5 results
Flux expulsion with dynamics
- Andrew D. Gilbert, Joanne Mason, Steven M. Tobias
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- Journal:
- Journal of Fluid Mechanics / Volume 791 / 25 March 2016
- Published online by Cambridge University Press:
- 24 February 2016, pp. 568-588
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In the process of flux expulsion, a magnetic field is expelled from a region of closed streamlines on a
$TR_{m}^{1/3}$ time scale, for magnetic Reynolds number
$R_{m}\gg 1$ (
$T$ being the turnover time of the flow). This classic result applies in the kinematic regime where the flow field is specified independently of the magnetic field. A weak magnetic ‘core’ is left at the centre of a closed region of streamlines, and this decays exponentially on the
$TR_{m}^{1/2}$ time scale. The present paper extends these results to the dynamical regime, where there is competition between the process of flux expulsion and the Lorentz force, which suppresses the differential rotation. This competition is studied using a quasi-linear model in which the flow is constrained to be axisymmetric. The magnetic Prandtl number
$R_{m}/R_{e}$ is taken to be small, with
$R_{m}$ large, and a range of initial field strengths
$b_{0}$ is considered. Two scaling laws are proposed and confirmed numerically. For initial magnetic fields below the threshold
$b_{core}=O(UR_{m}^{-1/3})$, flux expulsion operates despite the Lorentz force, cutting through field lines to result in the formation of a central core of magnetic field. Here
$U$ is a velocity scale of the flow and magnetic fields are measured in Alfvén units. For larger initial fields the Lorentz force is dominant and the flow creates Alfvén waves that propagate away. The second threshold is
$b_{dynam}=O(UR_{m}^{-3/4})$, below which the field follows the kinematic evolution and decays rapidly. Between these two thresholds the magnetic field is strong enough to suppress differential rotation, leaving a magnetically controlled core spinning in solid body motion, which then decays slowly on a time scale of order
$TR_{m}$.
15 - Proteolytic Cascades in Invasion and Metastasis
- from STROMAL CELLS/EXTRACELLULAR MATRIX
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- By Steven D. Mason, Memorial Sloan-Kettering Cancer Center, United States, Johanna A. Joyce, Memorial Sloan-Kettering Cancer Center, United States
- Edited by David Lyden, Danny R. Welch, Bethan Psaila
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- Book:
- Cancer Metastasis
- Published online:
- 05 June 2012
- Print publication:
- 25 April 2011, pp 167-182
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Summary
During tumor progression, there are several key stages that require the action of proteases (Figure 15.1). First, the induction of angiogenesis, or new blood vessel growth, involves degradation of the vascular basement membrane and the release and/or activation of matrix-bound proangiogenic growth factors. Second, invasion of cancer cells into the surrounding tissue requires the dissolution of cell–cell junctions and degradation of the epithelial basement membrane/extracellular matrix (BM/ECM) for cancer cells to spread from the primary tumor. Third, at least two key steps in metastasis require proteolysis: intravasation of cancer cells into the blood or lymphatic circulation at the primary site, and extravasation at the secondary site, where proteases can again play a role in promoting the colonization and growth of cancer cells as they do in the primary tumor.
Proteases not only are essential for the degradation of BM/ECM proteins, however; they also have more specialized processing roles that are important for cell signaling, such as in the restricted cleavage of pro-domains and subsequent activation of growth factors and cytokines. These functions are tightly regulated in a cascade of proteolytic interactions, allowing for control and amplification of proteolysis in metastasis.
The realization that proteolysis is necessary for multiple stages in metastasis emphasizes the importance of identifying the key tumor-promoting proteases, determining how individual proteases interact with each other, and developing therapeutic strategies to inhibit their actions.
Contributors
-
- By Rose Teteki Abbey, K. C. Abraham, David Tuesday Adamo, LeRoy H. Aden, Efrain Agosto, Victor Aguilan, Gillian T. W. Ahlgren, Charanjit Kaur AjitSingh, Dorothy B E A Akoto, Giuseppe Alberigo, Daniel E. Albrecht, Ruth Albrecht, Daniel O. Aleshire, Urs Altermatt, Anand Amaladass, Michael Amaladoss, James N. Amanze, Lesley G. Anderson, Thomas C. Anderson, Victor Anderson, Hope S. Antone, María Pilar Aquino, Paula Arai, Victorio Araya Guillén, S. Wesley Ariarajah, Ellen T. Armour, Brett Gregory Armstrong, Atsuhiro Asano, Naim Stifan Ateek, Mahmoud Ayoub, John Alembillah Azumah, Mercedes L. García Bachmann, Irena Backus, J. Wayne Baker, Mieke Bal, Lewis V. Baldwin, William Barbieri, António Barbosa da Silva, David Basinger, Bolaji Olukemi Bateye, Oswald Bayer, Daniel H. Bays, Rosalie Beck, Nancy Elizabeth Bedford, Guy-Thomas Bedouelle, Chorbishop Seely Beggiani, Wolfgang Behringer, Christopher M. Bellitto, Byard Bennett, Harold V. Bennett, Teresa Berger, Miguel A. Bernad, Henley Bernard, Alan E. Bernstein, Jon L. Berquist, Johannes Beutler, Ana María Bidegain, Matthew P. Binkewicz, Jennifer Bird, Joseph Blenkinsopp, Dmytro Bondarenko, Paulo Bonfatti, Riet en Pim Bons-Storm, Jessica A. Boon, Marcus J. Borg, Mark Bosco, Peter C. Bouteneff, François Bovon, William D. Bowman, Paul S. Boyer, David Brakke, Richard E. Brantley, Marcus Braybrooke, Ian Breward, Ênio José da Costa Brito, Jewel Spears Brooker, Johannes Brosseder, Nicholas Canfield Read Brown, Robert F. Brown, Pamela K. Brubaker, Walter Brueggemann, Bishop Colin O. Buchanan, Stanley M. Burgess, Amy Nelson Burnett, J. Patout Burns, David B. Burrell, David Buttrick, James P. Byrd, Lavinia Byrne, Gerado Caetano, Marcos Caldas, Alkiviadis Calivas, William J. Callahan, Salvatore Calomino, Euan K. Cameron, William S. Campbell, Marcelo Ayres Camurça, Daniel F. Caner, Paul E. Capetz, Carlos F. Cardoza-Orlandi, Patrick W. Carey, Barbara Carvill, Hal Cauthron, Subhadra Mitra Channa, Mark D. Chapman, James H. Charlesworth, Kenneth R. Chase, Chen Zemin, Luciano Chianeque, Philip Chia Phin Yin, Francisca H. Chimhanda, Daniel Chiquete, John T. Chirban, Soobin Choi, Robert Choquette, Mita Choudhury, Gerald Christianson, John Chryssavgis, Sejong Chun, Esther Chung-Kim, Charles M. A. Clark, Elizabeth A. Clark, Sathianathan Clarke, Fred Cloud, John B. Cobb, W. Owen Cole, John A Coleman, John J. Collins, Sylvia Collins-Mayo, Paul K. Conkin, Beth A. Conklin, Sean Connolly, Demetrios J. Constantelos, Michael A. Conway, Paula M. Cooey, Austin Cooper, Michael L. Cooper-White, Pamela Cooper-White, L. William Countryman, Sérgio Coutinho, Pamela Couture, Shannon Craigo-Snell, James L. Crenshaw, David Crowner, Humberto Horacio Cucchetti, Lawrence S. Cunningham, Elizabeth Mason Currier, Emmanuel Cutrone, Mary L. Daniel, David D. Daniels, Robert Darden, Rolf Darge, Isaiah Dau, Jeffry C. Davis, Jane Dawson, Valentin Dedji, John W. de Gruchy, Paul DeHart, Wendy J. 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Yee, Viktor Yelensky, Yeo Khiok-Khng, Gustav K. K. Yeung, Angela Yiu, Amos Yong, Yong Ting Jin, You Bin, Youhanna Nessim Youssef, Eliana Yunes, Robert Michael Zaller, Valarie H. Ziegler, Barbara Brown Zikmund, Joyce Ann Zimmerman, Aurora Zlotnik, Zhuo Xinping
- Edited by Daniel Patte, Vanderbilt University, Tennessee
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- Book:
- The Cambridge Dictionary of Christianity
- Published online:
- 05 August 2012
- Print publication:
- 20 September 2010, pp xi-xliv
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Correlation Between Bulk Morphology and Luminescence in Porous Silicon Investigated by Evaporation Induced Pore Collapse
- Donald J. Sirbuly, Michael D Mason, Steven K. Buratto
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- Journal:
- MRS Online Proceedings Library Archive / Volume 638 / 2000
- Published online by Cambridge University Press:
- 17 March 2011, F5.21.1
- Print publication:
- 2000
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We use a combination of scanning electron microscopy, laser scanning confocal microscopy and luminescence spectroscopy to correlate the emission properties of anodized porous silicon (PS) with film morphology in samples that have undergone evaporation induced collapse of the underlying porous structure. Several PS samples were investigated as a function of the current density (J) and total etch time, while the total charge (Q) injected per unit area (and the total Si removed) was kept constant during etching. From this data two classes of PS samples emerge. Porous silicon samples produced at high current density have a 3-dimensional pore network with a narrow distribution of blue-green emitting chromophores. In contrast, low current density samples form a 2-dimensional pore network normal to the Si substrate with larger chromophores and exhibit broad red luminescence.
Luminescence Intermittency and Quantum Efficiency of Individual Porous Si Nanoparticles.
- Michael D. Mason, Grace M. Credo, Paul J. Carson, Steven K. Buratto
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- Journal:
- MRS Online Proceedings Library Archive / Volume 560 / 1999
- Published online by Cambridge University Press:
- 10 February 2011, 151
- Print publication:
- 1999
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We have recently observed spectrally resolved vibronic structure and luminescence intermittency from nanometer-size porous silicon nanocrystals. In this study we examine the quantum efficiency of a single nanoparticle and show that emitting nanoparticles do so with near unity quantum efficiency. This result suggests that the emission from porous Si nanoparticles, and thus bulk porous Si, results from a small number of high quantum efficiency emitters. In our previous work we have shown that our nanoparticles contain more than one coupled chromophore. In order to examine these effects more closely we employ several spectroscopy and microscopy techniques including: 1) single-particle spectroscopy, 2) shear-force microscopy, and 3) time-resolved spectroscopy, on a colloidal suspension of size-selected, surface-oxidized nanoparticles. In addition we apply statistical techniques to provide a more complete picture of the coupling between chromophores in a given nanoparticle.
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