Effects of electron beam irradiation on binary polyamide-6 blends with metallocene copolymers

The effect of electron beam irradiation on thermal and mechanical properties, and SEM morphology of polyamide-6 (PA-6) blends with grafted copolymers was investigated. High toughness materials were obtained with ethylene-polypropylene-diene grafted copolymers without significant variations in their thermal properties and Izod impact strength at room temperature and −30 °C with the irradiation doses used.     

Open cross-section beams under pure bending. I. Experimental investigations

An experimental study of open thin-walled section beams subjected to pure bending is presented. The aim of the study was to analyse the post-collapse behaviour of U-sections and Ω-sections. The beams were made of cold-formed steel, the thickness being 0.6 and 1.5 mm and the grades of the steel S275 and S325. Twenty-two specimens were tested in a four-point bending configuration. A special bending outfit was designed and built, taking into account the slenderness of the beams. Accurate moment-rotation graphs were thus obtained up to angles of rotation in the plastic hinges near to 20°, allowing for a complete development of the plastic mechanism after the collapse. In parallel, a finite element analysis methodology was implemented to simulate the post-collapse behaviour. The comparison with the experimental results validated this methodology (explained in Part II. Finite Element Simulation).     

The effects of soluble gas stabilisation on the quality of packed sardine fillets (Sardina pilchardus) stored in air,VP and MAP

Sardine (Sardina pilchardus) is a species that for its abundance assumes great importance in the Portuguese fishing sector. In order to contribute for a better utilisation of this species, the aim of this study was to investigate the effect of the pre‐treatment with soluble gas stabilisation (SGS) (100% CO₂ at 2 bar, during 15 and 30 min) on the quality and shelf‐life of sardine fillets, packed in air (AP), vacuum (VP) and modified atmosphere (MAP: 5% O₂/35% CO₂/60% N₂). During the chilled storage, the quality changes were evaluated by sensory evaluation, chemical and microbiological analysis. The total volatile basic nitrogen content remained almost constant, between 16 and 19 mg N/100 g muscle, during the storage period, for all samples. The TBARs values increased with storage time, for all batches and storage conditions. The application of SGS treatment to sardine fillets, resulted in a bacteriostatic effect, contributing to the improvement of the microbiological quality of fillets. Considering a sensory criteria, the shelf‐life of SGS pre‐treated sardine fillets was found to be 5 days in AP and MAP while in VP‐treated fillets a shelf‐life of 8 days was reported. At sensory rejection, sardine fillets presented a K‐value of 30% in AP and MAP batches and 40% in VP batch.     

Soil degradation in the tropical forests of the Dominican Republic's Pedernales province in relation to heavy metal contents

Two of the National Parks of the only Biosphere Reserve in the Caribbean Islands, the Jaragua-Bahoruco-Enriquillo reserve, occur mostly within the Pedernales province (Dominican Republic). In these National Parks, Jaragua and Bahoruco, almost every tropical forest ecosystem is represented, as are the land uses most common to the Dominican Republic. Despite soil being a key natural resource that needs to be considered in any sustainable development programme, the literature contains very little information on the soils of this region. In this study, we analysed 41 topsoil samples representing the main forest types and land uses of the province. The factors examined were fertility (OM, N, P, K) and heavy metal contents (Cu, Cr, Pb, Cd, Ni, Zn). Mean OM, N and total and available metal levels were almost invariably higher in the natural forest soils compared to those given over to human activities, especially cultivated soils. This difference suggests the uptake of metals by the crops and, to a lesser extent, by animals feeding on crop remains and grassland plants. This hypothesis is supported by high total and available metal contents, especially of Zn, Cu, Pb and, in smaller measure, of Cr recorded in the solid waste landfill of the city of Pedernales. It appears that the cutting down and burning practices of a nomad type of cultivation, as well as the pressures of intensive agriculture and livestock rearing have resulted in heavy metals bound to the soil's OM. We propose this is an important point to consider for the management of these lands.     

Calcium3D: a visual software package for the simulation of calcium buffered diffusion in neuroendocrine cells

We present Calcium3D, a user-friendly software package for simulating calcium triggered processes in neuroendocrine cells. We use Monte Carlo methods for the simulation of the basic processes involved: entry of calcium into the cytoplasm, the diffusion of ions and mobile intracellular calcium buffers inside the intracellular medium, and the kinetics of the reaction of calcium with these buffers. The outputs of the simulation are calcium and buffer concentrations as a function of time and for different depths from the cellular membrane.     

Polycystic ovary syndrome: evidence for reduced sensitivity of the gonadotropin-releasing hormone pulse generator to inhibition by estradiol and progesterone

Plasma LH is commonly elevated in women with the polycystic ovary syndrome (PCOS), but the underlying mechanisms are uncertain. We tested the hypothesis that the elevated LH in part reflects a reduced sensitivity of the hypothalamic GnRH pulse generator to suppression by estradiol (E2) and progesterone (P). In an initial protocol, normal controls (beginning on cycle days 8-10) and women with PCOS were given E2 transdermally and P by vaginal suppository (three times daily), to achieve plasma concentrations similar to those in the midluteal phase of an ovulatory cycle, for 21 days. Blood was obtained at 10-min intervals for 12 h before and on days 5, 10, 20, and 28 (7 days after E2 and P were discontinued). LH pulse amplitude and LH pulse frequency were suppressed in both PCOS and normal controls, but LH pulse frequency fell more rapidly in controls and was lower by day 10 (P < 0.05). Based on this time course a dose-response study was performed, in which E2 in constant dosage and varying concentrations of P were administered for 7 days. Pulsatile LH release was appraised on days 1 and 7. The frequency of LH pulse secretion was reduced in controls and was lower than that in patients with PCOS on day 7 (P < 0.0001). Plasma P concentrations of 13-15 ng/mL suppressed LH pulse frequency to a similar degree in PCOS and controls. In contrast, lower concentrations (P < 10 ng/mL) were more effective in suppressing GnRH/LH pulse frequency in controls (by > 45% of basal) than in PCOS (< 40%; P < 0.01). The data indicate that E2 and P can inhibit the activity of the hypothalamic GnRH pulse generator in women with PCOS. However, higher plasma concentrations of P were required to reduce GnRH/LH pulse frequency in PCOS compared to controls, suggesting an insensitivity of the GnRH pulse generator to suppression by E2 and P. These results suggest that an abnormality in the regulation of hypothalamic GnRH secretion is present in PCOS and may be a factor in the etiology of the disorder in adolescence.     

Measuring femtosecond lifetimes of free charge carriers in gallium arsenide

Peculiarities of the measurement of femtosecond lifetimes of free charge carriers in gallium arsenide grown by the method of molecular beam epitaxy are considered. The carrier lifetime is determined by a variant of the pump-probe method in which the pumping and probing radiation beams are incident onto the semiconductor sample surface at the Brewster angle. The proposed variant ensures the detection of a change in the induced refractive index even in the case of very small response signals, thus providing for a high sensitivity of measurements. It is shown that the relative signal changes near the Brewster angle reach a maximum level.     

A microhardness test for monitoring the thermal stabilization of solid PVC

The Vickers microhardness test has been found to be a new and attractive analytical tool for the study of the thermal degradation of rigid poly(vinyl chloride) sheets stabilized with different ratios of calcium/zinc carboxylates.