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Thermal properties of Jojoba wax

II. Oxidation behaviour by differential scanning calorimetry

Journal of Thermal Analysis and Calorimetry
Authors:
V. González-González
and
E. Campos-López

The thermo-oxidative stability of Jojoba wax (Simmondsia chinensis) was studied by differential scanning calorimetry in a dynamic oxygen atmosphere. The thermo-oxidation activation energy (Ea) was calculated by determining the maximum reaction temperature (Tm) at different heating rates (Hr) and using mathematical models previously proposed for dynamic systems. The value obtained was 21.84 Kcal/mol. The oxidation enthalpiesδH ox were also calculated and a lineal relationship was found with the square root of the heating rate and the initial temperature of thermo-oxidation

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The behavior of the horizontal component of the magnetic field obtained by ground magnetometers for three intense magnetic storms that happened during the occurrence of continual auroral activity (HILDCAAs) was studied through a UT-LT analysis. The considered storm periods were August 26–28, 1998, October 21–23, 1999 and April 6–8, 2000. Five minute resolution data were taken from six magnetic observatories, with approximately uniform longitudinal distribution. The results were compared with some interplanetary parameters such as velocity of solar wind, south component of interplanetary magnetic field.

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Thermal properties of jojoba wax

I. Crystallization behaviour

Journal of Thermal Analysis and Calorimetry
Authors:
V. González-González
,
R. O. Valero-Coss
, and
E. Campos-López

The thermal behaviour of Jojoba (Simmondsia chinensis) liquid wax was studied by differential scanning calorimetry (DSC), varying the annealing conditions. The fusion enthalpy (ΔHf) of the unannealed material was 27.1 cal/g; the relationship between heat capacity (Cp) and temperature could be expressed by the following equation:Cp=9.51×10−4 T+0.129. It was found that Jojoba wax presents four endothermic transitions (α, β, γ andδ) including fusionα, estimable at low heating rates (1 K/min); the activation energies (Ea) for transitionsα andγ were 51.18 and 64.82 Kcal/mole respectively; and it was observed that the transition temperaturesα andγ maintained a lineal relationship with the square root of the heating rate (Hr).

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Benzenesulfenamides with the formula R-S-N-(R′)2 (R=C6H5 andR′=NC4H8O, C7H7 and C6H11) and their chromium carbonyl complexes were studied by means of TG and mass spectrometric methods. The thermal behaviour of the compounds the stabilities of free sulfenamides are lower than those observed for the corresponding chromium carbonyl complexes. Combined thermogravimetry — mass spectrometry results suggest that the fragmentation mechanism of the carbonyl complexes involves cleavage of the Cr-S and Cr-CO bonds while that of sulfenamide depends mainly on the dissociation rates of the NR2 groups.

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Four new derivatives of uranium with propionic acid, ammonium and various divalent cations have been synthesized, whose general formula corresponds to NH4M[UO2(C2H5COO)3]3nH2O, (M=Mn++, Co++, Ni++ and Zn++). These compounds have been studied by X-ray diffraction, differential thermal and thermogravimetric analysis, so as to identify the different solid phases isolated during heat treatment. The existence of a new double oxide of uranium and cobalt with fluorite type structure has also been shown.

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Abstract  

Artefacts of pottery belonging to the Guarani ethnic group were investigated by XRF techniques. The Tupi-Guarani, is one of the three main representatives of the Neolithic culture in the Amazonian scope. Such an ethnic group dispersed towards the South; in the Paraguayan area between the Paraguay and the Parana Rivers several Guarani ethnic movements by both rivers and their tributaries are perceived. The lithology and ceramics typology have contributed to support that perception. The archaeological findings help to clarify prehistoric cultural aspects and dispersal areas. In that context, the knowledge of the chemical composition of the found ceramic devices, in particular of the rare earth elements (REE) and other refractory ones provide information on this dispersion and its expansion. Selected trace elements (Rb, Sr, Y, Zr, Nb, Ba, La, Ce, and Nd) were determined in samples from thirteen archaeological sites with XRF using an Am-241 source. Their spidergrams have allowed identifying four different sets of samples according to their areas of provenance.

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The purpose of this study was to investigate the effects of three different distributions of aerobic training on the isokinetic strength and vertical jump performance [SJ, CMJ and Abalakov (ABA)] in thirty middle-aged endurance athletes (38.7 ± 9.8 yrs; 174.7 ± 6.5 cm; 72.0 ± 9.8 kg). Three zones of training were required to quantify volume of training: Zone 1, low-intensity-training < VT1; Zone 2, threshold-training, between VT1 and VT2; and Zone 3, high-intensity-training > VT2. The INC group (n = 10) began training in the Zone 1 and then gradually built up training in Zone 2 and Zone 3, thereby increasing the intensity of aerobic activity over the 4-week training period. The CON group (n = 10) performed the same activity every week in Zones 1, 2 and 3. The FRE group followed a free distribution of endurance training loads (n = 10). The results showed significant decreases in peak torque knee extension 30° (p < 0.05) in CON group and significant decreases (p < 0.05) in ABA in FRE group. Results provide a physiological basis to support several performance studies that consistently indicate 5 d·wk−1 endurance training does not impair strength development over the short term. In conclusion, variations in volume and intensity in training groups did not interfere with isokinetic strength and vertical jump performance.

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Journal of Thermal Analysis and Calorimetry
Authors:
J. Galán
,
J. Del Castillo
,
A. González-Pérez
,
V. Fuentes-Vázquez
, and
J. Rodríguez

Abstract  

The specific conductivities of dodecylpyridinium chloride have been determinated in water-butanol/pentanol/hexanol solutions in the temperature range of 10 to 35C, and butanol, pentanol and hexanol concentrations up to 0.05 mol kg–1. From these data the temperature dependence of the critical micelle concentration, (cmc), was determined. The molar fraction of alcohol in the micelle was estimated using the theory suggested by Motomura et al. for surfactant binary mixtures. The standard Gibbs free energy of solubilization of alcohols in the micelles was worked out using the phase separation model.

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Journal of Radioanalytical and Nuclear Chemistry
Authors:
T. Martinez
,
J. Lartigue
,
M. Navarrete
,
L. Cabrera
,
P. Gonzalez
,
A. Ramirez
, and
V. Elizarraras

Abstract  

This paper presents the annual radon gas concentrations obtained during the 1994–1995 monitoring campaign using passive electret system (type E-PERM). Radon levels were measured in 154 single family dwellings, in normal occupancy conditions (open house condition) in the metropolitan zone of Mexico City. At the same time radon monitoring was performed outdoors. The results show the general log-normal distribution of integrated indoor radon concentration with an annual indoor mean of 3.8 pCi·l−1. The seasonal variations show the minimum mean values in the summer season which are 39% lower than that in autumn. Equilibrium factors (F) were measured in 12 typical houses both in autumn and winter using a continuous working level monitor for short-lived radon decay products and H-chamber loaded with a short term electret (HST, E-PERM) for radon gas. The obtained total mean equilibrium factors are:F=0.41±0.17 andF=0.29±0.04 for indoor and outdoor, respectively. A quality program was also improved.

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A high-performance thin-layer chromatographic (HPTLC) method has been developed for determination of polyamines in beers. Beer samples, previously degassed, were derivatized with dansyl chloride and the dansyl derivatives were separated by HPTLC with silica gel as stationary phase and chloroform–triethylamine, 2 + 1 (v/v), containing 5% (m/v) polyoxyethylene-10-lauryl ether, as mobile phase. Quantitative analysis was achieved by in-situ fiberoptic-based fluorescence scanning. The compounds were determined over the range 0.5–85 ng, with relative standard deviations between 0.44–1.16% and detection limits in the range 0.28–0.39 ng. The simple preparation of the sample and the rapid microwave-assisted dansylation considerably reduce analysis time and effort.

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