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Grit, or passion and perseverance in pursuing long-term goals, is a non-cognitive factor positively related to age and education level, and inversely related to frequent career changes (Duckworth, Peterson, Matthews, & Kelly, 2007; Duckworth & Quinn, 2009). It is less clear, however, whether undergraduate students in the midst of college study show more grit the further along they are in their program. Furthermore, for students in science, technology, engineering, and mathematics (STEM), low within-major grades, concerns over ill-preparedness after high school, and lack of confidence in laboratory skills, time management, and maintaining enthusiasm, may contribute to differences in grit between STEM and non-STEM majors during the early years of study (King, 2015; Otrel-Cass, Cowie, & Campbell, 2009; Seymour & Hewitt, 1997). With greater rates of students switching from STEM to non-STEM majors than in the opposite direction, despite little difference in grades between STEM majors who switch and those who persist, it seems that STEM majors with higher grit may remain in STEM programs, while those with lower grit may accumulate in non-STEM programs (Ackerman, Kanfer, & Calderwood, 2013; Brainard & Carlin, 1998; Kokkelenberg & Sinha, 2010; Seymour & Hewitt, 1997; Thompson & Bolin, 2011). Differences in STEM versus non-STEM grit also may depend upon whether social and behavioral science disciplines, and health science disciplines, are included in STEM (Chen, 2013; Langdon, McKittrick, Beede, Khan, & Doms, 2011; National Science Board, 2015, 2016; U.S. Census Bureau, 2014, July 10). The goal of this study is to test the following hypotheses: 1) undergraduates report increasing grit in going from freshman to senior level; 2) undergraduate STEM majors report lower grit than non-STEM majors early in college, but higher grit than non-STEM majors later in college; and 3) this difference is increased when social and behavioral sciences or health sciences are considered STEM, and decreased when considered non-STEM. Subjects for the study were undergraduate college students recruited through Mechanical Turk ("Amazon Mechanical Turk [Website]," 2018), as well as at a Pacific Northwest community college through posting of flyers, announcements in class, and general calls for participation via college email. Through online self-report, participants completed the eight-item Short Grit (Grit-S) Scale (Duckworth & Quinn, 2009), while also providing GPA and major field of study by self-report. In general, this study finds that 1) four-year undergraduate subjects show higher scores in total Grit-S and the Consistency of Interest grit dimension when upper division (junior, senior) compared to lower division (freshman, sophomore), while community college students show higher Consistency of Interest when sophomore compared to freshman. Also, 2) STEM students generally show lower total Grit-S and Consistency of Interest compared to non-STEM students throughout college, but higher scores in the Perseverance of Effort grit dimension in the upper division. Additionally, 3) when considered STEM rather than non-STEM, health science students generally narrow the difference between STEM and non-STEM S-Grit and Consistency of Interest at the lower division, while social science students generally narrow that difference at the upper division. Findings from this study will help post-secondary educators identify academic disciplines where persistence is more highly correlated to grit than other disciplines. Educators then can focus on modifying those identified programs, such as through academic and career advising, tutoring services, and teaching methods that may raise student engagement (e.g., use of internet-based components, in-class poll-taking activities, and in-class group exercises), to better address student grit levels and match students to programs of best fit (Brint, Cantwell, & Saxena, 2012; Community College Research Center & American Association of Community Colleges, n.d.; Gasiewski, Eagan, Garcia, Hartado, & Chang, 2012; Maltese & Tai, 2011).

Ameloblasts continuously differentiate from epithelial stem cells to maturation stage ameloblasts, modulating and directing the formation of a mineralized enamel matrix. Calcium is required for enamel mineralization, however, as in other epithelial tissues; calcium may also be a modulator for ameloblast differentiation. Several studies have suggested a role for the calcium sensing receptor (CaSR) in ameloblast differentiation. Hypothesis: Calcium regulates ameloblast differentiation through the activity of the calcium sensing receptor. Methods: A primary ameloblast cell culture model was used to determine whether calcium could direct ameloblast differentiation, cellular morphology, and gene expression. Gene expression in response to calcium was assessed via microarray analysis. In vivo studies using K14-Cre-CaSR-/- mice treated with a normal diet, low calcium diet or high fluoride diet were completed to determine the role of the CaSR on ameloblast differentiation. Enamel formation, mineralization, and ameloblast differentiation were imaged by microCT, histochemistry, and immunohistochemistry. Gene expression was compared by qPCR. Results: In vitro primary cell culture data showed that elevated levels of calcium could induce mineralization, changes in cell morphology and gene expression related to dose and time of exposure. Primary ameloblast lineage cells is very heterogeneous, with a proportion of stellate reticulum cells, which accounts for the high levels of collagen Type I levels found in the microarray study. In vivo K14-Cre-CaSR-/- mouse model data showed earlier enamel formation compared to wild type mice, with no effects on ameloblast morphology and gene expression. The early enamel formation phenotype in K14-Cre-CaSR-/- mice was enhanced in the presence of fluoride and in the absence of calcium in the diet. Conclusion: Calcium can modulate expression of extracellular matrix proteins in a mixed primary cell culture. CaSR activity can influence the timing of enamel formation, but has a limited role in regulating ameloblast differentiation. Calcium mediated changes in gene expression and ameloblast cellular function appears to be controlled through mechanisms other than CaSR.

The objective of this investigation is to study experimentally millimeter-wave BARITT mixers and detectors, to find the limits of operation, and to improve BARITT mixer theory. Existing mixer analysis computer programs for transit-time diodes were modified to include the injection characteristic under the effect of mobile space charge in the drift region. Also they were extended to study the spontaneous punch-through BARITTs, i.e., punch through at zero dc bias, as potential millimeter-wave subharmonic mixers. Mixer parameters, such as conversion loss, noise figure, input impedance and output impedance, were studied for the subharmonic mixing application. Excellent quantitative agreement with the experimental results for low-frequency operation was obtained. Experiments were carried out to investigate the characteristics of millimeter-wave BARITT mixers and detectors. Several groups of high-quality BARITTs were successfully designed, fabricated and operated as millimeter-wave mixers and detectors. A conversion loss and noise figure of 5.5 dB and 7 dB, respectively, were measured at 35 GHz. A tangential signal sensitivity of -48 dBm was also measured. It was shown that the important parameters for frequency conversion applications are comparable to those of Schottky-barrier diodes. The burnout level of the BARITT device was also determined and was at least ten times higher than that of the best Schottky-barrier diode. In brief, this study presents the results of a highly sensitive and rugged millimeter-wave mixer and detector with a high burnout level and large dynamic range. It excels over Schottky-barrier mixers by eliminating the need for TR tubes or solid-state limiters in millimeter-wave communication and radar system applications and over Schottky-barrier diode pairs with regard to the symmetry of the I-V characteristic in subharmonic mixing applications.