Ideally, a measure of the security of a system should capture quantitatively the intuitive notion of 'the ability of the system to resist attack'. That is, it should be operational, reflecting the degree to which the system can be expected to remain free of security breaches under particular conditions of operation (including attack). Instead, current security levels at best merely reflect the extensiveness of safeguards introduced during the design and development of a system. Whilst we might expect a system developed to a higher level than another to exhibit 'more secure behaviour' in operation, this cannot be guaranteed; more particularly, we cannot infer what the actual security behaviour will be from knowledge of such a level. In the paper we discuss similarities between reliability and security with the intention of working towards measures of 'operational security' similar to those that we have for reliability of systems. Very informally, these measures could involve expressions such as the rate of occurrence of security breaches (cf rate of occurrence of failures in reliability), or the probability that a specified 'mission' can be accomplished without a security breach (cf reliability function). This new approach is based on the analogy between system failure and security breach. A number of other analogies to support this view are introduced. We examine this duality critically, and have identified a number of important open questions that need to be answered before this quantitative approach can be taken further. The work described here is therefore somewhat tentative, and one of our major intentions is to invite discussion about the plausibility and feasibility of this new approach.

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Objectives-This study is the first to use magnetisation transfer imaging (MTI), a technique sensitive to myelin and axonal abnormalities, to investigate the white matter in vivo in patients with schizophrenia. Conclusions-Subtle white matter pathology, most likely related to myelin and axonal abnormalities, can be detected in the temporal lobes in schizophrenic patients. MTI may be a useful tool in investigating the white matter in schizophrenia. (J Neurol Neurosurg Psychiatry 2000;68:70-74) Methods-MTI

Dermanyssus gallinae (De Geer), the poultry red mite, is a blood-feeding ectoparasite that infests many bird species. We have used an in vitro feeding assay to allow the identification of protective D. gallinae antigens that may have potential as vaccine candidates. Homogenised mites were extracted sequentially with PBS, Tween 20, Triton X100 and urea giving four protein fractions. Five experimental groups of Lohmann Brown hens were used to generate antibodies; four groups were injected with one of each of the protein fractions in QuilA adjuvant and a control group was injected with adjuvant only. Booster injections were administered 2 and 4 weeks after initial immunisation. Eggs were collected throughout the experiment and soluble IgY antibodies were extracted from a pool of egg yolks collected at week six post-injection. Western blots, performed using post vaccination antibodies from test and control groups, revealed a strong antibody response against a range of injected proteins. Fresh chicken blood, supplemented with antibodies raised against these protein fractions, was fed to mites in an in vitro feeding assay in order to determine whether the antibodies had an anti-mite effect. Although there was variability in the numbers of feeding mites, it was found that the strongest anti-mite effect was seen with the PBS protein fraction, which had a cumulative average mortality of 34.8% 14 days after feeding compared with 27.3% for the control group (P = 0.043).

The effects of sex, genotype, and adipose depot on lipogenic enzyme activity have been investigated in Holstein and Pirenaican bulls and heifers, taking into account differences in adipocyte size. Fifteen Pirenaican bulls and 15 heifers and 15 Holstein bulls and 13 heifers were fattened until slaughter (12 to 13 mo old and 450 to 500 kg of body weight). During the fattening period, animals had ad libitum access to commercial concentrates and straw. The 10th rib was dissected to determine the fat content. Adipocyte size and activities of the following lipogenic enzymes were determined: glycerol 3-phosphate dehydrogenase, fatty acid synthase, nicotinamide adenine dinucleotide phosphate (NADP)-malate dehydrogenase, glucose 6-phosphate dehydrogenase, and NADP-isocitrate dehydrogenase, in the omental, perirenal, subcutaneous, and intermuscular adipose depots, respectively. Because adipocyte mean cell volume varied with sex, breed, and depot, regression analyses of log(e) activity per cell and log(e) cell volume were used to compare activities per unit volume. Sex, breed and depot had no effect (P > 0.05) on the gradients of regressions, which did not differ significantly from 1. Thus, activity per unit volume did not vary with cell size. Consequently, sex, breed, and depot effects on the regression analyses were equivalent to effects on activity per unit volume. Females had greater amounts of fat in the 10th rib (P < 0.001), larger adipocytes (P < 0.001) and, in general, greater (P < 0.05) lipogenic activity per cell, even when adjusted for cell size, than males. These findings suggest that differences in adiposity between sexes are mainly due to females having a greater capacity for lipid synthesis, and hence, hypertrophy, than males. When adjusted for differences in carcass weight, Holsteins had larger adipocytes than Pirenaicans. The abdominal depots, omental and perirenal, had a greater adipocyte size (P < 0.001) and, in general, greater lipogenic enzyme activities per cell (P < 0.05) than the subcutaneous and intermuscular carcass depots. However, when activity per cell was adjusted for cell size, subcutaneous depots had greater fatty acid synthae, glucose 6-phosphate dehydrogenase, and NADP-malate dehydrogenase activities than omental and perirenal, indicating that other factors such as nutrient supply may restrict hypertrophy of carcass adipocytes.

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