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Appearance of Negative Differential Conductivity in Graphene Nanoribbons at High-Harmonics

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Graphene 2013年第2期2卷 61-65页

作者： musah rabiu Samuel Y. Mensah Sulemana S. Abukari Department of Applied Physics University for Development Studies Navrongo Ghana Physics Department Center for Laser and Fiber Optics University of Cape Coast Cape Coast Ghana

We theoretically study current dynamics of graphene nanoribbons subject to DC-AC driven fields. We show that graphene exhibits negative differential conductivity (NDC) at high-harmonics. NDC occurs in the neighborhood where a constant electric field is equal to amplitude of ac field. We also observe NDC at both even and odd harmonics and at wave mixing of two commensurate frequencies. The even harmonics are more pronounced than the odd harmonics. A possible use of the present method for generating terahertz frequencies at even harmonics in graphene is suggested.

关键词： Graphene Nanoribbon Energy Spectrum Electronic Conductivity Terahertz Negative Differential Conductivity

Generation and Propagation of Ultrasonic Waves in Piezoelectric Graphene Nanoribbon

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Open Journal of Acoustics 2013年第3期3卷 38-42页

作者： musah rabiu Samuel Y. Mensah Sulemana S. Abukari Matthew Amekpewu Baah Sefa-Ntiri Anthony Twum University for Development Studies Faculty of Applied Science Department of Applied Physics Navrongo Ghana University of Cape Coast Center for Laser and Fiber Optics Physics Department Cape Coast Ghana

Generation and propagation of ultrasonic waves in single layer Graphene Nanoribbon is studied using semi-classical approach. When piezoelectric Graphene Nanoribbon (GNR) is exposed to time varying light beam, ultrasonic waves are produced which propagate in the medium. At low frequencies, we observed oscillations of the ultrasonic observables, velocity change and attenuation which are characteristics of massless Dirac fermions in graphene. Exploiting this oscillatory behavior, we estimate graphene’s electronic mobility to be around . Propagating ultrasonic waves can be amplified, depending on the electric field amplitude. Specifically, amplification occurs when drift velocity exceeds sound velocity. This scheme can be employed for efficient ultrasonic amplifier device operation.

关键词： Current Density Negative Differential Conductivity Commensurable Frequencies

External Electric Field Effect on Electrons Transport in Carbon Nanotubes

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World Journal of Condensed Matter Physics 2013年第4期3卷 169-172页

作者： Sulemana S. Abukari Samuel Y. Mensah musah rabiu Kofi W. Adu Natalia G. Mensah Kwadwo A. Dompreh Anthony Twum Matthew Amekpewu Department of Applied Physics University for Development Studies Navorongo Ghana Department of Mathematics University of Cape Coast Cape Coast Ghana Department of Physics Laser and Fibre Optics Centre University of Cape Coast Cape Coast Ghana Department of Physics The Pennsylvania State University Altoona USA Materials Research Institute The Pennsylvania State University University Park USA

We consider a simple model of carbon nanotubes (CNTs) subject to external electric field E(t). Using a tight-binding approximation for the description of energy bands of CNTs, together with the standard Boltzmann transport equation and constant relaxation time, we predict the effect of self-induced transparency and absolute negative conductivity. The predicted effects may be useful in diagnostics of carbon nanotubes as well as in the amplification and efficiency conversion of electromagnetic signals.

关键词： Carbon Nanotubes Electric Field Electric Current Density Negative Differential Conductivity

High-Frequency Electric Field Induced Nonlinear Electron Transport in Chiral Carbon Nanotubes

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World Journal of Condensed Matter Physics 2015年第4期5卷 294-300页

作者： Sulemana S. Abukari Samuel Y. Mensah musah rabiu Kofi W. Adu Natalia G. Mensah Anthony Twum Alfred Owusu Kwadwo A. Dompreh Patrick Mensah-Amoah Matthew Amekpewu Department of Physics Laser and Fibre Optics Centre University of Cape Coast Cape Coast Ghana Department of Applied Physics University for Development Studies Navorongo Ghana Department of Physics The Pennsylvania State University-Altoona Altoona USA Materials Research Institute The Pennsylvania State University University Park USA Department of Mathematics University of Cape Coast Cape Coast Ghana

We investigate theoretically the high frequency complex conductivity in carbon nanotubes that are stimulated axially by a strong inhomogeneous electric field of the form E(t)=E0+E1cos(ωt). Using the kinetic approach based on Boltzmann’s transport equation with constant relaxation time approximation and the energy spectrum of the electron in the tight-binding approximation, together with Bhatnagar-Gross-Krook collision integral, we predict high-frequency nonlinear effects along the axial and the circumferential directions of the carbon nanotubes that may be useful for the generation of high frequency radiation in the carbon nanotubes.

关键词： Carbon Nanotubes High Frequency Electric Field Electric Current Density Complex Conductivity

Domain Suppression in the Negative Differential Conductivity Region of Carbon Nanotubes by Applied AC Electric Field

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World Journal of Condensed Matter Physics 2012年第4期2卷 274-277页

作者： Sulemana S. Abukari Samuel Y. Mensah Kofi W. Adu Natalia G. Mensah Kwadwo A. Dompreh Anthony Twum Chales L. Y. Amuah Matthew Amekpewu musah rabiu Department of Applied Physics University for Development Studies Navorongo Ghana Department of Physics Laser and Fibre Optics Centre University of Cape Coast Cape Coast Ghana Department of Physics The Pennsylvania State University Altoona USA Materials Research Institute The Pennsylvania State University University Park USA National Centre for Mathematical Sciences Ghana Atomic Energy Commission Accra Ghana Department of Mathematics University of Cape Coast Cape Coast Ghana

We study theoretically the electron transport properties in achiral carbon nanotubes under the influence of an external electric field E(t) using Boltzmann’s transport equation to derive the current-density. A negative differential conductivity (NDC) is predicted in quasi-static approximation i.e., ωτ 0 is equal to the amplitude of the AC electric field E1. The peak of the NDC intensity occurs at very weaker fields than that of superlattice under the same conditions. The peak intensity decreases and shifts to right with the increase in the amplitude of the ac field. This mechanism suppresses the domain formation and therefore could be used in terahertz frequency generation.

关键词： Carbon Nanotubes Negative Differential Conductivity and Generation of Terahertz Radiation

Anomalous Viscosity of Vortex Hall States in Graphene

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Journal of Applied Mathematics and Physics 2015年第12期3卷 1654-1661页

作者： rabiu musah Samuel Y. Mensah Ibrahim Y. Seini Sulemana S. Abukari Department of Applied Mathematics Faculty of Mathematical Sciences University for Development Studies Navrongo Campus Upper East Ghana Department of Physics Laser and Fiber Optics Center University of Cape Coast Cape Coast Ghana

We study temperature effect on anomalous viscosity of Graphene Hall fluid within quantum many-vortex hydrodynamics. The commonly observed filling fraction, in the range is considered. An expression for anomalous viscosity dependent on a geometric parameter-Hall expansion coefficient is obtained at finite temperatures. It arises from strained induced pseudo-magnetic field in addition to an anomalous term in vortex velocity, which is responsible for renormalization of vortex-vortex interactions. We observed that both terms greatly modify the anomalous viscosity as well as an enhancement of weakly observed v fractions. Finite values of the expansion coefficient produce constant and infinite viscosities at varying temperatures. The infinities are identified as energy gaps and suggest temperatures at which new stable quantum hall filling fractions could be seen. This phenomenon is used to estimate energy gaps of already measured fractional Quantum Hall States in Graphene.

关键词： Euler Hydrodynamics Quantum Hall Fluid Vortex Dynamics Fractional Quantum Hall Effect Anomalous Viscosity Hall Expansion Coefficient

Assessment of the performance of the TOPGNSS and ANN-MB antennas for ionospheric measurements using low-cost u-blox GNSS receivers

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Geodesy and Geodynamics 2024年第3期15卷 291-301页

作者： Daniel Okoh Aderonke Obafaye Oluwakemi Dare-Idowu Babatunde rabiu Anton Kashcheyev Claudio Cesaroni John Bosco Habarulema Bruno Nava United Nations African Regional Centre for Space Science and Technology Education-English(UN-ARCSSTE-E) Obafemi Awolowo University CampusIle IfeNigeria National Institute for Geophysics and Volcanology(INGV) 00143 RomeItaly Institute for Space Science and Engineering African University of Science and TechnologyAbujaNigeria University of New Brunswick FrederictonCanada South African National Space Agency(SANSA) P.O Box 32Hermanus 7200South Africa Department of Physics and Electronics Rhodes University6140 MakhandaSouth Africa The Abdus Salam International Centre for Theoretical Physics Strada Costiera11I-34151 TriesteItaly

Low-cost GNSS receivers have recently been gaining reliability as good candidates for ionospheric studies. In line with these gains are genuine concerns about improving the performance of these receivers. In this work, we present a comprehensive investigation of the performances of two antennas(the u-blox ANN-MB and the TOPGNSS TOP-106) used on a low-cost GNSS receiver known as the u-blox ZED-F9P. The two antennas were installed on two identical and co-located u-blox receivers. Data used from both receivers cover the period from January to June 2022. Results from the study indicate that the signal strengths are dominantly greater for the receiver with the TOPGNSS antenna than for the receiver with the ANN-MB antenna, implying that the TOPGNSS antenna is better than the ANN-MB antenna in terms of providing greater signal strengths. Summarily, the TOPGNSS antenna also performed better in minimizing the occurrence of cycle slips on phase TEC measurements. There are no conspicuous differences between the variances(computed as 5-min standard deviations) of phase TEC measurements for the two antennas, except for a period around May-June when the TOPGNSS gave a better performance in terms of minimizing the variances in phase TEC. Remarkably, the ANN-MB antenna gave a better performance than the TOPGNSS antenna in terms of minimizing the variances in pseudorange TEC for some satellite observations. For precise horizontal(North and East) positioning, the receiver with the TOPGNSS antenna gave better results, while the receiver with the ANN-MB antenna gave better vertical(Up) positioning. The errors for the receivers of both antennas are typically within about 5 m(the monthly mean was usually smaller than 1 m) in the horizontal direction and within about 10 m(the monthly mean was usually smaller than 4 m) in the vertical direction.

关键词： GNSS Ionosphere Low-cost Antenna TOPGNSS U-blox

Direct Current Generation in Carbon Nanotubes by Terahertz Field

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World Journal of Condensed Matter Physics 2016年第1期6卷 56-62页

作者： Sulemana S. Abukari Frederick Sam Samuel Y. Mensah Natalia G. Mensah rabiu musah Anthony Twum Patrick M. Amoah Alfred Owusu Department of Physics Laser and Fibre Optics Centre University of Cape Coast Cape Coast Ghana Department of Mathematics University of Cape Coast Cape Coast Ghana Department of Applied Physics University for Development Studies Navorongo Ghana

We report on a theoretical investigation of a direct current generation in carbon nanotubes (CNTs) that are stimulated axially by terahertz (THz) field. We consider the kinetic approach based on the semiclassical Boltzmann’s transport equation with constant relaxation time approximation, together with the energy spectrum of an electron in the tight-binding approximation. Our results indicate that for strong THz-fields, there is simultaneous generation of DC current in the axial and circumferential directions of the CNTs, even at room temperature. We found that a THz-field can induce a negative conductivity in the CNTs that leads to the THz field induced DC current. For varying amplitude of the THz-field, the current density decreases rapidly and modulates around zero with interval of negative conductivity. The interval decreases with increasing the amplitude of the THz-field. We show that the THz-field can cause fast switching from a zero DC current to a finite DC current due to the quasi-ballistic transport, and that electron scattering is a necessary condition for switching.

关键词： Carbon Nanotubes Terahertz Fields DC Voltage Generation Negative Conductivity Electron Scattering Ballistic Transport

Activated Protein C Resistance in Patients with Pre-Eclampsia in Lagos, Nigeria

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Open Journal of Obstetrics and Gynecology 2024年第4期14卷 575-590页

作者： Nosimot O. Davies Titilope A. Adeyemo Sunday I. Omisakin Akaninyene A. Udousoro Kabiru A. rabiu Department of Haematology and blood Transfusion College of Medicine University of Lagos Lagos Nigeria Department of Obstetrics and Gynaecology College of Medicine University of Lagos Lagos Nigeria Department of Obstetrics and Gynaecology Lagos State University Teaching Hospital Lagos Nigeria Department of Obstetrics and Gynaecology College of Medicine Lagos State University Lagos Nigeria

Background: Preeclampsia is reported to complicate 2% - 8% of pregnancies globally and is an important cause of maternal and perinatal morbidity and mortality. The aetiology and pathogenesis are still poorly understood and substantial improvement has not been made in the prediction, prevention and treatment of the disease. Objective: To compare the frequency of activated protein C resistance (APC-R) in patients with pre-eclampsia to that of normotensive pregnant women and to determine the correlation between activated protein ratio (APC-ratio) and the severity of pre-eclampsia. Methodology: A cross-sectional study was carried out in 100 pre-eclamptic patients and 100 normotensive pregnant controls. The APC-ratio was determined using the modified activated partial thromboplastin time. Study participants with APC-ratio of less than 2.0 were defined as having APC-R. Data was analyzed using SPSS version 22.0. Results: Mean APC-ratio was significantly lower in pre-eclamptics (2.89 ± 1.70) compared to normotensive pregnant women (3.57 ± 1.06) (p = 0.0008) and the levels were also higher in mild (2.95 ± 1.15) compared to severe pre-eclamptics (2.62 ± 1.14). The frequency of APC-R was 26% among women with pre-eclampsia compared to 4% among normotensive controls (p = 0.000). Among 100 pre-eclamptic women 7 (21.2%) out of 33 with mild pre–eclampsia had APC-R, while 19 (28.4%) out of 67 with severe pre-eclampsia had APC-R. APC-ratio had a significant negative correlation with mean arterial blood pressure (r = −0.324;p = 0.000) and proteinuria (r = −0.379;p = 0.000) among study participants. Conclusion: The frequency of activated protein c resistance is significantly higher in pre-eclamptics compared to normotensive pregnant women and this is more pronounced in those with severe pre-eclampsia compared with those with mild disease. APC-R may therefore be used as a marker of severity in the disease.

关键词： Activated Protein C Resistance Activated Protein C Ratio Pre-Eclampsia