Flux Bias Research Articles

Investigating and comparing the IRIS spectral lines Mg II, Si IV, and C II for flare precursor diagnostics

Context. Reliably predicting solar flares can mitigate the risks of technological damage and enhance scientific output by providing reliable pointings for observational campaigns. Flare precursors in the spectral line Mg II have been identified. Aims. We extend previous studies by examining the presence of flare precursors in additional spectral lines, such as Si IV and C II, over longer time windows, and for more observations. Methods. We trained neural networks and XGBoost decision trees to distinguish spectra observed from active regions that lead to a flare and those that did not. To enhance the information within each observation, we tested different masking methods to preprocess the data. Results. We find average classification true skill statistics (TSS) scores of 0.53 for Mg II, 0.44 for Si IV, and 0.42 for C II. We speculate that Mg II h&k performs best because it samples the highest formation height range, and is sensitive to heating and density changes in the mid- to upper chromosphere. The flaring area relative to the field of view has a large effect on the model classification score and needs to be accounted for. Combining spectral lines has proven difficult, due to the difference in areas of high probability for an imminent flare between different lines. Conclusions. Our models extract information from all three lines, independent of observational bias or GOES X-ray flux precursors, implying that the physics encoded in a combination of high resolution spectral data could be useful for flare forecasting.

GRAVITY for MATISSE

Context. MATISSE, the mid-infrared spectro-imaging instrument of VLTI, was designed to deliver its designed performance when paired with an external second-generation fringe tracker. Science observations started in 2019, demonstrating imaging capabilities and faint science target observations. Now, the GRAVITY fringe tracker stabilises the MATISSE fringes, which allows the use of all spectroscopic modes and improves sensitivity and data accuracy. Aims. We present how the MATISSE and GRAVITY instruments were adapted to make the GRAVITY fringe tracker work with MATISSE, under the umbrella of the aptly named GRA4MAT project, led by ESO in collaboration with the two instrument consortia. Methods. We detail the software modifications needed to implement an acquisition and observing sequence specific to GRA4MAT, including simultaneous fringe tracking and chopping and a narrow off-axis capability inspired by the Galactic Centre and exoplanet capability of GRAVITY. We explain the modified data collection and reduction processes. We show how we leveraged the recent fringe tracker upgrade to implement features specific to its use with MATISSE, for example mitigation of fringe jumps with an improved group delay control, and simultaneous fringe tracking and chopping with a new state machine. Results. We successfully demonstrate significant improvements to the MATISSE instrument. Observations can now be performed at higher spectral resolutions of up to R ~ 3300 and across the full LM bands at once. Long detector integration times, made possible with stabilised fringes, have improved the LM-band sensitivity by a factor of 10. Low flux biases in coherently reduced N-band data have been eliminated. The L-band transfer function is now higher and more stable. We finally illustrate the scientific potential of GRA4MAT with a preview of the first exoplanet observation made by MATISSE on β Pictoris b.

Aerosol interference with open-path eddy covariance measurement in a lake environment

Open-path eddy covariance (OPEC) is widely used for measuring trace gas fluxes between the surface and the atmosphere. At a lake in Eastern China (Lake Taihu), the CO2 flux measured with OPEC was often negative at night (with values as low as −22.1 μmol m−2 s−1) and was coherent across the whole lake, as if the lake were a large sink of atmospheric CO2. The purpose of this study is to investigate the cause of this negative flux phenomenon. In addition to OPEC, we also used closed-path eddy covariance (CPEC) and the transfer coefficient (TC) method to measure the flux. The results show that the persistent negative CO2 flux phenomenon was observed with OPEC but not with CPEC or TC. Because air drawn into the CPEC analyzer was filtered but the OPEC analyzer was influenced by aerosol contamination, the most logical explanation was that particles deposited on the optical lens of the OPEC analyzer changed its cross-sensitivity to water vapor. The direct evidence of this interference was a strong positive correlation between the OPEC analyzer's signal strength and the CO2 mixing ratio observed at 10 Hz. We suggest that it is possible to perform post-field correction to this negative flux bias using the 10 Hz signal strength data. In comparison, an OPEC system at a nearby land site did not experience aerosol interference due to low water vapor flux at night and lack of hygroscopic growth of particles on the optical lens in low humidity conditions. The type of aerosol interference reported here may also occur in high humidity and high pollution conditions elsewhere.

Experimenting with D-Wave quantum annealers on prime factorization problems

This paper builds on top of a paper we have published very recently, in which we have proposed a novel approach to prime factorization (PF) by quantum annealing, where 8, 219, 999 = 32, 749 × 251 was the highest prime product we were able to factorize—which, to the best of our knowledge is the largest number which was ever factorized by means of a quantum device. The series of annealing experiments which led us to these results, however, did not follow a straight-line path; rather, they involved a convoluted trial-and-error process, full of failed or partially-failed attempts and backtracks, which only in the end drove us to find the successful annealing strategies. In this paper, we delve into the reasoning behind our experimental decisions and provide an account of some of the attempts we have taken before conceiving the final strategies that allowed us to achieve the results. This involves also a bunch of ideas, techniques, and strategies we investigated which, although turned out to be inferior wrt. those we adopted in the end, may instead provide insights to a more-specialized audience of D-Wave users and practitioners. In particular, we show the following insights: (i) different initialization techniques affect performances, among which flux biases are effective when targeting locally-structured embeddings; (ii) chain strengths have a lower impact in locally-structured embeddings compared to problem relying on global embeddings; (iii) there is a trade-off between broken chain and excited CFAs, suggesting an incremental annealing offset remedy approach based on the modules instead of single qubits. Thus, by sharing the details of our experiences, we aim to provide insights into the evolving landscape of quantum annealing, and help people access and effectively use D-Wave quantum annealers.

Stepwise Calibration of Age‐Dependent Biomass in the Integrated Biosphere Simulator (IBIS) Model

AbstractMany land surface models (LSMs) assume a steady‐state assumption (SS) for forest growth, leading to an overestimation of biomass in young forests. Parameters inversion under SS will potentially result in biased carbon fluxes and stocks in a transient simulation. Incorporating age‐dependent biomass into LSMs can simulate real disequilibrium states, enabling the model to simulate forest growth from planting to its current age, and improving the biased post‐calibration parameters. In this study, we developed a stepwise optimization framework that first calibrates “fast” light‐controlled CO2 fluxes (gross primary productivity, GPP), then leaf area index (LAI), and finally “slow” growth‐controlled biomass using the Global LAnd Surface Satellite (GLASS) GPP and LAI products, and age‐dependent biomass curves for the 25 forests. To reduce the computation time, we used a machine learning‐based model to surrogate the complex integrated biosphere simulator LSM during calibration. Our calibrated model led to an error reduction in GPP, LAI, and biomass by 28.5%, 35.3% and 74.6%, respectively. When compared with net biome productivity (NBP) using no‐age‐calibrated parameters, our age‐calibrated parameters increased NBP by an average of 50 gC m−2 yr−1 across all forests, especially in the boreal needleleaf evergreen forests, the NBP increased by 118 gC m−2 yr−1 on average, increasing the estimate of the carbon sink in young forests. Our work highlights the importance of including forest age in LSMs, and provides a novel framework for better calibrating LSMs using constraints from multiple satellite products at a global scale.

The Effect of Indian Ocean Surface Freshwater Flux Biases On the Multi-Stable Regime of the AMOC

The Effect of Indian Ocean Surface Freshwater Flux Biases On the Multi-Stable Regime of the AMOC

Modeling Land–Atmosphere Interactions over Semiarid Plains in Morocco: In-Depth Assessment of GCM Stretched-Grid Simulations Using In Situ Data

Abstract Land surface–atmosphere interactions are a key component of climate modeling. They are particularly critical to understand and anticipate the climate and the water resources over the semiarid and arid North African regions. This study uses in situ observations to assess the ability of the IPSL-CM global climate model to simulate the land–atmosphere interactions over the Moroccan semiarid plains. A specific configuration with a grid refinement over the Haouz Plain, near Marrakech, and nudging outside Morocco has been performed to properly assess the model’s performances. To ensure reliable model–observation comparisons despite the fact that station measurements are not representative of a mesh-size area, we carried out experiments with adapted vegetation properties. Results show that the CMIP6 version of the model’s physics represents the near-surface climate over the Haouz Plain reasonably well. Nonetheless, the simulation exhibits a nocturnal warm bias, and the wind speed is overestimated in tree-covered meshes and underestimated in the wheat-covered region. Further sensitivity experiments reveal that LAI-dependent parameterization of roughness length leads to a strong surface wind drag and to underestimated land surface atmosphere thermal coupling. Setting the roughness heights to the observed values improves the wind speed and, to a lesser extent, the nocturnal temperature. A low bias in latent heat flux and soil moisture coinciding with a pronounced diurnal warm bias at the surface is still present in our simulations. Including a first-order irrigation parameterization yields more realistic simulated evapotranspiration flux and daytime skin surface temperatures. This result raises the importance of accounting for the irrigation process in present and future climate simulations over Moroccan agricultural areas.

Broadband coplanar-waveguide-based impedance-transformed Josephson parametric amplifier

Quantum-limited Josephson parametric amplifiers play a pivotal role in advancing the field of circuit quantum electrodynamics by enabling the fast and high-fidelity measurement of weak microwave signals. Therefore, it is necessary to develop robust parametric amplifiers with low noise, broad bandwidth, and reduced design complexity for microwave detection. However, current broadband parametric amplifiers either have degraded noise performance or rely on complex designs. Here, we present a device based on the broadband impedance-transformed Josephson parametric amplifier that integrates a hornlike coplanar waveguide transmission line, which significantly decreases the design and fabrication complexity while keeping comparable performance. The device shows an instantaneous bandwidth of 700 (200) MHz for 15 (20) dB gain with an average input saturation power of −110 dBm and near quantum-limited added noise. The operating frequency can be tuned over 1.4 GHz using an external flux bias. We further demonstrate the negligible backaction from our device on a transmon qubit. The amplification performance and simplicity of our device promise its wide adaptation in quantum metrology, quantum communication, and quantum information processing. Published by the American Physical Society 2024

Drivers of coupled climate model biases in representing Labrador Sea convection

This study investigates the representation of ocean convection in the Labrador Sea in seven Earth System Models (ESMs) from the Coupled Model Intercomparison Project Phase 5 and 6 datasets. The relative role of the oceanic and atmospheric biases in the subpolar North Atlantic gyre are explored using regional ocean simulations where the atmospheric forcing or the ocean initial and boundary conditions are replaced by reanalysis data in the absence of interactive air-sea coupling. Commonalities and differences among model behaviors are discussed with the objective of finding a pathway forward to improve the representation of the ocean mean state and variability in a region of fundamental importance for climate variability and change. Results highlight that an improved representation of ocean stratification in the North Atlantic subpolar gyre is urgently needed to constrain future climate change projections. While improving the ocean model resolution in the North Atlantic alone may contribute a better representation of both boundary currents and propagation of heat and freshwater anomalies into the Labrador Sea, it may not be sufficient. Addressing the atmospheric heat flux bias with better resolution in the atmosphere and land topography may allow for deep convection to occur in the Labrador Sea in some of the models that miss it entirely, but the greatest priority remains improving the representation of ocean stratification.

Neutral Tropical African CO2 Exchange Estimated From Aircraft and Satellite Observations

AbstractTropical lands play an important role in the global carbon cycle yet their contribution remains uncertain owing to sparse observations. Satellite observations of atmospheric carbon dioxide (CO2) have greatly increased spatial coverage over tropical regions, providing the potential for improved estimates of terrestrial fluxes. Despite this advancement, the spread among satellite‐based and in‐situ atmospheric CO2 flux inversions over northern tropical Africa (NTA), spanning 0–24°N, remains large. Satellite‐based estimates of an annual source of 0.8–1.45 PgC yr−1 challenge our understanding of tropical and global carbon cycling. Here, we compare posterior mole fractions from the suite of inversions participating in the Orbiting Carbon Observatory 2 (OCO‐2) Version 10 Model Intercomparison Project (v10 MIP) with independent in‐situ airborne observations made over the tropical Atlantic Ocean by the National Aeronautics and Space Administration (NASA) Atmospheric Tomography (ATom) mission during four seasons. We develop emergent constraints on tropical African CO2 fluxes using flux‐concentration relationships defined by the model suite. We find an annual flux of 0.14 ± 0.39 PgC yr−1 (mean and standard deviation) for NTA, 2016–2018. The satellite‐based flux bias suggests a potential positive concentration bias in OCO‐2 B10 and earlier version retrievals over land in NTA during the dry season. Nevertheless, the OCO‐2 observations provide improved flux estimates relative to the in situ observing network at other times of year, indicating stronger uptake in NTA during the wet season than the in‐situ inversion estimates.

Enhancing nickel grade and recovery with counter-current washing of the concentrated bubbly-zone of a single stage REFLUX™ Flotation Cell

The recovery and concentration of the nickel sulphide mineral, pentlandite, present several challenges due to its relatively slow flotation, leading to excessive hydrophilic gangue minerals in the concentrate. The REFLUX™ Flotation Cell (RFC™) offers the potential for a significant hydrodynamic advantage over conventional flotation. Much of this advantage is due to the replacement of the pulp and froth phases with a concentrated bubbly zone, which in turn supports more intense counter-current washing by permitting a powerful and effective positive bias flux. Thus, the aim of this study was to investigate the nickel recovery and silica rejection in the RFC™, by applying a wide range of positive bias fluxes. The focus was on a single stage of separation in the RFC™ using a feed flux of 0.63 cm/s at a feed nickel grade of 2.1%. At the lowest bias flux of 0.1 cm/s, a nickel grade of 7.5% was obtained at a single stage recovery of 70.2%. By increasing the bias flux to 0.42 cm/s, the grade increased to 9.7% but the recovery fell to 64.9%. With an extreme bias flux of 1.04 cm/s, the grade reached 12.3%, while the recovery fell to 54.7%. The selectivity, given by the nickel recovery relative to the silica recovery, was estimated to be 121 at the highest bias flux, declining sharply with a reduction in the bias flux. The performance ratio proposed by Parkes et al (2022) was quantified by comparing the RFC™ performance with the batch kinetic results from a mechanical cell, the product grade being ∼7%. The performance ratio was based on the experiment at the lowest bias flux used in the RFC™, and found to be at least 6, meaning the RFC™ footprint would be reduced by a factor of ∼6 for a similar product grade. Based on the higher product grades achieved in the RFC™ using the higher positive bias fluxes, the performance ratio would likely exceed 10-fold given the need for the mechanical cell concentrate to undergo at least one further stage of flotation.

Synthetic complex Weyl superconductors, chiral Josephson effect and synthetic half-vortices

We show that the most generic form of spin-singlet superconducting order parameter for chiral fermions in systems with broken time reversal symmetry and inversion symmetry is of the Delta _s+igamma ^5Delta _5 where Delta _s is the usual order parameter and Delta _5 is the pseudo-scalar order parameter. After factoring out the U(1) phase e^{iphi }, this form of superconductivity admits yet additional complex structure in the plane of (Delta _s,Delta _5). The polar angle chi in this plane, which we call the chiral angle, can be controlled by the external flux bias. We present a synthetic setup based on stacking of topological insulators (TIs) and superconductors (SCs). Alternatively flux biasing the superconductors with a fluxes pm Phi leads to Delta _5=Delta _0 sin (chi ), where Delta _0 is the superconducting order parameter of the SC layers, and the chiral angle chi ={2pi }Phi /Phi _0 is directly given by the flux Phi in units of the flux quantum Phi _0=h/(2e). This can be used as a building block to construct a two-dimensional Josephson array. In this setup chi will be a background field defining a pseudoscalar Delta _5 that can be tuned to desired configuration. While in a uniform background field Delta _5 the dynamics of phi is given by standard XY model and its associated vortices, a staggered background pm Delta _5 (or equivalently chi and chi +pi in alternating lattice sites) creates a new set of minima for the phi field that will support half-vortex excitations. An isolated single engineered “half-vortex” in the chi field in an otherwise uniform background will bind a phi -half-vortex. This is similar to the way a p-wave superconducting vortex core binds a Majorana fermion.

Hardware Implementation of Quantum Stabilizers in Superconducting Circuits.

Stabilizer operations are at the heart of quantum error correction and are typically implemented in software-controlled entangling gates and measurements of groups of qubits. Alternatively, qubits can be designed so that the Hamiltonian corresponds directly to a stabilizer for protecting quantum information. We demonstrate such a hardware implementation of stabilizers in a superconducting circuit composed of chains of π-periodic Josephson elements. With local on-chip flux and charge biasing, we observe a progressive softening of the energy band dispersion with respect to flux as the number of frustrated plaquette elements is increased, in close agreement with our numerical modeling.

Compact superconducting transmon qubit circuits made of ultrathin NbN

We design and fabricate a compact superconducting qubit circuit made of nano-thick NbN film on a high-resistivity silicon substrate, carrying seven transmon qubits. By comparing with the conventional superconducting qubit circuits made of superconducting films with hundred-nanometer thickness, our superconducting qubit circuit has much smaller size in the readout circuit, whose resonator length is only about 1/20 of that in a conventional superconducting circuit. Transmons are measured and characterized in the frequency and time domains with different flux bias. The transition frequency f01 can be adjusted in the range of several GHz. The qubit circuits made of such nano-thick material with high kinetic inductance are promising in the integration of quantum circuits.

Recent variations in oceanic transports across the Greenland–Scotland Ridge

Abstract. Oceanic exchanges across the Greenland–Scotland Ridge (GSR) play a crucial role in shaping the Arctic climate and linking with the Atlantic meridional overturning circulation. Most considered ocean reanalyses underestimate the observed 1993–2020 mean net inflow of warm and saline Atlantic Water of 8.0 ± 0.5 Sv by up to 15 %, with reanalyses at 0.25∘ resolution additionally exhibiting larger biases in the single inflow branches compared to higher-resolution products. The underestimation of Atlantic Water inflow translates into a low bias in mean oceanic heat flux at the GSR of 5 %–22 % in reanalyses compared to the observed value of 280 ± 18 TW. Interannual variations in reanalysis transports correlate reasonably well with observed transports in most branches crossing the GSR. Observations and reanalyses with data assimilation show a marked reduction in oceanic heat flux across the GSR of 4 %–9 % (compared to 1993–2020 means) during a biennial (2-year-long) period centered on 2018, a record low for several products. The anomaly was associated with a temporary reduction in geostrophic Atlantic Water inflow through the Faroe–Shetland branch and was augmented by anomalously cool temperatures of Atlantic Water arriving at the GSR. The latter is linked to a recent strengthening of the North Atlantic subpolar gyre and illustrates the interplay of interannual and decadal changes in modulating transports at the GSR.

Effects of toroidally-distributed-divertor biasing on scrape-off-layer (SOL) current drive, divertor particle flux and fast electron confinement in the QUEST spherical tokamak

A novel divertor biasing by four biasing plates distributed toroidally (TDDB) on the upper divertor target plate is applied to low density tokamak plasmas started-up by 28 GHz 2nd harmonic electron cyclotron current drive (ECCD) in a quasi-double null configuration of the QUEST spherical tokamak (ST). In the ST plasmas of line averaged electron density < ne > ∼0.7–1 × 1018 m−3, about 20%–40% of the current Ibias driven by ∼85 V sawtooth bias voltage reaches the lower divertor plate along the biased scrape-off-layer (SOL) flux tube as the SOL current ISOL . The fact ISOL is noticeably lower than Ibias indicates an appreciable leakage of parallel current from the biased SOL flux tube. The leakage currents in the toroidal and radial directions are confirmed by detection of them using the unbiased plates in the TDDB experiments. From the ion saturation current density profile obtained by a divertor Langmuir probe array, the fall-off lengths of divertor particle flux are estimated together with the strike line position. Total particle flux to the upper divertor, evaluated by the integrated ion saturation current density profile is reduced by up to 45% during positive biasing of the TDDB, depending on the position of the strike line to the biased plate. In addition, the TDDB also induces a noticeable loss of fast electrons produced by ECCD, leading to an ∼2% reduction in the maximum toroidal current of the ST plasma compared to a shot without the TDDB. Reduction of the divertor particle flux and enhancement of the fast electron losses are thought to be dominantly caused by E ×B drift induced by the TDDB. In the present experimental conditions, the effects of magnetic perturbations produced by the SOL currents on the fast electron losses can be neglected because of a too small SOL current.

Microwave Switch Architecture for Superconducting Integrated Circuits Using Magnetic Field-Tunable Josephson Junctions

We report on the design, fabrication, and measurement of a low-temperature microwave switch architecture that can be fully integrated on chip using single Josephson junctions and superconducting bias lines. The basic switching element used is a reflective single-pole-single-throw switch that is realized by tuning the critical current of a single Josephson junction by way of a local flux bias. A single-pole-single-throw switch is demonstrated at 4.2 K to have an on/off ratio in excess of 20 dB up to 12 GHz. This element is then incorporated into the design of a single-pole-double-throw switch that exhibits an on/off ratio above 20 dB up to 10 GHz. The switches require no intrinsic power dissipation in either state, and their performance was verified for input powers of -100 dBm to -60 dBm. S-parameter simulations using a simple lumped element model are in good agreement with the experimental data, allowing for the design to be extended to larger switch architectures.

Magnetic Flux Bias Compensation Based on Voltage Injection Method With an Auxiliary DC/DC Converter

DC bias will make the transformer core saturated, causing local overheating and insulation materials aging. Therefore, it is great of significance to study the suppression of DC bias in transformers. In this paper, a magnetic compensation scheme of DC bias based on a hybrid transformer (HT) integrated an auxiliary DC/DC converter is proposed. Firstly, a compensation mechanism is established by designing a novel HT topology structure, which lays the magnetic circuit foundation of DC bias compensation. Secondly, the mathematical model of transformer DC bias is established, and the DC compensation amount of HT is derived. A transient simulation model of three-phase HT is established by the finite element model, and the situation of the DC bias before and after the compensation is analyzed. Finally, the platform of the DC bias compensation scheme is built. The full compensation experiment of DC bias is simulated by two parallel HT. The experimental results show the DC bias compensation effect is obvious, the distortion of excitation current, temperature rise and flux density distribution drop obviously, which verifies the correctness of the scheme proposed in this paper. It provides a reference for solving the problem of DC bias.

Weak Radio Frequency Signal Reception Sensitivity Based on DC Superconducting Quantum Interference Devices

Superconducting quantum interference devices (SQUIDs) are promising for detection of extremely weak power regimes for the Internet of Things (IoT) and long-distance satellite networks. In low-frequency magnetic signal measurements, it has demonstrated superior performance over traditional systems. We review the resistively-and-capacitively-shunted junction (RCSJ) model of DC SQUIDs and investigate its transfer function to magnetic flux signals while taking thermal fluctuation into account. We numerically evaluate the influence of bias current and bias flux signal to determine the operating parameters of the device. The performances related to SQUID ring inductance operating at 4.2 K and 77 K are demonstrated. Combined with common radio frequency (RF) front-end modules, including low-noise amplifier (LNA) and low-pass filter, we evaluate the bit-error-rate (BER) performance of the system under different inductance values and inferred that the sensitivity of the system can reach -99 dBm at 100 MHz bandwidth.

Performance Analysis of Outer Rotor Multi-Tooth Biased Flux Permanent Magnet Motors

This paper proposes two biased flux permanent magnet (BFPM) motors in which the torque ripple issue of conventional doubly salient permanent magnet (DSPM) motor, as its predecessor, is greatly suppressed and the torque density of the BFPM structures has been improved. The permanent magnets (PMs) are positioned where they are easily accessible for an even better temperature management compared to other stator-PM structures. The second structure utilizes the available space between stator poles in which two sets of PMs are embedded between stator modules. This increases the torque density even more. The operation principles of these two structures are deeply discussed by identifying working harmonics of each flux source and then evaluated by the finite element method (FEM). An analytical procedure by deriving sizing equations of the structures is introduced and the effect of different design parameters on the electromagnetic performance is comprehensively studied. The performances of the structures are analysed by FEM. To better evaluate the superiority of the proposed structures, a demagnetization analysis is conducted and it is shown that even in high temperatures, the performance degradation of the proposed structures is much lower compared to other stator-PM structures. Finally, the proposed structures are prototyped to verify the simulation results.