Cholesterol feeding strongly reduces hepatic VLDL-triglyceride production in mice lacking the liver X receptor alpha

The oxysterol-activated nuclear receptor liver X receptor alpha (LXR alpha) has been implicated in the control of both cholesterol and fatty acid metabolism. In this study, we have evaluated the effects of excess dietary cholesterol on hepatic cholesterol metabolism, lipogenesis, and VLDL production in homozygous (Lxr alpha(-/-)), heterozygous (Lxr alpha(+/-)), and wild-type mice. Mice were fed either chow or a cholesterol-enriched diet (1%, w/w) for 2 weeks. On the high-cholesterol diet, fractional cholesterol absorption was higher in Lxr alpha(-/-) mice than in controls, leading to delivery of more dietary cholesterol to the liver. Lxr alpha(-/-) mice were not able to induce expression of hepatic Abcg5/Abcg8, and massive accumulation of free cholesterol and cholesteryl esters (CEs) occurred. Interestingly, despite the inability to upregulate Abcg5/Abcg8, the highly increased hepatic free cholesterol content did stimulate biliary cholesterol output in Lxr alpha(-/-) mice. Hepatic cholesterol accumulation was accompanied by decreased hepatic expression of lipogenic genes, probably caused by impaired sterol-regulatory element binding protein 1c processing, lower hepatic triglyceride (TG) contents, strongly reduced plasma TG concentrations (290%), and reduced VLDL-TG production rates (-60%) in Lxr alpha(-/-) mice. VLDL particles were smaller and CE-enriched under these conditions. Lxr alpha deficiency did not affect VLDL formation under chow-fed conditions. Hepatic stearyl coenzyme A desaturase 1 expression was decreased dramatically in Lxr alpha(-/-) mice and did not respond to cholesterol feeding, but fatty acid profiles of liver and VLDL were only slightly different between Lxr alpha(-/-) and wild-type mice. Our data indicate that displacement of TGs by CEs during the VLDL assembly process underlies hypotriglyceridemia in cholesterol-fed Lxr alpha(-/-) mice. - van der Veen, J. N., R. Havinga, V. W. Bloks, A. K. Groen, and F. Kuipers. Cholesterol feeding strongly reduces hepatic VLDL-triglyceride production in mice lacking the liver X receptor a

LOFAR early-time search for coherent radio emission from GRB 180706A

© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.The nature of the central engines of gamma-ray bursts (GRBs) and the composition of their relativistic jets are still under debate. If the jets are Poynting flux dominated rather than baryon dominated, a coherent radio flare from magnetic re-connection events might be expected with the prompt gamma-ray emission. There are two competing models for the central engines of GRBs; a black hole or a newly formed milli-second magnetar. If the central engine is a magnetar it is predicted to produce coherent radio emission as persistent or flaring activity. In this paper, we present the deepest limits to date for this emission following LOFAR rapid response observations of GRB 180706A. No emission is detected to a 3$\sigma$ limit of 1.7 mJy beam$^{-1}$ at 144 MHz in a two-hour LOFAR observation starting 4.5 minutes after the gamma-ray trigger. A forced source extraction at the position of GRB 180706A provides a marginally positive (1 sigma) peak flux density of $1.1 \pm 0.9$ mJy. The data were time-sliced into different sets of snapshot durations to search for FRB like emission. No short duration emission was detected at the location of the GRB. We compare these results to theoretical models and discuss the implications of a non-detection.Peer reviewedFinal Accepted Versio

HST Snapshot Survey of Post-AGB Objects

The results from a Hubble Space Telescope (HST) snapshot survey of post-AGB objects are shown. The aim of the survey is to complement existing HST images of PPN and to connect various types of nebulosities with physical and chemical properties of their central stars. Nebulosities are detected in 15 of 33 sources. Images and photometric and geometric measurements are presented. For sources with nebulosities we see a morphological bifurcation into two groups, DUPLEX and SOLE, as previous studies have found. We find further support to the previous results suggesting that this dichotomy is caused by a difference in optical thickness of the dust shell. The remaining 18 sources are classified as stellar post-AGB objects, because our observations indicate a lack of nebulosity. We show that some stellar sources may in fact be DUPLEX or SOLE based on their infrared colors. The cause of the differences among the groups are investigated. We discuss some evidence suggesting that high progenitor-mass AGB stars tend to become DUPLEX post-AGB objects. Intermediate progenitor-mass AGB stars tend to be SOLE post-AGB objects. Most of the stellar sources probably have low mass progenitors and do not seem to develop nebulosities during the post-AGB phase and therefore do not become planetary nebulae.Comment: 21 pages, 11 figure

Doped GeSe materials for selector applications

We report on the thermal and electrical performance of nitrogen (N) and carbon (C) doped GeSe thin films for selector applications. Doping of GeSe successfully improved its thermal stability to 450 degrees C. N doping led to a decrease in the off-state leakage and an increase in threshold voltage (V-th), while C doping led to an increase in leakage and reduced V-th. Hence, we show an effective method to tune the electrical parameters of GeSe selectors by using N and C as dopants

Developing hierarchically porous MnO_<em>x</em>/NC hybrid nanorods for oxygen reduction and evolution catalysis

Electrochemical oxygen reduction and evolution reactions (ORR and OER) play a vital role in the field of energy conversion and storage. The problem is that both processes are sluggish, requiring precious-metal catalysts. Here, starting from abundant precursors and using a simple synthesis approach, we report the preparation of a good bifunctional oxygen electro-catalyst: a composite nanorod of manganese oxides and nitrogen-doped carbon. This material has hierarchical porosity, facilitating the mass transfer within the electrode. The nitrogen-doped carbon forms contiguous 3D network, connecting the isolated MnOx nanoparticles and ensuring superior electrical conductivity. Importantly, the MnOx particles contain manganese of mixed oxidation states; aligned with the nitrogen-doped carbon, this hybrid is among the best non-noble-metal ORR/OER catalysts in alkaline media, outperforming even Pt and RuO2 catalysts.Peer reviewed: YesNRC publication: Ye

The unusual hydrocarbon emission from the early carbon star HD 100764: The connection between aromatics and aliphatics

We have used the Infrared Spectrograph (IRS) on the Spitzer Space Telescope to obtain spectra of HD 100764, an apparently single carbon star with a circumstellar disk. The spectrum shows emission features from polycyclic aromatic hydrocarbons (PAHs) that are shifted to longer wavelengths than normally seen, as characteristic of ``class C'' systems in the classification scheme of Peeters et al. All seven of the known class C PAH sources are illuminated by radiation fields that are cooler than those which typically excite PAH emission features. The observed wavelength shifts are consistent with hydrocarbon mixtures containing both aromatic and aliphatic bonds. We propose that the class C PAH spectra are distinctive because the carbonaceous material has not been subjected to a strong ultraviolet radiation field, allowing relatively fragile aliphatic materials to survive.Comment: 11 pages (in emulateapj), 5 tables, 7 figures. Accepted for publication in Ap