Thermal conductivity of bulk ZnO after different thermal treatments

Thermal conductivities (κ) of melt-grown bulk ZnO samples thermally treated under different conditions were measured using scanning thermal microscopy. Samples annealed in air at 1050°C for 3 h and treated with N-plasma at 750°C for 1 min. exhibited κ=1.35±0.08 W/cm-K and κ=1.47±0.08 W/cm-K, respectively. These are the highest values reported for ZnO. Atomic force microscopy (AFM) and conductive-AFM measurements revealed that surface carrier concentration as well as surface morphology affected the thermal conductivity.     

Diffractive light trapping in crystal-silicon films: experiment and electromagnetic modeling

Diffractive light trapping in 1.5 μm thick crystal silicon films is studied experimentally through hemispherical reflection measurements and theoretically through rigorous coupled-wave analysis modeling. The gratings were fabricated by nanoimprinting of dielectric precursor films. The model data, which match the experimental results well without the use of any fitting parameters, are used to extract the light trapping efficiency. Diffractive light trapping is studied as a function of incidence angle, and an enhancement of light absorption is found for incidence angles up to 50° for both TE and TM polarizations.     

Degradation kinetics of DMP 777, an elastase inhibitor

PURPOSE: The objective was to evaluate the degradation profile of the elastase inhibitor DMP 777 and lay the foundation for formulation development. METHODS: The pKa was determined by potentiometric titration in mixed-aqueous solvents. The degradation kinetics were studied as a function of pH, buffer concentration, ionic strength, methanol concentration and temperature using a stability-indicating HPLC assay. The degradation products were identified by LC-MS, NMR, and by comparison with authentic samples. RESULTS: The pKa for the protonated piperazine nitrogen was estimated to be 7.04. The pH-rate profile is described by specific acid-, water-, and specific base-catalyzed pathways. The pH of maximum stability is in the range of 4 to 4.5 where water is the principal catalyst in the reaction. Buffer catalysis, primary salt effects and medium effects were observed. The proposed mechanism for acid catalyzed degradation is the rarely observed AAL1 which involves alkyl-nitrogen heterolysis. The driving force for the reaction appears to lie in the stability of the benzylic carbocation. The proposed mechanism for base catalyzed degradation is BAC2 which involves beta-lactam ring opening. The beta-lactam ring of DMP 777, a monolactam, appears to be as reactive as that in benzylpenicillin in the KOH controlled region where a similar mechanism of hydrolysis should be operative. A contributing factor to this increased reactivity may lie in the reduced basicity of the beta-lactam nitrogen making it a good leaving group. CONCLUSIONS: The degradation profile indicates that development of a solution dosage form of DMP 777 with adequate shelf-life stability at room temperature is feasible.     

Thermal polycondensation of ammonium paratungstate, (NH4)10[W12O40(OH)2].4H2O

Connected with the examination of the thermal polycondensation of ammonium paratungstate pentahydrate the chemical and morphological properties of intermediate phases formed during the thermal decomposition of APT have been investigated. We have studied the pH and the turbidity of the aqueous solutions of the intermediate phases, the solubility of the phases, and their rehydratation capability as well as the morphology of the crystallite granules and the grain size distribution. These properties of the original APT have been related to the same properties of the products of decomposition formed between different temperature ranges. The results obtained show unambiguously that each of the above mentioned properties suddenly changes in the temperature range 225 to 250°C. This temperature range coincides with the formation temperature of a new phase called APT II. The most probable formula of APT II is (NH₄)₈ [H₂W₁₃O₄₃(OH)₂]·H₂O.     

Effect of a prolonged-release formulation of N-methionyl bovine somatotropin (sometribove) on milk fat.

Nine Holstein cows were injected bi-weekly with a prolonged-release formulation of N-methionyl bST, and 9 cows were injected with excipient. Intramuscular injections began at 60 +/- 3 d postpartum and continued at 14-d intervals for the full lactation. Administration of bST increased production of milk, total fat, and all milk fat components measured. Average fatty acid composition of milk fat was not influenced by bST treatment. Stage of lactation had a large influence on production and percentage of individual fatty acids in milk fat from both bST-treated and control cows. The stage of lactation impact on the fatty acid composition of milk fat reflected changes in the relative contributions of body fat mobilization and de novo synthesis of milk fat components in response to changes in energy balance. Initiation of bST treatment caused some transient changes in milk fatty acid composition that were related to energy balance. These changes were small compared with the normal changes because of stage of lactation in all cows. Phospholipid and cholesterol content of milk also changed with stage of lactation but were not influenced by bST treatment. Melting properties of milk fat were influenced greatly by stage of lactation. Bovine somatotropin did not cause any changes in composition or physical properties of milk fat that were outside the range of normal variation.