| 1. |
- Calleecharan, Yogeshwarsing, et al.
(författare)
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Towards a general method for estimating the unbalanced magnetic pull in mixed eccentricities motion including sufficiently large eccentricities in a hydropower generator and their validation against EM simulations
- 2013
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Ingår i: European Physical Journal. - : EDP Sciences. - 1286-0042 .- 1286-0050. ; 63:2
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Tidskriftsartikel (refereegranskat)abstract
- Electromagnetic (EM) analysis of hydropower generators is common practice but rotor whirling is little studied. This paper suggests a novel semi-analytical method for estimating the steady state unbalanced magnetic pull (UMP) when the rotor centre is undergoing mixed eccentricities motion. The ability to estimate the UMP for mixed eccentricities motion in finite element method (FEM)-based modelling software packages is rare. The proposed methodology in its formulation takes advantage of the fact that a purely dynamic eccentricity motion including non-synchronous whirling and a purely static eccentricity motion can be more amenable to implement in existing FEM-based EM modelling software products for UMP estimation. After these initial separate UMP results are obtained, the proposed method can be applied for virtually any mixed eccentricities motion cases up to sufficiently large eccentricities for quick analysis instead of running the mixed eccentricities simulations directly in a FEM-based software package. Good agreement between the UMP from the actual EM mixed eccentricities motion simulations in a commercial FEM-based software package and the UMP estimations by the novel method is made for a wide range of eccentricities that may commonly occur in practice. A modified feature selective validation (FSV) method, the FSV-UPC, is applied to assess the similarities and the differences in the UMP computations
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| 2. |
- Esebamen, Omeime Xerviar, et al.
(författare)
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Comparative Study of UV Radiation Hardness of n+p and p+n Duo-Lateral Position Sensitive Detectors
- 2014
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Ingår i: European Physical Journal. - : EDP Sciences. - 1286-0042 .- 1286-0050. ; 68:2, s. Art. no. 21301-
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Tidskriftsartikel (refereegranskat)abstract
- We report experimental results on the degree of radiation damage in two duo-lateral position sensitive detectors (LPSDs) exposed to 193 nm and253 nm ultraviolet (UV) beam. One of the detectors was an in-house fabricated n(+) p LPSD and the other was a commercially available p(+) n LPSD. We report that at both wavelengths, the degradation damage from the UV photons absorption caused a much more significant deterioration in responsivity in the p(+) n LPSD than in the n(+) p LPSD. By employing a simple method, we were able to visualize the radiation damage on the active area of the LPSDs using 3-dimensional graphs. We were also able to characterize the impact of radiation damage on the linearity and position error of the detectors.
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| 3. |
- Gao, Zhihao, et al.
(författare)
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Benchmark of a multi-physics Monte Carlo simulation of an ionguide for neutron-induced fission products
- 2022
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Ingår i: European Physical Journal. - : Springer Nature. - 1286-0042 .- 1286-0050. ; 58:2
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Tidskriftsartikel (refereegranskat)abstract
- To enhance the production of medium-heavy,neutron-rich nuclei, and to facilitate measurements of independentyields of neutron-induced fission, a proton-toneutronconverter and a dedicated ion guide for neutroninducedfission have been developed for the IGISOL facilityat the University of Jyväskylä. The ion guide holds thefissionable targets, and the fission products emerging fromthe targets are collected in helium gas and transported to thedownstream experimental stations.Acomputer model, basedon a combination of MCNPX for modeling the neutron production,the fission code GEF, and GEANT4 for the transportof the fission products, was developed. The model willbe used to improve the setup with respect to the productionand collection of fission products. In this paper we benchmarkthe model by comparing simulations to a measurementin which fission products were implanted in foils located atdifferent positions in the ion guide. In addition, the productsfrom neutron activation in the titanium foil and the uraniumtargets are studied. The result suggests that the neutron fluxat the high-energy part of the neutron spectrum is overestimatedby approximately 40%.However, the transportation offission products in the uranium targets agrees with the experimentwithin 10%. Furthermore, the simulated transportationof fission products in the helium gas achieves almost perfectagreement with the measurement. Hence, we conclude thatthe model, after correction for the neutron flux, is well suitedfor optimization studies of future ion guide designs.
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| 4. |
- Gogova, Daniela, et al.
(författare)
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Investigation of the structure of tungsten oxide films obtained by chemical vapor deposition
- 2000
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Ingår i: European Physical Journal. - 1286-0042 .- 1286-0050. ; 11:3, s. 167-174
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Tidskriftsartikel (refereegranskat)abstract
- Thin amorphous and polycrystalline tungsten oxide films have been prepared by Chemical Vapor Deposition (CVD) from metallorganic precursor - tungsten hexacarbonyl - at atmospheric pressure. The dependence of the composition and the structure of tungsten oxide films on the technological conditions has been investigated by XPS, XRD, DTA-TGA and Raman spectroscopy. As a result it has been established that: at high values of the flow-rates of the reaction gases amorphous films of very low density have been obtained, in the XPS spectra of the understoichiometric WO3-y (0 < y < 0.3) films besides W6+, also W5+ and W4+ states have been observed. First to observe in the Raman spectra of amorphous CVD-WO3 films is the band at similar to 950 cm(-1), characteristic for terminal W6+=O bonds in result of the presence of structural water. The existence of structural water in the amorphous material has been established by thermal analyze, also.
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| 5. |
- Grillo, SE, et al.
(författare)
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Monitoring the structural and chemical properties of CNx thin films during in situ annealing in a TEM
- 2001
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Ingår i: European Physical Journal. - 1286-0042 .- 1286-0050. ; 13:2, s. 97-105
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Tidskriftsartikel (refereegranskat)abstract
- Carbon nitride films synthesised by magnetron sputtering at different substrate temperatures have been studied using electron energy loss spectroscopy (EELS) during annealing performed in situ in a transmission electron microscope (TEM). The proportion of sp(2) hybridised carbon slightly decreases initially during heating, presumably because of the removal of defects in the structure, whilst it increases at higher temperatures when graphitisation tends to take place, as confirmed by high resolution electron microscopy (HREM). Substantial amounts of nitrogen (up to similar to 80%) are removed following annealing at 1000 degreesC. A corresponding decrease in the pre-peak of the nitrogen spectra suggests that pyridine-like N is released by annealing. As this peak component decreases, a second peak, of weaker intensity, is becoming apparent in the EELS spectra when the films are heated at temperatures above approximately 700 degreesC. The possibility has been suggested that this corresponds to N substituted for C in a graphitic structure, with possibly also some N-2 contributing to the peak.
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| 6. |
- Holmlid, Leif, 1942
(författare)
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Interaction between infrared laser modes in Rydberg Matter: redshifted modes in reflection and blueshifted in transmission
- 2004
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Ingår i: European Physical Journal-Applied Physics. - : EDP Sciences. - 1286-0042 .- 1286-0050. ; 26:2, s. 103-111
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Tidskriftsartikel (refereegranskat)abstract
- When an almost single-mode IR laser beam is reflected from an IR window with a deposit of Rydberg Matter on the inner, vacuum face, the laser modes appear red-shifted; thus their maxima are observed at lower laser current. This effect is complementary to the previously reported blue-shifts of IR laser modes in transmission through Rydberg Matter. Both types of shifts are due to interaction between the laser modes, now proved by using only two isolated modes both in reflection and transmission. The general process is stimulated Raman scattering. Rydberg Matter is here formed from Rydberg states of K atoms and nitrogen molecules inside a vacuum chamber. A theoretical description is given that involves slow decay or increase in the energy of the photons interacting with the Rydberg Matter, depending on the temperature of this matter. This means that the two isolated modes studied may become almost resonant within certain frequency ranges. The energy increase (frequency blue-shifting) of photons passing hot Rydberg Matter has been reported previously. The description used explains both the red-shifted reflection and the blue-shifted transmission results.
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| 7. |
- Hu, Xin, et al.
(författare)
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New Transmission Lines of Negative Refractive Index Basedon Periodically Loaded Negative-Impedance-Converted Inductors and Capacitors
- 2009
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Ingår i: European Physical Journal. - : EDP Sciences. - 1286-0042 .- 1286-0050. ; 46:3269
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Tidskriftsartikel (refereegranskat)abstract
- A new class of negative refractive index (NRI) transmission line is proposed. Differential operational amplifiers are used to form the required lumped elements, i.e., negative-impedance-converted (NIC) inductors and capacitors. When the gain of the differential operational amplifiers in the NIC circuits is very large over the entire frequency band, the equivalent material parameters are non-dispersive, and the phase response of the new NRI transmission line can be complimentary to that of a conventional transmission line over the entire frequency band. As an application example, a broadband 1:4 power divider based on the proposed NRI transmission line is studied.
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| 8. |
- Händel, S K, et al.
(författare)
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High voltage vacuum discharge characteristics
- 2001
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Ingår i: European Physical Journal. - 1286-0042 .- 1286-0050. ; 15:3, s. 207-212
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Tidskriftsartikel (refereegranskat)abstract
- Investigation of the high voltage vacuum discharge characteristics-current derivative (di/dt), current, voltage, and soft as well as hard X-rays-versus time has been carried out. Recorded traces indicate pinching of the interelectrode discharge column two or three times during which the voltage increases to values as high as the initial voltage or even higher. X-ray radiation of high penetration power is emitted during these events. In addition, sausage instabilities have been observed during the pinch giving rise to extreme penetrating X-rays caused partly by the pinch voltage and partly by the sausage voltage. Visible electrode studies show the fact that the discharge is restricted to a narrow column. Finally, a theoretical treatment of the discharge mechanism that seems to be in good agreement with the experimental result is also presented.
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| 9. |
- Karimipour, Masoud, et al.
(författare)
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Room temperature magnetization in Co-doped anatase phase of TiO2
- 2013
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Ingår i: European Physical Journal. - : EDP Sciences. - 1286-0042 .- 1286-0050. ; 61:1, s. 10601-
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Tidskriftsartikel (refereegranskat)abstract
- CoxTi1-xO2 films were deposited by spray pyrolysis technique on Si(1 0 0) substrates at 475 degrees C. A hydro-alcoholic solution containing titanium (iv) isopropoxide and Co(NO3)(2) with various Co doping levels from x = 0-0.015 in solution was used as spray solution. Grazing incident angle of X-ray diffraction illustrates that the CoxTi1-xO2 films are single phase and polycrystal with mixed orientations. Study of surface morphology of the films by atomic force microscope reveals that the annealing atmosphere does not significantly affect the grain size and the microstructure of the films. This study provides further insight into the importance of annealing atmosphere on magnetization of the films. Room temperature magneto-optical Kerr measurement was employed in polar mode. A hysteresis loop and a paramagnetic behavior have been recorded for samples annealed in H-2 ambient gas and air, respectively. Chemical composition analysis by X-ray photo-electron spectroscopy showed that Co atoms are bounded to oxygen and no metallic clusters are present. Moreover, it indicates the formation of high spin Co2+ for the sample x = 0.008 annealed in H-2 ambient gas. The origin of magnetization can be attributed to the contribution of oxygen vacancies in the spin polarization of the structure.
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| 10. |
- Leveque, P., et al.
(författare)
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Identification of hydrogen related defects in proton implanted float-zone silicon
- 2003
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Ingår i: European Physical Journal. - : EDP Sciences. - 1286-0042 .- 1286-0050. ; 23:1, s. 5-9
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen related defects in high purity n-type float zone silicon samples have been studied by means of Deep Level Transient Spectroscopy. They were introduced, as well as the characteristic vacancy-oxygen (VO) and divacancy (V-2) centers, by MeV proton implantation. Two hydrogen related defect levels were resolved at 0.32 eV and 0.45 eV below the conduction band edge (E-c). Careful annealing studies indicate strongly that a third hydrogen related level, overlapping with the singly negative charge state level of V-2, is also present in the implanted samples. The annealing behavior of the hydrogen related defects has been compared with literature data leading to a rather firm identification. The E-c-0.32 eV level originates from a VO center partly saturated with hydrogen (a VOH complex) while the E-c-0.45 eV level may be ascribed to a complex involving a monovacancy and a hydrogen atom ( a VH complex). The third hydrogen related defect is tentatively ascribed to a complex involving a hydrogen atom and a divacancy ( a V2H complex).
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| 11. |
- Lundström, Niklas L. P., et al.
(författare)
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Small shape deviations causes complex dynamics in large electric generators
- 2014
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Ingår i: European Physical Journal. - : EDP Sciences. - 1286-0042 .- 1286-0050. ; 66:2
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Tidskriftsartikel (refereegranskat)abstract
- We prove that combinations of small eccentricity, ovality and/or triangularity in the rotor and stator can produce complex whirling motions of an unbalanced rotor in large synchronous generators. It is concluded which structures of shape deviations that are more harmful, in the sense of producing complex whirling motions, than others. For each such structure, we derive simplified equations of motions from which we conclude analytically the relation between shape deviations and mass unbalance that yield non-smooth whirling motions. Finally we discuss validity of our results in the sense of modeling of the unbalanced magnetic pull force
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| 12. |
- Saers, Robert, 1977-, et al.
(författare)
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A set-up for flexible geometry optical lattices
- 2008
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Ingår i: European Physical Journal. - : EDP Sciences. - 1286-0042 .- 1286-0050. ; 42:3, s. 269-273
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Tidskriftsartikel (refereegranskat)abstract
- We have developed an alignment tool for optical lattices with arbitrary beam angles, allowing for optical potentials with a range of geometries and topographies. A calibration procedure has been introduced, giving a precision of 10 mrad in the chosen beam angle, and a high degree of flexibility. The tool has been tested in simplified experiments on the confinement and expansion of cold atoms in one-dimensional and two-dimensional optical lattices, and has proved to work well.
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| 13. |
- Samyn, P., et al.
(författare)
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Plasma deposition of polymer composite films incorporating nanocellulose whiskers
- 2011
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Ingår i: European Physical Journal. - : EDP Sciences. - 1286-0042 .- 1286-0050. ; 56:2
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Tidskriftsartikel (refereegranskat)abstract
- In a trend for sustainable engineering and functionalization of surfaces, we explore the possibilities of gas phase processes to deposit nanocomposite films. From an analysis of pulsed plasma polymerization of maleic anhydride in the presence of nanocellulose whiskers, it seems that thin nanocomposite films can be deposited with various patterns. By specifically modifying plasma parameters such as total power, duty cycle, and monomer gas pressure, the nanocellulose whiskers are either incorporated into a buckled polymer film or single nanocellulose whiskers are deposited on top of a polymeric film. The density of the latter can be controlled by modifying the exact positioning of the substrate in the reactor. The resulting morphologies are evaluated by optical microscopy, AFM, contact angle measurements and ellipsometry.
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| 14. |
- Öberg, Å., et al.
(författare)
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Conductive nanocomposite ceramics as tribological and electrical contact materials
- 2010
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Ingår i: European Physical Journal. - : EDP Sciences. - 1286-0042 .- 1286-0050. ; 49:2, s. 22902-
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Tidskriftsartikel (refereegranskat)abstract
- Conductive ceramics have widespread use in many industrial applications. One important application for such materials is electrical contact technology. Over the last few years, a new class of nanocomposite ceramic thin film materials has been developed with contact coatings as one key objective. This family of materials has proven to combine the favorable contact properties of metals, such as low electrical and thermal resistivity, and high ductility, with those of ceramics such as low friction and wear rate, high chemical integrity and good high-temperature properties. Furthermore, it is also found that the tribological properties of such materials can be tailored by alloying thus creating a triboactive system. The technology is now industrialized, and a practical example of a contact system utilizing a nanocomposite coating for improved performance is given.
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