Drift Velocity Research Articles

Electrically tunable graphene terahertz isolator assisted by nonreciprocal plasmon

Abstract Nonreciprocal isolators enable unidirectional light propagation without back reflection. Typical terahertz isolators require magnetic fields to break the time reversal symmetry. Here, we propose a nonmagnetic isolator in the terahertz range based on nonreciprocal graphene plasmon operated in reflection configuration. The bias voltage generates the drift current in graphene which breaks the time-reversal symmetry and induces the nonreciprocal reflection. The isolator device exhibits a high isolation beyond 20 dB with insertion loss less than 3 dB. Moreover, the bandwidth with isolation beyond 20 dB can be broadened by five times to 1.7 THz via tuning the carrier density. The indexes including isolation, insertion loss and bandwidth of the isolator show strong dependence on the drift velocity and mobility of graphene, as well as the air-gap thickness. Our work shows great potential in the burgeoning terahertz technology where nonmagnetic and electrically tunable isolators are still lacking.

Numerical Analysis of the Influence of 2D Dispersion Parameters on the Spread of Pollutants in the Coastal Zone

The transport of pollutants with flowing waters is one of the most common processes in the natural environment. In general, this process is described by a system of differential equations, including the continuity equation, dynamic equations, pollutant transport equations and equations of state. For the analyzed problem of pollutant migration in wide rivers and the coastal zone, a two-dimensional model is particularly useful because the velocity and mass concentration profile is vertically averaged. In this model, taking into account the dispersion flux leads to appropriate equations, and the dispersion process is described by the dispersion tensor. Due to the transverse isotropy of the dispersion process, the coordinates of this tensor are expressed in terms of local dispersion coefficients along the direction of the velocity and in the direction perpendicular to it. Commonly used methods for determining mass dispersion coefficients refer to a gradient velocity profile, typical for rivers. However, in the coastal zone, the velocity profile changes from gradient to drift when shear stresses on the surface caused by the wind begin to dominate. The drift profile also occurs in estuaries, where there is a difference in the density of fresh and salt water. This paper analyzes the numerical solution of the two-dimensional dispersion equations in the coastal zone for the dispersion coefficients adopted for the gradient and drift velocity profiles and then assesses how this affects the final result. Four typical scenarios of pollutant migration in the coastal zone of the Bay of Puck are presented. The calculated dispersion coefficients differ significantly depending on the adopted velocity profile: for the gradient, DLG = 0.17 [m2/s], and for the drift, DLD = 89.94 [m2/s].

An Interpretation Method of Gas–Water Two-Phase Production Profile in High-Temperature and High-Pressure Vertical Wells Based on Drift-Flux Model

With the increasing demand for oil and gas, the depth of some vertical gas wells can reach 6000 m. At this time, the downhole fluid is in a state of high temperature and pressure, and interpretation of the production logging output profile faces the problem of inaccurate production calculations and difficulty judging the water-producing layer. The drift-flux model is usually used to calculate the gas–water two-phase flow. The drift-flux model is widely used to describe the two-phase flow in pipelines and wells because of its accuracy and simplicity. The constitutive correlations used in drift-flux models, which specify the relative motion between phases, have been extensively studied. However, most of the correlations are only extended by laboratory data of small pipe diameters at standard temperature and pressure and do not apply to high-temperature and high-pressure large-diameter gas wells. Therefore, we improved the distribution coefficient and drift velocity of drift-flux correlations in this study for high-temperature and high-pressure gas wells with large pipe diameters. Therefore, this study improved the distribution coefficient and drift velocity of the drift-flux correlations for high-temperature and high-pressure gas wells with large pipe diameters. In practical application, the coincidence rates of gas production and water production calculated by the new drift-flux model were 12.68% and 19.39%, respectively. For high-temperature and high-pressure deep wells, the measurement errors of production logging instruments are significant, and surface laboratory pipelines are challenging to configure and equip with actual high-temperature and high-pressure conditions. Therefore, this study used the method of numerical simulation to study the flow characteristics of the two phases of high-temperature and high-pressure gas and water to provide a basis for identifying the water layer. Combined with the proposed drift-flux correlations and the new method of determining the water-producing layer, a new method of production profile interpretation of high-temperature and high-pressure gas wells is obtained.

The Ion Formation and Quantitative Response of Isoprene, Monoterpenes and Terpenoids in Ion Mobility Spectrometry with Atmospheric-Pressure Chemical Ionization as a Function of Temperature

Ion mobility spectrometry is successfully used as a sensor technology for different applications. A feature of this method is that characteristic ion mobility spectra are obtained for each measurement rather than a sum signal. The spectra result from the different drift velocities of ions in a drift tube at atmospheric pressure. In this study, we investigated the ion formation processes and the quantitative response of isoprene, monoterpenes and monoterpenoids as a function of the temperature of the spectrometer using a tritium ionization source. These substances are important target analytes in atmospheric monitoring and in the analysis of essential oils in different matrices. A drift tube temperature above 120 °C permitted the most sensitive detection of isoprene and monoterpenes, while 80 °C was sufficient for the sensitive detection of most terpenoids. Dimer ions were formed for isoprene over the whole temperature range. The ionization processes of monoterpenes and terpenoids were strongly influenced by the temperature. At temperatures of 40 °C, adduct ions were formed in addition to MH+ ions for monoterpenes. Enhanced temperatures provided a single peak with the same drift time for all monoterpenes. Structural differences influenced the ion formation of terpenoids, and much more complex spectra were obtained. The nature of the product ions changed depending on the temperature.

Estimation of the drift velocity of Equatorial Plasma Bubbles using GNSS and digisonde data

Equatorial Plasma Bubbles (EPBs) play a crucial role in modulating plasma density and electron content within the equatorial ionosphere. In this work, we present an advanced and more robust version of the method developed by \citet{Blanch2018} for detecting EPBs using data from the Global Navigation Satellite System (GNSS). The enhancements introduced in this version significantly improve the EPB detection process, achieving a notable reduction in the false positive rate compared to the previous approach. These refinements include the application of more rigorous statistical techniques to achieve a more accurate fit for the background Total Electron Content (TEC), leading to better characterization of EPBs through improved estimation of disturbance shapes. Applying the capabilities of this new method in a dense network of GNSS sensors, we have developed an interferometric procedure for estimating EPB drift velocities, including both speed and direction. This procedure provides valuable insights into the dynamic behavior of EPBs in the Caribbean region during 2014. Our analysis reveals a predominant eastward propagation pattern of EPBs, closely aligned with modified dip isolines. Furthermore, by integrating the results from the GNSS-based method with quasi co-located digisondes, we applied a conceptual model to estimate EPB velocities along their drift direction. This model has been tested across different geographical sectors and validated through comparisons with results from other independent studies. This cross-verification confirms the reliability of the methods for capturing EPB characteristics. This approach improves the precision of EPB detection and contributes to a deeper understanding of their spatiotemporal dynamics and behavior, providing a valuable framework for characterizing these phenomena in the equatorial ionosphere.

Incoherent scattering ion line spectra of vortex beams by magnetized ionospheric plasma with bi-Maxwellian distribution

Abstract Incoherent scattering theory is one of the important means of plasma parameter diagnosis. The incoherent scattering of vortex beams carrying orbital angular momentum can bring new incremental information to plasma diagnosis. Based on the angular spectrum theory of Bessel vortex beams and the theory of incoherent scattering, this paper studies the incoherent scattering of the ionospheric magnetized plasma to vortex electromagnetic waves under the bi-Maxwellian distribution along the magnetic field drift. The numerical results show that when the angle between the scattering wave vector and the magnetic field direction is small, the ion spectral lines have an obvious frequency shift. When the angle is close to 90°, the ion line spectra produce harmonic oscillation, and the drift speed restrains this oscillation phenomenon. The linear Doppler shift will shift the spectral line as a whole, while the rotating Doppler shift of the vortex beam will weaken the spectral line oscillation. This work may provide a possibility for further research on the scattering of vortex beams by magnetized plasma and the development of ionospheric plasma irregularities parameter inversion.

Transverse manipulation of an electron beam by circularly polarized Laguerre-Gaussian modes

This study investigates the modulation of the azimuthal velocity of electrons in an electron beam using circularly polarized Laguerre-Gaussian (LG) modes. The finite-difference time-domain particle-in-cell (FDTD-PIC) method is employed for this purpose. After obtaining the orbital and spin angular momenta of the LG mode, the distribution of the electrons’ azimuthal velocity (i.e., the distribution of angular momentum) exhibits 3D spiral patterns. The number of strands in these spirals corresponds to the sum of the quantum numbers associated with the orbital and spin angular momenta of the LG mode. Furthermore, these spiral patterns rotate in the same direction as the LG mode and move along with it. In contrast, the electrons in the beam undergo a gyromotion along their forward direction (without the application of an external magnetic field in this study). The rotation direction of the electrons is primarily determined by the sign of their initial azimuthal velocity after acquiring angular momenta from the LG mode. Additionally, all electrons share the same gyrofrequency, which is much lower than the LG mode’s frequency. This gyrofrequency can be manipulated by the frequency, electric field strength, and beam waist size of the LG mode. Moreover, increasing the electric field strength allows a larger-current electron beam to be confined within the LG mode. The gyromotion and confinement effects of electrons are primarily due to the transverse ponderomotive force generated by the LG mode. It is demonstrated that the manipulation of an electron beam can be realized by using circularly polarized LG modes.

A Study on Optimal Placement of Underwater Target Position Tracking System considering Marine Environment

The tracking accuracy of buoy-based LBL(Long Base Line) systems can be significantly influenced by sea environmental conditions. Particularly, the position of buoys that may have drifted due to sea currents. Therefore it is necessary to predict and optimize the drifted-buoy positions in the deploying step. This research introduces a free-drift simulation model using ocean data from the European CMEMS. The simulation model’s predictions are validated by comparing them to actual sea buoy drift tracks, showing a substantial match in averaged drift speed and direction. Using this drift model, we optimize the initial buoy layout and compare the tracking performance between the center hexagonal layout and close track layout. Our results verify that the optimized layout achieves lower tracking errors compared to the other two layout.

COMPLEX TECHNOLOGY OF THE CLEANING OF AGGLOMERATION GASES FROM DUST AND HARMFUL GASES WITH OBTAINING A GOOD PRODUCT

The purpose of the work is to improve the design of the dust-catching device of the sintering machine, to increase the efficiency of catching charged dust particles in laminar layers near the precipitating elements, the configuration and location of the elements of the precipitating elements, to establish the dependence of the effective (calculated) drift speed of charged dispersed particles on the speed of the medium being cleaned, with classical the process of electrogas purification and the combined flow of gases in electrofilters. It was established that the combined movement of gases in a modular unit ensures the charging of the entire population of dust particles to the limit values ​​by organizing a highly turbulent flow and keeping dust particles in the zones with the greatest tension in the corona charge covers, as well as effective trapping of charged dust particles in laminar layers near the precipitating elements . Mathematical modeling of the deposition block was carried out in order to optimize the configuration. The main dependences of the number and mutual location of precipitating elements to ensure maximum dust deposition were established. Studies of gas medium velocity spectra in models of new electrostatic precipitators have been carried out. The optimal live cross-sections of the aerodynamic partitions are determined to ensure favorable conditions for charging suspended particles and uniform distribution of the cleaned flow through the catching holes. The MV-2 modular type electric gas purification device with a capacity of 30 thousand nm3/h has been developed, based on innovative developments in the field of KEIT (combined electro-ion gas purification technology) in the field of conversion and control of cascade energy and aerodynamics of turbulent and laminar flows during inertial deposition dispersed suspension of flue gases. An apparatus for cleaning gases from a sinter machine with a capacity of up to 400,000 nm3/h is proposed. with an efficiency of 99 %, for replacing existing equipment (multicyclones). "MV-2JS" electric device was developed. This is a plasma-catalytic reactor, which allows you to produce the necessary amount of ozone in a low-cost way to oxidize the harmful components (SO2, NOx, CO) of the outgoing gases. The use of this device allows, in addition to the cleaning of flue gases from harmful gas impurities, to obtain commercial products (fertilizers, gypsum, sulfuric acid, etc.) at the output and to completely get rid of solid and liquid waste during gas desulfurization.

Numerical simulation of [formula omitted] drift effects on fueling pellet ablation and transport in EAST

The pellet injection technique is considered a primary method for fueling future fusion devices. The inclusion of the E×B particle drift effect is essential in the simulation to reproduce the actual particle transport of injected pellets and the changes in energy flux in the divertor region. In this study, the dynamic neutral gas shield model is coupled with the edge plasma code SOLPS-ITER, utilizing initial data referencing from EAST experiments. The investigation focuses on the effects of the E×B drift on the ablation of injected fuel pellets, particle transport, and heat flux in the divertor region. The simulation results show that the poloidal component of the E×B drift velocity causes the dispersion of ions and electrons produced by the ionization of ablated atoms from the pellet, which would accumulate around the pellet if the E×B drift is not considered. Under unfavorable toroidal magnetic field conditions, a significant accumulation of ions ▪ produced by the ionization of D atoms introduced by the injected pellet is observed near the outer target. Moreover, both the change and duration of energy flux variations in the outer target region are higher when compared with the case without E×B drift.

Observation of sporadic [formula omitted] layer altitude partially modulated by the Traveling Ionospheric Disturbances at high latitudes over Zhongshan station

At Zhongshan (69° S, 76° E) Antarctica we investigate the sporadic E (Es)-layer virtual height modulation, observed by an ionosonde, during the passage of the Medium-Scale Traveling Ionospheric Disturbances (MSTIDs), observed by a SuperDARN radar. Two events were identified, on 04 October 2011 at 07:00 - 12:00 UT and 29 February 2012 at 00:00 - 04:00 UT with periods of ∼15.0 and ∼12.0 min, respectively. The magnitude of average height modulation of the Es-layer was ∼3.7 to ∼17.1 and ∼0.5 to ∼7.3 km, respectively, with the same periods as the MSTIDs. Ray tracing during the events shows that the likely MSTID propagation was up to ∼300 km in the ionospheric F-region. The computed ion vertical drift velocity using SuperDARN radar and magnetometer data, and Es-layer altitude modulation observed by the ionosonde have moderate to strong positive correlation of 0.71 ± 0.22 and 0.51 ± 0.16, respectively. We show that the MSTIDs polarization electric field, which is mapped down from the F-region along the near-vertical magnetic field, moderately contributes to the modulation of the Es layer altitude via the E×B drift mechanism.

ARTEMIS Observations of Lunar Crustal Field‐Solar Wind Interaction and Impact on Reflected Plasma Under Weak Radial IMF

AbstractMagnetic anomalies or crustal fields are frequently observed close to the lunar surface, yet their interaction with the ambient plasma is not fully understood. Utilizing data from the Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) spacecraft, we perform case studies of such interactions under radial, weak interplanetary magnetic field. Our analysis shows that while the lunar crustal field direction did not directly affect the velocity and density of reflected ions, it locally increased their pitch angles, favoring growth of ultralow‐frequency waves. Additionally, we find that while the solar wind ions were demagnetized, retaining a nearly constant velocity, the magnetized electrons acquired significant perpendicular drift velocity due to the crustal field, resulting in a Hall current. This current altered the field strength near the lunar surface. The calculated loss cone angles of electrons reflected by the near‐surface field estimated from the Hall current are consistent with observations, suggesting that the crustal field was dominated by the Hall magnetic field. Our study advances our understanding of how lunar crustal fields interact with the solar wind and modify the nearby reflected plasma.

Observations of Preferential Heating and Acceleration of α-particles in the Young Solar Wind by Parker Solar Probe

Remote sensing observations of the nascent solar wind in the solar corona imply that heavy ions are often faster and hotter than the plasma protons. In situ observations of the near-Earth solar wind with low collisional age show that hotter and faster states of heavy ions usually do not occur at the same time: heavy ions are either faster or hotter than the protons. This discrepancy highlights the need to understand the competing effects of heating, acceleration, Coulomb collisions, and instabilities on heavy ions in the inner heliosphere, from the solar corona to Earth. The Parker Solar Probe (PSP) is currently the closest spacecraft to the Sun and is anticipated to cross the outer boundary of the preferential heating and acceleration zone. Using in situ measurements from PSP, we find that larger drift speeds between α-particles and protons (V α p ) correspond to larger α-to-proton temperature ratios ( TαTp ) in the young solar wind close to the corona. This observation differs from in situ observations farther from the Sun (e.g., with Helios and Wind at 0.3–1 au). We believe that this difference is related to the speed of the solar wind, as well as the distance from the Sun. The anti-correlation between V α p and TαTp in fast wind away from the Sun is potentially related to the energy transfer from the drift kinetic energy of α-particles to proton thermal energy due to drift instabilities. In the young slow wind, heavy ions exhibit signs of both preferential heating and preferential acceleration, but are not affected much by drift instabilities. We identify the outer boundary of the preferential heating and acceleration zone for heavy ions in the young slow wind to be at a distance of around 0.16 au, beyond which the effects of Coulomb collisions weaken the effects of preferential heating and acceleration.

Mechanism of a stepped leader in a negative lightning

The mechanism of a stepped leader not related to processes in the cloud is considered. The average leader speed is determined by the formation of a channel due to heating of one of the space stems in the electric field of the streamer corona. If the drift speed of the electrons in the formed channel is higher than the leader propagation speed, a drift wave arises which catches up with the boundary of the streamer zone. The electric field growth leads to a formation of the stepped leader. The mechanism is realized in case of a negative leader. Realism of this scenario has been checked by numerical simulations. For the negative leader the formation of the step with parameters close to those for natural leaders has been obtained. The estimated maximum speed of the electron drift at the stage of channel formation, which exceeds the negative leader propagation speed observed in the experiments, counts in favor of the above ideas.

Low-temperature electron transport in [110] and [100] silicon nanowires: a DFT-Monte Carlo study

The effects of very low temperature on the electron transport in a [110] and [100] axially aligned unstrained silicon nanowires (SiNWs) are investigated. A combination of semi-empirical 10-orbital tight-binding method, density functional theory and Ensemble Monte Carlo (EMC) methods are used. Both acoustic and optical phonons are included in the electron-phonon scattering rate calculations covering both intra-subband and inter-subband events. A comparison with room temperature (300 K) characteristics shows that for both nanowires, the average electron steady-state drift velocity increases at least 2 times at relatively moderate electric fields and lower temperatures. Furthermore, the average drift velocity in [110] nanowires is 50 percent more than that of [100] nanowires, explained by the difference in their conduction subband effective mass. Transient average electron velocity suggests that there is a pronounced streaming electron motion at low temperature which is attributed to the reduced electron-phonon scattering rates.

A high-resolution photoelectron spectroscopic and computational study of TaX− (X = C, N, O)

We report on the high-resolution photoelectron spectroscopy of diatomic molecules TaX− (X = C, N, O) anions using a cryogenic ion trap combined with the slow electron velocity imaging (cryo-SEVI) method. We determined the electron affinities of TaC, TaN, and TaO to be 2.098(2), 1.576(2), and 1.069(2) eV, respectively. In addition, the electron affinities of TaX molecules were calculated using the CCSD(T) method with the complete basis sets. To interpret the complicated photoelectron spectra, we predicted the excited states of TaX molecules using the MRCI + Q method, accounting for the spin–orbit coupling effects. Several new excited states of these molecules were observed.

Plasma potential shaping using end-electrodes in the Large Plasma Device

We perform experiments in the Large Plasma Device at the University of California, Los Angeles, studying how different end-electrode biasing schemes modify the radial potential profile in the machine. We impose biasing profiles of different polarities and gradient signs on a set of five concentric electrodes placed 12 m downstream from the plasma source. We find that imposing concave-down profiles (negative potential radial gradient) on the electrodes creates radial potential profiles halfway up the plasma column that are comparable to those imposed on the electrodes and a few electron temperature in height, regardless of the biasing polarity. On the other hand, imposing concave-up profiles (positive potential radial gradient) leads to non-monotonic radial potential profiles. This observation can be explained by the current drawn through the electrodes and the parallel plasma resistivity, highlighting their important role in controlling the rotation of plasma. Concave-down plasma potential profiles, obtained by drawing electrons on the axis, are predicted to drive azimuthal drift velocities that can approach significant fractions of the ion sound speed in the central region of the plasma column.

Dynamics of Viscous Jeffrey Fluid Flow Through Darcian Medium With Hall Current and Quadratic Buoyancy.

This contribution builds on existing studies by investigating the dynamics of Hall current in Jeffery fluid under radiative heat, convective boundary conditions, Joule heating, and Darcy dissipation. Hall current, an important phenomenon in engineering applications involving strong magnetic fields, highlights the impact of electromagnetic force in examining blood flow rate, determining charge drift velocity, density, and movement, and is used in power generators and high-voltage transformers. This analysis incorporates dissipative and thermal radiative heat and employs the effects of Hall current and Joule heating, resulting from porous medium resistance, to derive the partial differential equationsgoverning the dynamic systems. These equationsare then reduced to ordinary differential equations (ODEs) through similarity variables. The Galerkin weighted residual method (GWRM) is employed to examine the dynamics of Hall current and quadratic thermal buoyancy, shedding light on the thermal properties and hydrodynamics of Jeffrey fluid convection within a porous medium. The analysis reveals that in the presence of an applied magnetic field, the contribution of Hall current to flow and heat dynamics induces a magnetic force that enhances fluid motion and negatively impacts heat energy patterns. The imposition of dissipative heat physically increases the fluid temperature, owing to an increase in buoyancy current. The occurrence of thermal radiation, Hall current, viscous dissipation, and Joule heating can efficiently optimize the rate of heat transfer and shear stress. Moreover, the tabular results indicate that Jeffrey fluid, exhibiting higher relaxation time, will experience a lower friction coefficient and heat transferrate.

Impact of electron velocity modulation on microwave power performance for AlGaN/GaN HFETs

In this study, we demonstrate the effects of electron velocity modulation (Δve/ΔVgs) on the microwave power performance for AlGaN/GaN HFETs. In order to conduct the experiments, AlGaN/GaN HFETs with gate lengths ranging from 500 to 80 nm were fabricated. Electron transport was investigated by coupling a drift-diffusion solver with the Monte Carlo method. As gate lengths (Lg) varied from 500 to 200 nm, the increased polarization Coulomb field scattering led to an increase in Δve/ΔVgs and the stronger electric field (E) increased ve and enhanced the transconductance (gm), which in turn led to a greater power gain (Gp) in the HFETs. The higher power output (Pout) was also due to the increased ve that boosted the saturated output current (Ids,sat). The unique phenomenon that occurs from electron velocity modulation of AlGaN/GaN HFETs at electron densities (ns) < 3.42 × 1012cm−2 can be used as an effective mechanism to enhance the power gain of AlGaN/GaN HFETs.

A single-particle energy-conserving dissipative particle dynamics approach for simulating thermophoresis of nanoparticles in polymer networks.

The transport of nanoparticles in polymer networks has critical implications in biology and medicine, especially through thermophoresis in response to temperature gradients. This study presents a single-particle energy-conserving dissipative particle dynamics (seDPD) method by integrating a single-particle model into the energy-conserving DPD model to simulate the mesoscopic thermophoretic behavior of nanoparticles in polymer matrices. We first validate the newly developed seDPD model through comparisons with analytical solutions for nanoparticle viscosity, thermal diffusivity, and hydrodynamic drag and then demonstrate the effectiveness of the seDPD model in capturing thermophoretic forces induced by temperature gradients. The results show that nanoparticles driven by the Soret forces exhibit unique transport characteristics, such as drift velocity and diffusivity, leading to a significant acceleration of nanoparticle diffusion in the polymer network, which has been known as the giant acceleration of diffusion. Quantifying how nanoparticles move in flexible polymer networks sheds light on the interaction dynamics of nanoparticles within polymer networks, providing insight into nanoparticle behavior in complex environments that could be leveraged in various applications from drug delivery to material design.