1,678 research outputs found
Diurnal and annual variations of meteor rates at the arctic circle
Meteors are an important source for (a) the metal atoms of the upper atmosphere metal layers and (b) for condensation nuclei, the existence of which are a prerequisite for the formation of noctilucent cloud particles in the polar mesopause region. For a better understanding of these phenomena, it would be helpful to know accurately the annual and diurnal variations of meteor rates. So far, these rates have been little studied at polar latitudes. Therefore we have used the 33 MHz meteor radar of the ALOMAR observatory at 69° N to measure the meteor rates at this location for two full annual cycles. This site, being within 3° of the Arctic circle, offers in addition an interesting capability: The axis of its antenna field points (almost) towards the North ecliptic pole once each day of the year. In this particular viewing direction, the radar monitors the meteoroid influx from (almost) the entire ecliptic Northern hemisphere. <P style='line-height: 20px;'> We report on the observed diurnal variations (averaged over one month) of meteor rates and their significant alterations throughout the year. The ratio of maximum over minimum meteor rates throughout one diurnal cycle is in January and February about 5, from April through December 2.3±0.3. If compared with similar measurements at mid-latitudes, our expectation, that the amplitude of the diurnal variation is to decrease towards the North pole, is not really borne out. <P style='line-height: 20px;'> Observations with the antenna axis pointing towards the North ecliptic pole showed that the rate of deposition of meteoric dust is substantially larger during the Arctic NLC season than the annual mean deposition rate. The daylight meteor showers of the Arietids, Zeta Perseids, and Beta Taurids supposedly contribute considerably to the June maximum of meteor rates. We note, though, that with the radar antenna pointing as described above, all three meteor radiants are close to the local horizon but all three radiants were detected
Molecular gas heating in Arp 299
Understanding the heating and cooling mechanisms in nearby (Ultra) luminous
infrared galaxies can give us insight into the driving mechanisms in their more
distant counterparts. Molecular emission lines play a crucial role in cooling
excited gas, and recently, with Herschel Space Observatory we have been able to
observe the rich molecular spectrum. CO is the most abundant and one of the
brightest molecules in the Herschel wavelength range. CO transitions are
observed with Herschel, and together, these lines trace the excitation of CO.
We study Arp 299, a colliding galaxy group, with one component harboring an AGN
and two more undergoing intense star formation. For Arp 299 A, we present PACS
spectrometer observations of high-J CO lines up to J=20-19 and JCMT
observations of CO and HCN to discern between UV heating and alternative
heating mechanisms. There is an immediately noticeable difference in the
spectra of Arp 299 A and Arp 299 B+C, with source A having brighter high-J CO
transitions. This is reflected in their respective spectral energy line
distributions. We find that photon-dominated regions (PDRs) are unlikely to
heat all the gas since a very extreme PDR is necessary to fit the high-J CO
lines. In addition, this extreme PDR does not fit the HCN observations, and the
dust spectral energy distribution shows that there is not enough hot dust to
match the amount expected from such an extreme PDR. Therefore, we determine
that the high-J CO and HCN transitions are heated by an additional mechanism,
namely cosmic ray heating, mechanical heating, or X-ray heating. We find that
mechanical heating, in combination with UV heating, is the only mechanism that
fits all molecular transitions. We also constrain the molecular gas mass of Arp
299 A to 3e9 Msun and find that we need 4% of the total heating to be
mechanical heating, with the rest UV heating
The neutron time-of-flight facility n-TOF at CERN: Phase II
Neutron-induced reactions are studied at the neutron time-of-flight facility n-TOF at CERN. The facility uses 6∼ns wide pulses of 20 GeV/c protons impinging on a lead spallation target. The large neutron energy range and the high instantaneous neutron flux combined with high resolution are among the key characteristics of the facility. After a first phase of data taking during the period 2001-2004, the facility has been refurbished with an upgraded spallation target and cooling system for a second phase of data taking which started in 2009. Since 2010, the experimental area at 185 m where the neutron beam arrives, has been modified into a worksector of type A, allowing the extension of the physics program to include neutron-induced reactions on radioactive isotopes
Resolving the molecular gas around the lensed quasar RXJ0911.4+0551
We report on high angular resolution observations of the CO(7-6) line and
millimeter continuum in the host galaxy of the gravitationally lensed (z~2.8)
quasar RXJ0911.4+0551 using the Plateau de Bure Interferometer. Our CO
observations resolve the molecular disk of the source. Using a lens model based
on HST observations we fit source models to the observed visibilities. We
estimate a molecular disk radius of 10.2 kpc and an inclination of
696\deg, the continuum is more compact and is only marginally resolved by
our observations. The relatively low molecular gas mass, Msolar, and far infrared luminosity, Lsolar, of this quasar could be explained by its relatively low
dynamical mass, Msolar. It would be a
scaled-down version the QSOs usually found at high-z. The FIR and CO
luminosities lie on the correlation found for QSOs from low to high redshifts
and the gas-to-dust ratio () is similar to the one measured in the
z=6.4 QSO, SDSS J1148+5251. Differential magnification affects the
continuum-to-line luminosity ratio, the line profile and possibly the spectral
energy distribution.Comment: Accepted for publication in A&A, revised after language editin
Excitation of the molecular gas in the nuclear region of M82
We present high resolution HIFI spectroscopy of the nucleus of the
archetypical starburst galaxy M82. Six 12CO lines, 2 13CO lines and 4
fine-structure lines are detected. Besides showing the effects of the overall
velocity structure of the nuclear region, the line profiles also indicate the
presence of multiple components with different optical depths, temperatures and
densities in the observing beam. The data have been interpreted using a grid of
PDR models. It is found that the majority of the molecular gas is in low
density (n=10^3.5 cm^-3) clouds, with column densities of N_H=10^21.5 cm^-2 and
a relatively low UV radiation field (GO = 10^2). The remaining gas is
predominantly found in clouds with higher densities (n=10^5 cm^-3) and
radiation fields (GO = 10^2.75), but somewhat lower column densities
(N_H=10^21.2 cm^-2). The highest J CO lines are dominated by a small (1%
relative surface filling) component, with an even higher density (n=10^6 cm^-3)
and UV field (GO = 10^3.25). These results show the strength of multi-component
modeling for the interpretation of the integrated properties of galaxies.Comment: Accepted for publication in A&A Letter
Effects of Diversity on Multi-agent Systems: Minority Games
We consider a version of large population games whose agents compete for
resources using strategies with adaptable preferences. The games can be used to
model economic markets, ecosystems or distributed control. Diversity of initial
preferences of strategies is introduced by randomly assigning biases to the
strategies of different agents. We find that diversity among the agents reduces
their maladaptive behavior. We find interesting scaling relations with
diversity for the variance and other parameters such as the convergence time,
the fraction of fickle agents, and the variance of wealth, illustrating their
dynamical origin. When diversity increases, the scaling dynamics is modified by
kinetic sampling and waiting effects. Analyses yield excellent agreement with
simulations.Comment: 41 pages, 16 figures; minor improvements in content, added
references; to be published in Physical Review
Das exemte Bistum Bamberg 3. Die Bischofsreihe von 1522 bis 1693
Dieter J. Weiss, Das exemte Bistum Bamberg 3: Die Bischofsreihe von 1522 bis 1693 (Germania Sacra N. F. 38,1), Berlin/New York 2000
Das exemte Bistum Bamberg 4. Die Bamberger Bischöfe von 1693 bis 1802
Mit den Bischofsviten von 1693 bis 1802 liegt nun die vollständige Bischofsreihe des Bistums Bamberg vor. Der Band reicht vom Beginn des Pontifikats des Lothar Franz von Schönborn bis zur Säkularisation unter Christoph Franz von Buseck. Damit fallen der Barockkatholizismus, Ansätze zur absolutistischen Herrschaft und die Aufklärung in den Untersuchungszeitraum.
Mit Lothar Franz und Friedrich Karl von Schönborn, Adam Friedrich von Seinsheim und Franz Ludwig von Erthal werden Fürstbischöfe erfasst, die weit über den Bamberger Raum hinaus Bedeutung hatten. Die ebenso umfassenden wie markanten Bischofsporträts berücksichtigen auch literar- und kunstgeschichtliche Fragestellungen. Ein eigener Abschnitt enthält Kurzbiographien der Weihbischöfe, Generalvikare, Fiskale und Kanzler und stellt damit die eigentlichen Träger der geistlichen Verwaltung vor. Über die individuellen Biographien hinaus werden auch längerfristige Entwicklungen wie die Herausbildung absolutistischer Regierungsformen oder der Wandel des Bischofsideals im Zuge der Aufklärung deutlich.2018-10Dieter J. Weiß, Das exemte Bistum Bamberg 4: Die Bamberger Bischöfe von 1693 bis 1802 (Germania Sacra. Dritte Folge 12), Berlin/Boston 2015
Ammonia (J,K) = (1,1) to (4,4) and (6,6) inversion lines detected in the Seyfert 2 galaxy NGC 1068
We present the detection of the ammonia (NH3) (J,K) = (1,1) to (4,4) and
(6,6) inversion lines toward the prototypical Seyfert 2 galaxy NGC 1068, made
with the Green Bank Telescope (GBT). This is the first detection of ammonia in
a Seyfert galaxy. The ortho-to-para-NH3 abundance ratio suggests that the
molecule was formed in a warm medium of at least 20 K. For the NH3 column
density and fractional abundance, we find (1.09\pm0.23)\times10^14 cm^-2 and
(2.9\pm0.6)\times10^-8, respectively, from the inner 1.2 kpc of NGC 1068. The
kinetic temperature can be constrained to 80\pm20 K for the bulk of the
molecular gas, while some fraction has an even higher temperature of 140\pm30
K.Comment: 5 pages, 3 figures, accepted by A&
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