A parametrization for the symbols of a Hankel type operator

Hankel operators and their symbols, as generalized by V. Pták and P. Vrbová, are considered. In this more general framework, a linear operator X from a Hilbert space H1 to a Hilbert space H2 is said to be a Hankel operator for given contractions T1 on H1 and T2 on H2 if, and only if, XT ∗ 1 = T2X and X satisfies a boundedness condition that depends on the unitary parts of the minimal isometric dilations V1 of T1 and V2 of T2. A Hankel symbol of X is a dilation Z of X, with a certain norm constraint, such that ZV ∗ 1 = V2Z. The boundedness condition imposed to X has revealed to be essential, indeed necessary and sufficient, for X to admit Hankel symbols. As for a description of the symbols of X, this work provides a parametric labeling of all of them by means of Schur like formula. As a by-product, a new proof of the existence of Hankel symbols is obtained. The proof is established by associating to X, T1 and T2 a suitable isometry V so that there is a bijective correspondence between the symbols of X and the family of all minimal unitary extensions of V.Ministerio de Ciencia y TecnologíaJunta de AndalucíaFondo Nacional de Ciencia, Tecnología e Innovación (Venezuela

Data Descriptor : A European Multi Lake Survey dataset of environmental variables, phytoplankton pigments and cyanotoxins

Under ongoing climate change and increasing anthropogenic activity, which continuously challenge ecosystem resilience, an in-depth understanding of ecological processes is urgently needed. Lakes, as providers of numerous ecosystem services, face multiple stressors that threaten their functioning. Harmful cyanobacterial blooms are a persistent problem resulting from nutrient pollution and climate-change induced stressors, like poor transparency, increased water temperature and enhanced stratification. Consistency in data collection and analysis methods is necessary to achieve fully comparable datasets and for statistical validity, avoiding issues linked to disparate data sources. The European Multi Lake Survey (EMLS) in summer 2015 was an initiative among scientists from 27 countries to collect and analyse lake physical, chemical and biological variables in a fully standardized manner. This database includes in-situ lake variables along with nutrient, pigment and cyanotoxin data of 369 lakes in Europe, which were centrally analysed in dedicated laboratories. Publishing the EMLS methods and dataset might inspire similar initiatives to study across large geographic areas that will contribute to better understanding lake responses in a changing environment.Peer reviewe

Characterization of supplementary cementitious materials by thermal analysis

Working Group 1 of RILEM TC 238-SCM ‘Hydration and microstructure of concrete with supplementary cementitious materials (SCMs)’ is defining best practices for the physical and chemical characterization of SCMs, and this paper focusses on their thermal analysis. Thermogravimetric analysis (TGA) can provide valuable data on the chemical and mineralogical composition of SCMs. Loss-on-ignition (LOI) testing is a commonly used, standardized, but less sophisticated version of TGA that measures mass at endpoints only, with heating generally in air. In this paper we describe the use of TGA and LOI to characterize Portland cement with limestone additions, coal combustion fly ashes, ground-granulated blast furnace slag, calcined clays, and natural pozzolans. This paper outlines the value and limitations of TGA and LOI (in the formats defined in different standards regimes) for material characterization, and describes testing methods and analysis. TGA testing parameters affect the mass loss recorded at temperatures relevant for LOI measurements (700–1000 °C) of slags and fly ashes, mainly associated with oxidation reactions taking place upon heating. TGA of clays and natural pozzolans is utilized to identify optimal calcination conditions leading to dehydroxylation and consequent structural amorphization, particularly for kaolinite. However, dehydroxylation and amorphization do not occur at similar temperatures for all clays, limiting the applicability of TGA for this purpose. Although TGA is widely utilized for characterization of SCMs, the testing parameters significantly affect the results obtained, and TGA results require careful interpretation. Therefore, standardization of TGA testing conditions, particularly for LOI determination of slags and fly ashes, is required

Stratification strength and light climate explain variation in chlorophyll a at the continental scale in a European multilake survey in a heatwave summer

To determine the drivers of phytoplankton biomass, we collected standardized morphometric, physical, and biological data in 230 lakes across the Mediterranean, Continental, and Boreal climatic zones of the European continent. Multilinear regression models tested on this snapshot of mostly eutrophic lakes (median total phosphorus [TP] = 0.06 and total nitrogen [TN] = 0.7 mg L−1), and its subsets (2 depth types and 3 climatic zones), show that light climate and stratification strength were the most significant explanatory variables for chlorophyll a (Chl a) variance. TN was a significant predictor for phytoplankton biomass for shallow and continental lakes, while TP never appeared as an explanatory variable, suggesting that under high TP, light, which partially controls stratification strength, becomes limiting for phytoplankton development. Mediterranean lakes were the warmest yet most weakly stratified and had significantly less Chl a than Boreal lakes, where the temperature anomaly from the long-term average, during a summer heatwave was the highest (+4°C) and showed a significant, exponential relationship with stratification strength. This European survey represents a summer snapshot of phytoplankton biomass and its drivers, and lends support that light and stratification metrics, which are both affected by climate change, are better predictors for phytoplankton biomass in nutrient-rich lakes than nutrient concentrations and surface temperature

Treatment with tocilizumab or corticosteroids for COVID-19 patients with hyperinflammatory state: a multicentre cohort study (SAM-COVID-19)

Objectives: The objective of this study was to estimate the association between tocilizumab or corticosteroids and the risk of intubation or death in patients with coronavirus disease 19 (COVID-19) with a hyperinflammatory state according to clinical and laboratory parameters. Methods: A cohort study was performed in 60 Spanish hospitals including 778 patients with COVID-19 and clinical and laboratory data indicative of a hyperinflammatory state. Treatment was mainly with tocilizumab, an intermediate-high dose of corticosteroids (IHDC), a pulse dose of corticosteroids (PDC), combination therapy, or no treatment. Primary outcome was intubation or death; follow-up was 21 days. Propensity score-adjusted estimations using Cox regression (logistic regression if needed) were calculated. Propensity scores were used as confounders, matching variables and for the inverse probability of treatment weights (IPTWs). Results: In all, 88, 117, 78 and 151 patients treated with tocilizumab, IHDC, PDC, and combination therapy, respectively, were compared with 344 untreated patients. The primary endpoint occurred in 10 (11.4%), 27 (23.1%), 12 (15.4%), 40 (25.6%) and 69 (21.1%), respectively. The IPTW-based hazard ratios (odds ratio for combination therapy) for the primary endpoint were 0.32 (95%CI 0.22-0.47; p < 0.001) for tocilizumab, 0.82 (0.71-1.30; p 0.82) for IHDC, 0.61 (0.43-0.86; p 0.006) for PDC, and 1.17 (0.86-1.58; p 0.30) for combination therapy. Other applications of the propensity score provided similar results, but were not significant for PDC. Tocilizumab was also associated with lower hazard of death alone in IPTW analysis (0.07; 0.02-0.17; p < 0.001). Conclusions: Tocilizumab might be useful in COVID-19 patients with a hyperinflammatory state and should be prioritized for randomized trials in this situatio

Pre-treatments in silicate solutions to mitigate reinforcing steel corrosion in chloride-contaminated environments

Silicate ions were incorporated into a pre-treatment to mitigate corrosion in reinforcing steel bars. The efficiency of these pre-treatments was compared by testing steel samples in concrete pore simulating solutions contaminated with chloride ions. The study involved cyclic voltammetry, anodic polarisation curves and weight-loss tests following a 60-day immersion period. Surface analysis included micro-Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The electrical properties of the film were analyzed by impedance spectroscopy and Mott–Schottky plots. Polarisation curves show higher pitting potentials and lower corrosion current densities when pre-treating with silicate ions. Localised attack appears after 60 days of immersion in solutions containing chloride ions, but weight loss is reduced by 75% for coupons pre-treated in silicate solutions. XPS and Raman spectra indicate that the presence of silicate ions affects the composition of the passive film and the corrosion products. The results show that pre-treatments in silicate solutions are effective to minimise steel corrosion in aggressive environments.Fil: Rolandi, A. C.. Universidad Nacional de Mar del Plata; ArgentinaFil: Montes, F.. Universidad Nacional de Mar del Plata; ArgentinaFil: Morán Ayala, L.. Universidad Nacional de Mar del Plata; ArgentinaFil: Frontini, A.. Universidad Nacional de Mar del Plata; ArgentinaFil: Vázquez, M.. Universidad Nacional de Mar del Plata; ArgentinaFil: Valcarce, María Beatriz. Universidad Nacional de Mar del Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin

Adsorption of dyes with different molecular properties on activated carbons prepared from lignocellulosic wastes by Taguchi method

A design of experiments based in the Taguchi method was used to prepare activated carbons from different lignocellulosic residues with optimum properties for the removal of food and textile dyes (food yellow 4, food yellow 3, food red 17 and acid blue 74). A Taguchi L16 orthogonal array was devised for the design of experiments, using the dye removal percentage as response variable and several experimental factors, including the origin of the lignocellulosic precursor, type of chemical agent used for the impregnation of the precursors and other specific variables of the impregnation and thermal treatments. Statistical analysis of the results helped to identify the chemical agent and the final temperature of carbonization/activation as the experimental factors having the most relevant effect on the response (i.e., amount of dye adsorbed). Carbons obtained using the optimum conditions predicted by the Taguchi methodology for each dye were characterized using elemental analysis, FT-IR spectroscopy, adsorption isotherms of nitrogen at -196 °C and SEM/EDX analysis. The optimum carbons had a high specific surface area (∼1400 m 2/g) with a considerable amount of micropores (∼50%). Mesoporosity seemed also to play an important role in the adsorption of these dyes. © 2014 Elsevier Inc. All rights reserved