International Journal of Physics | Vol. 1, No. 8, August 2010 | pp. 57–64
Research Article
Title: Collective Excitations and Superfluid Density of Dipolar Bose-Einstein Condensates
Names of Authors: T. U. Vogel¹, U. V. Weber², V. W. Zeller¹
Authors’ Affiliations: ¹Institute for Theoretical Physics, University of Innsbruck, Innsbruck, Austria; ²Max Planck Institute of Quantum Optics, Garching, Germany
Abstract: We analyze the collective modes of an elongated Bose-Einstein condensate composed of chromium-52 atoms possessing strong magnetic dipole-dipole interactions. Using the extended Gross-Pitaevskii equation incorporating dipole orientation angles relative to the trap symmetry axis, we compute the dipole and quadrupole oscillation frequencies omega_z and omega_perp. Anisotropic dipole forces shift the resonant frequencies by up to 18% compared to standard contact-interaction gases. The normal-to-superfluid transition fraction evaluated via two-fluid hydrodynamic equations demonstrates suppression of critical velocity thresholds along the polarization axis. Damping rates measured through anisotropic expansion profiles show resonance peaks near aspect ratio thresholds epsilon_ar = 2.4. Our theoretical model accounts for dipolar relaxation losses and confirms stability regimes governed by the relative dipole-to-s-wave scattering length ratio epsilon_dd = mu_0 * d² * m / (12 * pi * hbar² * a_s).
Keywords: Bose-Einstein condensation, Dipolar gases, Collective excitations, Gross-Pitaevskii equation, Superfluidity
Manuscript Timeline: Received 05 May 2010, Revised 14 June 2010, Accepted 28 June 2010, Published 02 August 2010
Citation: Vogel, T. U., Weber, U. V., & Zeller, V. W. (2010). Collective Excitations and Superfluid Density of Dipolar Bose-Einstein Condensates. International Journal of Physics, 1(8), 57–64. DOI: 10.46882/2010/IJP/000008
International Journal of Physics | Vol. 1, No. 4, April 2010 | pp. 25–32
Research Article
Title: Spin-Orbit Coupling Effects on Exciton Binding Energies in Zinc-Blende Semiconductor Quantum Dots
Names of Authors: J. K. Dubois¹, K. L. Moreau²
Authors’ Affiliations: ¹Laboratoire de Physique de la Matière Condensée, École Polytechnique, Palaiseau, France; ²Institut Néel, CNRS, Grenoble, France
Abstract: We calculate the ground-state binding energy of excitons in spherical CdTe and ZnSe semiconductor quantum dots by incorporating the Dresselhaus and Rashba spin-orbit coupling Hamiltonians using a variational method within the effective mass approximation. As the dot radius R decreases from 20.0 nm to 2.0 nm, quantum confinement forces an enhancement of the electron-hole Coulomb interaction, raising the exciton binding energy E_x up to 48.5 meV. The inclusion of spin-orbit interactions splits the degenerate 1p-1p valence band states by an energy delta_so approximately 12.3 meV, inducing pronounced polarization anisotropy in the optical absorption spectra. Transition oscillator strengths show strong dependence on the applied external electric field F up to 50 kV/cm. The results correlate well with low-temperature photoluminescence measurements, clarifying the role of band-mixing phenomena in nanoscale heterostructures.
Keywords: Semiconductor quantum dots, Excitons, Spin-orbit coupling, Effective mass approximation, Optical properties
Manuscript Timeline: Received 04 January 2010, Revised 05 February 2010, Accepted 14 February 2010, Published 02 April 2010
Citation: Dubois, J. K., & Moreau, K. L. (2010). Spin-Orbit Coupling Effects on Exciton Binding Energies in Zinc-Blende Semiconductor Quantum Dots. International Journal of Physics, 1(4), 25–32. DOI: 10.46882/2010/IJP/000004
International Journal of Physics | Vol. 1, No. 11, November 2010 | pp. 87–94
DOI: 10.46882/2010/IJP/000011
Article Type: Original Research Paper
Title: Microscopic Simulation of Domain Wall Dynamics in Ferromagnetic Nanowires with Dzyaloshinskii-Moriya Interactions
Names of Authors: E. O. Amadi¹, G. B. Dupont²
Authors’ Affiliations: ¹Department of Physics, University of Nigeria, Nsukka, Nigeria; ²Laboratoire de Physique des Solides, Université Paris-Sud, Orsay, France
Abstract: Controlling the movement of domain walls in ferromagnetic nanowires is a foundational element for developing high-density racetrack memory and spintronic logic systems. This study utilizes micromagnetic simulations to investigate the velocity and stability of Néel-type domain walls driven by spin-orbit torques in the presence of interfacial Dzyaloshinskii-Moriya interactions (DMI). The system dynamics are modeled by solving the Landau-Lifshitz-Gilbert-Slonczewski equation via a high-performance finite-difference grid. The simulations explore nanowires with a width of 100 nm and a thickness of 2 nm, assuming DMI values ranging from 0.5 to 2.5 mJ/m². Our results show that strong interfacial DMI stabilizes the Néel domain wall configuration against the Walker breakdown phenomenon, allowing steady-state propagation speeds to exceed 450 m/s under an applied current density of 1.5 x 10¹² A/m². We find that the domain wall velocity depends linearly on the current density until reaching a critical injection threshold, where structural deformation occurs. Pinning effects caused by surface roughness and geometric notches are also evaluated, showing that a minimum depinning current of 0.35 x 10¹² A/m² is required to release trapped walls. These numerical insights provide useful parameter guidelines for optimizing the operational speed and power consumption of domain-wall-based non-volatile memory architectures.
Keywords: Micromagnetic simulation; Domain wall dynamics; Dzyaloshinskii-Moriya interaction; Spin-orbit torque; Ferromagnetic nanowires; Racetrack memory; Landau-Lifshitz-Gilbert equation; Spintronics.
Manuscript Timeline: Received: August 11, 2010; Revised: September 23, 2010; Accepted: October 14, 2010; Published: November 05, 2010.
Citation: Amadi, E. O., & Dupont, G. B. (2010). Microscopic Simulation of Domain Wall Dynamics in Ferromagnetic Nanowires with Dzyaloshinskii-Moriya Interactions. International Journal of Physics, 1(11), 87–94.
International Journal of Physics | Vol. 1, No. 2, February 2010 | pp. 9–16
Review Article
Title: Nonlinear Magnetohydrodynamic Wave Propagation in Solar Corona Plasma Loops
Names of Authors: D. E. Petrov¹, E. F. Varga²
Authors’ Affiliations: ¹Solar Physics Department, Sternberg Astronomical Institute, Moscow, Russia; ²Institute of Physics, Academy of Sciences, Budapest, Hungary
Abstract: This review synthesizes current theoretical and observational insights into nonlinear magnetohydrodynamic (MHD) wave dynamics within coronal loops. We examine the steepening of slow and fast magneto-acoustic waves into shock fronts under the influence of gravitational stratification and asymmetric magnetic field expansions B(z). Special attention is given to resonant absorption and phase mixing mechanisms that dissipate wave energy at rates exceeding Q_diss = 100 W/m² in active region loops. Utilizing the reductive perturbation method, we derive the generalized Burgers- Korteweg-de Vries equation governing velocity perturbations u(x, t) in low-beta plasma environments. Observational signatures from TRACE and SOHO spacecraft confirm fast-mode attenuation lengths lambda_att ranging from 5 to 20 Mm. We outline open challenges in modeling coronal heating via dissipation of turbulent MHD cascades and wave-particle interactions.
Keywords: Solar corona, Magnetohydrodynamics, Shock waves, Plasma loops, Wave dissipation
Manuscript Timeline: Received 12 November 2009, Revised 10 December 2009, Accepted 20 December 2009, Published 02 February 2010
Citation: Petrov, D. E., & Varga, E. F. (2010). Nonlinear Magnetohydrodynamic Wave Propagation in Solar Corona Plasma Loops. International Journal of Physics, 1(2), 9–16. DOI: 10.46882/2010/IJP/000002
International Journal of Physics | Vol. 1, No. 1, January 2010 | pp. 1–8
Research Article
Title: Quantum Phase Transitions in Ultra-Cold Fermi Gases with Tunable Interactions
Names of Authors: A. K. Sharma¹, B. R. Mehta², C. H. Liu³
Authors’ Affiliations: ¹Department of Physics, Indian Institute of Technology, New Delhi, India; ²Department of Applied Physics, University of Tokyo, Tokyo, Japan; ³Department of Physics, National University of Singapore, Singapore
Abstract: We investigate the quantum phase transitions in ultra-cold Fermi gases near a Feshbach resonance using a multi-channel functional renormalization group approach. By tuning the scattering length a from weak to strong coupling regimes, we evaluate the critical chemical potential mu_c and the pairing gap delta at T = 0 K. Our results indicate a smooth crossover from the Bardeen-Cooper-Schrieffer state to a Bose-Einstein condensate, exhibiting a non-monotonic behavior in the collective excitation frequency omega_b. The calculated critical exponent nu = 0.67 ± 0.03 aligns well with the universal scaling predictions for the unitary Fermi gas. Furthermore, we analyze the thermodynamic stability via the compressibility kappa and find suppressed fluctuations near the critical magnetic field B_c = 834.2 G. These findings provide robust theoretical benchmarks for ongoing optical lattice experiments involving lithium-6 and potassium-40 atomic mixtures.
Keywords: Ultra-cold gases, Feshbach resonance, Quantum phase transition, Renormalization group, Fermi-Bose crossover
Manuscript Timeline: Received 10 October 2009, Revised 15 November 2009, Accepted 02 December 2009, Published 05 January 2010
Citation: Sharma, A. K., Mehta, B. R., & Liu, C. H. (2010). Quantum Phase Transitions in Ultra-Cold Fermi Gases with Tunable Interactions. International Journal of Physics, 1(1), 1–8. DOI: 10.46882/2010/IJP/000001
International Journal of Physics | Vol. 2, No. 2, February 2011 | pp. 10–17
DOI: 10.46882/2011/IJP/000014
Article Type: Original Research Paper
Title: Atmospheric Aerosol Optical Depth and Angstrom Exponent Anomalies over Sub-Saharan West Africa
Names of Authors: V. A. Ezenwa¹, G. M. Jenkins²
Authors’ Affiliations: ¹Department of Physics, Nnamdi Azikiwe University, Awka, Nigeria; ²Department of Physics and Astronomy, Howard University, Washington DC, USA
Abstract: Characterizing atmospheric aerosols over West Africa is essential for understanding regional climate variation, radiative forcing, and dust transport patterns across the Atlantic. This paper analyzes variations in aerosol optical depth (AOD at 500 nm) and the Angstrom exponent (alpha at 440-870 nm) collected via multi-wavelength AERONET sun photometers over a five-year window, focusing on sub-Saharan monitoring stations. The dataset reveals a strong seasonal cycle dominated by the influx of mineral dust during the Harmattan season (December to March) and biomass burning plumes during the dry season. The mean AOD peaks dramatically in March at 1.42 ± 0.25, coinciding with a drop in the Angstrom exponent to 0.15 ± 0.04, which indicates the dominant presence of coarse-mode desert dust particles from the Bodélé Depression. In contrast, the wet season (June to September) displays a reduced mean AOD of 0.35 ± 0.12 and an elevated Angstrom exponent of 0.85 ± 0.18, signaling a shift toward fine-mode maritime and anthropogenic aerosols. Ground-based observations were validated against MODIS satellite data, yielding an 89% linear correlation coefficient. These empirical trends provide refined optical constraints for reducing uncertainty in regional climate projection models and atmospheric correction algorithms.
Keywords: Aerosol optical depth; Angstrom exponent; Sun photometer; Mineral dust; Radiative forcing; Sub-Saharan climate; Remote sensing; Atmospheric aerosols.
Manuscript Timeline: Received: November 02, 2010; Revised: December 14, 2010; Accepted: January 11, 2011; Published: February 03, 2011.
Citation: Ezenwa, V. A., & Jenkins, G. M. (2011). Atmospheric Aerosol Optical Depth and Angstrom Exponent Anomalies over Sub-Saharan West Africa. International Journal of Physics, 2(2), 10–17.