1,515 research outputs found
Spectroscopy of diffuse light in dust clouds. Scattered light and the solar neighbourhood radiation field
The optical surface brightness of dark nebulae is mainly due to scattering of
integrated starlight by classical dust grains. It contains information on the
impinging interstellar radiation field, cloud structure, and grain scattering
properties. We have obtained spectra of the scattered light from 3500 to 9000
Angstrom in two globules, the Thumbprint Nebula and DC303.8-14.2.
We use observations of the scattered light to study the impinging integrated
starlight spectrum as well as the scattered H-alpha and other line emissions
from all over the sky. We search also for the presence of other than scattered
light in the two globules.
We obtained long-slit spectra encompassing the whole globule plus adjacent
sky in a one-slit setting, thus enabling efficient elimination of airglow and
other foreground sky components. We calculated synthetic integrated starlight
spectra for the solar neighbourhood using HIPPARCOS-based stellar distributions
and the spectral library of Pickles.
Spectra are presented separately for the bright rims and dark cores of the
globules. The continuum spectral energy distributions and absorption line
spectra can be well modelled with the synthetic integrated starlight spectra.
Emission lines of H-alpha + NII, H-beta, and SII are detected and are
interpreted in terms of scattered light plus an in situ warm ionized medium
component behind the globules. We detected an excess of emission over the
wavelength range 5200-8000 Angstrom in DC303.8-14.2 but the nature of this
emission remains open
Coulomb blockade and Bloch oscillations in superconducting Ti nanowires
Quantum fluctuations in quasi-one-dimensional superconducting channels
leading to spontaneous changes of the phase of the order parameter by ,
alternatively called quantum phase slips (QPS), manifest themselves as the
finite resistance well below the critical temperature of thin superconducting
nanowires and the suppression of persistent currents in tiny superconducting
nanorings. Here we report the experimental evidence that in a current-biased
superconducting nanowire the same QPS process is responsible for the insulating
state -- the Coulomb blockade. When exposed to RF radiation, the internal Bloch
oscillations can be synchronized with the external RF drive leading to
formation of quantized current steps on the I-V characteristic. The effects
originate from the fundamental quantum duality of a Josephson junction and a
superconducting nanowire governed by QPS -- the QPS junction (QPSJ).Comment: 5 pages, 4 figure
The Spectral Energy Distribution of Self-gravitating Interstellar Clouds I. Spheres
We derive the spectral energy distribution (SED) of dusty, isothermal, self
gravitating, stable and spherical clouds externally heated by the ambient
interstellar radiation field. For a given radiation field and dust properties,
the radiative transfer problem is determined by the pressure of the surrounding
medium and the cloud mass expressed as a fraction of the maximum stable cloud
mass above which the clouds become gravitational unstable.
To solve the radiative transfer problem a ray-tracing code is used to
accurately derive the light distribution inside the cloud. This code considers
both non isotropic scattering on dust grains and multiple scattering events.
The dust properties inside the clouds are assumed to be the same as in the
diffuse interstellar medium in our galaxy. We analyse the effect of the
pressure, the critical mass fraction, and the ISRF on the SED and present
brightness profiles in the visible, the IR/FIR and the submm/mm regime with the
focus on the scattered emission and the thermal emission from PAH-molecules and
dust grains.Comment: accepted for publication in ApJS, May 2008, v176n1 issu
Centimetre continuum emission from young stellar objects in Cederblad 110
The low-mass star formation region associated with the reflection nebula
Cederblad 110 in the Chamaeleon I cloud was mapped with the Australian
Telescope Compact Array (ATCA) at 6 and 3.5cm. Altogether 11 sources were
detected, three of which are previously known low mass young stellar objects
associated with the nebula: the illuminating star IRS2 (Class III, Einstein
X-ray source CHX7), the brightest far-infrared source IRS4 (Class I), and the
weak X-ray source CHX10a (Class III). The other young stellar objects in the
region, including the Class 0 protostar candidate Cha-MMS1, were not detected.
The radio spectral index of IRS4 (alpha = 1.7 +/- 0.3) is consistent with
optically thick free-free emission arising from a dense ionized region,
probably a jet-induced shock occurring in the circumstellar material. As the
only Class I protostar with a 'thermal jet' IRS4 is the strongest candidate for
the central source of the molecular outflow found previously in the region. The
emission from IRS2 has a flat spectrum (alpha = 0.05 +/- 0.05) but shows no
sign of polarization, and therefore its origin is likely to be optically thin
free-free emission either from ionized wind or a collimated jet. The strongest
source detected in this survey is a new compact object with a steep negative
spectral index (-1.1) and a weak linear polarization (about 2 %), which
probably represents a background radio galaxy.Comment: 7 pages, 2 Postscript figures. Accepted for publication in Astronomy
& Astrophysic
Control of potato late blight by caraway oil in organic farming
Caraway (Carum carvi) seeds contain biologically active essential oils, which have shown potential in controlling Phytophthora infestans (P.i.). An attempt is being made to develop a P.i. control strategy for organic farming based on caraway oil
C18O (3-2) observations of the Cometary Globule CG 12: a cold core and a C18O hot spot
The feasibility of observing the C18O (3-2) spectral line in cold clouds with
the APEX telescope has been tested. As the line at 329.330 GHz lies in the wing
of a strong atmospheric H2O absorption it can be observed only at high altitude
observatories. Using the three lowest rotational levels instead of only two
helps to narrow down the physical properties of dark clouds and globules. The
centres of two C18O maxima in the high latitude low mass star forming region CG
12 were mapped in C18O (3-2) and the data were analyzed together with spectral
line data from the SEST. The T_MB(3-2)/T_MB(2-1) ratio in the northern C18O
maximum, CG 12 N, is 0.8, and in the southern maximum, CG 12 S, ~2. CG 12 N is
modelled as a 120'' diameter (0.4pc) cold core with a mass of 27 Msun. A small
size maximum with a narrow, 0.8 kms-1, C18O (3-2) spectral line with a peak
temperature of T_MB ~11 K was detected in CG 12 S. This maximum is modelled as
a 60'' to 80'' diameter (~0.2pc) hot (80 K < Tex < 200 K) ~1.6 Msun clump. The
source lies on the axis of a highly collimated bipolar molecular outflow near
its driving source. This is the first detection of such a compact, warm object
in a low mass star forming region.Comment: APEX A&A special issue, accepte
Using discriminant analysis as a nucleation event classification method
More than three years of measurements of aerosol size-distribution and different gas and meteorological parameters made in Po Valley, Italy were analysed for this study to examine which of the meteorological and trace gas variables effect on the emergence of nucleation events. As the analysis method, we used discriminant analysis with non-parametric Epanechnikov kernel, included in non-parametric density estimation method. The best classification result in our data was reached with the combination of relative humidity, ozone concentration and a third degree polynomial of radiation. RH appeared to have a preventing effect on the new particle formation whereas the effects of O<sub>3</sub> and radiation were more conductive. The concentration of SO<sub>2</sub> and NO<sub>2</sub> also appeared to have significant effect on the emergence of nucleation events but because of the great amount of missing observations, we had to exclude them from the final analysis
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