Nanoscale Charge Density and Dynamics in Graphene Oxide

Graphene oxide (GO) is widely used as a component in thin film optoelectronic device structures for practical reasons because its electronic and optical properties can be controlled. Progress critically depends on elucidating the nanoscale electronic structure of GO. However, direct experimental access is challenging because of its disordered and nonconductive character. Here, we quantitatively mapped the nanoscopic charge distribution and charge dynamics of an individual GO sheet by using Kelvin probe force microscopy (KPFM). Charge domains are identified, presenting important charge interactions below distances of 20 nm. Charge dynamics with very long relaxation times of at least several hours and a logarithmic decay of the time correlation function are in excellent agreement with Monte Carlo simulations, revealing an universal hopping transport mechanism best described by Efros-Shklovskii''s law. © 2021 The Authors. Published by American Chemical Society

Modelling TiO2 photoanodes for PEC water splitting: Decoupling the influence of intrinsic material properties and film thickness

Semiconductor metal oxides are intensively studied in electrodes for photoelectrochemical (PEC) water splitting. On a series of nanoparticulate TiO2 photoanodes, we analyze specific fabrication variables by means of data fitting. First, the experimental outcome is gathered using PEC characterization techniques, mostly cyclic voltammetry and transient photocurrent measurements. Subsequently, we apply models to gain insights into the involved charge trapping and transfer phenomena. We find that capacitance coefficients and the switch-on transient kinetics depend on the TiO2 layer thickness, respectively indicating surface mechanisms and stationary regimes that are mediated by light accessibility. On the contrary, exponential factors of capacitance are independent of thickness, but reflect changes in the density of electron states with different sintering atmospheres. Also, the transfer resistance in the electrolyte side is indirectly influenced by sintering. Through meticulous quantitative analysis of trends, we stablish simple mathematical relationships that connect thickness-dependent parameters. This knowledge delves into fundamental mechanisms governing the TiO2 photoelectrode behaviour, and aims to facilitate further improvements in the efficiency of materials and electrodes for green hydrogen production

Photoactivity improvement of TiO2 electrodes by thin hole transport layers of reduced graphene oxide

Nanostructured TiO2 and graphene-based materials constitute components of actual interest in devices related to solar energy conversion and storage. In this work, we show that a thin layer of electrochemically reduced graphene oxide (ECrGO), covering nanostructured TiO2 photoelectrodes, can significantly improve the photoactivity. In order to understand the working principle, ECrGO/TiO2 photoelectrodes with different ECrGO thicknesses were prepared and studied by a set of photoelectrochemical measurements. Methanol in alkaline conditions was employed as effective hole acceptor probe to elucidate the electronic phenomena in the electrode layers and interfaces. These studies underline the hole accepting properties of ECrGO and reveal the formation of a p-n junction at the interface between ECrGO and TiO2. It is shown for the first time that the resulting space charge region of about 10 nm defines the operational functionality of the ECrGO layer. Films thinner than the space charge region act as hole transport layer (HTL), which efficiently transfers holes to the liquid interface thus leading to enhanced photoactivity. Thicker films however act as hole blocking layer (HBL), resulting in a systematic decrease of the photoactivity. The finding of a thickness dependent threshold value for the operation of ECrGO as HTL and HBL is of general interest for the fabrication of optoelectronic devices with improved performance

Amebas de vida libre en aguas residuales de la cuenca del Ebro y su papel como reservorio natural de bacterias potencialmente patógenas

Las amebas de vida libre (AVL) son protozoos ubicuos, presentes en ecosistemas acuáticos naturales y artificiales y suelos,donde participan en los procesos de depuración alimenta´ndose de bacterias presentes en el medio y en biofilms. Acanthamoeba spp., Naegleria fowleri, Vermamoeba spp., Paravahlkamp a spp., Balamuthia mandrillaris y Sappinia spp. son los ge´neros descritos como pato´genos, causando queratitis, encefalitis granulomatosa o meningoencefalitis. Estas amebas suponen tambie´n un riesgo, ya que son un reservorio natural de bacterias pato´genas como Legionella pneumophila, Mycobacterium spp. o Pseudomonas spp., quedando ligada su patogenicidad a la presencia de bacterias en su interior. Cuando las AVL adoptan la forma de quiste, adquieren resistencia a las condiciones adversas y los desinfectantes actualmente utilizados en aguas, pudiendo superar los procesos de depuración y potabilización y colonizar los sistemas artificiales de agua. Algunas bacterias son capaces incluso de multiplicarse en su interior, aumentando su virulenci

A Multi-Fractal approach to soil thin sections in gray levels.

In the environment, as it is complex flows where Reynold number is quite high due to non-linear interactions in flows, several scales are developed. This type of hierarchy is detected in velocities as well as in the structure of scalar fields, as temperatures, tracer concentrations, density, etc. In these cases is interesting to relate in some way the geometrical o topological characteristics observed in flow images with their physical properties and dynamics. In the last decades many scientist has been applying fractal analysis to these types of images extracting several fractal dimensions for different intensity intervals. This type of analysis is what we call Multi-Fracta

Pulmonary Thrombosis or Embolism in a Large Cohort of Hospitalized Patients With Covid-19

Objective: We set out to analyze the incidence and predictive factors of pulmonary embolism (PE) in hospitalized patients with Covid-19. Methods: We prospectively collected data from all consecutive patients with laboratory-confirmed Covid-19 admitted to the Hospital de la Santa Creu i Sant Pau, a university hospital in Barcelona, between March 9 and April 15, 2020. Patients with suspected PE, according to standardized guidelines, underwent CT pulmonary angiography (CTPA). Results: A total of 1,275 patients with Covid-19 were admitted to hospital. CTPA was performed on 76 inpatients, and a diagnosis of PE was made in 32 (2.6% [95%CI 1.7-3.5%]). Patients with PE were older, and they exhibited lower PaO:FiO ratios and higher levels of D-dimer and C-reactive protein (CRP). They more often required admission to ICU and mechanical ventilation, and they often had longer hospital stays, although in-hospital mortality was no greater than in patients without PE. High CRP and D-dimer levels at admission (≥150 mg/L and ≥1,000 ng/ml, respectively) and a peak D-dimer ≥6,000 ng/ml during hospital stay were independent factors associated with PE. Prophylactic low molecular weight heparin did not appear to prevent PE. Increased CRP levels correlated with increased D-dimer levels and both correlated with a lower PaO:FiO. Conclusions: The 2.6% incidence of PE in Covid-19 hospitalized patients is clearly high. Higher doses of thromboprophylaxis may be required to prevent PE, particularly in patients at increased risk, such as those with high levels of CRP and D-dimer at admission. These findings should be validated in future studies

The effect of the temperature of graphene oxide reduction on low-temperature sorption of ⁴He

The sorption of⁴He by graphene oxide powders thermally reduced at T = 200, 300, 500, 700, 900 ºC has been investigated in the interval 1.5–290 K. The measured dependence of the quantity of sorbed helium upon the reduction temperature shows up as a nonmonotonic curve. The highest quantities of helium were sorbed by the samples reduced at T = 300 and 900 ºC. It is assumed that the thermal reduction of graphite oxide by heating it to 300 ºC causes evaporation of the water intercalated in the spacings of the carbon layers, this results in exfoliation of the graphene planes, which enhances the sorptive capacity. Heating the samples to 900 ºC generates numerous defects in the carbon planes, as a result, the interlayer spacings become accessible for sorption, which enhances the sorptive capacity

Amebas de vida libre en aguas residuales y fangos: Su papel como reservorio natural de bacterias potencialmente patógenas

Las amebas de vida libre (AVL) son protozoos ubicuos, presentes en suelos y en ecosistemas acuáticos naturales y artificiales. Participan en los procesos de depuración desarrollados en las Estaciones Depuradoras de Aguas Residuales (EDAR), convirtiéndolas en un nicho ecológico idóneo para la proliferación de AVL, que las colonizan e instauran en ellas su hábitat, ya que se alimentan de bacterias presentes en el medio. Los procesos de depuración biológica no están diseñados con el fin de eliminar la contaminación microbiológica, aunque ayudan a reducir algunas poblaciones bacterianas. Hasta la fecha, sólo algunas especies y géneros de AVL han sido descritos como patógenos, pero todas ellas suponen un riesgo como reservorio de bacterias patógenas. Su forma quística, les confiere resistencia frente a las condiciones adversas y desinfectantes comunes, permitiéndoles superar los procesos de depuración y potabilización y colonizar sistemas artificiales de agua. En este trabajo, se estudió la presencia de AVL en aguas y fangos de 5 EDAR que vierten sus aguas a la cuenca del Ebro, analizando un total de 20 puntos de muestreo. Para ello, se llevó a cabo el aislamiento AVL y la posterior identificación de género y especie, así como de las bacterias endosimbiontes, mediante la reacción en cadena de la polimerasa (PCR). De las 41 amebas aisladas en el 85 % de las muestras, 21 fueron identificadas genéticamente. Trece de ellas, pertenecieron al género Acanthamoeba spp., 6 a Naegleria spp. y 2 se identificaron como Vermamoeba vermiformis. El 53,66 % de las AVL albergaba en su interior Mycobacterium spp., el 29,27 % Legionella pneumophila y el 14,63 % Pseudomonas spp. Free-living amoebae (FLA) are ubiquitous protozoa, present in soils and in natural and artificial aquatic ecosystems. They take part in the purification processes that take place in Wastewater Treatment Plants (WWTPs), thereby turning these plants into ecological niches suitable for proliferation of FLAs, which they colonize and in which they establish their habitat, since they feed on bacteria present in the environment. Biological purification processes are not designed to remove microbiological contamination, although they help to reduce some microbial populations. At present only some genera and species of FLAs have been described as pathogenic, but all of them pose a risk as reservoirs of pathogenic bacteria. Their cystic stage gives them resistance to adverse conditions and common disinfectants, allowing them to withstand water purification processes and colonize artificial water systems. The presence of FLAs in waters and sludges from 5 WWTPs that discharge their waters into the Ebro river basin has been studied in this work. To this end, a total of 20 sample points were analysed by isolating the FLAs and subsequently identifying their genus and species. The same was done for endosymbiotic bacteria, by Polymerase Chain Reaction (PCR). Out of 41 FLAs that were isolated in 85 % of the samples, 21 were genetically identified. Thirteen belonged to the genus Acanthamoeba spp., 6 to Naegleria spp. and 2 were identified as Vermamoeba vermiformis. 53.66 % of FLAs hosted Mycobacterium spp., 29.27 % Legionella pneumophila, and 14.63 % Pseudomonas spp

De la gran urbe a la modesta villa: aplicación de la prospección magnética a la arqueología romana

La caracterización de yacimientos arqueológicos es una de las aplicaciones más extendidas de la prospección magnética, por su carácter no invasivo, que permite explorar sin destruir superficies de extensión considerable, y debido al carácter ferromagnético de muchos elementos asociados a la actividad humana (instrumentos de hierro, componentes minerales de tejas, ladrillos, hornos de cocción, etc...). Habitualmente, en prospección magnética se mide la intensidad total del campo magnético terrestre (realizando las correcciones de las oscilaciones debidas a la variación diurna y las micropulsaciones) y el gradiente horizontal o vertical (diferencia entre las medidas tomadas simultáneamente en posiciones cercanas mediante dos sensores, ver figura 1), que resulta muy útil cuando se trata de detectar anomalías debidas a cuerpos cercanos a la superficie. Frente a la sistemática de trabajo en prospecciones geológicas, el mallado de la prospección magnética en arqueología suele ser muy denso, con 1 m o 0,5 m de espaciado entre perfiles en muchas ocasiones