Assurance of lubricant supply in wet-lubricated space bearings

Conventional lubrication techniques appear to be satisfactory, but rigorous proof of meeting a ten-year life requirement is lacking. One approach provides additional lubricant only when commanded from ground control, while the other passively augments lubrication at all times. Each technique has specific advantages, and selection should be related to the application to obtain optimum performance

Is inequitable teacher sorting on the rise? Cross-national evidence from 20 years of TIMSS

Unequal access to qualified teachers for children of different socioeconomic status—also known as inequitable teacher sorting—has been increasingly put forth as one potential factor contributing to the socioeconomic achievement gap. Despite this, few studies have investigated cross-national differences in teacher sorting, and none have examined it within-countries over time. International large-scale assessments in education are uniquely positioned to answer such questions due to their longitudinal nature at the system level. This study uses six waves of data from the Trends in International Mathematics and Science Study (TIMSS) from 1999 to 2019 for 32 education systems. We compare differences in grade 8 mathematics teacher qualifications for each country at each time point, across top and bottom groups on the student socioeconomic spectrum. Results show that on the whole many countries display negligible gaps in access to teacher quality, with some key exceptions. With respect to inequity in novice teacher sorting, the problem is most prevalent in low- and middle- income education systems (i.e. in Turkey, Morocco, Tunisia and Indonesia). Inequity in sorting based on mathematics education is less common, with no clear pattern in regards to level of economic development (i.e. in Chile, Australia, New Zealand, and Chinese Taipei). Socio-economic inequality in teacher sorting has also remained broadly stable over time. Based on experience and mathematics education, less than a handful of systems show systematic upward trends in teacher sorting inequity (i.e. in Chile, Morocco, Singapore, and New Zealand). Given the increasing focus on inequity in access to teacher competence, these results have economic and policy implications for tackling the socioeconomic achievement gap

Measurement of Population Growth and Decline During California Prehistory

The distribution through time of radiocarbon dates is an important source of information about regional population fluctuation. However, a number of factors affecting distributional patterns must be considered when inferring changes in relative population size. Because these factors often are difficult to control, fluctuation in a date distribution is best considered a source of hypotheses about population growth and decline that should be tested against other sources of data. Three date distributions pertaining to the Santa Barbara Channel mainland coast, the northern Channel Islands, and the Vandenberg region exemplify the potential of this approach. These areas show similarities that may be linked to the impact of environmental events affecting broad geographic areas, as well as to differences that appear to reflect the impact of differing environments on cultural development. Future use of radiocarbon date distributions will be enhanced if archaeologists make every effort to obtain dates for every site investigated, take greater care in selecting samples, and report dating results in a systematic format