Radial Distributions of Coronal Electron Temperatures: specificities of the DYN model

This paper is a follow up of the article where Lemaire and Stegen (2016) introduced their DYN method to calculate coronal temperature profiles from given radial distributions of the coronal and solar wind (SW) electron densities. Several such temperature profiles are calculated and presented corresponding to a set of given empirical density models derived from eclipse observations and in-situ measurements of the electron density and bulk velocity at 1 AU. The DYN temperature profiles obtained for the equatorial and polar regions of the corona challenge the results deduced since 1958 from singular hydrodynamical models of the SW. In these models - where the expansion velocity transits through a singular saddle point - the maximum coronal temperature is predicted to be located at the base of the corona, while in all DYN models the altitude of the maximum temperature is found at significantly higher altitudes in the mid-corona. Furthermore, the maximum of the DYN-estimated temperatures is found at much higher altitudes over the polar regions and coronal holes, than over the equator. However, at low altitudes, in the inner corona, the DYN temperatures are always smaller at high latitudes, than at low equatorial latitudes. This appears well in agreement with existing coronal hole observations. These findings have serious implications on the open questions: what is the actual source of the coronal heating, and where is the maximum energy deposited within the solar corona?Comment: 13 pages, 3 figures. Submitted to the Solar Physics journa

ORIGAMIX, a CdTe-based spectro-imager development for nuclear applications

The Astrophysics Division of CEA Saclay has a long history in the development of CdTe based pixelated detection planes for X and gamma-ray astronomy, with time-resolved imaging and spectrometric capabilities. The last generation, named Caliste HD, is an all-in-one modular instrument that fulfills requirements for space applications. Its full-custom front-end electronics is designed to work over a large energy range from 2 keV to 1 MeV with excellent spectroscopic performances, in particular between 10 and 100 keV (0.56 keV FWHM and 0.67 keV FWHM at 13.9 and 59.5 keV). In the frame of the ORIGAMIX project, a consortium based on research laboratories and industrials has been settled in order to develop a new generation of gamma camera. The aim is to develop a system based on the Caliste architecture for post-accidental interventions or homeland security, but integrating new properties (advanced spectrometry, hybrid working mode) and suitable for industry. A first prototype was designed and tested to acquire feedback for further developments. In this study, we particularly focused on spectrometric performances with high energies and high fluxes. Therefore, our device was exposed to energies up to 700 keV (133Ba, 137Cs) and we measured the evolution of energy resolution (0.96 keV at 80 keV, 2.18 keV at 356 keV, 3.33 keV at 662 keV). Detection efficiency decreases after 150 keV, as Compton effect becomes dominant. However, CALISTE is also designed to handle multiple events, enabling Compton scattering reconstruction, which can drastically improve detection efficiencies and dynamic range for higher energies up to 1408 keV (22Na, 60Co, 152Eu) within a 1-mm thick detector. In particular, such spectrometric performances obtained with 152Eu and 60Co were never measured before with this kind of detector.Comment: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. Available online 9 January 2015, ISSN 0168-9002 (http://www.sciencedirect.com/science/article/pii/S0168900215000133). Keywords: CdTe; X-ray; Gamma-ray; Spectrometry; Charge-sharing; Astrophysics Instrumentation; Nuclear Instrumentation; Gamma-ray camera

In vitro expansion of U87-MG human glioblastoma cells under hypoxic conditions affects glucose metabolism and subsequent in vivo growth

Hypoxia is a characteristic feature of solid tumors leading to the over expression of hypoxia-inducible factor (HIF)-1α protein and therefore to a specific cellular behavior. However, even though the oxygen tension in tumors is low (<5 %), most of the cell lines used in cancer studies are grown under 21 % oxygen tension. This work focuses on the impact of oxygen conditions during in vitro cell culture on glucose metabolism using 1-13C-glucose. Growing U87-MG glioma cells under hypoxic conditions leads to a two- to threefold reduction of labeled glutamine and an accumulation of fructose. However, under both hypoxic and normoxic conditions, glucose is used for de novo synthesis of pyrimidine since the 13C label is found both in the uracil and ribose moieties. Labeling of the ribose ring demonstrates that U87-MG glioma cells use the reversible branch of the non-oxidative pentose phosphate pathway. Interestingly, stereotactic implantation of U87-MG cells grown under normoxia or mild hypoxia within the striatum of nude mice led to differential growth; the cells grown under hypoxia retaining an imprint of the oxygen adaptation as their development is then slowed down

Susceptibility gradient quantization by MRI signal response mapping (SIRMA) to dephaser

Purpose: Susceptibility effects are a very efficient source of contrast in magnetic resonance imaging. However, detection is hampered by the fact the induced contrast is negative. In this work, the SIgnal Response MApping (SIRMA) to dephaser method is proposed to map susceptibility gradient to improve visualization. Methods: In conventional gradient echo acquisitions, the echo formation of susceptibility affected spins is shifted in k -space, the shift being proportional to the susceptibility gradient. Susceptibility gradients map can be produced by measuring this induced shifts. The SIRMA method measures these shifts from a series of dephased images collected with additional incremental dephasers. These additional dephasers correspond either to a slice refocusing gradient offset or to a reconstruction window off-centering. The signal intensity profile as a function of the additional dephaser was determined on a pixel-by-pixel basis from the ensemble of dephased images. Susceptibility affected voxels presented a signal response profile maximum shifted compared to nonaffected voxels ones. Shift magnitude and sign were measured for each pixel to determine susceptibility gradients and produce a susceptibility gradient map. Results: In vitro experiments demonstrated the ability of the method to map gradient inhomogeneities induced by a cylinder. Quantization accuracy was evaluated comparing SIRMA images and simulations performed on the well-characterized air filled cylinder model. Performances of the SIRMA method, evaluated in vitro on cylinders filled with various superparamagnetic iron oxide SPIO concentrations, showed limited influence of acquisition parameters. Robustness of the method was then assessed in vivo after an infusion of SPIO-loaded nanocapsules into the rat brain using a convection-enhanced drug delivery approach. The region of massive susceptibility gradient induced by the SPIO-loaded nanocapsules was clearly delineated on SIRMA maps and images were compared to T 2 weighted images, Susceptibility Gradient Map (SGM), and histological Perl\u27s staining slice. The potential for quantitative evaluation of SPIO distribution volume was demonstrated. Conclusions: The proposed method is a promising technique for a wide range of applications especially in molecular or cellular imaging with respect to its quantitative nature and its computational simplicity

Prenatal evaluation of kidney function in mice using dynamic contrast-enhanced magnetic resonance imaging

Glomerular differentiation starts as soon as embryonic stage 12 in mice and suggests that kidneys may be functional at this stage. Dynamic contrast-enhanced magnetic resonance microscopy, a noninvasive imaging technique, was used to assess renal function establishment in utero. Indeed, in adults (n = 3), an intravenous injection of gadolinium-DOTA induced in a first step a massive and rapid drop in kidney signal intensity followed, in a second step, by a drop in bladder signal intensity. The delay in signal changes between kidney and bladder reflected glomerular filtration. Pregnant mice underwent anatomical and dynamic contrast-enhanced magnetic resonance microscopy on postcoital days 12-13 (n = 2), 13-14 (n = 1), 14-15 (n = 3), 15-16 (n = 2), 16-17 (n = 3), 17-18 (n = 3), and 18-19 (n = 1). Kidneys and bladder were unambiguously depicted prior to contrast agent injection on stage 15-16 embryos. Contrast agent injection allowed kidney, detection as early as stage 12-13 but not bladder. Kinetics of signal changes demonstrated that glomerular filtration is established at embryonic stage 15-16 in mice. Thus, anatomical and dynamic contrast-enhanced magnetic resonance microscopy may be a powerful noninvasive method for in vivo prenatal developmental and functional studies

Quantitative MR renography using a calibrated internal signal (ERETIC)

To measure MR renograms, cortical and medullary kidney signal intensity evolution is followed after contrast agent injection. To obtain an accurate quantitative signal measurement, the use of a reference signal is necessary to correct the potential MRI system variations in time. The ERETIC method (Electronic Reference To access In vivo Concentrations) provides an electronic reference signal. It is synthesized as an amplitude modulated RF pulse applied during the acquisition. The ERETIC method was as precise as the external tube reference method but presents major advantages like its free adjustability (shape, location and magnitude) to the characteristics of the organ studied as well as its not taking room inside the magnet. Even though ERETIC showed a very good intrinsic stability, systems’ variations still affect its signal in the same way as real NMR signals are affected. This method can be easily implemented on any imaging system with two RF channels

Magic traits drive the emergence of pathogens

An important branch of evolutionary biology strives to understand how divergent selection for an ecologically important trait can foster the emergence of new species specialized on different niches. Such ecological speciation is usually difficult to achieve because recombination between different subsets of a population that are adapting to different environments counteracts selection for locally adapted gene combinations. Traits pleiotropically controlling adaptation to different environments and reproductive isolation are therefore the most favourable for ecological speciation, and are thus called “magic traits”. We used genetic markers and cross-inoculations to show that pathogenicity-related loci are responsible for both host adaptation and reproductive isolation in emerging populations of Venturia inaequalis, the fungus causing apple scab disease. Because the fungus mates within its host and because the pathogenicity-related loci prevent infection of the non-host trees, host adaptation pleiotropically maintains genetic differentiation and adaptive allelic combinations between sympatric populations specific to different apple varieties. Such “magic traits” are likely frequent in fungal pathogens, and likely drive the emergence of new diseases.