3,429 research outputs found
Metabolic costs of bat echolocation in a non-foraging context support a role in communication
The exploitation of information is a key adaptive behavior of social animals,
and many animals produce costly signals to communicate with conspecifics. In
contrast, bats produce ultrasound for auto-communication, i.e., they emit
ultrasound calls and behave in response to the received echo. However,
ultrasound echolocation calls produced by non-flying bats looking for food are
energetically costly. Thus, if they are produced in a non-foraging or
navigational context this indicates an energetic investment, which must be
motivated by something. We quantified the costs of the production of such
calls, in stationary, non-foraging lesser bulldog bats (Noctilio albiventris)
and found metabolic rates to increase by 0.021 ± 0.001 J/pulse (mean ±
standard error). From this, we estimated the metabolic rates of N. albiventris
when responding with ultrasound echolocation calls to playbacks of
echolocation calls from familiar and unfamiliar conspecific as well as
heterospecific bats. Lesser bulldog bats adjusted their energetic investment
to the social information contained in the presented playback. Our results are
consistent with the hypothesis that in addition to orientation and foraging,
ultrasound calls in bats may also have function for active communication
Shear modulus of the hadron-quark mixed phase
Robust arguments predict that a hadron-quark mixed phase may exist in the
cores of some "neutron" stars. Such a phase forms a crystalline lattice with a
shear modulus higher than that of the crust due to the high density and charge
separation, even allowing for the effects of charge screening. This may lead to
strong continuous gravitational-wave emission from rapidly rotating neutron
stars and gravitational-wave bursts associated with magnetar flares and pulsar
glitches. We present the first detailed calculation of the shear modulus of the
mixed phase. We describe the quark phase using the bag model plus first-order
quantum chromodynamics corrections and the hadronic phase using relativistic
mean-field models with parameters allowed by the most massive pulsar. Most of
the calculation involves treating the "pasta phases" of the lattice via
dimensional continuation, and we give a general method for computing
dimensionally continued lattice sums including the Debye model of charge
screening. We compute all the shear components of the elastic modulus tensor
and angle average them to obtain the effective (scalar) shear modulus for the
case where the mixed phase is a polycrystal. We include the contributions from
changing the cell size, which are necessary for the stability of the
lower-dimensional portions of the lattice. Stability also requires a minimum
surface tension, generally tens of MeV/fm^2 depending on the equation of state.
We find that the shear modulus can be a few times 10^33 erg/cm^3, two orders of
magnitude higher than the first estimate, over a significant fraction of the
maximum mass stable star for certain parameter choices.Comment: 22 pages, 12 figures, version accepted by Phys. Rev. D, with the
corrections to the shear modulus computation and Table I given in the erratu
Entanglement between a diamond spin qubit and a photonic time-bin qubit at telecom wavelength
We report on the realization and verification of quantum entanglement between
an NV electron spin qubit and a telecom-band photonic qubit. First we generate
entanglement between the spin qubit and a 637 nm photonic time-bin qubit,
followed by photonic quantum frequency conversion that transfers the
entanglement to a 1588 nm photon. We characterize the resulting state by
correlation measurements in different bases and find a lower bound to the Bell
state fidelity of F = 0.77 +/- 0.03. This result presents an important step
towards extending quantum networks via optical fiber infrastructure
MM4Drone: A Multi-spectral Image and mmWave Radar Approach for Identifying Mosquito Breeding Grounds via Aerial Drones
Mosquitoes spread diseases such as Dengue and Zika that affect a significant portion of the world population. One approach to hamper the spread of the diseases is to identify the mosquitoes' breeding places. Recent studies use drones to detect breeding sites, due to their low cost and flexibility. In this paper, we investigate the applicability of drone-based multi-spectral imagery and mmWave radios to discover breeding habitats. Our approach is based on the detection of water bodies. We introduce our Faster R-CNN-MSWD, an extended version of the Faster R-CNN object detection network, which can be used to identify water retention areas in both urban and rural settings using multi-spectral images. We also show promising results for estimating extreme shallow water depth using drone-based multi-spectral images. Further, we present an approach to detect water with mmWave radios from drones. Finally, we emphasize the importance of fusing the data of the two sensors and outline future research directions
Rotational modes in molecular magnets with antiferromagnetic Heisenberg exchange
In an effort to understand the low temperature behavior of recently
synthesized molecular magnets we present numerical evidence for the existence
of a rotational band in systems of quantum spins interacting with
nearest-neighbor antiferromagnetic Heisenberg exchange. While this result has
previously been noted for ring arrays with an even number of spin sites, we
find that it also applies for rings with an odd number of sites as well as for
all of the polytope configurations we have investigated (tetrahedron, cube,
octahedron, icosahedron, triangular prism, and axially truncated icosahedron).
It is demonstrated how the rotational band levels can in many cases be
accurately predicted using the underlying sublattice structure of the spin
array. We illustrate how the characteristics of the rotational band can provide
valuable estimates for the low temperature magnetic susceptibility.Comment: 14 pages, 7 figures, to be published in Phys. Rev.
Valley degeneracy in biaxially strained aluminum arsenide quantum wells
This paper details a complete formalism for calculating electron subband
energy and degeneracy in strained multi-valley quantum wells grown along any
orientation with explicit results for the AlAs quantum well case. A
standardized rotation matrix is defined to transform from the conventional-
cubic-cell basis to the quantum-well-transport basis whereby effective mass
tensors, valley vectors, strain matrices, anisotropic strain ratios, and
scattering vectors are all defined in their respective bases. The specific
cases of (001)-, (110)-, and (111)-oriented aluminum arsenide (AlAs) quantum
wells are examined, as is the unconventional (411) facet, which is of
particular importance in AlAs literature. Calculations of electron confinement
and strain in the (001), (110), and (411) facets determine the critical well
width for crossover from double- to single-valley degeneracy in each system.
The notation is generalized to include miscut angles, and can be adapted to
other multi-valley systems. To help classify anisotropic inter-valley
scattering events, a new primitive unit cell is defined in momentum space which
allows one to distinguish purely in-plane inter-valley scattering events from
those that requires an out-of-plane momentum scattering component.Comment: 17 pages, 4 figures, 2 table
A thermodynamic framework to develop rate-type models for fluids without instantaneous elasticity
In this paper, we apply the thermodynamic framework recently put into place
by Rajagopal and co-workers, to develop rate-type models for viscoelastic
fluids which do not possess instantaneous elasticity. To illustrate the
capabilities of such models we make a specific choice for the specific
Helmholtz potential and the rate of dissipation and consider the creep and
stress relaxation response associated with the model. Given specific forms for
the Helmholtz potential and the rate of dissipation, the rate of dissipation is
maximized with the constraint that the difference between the stress power and
the rate of change of Helmholtz potential is equal to the rate of dissipation
and any other constraint that may be applicable such as incompressibility. We
show that the model that is developed exhibits fluid-like characteristics and
is incapable of instantaneous elastic response. It also includes Maxwell-like
and Kelvin-Voigt-like viscoelastic materials (when certain material moduli take
special values).Comment: 18 pages, 5 figure
MEM-BRAIN gas separation membranes for zero-emission fossil power plants
The aim of the MEM-BRAIN project is the development and integration of gas separation membranes for zero-emission fossil power plants. This will be achieved by selective membranes with high permeability for CO2, O2 or H2, so that high-purity CO2 is obtained in a readily condensable form. The project is being implemented by the “MEM-BRAIN” Helmholtz Alliance consisting of research centres, universities and industrial partners.\ud
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The MEM-BRAIN project focuses on the development, process engineering, system integration and energy systems analysis of different gas separation membranes for the different CO2 capture process routes in fossil power plants
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