Slow magnetosonic waves and fast flows in active region loops

Recent EUV spectroscopic observations indicate that slow magnetosonic waves are present in active region (AR) loops. Some of the spectral data were also interpreted as evidence of fast (~100-300 km/s) quasi-periodic flows. We have performed three-dimensional magnetohydrodynamic (3D MHD) modeling of a bipolar AR that contains impulsively generated waves and flows in coronal loops. The model AR is initiated with a dipole magnetic field and gravitationally stratified density, with an upflow driven steadily or periodically in localized regions at the footpoints of magnetic loops. The resulting flows along the magnetic field lines of the AR produce higher density loops compared to the surrounding plasma by injection of material into the flux-tubes and the establishment of siphon flow. We find that the impulsive onset of flows with subsonic speeds result in the excitation of damped slow magnetosonic waves that propagate along the loops and coupled nonlinearly driven fast mode waves. The phase speed of the slow magnetosonic waves is close to the coronal sound speed. When the amplitude of the driving pulses is increased we find that slow shock-like wave trains are produced. When the upflows are driven periodically, undamped oscillations are produced with periods determined by the periodicity of the upflows. Based on the results of the 3D MHD model we suggest that the observed slow magnetosonic waves and persistent upflows may be produced by the same impulsive events at the bases of ARs.Comment: Accepted for publication in The Astrophysical Journa

Development of an Interpretive Simulation Tool for the Proton Radiography Technique

Proton radiography is a useful diagnostic of high energy density (HED) plasmas under active theoretical and experimental development. In this paper we describe a new simulation tool that interacts realistic laser-driven point-like proton sources with three dimensional electromagnetic fields of arbitrary strength and structure and synthesizes the associated high resolution proton radiograph. The present tool's numerical approach captures all relevant physics effects, including effects related to the formation of caustics. Electromagnetic fields can be imported from PIC or hydrodynamic codes in a streamlined fashion, and a library of electromagnetic field `primitives' is also provided. This latter capability allows users to add a primitive, modify the field strength, rotate a primitive, and so on, while quickly generating a high resolution radiograph at each step. In this way, our tool enables the user to deconstruct features in a radiograph and interpret them in connection to specific underlying electromagnetic field elements. We show an example application of the tool in connection to experimental observations of the Weibel instability in counterstreaming plasmas, using $\sim 10^8$ particles generated from a realistic laser-driven point-like proton source, imaging fields which cover volumes of $\sim10$ mm$^3$. Insights derived from this application show that the tool can support understanding of HED plasmas.Comment: Figures and tables related to the Appendix are included in the published journal articl

Sparse Bayesian mass mapping with uncertainties: peak statistics and feature locations

Weak lensing convergence maps – upon which higher order statistics can be calculated – can be recovered from observations of the shear field by solving the lensing inverse problem. For typical surveys this inverse problem is ill-posed (often seriously) leading to substantial uncertainty on the recovered convergence maps. In this paper we propose novel methods for quantifying the Bayesian uncertainty in the location of recovered features and the uncertainty in the cumulative peak statistic – the peak count as a function of signal-to-noise ratio (SNR). We adopt the sparse hierarchical Bayesian mass-mapping framework developed in previous work, which provides robust reconstructions and principled statistical interpretation of reconstructed convergence maps without the need to assume or impose Gaussianity. We demonstrate our uncertainty quantification techniques on both Bolshoi N-body (cluster scale) and Buzzard V-1.6 (large-scale structure) N-body simulations. For the first time, this methodology allows one to recover approximate Bayesian upper and lower limits on the cumulative peak statistic at well-defined confidence levels

Decreased defluorination using the novel beta-cell imaging agent [18F]FE-DTBZ-d4 in pigs examined by PET

The aim of the thesis was twofold. The first aim was to radiolabel small molecules by using carbon-11 and fluorine-18 for visualising beta cell mass (BCM) in the pancreas by PET. Diabetes Mellitus (DM) is a chronic metabolic disorder that results from an absolute or relative lack of BCM of endocrine pancreas. The lack of an adequate non-invasive imaging PET probe prevents detailed examination of beta cell loss during onset and progression of DM as well as development of novel treatments and islets transplantation progress. The second aim of the thesis was to radiolabel peptide molecules with fluorine-18 to visualise beta amyloid in Alzheimer’s disease (AD) brain. AD is a chronic, progressive neurodegenerative disorder. Brain penetration study of a labelled peptide, specific for beta amyloid that can cross blood-brain-barrier (BBB), is important to gain knowledge about the fate of the molecule as a diagnostic probe. A series of three novel radioligands for BCM imaging has been developed in this thesis. In paper I, a vesicular monoamine transporter type 2 (VMAT2) specific radioligand [18F]FE-DTBZ-d4 was synthesised in two steps. First step is the nucleophilic [18F]fluorination to produce deuterated-[18F]fluoroethylbromide followed by the O- alkylation of desmethyl-DTBZ precursor to produce [18F]FE-DTBZ-d4. The in vivo pharmacokinetics (PK) studies in pigs by PET/CT demonstrated reduced in vivo defluorination; therefore, it may be an improved potential candidate for imaging VMAT2 dense tissue i.e. islets transplantation in proximity to cortical bone structure. In Paper II, a glucokinase (GK) specific radioligand, [11C]AZ12504948, was synthesised in one step via alkylation of O-desmethyl precursor using [11C]methyl iodide. Both in vitro and in vivo (pig and monkey) studies with [11C]AZ12504948 for imaging GK in the pancreas and liver indicated low specificity. Increased target specificity is required for further progress in GK imaging using PET radioligands. In Paper III, a radioligand for G-protein coupled receptor 44 (GPR44), [11C/3H]AZ Compound X, was synthesised via S-methylation of sodium sulfinate salt in one step using [11C/3H]methyl iodide. In vitro binding of the radioligand, evaluated by autoradiography (ARG) on human and rat pancreatic tissues, confirmed higher specific binding in islets of human pancreatic tissue and no measurable binding in rat pancreas, which is devoid of GPR44. These studies indicate that the radioligand has suitable properties for beta cell imaging with high potential for further preclinical and clinical evaluation. Three novel D-peptides were radiolabelled with fluorine-18 ([18F]ACI-87, [18F]ACI- 88, [18F]ACI-89) by using prosthetic group N-succinimidyl-4-[18F]fluorobenzoate, [18F]SFB, with epsilon (ε)-amino groups of lysine residues of peptide precursors in two steps. First step is the synthesis of [18F]SFB followed by the addition of [18F]SFB via acylation to the peptide molecule. Trimethylammonium salt [N(CH3)3+] precursor for synthesising [18F]SFB as well as the reference standard SFB were synthesised with good yields. Three 19F-peptide reference standards were also synthesised by using SFB. Preliminary ARG measurements were performed in AD and control human brains. ARG demonstrated higher radioligand uptake in the AD brain compared to age-matched control brain, which makes them potential for further use in in vivo testing by PET. However, preliminary PET (in vivo) studies in cynomolgus monkey brain, using these 18F-D-peptides, confirmed too low BBB penetration, making them unsuitable for further use as in vivo PET probes

Temperature structure of the intergalactic medium within seven nearby and bright clusters of galaxies observed with XMM-Newton

Aims. We map the temperature structure of the intra-cluster medium (ICM) within a nearly complete X-ray flux limited sample of galaxy clusters in the redshift range z=[0.045,0.096]. Our sample contains seven bright clusters of galaxies observed with XMM-Newton: Abell 399, Abell 401, Abell 478, Abell 1795, Abell 2029, Abell 2065, Abell 2256. Methods. We use a multi-scale spectral mapping algorithm especially designed to map spectroscopic observables from X-ray extended emission of the ICM. Derived from a former algorithm using Haar wavelets, our algorithm is now implemented with B-spline wavelets in order to perform a more regular analysis of the signal. Results. For the four clusters in our sample that are major mergers, we find a complex thermal structure with strong thermal variations consistent with their dynamics. For two of them, A2065 and A2256, we perform a 3-d analysis of cold front features evidenced from the gas temperature and brightness maps. Furthermore, we detect a significant non-radial thermal structure outside the cool core region of the other 3 more "regular" clusters, with relative amplitudes of about about 10%. We investigate possible implications of this structure on the mass estimates of the "regular" clusters A1795 and A2029, by extracting surface brightness and temperature profiles from sectors correspondings to the hottest and coldest regions in the maps. While compensating with surface brightness for A2029, leading to consistent mass profiles, the temperature structure leads to significant mass discrepancies in the innermost region of A1795.Comment: published in A&

Global Facilitation of Attended Features Is Obligatory and Restricts Divided Attention

Peer reviewedPublisher PD