Diffusion in supersonic, turbulent, compressible flows

We investigate diffusion in supersonic, turbulent, compressible flows. Supersonic turbulence can be characterized as network of interacting shocks. We consider flows with different rms Mach numbers and where energy necessary to maintain dynamical equilibrium is inserted at different spatial scales. We find that turbulent transport exhibits super-diffusive behavior due to induced bulk motions. In a comoving reference frame, however, diffusion behaves normal and can be described by mixing length theory extended into the supersonic regime.Comment: 11 pages, incl. 5 figures, accepted for publication in Physical Review E (a high-resolution version is available at http://www.aip.de./~ralf/Publications/p21.abstract.html

Large-scale energy and pressure dynamics in decaying 2D incompressible isotropic turbulence.

Numerical simulations using either molecular or hyper-viscosity are carried out to study the temporal evolution of large-scale energy and pressure statistics in decaying two-dimensional incompressible isotropic turbulence. Initial Gaussian velocity fields peaking at small scales are considered. For each set of initial parameters, multiple realizations are performed to achieve reasonable statistical convergence. A wide range of Reynolds numbers (based on an equivalent Taylor microscale) is explored. For an initial energy spectrum E(k,0) ∝ k s 0 as k → 0 with s 0 ≥ 3, and at high enough Reynolds number, the numerical simulations display an important energy backscatter at subsequent times: E(k,t) ∝ t γ e k s , where s ≈ 3 and γ e converges at high times towards 2.5. The pressure spectrum E pp (k,0) is initially proportional to k 1 at small wavenumbers, in agreement with the predictions of quasi-normal theory. After a short transient decay, the infrared pressure spectrum increases significantly with time, while becoming steeper than k 1. However, a Gaussian randomization of the velocity allows the k 1 pressure spectrum to be recovered. In the high-Reynolds-number regime, the infrared pressure spectrum increases enough to induce a temporal growth of the pressure variance. We examine self-similar behaviours based on Taylor, integral and dissipative scales. Finally, we determine pressure pdf's, which compare favourably with earlier analytic predictions based on shell models made by Holzer and Siggia

A comparison of spectral and vortex methods in three-dimensional incompressible flows

We present a comparison of the performance of vortex and pseudospectral methods in two reference flows: a homogeneous turbulent flow at low Reynolds number and a vortex reconnection case at a moderate Reynolds number. The results should contribute to a better understanding of the accuracy of vortex methods in both resolved and underresolved simulations. (C) 2002 Elsevier Science (USA)

Co-existence of BRAF and NRAS driver mutations in the same melanoma cells results in heterogeneity of targeted therapy resistance

Acquired chemotherapeutic resistance of cancer cells can result from a Darwinistic evolution process in which heterogeneity plays an important role. In order to understand the impact of genetic heterogeneity on acquired resistance and second line therapy selection in metastatic melanoma, we sequenced the exomes of 27 lesions which were collected from 3 metastatic melanoma patients treated with targeted or non-targeted inhibitors. Furthermore, we tested the impact of a second NRAS mutation in 7 BRAF inhibitor resistant early passage cell cultures on the selection of second line therapies.We observed a rapid monophyletic evolution of melanoma subpopulations in response to targeted therapy that was not observed in non-targeted therapy. We observed the acquisition of NRAS mutations in the BRAF mutated patient treated with a BRAF inhibitor in 1 of 5 of his post-resistant samples. In an additional cohort of 5 BRAF-inhibitor treated patients we detected 7 NRAS mutations in 18 post-resistant samples. No NRAS mutations were detected in pre-resistant samples. By sequencing 65 single cell clones we prove that NRAS mutations co-occur with BRAF mutations in single cells. The double mutated cells revealed a heterogeneous response to MEK, ERK, PI3K, AKT and multi RTK - inhibitors.We conclude that BRAF and NRAS co-mutations are not mutually exclusive. However, the sole finding of double mutated cells in a resistant tumor is not sufficient to determine follow-up therapy. In order to target the large pool of heterogeneous cells in a patient, we think combinational therapy targeting different pathways will be necessary

Kissing Cuisines: Exploring Worldwide Culinary Habits on the Web

Food and nutrition occupy an increasingly prevalent space on the web, and dishes and recipes shared online provide an invaluable mirror into culinary cultures and attitudes around the world. More specifically, ingredients, flavors, and nutrition information become strong signals of the taste preferences of individuals and civilizations. However, there is little understanding of these palate varieties. In this paper, we present a large-scale study of recipes published on the web and their content, aiming to understand cuisines and culinary habits around the world. Using a database of more than 157K recipes from over 200 different cuisines, we analyze ingredients, flavors, and nutritional values which distinguish dishes from different regions, and use this knowledge to assess the predictability of recipes from different cuisines. We then use country health statistics to understand the relation between these factors and health indicators of different nations, such as obesity, diabetes, migration, and health expenditure. Our results confirm the strong effects of geographical and cultural similarities on recipes, health indicators, and culinary preferences across the globe

Human eccrine sweat gland cells turn into melanin-uptaking Keratinocytes in dermo-epidermal skin substitutes

Recently, Biedermann et al. (2010) have demonstrated that human eccrine sweat gland cells can develop a multilayered epidermis. The question still remains whether these cells can fulfill exclusive and very specific functional properties of epidermal keratinocytes, such as the incorporation of melanin, a feature absent in sweat gland cells. We added human melanocytes to eccrine sweat gland cells to let them develop into an epidermal analog in vivo. The interaction between melanocytes and sweat gland-derived keratinocytes was investigated. The following results were gained: (1) macroscopically, a pigmentation of the substitutes was seen 2-3 weeks after transplantation; (2) we confirmed the development of a multilayered, stratified epidermis with melanocytes distributed evenly throughout the basal layer; (3) melanocytic dendrites projected to suprabasal layers; and (4) melanin was observed to be integrated into former eccrine sweat gland cells. These skin substitutes were similar or equal to skin substitutes cultured from human epidermal keratinocytes. The only differences observed were a delay in pigmentation and less melanin uptake. These data suggest that eccrine sweat gland cells can form a functional epidermal melanin unit, thereby providing striking evidence that they can assume one of the most characteristic keratinocyte properties