T2 Relaxation time study of the pig renal allografts

A previous study showed the possibility of the dependence of theT ₂ maps measured by Siemens Magnetom MR imager 1.5 T on the viability of the cadaveric kidney. For theT ₂ relaxometry study the pig model was used. Ten pig renal allografts were examined during 68 h after removal. Significant differences were found in the change of the initialT ₂ ⁱⁿⁱ values in the histogram within the first 20 h [₁=T ₂ ⁱⁿⁱ (2)–T ₂ ⁱⁿⁱ (20)] or 8 h [₂=T ₂ ⁱⁿⁱ (2)–T ₂ ⁿⁱ (8)] after removal between the groups of the damaged kidneys (₁=20.2±6.8 ms, ₂=19.4±3.0) and the kidneys without apparent damage (₁=9.4±8.5 ms, ₂=5.4±5.8).     

SrLnAlO4 (Ln=Nd and Sm) Microwave Dielectric Ceramics

SrLnAlO₄ (Ln=Nd and Sm) ceramics with K₂NiF₄ structure were prepared by a solid state reaction approach, and their microwave dielectric characteristics were evaluated together with the microstructures. The single phase dense SrNdAlO₄ and SrSmAlO₄ ceramics were obtained by sintering at 1450–1475°C and 1475–1500°C, respectively, and the good microwave dielectric characteristics were achieved: (1) = 17.8, Q · f = 25,700 GHz, _f = –9 ppm/°C for SrNdAlO₄; and (2) = 18.8, Q · f = 54,880 GHz, _f = 2 ppm/°C for SrSmAlO₄ dense ceramics. The Qf value significantly increased with increasing sintering temperature.     

Electrical Properties of 6H-BaTi0.95M0.05O3−δ Ceramics where M = Mn, Fe, Co and Ni

Hexagonal BaTiO₃ materials have been stabilised at room temperature according to the formula BaTi_0.95M_0.05 O_3– where M = Mn, Fe, Co and Ni. Dense ceramics (> 96% of the theoretical X-ray density) were sintered at 1450C in flowing O₂ gas from calcined powders prepared by the mixed oxide route at 1300C. All samples were single-phase and the bulk conductivity, _b, measured by Impedance Spectroscopy and Q.f measured by microwave dielectric resonance methods showed a strong dependence on the type of dopant. _b at 300C was 10^–7, 10^–5.5, 10^–5.5 and 10^–4 Scm^–1 for M = Mn, Fe, Ni and Co, respectively and Q.f at 5 GHz was 7790, 6670, 2442 and 1291 GHz, for M = Mn, Fe, Ni and Co, respectively. The correlation between _b and Q.f is attributed to the presence of oxygen vacancies and/or mixed valency of the dopant ions.     

The Influence of Bi2O3 and Sb2O3 on the Electrical Properties of ZnO-Based Varistors

This work presents a study of the influence of both Bi content and Sb/Bi ratio on the electrical characteristics of a commercial-type ZnO varistor. In contrast to previous studies two nonlinear coefficients, the breakdown fields and energy absorption abilities were measured after sintering at 970°C or 930°C. The Bi-content was varied from 0.9 to 1.8 at% while the Sb/Bi ratio was varied from 0.8 to 1.5, leading to values of up to 104 for the nonlinear coefficient 1, 1100 V mm^–1 for the breakdown field and 1137 J cm^–3 for the energy absorption ability. The highest value was measured for the highest Bi-content and the lowest Sb/Bi ratio and vice versa. The breakdown field E _V increased with lower sintering temperature, increased Sb/Bi ratio (at a given Bi-content) and increased Bi-content (at a given Sb/Bi ratio). The energy absorption coefficient increased at the higher sinter temperature and with lower Sb and Bi concentrations.The observed effects were related to the amount of spinel phase (Zn₇Sb₂O₁₂) formed during the sintering process and the amount of liquid phase present during early stages of the sintering process.     

Synthesis and Dielectric Characterization of Pyrochlore-Free Pb1−x Ba x (Zn1/3Nb2/3)O3 Ceramics

The dielectric properties and synthesis of pyrochlore-free lead zinc niobate ceramics with Ba substituting for Pb were investigated. Ba partial substitution for Pb was effective in stabilizing the perovskite structure in PZN ceramics, where the minimum amount of Ba substitution needed was about 20 mol%. The dielectric loss and the temperature coefficient of dielectric constant of PZN were reduced markedly with Ba substitution, while the dielectric constant was greater than 110. Good dielectric properties were obtained for the composition of Pb_0.3Ba_0.7(Zn_1/3Nb_2/3)O₃: = 133.5, tan = 0.0009, = –811 ppm/°C.     

P-Type Partial Conductivity of Donor(La)-Doped BaTiO3

P-type partial conductivity has been determined on donor (La _Ba )-doped BaTiO₃ in full thermodynamic equilibrium state at a fixed temperature of 1200°C: For the nominal compositions of Ba_0.99La_0.01Ti_0.9975O₃, Ba_0.99La_0.01TiO₃ and Ba_0.985La_0.01TiO₃, the p-type conductivity is found to vary with oxygen activity as _p = (_m/2)(a _{O 2}/a _{O 2}*)^+1/4 with _m 0.01 S cm^–1 and a _{O 2}* 32, 120, 310, respectively, in the a _{O 2} region where conventionally the electronic conductivity varies as a_{O 2} ^–1/4 and hence, the doped donors are believed to be compensated by cation vacancies (say, [La_Ba ] 4[VPrime;_Ti]). This experimental fact supports that in the vicinity of the stoichiometric composition of the system which falls approximately at a _{O 2} = a _{O 2}*, while cation vacancy concentration is fixed by the donor concentration, oxygen vacancy concentration in the minority is also essentially fixed, thus, keeping the activity of TiO₂ (or BaO) fixed. It is consequently suggested that donor-doped BaTiO₃ contains a second phase even in its stoichiometric regime.     

Development of Ferroelectric Ceramics with High Dielectric Constant and Low Dissipation Factor for High-Voltage Capacitors

Both ferroelectric BaTiO₃-based and SrTiO₃-based dielectric ceramics with high dielectric constant and low dissipation factor have been successfully developed, and applied into mass production for high-voltage ceramic capacitors. Crystalline phases of the ceramics were identified by XRD. STEM study of the ceramics was also conducted. Based on the computer simulation of a shell-core and two-phase mixed structural model proposed, a novel processing method was employed to produce SrTiO₃-based ceramics with the following satisfactory dielectric properties: dielectric constant at room temperature _20C=2000, dissipation factor at room temperature D _20C=0.003, temperature coefficient of dielectric constant = –8% (–25°C to 85°C), and, breakdown electric field E _b=10kV/mm(dc). Optional composition of BaTiO₃-based ceramics has been obtained through the orthogonal design experimentation: BaTiO₃-xBaZrO₃-yBaSnO₃, where x = 8wt% and y = 6wt%, with minor additions of MnSiO₃, WO₃, CeO₂, Bi₂(SnO₃)₃ and ZnO. Its major properties are as follows: Curie temperature T _c = 21°C, _20C=18,000, D _20'C = 0.008, =–80% (–25°C+85°C) and E _b = 8kV/mm (dc).     

Auswirkungen der Pulsweitenmodulation hoher Taktzahl auf die Oberschwingungsbelastung einer Asynchronmaschine bei Speisung durch einenU-Wechselrichter

Übersicht Für ein charakteristisches Ersatzschaltbild der Asynchronmaschine wird die Oberschwingungsbelastung bestimmt, die sich bei Pulsweitenmodulation hoher Taktzahl ergibt. Hierzu werden die Oberschwingungskupferverluste und die Pendelmomente ermittelt. Die Rechnung erfolgt im Zeitbereich und die Ergebnisse haben rein analytische Form. Obwohl hierbei von sehr hoher Taktzahl ausgegangen wird, kann man die entstandenen Gleichungen auch auf niedrige Taktzahlen übertragen. Es wird gezeigt, daß die Strom verdrängung mit in die Rechnung einbezogen werden kann. Ferner können auch die Oberschwingungseisenverluste in vereintachter Form analytisch bestimmt werden.

---

The effect of pulse width modulation with high switching frequency on the harmonic effects in an induction machine, fed from a voltage fed inverterPart 1. Fundamental considerations and single phase calculations

Contents The harmonic effects resulting from pulse width modulation with high switching frequency are determined from a characteristic equivalent circuit of an induction machine. The harmonic copper losses and torque pulsations are evaluated. The calculations are done in the time domain and the results are of exact analytical form. Although the original assumption is high switching frequency, the resulting equations may be adapted for lower switching frequencies as well. It is shown that skin effects may be taken into account in these calculations. The harmonic magnetising losses may also be determined in a simplified form.

---

Wichtige Formelzeichen U (t) Spannung (hier immer pulsförmig), Zeitbereich - U _.1 (t) Grundschwingung der SpannungU (t) - normierter Spannungsmittelwert für die Zeit =1/f _s - Û(vf ₁) Scheitelwert derv. Spannungsharmonischen - 2·U _B Wechselrichtereingangsspannung - I(t, ) Oberschwingungsstrom im Bereich =1/f _s als Funktion von - Î(vf ₁) Scheitelwert derv. Stromharmonischen - Magnetischer Fluß - f ₁=1/T Frequenz der Grundschwingung - ₁=2f ₁ Kreisfrequenz der Grundschwingung - _G Kreisfrequenz bei Grundfrequenztaktung - f _s =1/ Schaltfrequenz - z _T =f _s /f ₁ Taktzahl bzw. Frequenzverhältnis - m=Û ₁(f ₁)/U _B Modulationsgrad - v Ordnungszahl der Harmonischen - Oberschwingungskupferverluste als Funktion von - P _v Mittlere Oberschwingungskupferverluste über einer Periode - P _VFe Mittlere Oberschwingungseisenverluste über einer Periode - M Pendelmoment - M _H Hüllkurve der Pendelmomente - Scheitelwert der Pendelmomente - R _E =R _S +R _r L _h /(L _r +L _h ) wirksamer Widerstand für die Oberschwingungen ohne Stromverdrängung - R _E Widerstand unter Berücksichtigung der Stromverdrängung - L =L _S +L _r L _h /(L _r +L _h ) wirksame Induktivität für die Berechnung des Oberschwingungsstromes - L ^* =L L _h /(L _h +L _r ) wirksame Induktivität für die Berechnung der Pendelmomente     

Nanocrystalline Alkaline Earth Titanates and Their Conductivity Characteristics Under Changing Oxygen Ambients

This work presents the first systematic study of conductivity characteristics of alkaline earth titanates in the form of polycrystalline and heteroepitaxial thin films as well as nanocrystalline ceramics as a function of temperature (between 600_C and 1000_C) and continuously adjustable oxygen partial pressures ranging from 10^{– 20} bar to 1 bar. Compared to the well-known log,-log, pO₂ profiles of single crystals, the conductivity behavior of CSD-prepared, polycrystalline SrTiO₃ thin films with a feature size of about 50 nm differs radically. The most prominent characteristics are a sharp drop under reducing conditions followed by a broad plateau region. Tailored investigations on heteroepitaxial as well as polycrystalline thin films grown by PLD and especially by studies on nanocrystalline BaTiO₃ ceramics with a mean grain size of 100 nm allowed an unambiguous assignment of the described effects to the nanocrystalline morphology of the samples.     

Der Asynchronmotor mit drei und sechs Wicklungssträngen am stromeinprägenden Wechselrichter

Übersicht Für Drehzahlstellantriebe größerer Leistung bietet der Käligläufermotor mit 6 Wicklungsphasen und Versorgung durch zwei Stromumrichter deutliche Vorteile gegen-fiber dem 3-Phasenmotor mit 6-pulsiger oder auch 12-pulsiger Umrichterspeisung. Es werden die Größen untersucht und verglichen, die für die Wechselwirkung zwischen Motor und Umrichter charakteristisch sind:Die Induktivitäten und Phasenkopplungen, das Ersatzschahbild, die Pendelmomente und die Wirbelstromverluste.

---

The current-source inverter-supplied induction motor with three and six phases

Contents For speed control drives of greater power ratings the induction motor with 6 phases supplied by two current source inverters is superior to the 3-phases motor supplied by an inverter working in 6- or 12-pulse mode. All quantities characteristic for interactions between motor and inverter are analysed.The inductances and phase couplings, the electrical equivalent circuit, the torque harmonics and the eddy current losses.

---

Verwendete Symbole d _L Leiterdurchmesser - f, f ₁ Speisefrequenz - k() Kopplungsfaktor zweier um den Winkel versetzter Stränge - Widerstandserhöhung der in Nuten liegenden Leiter - Widerstandserhöhung der gesamten Wicklung - l _i ideelle Eisenlänge - l _s mittlere Länge der Stirnverbindungen - L _h Hauptinduktivität - L _K Kurzschlußinduktivität - L ₁,L ₂ Ständer- bzw. Läuferstreuinduktivität - L _N Nutstreuinduktivität - L _oS Stirnstreuinduktivität - L _oW Induktivität der doppelt verketteten Streuung - m Strangzahl - m _el Luftspaltmoment (als Zeitfunktion) - M _N Nennmoment - n Drehzahl - n Ordnungszahl für (räumliche) Oberwellen des Luftspaltfeldes - N Nutzahl - p Polpaarzahl - q Zahl der Ständernuten je Pol und Strang - s Sehnung in Nutteilungen - t _smin minimale Schonzeit der Thyristoren - V Magnetisierungsdurchflutung eines Pols - Windungszahl eines Stranges - _Sp Windungszahl einer Spule - W _S Spulenweite - Operatorimpedanz - Phasenverschiebung zwischen den Strömen der Ober- und Unterschicht - _res magnetisch wirksamer Luftspalt - ... Beiwert des magnetischen Leitwerts - Ordnungszahl der (zeitlichen) Oberschwingungen der Ströme und des Drehmoments - reduzierte Leiterhöhe nach [10] - _(n ) Wicklungsfaktor fürn-te Oberwelle des Luftspaltfelds - _K für die Kommutierung wirksamer totaler Streufaktor - _p Polteilung - (), () Hilfsfunktionen, siehe Gleichungen (54), (57) - Polfluß - verketteter Fluß - , Winkel, siehe Bild 9 - , ₁ Speisefrequenz - ₂ Läuferkreisfrequenz - ₀ Eigenkreisfrequenz des Kommutierungskreises Indizierung u ₁,i ₁,U ₁,... Ständergrößen - u ₂,i ₂,U ₂,... Läufergrößen - L _..a Stranginduktivität - L _..b Koppelinduktivität zweier um 30° versetzter Stränge - L _..c Sternpunktinduktivität - I _..(), Î_..(), M_..(),... Anteil der -ten Oberschwingung - Anteil dern-ten Oberwelle     

Electrical Conduction and Magnetoelectric Effect in CuFe1.8Cr0.2O4–Ba0.8Pb0.2TiO3 Composites

Magnetoelectric composites of CuFe_1.8Cr_0.2O₄– Ba_0.8Pb_0.2TiO₃ were prepared using high temperature solid-state reaction technique. X-ray structural analysis of these composites confirms the presence of both the phases in the composite. Detailed studies of dielectric properties (, tan and _ac ) as a function of frequency (100 Hz to 1 MHz) and temperature (30°C to 250°C) show that these compounds exhibit diffuse ferroelectric phase transitions. Results of ac conductivity, dc resistivity and thermoelectric power measurements show that conduction occurs by hopping of charge carriers. The magnetoelectric effect has been studied as a function of intensity of magnetic field. The electrical polarisation was induced in piezoelectric (Ba_0.8Pb_0.2TiO₃) phase as result of strain induced in the ferrite (CuFe_1.8Cr_0.2O₄) phase by the applied magnetic field. The Jahn-Teller distortion caused in the ferrite lattice by Jahn-Teller ions like Cu²⁺ and Cr³⁺ is also responsible for the elastic coupling of strain to the Ba_0.8Pb_0.2TiO₃ phase.     

Electrodynamic forces at thin non-magnetic tapes placed above ferromagnetic plates

Contents A method of calculation of the current density and electrodynamic forces at thin non-magnetic tapes placed in parallel to thick ferromagnetic plate is presented. The integral equation approach is applied, which permits to obtain an approximate solution of the problem considered. The tapes of finite width are considered. As an example, forces as a function of position and time are given.

---

Elektrodynamische Kräfte auf dünne, nicht-magnetische Bänder, die parallel zu einer ferromagnetischen Platte angeordnet sind

Übersicht Es wird eine Methode zur Berechnung der Stromdichte und der elektrodynamischen Kräfte bei parallel zu einer dicken ferromagnetischen Platte angeordneten dünnen, nichtmagnetischen Bändern dargestellt. Eine Näherungslösung des betrachteten Problems wird mit Hilfe einer Integralgleichungsmethode erhalten, wobei ein Band mit endlicher Breite betrachtet wird. Als Beispiel werden die Kräfte in Abhängigkeit von Ort und Zeit angegeben.

---

List of Symbols A vector potential - B magnetic density - 2d width of tape - h height of conductor above tape - l current in tape - J current density - k ² j _{0 s} - thickness of tape - ₀ permeability of vacuum - _r relative permeability of the ferromagnetic plate - conductivity of tape - _s conductivity of steel plate - _ij Kronecker delta - angular frequency     

Watt-hour efficiency of system loop inductor-ferromagnetic plate

Contents A numerical method of calculation of Watt-hour efficiency of a system loop inductor-ferromagnetic plate is presented. The integral equation approach is applied. The presented method permits to compute the eddy-current losses in the ferromagnetic plate without integrating the Poynting vector. As an example the watt-hour efficiency as a function of angular frequency is calculated.

---

Elektrischer Wirkungsgrad im System Induktionsschleife — Ferromagnetische Platte

Übersicht In der Arbeit wird eine numerische Berechnungs-methode des elektrischen Wirkungsgrades in dem System Induktionsschleife—ferromagnetische Platte dargestellt.Es wird die Methode der Integralgleichungen angewendet. Die Methode gestattet die Berechnung der Wirbelstromverluste in einer ferromagnetischen Platte ohne den Poynting-Vector zu integrieren. Ein Berechnungsbeispiel zeigt den elektrischen Wirkungsgrad als Funktion der Kreisfrequenz.

---

List of principal symbols A vector potential - I total current in the loop-inductor - J current density - k ² j _{0 f f} - P active power loss - R _{l, m} mutual resistance of conductorsl andm - Z _{l, m} mutual impedances of conductorsl andm - _c conductivity of the conductors - _f conductivity of the ferromagnetic plate - ₀ Kronecker delta - _f relative permeability of the ferromagnetic plate - ₀ permeability of the vacuum - angular frequency - watt-hour efficiency     

Temperature-Stable High-ε Dielectrics Ceramics Based on (1 − x) Ba5NdTi3Ta7O30/xBi4Ti3O12

Modification of Ba₅NdTi₃Ta₇O₃₀ dielectric ceramics was investigated through introducing Bi₄Ti₃O₁₂. With increasing of Bi₄Ti₃O₁₂ content, the dielectric constant increased, and the temperature coefficient of the dielectric constant changed from negative to positive. The small temperature coefficient ( < 50 ppm/°C) combined with high dielectric constant ( = 178) and low dielectric loss (tan = 0.007 at 1 MHz) was achieved in the composition x = 0.6.     

Leistungsbilanz und statische Stabilität der einphasigen elektrischen Welle

Übersicht Es wird das stationäre Verhalten einer einphasigen elektrischen Welle aus zwei gleichen Drehstromasynchronmaschinen mit Schleifringläufern unter Verwendung der Methode der symmetrischen Komponenten untersucht.Die Leistungsbilanz und die Stabilität einer Einphasenwelle unter Vernachlässigung der Dämpfung (statische Stabilität) werden behandelt und in eine Formel dafür abgeleitet. Ferner die daraus gewonnenen Rechenergebnisse werden mit Meßwerten verglichen. Es wird festgestellt, daß sich die die Einphasenwelle im Stillstand für Drehmomentübertragung mit Vorteil verwenden läßt.Zusammenstellung der benutzten Bezeichnungen U _N Netzspannung (V) - U _m ,U _g ,U ₀ Spannung des Mit-, Gegen- und Nullsystems (V) - j - P Polpaarzahl - Verdrehungswinkel des Läufers derten Wellenmaschine in Richtung des Drehfeldes des Mitsystems (=1,2) - ₁₀, ₂₀ Gleichgewichtswerte (^oel.) - P ₂- ₂ = gegenseitiger Verdrehungswinkel der Läufer (^oel.) - Winkelgeschwindigkeit des Läufers der -ten Wellenmaschine (s^–1) - Drehbeschleunigung des Läufers der -ten Wellenmaschine (s^–2) - m Mitsystem - g Gegensystem - o Nullsystem - 1 Wellenmaschine 1 - 2 Wellenmaschine 2 - Primärseite (Ständer) - Sekundärseite (Läufer) - J ₁ Primärstrom (Netzstrom) (A) - J _m ,J _g Strom des Mit- und Gegensystems (A) - J _re ,J _im reeller bzw. imaginärer Anteil des Primärnetzstromes der -ten Wellenmaschine (A) - J Läuferstrom der einphasigen elektrischen Welle (A) - , Ständer- bzw. Läufer-Streukoeffizient - totaler Streukoeffizient - R ohmscher Widerstand () - Streublindwiderstand () - _l Nutz-(Magnetisierungs-)blindwiderstand () - L l(1+)=Drehfeldinduktivität (H) - l Drehfeldhauptinduktivität (H) - l Streuinduktivität (H) - n Drehzahl (U/min) - n ₀ synchrone Drehzahl (U/min) - s Schlupf - s _K Kippschlupf der dreiphasigen Asynchronmaschine - M Drehmoment eines Wellenmotors(mkg) - M _K Kippmoment der dreiphasigen Asynchronmaschine (mkg) - N _d Drehfeldleistung einer Wellenmaschine (W) - N Vom Netz aufgenommene Leistung eines Motors der Einphasenwelle (W) - V undV Ständer- und Läuferkupferverluste (W) - N _m abgegebene mechanische Leistung (W) - N _s abgegebene Wirkleistung an den Schleifringen (W) - N _Gs gesamte vom Netz aufgenommene Leistung der einphasigen elektrischen Welle (W) - Winkelabweichungen von der Gleichgewichtslage - Trägheitsmoment (mkg s²) - Kreisfrequenz der ungedampften Schwingung (s ^–1) - N _bs Schleifringblindleistung (bkW) - N _b Blindleistung (bkW) - N Läuferblindstreuleistung (bkW) - N Statorstreuverluste (bkW) - f _b berechnete Frequenz (Hz) - f _m gemessene Frequenz (Hz) Mit 13 Textabbildungen     

The Electrical Conductance of SrFeO2.5+x Thin Films

Thin films of the non-stoichiometric perovskite SrFeO_2.5+x have been grown by the pulsed excimer laser deposition technique onto sapphire substrates. The electrical conductance properties of the thin films have been determined in a series of experiments done both isothermally and with programmed temperature changes from ambient to 490°C and under O₂/N₂ atmospheres with oxygen concentrations in the range from 100 ppm to 100%. Over these ranges of temperature and oxygen partial pressure a wide range of oxygen stoichiometry in SrFeO_2.5+x occurs (approximately 0 < x < 0.5), which includes all four known phases in the SrFeO_{2.5 + x} + O₂ system. The experimentally measured values for the activation energy of conduction, _A, for SrFeO_2.5+x films at temperatures 100 < T < 200°C are in the range 0.30 < _A < 0.47 eV under oxygen at partial pressures 0.001 O ₂)< 0.05 atm and 0.18 < _A < 0.28 eV for 0.2 O ₂)< 1 atm. These values for _A are typical for compositions of SrFeO_2.5+x with stoichiometries in the range 0.25 < x < 0.45. For T < 300°C and for P(_{O 2})< 0.001 atm the films were essentially insulators. For T > 250^°C and P(_{O 2})> 0.001 atm, the oxygen stoichiometries of the films change during the programmed temperature ramps. For these conditions, the values _A/ T exhibit minima/maxima in the temperature range 250 < T < 320^°C which are interpreted as being due to the onset of the order-disorder phase transition from the cubic to the tetragonal and orthorhombic ordered phases of SrFeO_2.5+x with oxygen stoichiometry in the range 0.08 < x < 0.38. The SrFeO_2.5+x thin films have application as oxygen sensing materials, and a relationship between conductance and oxygen sensitivity, S _ox , has been derived. The values of S _ox for SrFeO_2.5+x thin films increases by more than an order of magnitude for compositions close to the lower stoichiometric limit where the principal phase conversion is between the cubic perovskite and the brownmillerite forms.     

High-ε Microwave Dielectrics in Pb0.6Ca0.4Zr0.6+x (Fe1/2Nb1/2)0.4−x O3 System

Modification of Pb_0.6Ca_0.4Zr_0.6(Fe_1/2Nb_1/2)_0.4O₃ dielectric ceramics was performed by Zr substitution for (Fe, Nb). The XRD patterns showed that the single phase with orthorhombic distortion unit cell was obtained in the present ceramics. The decreasing dielectric constant by Zr substitution was due to its smaller value of /r ³ _ion. The calculated polarizability was compared with the observed one, and the results showed a good fit, considering the polarizability of oxygen dependent on the V _ox. The Zr substitution on B-site reduced the temperature coefficient of dielectric constant effectively due to the reduced dielectric constant. The effects of tilting transition on the temperature coefficient of dielectric constant were also discussed. The modified microwave dielectric properties were obtained in Pb_0.6Ca_0.4Zr_0.6+x (Fe_1/2Nb_1/2)_0.4–x O₃ for x = 0.3: _r = 100, Q × f = 3,300 to 3,600 GHz, _f = 6–8 ppm/°C.     

Improved lyapunov function for synchronous machine transient stability study

Contents The transient stability of a synchronous machine is analysed by utilizing Lyapunov's direct method. Lyapunov functions of Lur'e-type are developed, which include the effects of first and second-order speed governor. The used Lyapunov functions have been developed essentially by a systematic procedure based on the nonlinear control theory, Kalman's transformation and the second Lyapunov theorem. The paper evaluates the maximum region of asymptotic stability in the state-plane of a swinging synchronous machine while the computed critical clearing times are compared with those obtained by numerical integration. A numerical example is given.

---

Verbesserte Lyapunovsche Funktion zur Untersuchung der transienten Stabilität von Synchronmaschienen

Übersicht Die transiente Stabilität einer Synchronmaschine wird mittels des Lyapunov'schen Direktverfahrens untersucht. Es werden Lyapunov'sche Funktionen Lur'scher Art entwickelt, die die Folgen des Geschwindigkeitsreglers erster und zweiter Ordnung beibehalten. Die benutzten Lyapunov'schen Funktionen sind im wesentlichen nach einer systematischen Prozedur auf der Grundlage der Theorie der nichtlinearen Kontrolle, der Kalman'schen Transformation und des zweiten Lyapunov'schen Ansatzes entwickelt worden. Es ist Ziel dieser Veröffentlichung, die Frage zu beantworten, was der größte Bereich der asymptotischen Stabilität auf der Zustandsebene einer schwingenden Synchronmaschine ist. Die berechneten kritischen Fehlerlöschzeiten werden mit denen verglichen, die durch numerische Integration erhalten werden. Es wird ein numerisches Beispiel angegeben.

---

List of principal symbols E internal voltage of generator - E voltage of infinite bus - x _d transient reactance of generator - x _l reactance of each of the two transmission lines - ₀ 2f _o ,f _o=50 Hz - angle betweenE andE - ₀ , ₀ before and after-fault respectively steady-state value of - x _o x ₁₂+x _d - x ₁₂ total reactance between generator terminals and infinite bus - M inertia constant of generator - K _d mechanical damping coefficient - P _i instantaneous input power to generator - P _o post-fault steady-state input to generator - K _g the loop gain of the governing system - T _g equivalent time constant of governor - T _h time constant of the prime mover - V(x) Lyapunov function - V _mx critical maximum value ofV(x) - t _cl clearing time - t _er critical time