Velocity Modulation Research Articles

A seesaw in the South Pacific western and eastern subtropical mode waters

Abstract The South Pacific Western Subtropical Mode Water (WSTMW) and Eastern Subtropical Mode Water (ESTMW) are important components of the subtropical meridional overturning cells. By synthesizing observations, reanalysis products, and eddy-resolving ocean model results, we find an interannual volume seesaw in the WSTMW and ESTMW during 1980-2020. Further analysis of the data and model outputs indicates that this volume seesaw is closely related to the El Niño–Southern Oscillation (ENSO) through its modulation of the Ekman pumping velocity, buoyancy fluxes, and mixed layer depth over the formation regions of the two water masses. This negative correlation between the WSTMW and ESTMW modulates the depth of the permanent pycnocline and directly contributes to the east-west contrast between the two water masses in their core layer properties, especially, during negative phase of the Interdecadal Pacific Oscillation (IPO) since 2000.

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 novel gyroscope based on the slow surface acoustic wave in a phononic metamaterial

Limited to the direct modulation on the surface acoustic wave (SAW) by the rotation, the conventional SAW gyroscopes incur weak Coriolis effects and gyroscopic effects. In this paper, we innovatively utilize a phononic metamaterial (PM) operated at whispering-gallery modes (WGMs) as the vehicle for the Coriolis effect rather than SAW itself. The gyroscopic effects of this PM are investigated, and a new SAW gyroscope is subsequently proposed based on the slow SAW in PM. We show, combining theoretical modeling and finite element method simulation, that the rate of rotation can linearly induce the splitting of WGMs and modulate the phase velocity of SAW down to 4600 m/s (initial phase velocity of 5355 m/s); the direction of rotation results in the chiral symmetry of the PM vibration and the asymmetric distribution of the transmissive SAW. Besides, the proposed SAW gyroscope measures the angular velocity by detecting the phase shift resulting from rotation-dependent slow SAW in PM, obtaining a sensitivity of 0.016 deg/Hz when 50-cell PM. Compared with the existing SAW gyroscopes based on phase velocity modulation, the gyroscopic gain factor in this paper is enhanced by 430–1600 times. This work jumps out of the framework of directly modulating SAW in gyroscopes and provides an innovative scheme of the indirect modulations from the rotation-dependent PM on SAW, showing excellent performance and potential for angular velocity measurement in extreme environments.

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.

Coherent-synchrotron-radiation-free longitudinal shaping of a high-charge electron bunch based on velocity modulation

Beam-driven plasma wakefield acceleration (PWFA) is a promising technique to generate high-energy electron bunches for future electron-positron colliders. Longitudinal shaping of high-charge drive beam is highly desired for achieving high-transformer ratio and loading high-charge witness beam. However, the existing shaping schemes either focused on relatively low-charge bunch shaping or accompanied with significant charge-loss rate (typically over 50%). In this paper, a coherent-synchrotron-radiation-free shaping scheme based on velocity modulation is proposed to generate a high-charge beam with a linearly ramped profile. A >10 kA-peak-current shaped beam containing >50 nC charge with a low charge-loss rate is demonstrated by a start-to-end simulation, and the tunabilities of the beam charge and the peak current, and the robustness of the proposed shaping scheme are also discussed. When loaded by a 3 nC witness beam, a >GV/m accelerating electric field with a transformer ratio larger than 4 can be achieved in a uniform plasma for the shaped drive beam, providing the possibility of high-transformer-ratio PWFA for a high-charge beam. Published by the American Physical Society 2024

Light-regulated soliton dynamics in liquid crystals

Electrically powered solitons are particle-like field configurations in out-of-equilibrium nematics that have garnered significant interest. However, their random generation and lack of controllable motion have limited their application. Here, we present a reconfigurable optoelectronic approach capable of regulating the entire lifecycle of solitons by utilizing multi-strategy digital light projection to construct delicate patterning of virtual electrode. We demonstrate that optically actuated domains with diverse geometry enable the generation of multiple solitons and further allow in-situ formation of individual soliton by matching the light pattern to its dimension. Exquisitely engineered light intensity of patterns facilitates modulation of soliton velocity and transformation of propagating direction. The utilization of a light-guided channel enables the on-demand control of soliton trajectories along customized paths. Furthermore, dynamic light patterns that vary in space and time allow for collective motion such as migration, mimicking phototaxis in biological systems. This reconfigurable manipulation strategy, grounded in the photoconductive effect, proves highly versatile and effective in directing soliton dynamics, heralding the potential for their programmable control and offering a significant advantage in multitasking scenarios.

Influence of heart failure (HF) comorbidity in chronic obstructive pulmonary disease (COPD) and isolated forms of HF and COPD on cardiovascular function during hospitalization

IntroductionCoexistence of chronic obstructive pulmonary disease(COPD) and heart failure(HF) is associated with systemic inflammation, myocardial injury, and arterial stiffening, impacting cardiovascular risk and prognosis in patients. Arterial stiffness, reduced nitric oxide synthesis, and altered cardiac autonomic control further link COPD and HF pathophysiology, emphasizing the need for comprehensive cardiovascular assessment. ObjectiveTo investigate a cardiovascular profile in patients hospitalized with exacerbation COPD(ECOPD) in coexistence with HF compared with isolated diseases. MethodsA cross-sectional study including patients diagnosed with ECOPD and decompensated HF, approached between 24 and 48 h after hospital admission. Assessments included: endothelial function by brachial artery flow-mediated vasodilation(FMD); hemodynamic through analysis of pulse wave and arterial stiffness by carotid-femoral pulse wave velocity(cfPWV) and cardiac autonomic modulation(CAM) by heart rate variability(HRV). ResultsThe mean FMD was 4.45 %, indicating endothelial dysfunction in all patients. Date is present in mean(confidence interval) sequency COPD(n = 12), COPD-HF(n = 21) and HF(n = 21). FMD: 5.47(3.96–6.91); 2.66(0.09–3.48); 4.60(2.30–6.43) p < 0.01. However, COPD-HF had worse FMD. Arterial stiffens (AIx: 29.0(19.0–42.6); 34.6(24.3–43.2); 14.5(8.0–24.0)p < 0.01; cfPWV: (6.5(5.4–7.2); 7.7(7.0–8.5); 6.0(5.0–6.5)); COPD-HF also showed greater activation of the sympathetic nervous system compared to patients with isolated diseases (PNS: 1.32(-2.53 to −0.62); −2.33(-2.60 to −2.12); −1.32(-1.42 to −1.01) p < 0.01; SNS: 3.50(1.40–8.55); 7.11(5.70–8.29); 2.32(1.78–5.01) p < 0.01). In addition, rMSSD, NN50, pNN50, and TINN also indicate worse CAM in the COPD-HF group compared to isolated diseases. ConclusionDuring hospitalization, the worst impairment in vascular function and cardiac autonomic modulation were found in patients with COPD and HF comorbidity compared to the isolated diseases(HF or COPD).

Armature Reaction Analysis and Suppression of Voice Coil Actuator Based on an Improved Magnetic Equivalent Circuit Model

The high thrust density voice coil actuator (VCA) is a key component for the deployers to determine the CubeSats' separation velocity in orbit directly. To improve the VCA's thrust density and power consumption, it is essential to analyze the armature reaction under heavy current work conditions. This paper proposes a dynamic splitting method of the magnetic equivalent circuit (MEC) model for analyzing the armature reaction of the VCA. This MEC model can effectively reveal the interaction mechanism between the dynamic winding field and the permanent magnet (PM) field, which provides an approach to readily and quickly analyze the armature reaction. Based on the understanding of the mechanism, we found an effective way to suppress the armature reaction and propose a new VCA with double PM flux circuits. The electromagnetic performances of the new configuration are evaluated by comparing it with the conventional one. Both the theoretical and experimental results show that the new structure achieves lower magnetic saturation, lower armature reaction, and higher thrust density. A research prototype was constructed and experimentally tested to verify the theoretical results of the armature reaction, magnetic field, thrust, separation velocity, and other performances. The new VCA realizes a wide and accurate modulation of separation velocity for the CubeSats.

High-resolution spectroscopy of the intermediate polar EX Hydrae

EX Hya is one of the best studied, but still enigmatic intermediate polars. We present phase-resolved blue VLT/UVES high-resolution (λ/Δλ ≃ 16.000) spectra of EX Hya taken in January 2004. Our analysis involves a unique decomposition of the Balmer line profiles into the spin-modulated line wings that represent streaming motions in the magnetosphere and the orbital-phase modulated line core that represents the accretion disk. Spectral analysis and tomography show that the division line between the two is solidly located at ∣υrad ∣ ≃ 1200 km s−1, defining the inner edge of the accretion disk at rin ≃ 7 × 109 cm or ∼10R1 (WD radii). This large central hole allows an unimpeded view of the tall accretion curtain at the lower pole with a shock height up to hsh ∼ 1R1 that is required by X-ray and optical observations. Our results contradict models that advocate a small magnetosphere and a small inner disk hole. Equating rin with the magnetospheric radius in the orbital plane allows us to derive a magnetic moment of the WD of μ1 ≃ 1.3 × 1032 G cm3 and a surface field strength B1 ∼ 0.35 MG. Given a polar field strength Bp ≲ 1.0 MG, optical circular polarization is not expected. With an accretion rate Ṁ = 3.9 × 10−11 M⊙ yr−1, the accretion torque is Gacc ≃ 2.2 × 1033 g cm2 s−2. The magnetostatic torque is of similar magnitude, suggesting that EX Hya is not far from being synchronized. We measured the orbital radial-velocity amplitude of the WD, K1 = 58.7 ± 3.9 km s−1, and found a spin-dependent velocity modulation as well. The former is in perfect agreement with the mean velocity amplitude obtained by other researchers, confirming the published component masses M1 ≃ 0.79 M⊙ and M2 ≃ 0.11 M⊙.

Enhancing and switching spin-valley filtered polarizations in a magnetic WSe2 superlattice induced by Fermi velocity modulation

The spin–valley transport is studied in a Fermi velocity-modulated monolayer WSe2 magnetic superlattice. Based on these results, a scheme that can achieve an enhancing and switching spin–valley filter is proposed in the superlattice system. We find the Fermi velocity enhanced and switched spin-valley dependent conductance transport gaps by increasing the number of Fermi velocity barriers, which are verified by the transmission probabilities and Bloch theorem. When compared to a mono-periodic superlattice, the maximum spin ↓ and valley K′ polarized conductance in a well-constructed superlattice structure are greatly improved to a detectable degree. More importantly, the crucial bias voltage or exchange field can dynamically flip and control the valley polarized conductance, something that is not possible in a mono-periodic superlattice. Our findings indicate that a Fermi velocity modulated superlattice structure can be a great way to improve the spin-valley filtered polarizations of devices based on transition metal dichalcogenides.

Motor Control Adherence to the Two-thirds Power Law Differs in Autistic Development.

Autistic individuals often exhibit motor atypicalities, which may relate to difficulties in social communication. This study utilized a smart tablet activity to computationally characterize motor control by testing adherence to the two-thirds power law (2/3 PL), which captures a systematic covariation between velocity and curvature in motor execution and governs many forms of human movement. Children aged 4-8 years old participated in this study, including 24 autistic children and 33 typically developing children. Participants drew and traced ellipses on an iPad. We extracted data from finger movements on the screen, and computed adherence to the 2/3 PL and other kinematic metrics. Measures of cognitive and motor functioning were also collected. In comparison to the typically developing group, the autistic group demonstrated greater velocity modulation between curved and straight sections of movement, increased levels of acceleration and jerk, and greater intra- and inter-individual variability across several kinematic variables. Further, significant motor control development was observed in typically developing children, but not in those with autism. This study is the first to examine motor control adherence to the 2/3 PL in autistic children, revealing overall diminished motor control. Less smooth, more varied movement and an indication of developmental stasis in autistic children were observed. This study offers a novel tool for computational characterization of the autism motor signature in children's development, demonstrating how smart tablet technology enables accessible assessment of children's motor performance in an objective, quantifiable and scalable manner.

Wind Velocity and Forced Heat Transfer Model for Photovoltaic Module

This study proposes a computational model to define the wind velocity of the environment on the photovoltaic (PV) module via heat transfer concepts. The effect of the wind velocity and PV module is mostly considered a cooling effect. However, cooling and controlling the PV module temperature leads to the capability to optimize the PV module efficiency. The present study applied a nominal operating cell temperature (NOCT) condition of the PV module as a reference condition to determine the wind velocity and PV module temperature. The obtained model has been examined in contrast to the experimental heat transfer equation and outdoor PV module performance. The results display a remarkable matching of the model with experiments. The model’s novelty defines the PV module temperature in relation to the wind speed, PV module size, and various ambient temperatures that were not included in previous studies. The suggested model could be used in PV module test specification and provide analytical evaluation.

(3+1)-dimensional Pearcey-Gaussian wave packet with arbitrary velocity driven by flying focus.

The group velocity (GV) modulation of space-time wave packets (STWPs) along the transverse and longitudinal directions in free space is constrained by various factors. To surmount this limitation, a technique called "flying focus" has been developed, which enables the generation of laser pulses with dynamic focal points that can propagate at arbitrary velocities independent of GV. In this Letter, we propose a (3+1)-dimensional Pearcey-Gauss wave packet based on the "flying focus" technique, which exhibits superluminal propagation, transverse focus oscillation, and longitudinal periodic autofocusing. By selecting appropriate parameters, we can flexibly manipulate the position, the size, and the number of focal points- or make the wave packet follow a desired trajectory. This work may pave the way for the advancement of space-time structured light fields.

STABILITY OF LIQUID-LIQUID INTERFACE IN UNEVENLY ROTATING HORIZONTAL CYLINDERS

The effect of rotational velocity modulation on the shape of the interface between liquids with high contrast of viscosities and of different densities in a rapidly rotating horizontal cylinder is experimentally investigated. During rotation, the more viscous fluid with higher density is located near the lateral boundary of the cavity, and it is found that modulation of the rotation rate leads to the loss of stability of the initially axisymmetric liquid-liquid interface. The instability manifests itself in the development of a spatially periodic quasi-stationary 2D "frozen" wavy pattern on the interface. The phenomenon has a threshold character; the critical amplitude of velocity modulation depends on the rotation rate and the frequency of velocity modulation. It is shown that the appearance of the frozen waves is associated with the Kelvin-Helmholtz oscillatory instability and is accompanied by the generation of intensive vortex flows near the interphase boundary.

Comprehension of the Shock Velocity Modulation Mechanism due to the Interaction with the Temperature Modulation Field

Comprehension of the Shock Velocity Modulation Mechanism due to the Interaction with the Temperature Modulation Field

A Single-Sensor Approach for Noninvasively Tracking Phase Velocity in Tendons during Dynamic Movement.

Shear wave tensiometry is a noninvasive method for directly measuring wave speed as a proxy for force in tendons during dynamic activities. Traditionally, tensiometry has used broadband excitation pulses and measured the wave travel time between two sensors. In this work, we demonstrate a new method for tracking phase velocity using shaped excitations and measurements from a single sensor. We observed modulation of phase velocity in the Achilles tendon that was generally consistent with wave speed measures obtained via broadband excitation. We also noted a frequency dependence of phase velocity, which is expected for dispersive soft tissues. The implementation of this method could enhance the use of noninvasive wave speed measures to characterize tendon forces. Further, the approach allows for the design of smaller shear wave tensiometers usable for a broader range of tendons and applications.

Static and dynamic study of the airflow behavior generated by two air assisted sprayers commonly used in 3D crops

Air-assisted sprayers, which are commonly used for pesticide application in three dimensional (3D) crops, are evolving towards increasingly innovative designs in terms of pneumatic system regulation with the aim of providing an adjusted amount of airflow to the target. As a result, it is currently possible to modify the characteristics of the airflow by remote control from the cab or manually. In this sense, characterizing the behavior of airflow in agricultural sprayers has become crucial to understand how the characteristics of the air velocity vector vary before reaching the crop when the main application parameters change. Therefore, the present study focuses on characterizing the airflow generated by both a multirow and an axial air-assisted sprayer as a function of different configurations associated with both the pneumatic system (fan gearbox position and diffuser air outlet section) and the application conditions (height, horizontal distance and forward speed) with the final objective of obtaining mathematical models to estimate the air speed in the vicinity of the crop as a function of these parameters (pneumatic system configurations and application conditions). Air velocity maps were generated for each sprayer in both static and dynamic situations under laboratory conditions and in the absence of wind. Airflow rate (m3 h−1) generated by the sprayers was first quantified in accordance with the ISO 9898: 2000 standard using a vane probe anemometer. Then, static and dynamic measurements were carried out using a 3D ultrasonic anemometer to analyze module and direction of the air velocity vector for all configurations. Results showed some similarities in the airflow behavior between sprayers under static conditions. As horizontal distance increased, the vertical distribution of airflow became more homogeneous across different heights. Furthermore, the adjusted deflectors of the Twister sprayer and the multirow design resulted in minimal variation in the direction associated with the lower magnitude components of the air velocity vector. As the forward speed increased, main factors had different effects on the response variables among the sprayers. Models with a high goodness of fit when predicting the air velocity module were achieved for both sprayers.

Flexural wave rainbow trapping effect in the periodic non-uniform Euler-Bernoulli beams and its application in energy harvesting

The rainbow trapping of elastic wave enables spatial frequency shunting and energy concentration phenomenon, which implies that the broadband vibration will forbid propagating forward and occur energy concentration at different positions of metamaterial structure. This paper proposes a novel metamaterial consisting of the periodic non-uniform Euler-Bernoulli beams with an arbitrary profile section to achieve the rainbow trapping effect of flexural wave and application in piezoelectric energy harvester. Firstly, the differential quadrature method is introduced to solve a partial differential equation with variable coefficients. The convergence of this method is systematically demonstrated, and the correctness of band structures is validated by comparing theoretical results calculated by the differential quadrature method with those from the finite element method for different profiles. Based on band structures analysis, the working mechanism of the flexural wave rainbow trapping effect is attributed to the group velocity modulation; thereby, the constructed periodic array of non-uniform beams achieves integration of specific-band vibration reduction and energy enhancement at specific positions. Secondly, simulations indicate that the resonance rainbow trapping frequencies demonstrate more intense concentration of flexural wave energy compared to the counterpart with initial frequencies. Finally, the resonance rainbow trapping phenomenon demonstrates superiority in vibration energy harvesting. Specifically, when piezoelectric films are pasted on specific-position with enhanced energy density, the maximum output voltage in the independent circuit connection reaches up to 2.30V for the resonance rainbow trapping frequency of 8752Hz and the PVDF film position of x = 670 mm. Furthermore, simulations illustrate that the maximum output voltage and power are up to 4.52V and 1894.12 nW for the Series-A circuit connection, respectively, which is approximately the sum of the individual maximum output electrical energy generated by independent circuit connection at positions A and B. The proposed metamaterial beams can offer new selection guidelines for high-performance vibration energy harvesters.

THE "LARGE BARYON PUMP OF THE EARTH" AS A NATURAL IMAGE OF THE "TREE OF LIFE" AND AN OBJECT OF ENVIRONMENTAL LAW, WHICH IS INTEGRATED WITH THE NATURAL ENVIRONMENT OF MAN

THE "LARGE BARYON PUMP OF THE EARTH" AS A NATURAL IMAGE OF THE "TREE OF LIFE" AND AN OBJECT OF ENVIRONMENTAL LAW, WHICH IS INTEGRATED WITH THE NATURAL ENVIRONMENT OF MAN

Bound states of Dirac fermions in the presence of a Fermi velocity modulation

We investigate the effect of a position-dependent Fermi velocity on the electronic properties of two-dimensional Dirac materials. A physical Fermi velocity distribution, which approaches a finite value at infinity and experiences a modulation near x = 0, is considered. Such a position-dependent Fermi velocity could be realized in the curved graphene or by applying strain. It is shown that the bound states are absent in the presence of a pure Fermi velocity modulation without an electrostatic potential well. However, an extra electrostatic potential modulation could produce the bound states. A set of discrete energy level spectrum and the corresponding wave functions are obtained by solving the Dirac equation exactly. Local probes such as scanning tunnel microscopy should be able to observe the predicted bound states in two-dimensional materials.