2,080 research outputs found
Anthropogenic nitrogen autotrophy and heterotrophy of the world's watersheds: Past, present, and future trends
Anthropogenic nitrogen autotrophy of a territory is defined as the nitrogen flux associated with local production of harvested crops and grass consumed by livestock grazing (in kg N/km(2)/yr). Nitrogen heterotrophy is the nitrogen flux associated with local food and feed consumption by humans and domestic animals. These two summarizing characteristics (anthropogenic nitrogen autotrophy and heterotrophy (ANAH)) indicate the degree of anthropogenic perturbation of the nitrogen cycle by agriculture and human consumption: their balance value provides information on either the potential for commercial export or the need to import agricultural goods; in a watershed, their vector sum is related to the nitrogen flux delivered to the sea. These indicators were calculated for all the watersheds in the Global Nutrient Export from Watersheds (NEWS) database for 1970 and 2000, as well as for 2030 and 2050, according to Millennium Ecosystem Assessment scenarios. During this 30 year period, many watersheds shifted from relatively balanced situations toward either more autotrophic or more heterotrophic conditions. This trend is predicted to become more pronounced over the next 50 year
The BIOEXPLOIT Project
The EU Framework 6 Integrated Project BIOEXPLOIT concerns the exploitation of natural plant biodiversity for the pesticide-free production of food. It focuses on the pathogens Phytophthora infestans, Septoria tritici, Blumeria graminis, Puccinia spp. and Fusarium spp. and on the crops wheat, barley, tomato and potato. The project commenced in October 2005, comprises 45 laboratories in 12 countries, and is carried out by partners from research institutes, universities, private companies and small-medium enterprises. The project has four strategic objectives covered in eight sub-projects. These objectives relate to (i) understanding the molecular components involved in durable disease resistance, (ii) exploring and exploiting the natural biodiversity in disease resistance, (iii) accelerating the introduction of marker-assisted breeding and genetic engineering in the EU plant breeding industry, and (iv) coordinating and integrating resistance breeding research, providing training in new technologies, disseminating the results, and transferring knowledge and technologies to the industry
The absence of the 10 um silicate feature in the isolated Herbig Ae star HD 100453
We analyse the optical and IR spectra, as well as the spectral energy
distribution (UV to mm) of the candidate Herbig Ae star HD100453. This star is
particular, as it shows an energy distribution similar to that of other
isolated Herbig Ae/Be stars (HAEBEs), but unlike most of them, it does not have
a silicate emission feature at 10 um, as is shown in Meeus (2001). We confirm
the HAEBE nature of HD100453 through an analysis of its optical spectrum and
derived location in the H-R diagram. The IR spectrum of HD100453 is modelled by
an optically thin radiative transfer code, from which we derive constraints on
the composition, grain-size and temperature distribution of the circumstellar
dust. We show that it is both possible to explain the lack of the silicate
feature as (1) a grain-size effect - lack of small silicate grains, and (2) a
temperature effect - lack of small, hot silicates, as proposed by Dullemond
(2001), and discuss both possibilities.Comment: 9 pages, 7 figures; accepted by A&
Connected digit recognition with class specific word models
This work focuses on efficient use of the training material by selecting the optimal set of model topologies. We do this by training multiple word models of each word class, based on a subclassification according to a priori knowledge of the training material. We will examine classification criteria with respect to duration of the word, gender of the speaker, position of the word in the utterance, pauses in the vicinity of the word, and combinations of these. Comparative experiments were carried out on a corpus consisting of Dutch spoken connected digit strings and isolated digits, which are recorded in a wide variety of acoustic conditions. The results show, that classification based on gender of the speaker, position of the digit in the string, pauses in the vicinity of the training tokens, and models based on a combination of these criteria perform significantly better than the set with single models per digit
ISO spectroscopy of circumstellar dust in 14 Herbig Ae/Be systems: towards an understanding of dust processing
We present Infrared Space Observatory (ISO) spectra of fourteen isolated
Herbig Ae/Be (HAEBE) stars, to study the characteristics of their circumstellar
dust. These spectra show large star-to-star differences, in the emission
features of both carbon-rich and oxygen-rich dust grains. The IR spectra were
combined with photometric data ranging from the UV through the optical into the
sub-mm region. We defined two key groups, based upon the spectral shape of the
infrared region. The derived results can be summarized as follows: (1) the
continuum of the IR to sub-mm region of all stars can be reconstructed by the
sum of a power-law and a cool component, which can be represented by a black
body. Possible locations for these components are an optically thick,
geometrically thin disc (power-law component) and an optically thin flared
region (black body); (2) all stars have a substantial amount of cold dust
around them, independent of the amount of mid-IR excess they show; (3) also the
near-IR excess is unrelated to the mid-IR excess, indicating different
composition/location of the emitting material; (4) remarkably, some sources
lack the silicate bands; (5) apart from amorphous silicates, we find evidence
for crystalline silicates in several stars, some of which are new detections;
(6) PAH bands are present in at least 50% of our sample, and their appearance
is slightly different from PAHs in the ISM; (7) PAH bands are, with one
exception, not present in sources which only show a power-law continuum in the
IR; their presence is unrelated to the presence of the silicate bands; (8) the
dust in HAEBE stars shows strong evidence for coagulation; this dust processing
is unrelated to any of the central star properties (such as age, spectral type
and activity).Comment: 15 pages, accepted by A&
On the interplay between flaring and shadowing in disks around Herbig Ae/Be stars
Based on the SED, Herbig stars have been categorized into two observational
groups, reflecting their overall disk structure: group I members have disks
with a higher degree of flaring than their group II counterparts. We
investigate the 5-35 um Spitzer IRS spectra of a sample of 13 group I sources
and 20 group II sources. We focus on the continuum emission to study the
underlying disk geometry. We have determined the [30/13.5] and [13.5/7]
continuum flux ratios. The 7-um flux excess with respect to the stellar
photosphere is measured, as a marker for the strength of the near-IR emission
produced by the inner disk. We have compared our data to self-consistent
passive-disk model spectra, for which the same quantities were derived. We
confirm the literature result that the difference in continuum emission between
group I and II sources can largely be explained by a different amount of small
dust grains. However, we report a strong correlation between the [30/13.5] and
[13.5/7] flux ratios for Meeus group II sources. Moreover, the [30/13.5] flux
ratio decreases with increasing 7-um excess for all targets in the sample. To
explain these correlations with the models, we need to introduce an artificial
scaling factor for the inner disk height. In roughly 50% of the Herbig Ae/Be
stars in our sample, the inner disk must be inflated by a factor 2 to 3 beyond
what hydrostatic calculations predict. The total disk mass in small dust grains
determines the degree of flaring. We conclude, however, that for any given disk
mass in small dust grains, the shadowing of the outer (tens of AU) disk is
determined by the scale height of the inner disk (1 AU). The inner disk
partially obscures the outer disk, reducing the disk surface temperature. Here,
for the first time, we prove these effects observationally.Comment: 4 pages, 3 figures, accepted by A&
Photochemistry of the PAH pyrene in water ice: the case for ion-mediated solid-state astrochemistry
Context. Icy dust grains play an important role in the formation of complex
inter- and circumstellar molecules. Observational studies show that polycyclic
aromatic hydrocarbons (PAHs) are abundantly present in the ISM in the gas
phase. It is likely that these non-volatile species freeze out onto dust grains
as well and participate in the astrochemical solid-state network, but
experimental PAH ice studies are largely lacking. Methods. Near UV/VIS
spectroscopy is used to track the in situ VUV driven photochemistry of pyrene
containing ices at temperatures ranging from 10 to 125 K. Results. The main
photoproducts of VUV photolyzed pyrene ices are spectroscopically identified
and their band positions are listed for two host ices, \water and CO. Pyrene
ionisation is found to be most efficient in \water ices at low temperatures.
The reaction products, triplet pyrene and the 1-hydro-1-pyrenyl radical are
most efficiently formed in higher temperature water ices and in low temperature
CO ice. Formation routes and band strength information of the identified
species are discussed. Additionally, the oscillator strengths of Py, Py^+ and
PyH are derived and a quantitative kinetic analysis is performed by fitting a
chemical reaction network to the experimental data. Conclusions. Pyrene is
efficiently ionised in water ice at temperatures below 50 K. Hydrogenation
reactions dominate the chemistry in low temperature CO ice with trace amounts
of water. The results are put in an astrophysical context by determining the
importance of PAH ionisation in a molecular cloud. The photoprocessing of a
sample PAH in ice described in this manuscript indicates that PAH
photoprocessing in the solid state should also be taken into account in
astrochemical models.Comment: 11 pages, 8 figures, accepted for publication in A&
The characteristics of the IR emission features in the spectra of Herbig Ae stars: Evidence for chemical evolution
Herbig Ae/Be stars are a class of young pre-main sequence stellar objects of
intermediate mass and are known to have varying amounts of natal cloud material
still present in their direct vicinity. We characterise the IR emission bands,
due to fluorescence by PAH molecules, in the spectra of Herbig Ae/Be stars and
link observed variations to spatial aspects of the mid-IR emission. We analysed
two PAH dominated spectra from a sample of 15 Herbig Ae/Be stars observed with
Spitzer and derive profiles of the major PAH bands. The shape and the measured
band characteristics show pronounced variations between the two Spitzer
spectra. Those variations parallel those found between three ISO spectra of
other, well-studied, Herbig Ae/Be stars. The derived profiles are compared to
those from a broad sample of sources. The Spitzer and ISO spectra exhibit
characteristics commonly interpreted respectively as interstellar matter-like
(ISM), non-ISM-like, or a combination of the two. We argue that the PAH
emission detected from the sources exhibiting a combination of ISM-like and
non-ISM-like characteristics indicates the presence of two dissimilar,
spatially separated, PAH families. As the shape of the individual PAH band
profiles reflects the composition of the PAH molecules involved, this
demonstrates that PAHs in subsequent, evolutionary linked stages of star
formation are different from those in the general ISM, implying active
chemistry. None of the detected PAH emission can be associated with the
(unresolved) disk and is thus associated with the circumstellar cloud. This
implies that chemical changes may already occur in the natal cloud and not
necessarily in the disk
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