Voltammetric Electronic Tongue Based on Carbon Paste Electrodes Modified with Biochar for Phenolic Compounds Stripping Detection

Biochar is a charcoal produced from the biomass pyrolysis process that presents a highly porous and functionalized surface. In the present work an array of carbon paste electrodes (CPE) made of different forms of carbon (graphite, carbon nanotubes and activated biochar) was evaluated in the development of an electronic tongue for discrimination and stripping voltammetric determination of catechol (CAT), 4‐ethylcatechol (4‐EC) and 4‐ethylguaiacol (4‐EG) phenolic compounds. Morphological characterization of carbon materials and electrodes surfaces was performed by scanning electron microscopy (SEM) and semi‐quantitative elemental composition by energy dispersive spectroscopy (EDS). Electrochemical Impedance Spectroscopy (EIS) measurements were used for electrochemical characterization of electrodes. Cyclic voltammetry measurements were performed for the phenolic compounds evaluated using different concentrations. Principal component analysis (PCA) was performed to evaluate the qualitative analysis. Quantitative data modeling was done using artificial neural networks (ANN). The proposed sensor array presented analytical potentiality allowing the distinction and determination of CAT, 4‐EC and 4‐EG by using chemometric processing. The method showed sensibility, reproducibility and a good linearity (R²>0.9940) for three compounds evaluated. Spontaneous preconcentration of three compounds was possible using all three sensors, which can allow the application of these as passive samplers for remote determinations of phenolic compounds in wine and food samples.     

X-ray and mössbauer studies of tricyclohexyltin(IV) halides. The crystal structures of (cyclo-C6H11)3SnX (X = F,Br and I)

The structures of tricyclohexyltin fluoride (I), bromide (II) and iodide (III) have been determined by X-ray analysis. Compound I crystallizes in the space group P2₁/m with a = 10.422(6), b = 17.238(9), c = 5.769(3) Å, β = 104.6(1)° and Z = 2. Compounds II and III crystallize in the space group Pcmn with a = 10.427(6), b = 16.914(9), c = 11.366(6) Å, Z = 4; and a = 10.400(6), b = 16.900(10), c = 11.400(4) Å, Z = 4, respectively. All three structures consist of discrete tetrahedral (cyclo-C₆H₁₁)₃SnX units.The temperature dependence of the Mössbauer resonance areas has been examined in order to obtain information about the relationship between chemical structure and lattice dynamics.     

Stick-slip instability analysis

A theoretical investigation of friction-induced self-excited oscillations for systems with one degree of freedom is proposed. The friction force is assumed as an odd function of the relative sliding velocity with a jump discontinuity at a value of zero for the relative sliding velocity. The friction characteristic is approximated with a piecewise linear function, i.e. straight line segments with a suitable slope. For the generic system belonging to the class in question, the stick-slip instability region is located on a suitable dimensionless map.

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Sommario Viene proposta un'indagine teorica sulle oscillazioni autoeccitate indotte dall'attrito per sistemi ad un grado di libertà. La forza d'attrito viene assunta come funzione dispari della velocità relativa tra le superfici accoppiate, con una discontinuità di prima specie in corrispondenza del valore nullo della velocità. La caratteristica d'attrito viene approssimata mediante una funzione lineare a tratti con segmenti di opportuna pendenza. Per il generico sistema appartenente alla classe in esame, si perviene all'individuazione, su opportuna mappa adimensionale, della regione di instabilità da stick-slip.

     

Rheological behavior in the transient state of PP/EPDM blends with carbon nanofillers

The rheological properties in the transient state of PP/EPDM blends with carbon nanofillers had been studied. The carbon nanofillers were incorporated into molten EPDM in an internal mixer at 150 °C. The rheological variables were determined in rotational rheometry at constant temperature of 200 °C. The results suggest that the magnitude of the difference of the normal stress differences (N₁-N₂) of PP/EPDM blends through the time, with and without nanofillers, and has a transition cycle from positive to negative values and vice versa, at constant and at zero shear rate in previously sheared samples. At constant shear rate, the transition cycle is random; meanwhile, it is constant at zero shear rate. This behavior is attributed to the polymeric chain movement, considering that the sheared samples have two molecular reorder processes: an immediate mechanism and another one slower. The fastest reorder process is attributed to the polymeric chains entanglement forming non-stable and stressed molecular structures. In the other hand, the second process is referred to the molecular mobility that takes place inside the stressed entangled polymer, in such a way that its structure tends to molecular stability as the rest time increases.     

A canonical treatment of nonautonomous systems of type\dot \upsilon = f(t) + c.

We solve by canonical methods, the Hamilton-Jacobi equation and the Poisson bracket technique, the special type of nonautonomous systems described by the equation . The general expressions so obtained are applied to the free rocket and the rocket in a uniform gravitational field, which serve as illustrations and test of the general results.     

Synthesis,structural, and spectroscopic characterization of hexakis (dimethyl sulfoxide)cobalt(II) tetrachlorocobaltate(II), [Co(Me2SO)6][CoCl4]

Well-formed single crystals of a compound having the empirical formula CoCl₂·3Me₂SO have been prepared using a vapour diffusion technique. X-ray diffraction methods confirm the previous spectrophotometric results of Cotton and Francis (1960a) and unequivocally demonstrate that this compound must be formulated as [Co(Me₂SO)₆]²⁺[CoCl₄]^2–. The compound crystallizes in the triclinic space groupP¯1 witha=18.601(3),b=9.613(2),c=9.044(2),=87.50(2)°,=98.64(2)°, =98.44(2)° andZ=2. Although a significant decrease of crystal quality with time and severe molecular disorder of Me₂SO are present, we have determined the coordination geometry around the cobalt centers. One cobalt atom is bound to six oxygen atoms of the Me₂SO moiety in a slightly distorted octahedral configuration; the mean Co-O distance is 2.083(12)Å. The second cobalt atom is surrounded by four chloride anions in an approximately tetrahedral configuration; the mean Co-Cl distance is 2.284(6) Å. The structure of the complex has been also investigated by means of ir measurements in the 4000-200 cm^–1 range.     

Wavelet neural networks to resolve the overlapping signal in the voltammetric determination of phenolic compounds

Three phenolic compounds, i.e. phenol, catechol and 4-acetamidophenol, were simultaneously determined by voltammetric detection of its oxidation reaction at the surface of an epoxy-graphite transducer. Because of strong signal overlapping, Wavelet Neural Networks (WNN) were used in data treatment, in a combination of chemometrics and electrochemical sensors, already known as the electronic tongue concept. To facilitate calibration, a set of samples (concentration of each phenol ranging from 0.25 to 2.5mM) was prepared automatically by employing a Sequential Injection System. Phenolic compounds could be resolved with good prediction ability, showing correlation coefficients greater than 0.929 when the obtained values were compared with those expected for a set of samples not employed for training.     

Pandemic simulation of antivirals + school closures: buying time until strain-specific vaccine is available

A strain-specific vaccine is unlikely to be available in the early phases of a potential H5N1 avian influenza pandemic. It could be months and at the current production rate may not provide timely protection to the population. Intervention strategies that control the spread of infection will be necessary in this situation, such as the use of the US stockpile of antiviral medication coupled with a 6-month school closure. The agent-based simulation model, EpiSimS, was used to assess the impact of this intervention strategy followed by three different vaccine approaches: (1) 2-dose, 80% effective, (2) 1-dose, 30% effective, and (3) 1 dose, 80% effective. Simulations show that the combination of antivirals, school closures, and a strain-specific vaccine can reduce morbidity and mortality while in effect. A significant second infection wave can occur with current vaccine technology once school closures are relaxed, though an ideal vaccine is able to contain it. In our simulations, worker absenteeism increases in all cases mostly attributed to household adults staying home with children due to the school closures.

Tightness for the interfaces of one-dimensional voter models

We show that for the voter model on {0, 1} corresponding toa random walk with kernel p(·) and starting from unanimityto the right and opposing unanimity to the left, a tight interfacebetween zeros and ones exists if p(·) has finite secondmoment but does not if p(·) fails to have finite momentof order for some < 2.