Results of plasma radiative compression investigation in the PF-24 device operated with D2, Ar and (100%-x)D2+x%Ar mixtures obtained using the 5-phase Lee model code.

The article presents new results for plasma radiative compression in high-current discharges in the z-pinch configuration. The results are based on the 113 discharges performed in the plasma-focus PF-24 device operated with D2, Ar and (100%-x)D2+xAr mixtures, with Ar pressure fractions x ≈ 3-60% (mole fractions). The constant initial total pressure is about 2.9 mbar and the constant initial pressure of Ar is 1.2 mbar. Each experimental discharge was simulated individually using the 5-phase Lee model code to carry out the fitting procedure of the total discharge current waveform. The results from these 113 computed discharges fitted to the corresponding 113 experimental discharges show that the increase of the effective atomic number of the gas mixture increases the probability of occurrence of plasma radiative compression phenomenon. Relatively weak radiative compression was found for part of the discharges in 15-60% range of Ar mole fractions and in Ar, while the stronger radiative compression occurred for part of discharges in Ar only. This is because there was too little total x-ray line radiation emission during the equilibrium pinch lifetime related to the very small amount of swept up mass and the low current flow through pinched plasma, represented by the decreasing values of model parameters as the Ar mole fraction increases. The results show that the main pinch parameters influencing the occurrence and strength of radiative compression are: total x-ray line emission yield, effective atomic number, initial pinch radius, initial pinch ion number density and initial pinch ion/electron temperature.

In situ determination of the static inductance and resistance of a plasma focus capacitor bank.

The static (unloaded) electrical parameters of a capacitor bank are of utmost importance for the purpose of modeling the system as a whole when the capacitor bank is discharged into its dynamic electromagnetic load. Using a physical short circuit across the electromagnetic load is usually technically difficult and is unnecessary. The discharge can be operated at the highest pressure permissible in order to minimize current sheet motion, thus simulating zero dynamic load, to enable bank parameters, static inductance L(0), and resistance r(0) to be obtained using lightly damped sinusoid equations given the bank capacitance C(0). However, for a plasma focus, even at the highest permissible pressure it is found that there is significant residual motion, so that the assumption of a zero dynamic load introduces unacceptable errors into the determination of the circuit parameters. To overcome this problem, the Lee model code is used to fit the computed current trace to the measured current waveform. Hence the dynamics is incorporated into the solution and the capacitor bank parameters are computed using the Lee model code, and more accurate static bank parameters are obtained.

Ethnic fertility differentials in Peninsular Malaysia and Singapore.

Differences in fertility between the three major ethnic groups (Malays, Chinese and Indians) in Peninsular Malaysia and Singapore have existed since before the onset of fertility decline in the late 1950s and remain today, although the relative positions and the actual differences have changed due to the varying rates of decline. By 1987, the Malays experienced the highest fertility and the Chinese the lowest in both countries but in Singapore the Malay fertility was lower than the Chinese fertility in Peninsular Malaysia. The fertility differentials will lead to changes in the ethnic composition in both countries but more so in Peninsular Malaysia.

PIP: Ethnic fertility differentials are compared in Peninsular Malaysia and Singapore for Malays, Chinese, and Indians from 1947-87. These 2 neighboring countries have similar ethnic compositions and historical experiences. Both were part of a combined colonial territory under British rule until the late 1940s. By 1987, the Malays experienced the highest fertility rate in Peninsular Malaysia, while the Chinese had the lowest rate in both countries. It is noted that the Chinese fertility rate in peninsular Malaysia (Malays 4.51, Chinese 2.25, Indians 2.77) is greater than the Malay's fertility in Singapore (Malays 2.16, Chinese 1.48, Indians 1.95). These fertility differentials will lead to a shift in ethnic composition in both countries. Both governments have shifted from strictly antinatalist policies to a relaxed pronatalist influence.

A decade of fertility below replacement level in Singapore.

PIP: This paper discusses fertility trends in Singapore during the decade 1975-1984. Fertility 1st dropped below the replacement level in 1975 when the gross reproduction rate reached 1.006 and fell further to the low of 0.772 in 1984. During the same period all of the 3 main races, Chinese, Malays, and Indians, experienced fertility below replacement level. The shortfall in the number of births required to ensure replacement fertility increased during the decade until it approached 1/4 in 1984. This indicates that Singapore has more than achieved its national demographic goal of fertility to attain 0 growth and to stabilize the population in the future. This study shows that the newly introduced population policies designed to improve the quality of the population may well in practice lead to fewer births. A declining population in the 21st century is very likely.^ieng

The dynamics of ageing in Singapore's population.

This paper beings by explaining with the aid of the stable population theory that the ageing of a population is chiefly, if not entirely, the result of a decline in mortality. It shows that the decline in fertility is the major determinant of an ageing population. In Singapore the ageing of our population has commenced and will gather momentum in the future: there is little that can be done to arrest this trend caused by the past rapid decline in fertility and the maintenance of fertility below replacement level since 1975. Some of the more significant consequences in the areas of level of living, consumption pattern, savings, labour shortage, and ageing work force are discussed briefly.

Population growth and redistribution in Hong Kong, 1841-1975.

PIP: The authors analyze trends and patterns of population growth and redistribution in Hong Kong from 1841 to 1975. Causes of population growth, including migration, policies regulating growth, land acquisition, political circumstances, and conditions on the Chinese mainland, are examined. Population redistribution patterns are investigated with respect to geographical divisions and to changes in population density at district levels; factors influencing distribution variations are discussed^ieng