Drift Characteristics Research Articles

Multibeam Blind Search of Targeted SETI Observations toward 33 Exoplanet Systems with FAST

The search for extraterrestrial intelligence (SETI) is to search for technosignatures associated with extraterrestrial life, such as engineered radio signals. In this paper, we apply the multibeam coincidence matching (MBCM) strategy, and propose a new search mode based on the MBCM which we call the MBCM blind search mode. In our recent targeted SETI research, 33 exoplanet systems are observed by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). With this blind search mode, we search for narrowband drifting signals across 1.05–1.45 GHz in two orthogonal linear polarization directions separately. There are two special signals, one of which can only be detected by the blind search mode while the other can be found by both blind and targeted search modes. This result reveals huge advantages of the new blind search mode. However, we eliminate the possibility of the special signals being ETI signals based on much evidence, such as the polarization, drift, frequency, and beam coverage characteristics. Our observations achieve an unprecedented sensitivity and our work provides a deeper understanding to the polarization analysis of extraterrestrial signals.

Strategies for ultra-fast bit generation of two-terminal threshold switch-based true random number generator using drift-free Ge-doped SiO2 threshold switch device

To achieve fast random bit generation under 50 ns per bit by employing the threshold voltage (Vth) variation of a simple two-terminal threshold switch (TS) device, we have confirmed that Vth drift-free switching characteristics, along with large Vth variation and fast switching speed, are key factors for implementing true random number generator (TRNG) devices. We analyzed the drift-switching characteristics of various TS devices together with our innovative oxide TS device for TRNG applications. Our findings show that stochastic switching is degraded by the Vth drift characteristics of a conventional ovonic threshold switch (OTS) for fast random bit generation. Conversely, the drift-free insulating-to-metal transition (IMT)-based TS device has very tight Vth variation, which is not suitable as a dynamic entropy source for TRNG. However, the Ge-doped SiO2-based TS device operates with drift-free and large Vth variation switching characteristics. Finally, we successfully demonstrated the potential of a Ge:SiO2-based TS device for TRNG application pertaining to fast random bit generation under 50 ns per bit without a complex circuit system.

Modeling the leeway drift characteristics of persons-in-water at a sea-area scale in the seas of China

Drowning events are becoming more common. It is important to accurately predict the drift trajectory of floating objects. This study proposes a sea-area-scale drift modeling method to determine the drift trajectory of persons-in-water in offshore China. The proposed method divided offshore China into 18 areas, and field experiments were carried out in the northern East China Sea (N_ES) and the Taiwan Strait (TS). First, a series of models were created, namely N_ES_I (N_ES upright), N_ES_II (N_ES facedown), TS_I (TS upright), TS_II (TS facedown), C_I (comprehensive upright), and C_II (comprehensive facedown). The leeway coefficients and jibing frequencies were then determined, and the positive crosswind speed (+CWL) probabilities under different marine environments were analyzed. A large volume of information from open-source channels was used to establish a database of historical drift cases. The driven model was validated using a combination of field experiments and historical drift information. The results indicate that the trajectories simulated using the sea-area-scale models proposed in this study are more consistent with the actual trajectories than those using the constant coefficients. The prediction areas are sensitive to the +CWL probability and the jibing frequencies. This study can help to improve the ability of the drift trajectory in China.

Feature Drift in Fake News Detection: An Interpretable Analysis

In recent years, fake news detection and its characteristics have attracted a number of researchers. However, most detection algorithms are driven by data rather than theories, which causes the existing approaches to only perform well on specific datasets. To the extreme, several features only perform well on specific datasets. In this study, we first define the feature drift in fake news detection methods, and then demonstrate the existence of feature drift and use interpretable models (i.e., Shapley Additive Explanations and Partial Dependency Plots) to verify the feature drift. Furthermore, by controlling the distribution of tweets’ creation times, a novel sampling method is proposed to explain the reason for feature drift. Finally, the Anchors method is used in this paper as a supplementary interpretation to exhibit the potential characteristics of feature drift further. Our work provides deep insights into the temporal patterns of fake news detection, proving that the model’s performance is also highly related to the distribution of datasets.

Analysis and Verification of the Temperature Drift Characteristics of MEMS Resonant Sensors During Power-On Startup

Analysis and Verification of the Temperature Drift Characteristics of MEMS Resonant Sensors During Power-On Startup

A baseline drift removal algorithm based on cumulative sum and downsampling for hydroacoustic signal

Baseline drift is a widespread problem in a wide variety of signals and is traditionally handled by using high-pass filtering to filter out the low-frequency portion. However, the frequency of hydroacoustic signals is also very low, and filtering can cause distortion of the signal. In recent years, with the maturity of signal modal theory, variational modal decomposition (VMD) has become a widely used signal modal decomposition algorithm. VMD is effective in eliminating baseline drift, but the calculation steps of VMD are too complicated. In this paper, a baseline drift elimination algorithm based on cumulative sum and downsampling is proposed for the baseline drift characteristics of hydroacoustic signals. Its baseline is fitted to the signal to be processed. The algorithm is simple, can achieve better results than VMD in simulated experiments and actual hydroacoustic signal processing, and has good prospects for application in hydroacoustic signal processing.

Study on Spray Deposition and Drift Characteristics of UAV Agricultural Sprayer for Application of Insecticide in Redgram Crop (Cajanus cajan L. Millsp.)

Insecticide applications are typically being carried out with traditional manual spraying equipment in redgram, which leads to inadequate control of insects due to higher crop height. The modern deployment of tractor-drawn spray machines causes serious damage to the crop. In this connection, unmanned aerial vehicle (UAV) spray technology has great potential for precise insecticide application in redgram crops. One of the important machine parameters influencing droplet deposition and drift characteristics in UAV sprayers is downwash airflow generated by a multi-rotor propeller. A field experiment was carried out at the redgram research field (N11.01, E76.92), Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu, during 2021–2022 to study the spray drift and deposition characteristics of an autonomous UAV sprayer. The Imidacloprid (a.i. 17.8SL) insecticide mixed with water in a ratio of 1 mL per liter was sprayed with a UAV sprayer. Water-sensitive paper samples were kept at upper, middle, and bottom positions on the leaves, and data were analyzed for the spray droplet size, deposition rate, droplet density, and area coverage both in target and non-target areas using Spray Deposit Scanner software. UAV spray droplet deposition rate (2.93 ± 0.17, 2.01 ± 0.08, and 2.21 ± 0.162.38 μL cm−2), droplet density (47 ± 4.04, 53 ± 3.61, and 52 ± 8.74 droplets cm−2), and area coverage (15.72 ± 0.39, 16.60 ± 0.71, and 14.99 ± 0.39%) were highest in the upper layer as compared to the middle layer (droplet deposition rate: 1.21 ± 0.08, 1.07 ± 0.03, and 0.77 ± 0.02 μL cm−2; droplet density: 42 ± 2.52, 43 ± 8.50, and 38 ± 2.52 droplets cm−2; area coverage: 10.95 ± 0.81, 11.22 ± 0.56, and 8.57 ± 0.44%) and bottom layer (droplet deposition rate: 0.41 ± 0.06, 0.35 ± 0.03, and 0.33 ± 0.03 μL cm−2; droplet density: 22 ± 4.36, 17 ± 3.51, and 19 ± 4.51 droplets cm−2; area coverage: 2.78 ± 0.29, 2.95 ± 0.45, and 2.46 ± 0.20%, respectively). In the spray drift test, there was a higher droplet deposition rate (1.63 ± 0.09, 1.93 ± 0.05, and 1.82 ± 0.06 μL cm−2), area coverage (14.40 ± 0.07, 17.54 ± 0.36, and 16.42 ± 0.30%), and droplet density (46 ± 3.61, 54 ± 2.08, and 45 ± 3.21 No’s cm−2) in the target area as compared to the non-target area (droplet deposition rate: 0.88 ± 0.02, 0.46 ± 0.03, 0.22 ± 0.05, and 0.00 μL cm−2; droplet density: 23 ± 1.53, 11 ± 2.08, 6 ± 1.53, and 0.00 droplets cm−2; area coverage: 7.58 ± 0.34, 4.41 ± 0.19, 2.16 ± 0.05, and 0.00%, respectively), which may have been due to the downwash airflow produced by the multi-rotor propeller of the UAV sprayer. Finally, the UAV-based spraying technology results showed that the downwash air produced by the six-rotor propeller improved the penetrability of insecticide to crop leaves and led to a higher droplet deposition rate, droplet density, area coverage, and droplet penetrability on the upper layer, middle layer, and bottom layer of the plants.

Eye drift during fixation predicts visual acuity

Visual acuity is commonly assumed to be determined by the eye optics and spatial sampling in the retina. Unlike a camera, however, the eyes are never stationary during the acquisition of visual information; a jittery motion known as ocular drift incessantly displaces stimuli over many photoreceptors. Previous studies have shown that acuity is impaired in the absence of retinal image motion caused by eye drift. However, the relation between individual drift characteristics and acuity remains unknown. Here, we show that a) healthy emmetropes exhibit a large variability in their amount of drift and that b) these differences profoundly affect the structure of spatiotemporal signals to the retina. We further show that c) the spectral distribution of the resulting luminance modulations strongly correlates with individual visual acuity and that d) natural intertrial fluctuations in the amount of drift modulate acuity. As a consequence, in healthy emmetropes, acuity can be predicted from the motor behavior elicited by a simple fixation task, without directly measuring it. These results shed new light on how oculomotor behavior contributes to fine spatial vision.

Precision Feedback Control Design of Miniature Microwave Discharge Ion Thruster for Space Gravitational Wave Detection

The space gravitational wave detection mission has put forward multiple performance requirements for micro-newton thrusters, such as “fast response, high resolution, and low noise”. In order to solve the problem that the traditional open-loop propulsion system can hardly meet the high-precision performance, the microwave ion thruster with high accuracy and controllability of thrust estimation is adopted as the research object, and the precision feedback control method combining analog circuit and digital control technology is adopted to achieve a resolution of less than 0.1 μN, fast response of 20 ms, and 10−3~1 Hz frequency band noise less than 0.05 μN/Hz1/2 of the thrust performance. Experimental results show that, compared with open-loop regulation, the feedback control can effectively suppress various noises and disturbances caused by device temperature drift and complex operating characteristics of the thruster, and the anti-aliasing filter scheme adopted in this paper can suppress the folding of high-frequency data in the low- and medium-frequency bands during the digital control process, while it can effectively improve the system performance and reduce the impact of thrust noise. The feedback control strategy proposed in this paper verifies the possibility of a microwave ion thruster as an actuator for super “static and precise” space experiment satellites and provides a feasible solution for the application of a microwave ion thruster in deep space science experiment missions such as gravitational wave detection.

Determining the drift characteristics of open lifeboats based on large-scale drift experiments

Lifeboat is one of the most important life-saving equipment for escaping at sea when a ship is abandoned in an extreme emergency. An accurate drift model can help rescuers find the drift position of lifeboat in the shortest time, thus improving the efficiency of marine search and rescue (SAR) at sea and ensuring the safety of wrecked people. The purpose of this paper is to investigate the drift characteristics and to develop an accurate drift prediction model for the open lifeboat. First, large-scale drift experiments were conducted to analyze the drift characteristics with three 6.5-meter-long real-size open lifeboats in the South China Sea. Next, three drift prediction models of the lifeboats were developed using the least squares method based on the drift experimental data. Finally, the drift prediction models of the lifeboats were compared and evaluated using the Lagrangian method and Monte Carlo technique, respectively. Results indicate that the probability of positive crosswind leeway (CWL) of the open lifeboat is 47.5%. The jibing frequency is 6% per hour, and the maximum leeway divergence angle is 45°. These drift characteristics are very important for the prediction of the open lifeboat drift trajectory. The comparison results of three drift models show that the improved drift model is more accurate than the other two drift models for predicting drift trajectories of the open lifeboat, which can be directly applied to maritime search and rescue operations in the South China Sea.

Design of a high-precision, high environmental adaptability temperature measurement system for environments with large temperature variations

A high-precision, high environmental adaptability thermometer based on proportional divider resistance is proposed for high-precision temperature measurement in a spaceborne environment subjected to large temperature variations. In this method, a constant voltage source was used instead of the traditional current source to increase the short-term stability of the proportional divider resistance measurement. The temperature drift characteristics of the measurement system were analyzed and compensated by the self-calibration of the reference resistance method. Based on the above-mentioned method, the minimum noise requirements were analyzed and designed for each unit of the thermometer. The temperature measurement performance of the thermometer was tested by an equivalent temperature measurement experiment with a precision resistance box and a temperature comparison experiment with platinum resistance (PT1000). The equivalent experimental results showed that the resolution of the thermometer was 0.3 mK at an ambient temperature of 20 °C and the maximum deviation of the measurement error was less than 1 mK in a large working range of 10–40 °C. The comparison experiment using a Fluke thermometer 1594A as the reference instrument showed that the standard deviation of temperature measurement was within 0.8 mK in the range of 17–23 °C.

Drift characteristics and the multi-field coupling stress mechanism of the pantograph-catenary arc under low air pressure

The fault caused by a pantograph-catenary arc is the main factor that threatens the stability of high-speed railway energy transmission. Pantograph-catenary arc vertical drift is more severe than the case under normal pressure, as it is easy to develop the rigid busbar, which may lead to the flashover occurring around the support insulators. We establish a pantograph-catenary arc experiment and diagnosis platform to simulate low pressure and strong airflow environment. Meanwhile, the variation law of arc drift height with time under different air pressures and airflow velocities is analyzed. Moreover, arc drift characteristics and influencing factors are explored. The physical process of the arc column drifting to the rigid busbar with the jumping mechanism of the arc root on the rigid busbar is summarized. In order to further explore the mechanism of the above physical process, a multi-field stress coupling model is built, as the multi-stress variation law of arc is quantitatively evaluated. The dynamic action mechanism of multi-field stress on arc drifting characteristics is explored, as the physical mechanism of arc drifting under low pressure is theoretically explained. The research results provide theoretical support for arc suppression in high-altitude areas.

Geometrical and electrical modulation of cracked metal films based on metal nanowire/elastomer composites for high-performance wearable strain sensing

This work presents a simple yet highly efficient strategy to geometrically and electrically modulate mechanical cracks in a thin metal film for the fabrication of high-performance stretchable strain sensors. This is accomplished using a silver nanowire (AgNW)/dragon skin (DS) composite with a customizable surface structure. The AgNW/DS composite layer formed between a platinum (Pt) film and elastomeric DS substrate plays a vital role in redistributing the surface strain upon stretching, leading to a unique crack morphology comprising network-shaped Pt cracks coupled with conductive AgNW bridges. The Pt/AgNW/DS (PAD) strain sensor exhibits balanced sensing performance with large stretchability (75%), high sensitivity (maximum gauge factor of ∼493.2), negligible hysteresis and drift characteristics, fast response (∼205 ms), and long-term durability (1000 cycles at 30%). Finally, the PAD sensor is successfully demonstrated as a wearable device that can detect strains caused by various human activities and the volumetric change in a balloon in real time.

Predicting drift characteristics of life rafts: Case study of field experiments in the South China Sea

Every year, hundreds of people die at sea because of vessel and airplane accidents. As marine emergency evacuation equipment, life rafts are highly used in case of maritime accidents. Accurate predictions of drift trajectories and search and rescue (SAR) areas for life rafts at sea can enhance the efficiency and success rate of maritime SAR operations to save human lives. The objective of this study is to determine the drift characteristics of aviation and marine life rafts in the South China Sea, and develop an accurate drift prediction model. A series of maritime drift experiments were conducted in the South China Sea using the standard 6-person life raft (aviation life raft) and the standard 10-person life raft (marine life raft) to obtain 550 drift samples. This data was used to establish three drift models of life rafts: the AP98 leeway drift model, the dynamics drift model and the improved drift model. Finally, Lagrangian particle tracking method and Monte Carlo simulations were used to compare the drift models for 6-person and 10-person life raft. Results indicate that the probability of positive crosswind leeway (CWL) for 6-person and 10-person life raft is 61% and 31.4%, respectively. The jibing frequency is 2% per hour for 6-person and 4% per hour for 10-person life raft. The maximum divergence angle is 11.3° for 6-person and 20.5° for 10-person life raft, indicating that 10-person life raft is more sensitive to the wind speed in the crosswind direction. The improved drift model is more accurate than AP98 leeway drift model and dynamics drift model for predicting drift trajectories of both 6-person and 10-person life rafts. The results of this work may provide effective guidance for drift prediction of aviation life rafts and marine life rafts, which is of great significance for the maritime search and rescue (SAR) operations in the South China Sea.

Characteristics of unmanned aerial spraying systems and related spray drift: A review.

Although drift is not a new issue, it deserves further attention for Unmanned Aerial Spraying Systems (UASS). The use of UASS as a spraying tool for Plant Protection Products is currently explored and applied worldwide. They boast different benefits such as reduced applicator exposure, high operating efficiency and are unconcerned by field-related constraints (ground slope, ground resistance). This review summarizes UASS characteristics, spray drift and the factors affecting UASS drift, and further research that still needs to be developed. The distinctive features of UASS comprise the existence of one or more rotors, relatively higher spraying altitude, faster-flying speed, and limited payload. This study highlights that due to most of these features, the drift of UASS may be inevitable. However, this drift could be effectively reduced by optimizing the structural layout of the rotor and spraying system, adjusting the operating parameters, and establishing a drift buffer zone. Further efforts are still necessary to better assess the drift characteristics of UASS, establish drift models from typical models, crops, and climate environments, and discuss standard methods for measuring UASS drift.

Study on Dynamic Characteristics of Single-Phase Grounding Fault of 1000 MW Hydro Generator under Different Grounding Modes

The continuous operation of 1000 MW large hydro generators in China is of great value to the implementation of “double carbon strategy” and power grid safety. However, with the continuous increase of single unit capacity of the hydro generator, the problems of unit fault grounding current and neutral point voltage drift become more and more prominent, and the traditional analysis methods cannot accurately obtain the fault dynamic data. Therefore, starting from the neutral point grounding mode of the large hydro generator, taking a 1000 MW hydro generator as the research object, this paper establishes the single-phase grounding fault model under the condition of three-phase parameter asymmetry of stator winding and analyzes the dynamic characteristics of fault current, transient overvoltage, and neutral point voltage drift under different grounding modes by using transient analysis method; the influence of frequency offset on neutral voltage drift and the dynamic characteristics of single-phase grounding fault of the large hydro generator under different grounding modes are also obtained. Finally, according to the analysis results, the selection and optimization method of neutral grounding parameters are proposed, which provides a reference for the selection of neutral grounding mode and the research of protection strategy of the large hydro generator.

MeerKAT Observations of the Reversing Drifting Subpulses in PSR J1750-3503

We present an analysis of the subpulse drift in PSR J1750−3503, which is characterized by abrupt transitions of drift direction. As the pulsar does not exhibit other mode changes or clear nulling, it is an ideal candidate system for studying the phenomenon of drift direction change. For ∼80% of the time, the subpulses are characterized by positive drift—from early to later longitudes—while the drift direction is negative in the other ∼20%. The subpulse separation for single pulses with positive drift, P 2 = (18.8 ± 0.1)°, is higher than for single pulses with negative drift, P 2 = (17.5 ± 0.2)°. When the drift is stable, the measured repetition time of the drift pattern is P 3 obs = (43.5 ± 0.4)P, where P is the pulsar period. We show that the observed data can be reproduced by a carousel models with subpulse rotation around the magnetic axis using a purely dipolar configuration of the surface magnetic field. The observed drift characteristics can be modeled assuming that the actual repetition time P 3 < 2P, such that we observe its aliased value. A small variation in P 3, of the order of 6% (or less assuming higher alias orders), is enough to reproduce the characteristic drift direction changes we observe.

Effect of Physical Properties of an Emulsion Pesticide on the Atomisation Process and the Spatial Distribution of Droplet Size

In the process of applying plant protection sprays, the atomisation process of complex pesticide components such as emulsion pesticides is different from that of water. Indeed, emulsion is often used as an additive to spray to reduce drift. Therefore, this study investigated the different morphological characteristics that occur between emulsions and water during atomisation at different pressures through visualisation experiments and interpreting the formation of structural differences between the two fragmentation mechanisms. The effect of liquid sheet structure on droplet size distribution was analysed in three-dimensional space, not only from one spatial perspective, but how it alters the morphological structures of liquid sheet leading to different potential droplet drift characteristics. It was found that the smaller the liquid sheet disturbance, the more concentrated the droplet size distribution, the more intense the liquid sheet disturbance, the more dispersed the droplet size distribution. The addition of 0.02% emulsion significantly reduced the proportion of V100 (the ratio of volume with drops smaller than 100 μm to the total volume of all droplets) from 21.33% to 10.24%, and the higher the emulsion concentration, the smaller the V100. The ability of the emulsion to increase V400 decreased with increasing pressure.

A Novel Machine-Learning Framework With a Moving Platform for Maritime Drift Calculations

A novel data-driven conceptual framework using a moving platform was developed to accurately estimate the drift of objects in the marine environment in real time using a combination of a perception-based sensing technology and deep-learning algorithms. The framework for conducting field experiments to establish the drift properties of moving objects is described. The objective of this study was to develop and test the integrated technology and determine the leeway drift characteristics of a full-scale three-dimensional mannequin resembling a person in water (PIW) and of a rectangular pelican box to accurately forecast the trajectory and the drift characteristics of the moving objects in real time. The wind and ocean current speeds were measured locally for the entire duration of the tests. A sensor hardware platform with a light detector and ranging sensor (LiDAR), stereoscopic depth cameras, a global positioning system, an inertial measurement unit, and operating software was designed and constructed by the team. It was then mounted on a boat (mobile test platform) to collect data. Tests were conducted by deploying the drifting objects from the mobile test platform into Galveston Bay and tracking them in real time. A framework was developed for applying machine learning and localization concepts on the data obtained from the sensors to determine the leeway trajectory, drift velocity, and leeway coefficients of the drifting objects in real time. Consistent trends in the downwind and crosswind leeway drift coefficients were observed for the pelican (significantly influenced by the wind) and PIW (influenced by the winds and currents).

Drift Potential Characteristics of a Flat Fan Nozzle: A Numerical and Experimental Study

This study explores the drift potential characteristics of a flat fan nozzle. The atomization and drift characteristics of fan-shaped pressure nozzles were studied at a spraying height of 0.6 m and a lateral wind speed of 0–6 m/s through a combination of computational fluid dynamics (CFD) analyses and wind tunnel experiments. The nozzle Lu 120-03 had a spraying pressure of 0.3 MPa. The results show that as the wind speed varies from 0 m/s to 6 m/s, the spray droplet spectrum also changes, and the droplet volume medium diameter increases. The cumulative droplet ratio and droplet spectral width of M oscillate within certain ranges. The amount of spray drift increases at higher wind speeds. The concentration of droplet deposition on the bottom of the wind tunnel gradually spreads downward in the wind direction. The determination coefficient R2 of the straight-line fitting of the drift characteristics is 0.982, which is highly consistent with the CFD simulation results. A CFD simulation-assisted wind tunnel test method, which is more convenient and repeatable than traditional field tests, is proposed to analyze the droplet spectrum and drift of Lechler series nozzles. The program can accurately simulate the actual drift and provide theoretical and data support for the optimization of atomization and drift characteristics of several types of flat fan nozzles under different spraying pressures and crosswinds in practical applications.