Determination of activation energy distributions for chemisorption of oxygen on carbon: an improved approach

The present paper proposes an approach to obtaining the activation energy distribution for chemisorption of oxygen onto carbon surfaces, while simultaneously allowing for the activation energy dependence of the pre-exponential factor of the rate constant. Prior studies in this area have considered this factor to be uniform, thereby biasing estimated distributions. The results show that the derived activation energy distribution is not sensitive to the chemisorption mechanism because of the step function like property of the coverage. The activation energy distribution is essentially uniform for some carbons, and has two or possibly more discrete stages, suggestive of at least two types of sites, each with its own uniform distribution. The pre-exponential factors of the reactions are determined directly from the experimental data, and are found not to be constant as assumed in earlier work, but correlated with the activation energy. The latter results empirically follow an exponential function, supporting some earlier statistical and experimental work. The activation energy distribution obtained in the present paper permits improved correlation of chemisorption data in comparison to earlier studies. (C) 2000 Elsevier Science Ltd. All rights reserved.

Review of "Comorbidity, disability and the need for treatment for DSM-IV psychiatric disorders in an insured population"

Background: This study presents estimates of 12 month and current prevalences of DSM-IV disorders, and the related comor-bidity, disability and service utilization, derived from a national probability sample in Australia. Methods: The DSM-IV psychiatric disorders among persons aged 18 and over in the Australian population were assessed with data collected by lay interviewers using the Composite International Diagnostic Interview, other screening interviews and measures of disability and service utilization. The response rate was 78.1% and the final sample size was 10,641 adults. Results: Close to 20% reported at least one twelve month disorder and 13% a disorder current within the past 30 days. ICD-10 diagnoses were also derived, DSM-IV was the more conservative classification whether or not the new clinical significance criteria was applied. Major depression, any personality disorder, and alcohol dependence were the three most common twelve month disorders, generalized anxiety disorder replaced alcohol dependence as the third most common current disorder. The sexes has similar rates of any disorder, but women had higher rates of affective and anxiety disorders, men higher rates of substance use disorders. Prevalence of most disorders declined with age and education, and were lower among those employed or married. Respondents whose symptoms met criteria for three or more disorders in the past year had greatly increased rates of disability and of mental health consultations. The affective and somatoform disorders were associated with the highest rates of disability. Only 36% of people with a mental disorder this year had consulted for a mental problem, and most had seen a general practitioner. We identified those with a current disorder who were disabled or multiply comorbid - only half had consulted and of those who had not, more than half said they did not need treatment. Conclusions: The 12 month prevalence was lower than reported in the US National Comorbidity Survey but method factors might account for this. The relationships between prevalence and demographic variables, and between comorbidity, disability and service utilization were similar to those found in the US survey. Australia has a national health insurance scheme with total coverage and access to medical help is available to all, commonly at little or no cost. We identify the high rate of not consulting among those with a current disorder, and additional disability or multiple comorbidity, as an important public health problem. Kessler argued for more research on barriers to professional help seeking. This report reinforces his conclusion and shows that economic barriers are not the dominant issue.

The potential for a selective screening strategy for abdominal aortic aneurysm

Objectives-To investigate the feasibility of selective screening for abdominal aortic aneurysm (AAA) based on identification of a target group of manageable size defined by risk factors for AAA. Setting-Male residents of Perth, Western Australia, aged 65-83 years, who participated in a randomised controlled trial of ultrasound screening for AAA. Methods-Eligible men were identified from the electoral roll and invited to attend a screening clinic. Those who attended completed a questionnaire, had a limited physical examination, and underwent an ultrasound examination to identify the maximum diameter of the infrarenal aorta. Data on risk factors collected from the first 8995 men seen were used to calculate a multivariate risk score for the remaining 2755 men who were screened. Gentiles of the risk score were used to define potential target groups for screening and the sensitivity and specificity of each of these selective screening strategies were calculated. We repeated the calculation separately for AAAs of at least 30 mm, 40 mm, and 50 mm in diameter. Results-We found that screening half of the male population aged 65-83 years would find approximately 75% of AAAs, regardless of their size, whereas screening only current smokers in this population would find approximately 20% of AAAs. Conclusions-Selective screening for AAA using easily recognisable risk factors is feasible but is not worthwhile as approximately 25% of clinically significant cases would be missed.

Age-related differences in physical activity levels of young adults

Purpose: To examine age-related differences in the physical activity behaviors of young adults. Methods: We examined rates of participation in vigorous- and moderate-intensity leisure-time activity and walking, as well as an index of physical activity sufficient for health benefits in three Australian cross-sectional samples, for the age ranges of 18-19, 20-24, and 25-29 yr. Data were collected in 1991, 1996, and 1997/8. Results: There was at least a 15% difference in vigorous-intensity leisure-time physical activity from the 18-19 yr to the 25-29 yr age groups, and at least a 10% difference in moderate-intensity leisure-time physical activity. For the index of sufficient activity there was a difference between 9 and 21% across age groups. Differences in rates of walking were less than 8%. For all age groups, males had higher rates of participation for vigorous and moderate-intensity activity than did females, bur females had much higher rates of participation in walking than males. Age-associated differences in activity levels were more apparent for males. Conclusions: Promoting walking and various forms of moderate-intensity physical activities to young adult males, and encouraging young adult females to adopt other forms of moderate-intensity activity to complement walking may help to ameliorate decreases in physical activity over the adult lifespan.

Personality disorders in the community: a report from the Australian national survey of mental health and wellbeing

Background: The first set of aims of the present study was to determine the prevalence of personality disorders (PDs) in a nation, and gender differences in the types and numbers of PDs endorsed. The second set of aims was to establish the relationship of PD to other, non-PD disorders, physical conditions, and disability. Method: Data were obtained from the Australian National Survey of Mental Health and Wellbeing, conducted between May and August 1997. A stratified random sample of households was generated, from which all those aged 18 or over were considered potential interviewees. There were 10,641 respondents to the survey, and this represented a response rate of 78%. Each interviewee was asked 59 questions indexing specific ICD-10 PD criteria. Results: Of the total survey sample, 704 persons had at least one PD. Using weighted replicate weights, it was estimated that approximately 6.5% of the adult population of Australia have one or more PDs (lifetime prevalence). Persons with PD were more likely to be younger, male, and not married, and to have an anxiety disorder, an affective disorder, a substance use disorder, or a physical condition. They were also more likely to have greater disability than those without PD. Conclusion: The study is the first nationwide survey of mental disorders conducted within Australia. It provides an estimate of the prevalence of the various types of PD. The survey has considerable limitations, however, and these are discussed.

Disruptive vocalization and depression in older nursing home residents

Screaming and other types of disruptive vocalization are commonly observed among nursing home residents. Depressive symptoms are also frequently seen in this group, although the relationship between disruptive vocalization and depressive symptoms is unclear. Accordingly, we sought to examine this relationship in older nursing home residents. We undertook a controlled comparison of 41 vocally disruptive nursing home residents and 43 non-vocally-disruptive nursing home residents. All participants were selected to have Mini-Mental State Examination (MMSE) scores of at least 10. Participants had a mean age of 81.0 years (range 63-97 years) and had a mean MMSE score of 17.8 (range 10-29). Nurse ratings of disruptive vocalization according to a semioperationalized definition were validated against the noisy behavior subscale of the Cohen-Mansfield Agitation Inventory. Subjects were independently rated for depressive symptoms by a psychiatrist using the Dementia Mood Assessment Scale, the Cornell Scale for Depression in Dementia, and the Depressive Signs Scale. Vocally disruptive nursing home residents scored significantly higher than controls on each of these three depression-in-dementia scales. These differences remained significant when the effects of possible confounding variables of cognitive impairment, age, and sex were removed. We conclude that depressive symptoms are associated with disruptive vocalization and may have an etiological role in the generation of disruptive vocalization behaviors in elderly nursing home residents.

In vivo measurement of the effect of intra-abdominal pressure on the human spine

In humans, intra-abdominal pressure (IAP) is elevated during many everyday activities. This experiment aimed to investigate the extent to which increased IAP-without concurrent activity of the abdominal or back extensor muscles-produces an extensor torque. With subjects positioned in side lying on a swivel table with its axis at L3, moments about this vertebral level were measured when IAP was transiently increased by electrical stimulation of the diaphragm via the phrenic nerve. There was no electromyographic activity in abdominal and back extensor muscles. When IAP was increased artificially to similar to 15% of the maximum IAP amplitude that could be generated voluntarily with the trunk positioned in flexion, a trunk extensor moment (similar to6 Nm) was recorded. The size of the effect was proportional to the increase in pressure. The extensor moment was consistent with that predicted from a model based on measurements of abdominal cross-sectional area and IAP moment arm. When IAP was momentarily increased while the trunk was flexed passively at a constant velocity, the external torque required to maintain the velocity was increased. These results provide the first in vivo data of the amplitude of extensor moment that is produced by increased IAP. Although the net effect of this extensor torque in functional tasks would be dependent on the muscles used to increase the IAP and their associated flexion torque, the data do provide evidence that IAP contributes, at least in part, to spinal stability. (C) 2001 Elsevier Science Ltd. All rights reserved.

Mutant GABA(A) receptor gamma 2-subunit in childhood absence epilepsy and febrile seizures

Epilepsies affect at least 2% of the population at some time in life, and many forms have genetic determinants(1,2). We have found a mutation in a gene encoding a GABA, receptor subunit in a large family with epilepsy. The two main phenotypes were childhood absence epilepsy (CAE) and febrile seizures (FS), There is a recognized genetic: relationship between FS and CAE, yet the two syndromes have different ages of onset, and the physiology of absences and convulsions is distinct. This suggests the mutation has age-dependent effects on different neuronal networks that influence the expression of these clinically distinct, but genetically related, epilepsy phenotypes. We found that the mutation in GABRG2 (encoding the gamma2-subunit) abolished in vitro sensitivity to diazepam, raising the possibility that endozepines do in fact exist and have a physiological role in preventing seizures.

Identifying rate-limiting nodes in large-scale cortical networks for visuospatial processing: an illustration using fMRI

With the advent of functional neuroimaging techniques, in particular functional magnetic resonance imaging (fMRI), we have gained greater insight into the neural correlates of visuospatial function. However, it may not always be easy to identify the cerebral regions most specifically associated with performance on a given task. One approach is to examine the quantitative relationships between regional activation and behavioral performance measures. In the present study, we investigated the functional neuroanatomy of two different visuospatial processing tasks, judgement of line orientation and mental rotation. Twenty-four normal participants were scanned with fMRI using blocked periodic designs for experimental task presentation. Accuracy and reaction time (RT) to each trial of both activation and baseline conditions in each experiment was recorded. Both experiments activated dorsal and ventral visual cortical areas as well as dorsolateral prefrontal cortex. More regionally specific associations with task performance were identified by estimating the association between (sinusoidal) power of functional response and mean RT to the activation condition; a permutation test based on spatial statistics was used for inference. There was significant behavioral-physiological association in right ventral extrastriate cortex for the line orientation task and in bilateral (predominantly right) superior parietal lobule for the mental rotation task. Comparable associations were not found between power of response and RT to the baseline conditions of the tasks. These data suggest that one region in a neurocognitive network may be most strongly associated with behavioral performance and this may be regarded as the computationally least efficient or rate-limiting node of the network.

Residence time distributions of gas flowing through rotating drum bioreactors

Residence time distribution studies of gas through a rotating drum bioreactor for solid-state fermentation were performed using carbon monoxide as a tracer gas. The exit concentration as a function of time differed considerably from profiles expected for plug flow, plug flow with axial dispersion, and continuous stirred tank reactor (CSTR) models. The data were then fitted by least-squares analysis to mathematical models describing a central plug flow region surrounded by either one dead region (a three-parameter model) or two dead regions (a five-parameter model). Model parameters were the dispersion coefficient in the central plug flow region, the volumes of the dead regions, and the exchange rates between the different regions. The superficial velocity of the gas through the reactor has a large effect on parameter values. Increased superficial velocity tends to decrease dead region volumes, interregion transfer rates, and axial dispersion. The significant deviation from CSTR, plug flow, and plug flow with axial dispersion of the residence time distribution of gas within small-scale reactors can lead to underestimation of the calculation of mass and heat transfer coefficients and hence has implications for reactor design and scaleup. (C) 2001 John Wiley & Sons, Inc.

Quasars from a complete spectroscopic survey

With the advent of multi-fibre spectrographs such as the 'Two-Degree Field' (2dF) instrument at the Angle-Australian Telescope, quasar surveys that are free of any preselection of candidates and any biases this implies have become possible for the first time. The first of these is that which is being undertaken as part of the Fornax Spectroscopic Survey, a survey of the area around the Fornax Cluster of galaxies, and aims to obtain the spectra of all objects in the magnitude range 16.5 < b(j) < 19.7. To date, 3679 objects in the central pi -deg(2) area have been successfully identified from their spectral characteristics. Of these, 71 are found to be quasars, 61 with redshifts 0.3 < z < 2.2 and 10 with redshifts z > 2.2. Using this complete quasar sample, a new determination of quasar number counts is made, enabling an independent check of existing quasars surveys. Cumulative counts per square degree at a magnitude limit of b(j) < 19.5 are found to be 11.5 +/- 2.2 for 0.3 < z < 2.2, 2.22 +/- 0.93 for z > 2.2 and 13.7 +/- 3.1 for z > 0.3. Given the likely detection of extra quasars in the Fornax survey, we make a more detailed examination of existing quasar selection techniques. First, looking at the use of a stellar criterion, four of the 71 quasars are 'non-stellar' on the basis of the automated plate measuring facility (APM) b(j) classification, however inspection shows all are consistent with stellar, but misclassified due to image confusion. Examining the ultraviolet excess and multicolour selection techniques, for the selection criteria investigated, ultraviolet excess would find 69 +/- 6 per cent of our 0.3 < z < 2.2 quasars and only 50(-18)(+14), per cent of our z > 2.2 quasars, while the completeness level for multicolour selection is found to be 90(-4)(+3) per cent for 0.3 < z < 2.2 quasars and 80(-12)(+14) per cent for z > 2.2 quasars. The extra quasars detected by our all-object survey thus have unusually red star-like colours, and this appears to be a result of the continuum shape rather than any emission features. An intrinsic dust extinction model may, at least partly, account for the red colours.

Using the 6dF galaxy redshift survey to detect gravitationally-lensed quasars

It is possible to detect gravitationally-lensed quasars spectroscopically if the spectra obtained during galaxy surveys are searched for the presence of quasar emission lines. The up-coming 6 degree Field (6dF) redshift survey on the United Kingdom Schmidt Telescope will involve obtaining similar to 10(5) spectra of near-infrared selected galaxies to a magnitude limit of K = 13. Applying previously developed techniques implies that at least one lens should be discovered in the 6dF survey, but that as many as ten could be found if quasars typically have B-J - K similar or equal to 8. In this model there could be up to fifty lensed quasars in the, sample, but most of them could only be detected by infrared spectroscopy.

Stochastic structure and individual-tree growth models

The majority of past and current individual-tree growth modelling methodologies have failed to characterise and incorporate structured stochastic components. Rather, they have relied on deterministic predictions or have added an unstructured random component to predictions. In particular, spatial stochastic structure has been neglected, despite being present in most applications of individual-tree growth models. Spatial stochastic structure (also called spatial dependence or spatial autocorrelation) eventuates when spatial influences such as competition and micro-site effects are not fully captured in models. Temporal stochastic structure (also called temporal dependence or temporal autocorrelation) eventuates when a sequence of measurements is taken on an individual-tree over time, and variables explaining temporal variation in these measurements are not included in the model. Nested stochastic structure eventuates when measurements are combined across sampling units and differences among the sampling units are not fully captured in the model. This review examines spatial, temporal, and nested stochastic structure and instances where each has been characterised in the forest biometry and statistical literature. Methodologies for incorporating stochastic structure in growth model estimation and prediction are described. Benefits from incorporation of stochastic structure include valid statistical inference, improved estimation efficiency, and more realistic and theoretically sound predictions. It is proposed in this review that individual-tree modelling methodologies need to characterise and include structured stochasticity. Possibilities for future research are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.

Suicidal ideation and suicide attempts as predictors of mental health service use

Objective: To examine the extent to which suicidal ideation and suicide attempts are predictive of service use. Design and setting: The National Survey of Mental Health and Wellbeing considered service utilisation in relation to self-reported mental health problems. Service utilisation was inquired of in relation to hospital-based care (including both specialist mental health and general care settings), as well as consultations with a range of health professionals (both specialist and non-specialist mental health professionals, including psychiatrists, psychologists and general practitioners) on an outpatient basis. Participants: Secondary analysis of self-report data from 10 641 randomly selected Australian adults who participated in the National Survey of Mental Health and Wellbeing in 1997. The key predictor variables were reported suicidal ideation and suicide attempts over the past 12 months. Main outcome measures: Use of services for mental health problems (past 12 months). Results: When considered in isolation, individuals reporting suicidal ideation were more likely to make use of at least one type of service for mental health problems than non-suicidal individuals (OR, 17.3; 95% Cl, 13.2-22.6), and individuals reporting suicide attempts were even more likely to do so (OR, 32.3; 95% CI, 9.0-115.4). In the case of suicidal ideation, this effect remained significant after controlling for a range of potential confounders. For suicide attempts, the effect of mental health service use was no longer significant after other variables were taken into account. Conclusions: Suicidal individuals are likely to make use of services, and a high proportion of suicides may be preventable through appropriate healthcare system responses.

Redating the onset of burning at Lynch's Crater (North Queensland): implications for human settlement in Australia

Lynch's Crater preserves a continuous, high-resolution record of environmental changes in north Queensland. This record suggests a marked increase in burning that appears to be independent of any known major climatic boundaries. This increase is accompanied, or closely followed, by the virtually complete replacement of rainforest by sclerophyll vegetation. The absence of any major climatic shift associated with this increase in fire frequency therefore has been interpreted as a result of early human impact in the area. The age for this increase in burning, on the basis of conventional radiocarbon dating, was previously thought to be approximately 38000 C-14 yr BP, supporting the traditional model for human arrival in Australia at 40 000 C-14 yr BP Here we have applied a more rigorous pre-treatment and graphitisation procedure for radiocarbon dating samples from the Lynch's Crater sequence. These new dates suggest that the increase in fire frequency occurred at 45 000 C-14 yr BP, supporting the alternative view that human occupation of Australia occurred by at least 45 000-55 000 cal. yr BP. Copyright (C) 2001 John Wiley & Sons, Ltd.