1,303 research outputs found
Small-signal modeling of digitally controlled grid-connected inverters with <em>LCL</em> filters
Comparison of Image Registration Based Measures of Regional Lung Ventilation from Dynamic Spiral CT with Xe-CT
Purpose: Regional lung volume change as a function of lung inflation serves
as an index of parenchymal and airway status as well as an index of regional
ventilation and can be used to detect pathologic changes over time. In this
article, we propose a new regional measure of lung mechanics --- the specific
air volume change by corrected Jacobian.
Methods: 4DCT and Xe-CT data sets from four adult sheep are used in this
study. Nonlinear, 3D image registration is applied to register an image
acquired near end inspiration to an image acquired near end expiration.
Approximately 200 annotated anatomical points are used as landmarks to evaluate
registration accuracy. Three different registration-based measures of regional
lung mechanics are derived and compared: the specific air volume change
calculated from the Jacobian (SAJ); the specific air volume change calculated
by the corrected Jacobian (SACJ); and the specific air volume change by
intensity change (SAI).
Results: After registration, the mean registration error is on the order of 1
mm. For cubical ROIs in cubes with size 20 mm 20 mm 20 mm,
the SAJ and SACJ measures show significantly higher correlation (linear
regression, average and ) with the Xe-CT based measure of
specific ventilation (sV) than the SAI measure. For ROIs in slabs along the
ventral-dorsal vertical direction with size of 150 mm 8 mm 40
mm, the SAJ, SACJ, and SAI all show high correlation (linear regression,
average , and ) with the Xe-CT based sV without
significant differences when comparing between the three methods.
Conclusion: Given a deformation field by an image registration algorithm,
significant differences between the SAJ, SACJ, and SAI measures were found at a
regional level compared to the Xe-CT sV in four sheep that were studied
Techno-economic assessment and sustainability impact of hybrid energy systems in Gilgit-Baltistan, Pakistan
Pairing fluctuations and pseudogaps in the attractive Hubbard model
The two-dimensional attractive Hubbard model is studied in the weak to
intermediate coupling regime by employing a non-perturbative approach. It is
first shown that this approach is in quantitative agreement with Monte Carlo
calculations for both single-particle and two-particle quantities. Both the
density of states and the single-particle spectral weight show a pseudogap at
the Fermi energy below some characteristic temperature T*, also in good
agreement with quantum Monte Carlo calculations. The pseudogap is caused by
critical pairing fluctuations in the low-temperature renormalized classical
regime of the two-dimensional system. With increasing temperature
the spectral weight fills in the pseudogap instead of closing it and the
pseudogap appears earlier in the density of states than in the spectral
function. Small temperature changes around T* can modify the spectral weight
over frequency scales much larger than temperature. Several qualitative results
for the s-wave case should remain true for d-wave superconductors.Comment: 20 pages, 12 figure
TESS Discovery of a Transiting Super-Earth in the Mensae System
We report the detection of a transiting planet around Mensae (HD
39091), using data from the Transiting Exoplanet Survey Satellite (TESS). The
solar-type host star is unusually bright (V=5.7) and was already known to host
a Jovian planet on a highly eccentric, 5.7-year orbit. The newly discovered
planet has a size of and an orbital period of 6.27
days. Radial-velocity data from the HARPS and AAT/UCLES archives also displays
a 6.27-day periodicity, confirming the existence of the planet and leading to a
mass determination of . The star's proximity and
brightness will facilitate further investigations, such as atmospheric
spectroscopy, asteroseismology, the Rossiter--McLaughlin effect, astrometry,
and direct imaging.Comment: Accepted for publication ApJ Letters. This letter makes use of the
TESS Alert data, which is currently in a beta test phase. The discovery light
curve is included in a table inside the arxiv submissio
Genomic epidemiology of Mycobacterium bovis infection in sympatric badger and cattle populations in Northern Ireland
Bovine tuberculosis (bTB) is a costly, epidemiologically complex, multi-host, endemic disease. Lack of understanding of transmission dynamics may undermine eradication efforts. Pathogen whole-genome sequencing improves epidemiological inferences, providing a means to determine the relative importance of inter- and intra-species host transmission for disease persistence. We sequenced an exceptional data set of 619 Mycobacterium bovis isolates from badgers and cattle in a 100âkm2 bTB 'hotspot' in Northern Ireland. Historical molecular subtyping data permitted the targeting of an endemic pathogen lineage, whose long-term persistence provided a unique opportunity to study disease transmission dynamics in unparalleled detail. Additionally, to assess whether badger population genetic structure was associated with the spatial distribution of pathogen genetic diversity, we microsatellite genotyped hair samples from 769 badgers trapped in this area. Birth death models and TransPhylo analyses indicated that cattle were likely driving the local epidemic, with transmission from cattle to badgers being more common than badger to cattle. Furthermore, the presence of significant badger population genetic structure in the landscape was not associated with the spatial distribution of M. bovis genetic diversity, suggesting that badger-to-badger transmission is not playing a major role in transmission dynamics. Our data were consistent with badgers playing a smaller role in transmission of M. bovis infection in this study site, compared to cattle. We hypothesize, however, that this minor role may still be important for persistence. Comparison to other areas suggests that M. bovis transmission dynamics are likely to be context dependent, with the role of wildlife being difficult to generalize.ISSN:2057-585
Squeezed by a Habitat Split: Warm Ocean Conditions and Oldâforest Loss Interact to Reduce Longâterm Occupancy of a Threatened Seabird
Theory predicts that species requiring multiple habitat types simultaneously should have heightened sensitivity to anthropogenic pressures, yet tests of this prediction are especially rare. We tested whether breeding site occupancy of the threatened marbled murrelet (Brachyramphus marmoratus) was driven by the synergistic effects of nesting habitat loss in forests, and changing ocean condi- tions. We paired 70,700 murrelet surveys at 19,837 sites across 20 years from the Oregon Coast Range with annual data on the extent of old forest and biophysical ocean conditions. Dynamic occupancy models indicated that local murrelet col- onization rates were strongly reduced during warm ocean conditions with low prey availability. Landscapes that contained more old forest and were closer to the ocean showed reduced rates of local extinction. Given predictions of accel- erated ocean warming and increased global timber demand, our results suggest murrelets may continue to be imperiled by deterioration of the two habitats upon which they depend
Toward a Coordinated Understanding of Hydro-Biogeochemical Root Functions in Tropical Forests for Application in Vegetation Models
Tropical forest root characteristics and resource acquisition strategies are underrepresented in vegetation and global models, hampering the prediction of forestâclimate feedbacks for these carbon-rich ecosystems. Lowland tropical forests often have globally unique combinations of high taxonomic and functional biodiversity, rainfall seasonality, and strongly weathered infertile soils, giving rise to distinct patterns in root traits and functions compared with higher latitude ecosystems. We provide a roadmap for integrating recent advances in our understanding of tropical forest belowground function into vegetation models, focusing on water and nutrient acquisition. We offer comparisons of recent advances in empirical and model understanding of root characteristics that represent important functional processes in tropical forests. We focus on: (1) fine-root strategies for soil resource exploration, (2) coupling and trade-offs in fine-root water vs nutrient acquisition, and (3) abovegroundâbelowground linkages in plant resource acquisition and use. We suggest avenues for representing these extremely diverse plant communities in computationally manageable and ecologically meaningful groups in models for linked abovegroundâbelowground hydro-nutrient functions. Tropical forests are undergoing warming, shifting rainfall regimes, and exacerbation of soil nutrient scarcity caused by elevated atmospheric CO2. The accurate model representation of tropical forest functions is crucial for understanding the interactions of this biome with the climate
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