Time Data Sequential Processor /TDSP/

Time Data Sequential Processor /TDSP/ computer program provides preflight predictions for lunar trajectories from injection to impact, and for planetary escape trajectories for up to 100 hours from launch. One of the major options TDSP performs is the determination of tracking station view periods

Overexpression of Akt1 Enhances Adipogenesis and Leads to Lipoma Formation in Zebrafish

<div><h3>Background</h3><p>Obesity is a complex, multifactorial disorder influenced by the interaction of genetic, epigenetic, and environmental factors. Obesity increases the risk of contracting many chronic diseases or metabolic syndrome. Researchers have established several mammalian models of obesity to study its underlying mechanism. However, a lower vertebrate model for conveniently performing drug screening against obesity remains elusive. The specific aim of this study was to create a zebrafish obesity model by over expressing the insulin signaling hub of the <em>Akt1</em> gene.</p> <h3>Methodology/Principal Findings</h3><p><em>Skin oncogenic transformation screening shows that a stable zebrafish transgenic of Tg(krt4Hsa.myrAkt1</em>)^cy18 displays severely obese phenotypes at the adult stage. In Tg(<em>krt4:Hsa.myrAkt1</em>)^cy18, the expression of exogenous human constitutively active Akt1 (myrAkt1) can activate endogenous downstream targets of mTOR, GSK-3α/β, and 70S6K. During the embryonic to larval transitory phase, the specific over expression of myrAkt1 in skin can promote hypertrophic and hyperplastic growth. From 21 hour post-fertilization (hpf) onwards, myrAkt1 transgene was ectopically expressed in several mesenchymal derived tissues. This may be the result of the integration position effect. Tg(<em>krt4:Hsa.myrAkt1</em>)^cy18 caused a rapid increase of body weight, hyperplastic growth of adipocytes, abnormal accumulation of fat tissues, and blood glucose intolerance at the adult stage. Real-time RT-PCR analysis showed the majority of key genes on regulating adipogenesis, adipocytokine, and inflammation are highly upregulated in Tg(<em>krt4:Hsa.myrAkt1</em>)^cy18. In contrast, the myogenesis- and skeletogenesis-related gene transcripts are significantly downregulated in Tg(<em>krt4:Hsa.myrAkt1</em>)^cy18, suggesting that excess adipocyte differentiation occurs at the expense of other mesenchymal derived tissues.</p> <h3>Conclusion/Significance</h3><p>Collectively, the findings of this study provide direct evidence that Akt1 signaling plays an important role in balancing normal levels of fat tissue in vivo. The obese zebrafish examined in this study could be a new powerful model to screen novel drugs for the treatment of human obesity.</p> </div

Recent advances in computer modelling of granular systems

We present simple computer algorithms able to build random packings of spheres using the ballistic deposition model and we show how they can be used to investigate several size segregation phenomena occuring in granular systems : 1) penetration of a small sphere in a packing of large ones, 2) size-segregation in the formation of a heap or when pouring a silo, 3) size-segregation by shaking. In the last case, the computer simulation provides a very simple geometrical explanation of the phenomenon

Penrose tiling approximants

The modification of the Penrose tiling into a periodic structure is considered. Detailed analysis of the strip method and the dual transformation which yield approximants of the perfect tiling is presented in such a way that a complete classification of approximants is provided. The defects introduced to change the aperiodic order into a periodic one are discussed, their number per unit cell is derived, and the tile density is calculated. Our model implies also a fundamental similarity between the partial dislocations of the approximants and the elementary dislocations of quasi-crystals, which might result in comparable plasticity properties.Nous considérons les structures obtenues en modifiant un pavage de Penrose en un pavage périodique. Les analyses détaillées de la méthode de la bande et de la transformation duale sont présentées de façon à produire une classification générale des approximants. La nature des défauts qu'il est nécessaire d'introduire pour transformer un cristal apériodique en un cristal périodique est discutée ; nous calculons en outre leur nombre par cellule unité ainsi que la densité des tuiles. Notre modèle implique que les dislocations partielles des approximants et les dislocations élémentaires des quasi-cristaux sont des objets fondamentalement similaires ; cette similarité devrait conduire à des propriétés de déformation plastique comparables

Stress distributions in flowing aggregated colloidal suspensions

Simulations of the flow of concentrated aggregated colloidal systems, at the particulate level, are used to investigate the distribution of stresses in the shear-thinning regime. It is found that the distribution of shear stress carried by interparticle bonds decays approximately exponentially at large stresses, but with a double-exponential distribution for values of positive stress. The microstructural mechanisms associated with large stresses are manifested in clusters which dominate the positive contribution to the stress in the system. Towards the end of shear thinning the highest forces occur along bonds defining rods of particles aligned approximately along the flow-compression direction. We propose that the rheology of such systems is determined by a rupture-reformation process of these clusters of stress concentration during the flow. The aggregation forces play the role of enhancing such stress concentration by stabilizing clusters against buckling. (C) 1999 American Institute of Physics. [S0021-9606(99)51934-X]