1,948 research outputs found
Treibhausgasflüsse beim Anbau von Winterweizen und Kleegras
At the experimental station Viehhausen, 30 km north of Munich in southern Germany, N2O, CO2 and CH4 fluxes between soil and atmosphere were measured to investigate the influence of site-related factors and cultivation-technique on the emissions of these greenhouse gases. Clover-grass as well as several wheat cropping systems (with and without biogas slurry) were analyzed under the conditions of organic farming. This paper shows the results of the vegetation period of 2009. The N2O emissions from the wheat fields were higher than those from clover-grass fields. Ploughing-in of the legume-grass biomass resulted in releasing distinctive N2O emissions. For CH4 fluxes the arable soils were a net sink, especially in cropping systems with winter wheat
Physical Conditoins in Orion's Veil II: A Multi-Component Study of the Line of Sight Toward the Trapezium
Orion's Veil is an absorbing screen that lies along the line of sight to the
Orion H II region. It consists of two or more layers of gas that must lie
within a few parsecs of the Trapezium cluster. Our previous work considered the
Veil as a whole and found that the magnetic field dominates the energetics of
the gas in at least one component. Here we use high-resolution STIS UV spectra
that resolve the two velocity components in absorption and determine the
conditions in each. We derive a volume hydrogen density, 21 cm spin
temperature, turbulent velocity, and kinetic temperature, for each. We combine
these estimates with magnetic field measurements to find that magnetic energy
significantly dominates turbulent and thermal energies in one component, while
the other component is close to equipartition between turbulent and magnetic
energies. We observe molecular hydrogen absorption for highly excited v, J
levels that are photoexcited by the stellar continuum, and detect blueshifted S
III and P III. These ions must arise from ionized gas between the mostly
neutral portions of the Veil and the Trapezium and shields the Veil from
ionizing radiation. We find that this layer of ionized gas is also responsible
for He I absorption in the Veil, which resolves a 40-year-old debate on the
origin of He I absorption towards the Trapezium. Finally, we determine that the
ionized and mostly atomic layers of the Veil will collide in less than 85,000
years.Comment: 43 pages, 15 figures, to be published in Ap
Hubble Space Telescope Images of Magellanic Cloud Planetary Nebulae: Data and Correlations across Morphological Classes
The morphology of planetary nebulae (PNe) provides an essential tool for
understanding their origin and evolution, as it reflects both the dynamics of
the gas ejected during the TP-AGB phase, and the central star energetics. Here
we study the morphology of 27 Magellanic Cloud planetary nebulae (MCPNe) and
present an analysis of their physical characteristics across morphological
classes. Similar studies have been successfully carried out for galactic PNe,
but were compromised by the uncertainty of individual PN distances. We present
our own HST/FOC images of 15 Magellanic Cloud PNe (MCPNe) acquired through a
narrow-band lambda 5007 [O III] filter. We use the Richardson-Lucy
deconvolution technique on these pre-COSTAR images to achieve post-COSTAR
quality. Three PNe imaged before and after COSTAR confirm the high reliability
of our deconvolution procedure. We derive morphological classes, dimensions,
and surface photometry for all these PNe. We have combined this sample with
HST/PC1 images of 15 MCPNe, three of which are in common with the FOC set,
acquired by Dopita et al. (1996), to obtain the largest MCPN sample ever
examined from the morphological viewpoint. By using the whole database,
supplemented with published data from the literature, we have analyzed the
properties of the MCPNe and compared them to a typical, complete galactic
sample. Morphology of the MCPNe is then correlated with PN density, chemistry,
and evolution.Comment: text file lstanghe_mcpn.tex (LaTex); Figures 2 through 10, Figure 5
is in 3 parts (a,b,c); Figure 1 available by regular mail only; ApJ, in
press, November 10, 199
Stresses in silos: Comparison between theoretical models and new experiments
We present precise and reproducible mean pressure measurements at the bottom
of a cylindrical granular column. If a constant overload is added, the pressure
is linear in overload and nonmonotonic in the column height. The results are
{\em quantitatively} consistent with a local, linear relation between stress
components, as was recently proposed by some of us. They contradict the
simplest classical (Janssen) approximation, and may pose a rather severe test
of competing models.Comment: 4 pages, 2 figures, final version to appear in Phys. Rev. Let
Independent measurement of the Hoyle state feeding from 12B using Gammasphere
Using an array of high-purity Compton-suppressed germanium detectors, we
performed an independent measurement of the -decay branching ratio from
to the second-excited (Hoyle) state in . Our
result is , which is a factor smaller than the previously
established literature value, but is in agreement with another recent
measurement. This could indicate that the Hoyle state is more clustered than
previously believed. The angular correlation of the Hoyle state
cascade has also been measured for the first time. It is consistent with
theoretical predictions
Exploring CEvNS with NUCLEUS at the Chooz Nuclear Power Plant
Coherent elastic neutrino-nucleus scattering (CENS) offers a unique way
to study neutrino properties and to search for new physics beyond the Standard
Model. Nuclear reactors are promising sources to explore this process at low
energies since they deliver large fluxes of (anti-)neutrinos with typical
energies of a few MeV. In this paper, a new-generation experiment to study
CENS is described. The NUCLEUS experiment will use cryogenic detectors
which feature an unprecedentedly low energy threshold and a time response fast
enough to be operated in above-ground conditions. Both sensitivity to
low-energy nuclear recoils and a high event rate tolerance are stringent
requirements to measure CENS of reactor antineutrinos. A new experimental
site, denoted the Very-Near-Site (VNS) at the Chooz nuclear power plant in
France is described. The VNS is located between the two 4.25 GW
reactor cores and matches the requirements of NUCLEUS. First results of on-site
measurements of neutron and muon backgrounds, the expected dominant background
contributions, are given. In this paper a preliminary experimental setup with
dedicated active and passive background reduction techniques is presented.
Furthermore, the feasibility to operate the NUCLEUS detectors in coincidence
with an active muon-veto at shallow overburden is studied. The paper concludes
with a sensitivity study pointing out the promising physics potential of
NUCLEUS at the Chooz nuclear power plant
A Cryogenic Silicon Interferometer for Gravitational-wave Detection
The detection of gravitational waves from compact binary mergers by LIGO has opened the era of gravitational wave astronomy, revealing a previously hidden side of the cosmos. To maximize the reach of the existing LIGO observatory facilities, we have designed a new instrument that will have 5 times the range of Advanced LIGO, or greater than 100 times the event rate. Observations with this new instrument will make possible dramatic steps toward understanding the physics of the nearby universe, as well as observing the universe out to cosmological distances by the detection of binary black hole coalescences. This article presents the instrument design and a quantitative analysis of the anticipated noise floor
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