1,347 research outputs found

    The impact of sea-level rise on tidal characteristics around Australia

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    An established tidal model, validated for present-day conditions, is used to investigate the effect of large levels of sea-level rise (SLR) on tidal characteristics around Australasia. SLR is implemented through a uniform depth increase across the model domain, with a comparison between the implementation of coastal defences or allowing low-lying land to flood. The complex spatial response of the semi-diurnal M2 constituent does not appear to be linear with the imposed SLR. The most predominant features of this response are the generation of new amphidromic systems within the Gulf of Carpentaria and large-amplitude changes in the Arafura Sea, to the north of Australia, and within embayments along Australia's north-west coast. Dissipation from M2 notably decreases along north-west Australia but is enhanced around New Zealand and the island chains to the north. The diurnal constituent, K1, is found to decrease in amplitude in the Gulf of Carpentaria when flooding is allowed. Coastal flooding has a profound impact on the response of tidal amplitudes to SLR by creating local regions of increased tidal dissipation and altering the coastal topography. Our results also highlight the necessity for regional models to use correct open boundary conditions reflecting the global tidal changes in response to SLR.</p

    Continuation method for nonlinear complementarity problems via normal maps

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    Cataloged from PDF version of article.In a recent paper by Chen and Mangasarian (C. Chen, O.L. Mangasarian, A class of smoothing functions for nonlinear and mixed complementarity problems, Computational Optimization and Applications 2 (1996), 97±138) a class of parametric smoothing functions has been proposed to approximate the plus function present in many optimization and complementarity related problems. This paper uses these smoothing functions to approximate the normal map formulation of nonlinear complementarity problems (NCP). Properties of the smoothing function are investigated based on the density functions that de®nes the smooth approximations. A continuation method is then proposed to solve the NCPs arising from the approximations. Su cient conditions are provided to guarantee the boundedness of the solution trajectory. Furthermore, the structure of the subproblems arising in the proposed continuation method is analyzed for di erent choices of smoothing functions. Computational results of the continuation method are reported. Ó 1999 Elsevier Science B.V. All rights reserved

    Changes in ESCRT-III filament geometry drive membrane remodelling and fission in silico

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    BACKGROUND: ESCRT-III is a membrane remodelling filament with the unique ability to cut membranes from the inside of the membrane neck. It is essential for the final stage of cell division, the formation of vesicles, the release of viruses, and membrane repair. Distinct from other cytoskeletal filaments, ESCRT-III filaments do not consume energy themselves, but work in conjunction with another ATP-consuming complex. Despite rapid progress in describing the cell biology of ESCRT-III, we lack an understanding of the physical mechanisms behind its force production and membrane remodelling. // RESULTS: Here we present a minimal coarse-grained model that captures all the experimentally reported cases of ESCRT-III driven membrane sculpting, including the formation of downward and upward cones and tubules. This model suggests that a change in the geometry of membrane bound ESCRT-III filaments-from a flat spiral to a 3D helix-drives membrane deformation. We then show that such repetitive filament geometry transitions can induce the fission of cargo-containing vesicles. // CONCLUSIONS: Our model provides a general physical mechanism that explains the full range of ESCRT-III-dependent membrane remodelling and scission events observed in cells. This mechanism for filament force production is distinct from the mechanisms described for other cytoskeletal elements discovered so far. The mechanistic principles revealed here suggest new ways of manipulating ESCRT-III-driven processes in cells and could be used to guide the engineering of synthetic membrane-sculpting systems

    Application of Beamforming Methods to Full-Scale Military Jet Noise

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    Over the past decade, beamforming in aeroacoustics applications have undergone significant advances. Cross beamforming methods improve upon traditional beamforming in that they relax the assumption of multiple-source incoherence. This paper compares the abilities of three cross beamforming methods to reproduce source and field characteristics for an extended, partially correlated source that mimics supersonic jet noise radiation. Standard cross beamforming and two related methods that involve regularization—the hybrid method and improved generalized inverse beamforming—are applied to a numerically generated dataset along a near-field line. Estimated levels and coherence lengths are compared with benchmarks at the source as well as near and far-field locations. All three methods are successful in reproducing the field and source properties in high-amplitude regions. Although regularization generally helps to improve both source and field reconstructions, results are sensitive to regularization parameters, particularly for the generalized inverse method. The successful application of the three methods demonstrate the utility of cross-beamforming in formulating equivalent source models for accurate field prediction of complex sources, including jet noise

    Cosmic Dawn and Epoch of Reionization Foreground Removal with the SKA

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    The exceptional sensitivity of the SKA will allow observations of the Cosmic Dawn and Epoch of Reionization (CD/EoR) in unprecedented detail, both spectrally and spatially. This wealth of information is buried under Galactic and extragalactic foregrounds, which must be removed accurately and precisely in order to reveal the cosmological signal. This problem has been addressed already for the previous generation of radio telescopes, but the application to SKA is different in many aspects. In this chapter we summarise the contributions to the field of foreground removal in the context of high redshift and high sensitivity 21-cm measurements. We use a state-of-the-art simulation of the SKA Phase 1 observations complete with cosmological signal, foregrounds and frequency-dependent instrumental effects to test both parametric and non-parametric foreground removal methods. We compare the recovered cosmological signal using several different statistics and explore one of the most exciting possibilities with the SKA --- imaging of the ionized bubbles. We find that with current methods it is possible to remove the foregrounds with great accuracy and to get impressive power spectra and images of the cosmological signal. The frequency-dependent PSF of the instrument complicates this recovery, so we resort to splitting the observation bandwidth into smaller segments, each of a common resolution. If the foregrounds are allowed a random variation from the smooth power law along the line of sight, methods exploiting the smoothness of foregrounds or a parametrization of their behaviour are challenged much more than non-parametric ones. However, we show that correction techniques can be implemented to restore the performances of parametric approaches, as long as the first-order approximation of a power law stands.Comment: Accepted for publication in the SKA Science Book 'Advancing Astrophysics with the Square Kilometre Array', to appear in 201

    Transitions between lifetime alcohol use, regular use and remission: Results from the 2004 South African Stress and Health Survey

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    Background. Hazardous alcohol consumption presents a serious threat to the health and wellbeing of all people and is linked to chronic and acute health problems.Objectives. To: (i) estimate the prevalence of alcohol use disorders and remission from alcohol abuse and dependence in the South African (SA) population; and (ii) determine whether age of onset, education, sex and level of cohort alcohol use are associated with commencement of use, regularity of use, and transitions to and remission from more harmful levels of use.Methods. The study was a nationally representative sample of 4 315  individuals aged ≥18 years. In a multistage, area probability sample of adults, data were collected from 4 311 alcohol users using the World Mental Health Survey Initiative version of the Composite International Diagnostic Interview version 3.0. All analyses were carried out using SAS version 9.4.Results. Of the respondents, 40.6% indicated lifetime use of alcohol,  35.3% reported regular use, and 8.8% met diagnostic criteria for alcohol abuse and 2.7% for alcohol dependence. The prevalence of remission from lifetime abuse without dependence was 55.9%. The median age of onset of alcohol use was 20 years, with transition from use to regular use occurring within ~1 - 3 years. The results suggest that males, students (compared with those who had completed a high level of education) and greater  alcohol use in the respondent’s birth cohort were all associated with increased odds of commencing alcohol use. For transitions from use to regular use, increased odds were associated with males, greater birth cohort alcohol use, low education and later (&gt;21 years) onset of first alcohol use.Conclusions. Our findings suggest that cohort alcohol use is associated with transition to commencement of use and from use to regular use in the general SA population. The study further highlighted the need for  interventions among males and university students, given that hazardous alcohol consumption seems to be the most prevalent public health issue encountered by university students and males

    Development and mapping of SNP assays in allotetraploid cotton

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    A narrow germplasm base and a complex allotetraploid genome have made the discovery of single nucleotide polymorphism (SNP) markers difficult in cotton (Gossypiumhirsutum). To generate sequence for SNP discovery, we conducted a genome reduction experiment (EcoRI, BafI double digest, followed by adapter ligation, biotin–streptavidin purification, and agarose gel separation) on two accessions of G. hirsutum and two accessions of G. barbadense. From the genome reduction experiment, a total of 2.04 million genomic sequence reads were assembled into contigs with an N50 of 508 bp and analyzed for SNPs. A previously generated assembly of expressed sequence tags (ESTs) provided an additional source for SNP discovery. Using highly conservative parameters (minimum coverage of 8× at each SNP and 20% minor allele frequency), a total of 11,834 and 1,679 non-genic SNPs were identified between accessions of G. hirsutum and G. barbadense in genome reduction assemblies, respectively. An additional 4,327 genic SNPs were also identified between accessions of G. hirsutum in the EST assembly. KBioscience KASPar assays were designed for a portion of the intra-specific G. hirsutum SNPs. From 704 non-genic and 348 genic markers developed, a total of 367 (267 non-genic, 100 genic) mapped in a segregating F2 population (Acala Maxxa × TX2094) using the Fluidigm EP1 system. A G. hirsutum genetic linkage map of 1,688 cM was constructed based entirely on these new SNP markers. Of the genic-based SNPs, we were able to identify within which genome (‘A’ or ‘D’) each SNP resided using diploid species sequence data. Genetic maps generated by these newly identified markers are being used to locate quantitative, economically important regions within the cotton genome

    Prophylactic balloon angioplasty fails to prolong the patency of expanded polytetrafluoroethylene arteriovenous grafts: Results of a prospective randomized study

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    AbstractPurpose: Maintenance of hemodialysis access grafts represents an enormous social and clinical problem. Current grafts and graft salvage techniques are inadequate. Consequently, there has been increasing interest in the use of minimally invasive catheter techniques to prophylactically treat stenoses in functioning arteriovenous grafts. Prophylactic balloon angioplasty has been widely suggested as prolonging assisted primary patency. We have performed a prospective randomized trial to compare patients who underwent percutaneous transluminal angioplasty (PTA) for graft stenoses >50% with a control group that received no intervention. Our hypothesis was that to be efficacious a minimal benefit of 20% prolongation in patency would be necessary.Methods: Color flow duplex scanning was used to detect >50% stenoses in functioning expanded polytetrafluoroethylene grafts. Patients were then subjected to confirmatory angiographic evaluation. Those who had angiographic stenoses >50% were randomized to balloon angioplasty or observation. Patients were followed-up with duplex scanning every 2 months. Statistical analysis was performed using the Kaplan-Meier technique. Although demographically the patient groups were well matched, there were more prior interventions and concurrent central stenoses in the treatment group. Outcomes were graft thrombosis, graft dysfunction that precluded dialysis, and six or more PTA procedures within 18 months.Results: In the treatment and observation groups, the 6-month patency rates were 69% ± 7% and 70% ± 7%, respectively. The 12-month patency rates for the treatment and observation groups were 51% ± 6% and 47% ± 4%, respectively. There was no significant difference between these two groups ( p = 0.97), with an 80% confidence limit for detection of a difference greater than 20%.Conclusions: This study demonstrates that a generic approach of PTA to treat all polytetrafluoroethylene grafts with stenoses >50% does not prolong patency and cannot be supported

    Foregrounds for observations of the cosmological 21 cm line: II. Westerbork observations of the fields around 3C196 and the North Celestial Pole

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    In the coming years a new insight into galaxy formation and the thermal history of the Universe is expected to come from the detection of the highly redshifted cosmological 21 cm line. The cosmological 21 cm line signal is buried under Galactic and extragalactic foregrounds which are likely to be a few orders of magnitude brighter. Strategies and techniques for effective subtraction of these foreground sources require a detailed knowledge of their structure in both intensity and polarization on the relevant angular scales of 1-30 arcmin. We present results from observations conducted with the Westerbork telescope in the 140-160 MHz range with 2 arcmin resolution in two fields located at intermediate Galactic latitude, centred around the bright quasar 3C196 and the North Celestial Pole. They were observed with the purpose of characterizing the foreground properties in sky areas where actual observations of the cosmological 21 cm line could be carried out. The polarization data were analysed through the rotation measure synthesis technique. We have computed total intensity and polarization angular power spectra. Total intensity maps were carefully calibrated, reaching a high dynamic range, 150000:1 in the case of the 3C196 field. [abridged]Comment: 20 pages, 22 figures, accepted for publication in A&A. A version with full resolution figures is available at http://www.astro.rug.nl/~bernardi/NCP_3C196/bernardi.pd