Space-based Aperture Array For Ultra-Long Wavelength Radio Astronomy

The past decade has seen the rise of various radio astronomy arrays, particularly for low-frequency observations below 100MHz. These developments have been primarily driven by interesting and fundamental scientific questions, such as studying the dark ages and epoch of re-ionization, by detecting the highly red-shifted 21cm line emission. However, Earth-based radio astronomy below frequencies of 30MHz is severely restricted due to man-made interference, ionospheric distortion and almost complete non-transparency of the ionosphere below 10MHz. Therefore, this narrow spectral band remains possibly the last unexplored frequency range in radio astronomy. A straightforward solution to study the universe at these frequencies is to deploy a space-based antenna array far away from Earths' ionosphere. Various studies in the past were principally limited by technology and computing resources, however current processing and communication trends indicate otherwise. We briefly present the achievable science cases, and discuss the system design for selected scenarios, such as extra-galactic surveys. An extensive discussion is presented on various sub-systems of the potential satellite array, such as radio astronomical antenna design, the on-board signal processing, communication architectures and joint space-time estimation of the satellite network. In light of a scalable array and to avert single point of failure, we propose both centralized and distributed solutions for the ULW space-based array. We highlight the benefits of various deployment locations and summarize the technological challenges for future space-based radio arrays.Comment: Submitte

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

Surface roughness over the northern half of the Greenland Ice Sheet from airborne laser altimetry

This is the published version, also available here: http://dx.doi.org/10.1029/2008JF001067.Surface roughness, defined as the standard deviation of small-scale elevation fluctuations from the linear trend over 0.5 km, can be estimated from high-resolution airborne laser altimetry. Here we present results for the northern half of the Greenland Ice Sheet using laser data collected in May 1995. Roughness is smallest in the central region straddling the ice divide, increases in amplitude toward the coast, and appears to be correlated with slope of the ice surface. For most of the study region surface roughness is 8 cm or less (<2.5 cm water equivalent). In smaller regions associated with fast flow, larger values are found. Comparison of the size of small-scale topographic disturbances with the spatial noise estimated from five closely spaced ice cores drilled in northwest Greenland shows good agreement. Similar correspondence was found earlier using nine ice cores from the Summit region. These results indicate that the airborne laser altimeter provides an efficient platform for characterizing the statistical nature of the snow surface over large areas of the polar ice sheets

Orbiting low frequency antennas for radio astronomy(OLFAR): Distributing signal processing

Recently, new and interesting science drivers have emerged in the ultra low frequency range of 0.3-30 MHz ranging from the epoch of re-ionization, exo-planets, ultra-high energy cosmic rays and studies of the astronomical dark ages. However at these wavelengths, ground based observations are severely limited due to ionospheric distortions below 50MHz, manmade interference, complete reflection of radio waves below 30MHz and even solar flares (1)

Around the Tables – Contextual Factors in Healthcare Coverage Decisions Across Western Europe

Background: Across Western Europe, procedures and formalised criteria for taking decisions on the coverage (inclusion in the benefits basket or equivalent) of healthcare technologies vary substantially. In the decision documents, which display the justification of, the rationale for, these decisions, national healthcare institutes may employ ‘contextual factors,’ defined here as situation-specific considerations. Little is known about how the use of such contextual factors compares across countries. We describe and compare contextual factors as used in coverage decisions generally and 4 decision documents specifically in Belgium, England, Germany, and the Netherlands. Methods: Four group interviews with 3 experts from the national healthcare institute of each country, document and web site analysis, and a workshop with 1 to 2 of these experts per country were followed by the examination of the documents of 4 specific decisions taken in each of the 4 countries, sampled to vary widely in type of technology and decision outcome. Results: From the available decision documents, we conclude that in every country studied, contextual factors are established ‘around the table,’ ie, in deliberation. All documents examined feature contextual factors, with similar contextual factor patterns leading to similar decisions in different countries. The Dutch decisions employ the widest variety of factors, with the exception of the societal functioning of the patient, which is relatively common in Belgium, England, and Germany. Half of the final decisions were taken in another setting, with the consequence that no documentation was retrievable for 2 decisions. Conclusion: First, we conclude that in these countries, contextual factors are actively integrated in the decision document, and that this is achieved in deliberation. Conceptualising contextual factors as both situation-specific and actively-integrated affords insight into practices of contextualisation and provides an encouragement for exchange between decision-makers on more qualitative aspects of decisions. Second, the decisions that lacked a publicly acc

Biomechanical assessment of the effects of decompressive surgery in non-chondrodystrophic and chondrodystrophic canine multisegmented lumbar spines

Purpose Dogs are often used as an animal model in spinal research, but consideration should be given to the breed used as chondrodystrophic (CD) dog breeds always develop IVD degeneration at an early age, whereas nonchondrodystrophic (NCD) dog breeds may develop IVD degeneration, but only later in life. The aim of this study was to provide a mechanical characterization of the NCD [non-degenerated intervertebral discs (IVDs), rich in notochordal cells] and CD (degenerated IVDs, rich in chondrocyte-like cells) canine spine before and after decompressive surgery (nucleotomy). Methods The biomechanical properties of multisegmented lumbar spine specimens (T13-L5 and L5-Cd1) from 2-year-old NCD dogs (healthy) and CD dogs (early degeneration) were investigated in flexion/extension (FE), lateral bending (LB), and axial rotation (AR), in the native state and after nucleotomy of L2-L3 or dorsal laminectomy and nucleotomy of L7-S1. The range of motion (ROM), neutral zone (NZ), and NZ stiffness (NZS) of L1-L2, L2- L3, L6-L7, and L7-S1 were calculated. Results In native spines in both dog groups, the greatest mobility in FE was found at L7-S1, and the greatest mobility in LB at L2-L3. Surgery significantly increased the ROM and NZ, and significantly decreased the NZS in FE, LB, and AR in both breed groups. However, surgery at L2-L3 resulted in a significantly larger increase in NZ and decrease in NZS in the CD spines compared with the NCD spines, whereas surgery at L7-S1 induced a significantly larger increase in ROM and decrease in NZS in the NCD spines compared with the CD spines. Conclusions Spinal biomechanics significantly differ between NCD and CD dogs and researchers should consider this aspect when using the dog as a model for spinal research. © Springer-Verlag 2012

Effects of an early life diet containing large phospholipid-coated lipid globules on hepatic lipid metabolism in mice

We recently reported that feeding mice in their early life a diet containing a lipid structure more similar to human milk (eIMF, Nuturis) results in lower body weights and fat mass gain upon high fat feeding in later life, compared to control (cIMF). To understand the underlying mechanisms, we now explored parameters possibly involved in this long-term effect. Male C57BL/6JOlaHsd mice, fed rodent diets containing eIMF or cIMF from postnatal (PN) day 16–42, were sacrificed at PN42. Hepatic proteins were measured using targeted proteomics. Lipids were assessed by LC–MS/MS (acylcarnitines) and GC-FID (fatty-acyl chain profiles). Early life growth and body composition, cytokines, and parameters of bile acid metabolism were similar between the groups. Hepatic concentrations of multiple proteins involved in β-oxidation (+ 17%) the TCA cycle (+ 15%) and mitochondrial antioxidative proteins (+ 28%) were significantly higher in eIMF versus cIMF-fed mice (p < 0.05). Hepatic l-carnitine levels, required for fatty acid uptake into the mitochondria, were higher (+ 33%, p < 0.01) in eIMF-fed mice. The present study indicates that eIMF-fed mice have higher hepatic levels of proteins involved in fatty acid metabolism and oxidation. We speculate that eIMF feeding programs the metabolic handling of dietary lipids