A new contribution to periodic competition systems with delays

A delayed competition system of Lotka–Volterra type, with periodic coefficients, is considered. The topics of existence and global asymptotic stability of a periodic solution are investigated. The novelty of our results consists in the fact that they require only average conditions. In the study of global attractivity an unusual Lyapunov function is introduced. Our method takes advantage of the fact that there is no deviating argument in the negative feedback terms.     

Ultraviolet-B radiation effects on the structure and function of lower trophic levels of the marine planktonic food web

The impact of UV-B radiation (UVBR; 280-320 nm) on lower levels of a natural plankton assemblage (bacteria, phytoplankton and microzooplankton) from the St. Lawrence Estuary was studied during 9 days using several immersed outdoor mesocosms. Two exposure treatments were used in triplicate mesocosms: natural UVBR (N treatment, considered as the control treatment) and lamp-enhanced UVBR (H treatment, simulating 60% depletion of the ozone layer). A phytoplankton bloom developed after day 3, but no significant differences were found between treatments during the entire experiment for phytoplankton biomass (chlorophyll a and cell carbon) nor for phytoplankton cell abundances from flow cytometry and optical microscopy of three phytoplankton size classes (picoplankton, nanoplankton and microplankton). In contrast, bacterial abundances showed significantly higher values in the H treatment, attributed to a decrease in predation pressure due to a dramatic reduction in ciliate biomass (approximately 70-80%) in the H treatment relative to the N treatment. The most abundant ciliate species were Strombidinium sp., Prorodon ovum and Tintinnopsis sp.; all showed significantly lower abundances under the H treatment. P. ovum was the less-affected species (50% reduction in the H treatment compared with that of the N control), contrasting with approximately 90% for the other ones. Total specific phytoplanktonic and bacterial production were not affected by enhanced UVBR. However, both the ratio of primary to bacterial biomass and production decreased markedly under the H treatment. In contrast, the ratio of phytoplankton to bacterial plus ciliate carbon biomass showed an opposite trend than the previous results, with higher values in the H treatment at the end of the experiment. These results are explained by the changes in the ciliate biomass and suggest that UVBR can alter the structure of the lower levels of the planktonic community by selectively affecting key species. On the other hand, linearity between particulate organic carbon (POC) and estimated planktonic carbon was lost during the postbloom period in both treatments. On the basis of previous studies, our results can be attributed to the aggregation of carbon released by cells to the water column in the form of transparent exopolymer particles (TEPs) under nutrient limiting conditions. Unexpectedly, POC during such a period was higher in the H treatment than in controls. We hypothesize a decrease in the ingestion of TEPs by ciliates, in coincidence with increased DOC release by phytoplankton cells under enhanced UVBR. The consequences of such results for the carbon cycle in the ocean are discussed.     

Thorough small‐angle X‐ray scattering analysis of the instability of liquid micro‐jets in air

Liquid jets are of interest, both for their industrial relevance and for scientific applications (more important, in particular for X‐rays, after the advent of free‐electron lasers that require liquid jets as sample carrier). Instability mechanisms have been described theoretically and by numerical simulation, but confirmed by few experimental techniques. In fact, these are mainly based on cameras, which is limited by the imaging resolution, and on light scattering, which is hindered by absorption, reflection, Mie scattering and multiple scattering due to complex air/liquid interfaces during jet break‐up. In this communication it is demonstrated that synchrotron small‐angle X‐ray scattering (SAXS) can give quantitative information on liquid jet dynamics at the nanoscale, by detecting time‐dependent morphology and break‐up length. Jets ejected from circular tubes of different diameters (100–450 µm) and speeds (0.7–21 m s^?1) have been explored to cover the Rayleigh and first wind‐induced regimes. Various solvents (water, ethanol, 2‐propanol) and their mixtures have been examined. The determination of the liquid jet behaviour becomes essential, as it provides background data in subsequent studies of chemical and biological reactions using SAXS or X‐ray diffraction based on synchrotron radiation and free‐electron lasers.     

DFT/TDDFT investigation of the stepwise deprotonation in tetracycline: pK<Subscript>a</Subscript> assignment and UV–vis spectroscopy

Tetracyclines are a class of derivatives of polycyclic naphthacene carboxamide, which have attracted wide interest in the pharmaceutical field for their use as antibiotics. These molecules are characterized by a substantial conformational flexibility and by the presence of different binding sites which endow tetracycline with a noticeable capability in binding biological targets. A salient property of tetracyclines is the presence of multiple acidic groups: four equilibrium constants have been measured for the fully protonated tetracycline (TCH₃ ⁺) but so far no clear information concerning the pK_as of the various sites has been reported. We present here a computational investigation on the correlation between the acid–base and the spectroscopic properties of this important class of compounds. Starting from the TCH₃ ⁺ species, the pK_a of all the possible deprotonation sites has been computed by DFT calculations. The computed pK_as nicely compare with the experimental data, within 1 pK_a unit, allowing us to individuate the products of the first deprotonation. This procedure has been iteratively repeated using as starting species the products singled out from the previous deprotonation, thus individuating the stepwise products of each deprotonation step. Then, the optical absorption spectra have been computed for all the species involved in the protonation/deprotonation equilibria, comparing the results with the experimental data. The good agreement between theory and experiment has allowed us to rationalize the correlation between the solution pH and the absorption spectra.     

Complexes of tetracyclines with divalent metal cations investigated by stationary and femtosecond-pulsed techniques

Spectroscopic techniques both in steady-state (in absorption and emission) and pulsed (absorption of excited states with femtosecond resolution) conditions were used to study the complexation process between six molecules belonging to the tetracycline family and Mg(2+); in the case of TC the study was extended to the metal ions Ca(2+) and Cu(2+). The study was carried out in aqueous solution at various pH values, where one acid-base form of the substrate prevails over the others. The processing of experimental results, performed by means of Singular Value Decomposition and Global Analysis methods, allowed us to evaluate the extent of interaction through the association constants, to identify the number of equilibria present in solution and the stoichiometry (1:1 or 1:2) of the tetracycline:metal ion complex, and to define the spectral and photophysical properties of the latter (in terms of fluorescence quantum yields, lifetimes and rate constants). In fact, the (allowed) radiative decay process is a minor root for the lowest excited state of the complexes which mainly decay to the ground state by internal conversion. Details of the complexation sites are proposed for the various protonated forms of tetracyclines, and for the various cations in the case of TC. In particular, the molecular structure seems to affect significantly the dynamics of interaction when the upper peripheral region of tetracycline is rich in additional hydroxyl groups. Moreover, the state of protonation of the substrate produces changes in the order of the complexation sites, whose affinity for the cation increases significantly when they are negatively charged owing to the loss of protons. Magnesium and calcium (hard cations) give similar interactions, at least in acid solution, while copper(ii) (borderline cation) binds more efficiently on different sites, thus forming complexes with different properties.     

Top-down patterning of zeolitic imidazolate framework composite thin films by deep X-ray lithography

For the first time a top-down process was used to control the spatial location of Metal-Organic Frameworks on a surface. Deep X-ray lithography was utilised to micropattern a Zeolitic Imidazolate Framework layer on a sol-gel surface, with exposure hardening the sol-gel by inducing crosslinking while leaving the frameworks intact.     

Effect of Extraction Solvent and Temperature on Polyphenol Profiles,Antioxidant and Anti-Inflammatory Effects of Red Grape Skin By-Product

A fully-detailed LC-MS qualitative profiling of red grape skin, extracted with a mixture of ethanol and water (70:30 v:v) has permitted the identification of 65 compounds which can be classified into the following chemical classes: organic and phenolic acids (14 compounds), stilbenoids (1 compound), flavanols (21 compounds), flavonols (15 compounds) and anthocyanins (14 compounds). The extraction yield obtained with water at different temperatures (100 °C, 70 °C, room temperature) was then evaluated and the overall polyphenol content indicates that EtOH:H₂O solvent is the most efficient and selective for polyphenol extraction. However, by analyzing the recovery yield of each single polyphenol, we found that water extraction under heating conditions is effective (extraction yield similar or even better in respect to the binary solvent) for some polyphenolic classes, such as hydrophilic procyanidins, phenolic acids, flavonol glucosides and stilbenoids. However, according to their lipophilic character, a poor yield was found for the most lipophilic components, such as flavonol aglycones, and in general for anthocyanins. The radical scavenging activity was in accordance with the polyphenol content, and hence, much higher for the extract obtained with the binary solvent in respect to water extraction. All the tested extracts were found to have an anti-inflammatory activity in the R3/1 cell line with NF-kb reporter challenged with 0.01 µg/mL of IL-1α, in a 1 to 250 µg/mL concentration range. An intriguing result was that the EtOH:H₂O extract was found to be superimposable with that obtained using water at 100 °C despite the lower polyphenol content. Taken together, the results show the bioactive potentialities of grape skin extracts and the possibility to exploit this rich industrial waste. Water extraction carried out by heating is an easy, low-cost and environmentally friendly extraction method for some polyphenol classes and may have great potential for extracts with anti-inflammatory activities.     

Parametric study of a ramanp-H2 laser with over 30 MW emission at 16 μm

Summary In this work the main parameters which define the threshold, the temporal shape and the stability ofp-H₂ Raman laser have been investigated. Our results show a very high-power conversion efficiency (130%) and for each pump CO₂ line we can dispose of a correspondent line (pulse≥1J/50 ns) in the 16 μm range. This is foundamental as far as UF₆ isotopic separation is concerned.

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Riassunto In questo lavoro sono stati studiati i principali parametri che definiscono la soglia, la forma temporale e la stabilità di un laser Raman a para-idrogeno (16 μm). I nostri risultati mostrano un'alta efficienza di conversione di potenza (130%) per ciascuna riga del laser a CO₂ permettendo una buona tunabilità nel range dei 16 μm. Questo è fondamentale per la separazione isotopica di UF₆.

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Резюме В этой работе исследуются основные параметры, которые определяют порог, временную форму и стабильностьp-H₂ рамановского лазера. Наши результаты показывают очень высокую эффективность конверсии (130%). Для каждой линии CO₂ накачки мы можем сопоставить соответствующую линию (импульс≥1 Дж/50 нс) в диапазоне 16 мкм. Это является основой для разделения изотопов UF₆.

     

Separability of completely integrable dynamical systems admitting alternative Lagrangian descriptions

It is shown that whenever a (1, 1)-type tensor field, defined through two alternative Lagrangians, implies complete integrability for a second-order Lagrangian vector field Γ on the tangent bundle of a given configuration manifold, then a bundle atlas can be found in which both Γ and a class of equivalent Lagrangians are completely separated into a sum of second-order vector fields and Lagrangians, each one corresponding to a single degree of freedom.