162 research outputs found
Selective Visualization of Fluorescent Sterols in Caenorhabditis elegans by Bleach-Rate-Based Image Segmentation
The nematode Caenorhabditis elegans is a genetically tractable model organism to investigate sterol transport. In vivo imaging of the fluorescent sterol, dehydroergosterol (DHE), is challenged by C. elegans' high autofluorescence in the same spectral region as emission of DHE. We present a method to detect DHE selectively, based on its rapid bleaching kinetics compared to cellular autofluorescence. Worms were repeatedly imaged on an ultraviolet-sensitive wide field (UV-WF) microscope, and bleaching kinetics of DHE were fitted on a pixel-basis to mathematical models describing the intensity decay. Bleach-rate constants were determined for DHE in vivo and confirmed in model membranes. Using this method, we could detect enrichment of DHE in specific tissues like the nerve ring, the spermateca and oocytes. We confirm these results in C. elegans gut-granule-loss (glo) mutants with reduced autofluorescence and compare our method with three-photon excitation microscopy of sterol in selected tissues. Bleach-rate-based UV-WF imaging is a useful tool for genetic screening experiments on sterol transport, as exemplified by RNA interference against the rme-2 gene coding for the yolk receptor and for worm homologues of Niemann-Pick C disease proteins. Our approach is generally useful for identifying fluorescent probes in the presence of high cellular autofluorescence
Instantons for Vacuum Decay at Finite Temperature in the Thin Wall Limit
In dimensions, false vacuum decay at zero temperature is dominated by
the symmetric instanton, a sphere of radius , whereas at
temperatures , the decay is dominated by a `cylindrical' (static)
symmetric instanton. We study the transition between these two regimes
in the thin wall approximation. Taking an symmetric ansatz for the
instantons, we show that for and new periodic solutions exist in a
finite temperature range in the neighborhood of . However,
these solutions have higher action than the spherical or the cylindrical one.
This suggests that there is a sudden change (a first order transition) in the
derivative of the nucleation rate at a certain temperature , when the
static instanton starts dominating. For , on the other hand, the new
solutions are dominant and they smoothly interpolate between the zero
temperature instanton and the high temperature one, so the transition is of
second order. The determinantal prefactors corresponding to the `cylindrical'
instantons are discussed, and it is pointed out that the entropic contributions
from massless excitations corresponding to deformations of the domain wall give
rise to an exponential enhancement of the nucleation rate for .Comment: 24 pages, 7 figures available upon request, DAMTP-R-94/
Quintessential Maldacena-Maoz Cosmologies
Maldacena and Maoz have proposed a new approach to holographic cosmology
based on Euclidean manifolds with disconnected boundaries. This approach
appears, however, to be in conflict with the known geometric results [the
Witten-Yau theorem and its extensions] on spaces with boundaries of
non-negative scalar curvature. We show precisely how the Maldacena-Maoz
approach evades these theorems. We also exhibit Maldacena-Maoz cosmologies with
[cosmologically] more natural matter content, namely quintessence instead of
Yang-Mills fields, thereby demonstrating that these cosmologies do not depend
on a special choice of matter to split the Euclidean boundary. We conclude that
if our Universe is fundamentally anti-de Sitter-like [with the current
acceleration being only temporary], then this may force us to confront the
holography of spaces with a connected bulk but a disconnected boundary.Comment: Much improved exposition, exponent in Cai-Galloway theorem fixed,
axionic interpretation of scalar explained, JHEP version. 33 pages, 3 eps
figure
A system for accurate and automated injection of hyperpolarized substrate with minimal dead time and scalable volumes over a large range
Over recent years hyperpolarization by dissolution dynamic nuclear polarization has become an established
technique for studying metabolism in vivo in animal models. Temporal signal plots obtained from
the injected metabolite and daughter products, e.g. pyruvate and lactate, can be fitted to compartmental
models to estimate kinetic rate constants. Modeling and physiological parameter estimation can be made
more robust by consistent and reproducible injections through automation. An injection system previously
developed by us was limited in the injectable volume to between 0.6 and 2.4 ml and injection
was delayed due to a required syringe filling step. An improved MR-compatible injector system has been
developed that measures the pH of injected substrate, uses flow control to reduce dead volume within the
injection cannula and can be operated over a larger volume range. The delay time to injection has been
minimized by removing the syringe filling step by use of a peristaltic pump. For 100 ll to 10.000 ml, the
volume range typically used for mice to rabbits, the average delivered volume was 97.8% of the demand
volume. The standard deviation of delivered volumes was 7 ll for 100 ll and 20 ll for 10.000 ml demand
volumes (mean S.D. was 9 ul in this range). In three repeat injections through a fixed 0.96 mm O.D. tube
the coefficient of variation for the area under the curve was 2%. For in vivo injections of hyperpolarized
pyruvate in tumor-bearing rats, signal was first detected in the input femoral vein cannula at 3–4 s
post-injection trigger signal and at 9–12 s in tumor tissue. The pH of the injected pyruvate was
7.1 ± 0.3 (mean ± S.D., n = 10). For small injection volumes, e.g. less than 100 ll, the internal diameter
of the tubing contained within the peristaltic pump could be reduced to improve accuracy. Larger injection
volumes are limited only by the size of the receiving vessel connected to the pump
Prospects for dedicated energy crop production and attitudes towards agricultural straw use: the case of livestock farmers
Second generation biofuels utilising agricultural by-products (e.g. straw), or dedicated energy crops (DECs) produced on ‘marginal’ land, have been called for. A structured telephone survey of 263 livestock farmers, predominantly located in the west or ‘marginal’ upland areas of England captured data on attitudes towards straw use and DECs. Combined with farm physical and business data, the survey results show that 7.2% and 6.3% of farmers would respectively consider growing SRC and miscanthus, producing respective maximum potential English crop areas of 54,603 ha and 43,859 ha. If higher market prices for straw occurred, most livestock farmers would continue to buy straw. Reasons for not being willing to consider growing DECs include concerns over land quality, committing land for a long time period, lack of appropriate machinery, profitability, and time to financial return; a range of moral, land quality, production conflict and lack of crop knowledge factors were also cited. Results demonstrate limited potential for the production of DECs on livestock farms in England. Changes in policy support to address farmer concerns with respect to DECs will be required to incentivise farmers to increase energy crop production. Policy support for DEC production must be cognisant of farm-level economic, tenancy and personal objectives
Increased dietary protein in the second trimester of gestation increases live weight gain and carcass composition in weaner calves to 6 months of age
Genetically similar nulliparous Polled Hereford heifers from a closed pedigree herd were used to evaluate the effects of dietary protein during the first and second trimester of gestation upon fetal, placental and postnatal growth. Heifers were randomly allocated into two groups at 35d post AI (35dpc) to a single bull and fed High (15.7%CP) or Low (5.9%CP) protein in the first trimester (T1). At 90dpc, half of each nutritional treatment group changed to a High or Low protein diet for the second trimester until 180dpc (T2). High protein intake in the second trimester increased birthweight in females (P = 0.05) but there was no effect of treatment upon birthweight when taken over both sexes. Biparietal diameter was significantly increased by high protein in the second trimester with the effect being greater in the female (P = 0.02) but also significant overall (P = 0.05). Placental weight was positively correlated with birth weight, fibroblast volume, and relative blood vessel volume (P < 0.05). Placental fibroblast density was increased and trophoblast volume decreased in the high protein first trimester treatment group (P <0.05). There was a trend for placental weight to be increased by high protein in the second trimester (P = 0.06). Calves from heifers fed the high protein treatment in the second trimester weighed significantly more on all occasions preweaning (at one month (P = 0.0004), 2 mths (P = 0.006), 3 mths (P = 0.002), 4 mths (P = 0.01), 5 mths (P = 41 0.03), 6 mths (P = 0.001)), and grew at a faster rate over the 6 month period. By 6 mths of age the calves from heifers fed high nutrition in the second trimester weighed 33kg heavier than those fed the low diet in the second trimester. These results suggest that dietary protein in early pregnancy alters the development of the bovine placenta and calf growth to weaning
Chondrules – ubiquitous chondritic solids tracking the evolution of the solar protoplanetary disk
The Physics of Star Cluster Formation and Evolution
© 2020 Springer-Verlag. The final publication is available at Springer via https://doi.org/10.1007/s11214-020-00689-4.Star clusters form in dense, hierarchically collapsing gas clouds. Bulk kinetic energy is transformed to turbulence with stars forming from cores fed by filaments. In the most compact regions, stellar feedback is least effective in removing the gas and stars may form very efficiently. These are also the regions where, in high-mass clusters, ejecta from some kind of high-mass stars are effectively captured during the formation phase of some of the low mass stars and effectively channeled into the latter to form multiple populations. Star formation epochs in star clusters are generally set by gas flows that determine the abundance of gas in the cluster. We argue that there is likely only one star formation epoch after which clusters remain essentially clear of gas by cluster winds. Collisional dynamics is important in this phase leading to core collapse, expansion and eventual dispersion of every cluster. We review recent developments in the field with a focus on theoretical work.Peer reviewe
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