Free Drift Research Articles

Calibration of a hybrid sea ice model during an expedition to the Arctic

AbstractWe describe the acquisition and evaluation of data during the ArcWatch II expedition into the Arctic Ocean on board of the icebreaker Polarstern. The data is used to calibrate a hybrid sea ice model that focuses on modeling the marginal ice zone, which is the transition zone between pack ice and the open ocean. We describe the experimental setup used to track the motion of individual ice floes as well as the measurement of the wind and the ocean current. In the literature, the motion of an ice floe in the free‐drift regime is often estimated by Nansen's rule of thumb, which assumes the sea ice drifts at of the wind speed, deflected up to in clockwise direction. Analyzing the first datasets, we noticed that observed small ice floes in free drift often have a larger relative angle to the wind direction. Based on numerical simulation we quantify that these larger angles are related to the geometry of larger sea ice floes in the vicinity of the observed ice floe. These large icefloes influence the ocean current, which in turn, impacts the motion of the small ice floes in the surrounding.

Roles of non-axisymmetric perturbations in free drift vertical displacement events on EAST

The safe operation of most tokamaks, especially the large ones, relies on the feedback control of vertical displacement events (VDEs). However, most of these feedback control systems are based on axisymmetric VDE models. In this study, we use NIMROD simulations to study the role of non-axisymmetric perturbations in free drift vertical displacement events on EAST. The high-n modes in the non-axisymmetric VDE grow first, which drives the formation of high-n magnetic island chains. Subsequently, the magnetic island chains grow and overlap with each other, leading to the destruction of the magnetic flux surface, which induces a minor disruption and accelerates the start of the following major disruption. The magnetic island and the stochastic magnetic field allow the toroidally non-axisymmetric poloidal plasma current to jet towards the hoop force direction, forming finger-like and filamentary structures. Such a plasma current non-axisymmetry strongly depends on the anisotropy in the thermal transport coefficients.

Using LQR controller for vertical position control on EAST

Vertical position control is essential for stabilizing plasma with elongated configurations. The EAST tokamak is equipped with a set of in-vessel control (IC) coils dedicated to this purpose. Currently, a PD controller with fixed parameters is used for the vertical position control of EAST plasma. However, the response of the plasma in the vertical position changes with changes in plasma configuration, which can result in different control parameter requirements. It is essential to develop a model-based fast-tuning control algorithm for ensuring stability in the vertical position under different configurations. In this study, a model-based vertical position controller tuning method based on a linear quadratic regulator algorithm (LQR) is proposed. Compared with contemporary PD controllers, the proposed model-based LQR controller can enable adjusting controller parameters based on the response of the system, achieving stable control under different vertical position responses. In the EAST experiment, the model-based LQR controller achieved stable control under a shot with a continuously increasing growth rate and reached a maximum controllable vertical displacement growth rate of 968 s−1. The robustness of the system was also demonstrated in a free drift experiment. The new vertical displacement control method can be adapted to different system states and plasma configurations and improve the controllability and safety of future devices.

Study of Focused Ions Beam Generated by a Plasma Source through a Series of C- Magnet Configuration

The beam transport system is an essential part of any accelerator. This research investigates how a charged particle beam extracted from a plasma source behaves as it passes through a virtual beam transport system consisting of a series of C-bending magnets. This is done by analyzing the equations of motion of charged particles through this system. In addition, the study investigates the effect of the free drift space regions between these magnets and studies the behavior of charged particles beam passing through the suggested system for both horizontal and vertical planes using a computer program designed for this purpose. The results indicate many focusing regions along the beam path (beam envelop) for both the horizontal and vertical planes. The presence of free drift regions between the magnets strongly affects the beam envelop for both horizontal and vertical planes.

Development of the Free Drift (FD) Method to Measure the Laser-thrust Generated on an Aluminum Droplet

Development of the Free Drift (FD) Method to Measure the Laser-thrust Generated on an Aluminum Droplet

On shifting the principal eigenvalue of Dirichlet problem to infinity with non-transversal incompressible drift

We prove that it is always possible to add some divergence free drift vector field to some two dimensional spherical Dirichlet problem, such that the resulting principal eigenvalue lies above a prescribed bound. By construction those drift vector fields vanish on the boundary and their flow lines individually stay away from the boundary. The capacity of those drift vector fields to accelerate diffusivity originates from high frequency oscillation of the associated flow lines. The lower bounds for the spectrum are obtained through isoperimetric inequalities for flow invariant functions.

Basic algorithm for approximation of the boundary trajectory of short-focus electron beam using the root-polynomial functions of the fourth and fifth order

The new iterative method of approximating the boundary trajectory of a short-focus electron beam propagating in a free drift mode in a low-pressure ionized gas under the condition of compensation of the space charge of electrons is considered and discussed in the article. To solve the given approximation task, the root-polynomial functions of the fourth and fifth order were applied, the main features of which are the ravine character and the presence of one global minimum. As an initial approach to solving the approximation problem, the values of the polynomial coefficients are calculated by solving the interpolation problem. After this, the approximation task is solved iteratively. All necessary polynomial coefficients are calculated multiple times, taking into account the values of the function and its derivative at the reference points. The final values of polynomial coefficients of high-order root-polynomial functions are calculated using the dichotomy method. The article also provides examples of the applying fourth-order and fifth-order root-polynomial functions to approximate sets of numerical data that correspond to the description of ravine functions. The obtained theoretical results are interesting and important for the experts who study the physics of electron beams and design modern industrial electron beam technological equipment.

Validation of the energy resource assessment with experimental data for the site selection of a tidal turbine in the Tagus River estuary.

Lisbon, the capital of Portugal, is located on the mouth of the Tagus River, where the current speed and direction are mainly governed by the local tides. The narrowest part of the river is located between Lisbon downtown and the western side of the city. This narrowing accelerates the water flow and makes it a potential site for a tidal energy system. A preliminary study based on numerical simulations using the software MOHID was conducted to assess potential energy yields throughout the estuary using freely available hindcast data. This allowed the selection of three potential sites for a tidal turbine in the Lisbon area based on yearly tidal and current energy density: off the coasts of Cacilhas, Bel´em, and Pa¸co de Arcos. However, even if the current model has been previously validated with experimental data, it was only done at two locations in the estuary that are far from the potential sites. Due to the complexity of the phenomena driving the current speed at these locations, additional validation is necessary before committing to a specific site. This paper presents the numerical analysis, the experimental campaign and the validation of the results at those three locations. Drifters with sails of 3.4m and 4.5m depth were released at least 8 times at each location and retrieved after 15 minutes of free drift. Each drifter was tracked with a GPS and the current speed and direction were derived from the drifters’ trajectory. The analysis of the experimental data shows good agreement with the model, even though an error of 0.3m/s is consistent throughout the tests. This paper concludes with a discussion on the model temporal and spatial discretisation and the forces included in the analysis that could be the source of the differences between the numerical and experimental data.

A convenient switch design for high time resolution and energy resolution in ion velocity imaging

Time-sliced velocity map imaging (VMI) has extensively been applied in photodissociation dynamics studies, thanks to its unique advantages, such as high energy resolution and no requirement of inverse Abel or Hankel transformations. However, its time resolution is generally insufficient for distinguishing adjacent m/z ions with a certain kinetic energy due to the overlapping of time-of-flight distributions. Herein, we have made a novel and convenient switch design for the common ion optics in three-dimensional (3D) VMI. By simply introducing two additional resistors out of the vacuum chamber, the strength ratio of the extraction and acceleration fields is easily changed from 3D VMI to two-dimensional (2D) VMI under optimized conditions, as well as a significant extension of free drift length, leading to a higher time resolution while maintaining the high energy resolution. As a result, 2D and 3D VMI can be quickly switched without breaking the vacuum and replacing the electrostatic plates.

Growth and Characterization of Lanthanum Germanide Thin Films by the Thermal Evaporation Technique

AbstractLanthanum germanide (La6Ge) thin films are successfully fabricated using the thermal evaporation technique under a vacuum pressure of 10−5 mbar. The resulting films display an orthorhombic structure, characterized by lattice parameters of a = 8.725 Å, b = 8.063 Å, and c = 5.569 Å. Optical analysis of the La6Ge thin films reveal their high transparency, with an energy bandgap of 3.75±0.04 eV. The bandgap exhibits indirect allowed transitions and featured energy band tails with widths measuring (1.64±0.14) eV. In addition, dielectric dispersion analyses indicate the presence of two dominant dielectric resonance peaks centered at 3.15 and 2.08 eV. Moreover, the La6Ge films demonstrate a terahertz (THz) cutoff frequency of 1.0 THz when illuminated with infrared and visible light. This cutoff frequency increases to 45.6 THz in the ultraviolet range. Furthermore, by utilizing the Drude–Lorentz method, the investigation of optical conductivity parameters reveals that the lanthanum germanide optical filters can achieve free hole density and drift mobility values of 14.44 cm2 V−1 s−1 and 2.8×1018 cm−3, respectively, under infrared light irradiation. The outstanding optical and dielectric properties exhibited by the La6Ge thin films make them excellent candidates for highly transparent optical filters suitable for terahertz technology.

La/Ge stacked nanosheets designed as optical resonators, microwave oscillators and 5 G/6 G gigahertz receivers

Glass/Ge and La/Ge stacked layers, 100 nm thick, were prepared via thermal evaporation under a vacuum pressure of 10−5 mbar. Structural analysis confirmed amorphous growth of Ge nanosheets. Optically coating Ge onto La improved light absorption, energy band gap, and dielectric responses. In addition, dielectric spectra fitting using Lorentz approach showed increased free electron density, plasmon frequency, and drift mobility (up to 1153 cm2/Vs) in Ge due to lanthanum presence. Moreover, LGA Schottky barrier devices (La/Ge/Au) exhibited tunneling-type current conduction with 0.815 eV barrier height and 40 nm width. Resistance spectra of these Schottky barriers displayed negative resistance near 0.40 GHz, while capacitance spectra showed resonance-antiresonance behavior. La/Ge and LGA interface can be utilized for optical receivers and microwave resonators in 5 G/6 G technologies.

Direct measurement of electron drift parameters in pixelated cadmium zinc telluride semiconductor detectors

The single-polarity charge-sensing electrode is widely used in wide-bandgap room-temperature CdZnTe detectors; in such systems, the drift of electrons is the primary contribution to the induced signal at the anode. Thus, it is important to accurately evaluate the parameters that describe the electron transport properties because they affect the performance of detectors. This paper proposes a method to directly measure the electron mobility and their mean free drift time in a pixelated CdZnTe detector using a depth-sensitive technique. The presented method considers the effect of the nonideal weighting potential in an actual detector, which has not been accounted for in previously proposed methods. In addition, by fitting the cathode waveform to avoid the effect of the time–amplitude walk due to the trigger threshold, improved measurement accuracy of the electron drift parameters can be achieved.

Kappa Free Light Chain Drift Prompts the Need for a New Upper Limit of Normal Free Light Chain Ratio to Avoid an Epidemic of Kappa Light Chain Monoclonal Gammopathy of Undermined Significance.

Multiple laboratory tests are employed for detection of monoclonal proteins in patients and include serum protein electrophoresis (SPEP), immunofixation electrophoresis, free light chain (FLC) immunoassay, and mass spectrometry (Mass-Fix). Recently, reports on a drift in FLC quantitation results have been brought to light. We studied a cohort of 16 887 patients whose sera were tested for a monoclonal protein by a FLC assay, serum protein electrophoresis, and Mass-Fix. This is a retrospective study designed to assess the impact of a drift on the performance of FLC ratio (rFLC) in groups of patients with and without detectable plasma cell disorders (PCDs). The results demonstrated that 63% of patients with monoclonal protein equal or higher than 2 g/L (by SPEP) had an abnormal rFLC (reference range 0.26-1.65). Conversely, 16% of patients with undetectable monoclonal protein by other methods (i.e., SPEP and Mass-Fix) who also had no record of treated PCD had an abnormal rFLC. In these cases, there was an imbalance in the number of kappa high rFLCs to lambda low rFLCs of 201 to 1. The results of this study suggest decreased specificity of rFLC for a monoclonal kappa FLC in the 1.65 to 3.0 range.

Tidal dissipation from free drift sea ice in the Barents Sea assessed using GNSS beacon observations

One of the major challenges facing global hydrodynamic tidal models is the modelling of the interaction between sea ice and tides in high-latitude waters. Recent studies have shown strong seasonal correlation between sea ice and tides. Hence, it is important to accurately model the effect of sea ice in a tidal model. Presence of sea ice leads to a frictional dissipation of tides. Most models either completely ignore sea ice or partly include it by assuming a fixed sea ice cover (landfast ice). However, sea ice can also be drifting and the nature of dissipation between drifting sea ice and tides is partly unknown. We assess the dissipation of tides due to free drift sea ice. In the absence of wind, this is negligible in the deeper and open ocean. For the shallow water regions, however, this dissipation is unknown. Here, we evaluate this dissipation for the Spitzbergen Shelf region using a beacon dataset showing strong free drift subdaily sea ice oscillations and a physics based point ice model. Two analyses were done which compared the model and observed motion. The analyses showed that for winds speeds below 8m/s and with low subdaily signals, the subdaily free drift sea ice motion is strongly connected to the tides and that the frictional dissipation is low. In the context of global tide and storm surge models, the dissipation from free drift sea ice on tides should be evaluated based on the region (deep ocean or shallow water) and existing wind conditions. In the presence of strong winds the dissipation between free drift sea ice and air can be significant on a subdaily scale even if there are no subdaily signals in the wind itself.

Representation of sea ice regimes in the Western Ross Sea, Antarctica, based on satellite imagery and AMPS wind data

Sea ice drift data at high spatial resolution and surface wind model output are used to explore atmosphere-sea ice interactions in the Western Ross Sea including the three main polynyas areas; McMurdo Sound polynya (MSP), Terra Nova Bay polynya (TNBP), and the Ross Sea polynya (RSP). This study quantifies the relationship between the winds and sea ice drift and observes the average and annual anomalies across the region. Sea ice drift velocities are based on high-resolution (150 m) Advanced Synthetic Aperture Radar (ASAR) images from Envisat for winters between 2002 and 2012. Sea ice motion vectors were first correlated with the corresponding Antarctic Mesoscale Prediction System (AMPS) surface wind velocities, and the sensitivity of the spatial correlations and residuals were examined. Four drift parameters were selected (mean drift, the correlation between drift and wind, drift to wind scaling factor, and the directional drift constancy) to perform an unsupervised k-means classification to automatically distinguish six zones of distinctive sea ice characteristics solely based on ice drift and wind information. Results indicate a heterogeneous pattern of sea ice movement at a rate ranging from 0.41 to 2.24% of the wind speed in different areas. We also find that the directional constancy of sea ice drift is closely related to the wind fields. Sea ice drift and wind velocities display the highest correlation in free-drift areas (R = 0.70), followed by deformational drift zones (R = 0.54), and more random drift areas (R = 0.28). The classification illustrates the significance of localized wind-driven sea ice drift in this coastal area resulting in zones of convergence, shear, and free drift. The results also indicate that the most persistent patterns of sea ice motion are near the RSP and TNBP areas, both being driven by strong localized winds. Our findings identify that large-scale sea ice motion is predominantly wind-driven over much of the study area while ocean currents play only a minor role.

Electron trapping & blocking effect enabled by MXene/TiO2 intermediate layer for charge regulation of triboelectric nanogenerators

As the existence of interfacial electric field, the surface charges of triboelectric nanogenerators (TENGs) would diffuse into air or tribo-material interior, resulting in the charge decay. Therefore, charge regulation from charge storage is crucial in addition to charge generation. In this work, a MXene/TiO2 hybrid film has been prepared through partial oxidation of MXene in a contact-separate mode TENG (MT-TENG) as an intermediate layer between negative tribo-material and bottom electrode. It demonstrates the electric outputs of 128 μC/m2 in charge density, 73.78 μW/cm3 and 63.78 μW/g in average power density with an energy conversion efficiency of 34.81%. The surface terminals in MXene nanosheets and the oxygen vacancies in TiO2 nanoparticles provide abundant electron trap sites. Moreover, the energy band bending resulting from the polarization effect of the hybrid film could further hinder the free electrons' drift to the bottom electrode, and consequently prevent the charge recombination. With the synergetic effect of electron storage and polarization, the MT-TENG with an intermediate layer rapidly reaches a charge dynamic equilibrium with a charge density of 80 μC/m2. It is expected to provide new insights for material science and structure design from the perspective of charge regulation to improve the output performance of TENGs.

A new state-dependent parameterization for the free drift of sea ice

Abstract. Free-drift estimates of sea ice motion are necessary to produce a seamless observational record combining buoy and satellite-derived sea ice motion vectors. We develop a new parameterization for the free drift of sea ice based on wind forcing, wind turning angle, sea ice state variables (thickness and concentration), and estimates of the ocean currents. Given the fact that the spatial distribution of the wind–ice–ocean transfer coefficient has a similar structure to that of the spatial distribution of sea ice thickness, we take the standard free-drift equation and introduce a wind–ice–ocean transfer coefficient that scales linearly with ice thickness. Results show a mean bias error of −0.5 cm s−1 (low-speed bias) and a root-mean-square error of 5.1 cm s−1, considering daily buoy drift data as truth. This represents a 35 % reduction of the error on drift speed compared to the free-drift estimates used in the Polar Pathfinder dataset (Tschudi et al., 2019b). The thickness-dependent transfer coefficient provides an improved seasonality and long-term trend of the sea ice drift speed, with a minimum (maximum) drift speed in May (October), compared to July (January) for the constant transfer coefficient parameterizations which simply follow the peak in mean surface wind stresses. Over the 1979–2019 period, the trend in sea ice drift in this new model is +0.45 cm s−1 per decade compared with +0.39 cm s−1 per decade from the buoy observations, whereas there is essentially no trend in a free-drift parameterization with a constant transfer coefficient (−0.09 cm s−1 per decade) or the Polar Pathfinder free-drift input data (−0.01 cm s−1 per decade). The optimal wind turning angle obtained from a least-squares fitting is 25∘, resulting in a mean error and a root-mean-square error of +3 and 42∘ on the direction of the drift, respectively. The ocean current estimates obtained from the minimization procedure resolve key large-scale features such as the Beaufort Gyre and Transpolar Drift Stream and are in good agreement with ocean state estimates from the ECCO, GLORYS, and PIOMAS ice–ocean reanalyses, as well as geostrophic currents from dynamical ocean topography, with a root-mean-square difference of 2.4, 2.9, 2.6, and 3.8 cm s−1, respectively. Finally, a repeat of the analysis on two sub-sections of the time series (pre- and post-2000) clearly shows the acceleration of the Beaufort Gyre (particularly along the Alaskan coastline) and an expansion of the gyre in the post-2000s, concurrent with a thinning of the sea ice cover and the observed acceleration of the ice drift speed and ocean currents. This new dataset is publicly available for complementing merged observation-based sea ice drift datasets that include satellite and buoy drift records.

An Assessment of Sea Ice Motion Products in the Robeson Channel Using Daily Sentinel-1 Images

Sea ice motion is an essential parameter when determining sea ice deformation, regional advection, and the outflow of ice from the Arctic Ocean. The Robeson Channel, which is located between Ellesmere Island and northwest Greenland, is a narrow but crucial channel for ice outflow. Only three Eulerian sea ice motion products derived from ocean/sea ice reanalysis are available: GLORYS12V1, PSY4V3, and TOPAZ4. In this study, we used Lagrangian ice motion in the Robeson Channel derived from Sentinel-1 images to assess GLORYS12V1, PSY4V3, and TOPAZ4. The influence of the presence of ice arches, and wind and tidal forcing on the accuracies of the reanalysis products was also investigated. The results show that the PSY4V3 product performs the best as it underestimates the motion the least, whereas TOPAZ4 grossly underestimates the motion. This is particularly true in regimes of free drift after the formation of the northern arch. In areas with slow ice motion or grounded ice floes, the GLORYS12V1 and TOPAZ4 products offer a better estimation. The spatial distribution of the deviation between the products and ice floe drift is also presented and shows a better agreement in the Robeson Channel compared to the packed ice regime north of the Robeson Channel.

Моделювання електродних систем газорозрядних гармат з фокусуванням електронного пучка в магнітному полі короткої лінзи

In the article, based on the analysis of the basic provisions of the theory of high - voltage glow discharge (HVGD), a method of modeling electrode systems of gas discharge guns with focusing of the electron beam in the field of a short magnetic lens is proposed. To calculate the electric field in the electrode system the finite-difference Poisson equation has been used, which, to simplify its using in the software, is written in the form of an arithmetic-logical expression. Analysis of the guiding of the electron beam in the free drift region was performed with using a system of equations of discrete mathematics based on the Rutherford scattering model. A numerical algorithm for calculating the focus position of the electron beam and its focal diameter is also proposed. To estimate the position of the plasma boundary, a simulation method based on the conversion of the anode plasma volume from a one-dimensional system to the actual spatial geometry of the electrodes was used. In this case, the calculation of the height of the anode plasma in a real electrode system is reduced to the analytical solution of the cubic equation. The calculation of the magnetic field of a short lens was performed using the Yavor model. To implement the proposed methods of modeling HVGD guns, it is proposed to use arithmetic and logical expressions and methods of matrix programming. The obtained results of calculations on the distribution of the electric field in the electrode system, the boundary trajectories of the electron beam in the field of magnetic lense, as well as the distribution of the current density in the focal plane of the hollow electron beam with the ring focus are presented.

The Shoreline Deformation in Convex Beach due to Sea Level Rise

Sea level rise (SLR) is become more serious on a global scale and has become one of the main reasons causes shoreline changes, and erosion, even on an extreme scale can cause the sinking of coastal areas and islands. It was recorded that many big cities were damaged by SLR. The Bruun rule is the most widely used method for predicting the horizontal translation of the shoreline associated with a given rise in sea level. In this study, however, the change in the average shoreline at the convex beach, which is more vulnerable to erosion due to sea level rise, is investigated. The increase in water depth by sea level rise causes a change in the wave crestline, ultimately leading to a linearization of the shoreline. In general, it is assumed that the annual average shoreline is parallel to the annual mean wave crestline. Moreover, assuming that the equilibrium depth contour is formed according to the crestline, the retreat of the shoreline is predicted. The shoreline change is indirectly predicted through the wave crestline deformation obtained from a wave model and this method is applied to the convex beach. Our result showed that for a convex beach with a length of 1 km has open ends with free littoral drift at both ends, the sea level rise of 1 m cause the erosion of 10 m in the protruding area, and the sea level rise of 2 m causes erosion of 23 m. However, if the convex beach is blocked at both ends, sea level rise of 1 m causes the erosion of 6.3 m in the convex area, but the shoreline advance of 3.8 m at both ends, and if the sea level rise of 2 m occurs, the erosion of 14.3 m can occur in the convex area and shoreline advance of 8.6 m can occur at both ends.