23 research outputs found
The potentiostatic transient, for 3D nucleation with diffusion-controlled growth: theory and experiment for progressive nucleation
No full textThe theory of the potentiostatic transient for 3D nucleation with diffusion-controlled growth is discussed. It is shown that the theoretical model of Mirkin and Nilov [J. Electroanal. Chem., 283 (1990) 35] and Heerman and Tarallo [J. Electroanal. Chem., 470 (1999) 70] predicts too high values of the current, which becomes very apparent for high values of the site density and low values of the nucleation rate constant (progressive nucleation). For example, the model then predicts that the current in the limit of long times will be higher than the Cottrell limit by a factor of 4/3 which is physically unacceptable. Therefore, a modification to this model is proposed which is based on a careful analysis of the Kolmogorov-Avrami theorem. The "extended area" in the Kolmogorov-Avrami theorem includes contributions from "phantom nuclei" that are born inside already existing zones but do not exist physically. This is necessary to preserve the randomness of the system and allows the correct calculation of the appearance rate of the nuclei and the nucleus saturation density. The "extended current", defined in analogy with the "extended area", then also attributes current to the phantom nuclei. It follows that the ratio j(ex)(t)/theta(ex)(t) which appears in the model of Mirkin and Nilov and Heerman and Tarallo does not correspond to the actual number of nuclei formed on the electrode. Therefore, the "extended quantities" in this ratio must be replaced with quantities that relate directly to the real number of clusters (this implies what is fairly obvious, that the appearance rate of the clusters must be calculated first). This makes it is possible to derive an equation that predicts correctly the current in the limits of both short and long times which is directly linked to the N-a(t) vs. time relation (where N-a(t) is the actual number of nuclei on the electrode). Experiments for the nucleation of silver on glassy carbon electrodes, with the simultaneous recording of both j(t) vs. time and N-a(t) vs. time relations, are described. The experimental results obtained from the transients and the direct visual counting of nuclei are compared with the theoretical predictions. (C) 2004 Elsevier B.V. All rights reserved.status: Publishe
Filmes poliméricos com adição de agente antimicrobiano a base de prata: desenvolvimento, caracterização e aplicação em cortes de carne bovina
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Química, Florianópolis, 2009.Embalagens ativas, especialmente os filmes antimicrobianos vêm sendo estudados e avaliados como método auxiliar de conservação de alimentos, principalmente por aumentar a vida-de-prateleira e reduzirem os níveis de conservantes adicionados diretamente ao alimento. Neste trabalho, foram desenvolvidos filmes antimicrobianos de Polietileno de Baixa Densidade (PEBD), preparados por extrusão industrial, adicionados de antimicrobiano à base de prata (AlphaSan®) a concentrações de 0, 0,1, 0,5 e 1,0% (m/m). Os filmes extrusados foram avaliados quanto à espessura, distribuição da partícula de prata nos filmes e propriedades de tração, resistência a perfuração e barreira ao oxigênio (TPO2). O potencial antimicrobiano in-vitro de cada filme em relação aos microrganismos patogênicos Staphylococcus aureus spp.e Salmonella spp. foi testado. Amostras de carne bovina (contrafilé) foram acondicionadas em embalagens a vácuo elaboradas com os filmes nas concentrações citadas, para verificação da ação antimicrobiana em relação à Contagem Bacteriana Total-CBT e bactérias do gênero Pseudomonas por 10 dias, em condições de refrigeração comercial (3±1ºC). Adicionalmente, foi realizada a análise de cor utilizando colorímetro e metodologia digital, além da avaliação do teor de prata no alimento. O aditivo a base de prata inserido nos filmes de PEBD não modificou de forma significativa as propriedades de tração, resistência à perfuração e barreira ao oxigênio, mostrando dispersão homogênea das partícula de prata nos filmes. As embalagens com as três concentrações de antimicrobiano estudadas mostraram-se eficientes na inibição do crescimento in-vitro de Staphylococcus aureus., porém, apenas o filme com maior concentração de prata (1%) apresentou inibição de Salmonella spp. Este filme também mostrou melhor desempenho na redução de microrganismos Contagem bacteriana total-CBT e contagem de Pseudomonas, apresentando, ao final de um tempo de avaliação de 10 dias, uma redução de 2 ciclos logarítmicos para CBT e 1 ciclo para Pseudomonas, em relação à carne acondicionada no filme sem adição de agente antimicrobiano. A cor da carne acondicionada nos filmes antimicrobianos contendo 0,5 e 1% adquiriu coloração vermelho-cereja, enquanto que as amostras acondicionadas a 0,1% de prata e no filme controle mostraram intensificação da coloração marrom referente à formação de metamioglobina, cor típica de carne embalada a vácuo. O método digital para obtenção dos parâmetros de cor mostrou ser mais fiel à observação visual do produto quando comparado com os resultados obtidos pelo colorímetro. Foi observado um teor máximo de prata presente no alimento de 0,0375 ± 0,0028 mg de Ag.kg-1, correspondente ao filme com adição 1% de prata. Este valor, porém, não excedeu a quantidade determinada pela legislação vigente, que é de 0,05 mg.kg-1.Abstract : Active packages, specially antimicrobial films, are being studied and evaluated as auxiliary methods of food conservation, mainly for increasing shelf-life and reducing the levels of addictives added directly in the foods. In this work, antimicrobial films made of Low Density Polyethylene Films (LDPE), prepared by industrial extrusion with silver addition (AlphaSan®). The films produced were evaluated regarding to thickness, silver particle distribution and traction properties, resistance to perforation and oxygen barrier (O2PT). The in-vitro microbial potential of each film related to the pathogenical microorganisms Staphylococcus aureus spp.and Salmonella spp. were tested. Samples of beef, Striploin (m. Longissimus dorsi) were packed for microbial action verification on Total Bacterial Counting (TBC) and growth of Pseudomonas for 10 days in chilled commercial conditions (3±1 ºC). Additionally, a meat color study in each treatment was done by traditional colorimetric methods, using a colorimeter, and by digital and computational method. Determination of the silver content was evaluated in the meat. The addition of the silver-based addictive has not significantly modified (p>0,05) the traction properties, perforation resistance and oxygen barrier, showing also a good homogeneity in the silver particle distribution and thickness of the film. The antimicrobial films in the three concentrations were evaluated and considered efficient on the in-vitro growth inhibition of Staphylococcus aureus. Considering the other microorganisms tested, just the 1% silver-based film F3 film (film with greater concentration of silver (1%)) showed inhibition against Salmonella spp. It The F3 film also had a better performance on the psychotrophic microorganism reduction and counting of Pseudomonas reducing 2 logarithmic cycles for TBC and 1 cycle for Pseudomonas in ten days, the end of the evaluation time. The color of meat packaged using 0,5% and 1% antimicrobial films showed to keep the bright red coloration, while the samples packed in the Control or 0,1% silver films showed a brownish color,characteristic of the metamioglobina formation, a typical compound found in vacuum packed meat. The digital color meter method gave better informations about the meat color in the storage time. Colorimetric measures given by a colorimeter did not correspond to the meat color as observed by eyes. Silver maximum contents detected in meat packed using films with 0,5 and 1% m:m silver amount was 0,0375 ± 0,0028 mg Ag.kg-1, and.did not exceeded that one determined by Brazilian Food Law (0,05mg.kg-1), in the evaluated times
Development of a Merged CO Climate Data Record from IASI and MOPITT Observations
No full textInternational audienceCarbon monoxide (CO) is a key atmospheric compound that can be remotely sensed by satellite on a global scale. Continuous observations have been available since 2000 from the MOPITT/Terra instrument. Since 2007, the IASI/Metop instrument series has provided another homogeneous CO data record, thanks to the recent reprocessing of Metop-A and Metop-B data by EUMETSAT, resulting in the IASI CO Climate Data Record (IASI CO-CDR). Measuring the variability and trends of CO on a global scale is crucial as it serves as a precursor for ozone and carbon dioxide and regulates the troposphere's oxidizing capacity through its destruction cycle involving the hydroxyl radical (OH). As part of the ESA CCI+ Ozone Precursors project, we have been developing a merged CO Climate Data Record dataset combining IASI and MOPITT data to analyze long-term variability and trends. Monthly averaged gridded CO total columns (Level 3, 1°x1° resolution) are used as input. For IASI, we first apply an additional cloud mask to the Level 2 official data available on the Aeris French Database (https://iasi.aeris-data.fr/). We then compute monthly averages using IASI CO data from all Metop satellites, resulting in an intermediate (non-public) IASI CO monthly Level 3 product. For MOPITT, we use the official monthly Level 3 (version 9T) data available on the NASA Earth Data Portal (https://www.earthdata.nasa.gov/). We tested various methodologies for merging IASI and MOPITT CO Level 3 monthly grids. We performed averages with weighting schemes based on MOPITT priors and/or IASI/MOPITT uncertainties. In this poster, we will present the final version of the CO CCI merged product, which uses MOPITT CO total column/MOPITT prior ratios as weights for averaging. Among the different algorithm versions tested, this approach showed the best performance when validated against ground-based FTIR NDACC measurements, achieving a mean absolute bias below 5%, low standard deviation, and excellent correlation
Feasibility of robust estimates of ozone production rates using a synergy of satellite observations, ground-based remote sensing, and models
No full textOzone pollution is secondarily produced through a complex, non-linear chemical process. Our understanding of the spatiotemporal variations in photochemically produced ozone (i.e., PO₃) is limited to sparse aircraft campaigns and chemical transport models, which often carry significant biases. Hence, we present a novel satellite-derived PO₃ product informed by bias-corrected TROPOspheric Monitoring Instrument (TROPOMI) HCHO, NO₂, surface albedo data, and various models. These data are integrated into a parameterization that relies on HCHO, NO₂, HCHO / NO₂, jNO₂, and jO¹D. Despite its simplicity, it can reproduce ∼ 90 % of the variance in observationally constrained PO₃, with minimal biases in moderately to highly polluted regions. We map PO₃ across various regions with respect to July 2019 at a 0.1° × 0.1° spatial resolution, revealing accelerated values (> 8 ppbv h⁻¹) for numerous cities throughout Asia and the Middle East, resulting from elevated ozone precursors and enhanced photochemistry. In Europe and the United States, such high levels are only detected over Benelux, Los Angeles, and New York City. PO₃ maxima are observed in various seasons and are attributed to changes in photolysis rates, non-linear ozone chemistry, and fluctuations in HCHO and NO₂. Satellite errors result in moderate errors (10 %–20 %) in PO₃ estimates over cities on a monthly average basis, while these errors exceed 50 % in clean areas and under low light conditions. Using the current algorithm, we demonstrate that satellite data can provide valuable information for robust PO₃ estimation. This capability expands future research through the application of data to address significant scientific questions about locally produced ozone hotspots, seasonality, and long-term trends.This research has been supported by the National Aeronautics and Space Administration (grant no. 80NSSC23K1250). Funders facilitating the collection of data used in this article (rather than funders of this work specifically) are included in the Acknowledgementshttps://acp.copernicus.org/articles/25/2061/2025
Realization and characterization of porous gold for increased protein coverage on acoustic sensors
No full textImmunosensors show great potential for the direct detection of biological molecules. The sensitivity of these affinity-based biosensors is dictated by the amount of receptor molecules immobilized on the sensor surface. An enlargement of the sensor area would allow for an increase of the binding capacity, hence a larger amount of immobilized receptor molecules. To this end, we use electrochemically deposited "gold black" as a porous sensor surface for the immobilization of proteins. In this paper, we have analyzed the different parameters that define the electrochemical growth of porous gold, starting from flat gold surfaces, using different characterization techniques. Applied potentials of -0.5 V versus a reference electrode were found to constitute the most adequate conditions to grow porous gold surfaces. Using cyclic voltammetry, a 16 times increase of the surface area was observed under these electrochemical deposition conditions. In addition, we have assessed the immobilization degree of alkanethiols and of proteins on these different porous surfaces. The optimized deposition conditions for realizing porous gold substrates lead to a 11.4-fold increase of thiol adsorption and a 3.3-fold increase of protein adsorption, using the quartz crystal microbalance (QCM-D) as a biological transducer system. Hence, it follows that the high specific area of the porous gold can amplify the final sensitivity of the original flat surface device.status: Publishe
Realization and characterization of porous gold for increased protein coverage on acoustic sensors
No full textHow quickly they forget:The relationship between forgetting and working memory performance
No full textThis study examined the contribution of individual differences in rate of forgetting to variation in working memory performance in children. One hundred and twelve children (mean age 9 years 4 months) completed 2 tasks designed to measure forgetting, as well as measures of working memory, processing efficiency, and short-term storage ability. Individual differences in forgetting rate accounted for unique variance in working memory performance over and above variance explained by measures of processing efficiency and storage ability. In addition, the nature of the variation in forgetting was more consistent with a nonexecutive forgetting parameter than an executive ability associated with resistance to interference. These findings indicate that individual differences in the rate at which information is lost from memory is an important constraint on children's working memory performance, which has implications for current models of working memory that do not incorporate such a factor.</p
Assessment of TROPOMI HCHO Vertical Columns: evaluating the use of CAMS vertical profiles and new TROPOMI surface albedo climatologies for air mass factor determination
No full texthe ESA Climate Change Initiative (CCI) Ozone and Aerosols Precursors project is developing long-term climate data records (CDRs) of the Global Climate Observing System (GCOS) Precursors for Aerosol and Ozone Essential Climate Variables. These precursors include short-lived atmospheric trace gases such as formaldehyde (HCHO), glyoxal (CHOCHO), nitrogen dioxide (NO2), sulphur dioxide (SO2), carbon monoxide (CO), and ammonia (NH3). The project aims to create consistent and harmonized CDRs from multiple satellite missions, including GOME, SCIAMACHY, GOME-2, OMI, TROPOMI, IASI, and MOPITT.
This work presents selected findings of a round robin exercise conducted for UV-VIS retrievals. We focus on two key factors that influence HCHO air mass factor determination: the surface albedo climatology and the model a priori profiles. The impact of these factors on the HCHO vertical columns is evaluated by comparing the use of recent auxiliary datasets. Results are presented for TROPOMI HCHO columns and compared to the operational product.
The recent reprocessing of TROPOMI Level 1 data has enabled the development of new albedo climatologies in the UV, offering a finer spatial resolution than the previously used OMI albedo climatology. Additionally, we evaluate the use of a priori vertical profiles from the CAMS reanalysis dataset (spanning the 2003-2022 period) instead of the current TM5-MP profiles used in the TROPOMI operational product. We assess the impact of these alternative datasets on the TROPOMI HCHO vertical columns and on their validation towards ground-based data.
The generation of the ESA CCI HCHO CDR will be based on these findings. This comprehensive assessment not only contributes to the ongoing improvement of TROPOMI data quality but also provides deeper insights into the factors influencing HCHO vertical columns
Realization and Characterization of Porous Gold for Increased Protein Coverage on Acoustic Sensors
No full textImmunosensors show great potential for the direct detection of biological molecules. The sensitivity of these
affinity-based biosensors is dictated by the amount of
receptor molecules immobilized on the sensor surface.
An enlargement of the sensor area would allow for an
increase of the binding capacity, hence a larger amount
of immobilized receptor molecules. To this end, we use
electrochemically deposited “gold black” as a porous
sensor surface for the immobilization of proteins. In this
paper, we have analyzed the different parameters that
define the electrochemical growth of porous gold, starting
from flat gold surfaces, using different characterization
techniques. Applied potentials of −0.5 V versus a reference electrode were found to constitute the most adequate
conditions to grow porous gold surfaces. Using cyclic
voltammetry, a 16 times increase of the surface area was
observed under these electrochemical deposition conditions. In addition, we have assessed the immobilization
degree of alkanethiols and of proteins on these different
porous surfaces. The optimized deposition conditions for
realizing porous gold substrates lead to a 11.4-fold
increase of thiol adsorption and a 3.3-fold increase of
protein adsorption, using the quartz crystal microbalance
(QCM-D) as a biological transducer system. Hence, it
follows that the high specific area of the porous gold can
amplify the final sensitivity of the original flat surface
device
