MEMS Electrostatically Actuated Resonator

A MEMS electrostatically actuated resonator with fixed-fixed and fixed-free cantilever beams is designed, simulated, fabricated, and tested. The fabrication of the MEMS resonators uses RIT’s MEMS fabrication 2016 process flow which is a surface micromachining process. The released fixed-free devices tested showed an increasing change in capacitance with an increasing actuation voltage. Inspection of the released fixed-fixed devices has a compressive stress in the second polysilicon film that causes the cantilever beam to bend above the actuation and sensing pads. Testing for resonance has not been successful. Some new considerations for the MEMS fabrication process and design are discussed

The Role of Mechanical Forces in Patterning and Morphogenesis of the Vertebrate Gut

The vertebrate small intestine is responsible for nutrient absorption during digestion. To this end, the surface area of the gut tube is maximally expanded, both through a series of loops extending its length and via the development of a complex luminal topography. Here, I first examine the mechanism behind the formation of intestinal loops. I demonstrate that looping morphogenesis is driven by mechanical forces that arise from differential growth between the gut tube and the anchoring dorsal mesenteric sheet. A computational model based on measured parameters not only quantitatively predicts the looping pattern in chick, verifying that these physical forces are sufficient to explain the process, but also accounts for the variation in the gut looping patterns seen in other species. Second, I explore the formation of intestinal villi in chick. I find that intestinal villi form in a stepwise process as a result of physical forces generated as proliferating endodermal and mesenchymal tissues are constrained by sequentially differentiating layers of smooth muscle. A computational model incorporating measured differential growth and the geometric and physical properties of the developing chick gut recapitulates the morphological patterns seen during chick villi formation. I also demonstrate that the same basic biophysical processes underlie the formation of intestinal folds in frog and villi in mice. Finally, I focus on the process by which intestinal stem cells are ultimately localized to the base of each villus. The endoderm expresses the morphogen, Sonic hedgehog (Shh). As the luminal surface of the gut is deformed during villus formation there are resulting local maxima of Shh signaling in the mesenchyme. This results, at high threshold, in the induction of a new signaling center under the villus tip termed the villus cluster. This, in turn, feeds back to restrict proliferating progenitors in the endoderm, the presumptive precursors of the stem cells, to the base of each villus. Together, these studies provide new insight into the formation of the small intestine as a functional organ and highlight the interplay between physical forces, tissue-level growth, and signaling during development

Einstein on the beach: A study in temporality

This is an Author's Accepted Manuscript of an article published in Performance Research, 17(5), 34 - 40, 2012, copyright @ Taylor & Francis, available online at: http://www.tandfonline.com/10.1080/13528165.2012.728438.In this paper I seek to examine and analyse the sense of duration induced by performances of Einstein on the Beach, and the entailed sense of time which its internal structure creates. I initially sketch out the stylistic context and artistic intentions of this work's creators, Glass and Wilson, and I briefly describe the process of its creation. Certain features of this process indicate how the work may be interpreted. Having cited the creators' thoughts on structure and temporality, I address directly aspects of Einstein's temporal effects, comparing it to works of similar lengths. I give the briefest synopsis of its staging and motifs. I then outline three kinds of devices which seem to inform our temporal sense of this work as spectators. In the final section I invoke two ideas which serve as analogies to help characterise this work's overall effect on us: Heidegger's notion of the ‘hermeneutic circle’ and, more speculatively, Nietzsche's ‘theory’ of Eternal Recurrence

Membranes by the Numbers

Many of the most important processes in cells take place on and across membranes. With the rise of an impressive array of powerful quantitative methods for characterizing these membranes, it is an opportune time to reflect on the structure and function of membranes from the point of view of biological numeracy. To that end, in this article, I review the quantitative parameters that characterize the mechanical, electrical and transport properties of membranes and carry out a number of corresponding order of magnitude estimates that help us understand the values of those parameters.Comment: 27 pages, 12 figure

Tissue stiffening coordinates morphogenesis by triggering collective cell migration in vivo.

Collective cell migration is essential for morphogenesis, tissue remodelling and cancer invasion. In vivo, groups of cells move in an orchestrated way through tissues. This movement involves mechanical as well as molecular interactions between cells and their environment. While the role of molecular signals in collective cell migration is comparatively well understood, how tissue mechanics influence collective cell migration in vivo remains unknown. Here we investigated the importance of mechanical cues in the collective migration of the Xenopus laevis neural crest cells, an embryonic cell population whose migratory behaviour has been likened to cancer invasion. We found that, during morphogenesis, the head mesoderm underlying the cephalic neural crest stiffens. This stiffening initiates an epithelial-to-mesenchymal transition in neural crest cells and triggers their collective migration. To detect changes in their mechanical environment, neural crest cells use mechanosensation mediated by the integrin-vinculin-talin complex. By performing mechanical and molecular manipulations, we show that mesoderm stiffening is necessary and sufficient to trigger neural crest migration. Finally, we demonstrate that convergent extension of the mesoderm, which starts during gastrulation, leads to increased mesoderm stiffness by increasing the cell density underneath the neural crest. These results show that convergent extension of the mesoderm has a role as a mechanical coordinator of morphogenesis, and reveal a link between two apparently unconnected processes-gastrulation and neural crest migration-via changes in tissue mechanics. Overall, we demonstrate that changes in substrate stiffness can trigger collective cell migration by promoting epithelial-to-mesenchymal transition in vivo. More broadly, our results raise the idea that tissue mechanics combines with molecular effectors to coordinate morphogenesis

A Glial Variant of the Vesicular Monoamine Transporter Is Required To Store Histamine in the Drosophila Visual System

Unlike other monoamine neurotransmitters, the mechanism by which the brain's histamine content is regulated remains unclear. In mammals, vesicular monoamine transporters (VMATs) are expressed exclusively in neurons and mediate the storage of histamine and other monoamines. We have studied the visual system of Drosophila melanogaster in which histamine is the primary neurotransmitter released from photoreceptor cells. We report here that a novel mRNA splice variant of Drosophila VMAT (DVMAT-B) is expressed not in neurons but rather in a small subset of glia in the lamina of the fly's optic lobe. Histamine contents are reduced by mutation of dVMAT, but can be partially restored by specifically expressing DVMAT-B in glia. Our results suggest a novel role for a monoamine transporter in glia that may be relevant to histamine homeostasis in other systems

Adult gastric stem cells and their niches.

Adult gastric stem cells replenish the gastric epithelium throughout life. Recent studies have identified diverse populations of stem cells, progenitor cells, and even differentiated cells that can regain stem cell capacity, so highlighting an unexpected plasticity within the gastric epithelium, both in the corpus and antrum. Two niches seem to co-exist in the gastric unit: one in the isthmus region and the other at the base of the gland, although the precise features of the cell populations and the two niches are currently under debate. A variety of gastric organoid models have been established, providing new insights into niche factors required by the gastric stem cell populations. Here we review our current knowledge of gastric stem cell populations, their markers and interactions, important niche factors, and different gastric organoid systems. WIREs Dev Biol 2017, 6:e261. doi: 10.1002/wdev.261 For further resources related to this article, please visit the WIREs website.Wellcome-Trus