Operating Regimes Research Articles

On the Noise Estimation in Super Dual Auroral Radar Network Data

AbstractThe Super Dual Auroral Radar Network (SuperDARN) currently consists of more than thirty high‐frequency (HF, 3–30 MHz) radars covering mid‐latitude to polar regions in both hemispheres. Their major task is to map ionospheric plasma circulation which provides information about the interactions between the solar wind and the near‐Earth's space plasma environment. One of the major factors defining radar data quality is the signal‐to‐noise ratio (SNR), which requires an accurate characterization of the HF noise. The standard SuperDARN data analysis software uses the SNR as part of a set of empirical procedures designed to remove low‐quality data from further analysis. In this study we found that the currently used empirical algorithm systematically underestimates the noise level by up to 40%. Based on comparison of theoretical and observational noise statistics, we resolve this issue by designing and validating a procedure for accurate background noise level estimation. We then propose a simple SNR threshold to replace the existing criteria for excluding low‐quality data. In addition, we show that several aspects of the radar operational regime design, as well as short‐lived anthropogenic radio interference, can adversely affect the quality of the noise estimates at selected radar sites, and we propose ways to mitigate these problems.

Effects of surfactant size and concentration on the internal flow fields of moving slug and Disk-like droplets via μ-PIV

• • A laser-based phase-locking system is developed and integrated with a Micro Particle Image Velocimetry system enabling quantitative measurement of the internal velocity of moving droplets. • • Effects of surfactant size on the flow field of moving droplets are investigated by choosing two surfactants, Sodium Dodecyl Sulphate (SDS) and Tween 20, which have a large difference in adsorption timesale. • • Effects of surfactant concentration (zero to 10X) on the internal flow field of moving droplets are evaluated and discussed. • • Effects of droplet shape (slug and spherical) and droplet generation regimes on the internal flow field of moving droplets with surfactant are investigated and discussed. • • It is revealed that achievement of complete remobilisation in the internal flow depends on surfactant type, concentration, and droplet operating regime. Understanding the effects of surfactant on the internal flow field of moving droplets is of fundamental and practical importance. A laser-based phase-locking system was developed and coupled with a micro particle image velocimetry system enabling quantitative measurement of the internal droplet flow filed. Five concentrations (zero to 10X critical micelle concentration) of each of the two surfactants, Sodium Dodecyl Sulphate (SDS) and Tween 20, which present a large difference in adsorption timescale, were evaluated. Slug- and disk-shaped droplets were considered because of their different contact area with channel walls and thus the resulted friction. Squeezing and transition droplet formation regimes which normally yield monodispersed droplets were evaluated using SDS. Flow retardation was observed at low surfactant concentrations for slug droplets, which was primarily attributed to the induced Marangoni flow opposing the internal flow. Achievement of complete remobilisation in the internal flow depends on surfactant type, concentration, and droplet operating regime.

Turbine blade strike tests for evaluation and optimization of fish-friendly turbine

Widening the knowledge for fish injury and mortality mechanism caused by pressure, shear stress and blade strikes inside turbine was constructive for optimizing fish-friendly turbine design and turbine operation regime. A special designed test equipment was applied for simulating the rotating blade inside turbine passage, anesthetized fish (crucian carp) was placed on the route of the blade for strike tests. The fish length, blade thickness, strike angle, and strike speed were independent variables during the tests, the injury rate, degree of injury and mortality rate were analysed according to observation or anatomical examination after repeated tests. The injury types were classified into: imbalance, ribs broken, gill cover broken, internal hemorrhage and death. The injury severity was directly affected by strike speed under same blade thickness and fish length. The ratio of blade thickness and fish length also affect the injury rate. Multiple injuries can be observed on one fish after tests, and combined injuries are more likely to lead to death. In the fish-friendly turbine design, blade thickness in the leading edge and blade numbers shall be carefully considered and the rotational speed shall be calculated.

Superconducting hot-electron bolometer mixers and their applications

Superconducting hot electron bolometer (HEB) mixers are the most sensitive heterodyne detectors at frequencies beyond 1 THz, and are used for many astronomical observations. HEB, consisting of a narrow and short superconducting thin film patch connected to an antenna via contact pads, is brought into a highly sensitive operating regime by applying a DC current and a certain amount of local-oscillator power. Potentially, superconducting HEB mixers are capable of exhibiting high sensitivity for frequencies up to several tens of THz, as their output noise and conversion gain are nearly frequency independent according to the mixing mechanism. Moreover, the understanding of mixing mechanism has evolved over time from lumped-element model to distributed hot-spot model. In this review, we provide an overview of theoretical and experimental studies on HEBs and their applications, especially in astronomical observations on ground, airborne and space telescopes.

Dense velocity reconstruction with VIC-based time-segment assimilation

The vortex-in-cell time-segment assimilation (VIC-TSA) method is introduced. A particle track is obtained from a finite number of successive time samples of the tracer’s position and velocity can be used for reconstruction on a Cartesian grid. Similar to the VIC + technique, the method makes use of the vortex-in-cell paradigm to produce estimates of the flow state at locations and times other than the measured ones. The working principle requires time-resolved measurements of the particles’ velocity during a finite time interval. The work investigates the effects of the assimilated length on the spatial resolution of the velocity field reconstruction. The working hypotheses of the VIC-TSA method are presented here along with the numerical algorithm for its application to particle tracks datasets. The novel parameter governing the reconstruction is the length of the time-segment chosen for the data assimilation. Three regimes of operation are identified, based on the track length and the geometrical distance between neighbouring tracks. The regime of adjacent tracks arguably provides the optimal trade-off between spatial resolution and computational effort. The VIC-TSA spatial resolution is evaluated first by a numerical exercise; a 3D sine wave lattice is reconstructed at different values of the particles concentration. The modulation appears to reduce (cut-off delay) when the time-segment length is increased. Large-scale PIV experiments in the wake of a circular cylinder at Red = 27,000 are used to evaluate the method’s suitability to real data, including noise and data outliers. Both primary vortex structures in the Kármán wake as well as interconnecting ribs are present in this complex flow field, with a typical diameter close to the average inter-particle distance. When the time-segment is increased to adjacent tracks and beyond, a more regular time dependence of local and Lagrangian properties is observed, confirming the suitability of the time-segment assimilation for accurate reconstruction of sparse velocity data.Graphical abstract

Single-flow multiphase flow batteries: Experiments

The share of electricity generated from renewable sources is growing rapidly, and thus grid-scale battery storage is becoming more prevalent. Aqueous redox flow batteries have the potential to provide safe and scalable energy storage, but the high cost of storage, particularly the membrane and balance of plant costs, has inhibited commercialization. The recently developed single-flow battery leveraging a multiphase electrolyte promises a low-cost system, as it is membraneless and uses only one tank and flow loop, but suffers from low Coulombic efficiency. To unlock the potential of such a system, the interplay between interphase mass transport, multiphase flow phenomena, and battery performance must be unraveled. Here, we compare our previously developed theoretical battery model derived from a boundary layer analysis to results from a dedicated experimental program. This led to several key findings, including that our battery operates in a regime characterized by a high Stanton number, and that our analytical solutions led to excellent predictions in various operational regimes when using the interphase mass transport coefficient as a single-valued fitting parameter. In other regimes, such as at low electrolyte velocity, results indicate that gravity acting on the denser polybromide phase played a significant role, and thus gravitational effects should be incorporated in future models.

Universal Deterministic Quantum Operations in Microwave Quantum Links

We propose a realistic setup, inspired by already existing experiments, within which we develop a general formalism for the implementation of distributed quantum gates. Mediated by a quantum link that establishes a bidirectional quantum channel between distant nodes, our proposal works both for inter- and intra node communication and handles scenarios ranging from the few to the many modes limit of the quantum link. We are able to design fast and reliable state transfer protocols in every regime of operation, which, together with a detailed description of the scattering process, allows us to engineer two sets of deterministic universal distributed quantum gates. Gates whose implementation in quantum networks does not need entanglement distribution nor measurements. By employing a realistic description of the physical setup we identify the most relevant imperfections in the quantum links as well as optimal points of operation with resulting infidelities of $1-F \approx 10^{-2}-10^{-3}$.

Information processing second law for an information ratchet with finite tape.

We model a class of discrete-time information ratchet with a finite tape and explore its thermodynamic consequence as a Maxwell demon. We found that, although it supports the operational regime of an engine or eraser, it cannot typically sustain these thermodynamic functionalities due to eventual equilibration as a result of the finite information capacity of the tape. Nonetheless, cumulative work can be accrued or expended through successive tape scans and we prove that at all time the ratchet obeys the information processing second law (IPSL). Unlike the IPSL for the infinite-tape ratchet which operates only at the stationary state, the IPSL here is applicable also at the transient phase of the ratchet operation. We explore two ratchet designs with the single-state perturbed coin (PC) ratchet being the simplest ratchet without memory, while the double-state modified Boyd's (MB) ratchet is the simplest ratchet with memory. Our analysis shows that the MB ratchet can harness correlation to accumulate more work by having a larger time constant to reach steady state relative to the PC ratchet.

Retrospective quality by design r(QbD) for lactose production using historical process data and design of experiments

Quality by Design (QbD) is a popular formal approach for designing, upscaling and optimizing industrial production facilities towards guaranteed quality. To avoid the many costly experiments required for QbD, historical production data may be exploited for optimization instead in what is known as a retrospective QbD (rQbD) study. Current rQbD literature does limitedly discuss data-driven identification of Critical Process Parameters (CPPs) to optimize limited process knowledge availability, and does not cover situations where technical operation limits have not yet been fully explored and/or where parallel equipment (lines) are used. This work presents a new rQbD strategy that addresses these challenges by balancing knowledge that can be obtained from statistical analysis of historical data, together with process experts with a carefully designed set of plant-scale experiments within current operational limits. This novel strategy is demonstrated on a long-running industrial lactose production facility. By digitally and experimentally exploring historical operation variability, we found new operational regimes for this production that may lead to up to 7% product quality improvement, reduced energy consumption and increased process understanding. Although optimizing a specific process by necessity requires a process-specific approach, the way in which we systematically optimize the current process with Hybrid AI (combining available knowledge with new insights from historical data) shows that approaches that are currently used in prospective process upscaling may be modified to be invaluable for optimization of full-scale processes with a long operational history.

Implementation of free-space Fourier Ptychography with near maximum system numerical aperture.

Over the past decade, the research field of Fourier Ptychographic Microscopy (FPM) has seen numerous innovative developments that significantly expands its utility. Here, we report a high numerical aperture (NA) FPM implementation that incorporates some of these innovations to achieve a synthetic NA of 1.9 - close to the maximum possible synthetic NA of 2 for a free space FPM system. At this high synthetic NA, we experimentally found that it is vital to homogenize the illumination field in order to achieve the best resolution. Our FPM implementation has a full pitch resolution of 266 nm for 465 nm light, and depth of field of 3.6 µm. In comparison, a standard transmission microscope (incoherent) with close to maximum possible NA of 0.95 has a full pitch resolution of 318 nm for 465 nm light, and depth of field of 0.65 µm. While it is generally assumed that a free-space coherent imaging system and a free-space incoherent imaging system operating at their respective maximum NA should give comparable resolution, we experimentally find that an FPM system significantly outperforms its incoherent standard microscopy counterpart in resolution by a factor of 20%. Coupled with FPM's substantially longer effective depth of field (5.5 times longer), our work indicates that, in the near-maximum NA operation regime, the FPM has significant resolution and depth of field advantages over incoherent standard microscopy.

Fluid–structure interactions of energy-harvesting membrane hydrofoils

We study the kinematics, dynamics and flow fields generated by an oscillating, compliant membrane hydrofoil extracting energy from a uniform water stream at a chord-based Reynolds number $Re \approx 3 \times 10^4$ . Hydrodynamic forces during the foil's motion cause the membrane to dynamically morph its shape, effectively increasing the camber during the oscillation cycle. The membrane's deflection is modelled using the Young–Laplace equation, with pressure term approximated from thin-airfoil theory. Simultaneous tracking of the membrane deformation and the surrounding flow field using laser profiling and particle image velocimetry, respectively, reveals the role of dynamic cambering in stabilizing the leading-edge vortices on the membrane. In this regime of operation, we obtain up to 160 % higher power extraction when compared to a rigid, symmetric hydrofoil. The present work provides a demonstration of how passive compliance of soft materials interacting with fluids may be exploited in tidal and fluvial energy extraction.

Generation of cylindrical vector beams in a linear cavity mode-locked fiber laser based on nonlinear multimode interference.

In this paper, a linear cavity mode-locked pulsed fiber laser generating cylindrical vector beams (CVBs) is proposed and demonstrated based on a nonlinear multimode interference. A homemade long-period fiber grating with a broad bandwidth of 121 nm is used as a mode converter inside the cavity. The saturable absorber was formed by single-mode fiber-graded index multimode fiber-single mode fiber (SMF-GIMF-SMF) structure. By controlling the pump power, the operation states are switchable among continuous-wave, Q-switched mode-locked (QML), and mode-locked regimes. The repetition rate of the QML CVB pulse envelope varies from 57.4 kHz to 102.7 kHz at the pump range of 118 to 285 mW. When increasing pump power to 380 mW, mode-locked CVB pulse repetition rate of 3.592 MHz, and pulse duration of 4.62 ns are achieved. In addition, the maximum single-pulse envelope energy can reach 510 nJ, and 142 mW average-power CVBs with a slope efficiency of as high as 20.2% can be obtained. Moreover, azimuthally and radially polarized beams can be obtained with mode purity over 95% in different operating regimes. The proposed fiber laser has a simple structure, and the operation is controllable in both temporal and spatial domains, which presents a flexible pulsed CVB source for application of laser processing, time or mode division multiplexing system, and spatiotemporal nonlinear optics.

Demonstration of a flexible electro-optic polymer modulator with a low half-wave voltage for ECG signals acquisition

Polymer-based electro-optic (EO) modulators have the advantages of low half-wave voltages and a low-cost preparation process and thus have extensive application prospects. A flexible, low half-wave voltage SU-8 Mach–Zehnder (M-Z) EO polymer modulator was proposed for human electrocardiogram (ECG) signal detection; polydimethylsiloxane (PDMS) was used as the substrate, and crosslinked polymer disperse red 1 (DR1)/SU-8 was used as the waveguide core layer. PDMS surface modification and SU-8 polarization were achieved, and the device was prepared by spin coating, ultraviolet (UV) lithography, wet etching and low-temperature sputtering. The experimental results show that the modulator initially operates in a linear operating regime under unbiased voltage conditions, and direct linear modulation of the voltage can be realized. After the preparation process, the low half-wave voltage was measured to be 2 V with a core size of 4000 μm×22000 μm, and the loss of the device was −2.1 dB.

The determination of the measurement beam source in a chromatic confocal displacement sensor integrated with an optical laser head

The intensity of the measurement beam reaching the detector of the optical measurement system is important with regards to its functionality. This intensity is even more critical, due to the limited range of generated power, in the case of optical systems based on a broadband source of the measurement beam due to the limited range of generated power. In this paper, we proposed an approach for determining such an intensity in the case of an optical system consisting of a chromatic confocal displacement sensor integrated with an optical laser head. Two system operation regimes (off-line and on-line) were investigated, i.e. before/after and during laser material processing, respectively. The issues affecting the investigated intensity, such as the transmission of the optical path, the reflection from the sample, and the influence of radiation that occurs during laser material processing were comprehensively described and analyzed. Subsequently, the numerically achieved results were experimentally verified. Finally, the power of the measurement beam’s source, as well as its spectral characteristics, were determined separately for the optical system operating in the off-line and on-line regime, respectively.

Operational regimes of lasers based on gain media with a large Raman scattering cross-section

We report on unusual regimes of operation of a laser with a gain medium with a large Raman scattering cross-section, which is often inherent in new types of gain media such as colloidal and epitaxial quantum dots and perovskite materials. These media are characterized by a strong electron–phonon coupling. Using the Fröhlich Hamiltonian to describe the electron–phonon coupling in such media, we analyze the operation of the system above the lasing threshold. We show that below a critical value of the Fröhlich constant, the laser can only operate in the conventional regime: namely, there are coherent cavity photons but no coherent phonons. Above the critical value, a new pump rate threshold appears. Above this threshold, either joint self-oscillations of coherent phonons in the gain medium and photons in a cavity or a chaotic regime are established. We also find a range of the values of the Fröhlich constant, the pump rate, and the resonator eigenfrequency, in which more than one dynamical regime of the system is stable. In this case the laser dynamics is determined by the initial values of the resonator field, the active medium polarization, the population inversion, and phonon amplitude.

Nonlinear analysis and control of an underactuated 3-DOF control moment gyroscope with experimental validation

Nonlinear controllers have been extensively abstracted in recent times. Nevertheless, real time implementation for underactuated MIMO physical systems is rarely attempted. This work proposes a nonlinear framework based on dynamical analysis and the sliding mode based control technique to control a highly coupled and nonlinear MIMO underactuated control moment gyroscope. First, an analytical formulation based on dynamic characterization is proposed to understand both the unactuated dynamics and the performance constraints of the gyroscope. This characterization helps in designing a feasible nonlinear sliding mode controller which helps in a simple and straightforward control of the system through the entire operating regime. The effectiveness of the proposed nonlinear control and analytical framework is established by successful implementation on the experimental gyroscope setup.

Resonantly induced mitigation of supermode noise in a harmonically mode-locked fiber laser: revealing the underlying mechanisms.

We have performed experimental and numerical studies enabling clear insight into the physical mechanisms underlying the super-mode noise mitigation in harmonically mode-locked (HML) fiber lasers using the resonant continuous wave (CW) injection. New experiments have refined the requirements to the positions inside the laser spectrum assigned to the injected CW component, a Kelly sideband, and the transparency peaks of the birefringent fiber filter. In particular, we have proved experimentally that the noise mitigation effect is dominating with the CW injected to the long-wavelength side of laser spectrum. Injection to the opposite side destroys the HML operation regime. Our numerical simulations confirm these specific features. To get the result, we have simulated phase-locking between the CW and a single soliton. Then, the developed model has been applied to the laser cavity operating multiple pulses in the presence of the gain depletion and recovery mechanism responsible for harmonic pulse arrangement. We clearly demonstrate how the CW injection accelerates or slows down the HML process enabling the generation of additional inter-pulse forces.

Manipulating thermal light via displaced-photon subtraction

Thermal radiation played a pivotal role in the preliminary development of quantum physics where it helped resolve the apparent incongruity of the ultraviolet catastrophe. In contemporary physics, thermal state generation and manipulation finds new application in fields such as quantum imaging and quantum illumination and as a practical realization of Maxwell's demon. These applications often go hand in hand with photon subtraction operations which probabilistically amplify the mean photon number (MPN) of thermal light as a result of its super-Poissonian photon statistics. In this article, we introduce an operation for thermal states of light based on a generalized photon subtraction scheme. Displaced-photon subtraction (DPS) makes use of coherent state displacement followed by a subsequent anti-displacement in combination with single-photon detection to probe the MPN of a thermal state. We find regimes in which the output of a successful DPS is amplified, unchanged, or attenuated relative to the unconditioned output state. The regime of operation is controlled via the magnitude of the coherent displacement. A theoretical description of generalized photon subtraction of a displaced thermal state is derived via a two-mode moment-generating function (MGF) and used to describe generalized DPS. We perform a proof of principle experimental implementation of DPS for the case of a balanced beam splitter for which results demonstrate good agreement with the model.

Скрининг активности инкорпорированных радионуклидов у персонала научно-исследовательской организации

Studying the features of radiological situation in the workplace and assessing the individual effective doses in employees of research organizations working with open radiation sources (RS) are an urgent scientific task due to additional risks resulting from variability in the conditions and regimes of the technological operations. The study was aimed to assess the working conditions and intake of radionuclides by the employees of the V. G. Khlopin Radium Institute working with open RS. The data on exposure to work-related radiation factors were obtained by dosimetry, radiometry, and spectrometry. It was found that radiological situation in the employees' workplaces was characterized by the broad range of the gamma ambient dose equivalent rate values (0.10–122 µSv/h), alpha and beta working surface contamination, radioactive pollution of air in the working areas. In some individuals, spectrometry revealed the following: 125I in the thyroid gland (up to 9,850 Bq), 90Sr in the skeleton (up to 16,500 Bq), 137Сs in the whole body (up to 1,100 Bq), etc. The findings can provide the basis for developing the measures to improve the quality of individual internal dose control and the efficiency of medical care provision to the research organization employees dealing with open RS.

Large eddy simulation of an onshore wind farm under different operating regimes including topographic effects

High-fidelity simulations of actual wind farms with the Actuator Line Model, in a Large Eddy Simulation framework, have been performed in the past years, for both onshore and offshore sites. It has become the state of the art to simulate the wind flow through wind turbines and wind farms and it could be a powerful tool to assess the operation of actual wind farms and potential improvements. The objective of the present paper is two-fold: develop a high-fidelity numerical model of an onshore wind farm to be used to assess the influence of different environmental and aerodynamic conditions in its power performance and analyze, as case study, the effect of the topography in the wind flow and power production.