We report on a study of our students’ understanding of gravity using the Newtonian Gravity Concep... more We report on a study of our students’ understanding of gravity using the Newtonian Gravity Concept Inventory (NGCI). This article is supposed to serve two purposes: as a proof of applicability of the test to first year medical students outside the United States and as a general survey of our students’ understanding of gravity. The motivation for this work came initially from students’ misconceptions of gravity and related topics noticed in classrooms. NGCI has 26 multiple-choice questions probing students’ knowledge of gravity in four different domains: Directionality, Gravity as a force, Independence from other forces and threshold. Results confirmed weak overall performance of the 684 students participated in this study (average score of only 38.48%) with misconceptions related to gravity in all four domains. We were able to prove the applicability of the NGCI to our students through calculations of Classical Test Theory statistics and Cronbach’s alpha. We got a Cronbach’s alpha o...
Journal of Superconductivity and Novel Magnetism, 2017
In this article, Gd3−xErxFe5O12 powders with x= 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 were prepar... more In this article, Gd3−xErxFe5O12 powders with x= 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 were prepared by solid-state reaction method. The properties of the prepared samples were examined by X-ray diffraction, Mössbauer spectroscopy, vibrating sample magnetometry, and differential scanning calorimetry. The XRD patterns of the powders show a single-phase structure and were found to agree with the standard pattern of rare earth iron garnet. Room temperature Mössbauer spectra of the powders indicate that iron is present in three magnetic sites corresponding to two octahedral sites and one tetrahedral site. The saturation magnetization increased with increasing erbium substitution, and the Curie temperature decreased slightly.
Abstract BaFe 12− x Cu x O 19 hexaferrites were prepared using ball milling and sintering at 1100... more Abstract BaFe 12− x Cu x O 19 hexaferrites were prepared using ball milling and sintering at 1100 °C. Refinement of the X-ray diffraction patterns was carried out to determine the structural parameters and the ionic distribution over the crystallographic sites. The preferential site occupation and valence state of Cu was consistent with the results obtained from the analysis of Mossbauer spectra. Further, the magnetic parameters of the samples were discussed in light of the structural and Mossbauer analyses. The magnetic phase transition temperature was found to decrease with the level of Cu substitution, in accordance with the reduction of the superexchange interactions. Further, the magnetic softening of the hexaferrite and the significant reduction in magnetocrystalline anisotropy with Cu substitution was consistent with the ionic distribution in the lattice. This study clearly demonstrated the feasibility of using a simple method to fabricate hexaferrites with a modified coercivity, while maintain the saturation magnetization high enough for practical applications.
ABSTRACT The thermodynamic behavior of the one-dimensional Bose-gas-attractive-delta impurity sys... more ABSTRACT The thermodynamic behavior of the one-dimensional Bose-gas-attractive-delta impurity system is studied in this paper. The system is shown to undergo the Bose-Einstein condensation and the cause of the phase transition is attributed to the bound state introduced by the impurity in the free-particle energy spectrum. The condensed phase is composed of particles captured by the impurity, forming a drop of particles well localized in space. This gives to the Bose-Einstein condensation in this system the appearance of the ordinary vapor-liquid phase transition. The expression for the pressure is obtained and is plotted as a function of the temperature and the system length. The shapes of the isothermal curves reinforce the interpretation of a vapor-liquid transition. The evaluation of the heat capacity at constant length shows the existence of a finite discontinuity at the transition temperature.
In this article we report on the structural and magnetic properties of BaFe12-4xMoxZn3xO19 hexafe... more In this article we report on the structural and magnetic properties of BaFe12-4xMoxZn3xO19 hexaferrites with Mo-Zn substitution for Fe ions. The starting materials were commensurate with the BaM stoichiometry, and the Mo:Zn ratio was 1:3. The powder precursors were prepared by high energy ball milling, and subsequently sintered at temperatures from 1100 to 1300° C. The structural analyses indicated that all samples sintered at 1100° C were dominated by a major M-type hexaferrite phase. The relative abundance of the BaMoO4 and Zn-spinel secondary phases increased with increasing the concentration of the substituents, resulting in a decrease of the saturation magnetization from about 67 emu/g (for x = 0.0) to 55 emu/g (for x = 0.3). The coercivity also decreased from 3275 Oe (for x = 0.0) to 900 Oe (for x = 0.3), demonstrating the ability to tune the coercivity to the range useful for magnetic recording by the substitution process. The saturation magnetization improved significantly w...
The present study is concerned with the fabrication and characterization of Me 2 Y substituted he... more The present study is concerned with the fabrication and characterization of Me 2 Y substituted hexaferrites, Ba 2 Me 2 Fe 12-x T x O 22 (Me = Co 2+ , Mg 2+ , and Cr 2+ , and T = Fe 3+ , and Ga 3+). The samples were prepared by the conventional ball milling technique and sintering at 1200° C. The effect of the choices of Me and T ions on the structural and magnetic properties of the hexaferrites were investigated. XRD patterns, magnetic parameters, and Mössbauer spectra of the Co 2 Y were consistent with a single phase Y-type hexaferrite. However, the CoCr-Y sample was found to be dominated by the Y-type hexaferrite, and M-type and BaCrO 4 minority phases were observed in the XRD pattern of the sample. The small increase in saturation magnetization from about 34 emu/g up to 37.5 emu/g was therefore attributed to the development of the M-type phase. On the other hand, XRD pattern of the Cr 2 Y sample indicated the dominance of the M-type phase in this sample. The high coercivity (1445...
We report on a study of our students’ understanding of gravity using the Newtonian Gravity Concep... more We report on a study of our students’ understanding of gravity using the Newtonian Gravity Concept Inventory (NGCI). This article is supposed to serve two purposes: as a proof of applicability of the test to first year medical students outside the United States and as a general survey of our students’ understanding of gravity. The motivation for this work came initially from students’ misconceptions of gravity and related topics noticed in classrooms. NGCI has 26 multiple-choice questions probing students’ knowledge of gravity in four different domains: Directionality, Gravity as a force, Independence from other forces and threshold. Results confirmed weak overall performance of the 684 students participated in this study (average score of only 38.48%) with misconceptions related to gravity in all four domains. We were able to prove the applicability of the NGCI to our students through calculations of Classical Test Theory statistics and Cronbach’s alpha. We got a Cronbach’s alpha o...
Journal of Superconductivity and Novel Magnetism, 2017
In this article, Gd3−xErxFe5O12 powders with x= 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 were prepar... more In this article, Gd3−xErxFe5O12 powders with x= 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 were prepared by solid-state reaction method. The properties of the prepared samples were examined by X-ray diffraction, Mössbauer spectroscopy, vibrating sample magnetometry, and differential scanning calorimetry. The XRD patterns of the powders show a single-phase structure and were found to agree with the standard pattern of rare earth iron garnet. Room temperature Mössbauer spectra of the powders indicate that iron is present in three magnetic sites corresponding to two octahedral sites and one tetrahedral site. The saturation magnetization increased with increasing erbium substitution, and the Curie temperature decreased slightly.
Abstract BaFe 12− x Cu x O 19 hexaferrites were prepared using ball milling and sintering at 1100... more Abstract BaFe 12− x Cu x O 19 hexaferrites were prepared using ball milling and sintering at 1100 °C. Refinement of the X-ray diffraction patterns was carried out to determine the structural parameters and the ionic distribution over the crystallographic sites. The preferential site occupation and valence state of Cu was consistent with the results obtained from the analysis of Mossbauer spectra. Further, the magnetic parameters of the samples were discussed in light of the structural and Mossbauer analyses. The magnetic phase transition temperature was found to decrease with the level of Cu substitution, in accordance with the reduction of the superexchange interactions. Further, the magnetic softening of the hexaferrite and the significant reduction in magnetocrystalline anisotropy with Cu substitution was consistent with the ionic distribution in the lattice. This study clearly demonstrated the feasibility of using a simple method to fabricate hexaferrites with a modified coercivity, while maintain the saturation magnetization high enough for practical applications.
ABSTRACT The thermodynamic behavior of the one-dimensional Bose-gas-attractive-delta impurity sys... more ABSTRACT The thermodynamic behavior of the one-dimensional Bose-gas-attractive-delta impurity system is studied in this paper. The system is shown to undergo the Bose-Einstein condensation and the cause of the phase transition is attributed to the bound state introduced by the impurity in the free-particle energy spectrum. The condensed phase is composed of particles captured by the impurity, forming a drop of particles well localized in space. This gives to the Bose-Einstein condensation in this system the appearance of the ordinary vapor-liquid phase transition. The expression for the pressure is obtained and is plotted as a function of the temperature and the system length. The shapes of the isothermal curves reinforce the interpretation of a vapor-liquid transition. The evaluation of the heat capacity at constant length shows the existence of a finite discontinuity at the transition temperature.
In this article we report on the structural and magnetic properties of BaFe12-4xMoxZn3xO19 hexafe... more In this article we report on the structural and magnetic properties of BaFe12-4xMoxZn3xO19 hexaferrites with Mo-Zn substitution for Fe ions. The starting materials were commensurate with the BaM stoichiometry, and the Mo:Zn ratio was 1:3. The powder precursors were prepared by high energy ball milling, and subsequently sintered at temperatures from 1100 to 1300° C. The structural analyses indicated that all samples sintered at 1100° C were dominated by a major M-type hexaferrite phase. The relative abundance of the BaMoO4 and Zn-spinel secondary phases increased with increasing the concentration of the substituents, resulting in a decrease of the saturation magnetization from about 67 emu/g (for x = 0.0) to 55 emu/g (for x = 0.3). The coercivity also decreased from 3275 Oe (for x = 0.0) to 900 Oe (for x = 0.3), demonstrating the ability to tune the coercivity to the range useful for magnetic recording by the substitution process. The saturation magnetization improved significantly w...
The present study is concerned with the fabrication and characterization of Me 2 Y substituted he... more The present study is concerned with the fabrication and characterization of Me 2 Y substituted hexaferrites, Ba 2 Me 2 Fe 12-x T x O 22 (Me = Co 2+ , Mg 2+ , and Cr 2+ , and T = Fe 3+ , and Ga 3+). The samples were prepared by the conventional ball milling technique and sintering at 1200° C. The effect of the choices of Me and T ions on the structural and magnetic properties of the hexaferrites were investigated. XRD patterns, magnetic parameters, and Mössbauer spectra of the Co 2 Y were consistent with a single phase Y-type hexaferrite. However, the CoCr-Y sample was found to be dominated by the Y-type hexaferrite, and M-type and BaCrO 4 minority phases were observed in the XRD pattern of the sample. The small increase in saturation magnetization from about 34 emu/g up to 37.5 emu/g was therefore attributed to the development of the M-type phase. On the other hand, XRD pattern of the Cr 2 Y sample indicated the dominance of the M-type phase in this sample. The high coercivity (1445...
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