SYNTHESIS OF A NOVEL POLYSACCHARIDE HYDROGEL

ABSTRACT

A modified hyaluronic acid (HA) biopolymer was synthesized that can be photocrosslinked to form a stable hydrogel. The chemical and physical properties including the amount of modification of the polymer with methacrylate anhydride, the viscosity of the modified biopolymer, and the solute diffusion characteristics of the polymer have been determined.     

GROWTH AND MEASUREMENT UNCERTAINTY IN AN UNREGULATED FISHERY

Abstract Complete information is usually assumed in harvesting models of marine and terrestrial resources. In reality, however, complete information never exists. Fish and wildlife populations often fluctuate unpredictably in numbers, and measurement problems are frequent. In this paper, we analyze a time‐discrete fishery model that distinguishes between uncertain natural growth and measurement error and in which exploitation takes place in an unregulated manner. Depending on the parameterization of the model and at which point of time uncertainty is resolved, it is shown that expected harvest under ecological uncertainty may be below or above that of the benchmark model with no uncertainty. On the other hand, when stock measurement is uncertain, expected harvest never exceeds the benchmark level. We also demonstrate that the harvesting profit, or rent, under uncertainty may be above that of the benchmark situation of complete information. In other words, less information may be beneficial for the fishermen.     

Temperature Dependence Kinetic Studies of the Reaction of O(3P) with CHI3 and C2H5I and the 298 K Reaction of OH(X2Π) with CHI3

A flash photolysis–resonance fluorescence technique was used to investigate the kinetics of the OH(X²Π) radical and O(³P) atom‐initiated reactions with CHI₃ and the kinetics of the O(³P) atom‐initiated reaction with C₂H₅I. The reactions of the O(³P) atom with CHI₃ and C₂H₅I were studied over the temperature range of 296 to 373 K in 14 Torr of helium, and the reaction of the OH (X²Π) radical with CHI₃ was studied at T = 298 K in 186 Torr of helium. The experiments involved time‐resolved resonance fluorescence detection of OH (A²Σ⁺ → X²Π transition at λ = 308 nm) and of O(³P) (λ = 130.2, 130.5, and 130.6 nm) following flash photolysis of the H₂O/He, H₂O/CHI₃/He, O₃/He, and O₃/C₂H₅I/He mixtures. A xenon vacuum UV (VUV) flash lamp (λ > 120 nm) served as a photolysis light source. The OH radicals were produced by the VUV flash photolysis of water, and the O(³P) atoms were produced by the VUV flash photolysis of ozone. Decays of OH radicals and O(³P) atoms in the presence of CHI₃ and C₂H₅I were observed to be exponential, and the decay rates were found to be linearly dependent on the CHI₃ and C₂H₅I concentrations. Measured rate coefficients for the reaction of O(³P) atoms with CHI₃ and C₂H₅I are described by the following Arrhenius expressions (units are cm³ s^?1): k_O+C2H5I(T) = (17.2 ± 7.4) × 10^?12 exp[?(190 ± 140)K/T] and k_O+CHI3(T) = (1.80 ± 2.70) × 10^?12 exp[?(440 ± 500)K/T]; the 298 K rate coefficient for the reaction of the OH radical with CHI₃ is k_OH+CHI3(298 K) = (1.65 ± 0.06) × 10^?11 cm³ s^?1. The listed uncertainty values of the Arrhenius parameters are 2σ‐standard errors of the calculated slopes by linear regression.     

Assessing isomeric structures of pincer-ligated ruthenium and osmium polyhydrides using density functional calculations

DFT calculations on a [N(SiH₂CH₂PH₂)₂]MH₃ model (M = Ru and Os) of experimentally known compounds show that the three H have different bonding modes for Ru (H + H₂) and for Os (three independent H). Calculation shows that the Ru(H)(H₂) compound adds H₂ to give an RuH(H₂)₂ substructure; the Os(H)₂ species adds H₂ to give the Os(H)₃(H₂) substructure. The impact of these intramolecular redox processes on bond lengths is discussed, as are attempts to provide an improved computational model of P(alkyl) _n without the introduction of additional alkyl atoms.