Cryogenic seal remains leaktight during thermal displacement

Cryogenic seals protect the surfaces of a plastic member in a low-pressure system subjected to extreme temperature changes. The outer seal is an aluminum expansion ring bonded to the lens outer surface and the inner seal consists of a resin-filled aluminum U-ring bonded to the inner surface

Physical Performance Assessments of Strength and Power in Women Collegiate Athletes

International Journal of Exercise Science 14(6): 984-993, 2021. Limited research exists on physical performance assessments for women collegiate athletes. The current cross-sectional study compared field-based tests of muscular strength and power and investigated their relationship. Sports included field hockey, volleyball, soccer, and softball. Tests of one repetition maximum (1-RM) back squat, 1-RM bench press, vertical jump, and standing long jump were administered. A one-way analysis of variance (ANOVA) assessed differences across sports. Bivariate Pearson correlation coefficients examined relationships among tests. It was hypothesized sports with a higher anaerobic nature (volleyball, softball) would outperform those with higher aerobic nature (field hockey, soccer). Softball had the highest 1-RM bench press and 1-RM back squat (p \u3c 0.001) compared to field hockey, volleyball, and soccer. Further, softball had the highest vertical jump (p \u3c 0.001) compared to field hockey and soccer, but did not differ from volleyball. There were no differences across sports for standing long jump. Correlations (p \u3c 0.001) existed between 1-RM back squat and 1-RM bench press (n = 663, r = 0.56), and vertical jump and standing long jump (n = 160, r = 0.64). Results demonstrate strength and power differences among collegiate women’s sports. Softball consistently outperformed others in bench press, back squat, and vertical jump, which may be due to the demand of power embedded in the nature of the sport. These data provide descriptive measures of physical performance assessments and may assist practitioners with goal setting and program design

Radioactive Probes of the Supernova-Contaminated Solar Nebula: Evidence that the Sun was Born in a Cluster

We construct a simple model for radioisotopic enrichment of the protosolar nebula by injection from a nearby supernova, based on the inverse square law for ejecta dispersion. We find that the presolar radioisotopes abundances (i.e., in solar masses) demand a nearby supernova: its distance can be no larger than 66 times the size of the protosolar nebula, at a 90% confidence level, assuming 1 solar mass of protosolar material. The relevant size of the nebula depends on its state of evolution at the time of radioactivity injection. In one scenario, a collection of low-mass stars, including our sun, formed in a group or cluster with an intermediate- to high-mass star that ended its life as a supernova while our sun was still a protostar, a starless core, or perhaps a diffuse cloud. Using recent observations of protostars to estimate the size of the protosolar nebula constrains the distance of the supernova at 0.02 to 1.6 pc. The supernova distance limit is consistent with the scales of low-mass stars formation around one or more massive stars, but it is closer than expected were the sun formed in an isolated, solitary state. Consequently, if any presolar radioactivities originated via supernova injection, we must conclude that our sun was a member of such a group or cluster that has since dispersed, and thus that solar system formation should be understood in this context. In addition, we show that the timescale from explosion to the creation of small bodies was on the order of 1.8 Myr (formal 90% confidence range of 0 to 2.2 Myr), and thus the temporal choreography from supernova ejecta to meteorites is important. Finally, we can not distinguish between progenitor masses from 15 to 25 solar masses in the nucleosynthesis models; however, the 20 solar mass model is somewhat preferred.Comment: ApJ accepted, 19 pages, 3 figure

Relationships Among Metabolic-Risk, Body Fatness, and Muscular Fitness in Young Obese Latino Children

International Journal of Exercise Science 13(3): 488-500, 2020. Given the high prevalence of obesity in Latino children and potential health risks, the purpose of this study was to: 1) evaluate relationships among metabolic-risk, fitness, and body fatness; 2) determine sex differences in cardio-metabolic risk factors and fitness of obese children of Latino descent. Sixty children (boys, n= 39, 7.8 ± 1.5 years; girls, n= 21, 7.2 ± 1.5 years; body mass index, 97.8 ± 2.5thpercentile) completed assessments of height, weight, and body fat, prior to fasted blood draws and a battery of fitness tests. Cardio-metabolic markers were analyzed, and a metabolic risk score created. Correlations and regression analyses evaluated the relationships among body fatness, metabolic-risk, and fitness. Independent samples t-tests determined sex differences (p \u3c 0.05). Body fat related negatively to lower body power (p \u3c 0.016), but positively to upper body power (p= 0.049). After controlling for age and sex, body fat (p\u3c 0.001) was a positive predictor of variance in metabolic-risk scores, (R2 = 0.39, p \u3c 0.001). Further, the association between body fat and metabolic-risk was not moderated by sex. Metabolic-risk scores and body fat were similar for both sexes, but boys performed better on muscular fitness tests, even after accounting for fat free mass (p \u3c 0.05). Higher body fatness in obese Latino children may result in greater metabolic-risk and difficulty performing weight-bearing tasks. Therefore, culturally adapted weight management programs should employ a multifaceted approach to improve metabolic-risk and fitness

Halo White Dwarfs and the Hot Intergalactic Medium

We present a schematic model for the formation of baryonic galactic halos and hot gas in the Local Group and the intergalactic medium. We follow the dynamics, chemical evolution, heat flow and gas flows of a hierarchy of scales, including: protogalactic clouds, galactic halos, and the Local Group itself. Within this hierarchy, the Galaxy is built via mergers of protogalactic fragments. We find that early bursts of star formation lead to a large population of remnants (mostly white dwarfs), which would reside presently in the halo and contribute to the dark component observed in the microlensing experiments. The hot, metal-rich gas from early starbursts and merging evaporates from the clouds and is eventually incorporated into the intergalactic medium. The model thus suggests that most microlensing objects could be white dwarfs (m \sim 0.5 \msol), which comprise a significant fraction of the halo mass. Furthermore, the Local Group could have a component of metal-rich hot gas similar to, although less than, that observed in larger clusters. We discuss the known constraints on such a scenario and show that all local observations can be satisfied with present data in this model. The best-fit model has a halo that is 40% baryonic, with an upper limit of 77%.Comment: 15 pages, LaTex, uses aas2pp4.sty, 7 postscript figures. Substantially revised and enlarged to a full-length article. Somewhat different quantitative results, but qualitative conclusions unchange

Communicating Computational Concepts and Practices Within High School Students’ Portfolios of Making Electronic Textiles

Portfolios have recently gained traction within computer science education as a way to assess students’ computational thinking and practices. Whereas traditional assessments such as exams tend to capture learning within artificial settings at a single point in time, portfolios provide more authentic opportunities to document a trajectory of students’ learning and practices in everyday contexts. Furthermore, because communication itself has been defined as an important computational thinking practice, portfolios give students a place to practice this skill in the classroom. In this study, we report on the implementation of a digital portfolio with a class of 21 high school students used to capture the process of creating of an electronic textile mural project. While students’ understanding of computational concepts were only partially captured within the portfolios, their engagements with computational practices—such as debugging and iteration—were better highlighted. Much of this was due to the students’ existing communicative strategies themselves, both in terms of how precise they were in describing issues, as well as how they leveraged images and code to explain their process. Recommendations for designing more effective portfolio assessments are discussed, which include greater emphasis on creating shared classroom discourse, and leveraging students’ existing experiences with multimedia

QCD near the Light Cone

Starting from the QCD Lagrangian, we present the QCD Hamiltonian for near light cone coordinates. We study the dynamics of the gluonic zero modes of this Hamiltonian. The strong coupling solutions serve as a basis for the complete problem. We discuss the importance of zero modes for the confinement mechanism.Comment: 32 pages, ReVTeX, 2 Encapsulated PostScript figure

Fat-Free Mass Index in a Large Sample of Collegiate American Football Athletes

International Journal of Exercise Science 17(4): 129-139, 2024. High levels of fat-free mass (FFM) are favorable for athletes and are related to sport performance. However, fat-free mass index (FFMI), which includes adjustments for height, may offer a better way to characterize FFM beyond raw values. As FFMI is understudied relative to sport, the purpose of the current study was to assess position and age group differences in FFMI among collegiate American football players. National Collegiate Athletic Association DIII (n=111) football players underwent body composition assessment via bioelectrical impedance analysis. FFMI was calculated by dividing FFM by height squared. One-way analyses of variance with Bonferroni post-hoc tests were conducted to evaluate differences in FFMI by position and age groups (α\u3c0.05). The overall mean FFMI was 23.50 ± 2.04 kg· m−2, with values ranging from 18.1–27.7 kg· m−2. FFMI was highest in linemen (24.8 ± 1.5 kg· m−2) and lowest in specialty players (20.6 ± 1.4 kg· m−2) (p\u3c0.05). No differences in FFMI were apparent across age groups (p\u3e0.05). Current findings demonstrate that an athlete’s upper limit for FFMI may exceed 25 kg· m−2, and differences exist across positions, likely due to position-specific demands. These measurements serve as a foundation for tailoring nutritional and exercise plans, forecasting athletic performance, and supplying coaches with standardized data about the potential for additional FFM accretion in collegiate American football players