366 research outputs found
Changes in specific metabolic pathways are essential steps in the early apoptotic process in the liver
the immunosuppressant Cyclosporine A (CsA), we used multinuclear NMR spectroscopy and molecular studies to characterize metabolic pathways in mice liver during anti-Fas-induced apoptosis. An upregulation of specific metabolic pathways of glucose was the earliest indicator of the effect of Fas on the liver. CsA prevented apoptosis and energy failure at late stages, while the reversal of Fas-induced metabolic upregulation at early stages preceded the protective effect of EGF on programmed cell death. These phenomena provide useful hints for the understanding of early mechanisms controlling apoptotic cell death
Outcome and predictors for successful resuscitation in the emergency room of adult patients in traumatic cardiorespiratory arrest
Correction to:Regular participation in leisure time activities and high cardiovascular fitness improve motor sequence learning in older adults (Psychological Research, (2021), 85, 4, (1488-1502), 10.1007/s00426-020-01351-y)
Magnetohydrodynamics dynamical relaxation of coronal magnetic fields. II. 2D magnetic X-points
We provide a valid magnetohydrostatic equilibrium from the collapse of a 2D
X-point in the presence of a finite plasma pressure, in which the current
density is not simply concentrated in an infinitesimally thin, one-dimensional
current sheet, as found in force-free solutions. In particular, we wish to
determine if a finite pressure current sheet will still involve a singular
current, and if so, what is the nature of the singularity. We use a full MHD
code, with the resistivity set to zero, so that reconnection is not allowed, to
run a series of experiments in which an X-point is perturbed and then is
allowed to relax towards an equilibrium, via real, viscous damping forces.
Changes to the magnitude of the perturbation and the initial plasma pressure
are investigated systematically. The final state found in our experiments is a
"quasi-static" equilibrium where the viscous relaxation has completely ended,
but the peak current density at the null increases very slowly following an
asymptotic regime towards an infinite time singularity. Using a high grid
resolution allows us to resolve the current structures in this state both in
width and length. In comparison with the well known pressureless studies, the
system does not evolve towards a thin current sheet, but concentrates the
current at the null and the separatrices. The growth rate of the singularity is
found to be tD, with 0 < D < 1. This rate depends directly on the initial
plasma pressure, and decreases as the pressure is increased. At the end of our
study, we present an analytical description of the system in a quasi-static
non-singular equilibrium at a given time, in which a finite thick current layer
has formed at the null
Continental weathering and recovery from ocean nutrient stress during the Early Triassic Biotic Crisis
Following the latest Permian extinction ∼252 million years ago, normal marine and terrestrial
ecosystems did not recover for another 5-9 million years. The driver(s) for the Early Triassic
biotic crisis, marked by high atmospheric CO2 concentration, extreme ocean warming, and
marine anoxia, remains unclear. Here we constrain the timing of authigenic K-bearing mineral
formation extracted from supergene weathering profiles of NW-Pangea by Argon geochronology,
to demonstrate that an accelerated hydrological cycle causing intense chemical
alteration of the continents occurred between ∼254 and 248 Ma, and continued throughout
the Triassic period. We show that enhanced ocean nutrient supply from this intense continental
weathering did not trigger increased ocean productivity during the Early Triassic
biotic crisis, due to strong thermal ocean stratification off NW Pangea. Nitrogen isotope
constraints suggest, instead, that full recovery from ocean nutrient stress, despite some brief
amelioration ∼1.5 million years after the latest Permian extinction, did not commence until
climate cooling revitalized the global upwelling systems and ocean mixing ∼10 million years
after the mass extinction
Locating current sheets in the solar corona
Current sheets are essential for energy dissipation in the solar corona, in
particular by enabling magnetic reconnection. Unfortunately, sufficiently thin
current sheets cannot be resolved observationally and the theory of their
formation is an unresolved issue as well. We consider two predictors of coronal
current concentrations, both based on geometrical or even topological
properties of a force free coronal magnetic field. First, there are
separatrices related to magnetic nulls. Through separatrices the magnetic
connectivity changes discontinuously. Coronal magnetic nulls are, however, very
rare. At second, inspired by the concept of generalized magnetic reconnection
without nulls, quasi-separatrix layers (QSL) were suggested. Through QSL the
magnetic connectivity changes continuously, though strongly. The strength of
the connectivity change can be quantified by measuring the squashing of the
flux tubes which connect the magnetically conjugated photospheres.
We verify the QSL and separatrix concepts by comparing the sites of magnetic
nulls and enhanced squashing with the location of current concentrations in the
corona. Due to the known difficulties of their direct observation we simulated
the coronal current sheets by numerically calculating the response of the
corona to energy input from the photosphere heating a simultaneously observed
EUV Bright Point. We did not find coronal current sheets not at the
separatrices but at several QSL locations. The reason is that although the
geometrical properties of force free extrapolated magnetic fields can indeed,
hint at possible current concentrations, a necessary condition for current
sheet formation is the local energy input into the corona
Regression toward the mean – a detection method for unknown population mean based on Mee and Chua's algorithm
<p>Abstract</p> <p>Background</p> <p>Regression to the mean (RTM) occurs in situations of repeated measurements when extreme values are followed by measurements in the same subjects that are closer to the mean of the basic population. In uncontrolled studies such changes are likely to be interpreted as a real treatment effect.</p> <p>Methods</p> <p>Several statistical approaches have been developed to analyse such situations, including the algorithm of Mee and Chua which assumes a known population mean <it>μ</it>. We extend this approach to a situation where <it>μ </it>is unknown and suggest to vary it systematically over a range of reasonable values. Using differential calculus we provide formulas to estimate the range of <it>μ </it>where treatment effects are likely to occur when RTM is present.</p> <p>Results</p> <p>We successfully applied our method to three real world examples denoting situations when (a) no treatment effect can be confirmed regardless which <it>μ </it>is true, (b) when a treatment effect must be assumed independent from the true <it>μ </it>and (c) in the appraisal of results of uncontrolled studies.</p> <p>Conclusion</p> <p>Our method can be used to separate the wheat from the chaff in situations, when one has to interpret the results of uncontrolled studies. In meta-analysis, health-technology reports or systematic reviews this approach may be helpful to clarify the evidence given from uncontrolled observational studies.</p
[2,4-13C]β-hydroxybutyrate Metabolism in Astrocytes and C6 Glioblastoma Cells
This study was undertaken to determine if the ketogenic diet could be useful for glioblastoma patients. The hypothesis tested was whether glioblastoma cells can metabolize ketone bodies. Cerebellar astrocytes and C6 glioblastoma cells were incubated in glutamine and serum free medium containing [2,4-13C]β-hydroxybutyrate (BHB) with and without glucose. Furthermore, C6 cells were incubated with [1-13C]glucose in the presence and absence of BHB. Cell extracts were analyzed by mass spectrometry and media by 1H magnetic resonance spectroscopy and HPLC. Using [2,4-13C]BHB and [1-13C]glucose it could be shown that C6 cells, in analogy to astrocytes, had efficient mitochondrial activity, evidenced by 13C labeling of glutamate, glutamine and aspartate. However, in the presence of glucose, astrocytes were able to produce and release glutamine, whereas this was not accomplished by the C6 cells, suggesting lack of anaplerosis in the latter. We hypothesize that glioblastoma cells kill neurons by not supplying the necessary glutamine, and by releasing glutamate
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