6,132 research outputs found
Mechanical and SEM analysis of artificial comet nucleus samples
Since 1987 experiments dealing with comet nucleus phenomena have been carried out in the DFVLR space simulation chambers. The main objective of these experiments is a better understanding of thermal behavior, surface phenomena and especially the gas dust interaction. As a function of different sample compositions and exposure to solar irradiation (xenon-bulbs) crusts of different hardness and thickness were measured. The measuring device consists of a motor driven pressure foot (5 mm diameter), which is pressed into the sample. The applied compressive force is electronically monitored. The microstructure of the crust and dust residuals is investigated by scanning electron microscopy (SEM) techniques. Stress-depth profiles of an unirradiated and an irradiated model comet are given
Plasma lecithin/cholesterol acyltransferase (LCAT) activity in multipe-organ donors: A predictor of allograft viability in clinical liver transplantation
Microbial production of 1-octanol: a naturally excreted biofuel with diesel-like properties
The development of sustainable, bio-based technologies to convert solar energy and carbon dioxide into fuels is a grand challenge. A core part of this challenge is to produce a fuel that is compatible with the existing transportation infrastructure. This task is further compounded by the commercial desire to separate the fuel from the biotechnological host. Based on its fuel characteristics, 1-octanol was identified as an attractive metabolic target with diesel-like properties. We therefore engineered a synthetic pathway specifically for the biosynthesis of 1-octanol in Escherichia coli BL21(DE3) by over-expression of three enzymes (thioesterase, carboxylic acid reductase and aldehyde reductase) and one maturation factor (phosphopantetheinyl transferase). Induction of this pathway in a shake flask resulted in 4.4 mg 1-octanol L(-1) h(-1) which exceeded the productivity of previously engineered strains. Furthermore, the majority (73%) of the fatty alcohol was localised within the media without the addition of detergent or solvent overlay. The deletion of acrA reduced the production and excretion of 1-octanol by 3-fold relative to the wild-type, suggesting that the AcrAB-TolC complex may be responsible for the majority of product efflux. This study presents 1-octanol as a potential fuel target that can be synthesised and naturally accumulated within the media using engineered microbes
Lipid droplets: A dynamic organelle moves into focus.
Lipid droplets (LDs) were perceived as static storage deposits, which passively participate in the energy homeostasis of both cells and entire organisms. However, this view has changed recently after the realization of a complex and highly dynamic LD proteome. The proteome contains key components of the fat mobilization system and proteins that suggest LD interactions with a variety of cell organelles, including the endoplasmic reticulum, mitochondria and peroxisomes. The study of LD cell biology, including cross-talk with other organelles, the trafficking of LDs in the cell and regulatory events involving the LD coat proteins is now on the verge of leaving its infancy and unfolds that LDs are highly dynamic cellular organelles
Ischemic preconditioning attenuates portal venous plasma concentrations of purines following warm liver ischemia in man
Background/Aims: Degradation of adenine nucleotides to adenosine has been suggested to play a critical role in ischemic preconditioning (IPC). Thus, we questioned in patients undergoing partial hepatectomy whether (i) IPC will increase plasma purine catabolites and whether (ii) formation of purines in response to vascular clamping (Pringle maneuver) can be attenuated by prior IPC. Methods: 75 patients were randomly assigned to three groups: group I underwent hepatectomy without vascular clamping; group II was subjected to the Pringle maneuver during resection, and group III was preconditioned (10 min ischemia and 10 min reperfusion) prior to the Pringle maneuver for resection. Central, portal venous and arterial plasma concentrations of adenosine, inosine, hypoxanthine and xanthine were determined by high-performance liquid chromatography. Results: Duration of the Pringle maneuver did not differ between patients with or without IPC. Surgery without vascular clamping had only a minor effect on plasma purine transiently increased. After the Pringle maneuver alone, purine plasma concentrations were most increased. This strong rise in plasma purines caused by the Pringle maneuver, however, was significantly attenuated by IPC. When portal venous minus arterial concentration difference was calculated for inosine or hypoxanthine, the respective differences became positive in patients subjected to the Pringle maneuver and were completely prevented by preconditioning. Conclusion: These data demonstrate that (i) IPC increases formation of adenosine, and that (ii) the unwanted degradation of adenine nucleotides to purines caused by the Pringle maneuver can be attenuated by IPC. Because IPC also induces a decrease of portal venous minus arterial purine plasma concentration differences, IPC might possibly decrease disturbances in the energy metabolism in the intestine as well. Copyright (C) 2005 S. Karger AG, Basel
The chaotic behavior of the black hole system GRS 1915+105
A modified non-linear time series analysis technique, which computes the
correlation dimension , is used to analyze the X-ray light curves of the
black hole system GRS 1915+105 in all twelve temporal classes. For four of
these temporal classes saturates to which indicates that
the underlying dynamical mechanism is a low dimensional chaotic system. Of the
other eight classes, three show stochastic behavior while five show deviation
from randomness. The light curves for four classes which depict chaotic
behavior have the smallest ratio of the expected Poisson noise to the
variability () while those for the three classes which depict
stochastic behavior is the highest (). This suggests that the temporal
behavior of the black hole system is governed by a low dimensional chaotic
system, whose nature is detectable only when the Poisson fluctuations are much
smaller than the variability.Comment: Accepted for publication in Astrophysical Journa
The backbone of the climate network
We propose a method to reconstruct and analyze a complex network from data
generated by a spatio-temporal dynamical system, relying on the nonlinear
mutual information of time series analysis and betweenness centrality of
complex network theory. We show, that this approach reveals a rich internal
structure in complex climate networks constructed from reanalysis and model
surface air temperature data. Our novel method uncovers peculiar wave-like
structures of high energy flow, that we relate to global surface ocean
currents. This points to a major role of the oceanic surface circulation in
coupling and stabilizing the global temperature field in the long term mean
(140 years for the model run and 60 years for reanalysis data). We find that
these results cannot be obtained using classical linear methods of multivariate
data analysis, and have ensured their robustness by intensive significance
testing.Comment: 6 pages, 5 figure
An isolated complete intestinal transplantation in an adult: A complicated postoperative course
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