Energy-efficient adjustable speed double inverter-fed woundrotor induction motor drive

The mathematical and analytical models of adjustable speed electric drive based on double inverter-fed induction motor are considered and analyzed in the article, the main equations which describe energy performances of such type of AC electric drive system are determined. The influence of excitation frequency on energy performances of double inverter-fed induction motor in steady-state at orthogonal flux vector control is considered in the article. The condition ensures minimum of stator steel losses at a predetermined rotor speed and can operate at speeds up to double rated without the magnetic flux reducing is presented. This possibility is one of the most important advantages of this type of electric drive over others types of AC drives for many technological processes.Keywords: power, double-fed wound-rotor induction motor drive, steel and total losses, efficiency, energy-efficient control algorith

Latitudinal Diversity Gradients in Free-living Microorganisms - Hoogenraadia a Key Genus in Testate Amoebae Biogeography

The extent to which free-living microorganisms show cosmopolitan distributions has been a contentious aspect of microbial ecol¬ogy over the last few decades. Testate amoebae are a group of free living protists that can provide important evidence for the nature of the biogeography of microorganisms because there are relatively good data on the distribution of their morpho-species (compared to many other microbial groups). Many testate amoebae appear to exhibit ubiquitous distributions, while some taxa have proven to be endemic to limited regions. The genus Hoogenraadia (Gauthier-Lièvre and Thomas 1958) is of particular interest in this context as it appears to be restricted to relatively low latitudes. There are six described species of the genus: H. africana Gauthier-Lièvre and Thomas 1958, H. asiatica Wang and Min 1987, H. cryptostoma Gauthier-Lièvre and Thomas 1958, H. humicola Bonnet 1976, H. ovata Bonnet 1976, and H. sylvatica Vucetich 1974. However, information on these taxa is scattered through a number of different papers – here we provide a summary of what is known about the taxonomy and ecology of this genus. We also reinterpret recent new records of putative H. africana from China (suggesting this identification is not reliable). As an example of a protist taxon largely restricted to the tropics this genus is of particular interest in microbial biogeography and this paper discusses its morphology, ecology and distribution in this context

Exact limiting relation between the structure factors in neutron and x-ray scattering

The ratio of the static matter structure factor measured in experiments on coherent X-ray scattering to the static structure factor measured in experiments on neutron scattering is considered. It is shown theoretically that this ratio in the long-wavelength limit is equal to the nucleus charge at arbitrary thermodynamic parameters of a pure substance (the system of nuclei and electrons, where interaction between particles is pure Coulomb) in a disordered equilibrium state. This result is the exact relation of the quantum statistical mechanics. The experimental verification of this relation can be done in the long wavelength X-ray and neutron experiments.Comment: 7 pages, no figure

The Superconducting Gap Behavior in the Antiferromagnetic Nickel-Borocarbide Compounds RNi2B2C (R=Dy, Ho, Er, Tm) Studied by Point-Contacts Spectroscopy

An general survey of the superconducting (SC) gap study in the title compounds by point-contact (PC) spectroscopy is presented. The SC gap was determined from dV/dI of PCs employing the well-known theory of conductivity for normal metal-superconductor PCs accounting Andreev reflection. The theory was modified by including pair-breaking effects considering the presence of magnetic rare-earth ions. A possible multiband structure of these compounds was also taken into account. The PC study of the gap in the Er-compound (TN=6K<Tc=11K) gives =evidence for the presence of two SC gaps. Additionally, a distinct decrease of both gaps is revealed for R = Er in the antiferromagnetic (AF) state. For R = Tm (TN=1.5K<Tc=10.5K) a decrease of the SC gap is observed below 4-5K, while for R = Dy (TN=10.5K>Tc=6.5K) the SC gap has a BCS-like dependence in the AF state. The SC gap for R = Ho (TN=5.2K<Tc=8.5K) exhibits below T*=5.6K a single-band BCS-like dependence vanishing above T*, where a specific magnetic order occurs. The difference in the SC gap behavior in the title compounds is attributed to different AF ordering.Comment: 4 pages, 4 figs., submitted to LT25; V2. missed author is adde

Effect of the Sc/Zr ratio on the corrosion resistance of Al-Mg cast alloys

The results of investigations of the corrosion resistance of Al-Mg-Sc-Zr alloys with varying Mg content and different Sc/Zr ratios are presented. The objects of investigations were the Al-Mg-Sc-Zr alloys with total Sc + Zr content of 0.32 wt%. The concentration of Sc and Zr in the alloys varied with the increments of 0.02 wt%. The alloys were produced by induction casting. The effect of annealing temperature on the microhardness and electrical resistivity of the Al-Mg-Sc-Zr alloys was investigated. Corrosion tests were carried out in a medium simulating intergranular corrosion in aluminum alloys. Electrochemical studies and mass loss tests were performed. An increase in the Sc concentration and a decrease in the Zr one were shown to result in an increase in the corrosion rate. The primary Al3(ScxZr1-x) particles were found to have the main effect on the corrosion resistance of Al-Mg-Sc-Zr alloys. The dependence of the corrosion current on the annealing temperature of the Al-Mg-Sc-Zr alloy was found to have a non-monotonous character (with a maximum).Comment: 29 pages, 2 tables, 11 figures, 58 reference

Point Contact Spectroscopy of Superconducting Gap Anisotropy in Nickel Borocarbide Compound LuNi2B2C

Point contacts are used to investigate the anisotropy of the superconducting energy gap in LuNi2B2C in the ab plane and along the c axis. It is shown that the experimental curves should be described assuming that the superconducting gap is non-uniformly distributed over the Fermi surface. The largest and the smallest gaps have been estimated by two-gap fitting models. It is found that the largest contribution to the point-contact conductivity in the c direction is made by a smaller gap and, in the ab plane by a larger gap. The deviation from the one-gap BCS model is pronounced in the temperature dependence of the gap in both directions. The temperature range, where the deviation occurs, is for the c direction approximately 1.5 times more than in the ab plane. The \Gamma parameter, allowing quantitatively estimate the gap anisotropy by one-gap fitting, in c direction is also about 1.5 times greater than in the ab plane. Since it is impossible to describe satisfactorily such gap distribution either by the one- or two-gap models, a continuous, dual-maxima model of gap distribution over the Fermi surface should be used to describe superconductivity in this material.Comment: 10 pages, 14 Figs, accepted in PR

SunbYte: an autonomous pointing framework for low-cost robotic solar telescopes on high altitude balloons

The design and usability of a fully autonomous robotic control system (SunbYte - Sheffield University Balloon “lYfted” TElescope) for solar tracking and observational applications onboard high-altitude balloons are addressed here. The design is based on a six-step development plan balancing scientific objectives and practical engineering requirements. The high-altitude solar observational system includes low-cost components such as a Cassegrain-type telescope, stepper motors, harmonic drives, USB cameras and microprocessors. OpenCV installed from ROS (Robotic Operating System), python and C facilitated the collection, compression, and processing of housekeeping and scientific data. This processed data was then transmitted to the ground station through the launch vehicle’s telecommunication link. The SunbYte system allows the brightest spot in the sky, the sun, to be identified, and a telescope pointed towards it with high enough accuracy that a scientific camera can capture images. This paper gathers and presents the results from primarily two missions with the High-Altitude Student Platform (HASP, NASA Balloon Program office and LaSpace). Additionally, a discussion will be made comparing these with an earlier iteration flown with the German-Swedish “REXUS/BEXUS” programme coordinated by the European Space Agency. By capturing and analysing a series of tracking images with the location of the Sun at the calibrated centre, the system demonstrated the tracking capabilities on an unstable balloon during ascent. Housekeeping sensor data was collected to further analyse the thermal and mechanical performance. The low temperature increased friction in the drive train and reduced the responsiveness of the harmonic drive actuation system. This caused some issues which require further work in future missions, for example, with SunbYte 4 and its work when flying with the HEMERA ZPB (Zero Pressure Balloon) program

Point-contact study of ReFeAs(1-x)Fx (Re=La, Sm) superconducting films

Point-contact (PC) Andreev-reflection (AR) measurements of the superconducting gap in iron-oxipnictide ReFeAsO_{1-x}F_x (Re=La, Sm) films have been carried out. The value of the gap is distributed in the range 2\Delta \simeq 5-10 meV (for Re=Sm) with a maximum in the distribution around 6 meV. Temperature dependence of the gap \Delta(T) can be fitted well by BCS curve giving reduced gap ratio 2\Delta /kT_c^*\simeq 3.5 (here T_c^* is the critical temperature from the BCS fit). At the same time, an expected second larger gap feature was difficult to resolve distinctly on the AR spectra making determination reliability of the second gap detection questionable. Possible reasons for this and the origin of other features like clear-cut asymmetry in the AR spectra and current regime in PCs are discussed.Comment: 6 two-column pages, 6 figs., 26 Refs., to be published in Superconductor Science and Technolog