We have experience of two methods for the analysis of 14C in environmental samples and have used this experience to directly compare these two techniques. Nine vegetation samples and a sucrose standard were analyzed using the benzene synthesis and combustion techniques. The results obtained using both methods were in good agreement and show that 14C data obtained using either technique are comparable. The analytical requirements for the two techniques vary considerably. In choosing a technique, a variety of factors such as sensitivity, sample size, sample type, carbon content and how the results are to be expressed, need to be considered.
The analysis of99Tc was carried out in filter, peat and rainwater samples. A solvent extraction technique was used to separate Tc from them, where tributylphosphate was the extracting agent. Radiochemical yield was obtained by using99mTc as an internal tracer. A typical value of 60% was found for it. However, problems encountered in its determination are discussed in the text. Additionally, rainwater samples were analyzed for137Cs. This was adsorbed in ammonium phosphomolibdate. Radiochemical yield was obtained by using134Cs as an internal tracer.
In the tropics, maize (
L.) is often grown under low N conditions. Information on the respective role of N uptake and partitioning at anthesis in determining grain yield under low N is scarce. Senescence traits have been proposed as secondary traits to select for low N tolerance, but the stability of their association with yield under different environmental conditions has been rarely described. In the present study we analyzed the associations between grain yield, N uptake and partitioning at anthesis, dry matter matter partitioning, and senescence traits during two seaons in QPM (quality protein maize) hybrids. Association between grain yield and N uptake at anthesis, when found, was mainly explained by a close relationship between grain yield and above-ground biomass. No relationship was found between grain yield and N partitioning at anthesis. In both seasons grain yield was significantly positively associated with ear to above-ground biomass and ear to tassel weight ratios. The magnitude of the correlation between grain yield and senescence traits highly depended on climatic conditions.
Authors:Nuria Sánchez-Sánchez and Adolfo C. Fernández Puente
This paper examines the paradox between high relative levels of job satisfaction and the characteristics of women's jobs compared to men's in Spain. Three hypothesis are considered: i) the existence of a selection bias when participating in the labour market; ii) of the presence of adaptive job satisfaction; and iii) the existence of differences related to preferences of different nature to strictly labour issues.
The study shows that, although having lower working conditions, women are more likely to be satisfied at work than men are. This paradox persists regardless of the inclusion of a great range of variables of different nature (objective and subjective), the age group and educational level under consideration. The Oaxaca-Blinder decomposition suggests that women's preferences are actually influencing the differences in job satisfaction. However, it is not demonstrated that these differences disappear as age decreases or educational level increases. The probable existence of a “glass ceiling” that prevents women from having access to posts of greater responsibility and higher wages could cause that women who actually reach them are more satisfied than their male colleagues. As the labour market and society become more equal, this paradox might dilute.
Authors:P. Sánchez-Soto, E. Morillo, J. Pérez-Rodríguez, and C. Real
Thermoanalytical study of the pesticide 3-amino-1,2,4-triazole (ATA) has been carried out, using simultaneous DTA-TG in nitrogen
flow, in order to know its thermal behaviour and stability. These techniques have been further complemented using evolved
gas analysis and mass spectroscopy (EGA-MS). Two different stages of ATA decomposition were observed: after the first decomposition
step, a mixture of compounds is obtained, according to MS data, being the principal component a compound of molecular weight
126. It is formed by a first order reaction mechanism, according to the kinetic study, withEa=124±8 kJ·mol−1. The second decomposition step takes place about 735°C, with evolution of HCN and NH3, being the final weight loss 96%.
Authors:E. Morillo, J. Pérez-Rodríguez, C. Real, and P. Sánchez-Soto
In the present investigation, DTA and TG techniques were used to study the thermal behaviour of montmorillonite treated with
solutions of the pesticide aminotriazole (AMT), in nitrogen flow. These techniques have been complemented by mass spectrometry of the evolved gases (EGA-MS).
AMT is adsorbed in the interlamellar space of montmorillonite as a cation. Results obtained in this study show that this provokes
a shift of the dehydroxylation peak of montmorillonite to lower temperatures than those of the untreated clay. Montmorillonite
protects the adsorbedAMT, delaying its first decomposition step, and catalysesAMT final decomposition at lower temperatures.
The DTA curve of montmorillonite-AMT mechanical mixture differs from the sum of those of the clay mineral and the pesticide heated individually. Montmorillonite
dehydroxylation occurs at lower temperature, indicating a complex formation betweenAMT and the mineral during the heating process. However the DTA of the mixture is different from that of the complex previously
studied, indicating that in the complex obtained by heating the physical mixtureAMT is adsorbed as neutral molecule or as a product of its decomposition.
Authors:C. del Hoyo, C. Dorado, M. Rodríguez-Cruz, and M. Sánchez-Martín
A physicochemical study of the systems formed by the clay minerals, montmorillonite and kaolinite (layered) and sepiolite
(non-layered) and the surfactants Triton X-100 (TX100, non-ionic), dodecyl sodium sulfate (SDS, anionic) and trimethyloctadecyl-ammonium
bromide (ODTMA, cationic), with different chemical structure, was carried out by X-ray diffraction (XRD), infrared spectroscopy
(FTIR) and thermogravimetric and differential thermal analysis (TG/DTA). TG/DTA results indicated an increase in the thermal
stabilization of non-ionic (TX100) and cationic (ODTMA) surfactants adsorbed by all clay minerals in relation to pure compounds.
This effect was greater in montmorillonite and sepiolite than in kaolinite owing to these minerals must allow the establishment
of a stronger bond with the surfactants as indicated by XRD and FTIR results. Differences in decomposition of anionic surfactant
SDS are not emphasized due to the low adsorbed amount of this surfactant by all systems. The results obtained indicate the
interest of taking into account the structure of surfactant and the clay mineral type when preparing customized surfactant-clay
mineral systems which contribute to establish more efficient soil and water remediation strategies based in the use of these
Authors:L. Franco, C. Sánchez, R. Bravo, A. Rodriguez, C. Barriga, and Javier Juánez
The hop (Humulus lupulus), a component of beer, is a sedative plant whose pharmacological activity is due principally to its bitter resins, especially to the α-acid component 2-methyl-3-buten-2-ol. The mechanism of action of the resin of hop consists of increasing the activity of the neurotransmitter γ-aminobutyric (GABA), inhibiting the central nervous system (CNS). Objectives: To analyze in an experimental model of diurnal animal the sedative effect of hop, a component of beer, on the activity/rest rhythm. Methods: Experiments were performed with common quail (Coturnix coturnix) similar to humans in the sleep-wake rhythm, isolated in 25 × 25 × 25 cm methacrylate cages, with food and water ad libitum, in a room with artificial ventilation (22 ± 1 °C) and a lighting cycle of 12L/12D (n = 5). The doses administered, close to the content of non-alcoholic beer, were 1, 2 and 11 mg extract of hop as one capsule per day, at 18:00 h for one week. A control group received capsules only with a methylcellulose excipient and a basal group received no treatment. The chronobiological analysis of the animals’ activity captured and logged by the software DAS24 was performed using the Ritme computer program (cosinor methods). Results: With the dose of 2 mg, there was a statistically significant (p < 0.05) reduction of the arithmetic mean nocturnal activity (23 ± 3.0) with respect to the basal (38.56 ± 2.79), control (38.1 ± 2.8) and other doses groups 1 mg (52.04 ± 3.65) and 11 mg (47.47 ± 5.88). This dose of 2 mg, similar to the concentration in beer, was more effective in reducing nocturnal activity than the other doses of 1 and 11 mg, as well as preserving the circadian activity/rest rhythm. Conclusion: The concentration of 2 mg of hop extract effectively decreased nocturnal activity in the circadian activity rhythm. On the basis of this investigation, administration of non-alcoholic beer would be recommended due to its hop content and consequent sedative action, which would be an aid to nocturnal sleep.
Authors:C. Wehenkel, A. Reyes-Martínez, J. H. Martínez-Guerrero, C. Pinedo-Alvarez, and C. A. López-Sánchez
Bird migration constitutes a redistribution of bird diversity that radically changes the composition of the bird community worldwide. It comprises about 19% of the world’s bird species. Several studies have indicated that changes in avian community structure and differences in bird richness in different seasons are mainly driven by seasonality and by winter harshness, and that the associated costs increase with the distance involved. Western Mexico is an important wintering area for most passerines that breed in western North America, and that travel long on the long-distance Central and Pacific migration routes. In this study, we examined bird species richness and diversity during the breeding and wintering seasons in the Central Sierra Madre Occidental (SMO), North Durango (Mexico) in relation to i) tree species diversity, ii) tree dimension, iii) forest stand density and site quality, iv) density and dimension of snag trees, and v) various climate variables. The overall aim of the study was to determine how the observed associations between bird species diversity and variables i-v are affected by the season considered (breeding or wintering). The diversity of bird species in the breeding season was not affected by any of the climate and forest stand variables considered. In contrast, bird species diversity in the wintering season was significantly and weakly to moderately associated with climate variables, tree species diversity and stand density, although not with density or dimension of snag trees. Bird species diversity was higher at lower elevations and in drier and warmer locations of the SMO. The association detected is therefore mainly a local migratory phenomenon.
Authors:J. Cubero, V. Valero, D. Narciso, J. Sánchez, A. Rodríguez, and C. Barriga
The use of melatonin as antioxidant has been extensively established. But what would the antioxidant function be if one were to go one step back in the anabolism of that amine, and orally administer its precursor — the amino acid tryptophan? Diurnal animals (
) were administered orally capsules containing 125 or 300 mg L-tryptophan/kg b.w. for 7 days at the end of the light period (20
). A control group received capsules with methylcellulose. The antioxidant function was studied through the reduction of nitroblue tetrazolium (NBT) by superoxide anion, and through the levels of malonaldehyde (MDA) produced in the lipoperoxidation that occurs from the respiratory burst in response to the presence of a foreign particle in phagocytic cells (heterophils), which were extracted at 2
— at the acrophase of melatonin in the blood stream. In the heterophils extracted from the group that received 125 mg kg
b.w. tryptophan, there was less oxidative stress as determined by the NBT reduction than in those from the 300 mg kg
b.w. group. In the study of the lipoperoxidation of the membranes as determined by the levels of MDA, however, no significant variations were observed between the different groups. The lower concentration (125 mg L-tryptophan/kg b.w.), administered orally, succeeded in diminishing the free radicals produced in the heterophils for the destruction of the ingested foreign agent, but not fully or maximally. The possible solution to this prooxidant/antioxidant imbalance would be to administer a lower concentration of tryptophan to attain the perfect balance for application in nutritional treatments.