3,297 research outputs found
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)
Faster Base64 Encoding and Decoding Using AVX2 Instructions
Web developers use base64 formats to include images, fonts, sounds and other
resources directly inside HTML, JavaScript, JSON and XML files. We estimate
that billions of base64 messages are decoded every day. We are motivated to
improve the efficiency of base64 encoding and decoding. Compared to
state-of-the-art implementations, we multiply the speeds of both the encoding
(~10x) and the decoding (~7x). We achieve these good results by using the
single-instruction-multiple-data (SIMD) instructions available on recent Intel
processors (AVX2). Our accelerated software abides by the specification and
reports errors when encountering characters outside of the base64 set. It is
available online as free software under a liberal license.Comment: software at https://github.com/lemire/fastbase6
Triggered/sequential star formation? A multi-phase ISM study around the prominent IRDC G18.93-0.03
G18.93-0.03 is a prominent dust complex within an 0.8deg long filament, with
the molecular clump G18.93/m being IR dark from near IR wavelength up to 160mu.
Spitzer composite images show an IR bubble spatially associated with G18.93. We
use GRS 13CO and IRAM 30m H13CO+ data to disentangle the spatial structure of
the region. From ATLASGAL submm data we calculate the gas mass, while we use
the H13CO+ line width to estimate its virial mass. Using HERSCHEL data we
produce temperature maps from fitting the SED. With the MAGPIS 20cm and
SuperCOSMOS Halpha data we trace the ionized gas, and the VGPS HI survey
provides information on the atomic hydrogen gas. We show that the bubble is
spatially associated with G18.93, located at a kinematic near distance of
3.6kpc. With 280Msun, the most massive clump within G18.93 is G18.93/m. The
virial analysis shows that it may be gravitationally bound and has neither
Spitzer young stellar objects nor mid-IR point sources within. Fitting the SED
reveals a temperature distribution that decreases towards its center, but
heating from the ionizing source puts it above the general ISM temperature. We
find that the bubble is filled by HII gas, ionized by an O8.5 star. Between the
ionizing source and the IR dark clump G18.93/m we find a layered structure,
from ionized to atomic to molecular hydrogen, revealing a PDR. Furthermore, we
identify an additional velocity component within the bubble's 8mu emission rim
at the edge of the infrared dark cloud and speculate that it might be shock
induced by the expanding HII region. While the elevated temperature allows for
the build-up of larger fragments, and the shock induced velocity component may
lead to additional turbulent support, we do not find conclusive evidence that
the massive clump G18.93/m is prone to collapse because of the expanding HII
region.Comment: Accepted for publication in A&
Inelastic light scattering and the excited states of many-electron quantum dots
A consistent calculation of resonant inelastic (Raman) scattering amplitudes
for relatively large quantum dots, which takes account of valence-band mixing,
discrete character of the spectrum in intermediate and final states, and
interference effects, is presented. Raman peaks in charge and spin channels are
compared with multipole strengths and with the density of energy levels in
final states. A qualitative comparison with the available experimental results
is given.Comment: 5 pages, accepted in J. Phys.: Condens. Matte
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