3,837 research outputs found
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The solar influence on the probability of relatively cold UK winters in the future
Recent research has suggested that relatively cold UK winters are more common when solar activity is low (Lockwood et al 2010 Environ. Res. Lett. 5 024001). Solar activity during the current sunspot minimum has fallen to levels unknown since the start of the 20th century (Lockwood 2010 Proc. R. Soc. A 466 303–29) and records of past solar variations inferred from cosmogenic isotopes (Abreu et al 2008 Geophys. Res. Lett. 35 L20109) and geomagnetic activity data (Lockwood et al 2009 Astrophys. J. 700 937–44) suggest that the current grand solar maximum is coming to an end and hence that solar activity can be expected to continue to decline. Combining cosmogenic isotope data with the long record of temperatures measured in central England, we estimate how solar change could influence the probability in the future of further UK winters that are cold, relative to the hemispheric mean temperature, if all other factors remain constant. Global warming is taken into account only through the detrending using mean hemispheric temperatures. We show that some predictive skill may be obtained by including the solar effect
Controlling for individual heterogeneity in longitudinal models, with applications to student achievement
Longitudinal data tracking repeated measurements on individuals are highly
valued for research because they offer controls for unmeasured individual
heterogeneity that might otherwise bias results. Random effects or mixed models
approaches, which treat individual heterogeneity as part of the model error
term and use generalized least squares to estimate model parameters, are often
criticized because correlation between unobserved individual effects and other
model variables can lead to biased and inconsistent parameter estimates.
Starting with an examination of the relationship between random effects and
fixed effects estimators in the standard unobserved effects model, this article
demonstrates through analysis and simulation that the mixed model approach has
a ``bias compression'' property under a general model for individual
heterogeneity that can mitigate bias due to uncontrolled differences among
individuals. The general model is motivated by the complexities of longitudinal
student achievement measures, but the results have broad applicability to
longitudinal modeling.Comment: Published at http://dx.doi.org/10.1214/07-EJS057 in the Electronic
Journal of Statistics (http://www.i-journals.org/ejs/) by the Institute of
Mathematical Statistics (http://www.imstat.org
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Texas Business Review, May 1975
The Business Situation in Texas; Nuclear Power in Texas 1954-1975; Texas ConstructionBureau of Business Researc
ON LIST STRUCTURES AND THEIR USE IN THE PROGRAMMING OF UNIFICATION
The notion of list structure is discussed, and a new construct is introduced into LISP which permits the computation of list structures containing cycles without recourse to operations which alter existing structures. It is shown that list structures can be used to represent both finite and “rational” infinite terms. Substitutions (generalized for a term algebra which includes infinite terms) are discussed, “tables” are introduced as an abstract data type, and two methods of representing substitutions by tables, together with their interrelation, are considered. Concise programs are given for a succession of forms of Robinson’s unification algorithm, including one which operates in almost linear time, and for the application of substitutions to terms
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Comment on “Mapping the dayside ionosphere to the magnetosphere according to particle precipitation characteristics” by Newell and Meng
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The variation of reconnection rate at the dayside magnetopause and cusp ion precipitation
A method is presented which allows estimation of the variation of the rate of magnetic reconnection at the day side magnetopause. This is achieved using observations of the cusp particle precipitation made by low-altitude polar-orbiting spacecraft. In this paper we apply the technique to a previously published example of a cusp intersection by the DMSP F7 satellite. It is shown that the cusp signature in this case was produced by three separate bursts of reconnection which were of the order of 10 min apart, each lasting roughly 1 min. This is similar to the variation of reconnection rate which is required to explain typical flux transfer event signatures at the magnetopause
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The pulsating cusp
Recent observations at the magnetopause and of the high-latitude ionosphere, suggest that the cusp may be pulsed in nature. Specifically ground-based observations in the dayside auroral oval reveal transient optical features accompanied by bursts of enhanced plasma flow. Also, recent interpretation has shown cusp satellite data to be consistent with a burst of enhanced reconnection. In this paper we use these observations to produce a scenario in which both the satellite and ground-based observations can be fitted. The scenario we develop is based on the flux transfer event (FTE) models of Southwood et al. and Scholer and shows that the signatures, at both low and high altitudes, can be interpreted in terms of FTEs
Computing Cyclic List Structures
It is argued that list structures containing cycles are useful and unobjectionable Lisp entities. If this is so, it is desirable to have a means of computing them less foreign to the equational-definition style characteristic of Lisp than are the list-structure-altering primitives rplaca and rplacd. A notion is developed of a reasonable system of mutually recursive equations, guaranteed to have a unique solution in list structures. The notion is given in terms of the computations invoked by the equations, without reference to the forms of expressions appearing in them. A variety of programming examples are presented, including a curious implementation of the Knuth-Morris-Pratt string matching algorithm. Two methods of implementing the recursive definitions facility are discussed
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Reply to Comment on: ’Low-altitude signatures of the cusp and flux transfer events’ by Mike Lockwood and Mark F. Smith
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