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We investigate a theoretical framework for modelling fluid turbulence based on the formalism of exact coherent structures (ECSs). Although highly promising, existing evidence for the role of ECSs in turbulent flows is largely circumstantial and comes primarily from idealized numerical simulations. In particular, it remains unclear whether three-dimensional turbulent flows in experiment shadow any ECSs. In order to conclusively answer this question, a hierarchy of ECSs should be computed on a domain and with boundary conditions exactly matching experiment. The present study makes the first step in this direction by investigating a small-aspect-ratio Taylor–Couette flow with naturally periodic boundary conditions in the azimuthal direction. We describe the structure of the chaotic set underlying turbulent flow driven by counter-rotating cylinders and present direct numerical evidence for shadowing of a collection of unstable relative periodic orbits and a travelling wave, setting the stage for further experimental tests of the framework.
The cognitive process of worry, which keeps negative thoughts in mind and elaborates the content, contributes to the occurrence of many mental health disorders. Our principal aim was to develop a straightforward measure of general problematic worry suitable for research and clinical treatment. Our secondary aim was to develop a measure of problematic worry specifically concerning paranoid fears.
An item pool concerning worry in the past month was evaluated in 250 non-clinical individuals and 50 patients with psychosis in a worry treatment trial. Exploratory factor analysis and item response theory (IRT) informed the selection of scale items. IRT analyses were repeated with the scales administered to 273 non-clinical individuals, 79 patients with psychosis and 93 patients with social anxiety disorder. Other clinical measures were administered to assess concurrent validity. Test-retest reliability was assessed with 75 participants. Sensitivity to change was assessed with 43 patients with psychosis.
A 10-item general worry scale (Dunn Worry Questionnaire; DWQ) and a five-item paranoia worry scale (Paranoia Worries Questionnaire; PWQ) were developed. All items were highly discriminative (DWQ a = 1.98–5.03; PWQ a = 4.10–10.7), indicating small increases in latent worry lead to a high probability of item endorsement. The DWQ was highly informative across a wide range of the worry distribution, whilst the PWQ had greatest precision at clinical levels of paranoia worry. The scales demonstrated excellent internal reliability, test-retest reliability, concurrent validity and sensitivity to change.
The new measures of general problematic worry and worry about paranoid fears have excellent psychometric properties.
Chlamydia gallinacea, a new chlamydial agent, has been reported in four European countries as well as Argentina and China. Experimentally infected chickens with C. gallinacea in previous study showed no clinical signs but had significantly reduced gains in body weight (6·5–11·4%). Slaughterhouse workers exposed to infected chickens have developed atypical pneumonia, indicating C. gallinacea is likely a zoonotic agent. In this study, FRET-PCR confirmed that C. gallinacea was present in 12·4% (66/531) of oral–pharyngeal samples from Alabama backyard poultry. Phylogenetic comparisons based on ompA variable domain showed that 16 sequenced samples represented 14 biotypes. We report for the first time the presence of C. gallinacea in North America, and this warrants further research on the organism's pathogenicity, hosts, transmission, and zoonotic potential.
Exposure to volatile organic compounds can lead to asphyxiation, pneumonia like conditions, comas, seizures and irreversible lung, kidney and central nervous system damage. Volatile organics are additionally extremely flammable and explosive, making their early detection in the immediate environment increasingly important. Metal oxide semiconductor (MOS) gas sensors present a potential technology to detect such gases.
Metal oxide semiconducting (MOS) gas sensors represent a cheap, robust and sensitive technology for detecting volatile organic compounds. An array of five thick film MOS gas sensors was fabricated, based on vanadium pentoxide inks. Production took place using a commercially available screen printer, a 3 x 3 mm alumina substrate containing interdigitated electrodes and a platinum heater track. V2O5 inks were modified using zeolite beta, zeolite Y, mordenite & ZSM5 admixtures. Sensors were exposed to three common reducing gases, namely acetone, ethanol, and toluene, and a machine learning technique was applied to differentiate between the different gases. Sensors produced strong responses to all gases. Zeolite modified sensors were found to increase the responsiveness of the sensors compared to umodified V2O5 in a number of cases. Machine learning techniques were incorporated to test the selectivity of the sensors. A high level of accuracy was achieved in determining the class of gas observed.
Cannabis use is associated with an increased risk of developing a psychotic disorder but the temporal relationship between cannabis use and onset of illness is unclear. The objective of this study was to assess prospectively the influence of cannabis use on transition to psychosis in people at ultra-high risk (UHR) for the disorder.
Lifetime and continued cannabis use was assessed in a consecutively ascertained sample of 182 people (104 male, 78 female) at UHR for psychosis. Individuals were then followed clinically for 2 years to determine their clinical outcomes.
Lifetime cannabis use was reported by 134 individuals (73.6%). However, most of these individuals had stopped using cannabis before clinical presentation (n = 98, 73.1%), usually because of adverse effects. Among lifetime users, frequent use, early-onset use and continued use after presentation were all associated with an increase in transition to psychosis. Transition to psychosis was highest among those who started using cannabis before the age of 15 years and went on to use frequently (frequent early-onset use: 25%; infrequent or late-onset use: 5%; χ21 = 10.971, p = 0.001). However, within the whole sample, cannabis users were no more likely to develop psychosis than those who had never used cannabis (cannabis use: 12.7%; no use: 18.8%; χ21 = 1.061, p = 0.303).
In people at UHR for psychosis, lifetime cannabis use was common but not related to outcome. Among cannabis users, frequent use, early-onset use and continued use after clinical presentation were associated with transition to psychosis.
This paper describes sentinel laboratory surveillance of hepatitis C antibody testing in England. Demographic and test result data were supplemented by follow-up questionnaires sent to the requesting clinician. Between October 2002 and September 2003 almost 75000 anti-HCV tests were performed in eight sentinel centres. More males were tested than females and over half of those tested were aged 25–44 years. Overall 5·7% (3333/58144, range 2·8–7·7%) individuals tested positive. Follow-up questionnaire data showed that 82% (1043/1277) of the positives had injecting drug use reported as the main risk exposure. The majority of negative individuals were undergoing routine screening as recommended for specific patient groups. Most individuals were asymptomatic. Antibody prevalence was estimated to be 34% in current injecting drug users and 42% in former injectors. Comparing positives to routine national surveillance suggests that only 53% (1782/3333) of diagnosed cases were reported. Sentinel laboratory data can provide valuable supplementary data to national surveillance.
This paper proves a theorem about bounding orbits of a time dependent dynamical system. The maps that are involved are examples in convex dynamics, by which we mean the dynamics of piecewise isometries where the pieces are convex. The theorem came to the attention of the authors in connection with the problem of digital halftoning. Digital halftoning is a family of printing technologies for getting full-color images from only a few different colors deposited at dots all of the same size. The simplest version consists in obtaining gray-scale images from only black and white dots. A corollary of the theorem is that for error diffusion, one of the methods of digital halftoning, averages of colors of the printed dots converge to averages of the colors taken from the same dots of the actual images. Digital printing is a special case of a much wider class of scheduling problems to which the theorem applies. Convex dynamics has roots in classical areas of mathematics such as symbolic dynamics, Diophantine approximation, and the theory of uniform distributions.
The biogeochemical dynamics of Si in temperate lakes is well documented and the role of biological uptake and recycling is well known. In this paper we examine the Si dynamics of a series of ice-covered, closed-basin lakes in the McMurdo Dry Valley region (~78° S) of Antarctica. Our data and calculations indicate that biological uptake of Si is not a major process in these lakes. Mass balance considerations in Lake Hoare, the youngest and the freshest lake, suggest that annual stream input during relatively low-flow years is minor and that Si dynamics is greatly influenced by hydrological variation and hence climatic changes affecting stream flow and lake level. The data imply that the Si input during high-flow years must dominate the system. Subtle changes in climate have a major control on Si input into the lake, and Si dynamics are not controlled by biogeochemical processes as in temperate systems.
We consider nonnegative steady-state solutions of the evolution equation
Our class of coefficients f, g allows degeneracies at h = 0,
such as f(0) = 0, as well as divergences like g(0) = ±∞. We first construct steady states and study their regularity. For
f, g > 0 we construct positive periodic steady states, and non-negative steady states with either
zero or nonzero contact angles. For f > 0 and g < 0, we prove there are no non-constant
positive periodic steady states or steady states with zero contact angle, but we do construct
non-negative steady states with nonzero contact angle. In considering the volume, length (or
period) and contact angle of the steady states, we find a rescaling identity that enables us to
answer questions such as whether a steady state is uniquely determined by its volume and
contact angle. Our tools include an improved monotonicity result for the period function of
the nonlinear oscillator. We also relate the steady states and their scaling properties to a
recent blow-up conjecture of Bertozzi and Pugh.
In interplanetary travel and high altitude flight, humans will be exposed to high energy charged particles from solar flares and galactic cosmic rays. These particles lose energy in a material by Coulomb interactions and nuclear collisions. In nuclear collisions, large amounts of energy are transferred and secondary particles are formed from both the projectile and the struck nucleus. A significant portion of these particles are neutrons which can only lose energy by collisions or reactions with a nucleus. Hydrogen-containing materials, such as polymers, are most effective in reducing the neutron energy. When reduced to very low energies, neutrons have a high probability of reacting with a nucleus. Such reactions are dangerous in the human body, and can cause electronic equipment failure. Low energy neutrons react particularly well with a stable isotope of boron, 10B. To test structural materials which contain both hydrogen to reduce the energy of neutrons and boron to absorb neutrons of reduced energy, samples of two polyimides were made which contained varying amounts of either amorphous boron powder or boron carbide whiskers. The polymers used were a thermoset, PETI-5 from Imitec, and a thermoplastic, K3B from Fiberite. Both materials were made in pure form and with up to 20% by weight of the boron additives. The addition of boron in either form did not change the thermal properties of these materials significantly. However, the compressive yield strength and the tensile strength were both affected by the addition of the boron materials. A neutron absorption test using a PuBe thermal neutron source showed that a 0.5 cm thick sample of K3B containing 15% amorphous boron powder absorbed over 90% of the incident neutrons.
Increasing complexity of design in automotive electrical systems has been paralleled by increased demands for analysis of the safety and reliability aspects of those designs. Such demands can place a great burden on the engineers charged with carrying
out the analysis. This paper describes how the intended functions of a circuit design can be combined with a qualitative model of the electrical circuit that fulfils the functions, and used to analyse the safety of the design. FLAME, an automated failure
mode and effects analysis system based on these techniques, is described in detail. FLAME has been developed over several years, and is capable of composing an FMEA report for many different electrical subsystems. The paper also addresses the issue of how
the use of functional and structural reasoning can be extended to sneak circuit analysis and fault tree analysis.
Films of copper(II) imidazolate, an aromatic, heterocyclic hydrocarbon polymer, have been synthesized in situ at room temperature on copper surfaces. The films were made using a copper(II) salt formed as a thin film on an metallic copper substrate with subsequent complexation and deprotonation of the imidazole molecule. The in-situ formed copper(II) imidazolate polymer films have been studied by elemental analyses, scanning electron microscopy, and x-ray photoelectron and Auger spectroscopy. The copper Auger parameter has been derived for the films.
Calcium phosphate based thin films prepared by colloidal sol-gel slow draw dipping of quartz substrates are bioactive to both osteoclast resorption and osteoblast deposition. The bioactivity is related to the presence of mixed crystalline phases in the films generated under different sintering conditions. As the sintering temperature was increased from 800°C to 1000°C, a transition in film composition from calcium hydroxylapatite to alpha-tricalcium phosphate is achieved.
The aim of this study was to determine whether HIV infection is associated with increased psychosocial distress in the asymptomatic and early symptomatic stages of disease and to determine the factors associated with reporting health symptoms. Subjects included 61 gay men (41 HIV −, 20 HIV +) who were assessed at the time of requesting their first HIV test and again 12 months later. Measures included a detailed standardized psychiatric interview (Present State Examination, PSE), a range of psychosocial self-report measures and a physical symptom checklist. There were no differences between the HIV + and HIV − groups in terms of self-reported symptoms. Multiple regression analysis showed that the symptom reporting was not associated with clinical or immunological markers of disease progression but was associated with measures of psychosocial distress. Although both groups showed elevated levels of psychosocial distress at the time of HIV testing, there were no differences between serostatus groups at follow-up. Multiple regression analysis indicated that the best predictors of PSE scores at follow-up were baseline PSE score and a history of psychiatric illness. Early HIV disease is not associated with increased psychosocial distress and symptom reporting is more closely related to psychological measures than to clinical or immunological markers of disease.
The aim of this study was to determine whether HIV infection is associated with neurological or neuropsychological impairment in the asymptomatic and early symptomatic stages of disease. Subjects included 61 gay men (41 HIV −, 20 HIV +) who were assessed at the time of requesting their first HIV test and again 12 months later. The assessments at baseline were conducted double-blind to HIV serostatus. Measures included a neuropsychological battery, neurological examination and full psychiatric assessment. There were no differences between the asymptomatic HIV + and HIV − groups at baseline or at follow-up in terms of mean scores on neuropsychological tests. Mean scores were within the normal range for all neuropsychological tests for both groups. Multiple regression analysis was used to predict each individual's performance at follow-up on the basis of their baseline performance, psychiatric state, neurological history and drug use for each of the neuropsychological tests. HIV + subjects were more likely than control subjects to perform at a significantly lower level at follow-up on one or more tests than predicted on the basis of their baseline performance.
D. R. Pugh, Department of Computer Science University of Wales Aberystwyth Dyfed SY23 3DB United Kingdom,
C. J. Price, Department of Computer Science University of Wales Aberystwyth Dyfed SY23 3DB United Kingdom
This paper describes work on the construction of a configurable knowledge acquisition tool, Jigsaw. Unlike automated knowledge acquisition programs such as MORE [Kahn, 1988], MOLE [Eshelman, 1988], and OPAL [Musen, 1989], each of which automates elicitation for just one problem solving method, it is possible to alter Jigsaw's knowledge acquisition strategy to match different problem solving methods.
The work is based upon eliciting knowledge for problem solvers made up from different combinations of generic task (as denned in [Chandrasekaran, 1986] and [Chandrasekaran, 1988]). Each combination of generic tasks defines the functionality of a different problem solving method. However, the eventual aim of this work is that it will be possible to adapt it to a range of different KADS [Schreiber et. al., 1987] interpretation models and thus it will be part of a complete knowledge acquisition methodology.
The paper outlines the requirements for such a knowledge acquisition tool and details the distributed architecture which allows the tool, Jigsaw, to achieve the required flexibility to elicit knowledge for such problem solvers. An important part of this flexibility is the way in which Jigsaw can be configured to match different types of problem solver. This is described in some detail.
Jigsaw has been used to reproduce the MDX2 [Sticklen, 1987] knowledge base, which was initially constructed by using manual knowledge acquisition techniques. The paper gives a description of how Jigsaw elicited this knowledge.
Let ϕ be a flow on a compact metric space Λ and let p ∈ Λ be chain recurrent. We show that (Λ; ℝ) ≠ 0 if dimp Λ = 1 or if p belongs to a section of ϕ. Applications to planar flows and to smooth flows are given.