A comparative study on the single-scan and multiple-scan techniques in differential scanning calorimetry: Application to the crystallization of the semiconducting Ge0.13Sb0.23Se0.64 alloy

A method has been developed for analysing the evolution with time of the volume fraction transformed and for calculating the kinetic parameters at non-isothermal reactions in materials involving formation and growth of nuclei. By considering the assumptions of extended volume and random nucleation, a general expression of the fraction transformed as a function of time has been obtained in isothermal crystallization processes. Considering the mutual interference of regions growing from separate nuclei the Johnson–Mehl–Avrami equation has been deduced as a particular case. The application of the transformation rate equation to the non-isothermal processes has been carried out under the restriction of a nucleation which takes place early in the transformation and the nucleation frequency is zero thereafter. Under these conditions, the kinetic parameters have been deduced by using the techniques of data analysis of single-scan and multiple-scan. The theoretical method developed has been applied to the glass-crystal transformation kinetics of the semiconducting Ge_0.13Sb_0.23Se_0.64 alloy. The kinetic parameters obtained according to both techniques differ by only about 2.5%, which confirms the reliability and accuracy of the single-scan technique when calculating the above-mentioned parameters in non-isothermal transformation processes. The phases at which the above-mentioned semiconducting glass crystallizes after the thermal process have been identified by X-ray diffraction. The diffractogram of the transformed material shows that microcrystallites of Sb₂Se₃ and GeSe are associated with the crystallization process, remaining a residual amorphous matrix.     

Multiresidue liquid chromatography tandem mass spectrometry determination of 52 non gas chromatography-amenable pesticides and metabolites in different food commodities

A multiresidue method is developed for the screening, quantification and confirmation of 43 pesticides, belonging to different chemical families of insecticides, acaricides, fungicides, herbicides and plant growth regulators, and 9 pesticide metabolites in four fruit and vegetable matrices. Pesticide residues are extracted from the samples with MeOH:H2O (80:20, v/v) 0.1% HCOOH, and then a cleanup step using OASIS HLB SPE cartridges is applied. The SPE eluate is concentrated and the final volume adjusted to 1 mL with MeOH:H2O (10:90, v/v) before injection into LC-MS/MS. Analyses are performed using electrospray ionization (ESI) and triple quadrupole (QqQ) analyzer. The method has been validated based on the SANCO European Guidelines for representative samples that were chosen to study the influence of different matrices: high water content (tomato), high acidic content (lemon), high sugar content (raisin) and high lipidic content (avocado). Special attention has been given to minimize the degradation of some pesticides into their metabolites and the losses observed in the evaporation step. Under the optimized conditions, the recoveries were, with a few exceptions, in the range 70-110% with satisfactory precision (CV < or = 15%). The quantification of analytes was carried out using the most sensitive transition for every compound and by "matrix-matched" standards calibration. The method can be used for the accurate determination of 52 pesticides and metabolites in one single determination step at the 0.01 mg/kg level. Confirmation of residues detected in samples is performed by an independent injection into the LC-MS/MS system by acquiring additional MS/MS transitions to that used for quantification. The acquisition of the highest number of available transitions is suggested for unequivocal confirmation of the analyte.     

The direct and indirect roles of fundamental frequency in vowel perception

Several experiments have found that changing the intrinsic f0 of a vowel can have an effect on perceived vowel quality. It has been suggested that these shifts may occur because f0 is involved in the specification of vowel quality in the same way as the formant frequencies. Another possibility is that f0 affects vowel quality indirectly, by changing a listener's assumptions about characteristics of a speaker who is likely to have uttered the vowel. In the experiment outlined here, participants were asked to listen to vowels differing in terms of f0 and their formant frequencies and report vowel quality and the apparent speaker's gender and size on a trial-by-trial basis. The results presented here suggest that f0 affects vowel quality mainly indirectly via its effects on the apparent-speaker characteristics; however, f0 may also have some residual direct effects on vowel quality. Furthermore, the formant frequencies were also found to have significant indirect effects on vowel quality by way of their strong influence on the apparent speaker.     

Design, construction and testing of a system for detection of toxic gases based on piezoelectric crystals

A system for static operation of toxic gas sensors based on piezoelectric crystals was constructed as a preliminary step in the development of this type of sensor. The sensing part of the setup consists of a twin oscillating circuit assembled from commercially available electronic parts mounted on a motherboard. The oscillating circuits can accommodate two piezoelectric crystals, of which one or both can be coated with different materials, or a single one, as required. The sensing assembly (crystals plus oscillating circuits) is placed in a customized test chamber that allows one to control and reproduce its internal environment. Once assembled and fine-tuned, the proposed setup was used to test a commercially available piezoelectric crystal for sensing formaldehyde in order to expand available information on this type of sensor.     

A formulation to obtain semi-analytical planetary theories using true anomalies as temporal variables

The main methods used to obtain analytical theories of perturbed motion in celestial mechanics are based on the expansion of the disturbing function in trigonometric series of the mean anomalies (or longitudes). In this paper a new method based on the double Fourier series expansion using the true anomalies (or longitudes) is developed. The method involves a semi-analytical technique to allow the expansion of the inverse of the distance with great accuracy, and a new integration technique using a linear combination of the true anomalies based on an iterative method to integrate each term of the expansion of the Lagrange planetary equations.     

Relation between quasirigidity andL-rigidity in space-times of constant curvature and weak fields

The relation between quasirigidity andL-rigidity in space-times of constant nonzero curvature and in space-times with small curvature (weak fields) is studied. The covariant expansion of bitensors about a point is considered. We obtain an increase in the order of magnitude, underL-rigidity conditions, of the rate of change with respect to a comoving orthonormal frame of the linear momentum, angular momentum, and reduced multipole moments of the energy-momentum tensor. Thus,L-rigidity leads to quasirigidity in such space-times.     

Rigid motions relative to an observer:L-rigidity

A new definition of rigidity,L-rigidity, in general relativity is proposed. This concept is a special class of pseudorigid motions and therefore it depends on the chosen curveL. It is shown that, for slow-rotation steady motions in Minkowski space, weak rigidity andL-rigidity are equivalent. The methods of the PPN approximation are considered. In this formalism, the equations that characterizeL-rigidity are expressed. As a consequence, the baryon mass density is constant in first order, the stress tensor is constant in the comoving system, the Newtonian potential is constant along the lineL, and the gravitational field is constant along the lineL in the comoving system.     

Multiresidue pesticide analysis of fruits by ultra-performance liquid chromatography tandem mass spectrometry

Ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC–MS–MS) has been used for screening and quantification of 32 pesticides and metabolites in two fruit matrices. The compounds investigated belonged to different chemical families of insecticides, acaricides, fungicides, and herbicides; several metabolites were also included. Quantification was conducted using matrix-matched standards calibration; response was a linear function of concentration in the range tested (10–500 ng mL⁻¹). The method was validated with blank samples of lemon and raisin spiked at 0.01 and 0.1 mg kg⁻¹, and recoveries were satisfactory, between 70 and 110%, for most of the pesticides tested and relative standard deviations were below 15% (n = 5 at each spiking level). Excellent sensitivity resulted in limits of detection for all compounds well below 0.01 mg kg⁻¹, with the limit of quantification being validated at 0.01 mg kg⁻¹. The UPLC system generates narrow peaks (approx. 5 s), thus increasing peak height and improving sensitivity. This improved separation efficiency facilitates adequate resolution not only of the analytes but also of matrix interferences compared with conventional HPLC. The method developed could also resolve some geometric isomers. The main advantage of this approach is the high sample throughput achieved because of the short analysis time, which enables satisfactory separation of all the compounds in less than 5 min per sample.     

Residue determination of captan and folpet in vegetable samples by gas chromatography/negative chemical ionization-mass spectrometry

A gas chromatography/negative chemical ionization-mass spectrometry (GC/NCI-MS) method has been developed for the simultaneous determination of the fungicides captan and folpet in khaki (persimmon; flesh and peel) and cauliflower. Samples were extracted with acetone in the presence of 0.1 M zinc acetate solution in order to avoid degradation of fungicides and were purified using solid-phase extraction with divinylbenzene polymeric cartridges. Purified extracts were evaporated and dissolved in hexane prior to injection into the GC/NCI-MS system. Isotope-labeled captan and folpet were used as surrogate/internal standards, and quantification was performed using matrix-matched calibration. The method showed linear response in the concentration range tested (50-2500 ng/mL). The method was fully validated with untreated blank samples of khaki (flesh and peel) and cauliflower spiked at 0.05 and 0.5 mg/kg. Satisfactory recoveries between 82 and 106% and relative standard deviations lower than 11% in all cases (n = 5) were obtained. The limit of detection for both compounds were estimated to be 0.01 mg/kg. The developed method has been applied to treated and untreated samples collected from residue trials.     

A comparative study on the glass-forming ability of some alloys in the Sb-As-Se system by differential scanning calorimetry

The glass-forming ability and devitrification of alloys in the Sb-As-Se system have been studied by differential scanning calorimetry (DSC). A comparison of various simple quantitative methods to assess the level of stability of glassy materials in the above-mentioned system is presented. All these methods are based on the characteristic temperatures, obtained by heating of the samples in non-isothermal regime, such as the glass transition temperature, T_g, the temperature at which crystallization begins, T_in, the temperature corresponding to the maximum crystallization rate, T_p, or the melting temperature, T_m. In this work, a kinetic parameter K_r(T) is added to the stability criteria. The thermal stability of some ternary compounds of Sb_xAs_{0.60−(2x+y)}Se_0.40+x+y-type has been evaluated experimentally and correlated with the activation energies of crystallization by this kinetic criterion and compared with those evaluated by other criteria.