91,680 results

  • The death of massive stars - I. Observational constraints on the progenitors of Type II-P supernovae

    Smartt, SJ; Eldridge, John; Crockett, RM; Maund JR (2009)

    Journal article
    The University of Auckland Library

    We present the results of a 10.5-yr, volume-limited (28-Mpc) search for supernova (SN) progenitor stars. In doing so we compile all SNe discovered within this volume (132, of which 27 per cent are Type Ia) and determine the relative rates of each subtype from literature studies. The core-collapse SNe break down into 59 per cent II-P and 29 per cent Ib/c, with the remainder being IIb (5 per cent), IIn (4 per cent) and II-L (3 per cent). There have been 20 II-P SNe with high-quality optical or near-infrared pre-explosion images that allow a meaningful search for the progenitor stars. In five cases they are clearly red supergiants, one case is unconstrained, two fall on compact coeval star clusters and the other twelve have no progenitor detected. We review and update all the available data for the host galaxies and SN environments (distance, metallicity and extinction) and determine masses and upper mass estimates for these 20 progenitor stars using the STARS stellar evolutionary code and a single consistent homogeneous method. A maximum likelihood calculation suggests that the minimum stellar mass for a Type II-P to form is mmin = 8.5+1-1.5Msolar and the maximum mass for II-P progenitors is mmax = 16.5 +/- 1.5Msolar, assuming a Salpeter initial mass function holds for the progenitor population (in the range ?? = -1.35+0.3-0.7). The minimum mass is consistent with current estimates for the upper limit to white dwarf progenitor masses, but the maximum mass does not appear consistent with massive star populations in Local Group galaxies. Red supergiants in the Local Group have masses up to 25Msolar and the minimum mass to produce a Wolf-Rayet star in single star evolution (between solar and LMC metallicity) is similarly 25-30Msolar. The reason we have not detected any high-mass red supergiant progenitors above 17Msolar is unclear, but we estimate that it is statistically significant at 2.4?? confidence. Two simple reasons for this could be that we have systematically underestimated the progenitor masses due to dust extinction or that stars between 17-25Msolar produce other kinds of SNe which are not II-P. We discuss these possibilities and find that neither provides a satisfactory solution. We term this discrepancy the `red supergiant problem' and speculate that these stars could have core masses high enough to form black holes and SNe which are too faint to have been detected. We compare the 56Ni masses ejected in the SNe to the progenitor mass estimates and find that low-luminosity SNe with low 56Ni production are most likely to arise from explosions of low-mass progenitors near the mass threshold that can produce a core-collapse.

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  • A general thermolabile protecting group strategy for organocatalytic metal-organic frameworks

    Lun, DJ; Waterhouse, Geoffrey; Telfer, SG (2011)

    Journal article
    The University of Auckland Library

    We present a general strategy for incorporating organocatalytic moieties into metal organic frameworks (MOFs). The organocatalytic units are protected by a thermolabile protecting group during MOF synthesis and then unveiled by a simple postsynthetic heating step. The strategy is exemplified using a thermolabile tert-butoxycarbonyl (Boc) protecting group for a proline moiety, the removal of which endows the resulting cubic zinc(II) IRMOF with catalytic activity for asymmetric aldol reactions. The bulky Boc groups also prevent framework interpenetration, producing openMOFs that can admit relatively large substrates.

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  • Spectral population synthesis including massive binaries

    Eldridge, John; Stanway, ER (2009)

    Journal article
    The University of Auckland Library

    We have constructed a new code to produce synthetic spectra of stellar populations that includes massive binaries. We have tested this code against the broad-band colours of unresolved young massive stellar clusters in nearby galaxies, the equivalent widths of the Red and Blue Wolf-Rayet bumps in star-forming Sloan Digital Sky Survey galaxies and the ultraviolet and optical spectra of the star-forming regions Tol-A and B in NGC 5398. In each case, we find a good agreement between our models and observations. We find that in general binary populations are bluer and have fewer red supergiants, and thus significantly less flux in the I band and at longer wavelengths, than single star populations. Also we find that Wolf-Rayet stars occur over a wider range of ages up to 107yr in a stellar population including binaries, increasing the ultraviolet flux and Wolf-Rayet spectral features at later times. In addition, we find that nebula emission contributes significantly to these observed properties and must be considered when comparing stellar models with observations of unresolved stellar populations. We conclude that incorporation of massive stellar binaries can improve the agreement between observations and synthetic spectral synthesis codes, particularly for systems with young stellar populations.

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  • Physical and Optical Properties of Inverse Opal CeO2 Photonic Crystals.

    Waterhouse, Geoffrey; Metson, James; Idriss, H; Sun-Waterhouse, Dongxiao (2008)

    Journal article
    The University of Auckland Library

    Inverse opal ceria (CeO2) films and powders, exhibiting three-dimensional ordered macroporous (3DOM) structures and a photonic band gap (PBG) in the visible region, were successfully fabricated using the colloidal crystal template approach. Colloidal crystals templates, comprising polymethylmethacrylate (PMMA) spheres of diameter ???325 nm arranged on a face-centered cubic (fcc) lattice, were prepared by self-assembly from aqueous colloidal suspensions of PMMA spheres. After drying, the interstitial spaces in the PMMA colloidal crystals were filled with a ceria sol???gel precursor, and then the resulting structure calcined at 400 ??C to remove the polymer template. The ceria inverse opals obtained were characterized by SEM, XRD, BET, porosity, and UV???vis transmittance measurements and showed fcc ordering of macropores (diameter around 240 nm) within a CeO2 nanocrystal matrix. The CeO2 volume fraction in the inverse opals was 17???18 vol %, and its surface area was 51 m2 g-1. Both the PMMA colloidal crystals and CeO2 inverse opals behaved as 3-dimensional photonic crystals, with PBGs at 877 and 485 nm, respectively. Filling the macropores of the CeO2 inverse opal with solvent caused a redshift in the position of the PBG, with the magnitude of the shift being directly proportional to the refractive index of the solvent. Refractive index sensing with a sensitivity of n ) 0.001 or better is achievable using inverse opal CeO2 thin films. Inverse opal CeO2 powders showed improved thermal stability at 800 ??C compared to non-networked ceria nanoparticles of similar initial crystallite size and surface area, suggesting that inverse opal architectures may be useful in applications where retention of large surface area during high temperature operation is important (e.g., heterogeneous catalysis).

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  • Effect of mixture ratio, solids concentration and hydraulic retention time on the anaerobic digestion of the organic fraction of municipal solid waste

    Fongsatitkul, P; Elefsiniotis, Panagiotis; Wareham, DG (2010)

    Journal article
    The University of Auckland Library

    This paper describes how the degradation of the organic fraction of municipal solid waste (OFMSW) is affected through codigestion with varying amounts of return activated sludge (RAS). Solid waste that had its inorganic fraction selectively removed was mixed with RAS in ratios of 100% OFMSW, 50% OFMSW/50% RAS, and 25% OFMSW/75% RAS. The total solids (TS) concentration was held at 8% and three anaerobic digester systems treating the mixtures were held (for the first run) at a total hydraulic retention time (HRT) of 28 days. Increasing amounts of RAS did not however improve the mixture???s digestability, as indicated by little change and/or a drop in the main performance indices [including percentage volatile solids (VS) removal and specific gas production]. The optimum ratio in this research therefore appeared to be 100% OFMSW with an associated 85.1 ?? 0.6% VS removal and 0.72 ?? 0.01 L total gas g ???1 VS. In the second run, the effect of increasing percentage of TS (8, 12% and 15%) at a system HRT of 28 days was observed to yield no improvement in the main performance indices (i.e. percentage VS removal and specific gas production). Finally, during the third run, variations in the total system HRT were investigated at an 8% TS, again using 100% OFMSW. Of the HRTs explored (23, 28 and 33 days), the longest HRT yielded the best performance overall, particularly in terms of specific gas production (0.77 ?? 0.01 L total gas g ???1 VS).

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  • Leadership as Practice: Challenging the Competency Paradigm

    Carroll, Brigid; Levy, Lester; Richmond, D (2008)

    Journal article
    The University of Auckland Library

    Competency frameworks, models, instruments and thinking have long been ingrained and utilized in management and organizational life. Not surprisingly they have been transplanted both swiftly and seemingly easily into the leadership domain. While there certainly have been discomfort and critique from academic and practitioner sources, nothing has emerged strongly enough to date that would provide an alternative mode of framing and translating both leadership and leadership development in the different contexts that seek to make it visible. In this article, consequently, we submit leadership and its development to the `practice turn' to enable a radically different perspective from a competency orientated one. The ontology, epistemology and methodologies of practice are examined and translated to the leadership field. We argue that a focus on praxis, practitioner and practice offers both challenge and transformation to the ways that leadership is bounded and constrained by current organizational and managerial conventions.

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  • Accuracy of surface landmark identification for cannula cricothyroidotomy.

    Elliott, DS; Baker, Paul; Scott, MR; Birch, CW; Thompson, John (2010-09)

    Journal article
    The University of Auckland Library

    Cannula cricothyroidotomy is recommended for emergency transtracheal ventilation by all current airway guidelines. Success with this technique depends on the accurate and rapid identification of percutaneous anatomical landmarks. Six healthy subjects underwent neck ultrasound to delineate the borders of the cricothyroid membrane. The midline and bisecting transverse planes through the membrane were marked with an invisible ink pen which could be revealed with an ultraviolet light. Eighteen anaesthetists were then invited to mark an entry point for cricothyroid membrane puncture. Only 32 (30%) attempts by anaesthetists accurately marked the skin area over the cricothyroid membrane. Of these only 11 (10%) marked over the centre point of the membrane. Entry point accuracy was not significantly affected by subjects' weight, height, body mass index, neck circumference or cricothyroid dimensions. Consultant and registrar anaesthetists were significantly more accurate than senior house officers at correctly identifying the cricothyroid membrane. Accuracy of percutaneously identifying the cricothyroid membrane was poor. Ultrasound may assist in identifying anatomical landmarks for cricothyroidotomy.

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  • Effects of perindopril-indapamide on left ventricular diastolic function and mass in patients with type 2 diabetes: the ADVANCE Echocardiography Substudy

    Doughty, Robert; Whalley, Gillian; Gamble, Gregory; Baker, J; Chalmers, J; Cooper, M; Cruickshank, K; Dixon, P; Dunne, P; Eccleston, D; Jerums, G; Luke, R; McGrath, B; Nolan, C; Patel, A; Poulter, N; Phillips, P; Scott, R; Singh, J; Smith, R; Stanton, A; Suranyi, M; Thom, S; Woodward, M (2011-07-01)

    Journal article
    The University of Auckland Library

    Background The Action in Diabetes and Vascular Disease (ADVANCE) Study demonstrated that a fixed combination of perindopril and indapamide reduced the risk of major vascular events and mortality in patients with type 2 diabetes. This Echocardiographic Substudy was designed to determine the effects of this treatment on left ventricular diastolic function and left ventricular mass.Methods Five hundred and fifty-five patients entering ADVANCE underwent quantitative echocardiography prior to randomization and after 6 months and 4 years of treatment with perindopril-indapamide or placebo. Main end points were left ventricular diastolic function (ratio of mitral E velocity/early medial mitral annular tissue Doppler velocity, E/Em, and left atrial volume index) and left ventricular mass index.Results Overall, blood pressure was reduced in the perindopril-indapamide group compared with placebo. E/Em and left atrial volume index both increased over the 4 years. There was no effect of perindopril-indapamide on E/Em, although there was a small attenuation of the increase in left atrial volume index with active treatment. Left ventricular mass index was reduced by 2.7 g/m(2) with active treatment (95% confidence interval -5.0 to -0.1, P=0.04).Conclusion Compared with placebo, the perindopril-indapamide combination reduced blood pressure and left ventricular mass in patients with diabetes, but did not improve left ventricular diastolic function. Left ventricular diastolic function worsened in both groups over 4 years, despite blood pressure reduction and reduction in left ventricular mass. Improving left ventricular diastolic function remains a challenge in patients with diabetes. J Hypertens 29:1439-1447 (C) 2011 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.

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  • Angiotensin-converting enzyme 2 A1075G 3 polymorphisam is assocaited with survival in an acute coronary syndromes cohort.

    Palmer, BR; Jarvis, MD; Pilbrow, AP; Ellis, KL; Frampton, CM; Skelton, L; Yandle, TG; Doughty, Robert; Whalley, Gillian; Ellis, CJ; Troughton, RW; Richards, AM; Cameron, VA (2008)

    Journal article
    The University of Auckland Library

    Background Polymorphisms of the angiotensin-converting enzyme 2 (ACE2) gene, which is located on the X chromosome, have been associated with hypertension and left ventricular hypertrophy in previous studies. We tested the hypothesis that the rare allele of an ACE2 gene polymorphism was associated with risk factors for and adverse outcome after acute coronary syndrome (ACS) events. Methods Patients (n = 1,042) were recruited after admission for an ACS event and were genotyped for the A1075G polymorphism of the angiotensin-converting enzyme 2 gene. This genetic marker was tested for association with baseline measurements, echocardiographic measurements, and clinical outcome, over a median 2.19 years follow-up. As the ACE2 gene is X-linked, analyses were performed separately for males and females. Patients were predominantly of European ethnicity (90.1%). Results The A1075 allele was significantly associated with covariate-adjusted mortality in male patients (hazard ratio 1.95, 95% CI 1.10-3.46, P = .047) but not unadjusted (hazard ratio 1.14, 95% CI 0.736-1.76, P = .56). The G1075 (P < .035) allele was more frequent in patients of Maori compared to European ancestry. E/E???, an echocardiographic index of left ventricular diastolic function and filling pressure, was higher in males in the A1075 group (G allele group 10.5 [95% CI 10.0-11.0], A allele group 11.4 [95% CI 10.8-12.1], P = .024). A1075 genotype was significantly associated with male survival in the absence of (mortality: A 12.8%, n = 39; G 29.2%, n = 48; P = .037) but not in the presence of ??-blocker treatment (mortality: A 13.5% n = 273; G 8.2% n = 304, P = nonsignificant). Conclusions The A1075 allele was associated with covariate-adjusted mortality in male patients.

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  • Trophoblast deportation part I: review of the evidence demonstrating trophoblast shedding and deportation during human pregnancy.

    Askelund, Kathryn; Chamley, Lawrence (2011-10)

    Journal article
    The University of Auckland Library

    Trophoblast deportation was first described before the turn of the 20th Century by the German Scientist Schmorl and is now considered a normal physiological process during human pregnancy. Increased shedding and deportation of placental trophoblast is well documented in preeclampsia, one of the most common diseases of pregnancy. This review summarises the seminal historical and contemporary publications that have contributed to our knowledge of trophoblast deportation to the maternal lungs, their presence and quantity in the maternal circulation during normal pregnancy and during preeclampsia, and the range of morphologies deported trophoblasts display. Finally, the contentious nature of the deported multinucleated trophoblasts' current nomenclature (syncytial knots vs. sprouts) is considered.

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  • Doing 'it' differently: Relinquishing the disease and pregnancy prevention focus of sexuality education

    Allen, Louisa (2007)

    Journal article
    The University of Auckland Library

    Despite policy provision enabling sexuality education to address more than disease and pregnancy prevention, this focus continues to permeate many school programmes. This paper problematises the danger prevention emphasis in sexuality education, examines school's investment in it and asks how useful it is. The ways this kind of sexuality education may inhibit the reduction of 'negative' sexual outcomes and fail to support young people's sexual well-being is explored. Suggesting sexu- ality education might be conceptualisxed without this danger prevention emphasis necessitates an exploration of what might replace it. Foucault's work around an ethics of pleasure is drawn on as one example of how the objectives of sexuality education might be re-envisaged.

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  • A multi-proxy record of changing environments from ca. 30000 to 9000 cal. a BP: Onepoto maar palaeolake, Auckland, New Zealand

    Augustinus, Paul; D'costa, D; Deng, Y; Hagg, J; Shane, Philip (2011)

    Journal article
    The University of Auckland Library

    We present a high-resolution record of lacustrine sedimentation spanning ca. 30 000 to 9000 cal. a BP from Onepoto maar, northern North Island, New Zealand. The multi-proxy record of environmental change is constrained by tephrochronology and accelerator mass spectrometric 14C ages and provides evidence for episodes of rapid environmental change during the Last Glacial Coldest Period (LGCP) and Last Glacial???Interglacial Transition (LGIT) from northern New Zealand. The multi-proxy palaeoenvironmental record from Onepoto indicates that the LGCP was cold, dry and windy in the Auckland region, with vegetation dominated by herb and grass in a beech forest mosaic between ca. 28 500 and 18 000 cal. a BP. The LGCP was accompanied by more frequent fires and influx of clastic sediment indicating increased erosion during the LGCP, with a mid-LGCP interstadial identified between ca. 25 000 and 23 000 cal. a BP. Rapid climate amelioration at ca. 18 000 cal. a BP was accompanied by increased terrestrial biomass exemplified by the expansion of lowland podocarp forest, especially Dacrydium cupressinum. Increasing biomass production is reversed briefly by LGIT perturbations which are apparent in many of the proxies that span ca. 14 000???10 500 cal. a BP, suggesting generally increased wetness and higher in situ aquatic plant productivity with reduced terrestrial organic matter and terrigenous detrital influx. Furthermore, conditions at that time were probably warmer and frosts rare based on the increasing importance of Ascarina. The subsequent early Holocene is characterised by podocarp conifer forest and moist mild conditions. Postglacial sea-level rise breached the crater rim and deposited 36m of estuarine mud after ca. 9000 cal. a BP.

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  • A conclusive scalable model for the complete actuation response for IPMC transducers

    McDaid, Andrew; Aw, Kean; Haemmerle, Enrico; Xie, Sheng (2010-06-01)

    Journal article
    The University of Auckland Library

    Abstract This paper proposes a conclusive scalable model for the complete actuation response for ionic polymer metal composites (IPMC). This single model is proven to be able to accurately predict the free displacement/velocity and force actuation at varying displacements, with up to 3 V inputs. An accurate dynamic relationship between the force and displacement has been established which can be used to predict the complete actuation response of the IPMC transducer. The model is accurate at large displacements and can also predict the response when interacting with external mechanical systems and loads. This model equips engineers with a useful design tool which enables simple mechanical design, simulation and optimization when integrating IPMC actuators into an application. The response of the IPMC is modelled in three stages: (i) a nonlinear equivalent electrical circuit to predict the current drawn, (ii) an electromechanical coupling term and (iii) a segmented mechanical beam model which includes an electrically induced torque for the polymer. Model parameters are obtained using the dynamic time response and results are presented demonstrating the correspondence between the model and experimental results over a large operating range. This newly developed model is a large step forward, aiding in the progression of IPMCs towards wide acceptance as replacements to traditional actuators.

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  • Measurement of replication structures at the nanometer scale using super-resolution light microscopy

    Baddeley, David; Chagin, VO; Schermelleh, L; Martin, S; Pombo, A; Carlton, PM; Gahl, A; Domiang, P; Birk, U; Leonhardt, H; Cremer, C; Cardoso, C (2009)

    Journal article
    The University of Auckland Library

    DNA replication, similar to other cellular processes, occurs within dynamic macromolecular structures. Any comprehensive understanding ultimately requires quantitative data to establish and test models of genome duplication. We used two different super-resolution light microscopy techniques to directly measure and compare the size and numbers of replication foci in mammalian cells. This analysis showed that replication foci vary in size from 210nm down to 40 nm. Remarkably, spatially modulated illumination (SMI) and 3Dstructured illumination microscopy (3D-SIM) both showed an average size of 125nm that was conserved throughout S-phase and independent of the labeling method, suggesting a basic unit of genome duplication. Interestingly, the improved optical 3D resolution identified 3- to 5-fold more distinct replication foci than previously reported. These results show that optical nanoscopy techniques enable accurate measurements of cellular structures at a level previously achieved only by electron microscopy and highlight the possibility of high-throughput, multispectral 3D analyses.

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  • Optical single-channel resolution imaging of the ryanodine receptor distribution in rat cardiac myocytes

    Baddeley, David; Jayasinghe, Isuru; Lam, Chi; Rossberger, Sabrina; Cannell, Mark; Soeller, Christian (2009)

    Journal article
    The University of Auckland Library

    We have applied an optical super-resolution technique based on single-molecule localization to examine the peripheral distribution of a cardiac signaling protein, the ryanodine receptor (RyR), in rat ventricular myocytes. RyRs form clusters with a mean size of approximately 14 RyRs per cluster, which is almost an order of magnitude smaller than previously estimated. Clusters were typically not circular (as previously assumed) but elongated with an average aspect ratio of 1.9. Edge-to-edge distances between adjacent RyR clusters were often <50 nm, suggesting that peripheral RyR clusters may exhibit strong intercluster signaling. The wide variation of cluster size, which follows a near-exponential distribution, is compatible with a stochastic cluster assembly process. We suggest that calcium sparks may be the result of the concerted activation of several RyR clusters forming a functional ??????supercluster?????? whose gating is controlled by both cytosolic and sarcoplasmic reticulum luminal calcium levels.

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  • Monks and lay communities in late antique Gaul: the evidence of the Eusebius Gallicanus sermons

    Bailey, Lisa (2006)

    Journal article
    The University of Auckland Library

    The Eusebius Gallicanus sermons reveal the congruity in late antique Gaul between the models of pastoral care for monks and lay Christians. For these Gallic clergy, there was little antagonism between monastery and world. Preachers to both audiences share a common central concern with the defence of community and in this respect they differ from some of their contemporaries. The sermon collection demonstrates that the ascetic world in Gaul was far from monolithic and that pastoral care could be highly individualised and responsive to the demands of local communities.

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  • Crystal structures of F-420-dependent glucose-6-phosphate dehydrogenase FGD1 involved in the activation of the anti-tuberculosis drug candidate PA-824 reveal the basis of coenzyme and substrate binding

    Bashiri, Ghader; Squire, Christopher; Moreland, Nicole; Baker, Edward (2008)

    Journal article
    The University of Auckland Library

    The modified flavin coenzyme F420 is found in a restricted number of microorganisms. It is widely distributed in mycobacteria, however, where it is important in energy metabolism, and in Mycobacterium tuberculosis (Mtb) is implicated in redox processes related to non-replicating persistence. In Mtb, the F420- dependent glucose-6-phosphate dehydrogenase FGD1 provides reduced F420 for the in vivo activation of the nitroimidazopyran prodrug PA-824, currently being developed for anti-tuberculosis therapy against both replicating and persistent bacteria. The structure of M. tuberculosis FGD1 has been determined by x-ray crystallography both in its apo state and in complex with F420 and citrate at resolutions of 1.90 and 1.95 A?? , respectively. The structure reveals a highly specific F420 binding mode, which is shared with several other F420-dependent enzymes. Citrate occupies the substrate binding pocket adjacent to F420 and is shown to be a competitive inhibitor (IC50 43 M). Modeling of the binding of the glucose 6-phosphate (G6P) substrate identifies a positively charged phosphate binding pocket and shows that G6P, like citrate, packs against the isoalloxazine moiety of F420 and helps promote a butterfly bend conformation that facilitates F420 reduction and catalysis.

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  • Rethinking the admission criteria to nursing school

    Boaz, S; Wang, G; Zhao, Y; Baker, Heather (2011)

    Journal article
    The University of Auckland Library

    The main objective of this study was to identify the best predictors for student achievements (Undergraduate Grade Point Average (UGPA)) in their first year in an undergraduate nursing programme. Data were acquired from the Tracking Project database which is held by the Faculty of Medical and Health Sciences at the University of Auckland. The data (n = 134) included information on student demographics, final year secondary school achievements (National Certificate of Educational Achievement Grade Point Average (NCEAGPA) & NCEA Credits), university admission ranking scores, and achievements in first year in the undergraduate nursing programme (UGPA). Linear regression models were used to identify the best predictors for first year students' UGPA in the nursing programme. The regression models suggest that the best predictor for the first year GPA is the NCEAGPA (beta = .488; R2(for the entire model) = .53), followed by the admission ranking scores (beta = .308; R2 = .40). Based on these findings, it is suggested that a Dual Admission Model (DAM) be utilised whereby students could be admitted either by the current university admission criteria or by an alternative model, which is purely based on the predictability of achievement within the nursing programme. Application of the DAM to other institutions/countries was discussed.

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  • The crystal structure of staphylococcal superantigen-like protein 11 (SSL11) in complex with sialyl Lewis X reveals the mechanism for cell binding and immune inhibition.

    Chung, MC; Wines, BD; Baker, Heather; Langley, Ries; Baker, Edward; Fraser, John (2007)

    Journal article
    The University of Auckland Library

    Staphylococcus aureus is a major pathogen that produces a family of 14 staphylococcal superantigen-like (SSL) proteins, which are structurally similar to superantigens but do not stimulate T cells. SSL11 is one member of the family that is found in all staphylococcal strains. Recombinant SSL11 bound to granulocytes and monocytes through a sialic aciddependent mechanism and was rapidly internalized. SSL11 also bound to sialic acid-containing glycoproteins, such as the Fc receptor for IgA (FcaRI) and P-selectin glycoprotein ligand-1 (PSGL-1), and inhibited neutrophil attachment to a P-selectin-coated surface. Biosensor analysis of two SSL11 alleles binding to sialyl Lewis X [sLex ??? Neu5Aca2-3Galb1- 4(Fuc1-3)GlcNAc] coupled to bovine serum albumin gave dissociation constants of 0.7 and 7 mm respectively. Binding of SSL11 to a glycan array revealed specificity for glycans containing the trisaccharide sialyllactosamine (sLacNac ??? Neu5Aca2- 3Galb1-4GlcNAc). A 1.6 ?? resolution crystal structure of SSL11 complexed with sLex revealed a discrete binding site in the C-terminal b-grasp domain, with predominant interactions with the sialic acid and galactose residues. A single amino acid mutation in the carbohydrate binding site abolished all SSL11 binding. Thus, SSL11 is a staphylococcal protein that targets myeloid cells by binding sialyllactosaminecontaining glycoproteins.

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  • Crystal structures of the Staphylococcal toxin SSL5 complex with sialyl-Lewis X revel conserved binding site that shares common features with viral and bacterial sialic acid-binding proteins.

    Baker, Heather; Basu, I; Chung, MC; Caradoc-Davies, TT; Fraser, John; Baker, Edward (2007)

    Journal article
    The University of Auckland Library

    Staphylococcus aureus is a significant human pathogen. Among its large repertoire of secreted toxins is a group of staphylococcal superantigen-like proteins (SSLs). These are homologous to superantigens but do not have the same activity. SSL5 is shown here to bind to human granulocytes and to the cell surface receptors for human IgA (Fc??RI) and P-selectin [P-selectin glycoprotein ligand-1 (PSGL-1)] in a sialic acid (Sia)-dependent manner. Cocrystallization of SSL5 with the tetrasaccharide sialyl Lewis X (sLeX), a key determinant of PSGL-1 binding to P-selectin, led to crystal structures of the SSL5???sLeX complex at resolutions of 1.65 and 2.75 ?? for crystals at two pH values. In both structures, sLeX bound to a specific site on the surface of the C-terminal domain of SSL5 in a conformation identical with that bound by P-selectin. Conservation of the key carbohydrate binding residues indicates that this ability to bind human glycans is shared by a substantial subgroup of the SSLs, including SSL2, SSL3, SSL4, SSL5, SSL6, and SSL11. This indicates that the ability to target human glycans is an important property of this group of toxins. Structural comparisons also showed that the Sia binding site in SSL5 contains a substructure that is shared by other Sia binding proteins from bacteria as well as viruses and represents a common binding motif.

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