5,436 research outputs found
Dynamical quark recombination in ultrarelativistic heavy-ion collisions and the proton to pion ratio
We study quark thermal recombination as a function of energy density during
the evolution of a heavy-ion collision in a numerical model that reproduces
aspects of QCD phenomenology. We show that starting with a set of free quarks
(or quarks and antiquarks) the probability to form colorless clusters of three
quarks differs from that to form colorless clusters of quark-antiquark and that
the former has a sharp jump at a critical energy density whereas the latter
transits smoothly from the low to the high energy density domains. We interpret
this as a quantitative difference in the production of baryons and mesons with
energy density. We use this approach to compute the proton and pion spectra in
a Bjorken scenario that incorporates the evolution of these probabilities with
energy density, and therefore with proper time. From the spectra, we compute
the proton to pion ratio and compare to data at the highest RHIC energies. We
show that for a standard choice of parameters, this ratio reaches one, though
the maximum is very sensitive to the initial evolution proper time.Comment: 10 pages, 12 figures, version to appear in Phys. Rev.
El aprendizaje de la Física en bachillerato : investigación con simuladores informáticos versus aula tradicional
Transpiración nocturna en vid
Se presentan las medidas de transpiración media cada quince minutos, de la vid
(Vitis vinifera cv. Tempranillo), en tres periodos fenológicos del cultivo: cerrado de racimo,
envero y maduración. El estudio se realizó en dos plantas de 16 años de edad, a un marco
de plantación de 3 m x 1,5 m, regadas mediante goteo y plantadas en un lisímetro de
pesada continua monolítico de 9 m2 de superficie. Con la finalidad de poder medir la
transpiración, la superficie del lisímetro fue cubierta con una lona impermeable, para evitar la
pérdida de agua por evaporación, dejándose únicamente al aire libre el cultivo; de esta
manera, las medidas registradas de pérdida de peso se debieron únicamente al efecto de la
transpiración. Los resultados indicaron transpiración antes y después de la salida del sol,
oscilando los valores de un 7% a un 16%, con respecto a la transpiración total del día.Ministerio de Economía y Competitividad AGL2014- 54201-C4-4-RMinisterio de Economía y Competitividad RTA2011-00100-C05-04Ministerio de Economía y Competitividad RTA 2014-00049-C05-0
Self-pulsing dynamics of ultrasound in a magnetoacoustic resonator
A theoretical model of parametric magnetostrictive generator of ultrasound is
considered, taking into account magnetic and magnetoacoustic nonlinearities.
The stability and temporal dynamics of the system is analized with standard
techniques revealing that, for a given set of parameters, the model presents a
homoclinic or saddle--loop bifurcation, which predicts that the ultrasound is
emitted in the form of pulses or spikes with arbitrarily low frequency.Comment: 5 pages, 5 figure
Excitability in a nonlinear magnetoacoustic resonator
We report a nonlinear acoustic system displaying excitability. The considered
system is a magnetostrictive material where acoustic waves are parametrically
generated. For a set of parameters, the system presents homoclinic and
heteroclinic dynamics, whose boundaries define a excitability domain. The
excitable behaviour is characterized by analyzing the response of the system to
different external stimuli. Single spiking and bursting regimes have been
identified.Comment: 4 pages, 5 figure
¿Es posible mejorar la eficiencia en el uso del agua de un viñedo mediante un acolchado orgánico del suelo?
El objetivo de este trabajo fue evaluar el efecto que un acolchado orgánico del suelo
(restos de poda) puede tener sobre la evapotranspiración del cultivo (ETc) de la vid con el fin
de mejorar la eficiencia en el uso del agua. El estudio se realizó durante la campaña de
2015 en la finca “Las Tiesas”, Albacete (España). Las medidas se llevaron a cabo en un
lisímetro monolítico de pesada ubicado en el centro de una parcela de vid (Vitis vinífera L.,
cv. Tempranillo) de 1 ha de superficie, y con cepas plantadas a un marco de 3 x 1,5 m y
conducción en espaldera. Se llevaron a cabo tres ciclos de medidas, cada uno consistió en
mantener el suelo desnudo durante los dos primeros días, los dos siguientes se cubrió la
superficie del lisímetro con un acolchado orgánico (restos de poda de la vid) y los dos
últimos días se cubrió el lisímetro con un acolchado inorgánico (lona de plástico). Los
resultados indican que para la misma demanda evaporativa y fracción de cubierta vegetal, el
acolchado orgánico redujo la ETc de la vid algo más de un 17%, mientras que el plástico la
redujo un 25%. Los resultados obtenidos indican que con el acolchado orgánico sigue
produciéndose una cierta evaporación de agua desde el suelo, pero se reduce
considerablemente la ETc pudiéndose mejorar la eficiencia en el uso del agua.Ministerio de Economía y Competitividad FEDER AGL2014-54201-C4-4- RRTA 2011-00100-C05-04RTA 2014-00049-C05-0
Preliminary linkage map in turbot (Scophthalmus maximus) with AFLPs and Microsatellite markers.
Wildlife and Antibiotic Resistance
Antibiotic resistance is a major human health problem. While health care facilities are main contributors to the emergence, evolution and spread of antibiotic resistance, other ecosystems are involved in such dissemination. Wastewater, farm animals and pets have been considered important contributors to the development of antibiotic resistance. Herein, we review the impact of wildlife in such problem. Current evidence supports that the presence of antibiotic resistance genes and/or antibiotic resistant bacteria in wild animals is a sign of anthropic pollution more than of selection of resistance. However, once antibiotic resistance is present in the wild, wildlife can contribute to its transmission across different ecosystems. Further, the finding that antibiotic resistance genes, currently causing problems at hospitals, might spread through horizontal gene transfer among the bacteria present in the microbiomes of ubiquitous animals as cockroaches, fleas or rats, supports the possibility that these organisms might be bioreactors for the horizontal transfer of antibiotic resistance genes among human pathogens. The contribution of wildlife in the spread of antibiotic resistance among different hosts and ecosystems occurs at two levels. Firstly, in the case of non-migrating animals, the transfer will take place locally; a One Health problem. Paradigmatic examples are the above mentioned animals that cohabit with humans and can be reservoirs and vehicles for antibiotic resistance dissemination. Secondly, migrating animals, such as gulls, fishes or turtles may participate in the dissemination of antibiotic resistance across different geographic areas, even between different continents, which constitutes a Global Health issue. Copyright © 2022 Laborda, Sanz-García, Ochoa-Sánchez, Gil-Gil, Hernando-Amado and Martínez
A new pathogenicity island carrying an allelic variant of the Subtilase cytotoxin is common among Shiga toxin producing Escherichia coli of human and ovine origin
AbstractSubtilase (SubAB) is a cytotoxin elaborated by some Shiga Toxin (Stx)-producing Escherichia coli (STEC) strains usually lacking the locus of enterocyte effacement (LEE). Two variants of SubAB coding genes have been described: subAB1, located on the plasmid of the STEC O113 98NK2 strain, and subAB2, located on a pathogenicity island (PAI) together with the tia gene, encoding an invasion determinant described in enterotoxigenic E. coli. In the present study, we determined the entire nucleotide sequence of the PAI containing the subAB2 operon, termed Subtilase-Encoding PAI (SE-PAI), and identified its integration site in the pheV tRNA locus. In addition, a PCR strategy for discriminating the two subAB allelic variants was developed and used to investigate their presence in E. coli strains belonging to different pathotypes and in a large collection of LEE-negative STEC of human and ovine origin. The results confirmed that subAB genes are carried predominantly by STEC and showed their presence in 72% and 86% of the LEE-negative strains from human cases of diarrhoea and from healthy sheep respectively. Most of the subAB-positive strains (98%) identified possessed the subAB2 allelic variant and were also positive for tia, suggesting the presence of SE-PAI. Altogether, our observations indicate that subAB2 is the prevalent SubAB-coding operon in LEE-negative STEC circulating in European countries, and that sheep may represent an important reservoir for human infections with these strains. Further studies are needed to assess the role of tia and/or other genes carried by SE-PAI in the colonization of the host intestinal mucosa
On-surface synthesis of metal–organic frameworks: the critical role of the reaction conditions
Two different metal–organic frameworks with either a honeycomb or Kagome structure were grown on Cu(111) using para-aminophenol molecules and native surface adatoms. Although both frameworks are made up from the same chemical species, they are structurally different emphasizing the critical role being played by the reaction conditions during their growth. This work highlights the importance of the balance between thermodynamics and kinetics in the final structure of surface-supported metal–organic networks
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