Comparison of nutrient cycling in a surface-flow constructed wetland and in a facultative pond treating secondary effluent.

There is a growing interest in the possibilities offered by combinations of waste stabilisation ponds (WSP) and constructed wetlands (CW). The purpose of our study was to compare treatment performances and nutrient cycling in a surface-flow wetland (SFW) and in a WSP treating secondary effluent. In the period between 2000 and 2003, a pilot SFW and a pilot WSP were constructed at the outlet of the wastewater treatment plant and their performance monitored while both were active under the same conditions. The SFW was planted with Phragmites australis and Eichhornia crassipes, while in the WSP development of algae was spontaneous. Performance efficiency was monitored by means of evaluation of physical and chemical parameters in water, by measurement of plant productivity and by analysis of N and P contents in biomass. The SFW with macrophytes proved more efficient in decreasing the suspended solids (64.6%), settleable solids (91.8%), organic N (59.3%), total N (38%), COD (67.2%) and BOD5 (72.1%) than the WSP. The WSP with algae was more efficient in treatment of ammonia nitrogen (48.9%) and ortho-phosphate (43.9%). The results of this study provide data that are of help in optimising combinations of SFW and WSP.     

JETS,PLUMES AND BUOYANT JETS IN STATIC ENVIRONMENT

Turbulence represents an essential aspect in atmospheric and oceanic circulations.In particu-lar,it is a preponderant factor in the dispersion of pollutants of artificial or natural origin.Thevertical turbulent jets,plumes and buoyant jets discharging into static environment is one of themost important and basic flow patterns related with the environment pollution.These flows havenumerous important applications,for example,thrust augmentors,waste disposal plumes fromstacks and combustion systems,and significant problems of turbulent diffusion.     

EXPERIMENTAL STUDIES AND NUMERICAL CALCULATION ON TURBULENT BOUNDARY LAYER OF WATER FLOW ALONG CURVED SURFACE

This paper will introduce experimental studies and numerical calculation onturbulent boundary layer of water flow along curved surface in our country in recent years.Onthe basis of the experimental studies,the effects of curvature and roughness on velocitydistribution and pressure distribution and the change of turbulent flow boundary layer onoverflow bucket concave surface is discussed.We proposed the empirical formula of velocity,pressure and the change of turbulent flow boundary layer on outlet bucket concave.According tothe momentum principle,we have deduced the momentum integral equation full water depthboundary layer and using the element as control unit inside the boundary layer on concavesurface of bucket.Combining with continuity equation,we have computed the boundary layerdevelopment on the bucket of a spillway.Compared with the field experimental data,thecalculation results are available.Under polar coordinates,a mathematical model for simulatingtime-averaged flow characteristics in concave surface of bucket is established.The turbulent flowfield on concave surface of bucket is calculated by SIMPLE method and this mathematicalmodel.The flow velocity field,pressure field,distribution of turbulent kinetic energy,distribution of turbulent energy dissipating rate and distribution of shear stress are available.Thecalculation value is consistent with measured test data.     

Unemployment compensation and episodes of nonemployment

This paper examines the influence of unemployment insurance (UI) on the length of nonemployment spells experienced by young workers. The analysis introduces a flexible duration model to estimate the effects of the weekly benefit amount and weeks of eligibility on the amount of time spent between jobs by men, distinguishing between the experiences of UI and non-UI recipients. The empirical findings suggest three conclusions: (1) UI recipients experience longer spells of nonemployment than their non-UI recipient counterparts, at least up to the point of exhaustion of UI benefits; (2) the level of the weekly benefit amount does not significantly affect the length of nonemployment spells; and (3) increasing the number of weeks of eligibility offered by a UI program leads to longer episodes of nonemployment.     

The Distribution of Multifamily Mortgage Originations: What We Know and Why We Care

Three policy-relevant questions about multifamily mortgage originations (MFOs) are addressed. First, what is the annual volume of MFOs? This analysis highlights differences and problems among three publicly available multifamily lending surveys; the 1993 volume is estimated at $30 billion. Second, what is the size distribution of multifamily mortgages? Using kernel density estimation, variation in this distribution among central cities and suburbs, underserved areas, and lender type is examined. Third, what are the primary determinants of the variation in multifamily lending? A relatively simple regression model is estimated to shed light on the variables most highly correlated with multifamily lending. Tract income relative to MSA median income and minority concentrations are shown to be highly correlated with lending volume, but the largest source of variation is the number of multifamily rental units in the tract.     

The Role of Multinational Firms in the Wage-Gap Debate

The observation of an increase in the ratio of skilled to unskilled wages in the high-income countries and in some cases in low/middle-income countries has led to considerable discussion and controversy as to its cause. Virtually none of the analyses have considered a role for multinational investment in explaining the wage-gap phenomenon. This paper adapts the authors' earlier work to consider what role multinationals might play in factor markets. It identifies circumstances under which investment liberalization is likely to raise the wage gap in both the skilled-labor abundant and the unskilled-labor abundant country.