NMR and sedimentation studies of a polymeric steric stabilizer for alumina

The sedimentation behavior of alumina powder has been studied in the presence of poly-vinylpyrrolidone (PVP) and poly(vinylpyrrolidone-co-vinyl acetate) (PVP/VA) in both thermodynamically “good” and “poor” solvents for the PVP homopolymer. PVP/VA provides higher sediment densities than does its PVP homopolymer counterpart. Solutionstate ¹³C-T₁ spin-lattice relaxation measurements were made on analogous mixtures both with and without alumina powder. The NMR results suggest that the PVP/VA copolymer is anchored to the alumina powder surface by means of VA moieties, whereas the PVP moieties extend into the continuous phase of the slurry medium. Thus, the higher settling densities that are observed in the presence of PVP/VA can be attributed to a steric stabilization mechanism. © 1993 John Wiley & Sons, Inc.     

Solvation of ions—XX. The ferrocene—ferricinium couple and its role in the estimation of free energies of transfer of single ions

The ferrocene-ferricinium electrode (Pt/Foc, Fic⁺) was investigated in water, acetonitrile, ethanol, DMSO and DMF using single scan cyclic voltammetry and phase sensitive ac polarography. The oxidation-reduction is pseudo-reversible in all five solvents with an electrochemical rate constant of approximately 10⁻² cm/s. In all solvents a slow irreversible chemical step involving the ferricinium cation follows electron transfer, so that slow cyclic voltammetry or polarography rather than potentiometry is preferred if ferrocene is to be used as a reference electrode in non-aqueous solvents.

The Strehlow assumption, ΔG_tr(Foc) = ΔG_tr(Fic⁺ gives very different free energies of transfer of single ions from non-aqueous solvents to water when compared with the TATB assumption that ΔG_tr(Ph₄As⁺) = ΔG_tr(Ph₄B⁻). This discrepancy is likely to be because ferricinium is only a moderately large cation, so that ΔG_tr(Fic⁺) is less positive than ΔG_tr(Foc) for transfer to water. The discrepancy is not because of abnormal electrochemical behavior of the Pt/Foc, Fic⁺ electrode in water or other solvents. Values of E° vs nhe, H₂O in a variety of solvents based on the TATB assumption are presented.     

Mechanical properties and transition temperatures of copolymers of N-n-alkylacrylamides and vinylidene chloride

Mechanical and solution properties, melting transitions, torsional stiffness temperatures, T_f, and selected modulus-temperature curves are presented for copolymers of the N-n-alkylacrylamides with vinylidene chloride. Copolymers were prepared at 60°C across the range of compositions, using as comonomers N-n-butyl-, octyl-, dodecyl- and oleyl-acrylamide, which have amorphous side-chains, and N-n-octadecyl acrylamide and n-octadecyl acrylate whose side-chains are crystalline. The mechanical properties reflected the effect of the decline in backbone crystallinity and the simultaneous development of strong intermolecular interactions in the amorphous stage. Copolymers were stiff or showed brittle failure across the compositional range except when intermolecular forces were reduced (with n-octadrcyl acrylate) and side-chain crystallization eliminated (with N-oleylacrylamide). These systems and the n-dodecylacrylamide copolymers had yield strengths less than brittle strengths and substantial elongations. Backbone crystallinity was eliminated at about 15 mole % amide and side-chain crystallinity vanished at less than 10 mole % of the amide in the N-n-octadecylacrylamide series. No depression in side-chain melting point occurred with dilution by segments of vinylidene chloride. Over-all decline in the flex-temperature was the normal monotonic function of composition except that values increased in magnitude at high vinylidene chloride contents, the effect presumably being caused by the presence of crystallinity. An empirical equation was developed which permitted the calculation of T_f for any N-n-alkylacrylamide composition with any number of carbon atoms in the side-chain, above 3.     

Viscosity index. I. Evaluation of selected copolymers incorporating n-octadecyl acrylate as viscosity index improvers

Compositionally and structurally varied copolymers all containing n-octadecyl acrylate were prepared and evaluated as viscosity index improvers in a common base oil under conditions of low shear. Systems evaluated over a range of copolymer and blend composition were: copolymers of n-octadecyl acrylate with, respectively, methyl methacrylate, 2-ethylhexyl acrylate, and n-dodecyl acrylate; and homopolymers of poly(n-octadecyl acrylate), prepared with a wide range of molecular weights. Properties were compared with those of blends of commercial methacrylate copolymers (acryloids) which had been freed of their entraining liquid. Mixtures of base oil with copolymers of n-octadecyl acrylate and methyl methacrylate, compared at fixed SAE viscosities, were the most efficient of all blends studied. They had the smallest rate of change of viscosity with temperature (as measured by their ASTM slopes), particularly in the composition region of incipient polymer precipitation at room temperature. Efficiency of certain of these composition was somewhat greater than that of the acryloids. A parameter that related concentration and weight-average molecular weight was used to correlate all of the data for ASTM slope and viscosity. Empirical relations developed by using this parameter enabled rheological data to be estimated that agree within 6% of experimental values for the case of thermodynamically good base oil solvents. These data demonstrated the relatively small contributions of copolymer structure to viscosity index improvement.     

Pulmonary infiltrates in neutropenic patients with acute leukemia during chemotherapy: outcome and prognostic factors

STUDY OBJECTIVE: To determine predictors of mortality from pulmonary infiltrates in neutropenic patients with acute leukemia during chemotherapy, and the significance of those factors related to the underlying malignancy and its therapy as well as of those related to the severity of the illness associated with pulmonary infiltrates. DESIGN: A historical cohort study. SETTING: A university teaching hospital and tertiary referral center. PATIENTS AND METHODS: Overall, 53 patients with neutropenia during chemotherapy and with first episodes of pulmonary infiltrates during a 4-year period were studied. Prognostic analysis included 38 variables. Multivariate analyses were performed by logistic regression. RESULTS: The survival rate from pneumonia was 57% (30/53). The following eight parameters were significantly associated with death in univariate analysis: comorbidity present; development of "late" pulmonary infiltrates (> or = 14 days after hospital admission); heart rate > or = 100 beats/min; a ratio heart rate/systolic blood pressure (HR/SBP) > or = 1.2; urea nitrogen > 7 mmol/L; radiographic score > or = 3; neutropenia < 1.0x10(9)/L at the treatment end point; and failed complete remission. In a multivariate model including only parameters available at diagnosis of pulmonary infiltrates, the presence of a ratio HR/SBP > or = 1.2 and of a radiographic score > or = 3 remained independently associated with death. In a second model also including the evolutionary parameter neutropenia < or = 1.0x10(9)/L at the treatment end point, both parameters remained significant together with neutropenia <1.0x 10(9)/L at the treatment end point. The presence of a ratio HR/SBP > or = 1.2 was a strong marker of early death. CONCLUSION: Both therapy- and malignancy-associated neutropenia as well as the severity of illness associated with pulmonary infiltrates are independent prognostic factors. Patients with a ratio HR/SBP > or = 1.2 at diagnosis of pulmonary infiltrates suffer from potentially reversible acute illness, are at risk for early death and, therefore, may be appropriate candidates for treatment in an ICU.     

Interactive display of isosurfaces with global illumination

In many applications, volumetric data sets are examined by displaying isosurfaces, surfaces where the data, or some function of the data, takes on a given value. Interactive applications typically use local lighting models to render such surfaces. This work introduces a method to precompute or lazily compute global illumination to improve interactive isosurface renderings. The precompiled illumination resides in a separate volume and includes direct light, shadows, and intersections. Using this volume, interactive globally illuminated renderings of isosurfaces become feasible while still allowing dynamic manipulation of lighting, viewpoint and isovalue.     

Grafting of enzymes on collagen films using Woodward''s reagent "K" and a water-soluble carbodiimide derivative

Two new methods of activation were developed to graft enzymes on collegen films. They involved chemical modifications of surface groups of collagen either by Woodward's reagent "K" or by EDC, a water-soluble derivative of carbodiimide. EDC was a better coupling agent and a detailed study was conducted with this agent. It could be used either in a global method of activation and coupling, or in a two-step procedure of activation of collagen, followed by spontaneous coupling of enzyme. All enzymes tested were successfully bound: malate dehydrogenase, lactate dehydrogenase, aspartate aminotransferase, urease, creatine kinase, hexokinase. The influence on the yield of grafted enzyme, of pretreatment of films, time and temperature of EDC activation, concentration of EDC and enzyme, protecting agents was studied. Stability of enzyme activity on storage was greatly increased after grafting. A co-grafted dual system creatine kinase/heoxkinase, was achieved which exhibited a good efficiency. A striking renaturing process at 0-4degreesC after thermal denaturation, was observed with hexokinase.