General Relativistic Simulations of Jet Formation in a Rapidly Rotating Black Hole Magnetosphere

To investigate the formation mechanism of relativistic jets in active galactic nuclei and micro-quasars, we have developed a new general relativistic magnetohydrodynamic code in Kerr geometry. Here we report on the first numerical simulation of jet formation in a rapidly-rotating (a=0.95) Kerr black hole magnetosphere. We study cases in which the Keplerian accretion disk is both co-rotating and counter-rotating with respect to the black hole rotation. In the co-rotating disk case, our results are almost the same as those in Schwarzschild black hole cases: a gas pressure-driven jet is formed by a shock in the disk, and a weaker magnetically-driven jet is also generated outside the gas pressure-driven jet. On the other hand, in the counter-rotating disk case, a new powerful magnetically-driven jet is formed inside the gas pressure-driven jet. The newly found magnetically-driven jet in the latter case is accelerated by a strong magnetic field created by frame dragging in the ergosphere. Through this process, the magnetic field extracts the energy of the black hole rotation.Comment: Co-rotating and counter-rotating disks; 8 pages; submitted to ApJ letter

U redox state and speciation of U in contact with magnetite nanoparticles : High resolution XANES, EXAFS, XPS and TEM study

Long-term storage of high-level radioactive waste is associated with potential radioecological hazards. One chemical element of high interest is uranium (U), which can mainly exists as a mobile U(VI) (oxidizing conditions) and sparingly soluble U(IV) (reducing conditions) species. It is expected that the main inorganic reducing agent for U(VI) in the environment are ferrous species in magnetite, formed on the steel canisters surface as an intermediate iron (Fe) corrosion product [1]. Results obtained from laboratory experiments for the interaction of U(VI) with magnetite nanoparticles point to partial reduction of U(VI) [2] or the formation of ~3 nm uranium dioxide (UO₂) particles on the surface layer [3]. The evidence for U(VI) reduction to intermediate U(V) state was found with no direct evidence of U(IV), which is in contradiction with thermodynamic calculations [4]. Continuous interaction and related phase dissolution/recrystallization processes can also lead to U redox changes and structural U incorporation into Fe oxides, resulting in U immobilization [5]. U redox state and speciation analyses are still very challenging due to simultaneous formation of several different species in such mineral systems. New advanced spectroscopic methods for characterization of such systems will provide more precise results from speciation studies. The main goal of our investigation is to assess the U M4 edge high energy resolution X-ray absorption near edge structure (HR-XANES) spectroscopy technique for detection of U(V) possibly co-existing with U(IV) and U(VI) under reducing conditions on/in Fe containing minerals. The U M4 edge HR-XANES has an advantage compared to the conventional U L3 edge XANES, as the measured spectra are less dominated by corehole lifetime broadening effects and therefore have narrower spectral features [6-8]. This technique facilitates the detection of minor contribution of one oxidation state in mixtures. We have investigated the U redox states and speciation in a set of samples where U coprecipitated with magnetite nanoparticles (~ 20 nm) with U concentrations varying in the 1000-10000 ppm range (1000, 3000, 6000 and 10000 ppm). In addition to U M4 edge HR-XANES, U L3 edge extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) techniques have been applied. The studied system models the interaction of U(VI) with magnetite in aqueous solution, important for the understanding of the retarding effect of Fe corrosion products on U in the context of deep geological spent nuclear fuel disposal. These spectroscopic results can be compared with thermodynamic calculations and geochemical models describing this interaction. After 10 days U interaction with magnetite U M4 edge HR-XANES results indicate the formation of U(IV), U(V) and U(VI) mixtures in varying ratios, depending on the initial U loading. Going from 10000 to 3000 ppm, the U(VI) content decreases continuously and is no longer found in the 1000 ppm sample. At the same time the U(IV) and U(V) fractions increase. U(V) is stabilized as the main U redox state in the 1000 ppm sample along with a smaller U(IV) contribution. After 20 days of contact time XPS data show the predominance of U(IV) and U(V) species in the 6000 ppm sample. However, mostly U(V) and some U(IV) is found for the 1000 ppm sample. For all samples aged for 240 days U L3 XANES and EXAFS strongly suggest the formation of a UO₂ phase, UO₂ is the dominating species in the 10000 ppm sample with U-O bond distance 2.33. Å as determined by EXAFS. UO₂ crystalline clusters with about 5 nm size formed on the surface of the magnetite nanoparticles are also found by TEM in the 10000 and 3000 ppm samples. The major and minor contributions of U(V) and U(IV), respectively, for the 1000 ppm sample after 240 days confirm the assumption that the U redox kinetics has completed within less than 10 days at this U concentration. EXAFS analyses reveal U(V)-Fe interaction in the second U coordination sphere, which substantially increases from the 10000 to 1000 ppm sample and is the dominating species in the 1000 ppm sample

Magnetohydrodynamics in full general relativity: Formulation and tests

A new implementation for magnetohydrodynamics (MHD) simulations in full general relativity (involving dynamical spacetimes) is presented. In our implementation, Einstein's evolution equations are evolved by a BSSN formalism, MHD equations by a high-resolution central scheme, and induction equation by a constraint transport method. We perform numerical simulations for standard test problems in relativistic MHD, including special relativistic magnetized shocks, general relativistic magnetized Bondi flow in stationary spacetime, and a longterm evolution for self-gravitating system composed of a neutron star and a magnetized disk in full general relativity. In the final test, we illustrate that our implementation can follow winding-up of the magnetic field lines of magnetized and differentially rotating accretion disks around a compact object until saturation, after which magnetically driven wind and angular momentum transport inside the disk turn on.Comment: 28 pages, to be published in Phys. Rev.

Structural tale of two novel (Cr, Mn)C carbides in steel

Chromium (Cr), manganese (Mn) and carbon (C) are well known alloying elements used in technologically important alloy steels and advanced high strength steels. It is known that binary CrCx and MnCx carbides can be formed in steels, but in this study we reveal for the first time that Cr and Mn were found combined in novel ternary cementite type (Cr, Mn)C carbides. Electron diffraction experiments showed that Cr, Mn and C formed two distinct carbide phases possessing orthorhombic and monoclinic crystal structures. Density functional theory calculations were performed on these phases and excellent agreement was found between calculations and experiments on the lattice parameters and relative atomic positions. The calculations showed that the combination of Mn and Cr resulted in a very high thermodynamic stability of the (Cr, Mn)C carbides, and that local structural relaxations are associated with carbon additions. Possible implications of these ternary carbides for novel applications in steel design and manufacturing are discussed

Three-dimensional magnetic resonance imaging of the anterolateral ligament of the knee: an evaluation of intact and anterior cruciate ligament–deficient knees from the scientific anterior cruciate ligament network international (SANTI) Study Group

Purpose: The aim of this study was to determine the visualisation rate of the ALL in uninjured and ACL deficient knees when using 3D-MRI. In addition, it was sought to characterize the spectrum of ALL injury in acute and chronically ACL deficient knees, and also to determine the inter and intra-observer reliability of a 3D-MRI classification of ALL injury. Methods: 100 knees underwent 3D-MRI (60 with ACL rupture and 40 non-injured knees). The ALL was evaluated by two blinded orthopaedic surgeons. The ALL was classified as Type A: continuous, clearly defined low-signal band, Type B: with warping, thinning, or iso-signal changes, Type C: without clear continuity. Comparison between acute (<1 month) and chronically ACL injured knees was evaluated as well as intra and inter-observer reliability. Results: Complete visualisation of the full path of the ALL was achieved in all non-injured knees. In the ACL injured group, 24 acutely injured knees were imaged: 87.5% showed evidence of injury (3 knees were normal/Type A (12.5%), 18 Type B (75.0%), and 3 Type C (12.5%)). 36 knees chronically ACL injured knees were imaged: 55.6% showed evidence of injury (16 Type A (44.4%), 18 Type B (50.0%), and 2 Type C (5.6%)). The difference in the rate of injury between the two groups was significant (p = 0.03). Multivariate analysis demonstrated that the delay from ACL injury to MRI was the only factor (negatively) associated with the rate of injury to the ALL. Inter- and intra-observer reliability of the classification of ALL type were good (kappa 0.86 and 0.93 respectively). Conclusion: 3D-MRI allows full visualisation of the ALL in all knees. The rate of injury to the ALL in acutely ACL injured knees identified on 3D-MRI is higher than previous reports using standard MRI techniques. This rate is significantly higher than the rate of injury to the ALL identified in chronically ACL injured knees. Level of Evidence: IV, Diagnostic, case control study