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Search Results: 1 - 10 of 191346 matches for " D. Zahnow "
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Aggregation and fragmentation dynamics of inertial particles in chaotic flows
Jens C. Zahnow,Rafael D. Vilela,Ulrike Feudel,Tamas Tel
Physics , 2008, DOI: 10.1103/PhysRevE.77.055301
Abstract: Inertial particles advected in chaotic flows often accumulate in strange attractors. While moving in these fractal sets they usually approach each other and collide. Here we consider inertial particles aggregating upon collision. The new particles formed in this process are larger and follow the equation of motion with a new parameter. These particles can in turn fragment when they reach a certain size or shear forces become sufficiently large. The resulting system consists of a large set of coexisting dynamical systems with a varying number of particles. We find that the combination of aggregation and fragmentation leads to an asymptotic steady state. The asymptotic particle size distribution depends on the mechanism of fragmentation. The size distributions resulting from this model are consistent with those found in rain drop statistics and in stirring tank experiments.
Coagulation and fragmentation dynamics of inertial particles
Jens C. Zahnow,Rafael D. Vilela,Ulrike Feudel,Tamás Tél
Physics , 2009, DOI: 10.1103/PhysRevE.80.026311
Abstract: Inertial particles suspended in many natural and industrial flows undergo coagulation upon collisions and fragmentation if their size becomes too large or if they experience large shear. Here we study this coagulation-fragmentation process in time-periodic incompressible flows. We find that this process approaches an asymptotic, dynamical steady state where the average number of particles of each size is roughly constant. We compare the steady-state size distributions corresponding to two fragmentation mechanisms and for different flows and find that the steady state is mostly independent of the coagulation process. While collision rates determine the transient behavior, fragmentation determines the steady state. For example, for fragmentation due to shear, flows that have very different local particle concentrations can result in similar particle size distributions if the temporal or spatial variation of shear forces is similar.
CCAAT/enhancer binding proteins in normal mammary development and breast cancer
Cynthia A Zahnow
Breast Cancer Research , 2002, DOI: 10.1186/bcr428
Abstract: Breast cancer is, in part, a result of the overexpression of transcription factors that disrupt the delicate balance between cellular proliferation, terminal differentiation and programmed cell death. Yet, when expressed at physiologic levels, many of these same transcription factors are critical for normal development of the mammary gland. The C/EBPs play a pivotal role in controlling growth and differentiation of the mammary gland. Accordingly, this review focuses on the role that the C/EBPs play in both breast cancer and in normal mammary development.The C/EBPs together form a highly conserved family of transcription factors that bind to sequence-specific DNA sequences as dimers and that regulate the transcription of genes involved in proliferation and differentiation. Six C/EBP genes have thus far been identified, and they are designated C/EBPα, C/EBPβ, C/EBPγ, C/EBPδ, C/EBPε, and C/EBPζ (also known as CHOP [C/EBP homologous protein-10] or GADD153) (for a review of the nomenclature, see [1]). Of these genes, C/EBPβ, C/EBPα, and C/EBPδ have been the most thoroughly studied in rodent and human mammary tissue, and will be the focus of this review.C/EBPs belong to the leucine zipper class of DNA-binding proteins. They contain an amino-terminal transactivation domain and a highly basic DNA-binding region immediately adjacent to the carboxyl-terminal, leucine-rich dimerization domain (Fig. 1).The dimerization domain is characterized as an amphipathic, α-helix containing a heptad repeat of leucines that project uniformly along the hydrophobic side of the helix and that interdigitate with the leucine residues of a dimerization partner [2]. Dimerization can occur within a C/EBP family, between different C/EBP family members, or between different groups of leucine zipper proteins [3]. Dimerization of these helices has been proposed to bring into close proximity the basic amino acids associated with the DNA binding domain from the two polypeptide chains [2,4]. Dimerization
What determines size distributions of heavy drops in a synthetic turbulent flow?
J. C. Zahnow,U. Feudel
Nonlinear Processes in Geophysics (NPG) , 2009,
Abstract: We present results from an individual particle based model for the collision, coagulation and fragmentation of heavy drops moving in a turbulent flow. Such a model framework can help to bridge the gap between the full hydrodynamic simulation of two phase flows, which can usually only study few particles and mean field based approaches for coagulation and fragmentation relying heavily on parameterization and are for example unable to fully capture particle inertia. We study the steady state that results from a balance between coagulation and fragmentation and the impact of particle properties and flow properties on this steady state. We compare two different fragmentation mechanisms, size-limiting fragmentation where particles fragment when exceeding a maximum size and shear fragmentation, where particles break up when local shear forces in the flow exceed the binding force of the particle. For size-limiting fragmentation the steady state is mainly influenced by the maximum stable particle size, while particle and flow properties only influence the approach to the steady state. For shear fragmentation both the approach to the steady state and the steady state itself depend on the particle and flow parameters. There we find scaling relationships between the steady state and the particle and flow parameters that are determined by the stability condition for fragmentation.
What Determines Size Distributions of Heavy Drops in a Synthetic Turbulent Flow?
Jens C. Zahnow,Ulrike Feudel
Physics , 2009,
Abstract: We present results from an individual particle based model for the collision, coagulation and fragmentation of heavy drops moving in a turbulent flow. Such a model framework can help to bridge the gap between the full hydrodynamic simulation of two phase flows, which can usually only study few particles and mean field based approaches for coagulation and fragmentation relying heavily on parameterization and are for example unable to fully capture particle inertia. We study the steady state that results from a balance between coagulation and fragmentation and the impact of particle properties and flow properties on this steady state. We compare two different fragmentation mechanisms, size-limiting fragmentation where particles fragment when exceeding a maximum size and shear fragmentation, where particles break up when local shear forces in the flow exceed the binding force of the particle. For size-limiting fragmentation the steady state is mainly influenced by the maximum stable particle size, while particle and flow properties only influence the approach to the steady state. For shear fragmentation both the approach to the steady state and the steady state itself depend on the particle and flow parameters. There we find scaling relationships between the steady state and the particle and flow parameters that are determined by the stability condition for fragmentation.
Moving Finite Size Particles in a Flow: A Physical Example for Pitchfork Bifurcations of Tori
Jens C. Zahnow,Ulrike Feudel
Physics , 2008, DOI: 10.1103/PhysRevE.77.026215
Abstract: The motion of small, spherical particles of finite size in fluid flows at low Reynolds numbers is described by the strongly nonlinear Maxey-Riley equations. Due to the Stokes drag the particle motion is dissipative, giving rise to the possibility of attractors in phase space. We investigate the case of an infinite, cellular flow field with time-periodic forcing. The dynamics of this system are studied in a part of the parameter space. We focus particularly on the size of the particles whose variations are most important in active, physical processes, for example for aggregation and fragmentation of particles. Depending on their size the particles will settle on different attractors in phase space in the long term limit, corresponding to periodic, quasiperiodic or chaotic motion. One of the invariant sets that can be observed in a large part of this parameter region is a quasiperiodic motion in form of a torus. We identify some of the bifurcations that these tori undergo, as particle size and mass ratio relative to the fluid are varied. This way we provide a physical example for sub- and supercritical pitchfork bifurcations of tori.
Particle-based modelling of aggregation and fragmentation processes: Fractal-like aggregates
Jens C. Zahnow,Joeran Maerz,Ulrike Feudel
Physics , 2009, DOI: 10.1016/j.physd.2011.01.003
Abstract: The incorporation of particle inertia into the usual mean field theory for particle aggregation and fragmentation in fluid flows is still an unsolved problem. We therefore suggest an alternative approach that is based on the dynamics of individual inertial particles and apply this to study steady state particle size distributions in a 3-d synthetic turbulent flow. We show how a fractal-like structure, typical of aggregates in natural systems, can be incorporated in an approximate way into the aggregation and fragmentation model by introducing effective densities and radii. We apply this model to the special case of marine aggregates in coastal areas and investigate numerically the impact of three different modes of fragmentation: large-scale splitting, where fragments have similar sizes, erosion, where one of the fragments is much smaller than the other and uniform fragmentation, where all sizes of fragments occur with the same probability. We find that the steady state particle size distribution depends strongly on the mode of fragmentation. The resulting size distribution for large-scale fragmentation is exponential. As some aggregate distributions found in published measurements share this latter characteristic, this may indicate that large-scale fragmentation is the primary mode of fragmentation in these cases.
LIP expression is regulated by IGF-1R signaling and participates in suppression of anoikis
Huili Li, Brenda R Baldwin, Cynthia A Zahnow
Molecular Cancer , 2011, DOI: 10.1186/1476-4598-10-100
Abstract: Our data provide the first evidence that IGF-1R signaling regulates LIP expression in an EGFR independent manner to increase the LIP/LAP ratio in mammary epithelial cells. Although crosstalk between IGF-1R signaling and EGFR signaling is detectable in MCF10A cells, this crosstalk is not required for the IGF-1 mediated regulation of LIP expression. Rather, the critical regulator of IGF-1 induced LIP expression appears to be EGFR-independent, Akt activity. Our data also demonstrate that increases in LIP expression promote cell survival via suppression of anoikis. Likewise, knockdown of total C/EBPβ leads to increased cell death and suggest that C/EBPβ expression is important for survival and resistance to anoikis. IGF-1 treatment can partially rescue vector control cells from anoikis; however, cells with reduced C/EBPβ expression do not survive anoikis.Taken together, our data demonstrate that IGF-1R signaling regulates LIP expression in an EGFR independent manner to increase the LIP/LAP ratio in mammary epithelial cells. C/EBPβ expression and elevations in LIP play an important role in regulating cellular survival via suppression of anoikis, in an IGF-1R mediated context or in a manner independent of IGF-1R signaling.The transcription factor, CCAAT/Enhancer binding protein β (C/EBPβ) is an important mediator of mammary development [1,2] and breast tumorigenesis [3,4]. Encoded by an intronless gene, C/EBPβ is expressed as several distinct protein isoforms (LAP1, LAP2 and LIP) whose expression is tightly regulated by the differential use of a number of in-frame translation start sites [5-7]. All of the C/EBPβ isoforms share the same C-terminal DNA binding and leucine zipper dimerization domains, but LIP lacks all of the N-terminal transactivation domain and much of the inhibitory domains. Consequently, LIP can act as a dominant-negative [5] to inhibit gene transcription or as an activator of transcription, depending upon the nature of its interaction with other C/EBP f
The Cross Section of 3He(3He,2p)4He measured at Solar Energies
The LUNA Collaboration,M. Junker,A. D'Alessandro,S. Zavatarelli,C. Arpesella,E. Bellotti,C. Broggini,P. Corvisiero,G. Fiorentini,A. Fubini,G. Gervino,U. Greife,C. Gustavino,J. Lambert,P. Prati,W. S. Rodney,C. Rolfs,F. Strieder,H. P. Trautvetter,D. Zahnow
Physics , 1997, DOI: 10.1103/PhysRevC.57.2700
Abstract: We report on the results of the \hethet\ experiment at the underground accelerator facility LUNA (Gran Sasso). For the first time the lowest projectile energies utilized for the cross section measurement correspond to energies below the center of the solar Gamow peak ($E_{\rm 0}$=22 keV). The data provide no evidence for the existence of a hypothetical resonance in the energy range investigated. Although no extrapolation is needed anymore (except for energies at the low-energy tail of the Gamow peak), the data must be corrected for the effects of electron screening, clearly observed the first time for the \hethet\ reaction. The effects are however larger than expected and not understood, leading presently to the largest uncertainty on the quoted $S_{\rm b}(E_{\rm 0})$ value for bare nuclides (=5.40 MeV b).
Methylation of the Claudin 1 Promoter Is Associated with Loss of Expression in Estrogen Receptor Positive Breast Cancer
Francescopaolo Di Cello, Leslie Cope, Huili Li, Jana Jeschke, Wei Wang, Stephen B. Baylin, Cynthia A. Zahnow
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0068630
Abstract: Downregulation of the tight junction protein claudin?1 is a frequent event in breast cancer and is associated with recurrence, metastasis, and reduced survival, suggesting a tumor suppressor role for this protein. Tumor suppressor genes are often epigenetically silenced in cancer. Downregulation of claudin?1 via DNA promoter methylation may thus be an important determinant in breast cancer development and progression. To investigate if silencing of claudin?1 has an epigenetic etiology in breast cancer we compared gene expression and methylation data from 217 breast cancer samples and 40 matched normal samples available through the Cancer Genome Atlas (TCGA). Moreover, we analyzed claudin?1 expression and methylation in 26 breast cancer cell lines. We found that methylation of the claudin?1 promoter CpG island is relatively frequent in estrogen receptor positive (ER+) breast cancer and is associated with low claudin?1 expression. In contrast, the claudin?1 promoter was not methylated in most of the ER-breast cancers samples and some of these tumors overexpress claudin?1. In addition, we observed that the demethylating agents, azacitidine and decitabine can upregulate claudin?1 expression in breast cancer cell lines that have a methylated claudin?1 promoter. Taken together, our results indicate that DNA promoter methylation is causally associated with downregulation of claudin?1 in a subgroup of breast cancer that includes mostly ER+ tumors, and suggest that epigenetic therapy to restore claudin?1 expression might represent a viable therapeutic strategy in this subtype of breast cancer.
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