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P r e f a c e I n t e r e s t i n human s e t t l e m e n t systems and p o l i c i e s h a s been a c r i t i c a l p a r t o f u r b a n -r e l a t e d work a t IIASA s i n c e i t s incept i o n .Recently t h i s i n t e r e s t h a s given r i s e t o a c o n c e n t r a t e d r e s e a r c h e f f o r t f o c u s i n g on m i g r a t i o n dynamics and s e t t l e m e n t p a t t e r n s .Four s u b -t a s k s form t h e c o r e of t h i s r e s e a r c h e f f o r t :I .t h e s t u d y of s p a t i a l p o p u l a t i o n dynamics;11. t h e d e f i n i t i o n and e l a b o r a t i o n of a new r e s e a r c h a r e a c a l l e d demometrics and i t s a p p l i c a t i o n t o m i g r a t i o n a n a l y s i s and s p a t i a l p o p u l a t i o n f o r ec a s t i n g ;111. t h e a n a l y s i s and d e s i g n o f m i g r a t i o n and s e t t l ement p o l i c y ;a comparative s t u d y of n a t i o n a l m i g r a t i o n and s e t t l e m e n t p a t t e r n s and p o l i c i e s .T h i s p a p e r , t h e t h i r t e e n t h i n t h e dynamics s e r i e s , i s a summary review of 1IASA1s work on model m i g r a t i o n s c h e d u l e s . I t combines t h e major f i n d i n g s of two e a r l i e r p u b l i c a t i o n s (RM-75-57 and RR-76-09) w i t h more r e c e n t , a s y e t , u n p u b l i s h e d work. R e l a t e d p a p e r s i n t h e dynamics s e r i e s , and o t h e r p u b l i c at i o i l s o f t h e m i g r a t i o n and sett1emer.t s t u d y , a r e l i s t e d on t h e back page of t h i s r e p o r t .Andrei Rogers Chairman Human S e t t l e m e n t s and S e r v i c e s Area. November 1977 A b s t r a c t T h i s p a p e r c o n s i d e r s and c o n t r a s t s two a l t e r n a t i v e a p p r o a c h e s f o r c a p t u r i n g t h e r e g u l a r i t i e s e x h i b i t e d by age p a t t e r n s i n ob-s e r v e d m i g r a t i o n r a t e s .The m o r t a l i t y approach i s c o n s i d e r e d f i r s t and it i s shown how s u c h a n approach may be used t o i n f e r m i g r a t i o n f l o w s from two c o n s e c u t i v e p l a c e -o f -r e s i d e n c e -b y -p l a c eo f -b i r t h c e n s u s a g e d i s t r i b u t i o n s .The f e r t i l i t y approach i s c o n s i d e r e d n e x t , and t e c h n i q u e s f o r g r a d u a t i n g m i g r a t i o n age p r o f i l e s a r e d e s c r i b e d .The a d v a n t a g e s and d i s a d v a n t a g e s o f b o t h a p p r o a c h e s a r e t h e n b r i e f l y a s s e s s e d .The a u t h o r s g r a t e f u l l y acknowledge t h e c o m p u t a t i o n a l a s s i s t a n c e of F r a n s W i l l e k e n s .I n c a r r y i n g o u t t h i s r e s e a r c h

Scores of papers published over the past two decades have reported on efforts to identify the determinants and project the consequences of interregional migration within various nations. Generally, such studies have sought to associate data on migration streams between pairs of regions and such variables as wage rates, unemployment rates, income levels, education, degrees of urbanization, and the distances separating origin and destination regions. Among the several ways of adjusting for relative differences in regional population levels, the division of stream totals by population size to define rates has been especially popular. When the stream is directional and divided by the origin "at risk population, it is called a gross migration rate or probability. When the difference between an in-flow and an out-flow stream is divided by the population experiencing both, the resulting measure is called a net migration rate, even though its interpretation as a rate is ambiguous.' rates rather than counts of the absolute numbers of events, even though some published studies ofnet migration have used the latter.Throughout this paper, I focus on analyses carried out usin

The ability to understand and monitor the distributed behaviour of extended, critical structures is recognized as a matter of increasing importance. Optical fibres offer unique advantages for spatially distributed measurement. This article reviews the field of distributed optical-fibre sensing (DOFS), tracing its origins and its evolution, and discussing the present and future positions. Examples of the use of both linear and non-linear optics in pursuit of DOFS development are presented, together with details of a range of systems which have been investigated for particular applications.