998 research outputs found
Ertragsentwicklung von Erbsen sowie Sommergerste in Reinsaat und in Mischung mit Leindotter oder Koriander im Ă–kologischen Landbau
Mischkulturen können unterschiedliche Wachstumsbedingungen besser ausschöpfen als Monokulturen. Im Gemenge mit Leguminosen können Nicht-Leguminosen überschüssigen Stickstoff aus der Bodenlösung aufnehmen. Ein ökonomischer Zusatzertrag wird bei einer Beimengung von Leindotter zu Erbsen oder Sommergerste diskutiert. Erbsenreinsaaten erreichten im Vergleich zu beiden Leindotter-Varianten gesichert höhere Erträge; Erbsen mit resp. ohne Koriander unterschieden sich nicht. Sommergerste – Reinsaaten waren bezüglich dem Ertrag den Mischungen mit Leindotter überlegen; Koriander wurde von der Sommergerste vollständig unterdrückt. Abschließend kann festgehalten werden, dass unter limitierenden Niederschlägen im pannonischen Klimaraum dem Mischkulturanbau enge Grenzen gesetzt sind
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Enrollment of adolescents and young adults onto SWOG cancer research network clinical trials: A comparative analysis by treatment site and era.
BackgroundFew adolescents and young adults (AYAs, 15-39 years old) enroll onto cancer clinical trials, which hinders research otherwise having the potential to improve outcomes in this unique population. Prior studies have reported that AYAs are more likely to receive cancer care in community settings. The National Cancer Institute (NCI) has led efforts to increase trial enrollment through its network of NCI-designated cancer centers (NCICC) combined with community outreach through its Community Clinical Oncology Program (CCOP; replaced by the NCI Community Oncology Research Program in 2014).MethodsUsing AYA proportional enrollment (the proportion of total enrollments who were AYAs) as the primary outcome, we examined enrollment of AYAs onto SWOG therapeutic trials at NCICC, CCOP, and non-NCICC/non-CCOP sites from 2004 to 2013 by type of site, study period (2004-08 vs 2009-13), and patient demographics.ResultsOverall, AYA proportional enrollment was 10.1%. AYA proportional enrollment decreased between 2004-2008 and 2009-2013 (13.1% vs 8.5%, P < .001), and was higher at NCICCs than at CCOPs and non-NCICC/non-CCOPs (14.1% vs 8.3% and 9.2%, respectively; P < .001). AYA proportional enrollment declined significantly at all three site types. Proportional enrollment of AYAs who were Black or Hispanic was significantly higher at NCICCs compared with CCOPs or non-NCICC/non-CCOPs (11.5% vs 8.8, P = .048 and 11.5% vs 8.6%, P = .03, respectively).ConclusionNot only did community sites enroll a lower proportion of AYAs onto cancer clinical trials, but AYA enrollment decreased in all study settings. Initiatives aimed at increasing AYA enrollment, particularly in the community setting with attention to minority status, are needed
Tumor growth instability and the onset of invasion
Motivated by experimental observations, we develop a mathematical model of
chemotactically directed tumor growth. We present an analytical study of the
model as well as a numerical one. The mathematical analysis shows that: (i)
tumor cell proliferation by itself cannot generate the invasive branching
behaviour observed experimentally, (ii) heterotype chemotaxis provides an
instability mechanism that leads to the onset of tumor invasion and (iii)
homotype chemotaxis does not provide such an instability mechanism but enhances
the mean speed of the tumor surface. The numerical results not only support the
assumptions needed to perform the mathematical analysis but they also provide
evidence of (i), (ii) and (iii). Finally, both the analytical study and the
numerical work agree with the experimental phenomena.Comment: 12 pages, 8 figures, revtex
When the optimal is not the best: parameter estimation in complex biological models
Background: The vast computational resources that became available during the
past decade enabled the development and simulation of increasingly complex
mathematical models of cancer growth. These models typically involve many free
parameters whose determination is a substantial obstacle to model development.
Direct measurement of biochemical parameters in vivo is often difficult and
sometimes impracticable, while fitting them under data-poor conditions may
result in biologically implausible values.
Results: We discuss different methodological approaches to estimate
parameters in complex biological models. We make use of the high computational
power of the Blue Gene technology to perform an extensive study of the
parameter space in a model of avascular tumor growth. We explicitly show that
the landscape of the cost function used to optimize the model to the data has a
very rugged surface in parameter space. This cost function has many local
minima with unrealistic solutions, including the global minimum corresponding
to the best fit.
Conclusions: The case studied in this paper shows one example in which model
parameters that optimally fit the data are not necessarily the best ones from a
biological point of view. To avoid force-fitting a model to a dataset, we
propose that the best model parameters should be found by choosing, among
suboptimal parameters, those that match criteria other than the ones used to
fit the model. We also conclude that the model, data and optimization approach
form a new complex system, and point to the need of a theory that addresses
this problem more generally
Interplay between distribution of live cells and growth dynamics of solid tumours
Experiments show that simple diffusion of nutrients and waste molecules is not sufficient to explain the typical multilayered structure of solid tumours, where an outer rim of proliferating cells surrounds a layer of quiescent but viable cells and a central necrotic region. These experiments challenge models of tumour growth based exclusively on diffusion. Here we propose a model of tumour growth that incorporates the volume dynamics and the distribution of cells within the viable cell rim. The model is suggested by in silico experiments and is validated using in vitro data. The results correlate with in vivo data as well, and the model can be used to support experimental and clinical oncology
Massive stars and the energy balance of the interstellar medium. II. The 35 solar mass star and a solution to the "missing wind problem"
We continue our numerical analysis of the morphological and energetic
influence of massive stars on their ambient interstellar medium for a 35 solar
mass star that evolves from the main sequence through red supergiant and
Wolf-Rayet phases, until it ultimately explodes as a supernova. We find that
structure formation in the circumstellar gas during the early main-sequence
evolution occurs as in the 60 solar mass case but is much less pronounced
because of the lower mechanical wind luminosity of the star. Since on the other
hand the shell-like structure of the HII region is largely preserved, effects
that rely on this symmetry become more important. At the end of the stellar
lifetime 1% of the energy released as Lyman continuum radiation and stellar
wind has been transferred to the circumstellar gas. From this fraction 10% is
kinetic energy of bulk motion, 36% is thermal energy, and the remaining 54% is
ionization energy of hydrogen. The sweeping up of the slow red supergiant wind
by the fast Wolf-Rayet wind produces remarkable morphological structures and
emission signatures, which are compared with existing observations of the
Wolf-Rayet bubble S308. Our model reproduces the correct order of magnitude of
observed X-ray luminosity, the temperature of the emitting plasma as well as
the limb brightening of the intensity profile. This is remarkable, because
current analytical and numerical models of Wolf-Rayet bubbles fail to
consistently explain these features. A key result is that almost the entire
X-ray emission in this stage comes from the shell of red supergiant wind swept
up by the shocked Wolf-Rayet wind rather than from the shocked Wolf-Rayet wind
itself as hitherto assumed and modeled. This offers a possible solution to what
is called the ``missing wind problem'' of Wolf-Rayet bubbles.Comment: 52 pages, 20 figures, 2 tables, accepted for publication in the
Astrophysical Journa
The influence of residual gas expulsion on the evolution of the Galactic globular cluster system and the origin of the Population II halo
We present new results on the evolution of the mass function of the globular
cluster system of the Milky Way, taking the effect of residual gas expulsion
into account. We assume that gas embedded star clusters start with a power-law
mass function with slope \beta=2. The dissolution of the clusters is then
studied under the combined influence of residual gas expulsion driven by energy
feedback from massive stars, stellar mass-loss, two-body relaxation and an
external tidal field. The influence of residual gas expulsion is studied by
applying results from a large grid of N-body simulations computed by Baumgardt
& Kroupa (2007).
In our model, star clusters with masses less than 10^5 M_sun lose their
residual gas on timescales much shorter than their crossing time and residual
gas expulsion is the main dissolution mechanism for star clusters, destroying
about 95% of all clusters within a few 10s of Myr. We find that in this case
the final mass function of globular clusters is established mainly by the gas
expulsion and therefore nearly independent of the strength of the external
tidal field, and that a power-law mass function for the gas embedded star
clusters is turned into a present-day log-normal one.
Another consequence of residual gas expulsion and the associated strong
infant mortality of star clusters is that the Galactic halo stars come from
dissolved star clusters. Since field halo stars would come mainly from
low-mass, short-lived clusters, our model provides an explanation for the
observed abundance variations of light elements among globular cluster stars
and the absence of such variations among the halo field stars.Comment: 12 pages, 9 figures, MNRAS accepte
A deep wide-field sub-mm survey of the Carina Nebula complex
The Great Nebula in Carina is a superb location in which to study the physics
of violent massive star-formation and the resulting feedback effects, including
cloud dispersal and triggered star-formation. In order to reveal the cold dusty
clouds in the Carina Nebula complex, we used the Large APEX Bolometer Camera
LABOCA at the APEX telescope to map a 1.25 deg x 1.25 deg (= 50 x 50 pc^2)
region at 870 micrometer. From a comparison to Halpha images we infer that
about 6% of the 870 micrometer flux in the observed area is likely free-free
emission from the HII region, while about 94% of the flux is very likely
thermal dust emission. The total (dust + gas) mass of all clouds for which our
map is sensitive is ~ 60 000 Msun, in good agreement with the mass of the
compact clouds in this region derived from 13CO line observations. We generally
find good agreement in the cloud morphology seen at 870 micrometer and the
Spitzer 8 micrometer emission maps, but also identify a prominent infrared dark
cloud. Finally, we construct a radiative transfer model for the Carina Nebula
complex that reproduces the observed integrated spectral energy distribution
reasonably well. Our analysis suggests a total gas + dust mass of about 200000
Msun in the investigated area; most of this material is in the form of
molecular clouds, but a widely distributed component of (partly) atomic gas,
containing up to ~ 50% of the total mass, may also be present. Currently, only
some 10% of the gas is in sufficiently dense clouds to be immediately available
for future star formation, but this fraction may increase with time owing to
the ongoing compression of the strongly irradiated clouds and the expected
shockwaves of the imminent supernova explosions.Comment: Accepted for publication in Astronomy & Astrophysics; high-quality
pre-prints can be obtained from
http://www.usm.uni-muenchen.de/people/preibisch/publications.htm
Research on Layer Manufacturing Techniques at Fraunhofer
Within the German Fraunhofer-Gesellschaft, the Fraunhofer Alliance Rapid Prototyping
unites the competences of 12 institutes in the field of solid freeform fabrication. Covered
competences are virtual and computer-aided product planning methods and techniques, the
development and integration of materials and processes for different industrial sectors. This
paper presents actual research results on layer manufacturing within the Fraunhofer-
Gesellschaft based on examples from Fraunhofer ILT »Laser Melting - Direct
manufacturing of metal parts with unique properties«, Fraunhofer IFAM »ecoMold - A
novel concept to produce molds for plastic injection molding and pressure die casting« and
Fraunhofer IPT »Quick manufacture, repair and modification of steel molds using
Controlled Metal Build Up (CMB)«.Mechanical Engineerin
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