Understanding the role of iron in the magnetism of Fe doped ZnO nanoparticles.

The actual role of transition metals like iron in the room temperature ferromagnetism (RTFM) of Fe doped ZnO nanoparticles is still an unsolved problem. While some studies concluded that the Fe ions participate in the magnetic interaction, others in contrast do not believe Fe to play a direct role in the magnetic exchange interaction. To contribute to the understanding of this issue, we have carefully investigated the structural, optical, vibrational and magnetic properties of sol-gel synthesized Zn1-xFexO (0 < x < 0.10) nanoparticles. No Fe(2+) was detected in any sample. We found that high spin Fe(3+) ions are substitutionally incorporated at the Zn(2+) in the tetrahedral-core sites and in pseudo-octahedral surface sites in ZnO. Superficial OH(-) was observed in all samples. For x ≤ 0.03, an increment in Fe doping concentration decreased a and c lattice parameters, average Zn-O bond length, average crystallite size and band gap; while it increased the degree of distortion and quadrupole splitting. Undoped ZnO nanoparticles exhibited very weak RTFM with a saturation magnetization (Ms) of ∼0.47 memu g(-1) and this value increased to ∼2.1 memu g(-1) for Zn0.99Fe0.01O. Very interestingly, the Ms for Zn0.99Fe0.01O and Zn0.97Fe0.03O increased by a factor of about ∼2.3 by increasing annealing for 1 h to 3 h. For x ≥ 0.05, ferrimagnetic disordered spinel ZnFe2O4 was formed and this phase was found to become more ordered with increasing annealing time. Fe does not contribute directly to the RTFM, but its presence promoted the formation of additional single charged oxygen vacancies, zinc vacancies, and more oxygen-ended polar terminations at the nanoparticle surface. These defects, which are mainly superficial, altered the electronic structure and are considered as the main sources of the observed ferromagnetism.

[Continuous epidural perfusion with meperidine on demand for the treatment of postoperative pain]. / Perfusión continua más demanda de meperidina por vía peridural en el tratamiento del dolor postoperatorio.

OBJECTIVE: To determine whether epidural administration of meperidine through a system affording patient-controlled analgesia (PCA) is appropriate for postoperative pain. PATIENTS AND METHODS: A prospective double-blind study of 30 patients undergoing high abdominal surgery randomly into two groups. After surgery with the same type of general anesthesia for both groups, group A received epidural meperidine through a PCA pump (initial boluses of 50 mg + infusion of 10 mg/h with additional doses of 25 mg upon patient demand and closure time of 90 min). Control group B received 0.9% saline serum through an epidural PCA system with identical perfusion characteristics. All patients had access to additional analgesia with subcutaneous meperidine (1 mg/kg weight). RESULTS: There was a wide interindividual variation in meperidine consumption in group A, with a mean total dose of 301.4 +/- 73 mg in 24 hours and no patient requiring additional subcutaneous meperidine. Subcutaneous meperidine required in group B reached 273 +/- 65.8 mg in 24 hours, with no significant differences between groups A and B for total dose given. No side effects inherent to the technique were found. Sufficient control of pain was achieved for all patients receiving epidural meperidine. CONCLUSIONS: Epidurally administered PCA with meperidine affords better pain relief with greater patient satisfaction than the same amount of drug given subcutaneously in successive doses upon patient request.

Growth patterns of two lines of Angus cattle selected using predicted growth parameters.

Linear functions of body weight and condition score at weaning and 18 mo of age were used to predict the mature weight (A) and maturing rate (k) parameters of an asymptotic growth model of Angus cows at the Subtropical Agricultural Research Station, Brooksville, FL. From 1981 through 1988 a heavy-mature-weight line (Line A) and a rapid-maturing line (Line K) were selected based on predicted A and k values. Linear contrasts (A-K) of least squares means for weight at fixed ages indicated that the weight difference between lines increased from birth to maturity during the period of the study. Animals from Line A were heavier (P less than .01) at all ages. A negative response in maternal ability, relative to increased growth potential of their calves, seems to have occurred in the cows of Line A. Mature weight was reached at approximately 4.5 yr of age in Line K and at approximately 5.5 yr in Line A. Brody's three-parameter and Richards' four-parameter functions were fitted to 2,855 quarterly weights of cows, from birth to 6.5 yr of age, to estimate the average growth curve for each line. Brody's model gave better estimates of weights from 18 mo to maturity, but the asymptotic residual mean squares were slightly higher because early weights were overestimated. Linear and nonlinear regression analyses of weight-age data and comparisons of degree of maturity at different premature ages showed differences in the growth patterns of the two lines selected for early predicted values of A and k.