Carrier Velocity Research Articles

Research on Inertial Isolation Rotation Modulation of Dual-Axis Inertial Navigation Based on Multi-Error Coupling Characteristics

Currently, research on the rotational modulation of dual-axis inertial navigation for isolated carrier motion does not provide sufficient solutions for the compensation of the gyroscope scale factor error caused by the Earth’s rotation. Moreover, it is primarily applied to ships with low maneuverability and has not yet been implemented in the field of pure inertial guidance weapons. A dual-axis inertial isolation rotation modulation method is proposed to address this issue, taking into account the application characteristics of long-endurance guided weapons. An analysis of the system error characteristics under the coupling of multiple error sources acting on IMU was conducted, and it was found that the angular velocity of the inertial isolation carrier can significantly reduce the output error of the IMU. A dual-axis inertial isolation shaft system installation error compensation algorithm was designed, and an improvement was made based on the traditional sixteen-sequence rotation scheme to compensate for the projection components of the Earth’s rotation and carrier motion on the inner and outer frame rotation axes, achieving the inertial isolation rotation modulation function of dual-axis inertial navigation. Based on the attitude changes in long-range guided weapons, Monte Carlo simulation verification was conducted, and the results showed that this scheme can improve inertial navigation accuracy by 10% to 20%.

In-Plane Anisotropy in van der Waals NiTeSe Ternary Alloy.

The anisotropic properties of materials profoundly influence their electronic, magnetic, optical, and mechanical behaviors and are critical for a wide range of applications. In this study, the anisotropic characteristics of Ni-based van der Waals materials, specifically NiTe2 and its alloy NiTeSe, utilizing a combination of comprehensive scanning tunneling microscopy (STM), angle-resolved photoemission spectroscopy (ARPES), and density functional theory (DFT) calculations, are explored. Unlike 1T-NiTe2, which exhibits trigonal in-plane symmetry, the substitution of Te with Se in NiTe2 (resulting in the NiTeSe alloy) induces a pronounced in-plane anisotropy. This anisotropy is clear in the STM topographs, which reveal a distinct linear order of charge distribution. Corroborating these observations, ARPES measurements and DFT calculations reveal an anisotropic Fermi surface centered at the point, which is notably elongated along the ky direction, leading to directional variations in in-plane carrier velocities. Consequently, the Fermi velocity is highest along the kx direction where the linear charge distribution aligns in real space and is lowest along the ky direction. These findings offer valuable insights into the tunability of anisotropic properties in ternary transition metal dichalcogenide systems, highlighting their potential applications in the development of anisotropic electronic and optoelectronic devices.

An investigation into the relationships between technical collision behaviours and physical characteristics in world-class, international female rugby players

ABSTRACT This study first investigated how the probability of winning collision events is affected by technical characteristics among world-class, international female rugby union players, and second, whether enhanced performance of these technical characteristics was related to physical attributes. Carry and tackle events from 16 international matches played by a top-two world ranking team were coded according to technical characteristics and performance outcomes. Binary classification tree models revealed that carry performance was successfully predicted (p < 0.01) by combinations of the variables: carrier velocity at the line, change of direction and straightening angle, leg drive, body mass and system mass (carrier combined with assistance from team-mate(s)). Tackle performance was predicted by combinations of the variables: initial line-speed, tackle direction, tackle type, collision zone entry, body mass, system mass, arm use and leg drive. Cumulative link mixed effects models subsequently revealed that performance increases of ~2% in single-leg isometric squat, counter-movement jump, bench press, single-leg drop jump, 10 m acceleration momentum and velocity, and skinfolds and body mass; were associated with increasing and decreasing likelihoods of superior technical performance, depending on the investigated variable. These findings may increase the precision of practices, physical training and assessment methods, among elite-standard female rugby union players.

Crystal facet regulation enhances the photocatalytic performance for gaseous toluene degradation in BiOCl by promoting the activation of the methyl C(sp3)-H bond

In the field of heterogeneous photocatalysis, the exposure and arrangement of surface atoms exert a profound impact on the reactivity of photocatalysts, dictating the formation of various active sites and reaction pathways. Utilizing crystal facet engineering and surface modification under standard temperature and pressure conditions, we have synthesized BiOCl photocatalysts with an increased exposure of (110) facets, denoted as oxygen vacancy (Ov). The coordination of Bi3+ with thiourea and acetic acid governed the growth direction of BiOCl, inducing lattice distortion andin synergy with ethylene glycol (EG), promoting the preferential formation of Ov. This innovative strategy not only fine-tuned the bandgap of BiOCl by adjusting the conduction band (CB) position but also significantly augmented the migration velocity and separation efficiency of surface charge carriers. In the photocatalytic interaction with toluene, BiOCl demonstrated an enhanced adsorption capacity and a more potent activation of methyl C (sp3)-H bonds, concomitant with the production of substantial superoxide anion radicals (·O2–), which expedited the degradation of toluene. Theoretical computations and detailed characterizations have unveiled the corresponding mechanism and the degradation pathways of toluene at the photocatalytic interface.

Hetero dielectric based dual material gate AlGaN channel MISHEMT for enhanced electrical characteristics

Herein, we report an AlGaN channel metal insulator semiconductor high electron mobility transistor (MISHEMT) in dual material gate (DMG) architecture with two different dielectrics as gate insulator for enhancing the DC performance of the device. The use of a high-k dielectric material as gate insulator below gate metal 1 and a low-k dielectric below gate metal 2 results in significant threshold voltage variation along the channel. This contributes to improved average carrier velocity which in turn results in better current drive. The proposed device exhibits a peak current of 162 mA/mm at zero gate bias, whereas, the DMG and single material gate (SMG) AlGaN channel HEMTs offer currents of 137 mA/mm and 125 mA/mm respectively. The peak transconductances are about 24.66 mS/mm, 23.68 mS/mm and 22.71 mS/mm respectively for the proposed device, DMG and SMG HEMTs. The proposed device reduces the OFF current by an order of 106 compared to that of DMG HEMT.

Theory of quasi-ballistic FET: steady-state regime and low-frequency noise

Abstract We present a theoretical analysis of steady state regimes and low-frequency noise in quasi-ballistic field effect transistors (FETs). The noise analysis is based on the Langevin approach, which accounts for the microscopic sources of fluctuations originating from intrachannel electron scattering. The general formulas for local fluctuations of the carrier concentration, velocity and electrostatic potential, as well as their distributions along the channel, are found as functions of applied voltage/current. Two circuit regimes with stabilized current and stabilized voltage are considered. The noise intensities for devices with different electron ballisticity in the channel are compared. We suggest that the presented analysis allows a better comprehension of the physics of electron transport and fluctuations in quasi-ballistic FETs, improves their theoretical description and can be useful for device simulation and design.

Heat Transfer Performance Factors in a Vertical Ground Heat Exchanger for a Geothermal Heat Pump System

Ground heat pump systems (GHPSs) are esteemed for their high efficiency within renewable energy technologies, providing effective solutions for heating and cooling requirements. These GHPSs operate by utilizing the relatively constant temperature of the Earth’s subsurface as a thermal source or sink. This feature allows them to perform greater energy transfer than traditional heating and cooling systems (i.e., heating, ventilation, and air conditioning (HVAC)). The GHPSs represent a sustainable and cost-effective temperature-regulating solution in diverse applications. The ground heat exchanger (GHE) technology is well known, with extensive research and development conducted in recent decades significantly advancing its applications. Improving GHE performance factors is vital for enhancing heat transfer efficiency and overall GHPS performance. Therefore, this paper provides a comprehensive review of research on various factors affecting GHE performance, such as soil thermal properties, backfill material properties, borehole depth, spacing, U-tube pipe properties, and heat carrier fluid type and velocity. It also discusses their impact on heat transfer efficiency and proposes optimal solutions for improving GHE performance.

Coulomb Contribution to Shockley-Read-Hall Recombination.

A nonradiative recombination channel is proposed, which does not vanish at low temperatures. Defect-mediated nonradiative recombination, known as Shockley-Read-Hall (SRH) recombination, is reformulated to accommodate Coulomb attraction between the charged deep defect and the approaching free carrier. It is demonstrated that this effect may cause a considerable increase in the carrier velocity approaching the recombination center. The effect considerably increases the carrier capture rates. It is demonstrated that, in a typical semiconductor device or semiconductor medium, the SRH recombination rate at low temperatures is much higher and cannot be neglected. This effect renders invalid the standard procedure of estimating the radiative recombination rate by measuring the light output in cryogenic temperatures, as a significant nonradiative recombination channel is still present. We also show that SRH is more effective in the case of low-doped semiconductors, as effective screening by mobile carrier density could reduce the effect.

Evidence of topological surface states with upward band bending in (Bi[formula omitted]Sb[formula omitted])[formula omitted]Te[formula omitted] topological insulator

Significant efforts have been put in the past to minimize the bulk conduction to probe the exotic surface states of topological insulators (TIs), nevertheless, the surface transport is usually hindered by the presence of bulk conduction. The identification and separation of the contribution of topological surface states (TSS) by electrical transport is important for understanding the unique properties of TIs and developing new electronic devices based on these materials. In this report we have studied Shubnikov-de Haas (SdH) oscillations, magneto-resistance (MR) and hall resistivity under high magnetic field in (Bi0.45Sb0.60)2Te3 single crystal grown by modified Bridgman method. Our results show the existence of SdH oscillations which arise from TSS. The obtained Fermi wave vector and Fermi velocity of surface charge carriers show a good agreement with those found by angle-resolved photoemission spectroscopy experiments. Two band model fit to hall resistivity confirms the high mobility of surface bands and low mobility of bulk bands. Band bending effect is investigated which exhibits a depletion of carriers from near by bulk towards the surface states resulting in an upward band bending. A large non-saturating MR (∼347)% is observed as a result of multichannel quantum coherent transport mechanism.

A Compact Model for Carbon Nanotube Field Effect Transistors Incorporating Temperature Effects and Application for Operational Amplifier Design

Semiconducting carbon nanotubes (CNTs), characterized by high carrier mobility and atomic thickness, are considered ideal channel materials for building high-performance and ultimate-scale field-effect transistors for future electronics. Here, we present a data-calibrated compact model of CNT field-effect transistors (CNTFETs) that incorporates temperature effects using the virtual source approach. The proposed model also includes the self-heating effect. Temperature effect was characterized by the influence of temperature on devices, achieved through establishing a temperature-dependent semi-empirical model of carrier mobility and carrier velocity. The proposed model can be easily implemented in a simulator. We designed a two-stage operational amplifier (OPAMP) using the proposed model at 32 nm technology. Compared with other studies, the designed CNTFET-based OPAMP demonstrates lower power consumption, which is beneficial for exploring the biological applications of low-power analog circuits in portable electronic devices. Furthermore, the impact of thermal variations on the design of OPAMP, as per the proposed model, was delineated. Investigations revealed that our circuit maintains a high common mode rejection ratio, which diminishes as the temperature increases and exhibits a moderate gain value that escalates with temperature.

Orbitronics: light-induced orbital currents in Ni studied by terahertz emission experiments

Orbitronics is based on the use of orbital currents as information carriers. Orbital currents can be generated from the conversion of charge or spin currents, and inversely, they could be converted back to charge or spin currents. Here we demonstrate that orbital currents can also be generated by femtosecond light pulses on Ni. In multilayers associating Ni with oxides and nonmagnetic metals such as Cu, we detect the orbital currents by their conversion into charge currents and the resulting terahertz emission. We show that the orbital currents extraordinarily predominate the light-induced spin currents in Ni-based systems, whereas only spin currents can be detected with CoFeB-based systems. In addition, the analysis of the time delays of the terahertz pulses leads to relevant information on the velocity and propagation length of orbital carriers. Our finding of light-induced orbital currents and our observation of their conversion into charge currents opens new avenues in orbitronics, including the development of orbitronic terahertz devices.

Improved reference condition independent method for output performance estimation of PV modules under varying operating conditions

Traditional methods for estimating output property of the photovoltaic (PV) modules are strongly influenced by the selection of reference condition and transforming equations, which determine the calculated physical parameters under real operating conditions. The differences in the carrier transport properties of PV cells under varying operating conditions, such as the number and velocity of minority carriers at the junction edge and their recombination speed, lead to large deviations in the estimation of the output characteristics, especially under low irradiance conditions. To enhance the accuracy of performance estimation, we propose an improved method that is independent of reference condition. This method eliminates the impact of reference conditions and improves the transformation equations under all irradiance levels. Transformation equations of single diode model are established in different irradiance intervals based on the dependence of physical parameter on irradiance and temperature. Especially in the low irradiance range, all effects of irradiance and temperature are considered for each physical parameter in improved transformation equations. To optimize the unknown parameters in the transformation equations, the artificial hummingbird algorithm is used to fit experimental I–V data. The experimental results of six different types PV modules under a wide range of operating conditions are used to verify the effectiveness of the proposed method. The proposed method offers immediate benefits, including independence from reference condition and a more precise relationship between physical parameters and environmental factors in the estimation of PV output properties. Comparing the results to the traditional method by Laudani, the proposed method demonstrates superior capability in estimating I–V characteristics and accurately identifies the maximum power point under various operating conditions, which is of significant value for engineering applications.

Boost in Carrier Velocity Due to Electrostatic Effects of Negative Capacitance Gate Stack

Boost in Carrier Velocity Due to Electrostatic Effects of Negative Capacitance Gate Stack

Origin of linear magnetoresistance in Bi2Te3 topological insulator: Role of surface state and defects

Connection between topological surface states (TSS) and large linear magnetoresistance (LMR) is established in tetradymite Bi2Te3 through tuning of native defects. Thorough analysis of temperature dependent synchrotron X-ray diffraction data quantifies 0-D, 1-D and 2-D defect concentrations. Plausible variation of antisite defects is explained via carrier concentration data. Resistivity data divulge contribution of mixed bulk and surface states in the synthesized samples. High Fermi velocity (∼106 ms−1) and low Fermi energy (∼14 meV) of carriers are obtained. Lower defect concentration sample emerges with high magnetoresistance (MR) and higher mobility. Weak antilocalization (WAL) effect, signature of TSS, is revealed from MR. Large (80%), non-saturating LMR along with ultrahigh mobility (∼1 m2V−1s−1) in Bi2Te3 supports the presence of TSS. Magnetoconductance data are fitted with Hikami-Larkin-Nagaoka equation, obtaining further insight on WAL effect. In addition, extracted parameters like disorder correlation length and coherence length explicate the role of defect density on LMR.

A water track laser Doppler velocimeter for use in underwater navigation

Doppler velocity log (DVL) is usually employed to suppress the divergency of the Strapdown Inertial Navigation System (SINS) in underwater navigation, which is not concealable due to high transmittance for acoustic wave in the water. To conduct underwater navigation task with high concealment, a differential laser Doppler velocimeter (LDV) working at water track mode is integrated with SINS in this paper. The developed LDV measures the advance velocity of the underwater carrier with respect to the surrounding water in underwater navigation scenario with advantages of high concealment, high real-time performance, high update rate, light weight, and small dimension. A dynamic river test was conducted to validate the underwater navigation performance of SINS/LDV integrated system. The experimental results show that during the voyage of 4493s and 5271.8 m, the maximum horizontal positioning errors of the proposed SINS/LDV integrated underwater navigation system is 27.8 m and the relative position error is less than 0.6% with respect to total distance. Therefore, the water track LDV is practical to aid SINS in underwater navigation environment.

Doppler-Shift-Based Sybil Attack Detection for Mobile IoT Networks

The rapid growth of Internet of Things (IoT) networks brings new security challenges for service providers. Due to the resource constrained nature of IoT networks, conventional security methods are not always suitable. Therefore, physical layer security (PLS) has come to the forefront, providing a high level of security while respecting the limited resources of IoTs. A Sybil attack is an insider attack in which a malicious node illegitimately fakes multiple identities, to impersonate legitimate nodes in the IoT network. This study introduces a novel Sybil attack detection scheme for mobile IoT networks that corresponds to time-varying channel. Doppler shift caused by mobile IoT nodes is considered as a novel detection metric to identify available Sybil attacks. The proposed scheme is analyzed by both the true positive rate and the false positive rate, which are mathematically formulated to verify the simulation results. Results demonstrate that as the randomness in the mobility pattern of IoT nodes increases, the proposed detection mechanism based on Doppler shift offers improved identification of the Sybil nodes. Moreover, this work provides receiver operating characteristics (RoCs) for mobile IoT networks to evaluate the effect of different system parameters including carrier frequency, velocity, subcarrier spacing (SCS), and the size of cyclic prefix (CP). The performance of the proposed scheme improves with an increase in both the carrier frequency and velocity, as the Doppler shift becomes more pronounced.

Quantum Transport Properties of Monolayer MoS2, WS2, and Black Phosphorus: A Comparative Study

A comparative study of the performance analysis of dual-gate ballistic monolayer Molybdenum disulfide (MoS2), tungsten disulfide (WS2), and black phosphorus (BP) field-effect transistors (FETs) is presented. A thorough investigation of output and transfer characteristics infers that WS2 FET exhibits better performance as compared to MoS2 and BP. Furthermore, among all three FETs (MoS2, WS2, and BP), the WS2 based FET has a higher carrier velocity. However, variation of gate capacitance (CG) with gate voltage (VG) reflects a very good electrostatic gate control of MoS2 FET due to higher surface charge accumulation. Except for CG, the overall performance of WS2 based FET is better than MoS2 and BP.

Terahertz Generation through Coherent Excitation of Slow Surface Waves in an Array of Carbon Nanotubes

In this paper, we present a scheme for generating terahertz (THz) radiation using an array of parallel double-walled carbon nanotubes (DWCNTs) subjected to a direct current (DC). The longitudinal surface plasmon polaritons (SPPs) in the DWCNTs are coherently excited by two near-infrared laser beams with slightly different frequencies. Through numerical methods, we investigate the spectral characteristics of the SPPs in the presence of a DC current in the nanotubes. We identify high-quality plasmonic modes with a slowdown factor exceeding 300 in the terahertz frequency region. The amplification of these slow SPP modes is facilitated by the DC current in the DWCNTs, fulfilling a synchronism condition. This condition ensures that the phase velocity of the SPPs is closely matched to the drift velocity of the charge carriers, allowing for an efficient energy exchange between the current and the surface electromagnetic wave. The high-frequency currents on the nanotube walls in the DWCNT array enable the emission of THz radiation into the far field, owing to an antenna effect.

Topological nonsymmorphic insulator versus Dirac semimetal in KZnBi

KZnBi was discovered recently as a new three-dimensional Dirac semimetal with a pair of bulk Dirac fermions in contrast to the trivial insulator reported earlier. In order to address this discrepancy, we have performed electronic structure and topological state analysis of KZnBi using the local, semilocal, and hybrid exchange-correlation (XC) functionals within the density functional theory framework. We find that various XC functionals, including the SCAN meta-GGA and hybrid functional with 25% Hartree–Fock (HF) exchange (HSE06), resolve a topological nonsymmorphic insulator state with the glide-mirror protected hourglass surface Dirac fermions. By carefully tuning the XC strength in modified Becke-Johnson (mBJ) potential, we recover the correct orbital ordering and Dirac semimetal state of KZnBi. We further show that increasing the default HF exchange in hybrid functional (40%) can also capture the desired Dirac semimetal state with the correct orbital ordering of KZnBi. The calculated energy dispersion and carrier velocities of Dirac states are found to be in excellent agreement with the available experimental results. Our results demonstrate that KZnBi is a unique topological material where large XC effects are crucial to producing the Dirac semimetal state.

First-principles prediction of intrinsic piezoelectricity, spin-valley splitting and magneto-crystal anisotropy in 2H-VS2 magnetic semiconductor

The piezoelectricity, valley character and magnetic properties of intrinsic ferrovalley 2H-VS2 monolayer are studied using density functional theory. The results suggest that 2H-VS2 monolayer exhibits obvious bipolar magnetic semiconductor characters with Curie temperature (TC) of 278 K, large piezoelectric coefficient d11 of 3.925 pm/V, in-plane magneto-crystal anisotropy (MA) and large valley splitting (ΔKK′) of 75.1 meV. Applying in-plane strain (-6% to 6 %) can well adjust the ΔKK′ and TC from 72 meV to 76.7 meV and from 98 K to 397 K, respectively, resulting an obvious change of electronic structures from bipolar magnetic semiconductor to spin gapless semiconductor phase. The magnetic anisotropy energy (MAE) of 2H-VS2 monolayer firstly increases and then decreases as the strain increases from −6% to 6 %, which mainly originates from the contribution of V dx2-y2 and dxy orbitals. In addition, 2H-VS2 monolayer retains a large valley-contrasting Berry curvature and non-zero anomalous Hall conductivity, indicating that the transverse velocity of carriers is opposite to the effect of in-plane longitudinal electric field. These results suggest that the 2H-VS2 monolayer can become good candidates for the spintronic and valleytronic applications.