Marcelo Otero

Study of atmospheric particulate matter in Buenos Aires city

Abstract The data reported here constitute the results of the first long-term monitoring campaign of daily PM10 and PM2.5 concentration levels in Buenos Aires city. Twenty-four hour averages atmospheric concentrations of PM10 and PM2.5 were measured (not simultaneously) at a site near downtown Buenos Aires, since December 1998–September 1999. The values of PM2.5 concentrations correlate well with the concentrations of carbon monoxide (CO) during the winter period, indicating that direct traffic emissions have an important contribution to PM2.5. The data are less correlated for the case of PM10, indicating that the sources of the coarse fraction are not only traffic emissions, with an important contribution of other sources, for example re-suspended material. Scanning electron microscopy and atomic force microscopy images of atmospheric particles on nucleopore filters are shown. Information about the ion and metal content of these particles is reported.

A Stochastic Spatial Dynamical Model for Aedes Aegypti

We develop a stochastic spatial model for Aedes aegypti populations based on the life cycle of the mosquito and its dispersal. Our validation corresponds to a monitoring study performed in Buenos Aires. Lacking information with regard to the number of breeding sites per block, the corresponding parameter (BS) was adjusted to the data. The model is able to produce numerical data in very good agreement with field results during most of the year, the exception being the fall season. Possible causes of the disagreement are discussed. We analyzed the mosquito dispersal as an advantageous strategy of persistence in the city and simulated the dispersal of females from a source to the surroundings along a 3-year period observing that several processes occur simultaneously: local extinctions, recolonization processes (resulting from flight and the oviposition performed by flyers), and colonization processes resulting from the persistence of eggs during the winter season. In view of this process, we suggest that eradication campaigns in temperate climates should be performed during the winter time for higher efficiency.

Layer-by-layer electrostatic deposition of biomolecules on surfaces for molecular recognition, redox mediation and signal generation

Layer-by-layer supramolecular structures composed of alternate layers of negatively charged enzymes and cationic redox polyelectrolyte have been assembled. Glucose oxidase (GOx), lactate oxidase (LOx) and soybean peroxidase (SBP) have been electrically wired to the underlying electrode by means of poly(allylamine) with [Os(bpy)2ClPyCOH]+ covalently attached (PAA-Os) in organized structures with high spatial resolution. Biotinylated glucose oxidase has also been used to assemble step-by-step on antibiotin goat immunoglobulin (IgG) layers and the enzyme was electrically wired by PAA-Os. These spatially organized multilayers with mono- and bienzymatic schemes can work efficiently in molecular recognition, redox mediation and generation of an electrical signal. The concentration of redox mediator integrated into the multilayers, obtained from the voltammetric charge and an estimation of the layer thickness, exceeds by 100-fold the amount of deposited enzyme assessed by quartz crystal microbalance. Differences in GOx electrical wiring efficiency have been detected with the different assembling strategies. The surface concentration of electrically wired enzyme represents a small proportion of all the enzyme molecules present in the multilayers which can be oxidized by the soluble mediator [Os(bpy)2Cl PyCOOH]Cl. This proportion, as well as the rate of FADH2 oxidation by PAA-Os, increases with the number of electrically wired enzyme layers and with the spatial accessibility of the Os moiety to the enzyme active center.

Stochastic eco-epidemiological model of dengue disease transmission by Aedes aegypti mosquito

We present a stochastic dynamical model for the transmission of dengue that takes into account seasonal and spatial dynamics of the vector Aedes aegypti. It describes disease dynamics triggered by the arrival of infected people in a city. We show that the probability of an epidemic outbreak depends on seasonal variation in temperature and on the availability of breeding sites. We also show that the arrival date of an infected human in a susceptible population dramatically affects the distribution of the final size of epidemics and that early outbreaks have a low probability. However, early outbreaks are likely to produce large epidemics because they have a longer time to evolve before the winter extinction of vectors. Our model could be used to estimate the risk and final size of epidemic outbreaks in regions with seasonal climatic variations.

An EQCM electroacoustic study of poly(vinylferrocene) modified electrodes in different aqueous electrolytes

Abstract In this paper we report the study of poly(vinylferrocene) films cast on Au electrodes by the electrochemical quartz crystal microbalance (EQCM) electroacoustic impedance technique. The simultaneous recording of the quartz resonant frequency and the surface electro-acoustic impedance of the quartz-film-liquid electrolyte composite system and a viscoelastic analysis of these parameters provide an estimate of the viscoelastic changes as a function of redox conversion and the mass changes as a result of solvent and ion exchange with the electrolyte. The changes in mass obtained by this method have been compared to the values calculated with the Sauerbrey approximation. By comparison of this information with results of probe beam deflection (PBD) technique under similar conditions for different electrolytes, the number of water molecules exchanged per electron/ion transferred, the ionic exchange mechanism and the shear modulus could be obtained. It has been found that they depend on the nature of the anion in the electrolyte. While the EQCM is sensitive to the total mass of ions and solvent exchanged with the electrolyte, the PBD detects the flux of ions exchanged but it is insensitive to the flux of solvent. We also describe for the first time the viscoelastic changes that take place during film conditioning by incorporation of solvent and ions during ‘break in’. Solvation of PVF+ produces an increase in the shear modulus at 10 MHz as a result of viscoelastic losses in the swollen polymer film with segmental motion of polyion strands and electrolyte trapped in the polymer structure.

Viscoelastic Characterization of Electrochemically Prepared Conducting Polymer Films by Impedance Analysis at Quartz Crystal Study of the Surface Roughness Effect on the Effective Values of the Viscoelastic Properties of the Coating

An electrochemical quartz crystal microbalance is used for a continuous monitoring of the growth of the polymer poly(3,4-ethylenedioxy) thiophene tetrabutylammonium perchlorate (PEDOT-TBAP), electropolymerized in acetonitrile on a gold electrode of a 10 MHz AT-cut quartz crystal resonator. The surface acoustic impedance of the resonator is analyzed starting from the electrical admittance continuously measured by means of a network analyzer. Changes in the acoustic impedance suggest that a mechanical resonance phenomenon occurs during the electrodeposition. To determine the origin of this effect, the evolution of the physical properties of the coating is analyzed. This analysis shows a significant change of the viscoelastic properties of the coating during the electropolymerization and especially during the time interval of the suspected mechanical resonance. The effect of the surface roughness on the mechanical impedance of the coating is analyzed. This study seems to indicate that the changes in the effective viscoelastic properties of the coating are due to the changes in the surface roughness. The mechanical resonance effect also seems to be more a result of this change in the coating effective viscoelastic properties than of the growth of the coating thickness where coating viscoelastic properties are maintained constant.

Dengue epidemics and human mobility

In this work we explore the effects of human mobility on the dispersion of a vector borne disease. We combine an already presented stochastic model for dengue with a simple representation of the daily motion of humans on a schematic city of 20 × 20 blocks with 100 inhabitants in each block. The pattern of motion of the individuals is described in terms of complex networks in which links connect different blocks and the link length distribution is in accordance with recent findings on human mobility. It is shown that human mobility can turn out to be the main driving force of the disease dispersal.

Modeling dengue outbreaks

We introduce a dengue model (SEIR) where the human individuals are treated on an individual basis (IBM) while the mosquito population, produced by an independent model, is treated by compartments (SEI). We study the spread of epidemics by the sole action of the mosquito. Exponential, deterministic and experimental distributions for the (human) exposed period are considered in two weather scenarios, one corresponding to temperate climate and the other to tropical climate. Virus circulation, final epidemic size and duration of outbreaks are considered showing that the results present little sensitivity to the statistics followed by the exposed period provided the median of the distributions are in coincidence. Only the time between an introduced (imported) case and the appearance of the first symptomatic secondary case is sensitive to this distribution. We finally show that the IBM model introduced is precisely a realization of a compartmental model, and that at least in this case, the choice between compartmental models or IBM is only a matter of convenience.

Gravimetric and viscoelastic changes during the oxidation–reduction of layer-by-layer self assembled enzyme multilayers wired by an Os-containing poly(allylamine) polymer

The ellipsometric and mass increase during the oxidation � /reduction cycles of self-assembled layer-by-layer osmium complex derivatized poly(allylamine) and glucose oxidase multilayers due to the exchange of anions and solvent with the electrolyte and viscoelastic changes of the surface layer have been studied using the electrochemical quartz crystal microbalance (EQCM) technique. From the measurement of the quartz crystal impedance spectrum of films deposited on a thiolate Au-quartz crystal immersed in viscous aqueous electrolyte, simultaneously with cyclic voltammetry and potential steps, the real (RS) and imaginary components (XLS � /vLS) of the quartz complex impedance load have been derived. It has been shown that the quartz crystal impedance of the composite resonator (film and liquid) increases with the number of deposited layers due to increase of both the film thickness and the shear modulus. The reduced polymer multilayers, with ellipsometric thickness ranging from 200 to 600 nm behave as acoustically thin films, while in the oxidized Os(III) films viscoelastic characteristics are apparent at 10 MHz. Using a viscoelastic model for the enzyme/polymer film we conclude that the film acoustic impedance increases with the number of self-assembled layers due to the thickness increase, and also to the increase of the shear modulus due to oxidation. The values of the shear modulus and loss tangent were estimated from the acoustic impedance, the film density and the ellipsometric thickness; the latter follows a linear dependence with the degree of oxidation. The increase of loss modulus, and hence loss tangent, is more pronounced, the larger the degree of polymer oxidation. # 2002 Elsevier Science B.V. All rights reserved.

Modelling interventions during a dengue outbreak

We present a stochastic dynamical model for the transmission of dengue that considers the co-evolution of the spatial dynamics of the vectors (Aedes aegypti) and hosts (human population), allowing the simulation of control strategies adapted to the actual evolution of an epidemic outbreak. We observed that imposing restrictions on the movement of infected humans is not a highly effective strategy. In contrast, isolating infected individuals with high levels of compliance by the human population is efficient even when implemented with delays during an ongoing outbreak. We also studied insecticide-spraying strategies assuming different (hypothetical) efficiencies. We observed that highly efficient fumigation strategies seem to be effective during an outbreak. Nevertheless, taking into account the controversial results on the use of spraying as a single control strategy, we suggest that carrying out combined strategies of fumigation and isolation during an epidemic outbreak should account for a suitable strategy for the attenuation of epidemic outbreaks.