Vergleich genormter Verfahren zur Bestimmung des Wirkungsgrades von Induktionsmaschinen

Übersicht Dieser Beitrag beschäftigt sich mit der meßtechnischen Bestimmung des Wirkungsgrades von Induktionsmotoren mit Käfigläufer mit dem Einzelver-lustverfahren nach IEC 60034-2 und der Methode B nach IEEE 112. Für beide Verfahren werden die Verlustanteile und deren Ermittlung diskutiert und dabei insbesondere die Unterschiede in der Berechnung der lastabhängigen Zusatzverluste aufgezeigt. Die Arbeit stützt sich auf Messungen an Käfigläufermotoren unterschiedlicher Leistung.

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Determination of the efficiency of induction machines by different standardized methods

Contents This paper deals with the determination of the efficiency of squirrel-cage induction motors by both the loss-summation method of IEC 60034-2 and method B of IEEE 112. The proceedings according to both standardizations are described and compared, especially those parts regarding the determination of stray-load losses. The discussion is based on measurement results taken of squirrel-cage motors in a relatively wide range of rated output.

     

Wide-area fuzzy logic control of voltage/VAr under simulated onlineconditions

This work describes the development of a fuzzy logic tool capable of controlling system voltages and VAr resources, as well as processing alarms related to voltage stability. The fuzzy controller monitors voltages and VAr resources and generates appropriate control signals to each VAr source to maintain acceptable system voltage levels. The fuzzy alarm processor generates an individual alarm for each voltage region, and a general alarm signal that indicates the overall system condition. A prototype fuzzy controller/processor has been interfaced with power system simulation software to test its performance under simulated on-line conditions     

DES-GENERATED CHECKSUMS FOR ELECTRONIC SIGNATURES

Secrecy and authentication are two important features of a secure communication system. Public Key Cryptosystems, based, e.g., on the Rivest-Shamir-Adleman (RSA) algorithm, provide a very elegant solution to the problem of authenticity verification or true electronic signatures. Practical problems, however, mainly the lack of execution speed, prevent a straightforward application. In order to sign a long message it is much faster to first calculate a short digest or checksum and then sign the compressed message. For this checksum calculation the fast, inexpensive and extensively tested Data Encryption Standard (DES) can be used. But care must be taken that this additional processing step does not introduce any weakness into the signature scheme. This paper investigates two DES-based hashing methods. It is shown that neither method seems to introduce any statistical regularities in the generated checksums. The “Cipher/Message to Plain Feedback,” however, is not secure under a modification compensation attack. It is further shown how the second method, the “Cipher to Plain Feedback” proposed by Davies and Price, can be broken by a “meet in the middle attack.” This checksum method, however, can be used safely with a slight modification.     

A method to align the coordinate system of accelerometers to the axes of a human body: The depitch algorithm

One of the key problems in accelerometry based gait analyses is that it may not be possible to attach an accelerometer to the lower trunk so that its axes are perfectly aligned to the axes of the subject. In this paper we will present an algorithm that was designed to virtually align the axes of the accelerometer to the axes of the subject during walking sections. This algorithm is based on a physically reasonable approach and built for measurements in unsupervised settings, where the test persons are applying the sensors by themselves. For evaluation purposes we conducted a study with 6 healthy subjects and measured their gait with a manually aligned and a skewed accelerometer attached to the subject's lower trunk. After applying the algorithm the intra-axis correlation of both sensors was on average 0.89±0.1 with a mean absolute error of 0.05g. We concluded that the algorithm was able to adjust the skewed sensor node virtually to the coordinate system of the subject.     

Genetic relationships and additive genetic variation of productive and reproductive traits in Guernsey dairy cattle

Data were first lactation production and reproduction records initiated from 1958 to 1981 in two experiment station Guernsey herds. Heritability estimates using paternal half sib groups were .24 +/- .12 for milk yield, .27 +/- .12 for fat yield, and .77 +/- .15 for fat percentage. Heritability estimates for reproductive traits ranged from .01 to .04 for number of services, service period, conception rate, and days open, but were higher for days in milk at first breeding (.12) and age at first calving (.13). Except for age at first calving, coefficients of additive genetic variation were larger for reproductive traits than for productive traits. Genetic correlations between measures of production and reproduction were moderate to large and antagonistic, except that the relationship between production and age at first calving was favorable. Breeding value estimates for milk yield and reproduction were negatively correlated for sires with above average breeding values for milk yield. Huge phenotypic variances for reproductive traits masked substantial additive genetic variation for these traits. When all things are considered it seems unwise to ignore reproductive performance in selection programs for dairy cattle.     

It's a nano world after all

The nanotechnology module was designed to introduce nanotechnology and the ideas behind it to students who know little about the subject. Students participate In hands-on activities that give them a better sense of how small the nano world really is, and to learn about the various applications of nanotechnology at the same time.     

Mutagenesis of the conserved residue Glu259 of Gsalpha demonstrates the importance of interactions between switches 2 and 3 for activation

We previously reported that substitution of Arg258 within the switch 3 region of Gsalpha impaired activation and increased basal GDP release due to loss of an interaction between the helical and GTPase domains (Warner, D. R., Weng, G., Yu, S., Matalon, R., and Weinstein, L. S. (1998) J Biol. Chem. 273, 23976-23983). The adjacent residue (Glu259) is strictly conserved in G protein alpha-subunits and is predicted to be important in activation. To determine the importance of Glu259, this residue was mutated to Ala (Gsalpha-E259A), Gln (Gsalpha-E259Q), Asp (Gsalpha-E259D), or Val (Gsalpha-E259V), and the properties of in vitro translation products were examined. The Gsalpha-E259V was studied because this mutation was identified in a patient with Albright hereditary osteodystrophy. S49 cyc reconstitution assays demonstrated that Gsalpha-E259D stimulated adenylyl cyclase normally in the presence of GTPgammaS but was less efficient with isoproterenol or AlF4-. The other mutants had more severely impaired effector activation, particularly in response to AlF4-. In trypsin protection assays, GTPgammaS was a more effective activator than AlF4- for all mutants, with Gsalpha-E259D being the least severely impaired. For Gsalpha-E259D, the AlF4--induced activation defect was more pronounced at low Mg2+ concentrations. Gsalpha-E259D and Gsalpha-E259A purified from Escherichia coli had normal rates of GDP release (as assessed by the rate GTPgammaS binding). However, for both mutants, the ability of AlF4- to decrease the rate of GTPgammaS binding was impaired, suggesting that they bound AlF4- more poorly. GTPgammaS bound to purified Gsalpha-E259D irreversibly in the presence of 1 mM free Mg2+, but dissociated readily at micromolar concentrations. Sucrose density gradient analysis of in vitro translates demonstrated that all mutants except Gsalpha-E259V bind to beta gamma at 0 degreesC and were stable at higher temperatures. In the active conformation Glu259 interacts with conserved residues in the switch 2 region that are important in maintaining both the active state and AlF4- in the guanine nucleotide binding pocket. Although both Gsalpha Arg258 and Glu259 are critical for activation, the mechanisms by which these residues affect Gsalpha protein activation are distinct.