1,949 research outputs found
Ears adapted for the detection of motion, or how echolocating bats have exploited the capacities of the mammalian auditory system
Echo Delay and Overlap with Emitted Orientation Sounds and Doppler-shift Compensation in the Bat, Rhinolophus ferrumequinum
The compensation of Doppler-shifts by the bat, Rhinolophusferrumequinum,
functions only when certain temporal relations between the echo
and the emitted orientation sound are given. Three echo configurations
were used:
a) Original orientation sounds were electronically Doppler-shifted and
played back either cut at the beginning (variable delay) or at the end (variable
duration) of the echo.
b) Artificial constant frequency echoes with variable delay or duration
were clamped to the frequency of the emitted orientation sound at different
Doppler-shifts.
c) The echoes were only partially Doppler-shifted and the Doppler-shifted
component began after variable delays or had variable durations.
With increasing delay or decreasing duration of the Doppler-shifted echo
the compensation amplitude for a sinusoidally modulated + 3 kHz Dopplershift
(modulation rate 0.08 Hz) decreases for all stimulus configurations
(Figs. 1, 2, 3).
The range of the Doppler-shift compensation system is therefore limited
by the delay due to acoustic travel time to about 4 m distance between
bat and target. In this range the overlap duration of the echo with the
emitted orientation sound is always sufficiently long, when compared with
data on the orientation pulse length during target approach from Schnitzler
(1968) (Fig. 5)
Spin transitions in an incompressible liquid Coulomb coupled to a quantum dot
We report on our investigation of the low-lying energy spectra and charge
density of a two-dimensional quantum Hall liquid at that is
Coulomb coupled to a quantum dot. The dot contains a hole and two/three
electrons. We found that any external perturbation (caused by the close
proximity of the quantum dot) locally changes the spin polarization of the
incompressible liquid. The effect depends crucially on the separation distance
of the quantum dot from the electron plane. Electron density distribution in
the quantum Hall layer indicates creation of a quasihole that is localized by
the close proximity of the quantum dot. Manifestation of this effect in the
photoluminescence spectroscopy is also discussed.Comment: 4 pages, 3 figure
Foraging behavior and Doppler shift compensation in echolocating hipposiderid bats, I-Iipposideros bicolor and I-Iipposideros speoris
1. Two hipposiderid bats,H. bicolor andH. speoris, were observed in their natural foraging areas in Madurai (South India). Both species hunt close together near the foliage of trees and bushes but they differ in fine structure of preferred hunting space:H. bicolor hunts within the foliage, especially whenH. speoris is active at the same time, whereasH. speoris never flies in dense vegetation but rather in the more open area (Fig. 1, Table 1).
2. Both species emit CF/FM-sounds containing only one harmonic component in almost all echolocation situations. The CF-parts of CF/FM-sounds are species specific within a band of 127–138 kHz forH. speoris and 147–159 kHz forH. bicolor (Tables 2 and 3).
3. H. speoris additionally uses a complex harmonic sound during obstacle avoidance and during laboratory tests for Doppler shift compensation.H. bicolor consistently emits CF/FM-sounds in these same situations (Fig. 2).
4. Both hipposiderid bats respond to Doppler shifts in the returning echoes by lowering the frequency of the emitted sounds (Fig. 3). However, Doppler compensations are incomplete as the emitted frequencies are decreased by only 55% and 56% (mean values) of the full frequency shifts byH. speoris andH, bicolor, respectively.
5. The differences in Doppler shift compensation, echolocating and hunting behavior suggest thatH. speoris is less specialized on echolocation with CF/FM-sounds thanH. bicolor
Lubrication and performance of high-speed rolling-element bearings
Trends in aircraft engine operating speeds have dictated the need for rolling-element bearings capable of speeds to 3 million DN. A review of high-speed rolling-element bearing state-of-the-art performance and lubrication is presented. Through the use of under-race lubrication and bearing thermal management bearing operation can be obtained to speeds of 3 million DN. Jet lubricated ball bearings are limited to 2.5 million DN for large bore sizes and to 3 million DN for small bore sizes. Current computer programs are able to predict bearing thermal performance
ELECTRONIC EXCITATION OF K ATOMS IN COLLISIONS WITH DIATOMIC MOLECULES: THRESHOLDS AND ENERGY DEPENDENCE FROM 1-5 eV
Deconvoluting Reversal Modes in Exchange Biased Nanodots
Ensemble-averaged exchange bias in arrays of Fe/FeF2 nanodots has been
deconvoluted into local, microscopic, bias separately experienced by nanodots
going through different reversal modes. The relative fraction of dots in each
mode can be modified by exchange bias. Single domain dots exhibit a simple loop
shift, while vortex state dots have asymmetric shifts in the vortex nucleation
and annihilation fields, manifesting local incomplete domain walls in these
nanodots as magnetic vortices with tilted cores.Comment: 17 pages, 3 figures. Phys. Rev. B in pres
Dynamics of Spontaneous Magnetization Reversal in Exchange Biased Heterostructures
The dependence of thermally induced spontaneous magnetization reversal on
time-dependent cooling protocols was studied. Slower cooling and longer waiting
close to the N\`{e}el temperature of the antiferromagnet () enhances the
magnetization reversal. Cycling the temperature around leads to a thermal
training effect under which the reversal magnitude increases with each cycle.
These results suggest that spontaneous magnetization reversal is energetically
favored, contrary to our present understanding of positive exchange bias
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