On piecewise trivial Hopf—Galois extensions

We discuss a noncommutative generalization of compact principal bundles that can be trivialized relative to the finite covering by closed sets. In this setting we present bundle reconstruction and reduction

\pi^0 \pi^0 Production in Proton-Proton Collisions at Tp=1.4 GeV

The reaction pp->pppi0pi0 has been investigated at a beam energy of 1.4 GeV using the WASA-at-COSY facility. The total cross section is found to be (324 +- 21_systematic +- 58_normalization) mub. In order to to study the production mechanism, differential kinematical distributions have been evaluated. The differential distributions indicate that both initial state protons are excited into intermediate Delta(1232) resonances, each decaying into a proton and a single pion, thereby producing the pion pair in the final state. No significant contribution of the Roper resonance N*(1440) via its decay into a proton and two pions is foundComment: Submitted to PL

Total and differential cross sections of η-production in proton–deuteron fusion for excess energies between Qη = 13 MeV and Qη = 81 MeV

New data on both total and differential cross sections of the production of η mesons in proton–deuteron fusion to He3η in the excess energy region 13.6MeV≤Qη≤80.9MeV are presented. These data have been obtained with the WASA-at-COSY detector setup located at the Forschungszentrum Jülich, using a proton beam at 15 different beam momenta between pp=1.60GeV/c and pp=1.74GeV/c. While significant structure of the total cross section is observed in the energy region 20MeV≲Qη≲60MeV, a previously reported sharp variation around Qη≈50MeV cannot be confirmed. Angular distributions show the typical forward-peaking that was noted earlier. For the first time, it is possible to study the development of these angular distributions with rising excess energy over a wide interval

Transients of current and electromagnetic torque during start-up in high-speed induction motors

High-speed motors are produced in Poland outside the machine-building industry. Only a few motors, adapted to specific purposes, are manufactured, for example, by plants that produce rolling-element bearings. These motors have found their application in driving high-speed grinders in bearing ring raceway production lines. The properties of motors fed with high-frequency voltage result mainly from the use of a closed slot in the rotor and the high frequency of supply voltage. The use of the closed rotor slot causes strong saturation of the magnetic circuit by the leakage flux around the slot. Taking account of the phenomenon of saturation of the magnetic circuit due to the leakage flux around the closed rotor slots is a complex issue. In the present article, this phenomenon was taken into consideration by introducing into the mathematical model of the motor, derived for a linear magnetic circuit, rotor leakage inductance dependent on rotor current. The relation was determined experimentally

Indirect method applied to determine pull-out torque for induction motors

Pull-out torque and the corresponding pull-out slip of induction motors is determined, with a fair degree of accuracy, by measurements in the short-circuit and idle-running states. This refers to motors without the skin effect in the cage bar or those in which the phenomenon has been omitted. The paper compares analytical methods for determining pull-out torque based on the method of equivalent graphs and a simplified Kloss formula. The analysis was carried out for two induction motors: squirrel cage and slip ring. Pull-out slip and torque diagrams were used. An advantage of this method is the fact that determination of pull-out torque does not require the knowledge of pull-out slip

Influence of the saturation of the magnetic circuit and skin effect on the transients of electromagnetic torque and current during the start up of high-speed motors

High speed squirrel-cage motors are a relatively unknown group of machines, mainly due to their particular application. High rotational speed is achieved by supplying the motors with 400-1500Hz frequency voltage. Their operation in special conditions results in the fact that their structure and some properties differ from those of squirrel-cage induction machines supplied with 50Hz frequency voltage. The use of closed rotor slots causes strong saturation of the magnetic circuit for the slot leakage flux. Changes in the current in the slot causes a varying state of saturation and thus rotor leakage inductance is not a constant parameter. When determining the rotor winding leakage inductance for classic induction motors supplied with 50Hz frequency voltage, the influence of the saturation of the magnetic circuit for the leakage flux is usually omitted. This is a standard approach and an equivalent scheme, mentioned in literature, is used in such a case. Identification of the inductance in motors supplied with high frequency voltage, in which the phenomenon of core saturation occurs, is a relatively complex issue due to the complicated distribution of magnetic flux, and especially the leakage flux. The value of leakage inductance was determined experimentally. The paper presents differential equations describing a mathematical model and transients of the current and electromagnetic torque, obtained by simulating the start-up of a squirrel-cage high-speed motor

Slip characteristic of induction motor admittance stator obtained with the application of computer simulation

Slip characteristic of induction motor admittance is the admittance locus at varied slip and constant frequency of feeding voltage. Circle diagram can graphically represent the characteristic only in the case when electromagnetic parameters of a machine are constant. Circle diagram makes an important tool at the evaluation of an asynchronous motor operation. Based on the diagram it is possible to find for an arbitrary slip not only values of electrical parameters but also mechanical parameters such as torque, mechanical power and rotational speed. The paper presents a comparative analysis of classical methods for circle diagram elaboration and of their accuracy. Computer simulation of an admittance slip characteristic has been performed with the Matlab-Simulink software, based on dependences that determine admittance of a motor. The analysis concerns conditions when equivalent network parameters of an asynchronous motor are constant and the characteristic is represented by a circle. When electromagnetic parameters of a motor are not constant then the characteristic essentially differs from a typical circle diagram. It mainly concerns a squirrel-cage motor with closed slots in the rotor, fed with high-frequency voltage. In the mentioned case saturation of the closure occurs under the influence of a leakage flux. It has been shown that a shape of the characteristic depends on many parameters of a motor as well as on the way the leakage reactance changes

A method of determining the slipping characteristics of admittance of a squirrel-cage high-speed motor

High speed squirrel-cage induction motors are supplied with a high frequency voltage ranging from 400 to 1500Hz. The highest frequencies, i.e., the highest rotation speeds, arise from technological needs and are limited by manufacturing possibilities. These motors have a structure and electromagnetic properties that differentiate them from classic machines. In particular, they are distinguished by the high frequency of supply voltage, intensive cooling introduced to reduce the size of the motor, and closed rotor slots used to minimize vibrations and noise. The paper presents how slip characteristics of admittance of a squirrel-cage motor were determined on the basis of laboratory measurements conducted with current of variable frequency. This characteristic is the geometric locus of motor admittance with the slip ranging from + ∞ to - ∞ and an assumed constant frequency of supply voltage. The image of these characteristics differs considerably from a typical pie chart and it evidences the differences in electromagnetic properties in comparison with typical induction motors. Changes in the current in the slot causes a varying state of saturation and thus rotor leakage inductance is not a constant parameter