2,267 research outputs found
Moving out but keeping in touch : contacts between endoplasmic reticulum and lipid droplets
The formation of neutral lipid filled and phospholipid monolayer engulfed lipid droplets (LDs) from the bilayer of the endoplasmic reticulum (ER) is an active area of investigation. This process harnesses the biophysical properties of the lipids involved and necessitates cooperation of protein machineries in both organelle membranes. Increasing evidence suggests that once formed, LDs keep close contact to the mother organelle and that this may be achieved via several, morphologically distinct and potentially functionally specialized connections. These may help LDs to dynamically respond to changes in lipid metabolic status sensed by the ER. In this review, we will discuss recent progress in understanding how LDs interact with the ER.Peer reviewe
A sensitivity analysis of the prediction of the nitrogen fertilizer requirement of cauliflower crops using the HRI WELL_N computer model
HRI WELL_N is an easy to use computer model, which has been used by farmers and growers since 1994 to predict crop nitrogen (N) requirements for a wide range of agricultural and horticultural crops.
A sensitivity analysis was carried out to investigate the model predictions of the N fertilizer requirement of cauliflower crops, and, at that rate, the yield achieved, yield response to the fertilizer applied, N uptake, NO3-N leaching below 30 and 90 cm and mineral N at harvest. The sensitivity to four input factors – soil mineral N before planting, mineralization rate of soil organic matter, expected yield and duration of growth – was assessed. Values of these were chosen to cover ranges between 40% and 160% of values typical for field crops of cauliflowers grown in East Anglia. The assessments were made for three soils – sand, sandy loam and silt – and three rainfall scenarios – an average year and years with 144% or 56% of average rainfall during the growing season. The sensitivity of each output variable to each of the input factors (and interactions between them) was assessed using a unique ‘sequential' analysis of variance approach developed as part of this research project.
The most significant factors affecting N fertilizer requirement across all soil types/rainfall amounts were soil mineral N before planting and expected yield. N requirement increased with increasing yield expectation, and decreased with increasing amounts of soil mineral N before planting. The responses to soil mineral N were much greater when higher yields were expected. Retention of N in the rooting zone was predicted to be poor on light soils in the wettest conditions suggesting that to maximize N use, plants needed to grow rapidly and have reasonable yield potential.
Assessment of the potential impacts of errors in the values of the input factors indicated that poor estimation of, in particular, yield expectation and soil mineral N before planting could lead to either yield loss or an increased level of potentially leachable soil mineral N at harvest.
The research demonstrates the benefits of using computer simulation models to quantify the main factors for which information is needed in order to provide robust N fertilizer recommendations
How Much Is Enough? Optimal Support Payments in a Renewable-Rich Power System
The large-scale deployment of intermittent renewable energy sources may cause substantial power imbalance. Together with the transmission grid congestion caused by the remoteness of these sources from load centers, this creates a need for fast-adjusting conventional capacity
such as gas-fired plants. However, these plants have become unprofitable because of lower power prices due to the zero marginal costs of renewables. Consequently, policymakers are proposing new measures for mitigating balancing costs and securing supply. In this paper, we take the perspective of the regulator to assess the effectiveness of support payments to flexible generators. Using data on the German power system, we implement a
bi-level programming model, which shows that such payments for gas-fired plants in southern Germany reduce balancing costs and can be used as part of policy to integrate renewable energy
Comparison of bar strengths in optical and near-infrared for the OSUBSGS sample
We use a gravitational bar torque method to compare bar strengths (the
maximum tangential force normalized by radial force) in B and H-band images of
152 galaxies from the Ohio State University Bright Spiral Galaxy Survey. Our
main motivation is to check how much the difference in the rest-frame
wavelength could affect comparisons of bar strengths in low and high redshift
observations. Between these two bands we find an average bar strength ratio
Q_B/H= 1.25 which factor is nearly independent of the morphological type. We
show that Q_B/H > 1 is mostly due to reduced bulge dilution of radial forces in
the B-band. The bar torque method needs an estimate for the vertical scale
height of the galaxy, based on the radial scale length of the disk and the
galaxy's morphological type. Since these two might not always be possible to
determine at high redshifts in a reliable manner, we also checked that similar
results are obtained with vertical scale heights estimated from the radii
corresponding to the K-band surface brightness of 20 mag/arcsec^2. Also, we
made a simple test of the usability of the bar torque method at high redshifts
by checking the effects of image degradation (nearest neighbour sampling
without any adjustment of noise levels): we found that the estimated bar
strengths varied by +/- 10% at most as long as the total extent of the bar was
at least 10 pixels. Overall, we show that the gravitational bar torque method
should provide a proficient tool for quantifying bar strengths also at high
redshifts.Comment: 15 pages, 9 figures, 1 table, accepted to MNRA
Electronic properties of H on vicinal Pt surfaces: A first-principles study
In this work, we use the first-principle density-functional approach to study
the electronic structure of a H atom adsorbed on the ideal Pt(111) and vicinal
Pt(211) and Pt(331) surfaces. Full three-dimensional potential-energy surfaces
(3D PES's) as well as local electronic density of states on various adsorption
sites are obtained. The results show that the steps modify the PES
considerably. The effect is nonlocal and extends into the region of the (111)
terraces. We also find that different type of steps have different kind of
influence on the PES when compared to the one of the ideal Pt(111) surface. The
full 3D PES's calculated in this work provide a starting point for the
theoretical study of vibrational and diffusive dynamics of H adatoms adsorbed
on these vicinal surfaces.Comment: 8 pages with 5 figures and 3 tables. In version 2, there have been
made some minor changes and a bigger one in Section III.A.1 where the results
of the test calculations dealt with the accuracy of the present results have
been adde
Exponential instability in the fractional Calder\'on problem
In this note we prove the exponential instability of the fractional
Calder\'on problem and thus prove the optimality of the logarithmic stability
estimate from \cite{RS17}. In order to infer this result, we follow the
strategy introduced by Mandache in \cite{M01} for the standard Calder\'on
problem. Here we exploit a close relation between the fractional Calder\'on
problem and the classical Poisson operator. Moreover, using the construction of
a suitable orthonormal basis, we also prove (almost) optimality of the Runge
approximation result for the fractional Laplacian, which was derived in
\cite{RS17}. Finally, in one dimension, we show a close relation between the
fractional Calder\'on problem and the truncated Hilbert transform.Comment: 17 page
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