Porosity evolution at the brittle-ductile transition in the continental crust: Implications for deep hydro-geothermal circulation.

Recently, projects have been proposed to engineer deep geothermal reservoirs in the ductile crust. To examine their feasibility, we performed high-temperature (up to 1000 °C), high-pressure (130 MPa) triaxial experiments on granite (initially-intact and shock-cooled samples) in which we measured the evolution of porosity during deformation. Mechanical data and post-mortem microstuctural characterisation (X-ray computed tomography and scanning electron microscopy) indicate that (1) the failure mode was brittle up to 900 °C (shear fracture formation) but ductile at 1000 °C (no strain localisation); (2) only deformation up to 800 °C was dilatant; (3) deformation at 900 °C was brittle but associated with net compaction due to an increase in the efficiency of crystal plastic processes; (4) ductile deformation at 1000 °C was compactant; (5) thermally-shocking the granite did not influence strength or failure mode. Our data show that, while brittle behaviour increases porosity, porosity loss is associated with both ductile behaviour and transitional behaviour as the failure mode evolves from brittle to ductile. Extrapolating our data to geological strain rates suggests that the brittle-ductile transition occurs at a temperature of 400 ± 100 °C, and is associated with the limit of fluid circulation in the deep continental crust.

Fracture and compaction of andesite in a volcanic edifice.

The failure mode of lava-dilatant or compactant-depends on the physical attributes of the lava, primarily the porosity and pore size, and the conditions under which it deforms. The failure mode for edifice host rock has attendant implications for the structural stability of the edifice and the efficiency of the sidewall outgassing of the volcanic conduit. In this contribution, we present a systematic experimental study on the failure mode of edifice-forming andesitic rocks (porosity from 7 to 25 %) from Volcán de Colima, Mexico. The experiments show that, at shallow depths (<1 km), both low- and high-porosity lavas dilate and fail by shear fracturing. However, deeper in the edifice (>1 km), while low-porosity (<10 %) lava remains dilatant, the failure of high-porosity lava is compactant and driven by cataclastic pore collapse. Although inelastic compaction is typically characterised by the absence of strain localisation, we observe compactive localisation features in our porous andesite lavas manifest as subplanar surfaces of collapsed pores. In terms of volcano stability, faulting in the upper edifice could destabilise the volcano, leading to an increased risk of flank or large-scale dome collapse, while compactant deformation deeper in the edifice may emerge as a viable mechanism driving volcano subsidence, spreading and destabilisation. The failure mode influences the evolution of rock physical properties: permeability measurements demonstrate that a throughgoing tensile fracture increases sample permeability (i.e. equivalent permeability) by about a factor of two, and that inelastic compaction to an axial strain of 4.5 % reduces sample permeability by an order of magnitude. The implication of these data is that sidewall outgassing may therefore be efficient in the shallow edifice, where rock can fracture, but may be impeded deeper in the edifice due to compaction. The explosive potential of a volcano may therefore be subject to increase over time if the progressive compaction and permeability reduction in the lower edifice cannot be offset by the formation of permeable fracture pathways in the upper edifice. The mode of failure of the edifice host rock is therefore likely to be an important factor controlling lateral outgassing and thus eruption style (effusive versus explosive) at stratovolcanoes.

Slip on 'weak' faults by the rotation of regional stress in the fracture damage zone.

Slip on unfavourably oriented faults with respect to a remotely applied stress is well documented and implies that faults such as the San Andreas fault and low-angle normal faults are weak when compared to laboratory-measured frictional strength. If high pore pressure within fault zones is the cause of such weakness, then stress reorientation within or close to a fault is necessary to allow sufficient fault weakening without the occurrence of hydrofracture. From field observations of a major tectonic fault, and using laboratory experiments and numerical modelling, here we show that stress rotation occurs within the fractured damage zone surrounding faults. In particular, we find that stress rotation is considerable for unfavourably oriented 'weak' faults. In the 'weak' fault case, the damage-induced change in elastic properties provides the necessary stress rotation to allow high pore pressure faulting without inducing hydrofracture.

Differences in the progress of discharged and undischarged patients in a medium secure unit: a pilot study.

This study compared 15 patients ('undischarged' group) who were showing little sign of progress in a medium secure unit (MSU) after 2 years with 15 who had been discharged from the same unit 1-2 years following admission. The two groups were compared across a number of broadly defined behavioural indices during their first 6 months and first 12 months following admission. The measures used were indices of progress to wards of lower security (highest ward status and transfers to wards of higher security) and progress in terms of leave (highest leave status and reductions in leave status). In addition, the two groups were compared on number of recorded incidents attributable to them. Discharged patients were significantly older at the time of their admission than the undischarged patients (median ages 33 and 26 years, respectively). They made more progress in their first year in terms of ward security and leave status and were responsible for fewer recorded incidents. These results were also obtained at 6 months following admission with the exception that the difference for highest ward status was not statistically significant. The findings of this small-scale study suggest that within the first 6 months of admission, it may be possible to distinguish patients who will probably make good progress in a MSU from those whose progress is likely to be very slow. Implications of the study are discussed.

Acute right-to-left inter-atrial shunt; an important cause of profound hypoxia.

Three patients presented to our intensive care unit over a 3-yr period with profound hypoxia resulting from acute right-to-left inter-atrial shunt (RLIAS). Patient 1 was a 67-yr-old male with an atrial septal defect who became hypoxic and developed the rare sign of platypnoea following elective repair of an abdominal aortic aneurysm (breathlessness made worse when upright and relieved by lying flat). Patient 2 was a 38-yr-old female who developed platypnoea and hypoxia secondary to a patent foramen ovale (PFO) and pericardial effusion. Patient 3 was a 46-yr-old male with a PFO who developed hypoxia without platypnoea because of multiple pulmonary emboli following right hemicolectomy. These case reports illustrate the need to consider RLIAS as a cause of hypoxia of sudden onset. Early use of bubble contrast echocardiography is indicated.

Nestedness in assemblages of metazoan ecto- and endoparasites of marine fish.

Assemblages of metazoan ectoparasites of 79 species and gastrointestinal helminths of eight species of marine fishes were analysed to examine whether nestedness is related to sample size, abundance, species richness, and prevalence of infection, and whether the use of z-scores or Monte Carlo simulations yields different results. No significant differences in the number of nested assemblages were found with the two methods, and neither sample size nor abundance, but prevalence of infection of ectoparasites was correlated with nestedness. Species richness was significantly correlated with nestedness only when fish species with fewer than three parasite species were not excluded. Differential colonisation probabilities are the most likely cause of nestedness.

Latitudinal differences in species and community richness and in community structure of metazoan endo- and ectoparasites of marine teleost fish.

Relative species diversity of gastrointestinal helminths of 55 teleost fish species did not differ significantly at different latitudes, whereas relative species diversity of metazoan ectoparasites on the heads and gills of 108 teleost fish species showed a significant increase with decreasing latitude and from deep to surface waters. Abundance of endoparasites also was the same at all latitudes, whereas abundance of ectoparasites increased with decreasing latitude and from deep to shallow waters. A comparative analysis using phylogenetically independent contrasts supported these conclusions. Possible reasons for the differences between endo- and ectoparasites are discussed. A detailed analysis of the community structure of gastrointestinal helminths of five Antarctic and three tropical teleosts and of metazoan ectoparasites on the heads and gills of five Antarctic and seven tropical fish species showed the following: abundance and prevalence of infection of endoparasites are similar in Antarctic and tropical fish, but are much greater for tropical than for Antarctic ectoparasites. Relative species diversity of endoparasites is similar for Antarctic and tropical endoparasites, but much greater for tropical than Antarctic ectoparasites. In both Antarctic and tropical fish, different fish of the same species may have different dominant species of endo- and ectoparasites, although there is a greater range of dominant species of tropical ectoparasites, a consequence of the greater species pool available. The most dominant parasite (irrespective of species) represented 80-99% of all endoparasites of Antarctic, and about 50-80% of all endoparasites of tropical fish. The most dominant parasites (irrespective of species) represented about 90-100% of all ectoparasites of Antarctic, and about 20-70% of all ectoparasites of tropical fish, the difference a consequence of the greater species pool of tropical ectoparasites available. The data suggest that both endo- and ectoparasites live in assemblages not structured by interspecific competition.

Hypnotic pain control: some theoretical and practical issues.

Pain management programs assist patients to use their behavioral and cognitive skills for the purpose of rendering their experience of pain as more tolerable in some way. Hypnotic procedures may be included in this perspective. Thus, hypnosis may be best conceived as a set of skills to be deployed by the individual rather than as a state. The authors contend that such an emphasis is more compatible with the approaches of some pain management practitioners who have been generally slow to acknowledge the value of hypnosis and to incorporate hypnosis in their range of treatment skills. In this article, the authors present a minimal and atheoretical definition of hypnosis, and they list the basic properties of hypnosis that may be used in the treatment of pain. For a number of reasons, it is suggested that undertaking hypnosis as though the individual were indeed being placed into a special trance state may in some cases promote an effective outcome. However, it should be acknowledged that there may be instances when the relevant skills may be more effectively engaged at the expense of a strict special trance state by targeting the specific skills that are to be used for therapeutic benefit.

Are coagulation studies on blood sampled from arterial lines valid?

Coagulation tests were performed on two venous blood samples and two blood samples from arterial lines taken from 79 patients on an intensive care unit. For the first arterial sample the discard volume was 4.5 ml and for the second arterial sample the discard volume was 16 ml. From each pair of venous samples a mean venous coagulation value was calculated. There were statistically significant differences between arterial and venous results and between the two arterial samples for activated partial thromboplastin time and thrombin time assays but not for prothrombin time, reptilase time and fibrinogen assays. However, these differences were sufficiently small to be of little clinical significance. The bias for the difference in activated partial thromboplastin time values between the first arterial sample and the venous sample was +1.24 s (limits of agreement: -4.39 to +6.87 s) and between the second arterial sample and the venous sample the bias was +0.89 s (limits of agreement: -3.25 to +5.03 s). Only 3.8% of first arterial samples and 1.3% of second arterial samples produced activated partial thromboplastin time values that were more than 10% longer than the corresponding venous values. No heparin was detectable in these arterial samples using a heparin assay (< 0.02 iu.ml-1). The differences between arterial and venous activated partial thromboplastin times were slightly but not significantly greater in subgroups of patients with moderately or severely deranged coagulation compared with a group with normal coagulation. We conclude that samples from arterial lines provide valid activated partial thromboplastin time results using a discard volume of either 4.5 ml or 16 ml.

The nature of hypnosis.

This paper presents an overview of the essential nature of hypnosis as it is studied and practised today. Some theoretical controversies are mentioned and historical antecedents are briefly summarized. An overview is then presented of the ways in which hypnosis is applied therapeutically. It is concluded that although clinical hypnosis has yet to be informed by a strong academic base, progress is being made to that end and its potential scope and value in clinical practice have probably yet to be realized.

A survey of the physical health status of pupils aged 10-14 years in Standards 3-5 at three schools in New Crossroads, near Cape Town in the Western Cape.

Although adolescence is most commonly associated with risk-taking behaviour, mortality due to poverty-related conditions is high among black African children aged 10-14 years. This paper describes a study carried out in October 1991 to assess the physical health status of 860 underprivileged pupils aged 10-14 years in Standards 3-5 at three schools in New Crossroads, near Cape Town. Data on nutritional status, age at menarche, blood pressure, eyesight, physical abnormalities, injuries and use of hospitals were obtained. The response rate was 90%. Of all the children, 7.2% were below the 5th percentile weight-for-age. The proportion of boys (13.1%) below the 5th percentile weight-for-age was significantly higher than that of girls (3.7%). Of all the children, 19.5% were below the 5th percentile height-for-age. The proportion of boys (24.4%) below the 5th percentile height-for-age was also significantly higher than that of girls (16.7%). The average age at menarche was 13 years, similar to that (12.8 years) reported for the UK. In 5% of the children, the diastolic blood pressure was > 90 mmHg and the findings show some increase with age. Red Cross War Memorial Children's Hospital accounted for 30.9% of hospital attendances. 'Chest' complaints (19.5%) were frequent reasons for consultations, while 15.2% of the children reported being injured, with car accidents (16.0%), fractures (27.5%) and burns (20.6%) being the most common injuries. It is suggested that the provision of a 24-hour day hospital will ease the load on the referral hospital, i.e. Red Cross War Memorial Children's Hospital.(ABSTRACT TRUNCATED AT 250 WORDS)

Aspects of the ecology of metazoan ectoparasites of marine fishes.

Numerous (3947) individuals of 102 marine fish species from Papua New Guinea, New Zealand, the North Sea, Antarctica, the deepsea and coast of southeastern Australia, Pacific Canada, Brazil, Argentina and the Great Barrier Reef were examined for metazoan ectoparasites. Of the 102 fish species, 86 harboured at least 1 parasite species, and only in Antarctica and the deepsea were large proportions of fish species found to be free of ectoparasites. The mean prevalence of infection was 30.1%, the average of abundances was 6.7 parasites per fish, due to very heavy intensities of some parasite species (mean median abundance 4.31). Most parasite species exhibited a clustered distribution in the host populations, as measured by variance to mean ratios, i.e. some fish were more, and others less, heavily infected than if infection were random. Core and satellite species cannot be distinguished unambiguously, because numbers of parasites on almost all hosts are too small for any bimodality to become apparent. On average, the most dominant species represented 90% of all parasite individuals of a particular fish; different parasite species were often dominant on different fish individuals of a particular host species. Both abundances and maximum intensities of infection were positively correlated with prevalence of infection. Community richness varies greatly at and between localities, with the lowest richness found in Antarctic and deepsea fish and the highest richness in tropical fish. Species richness, abundance and prevalence of infection in many fish groups (with different ecological characteristics) are strongly correlated with temperature. If fish from all localities were pooled, pelagic fish had fewer intensities and (jointly with benthopelagic fishes) fewer species than benthic fish, and planktivorous fish had lower abundances and prevalences of infection than predatory and omnivorous fish. Prevalences of infection, abundance and parasite species richness were significantly correlated with host length. Fifteen positive and 1 negative associations among species were found. This and the generally low prevalences and abundances of infection indicate that competitive interactions are probably scarce. Overall, the findings indicate that most (if not all) metazoan ectoparasite communities of marine fish live in non-saturated, little-ordered assemblages.

A tropical assemblage of ectoparasites: gill and head parasites of Lethrinus miniatus (Teleostei, Lethrinidae).

Aspects of the community ecology of metazoan ectoparasites of Lethrinus miniatus (Teleostei. Lethrinidae) from 3 localities on the Great Barrier Reef were examined. Twelve species of Monogenea, 6 of Copepoda, 2 species of adult and several larval Isopoda and 1 leech were found. Total parasite numbers reach 3500 per host, and prevalence of infection with a particular parasite species reached 100% in some species. Numbers of parasite species per fish varied from 5 to 11. Four parasite species were most dominant on different fish if intensities of infection were used to calculate dominance, one species representing about 80% of all parasite individuals on a particular fish at 2 localities and about 50% at the third locality. Ten parasite species were most dominant on different fish, if volume (biomass) was used for calculating dominance, one species representing about 55% at one and 80% of total parasite volume at 2 localities. Parasites included at least 12 congeneric species of 4 or more genera, and those (of 2 genera) occurring on the gills showed much overlap in their distribution. Congeneric Monogenea of the families Dactylogyridae and Diplectanidae occurring in the same sites differ markedly in the size and structure of their copulatory sclerites. Positive associations between species were much more common than negative ones. The bony parts of the gills (gill arches) were never found to be infected, indicating the availability of empty niches.

Elderly patients' preferences concerning life-support treatment.

The preferences of 118 elderly patients, aged from 70 to 97 years, concerning the institution of artificial ventilation in the event of an overwhelming illness, were investigated using a questionnaire. Most patients wanted treatment if the outcome was likely to be good, but in approximately half, the desire for treatment declined as anticipated quality of life or chances of recovery fell. Forty percent wanted to make the decision about institution of artificial ventilation themselves if mentally competent and 24% wanted to use some form of advance directive if mentally incompetent.

Health status of hostel dwellers. Part I. Introduction, methodology and response rates.

A health status survey (October-November 1987) was carried out among the residents of the urban migrant council-built hostels outside Cape Town at Langa, Nyanga and Guguletu, at their request. The project is introduced and the basis for the interpretation of the findings is provided. Migrant labour and the resultant material and physical impoverishment provide the social context for this study. The hostel dwellers as a migrant or mobile population presented certain research challenges. The working concepts, including the notion of the 'bedhold', employed in this study to address the mobility of the population are outlined. the methodology describes how the range of criteria selected to measure health status was investigated in a single survey. The response rates suggest that surveys carried out in the urban location of a migrant labour situation do not access the poor in the broader migrant labour situation. Findings are treated with caution for what they infer for the broader migrant population.

Health status of hostel dwellers. Part III. Nutritional status of children 0--5 years.

The standards laid down by the National Center for Health Statistics in the USA were used to assess the nutritional status of children (0--5 years) in the Zones, an urban migrant council-built hostel complex in Langa, outside Cape Town. Of the children, 5.7% were below the 3rd percentile of weight-for-age (acute undernutrition). There was a significant difference between age categories and an increase in age was associated with an increase in proportion of children below the 3rd percentile. Acute undernutrition was significantly higher for children born outside Cape Town. There was a significant difference between age groups and percentage of children below the 3rd percentile of height-for-age (chronic undernutrition). Chronic nutritional levels were also significantly higher for children not born in Cape Town. Yet there were no significant differences between proportions of children under the 3rd percentile of height-for-weight (current nutritional status) for age category or place of birth. These results suggested that while in town children were adequately nourished, this was not the case at their home-base. Chronic undernutrition findings indicated an incremental negative effect of the poverty of the home-base on the long-term health status of hostel migrant children.

Health status of hostel dwellers. Part II. Infant mortality and prevalence of diabetes, hypertension and syphilis among adults.

The range of biomedical criteria selected to measure the health status of the residents of the urban migrant council-built hostels of Langa, Nyanga and Guguletu were investigated in a single survey. A single survey method screens health status and provides the opportunity to examine the interrelationship between findings on the different health criteria. Here a high infant mortality rate is examined against a low prevalence of diabetes, hypertension and syphilis and some of the effects of migrant labour on the health status of migrant hostel dwellers are identified. The low prevalence of disease among the Cape Town hostel residents suggests that migrant labour, by sifting out the able-bodied and employable, reproduces a 'healthy worker effect' among the migrant population with access to the city. The high infant mortality rate, in contrast, suggests that the disease burden of the migrants is being carried by the home-base population.

Health status of hostel dwellers. Part IV. Immunisation of children.

The immunisation status of children (0-5 years) living in the Zones, an urban migrant council-built hostel in Langa, was investigated to examine the effect of migrant labour and related to this, the effect of circular or oscillating migration between Cape Town and the eastern Cape (Transkei/Ciskei) on access to this preventive health care measure. 'Road-to-Health' cards were available for 69.4% of subjects--78.8% for those born in Cape Town and 50.8% for those born in Transkei. Immunisation of 'Road-to-Health' card holders ranged from 71.8% to 95%. The range dropped to 41-79.1% if it was assumed that children without 'Road-to-Health' cards (i.e. without positive proof of immunisation) had not been immunised. Children born in Cape Town have a significantly higher immunisation coverage than children born elsewhere (Transkei accounted for 82.7% of these children). Immunisations administered in Cape Town numbered 80.6%, while 62.6% of subjects were born in Cape Town. In Transkei, payment is required for immunisation, in Cape Town it is free. By implication, cost appeared to be an important reason for low coverage in Transkei. The findings of this study suggested that hostel migrant children who had access to the Cape Town health services through working parents had better immunisation coverage than children at the home-base who seldom or never reached the city.

Health status of hostel dwellers. Part V. Tuberculosis notifications.

Cape Town tuberculosis notification rates for the hostel dwellers of Langa and Guguletu emphasise the severity of the problem among the poor in the city. But the enormity of the problem for the broader dependent migrant population can only be surmised from these figures. It is not possible to compile a comprehensive tuberculosis profile for a geographically divided mobile population nor provide the necessary continuity of treatment under the present politically contrived disparate health care system. Control of tuberculosis cannot wait for a political solution.