Essential variables to consider for an efficient control strategy for invasive plants include dispersion pattern (i.e., satellite or invasion front) and patch expansion rate. These variables were demonstrated for buffelgrass [Pennisetum ciliare (L.) Link], a C4 perennial grass introduced from Africa, which has invaded broadly around the world. The study site was along a roadway in southern Arizona (USA). The P. ciliare plant distributions show the pattern of clumping associated with the satellite (nascent foci) colonization pattern (average nearest neighbor test, z-score −47.2, P<0.01). The distance between patches ranged from 0.743 to 12.8 km, with an average distance between patches of 5.6 km. Median patch expansion rate was 271% over the 3-yr monitoring period versus 136% found in other studies of established P. ciliare patches. Targeting P. ciliare satellite patches as a control strategy may exponentially reduce the areal doubling time, while targeting the largest patches may have less effect on the invasion speed.

A condition expressed in Eq. (7) is given which, with one simplifying regularity condition, ensures that the policy-improvement algorithm is equivalent to application of the Newton–Raphson algorithm to an optimality condition. It is shown that this condition covers the two known cases of such equivalence, and another example is noted. The condition is believed to be necessary to within transformations of the problem, but this has not been proved.

We show that the calculation of the infinite-horizon value function for a linear/quadratic Markov decision process by policy improvement is exactly equivalent to solution of the equilibrium Riccati equation by the Newton-Raphson method. The assertion extends to risk-sensitive and non-Markov forinulations and thus shows, for example, that the Newton-Raphson method provides an iterative algorithm for the canonical factorization of operators which shows second-order convergence and has a variational basis.

The most probable equilibrium configuration in a circuit-switched network is determined, in the limit of very large scale, by a primal optimization problem whose dual determines the blocking probabilities. This approximation can be inadequate for moderate scale, and so the blocking probabilities are usually determined by the Erlang fixed-point principle. In this paper, it is shown that there is a “softened” form of the dual natural to the problem. This gives determinations of the blocking probabilities agreeing with those derived from the Erlang principle as far as terms of order (scale)-1. It is more attractive than the Erlang principle, however, in that it has a mathematical basis, provides an extremal principle by its nature, yields immediately the geometric distribution of the numbers of free circuits, and clearly agrees with the “hard” dual in the limit of large scale.

A trial of protective efficacy which compared medium–titre Edmonston-Zagreb (EZ) measles vaccine (104.6 p.f.u.) from the age of 4 months with the standard Schwarz (SW) measles vaccine given from the age of 9 months was started in an urban community in Guinea-Bissau in 1985. Because trials of high–titre measles vaccine have found increased mortality among female recipients, we examined whether EZ medium–titre vaccine was associated with any long-term impact on mortality, suppression of T–cells, or growth. The mortality rate ratio over 5 years of follow–up was 1.12 for EZ children compared with children in the standard group (P = 0.63). Seventy–five percent of the children still residing in the area at 5 years of age took part in an immunological and anthropometric examination. There was no difference in T–cell subsets between the two groups. There was no difference in mid–upper–arm circumference, but EZ children were significantly shorter than the children in the standard group. In conclusion, medium–titre EZ was not associated with reduced survival or persistent immunosuppression.

Five-sixths of all the continental area on the Earth's surface has antipodes in oceanic regions. This proportion is not significantly different from what one would expect on the assumption that the continents are randomly situated.

Despite their potential utility, clinicians are skeptical about claims data as a substrate for clinical research. Clinicians' concerns are centered on two issues—the quality of the data and the fairness of comparisons that are made. To increase the impact of claims data research on clinical practice, several strategies should be pursued.

Two systems have been studied La2-xYxZr2O7 and La2-xYxHf2O7, as part of an on-going study of radiation tolerance in nuclear waste forms and related oxide materials. The structural effects of increasing Y content in La based zirconate and hafnate pyrochlores have been studied with neutron diffraction and electron microscopy. Results have shown a difference in structural stability for both the pyrochlore and fluorite phases within each system, including the presence of two-phase regions in both systems. In the zirconate, the two-phase region lies in the range x = 0.9-1.6. This is shifted to higher Y content in the hafnate system and lies in the range of x = 1.5 to approximately 1.8-1.9. In addition to the differences in phase stability, electron diffraction, predominantly down the [110] zone axis, has shown evidence for ordering in the form of structured diffuse scattering within the fluorite phases.

The aim of this study was to determine whether a temporary rise in sexual risk behaviour during war in Guinea–Bissau could explain the observed trends in HIV-1 and HIV-2 prevalence, and to explore the possible contribution of competitive elimination of HIV-2 by HIV-1. A simulation model of the heterosexual transmission of sexually transmitted infections was parameterized using demographic, behavioural and epidemiological data from rural Guinea–Bissau, and fitted to the observed HIV-1 and HIV-2 trends with and without a historic rise in risk behaviour. The observed trends could only be simulated by assuming a temporary rise in risk behaviour. Around 30% of the projected decline in HIV-2 prevalence from a peak of 8·7% to 4·3% in 2010 was due to competitive elimination by HIV-1. Importantly for public health, HIV-1 prevalence was predicted to continue increasing and to become the dominant HIV type by 2010. Data collection is required to validate this prediction.

The aim of this paper is to evaluate the performance of the optimal policy (the Gittins index policy) for open tax problems of the type considered by Klimov in the undiscounted limit. In this limit, the state-dependent part of the cost is linear in the state occupation numbers for the multi-armed bandit, but is quadratic for the tax problem. The discussion of the passage to the limit for the tax problem is believed to be largely new; the principal novelty is our evaluation of the matrix of the quadratic form. These results are confirmed by a dynamic programming analysis, which also suggests how the optimal policy should be modified when resources can be freely deployed only within workstations, rather than system-wide.

Hollandites with compositions Ba1.2-xCsxMg1.2-x/2Ti6.8+x/2 O16, and Ba1.2-xCsxAl2.4-xTi5.6+xO16 (x=0, 0.1, 0.25) have been synthesised using a modified alkoxide/acetate precursor route. The samples have been sintered using two procedures; hot isostatic pressing and sintering at ambient pressure. X-ray powder diffraction has shown samples from both systems to form tetragonal hollandites, with little change when pressed by both methods. Cs-133 MAS NMR spectra have been recorded showing the chemical shift in Al containing samples to be ∼250ppm, and in Mg hollandites ∼175ppm and 200ppm, with little change when prepared by both methods.

Respiratory syncytial virus (RSV) infection in The Gambia occurs seasonally in association with the rainy season. This study examined the genetic variability of RSV isolates from four consecutive epidemics from 1993–6. Each epidemic was made up of a number of variants which were replaced in subsequent epidemics. Analysis of attachment (G) protein gene sequences showed that isolates were closely related to those observed in the rest of the world. However, many isolates from 1993 and 1994 were unlike other isolates observed in the developed world during this period and were more similar to isolates from 1984 in Europe. In addition, the most commonly observed genotype in the UK in the 1990s was not detected in The Gambia during this period.

We consider the distribution of the free coordinates of a time-homogeneous Markov process at the time of its first passage into a prescribed stopping set. This calculation (for an uncontrolled process) is of interest because under some circumstances it enables one to calculate the optimal control for a related controlled process. Scaling assumptions are made which allow the application of large deviation techniques. However, the first-order evaluation obtained by these techniques is often too crude to be useful, and the second-order correction term must be calculated. An expression for this correction term as an integral over time is obtained in Equation (20). The integration can be performed in some cases to yield the conclusions of Theorems 1 and 2, expressed in Equations (7) and (9). Theorem 1 gives the probability density of the state vector (to the required degree of approximation) at a prescribed time for a class of processes we may reasonably term linear. Theorem 2 evaluates (without any assumption of linearity) the ratio of this density to the probability density of the coordinates under general stopping rules.

In well fed ewes with one or two lambs, large volumes of colostrum accumulate in the mammary glands during the last few days of pregnancy and copious milk secretion begins soon after birth. In underfed ewes, prenatal colostrum accumulation is reduced markedly, lactogenesis is delayed. (Mellor and Murray, 1985). Robinson (1985) has shown that there is a sharp increase in the ewe's net protein requirements for udder growth and colostrum production in the last two weeks pre-partum. McPherson, Robinson and Fraser (1981) found that the detrimental effects of a maternal energy deficit on the ewes colostrum supply at parturition can be ameliorated by increasing her supply of amino acids through the provision of a dietary supplement of rumen UDP. The peri-parturient transitions from udder growth to colostrum accumulation and then milk secretion depend largely on withdrawal of progesterone and surges in prolactin, Cortisol and oestrogen, with the progesterone inhibiting and Cortisol potentiating the lactogenic actions of prolactin (Delouis, 1978). The slower progesterone withdrawal in the underfed ewes was associated with a delay in lactogenesis. Thus the objective of this experiment was to study the effects of feeding different diets on ewe colostrum production and quality, and on progesterone concentration pre and post lambing.

The distribution (1) used previously by the author to represent polymerisation of several types of unit also prescribes quite general statistics for a random field on a random graph. One has the integral expression (3) for its partition function, but the multiple complex form of the integral makes the nature of the expected saddlepoint evaluation in the thermodynamic limit unclear. It is shown in Section 4 that such an evaluation at a real positive saddlepoint holds, and subsidiary conditions narrowing down the choice of saddlepoint are deduced in Section 6. The analysis simplifies greatly in what is termed the semi-coupled case; see Sections 3, 5 and 7. In Section 8 the analysis is applied to an Ising model on a random graph of fixed degree r + 1. The Curie point of this model is found to agree with that deduced by Spitzer for an Ising model on an r-branching tree. This agreement strengthens the conclusion of ‘locally tree-like' behaviour of the graph, seen as an important property in a number of contexts.