Effect of Hydration on Silk Film Material Properties

Effects of hydration on silk fibroin film properties were investigated for water‐annealed and MeOH‐treated samples. Hydration increased thickness by 60% for MeOH‐immersed films, while water‐annealed samples remained constant. MeOH‐immersed films showed an 80% mass loss due to water, while water‐annealed lost only 40%. O₂ permeability was higher in MeOH‐immersed films with Dk values of 10^?10 (mL O₂ · cm) · (cm^?1 · s^?1 · mmHg^?1), while those of water‐annealed films reached only one fifth of this value. All films showed a decrease in Young's modulus and increased plastic deformation by two orders of magnitude when submerged in saline solution. FT‐IR showed that β‐sheet content in water‐annealed films increased with increasing water vapor pressure, while MeOH‐immersed films showed no change.

     

Über zwei Fragen der Theorie des Extremums eines einfachen Integrals

Ohne Zusammenfassung     

Chirality, surface anchoring, and the cholesteric-smectic A phase transition

Magnetic Freedericksz transition measurements were performed on samples of chiral and racemic mixtures in the cholesteric/nematic phase. We found that the quantity Ф, which is defined as the threshold field H_th times the cell thickness, is larger for the chiral than for the racemic mixtures. This result is inconsistent with chiral contributions to the anchoring strength potential. Instead, the data support a model by Lubensky wherein the transition temperature to the smectic A phase is suppressed in a chiral liquid crystal.     

Differential and ergodic transforms

In this paper we consider weighted differences of ergodic averages and averages associated with differentiation. These weighted differences are shown to converge a.e., as well as in . These results have consequences for unconditional convergence of the series of differences, and give some information about how the averages converge. Received: 6 March 2000 / Published online: 4 April 2002     

Collapse dynamics of liquid bridges investigated by time-varying magnetic levitation

Using a novel technique that facilitates temporal control over the total body force on a liquid, an unexpected scaling relationship was discovered for the collapse time of a liquid bridge. A paramagnetic liquid was suspended between the tips of two collinear rods in a strong magnetic field gradient that was adjusted to compensate gravity. A sudden change of the magnet current, corresponding to a change of Bond number, resulted in a deformation and ultimate collapse of the liquid bridge. The collapse time was found to be independent of the bridge length when other parameters were held constant.     

Thermal diffusivities of group V semimetals

A flash method, employing a pulsed flashlamp-pumped dye laser has been used to determine the thermal diffusivities of elemental arsenic, antimony, and bismuth. Measurements were made both on poly-crystalline samples and on oriented single crystal (111) wafers in the form of small disks 3.0?7.0 mm in diameter, and 0.43–1.33 mm thick. Thermocouples (0.076 mm dia) monitor the back surface temperature as a function of time after the front of the sample is exposed to a single laser pulse of pulse width (τ) <1.0 μsec. The room temperature thermal diffusivities α (cm²/sec) of polycrystalline As, Sb and Bi are respectively: 0.234, 0.182 and 0.0651. The diffusivities parallel to the trigonal crystal axis α₁ are: 0.119,0.142 and 0.0350. Measurements on polycrystalline Cu, Al and Ti yield 1.13, 0.96 and 0.085 cm²/sec, in agreement with literature values.     

Control of release kinetics of macromolecules from polymers

Internal and external means for controlling the release rates of large molecules, such as proteins, from ethylene—vinyl acetate copolymer matrices are presented. Internal approaches include alteration of the polymer—drug design, such as changing drug loading and particle size, coating the matrix, or altering matrix geometry. Kinetic and microstructural analyses are discussed. Applications of these polymeric systems, for instance, in delivery of insulin for diabetes, improved immunization procedures, and in developing bioassays for informational macromolecules are considered. In addition, a new approach for externally controlling release rates of drugs using magnetism has been developed. Until now, drug delivery systems were capable of delivering drugs at either constant or decreasing rates. We sought a system that permitted delivery of increased doses on demand, and achieved this by incorporating magnetic particles and drugs into polymeric matrices. Drug release rates can then be increased by an appropriate application of an external magnetic field. Over a five-day period, the magnetic field was applied ten times and drug release rates increased by up to 100% each time. Initial results indicate that this system does not cause tissue damage.