Ventilation effects on humidity measurements in thermometer screens

Relative humidity (RH) measurements, as derived from wet-bulb and dry-bulb thermometers operated as a psychrometer within a thermometer screen, have limited accuracy because of natural ventilation variations. Standard RH calculations generally assume a fixed screen psychrometer coefficient, but this is too small during poor ventilation. By comparing a reference humidity probe—exposed within a screen containing a psychrometer—with wind-speed measurements under controlled conditions, a wind-speed correction for the screen psychrometer coefficient has been derived and applicable when 2-metre wind speeds fall below 3 ms–1. Applying this to hourly-averaged data reduced the mean moist RH bias of the psychrometer (over the reference probe) from 1.2% to 0.4%, and reduced the inter-quartile range of the RH differences from 2.0% to 0.8%. This correction is particularly amenable to automatic measurement systems

The origin of Sr segregation at La1-xSrxMnO3 surfaces

A uniform distribution of La and Sr in lanthanum-strontium manganites would lead to charged crystal planes, a charged surface, and arbitrarily large surface energy for a bulk crystal. This divergent energy can be eliminated by depleting the La concentration near the surface. Assuming an exponential form for segregation suggested by experiment, the total electrostatic energy is calculated, depending only upon the decay length and on an effective charge Z* associated with the La ion. It is found to be lower in energy than neutralization of the surface by changing Mn charge states, previously expected, and lower than simply readjusting the La concentration in the surface plane. The actual decay length obtained by minimizing this electrostatic energy is shorter than that observed. The extension of this mechanism to segregation near the surface in other systems is discussed

Leadership in Private Christian Schools: Perceptions of Administrators

The purpose of this exploratory qualitative study was to discover the perceptions of private Christian school administrators about leadership characteristics, roles, and teacher professional development. The co-researchers first conducted a demographic survey and focus group interviews with six administrators from K-12 or secondary private Christian schools in Oregon and Washington. Themes that surfaced from the data were who we are as leaders, success and celebration, and what we do as leaders. Results showed that administrators of private Christian schools tended to focus on the importance of the vision and mission of their schools, keeping in mind their influence as spiritual leaders and the importance of problem solving and decision making. Servant leadership was identified as well. However, little information was shared about how they supported teacher professional development or student academic achievement