Determination of efficiencies, loss mechanisms, and performance degradation factors in chopper controlled dc vehical motors. Section 2: The time dependent finite element modeling of the electromagnetic field in electrical machines: Methods and applications

The time dependent solution of the magnetic field is introduced as a method for accounting for the variation, in time, of the machine parameters in predicting and analyzing the performance of the electrical machines. The method of time dependent finite element was used in combination with an also time dependent construction of a grid for the air gap region. The Maxwell stress tensor was used to calculate the airgap torque from the magnetic vector potential distribution. Incremental inductances were defined and calculated as functions of time, depending on eddy currents and saturation. The currents in all the machine circuits were calculated in the time domain based on these inductances, which were continuously updated. The method was applied to a chopper controlled DC series motor used for electric vehicle drive, and to a salient pole sychronous motor with damper bars. Simulation results were compared to experimentally obtained ones

Compact frequency standard based on an intracavity sample of cold cesium atoms

We have demonstrated the possibility for a compact frequency standard based on a sample of cold cesium atoms. In a cylindrical microwave cavity, the atoms are cooled and interrogated during a free expansion and then detected. The operation of this experiment is different from conventional atomic fountains since all the steps are sequentially performed in the same position of space. In this paper we report the analysis of a Ramsey pattern observed to present a (47±5) Hz linewidth and a stability of (5±0.5)x10-13τ-1/2 for an integration time longer than 100 s. Some of the main limitations of the standard are analyzed. This present report demonstrates considerable improvement of our previous work [J. Opt. Soc. Am. B 25, 909 (2008)] where the atoms were in a free space and not inside a microwave cavity.FAPESPCNPqCAPESFAPESP-CNR

Determination of efficiencies, loss mechanisms, and performance degradation factors in chopper controlled dc vehical motors. Section 1: Test program results and recommendations

The conventional series motor model is discussed as well as procedures for obtaining, by test, the parameters necessary for calculating performance and losses. The calculated results for operation from ripple free DC are compared with observed test results, indicating approximately 5% or less error. Experimental data indicating the influence of brush shift and chopper frequency are also presented. Both factors have a significant effect on the speed and torque relationships. The losses and loss mechanisms present in a DC series motor are examined and an attempt is made to evaluate the added losses due to harmonic currents and fluxes. Findings with respect to these losses is summarized

Low-temperature infrared spectroscopy of H2 in crystalline C60

Diffuse reflectance infrared spectroscopy is used to measure the quantum dynamics of molecular hydrogen trapped within a C60 lattice at temperatures as low as 10 K. Crystal field effects in conjunction with rotational translational coupling lead to a rich spectrum with multiply split peaks that are more than an order of magnitude sharper than at room temperature. The induced redshifts in the vibrational-rotational mode frequencies are explained using a simple model in which the state dependence of the H2 polarizability leads to changes in the C60-H2 interaction potential

Cryogenic apparatus for diffuse reflection infrared spectroscopy with high-pressure capabilities

A cryogenic apparatus for obtaining diffuse reflection infrared spectra at liquid helium temperature is described. The system combines a commercially available reflection accessory and cold finger cryostat with a custom designed vacuum housing and high-pressure sample cell. This enables spectra to be obtained from room temperature to 10 K and at gas loading pressures as high as 100 bars. Initial experiments on H2 in solid C60 show the power of the system to obtain spectra that are significantly enhanced relative to those at room temperature

LOW-TEMPERATURE INFRARED SPECTROSCOPY OF H2_2 IN SOLID C60_{60}

Author Institution: Department of Physics and Astronomy, Oberlin College,; Oberlin, OH 44074Interstitial H$_2$ trapped in a C$_{60}$ lattice forms an ideal case of a single isolated molecule confined within a cavity. Diffuse reflectance infrared spectroscopy is used to probe the quantum dynamics of the trapped hydrogen at temperatures as low as 10 K. Crystal field effects in conjunction with rotational translational coupling lead to a rich spectrum with multiply split peaks that are more than an order of magnitude sharper than at room temperature. Analysis of the data allows us to put much greater constraints on the parameters governing the fundamental C--H intermolecular potential