2,291 research outputs found
A spatial model of calcification in scleractinian corals
Calcification in scleractinian corals is a highly complex process depending on a wide variety of physical, chemical and biological parameters that interact on a molecular, cellular, organismal and ecosystem level. Although many of these individual parameters have been identified during recent years, coral skeletogenesis on a systems level is still not well understood, limiting the possibility to accurately predict the effect of environmental changes. Therefore we have constructed a model of calcification in which existing knowledge on the factors influencing skeleton formation is integrated within a mathematical framework. In this model we have developed a spatial representation of the coral tissue where we simulate the relevant chemical reactions in the surrounding environment, the transport processes of inorganic carbon and calcium ions, photosymthesis, respiration and calcification in the different cell layers. We model the change in space and time of the different processes as a set of coupled reaction-diffusion equations. Simulations can also be employed to clarify the relative contribution of different individual processes such as ion transport, photosynthesis or mitochondrial respiration rates. Results of these simulations can be used to guide further experimental studies. In the future we hope to combine all these models in a multi-scale model of calcification which can be used to analyse the relations between the marine environment, genetic regulation, skeletogenesis and coral growth
Iron Depletion: An Ameliorating Factor for Sickle Cell Disease?
We report some observations from our laboratory practice that might be important for the treatment of sickle cell disease (SCD). We describe data from two cases indicating that iron depletion might have a beneficial effect diminishing the formation of HbS in
favor of HbF, possibly reducing the severity of the disease. We believe that it would be worthwhile to monitor the course of the disease comparing cases with identical genotypes with and without iron depletion, and we advise to consider chelation therapy to reduce iron overload in patients with SCD
Yields of oxidized volatile organic compounds during the OH radical initiated oxidation of isoprene, methyl vinyl ketone, and methacrolein under high-NO_x conditions
We present first-generation and total production yields of glyoxal, methylglyoxal, glycolaldehyde, and hydroxyacetone from the oxidation of isoprene, methyl vinyl ketone (MVK), and methacrolein (MACR) with OH under high NO_x conditions. Several of these first-generation yields are not included in commonly used chemical mechanisms, such as the Leeds Master Chemical Mechanism (MCM) v. 3.2. The first-generation yield of glyoxal from isoprene was determined to be 2.1 (±0.6)%. Inclusion of first-generation production of glyoxal, glycolaldehyde and hydroxyacetone from isoprene greatly improves performance of an MCM based model during the initial part of the experiments. In order to further improve performance of the MCM based model, higher generation glyoxal production was reduced by lowering the first-generation yield of glyoxal from C5 hydroxycarbonyls. The results suggest that glyoxal production from reaction of OH with isoprene under high NO_x conditions can be approximated by inclusion of a first-generation production term together with secondary production only via glycolaldehyde. Analogously, methylglyoxal production can be approximated by a first-generation production term from isoprene, and secondary production via MVK, MACR and hydroxyacetone. The first-generation yields reported here correspond to less than 5% of the total oxidized yield from isoprene and thus only have a small effect on the fate of isoprene. However, due to the abundance of isoprene, the combination of first-generation yields and reduced higher generation production of glyoxal from C5 hydroxycarbonyls is important for models that include the production of the small organic molecules from isoprene
Exploring the phase space of multiple states in highly turbulent Taylor-Couette flow
We investigate the existence of multiple turbulent states in highly turbulent
Taylor-Couette flow in the range of to ,
by measuring the global torques and the local velocities while probing the
phase space spanned by the rotation rates of the inner and outer cylinder. The
multiple states are found to be very robust and are expected to persist beyond
. The rotation ratio is the parameter that most strongly
controls the transitions between the flow states; the transitional values only
weakly depend on the Taylor number. However, complex paths in the phase space
are necessary to unlock the full region of multiple states. Lastly, by mapping
the flow structures for various rotation ratios in a Taylor-Couette setup with
an equal radius ratio but a larger aspect ratio than before, multiple states
were again observed. Here, they are characterized by even richer roll structure
phenomena, including, for the first time observed in highly turbulent TC flow,
an antisymmetrical roll state.Comment: 9 pages, 7 figure
Public exhibit for demonstrating the quantum of electrical conductance
We present a new robust setup that explains and demonstrates the quantum of
electrical conductance for a general audience and which is continuously
available in a public space. The setup allows users to manually thin a gold
wire of several atoms in diameter while monitoring its conductance in real
time. During the experiment, a characteristic step-like conductance decrease
due to rearrangements of atoms in the cross-section of the wire is observed.
Just before the wire breaks, a contact consisting of a single atom with a
characteristic conductance close to the quantum of conductance can be
maintained up to several seconds. The setup is operated full-time, needs
practically no maintenance and is used on different educational levels
Monte Carlo study of multiply crosslinked semiflexible polymer networks
We present a method to generate realistic, three-dimensional networks of
crosslinked semiflexible polymers. The free energy of these networks is
obtained from the force-extension characteristics of the individual polymers
and their persistent directionality through the crosslinks. A Monte Carlo
scheme is employed to obtain isotropic, homogeneous networks that minimize the
free energy, and for which all of the relevant parameters can be varied: the
persistence length, the contour length as well as the crosslinking length may
be chosen at will. We also provide an initial survey of the mechanical
properties of our networks subjected to shear strains, showing them to display
the expected non-linear stiffening behavior. Also, a key role for non-affinity
and its relation to order in the network is uncovered.Comment: 11 pages, revised figures, added extra information about the network
Simulation of spatial variability in crop leaf area index and yield using agroecosystem modeling and geophysics-based quantitative soil information
Agroecosystem models that simulate crop growth as a function of weather conditionsand soil characteristics are among the most promising tools for improving crop yield and achieving more sustainable agricultural production systems. This study aims at using spatially distributed crop growth simulations to investigate how field-scale patterns in soil properties obtained using geophysical mapping affect the spatial variability of soil water content dynamics and growth of crops at the square kilometer scale. For this, a geophysics-based soil map was intersected with land use information. Soilhydraulic parameters were calculated using pedotransfer functions. Simulations of soilwater content dynamics performed with the agroecosystem model AgroC were com-pared with soil water content measured at two locations, resulting in RMSE of 0.032and of 0.056 cm3cm−3, respectively. The AgroC model was then used to simulate thegrowth of sugar beet (Beta vulgaris L.), silage maize (Zea maysL.), potato (SolanumtuberosumL.), winter wheat (Triticum aestivumL.), winter barley (Hordeum vulgareL.), and winter rapeseed (Brassica napusL.) in the 1- by 1-km study area. It was found that the simulated leaf area index (LAI) was affected by the magnitude of simulated water stress, which was a function of both the crop type and soil characteristics. Simulated LAI was generally consistent with the observed LAI calculated from normalized difference vegetation index (LAINDVI) obtained from RapidEye satellite data. Finally, maps of simulated agricultural yield were produced for four crops, and it was found that simulated yield matched well with actual harvest data and literature values. Therefore, it was concluded that the information obtained from geophysics-based soilmapping was valuable for practical agricultural applications
Virtual-pion and two-photon production in pp scattering
Two-photon production in pp scattering is proposed as a means of studying
virtual-pion emission. Such a process is complementary to real-pion emission in
pp scattering. The virtual-pion signal is embedded in a background of
double-photon bremsstrahlung. We have developed a model to describe this
background process and show that in certain parts of phase space the
virtual-pion signal gives significant contribution. In addition, through
interference with the two-photon bremsstrahlung background, one can determine
the relative phase of the virtual-pion process
Increased genetic marker density reveals high levels of admixture between red deer and introduced Japanese sika in Kintyre, Scotland
Hybridization is a natural process at species range boundaries, but increasing numbers of species are hybridizing due to direct or indirect human activities. In such cases of anthropogenic hybridization, subsequent introgression can threaten the survival of native species. To date, many such systems have been studied with too few genetic markers to assess the level of threat resulting from advanced backcrossing. Here, we use 44,999 single nucleotide polymorphisms (SNPs) and the ADMIXTURE program to study two areas of Scotland where a panel of 22 diagnostic microsatellites previously identified introgression between native red deer (Cervus elaphus) and introduced Japanese sika (Cervus nippon). In Kintyre, we reclassify 26% of deer from the pure species categories to the hybrid category whereas in the NW Highlands we only reclassify 2%. As expected, the reclassified individuals are mostly advanced backcrosses. We also investigate the ability of marker panels selected on different posterior allele frequency criteria to find hybrids assigned by the full marker set and show that in our data, ancestry informative markers (i.e. those that are highly differentiated between the species, but not fixed) are better than diagnostic markers (those markers that are fixed between the species) because they are more evenly distributed in the genome. Diagnostic loci are concentrated on the X chromosome to the detriment of autosomal coverage
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