1,023 research outputs found
Coherence of terrestrial vertebrate species richness with external drivers across scales and taxonomic groups
Aim: Understanding connections between environment and biodiversity is crucial for conservation, identifying causes of ecosystem stress, and predicting population responses to changing environments. Explaining biodiversity requires an under-standing of how species richness and environment covary across scales. Here, we identify scales and locations at which biodiversity is generated and correlates with environment.Location: Full latitudinal range per continent.Time Period: Present day.Major Taxa Studied: Terrestrial vertebrates: all mammals, carnivorans, bats, song-birds, hummingbirds, amphibians.Methods: We describe the use of wavelet power spectra, cross- power and coherence for identifying scale-dependent trends across Earth's surface. Spectra reveal scale- and location-dependent coherence between species richness and topography (E), mean annual precipitation (Pn), temperature (Tm) and annual temperature range (ΔT).Results: >97% of species richness of taxa studied is generated at large scales, that is, wavelengths ≳103 km, with 30%–69% generated at scales ≳104 km. At these scales, richness tends to be highly coherent and anti-correlated with E and ΔT, and positively correlated with Pn and Tm. Coherence between carnivoran richness and ΔT is low across scales, implying insensitivity to seasonal temperature variations. Conversely, amphibian richness is strongly anti-correlated with ΔT at large scales. At scales ≲103 km, examined taxa, except carnivorans, show highest richness within the trop-ics. Terrestrial plateaux exhibit high coherence between carnivorans and E at scales ∼103 km, consistent with contribution of large-scale tectonic processes to biodiver-sity. Results are similar across different continents and for global latitudinal averages. Spectral admittance permits derivation of rules-of- thumb relating long-wavelength environmental and species richness trends.Main Conclusions: Sensitivities of mammal, bird and amphibian populations to envi-ronment are highly scale dependent. At large scales, carnivoran richness is largely in-dependent of temperature and precipitation, whereas amphibian richness correlates strongly with precipitation and temperature, and anti-correlates with temperature range. These results pave the way for spectral- based calibration of models that pre-dict biodiversity response to climate change scenarios
Non-intrusive reduced order modeling of natural convection in porous media using convolutional autoencoders: comparison with linear subspace techniques
Natural convection in porous media is a highly nonlinear multiphysical
problem relevant to many engineering applications (e.g., the process of
sequestration). Here, we present a non-intrusive reduced order
model of natural convection in porous media employing deep convolutional
autoencoders for the compression and reconstruction and either radial basis
function (RBF) interpolation or artificial neural networks (ANNs) for mapping
parameters of partial differential equations (PDEs) on the corresponding
nonlinear manifolds. To benchmark our approach, we also describe linear
compression and reconstruction processes relying on proper orthogonal
decomposition (POD) and ANNs. We present comprehensive comparisons among
different models through three benchmark problems. The reduced order models,
linear and nonlinear approaches, are much faster than the finite element model,
obtaining a maximum speed-up of because our framework is not
bound by the Courant-Friedrichs-Lewy condition; hence, it could deliver
quantities of interest at any given time contrary to the finite element model.
Our model's accuracy still lies within a mean squared error of 0.07 (two-order
of magnitude lower than the maximum value of the finite element results) in the
worst-case scenario. We illustrate that, in specific settings, the nonlinear
approach outperforms its linear counterpart and vice versa. We hypothesize that
a visual comparison between principal component analysis (PCA) or t-Distributed
Stochastic Neighbor Embedding (t-SNE) could indicate which method will perform
better prior to employing any specific compression strategy
Multiplexed dispersive readout of superconducting phase qubits
We introduce a frequency-multiplexed readout scheme for superconducting phase
qubits. Using a quantum circuit with four phase qubits, we couple each qubit to
a separate lumped-element superconducting readout resonator, with the readout
resonators connected in parallel to a single measurement line. The readout
resonators and control electronics are designed so that all four qubits can be
read out simultaneously using frequency multiplexing on the one measurement
line. This technology provides a highly efficient and compact means for reading
out multiple qubits, a significant advantage for scaling up to larger numbers
of qubits.Comment: 4 pages, 4 figure
Electron affinity of Li: A state-selective measurement
We have investigated the threshold of photodetachment of Li^- leading to the
formation of the residual Li atom in the state. The excited residual
atom was selectively photoionized via an intermediate Rydberg state and the
resulting Li^+ ion was detected. A collinear laser-ion beam geometry enabled
both high resolution and sensitivity to be attained. We have demonstrated the
potential of this state selective photodetachment spectroscopic method by
improving the accuracy of Li electron affinity measurements an order of
magnitude. From a fit to the Wigner law in the threshold region, we obtained a
Li electron affinity of 0.618 049(20) eV.Comment: 5 pages,6 figures,22 reference
Planar Superconducting Resonators with Internal Quality Factors above One Million
We describe the fabrication and measurement of microwave coplanar waveguide
resonators with internal quality factors above 10 million at high microwave
powers and over 1 million at low powers, with the best low power results
approaching 2 million, corresponding to ~1 photon in the resonator. These
quality factors are achieved by controllably producing very smooth and clean
interfaces between the resonators' aluminum metallization and the underlying
single crystal sapphire substrate. Additionally, we describe a method for
analyzing the resonator microwave response, with which we can directly
determine the internal quality factor and frequency of a resonator embedded in
an imperfect measurement circuit.Comment: 4 pages, 3 figures, 1 tabl
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