2,996 research outputs found
New data on the evolution of Mikrotia (Muridae, Rodentia) in the Late Miocene of Gargano (Apulia, Italy).
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LC compensators for power factor correction of nonlinear loads
No full textThis material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of Brunel University's products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to [email protected]. Copyright @ 2004 IEEEA method is presented for finding the optimum fixed LC compensator for power factor correction of nonlinear loads where both source voltage and load current harmonics are present. The LC combination is selected because pure capacitive capacitors alone would not sufficiently correct the power factor. Optimization minimizes the transmission loss, maximizes the power factor, and maximizes the efficiency. The performance of the obtained compensator is discussed by means of numerical examples
LC compensators based on transmission loss minimization for nonlinear loads
No full textThis material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of Brunel University's products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to [email protected]. Copyright @ 2004 IEEEThis paper presents a method employing the penalty function search algorithm to determine the LC compensator value for the optimal power factor correction in nonsinusoidal systems. The objective of the proposed method is to minimize the transmission loss while the power factor and efficiency are taken as constraints and utilized in order to solve the multiobjective optimization problem by transforming it into a single objective one. Examples show that the load nonlinearity can have a significant impact on optimal compensator sizes
Pleistocene mammal faunas from the Leffe Basin (Bergamo, Northern Italy): revision and new data
No full textIn this study, the mammal remains collected from the second half of the 19th century until the late 1950’s in the brown coal mine of Leffe (Bergamo, Northern Italy) are re-evaluated. We studied both the material preserved in the collections and the remains now lost but nonetheless well described in the literature. Along with Mammuthus meridionalis and Stephanorhinus ex gr. etruscus, several species not previously recorded from Leffe have been found in the collections (Pachycrocuta brevirostris, Hippopotamus cf. antiquus, Cervalces cf. carnutorum, and Megaloceros gr. verticornis-pliotarandoides). Furthermore, Mimomys savini, Capreolus s.l. sp. and ?Megaloceros cf. obscurus are recorded thanks to the descriptions and measurements given in the literature of specimens now lost. Also, the previous specific identifications of Leptobos etruscus and of a Dama-like cervid have been modified into Leptobos vallisarni and Axis eurygonos, respectively.
Three Early Pleistocene mammal groups are represented: one from the main brown coal level (subunit #5, Biogenic Unit), spanning the end of the Tasso FU (FU = Faunal Unit) to the beginning of the Farneta FU, one from subunit #6 and #7 (again Biogenic Unit), ranging from the latest part of the Farneta FU to the beginning of the Colle Curti FU, and one from the Upper Unit (subunit #9), which is attributed to the Colle Curti FU.
A Palaeoloxodon antiquus upper palate, which was found in the collections of the Civic Museum of Milan, belongs to a more recent period. In fact, its white light coloured surfaces and adhered red clay sediment imply that it comes from the red palaeosoils overlying the Leffe Formation
Evolutionary trends in arvicolids and the endemic murid Mikrotia - New data and a critical overview
No full textThe study of evolutionary rates dates back to the work of Simpson and Haldane in the 1940s. Small
mammals, especially Plio-Pleistocene arvicolids (voles and lemmings), are particularly suited for such
studies because they have an unusually complete fossil record and exhibit significant evolutionary
change through time. In recent decades, arvicolids have been the focus of intensive research devoted to
the tempo and mode of evolutionary change and the identification of trends in dental evolution that can
be used to correlate and date fossil sites. These studies have raised interesting questions about whether
voles and lemmings had unique evolutionary trajectories, or show convergent evolutionary patterns with
other hypsodont rodents. Here we review evolutionary patterns in selected arvicolid lineages and
endemic Messinian murids (Mikrotia spp.) and discuss reasons for convergence in dental morphology in
these two groups of hypsodont rodents. The results substantiate previously detected patterns, but the
larger dataset shows that some trends are less regular than previous studies have suggested. With the
exception of a pervasive and sustained trend towards increased hypsodonty, our results show that other
features do not follow consistent patterns in all lineages, exhibiting a mosaic pattern comprising stasis,
variable rate evolution and gradual unidirectional change through time. Evidence for higher evolutionary
rates is found in lineages apparently undergoing adaptations to new ecological niches. In the case of
Mikrotia, Microtus voles and the water vole (MimomyseArvicola) lineage, a shift to a fossorial lifestyle
appears to have been an important driving force in their evolution. For other characters, different causes
can be invoked; for example a shift to a semi-aquatic lifestyle may be responsible for the trend towards
increasing size in Arvicola. Biochronological application of the data should take into account the
complexity and biases of the data
Cost-effective applications of power factor correction for nonlinear loads
No full textThis material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of Brunel University's products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to [email protected]. Copyright @ 2005 IEEEThe objective of this paper is to propose a new approach for designing passive LC compensators by using the penalty function method as an optimization tool. The performance of the cost-effective passive LC compensator for a constant load depends on the appropriate inductor and capacitor selection. Several design methods are reviewed and a novel design methodology is proposed in this paper. By using the proposed method, the designer can quickly find appropriate parameter values to meet the desired circuit performance. Simulated results show that an appropriate combination of the inductor and capacitor selected by the proposed method can meet the desired power-quality requirement. Different cases of design examples are shown in this paper to verify the performance of the proposed design methodology
A 155W −95.6 dB THD+N GaN-based Class-D Audio Amplifier With LC Filter Nonlinearity Compensation
No full textSilicon MOSFETs-based medium-power (< 50W) Class-D amplifiers (CDAs) switching in the MHz range have gained popularity in recent years, which achieves better linearity thanks to a higher loop gain in the audio band while enabling the use of LC filters with higher cut-off frequencies. However, for high-power (>100 W) CDAs, such switching frequency and high load current could lead to significant power loss. Furthermore, in the presence of a large current and voltage applied to the load, the linearity of the system can quickly degrade due to LC filter component voltage/current dependency. Without any LC filter nonlinearity compensation technique, LC components with high voltage/current rating must be used to reach high system linearity, which are often expensive and bulky. This paper presents a CDA using a GaN-based output stage to achieve high switching frequency and good efficiency simultaneously, and an integrated controller implemented in a 180nm CMOS technology to compensate for the LC filter nonlinearity. Switching at 1.8 MHz, the CDA can deliver a maximum of 155W from a 50V supply into a load with a peak efficiency of 91.7%. It achieves a peak THD+N of −95.6 dB (0.0017%) while allowing the use of cheaper and smaller nonlinear LC components.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Components, Technology and MaterialsMicroelectronic
A - 121.5-dB THD Class-D Audio Amplifier With 49-dB LC Filter Nonlinearity Suppression
No full textClass-D audio amplifiers produce electromagnetic interference (EMI), which often needs to be suppressed by an external LC filter. However, due to component nonlinearity, this filter can itself cause significant distortion. This article presents a class-D amplifier that suppresses LC filter nonlinearity by 49 dB and is robust to ±30% variations in its cutoff frequency. This is achieved by a dual-loop architecture, in which an inner loop provides stability, while an outer loop provides the high gain needed to suppress the LC filter and output-stage nonlinearity. A prototype, implemented in a 180-nm BCD process, achieves -121.5-dB total harmonic distortion (THD) and -107.1-dB THD+N, which is maintained to within 3 dB even as the LC filter cutoff frequency is varied from 62 to 106 kHz. It can deliver a maximum of 21 W into a 4-Ω load with 87% efficiency and 12 W into an 8-Ω load with 91% efficiency, measured at 10% THD. Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic InstrumentationMicroelectronic
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