Statistics of Core Lifetimes in Numerical Simulations of Turbulent, Magnetically Supercritical Molecular Clouds

We present measurements of the mean dense core lifetimes in numerical simulations of magnetically supercritical, turbulent, isothermal molecular clouds, in order to compare with observational determinations. "Prestellar" lifetimes (given as a function of the mean density within the cores, which in turn is determined by the density threshold n_thr used to define them) are consistent with observationally reported values, ranging from a few to several free-fall times. We also present estimates of the fraction of cores in the "prestellar", "stellar'', and "failed" (those cores that redisperse back into the environment) stages as a function of n_thr. The number ratios are measured indirectly in the simulations due to their resolution limitations. Our approach contains one free parameter, the lifetime of a protostellar object t_yso (Class 0 + Class I stages), which is outside the realm of the simulations. Assuming a value t_yso = 0.46 Myr, we obtain number ratios of starless to stellar cores ranging from 4-5 at n_thr = 1.5 x 10^4 cm^-3 to 1 at n_thr = 1.2 x 10^5 cm^-3, again in good agreement with observational determinations. We also find that the mass in the failed cores is comparable to that in stellar cores at n_thr = 1.5 x 10^4 cm^-3, but becomes negligible at n_thr = 1.2 x 10^5 cm^-3, in agreement with recent observational suggestions that at the latter densities the cores are in general gravitationally dominated. We conclude by noting that the timescale for core contraction and collapse is virtually the same in the subcritical, ambipolar diffusion-mediated model of star formation, in the model of star formation in turbulent supercritical clouds, and in a model intermediate between the previous two, for currently accepted values of the clouds' magnetic criticality.Comment: 25 pages, 8 figures, ApJ accepted. Fig.1 animation is at http://www.astrosmo.unam.mx/~e.vazquez/turbulence/movies/Galvan_etal07/Galvan_etal07.htm

RETOS LOGÍSTICOS EN SSANGYONG MOTOR COLOMBIA S.A.

La revaluación del peso frente al dólary el importante crecimiento que tuvola economía colombiana en los años2005 y 2006, dispararon las ventasde vehículos en Colombia. Para poderaprovechar ese importante aumentode la demanda, SsangYong Motor ColombiaS.A., empresa especializadaen la importación y comercializaciónde vehículos diésel de última generación,se enfrentó a grandes retos logísticos,que se presentaron porque amediados del año 2007 se elevaron losprecios de los fl etes marítimos desdeel Lejano Oriente hacia Suramérica,lo cual incrementó los costos de trasladode vehículos en contenedores.De otro lado, la oferta de espacios enbuques especializados para transportarvehículos no creció y lo quehabía disponible estaba totalmentevendido. A lo anterior, se suma elproblema de congestión en el puertode Buenaventura que incrementó loscostos de desembalaje y transferenciade la carga, además que daban prioridadal depósito de zona franca. Pararesponder a estos retos, SsangYongse planteó tres posibles alternativasde solución. El caso profundiza encada una de ellas desde la perspectivalogística de los negocios internacionales,representa una situación reala la luz de la cual se puede analizarla cambiante situación del mercadoglobal y cómo Colombia interactúacon el mismo.Logística, SsangYong, venta vehículos,fl etes marítimos, puerto Buenaventura.

Mamíferos de Pamplona

En esta guía quedan recogidos todos los grupos de mamíferos que tienen presencia en el entorno de Pamplona, así como sus principales características

GT4Py: High Performance Stencils for Weather and Climate Applications using Python

All major weather and climate applications are currently developed using languages such as Fortran or C++. This is typical in the domain of high performance computing (HPC), where efficient execution is an important concern. Unfortunately, this approach leads to implementations that intermix optimizations for specific hardware architectures with the high-level numerical methods that are typical for the domain. This leads to code that is verbose, difficult to extend and maintain, and difficult to port to different hardware architectures. Here, we propose a different strategy based on GT4Py (GridTools for Python). GT4Py is a Python framework to write weather and climate applications that includes a high-level embedded domain specific language (DSL) to write stencil computations. The toolchain integrated in GT4Py enables automatic code-generation,to obtain the performance of state-of-the-art C++ and CUDA implementations. The separation of concerns between the mathematical definitions and the actual implementations allows for performance portability of the computations on a wide range of computing architectures, while being embedded in Python allows easy access to the tools of the Python ecosystem to enhance the productivity of the scientists and facilitate integration in complex workflows. Here, the initial release of GT4Py is described, providing an overview of the current state of the framework and performance results showing how GT4Py can outperform pure Python implementations by orders of magnitude.Comment: 12 page

Effects of rearing feeding programme on the young rabbit females’ behaviour and welfare indicators

[EN] Restriction of young rabbit females during rearing is a widespread management technique that could have negative consequences on their welfare and behaviour. In the present work, a total of 24 young rabbit females aged 9 wk were used to evaluate 3 rearing feeding programmes until first parturition: CAL, fed ad libitum with a control diet [C: 11.0 MJ digestible energy (DE) and 114 g digestible protein (DP) per kg dry matter (DM)]; CR, receiving the C diet restricted (140 g/d) from 12 wk of age; and F, fed ad libitum with a low energy/high fibre diet [F: 8.7 MJ DE and 88 g DP per kg DM]. F females presented lower body weight than CAL and CR females at week 18 (–0.4 kg and –0.2 kg; P<0.05), but differences in body weight disappeared at parturition. Feeding programme affected the daily feed intake of young females during rearing and gestation periods (on av. of 2 periods: 140, 127 and 179 g DM/d, for CAL, CR and F females, respectively; P<0.001). Blood levels of glucose and insulin decreased with the age of rabbits (from 97 to 73 mg/dL for glucose and from 11 to 6 μUI/mL for insulin at 13 and 20 wk, respectively; P<0.001). Concentration of non-esterified fatty acids was higher in the blood of CAL females (+0.13 mmol/L compared to F; P<0.05), while corticosterone was higher in F females (+0.7 μg/dL compared to CAL; P<0.05). The type of feeding schedule affected the lying still and eating behaviour (P<0.01) of CR females, especially before and after feeding supply, as well as their behavioural stressed indicators (stereotypies; P<0.01), which were more frequent in CR females before feeding supply at 20 weeks of age. Therefore, ad libitum use of a low energy/high fibre diet is an adequate feeding programme for young rabbit females, which does not alter their behavioural patterns.The authors thank the Spanish Ministry of Education and Science (Projects AGL2006-07596 and AGL2014-53405-C2-1-P) for the economic support to conduct this study.Martínez Paredes, EM.; Ródenas Martínez, L.; Pascual Amorós, JJ.; Blas Ferrer, E.; Brecchia, G.; Boiti, C.; Cervera Fras, MC. (2015). Effects of rearing feeding programme on the young rabbit females’ behaviour and welfare indicators. World Rabbit Science. 23(3):197-205. https://doi.org/10.4995/wrs.2015.3987SWORD19720523

Clouds as Turbulent Density Fluctuations. Implications for pressure confinement and spectral line data interpretation

We examine the idea that diffuse and giant molecular clouds and their substructure form as density fluctuations induced by large scale interstellar turbulence. We do this by investigating the topology of various fields in realistic simulations of the ISM. We find that a) the velocity field is continuous across threshold-defined cloud boundaries; b) such cloud boundaries are rather arbitrary, with no correspondence to any actual physical boundary, such as a density discontinuity; c) abrupt velocity jumps are coincident with the density maxima; d) the volume and surface kinetic terms in the Eulerian Virial Theorem for a cloud ensemble are comparable in general; e) the magnetic field exhibits bends and reversals highly correlated with similar density features. These results suggest that clouds are formed by colliding gas streams. Within this framework, we argue that thermal pressure equilibrium is irrelevant for cloud confinement in a turbulent medium, since inertial motions can still distort or disrupt a cloud. Turbulent pressure confinement appears self-defeating, because turbulence contains large-scale motions which necessarily distort cloud boundaries. Density-weighted velocity histograms show similar FWHMs and similar multi-component structure to those of observational line profiles, though the histogram features do not correspond to isolated "clumps", but rather to extended regions throughout a cloud. We argue that the results presented here may be also applicable to small scales with larger densities (molecular clouds and cores) and suggest that quasi- hydrostatic configurations cannot be produced from turbulent fluctuations unless the thermodynamic behavior of the flow becomes nearly adiabatic at late stages of collapse. We expect this to occur only at protostellar densities.Comment: 20 pages, 11 PostScript figures, LaTex, ApJ submitted. Added reference to Chandrasekhar & Munch (1952) and corresponding discussio

Thyrotropin-releasing hormone (TRH) promotes wound re-epithelialisation in frog and human skin

There remains a critical need for new therapeutics that promote wound healing in patients suffering from chronic skin wounds. This is, in part, due to a shortage of simple, physiologically and clinically relevant test systems for investigating candidate agents. The skin of amphibians possesses a remarkable regenerative capacity, which remains insufficiently explored for clinical purposes. Combining comparative biology with a translational medicine approach, we report the development and application of a simple ex vivo frog (Xenopus tropicalis) skin organ culture system that permits exploration of the effects of amphibian skin-derived agents on re-epithelialisation in both frog and human skin. Using this amphibian model, we identify thyrotropin-releasing hormone (TRH) as a novel stimulant of epidermal regeneration. Moving to a complementary human ex vivo wounded skin assay, we demonstrate that the effects of TRH are conserved across the amphibian-mammalian divide: TRH stimulates wound closure and formation of neo-epidermis in organ-cultured human skin, accompanied by increased keratinocyte proliferation and wound healing-associated differentiation (cytokeratin 6 expression). Thus, TRH represents a novel, clinically relevant neuroendocrine wound repair promoter that deserves further exploration. These complementary frog and human skin ex vivo assays encourage a comparative biology approach in future wound healing research so as to facilitate the rapid identification and preclinical testing of novel, evolutionarily conserved, and clinically relevant wound healing promoters

Investment in the long-tail of biodiversity data: from local research to global knowledge

In business, the "long-tail economy" refers to a market strategy where the gravity center shifts from a few high-demand products to many, varied products focused on small niches. Commercialization of individually low-demand products can be profitable as long as their production cost is low and, all taken together, they aggregate into a big chunk of the market. Similarly, in the "business" of biodiversity data acquisition, we can find several mainstream products that produce zillions of bits of information every year and account for most of the budget allocated to increase our primary data-based knowledge about Earth's biological diversity. These products play a crucial role in biodiversity research. However, along with these large global projects, there is a constellation of small-scale institutions that work locally, but whose contribution to our understanding of natural processes should not be dismissed. These information datasets can be collectively referred to as the "long-tail biodiversity data"