M K Wilkinson

Radioligand binding studies on hypothalamic noradrenergic receptors during the estrous cycle or after steroid injection in ovariectomized rats

Central catecholamines are associated with the regulation of ovulation in the rat 10. Aminergic terminals in the hypothalamus coincide with areas of steroid feedback which are thought to control gonadotrophin secretion la. In addition, catecholamine pathways are functionally linked to neuroendocrine activity through the observation that amine turnover rates are altered in steroid target areas of the brain 3. Despite a large body of information on the interaction of estrogen (E) with catecholamines there is a lack of fundamental knowledge as to how neurons mediate the feedback effect of steroids, though aand fl-adrenergic receptors are implicated. Since the development of methods for the quantification of receptor populations it is clear that variations in receptor sensitivity may contribute to physiological processes 12. We report here the effect of hormonal state on hypothalamic aand fl-adrenergic receptors. These were quantified by radioligand binding assays using [aH]dihydroalprenolol (DHA; a fl-antagonist) and [aH]dihydroergokryptine (DHE; an a-antagonist) according to published methods 1,4. Adult female Sprague-Dawley rats which had shown two consecutive 4-day cycles (lights on 05.00-19.00 h) were killed in groups of 8-10 at 10.00 h on each day of the third cycle (rats in each group had the same vaginal smear). Brains were removed and dissected as described below. In another experiment, ovariectomized rats (in groups of 10, at least one month postsurgery) were steroid-primed 2 as follows: rats were injected with estradiol benzoate (EB) at noon (20 #g; s.c.; in oil). This was followed 72 h later with an injection of progesterone (EB/P; 2.5 mg). This treatment gives a surge of LH 5 h after injection of P. Two control groups consisted of: (a) two injections of peanut oil and (b) one injection of EB followed by an injection of oil (EB/C). Neither control treatment results in an LH surge (checked by radioimmunoassay of blood plasma). Animals were killed 5 h after the final injection. Brains were removed and hypothalami (including pre-optic area but not mammillary bodies) were dissected and stored in ice-cold

Lattice models of branched polymers: statistics of uniform stars

The authors investigate the statistical properties of uniform star polymers with f branches, modelled on lattices in two and three dimensions. It is shown that the growth constant exists and is equal to mu f, where mu is the self-avoiding walk limit. The f dependence of the corresponding critical exponent gamma (f) is studied using exact enumeration and Monte Carlo techniques and the results are compared with the predictions of Miyake and Freed (1983) obtained using chain conformation space renormalisation group method.

Interpreting “systems architecting”

The UK Chapter of the International Council on Systems Engineering (INCOSE UK) commissioned research to illustrate the variety of usage of the terms architecture and architecting in the systems engineering community. These terms, though widely used, are rarely strictly defined, and the meaning attributed to the terms is not consistent even in formal publications. Using soft systems methodology, this research has analyzed three published sources (MODAF [http://www.modaf.org.uk, 2008], The Art of Systems Architecting by Maier and Rechtin [CRC Press, 2009], and ISO/IEC 42010 [2011]), and conducted a series of interviews with systems architecting practitioners. This research was set in context by a historical review of the use of the term systems architecting. Twelve contentious questions in systems architecting are discussed, and six perspectives on systems architecting presented, including three basic worldviews of the relationship between systems engineering and systems architecting. One model sees systems architecting as simply a rebranding of systems engineering to broaden its appeal with no change in content. Another model sees systems engineering restricted to its traditional processes, with systems architecting adding to systems engineering through external processes. The final model, and the most popular among the systems engineering community surveyed, sees systems architecting addressing shortcomings in traditional sequential lifecycle models by stretching the content of systems engineering to include new elements under the banner of systems architecting.

Derivation of series expansions for a study of percolation processes

The derivation of series expansions for a study of percolation processes for both site and bond mixtures is reviewed. For the bond problem, low density expansions for the mean size of clusters on the simple cubic and body-centred cubic lattices are given through p14. High density expansions for the mean number and size of finite clusters and the percolation probability are given for the simple cubic lattice through q41 and for the body-centred cubic lattice through q61.

Lattice models of branched polymers: uniform combs in two dimensions

The authors establish rigorously the relationship between the growth constant of uniform trees with two branch points and that of self-avoiding walks. For combs, they estimate the corresponding exponent and study the mean-square lengths of the internal and external branches.

Branched polymers: exact enumeration study of three-dimensional lattice animals classified by valence distribution

The partial generating function method is applied to the enumeration of lattice animals classified according to their valence distribution. This detailed information allows one to study the effects of the number and nature of branch points on the properties of branched polymers. Several series analysis techniques are applied to the data. Particular attention is given to the effects of correction-to-scaling terms.

Generating functions for connected embeddings in a lattice. V: Application to the simple cubic and body-centred cubic lattices

For pt.IV see ibid., vol.19, p.2431 (1986). The method of partial generating functions is used to derive, for the simple cubic lattice, the number of connected strong embeddings through 13 sites, the number of connected weak embeddings through 14 bonds and three new bond perimeter polynomials D10, D11, D12 for the bond percolation problem. For the body-centred cubic and simple cubic lattices an expression is derived for the mean number of clusters for the site percolation problem in powers of the probabilities of occupation of A and B sites.

Lattice statistics of branched polymers with specified topologies

The authors study the numbers of lattice animals with specified topologies. They prove that the growth constant for animals with c cycles and nk vertices of degree k (k=3, . . ., 2d), weakly embeddable in a d-dimensional hypercubic lattice, equal to mu , the growth constant for self-avoiding walks. For some particular topologies they derive upper and lower bounds for the corresponding critical exponents and estimate the values of these exponents by deriving and analysing new exact enumeration data. They conjecture that their previous result for trees with b branches (that the exponent is gamma +b-1, where gamma is the self-avoiding walk exponent) is also valid in the more general case in which the cyclomatic index (c) is non-zero; i.e. for b>or=1, the exponent does not depend on c. They show that their results are consistent with renormalisation group arguments that the universality class of branched polymers is independent of cycle and (non-zero) branching fugacities.

Belief systems in systems architecting: Method and preliminary applications

Architecting has become an important discipline within the broader context of systems engineering. The lack of a common understanding of the discipline amongst practitioners and other stakeholders, particularly in broad communities, can result in confusion, misunderstanding and inefficiencies. Methods and principles from the Soft Systems Methodology (SSM) are used to define a method for investigating different approaches to systems and system of systems architecting, which we characterize as distinct ‘belief systems’. This method is applied to a number of such ‘belief systems’ encountered in applied systems architecting with the aim of clarifying their key features and promoting mutual understanding across different architecting communities.

Absorption probability distribution for rough surfaces

The authors calculate the absorption probability distribution for particles diffusing onto perfectly absorbing boundaries. The boundaries studied are rough but not fractal; nevertheless, non-classical behaviour is evident in the singularities of the measure and their distribution.