Ad-hoc Nature Research Articles

Numerical analyses of operator-splitting algorithms for the two-dimensional advection-diffusion equation

Holly and Preissmann's (HP) scheme has been the basis of a large number of operator splitting algorithms for the solution of the advection-diffusion equation. However, these algorithms, including HP, are first-order accurate in time due to splitting errors. Error analyses of these algorithms, incorporating splitting error and errors resulting from numerical solutions of the split advection and diffusion equations, are lacking. In this paper, error analysis of a second-order accurate adaptation of the HP scheme (AHP) is presented for the two-dimensional advection-diffusion equation. A modified AHP scheme (MAHP) is suggested to remove the ad-hoc nature of boundary conditions during the diffusion step of computations in both HP and AHP. As boundary conditions specified for the advection-diffusion equation are not applicable to the split equations, second-order accurate boundary conditions for the split advection and diffusion equations are derived. An analysis of numerical dispersion and dissipation associated with the numerical procedure for the advection equation is presented. The analysis establishes a criterion so that computational errors are small in two-dimensional advection dominated transport problems. Several numerical examples are presented to verify the numerical analyses presented in the paper. In addition, a review of the current status of operator splitting algorithms for the advection-diffusion equation is presented. The objective of the review is to identify the issues that have not been addressed in the previous studies.

Floods of the Brahmaputra River in India

ABSTRACT Floods in the Brahmaputra basin of India are characterized by their extremely large magnitude, high frequency, and extensive devastation. During the last forty years of flood record at Pandu, the highest flood [72,748 cubic meters per second (m3s1)] occurred in 1962. But, more recently, the 1988 flood, characterized by the maximum flood height so far observed at Pandu, appears to be the most devastating one, causing inundation of 62 per cent of Assam's Brahmaputra valley. The mean annual flood discharge of the river at Pandu is 47,608 m3s' with a recurrence interval of 2.56 years. Floods on the Brahmaputra have been a recurring feature from early times. They may be attributed to the involvement of a host of related causes of a natural, hydrometeorological, and anthropogenic nature. But, in recent years floods of the river have become more severe, due to a variety of newly-emerged manmade causes, in addition to those generally recognized The flood control measures adopted in the basin since the early fifties are all of a short-term and ad-hoc nature and in fact, no proper floodplain management program is being implemented. Consequently, there have been regular flood onslaughts, adversely affecting the agrarian economy of the Brahmaputra valley.

Poland: The Social Safety Net During the Transition

This paper argues that the brunt of the reform-induced increase in Polish social expenditures has been borne by social insurance arrangements (mainly pensions and unemployment compensation) rather than by social assistance schemes targeted to the poor or more temporary social safety net schemes. This is largely due to ease of access to social security and its more attractive benefit structure. Much of recent social expenditure reform had an ad-hoc nature and was driven by the need to alleviate looming financial, distress. A major policy challenge is to avoid a further burdening of social security by needs that should be addressed by basic income support and emergency assistance policies or by general transfers (e.g., family allowances). Current reform needs are illustrated by using unemployment benefits and pensions as examples.

Poland: The Social Safety Net During the Transition

This paper argues that the brunt of the reform-induced increase in Polish social expenditures has been borne by social insurance arrangements (mainly pensions and unemployment compensation) rather than by social assistance schemes targeted to the poor or more temporary social safety net schemes. This is largely due to ease of access to social security and its more attractive benefit structure. Much of recent social expenditure reform had an ad-hoc nature and was driven by the need to alleviate looming financial distress. A major policy challenge is to avoid a further burdening of social security by needs that should be addressed by basic income support and emergency assistance policies or by general transfers (e.g., family allowances). Current reform needs are illustrated by using unemployment benefits and pensions as examples.