184 research outputs found
Multiphonon and ``hot''-phonon Isovector Electric-Dipole Excitations
We argue that a substantial increase in the cross section for Coulomb
excitation in the region of the Double Giant Dipole Resonance should be
expected from Coulomb excitation of excited states involved in the spreading of
the one-phonon resonance, in a manifestation of the Brink-Axel phenomenon. This
generates an additional fluctuating amplitude and a corresponding new term to
be added incoherently to the usual cross-section. The appropriate extension of
an applicable reaction calculation is considered in order to estimate this
effect.Comment: 6 pages, Latex, 1 figure available on reques
Skin-associated lactic acid bacteria from North American bullfrogs as potential control agents of batrachochytrium dendrobatidis
The fungal pathogen Batrachochytrium dendrobatidis (Bd) is the causative agent of chytridiomycosis and has been a key driver in the catastrophic decline of amphibians globally. While many strategies have been proposed to mitigate Bd outbreaks, few have been successful. In recent years, the use of probiotic formulations that protect an amphibian host by killing or inhibiting Bd have shown promise as an effective chytridiomycosis control strategy. The North American bullfrog (Lithobates catesbeianus) is a common carrier of Bd and harbours a diverse skin microbiota that includes lactic acid bacteria (LAB), a microbial group containing species classified as safe and conferring host benefits. We investigated beneficial/probiotic properties: anti-Bd activity, and adhesion and colonisation characteristics (hydrophobicity, biofilm formation and exopolysaccharide-EPS production) in two confirmed LAB (cLAB-Enterococcus gallinarum CRL 1826, Lactococcus garvieae CRL 1828) and 60 presumptive LAB (pLAB) [together named as LABs] isolated from bullfrog skin.We challenged LABs against eight genetically diverse Bd isolates and found that 32% of the LABs inhibited at least one Bd isolate with varying rates of inhibition. Thus, we established a score of sensitivity from highest (BdGPL AVS7) to lowest (BdGPL C2A) for the studied Bd isolates. We further reveal key factors underlying host adhesion and colonisation of LABs. Specifically, 90.3% of LABs exhibited hydrophilic properties that may promote adhesion to the cutaneous mucus, with the remaining isolates (9.7%) being hydrophobic in nature with a surface polarity compatible with colonisation of acidic, basic or both substrate types. We also found that 59.7% of LABs showed EPS synthesis and 66.1% produced biofilm at different levels: 21% weak, 29% moderate, and 16.1% strong. Together all these properties enhance colonisation of the host surface (mucus or epithelial cells) and may confer protective benefits against Bd through competitive exclusion. Correspondence analysis indicated that biofilm synthesis was LABs specific with high aggregating bacteria correlating with strong biofilm producers, and EPS producers being correlated to negative biofilm producing LABs. We performed Random Amplified Polymorphic DNA (RAPD)-PCR analysis and demonstrated a higher degree of genetic diversity among rod-shaped pLAB than cocci. Based on the LAB genetic analysis and specific probiotic selection criteria that involve beneficial properties, we sequenced 16 pLAB which were identified as Pediococcus pentosaceus, Enterococcus thailandicus, Lactobacillus pentosus/L. plantarum, L. brevis, and L. curvatus. Compatibility assays performed with cLAB and the 16 species described above indicate that all tested LAB can be included in a mixed probiotic formula. Based on our analyses, we suggest that E. gallinarum CRL 1826, L. garvieae CRL 1828, and P. pentosaceus 15 and 18B represent optimal probiotic candidates for Bd control and mitigation. © 2019 Niederle et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited149FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP2016/25358-3This research was supported by Consejo Nacional de Investigaciones Científicas y Técnicas (PIP 063 to SEP), Consejo de Investigaciones de la Universidad Nacional de Tucumán (PIUNT 26/D 414 and 26/D 645 to SEP, and PIUNT 528), Agencia Nacional de Promoción Científica y Tecnológica (PICT 2017-2244 to SEP, PICT 2015-2467 to CEA, and PICT2017-4324 to MENM), Ministerio de Economía y Competitividad de España (CGL2015-70070-R to JB), Fondo Nacional de Desarrollo Científico y Tecnológico (1181758 to CSA and 3180107 to AVS), Fundação de Amparo à Pesquisa do Estado de São Paulo (2016/25358-3 to LFT). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscrip
Theory of Multiphonon Excitation in Heavy-Ion Collisions
We study the effects of channel coupling in the excitation dynamics of giant
resonances in relativistic heavy ions collisions. For this purpose, we use a
semiclassical approximation to the Coupled-Channels problem and separate the
Coulomb and the nuclear parts of the coupling into their main multipole
components. In order to assess the importance of multi-step processes, we
neglect the resonance widths and solve the set of coupled equations exactly.
Finite widths are then considered. In this case, we handle the coupling of the
ground state with the dominant Giant Dipole Resonance exactly and study the
excitation of the remaining resonances within the Coupled-Channels Born
Approximation. A comparison with recent experimental data is made.Comment: 29 pages, 7 Postscript figures available upon reques
Projectile breakup dynamics for Li + Co: kinematical analysis of - coincidences
A study of the kinematics of the - coincidences in the Li +
Co system at a bombarding energy of MeV is presented.
With exclusive measurements performed over different angular intervals it is
possible to identify the respective contributions of the sequential projectile
breakup and direct projectile breakup components. A careful analysis using a
semiclassical approach of these processes provides information on both their
lifetime and their distance of occurrence with respect to the target. Breakup
to the low-lying (near-threshold) continuum is delayed, and happens at large
internuclear distances. This suggests that the influence of the projectile
breakup on the complete fusion process can be related essentially to direct
breakup to the Li high-lying continuum spectrum. %Comment: Revised version including new Fig.3 and Fig.4 with new CDCC
calculations. Accepted for publication at Eur. Phys. Jour. A. 11 pages, 6
figure
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