3,041 research outputs found
Mutualism supports biodiversity when the direct competition is weak
A key question of theoretical ecology is which properties of ecosystems favour their stability and help maintaining biodiversity. This qu estion recently reconsid- ered mutualistic systems, generating intense controversy about the role of mutu- alistic interactions and their network architecture. Here we show analytically and verify with simulations that reducing the effective intersp ecific competition and the propagation of perturbations positively influences struct ural stability against envi- ronmental perturbations, enhancing persistence. Notewor thy, mutualism reduces the effective interspecific competition only when the direct interspecific competition is weaker than a critical value. This critical competition i s in almost all cases larger in pollinator networks than in random networks with the same connectance. Highly connected mutualistic networks reduce the propagation of e nvironmental perturba- tions, a mechanism reminiscent of MacArthurâs proposal tha t ecosystem complexity enhances stability. Our analytic framework rationalizes p revious contradictory re- sults, and it gives valuable insight on the complex relation ship between mutualism and biodiversity
Stars and brown dwarfs in the sigma Orionis cluster. III. OSIRIS/GTC low-resolution spectroscopy of variable sources
Context. Although many studies have been performed so far, there are still
dozens of low-mass stars and brown dwarfs in the young sigma Orionis open
cluster without detailed spectroscopic characterisation. Aims. We look for
unknown strong accretors and disc hosts that were undetected in previous
surveys. Methods. We collected low-resolution spectroscopy (R ~ 700) of ten
low-mass stars and brown dwarfs in sigma Orionis with OSIRIS at the Gran
Telescopio Canarias under very poor weather conditions. These objects display
variability in the optical, infrared, Halpha, and/or X-rays on time scales of
hours to years. We complemented our spectra with optical and near-/mid-infrared
photometry. Results. For seven targets, we detected lithium in absorption,
identified Halpha, the calcium doublet, and forbidden lines in emission, and/or
determined spectral types for the first time. We characterise in detail a
faint, T Tauri-like brown dwarf with an 18 h-period variability in the optical
and a large Halpha equivalent width of -125+/-15 AA, as well as two M1-type,
X-ray-flaring, low-mass stars, one with a warm disc and forbidden emission
lines, the other with a previously unknown cold disc with a large inner hole.
Conclusions. New unrevealed strong accretors and disc hosts, even below the
substellar limit, await discovery among the list of known sigma Orionis stars
and brown dwarfs that are variable in the optical and have no detailed
spectroscopic characterisation yet.Comment: A&A, in press (accepted for publication in section 14. Catalogs and
data of Astronomy and Astrophysics
Interstitial cells of Cajal in the urethra as effectors of the nitric oxide action through the cyclic GMP pathway
OP07.05: Recurrence rate after ultrasoundâguided transvaginal aspiration of benign adnexal masses with and without sclerotherapy: a systematic review and metaâanalysis
Unit-cell design for antenna arrays efficiently matched to uni-travelling-carrier photodiodes
International audienceWe present an antenna array with a backing reflector that allows one to obtain efficient matching to integrated sources or loads with low input resistance. In the infinite array limit, it is possible to describe the proposed unit-cell as an equivalent network with closed-form expressions for its different constituents. This analytic approach enables the preliminary design of arrays with improved matching efficiency for optimum power transmission/reception. The proposed solution has enabled an improved matching to a uni-travelling-carrier photodiode with a maximum improvement of 3 dB in the radiated power with respect to a 72-⊠antenna, and featuring a 50% bandwidth
Manipulation and Generation of Supercurrent in Out-of-Equilibrium Josephson Tunnel Nanojunctions
We demonstrate experimentally manipulation of supercurrent in Al-AlO_x-Ti
Josephson tunnel junctions by injecting quasiparticles in a Ti island from two
additional tunnel-coupled Al superconducting reservoirs. Both supercurrent
enhancement and quenching with respect to equilibrium are achieved. We
demonstrate cooling of the Ti line by quasiparticle injection from the normal
state deep into the superconducting phase. A model based on heat transport and
non-monotonic current-voltage characteristic of a Josephson junction
satisfactorily accounts for our findings.Comment: 4 pages, 4 colour figures, published versio
Localization lengths of ultrathin disordered gold and silver nanowires
The localization lengths of ultrathin disordered Au and Ag nanowires are
estimated by calculating the wire conductances as functions of wire lengths. We
study Ag and Au monoatomic linear chains, and thicker Ag wires with very small
cross sections. For the monoatomic chains we consider two types of disorder:
bounded random fluctuations of the interatomic distances, and the presence of
random substitutional impurities. The effect of impurity atoms on the nanowire
conductance is much stronger. Our results show that electrical transport in
ultrathin disordered wires may occur in the strong localization regime, and
with relatively small amounts of disorder the localization lengths may be
rather small. The localization length dependence on wire thickness is
investigated for Ag nanowires with different impurity concentrations.Comment: 6 pages, postscript figures included, submitted to PR
Algal nutraceuticals: a perspective on metabolic diversity, current food applications, and prospects in the field of metabolomics
The current consumersâ demand for food naturalness is urging the search for new functional foods of natural
origin with enhanced health-promoting properties. In this sense, algae constitute an underexplored biological
source of nutraceuticals that can be used to fortify food products. Both marine macroalgae (or seaweeds) and
microalgae exhibit a myriad of chemical constituents with associated features as a result of their primary and
secondary metabolism. Thus, primary metabolites, especially polysaccharides and phycobiliproteins, present
interesting properties to improve the rheological and nutritional properties of food matrices, whereas secondary
metabolites, such as polyphenols and xanthophylls, may provide interesting bioactivities, including antioxidant
or cytotoxic effects. Due to the interest in algae as a source of nutraceuticals by the food and related industries,
novel strategies should be undertaken to add value to their derived functional components. As a result,
metabolomics is considered a high throughput technology to get insight into the full metabolic profile of biological
samples, and it opens a wide perspective in the study of algae metabolism, whose knowledge is still little
explored. This review focuses on algae metabolism and its applications in the food industry, paying attention to
the promising metabolomic approaches to be developed aiming at the functional characterization of these
organisms.The research leading to these results was supported by the European
Union through the âNextGenerationEUâ program supporting the
âMargarita Salasâ grant awarded to P. Garcia-Perez, by Xunta de Galicia
for supporting the program EXCELENCIA-ED431F 2020/12, the postdoctoral
grant of L. Cassani (ED481B-2021/152), and the pre-doctoral
grant of P. Garcia-Oliveira (ED481A-2019/295) and by MICINN supporting
the RamÂŽon y Cajal grant for M.A. Prieto (RYC-2017-22891) and
J. Xiao (RYC-2020-030365-I). Authors are grateful to Bio Based Industries
Joint Undertaking (JU) under grant agreement No 888003
UP4HEALTH Project (H2020-BBI-JTI-2019). The JU receives support
from the European Unionâs Horizon 2020 research and innovation
program and the Bio Based Industries Consortium. This work has also
received funding from the Argentinean Agency for the Scientific and
Technological Promotion (ANPCyT, Argentina) under the project PICT
(2020)/1602.info:eu-repo/semantics/publishedVersio
Free-electron Model for Mesoscopic Force Fluctuations in Nanowires
When two metal electrodes are separated, a nanometer sized wire (nanowire) is
formed just before the contact breaks. The electrical conduction measured
during this retraction process shows signs of quantized conductance in units of
G_0=2e^2/h. Recent experiments show that the force acting on the wire during
separation fluctuates, which has been interpreted as being due to atomic
rearrangements. In this report we use a simple free electron model, for two
simple geometries, and show that the electronic contribution to the force
fluctuations is comparable to the experimentally found values, about 2 nN.Comment: 4 pages, 3 figures, reference correcte
Challenges for future food systems: from the Green Revolution to food supply chains with a special focus on sustainability
Finding a food system to feed the growing worldwide population remains a challenge, especially in the current era, where natural resources are being dramatically depleted. From a historical point of view, the Green Revolution, together with biofortification and sustainable intensification, was established as a possible solution to counter hunger and malnutrition during the second half of the 20th century. As a solution, to overcome the limitations attributed to the Green Revolution, food supply chains were developed. The current food system, based on the long food supply chain (LFSC), is characterized by globalization, promoting several advantages for both producers and consumers. However, LFSC has been demonstrated to be unable to feed the global population and, furthermore, it generates negative ecological, environmental, logistical, and nutritional pressures. Thus, novel efficient food systems are required to respond to current environmental and consumers' demands, as is the case of short food supply chain (SFSC). As a recently emerging food system, the evaluation of SFSC sustainability in terms of environmental, economic, and social assessment is yet to be determined. This review is focused on the evolution of food supply systems, starting from the Green Revolution to food supply chains, providing a significant perspective on sustainability.The research leading to these results was supported by MICINN supporting
the RamĂłn y Cajal grant for M. A. Prieto (RYC-2017-22891),
the Juan de la Cierva IncorporaciĂłn for Hui Cao (IJC2020-04605-
5-I) and the FPU grant for A. Soria-Lopez (FPU2020/06140); by
Xunta de Galicia for supporting the program (EXCELENCIA-ED431F
2020/12) and by supporting the postdoctoral grant of M. Fraga-
Corral (ED481B-2019-096) and the predoctoral grants of M. Carpena
(ED481A 2021/313) and of P. Garcia-Oliveira (ED481A-2019/295);
and by the European Union through the âNextGenerationEUâ program
supporting the âMargarita Salasâ grant awarded to P. Garcia-Perez. The authors are grateful to Ibero-American Program on Science and
Technology (CYTEDâAQUA-CIBUS, P317RT0003), to the Bio Based
Industries Joint Undertaking (JU) under grant agreement No. 888003
UP4HEALTH Project (H2020-BBI-JTI-2019) that supports the work of
P. Otero and P. Garcia-Perez. The JU receives support from the European
Unionâs Horizon 2020 research and innovation program and the
Bio Based Industries Consortium. The project SYSTEMIC Knowledge
hub on Nutrition and Food Security, has received funding from national
research funding parties in Belgium (FWO), France (INRA), Germany
(BLE), Italy (MIPAAF), Latvia (IZM), Norway (RCN), Portugal (FCT), and
Spain (AEI) in a joint action of JPI HDHL, JPI-OCEANS and FACCE-JPI
launched in 2019 under the ERA-NET ERA-HDHL (No. 696295)
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