Direct application of UNIFAC activity coefficient computer programs to the calculation of solvent activities and .chi.-parameters for polymer solutions

Application of UNIFAC computer calculations to polymer solutions does not seem to make sense because of the value of the solvent activity: close to 1.000 over a considerable range of concentrations (up to 90% of polymer). A simple procedure is proposed to calculate solvent activity coefficients, and thus X-parameters, such that the easily available UNIFAC computer programs may be applied directly, without any modification

Instrumental Variable Estimation of the Causal Effect of Hunger Early in Life on Health Later in Life

Numerous studies have evaluated the effect of nutrition early in life on health much later in life by comparing individuals born during a famine to others. Nutritional intake is typically unobserved and endogenous, whereas famines arguably provide exogenous variation in the provision of nutrition. However, living through a famine early in life does not necessarily imply a lack of nutrition during that age interval, and vice versa, and in this sense the observed difference at most provides a qualitative assessment of the average causal effect of a nutritional shortage, which is the parameter of interest. In this paper we estimate this average causal effect on health outcomes later in life, by applying instrumental variable estimation, using data with self-reported periods of hunger earlier in life, with famines as instruments. The data contain samples from European countries and include birth cohorts exposed to various famines in the 20th century. We use two-sample IV estimation to deal with imperfect recollection of conditions at very early stages of life. The estimated average causal effects often exceed famine effects by a factor three.2SLS, obesity, high blood pressure, height, developmental origins, ageing, famine, nutrition, two-sample IV

Multi-walled microchannels: free-standing porous silicon membranes for use in µTAS

Electrochemically formed porous silicon (PS) can be released from the bulk silicon substrate by underetching at increased current density. Using this technique, two types of channels containing free-standing layers of PS were constructed, which were failed multi-walled microchannels (MW µCs). They can be used in devices like microsieves, microbatteries, and porous electrodes. Two types of MWµC were made: the 'conventional' version, consisting of two or more coaxially constructed microchannels separated by a suspended PS membrane, and the buried variety, where a PS membrane is suspended halfway in an etched cavity surrounded by silicon nitride walls. The latter is more robust. The pore size of the PS was measured using transmission electron microscopy and field emission gun scanning electron microscopy (FEGSEM) and found to be of the order of 7 n

Instrumental Variable Estimation of the Causal Effect of Hunger Early in Life on Health Later in Life

Numerous studies have evaluated the effect of nutrition early in life on health much later in life by comparing individuals born during a famine to others. Nutritional intake is typically unobserved and endogenous, whereas famines arguably provide exogenous variation in the provision of nutrition. However, living through a famine early in life does not necessarily imply a lack of nutrition during that age interval, and vice versa, and in this sense the observed difference at most provides a qualitative assessment of the average causal effect of a nutritional shortage, which is the parameter of interest. In this paper we estimate this average causal effect on health outcomes later in life, by applying instrumental variable estimation, using data with self-reported periods of hunger earlier in life, with famines as instruments. The data contain samples from European countries and include birth cohorts exposed to various famines in the 20th century. We use two-sample IV estimation to deal with imperfect recollection of conditions at very early stages of life. The estimated average causal effects often exceed famine effects by a factor three

The effect of electrical stimulation on the meat quality of impala Aepyceros melampus

The purpose of this research was to study the effect of electrical stimulation of carcasses on the meat quality of impala (Aepyceros melampus). The impala is one of the most important species in game meat production. A total of 40 impala (Aepyceros melampus) were harvested on Mara Research Station (23° 05' S and 29° 25' E; 961 m.a.s.l.) in the Limpopo province, South Africa. Animals were obtained during daytime by shooting from vehicles and by the walk and stalk method. Animals were shot high in the neck with .308 calibre scoped rifles and were immediately exsanguinated by cutting the jugular veins and carotid arteries with a sharp knife. The harvested animals were then taken to the processing facility at Mara Research Station, electrically stimulated, eviscerated and the carcasses cleaned according to standard South African and Zimbabwean practices. The animals were then hung by their Achilles tendon in a cold room at ca 4 ºC and left in the cold room for 24 hours with the skins on after which the skins were removed. The 40 animals were randomly grouped in the following groups and marked accordingly: Group 1: Electrical stimulation (ES) group consisting of 20 impala of which 10 were male and 10 were female (Experimental group). Group 2: Non-electrical stimulation (NES) group consisting of 20 impala of which 10 were male and 10 were female (Control group). Impala were electrically stimulated within 40 minutes after being shot. ES was applied using a Jarvis BV-80 unit (Jarvis Products Corporation, Middletown, CT) that delivered an electrical charge (230V; 50 Hz for 60 seconds) via a clamp attached to the nose and a steel hook (probe) inserted into the anus. The live mass (kg) of each animal was recorded and after dressing the carcass, the dressed out percentage (%) was calculated per individual animal. The average live mass of impala males was 55.5 kg which was significantly (p<0.001) higher compared to the females with an average live mass of 46.4 kg. The dressing percentage however did not differ significantly between the sexes where males had a 60 % dressing percentage and females a 59.4 % dressing percentage. ES, sex and muscle group had a significant (p<0.001) effect on muscle pH as measured at 45 min. 3, 6, and 12 hours post mortem. ES had a significant (p<0.001) effect on the pH of m. semimembranosus (SM), m. semitendinosus (ST), m. biceps femoris (BF) and m. longissimus dorsi (L1-L6) (LM) at 45 min., 3,6 and 12 hours post mortem. The pH of m. triceps brachii (TB) samples from impala in the ES group did not differ significantly (p=0.096) from samples from the NES group, samples from TB had a significantly (p<0.01) lower initial rate of pH decline compared to BF, LM, SM and ST. The interaction between ES x sex was significant (p<0.01). Muscle pH of samples from male impala in the NES group had lower initial pH values (at 45 min., 3,6 and 12 hours post mortem; p<0.001) than samples from the female impala in the NES group while there was no differences between samples from male and female impala in the ES group. Electrical stimulation influenced the pHu-value (p<0.05) of m. semitendinosus, with muscles from the ES group having a lower pHu (pH 5.52 ± 0.02) than muscles from the NES group (pH 5.59 ± 0.02). No significant differences were observed between ES and NES for the pHu-values of m. semimembranosus, m. biceps femoris, m. longissimus dorsi et lumborum and m. triceps brachii. Sex had a significant (p<0.05) effect on the pHu-value of the m. triceps brachii, with muscles from the male group having a higher pHu (pH 5.64 ± 0.02) than muscles from the female group (pH 5.58 ± 0.02). Electrical stimulation had a significant (p<0.05) effect on the L*24-value of the m. biceps femoris muscle, with muscles from the ES group (35.8 ± 0.08) being lighter than muscles from the NES group (33.1 ± 0.08). No significant differences were observed between ES and NES for the a*24- and b*24-values for all muscle groups. The L*-, a*- and b*-values of m. longissimus dorsi et lumborum muscle from ES and NES carcasses declined significantly (p<0.001) from 24 hours post-mortem to post freeze-thaw. ES also had no significant effect on the L*F- and a*F-values of the m. longissimus dorsi et lumborum muscle. ES however, had a significant (p<0.05) effect on the b*F-values. The b*F-value for ES meat (7.1 ± 0.1) was higher than NES meat (6.5 ± 0.2).The muscle x ES interaction was not significant. A significant difference (p<0.01) was found before and after freezing between the L*-values, a*-values and b*-values for both the ES and NES groups whereas the NES b*-value (p = 0.0638), showed a tendency to differ. No significant differences were observed between ES and NES for the thaw loss, drip loss, cooking loss, pH u, sarcomere length and shear force for the m. longissimus dorsi et lumborum muscle. Sex of the animal influenced (p<0.05) the thaw loss and cooking loss of the m. longissimus dorsi et lumborum muscle. No significant differences were observed between male and female for the drip loss, pHu, sarcomere length and shear force of the m. longissimus dorsi et lumborum muscle. In conclusion, it was found that ES did not have a significant effect on the meat quality of impala Aepyceros melampus ES however decreased muscle pH early post-mortem for impala by accelerating post-mortem glycolysis and hastening the onset of rigor mortis. This decrease in muscle pH probably reduced the possibility of cold shortening especially as impala have leaner carcasses. Thus ES may provide a commercial advantage with a decrease in processing and cooling time and an increase in meat production and shelf life. CopyrightDissertation (MSc(Agric))--University of Pretoria, 2009.Animal and Wildlife Sciencesunrestricte