518 research outputs found
Plant Enemy-derived Elicitors Increase the Foliar Tannin Concentration of Onobrychis viciifolia Without a Trade-off to Growth
Background and Aims Molecular experiments suggest that the regulation of the biosynthesis of condensed tannin (CT) is sensitive to the presence of plant enemies. The enemy-specific response of CT concentrations to simulated attacks by pathogenic fungi, bacteria or herbivores was studied in Onobrychis viciifolia grown at four levels of nutrient availability. It was hypothesized that CT concentrations increase in response to an attack, and that constitutive and induced levels of CT are higher at low than at high nutrient availability. Investment in CT was also predicted to be negatively related to plant growth. Methods Recently discovered substances by which plants recognize their opponents (i.e. elicitors) were used to simulate attacks to Onobrychis viciifolia grown at 0·0027, 0·075, 0·67 or 2 mm phosphorus in the nutrient solution. Key Results Relative growth rate and final biomass (P < 0·001) were highest at 0·67 mm of phosphorus. CT concentrations decreased with increasing phosphorus availability, from 94·9 to 69·0 mg g−1 leaf dry weight (P < 0·001). Compared with unscathed plants, sterile mere mechanical wounding reduced tannin concentrations from 83·8 to 69·3 mg g−1 leaf dry weight (P < 0·01). Local CT concentrations were higher when wounded leaves were additionally treated with fungal (+15·9 %), bacterial (+19·6 %) or insect (+31·0 %) elicitors (each elicitor; P < 0·05); however, only the insect elicitor (saliva of the lepidopteron Spodoptera littoralis) induced CT concentrations higher than those of unscathed leaves. Conclusions CT concentrations were inducible in the vicinity of the wound but the level of induction was unrelated to the nutrient status of the plant. There was no evidence of a growth-defence trade-off. The inverse relathionship between CT concentrations and nutrient availability appears to reflect passive growth dilution at high nutrient availability, rather than surplus CT production at low nutrient availabilit
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
The Effects of X-Ray Feedback from AGN on Host Galaxy Evolution
Hydrodynamic simulations of galaxies with active galactic nuclei (AGN) have
typically employed feedback that is purely local: i.e., an injection of energy
to the immediate neighborhood of the black hole. We perform GADGET-2
simulations of massive elliptical galaxies with an additional feedback
component: an observationally calibrated X-ray radiation field which emanates
from the black hole and heats gas out to large radii from the galaxy center. We
find that including the heating and radiation pressure associated with this
X-ray flux in our simulations enhances the effects which are commonly reported
from AGN feedback. This new feedback model is twice as effective as traditional
feedback at suppressing star formation, produces 3 times less star formation in
the last 6 Gyr, and modestly lowers the final BH mass (30%). It is also
significantly more effective than an X-ray background in reducing the number of
satellite galaxies.Comment: 9 emulateapj pages, 8 figures; accepted to Ap
Deep near-infrared imaging of the HE0450-2958 system
The QSO HE0450-2958 and the companion galaxy with which it is interacting,
both ultra luminous in the infrared, have been the subject of much attention in
recent years, as the quasar host galaxy remained undetected. This led to
various interpretations on QSO and galaxy formation and co-evolution, such as
black hole ejection, jet induced star formation, dust obscured galaxy, or
normal host below the detection limit. We carried out deep observations in the
near-IR in order to solve the puzzle concerning the existence of any host. The
object was observed with the ESO VLT and HAWK-I in the near-IR J-band for 8
hours. The images have been processed with the MCS deconvolution method
(Magain, Courbin & Sohy, 1998), permitting accurate subtraction of the QSO
light from the observations. The compact emission region situated close to the
QSO, called the blob, which previously showed only gas emission lines in the
optical spectra, is now detected in our near-IR images. Its high brightness
implies that stars likely contribute to the near-IR emission. The blob might
thus be interpreted as an off-centre, bright and very compact host galaxy,
involved in a violent collision with its companion.Comment: 4 pages, 3 figures, accepted for publication in A&
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
Galaxy Zoo: dust lane early-type galaxies are tracers of recent, gas-rich minor mergers
We present the second of two papers concerning the origin and evolution of
local early-type galaxies exhibiting dust features. We use optical and radio
data to examine the nature of active galactic nucleus (AGN) activity in these
objects, and compare these with a carefully constructed control sample. We find
that dust lane early-type galaxies are much more likely to host emission-line
AGN than the control sample galaxies. Moreover, there is a strong correlation
between radio and emission-line AGN activity in dust lane early-types, but not
the control sample. Dust lane early-type galaxies show the same distribution of
AGN properties in rich and poor environments, suggesting a similar triggering
mechanism. By contrast, this is not the case for early-types with no dust
features. These findings strongly suggest that dust lane early-type galaxies
are starburst systems formed in gas-rich mergers. Further evidence in support
of this scenario is provided by enhanced star formation and black hole
accretion rates in these objects. Dust lane early-types therefore represent an
evolutionary stage between starbursting and quiescent galaxies. In these
objects, the AGN has already been triggered but has not as yet completely
destroyed the gas reservoir required for star formation.Comment: 11 pages, 18 figures, 4 tables, MNRAS (Accepted for publication- 2012
January 19
A Powerful AGN Outburst in RBS 797
Utilizing ks of Chandra X-ray Observatory imaging, we present an
analysis of the intracluster medium (ICM) and cavity system in the galaxy
cluster RBS 797. In addition to the two previously known cavities in the
cluster core, the new and deeper X-ray image has revealed additional structure
associated with the active galactic nucleus (AGN). The surface brightness
decrements of the two cavities are unusually large, and are consistent with
elongated cavities lying close to our line-of-sight. We estimate a total AGN
outburst energy and mean jet power of erg and
erg s, respectively, depending on the
assumed geometrical configuration of the cavities. Thus, RBS 797 is apparently
among the the most powerful AGN outbursts known in a cluster. The average mass
accretion rate needed to power the AGN by accretion alone is
yr. We show that accretion of cold gas onto the AGN at this level is
plausible, but that Bondi accretion of the hot atmosphere is probably not. The
BCG harbors an unresolved, non-thermal nuclear X-ray source with a bolometric
luminosity of erg s. The nuclear emission is
probably associated with a rapidly-accreting, radiatively inefficient accretion
flow. We present tentative evidence that star formation in the BCG is being
triggered by the radio jets and suggest that the cavities may be driving weak
shocks () into the ICM, similar to the process in the galaxy
cluster MS 0735.6+7421.Comment: Accepted to ApJ; 20 pages, 11 low-resolution figure
The central black hole mass of the high-sigma but low-bulge-luminosity lenticular galaxy NGC 1332
The masses of the most massive supermassive black holes (SMBHs) predicted by
the M_BH-sigma and M_BH-luminosity relations appear to be in conflict. Which of
the two relations is the more fundamental one remains an open question. NGC
1332 is an excellent example that represents the regime of conflict. It is a
massive lenticular galaxy which has a bulge with a high velocity dispersion
sigma of ~320 km/s; bulge--disc decomposition suggests that only 44% of the
total light comes from the bulge. The M_BH-sigma and the M_BH-luminosity
predictions for the central black hole mass of NGC 1332 differ by almost an
order of magnitude. We present a stellar dynamical measurement of the SMBH mass
using an axisymmetric orbit superposition method. Our SINFONI integral-field
unit (IFU) observations of NGC 1332 resolve the SMBH's sphere of influence
which has a diameter of ~0.76 arcsec. The sigma inside 0.2 arcsec reaches ~400
km/s. The IFU data allow us to increase the statistical significance of our
results by modelling each of the four quadrants separately. We measure a SMBH
mass of (1.45 \pm 0.20) x 10^9 M_sun with a bulge mass-to-light ratio of 7.08
\pm 0.39 in the R-band. With this mass, the SMBH of NGC 1332 is offset from the
M_BH-luminosity relation by a full order of magnitude but is consistent with
the M_BH-sigma relation.Comment: 15 pages, 12 figures, accepted for publication in MNRA
Urea Activation by an External Brønsted Acid: Breaking Self-Association and Tuning Catalytic Performance
In this work, we hypothesize that Bronsted acids can activate urea-based catalysts by diminishing its self-assembly tendency. As a proof of concept, we used the asymmetric Friedel-Crafts alkylation of indoles with nitroalkenes as a benchmark reaction. The resulting 3-substituted indole derivatives were obtained with better results due to cooperative effects of the chiral urea and a Bronsted acid additive. Such synergy has been rationalized in terms of disassembly of the supramolecular catalyst aggregates, affording a more acidic and rigid catalytic complex
On the offset of barred galaxies from the black Hole MBH-σ relationship
We use collisionless N-body simulations to determine how the growth of a supermassive black hole (SMBH)
influences the nuclear kinematics in both barred and unbarred galaxies. In the presence of a bar, the increase in the
velocity dispersion σ (within the effective radius) due to the growth of an SMBH is on average �10%, whereas the
increase is only �4% in an unbarred galaxy. In a barred galaxy, the increase results from a combination of three
separate factors: (1) orientation and inclination effects; (2) angular momentum transport by the bar that results in an
increase in the central mass density; and (3) an increase in the vertical and radial velocity anisotropy of stars in the vicinity of the SMBH. In contrast, the growth of the SMBH in an unbarred galaxy causes the velocity distribution in the inner part of the nucleus to become less radially anisotropic. The increase in σ following the growth of the SMBH is insensitive to a variation of a factor of 10 in the final mass of the SMBH, showing that it is the growth process rather than the actual SMBH mass that alters bar evolution in a way that increases σ.We argue that using an axisymmetric stellar dynamical modeling code to measure SMBH masses in barred galaxies could result in a slight overestimate of the derived MBH, especially if a constant M/L ratio is assumed. We conclude that the growth of a black hole in the presence of a bar could result in an increase in σ that is roughly 4%–8% larger than the increase that occurs in an axisymmetric system. While the increase in σ due to SMBH growth in a barred galaxy might partially account for the claimed offset of barred galaxies and pseudo bulges from the MBH–σ relation obtained for elliptical galaxies and classical bulges in unbarred galaxies, it is inadequate to account for all of the offset
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