Multipole shimming of permanent magnets using harmonic corrector rings

Shimming systems are required to provide sufficient field homogeneity for high resolution nuclear magnetic resonance (NMR). In certain specialized applications, such as rotating-field NMR and mobile ex situ NMR, permanent magnet-based shimming systems can provide considerable advantages. We present a simple two-dimensional shimming method based on harmonic corrector rings which can provide arbitrary multipole order shimming corrections. Results demonstrate, for example, that quadrupolar order shimming improves the linewidth by up to an order of magnitude. An additional order of magnitude reduction is in principle achievable by utilizing this shimming method for z-gradient correction and higher order xy gradients.     

Simulation of Fluid Flow and Oscillation of the Argon Oxygen Decarburization (AOD) Process

The oscillation of argon oxygen decarburization (AOD) converters is flow related and depends on the process parameters (e.g., vessel geometry, melt fill height, process gas type and blowing rate, vessel tilting angle, as well as geometry, number, and arrangement of the side-wall nozzles). For a 120-ton AOD converter with seven submerged side-wall nozzles, plant tests, physical simulations on a 1:4 scale water model, and computational fluid dynamics simulations have been done. The investigations show that the penetration depth of an inert gas jet into the melt does not exceed approximately 0.4 m. The plumes are located close to the nozzle-side converter wall and induce a large-scale primary vortex as well as intensive surface movements; both are responsible for the oscillation. Several process mechanisms were investigated. The oscillation is highest in the last stage of the dynamic blow and is still high during the reduction stage. As the amount of inert gas increases, the vibration level also increases. Inert gas has a greater influence on the oscillation than oxygen. Tilting the converter around 8 deg clearly leads to more intensive oscillations. Increasing the blowing rate increases the forces and torques acting on the vessel, whereas the oscillation frequency remains nearly constant. A varying fill level does not influence the vibration level the same way as the blowing rate. The operational test shows, for example, that the maximum torque does not depend on the heat size when the latter varies between –8 pct and +21 pct of the nominal heat size. The water model test shows decreasing forces and torques with a rising fill level.     

An approach for determining the subsystem experiencing andproducing a bifurcation in a power system dynamic model

This paper presents a method for determining reduced-order subsystems called bifurcation subsystems, that experience bifurcation, and produce the bifurcation in the full power system dynamic model. The bifurcation subsystem is generally a subset of the center manifold subsystem. The bifurcation subsystem is in fact the singular perturbation determined slow subsystem within the center manifold dynamics that actually experiences and produces the bifurcation in the center manifold dynamics. The test procedure used to determine a bifurcation subsystem is described in this paper and does not require performing a nonlinear transformation required to determine the center manifold. The theory provides two singular perturbation based test conditions for existence of bifurcation subsystems. Examples that demonstrate the systematic use of this test procedure are presented for saddle-node and Hopf bifurcations in a single-machine-infinite-bus-model. Results when the test procedure for finding a bifurcation subsystem is applied to the large dominant elements of the tight eigenvector and the participation factor of a bifurcating eigenvalue are compared     

Identification of generic bifurcation and stability problems inpower system differential-algebraic model

Based on the structurally represented power system differential-algebraic model and its Jacobian matrix. This paper develops a much more complete and systematic classification of the types of bifurcation and stability problem in the power system model. It is theoretically shown that bifurcations cannot occur due to the row dependence of the network Jacobian matrix (causality matrix) associated with the rows of the active and reactive power balance equations at a single bus or at a subset of buses, resulting in several of the classified bifurcations being nongeneric. The generic types of bifurcation and instability problems are then identified: static bifurcation dynamic bifurcation, loss of causality, and loss of single-machine stability; the later two are further shown to be very improbable. This paper also proposes an equivalent test for static bifurcation-static/algebraic bifurcation test whose advantages are disclosed. The identification of generic bifurcation and stability problems in power systems provides the foundation of the further study on static and dynamic voltage-angle stability problems     

Structural and Magnetic Properties of Copper(II) Coordination Polymers Containing Fluoride-Based Anions and Ancillary Organic Ligands

The fluoride (F⁻) and bifluoride (HF₂⁻) anions have been little used in the self-assembly of molecular and polymeric magnets. We have recently synthesized several new compounds, namely CuF₂(3-OHpy)₄ (OHpy = hydroxypyridine) (1), Cu(SiF₆)(2,6-me₂pyz)₄ (me₂pyz = dimethylpyrazine) (2), CuF₂(H₂O)₂(pyz) (pyz = pyrazine) (3) and [Cu(HF₂)(pyz)₂]BF₄ (4). Compound 1 contains coordinate covalent and hydrogen bonding interactions that link the Cu(II) ions into 3D networks while 2 features square-pyramidal Cu(II) ions that are weakly bridged by SiF₆²⁻ anions into 1D chains. Preliminary structural data indicate that compound 3 contains 1D Cu-pyz-Cu chains while 4 contains two dimensional [Cu(pyz)₂]²⁺ layers, which held together via HF₂⁻ anions so as to form an unprecedented 3D network. The magnetic properties of each are briefly described herein.     

Outcome of transfusion of K:11 erythrocytes in a patient with anti-K11 antibody

Arteriovenous (AV) malformations are rare and may occur at various locations, like in the brain, liver, lungs, or in the subcutaneous tissue. This case report describes an AV malformation from the right occipital artery. The value of combined B-mode ultrasonography and color Doppler mode imaging of masses in the neck region is discussed.