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

Teacher sorting and the opportunity gap: a cross-national investigation of institutional differentiation and educational equity

Inequitable access to teacher competence (‘teacher sorting’ or the teacher ‘opportunity gap’) is increasingly the focus of international educational bodies worldwide but is still relatively underexplored empirically. The overarching purpose of this doctoral thesis is to investigate the relationship between teacher sorting and educational inequity from a cross-national perspective, while empirically addressing theoretical questions related to social reproduction and inequality of educational opportunities in school systems. A final aim is to provide empirically grounded policy recommendations related to the findings. With these aims in mind, the constituent studies in the thesis cover several facets of the phenomenon of teacher sorting: the magnitude and development cross-nationally over the past two decades, the impact on inequity in student test scores, as well as the associated institutional features. The data come from international large-scale assessments such as the Trends in International Mathematics and Science Study (TIMSS, 1999-2019) and the Teaching and Learning International Survey (TALIS, 2018), and include 32 and 46 education systems, respectively, with a special focus on mathematics and science teachers. The main analytical approaches include descriptive statistical methods, panel data regressions with country fixed effects, and hierarchical generalized linear modelling. The dissertation is comprised of four empirical studies. Study I investigates the magnitude of teacher sorting cross-nationally as well as its development since 1999. Results show that the magnitude of inequity varies by the country and teacher qualification in focus. Few countries show widening inequities in the teacher qualification gaps. Study II investigates the impact of teacher sorting on mathematics achievement inequity and finds that more pronounced sorting by specialization exacerbates inequity in student achievement, and that this finding remains marginally significant after controlling for increasing socioeconomic school segregation. Studies III and IV investigate policy- and institution-level correlates of teacher sorting and teacher turnover, respectively. The results of Study III show a general pattern of mixed results related to stratification, accountability, autonomy, and competition, depending on the teacher quality indicator in focus. National economic development level as well as school competition were positively related to the slope on more than one occasion, however. Study IV found a more pronounced relationship between teacher turnover intentions and classroom SES in school systems with more widespread use of external accountability practices with student performance data. The results point to several key conclusions. First, there was evidence of inequity in teacher sorting across many educational systems to varying degrees. The patterns varied depending on how teacher qualifications and socioeconomic status were measured as well as how students were grouped. Next, the studies provided mixed results regarding school autonomy, accountability, competition and stratification, indicating that the determinants of socioeconomic teacher sorting do not easily generalize according to cross-national patterns. School competition was the single system-level variable to be associated with both qualifications. Despite this, performance data-based accountability (teacher appraisal) was consistently associated with higher turnover intention rates in low-SES settings. Appraisal of teacher performance for those working in lower-SES classrooms should rely on metrics other than performance data and should be conducted by those with appropriate knowledge of the school context. With respect to inequity in student outcomes, socioeconomic teacher sorting by specialization was found to have a modest effect. In most cases, priority should be given to democratizing access to teachers with appropriate content knowledge, but educational systems must go beyond providing socioeconomically disadvantaged students with teachers with basic qualification levels. While incentivizing the most competent teachers to work in socioeconomically disadvantaged settings is an ongoing challenge for many educational systems, building upon the content knowledge of underqualified mathematics teachers currently working in hard-to-staff settings is a worthwhile endeavor. Last, while reducing teacher sorting by specialization is likely to alleviate some degree of inequity in educational outcomes, it is not a panacea in the wider context of rising income inequality and social segregation in many educational systems

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

The Occurrence of Red Abalone Shells in Northern Channel Island Archaeological Middens: Implications for Climatic Reconstruction

Certain archaeological sites on the northern Channel Islands dating between ca. 4,500 and 7,500 B.P. contain unusually high frequencies of red abalone (Haliotis rufescens) shells. Assuming that aboriginal peoples living at these sites collected shellfish principally from the intertidal zone, the high frequency of red abalone shells may reflect a time when sea water temperatures were cooler than present, allowing red abalone to be the dominant abalone species in the intertidal zone.Glassow, Michael A. "The Occurrence of Red Abalone Shells in Northern Channel Island Archaeological Middens: Implications for Climatic Reconstruction." In: 3rd California Islands Symposium. 1987. 567-576

Modeling of liquid flow in surface discontinuities

Polymer composite and metallic materials have found wide application in various industries such as aviation, rocket, car manufacturing, ship manufacturing, etc. Many design elements need permanent quality control. Ensuring high quality and reliability of products is impossible without effective nondestructive testing methods. One of these methods is penetrant testing using penetrating substances based on liquid penetration into defect cavities. In this paper, we propose a model of liquid flow to determine the rates of filling the defect cavities with various materials and, based on this, to choose optimal control modes