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This paper describes simple modifications to a demonstration Stirling engine that allows one to make quantitative measurements of the Stirling cycle. First, we describe measurements of the "P-V" diagram using an in-expensive pressure sensor and a common photogate. Then, as a supplement, the engine was run as a refrigerator by using a rotary tool to turn the flywheel of the engine. A small, but measurable, temperature difference developed across the body of the engine.

Cold clusters of molecular hydrogen were created using a pulsed nozzle. The thermodynamical states of the clusters were characterized by measuring the cluster beam velocity and the laser-induced fluorescence (LIF) spectra of embedded molecules. Two distinct velocity components were identified in the beam that originates from different clustering mechanisms. The fast velocity component corresponds to the expansion of H2 from the gas phase, while the slow velocity component corresponds to the expansion from the liquid phase. The velocity distribution of these two components showed no significant difference between the expansions of para and normal hydrogen. In this study, LIF spectroscopy of single Mg-phthalocyanine molecules embedded in the H2 clusters consisting of 105 H2 molecules was used to investigate the properties of the fast component. The observed peak frequencies of the LIF signals, compared to those observed in helium droplets, were used to infer the possible presence of the liquid phase in the fast component of the H2 clusters below 5 K. The shift, linewidth, and splitting in the spectra, which strongly depend on the ortho/para ratio, are attributed to the local configurations of hydrogen in the vicinity of the probe molecules. [ABSTRACT FROM AUTHOR]

Background: Cadherin‐associated protein p120 catenin regulates cell adhesion and migration in cell cultures and is required for axial elongation in embryos. Its roles in adhesion and cell migration are regulated by phosphorylation. We determined the effects of phosphorylation of six serine and three threonine residues in p120 catenin during zebrafish (Danio rerio) embryogenesis. Results: We knocked down endogenous p120 catenin‐δ1 with an antisense RNA‐splice‐site morpholino (Sp‐MO) causing defects in axis elongation. These defects were rescued by co‐injections of mRNAs for wildtype mouse p120 catenin‐δ1‐3A or various mutated forms. Several mRNAs containing serine or threonine codons singly or doubly mutated to phosphomimetic glutamic acid rescued, and some nonphosphorylatable mutants did not. Conclusions: We discovered that phosphorylation of serine residue S252 or S879 is required for convergent extension of zebrafish embryos, since rescue occurred only when these residues were mutated to glutamic acid. In addition, the phosphorylation of either S268 or S269 is required, not both, consistent with the presence of only a single one of these residues in two isoforms of zebrafish and Xenopus laevis. In summary, phosphorylation of multiple serine and threonine residues of p120 catenin activates migration of presomitic mesoderm of zebrafish embryos facilitating elongation of the dorsal axis. Key Findings: Knockdown of zebrafish p120 catenin‐δ1 with a morpholino blocks migration of presomitic mesoderm and extension of the dorsal axis.We compared rescue of morphology by injecting mouse p120 catenin‐δ1‐3A (CTNND1‐3A) mRNAs mutated to phosphomimetic (E) and nonphosphorylatable (F) versions of serine and threonine residues.Convergent extension of zebrafish embryos was partially rescued by phosphorylation of T310, S905, or T916. Importantly, it required phosphorylation of serine residues S252, S879, and either of S268 or S269.We see normal morphogenesis as a dynamic interplay of motile filopodia and lamellipodia forming at the leading edge of the presomitic mesoderm cell as well as turnover of new cadherin‐mediated anchoring adherens junctions that facilitate a treadmilling action used by presomitic cells to migrate toward the dorsal aspect of the embryo. [ABSTRACT FROM AUTHOR]

First-year physics laboratories are often driven by a mix of goals that includes the illustration or discovery of basic physics principles and a myriad of technical skills involving specific equipment, data analysis, and report writing. The sheer number of such goals seems guaranteed to produce cognitive overload, even when highly detailed "cookbook" instructions are given. Recent studies indicate that this approach leaves students with a poor conceptual understanding of one of the most important features of laboratory physics and of the real world of science, in general: the development of an understanding of the nature of measurement and its attendant uncertainty. While students might be able to reproduce certain technical manipulations of data, as novice thinkers they lack the mental scaffolding that allows an expert to organize and apply this knowledge. Our goal is to put novices on the path to expertise, so that they will be able to transfer their knowledge to novel situations.

The effect of buccolingual staggered implant placement on stress distribution within the supporting structure was examined photoelastically. Two photoelastic models of a human mandible, edentulous distal to the canine, were fabricated. Three screw-type implants were embedded into the edentulous region of each model. The implants were placed in a straight line in one model and in a buccolingual staggered configuration in the other. Vertical and lateral loads were applied to a fixed partial denture superstructure. No clear biomechanical advantage to a staggered 1.5 mm buccal and lingual offset placement configuration was observed. [ABSTRACT FROM AUTHOR]

Clusters of tetracene molecules with different numbers of attached (Ar)N, (Ne)N and (H2)N particles (N = 1-2000) are assembled inside superfluid He nanodroplets and studied via laser-induced fluorescence. The frequency shift of the fluorescence spectrum of the tetracene molecules is studied as a function of cluster size and pickup order of tetracene and cluster species. For (Ar)N and (Ne)N clusters, our results indicate that the tetracene molecules reside inside the clusters when tetracene is captured by the He nanodroplet before the cluster species; conversely, the tetracene molecules stay on the surface of the clusters when tetracene is captured after the cluster species. In the case of (H2)N clusters, however, tetracene molecules reside inside the (H2)N clusters irrespective of the pickup order. We conclude that (Ar)N and (Ne)N clusters are rigid at T = 0.38 K, while (H2)N clusters of up to N = 2000 remain fluxional at the same temperature. The results may also indicate the occurrence of heterogeneous nucleation of the (H2)N clusters, which is induced by the interaction with tetracene chromophore molecules. [ABSTRACT FROM AUTHOR]