Reynolds number limits for jet propulsion: A numerical study of simplified jellyfish

The Scallop Theorem states that reciprocal methods of locomotion, such as jet propulsion or paddling, will not work in Stokes flow (Reynolds number = 0). In nature the effective limit of jet propulsion is still in the range where inertial forces are significant. It appears that almost all animals that use jet propulsion swim at Reynolds numbers (Re) of about 5 or more. Juvenile squid and octopods hatch from the egg already swimming in this inertial regime. The limitations of jet propulsion at intermediate Re is explored here using the immersed boundary method to solve the two-dimensional Navier Stokes equations coupled to the motion of a simplified jellyfish. The contraction and expansion kinematics are prescribed, but the forward and backward swimming motions of the idealized jellyfish are emergent properties determined by the resulting fluid dynamics. Simulations are performed for both an oblate bell shape using a paddling mode of swimming and a prolate bell shape using jet propulsion. Average forward velocities and work put into the system are calculated for Reynolds numbers between 1 and 320. The results show that forward velocities rapidly decay with decreasing Re for all bell shapes when Re < 10. Similarly, the work required to generate the pulsing motion increases significantly for Re < 10. When compared actual organisms, the swimming velocities and vortex separation patterns for the model prolate agree with those observed in Nemopsis bachei. The forward swimming velocities of the model oblate jellyfish after two pulse cycles are comparable to those reported for Aurelia aurita, but discrepancies are observed in the vortex dynamics between when the 2D model oblate jellyfish and the organism

Leaf roll-up and aquaplaning in strong winds and floods

Flexible plants, fungi, and sessile animals are thought to reconfigure in the wind and water to reduce the drag forces that act upon them. In strong winds, for example, leaves roll up into cone shapes that reduce flutter and drag when compared to paper cut-outs with similar shapes and flexibility. During flash floods, herbaceous broad leaves aquaplane on the surface of the water which reduces drag. Simple mathematical models of a flexible beam immersed in a two-dimensional flow will also reconfigure in flow. What is less understood is how the mechanical properties of a two-dimensional leaf in a three-dimensional flow will passively allow roll up and aquaplaning. In this study, we film leaf roll-up and aquaplaning in tree and vine leaves in both strong winds and water flows

Recent progress in the synthesis of nanostructured magnesium hydroxide

This review highlights synthetic routes for producing nanostructured magnesium hydroxide and focuses on how these various preparative approaches can produce Mg(OH)2 nanoparticles with controlled size and morphology. Mg(OH)2 nanocrystals with rod-, needle-, hollow tube- or platelet-like morphology can be synthesised by the modification of chemical and physical experimental parameters such as the selection of magnesium precursor, solvent and temperature or by employing surface modifiers and templates. Techniques based on hydrothermal/solvothermal treatments, microwave heating and (co-)precipitation are dominant in the production of Mg(OH)2 at the nanoscale, but other materials design approaches are now emerging. Bulk Mg(OH)2 has been extensively studied over decades and finds use in a wide range of applications. Moreover, the hydroxide can also serve as a precursor for other commercially important materials such as MgO. Nanostructuring the material has proven extremely useful in modifying some of its most important properties – not least enhancing the performance of Mg(OH)2 as a non-toxic flame retardant – but equally it is creating new avenues of applied research. We evaluate herein the latest efforts to design novel synthesis routes to nano-Mg(OH)2, to understand the mechanisms of crystallite growth and to tailor microstructure towards specific properties and applications

Undergraduate students' attitudes toward older adults after an intergenerational service-learning project.

In the United States, adults are living longer, and working longer and negative attitudes toward older adults still exist. Attitudes of college students from various colleges and disciplines have been studied to assess their attitudes toward older adults. Current literature suggests that students who participated in intergenerational service-learning projects have a positive change in attitudes toward older adults. The purpose of this present study was to assess the difference in community/public health undergraduate college students' attitudes toward older adults before and after an intergenerational service-learning project. The refined Aging Semantic Differential (ASD) and the Student Assisted Independent Living (SAIL) Questionnaire were provided to undergraduate college students enrolled in a 4000 level health and aging course who also participated in an intergenerational service-learning project as a course requirement. Survey instruments were administered on three separate occasions to determine changes in attitudes toward older adults before, during, and after the intergenerational service-learning project. Due to a small sample size, changes in attitudes were not statistically significant but trended toward a positive change in undergraduate college students' attitudes toward older adults. Although results were not statistically significant, effect sizes ranged from weak to moderate. With minimal research found in community/public health students' attitudes toward older adults, a recommendation for future studies should include continued exploration of community/public health students' attitudes' toward older adults

“There’s a Double Meaning in That”: Heroism and Blessedness in Much Ado About Nothing

I have chosen to include this line “There’s a double meaning in that” (spoken by Benedick in Act 2 scene 3) in the title of this analysis as a way of introducing the play’s two heroines: Hero and Beatrice, and my argument that these women’s names at once symbolically exemplify and ironically contrast with their characters’ natures. While referring to scholarship on Shakesperean names, allegory, and societal and gender roles, I will consider the meaning of these names—Hero meaning “hero” and Beatrice meaning “blessed” or “blessing”—and examine the ways that these characters define and are defined by heroism, blessing, and womanhood. Moreover, I will argue that as these characters are so closely knit and supportive of each other, they define and are defined by each other’s names as well as their own. Although I will be focusing on these women, I will also refer to Benedick—whose name can also be translated as “blessed”—and his noteworthy decision to advocate for these women when they find themselves at odds with a male-led society. Ultimately, I will conclude that both Hero and Beatrice are as cursed as they are blessed, as heroic as they are victimized by circumstance, and that these loving and supportive cousins help each other to find happiness by making the most of their name-given, definitive strengths

Is the growth of the child of a smoking mother influenced by the father's prenatal exposure to tobacco? A hypothesis generating longitudinal study

OBJECTIVES: Transgenerational effects of different environmental exposures are of major interest, with rodent experiments focusing on epigenetic mechanisms. Previously, we have shown that if the study mother is a non-smoker, there is increased mean birth weight, length and body mass index (BMI) in her sons if she herself had been exposed prenatally to her mother's smoking. The aim of this study was to determine whether the prenatal smoke exposure of either parent influenced the growth of the fetus of a smoking woman, and whether any effects were dependent on the fetal sex. DESIGN: Population-based prebirth cohort study. SETTING: Avon Longitudinal Study of Parents and Children. PARTICIPANTS: Participants were residents of a geographic area with expected date of delivery between April 1991 and December 1992. Among pregnancies of mothers who smoked during pregnancy, data were available concerning maternal and paternal prenatal exposures to their own mother smoking for 3502 and 2354, respectively. PRIMARY AND SECONDARY OUTCOME MEASURES: Birth weight, length, BMI and head circumference. RESULTS: After controlling for confounders, there were no associations with birth weight, length or BMI. There was a strong adjusted association of birth head circumference among boys whose fathers had been exposed prenatally (mean difference −0.35 cm; 95% CI −0.57 to −0.14; p=0.001). There was no such association with girls (interaction p=0.006). Similar associations were found when primiparae and multiparae were analysed separately. In order to determine whether this was reflected in child development, we examined the relationships with IQ; we found that the boys born to exposed fathers had lower IQ scores on average, and that this was particularly due to the verbal component (mean difference in verbal IQ −3.65 points; 95% CI −6.60 to −0.70). CONCLUSIONS: Head size differences concerning paternal fetal exposure to smoking were unexpected and, as such, should be regarded as hypothesis generating

Ammonia borane-based nanocomposites as solid state hydrogen stores for portable power applications

Ammonia borane (AB) based nanocomposites have been investigated with the aim of developing a promising solid-state hydrogen store that complies with the requirements of a modular polymer electrolyte membrane fuel cell (PEM FC) in a portable power pack system. AB-carbon nanocomposites (prepared via ball milling or solution-impregnation) demonstrate improved hydrogen release performance compared to AB itself in terms of onset temperature and hydrogen purity, while maintaining a gravimetric density of more than 5 wt. % H2. The most promising of these materials is an AB-AC (activated carbon) composite, synthesised via solution-impregnation with an optimal dehydrogenation temperature of 96 °C. When combined with an external nickel chloride filter downstream, no evolved gaseous by-products can be detected above 100 ppb. The feasibility of an AB-AC storage tank has been further endorsed by simulations in which the reaction rate and the hydrogen flux was found to be almost constant as the temperature front propagated from the bottom to the top of the tank after initiation