Drift Current Research Articles

Geometry of deep and intermediate water breaking waves influenced by wind speed and direction

Wind effects on the evolution of a breaking wave group due to dispersive focusing are investigated using a two-phase flow Navier–Stokes solver. The Navier–Stokes equations are solved for both air and water, with the air–water interface captured by the Volume of Fluid method and the turbulence by the Smagorinsky subgrid-scale stress model. The two-phase model is first validated with the experimental measurements with and without following wind action. The following wind delays the breaking and shifts the breaking location downstream, and vice versa for the opposing wind. The wind-induced drift current is mainly responsible for these shifts of breaking time and location. The shift of breaking location and time is approximately linearly proportional to the wind speed (wind induced drift current) under weak winds, but the shift saturates under strong winds. The direct wind forcing, on the other hand, plays an increasingly larger role in the wave breaking process in the presence of stronger wind. It was found that the strong following wind forcing enhances the initiation of wave breaking, while the strong opposing wind forcing may change breaking type or suppress wave breaking of large intensity, such as plunging breaking. Accordingly, the wave shape at breaking onset is altered considerably under strong winds. The following wind increases the maximum wave height and wave skewness slightly. However, the opposing wind may also increase the maximum wave height initially because of the wind drift current induced upwave refocusing of the wave group. Eventually, stronger opposing wind decreases the wave height and wave skewness.

Forecasting seasonal sargassum events across the tropical Atlantic: Overview and challenges

Proliferation of sargassum across the tropical Atlantic since 2011 has motivated a range of forecasting methods. Statistical methods based on basin-scale satellite data are used to address seasonal timescales. Other methods involve explicit Lagrangian calculations of trajectories for particles that are representative of drifting sargassum over days-months. This computed sargassum drift is attributed to the combined action of surface currents, winds and waves, individually or in various combinations. Such calculations are undertaken with both observed surface drift and simulated currents, each involving strengths and weaknesses. Observed drift implicitly includes the action on sargassum of winds and waves, assumed equivalent between drifters and sargassum mats. Simulated currents provide large gridded datasets that facilitate computation of ensembles, enabling some quantification of the uncertainty inherent in an eddy-rich ocean, further subject to interannual variability. A more limited number of forecasts account for in situ growth or loss of sargassum biomass, subject to considerable uncertainty. Forecasts provide either non-dimensional indices or quantities of sargassum, accumulated in specified areas or counted across specified transects over a given time interval. Proliferation of different forecast methodologies may reduce uncertainty, if predictions for given seasons are consistent in broad terms, but there is scope to coordinate different approaches with common geographical foci and predicted variables, to facilitate direct inter-comparisons. In an example of forecasting westward sargassum flux into the Caribbean during the first half of 2022, challenges and opportunities are highlighted. In conclusion, prospects for closer alignment of complementary forecasting methods, and implications for sargassum management, are identified.

Unveiling the Effect of Superlattice Interfaces and Intermixing on Phase Change Memory Performance

Superlattice (SL) phase change materials have shown promise to reduce the switching current and resistance drift of phase change memory (PCM). However, the effects of internal SL interfaces and intermixing on PCM performance remain unexplored, although these are essential to understand and ensure reliable memory operation. Here, using nanometer-thin layers of Ge2Sb2Te5 and Sb2Te3 in SL-PCM, we uncover that both switching current density (Jreset) and resistance drift coefficient (v) decrease as the SL period thickness is reduced (i.e., higher interface density); however, interface intermixing within the SL increases both. The signatures of distinct versus intermixed interfaces also show up in transmission electron microscopy, X-ray diffraction, and thermal conductivity measurements of our SL films. Combining the lessons learned, we simultaneously achieve low Jreset ≈ 3-4 MA/cm2 and ultralow v ≈ 0.002 in mushroom-cell SL-PCM with ∼110 nm bottom contact diameter, thus advancing SL-PCM technology for high-density storage and neuromorphic applications.

The Dynamics of 0-Group Herring Clupea harengus and Sprat Sprattus sprattus Populations Along the Norwegian Skagerrak Coast

Coastal areas are important habitats for early life stages of many fish species. These habitats are used as nursery grounds and can provide a significant contribution to the recruitment of a fish population. In 1919, standardized sampling with a beach seine along the Norwegian Skagerrak coastline was established mainly to target 0-group fish. Here, we focus on Atlantic herring and European sprat to explore whether inter-annual variability in the abundance of these species is indicative of variability in recruitment. We investigated if the abundance of 0-group herring and sprat are affected by environmental factors. Further, the beach seine abundance indices were compared with recruitment estimates of neighboring stocks. There was a clear correlation between herring and sprat abundance in the beach seine samples. While sprat abundance was mainly affected by environmental factors such as temperature and current drift, herring abundance was positively affected by the recruitment of the neighboring stock of western Baltic spring spawners. One plausible explanation could be that sprat recruit to a more local component, while herring of the neighboring stock utilize the Skagerrak coastline as nursery grounds. This study demonstrates the importance of long time series and can provide new insight into the dynamics and structure of multiple fish species.

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.

Using light-emitting complex Ir(mppy)3 to detect acetone from 0.5 to 100 ppm by vertical-channel gas sensor

Acetone and ammonia are the gases in human breath with relatively high concentrations of 1–200 ppm and 0.5–2 ppm respectively. Gas sensors with vertical current channels covered with organic polymer semiconductors have been proved to have high sensitivity and reliability in breath ammonia detection. But the polymers have a large current drift in air and poor sensitivity to acetone. Here, the polymer is replaced by the iridium metal complex tris[2-( p -tolyl)pyridine]iridium(III), (Ir(mppy) 3 ), a common emitter in organic light-emitting diode (OLED). The vertical gas sensor now has good sensitivity to acetone in the important range of 0.5–100 ppm. The current of Ir(mppy) 3 sensor has a smaller drift in air during the measurement. In 800 s, the current drift of Ir(mppy) 3 device is only 3.2% percent, whereas the drift of PTB7 polymer device is 35% and P3HT polymer device is 29%. The good resolution of 0.5 ppm acetone is related to the stability of the current of Ir(mppy) 3 device. • OLED light emitter Ir(mppy) 3 is used as gas sensing material. • Vertical-channel gas sensor with Ir(mppy) 3 can resolve acetone down to 0.5 ppm. • The acetone sensor with Ir(mppy) 3 can be applied in medical diagnosis using breath.

Rival interpretations of hydride precipitation-dissolution hysteresis in zirconium: Rebuttal to Critical Comments to the Letter to the Editor of G.A. McRae and C.E. Coleman published in Journal of Nuclear Materials 556 (2021) 153169

Two models of precipitation-dissolution hysteresis in zirconium have been discussed recently. In one an elastic model for the hydrogen flux is written as the superposition of a diffusion current and a drift current. The solvus, TSS, is defined when the currents sum to zero at a hydride interface. Stable hydrides are surrounded by a cloud of hydrogen terminating at concentration C- calculated from another zero-flux condition. The temperature difference between TSS and C- agrees with the hysteresis. The second ‘traditional’ model invokes plastic deformation in zirconium caused by differences between the crystal axes in zirconium and those of the hydride.

Theory of drift-enabled control in nonlocal magnon transport

Electrically injected and detected nonlocal magnon transport has emerged as a versatile method for transporting spin as well as probing the spin excitations in a magnetic insulator. We examine the role of drift currents in this phenomenon as a method for controlling the magnon propagation length. Formulating a phenomenological description, we identify the essential requirements for existence of magnon drift. Guided by this insight, we examine magnetic field gradient, asymmetric contribution to dispersion, and temperature gradient as three representative mechanisms underlying a finite magnon drift velocity, finding temperature gradient to be particularly effective.

Current Drifts in Design and Development of Prodrugs

The design and development of prodrug is based on the objectivity to improve the pharmacokinetic and pharmacodynamic profiles including toxicity of the potent chemical entity. Currently, the prodrug approach is extended with conjugating the parent drug with a self immolating molecule or linker which itself assembles into nanoparticles and prolonged the blood circulation and having passive targeting ability. It also includes delivery of the drug at target site having specific pH condition, delivery of drug to brain by endogenous carrier molecule, NQO1 activable prodrug, prodrug with sustained release behavior, receptor targeted, dual action prodrug, activation via specific enzyme like human carboxylesterase, and phospholipase A2. Some other approaches to prodrug development are that the conversion of active pharmaceutical ingredient (API) into ionic liquids (ILs). In this the biocompatible ionic liquids include choline and amino acid esters are used. One of the anticancer drug methotrexate is formulated into ionic liquid form and used as potential anticancer prodrug. In addition to improvement in combination chemotherapy, there is photoresponsive hybrid prodrug that consists of a photoremovable protecting group. The release of doxorubicin and combrestatin A4 is mainly triggered by 405 nm light and 365 nm light respectively and displayed a quasi-sequential release behavior.

Space charge waves in a two-dimensional electron gas

This paper uses field theory to derive the exact dispersion relation of space charge waves in a two-dimensional electron gas (2DEG) located in a dielectric or a dissimilar dielectric waveguide. It is found that the dispersion of a 2DEG can be modeled accurately using the free-electron sheet model, which is further confirmed by the almost identical polarizability of a 2DEG and of a free-electron sheet with zero drift velocity. Transitions among the well-known 2DEG dispersion, the beam mode in vacuum electronics, and Gould–Trivelpiece mode in plasma physics are demonstrated by varying the 2DEG density and direct current drift velocity. The effects of waveguide dimensions are also presented. Our method is general and can be applied to find the dispersion relation of 2DEG with arbitrary drift velocity (governed by electric field and scattering) in more complex circuits. Our study provides insight into the design of electromagnetic wave devices and circuits involving a 2DEG.

A survey of active and passive concept drift handling methods

AbstractAt present, concept drift in the nonstationary data stream is showing trends with different speeds and different degrees of severity, which has brought great challenges to many fields like data mining and machine learning. In the past two decades, a lot of methods dedicated to handling concept drift in the nonstationary data stream have emerged. A novel perspective is proposed to classify these methods, and the current concept drift handling methods are comprehensively explained from the active handling methods and the passive handling methods. In particular, active handling methods are analyzed from the perspective of handling one specific type of concept drift and handling multiple types of concept drift, and passive handling methods are analyzed from the perspective of single learner and ensemble learning. Many concept drift handling methods in this survey are analyzed and summarized in terms of the comparing algorithms, learning model, applicable drift type, advantages, and disadvantages of the algorithms. Finally, further research directions are given, including the active and passive mixing methods, class imbalance, the existence of novel class in the data stream, and the noise in the data stream.

Improvement of the FEBIAD ion source at SPIRAL1

The behaviour of the Forced Electron Beam Induced Arc Discharge (FEBIAD) ion source used at GANIL within the Target Ion Source System (TISS) of the “Système de Production d’Ions Radioactifs Accélérés en Ligne” (SPIRAL1) has been recently investigated to improve its performances and render them reproducible. Off line systematic studies of the evolution of working parameters (cathode shape, cathode heating, anode current) with time and temperature configuration have clearly shown the origin of issues was mainly related to an excessive temperature of the anode insulators. Modifications of the TISS have allowed the reduction of the anode current drift and an ionisation efficiency of 40Ar of 15%, stable over more than eight days. The system is still under improvement to stabilize its Ar ionization efficiency to 25%, which is the maximum observed during testing.

Chemical Potential Diagram Guided Rational Tuning of Electrical Properties: A Case Study of CsPbBr3 for X-ray Detection.

Controlling the carrier polarity and concentration underlies most electronic and optoelectronic devices. However, for the intensively studied lead halide perovskites, the doping tunability is inefficient. In this work, taking CsPbBr3 as an example, it is revealed that the coexistence of metallic Pb or CsBr3 /Br2 , rather than the precursor ratio, can provide Pb-rich/Br-poor or Br-rich/Pb-poor chemical conditions, enabling the tunability of electrical properties from weak n-type, intrinsic, to moderate p-type. Experimentally, under Br2 -exposure treatment, a shift of the Fermi level as large as 1.00 eV is achieved, which is one of the highest value among all kinds of doping methods. The X-ray detector based on the intrinsic CsPbBr3 exhibits excellent performance, with a negligible dark-current drift of 7.1 × 10-4 nA cm-1 s-1 V-1 , a low detection limit of 103.6 nGyair s-1 , and a high sensitivity of 9085 μC Gyair -1 cm-2 . This work provides a critical understanding and guidance for tuning the electrical properties of lead halide perovskites, which establishes good foundations for achieving intrinsic perovskite semiconductors and also constructing potential homojunction devices.

Improved Low‐Temperature Solution‐Growth of CsPbBr3‐nCln Single Crystals for X‐Ray Detection

AbstractThe dark current drift caused by severe ion migration in all‐inorganic perovskite CsPbBr3 degrades the stability of X‐ray detection performance under a high electric field. The halogen doping is an effective method to improve the properties of the perovskites. In this work, the all‐inorganic Cl‐doped perovskites CsPbBr3‐nCln (n=0, 0.1 and 0.5) single crystals were grown by a modified low‐temperature inverse temperature crystallization (ITC) method with the growth temperature lower than the phase transition point. The trap density decreased to 3.05×1010 cm−3 and the carrier mobility increased to 124.75 cm2 V−1 s−1 for the optimum component of CsPbBr2.9Cl0.1. Furthermore, by designing the detector with an asymmetric electrode configuration, CsPbBr2.9Cl0.1 detector showed super low dark current and an outstanding hard X‐ray induced photo‐response under a high voltage of 200 V. Consequently, the CsPbBr2.9Cl0.1 perovskite detector delivers a high sensitivity (5593.24 μC Gyair−1 cm−2) and a low detection limit (0.68 μGyair s−1). Our low temperature solution grown Cl‐doped all‐inorganic perovskite single crystals efficiently improve the photoelectric properties and enhance the X‐ray detection performance.

SNR-efficient distortion-free diffusion relaxometry imaging using accelerated echo-train shifted echo-planar time-resolving imaging (ACE-EPTI).

To develop an efficient acquisition technique for distortion-free diffusion MRI and diffusion-relaxometry. A new accelerated echo-train shifted echo-planar time-resolved imaging (ACE-EPTI) technique is developed to achieve high-SNR, distortion-free diffusion, and diffusion-relaxometry imaging. ACE-EPTI uses a newly designed variable density spatiotemporal encoding with self-navigators for phase correction, that allows for submillimeter in-plane resolution using only 3-shot. Moreover, an echo-train-shifted acquisition is developed to achieve minimal TE, together with an SNR-optimal readout length, leading to ∼30% improvement in SNR efficiency over single-shot EPI. To recover the highly accelerated data with high image quality, a tailored subspace image reconstruction framework is developed, that corrects for odd/even-echo phase difference, shot-to-shot phase variation, and the B0 field changes because of field drift and eddy currents across different dynamics. After the phase-corrected subspace reconstruction, artifacts-free high-SNR diffusion images at multiple TEs are obtained with varying T2 * weighting. Simulation, phantom, and in vivo experiments were performed, which validated the 3-shot spatiotemporal encoding provides accurate reconstruction at submillimeter resolution. The use of echo-train shifting and optimized readout length improves the SNR-efficiency by 27%-36% over single-shot EPI. The level of image distortion was also evaluated, which shows no noticeable susceptibility and eddy-current distortions in ACE-EPTI images that are common in EPI. The time-resolved acquisition of ACE-EPTI also provides multi-TE images for diffusion-relaxometry analysis. ACE-EPTI was demonstrated to be an efficient and powerful technique for high-resolution diffusion imaging and diffusion-relaxometry, which provides high SNR, distortion- and blurring-free, and time-resolved multi-echo images by a fast 3-shot acquisition.

Channel Mobility Model of Nano-Node MOSFETs Incorporating Drain-and-Gate Electric Fields

A novel channel mobility model with two-dimensional (2D) aspect is presented covering the effects of source/drain voltage (VDS) and gate voltage (VGS), and incorporating the drift and diffusion current on the surface channel at the nano-node level, at the 28-nm node. The effect of the diffusion current is satisfactory to describe the behavior of the drive current in nano-node MOSFETs under the operations of two-dimensional electrical fields. This breakthrough in the model’s establishment opens up the integrity of long-and-short channel devices. By introducing the variables VDS and VGS, the mixed drift and diffusion current model effectively and meaningfully demonstrates the drive current of MOSFETs under the operation of horizontal, vertical, or 2D electrical fields. When comparing the simulated and experimental consequences, the electrical performance is impressive. The error between the simulation and experiment is less than 0.3%, better than the empirical adjustment required to issue a set of drive current models.

Tuning the Photon Sensitization Mechanism in Metal‐Halide‐Perovskite‐Based Nanocomposite Films Toward Highly Efficient and Stable X‐Ray Detection

AbstractMetal halide perovskites (MHPs) have emerged as promising X‐ray detection materials. However, most MHP‐based X‐ray detectors are incompatible for large‐area preparation and integration, and suffer from the serious ion migration issue. This work demonstrates a “perovskite‐in‐a‐host” nanocomposite structure for X‐ray detection, by embedding the perovskite nanocrystal (PNC) sensitizers in the organic interpenetrating charge transport channels to work as the X‐ray attenuation layer. Intriguingly, the photon sensitization mechanism can be readily tuned from indirect‐ to direct‐type X‐ray conversion by decreasing the ligand density on the PNC surface, which significantly increases the sensitivity to 5 696 µC Gyair–1 cm–2. Besides, the ion migration gets suppressed due to the ion blocking effect of the surrounding organic phase. Therefore, an ultra‐small dark current relative drift of 3.57 × 10–9 cm s–1 V–1 is achieved even under an extremely large electric field up to 5 100 V cm–1, ensuring a low detection limit down to 72 nGyair s–1. The superior sensitivity and biasing stability enable the high performance X‐ray imaging capability of the devices, which exhibit great potential in scaling up and integration for the flat panel imaging.

Ultrasensitive and Robust 120keV Hard X-Ray Imaging Detector based on Mixed-Halide Perovskite CsPbBr3- n In Single Crystals.

The relatively low resistivity and severe ion migration in CsPbBr3 significantly degrade the performance of X-ray detectors due to their high detection limit and current drift. The electrical properties and X-ray detection performances of CsPbBr3 -nIn single crystals are investigated by doping the iodine atoms into the melt-grown CsPbBr3 . The resistivity of CsPbBr3 -nIn single crystals increases from 3.6 × 109 (CsPbBr3 ) to 2.2 × 1011 (CsPbBr2 I) Ω cm, restraining the leak current and decreasing the detection limit of the detector. Additionally, CsPbBr3 -nIn single crystals exhibit stable dark currents, arising from their high ion migration activation energy. A record sensitivity of 6.3 × 104 µC Gy-1 cm-2 (CsPbBr2.9 I0.1 ) and a low detection limit of 54 nGy s-1 (CsPbBr2 I) are achieved by CsPbBr3 -nIn single crystals for the 120 keV hard X-ray detection under a 5000 V cm-1 electrical field. The CsPbBr2.9 I0.1 detector shows a stable current response with a dark current density of 0.58 µA cm-2 for 30 days and clear imaging for 120 keV Xrays at ambient conditions. The effective iodine atom doping strategy makes the CsPbBr3 -nIn single crystals promising for reproducible high-energy hard X-ray imaging systems.

Centimeter-Sized Stable Zero-Dimensional Cs3Bi2I9 Single Crystal for Mid-Infrared Lead-Free Perovskite Photodetector

The detection of broadband spectroscopy is a huge challenge for modern optoelectronics, especially for extremely high- or low-energy photons. For metal halide perovskites significant progress has been made in high-energy photons such as X-rays, but there is little exploration of the perovskites in the high-performance detection of low-energy photons, especially mid- or far-infrared photons. Most infrared photodetectors suffer large dark currents, and perovskite photodetectors’ performances are significantly limited by ion migration. Here, a facile solution evaporation method is developed to grow a centimeter-scale zero-dimensional (0D), lead-free perovskite Cs3Bi2I9 single crystal for high-performance mid-infrared photodetectors with ultralow dark current drifts. The 0D Cs3Bi2I9 perovskite single crystal (PSC) photodetector shows an ultralow dark current drift (1.67 × 10–17 A cm–2 V–1 s–1, 9 orders of magnitude smaller than that of MAPbI3) and ultralow power consumption (smaller than 1 pA at 1 V bias) for greatly inhibited ion migration. The photodetector achieves effective photodetection from the ultraviolet to the mid-infrared (from 343 to 4000 nm) at room temperature based on the photoelectric and photobolometric effects with the best responsivity of 3.15 mA/W and detectivity of 8.7 × 108 jones at the wavelength of 343 nm at 0.033 mW/cm2. This work opens a door for low-dimensional perovskite-based mid-infrared detectors and provides a new path for the development of infrared perovskite photonics.

Ultralow Detection Limit and Robust Hard X-ray Imaging Detector Based on Inch-Sized Lead-Free Perovskite Cs3Bi2Br9 Single Crystals.

Halide perovskites are promising candidates for soft X-ray detection (<80 keV) owing to their high X-ray absorption coefficient, resistivity, and mobility lifetime product. However, the lack of large high-quality single crystals (SCs) renders it challenging to manufacture robust hard X-ray imaging systems (>100 keV) with a low detection limit and stable dark current. Herein, high-quality inch-size two-dimensional (2D) Cs3Bi2Br9 (CBB) single crystals are grown from a melt via the Bridgman method. The crystal quality is enhanced by eliminating inclusions of CsBr-rich phases and restraining the trap-state density, leading to an enhanced resistivity of 1.41 × 1012 Ω cm and a mobility lifetime product of 8.32 × 10-4 cm2 V-1. The Au/CBB/Au single-crystal device exhibits a high sensitivity of 1705 μC Gyair-1 cm-2 in all-inorganic bismuth-based perovskites and an ultralow detection limit of 0.58 nGyair s-1 in all of the bismuth-based perovskites for 120 keV hard X-ray detection. The CBB detector exhibits high work stability with an ultralow dark current drift of 2.8 × 10-10 nA cm-1 s-1 V-1 and long-term air environment reliability under a high electric field of 10 000 V cm-1 owing to the ultrahigh ionic activation energy of the 2D structure. The proposed robust imaging system based on CBB SC is a promising tool for X-ray medical imaging and diagnostics.