1,721,051 research outputs found
Singularities of the curve shrinking flow for space curves
No full textAltschuler, Steven J.. (1991). Singularities of the curve shrinking flow for space curves. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/4439
Shortening space curves and flow through singularities
No full textAltschuler, Steven J.; Grayson, Matthew A.. (1991). Shortening space curves and flow through singularities. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/4606
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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Investigating signal integration in the intestinal epithelium
Get PDFMulticellular tissues arise from a complex collaboration between the constituent cell types. Proper coordination between cells through signal interactions is crucial for tissue renewal and response to environmental changes such as injury or infection. How do tissues integrate and interpret multiple signals? How does the design of tissues and their lineage structures guide response to perturbations? I investigate these questions in the context of the intestinal epithelium, the single cell layer lining the small intestine. Alongside post-docs in the Altschuler-Wu Lab, Curtis Thorne and Laura Sanman, I developed an enteroid monolayer culture system for high-throughput quantitative profiling of intestinal epithelial cell-type composition. I then employed this system to study how combinations of signals may interact and how lineage structure may guide tissue response in the intestinal epithelial.In Chapter 1, I describe the methods for establishing the enteroid monolayer platform, including the experimental culture methods and image quantification analysis. The approach outlined here forms the foundation for the subsequent investigations into signal feedback and coordination between cell types.
In Chapter 2, I dissect the intrinsic roles of two main proliferation regulators, Wnt and BMP, in shaping the intestinal epithelium. We discovered that intrinsic Wnt3a signals from the crypt is important for proper spatial patterning of progenitors. We also found that intrinsic BMP2 secreted by differentiated cells acts as a delayed negative feedback signal for self-regulating increased proliferation in the intestinal epithelium. This finding indicates that external signals can feed into intrinsic signaling circuits, which link distinct cell population compartments.
In Chapter 3, I expand the investigation to examine progenitor and differentiated cell types in the intestinal epithelium. We identified an unexpected mutual antagonism interaction between inhibition of the epidermal growth factor receptor and activation with the cytokine IL-4. We also uncovered a general relationship between transit-amplifying cell proliferation and the balance of secretory to absorptive cell types. We proposed a differential amplification model to explain how amplification of fated progenitors can be modulated to control lineage composition.
Finally, in Chapter 4, I synthesize the results from these studies and discuss the implications for how the intestinal epithelium integrates and responds to signals. I conclude with potential directions for future research
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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Role of cell identity in growth cone extension during Drosophila visual circuit development
Get PDFThe formation of repeated patterns is a recurring theme during tissue development. Well-studied models include the pigmentation of fish skins, the spacing and orientation of hair follicles, and the connection of sensory neurons. How do seemingly complex, yet highly organized patterns emerge? What rules underlie the development of these cellular patterns? A major challenge is to uncover rules in the face of “biological noise”, arising from stochastic variability of individual cells, local warping of the developing tissue, and specimen-to-specimen differences. Here, I investigated rules governing neuronal pattern formation in the context of Drosophila visual circuit development, where the outer photoreceptors, R1-R6, resort in the lamina layer of the brain to form the stereotyped neural superposition (NSP) circuit. To hunt for signals within the biological noise, I developed a data-driven, standardized coordinate system to characterize the ensemble behaviors of photoreceptors. With this, I was able to identify rules that govern cell-type-specific extension velocities of the photoreceptor pair R3/R4, which uniquely exhibit asymmetric targeting. Specifically, I found that the extension speeds of the R3 and R4 growth cones are inherent to their cell identities. Further, to showcase the predictive power of the coordinate system, I made a computational prediction that extension angles can be explained by a weighted nearest-neighbor repulsion model. My work provides a new case study of how pattern formation rules — hidden within phenotypic variability — can be inferred by quantitative analysis during the development of living organisms
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