11,561 research outputs found
Benjamin Franklin Simons
No full textPhoto of Benjamin Franklin Simons, Lansing. Born 506 South Grand Avenue, Lansing, Michigan 1869. Son of B. F. Simons and Mary Adeline Jennison Simons. Order of Temple, November 20, 1901
Dynamic heterogeneity as a strategy of stem cell self-renewal.
Get PDFTo maintain cycling adult tissue in homeostasis the balance between proliferation and differentiation of stem cells needs to be precisely regulated. To investigate how stem cells achieve perfect self-renewal, emphasis has been placed on models in which stem cells progress sequentially through a one-way proliferative hierarchy. However, investigations of tissue regeneration have revealed a surprising degree of flexibility, with cells normally committed to differentiation able to recover stem cell competence following injury. Here, we investigate whether the reversible transfer of cells between states poised for proliferation or differentiation may provide a viable mechanism for a heterogeneous stem cell population to maintain homeostasis even under normal physiological conditions. By addressing the clonal dynamics, we show that such models of "dynamic heterogeneity" may be equally capable of describing the results of recent lineage tracing assays involving epithelial tissues. Moreover, together with competition for limited niche access, such models may provide a mechanism to render tissue homeostasis robust. In particular, in 2D epithelial layers, we show that the mechanism of dynamic heterogeneity avoids some pathological dependencies that undermine models based on a hierarchical stem/progenitor organization
Extreme value statistics of mutation accumulation in renewing cell populations
Get PDFThe emergence of a predominant phenotype within a cell population is often triggered by the chance accumulation of a sequence of rare genomic DNA mutations within a single cell. For example, tumors may be initiated by a single cell in which multiple mutations cooperate to bypass their natural defense mechanism. The risk of such an event is thus determined by the extremal accumulation of mutations across tissue cells. To address this risk, here we study the statistics of the maximum mutation numbers in a generic, but tested, model of a renewing cell population. By drawing an analogy between the genealogy of a cell population and the theory of branching random walks, we obtain analytical estimates for the probability of exceeding a threshold number of mutations to trigger a proliferative advantage of a cell over its neighbors, and determine how the statistical distribution of maximum mutation numbers scales with age and cell population size
Three-dimensional model of glioblastoma by co-culturing tumor stem cells with human brain organoids.
Get PDFEmerging three-dimensional (3D) cultures of glioblastoma are becoming powerful models to study glioblastoma stem cell behavior and the impact of cell-cell and cell-microenvironment interactions on tumor growth and invasion. Here we describe a method for culturing human glioblastoma stem cells (GSCs) in 3D by co-culturing them with pluripotent stem cell-derived brain organoids. This requires multiple coordinated steps, including the generation of cerebral organoids, and the growth and fluorescence tagging of GSCs. We highlight how to recognize optimal organoid generation and how to efficiently mark GSCs, before describing optimized co-culture conditions. We show that GSCs can efficiently integrate into brain organoids and maintain a significant degree of cell fate heterogeneity, paving the way for the analysis of GSC fate behavior and lineage progression. These results establish the 3D culture system as a viable and versatile GBM model for investigating tumor cell biology and GSC heterogeneity.This article has an associated First Person interview with the first author of the paper
Scattering Amplitudes of Massive N=2 Gauge Theories in Three Dimensions
Get PDFWe study the scattering amplitudes of mass-deformed Chern-Simons theories and Yang-Mills-Chern-Simons theories with N=2 supersymmetry in three dimensions. In particular, we derive the on-shell supersymmetry algebras which underlie the scattering matrices of these theories. We then compute various 3 and 4-point on-shell tree-level amplitudes in these theories. For the mass-deformed Chern-Simons theory, odd-point amplitudes vanish and we find that all of the 4-point amplitudes can be encoded elegantly in superamplitudes. For the Yang-Mills-Chern-Simons theory, we obtain all of the 4-point tree-level amplitudes using a combination of perturbative techniques and algebraic constraints and we comment on difficulties related to computing amplitudes with external gauge fields using Feynman diagrams. Finally, we propose a BCFW recursion relation for mass-deformed theories in three dimensions and discuss the applicability of this proposal to mass-deformed N=2 theories
Deconstructing supersymmetric S matrices in D <= 2+1
Get PDFhttp://arxiv.org/abs/1206.1857v1archiveprefix: arXiv primaryclass: hep-th slaccitation: %%CITATION = ARXIV:1206.1857;%%archiveprefix: arXiv primaryclass: hep-th slaccitation: %%CITATION = ARXIV:1206.1857;%%D. Y. was supported by FNU through Grant No. 272-08-032
Evaluation as adventure: taking that risk
No full textHelen Simons traces the values that underpin her preferred methodology of case study and democratic evaluation to the central values she gained from the land of her birth. She looks back to consider what early experiences may have influenced her deep commitment to these values and how they impacted on her professional world as a teacher, a psychologist, and an evaluator. Her interview transcript which was a stimulus for this article is here: http://onlinelibrary.wiley.com/wol1/doi/10.1002/ev.20302/suppinfo. Read only. This should not be used in any form without explicit permission from the author.</p
Definition of Chern-Simons Terms in Thermal QED_3 Revisited
Get PDFWe present two compact derivations of the correct definition of the Chern-Simons term in the topologically non trivial context of thermal QED_3. One is based on a transgression descent from a D= 4 background connection, the other on embedding the abelian model in SU(2). The results agree with earlier cohomology conclusions and can be also used to justify a recent simple heuristic approach. The correction to the naive Chern-Simons term, and its behavior under large gauge transformations are displayed
Covariantly constant curvature tensors and D=3, N=4, 5, 8 Chern-Simons matter theories
No full textWe construct some examples of D = 3, N = 4 GW theory and N = 5 superconformal Chern-Simons matter theory by using the covariantly constant curvature of a quaternionic-Kahler manifold to construct the symplectic 3-algebra in the theories. Comparing with the previous theories, the N = 4, 5 theories constructed in this way possess a local Sp(2n) symmetry and a diffeomorphism symmetry associated with the quaternionic-Kahler manifold. We also construct a generalized N = 8 BLG theory by utilizing the dual curvature operator of a maximally symmetric space of dimension 4 to construct the Nambu 3-algebra. Comparing with the previous N = 8 BLG theory, the theory has a diffeomorphism invariance and a local SO(4) invariance associated with the symmetric space.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000301843500004&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Astronomy & AstrophysicsPhysics, Particles & FieldsSCI(E)2ARTICLE6null8
Higgs–Chern–Simons Gravity Models in d = 2n + 1 Dimensions
Get PDFWe consider a family of new Higgs–Chern–Simons (HCS) gravity models in 2n+1 dimensions (n=1,2,3). This provides a generalization of the (usual) gravitational Chern–Simons (CS) gravities resulting from non-Abelian CS densities in all odd dimensions, which feature vector and scalar fields, in addition to the metric. The derivation of the new HCS gravitational (HCSG) actions follows the same method as in the usual-CSG case resulting from the usual CS densities. The HCSG result from the HCS densities, which result through a one-step descent of the Higgs–Chern–Pontryagin (HCP), with the latter being descended from Chern-Pontryagin (CP) densities in some even dimension. A preliminary study of the solutions of these models is considered, with exact solutions being reported for spacetime dimensions d=3,5.publishe
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