Search Results
Abstract
The accelerated thermal degradation of low-density polyethylene (LDPE) was studied in air at atmospheric pressure and temperatures of 70, 80, 90 and 100C. The changes in elongation at break, traction resistance and density as a result of accelerated thermooxidative degradation were followed. Thermal analysis curves (TG, DTG and DTA) of non-aged and thermally aged LDPE were recorded, and the thermal analysis results were compared with those relating to the variations in the elongation at break, the traction resistance and the density as a consequence of accelerated thermal aging.
Summary
The age of a recent, i.e., fresh, nuclear event can be determined by measuring the activity of short-lived parent and daughter fission products. The event studied was a short irradiation, of a small sample of uranium, in a nuclear reactor. Two clocks were investigated, 92Sr-92Y and 135I-135Xe. Measurements of the source by gamma-spectrometry yielded very good agreement between true and measured ages. The upper and lower age limits of applicability for the clocks in question were defined. The half-life of 92Sr was found 2.635±0.008 hours and of 135I 6.65±0.04 hours.
Abstract
The physical aging of a system containing tetraglycidyl-4-4′-diaminodiphenylmethane (TGDDM), with a multifunctional novolac glycidyl ether resin hardened by 4,4′-diaminodiphenylsulphone (DDS) has been investigated by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Samples fully cured were aged at temperatures between 200 and 250C, during periods of time from 1 to a maximum of 336 h. Furthermore, the dynamic mechanical relaxation behaviour annealed at temperature of 220C, was studied, aging during 24 and 168 h. The effect of the enthalpy relaxation during DSC heating scan is shown by the presence of an endothermic peak whose position and intensity depends on the aging conditions, both temperature and time. DSC studies suggest that enthalpy relaxation increases gradually with aging time to a limiting value for each temperature where structural equilibrium is reached. DMA results show that the effect of aging is to cause chain stiffening and a decrease in the height of the peak value of the loss factor.
Summary
Scarce information is available on the content of metals and their molecules in the human brain. Iron, copper and other metals are involved in neurodegenerative disorders like Parkinson’s Disease (PD), however, their behavior in physiological conditions is poorly understood. In this study we have measured iron, copper and their major proteins (ferritins and ceruloplasmin) in substantia nigra (SN) of normal subjects at different ages, since this is the main target region of PD. An increasing trend for iron and copper concentration was found in aging. Ferritins were also increasing in aging while ceruloplasmin did not vary. These data show that the accumulation of these metals requires an increased expression of storage molecules to prevent toxic effects of iron and copper.
Abstract
The composition and the permeation properties of the skin are dependent on age. In the animal models for permation studies, age affects the mechanical as well as the permeation properties significantly. The time dependence of permeation of 147Pm3+ from aqueous solution was established by the animal skin model and the age dependence of promethium permeation through the skin was examined. The aim was to find the optimum rat skin age model for radionuclide permeation studies and to assess the relative importance of the main permeation pathways: transepidermal and transfollicular permeation. The skin from 5-day-old rats (5DR) was found to represent the optimum animal model to study transepidermal permeation of ions. The skin from 9-day-old rats (9DR) was selected to study transfollicular permeation of ions. Comparison of the permeated amounts of promethium through the skin without hairs (3 DR to 6 DR) and with hairs (7DR to 12DR) showed that the additional permation mode via follicles significantly contributed to the permeation rate and extent.
Abstract
Correlated measurements of the individual positron lifetimes (so-called positron ages) and of the Doppler shift of the 2
-annihilation photon energy (Age-Momentum Correlation, AMOC) allow the evolution of the positron states to be observed in the time domain. The AMOC technique is thus especially useful when 
chemical
reactions of positronium induce transitions between positron states. The full information contained in the AMOC data may be extracted from the two-dimensional AMOC histogramme, the so-called AMOC relief, by fitting a suitable two-dimensional model function. In this way quantitative information on the spin conversion of positronium by a paramagnetic radical in the systems HTEMPO/methanol and HTEMPO/benzene and on the formation of positron bound states in aqueous solutions of various sodium halides has been deduced.
Abstract
To study the behaviour of trace elements in dependence of age and environment, samples of skin, lung, heart, aorta, kidney, liver, and brain were assayed for concentrations of Fe, Zn, Rb, Co, Cr, Se, Sc, Sb, Cs, Al and partly Eu. Nearly all element concentrations changed with progressing age, but they showed no clear correlation to either parameter assessed. The non-essential elements Sc, Sb, and Sc were increasingly concentrated in all organs except the skin. Comparing lung samples of patients from highly industrialized regions with those of lesser industrialization, the elements Sc, Al, Sb, Eu and Co were accumulated by a factor of 10 to 100. Thus the concentrations of trace elements in human organism also depends on the degree of industrialization.
Abstract
Using differential scanning calorimetry (DSC) we have studied the physical aging of an epoxy resin based on the diglycidyl ether of bisphenol A (DGEBA) modified by two different contents of an acrylonitrile-butadiene-styrene (ABS) and cured with 1,3-bisaminomethylcyclohexane (1,3-BAC). Samples fully cured were annealed at temperature of 125C for periods of time of 72 and 120 h, to determine the process of physical aging. The apparent activation energy for the enthalpy relaxation, Dh*, is determined as the sample is heated at 10C min-1 following cooling at various rates through the glass transition region. DSC studies suggested that the presence of thermoplastic inhibits the process of relaxation.
Abstract
The mean squared slowing-down distance, <r
2>, and the age to themal capture (Migration Area),M
2, are direct measures of the slowing-down, and the spreading out, processes of neutrons in a medium. They also enter directly into reactor calculations. These parameters have been determined experimentally for Am-Be neutrons (mean energy 4.46 Me V), in a block of perpex, using the activities induced in thin indium foils from the115In(n,
)116In reactions.
Abstract
This paper presents the results on 20 minor and trace elements of a wide analytical programme — based on neutron activation and statistical analysis — which deals with the chemical characterization of pottery from the Cycladic islands and Crete, during the Bronze Age (Cycladic period), with particular reference to Akrotiri on Thera. Multivariate analysis of the neutron activation data showed that the majority of the pottery found in Akrotiri was locally made, by one type of clay. This in connection with the local style that Akrotiri had introduced, supports the idea of an autonomous development. Contacts with neighbouring islands were also confirmed.
