162 research outputs found
Neural coding of naturalistic motion stimuli
We study a wide field motion sensitive neuron in the visual system of the
blowfly {\em Calliphora vicina}. By rotating the fly on a stepper motor outside
in a wooded area, and along an angular motion trajectory representative of
natural flight, we stimulate the fly's visual system with input that approaches
the natural situation. The neural response is analyzed in the framework of
information theory, using methods that are free from assumptions. We
demonstrate that information about the motion trajectory increases as the light
level increases over a natural range. This indicates that the fly's brain
utilizes the increase in photon flux to extract more information from the
photoreceptor array, suggesting that imprecision in neural signals is dominated
by photon shot noise in the physical input, rather than by noise generated
within the nervous system itself.Comment: 15 pages, 4 figure
Lifecycle-Support in Architectures for Ontology-Based Information Systems
Ontology-based applications play an increasingly important role in the public and corporate Semantic Web. While today there exist a range of tools and technologies to support specific ontology engineering and management activities, architectural design guidelines for building ontology-based applications are missing. In this paper, we present an architecture for ontology-based applications—covering the complete ontology-lifecycle—that is intended to support
software engineers in designing and developing ontology based-applications.
We illustrate the use of the architecture in a concrete case study using the NeOn toolkit as one implementation of the architecture
Rotational spectroscopy of the thioformaldehyde isotopologues HCS and HCS in four interacting excited vibrational states and an account on the rotational spectrum of thioketene, HCCS
An investigation of the rotational spectrum of the interstellar molecule
thioformaldehyde between 110 and 377 GHz through a pyrolysis reaction revealed
a multitude of absorption lines assignable to HCS and HCS in
their lowest four excited vibrational states besides lines of numerous
thioformaldehyde isotopologues in their ground vibrational states reported
earlier as well as lines pertaining to several by-products. Additional
transitions of HCS in its lowest four excited vibrational states were
recorded in selected regions between 571 and 1386 GHz. Slight to strong
Coriolis interactions occur between all four vibrational states with the
exception of the two highest lying states because both are totally symmetric
vibrations. We present combined analyses of the ground and the four interacting
states for our rotational data of HCS and HCS. The HCS data
were supplemented with two sets of high-resultion IR data in two separate
analyses. The state has been included in analyses of Coriolis
interactions of low-lying fundamental states of HCS for the first time and
this improved the quality of the fits substantially. We extended furthermore
assignments in of transition frequencies of thioketene in its ground
vibrational state.Comment: 23 pages including figures, tables, and references; Mol. Phys.,
accepted (for the Tim Lee memorial issue
Investigation of the rotational spectrum of CDOD and an astronomical search toward IRAS 162932422
Solar-type prestellar cores and protostars display large amounts of
deuterated organic molecules. Recent findings on CHDOH and CDOH toward
IRAS 16293-2422 suggest that even fully deuterated methanol, CDOD, may be
detectable as well. However, searches for CDOD are hampered in particular
by the lack of intensity information from a spectroscopic model. The objective
of the present investigation is to develop a spectroscopic model of CDOD in
low-lying torsional states that is sufficiently accurate to facilitate searches
for this isotopolog in space. We carried out a new measurement campaign for
CDOD involving two spectroscopic laboratories that covers the 34 GHz-1.1
THz range. A torsion-rotation Hamiltonian model based on the rho-axis method
was employed for our analysis. Our resulting model describes the ground and
first excited torsional states of CDOD well up to quantum numbers and . We derived a line list for radio-astronomical
observations from this model that is accurate up to at least 1.1 THz and should
be sufficient for all types of radio-astronomical searches for this methanol
isotopolog. This line list was used to search for CDOD in data from the
Protostellar Interferometric Line Survey of IRAS 162932422 obtained with the
Atacama Large Millimeter/submillimeter Array. While we found several emission
features that can be attributed largely to CDOD, their number is still not
sufficiently high enough to establish a clear detection. Nevertheless, the
estimate of 2 cm derived for the CDOD column density
may be viewed as an upper limit that can be compared to column densities of
CDOH, CHOD, and CHOH. The comparison indicates that the CDOD
column density toward IRAS 16293-2422 is in line with the enhanced D/H ratios
observed for multiply deuterated complex organic molecules.Comment: 10 pages total, including figures, tables, and references; abstract
slightly shortened; Astron. Astrophys., accepte
Rotation-tunneling spectrum and astrochemical modeling of dimethylamine, CHNHCH, and searches for it in space
Methylamine has been the only simple alkylamine detected in the interstellar
medium for a long time. With the recent secure and tentative detections of
vinylamine and ethylamine, respectively, dimethylamine has become a promising
target for searches in space. Its rotational spectrum, however, has been known
only up to 45 GHz until now. Here we investigate the rotation-tunneling
spectrum of dimethylamine in selected regions between 76 and 1091 GHz using
three different spectrometers in order to facilitate its detection in space.
The quantum number range is extended to and , yielding an
extensive set of accurate spectroscopic parameters. To search for
dimethylamine, we refer to the spectral line survey ReMoCA carried out with the
Atacama Large Millimeter/submillimeter Array toward the high-mass star-forming
region Sagittarius B2(N) and a spectral line survey of the molecular cloud
G+0.6930.027 employing the IRAM 30 m and Yebes 40 m radio telescopes. We
report nondetections of dimethylamine toward the hot molecular cores Sgr
B2(N1S) and Sgr B2(N2b) as well as G+0.6930.027 which imply that
dimethylamine is at least 14, 4.5 and 39 times less abundant than methylamine
toward these sources, respectively. The observational results are compared to
computational results from a gas-grain astrochemical model. The modeled
methylamine to dimethylamine ratios are compatible with the observational
ratios. However, the model produces too much ethylamine compared with
methylamine which could mean that the already fairly low levels of
dimethylamine in the models may also be too high.Comment: Mon. Not. R. Astron. Soc., accepted. 33 pages including tables,
figures, and appendi
Interstellar detection of CCC and high-precision laboratory measurements near 2THz
ABSTRACT We describe more fully our original tentative interstellar detection of the triatomic pure carbon chain molecule, CCC, in absorption toward the Galactic center source Sgr B2
Accurate laboratory rest frequencies of vibrationally excited CO up to and up to 2 THz
Astronomical observations of (sub)millimeter wavelength pure rotational
emission lines of the second most abundant molecule in the Universe, CO, hold
the promise of probing regions of high temperature and density in the innermost
parts of circumstellar envelopes. The rotational spectrum of vibrationally
excited CO up to \varv = 3 has been measured in the laboratory between 220
and 1940 GHz with relative accuracies up to , corresponding
to kHz near 1 THz. The rotational constant and the quartic
distortion parameter have been determined with high accuracy and even the
sextic distortion term was determined quite well for \varv = 1 while
reasonable estimates of were obtained for \varv = 2 and 3. The present
data set allows for the prediction of accurate rest frequencies of
vibrationally excited CO well beyond 2 THz.Comment: Astron. Astrophys, accepted; 5 pages, 2 Figures, 2 Table
- …