Showing 741 - 750 of 2040 Items
Hedgehog signaling regulates dental papilla formation and tooth size during zebrafish odontogenesis
Date: 2015-04-01
Creator: Jeffrey C. Yu
Zachary D. Fox
James L. Crimp
Hana E. Littleford
Andrea L., Jowdry
William R. Jackman
Access: Open access
- Intercellular communication by the hedgehog cell signaling pathway is necessary for tooth development throughout the vertebrates, but it remains unclear which specific developmental signals control cell behavior at different stages of odontogenesis. To address this issue, we have manipulated hedgehog activity during zebrafish tooth development and visualized the results using confocal microscopy. Results: We first established that reporter lines for dlx2b, fli1, NF-κB, and prdm1a are markers for specific subsets of tooth germ tissues. We then blocked hedgehog signaling with cyclopamine and observed a reduction or elimination of the cranial neural crest derived dental papilla, which normally contains the cells that later give rise to dentin-producing odontoblasts. Upon further investigation, we observed that the dental papilla begins to form and then regresses in the absence of hedgehog signaling, through a mechanism unrelated to cell proliferation or apoptosis. We also found evidence of an isometric reduction in tooth size that correlates with the time of earliest hedgehog inhibition. Conclusions: We hypothesize that these results reveal a previously uncharacterized function of hedgehog signaling during tooth morphogenesis, regulating the number of cells in the dental papilla and thereby controlling tooth size.
Statement by Melinda (Mindy) Kane collected by Rachel George on September 11, 2014
Date: 2014-09-11
Creator: Melinda Kane
Access: Open access
Statement by Wendy Newell Dyer collected by Rachel George on January 12, 2015
Date: 2015-01-12
Creator: Wendy Newell Dyer
Access: Open access
Statement by Andrew Mead collected by Rachel George on August 21, 2014
Date: 2014-08-21
Creator: Andrew Mead
Access: Open access
Vertical Trade, Exchange Rate Pass-Through, and Exchange Rate Regime
Date: 2012-09-01
Creator: Yao Tang
Ke Pang
Access: Open access
- We compare the welfare of different combinations of monetary and currency policies in an open-economy macroeconomic model that incorporates two important features of many small economies: a high level of vertical international trade and a prevalent use of a large trade partner's currency as the invoicing currency for both imports and exports. In this environment, a small economy prefers a fixed exchange rate regime over a flexible regime, while the larger economy prefers a flexible exchange rate regime. There are two main causes underlying our results. First, in the presence of sticky prices, relative prices adjust through changes in the exchange rate. Multiple stages of production and trade make it more difficult for one exchange rate to balance the whole economy by adjusting several relative prices throughout the vertical chain of production and trade. Namely, there is a trade-off between delivering an efficient relative price between home and foreign final goods and delivering an efficient relative price between home and foreign intermediate goods. Second, because the small economy uses the larger economy's currency in trade, it faces a high degree of exchange rate pass-through under a flexible regime and hence suffers from the lack of efficient relative prices in vertical trade. The larger economy, however, does not face this problem because its level of exchange rate pass-through is low.
Learning cognitive maps: Finding useful structure in an uncertain world
Date: 2008-05-22
Creator: Eric Chown
Byron Boots
Access: Open access
- In this chapter we will describe the central mechanisms that influence how people learn about large-scale space. We will focus particularly on how these mechanisms enable people to effectively cope with both the uncertainty inherent in a constantly changing world and also with the high information content of natural environments. The major lessons are that humans get by with a "less is more" approach to building structure, and that they are able to quickly adapt to environmental changes thanks to a range of general purpose mechanisms. By looking at abstract principles, instead of concrete implementation details, it is shown that the study of human learning can provide valuable lessons for robotics. Finally, these issues are discussed in the context of an implementation on a mobile robot. © 2007 Springer-Verlag Berlin Heidelberg.
Kyanite preserves prograde and retrograde metamorphic events as revealed by cathodoluminescence, geochemistry, and crystallographic orientation
Date: 2021-01-01
Creator: Emily M. Peterman
Michael J. Jercinovic
Rachel J. Beane
Cameron B. de Wet
Access: Open access
- Cathodoluminescence (CL) images of kyanite reveal several internal textures, including sector zoning, oscillatory zoning, and cross-cutting relationships among different domains. Many textures observed in kyanite correspond to discrete events, thereby connecting kyanite textures to the pressure–temperature (P–T) history of the rock. To evaluate the record of metamorphism preserved by kyanite, metapelites were selected from three different orogens that reflect P–T conditions ranging from amphibolite to ultrahigh-pressure (UHP) facies. Cross-correlation of variations in CL intensity, chemistry, and crystal orientation within kyanite indicate the following findings. First, the preservation of original growth zones in kyanite from poly-metamorphic rocks demonstrates that growth zoning in kyanite persists through metamorphic events and is not erased by diffusion or complete recrystallization. In some samples, kyanite retains evidence of its reaction history during growth. Second, measured changes in absolute crystallographic orientation do not correspond with changes in CL intensity in any of the measured samples, including kyanite twins. Third, both kink banding and undulatory extinction are present across all samples, consistent with rotation about in the (100)[001] slip system. Kyanite from (U)HP samples exhibits higher amplitude undulations than kyanite from lower-grade lithologies, suggesting that crystallographic orientation data may provide complementary insight about deformation along the P–T path. Fourth, specific CL and trace element signatures in kyanite can be correlated with discrete metamorphic histories; yet, CL intensity and colour are affected by multiple elements, not a single controlling element. In sum, multiple generations of kyanite can be identified by careful cross-correlation of CL and geochemical data, and when combined with crystal orientation data, kyanite provides a robust record of a rock's P–T evolution.
The organization (re)invented by its blogs
Creator: Alex Primo
Access: Open access
- This article discusses how interactions in organizational blogs participate in the emergence of the organization itself. Based on the principles of The Montreal School of organizational communication, the paper reflects on how the recursive relationship between texts and conversations in blogs, according to their affordances, mobilizes the organization and contributes to its continuing creation. In order to conduct this argument, the concept of social media, uses of organizational blogs and the main contributions of The Montreal School are analyzed. Finally, this article demonstrates how blogs contribute to the definition of the organization. Beyond their promotional potential, the blog’ role as co-creator of the organization is highlighted.