1,721,034 research outputs found
De partibus irritabilibus humani corporis
No full textQvam ... Praeside D. Carolo Christiano Kravse ... Pro Gradv Doctoris Pridie Cal. Martii A.P.C.N. MDCCLXXVII H.L.Q.C. Ad Disceptandvm Proponit Ioannes Levi Benjamin Kergel Wallhavso-ThvringvsAutopsie nach Ex. der ULB DüsseldorfVorlageform der Veröffentlichungsangabe: Lipsiae Ex Officina LangenhemiaUniversität Leipzig, Dissertation, 177
An Experimentally Tuned Dynamic Model Predicting Cell Migration for Guidance of Sprouting Endothelial Cells
No full textEndothelial cells (ECs) create a vascular network with a tubular structure in response to growth factors diffused into the gel and interactions with the surrounding environment. Individual cells migrate in response to all of these cues, leading to network pattern formation. This paper presents a dynamic model predicting EC sprout growth that is tuned to time-lapse experimental cell migration data obtained from microfluidic 3D culture. Simple cell migration equations with just a few parameters are formulated and a Maximum Likelihood estimator is used for estimating model parameters from experimental data. The tuned model is used to evaluate the influence of different sprout elongation rates on cell density in the sprout stalk. This quantitative modeling approach will lead to input shaping and feedback control to optimize sprouting metrics such as stalk cell density. Copyright © 2011 by ASME.Singapore-MIT Alliance for Research and Technology (SMART
Stable control of distributed hysteretic systems using cellular broadcast stochastic feedback
No full textThis work develops a provably stable broadcast feedback approach to regulating the aggregate output of a collection of stochastically behaving cellular units with pronounced hysteresis. Similar to skeletal muscle, comprised of a number of muscle fibers, the cellular units are independent and each contributes to an aggregate system output. The control architecture consists of a central controller that only observes the aggregate system output and cell-level controllers that manage cell state on the hysteresis loop. The central controller stochastically recruits cells to reduce expected squared error. Stability analysis based on supermartingale theory guarantees that the control framework is stable.National Science Foundation (U.S.) (Grant no. NSF CMSI-0728162
Motion artifact reduction for wearable photoplethysmogram sensors using micro accelerometers and laguerre series adaptive filters
Get PDFThesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (p. 73-74).The photoplethysmogram (PPG) is an extremely useful wearable sensing medical diagnostic tool. However, the PPG signal becomes highly corrupted when the wearer is in motion, rendering the measured signal useless. This thesis develops an adaptive motion artifact reduction scheme to recover the underlying physiologic information from the corrupted signal using a collocated accelerometer as a motion reference and adaptively estimating the motion-to-artifact system dynamics. It has previously been shown that this artifact reduction scheme can be utilized, but many tunable parameters were required to model the system dynamics and performance was poor. This work quantifies algorithm performance based on confidence in the estimated system dynamics, which shows low confidence using the previous parameterization when the wearer is jogging. To improve confidence, the form of the system dynamics is established and a Laguerre series is implimented to compactly represent the system dynamics using just a few parameters that can be confidently estimated. Using the new model, heart rate and amplitude can be estimated from typical jogger data with variance similar to separate PPG sensors located on contralateral motionless hands. The standard artifact reduction scheme does not work when the physiologic signal is correlated with wearer motion. Since the signals may become correlated, this work develops a method of recovering the physiological signal even when it is correlated with wearer motion by adapting blind source seperation techniques. However, the success of this new method is limited.by Levi Benjamin Wood.S.M
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
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
Time Lapse Observation Based Modeling and Identification of Cell Behaviors in Angiogenic Sprout Development
No full textThis paper presents a method for deriving dynamic equations for Endothelial Cell (EC) motion and estimating parameters based on time lapse imagery of angiogenic sprout development. Angiogenesis is the process whereby a collection of endothelial cells sprout out from an existing blood vessel, degrade the surrounding scaffold and form a new blood vessel. Sprout formation requires that a collection of ECs all work together and coordinate their movements and behaviors. The process is initiated and guided by a collection of external growth factors. In addition, the individual cells communicate and respond to each other's movements to behave in a coordinated fashion. The mechanics of cell coordination are extremely complex and include both chemical and mechanical communication between cells and between cells and the matrix. Despite the complexity of the physical system, with many variables that cannot be measured in real time, the ECs behave in a predictable manner based on just a few quantities that can be measured in real time. This work presents a methodology for constructing a set of simple stochastic equations for cell motion dependent only on quantities obtained from time lapse data observed from in vitro experiments. Model parameters are identified from time lapse data using a Maximum Likelihood Estimator. Copyright © 2010 by ASME
Quantitative modeling and control of nascent sprout geometry in in vitro Angiogenesis
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 121-127).Nascent blood vessel growth in angiogenesis is a complex process involving cellular response to biochemical growth factors, degradation of the surrounding matrix, and coordinated migration of multiple endothelial cells up a growth factor gradient. Mechanistic understanding and quantitative modeling of the dominant dynamics involved in nascent vessel growth will enable new strategies for regulating vessel growth rate and geometry, and will have implications in controlling growth of complete vascular networks in many research areas, ranging from cancer treatment and wound healing to tissue engineering. In this thesis, we investigate the dynamics of nascent vessel growth in 3D microfluidic assays, formulate a quantitative process model based on our experimental characterization, and formulate a feedback approach to regulate growth. We begin by developing a new microfluidic assay consisting of a collagen gel scaffold with features to reduce assay-to-assay variability and increase experimental throughput. This high throughput assay reveals that there is an inverse relationship between nascent vessel elongation rate and diameter under diverse biochemical conditions. This finding is supported by immuno-fluorescent staining and biochemical inhibition studies, which give insight into the dominant mechanisms determining nascent vessel diameter. Based on our experimental characterization, we formulate a simple quantitative reaction-diffusion model that relates vessel diameter to elongation rate, and supports our understanding of the relevant dynamics. We conclude by formulating a model-based optimization approach for planning the optimal trajectory of elongation rate vs. time needed to obtain desired sprout geometry, and illustrate in simulation that model predictive feedback control can be used to correct for noise in the response of elongation rate to growth factor inputs.by Levi Benjamin Wood.Ph.D
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