553 research outputs found
Lehr- und Lernformen in der Hochschulbildung fĂĽr das Berufsfeld Ă–kolandbau
Organic farming requires specific skills and competences such as systems thinking or
action competence. Academic education should guide students in their development
of these skills. Problem based learning or learning in reality seem appropriate. An
innovative teaching module developed by the University of Applied Sciences
Eberswalde in close collaboration with a network of regional organic agribusinesses
for its Bachelor Programme “Organic Farming and Marketing” is discussed
Changes in bulk and surface properties of two biochar types during 12 months of field ageing in two West-African soils
The study investigated the changes in properties of rice husk and corn cob biochars applied in urban agricultural field soils in Tamale (northern Ghana) and Ouagadougou (Burkina Faso), respectively. The biochars were both pyrolyzed at 500 °C with a batch reactor. Fine polyethylene mesh (litter bags) filled with 10 g of each type of biochar were buried at 20 cm depth in urban fields trials with a 3 x 2 factorial layout replicated 4 times. Factor 1 involved soil management practices at 3 levels: (1) farmers’ practice (FP), (2) 20 t biochar ha-1 and (3) control (no biochar). The second factor was time (duration) at two levels (6 and 12 months). Aged and fresh biochars were analyzed for volatile matter (VM), ash and fixed carbon (FC) contents, pH, effective cation exchange capacity (ECEC), and total surface acidity (Sa) and basicity (Sb). Dissolved organic carbon contents were determined sequentially by cold (cDOC) and hot water extractions (hDOC), respectively and aromaticities of cold water DOC (cSUVA) and hot water DOC (hSUVA) were determined. There was no significant interaction effect of soil management practices and time on measured ageing biochar properties. Time significantly affected most biochar ageing properties except Sa and Sb in rice husk biochar and ECEC in corn cob biochars at 6 months of exposure. In both biochars, Ash content, Fixed carbon (FC), cDOC, hDOC, cSUVA and hSUVA increased whilst pH and volatile matter contents decreased significantly. The hDOC was 2-3 times higher than cDOC contents for both biochars. Aromaticity of DOC contents of aged rice husk biochar exposed to soil management practices and time in the experimental site in Tamale showed persistence with time compared to corn cob biochar exposed in Ouagadougou experimental site. The results imply that rainfall, soil organic matter contents with interplay of soil minerals are key drivers to ageing and sequestration of these biochars and that these forces act at different scales but driven by time
Entwicklung eines regionalen Ausbildungsmodells „Ökolandbau und Vermarktung“ an der Fachhochschule Eberswalde im Rahmen des Bundesförderprogramms Regionen Aktiv
In September 2004 a new B. Sc. study course for Organic Farming and Marketing started at the University of Applied Sciences Eberswalde. Supported by the Federal Ministry of Consumer Protection, Food and Agriculture program “Regionen Aktiv” an innovative education model was established. Focussing on rural development farmers, processors and trading partners were involved in the development of topics for the study programme
Spectroscopic Signatures of the Tidal Disruption of Stars by Massive Black Holes
During the tidal disruption of a star by a massive black hole (BH) of mass
MBH <~ 10^7 Msun, stellar debris falls back to the BH at a rate well above the
Eddington rate. A fraction of this gas is subsequently blown away from the BH,
producing an optically bright flare of radiation. We predict the spectra and
spectral evolution of tidal disruption events, focusing on the photoionized gas
outside this outflow's photosphere. The spectrum will show absorption lines
that are strongly blueshifted relative to the host galaxy, very broad
(0.01-0.1c), and strongest at UV wavelengths (e.g., C IV, Ly alpha, O VI),
lasting ~ 1 month for a 10^6 Msun BH. Meanwhile, supernovae in galactic nuclei
are a significant source of confusion in optical surveys for tidal disruption
events: we estimate that nuclear Type Ia supernovae are two orders of magnitude
more common than tidal disruption events at z ~ 0.1 for ground-based surveys.
Nuclear Type II supernovae occur at a comparable rate but can be excluded by
pre-selecting red galaxies. Supernova contamination can be reduced to a
manageable level using high-resolution follow-up imaging with adaptive optics
or the Hubble Space Telescope. Our predictions should help optical transient
surveys capitalize on their potential for discovering tidal disruption events.Comment: 14 pages, 5 figures; accepted for publication in MNRAS; some added
discussion in Section
Long term results of postoperative Intensity-Modulated Radiation Therapy (IMRT) in the treatment of Squamous Cell Carcinoma (SCC) located in the oropharynx or oral cavity
Background: To report our long-term results with postoperative intensity-modulated radiation therapy (IMRT) in patients suffering from squamous-cell carcinoma (SCC) of the oral cavity or oropharynx. Methods: Seventy five patients were retrospectively analyzed. Median age was 58 years and 84 % were male. 76 % of the primaries were located in the oropharynx. Surgery resulted in negative margins (R0) in 64 % of the patients while 36 % suffered from positive margins (R1). Postoperative stages were as follows: stage1:4 %, stage2:9 %, stage3:17 %, stage4a:69 % with positive nodes in 84 %. Perineural invasion (Pn+) and extracapsular extension (ECE) were present in 7 % and 29 %, respectively. All patients received IMRT using the step-and-shoot approach with a simultaneously integrated boost (SIB) in 84 %. Concurrent systemic therapy was applied to 53 patients, mainly cisplatin weekly. Results: Median follow-up was 55 months (5–150). 13 patients showed locoregional failures (4 isolated local, 4 isolated neck, 5 combined) transferring into 5-year-LRC rates of 85 %. Number of positive lymph nodes (n > 2) and presence of ECE were significantly associated with decreased LRC in univariate analysis, but only the number of nodes remained significant in multivariate analysis. Overall treatment failures occurred in 20 patients (9 locoregional only, 7 distant only, 4 combined), transferring into 3-and 5-year-FFTF rates of 77 % and 75 %, respectively. The 3-and 5-year-OS rates were 80 % and 72 %, respectively. High clinical stage, high N stage, number of positive nodes (n > 2), ECE and Pn1 were significantly associated with worse FFTF and OS in univariate analysis, but only number of nodes remained significant for FFTF in multivariate analysis. Maximum acute toxicity was grade 3 in 64 % and grade 4 in 1 %, mainly hematological or mucositis/dysphagia. Maximum late toxicity was grade 3 in 23 % of the patients, mainly long-term tube feeding dependency. Conclusion: Postoperative IMRT achieved excellent LRC and good OS with acceptable acute and low late toxicity rates. The number of positive nodes (n > 2) was a strong prognostic factor for all endpoints in univariate and the only significant factor for LRC and FFTF in multivariate analysis. Patients with feeding tubes due to postoperative complications had an increased risk for long-term feeding tube dependency
Are Radio AGN Powered by Accretion or Black Hole Spin?
We compare accretion and black hole spin as potential energy sources for
outbursts from AGN in brightest cluster galaxies (BCGs). Based on our adopted
spin model, we find that the distribution of AGN power estimated from X-ray
cavities is consistent with a broad range of both spin parameter and accretion
rate. Sufficient quantities of molecular gas are available in most BCGs to
power their AGN by accretion alone. However, we find no correlation between AGN
power and molecular gas mass over the range of jet power considered here. For a
given AGN power, the BCG's gas mass and accretion efficiency, defined as the
fraction of the available cold molecular gas that is required to power the AGN,
both vary by more than two orders of magnitude. Most of the molecular gas in
BCGs is apparently consumed by star formation or is driven out of the nucleus
by the AGN before it reaches the nuclear black hole. Bondi accretion from hot
atmospheres is generally unable to fuel powerful AGN, unless their black holes
are more massive than their bulge luminosities imply. We identify several
powerful AGN that reside in relatively gas-poor galaxies, indicating an
unusually efficient mode of accretion, or that their AGN are powered by another
mechanism. If these systems are powered primarily by black hole spin, rather
than by accretion, spin must also be tapped efficiently in some systems, i.e.,
, or their black hole masses must be substantially
larger than the values implied by their bulge luminosities. We constrain the
(model dependent) accretion rate at the transition from radiatively inefficient
to radiatively efficient accretion flows to be a few percent of the Eddington
rate, a value that is consistent with other estimates.Comment: Accepted for Publication in ApJ, January 2011, 21 pages, 4 figures;
One new data point added to figures; clarifications and minor corrections in
response to referee repor
Spectral and morphological properties of quasar hosts in SPH simulations of AGN feeding by mergers
We present a method for generating virtual observations from
smoothed-particle-hydrodynamics (SPH) simulations. This method includes stellar
population synthesis models and the reprocessing of starlight by dust to
produce realistic galaxy images. We apply this method and simulate the merging
of two identical giant Sa galaxies. The merger remnant is an elliptical galaxy.
The merger concentrates the gas content of the two galaxies into the nuclear
region. The gas that flows into the nuclear region refuels the central black
holes of the merging galaxies. We follow the refuelling of the black holes
during the merger semi-analytically.
In the simulation presented in this article, the black holes grow from 3 x
10^7 to 1.8X 10^8 Solar masses, with a peak AGN luminosity of M_B ~ -23.7. We
study how the morphological and spectral properties of the system evolve during
the merger and work out the predictions of this scenario for the properties of
host galaxies during the active phase. The peak of AGN activity coincides with
the merging of the two galactic nuclei and occurs at a stage when the remnant
looks like a lenticular galaxy. The simulation predicts the formation of a
circumnuclear starburst ring/dusty torus with an opening angle of 30-40 degrees
and made of clouds with n_H=10^24 cm^-2. The average optical depth of the torus
is quite high, but the obscuring medium is patchy, so that there still exist
lines of sight where the AGN is visible in a nearly edge-on view. For the same
reason, there are lines of sight where the AGN is completely obscured in the
face-on view.Comment: 14 pages, 11 figure
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