined. The radius of univalence and starlikeness is determined. The behavior off _α(z) = ∫ ₀ ^z [f'(t)]^α dt is determined for various classes of functions. It is shown that the image of |z|<1 underV _kfunctions contains the disc of radius 1/k centered at the origin, andV _k functions are continuous in |z|≦1 with the exception of at most [k/2+1] points on |z|=1.     

Integral means of analytic functions

Sharp bounds for general integral means of analytic functions in the unit disc are determined. These bounds depend only on the moduli of the points on the boundary of the image domain nearest to and farthest from the origin. The proof is shown to be a simple application of a deep theorem of A. Beurling in potential theory.     

Multi electron capture processes in slow collisions between X<Superscript>7+</Superscript> (X = N,O and Ne) ions with C<Subscript>60</Subscript>

Electron capture processes in collision between slow X⁷⁺ (X = N, O and Ne) ions and C₆₀ fullerene have been investigated using coincident measurements of the number n of ejected electrons, the mass and charge of the multicharged C₆₀ ^r+ recoil ions and their fragments C_m ⁱ⁺ and the final charge state of the outgoing projectiles X^(q-s)+ ( ). The collision velocity is about 0.4 a.u. The partial cross-sections σ_r ^s , corresponding to r electrons transferred to the projectile with only s electrons stabilized, have been measured. Cross-sections for collisions “inside” and those “outside” the C₆₀ cage have been separated by analyzing the kinetic energy of the outgoing projectile. The mean final charge state for frontal collisions has been measured to 3.1, 2.6 and 2.5 for N⁷⁺, O⁷⁺ and Ne⁷⁺ respectively. These results show the importance of the core effect on the stabilisation processes of captured electrons.     

Photophysics of Calix[4]biscrown-Based Ditopic Receptors of Caesium Containing One or Two Dioxocoumarin Fluorophores

The ditopic receptors Calix-COU1 and Calix-COU2 consist of a calix[4]biscrown containing one or two dioxycoumarin fluorophores, respectively, inserted into the crown. They can form 1:1 and 2:1 (metal:ligand) complexes with caesium ions. The photophysical properties of the 1:1 complexes can be explained by (i) cation tunneling through the tube-shaped cavity (composed of the four phenyl rings) of the calix[4]biscrown, (ii) photodisruption of the interaction between the bound cation and the oxygen atoms belonging to both the coumarin moiety and the crown, (iii) photoinduced motions of the cation.     

Thermal lensing of laser beams in optically transmitting materials

Detailed numerical computations of thermal lensing in optically transmitting materials are carried out. The time evolution of the transmitted beam intensity, revealing defocusing and degradation effects, is displayed for a variety of materials, under a variety of geometrical configurations and operating conditions. While the degradation is monotonic with increasing time or incident power for materials with small induced birefringence, it may display an oscillatory character when birefringence effects are large. From the intensity degradation, criteria are formulated for rating optical performance of materials under transient and steady-state conditions. Ratings are obtained for a variety of transmitting materials at 10.6 μm. As a class, ionic materials are found to substantially outperform semiconductors and glasses at 10.6 μm.