EFFECT OF COMPOSITION AND THERMAL HISTORY ON DIELECTRIC CONSTANTS OF SODA-BOROSILICATE GLASSES*

The dielectric constants, densities, and refractive indices of two series of soda-boro-silicate glasses were measured at 25° C. on some quenched specimens and on other specimens that were stabilized at different temperatures. The compositions of the two series were Na₂O-4.69 SiO₂-B₂O, (0 to 45%) and Na₂O B₂O₃-SiO₂ (30 to 100%), respectively. The structure of the glasses was found to depend on the ratio of oxygen atoms to the sum of the boron and silicon atoms and also on the concentration of the sodium ions. If the ratio of O to B + Si is greater than 2.0 or if the ratio of oxygen to sodium ions is less than 6.0, some of the oxygens are bonded only to one boron or to one silicon atom. The presence of “single-bonded” oxygen atoms in the glass structure leads to a lower density and a higher dielectric constant and refractive index. The dielectric constant decreases and the density increases continuously as the temperature of heat treatment is lowered. The effect of heat treatment is greater for the glasses which contain the larger number of “single-bonded” oxygen atoms and the higher concentration of sodium ions.     

Measuring concentrations of insulin-like growth factor-I with an enzyme-linked immunosorbent antibody assay in plasma samples from Holstein cows

This study describes the use of a commercial nonextraction ELISA to quantify total concentrations of insulin-like growth factor-I (IGF-I) in plasma samples from Holstein cows fed pasture-based diets varying in dry matter and metabolizable energy density. The assays were conducted using the protocols provided by the manufacturer. The ELISA was verified for linearity, accuracy in measuring IGF-I from spiked plasma samples, and precision involving variation within and between assays. Validation also involved comparing results of the ELISA against an established RIA after defatted plasma samples were subjected to acid gel HPLC to dissociate and separate IGF and IGF binding protein complexes. Validation results had low coefficients of variation (CV; intraassay CV of less than 6% and interassay CV of less than 8%) and a high recovery percentage of IGF-I (79%) from samples spiked with unbound IGF-I. The coefficients of determination between the ELISA and the RIA reference assay were 0.90 in 2 separate assays. Associations between the RIA and the ELISA were higher, and the limits of agreement at 95% confidence intervals were narrower compared with those between the RIA and a modified ELISA procedure in which IGF binding protein complexes were extracted using HPLC. The samples were obtained from cows sampled over a period of 5 wk. These results demonstrated that the DSL-10-2800 nonextraction IGF-I ELISA was acceptably specific and sufficiently sensitive to be used to measure the extent and patterns of change in the plasma concentrations of IGF-I in samples from lactating Holstein cows.     

Variation in plasma concentrations of insulin-like growth factor-I in pasture-fed Holstein cows

The objective of this 5-wk study was to determine dietary effects on plasma concentrations of insulin-like growth factor-I (IGF-I), as well as milk production and milk components in pasture-fed dairy cows. Thirty-two Holstein cows 4 to 5 wk postpartum were randomly assigned to 4 dietary subgroups. Feed was provided twice daily ad libitum at 0900 and 1600 h composed of fresh-cut pasture, meadow hay, and pelleted cereal grain to achieve differing levels of DMI and ME density (LL: 16.6 kg of DMI and 174 MJ of ME; HL: 17.3 kg of DMI and 181.1 MJ of ME; LH: 15.4 kg of DMI and 183.1 MJ of ME; HH: 17.9 kg of DMI and 213.3 MJ of ME, with the first letter indicating DMI and the second ME, and with H indicating high and L indicating low, respectively). The first day cows were placed on their diets was designated d 0. Concentrations of IGF-I were measured in frozen-thawed samples of plasma using a verified ELISA. Dietary treatment had affected plasma concentrations of IGF-I by d 7 with cows on high ME diets having greater IGF-I concentrations at d 14 (83.7 vs. 45.6 ng/mL) than cows on the low ME diets. The level of DMI had less effect on plasma concentrations of IGF-I at d 14 (72.2 vs. 57.1 ng/mL). Dietary treatment effects on these concentrations had stabilized by d 21. Day-to-day variation in mean plasma concentrations of IGF-I within each dietary treatment was low during an intensive period of daily sampling for 14 d (from d 22 to 35). Within-cow day-to-day variation was also low compared with that among cows within the same dietary group and was associated with a high repeatability in the day-to-day concentration of IGF-I in individual cows. Intraclass correlation coefficients for IGF-I ranged from 0.56 (± 0.14) to 0.88 (± 0.06) with a combined (pooled) value for the 4 subgroups of 0.77 (± 0.05). The ME and DMI effects (H vs. L) at d 35 were 79.3 vs. 41.4 and 62.0 vs. 55.7 ng/mL, respectively. Although the ME and DMI differences also affected milk yield and compositional parameters, the effects were not as proportionately great as those measured for IGF-I. Altering the ME or DMI components of the pasture-based diets produced changes in plasma IGF-I concentrations that did not become stabilized for 3 wk, but were then highly repeatable for individual cows within each dietary group. Both observations have relevance to interpreting data related to plasma concentrations of IGF-I in lactating Holstein cows.     

Incorporating the service accomplishments into pre-registration curriculum to enhance reflective practice

Much emphasis is being placed on the importance of reflective practice as a means to ensure that practitioners are competent in their practice. It is therefore important to ensure that student nurses acquire these reflective skills as part of their development throughout pre-registration curricula. Although reflective practice is seen as a major part of curricula activity, the style in which reflection is advocated takes many different formats. Strategies for developing reflection which focus on outcomes for students can become subjective and fail to place healthcare practice within the context of social structures and values. This paper offers a framework for reflection that promotes an outlook which is both objective and subjective, based on Mezirow's six levels of reflection (as adapted by Powell 1989) and O'Brien's (1987) five service accomplishments. Focus of reflection within the wider context of society and healthcare policy should enable development of a practitioner who is both competent in practice and can analyse and evaluate their practice.