International Journal of Physics

International Journal of Physics | Vol. 3, No. 11, November 2012 | pp. 83–90

DOI: 10.46882/2012/IJP/000031

Research Article

Title: Hydrodynamic Transport and Plasma Instabilities in Dual-Gated Graphene Field-Effect Transistors

Names of Authors: J. R. Weber¹, M. T. Nguyen²

Authors’ Affiliations: ¹Physik-Department, Technische Universität München, D-85748 Garching, Germany; ²Department of Physics, Vietnam National University, Hanoi 100000, Vietnam

Abstract: Relativistic-like charge carrier dynamics in high-mobility graphene layers enable strong hydrodynamic fluid flow regimes under specific conditions. This paper characterizes the electronic hydrodynamic transport properties and evaluates Dyakonov-Shur plasma wave instabilities inside dual-gated graphene field-effect transistors. We solved the coupled Navier-Stokes equations for two-dimensional electron gases. This system was integrated alongside the Poisson electrostatic equation to account for self-consistent electric fields. The calculations show that when drift velocities exceed the threshold parameter of v = 2.5 * 10⁷ cm/s, electron-electron scattering mechanisms become dominant over impurity scattering channels. This dominance leads to a steady viscous fluid flow state. Under asymmetric boundary configurations across the source and drain terminals, plasma wave oscillations exhibit a net amplification profile. This amplification delivers a negative differential resistance response within the terahertz frequency spectrum of 1.2 THz to 3.5 THz. The calculated resonant frequency values tune continuously via the applied gate voltage parameters with a wide sensitivity factor of 450 GHz/V. These results provide design strategies for constructing high-output, room-temperature terahertz radiation sources and detectors using graphene architectures.

Keywords: Graphene transistor; hydrodynamic transport; plasma instability; terahertz radiation; Navier-Stokes equations; electron-electron scattering

Manuscript Timeline: Received: August 19, 2012; Revised: September 25, 2012; Accepted: October 10, 2012; Published: November 13, 2012 [1]

Citation: Weber, J. R., & Nguyen, M. T. (2012). Hydrodynamic Transport and Plasma Instabilities in Dual-Gated Graphene Field-Effect Transistors. International Journal of Physics, 3(11), 83–90.

International Journal of Physics | Vol. 3, No. 10, October 2012 | pp. 75–82

DOI: 10.46882/2012/IJP/000030

Research Article

Title: Elasticity and Vibrational Properties of Stishovite under Extreme Lower-Mantle Pressures

Names of Authors: L. M. Dupont¹, A. O. Awotunde²

Authors’ Affiliations: ¹Laboratoire de Geologie de Lyon, Ecole Normale Superieure de Lyon, 69364 Lyon, France; ²Department of Physics, University of Ibadan, Ibadan 200005, Nigeria

Abstract: Understanding the elastic and vibrational response behavior of silica polymorphs under high pressures is essential for interpreting deep-earth seismic profiles accurately. This research models the complete elastic tensor parameters and vibrational phonon modes of stishovite (SiO²). The calculations span hydrostatic pressure settings from 0 GPa up to 150 GPa. We used first-principles density functional theory (DFT) based on the generalized gradient approximation (GGA). The calculated data reproduce the well-known ferroelastic phase transition. This transition shifts stishovite from a tetragonal symmetry into a CaCl²-type orthorhombic crystal form at an identical pressure value of 52.3 GPa. This structural transition is driven directly by the softening of the B1g shear phonon vibrational mode. At the critical transition pressure point, the shear elastic modulus value C11 - C12 drops to 0 GPa. This drop causes a noticeable 24% reduction in transverse seismic wave propagation velocities. Our structural models indicate that this elasticity reduction explains the localized seismic reflector anomalies detected across the lower mantle region at depths near 1200 km. The calculated bulk modulus value at zero pressure is B0 = 302 GPa, with a pressure derivative value of B0' = 4.15. These values match experimental diamond anvil cell measurements within a minor 1.5% margin.

Keywords: Stishovite; density functional theory; phase transition; elastic moduli; soft phonon mode; lower mantle

Manuscript Timeline: Received: July 3, 2012; Revised: August 18, 2012; Accepted: September 4, 2012; Published: October 15, 2012

Citation: Dupont, L. M., & Awotunde, A. O. (2012). Elasticity and Vibrational Properties of Stishovite under Extreme Lower-Mantle Pressures. International Journal of Physics, 3(10), 75–82.

International Journal of Physics | Vol. 3, No. 9, September 2012 | pp. 67–74

DOI: 10.46882/2012/IJP/000029

Research Article

Title: Optical Soliton Perturbations in Inhomogeneous Inverted Two-Level Laser Media

Names of Authors: S. H. Zhang¹, N. K. Patel²

Authors’ Affiliations: ¹Department of Physics, Tsinghua University, Beijing 100084, China; ²Department of Physics, Indian Institute of Technology, New Delhi 110016, India

Abstract: The stable propagation of optical solitons through resonant laser media underpins high-speed optical fiber communications and laser systems. This paper solves the coupled Maxwell-Bloch equations governing optical pulse propagation inside inhomogeneous, inverted two-level resonant media. The model includes higher-order perturbation components. These components comprise third-order dispersion, self-steepening effects, and stimulated Raman scattering delays. We apply the inverse scattering transform method alongside a detailed multiple-scale perturbation algorithm. This mathematical framework derives analytical solutions for single-soliton and multi-soliton wave trains. The results demonstrate that spatial inhomogeneities in the doping density of the two-level atoms introduce a variable gain profile. This profile balances out the dispersion-induced energy losses. The optical soliton exhibits an acceleration profile proportional to the density gradient of the resonant atoms. It maintains its structural stability over propagation distances exceeding 500 m. Numerical validation exercises using split-step Fourier simulations confirm the analytical predictions. The errors between the mathematical models and numerical runs remain bounded below 0.5%. These analytical insights help engineers optimize pulse shaping routines in fiber lasers and improve long-distance optical signal transmission pipelines.

Keywords: Optical solitons; Maxwell-Bloch equations; perturbation theory; resonant media; split-step Fourier method; Raman scattering

Manuscript Timeline: Received: June 14, 2012; Revised: July 20, 2012; Accepted: August 5, 2012; Published: September 11, 2012

Citation: Zhang, S. H., & Patel, N. K. (2012). Optical Soliton Perturbations in Inhomogeneous Inverted Two-Level Laser Media. International Journal of Physics, 3(9), 67–74.

International Journal of Physics | Vol. 3, No. 8, August 2012 | pp. 59–66

DOI: 10.46882/2012/IJP/000028

Research Article

Title: High-Energy Cosmogenic Neutrino Flux Anomalies and Dark Matter Decay Channels

Names of Authors: E. C. Vance¹, F. E. Colombo²

Authors’ Affiliations: ¹Department of Physics, University of California, Berkeley, California 94720, USA; ²Istituto Nazionale di Fisica Nucleare, Sezione di Roma, 00185 Rome, Italy

Abstract: High-energy neutrino telescopes collect vital data that can reveal physics signatures extending beyond the established Standard Model boundaries. This paper examines recent high-energy cosmogenic neutrino flux measurements that show statistical deviations in the energy range spanning 1.0 PeV to 10.0 PeV. We explore a theoretical model where these flux anomalies originate from the slow, non-thermal decay of heavy dark matter particles. These dark matter entities are hypothesized to reside within the galactic halo with an estimated mass scale of M = 20 PeV. Our calculated results match the observed isotropic neutrino background data closely. This match is achieved by setting the dark matter lifetime parameter at approximately τ = 3.5 * 10²⁸ seconds. The primary decay pathway analyzed involves a direct coupling to active neutrinos and standard Higgs bosons. This channel yields a distinctive monochromatic spectral peak superimposed over the continuous astrophysical power-law background spectrum. This specific decay topology produces a distinct flavor ratio balance at Earth detectors. The calculated flavor ratio matches the expected standard statistical proportion of νe : νμ : ντ = 1 : 1 : 1 due to long-baseline neutrino oscillation mechanics. This work establishes tighter constraints on the coupling parameters governing interactions between dark sector matter and standard leptons.

Keywords: Cosmogenic neutrinos; dark matter decay; galactic halo; standard model; neutrino telescope; flavor oscillation

Manuscript Timeline: Received: May 11, 2012; Revised: June 27, 2012; Accepted: July 11, 2012; Published: August 14, 2012

Citation: Vance, E. C., & Colombo, F. E. (2012). High-Energy Cosmogenic Neutrino Flux Anomalies and Dark Matter Decay Channels. International Journal of Physics, 3(8), 59–66.

International Journal of Physics | Vol. 3, No. 7, July 2012 | pp. 51–58

DOI: 10.46882/2012/IJP/000027

Research Article

Title: Magnetic Phase Transitions and Magnetocaloric Effects in Rare-Earth Intermetallic Compounds

Names of Authors: O. B. Ivanov¹, G. W. McKenzie²

Authors’ Affiliations: ¹L.D. Landau Institute for Theoretical Physics, Russian Academy of Sciences, Chernogolovka 142432, Russia; ²School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom

Abstract: Rare-earth intermetallic compounds draw substantial research attention due to their potential application in energy-efficient magnetic refrigeration technology. This investigation models the magnetic phase transitions and characterizes the magnetocaloric effect in Gd5(Si²Ge²-xSnx) compounds where x varies systematically from 0.0 to 0.5. We utilized a comprehensive combination of mean-field theory calculations, Monte Carlo simulations, and direct magnetizations measurements. The empirical data indicate a first-order magneto-structural phase transition shifting toward lower temperatures as the tin (Sn) content increases. For the specific composition where x = 0.1, we recorded a substantial magnetic entropy change value of -14.2 J/(kg*K) under an applied external magnetic field swing of 0 to 5 T. The corresponding adiabatic temperature adjustment was measured directly at ΔT = 5.4 K near the Curie temperature benchmark of 245 K. The calculations reveal that substituting silicon and germanium with tin atoms expands the host crystal lattice volume by 1.2%. This structural expansion modifies the indirect RKKY exchange interaction coupling constants significantly. Consequently, this material tuning effectively optimizes the operating window of the magnetocaloric effect for commercial climate control applications.

Keywords: Magnetocaloric effect; magnetic refrigeration; intermetallic compounds; phase transitions; Monte Carlo simulation; Curie temperature

Manuscript Timeline: Received: April 22, 2012; Revised: June 1, 2012; Accepted: June 15, 2012; Published: July 12, 2012

Citation: Ivanov, O. B., & McKenzie, G. W. (2012). Magnetic Phase Transitions and Magnetocaloric Effects in Rare-Earth Intermetallic Compounds. International Journal of Physics, 3(7), 51–58.

International Journal of Physics | Vol. 4, No. 6, June 2013 | pp. 41–48

DOI: 10.46882/2013/IJP/000038

Research Article

Title: Quantum Efficiency Enhancement in Organic Photovoltaic Cells via Surface Plasmon Resonance of Silver Nanoparticles

Names of Authors: A. M. Fernandes¹, H. K. Gupta²

Authors’ Affiliations: ¹Department of Physics, Federal University of Minas Gerais, Belo Horizonte 31270-901, Brazil; ²Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076, India

Abstract: Low light absorption coefficients within thin active layers limit the conversion efficiency of organic photovoltaic (OPV) devices. This study implements a method to enhance the internal quantum efficiency of bulk-heterojunction OPV cells by incorporating synthesized silver nanoparticles into the buffer layer. The solar cells were fabricated with a standard architecture consisting of indium tin oxide, a hole transport layer, and a blend active layer. We systematically adjusted the diameter of the silver nanoparticles from 20.0 nm to 60.0 nm to tune the localized surface plasmon resonance wavelength. Experimental UV-vis absorption spectra show a significant 35.0% increase in optical absorption within the 450.0 nm to 550.0 nm band when 40.0 nm nanoparticles are introduced. Under simulated solar illumination (AM 1.5G, 100.0 mW/cm²), the optimized plasmonic OPV device yielded a short-circuit current density of 11.42 mA/cm² and an open-circuit voltage of 0.62 V. This resulted in a maximum power conversion efficiency of 5.12%, representing a 28.0% improvement over the control cell. Finite-difference time-domain simulations confirm that the performance boost stems from strong near-field electromagnetic field enhancement and forward scattering. These results show that integrating plasmonic nanostructures is an effective approach for developing high-efficiency, thin-film organic solar cells.

Keywords: Organic photovoltaics; silver nanoparticles; localized surface plasmon resonance; light harvesting; power conversion efficiency; finite-difference time-domain

Manuscript Timeline: Received: March 02, 2013; Revised: April 14, 2013; Accepted: May 02, 2013; Published: June 12, 2013

Citation: Fernandes, A. M., & Gupta, H. K. (2013). Quantum Efficiency Enhancement in Organic Photovoltaic Cells via Surface Plasmon Resonance of Silver Nanoparticles. International Journal of Physics, 4(6), 41–48.