322 research outputs found
Effect of Nb and C Additives on the Microstructures and Magnetic Properties of Rapidly Solidified Sm-Co Alloys
Highly coercive Sm-Co-based permanent magnets have been achieved through simple modification of binary Sm12Co88 alloys with Nb, C or combined Nb and C at concentrations ranging from 1 to 10 atomic percent processed via rapid solidification. Melt spinning at 40 m/s resulted in the formation of the metastable TbCu7-type structure in all alloys. While the unalloyed, as-solidified Sm12Co88 alloy displayed a coercivity of 0.5 kOe, alloying additions resulted in a systematic and profound increase in coercivity. Nb additions resulted in as-solidified coercivities up to 9 kOe, C additions up to 37 kOe, and combined NbC additons 8 kOe. The Nb and NbC additions led to a reduction in grain size, while C additions altered the morphology, producing a grain-boundary phase that effectively isolated the magnetic grains from one another. The magnetization processes for Nb- and NbC-modified Sm–Co were determined to be nucleation-controlled, while a transition to pinning-controlled magnetization was observed for the C-modified alloy
COA6 facilitates cytochrome c oxidase biogenesis as thiol-reductase for copper metallochaperones in mitochondria.
The mitochondrial cytochrome c oxidase, the terminal enzyme of the respiratory chain, contains heme and copper centers for electron transfer. The conserved COX2 subunit contains the CuA site, a binuclear copper center. The copper chaperones SCO1, SCO2, and COA6 are required for CuA center formation. Loss of function of these chaperones and the concomitant cytochrome c oxidase deficiency cause severe human disorders. Here we analyzed the molecular function of COA6 and the consequences of COA6 deficiency for mitochondria. Our analyses show that loss of COA6 causes combined complex I and complex IV deficiency and impacts membrane potential driven protein transport across the inner membrane. We demonstrate that COA6 acts as a thiol-reductase to reduce disulphide bridges of critical cysteine residues in SCO1 and SCO2. Cysteines within the CX3CXNH domain of SCO2 mediate its interaction with COA6 but are dispensable for SCO2-SCO1 interaction. Our analyses define COA6 as thiol-reductase, which is essential for CuA biogenesis
Study of Kalman, Extended Kalman and Unscented Kalman Filter (An Approach to Design a Power System)
The accurate measurement of harmonics level is essential for designing harmonic filters,monitoring the stress to which the power system devices are subjected due to harmonics and specifying digital filtering techniques for phasor measurements for relaying. This project presents an integrated approach to design an optimal estimator of harmonic components of a power network in the presence of frequency variations. This has led to the study of Kalman,
Extended Kalman and Unscented Kalman filter characteristics and a subsequent implementation of the study to design the optimal filter. We have employed the Extended Kalman filter and Unscented Kalman filter algorithms to estimate the power system voltage magnitude in the presence of random noise and distortions again taking into account the measurement noise. Kalman filter being an optimal estimator track the signal corrupted with noise and bearing harmonic distortion quite accurately. Adaptive tracking of harmonic components of a power system can easily be done using these algorithm. The proposed approaches are tested for only
static signals. For a test signal both EKF and UKF algorithms are used and the results are compared
Statistical Isotropy violation of the CMB brightness fluctuations
Certain anomalies at large angular scales in the cosmic microwave background
measured by WMAP have been suggested as possible evidence of breakdown of
statistical isotropy(SI). Most CMB photons free-stream to the present from the
surface of last scattering. It is thus reasonable to expect statistical
isotropy violation in the CMB photon distribution observed now to have
originated from SI violation in the baryon-photon fluid at last scattering, in
addition to anisotropy of the primordial power spectrum studied earlier in
literature.
We consider the generalized anisotropic brightness distribution fluctuations,
(at conformal time ) in contrast to the
SI case where it is simply a function of and . The brightness fluctuations expanded in Bipolar Spherical Harmonic
(BipoSH) series, can then be written as where terms encode deviations from statistical isotropy. We
study the evolution of from
non-zero terms at last
scattering. Similar to the SI case, power at small spherical harmonic (SH)
multipoles of at the last
scattering, is transferred to at
larger SH multipoles. The structural similarity is more apparent in the
asymptotic expression for large values of the final SH multipoles. This
formalism allows an elegant identification of any SI violation observed today
to a possible origin in the SI violation present in the baryon-photon fluid
(eg., due to the presence of significant magnetic field).Comment: 14 pages, 4 figures, added illustrative example of SI violation in
baryon-photon fluid, matches version accepted for publication in Phys. Rev.
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Climate or land use? - Attribution of changes in river flooding in the Sahel zone
Comparing impacts of climate change on streamflow in four large African river basins
This study aims to compare impacts of climate change on streamflow in four large representative African river basins: the Niger, the Upper Blue Nile, the Oubangui and the Limpopo. We set up the eco-hydrological model SWIM (Soil and Water Integrated Model) for all four basins individually. The validation of the models for four basins shows results from adequate to very good, depending on the quality and availability of input and calibration data. For the climate impact assessment, we drive the model with outputs of five bias corrected Earth system models of Coupled Model Intercomparison Project Phase 5 (CMIP5) for the representative concentration pathways (RCPs) 2.6 and 8.5. This climate input is put into the context of climate trends of the whole African continent and compared to a CMIP5 ensemble of 19 models in order to test their representativeness. Subsequently, we compare the trends in mean discharges, seasonality and hydrological extremes in the 21st century. The uncertainty of results for all basins is high. Still, climate change impact is clearly visible for mean discharges but also for extremes in high and low flows. The uncertainty of the projections is the lowest in the Upper Blue Nile, where an increase in streamflow is most likely. In the Niger and the Limpopo basins, the magnitude of trends in both directions is high and has a wide range of uncertainty. In the Oubangui, impacts are the least significant. Our results confirm partly the findings of previous continental impact analyses for Africa. However, contradictory to these studies we find a tendency for increased streamflows in three of the four basins (not for the Oubangui). Guided by these results, we argue for attention to the possible risks of increasing high flows in the face of the dominant water scarcity in Africa. In conclusion, the study shows that impact intercomparisons have added value to the adaptation discussion and may be used for setting up adaptation plans in the context of a holistic approach
GW190814: Gravitational Waves from the Coalescence of a 23 Solar Mass Black Hole with a 2.6 Solar Mass Compact Object
We report the observation of a compact binary coalescence involving a 22.2 - 24.3 M⊙ black hole and a compact object with a mass of 2.50 - 2.67 M⊙ (all measurements quoted at the 90% credible level). The gravitational-wave signal, GW190814, was observed during LIGO\u27s and Virgo\u27s third observing run on August 14, 2019 at 21:10:39 UTC and has a signal-to-noise ratio of 25 in the three-detector network. The source was localized to 18.5 deg2 at a distance of 241+41−45 Mpc; no electromagnetic counterpart has been confirmed to date. The source has the most unequal mass ratio yet measured with gravitational waves, 0.112+0.008−0.009, and its secondary component is either the lightest black hole or the heaviest neutron star ever discovered in a double compact-object system. The dimensionless spin of the primary black hole is tightly constrained to ≤0.07. Tests of general relativity reveal no measurable deviations from the theory, and its prediction of higher-multipole emission is confirmed at high confidence. We estimate a merger rate density of 1-23 Gpc−3 yr−1 for the new class of binary coalescence sources that GW190814 represents. Astrophysical models predict that binaries with mass ratios similar to this event can form through several channels, but are unlikely to have formed in globular clusters. However, the combination of mass ratio, component masses, and the inferred merger rate for this event challenges all current models for the formation and mass distribution of compact-object binaries
Influence of heavy modes on perturbations in multiple field inflation
We investigate linear cosmological perturbations in multiple field
inflationary models where some of the directions are light while others are
heavy (with respect to the Hubble parameter). By integrating out the massive
degrees of freedom, we determine the multi-dimensional effective theory for the
light degrees of freedom and give explicitly the propagation matrix that
replaces the effective sound speed of the one-dimensional case. We then examine
in detail the consequences of a sudden turn along the inflationary trajectory,
in particular the possible breakdown of the low energy effective theory in case
the heavy modes are excited. Resorting to a new basis in field space, instead
of the usual adiabatic/entropic basis, we study the evolution of the
perturbations during the turn. In particular, we compute the power spectrum and
compare with the result obtained from the low energy effective theory.Comment: 24 pages, 13 figures; v2 substantial changes in sec.V; v3 matching
the published version on JCA
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