Browsing by Issue Date, starting with "2015-01-28"
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- Upscale and downscale energy transfer over the tropical Pacific revealed by scatterometer windsPublication . King, Gregory P.; Vogelzang, Jur; Stoffelen, AdThe direction of the energy cascade in the mesoscales of atmospheric turbulence is investigated using near-surface winds over the tropical Pacific measured by satellite scatterometers SeaWinds (QuikSCAT) and ASCAT (MetOp-A). The tropical Pacific was subdivided into nine regions, classified as rainy or dry. Longitudinal third-order along-track structure functions inline image and skewness inline image were calculated as a function of separation inline image for each region and month during the period November 2008 to October 2009. We find that the results support both downscale and upscale interpretations, depending on region and month. The results indicate that normally energy cascades downscale, but cascades upscale over the cold tongue in the cold season and over the west Pacific in summer months. An explanation is offered based on the heating or cooling of the air by the underlying sea surface temperature. It is also found that the signature of intermittent small-scale (<100 km) events could be identified in graphs of inline image, implying that this diagnostic may be useful in the studies of tropical disturbances.
- Model Checking to Assess T-Helper Cell PlasticityPublication . Abou-Jaoudé, Wassim; Monteiro, Pedro T.; Naldi, Aurélien; Grandclaudon, Maximilien; Soumelis, Vassili; Chaouiya, Claudine; Thieffry, DenisComputational modeling constitutes a crucial step toward the functional understanding of complex cellular networks. In particular, logical modeling has proven suitable for the dynamical analysis of large signaling and transcriptional regulatory networks. In this context, signaling input components are generally meant to convey external stimuli, or environmental cues. In response to such external signals, cells acquire specific gene expression patterns modeled in terms of attractors (e.g., stable states). The capacity for cells to alter or reprogram their differentiated states upon changes in environmental conditions is referred to as cell plasticity. In this article, we present a multivalued logical framework along with computational methods recently developed to efficiently analyze large models. We mainly focus on a symbolic model checking approach to investigate switches between attractors subsequent to changes of input conditions. As a case study, we consider the cellular network regulating the differentiation of T-helper (Th) cells, which orchestrate many physiological and pathological immune responses. To account for novel cellular subtypes, we present an extended version of a published model of Th cell differentiation. We then use symbolic model checking to analyze reachability properties between Th subtypes upon changes of environmental cues. This allows for the construction of a synthetic view of Th cell plasticity in terms of a graph connecting subtypes with arcs labeled by input conditions. Finally, we explore novel strategies enabling specific Th cell polarizing or reprograming events.
- Second-order structure function analysis of scatterometer winds over the Tropical PacificPublication . King, Gregory P.; Vogelzang, Jur; Stoffelen, AdKolmogorov second-order structure functions are used to quantify and compare the small-scale information contained in near-surface ocean wind products derived from measurements by ASCAT on MetOp-A and SeaWinds on QuikSCAT. Two ASCAT and three SeaWinds products are compared in nine regions (classified as rainy or dry) in the tropical Pacific between 10°S and 10°N and 140° and 260°E for the period November 2008 to October 2009. Monthly and regionally averaged longitudinal and transverse structure functions are calculated using along-track samples. To ease the analysis, the following quantities were estimated for the scale range 50 to 300 km and used to intercompare the wind products: (i) structure function slopes, (ii) turbulent kinetic energies ( inline image), and (iii) vorticity-to-divergence ratios. All wind products are in good qualitative agreement, but also have important differences. Structure function slopes and inline image differ per wind product, but also show a common variation over time and space. Independent of wind product, longitudinal slopes decrease when sea surface temperature exceeds the threshold for onset of deep convection (about 28°C). In rainy areas and in dry regions during rainy periods, ASCAT has larger divergent inline image than SeaWinds, while SeaWinds has larger vortical inline image than ASCAT. Differences between SeaWinds and ASCAT vortical inline image and vorticity-to-divergence ratios for the convectively active months of each region are large.