1,451 research outputs found
A scalar invariant and the local geometry of a class of static spacetimes
The scalar invariant, I, constructed from the "square" of the first covariant
derivative of the curvature tensor is used to probe the local geometry of
static spacetimes which are also Einstein spaces. We obtain an explicit form of
this invariant, exploiting the local warp-product structure of a 4-dimensional
static spacetime, , where is
the Riemannian hypersurface orthogonal to a timelike Killing vector field with
norm given by a positive function, on . For a static
spacetime which is an Einstein space, it is shown that the locally measurable
scalar, I, contains a term which vanishes if and only if is
conformally flat; also, the vanishing of this term implies (a)
is locally foliated by level surfaces of , , which are totally
umbilic spaces of constant curvature, and (b) is locally a
warp-product space. Futhermore, if is conformally flat it
follows that every non-trivial static solution of the vacuum Einstein equation
with a cosmological constant, is either Nariai-type or Kottler-type - the
classes of spacetimes relevant to quantum aspects of gravity.Comment: LaTeX, 13 pages, JHEP3.cls; The paper is completely rewritten with a
new title and introduction as well as additional results and reference
Comparison of a New bioprosthetic Mitral Valve to Other Commercially Available Devices Under Controlled Conditions in a Porcine Mode
BACKGROUND/AIM: To evaluate three mitral bioprostheses (of comparable measured internal diameters) under controlled, stable, hemodynamic and surgical conditions by bench, echocardiographic, computerized tomography and autopsy comparisons pre‐ and postvalve implantation. METHODS: Fifteen similar‐sized Yorkshire pigs underwent preprocedural computerized tomography anatomic screening. Of these, 12 had consistent anatomic features and underwent implantation of a mitral bioprosthesis via thoracotomy on cardiopulmonary bypass (CPB). Four valves from each of three manufacturers were implanted in randomized fashion: 27‐mm Epic, 27‐mm Mosaic, and 25‐mm Mitris bioprostheses. After CPB, epicardial echocardiographic studies were performed to assess hemodynamic function and define any paravalvular leaks, followed by postoperative gated contrast computerized tomography. After euthanasia, animals underwent necropsy for anatomic evaluation. RESULTS: All 12 animals had successful valve implantation with no study deaths. Postoperative echocardiographic trans‐valve gradients varied among bioprosthesis manufacturers. The 25‐mm Mitris (5.1 ± 2.7)/(2.6 ± 1.3 torr) had the lowest peak/mean gradient and the 27‐mm Epic bioprosthesis had the highest (9.2 ± 3.7)/(4.6 ± 1.9 torr). Surgical valve opening area (SOA) varied with the 25‐mm Mitris having the largest SOA (2.4 ± 0.15 cm(2)) followed by the 27‐mm Mosaic (2.04 ± 0.23 cm(2)) and the 27‐mm Epic (1.8 ± 0.27 cm(2)) valve. Bench device orthogonal internal diameter measurements did not match manufacturer device size labeling: 25‐mm Mitris (23 × 23 mm), 27‐mm Mosaic (23 × 22 mm), 27‐mm Epic (21 × 21 mm). CONCLUSIONS: Current advertisement/packaging of commercial surgical mitral valves is not uniform. This study demonstrates marked variations in hemodynamics, valve opening area and anatomic dimensions between similar sized mitral bioprostheses. These data suggest a critical need for standardization and close scientific evaluation of surgical mitral bioprostheses to ensure optimal clinical outcomes
The determination of the electron-phonon interaction from tunneling data in the two-band superconductor MgB2
We calculate the tunneling density of states (DOS) of MgB2 for different
tunneling directions, by directly solving the real-axis, two-band Eliashberg
equations (EE). Then we show that the numeric inversion of the standard
single-band EE, if applied to the DOS of the two-band superconductor MgB2, may
lead to wrong estimates of the strength of certain phonon branches (e.g. the
E_2g) in the extracted electron-phonon spectral function alpha^(2)F(omega). The
fine structures produced by the two-band interaction turn out to be clearly
observable only for tunneling along the ab planes in high-quality single
crystals. The results are compared to recent experimental data.Comment: 2 pages, 2 figures, proceedings of M2S-HTSC-VII conference, Rio de
Janeiro (May 2003
Risk factors associated with exposure to bovine respiratory disease pathogens during the peri-weaning period in dairy bull calves
peer-reviewedBackground
Bovine respiratory disease (BRD) remains among the leading causes of death of cattle internationally. The objective of this study was to identify risk factors associated with exposure to BRD pathogens during the peri-weaning period (day (d)-14 to d 14 relative to weaning at 0) in dairy bull calves using serological responses to these pathogens as surrogate markers of exposure.
Clinically normal Holstein-Friesian and Jersey breed bull calves (n = 72) were group housed in 4 pens using a factorial design with calves of different breeds and planes of nutrition in each pen. Intrinsic, management and clinical data were collected during the pre-weaning (d − 56 to d − 14) period. Calves were gradually weaned over 14 days (d − 14 to d 0). Serological analysis for antibodies against key BRD pathogens (BRSV, BPI3V, BHV-1, BHV-4, BCoV, BVDV and H. somni) was undertaken at d − 14 and d 14. Linear regression models (for BVDV, BPI3V, BHV-1, BHV-4, BCoV and H. somni) and a single mixed effect random variable model (for BRSV) were used to identify risk factors for changes in antibody levels to these pathogens.
Results
BRSV was the only pathogen which demonstrated clustering by pen. Jersey calves experienced significantly lower changes in BVDV S/P than Holstein-Friesian calves. Animals with a high maximum respiratory score (≥8) recorded significant increases in H. somni S/P during the peri-weaning period when compared to those with respiratory scores of ≤3.
Haptoglobin levels of between 1.32 and 1.60 mg/ml at d − 14 were significantly associated with decreases in BHV-1 S/N during the peri-weaning period. Higher BVDV S/P ratios at d − 14 were significantly correlated with increased changes in serological responses to BHV-4 over the peri-weaning period.
Conclusions
Haptoglobin may have potential as a predictor of exposure to BHV-1. BRSV would appear to play a more significant role at the ‘group’ rather than ‘individual animal’ level. The significant associations between the pre-weaning levels of antibodies to certain BRD pathogens and changes in the levels of antibodies to the various pathogens during the peri-weaning period may reflect a cohort of possibly genetically linked ‘better responders’ among the study population
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Use of a fluorinated probe to quantitatively monitor amino acid binding preferences of ruthenium(ii) arene complexes.
In order to address outstanding questions about ruthenium complexes in complex biological solutions, 19F NMR spectroscopy was used to follow the binding preferences between fluorinated RuII(η6-arene)(bipyridine) complexes and protected amino acids and glutathione. Reporting what ruthenium compounds bind to in complex environments has so far been restricted to relatively qualitative methods, such as mass spectrometry and X-ray spectroscopic methods; however, quantitative information on the species present in the solution phase cannot be inferred from these techniques. Furthermore, using 1H NMR, in water, to distinguish and monitor a number of different complex RuII(η6-arene) adducts forming is challenging. Incorporating an NMR active heteroatom into ruthenium organometallic complexes provides a quantitative, diagnostic 'fingerprint' to track solution-phase behaviour and allow for unambiguous assignment of any given adduct. The resulting 19F NMR spectra show for the first time the varied, dynamic behaviour of organoruthenium compounds when exposed to simple biomolecules in complex mixtures. The rates of formation of the different observed species are dramatically influenced by the electronic properties at the metal, even in a closely related series of complexes in which only the electron-donating properties of the arene ligand are altered. Preference for cysteine binding is absolute: the first quantitative solution-phase evidence of such behaviour
Cross-shift changes in pulmonary function and occupational exposure to particulate matter among e-waste workers in Ghana
IntroductionLittle is known on the association between cross-shift changes in pulmonary function and personal inhalation exposure to particulate matter (PM) among informal electronic-waste (e-waste) recovery workers who have substantial occupational exposure to airborne pollutants from burning e-waste.MethodsUsing a cross-shift design, pre- and post-shift pulmonary function assessments and accompanying personal inhalation exposure to PM (sizes <1, <2.5 μm, and the coarse fraction, 2.5–10 μm in aerodynamic diameter) were measured among e-waste workers (n = 142) at the Agbogbloshie e-waste site and a comparison population (n = 65) in Accra, Ghana during 2017 and 2018. Linear mixed models estimated associations between percent changes in pulmonary function and personal PM.ResultsDeclines in forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) per hour were not significantly associated with increases in PM (all sizes) among either study population, despite breathing zone concentrations of PM (all sizes) that exceeded health-based guidelines in both populations. E-waste workers who worked “yesterday” did, however, have larger cross-shift declines in FVC [−2.4% (95%CI: −4.04%, −0.81%)] in comparison to those who did not work “yesterday,” suggesting a possible role of cumulative exposure.DiscussionOverall, short-term respiratory-related health effects related to PM exposure among e-waste workers were not seen in this sample. Selection bias due to the “healthy worker” effect, short shift duration, and inability to capture a true “pre-shift” pulmonary function test among workers who live at the worksite may explain results and suggest the need to adapt cross-shift studies for informal settings
Export of malaria proteins requires co-translational processing of the PEXEL motif independent of phosphatidylinositol-3-phosphate binding
Acknowledgements We thank the Red Cross blood bank in Melbourne for human erythrocytes. We thank Svenja Gunther for expression of GBP130 66–196 proteins; Michelle Gazdik and Chris Burns for help in preparing lipids; Lachlan Whitehead (Centre for Dynamic Imaging, Walter and Eliza Hall Institute) for assistance with quantification of export; and David Bocher for help with generation of STEVOR constructs. This work was supported by the National Health and Medical Research Council of Australia (grants 637406, 1010326, 1049811 and 1057960), a Ramaciotti Foundation Establishment Grant (3197/2010), a Victorian State Government Operational Infrastructure Support and Australian Government NHMRC IRIISS, and the Canadian Institutes for Health Research (MOP#130359). J.A.B is an Australian Research Council QEII Fellow, SF was supported by the Research Training Group GRK1459 of the German Research Foundation, and AFC is a Howard Hughes International Scholar.Peer reviewedPublisher PD
An upper limit on the electron-neutrino flux from the HiRes detector
Air-fluorescence detectors such as the High Resolution Fly's Eye (HiRes)
detector are very sensitive to upward-going, Earth-skimming ultrahigh energy
electron-neutrino-induced showers. This is due to the relatively large
interaction cross sections of these high-energy neutrinos and to the
Landau-Pomeranchuk-Migdal (LPM) effect. The LPM effect causes a significant
decrease in the cross sections for bremsstrahlung and pair production, allowing
charged-current electron-neutrino-induced showers occurring deep in the Earth's
crust to be detectable as they exit the Earth into the atmosphere. A search for
upward-going neutrino-induced showers in the HiRes-II monocular dataset has
yielded a null result. From an LPM calculation of the energy spectrum of
charged particles as a function of primary energy and depth for
electron-induced showers in rock, we calculate the shape of the resulting
profile of these showers in air. We describe a full detector Monte Carlo
simulation to determine the detector response to upward-going
electron-neutrino-induced cascades and present an upper limit on the flux of
electron-neutrinos.Comment: 13 pages, 3 figures. submitted to Astrophysical Journa
Search for Correlations between HiRes Stereo Events and Active Galactic Nuclei
We have searched for correlations between the pointing directions of
ultrahigh energy cosmic rays observed by the High Resolution Fly's Eye
experiment and Active Galactic Nuclei (AGN) visible from its northern
hemisphere location. No correlations, other than random correlations, have been
found. We report our results using search parameters prescribed by the Pierre
Auger collaboration. Using these parameters, the Auger collaboration concludes
that a positive correlation exists for sources visible to their southern
hemisphere location. We also describe results using two methods for determining
the chance probability of correlations: one in which a hypothesis is formed
from scanning one half of the data and tested on the second half, and another
which involves a scan over the entire data set. The most significant
correlation found occurred with a chance probability of 24%.Comment: 13 pages, 1 table, 5 figure
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