| 1. |
- Moubah, Reda, et al.
(författare)
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Origin of the anomalous temperature dependence of coercivity in soft ferromagnets
- 2014
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 116:5
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Tidskriftsartikel (refereegranskat)abstract
- We report on the origin of the anomalous temperature dependence of coercivity observed in some soft ferromagnets by studying the magnetic and electronic properties of FeZr films doped using ion implantation by H, He, B, C, and N. The anomalous increase of the coercivity with temperature was observed only in the C- and B-doped samples. Using x-ray photoelectron spectroscopy, we show that the anomalous behavior of the coercivity coincides with the occurrence of an electron charge transfer for those implanted samples. The origin of the anomaly is discussed in terms of (i) magnetic softness, (ii) nature of the Fe-C and -B covalent bonds, and (iii) large charge transfer.
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| 2. |
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| 3. |
- Stener, Jan, et al.
(författare)
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Evaluation of the applicability of ultrasonic velocity profiling in conditions related to wet low intensity magnetic separation
- 2014
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Ingår i: Minerals Engineering. - : Elsevier BV. - 0892-6875 .- 1872-9444. ; 62, s. 2-8
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Tidskriftsartikel (refereegranskat)abstract
- The internal material transport and selection processes of the wet low-intensity magnetic separators (LIMS) are poorly understood; this calls for improved measurement techniques. In this work an ultrasonic velocity profiling (UVP) technique for measuring how material flow velocity varies with penetration depth is presented. A measurement depth of just a couple of centimetres would greatly improve the understanding of the separation process in a LIMS.When applied to flows of mineral suspensions with high volumetric solids concentration, similar to those in the separators, UVP is unique in combining:•Non-intrusive measurements.•Operates using just one sensor element (transducer).•Relatively good spatial resolution.•Penetrates opaque suspensions.•Fast sampling rate.Here, flows are studied in a rectangular duct (50 × 75 mm). Using magnetite suspensions, measurement through the whole depth of 50 mm is made with good accuracy. Velocity profiles are presented for solids concentrations of 5% and 9% solids by volume (20% and 36% by weight). Even at 9 vol% solids it is possible to reach a penetration depth of more than 25 mm.
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| 4. |
- Stener, Jan, et al.
(författare)
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Robust estimation of particle velocity profiles in high concentration magnetite suspensions
- 2013
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Ingår i: Proceedings of the 2013 International Congress on Ultrasonics. - Singapore : Research Publishing Services. - 9789810759384
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Konferensbidrag (refereegranskat)abstract
- In the mining industry magnetite particles are transported in aqueous suspension through different stages of the process. In some stages it is of interest to monitor both the concentration and particle velocity profiles over a cross-section of the flow. In this paper an ultrasonic flow meter method based on cross-correlation of backscattered sound is presented. High solid particle content (e.g. 20-40 wt%) makes this challenging and therefore the emphasis lies on developing robust signal processing techniques for particle velocity estimation. The developed method is evaluated in laboratory experiments on flows in a rectangular duct. Transducers with centre frequency 1, 2, 4 and 5 MHz are evaluated in flows with a solid content of 20% by weight (4.7 vol% solids). Using the 2 MHz transducer a penetration depth of 50 mm is reached.
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| 5. |
- Stener, Jan, et al.
(författare)
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Towards the measurement of local particle mass fractions in magnetite suspensions
- 2014
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Ingår i: 2014 IEEE International Ultrasonics Symposium, IUS 2014. - Piscataway, NJ : IEEE Communications Society. - 9781479970490 ; , s. 939-942
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Konferensbidrag (refereegranskat)abstract
- In the mining industry, magnetite particles are transported in suspensions with water through different stages of the process. In some of these stages, it is of interest to monitor both the concentration and particle velocity over a cross-section of the flow. High particle concentration makes development of flow measurement techniques challenging. An additional challenge is that the flow is often accessible from one side only, which further limits the selection of applicable techniques. Previous work by the authors focused on using pulse-echo ultrasound for flow velocity profile estimation. In this paper the same setup is used to simultaneously study local variations in solids concentration. Ultrasound pulses are transmitted into the suspension, and the resulting backscatter is recorded. The statistics of the backscatter depend on solids concentration, particle size distribution, particle density, etc. We demonstrate how a short-time (windowed) Power Spectral Density (PSD) estimate can be used to obtain qualitative information about local solids concentration variations. For demonstration, a magnetite suspension carrying up to 7.5 vol% particles (29 wt%, mean particle size 34 μm) is pumped through a closed rectangular channel. When the pump is stopped, pulse-echo ultrasound (with a center frequency of 2.25 or 3.5 MHz) is used to monitor the sedimentation process. Nine snapshots of the process are included. These show a time lapse of the sedimentation, with 5 s between each image. It is clear that the short-time PSD is a good indicator of local mass fraction variations.
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| 6. |
- Stener, Jan, et al.
(författare)
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Ultrasonic velocity profiling of flows related to wet low intensity magnetic separation
- 2013
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Ingår i: Conference in Minerals Engineering. - Luleå. ; , s. 157-168
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The internal workings of wet Low Intensity Magnetic Separators (LIMS) are poorly understood. In this work an Ultrasonic Velocity Profiling (UVP) technique for measuring material flow speed at varying depth. A measurement depth of just a couple of centimetres will greatly improve our understanding of the separation process.When applied to flows of high density mineral suspensions, similar to those in wet LIMS, UVP is unique in combining:• Non-intrusive measurements.• A single transceiver element is sufficient.• Relatively good spatial resolution.• Penetrates opaque suspensions.• Fast sampling rate.Here, flows are studied in a simple rectangular geometry (50x75 mm), using dilute magnetite suspensions; measurement through the whole depth of 50 mm is made with good accuracy. Velocity profiles are presented for different sensors at solids concentrations of 5 vol% solids.
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| 7. |
- Yao, Dao-Xin, et al.
(författare)
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Quantum phase transitions in disordered dimerized quantum spin models and the Harris criterion
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society (APS). - 1098-0121 .- 1550-235X. ; 82:17, s. 172409-
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Tidskriftsartikel (refereegranskat)abstract
- We use quantum Monte Carlo simulations to study effects of disorder on the quantum phase transition occurring versus the ratio g = J/J' in square-lattice dimerized S = 1/2 Heisenberg antiferromagnets with intradimer and interdimer couplings J and J'. The dimers are either randomly distributed (as in the classical dimer model), or come in parallel pairs with horizontal or vertical orientation. In both cases the transition violates the Harris criterion, according to which the correlation-length exponent should satisfy v >= 1. We do not detect any deviations from the three-dimensional O(3) universality class obtaining in the absence of disorder (where v approximate to 0.71). We discuss special circumstances which allow v < 1 for the type of disorder considered here.
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