552 research outputs found
Quantum gravitational corrections to a star metric and the black hole limit
No full textIn this paper we consider the full set of quantum gravitational corrections to a star metric to second order in curvature. As we use an effective field theoretical approach, these corrections apply to any model of quantum gravity that is based on general coordinate invariance. We then discuss the black hole limit and identify an interesting phenomenon which could shed some light on the nature of astrophysical black holes: while star metrics receive corrections at second order in curvature, vacuum solutions such as black hole metrics do not. What happens to these corrections when a star collapses
Quantum gravitational hair in gravastars and observational tests
Get PDFUsing the effective field theory of quantum gravity at second order in curvature,
we calculate quantum corrections to the metric of gravastars and the closely related dark
energy stars. We find that the quantum corrections in the exterior region depend on the
equation of state of the gravastar, thus providing an example of quantum gravitational
hair. We continue by calculating the induced quantum corrections to the photon sphere and
the bending of light rays in the weak field regime. These corrections, albeit Planck scale
suppressed, allow in principle to distinguish these objects from black holes observationally
Quantum corrected equations of motion in the interior and exterior Schwarzschild spacetimes
Get PDFIn this paper we derive the leading quantum gravitational corrections to the geodesics and the equations of motion for a scalar field in the spacetime containing a constant density star. It is shown that these corrections can be calculated in quantum gravity reliably and in a model independent way. Furthermore, we find that quantum gravity gives rise to an additional redshift that results from the gradient instead of the amplitude of the density profile
Singularities in quantum corrected space-times
Get PDFIn this paper we consider a static and regular fluid generating a locally spherically symmetric and time-independent space-time and calculate the leading quantum corrections to the metric to first order in curvature. Starting from a singularity free classical solution of general relativity, we show that singularities can be introduced in the curvature invariants by quantum gravitational corrections calculated using an effective field theory approach to quantum gravity. We identify non-trivial conditions that ensure that curvature invariants remain singularity free to leading order in the curvature expansion of the effective action
Quantum Hair from Gravity
Get PDFWe explore the relationship between the quantum state of a compact matter
source and of its asymptotic graviton field. For a matter source in an energy
eigenstate, the graviton state is determined at leading order by the energy
eigenvalue. Insofar as there are no accidental energy degeneracies there is a
one to one map between graviton states on the boundary of spacetime and the
matter source states. A typical semiclassical matter source results in an
entangled asymptotic graviton state. We exhibit a purely quantum gravitational
effect which causes the subleading asymptotic behavior of the graviton state to
depend on the internal structure of the source. These observations establish
the existence of ubiquitous quantum hair due to gravitational effects.Comment: 12 page
Quantum Hair During Gravitational Collapse
Get PDFWe consider quantum gravitational corrections to the Oppenheimer-Snyder
metric describing time-dependent dust ball collapse. The interior metric also
describes Friedmann-Lemaitre-Robertson-Walker cosmology and our results are
interpreted in that context. The exterior corrections are an example of quantum
hair, and are shown to persist throughout the collapse. Our results show the
quantum hair survives throughout the horizon formation and that the internal
state of the resulting black hole is accessible to outside observers.Comment: 13 page
Insulin sensitivity of hepatic glucose and lipid metabolism in animal models of hepatic steatosis
Get PDFDe lever is betrokken bij de regulatie van zowel het koolhydraat als het vet metabolisme. De lever slaat glucose op als glycogeen, scheidt glucose uit, kan glucose maken uit bijvoorbeeld melkzuur en aminozuren (‘gluconeogenese’), zet glucose om in vet (‘de novo lipogenese’), verbrandt vetzuren in de beta-oxidatie (levert energie voor de gluconeogenese) en scheidt triglycerides uit in de circulatie in ‘very low density lipoprotein’ (VLDL) deeltjes. Insuline remt de glucoseproductie door de lever en stimuleert de omzetting van glucose in glycogeen, vetzuren en vet (triglycerides). Daarnaast onderdrukt insuline de uitscheiding van triglyceride-rijke VLDL-deeltjes. Indirect remt insuline ook de beta-oxidatie omdat het de vrijmaking van vetzuren uit triglycerides remt.
Een verhoogde triglyceride concentratie in de lever (vette lever of hepatische steatose) is geassocieerd met diverse componenten van het metabool syndroom (dyslipidemie, insulineresistentie, obesitas, hypertensie) en kan een voorloper zijn van bijvoorbeeld levercirrose. Uit de klinische praktijk is gebleken dat hepatische steatose is geassocieerd met insulineresistentie en diabetes mellitus type 2. In de studies beschreven in het proefschrift van Aldo Grefhorst werd met behulp van muismodellen het effect van hepatische steatose op de insulinegevoeligheid van het glucose- en vetmetabolisme onderzocht. Op deze manier is getracht de onderliggende moleculaire processen behorende bij deze associatie op te helderen. De gebruikte modellen waren de leptine-deficiënte ob/ob muis, activering van de novo lipogenese met synthetische agonisten van de liver X receptor, farmacologische remming van de beta-oxidation met TDGA en farmacologische remming van glucose-6-phosphatase met S4048. Insulinegevoeligheid werd onder andere gemeten met behulp van hyperinsulinemische euglycemische clamps in combinatie met infusies van stabiele isotopen.
In alle onderzochte muismodellen is sprake van ernstige hepatische steatose. Met uitzondering van de ob/ob muis, werd in geen van de modellen een afgenomen insulinegevoeligheid waargenomen. Aan de hand van deze studies kan dan ook geconcludeerd worden dat de hoeveelheid triglycerides in de lever op zich weinig zegt over de mate van hepatische insulinegevoeligheid. Andere factoren zijn waarschijnlijk belangrijke determinanten voor het optreden van insulineresistentie bij hepatische steatose. Te denken valt bijvoorbeeld aan de oorsprong van de triglycerides, de duur van de hepatische steatose, de locatie van de triglycerides in de lever, de grootte van de vetdruppels in de cellen en verhoogde concentraties van andere soorten lipiden.
The Clinical Value of HDL Function Measurements
Get PDFLow levels of plasma high-density lipoprotein (HDL) cholesterol are independently associated with an increased risk of atherosclerotic cardiovascular disease (CVD). The mechanisms by which HDL protects against CVD are complex and multifactorial. Functions of HDL that may lead to protection from atherosclerosis include (i)removal of excess cholesterol from lipid-laden macrophage cells in the artery wall is generally believed to be the primary anti-atherogenic action of HDL, (ii) anti-oxidative properties, typically characterized by the ability of HDL to inhibit the pro-atherogenic oxidative modification of LDL and (iii) anti-inflammatory properties, such as its capacity to reduce cytokine-induced expression of adhesion molecules on endothelial cells. On the other hand, several studies have demonstrated that HDL can lose its ability to counteract the development of atherosclerosis in certain disease states and may even become pro-atherogenic. Together with the inconsistent relationship between plasma HDL cholesterol levels and CVD on the individual level as well as the disappointing results of recent clinical trials with HDL-raising agents, these data enforced the concept that the functional quality of HDL particles may be more important than absolute HDL cholesterol mass levels. However, the importance of HDL functionality for cardiovascular risk is still poorly investigated. Therefore, the aim of this thesis was to provide more insight into the importance of HDL functionality for cardiovascular risk. Overall, important information can be derived from measures of HDL functionality over mere HDL cholesterol mass levels. However, there is still an urgent need for large prospective studies exploring whether HDL functionality can predict disease in the general population
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