Topography of brain sodium accumulation in progressive multiple sclerosis

Object

Sodium accumulation is involved in neuronal injury occurring in multiple sclerosis (MS). We aimed to assess sodium accumulation in progressive MS, known to suffer from severe neuronal injury.

Materials and methods

3D-²³Na-MRI was obtained on a 3T-MR-scanner in 20 progressive MS patients [11 primary-progressive (PPMS) and nine secondary-progressive (SPMS)] and 15 controls. Total sodium concentrations (TSC) within grey matter (GM), normal-appearing white matter (WM) and lesions were extracted. Statistical mapping analyses of TSC abnormalities were also performed.

Results

Progressive MS patients presented higher GM–TSC values (48.8 ± 3.1 mmol/l wet tissue vol, p < 0.001) and T₂lesions-TSC values (50.9 ± 2.2 mmol/l wet tissue vol, p = 0.01) compared to GM and WM of controls. Statistical mapping analysis showed TSC increases in PPMS patients confined to motor and somatosensory cortices, prefrontal cortices, pons and cerebellum. In SPMS, TSC increases were associated with areas involving: primary motor, premotor and somatosensory cortices; prefrontal, cingulate and visual cortices; the corpus callosum, thalami, brainstem and cerebellum. Anterior prefrontal and premotor cortices TSC were correlated with disability.

Conclusion

Sodium accumulation is present in progressive MS patients, more restricted to the motor system in PPMS and more widespread in SPMS. Local brain sodium accumulation appears as a promising marker to monitor patients with progressive MS.     

Overvoltages caused by switching unloaded cable lines by a vacuum switch

The paper presents results of the studies on overvoltages generated while switching unloaded medium voltage (MV) power cable lines by a vacuum switch. The studies were carried out while switching real MV cable lines and their physical models. It has been found that overvoltages and overcurrents are generated during switching, and that under certain conditions they may reach significant values. These values depend on the source side circuit parameters, on kinematics vacuum switch parameters as well as on parameters of a switched cable line.Abbreviations AR Arc reignition - V_p Test voltages - t_bpn Time without current between subsequent ARs - k_szn Coefficient of ground overvoltage in the source side circuit after AR occurrence - k_swn Coefficient of ground overvoltage in the source side circuit after switching off n AR - k_czn Coefficient of overvoltage in the research circuit after AR occurrence - k_cwn Coefficient of overvoltage in the research circuit after switching off current of n AR - k_pcn Coefficient of overvoltage in the research circuit as an effect of overloading the capacity of the cable line or its physical model as a result of AR     

Tangentialkomponentenverlauf der magnetischen Feldstärke längs eines rechteck- oder vieleckförmigen Magnetkreises

Übersicht Wenn ein Stromleiter oder eine Wicklung von einem geschlossenen Magnetkreis idealer Permeabilität umgeben ist, ist die tangentielle Feldstärke längs der inneren Oberfläche des Eisens nur von den geometrischen Dimensionen des Magnetkreises, nicht aber von der Lage des Leiters abhängig. Es wird der Verlauf der Tangentialkomponente der magnetischen Intensität längs eines rechteckigen und polygonalen Rahmens mittels konformer Abbildungen untersucht und die theoretisch gewonnenen Ergebnisse werden mit experimentellen Messungen der Tangentialkomponente in einem Rechteckrahmen verglichen.

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Summary If a conductor or winding is surrounded by a closed magnetic circuit of ideal permeability, the tangential component of the intensity of the magnetic field along the inner surface of the iron depends only on the geometrical dimensions of the magnetic circuit and not on the position of the conductor inside it. Using the conformal mapping there is analysed the form of the tangential component of the magnetic intensity along a rectangular and polygonal frame and the theoretically derived results are compared with the experimental measurements of the tangential component in a rectangular frame.

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Übersicht der benutzten Formelzeichen B _no Normalkomponente der Induktion an der Oberfläche des Magnetkreises in derz-Ebene - H _to Tangentialfeldstärke an der Oberfläche des Magnetkreises in derz-Ebene - H _tow dasselbe, jedoch in derw-Ebene - Index I Innengebiet (Fensterraum) des Eisen-Rahmens oder-Polygons - II Außengebiet (Eisen) des Eisen-Rahmens oder-Polygons - I Gesamtstrom im Innenraum des Rahmens - z ₁–z _n Eckpunkte des Rahmens derz-Ebene - z ₀ Punkte des Rahmenumrisses - w ₁–w _n Den Eck-Punktenz ₁–z _n zugeordnete Punkte derw-Ebene - ₁– _n Außenwinkel des Rahmens - 2a, 2b Seitenlängen des Rahmens bzw. Polygons - Halbmesser des Polygonumkreises - Mittelpunktswinkel der Rahmen- oder Polygonseite - M Abbildungsmodul - F _m Magnetische Spannung - , , ^* Hilfsfunktionen Mit 7 Textabbildungen     

Lateralization of amygdala activation in fMRI may depend on phase-encoding polarity

Object

Susceptibility artifacts along the phase-encoding (PE) direction impact the activation pattern in the amygdala and may lead to systematic asymmetries. We implemented a triple-echo echo-planar imaging (EPI) sequence, acquiring opposite PE polarities along left?Cright PE direction in a single shot, to investigate its effects on amygdala lateralization.

Materials and Methods

Twelve subjects viewed emotional faces to evoke amygdala activation.

Results and Conclusion

A region of interest analysis revealed that the lateralization of amygdala responses depended on the PE polarity thus representing a pure method artifact. Alternating PE with multi-echo EPI reduced the artifact. Lateralized fMRI activation in areas with magnetic field inhomogeneities need to be interpreted with caution.     

Cardiac magnetic resonance T1 and extracellular volume mapping with motion correction and co-registration based on fast elastic image registration

Objective

Our aim was to investigate the technical feasibility of a novel motion compensation method for cardiac magntic resonance (MR) T1 and extracellular volume fraction (ECV) mapping.

Materials and methods

Native and post-contrast T1 maps were obtained using modified look-locker inversion recovery (MOLLI) pulse sequences with acquisition scheme defined in seconds. A nonrigid, nonparametric, fast elastic registration method was applied to generate motion-corrected T1 maps and subsequently ECV maps. Qualitative rating was performed based on T1 fitting-error maps and overlay images. Local deformation vector fields were produced for quantitative assessment. Intra- and inter-observer reproducibility were compared with and without motion compensation.

Results

Eighty-two T1 and 39 ECV maps were obtained in 21 patients with diverse myocardial diseases. Approximately 60% demonstrated clear quality improvement after motion correction for T1 mapping, particularly for the poor-rating cases (23% before vs 2% after). Approximately 67% showed further improvement with co-registration in ECV mapping. Although T1 and ECV values were not clinically significantly different before and after motion compensation, there was improved intra- and inter-observer reproducibility after motion compensation.

Conclusions

Automated motion correction and co-registration improved the qualitative assessment and reproducibility of cardiac MR T1 and ECV measurements, allowing for more reliable ECV mapping.

     

Use of Ritz and Bubnow-Galerkin methods for calculation of inductance and impedance of conductors

Contents It is shown that the Ritz and Bubnow-Galerkin methods can be applied for the calculation of the inductance and the impedance, respectively. Moreover it is shown that the calculation of the impedance by the Bubnow-Galerkin method is a generalization of the calculation of the inductance by the Ritz method in the case of a nonhomogeneous Neumann boundary problem. For the illustration of these methods the inductance of a rectangular ferromagnetic conductor and the inner impedance of a rectangular conductor placed in a semi-closed slot are calculated.

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Übersicht In der Arbeit wird bewiesen, daß man die Methoden von Ritz und Bubnow-Galerkin zur Berechnung der Induktivität und der Impedanz anwenden kann. Überdies wird gezeigt, daß die Berechnung der Impedanz mit Hilfe der Methode von Bubnow-Galerkin eine Verallgemeinung der Berechnung der Induktivität mit Hilfe der Ritz-Methode für die ungleichartigen Randbedingungen des Neumann-Problems bildet.Zur Illustration der Methoden werden die Induktivität des rechteckigen ferromagnetischen Leiters und die innere Impedanz des rechteckigen Leiters in der halbgeschlossenen Nut berechnet.

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Symbols A Component of the vector potential to thez-axis (complex v. m. s. value) - B _t,B _n Tangential and normal component of magnetic induction (complex r. m. s. values) - C,C ₀,K Operators in a Hilbert space - H Hilbert space - Energetic space of a positive definite operator - I=\I\e ⁱ Complex value of the current, |I|=r. m. s. value - Imaginary unit - J Current density (complex r. m. s. value) - l Conductor length - L, L() Inductance - Z Impedance - z ^* Dimension coupled with complex dimensionz - Magnetic permeability - Conductance - Pulsation - Derivative in normal external direction and tangential direction - Scalar Laplacian - 1 _t,1 _n Unit vectors, tangential and normal to the curve lying in thex,y-plane - (x/y) Scalar product of Hilbert space elementsx, y     

induktivitäten windschiefer Leitersysteme

Übersicht In der Abhandlung werden die Selbst- und Koppelinduktivitäten zweier kurzer Linienleiter aus dem Vektorpotential bestimmt. Die gefundenen Beziehungen werden für verschiedene Anordnungen ausgewertet und diskutiert. Weitere Leiter lassen sich durch Überlagerung der Flüsse berücksichtigen.Damit ist es möglich, die Induktivitäten komplizierter Leiterschleifen anzugeben, bzw. die Ströme und Spannungen in räumlichen Mehrleitersystemen zu berechnen. Gekrümmte Leiterschleifen werden durch Polygonzüge angenähert. Als einfache Beispiele werden Ringspulen, Zylinderspulen und kurze Leitungen untersucht. Die Ergebnisse werden mit den bekannten analytischen Lösungen verglichen. Es zeigt sich, daß das Verfahren bereits bei geringer Stückelung brauchbare Ergebnisse liefert.

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Induction coefficients of twisted conductors

Contents In this paper the self- and mutual inductances of two short line wires are defined by the vector potential. The figures obtained are evaluated and discussed for various arrangements. Further conductors can be considered by a superposition of flux. With this it is possible to indicate the inductances of complicated turns respectively to calculate the currents and voltages of multi-conductor systems in space arrangement. Curved conductors are approximated by the point-slope method. Toroidal coils, cylindric coils and finite lines are investigated according to this method. The values obtained are compared with the well-known analytic solutions. It appears that by the point-slope method suitable results can be obtained by replacing the conductor by few straight lines.

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Formelzeichen A Abstand zum fiktiven Rückleiter - a Querabstand - b Abstand - d Ersatzbreite - F Windungsfläche - f Frequenz - g mittlerer geometrischer Abstand m.g.A. - h mittlerer harmonischer Abstand m.h.A. - L Induktivität - i Länge - P Aufpunkt - Q Laufpunkt - R Radius einer kreisförmigen Leiterschleife - r Abstand zwischen zwei Punkten - mittlerer arithmetischer Abstand - R, s Strahl nach Bild 1 - , , , Winkel - Fluß - Leiterradius - ₀ Permeabilität des leeren Raumes     

Some characteristics of magnetic field patterns in air-gaps with double-sided slotting

Contents The conductance of air-gaps with double-sided slotting is generally considered with the assumption that the flux lines are radially directed only. Calculations allowing for the two-dimensional nature of air-gap fields, however, show a different situation with regard to the effect of slotting, especially at the higher harmonic orders. Calculated curves and tables are presented to illustrate the correlation between these two ways of approach for two slot combinations under excitation by a single coil, and also to establish the way in which the harmonics vary with changing rotor position.

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Einige Eigenschaften der magnetischen Feldverteilung in Luftspalten mit beiderseitiger Nutung

Übersicht Der Leitwert von Luftspalten mit beiderseitiger Nutung wird gewöhnlich unter der Voraussetzung betrachtet, daß die Feldlinien ausschließlich radial verlaufen. Berechnungen unter Berücksichtigung des zweidimensionalen Charakters des Luftspaltfeldes zeigen jedoch, insbesondere bei den höheren Harmonischen, bezüglich der Auswirkung der Nutung ein anderes Bild. Es werden berechnete Kurven und Tabellen vorgelegt, mit denen der Zusammenhang zwischen den beiden Methoden für zwei Nut-Kombinationen mit Erregung durch eine Spule untersucht wird. Außerdem werden die Änderungen der Harmonischen mit der veränderlichen Rotorposition betrachtet.

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List of principle symbols B _n ^s /B _n ^r stator/rotorn-th order flux densities - B _n ^rs n-th order flux density on rotor generated by stator coil - B _n ^sr n-th order flux density on stator generated by rotor coil - d distance large enough to extend into homogeneous flux region - g air-gap length - N ^s/N ^r number of teeth on stator/rotor - S ^s/N ^r stator/rotor slot opening - rotor position relative to stator - B _n ^s /B _n ^r stator/rotor tooth pitch - tangential position in air-gap     

Three-dimensional analysis of electromagnetic forces in some geometries with cylindrical symmetry

Contents The paper utilizes a three-dimensional analytical method in order to determine the values and distribution of electromagnetic forces acting on electrical systems provided with saddle coils. The method permits the calculation of the forces per unit volume, the pressures and the total forces acting on the coils, taking into account the end zones. Two application examples are given, referring to a dipole superconducting magnet and to a superconducting turboalternator.

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Dreidimensionale Analyse der elektromagnetischen Kräfte in verschiedenen rotationssymmetrischen Anordnungen

Übersicht Der Aufsatz benutzt eine dreidimensionale analytische Methode zur Berechnung der Werte und der Verteilung der elektromagnetischen Kräfte in elektrischen Systemen mit Sattelspulen. Die Methode erlaubt die Berechnung der Kräfte pro Volumeneinheit, der Drücke und die auf die Spulen wirkenden Gesamtkräfte unter Berücksichtigung der endlichen Länge. Die Methode wird auf einen zweipoligen supraleitenden Magnet und auf einen supraleitenden Synchrongenerator angewendet.

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List of main symbols A, C integration constants - m, n tangential and axial harmonics - p number of pole pairs - I, K modified Bessel functions of the first and second kind - s Lommel functions - I, K derivatives of Bessel functions with respect tor - q /g - ₀ absolute magnetic permeability - _z relative magnetic permeability of the axial shields - NI coil ampereturns     

Zahnbrüche und Zahnkräfte in Asynchronmotoren

Übersicht Die pulsierenden Tangential- und Radialkräfte auf die Rotorzähne werden mittels zweier verschiedener Methoden an einem 3000 kW-und einem 45 kW-Motor berechnet. Die Tangentialkraft auf den einzelnen Zahn ist besonders während des Anlaufes überraschend groß, etwa 46mal größer als es dem asynchronen Drehmomentanteil entspricht.Die an einem 4poligen 3000 kW-Motor beobachteten Zahnbrüche werden untersucht. In Resonanz mit 1266 Hz (bei 1055 U/min im Anlauf) wird die tangentiale Zahnschwingung 9mal größer als bei statischer Auslenkung und beträgt 0,31 mm. Dabei entstehen Biegewechselspannungen mit bis zu 440 N/mm², die zu einem Ermüdungsbruch führten. Die zulässige Betriebsdauer bis zum Eintritt eines Ermüdungsbruches wird berechnet.Die magnetische Radialkraft und die Fliehkraft sind von geringerer Bedeutung. Regeln zur Vermeidung von Zahnbrüchen werden angegeben.

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Tooth breakage and tooth forces in asynchronous motors

Contents The oscillating tangential and radial forces acting on rotor teeth are analysed by two different methods for motors rated 3000 kW and 45 kW. The maximal tangential force on a tooth during starting up can be especially large, e.g. 46 times larger than the asynchronous force per tooth.Tooth breakages which appeared in a 4pole motor rated 3000 kW are investigated. In tooth-resonance with 1266 Hz during starting up at 1055 rev/min the tangential tooth deflection becomes 9 times its static deflection and amounts to 0.31 mm. Thereby oscillating bending stresses occur up to values of 440 N/mm² which cause fractures by fatigue. The admissible operating time until failure is determined. The magnetic radial and centrifugal forces are of minor importance. Rules to avoid tooth breakage are given.

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Formelzeichen Polpaarzahl der MMK des Stator-Grundstromes, Ordnungszahl der Rotoroberströme - Polpaarzahl der MMK der Stator-Oberströme - Polpaarzahl der Rotor-MMK - p Polpaarzahl, oder Index für Pendelkraft - b Ordnungszahl=0, ±1, ±2 ...b _max - a 0, ±1, ±2 ...,c=0, ±1, ±2, ... - Z ₁,Z ₂ Nutenzahlen im Stator und Rotor - s (n ₀ –n)/n ₀ = Schlupf, oder Index für Stab - r Bohrungsradius - U _k Klemmenspannung des k-ten Stranges - ^b _1,k komplexer Statoroberstrom im Strang k mit der Ordnungszahl b - m Strangzahl - ₂ Rotorpositionswinkel (Startwinkel) siehe Bild 6, in rad - q Nutenzahl pro Pol und Strang - _g geometrischer Luftspalt - N Windungszahl pro Spule - magnetischer Leitwert des Stators für die Harmonischen ₁ - n ₁ ±0, ±1, ±2 ...n _{1 max} - Wicklungsfaktor für die Harmonische - ^v s Frequenzbeiwert für den Rotoroberstrom I _R - Verkürzung der Spulenweite in Nuten - ₁ Nutenwinkel im Stator - s ₂ Nutschlitzbreite im Rotor - l _e Einsenlänge - b _u /b ₀ Zahnbreite unten/oben - n ₀ synchrone Drehzahl - y _e Schwingungsausschlag am Zahnende - _b Biegespannung an der Zahnwurzel - x₂ Rotorkoordinate, Ursprung in Mitte von Zahn 1, in rad - _mec mechanische Winkelgeschwindigkeit - f _N Netzfrequenz - logarithmisches Dekrement der Dämpfung - Verhältnis Nutschlitzbreite zu Nutteilung - Kreisfrequenz von Schwingungen     

一种求解输电线路不均匀覆冰受力状态的新方法

在2种不同均布荷载同时作用下线索的悬垂函数以及弧垂、线长、张力的斜抛物线方程计算方法的基础上,提出"线路同时承受多个荷载所引起的线路状态变化增量等于分别承受这些荷载所引起的线路状态变化增量的叠加"的假设,利用该假设结合牛顿法得出一种便于实现电算化的求解线路不均匀覆冰复杂受力状态的新方法-分解法,该方法运用积分原理,将不均匀覆冰的复杂受力状态,划分为多个微段的均匀覆冰叠加,然后求解出最壮的受力状态。     

Finite-element method for field analysis in rectangular conductor carrying sinusoidal current

Contents On the basis of finite element method the analysis of skin effect occurring in the rectangular conductor carrying sinusoidal current has been performed. The conductor is surrounded by a cylindrical surface. Outside that surface the method of variable division has been applied and inside — the Bubnov-Galerkin method by means of numerical calculations with the use of finite-element method. — On the basis of the data obtained the numerical calculations were performed and the plots of resistance and reactance were drawn.

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Feldanalyse in einem rechteckigen den sinusoidalen Strom leitenden Leiter mit der Methode der finiten Elemente

Übersicht In diesem Beitrag wird in Anlehnung an die Methode der finiten Elemente eine zweidimensionale Analyse der Stromverdrängung in einem rechteckigen den sinusoidalen Strom leitenden Leiter durchgeführt. Der Leiter ist mit einer Zylinderfläche umgeben, in deren Inneren man die Variablentrennungsmethode verwendet und Außen — die Bubnov-Galerkin-Methode (eine nummerische Realisierung dieser Methode unter Benutzung der Methode der finiten Elemente). — Auf Grundlage der erhaltenen Abhängigkeiten werden digitale Berechnungen durchgeführt, die man zur Ausführung der Resistanz- und Reaktanz-Diagramme verwendet.

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Symbols A vector potential (complex r.m.s. value) - A z-component of A (complex r.m.s. value) - B magnetic induction vector (complex r.m.s. value) - tangential component of the magnetic induction vector (complex r.m.s. value) - normal component of the magnetic induction vector (complex r.m.s. value) - E electric field intensity (complex r.m.s. value) - i, j, k numbers of vertices of the considered finite element - J current (r.m.s. value) - imaginary unit - imaginary unit - R resistance - R ₀ D.C. resistance - S boundary of region - T finite element area - X reactance - Z impedance - z ^* conjugate complex number ofz - basis function - magnetic permeability - pulsation - _i, _j, _k function of finite element shape - conductivity - region - ^h region approximating the region - ^e finite element region - 3.141593... - ² scalar Laplacian - 1 _n ; 1 _t ; 1 _z unit vector in normal external, tangential andz-axis direction - x, y, z rectangular coordinates - r, ,z cylindrical coordinates     

Zero-sequence representation of overhead lines

Contents The zero sequence components of electrical quantities of overhead lines appearing at unsymmetrical ground faults are analysed, taking into account the mutual coupling among line phase circuits and earth wires as well as the conducting effects of line towers. The line model, developed using the Z-Transform, enables an accurate analysis of ground fault current distribution and magnitudes. As an illustration, the line model is applied for evaluation of various earthing system parameters of an EHV line connecting two substations. Analytical expressions for some of these parameters are also given.

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Nullsystem-Darstellung von Freileitungen

Übersicht Die Nullkomponente der elektrischen Größen, die etwa bei unsymmetrischen Erdkurzschlüssen auf Freileitungen vorkommen, werden unter Berücksichtigung der elektromagnetischen Kopplungen zwischen den Hauptleitern und den Erdseilen sowie der Mastströme analyisert. Das unter Verwendung der Z-Transformation entwickelte Leitungsmodell ermöglicht eine genaue Bestimmung der Verteilung und der Größe der Erdkurzschlußströme. Als Beispiel wird es zur Berechnung verschiedener Erdungsparameter einer Höchstspannungsfreileitung angewandt, die zwei Umspannwerke verbindet. Analytische Formeln für einige dieser Parameter werden angegeben.

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List of Principal Symbols i vector of triple zero-sequence currents of line circuits - i _ek total earth wire current at spank - i _ek vector of earth wire currents at spank - u _k vector of zero-sequence potentials of line circuits at towerk - u _ek potential of towerk - u _p voltage of the faulted phase, prior to fault occurence - z_p matrix of self- and mutual-impedances of line circuits, per line span - z _m matrix of mutual impedances among line circuits and earth wires, per line span - z matrix of self- and mutual-impedances of earth wires, per line span - Z ⁺,Z ^–,Z ⁰ positive-, negative- and zero-sequence impedances - Z _A (Z _B ) resistance to ground of substationA(B) carthing grid - Z _l carth wire ground resistance - R tower resistance to ground - earth wire coupling factor - r earth wire total screening factor - M(N) number of line circuits (earth wires) - M(N) M(N)-dimensional vector of units     

The response to rapid infusion of fentanyl in the human brain measured using pulsed arterial spin labelling

Objective

We evaluated the sensitivity of pulsed Arterial Spin Labelling (pASL) for the detection of changes in regional cerebral blood perfusion (CBP) during and after intra-venous (i.v.) infusion of an opioid agonist (fentanyl) and an opioid antagonist (naloxone).

Materials and methods

Twenty-three subjects were scanned four times, receiving i.v. infusion of fentanyl, naloxone, placebo and a second fentanyl administration, in four separate scanning sessions in randomised order. End-tidal CO₂, respiration rate and heart rate were recorded continuously throughout each scan. pASL time series were collected using single shot EPI for 15?min (including 5?min of baseline prior to infusion).

Results

Significant increases in CBP were detected during and after administration of fentanyl, (when compared to placebo and naloxone), in most areas of high concentration of mu-opioid receptors (thalamus, lingual gyrus, para-hippocampal gyrus, and insula); near-significant increases were also observed in the insula. No increases in perfusion were observed during or after naloxone infusion. No correlation was found between regional rCBF changes and end-tidal CO₂, respiration rate or heart rate. Good reliability was found between the first and second fentanyl sessions but the regions of high reliability did not overlap completely with those of highest perfusion change.

Conclusion

pASL is a suitable method for examining rapid, dynamic effects of opioid administration on brain physiology.     

Non-symmetrical shaped conductors located in a time-harmonic TM field

Contents In the work the method providing to determinate the power losses of long conductor of an arbitrary polygonal cross-section, placed in a time-harmonic transverse magnetic (TM) field. This method rests on the connection of the Bubnov-Galerkin method in its numerical version performed by means of finite element method for internal region with the method of division of variables for external region. — On the basis of theoretical considerations the numerical calculations were performed for several chosen cases of shaped conductors, on the basis of which the plots of Joule power losses in those conductors were made.

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Die in einem senkrechten harmonischen Magnetfeld (TM-Feld) lokalisierten nicht symmetrischen Profilleiter

Übersicht Im Beitrag wurde eine Methode zur Ermittlung der Leistungsverluste in einem langen Leiter mit einem beliebigen vielblätterigen Querschnitt angegeben. Der Leiter befindet sich in einem harmonischen senkrechten Magnetfeld (TM-Feld). Die Methode verbindet die Bubnov-Galerkin-Methode (es geht hier um nummerische Realisierung dieser Methode unter Verwendung der Methode finiter Elemente für den inneren Bereich) und die Variablentrennung-Methode (für den äußeren Bereich). — Auf der Grundlage theoretischer Erwägungen hat man numerische Berechnungen für einige gewählte Leiterprofile durchgeführt und die Joule-Diagramme der Leistungsverluste erhalten.

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List of main symbols A z-component of the vector potentialA (complex r.m.s. value) - B magnetic induction vector (complex r.m.s. value) - B _t =A/n tangential component of the magnetic induction vector (complexs r.m.s. value) - E electric field vector (complex r.m.s. value) - i, j, k numbers of vertices of the considered finite element - H magnetic field intensity vector (complex r.m.s. value) - Imaginary unit - l boundary of the region II - l ^h boundary of the region II approximated by broken line - P complex Poynting vector - P Joule's power losses - r ₀ radius - S boundary of the region - x, y, z rectangular coordinates - r, ,z cylindrical coordinates - =3.141593 ... - z ^* conjugate complex number ofz - basis function - magnetic permeability - pulsation - N _i ,N _j ,N _k function of finite element shape - conductivity - region - ^h region approximating the region - ^e finite element region - ² scalar Laplacian - finite element area     

Semi-automated myocardial segmentation of bright blood multi-gradient echo images improves reproducibility of myocardial contours and T2* determination

Objectives

Early detection of iron loading is affected by the reproducibility of myocardial contour assessment. A novel semi-automatic myocardial segmentation method is presented on contrast-optimized composite images and compared to the results of manual drawing.

Materials and methods

Fifty-one short-axis slices at basal, mid-ventricular and apical locations from 17 patients were acquired by bright blood multi-gradient echo MRI. Four observers produced semi-automatic and manual myocardial contours on contrast-optimized composite images. The semi-automatic segmentation method relies on vector field convolution active contours to generate the endocardial contour. After creating radial pixel clusters on the myocardial wall, a combination of pixel-wise coefficient of variance (CoV) assessment and k-means clustering establishes the epicardial contour for each segment.

Results

Compared to manual drawing, semi-automatic myocardial segmentation lowers the variability of T2* quantification within and between observers (CoV of 12.05 vs. 13.86% and 14.43 vs. 16.01%) by improving contour reproducibility (P < 0.001). In the presence of iron loading, semi-automatic segmentation also lowers the T2* variability within and between observers (CoV of 13.14 vs. 15.19% and 15.91 vs. 17.28%).

Conclusion

Application of semi-automatic myocardial segmentation on contrast-optimized composite images improves the reproducibility of T2* quantification.

     

Electrodynamic forces acting on a conductor with elliptic cross section in the slot of an electric machine

Contents In this paper, radial electrodynamic forces acting on a conductor entirely filling a semi-closed slot with elliptic cross section are investigated. The calculations have been made by using the Bubnow-Galerkin method. The results are compared with published data.

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Elektrodynamische Kräfte auf einen Leiter mit Ellipsen-form in der Nut elektrischer Maschinen

Übersicht In diesem Artikel wurden die Kräfte untersucht, die auf einen Leiter mit Ellipsenform in halbgeschlossener Nut wirken. Die Berechnungen wurden mit der Bubnow-Galerkin Methode vorgenommen. Die Berechnungsergebnisse wurden mit Literaturangaben verglichen.

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List of Symbols A z-component of vector potential (complex r.m.s. value) - B ,B normal and tangential components of the magnetic induction in the elliptic-cylindrical system of coordinates (r.m.s. value) - F electrodynamic force - F _m , F _a arythmetical mean and alternating components of the total force - J z-component of current density (complex r.m.s. value) - imaginary unit - 2a, 2b major and minor axis of ellipse - c distance of focus from center of cllipse - l conductor lenght - I=I e^j complex value of current, |I|=r.m.s. value - z,z ^* modulus of complex numberz and complex conjugate ofz - Rez, Im z real and imaginary part of complex numberz - ₁ angle of slot opening - conductivity - magnetic permeability - pulsation - cross section area     

The finite element method application to the slot impedance calculation

Contents The aim of this paper is to determine, by means of the finite element method, the impedance of the bar filling the semi-closed slot of an electric machine. As an example the slot of complex shape was chosen for calculations. The analysis of that case by means exact methods would have been totally impossible. An accuracy of the method has been evaluated on the basis of published data. The two-dimensional skin effect was taken into considerations.

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Anwendung der Methode der finiten Elemente in der Nut Impedanzen Berechnung

Übersicht Der Beitrag behandelt, mit Hilfe der Methode der finiten Elemente, die Bestimmung der Impedanzen von Leitern in der halbgeschlossenen Nut elektrischer Maschinen für den Fall kompliziert geformter Querschnitte, bei denen eine geschlossene analytische Berechnung unmöglich ist. Das Verfahren und die erreichbare Genauigkeit wird an einem Beispiel gezeigt, wobei die Stromverdrängung mit berücksichtigt wird.

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List of Symbols A z-component of vector potential (complex r.m.s. value) - B _t tangential component of induction - I=|I| e^j0 complex value of current, |I|=r.m.s. value - imaginary unit - |z|,z ^* modulus of complex numberz and complex conjugate ofz - Re [z], Jm [z] real and imaginary part of complex numberz - angle of slot opening - R _o d.c. resistance - magnetic permeability - conductivity - ² scalar Laplacian - /n derivative in normal external direction - cross section area - S boundary of area - H Hilbert's space - H–² energetic space of a positive definite ² - ^h region under triangulation - l _h boundary of ^h - W ₂ ¹ () Sobolev's space - S _h subspace ofW ₂ ¹ () - pulsation     

Distribution in TLM models for diffusion (Part II: multi‐dimensional treatment)

The signals obtained at each time step of a transmission line matrix (TLM) simulation of Gaussian diffusion are analysed for two‐ and three‐dimensional cases. A combinatorial formula is derived to provide the signal magnitude at any spatial position and any time step after a single‐shot excitation in the two‐dimensional link‐line model. Formulae for the expectation and variance of the axial positions of a particle are determined for two‐ and three‐dimensional link‐line and link‐resistor models. A generalization of these formulae is proposed for higher dimensions, and an entirely numerical proving scheme is devised. Finally, we briefly compare the resulting variances and that of the underlying diffusion process. Copyright © 2003 John Wiley & Sons, Ltd.     

SMOS: A CAD-compatible statistical model for analogue mos integrated circuit simulation

An analogue CAD tool capable of simulating MOS circuit performance variance caused by intra-die variability inherent to IC fabrication processes has been developed. the nucleus of this tool is a general, CAD-compatible, MOS statistical model called SMOS which comprehends the effects of device geometry, circuit layout and transistor bias on parameter variance. an example of the model calculation procedure is presented to illustrate both the modelling algorithms and the process characterization data required by the statistical model. the statistical model is verified through experimental data which show excellent agreement with performance variances predicted by simulation. Implementations of the statistical model in two circuit simulation environments, SPICE and APLAC, are also described. Statistical analysis and simulation of two basic analogue subcircuits, the current mirror and the source-coupled pair, are presented.