Torque Ripple Reduction of Switched Reluctance Motor with Non-Uniform Air-Gap and a Rotor Hole

A switched reluctance motor has a very simple structure which becomes its key signature and leads to various advantages. However, because of its double saliency and switching principle, the motor is also known to have a relatively high torque ripple, and this hinders its use as a high-performance drive. In this paper, a method to reduce torque ripple while maintaining average torque is introduced. Two elements are used to achieve this, namely, a non-uniform air-gap on the rotor-pole face and one hole in each non-uniform region, which maintains the saturation level of the air-gap. This approach preserves the mechanical simplicity of the motor and is easy to implement. Simulations and experiments were performed to verify the effectiveness of the proposed design.

Direct velocity measurements in high-temperature non-ideal vapor flows

Direct velocity measurements in a non-ideal expanding flow of a high temperature organic vapor were performed for the first time using the laser Doppler velocimetry technique. To this purpose, a novel seeding system for insemination of high-temperature vapors was specifically conceived, designed, and implemented. Comparisons with indirectly measured velocity, namely inferred from pressure and temperature measurements, are also provided. Nozzle flows of hexamethyldisiloxane (MM, C$$_6$$ 6 H$$_{18}$$ 18 OSi$$_2$$ 2 ) at temperature up to $$220\,^\circ \mathrm {C}$$ 220 ∘ C and pressure up to 10 bar were taken as representative of non-ideal compressible-fluid flows. The relative high temperature, high pressure and the need of avoiding contamination pose strong constraints on the choice of both seeding system design and tracer particle, which is solid. A liquid suspension of tracer particles in hexamethyldisiloxane is injected through an atomizing nozzle in a high-temperature settling chamber ahead of the test section. The spray droplets evaporate, while the particles are entrained in the flow to be traced. Three different test cases are presented: a subsonic compressible nozzle flow with a large uniform region at Mach number 0.7, a high velocity gradient supersonic flow at Mach number 1.4 and a near-zero velocity gradient flow at Mach number 1.7. Temperature, pressure and direct velocity measurements are performed to characterize the flow. Measured velocity is compared with both computational fluid dynamics (CFD) calculations and velocity computed from pressure and temperature measurements. In both cases, the thermodynamic model applied was a state-of-the-art Helmoltz energy equation of state. A maximum velocity deviation of 6.6% was found for both CFD simulations and computed velocity. Graphical abstract

Friedrich Richard Ulbricht’s Kugelphotometer

With the rapid development of many new and varied sources of light in the 19th century—Argand lamps of different designs and which burned various fuels, Carcel lamps, stearin candles, paraffin candles, and spermaceti candles, electric arc lamps, Drummond lamps, incandescent lamps with various filaments, Nernst glowbars, and many others —some method was needed to compare their output. But with the sources varying in spectral content and the angular distribution of the light, how could a meaningful comparison be made? After various fruitless attempts were made to concentrate the light onto a uniform region a surprisingly simple solution was proposed.

Formal and Informal Governance Arrangements to Boost Sustainable and Inclusive Rural-Urban Synergies: An Analysis of the Metropolitan Area of Styria

In the past, the contrasts between rural and urban regions were the primary feature of analysis, while today, spatial dynamics are realized by the interactions between spaces and focus on the dependencies of rural-urban areas. This implies that boundaries are not anymore perceived as fixed but as flexible and fluid. With rising spatial interrelations, the concept of the “city-region” has been increasingly regarded as a meaningful concept for the implementation of development policies. Governance arrangements working at the rural-urban interface are often highly complex. They are characterized by horizontal and vertical coordination of numerous institutional public and private actors. In general, they provide opportunities to reap benefits and try to ameliorate negative outcomes but, due to asymmetric power relations, rural areas are often challenged to make their voice heard within city-region governance structures which can too easily become focused on the needs of the urban areas. This paper addresses these issues of rural-urban partnerships through the case of the Metropolitan Area of Styria. It presents analyses on the core issue of how to recognize the structure and driving challenges for regional co-operation and inter-communal collaboration in this city-region. Data were collected through workshops with regional stakeholders and interviews with mayors. Although the Metropolitan Area of Styria occupies an increased reference in policy discourses, the city-region has not grown to a uniform region and there are still major differences in terms of economic performance, the distribution of decision-making power, accessibility and development opportunities. If there should be established a stronger material and imagined cohesion in the city-region, it requires enhanced assistance for municipalities with less financial and personal resources, and tangible good practices of inter-municipal co-operation. The ability to act at a city-regional level depends highly on the commitment for co-operation in the formal and informal governance arrangement, and on the willingness for political compromises as well as on the formulation of common future goals.

Finite time coverage tracking algorithm of maneuvering target by multiple mobile agents

In this paper, a problem regarding how multiple mobile agents track a high-speed maneuvering target is considered. Due to the uncertainties of the target caused by the background noises, we use a dynamic non-uniform region to describe the location of target. Therefore, the cooperative tracking problem is transformed into a problem to cover a known dynamic non-uniform region. In order to capture the high-speed maneuvering target, the mobile agents with global sensing areas and limited actuation region are designed to track and cover the dynamic region. Also, the probability that the target appear in the circle is denoted by a probability density function and a performance index function is given to describe the effectiveness of covering a moving target. With observer-based estimation and dynamic formation control, a coverage tracking algorithm is proposed so that the group of agents catch the target by a coverage tracking policy in finite time.

Statistical study of foreshock transients in a global hybrid-Vlasov magnetospheric simulation

<p>Upstream of Earth's bow shock lies the foreshock, a region permeated by bow shock-reflected electrons and ions propagating against the incoming solar wind. The interaction between the reflected ions and the solar wind leads to instabilities, which generate Ultra Low Frequency (ULF) waves in the foreshock. Another feature of the foreshock are various propagating transient structures. A particular type of transients are foreshock cavitons, which are characterized as simultaneous depressions of plasma density and magnetic field bounded by edges where these parameters are enhanced.<br>    Cavitons are proposed to form as a consequence of the non-linear evolution of two ULF wave types. They are carried by the solar wind towards the shock, but have been found to propagate sunward in the solar wind rest frame. Studies have shown that cavitons can accumulate reflected suprathermal ions inside them as they approach the bow shock, causing significant heating and bulk flow deflection in their interiors. These signatures resemble those of Hot Flow Anomalies (HFAs), transients which are associated with interplanetary magnetic field (IMF) discontinuities interacting with the bow shock. As the evolution of cavitons is independent of IMF discontinuities, the hot, evolved transients are classified as spontaneous HFAs (SHFAs). SHFAs arriving to the shock have been found to cause perturbations to the shock surface and the magnetosheath downstream of it.<br>    In this work, a numerical statistical study of cavitons and SHFAs is conducted with Vlasiator, a global hybrid-Vlasov code. Individual transients are tracked, allowing us to examine their formation rate, propagation characteristics and evolution in addition to their physical properties. Our results show that cavitons and SHFAs form in a uniform region near the bow shock, and there is a distinct distance to the shock within which cavitons can become SHFAs. The density and magnetic field depressions inside cavitons appear well correlated, although shallow compared to spacecraft measurements. We find that both transient types propagate sunwards in the solar wind rest frame, agreeing with earlier studies. Our statistical data set allows us to calculate the propagation velocity, which shows a similar value for all tracked transients. Our results also suggest that the velocity has a southward component. </p>

Dispersion of sausage waves in coronal waveguides with transverse density structuring

ABSTRACT We study dispersion properties of fast-sausage waves in a radially structured coronal magnetic tube with continuous radial density distribution. The models, containing either a non-uniform core or inhomogeneous external medium are considered. The dispersion relations are obtained for a power law density distribution in the corresponding non-uniform region, where the power-law index controls the steepness of the tube boundary. The governing wave equations with varying coefficients were solved with the Wentzel–Kramers–Brillouin (WKB) approximation. The model with the non-uniform core supports the existence of trapped and leaky sausage modes. The density non-uniformity in the core modifies the values of cut-off wave numbers kc. The smaller values of cut-offs, normalized to the effective tube radius r0, correspond to the smaller power index p. The wave dispersion (i.e. dVph/dk) decreases for smaller p. This occurs in the range of not too small longitudinal wave numbers k > kc. For the model, containing inhomogeneous environment the basic dispersion properties are generally identical to that for the monolithic tube model, studied in Lopin & Nagorny (2015b). The waves are trapped for all wave numbers, if the power-law index 0 < n < 2. There are both trapped and leaky regimes for n ≥ 2. The wave dispersion decreases for smaller n, in the range of the intermediate values of the longitudinal wave numbers k > kc. The seismological application of the obtained results is discussed.

Image quality assessment using NEMA NU 4/2008 standards in small animal PET scanner

In Brazil, there are few microPET in use and a quality control protocols standardization are needed to harmonize their use in the research field. Thus, the purpose of this study is to characterize the image quality performance of the microPET scanner (LabPET 4, GE healthcare Technologies, Waukesha, WI) using the NEMA NU 4/ 2008 standards and specific phantom. The NEMA image-quality (IQ) phantom consists of 3 different regions to analyze distinct characteristics: image noise (%SD), expressed as percentage SD in a uniform region (%SD), recovery coefficient (RC) and Spill-over (SOR) in air and water. The IQ phantom was filled with 18F-FDG calibrated at the beginning of acquisition, placed in the center of the field-of-view (FOV) and measured with the typical whole body imaging protocol. The images were reconstructed with different reconstruction methods (FBP-2D; MLEM-3D and OSEM-3D); with and without high resolution (HR) when possible. The results were compared. The LabPET 4 system produces appropriate image and with performance according to the literature. The present study is an initial step to verify the NEMA NU 4/2008 use in the Brazilian scenario for further standardization.

Image quality assessment using NEMA NU 4/2008 standards in small animal PET scanner

In Brazil, there are few microPET in use and a quality control protocols standardization are needed to harmonize their use in the research field. Thus, the purpose of this study is to characterize the image quality performance of the microPET scanner (LabPET 4, GE healthcare Technologies, Waukesha, WI) using the NEMA NU 4/ 2008 standards and specific phantom. The NEMA image-quality (IQ) phantom consists of 3 different regions to analyze distinct characteristics: image noise (%SD), expressed as percentage SD in a uniform region (%SD), recovery coefficient (RC) and Spill-over (SOR) in air and water. The IQ phantom was filled with 18F-FDG calibrated at the beginning of acquisition, placed in the center of the field-of-view (FOV) and measured with the typical whole body imaging protocol. The images were reconstructed with different reconstruction methods (FBP-2D; MLEM-3D and OSEM-3D); with and without high resolution (HR) when possible. The results were compared. The LabPET 4 system produces appropriate image and with performance according to the literature. The present study is an initial step to verify the NEMA NU 4/2008 use in the Brazilian scenario for further standardization.