Operating Regimes Research Articles

Diverse quantum interference regimes in intramolecular singlet fission chromophores with thiophene-based linkers.

An array of thiophene-based π-conjugated linkers in covalently linked pentacene dimers allow us to access diverse quantum interference (QI), modulating nonadiabatic coupling (NAC) in the singlet fission (SF) process. Simulations show that structural isomerism in terms of S atom orientation substantially alters NAC with relatively marginal impacts on energies. Extended curly arrow rules (ECARs) reveal sensitive dependence of QI on SF linker topologies and connectivity, categorizing regimes of constructive, destructive, and previously unrealized in SF research, shifted destructive QI. Drastic NAC changes in terms of S atom orientation are rationalized based on the nature of QI. Our results from nonequilibrium Green's function calculation using density functional theory corroborate the classification of QI regimes based on ECARs. Moreover, we found that the extent of charge resonance contribution in electronic states relevant to multiexciton formation and the appearance of optically allowed charge transfer excitation strongly depends on the operative QI regime. Notably, the magnitude of NAC effectively captures this influence. Our findings show that QI can rationalize and semi-quantitatively correlate with NAC for the multiexciton formation step in the SF process.

DESIGN AND VERIFICATION OF THE MODEL OF STRUCTURE FORMATION AND HEAT TRANSFER IN A FLUIDIZED BED APPARATUS WITH A HEAT JACKET

A one-dimensional mathematical model of the formation of a fluidized bed and the evolution of its thermal state during the heating of an ensemble of particles is proposed based on the mathematical apparatus of the Markov chain theory. When describing the thermal state of the system, the processes of interfacial heat exchange between the gas flow and particles, as well as between the wall of the apparatus and the gas suspension, were taken into account. The results of previous studies and known empirical regularities for the material constants of the process were used to identify the parameters of the model. The parametric identification made it possible to adapt and apply the mathematical model for calculating the process of heat treatment of the suspension of silicate sand particles in an apparatus with a fluidized bed of a periodic principle of operation equipped with a heating jacket. Verification of the predictive capabilities of the physicomathematical model adapted in this way was carried out by comparing the forecasts obtained by calculation with the results of the full-scale experiment conducted during the study. To conduct the full-scale experiment, a sample of sand particles was placed in the apparatus, which was previously output to the established thermal regime of operation. After loading the material, a set of thermocouples equidistant from each other was placed in the apparatus and temperature readings were taken at different heights from the level of the gas distributor. The temperature distributions obtained in this way along the bed height were in good agreement with the calculated forecasts and show a significant heterogeneity of the gas phase temperature fields. The temperature of the particles was estimated only as an integral characteristic by measurements of the heat content of the bulk medium after unloading from the apparatus. The integral temperature of the particles also turned out to be close to the predicted values. In addition, during the computational and experimental study, the kinetic characteristics of the heating of the suspension of the material were clarified. Thus, the proposed mathematical model has sufficient predictive efficiency for engineering tasks and can be considered as a basis for constructing a computer method for calculating heat exchangers with a heating jacket using the fluidization technique of bulk media.

A feasibility study into the quasi-frozen spin regime of operation of the NICA storage ring

This study is motivated by the search for the electric dipole moment (EDM) of elementary particles. The most promising idea in that regard is the “Frozen Spin” concept first proposed by the BNL. This concept, however, requires the building of a brand-new facility devoted to the EDM-search. NICA is not such a facility, hence the need for a modification compatible with the existing optics; one that wouldn’t disrupt the ring’s capability for parallel experiments. Such a modification is the “Quasi-Frozen Spin” idea, realized by adding transport channels, bypassing the ring’s straight sections. Wien-filters are placed in these channels in order to compensate spin-rotations caused by the ring’s arc dipoles, thus making its net spin-transfer matrix unitary. Even though, during its movement along the beam line, the beam’s polarization vector deviates from alignment with the momentum vector, this motion is regular and fits within one beam revolution, allowing for the buildup of the EDM-signal. The present study shows that the “Quasi-Frozen Spin”-specific optics is consistent with the existing NICA lattice and that the modified structure is capable of maintaining a requisite spin-coherence time.

Some practical approaches of the poultry slaughter wastewater treatment by apply physico-chemical treatment

As a result of slaughtering processes, large volumes of effluents with high concentrations of organic, inorganic and microbiological pollutants are generated. The pollutants composition must be reduced by apply simultaneous processes in order, to obtain an proper effluent before discharge. In this paper, the efficiency of the physico-chemical treatment process was determined, in which a rotary sieve and the Dissolved Air Flotation (DAF) system were used. The efficiency of the DAF process was determined by comparing the quality indicators of effluents from a poultry slaughterhouse, analyzed both before and after treatment. To carry out the analysis, the samples were taken in October and November 2023, and they were determined by using certified laboratory procedures. After setting the DAF process to an optimal operating regime and chemicals dosages, the quality indicators were significantly reduced, reaching a maximum of 99%, 98%, 93%, 92%, 85%, 84%, for TSS, PO4, NO3, TKN, BOD5 and COD.

Investigation of Plasma Flow Velocity in the Helical Magnetic Open Trap SMOLA

The physics of confinement of plasma rotating in the magnetic field with linear helical symmetry is studied at the SMOLA open trap at Budker Institute of Nuclear Physics of the Siberian Branch of the Russian Academy of Sciences. The factor characterizing the quality of plasma confinement in the system is its flow velocity. The paper describes the diagnostics applied, which is based on the Mach probe used under the conditions of nonmagnetized plasma; this diagnostics made it possible to determine the longitudinal flow velocity in the experiments. In different operating regimes of the device, the measured longitudinal flow velocity was (0.5−5) × 106 cm/s. It is discussed how the velocity depends on the magnetic field corrugation. The reverse flow of trapped particles returning to the confinement zone was detected.

Analysis of hydraulic parameters in determining the occurrence of cavitation in the spillways of the Furnas, Luiz Carlos Barreto de Carvalho and Batalha hydroelectric power plants

Analysis of hydraulic parameters in determining the occurrence of cavitation in the spillways of the Furnas, Luiz Carlos Barreto de Carvalho and Batalha hydroelectric power plants

Correction to Semi-Linear All-Polarization-Maintaining Yb-Doped Fiber Laser Oscillator Manifesting Dual Operation Regime at Net Anomalous Dispersion

Correction to Semi-Linear All-Polarization-Maintaining Yb-Doped Fiber Laser Oscillator Manifesting Dual Operation Regime at Net Anomalous Dispersion

Semi-Linear All-Polarization-Maintaining Yb-Doped Fiber Laser Oscillator Manifesting Dual Operation Regime at Net Anomalous Dispersion

Semi-Linear All-Polarization-Maintaining Yb-Doped Fiber Laser Oscillator Manifesting Dual Operation Regime at Net Anomalous Dispersion

Assessment of beam-intercepting device robustness for intensity increase in CERN’s North Area

CERN’s North Area comprises several target and experimental systems and is a zone of interest for future development. Provision of beam to this area relies upon several beam-intercepting devices located in various branched transfer lines from the Super Proton Synchrotron. In several lines, these include a primary production target system of beryllium plates followed by a combined collimation, attenuation and dump device made from a set of aluminum, copper and iron blocks and known as a ‘TAX’ (Target Attenuator [for] eXperimental areas). These may operate in a range of configurations depending on experimental needs. Future operational regimes with higher beam intensities (increased from a current specification of 1.5× 1013 to 4.0× 1013 p +/pulse), shorter pulse times (4.8 s reduced to 1.2 s), greater repetition rates (14.4 s cycle time reduced to 7.2 s) and ten times the annual intensity place more stringent thermo-structural demands on these existing devices, beyond their original specification. This contribution outlines the engineering analysis, including beam-matter interaction studies and thermo-structural simulations, carried out to assess their robustness under such conditions.

Смена режимов генерации в эрбиевых волоконных лазерах

Operation features of the erbium fiber lasers with short cavities near two phase transitions have been established experimentally for the first time. The power-law behavior of the system parameters in the vicinity of the critical point in a wide range of pump power values was revealed. The parameters and operation regimes dependence on the cavity length and pump power, namely the switching from pulsed to CW operation, was investigated. The pulse duration and frequency dependencies with varying cavity length have been investigated, which made it possible to experimentally establish the universal dependence of these parameters on the lasing power for passively Q-switched erbium fiber lasers. The critical indices for pulsed operation of the erbium fiber lasers are determined weakly depending on the cavity parameters. The results of the study can be used for designing high-coherent fiber laser sources.

Nanoscale Operando Characterization of Electrolyte-Gated Organic Field-Effect Transistors Reveals Charge Transport Bottlenecks.

Charge transport in electrolyte-gated organic field-effect transistors (EGOFETs) is governed by the microstructural property of the semiconducting thin film that is in direct contact with the electrolyte. Therefore, a comprehensive nanoscale operando characterization of the active channel is crucial to pinpoint various charge transport bottlenecks for rational and targeted optimization of the devices. Here, the local electrical properties of EGOFETs are systematically probed by in-liquid scanning dielectric microscopy (in-liquid SDM) and a direct picture of their functional mechanism at the nanoscale is provided across all operational regimes, starting from subthreshold, linear to saturation, until the onset of pinch-off. To this end, a robust interpretation framework of in-liquid SDM is introduced that enables quantitative local electric potential mapping directly from raw experimental data without requiring calibration or numerical simulations. Based on this development, a straightforward nanoscale assessment of various charge transport bottlenecks is performed, like contact access resistances, inter- and intradomain charge transport, microstructural inhomogeneities, and conduction anisotropy, which have been inaccessible earlier. Present results contribute to the fundamental understanding of charge transport in electrolyte-gated transistors and promote the development of direct structure-property-function relationships to guide future design rules.

Internal Flow Characteristics of Novel Turbine Performance Enhancement Method through Specific Fluid Injection

Gas turbine engines are an essential component for many industries, such as aerospace, marine propulsion, energy generation, etc., with modern engines capable of achieving high powers, efficiencies and reliability. However, these high performances are achieved on a narrow interval of working regimes; when operating at partial loads, a drastic decrease in performance is expected. In order to mitigate this drawback, a novel injection method has been proposed to improve axial turbine and gas turbine engine performance at these regimes. The method consists of the injection of a fluid in specific sections of turbine vanes to accelerate the flow, modify the velocity triangles and increase the generated power at partial loads. In this paper, the authors discuss the internal flow characteristics of the injection channels using numerical studies to determine the flow fields for different working regimes. The results show that the power generated by the rotor can be improved by 10% to 21% for different operating regimes without considering the internal geometries. The introduction of internal flow configurations led to smaller improvements in power generation, obtaining injection system pressure losses of between 10% and 20%. The paper concludes that the flow through channels is not uniform, with smaller dimensions of the internal geometries leading to higher pressures and an increased influence of the injection system.

An intelligent fault detection and diagnosis monitoring system for reactor operational resilience: Fault diagnosis

Various advanced reactor designs proposed in recent years envision deployment scenarios which feature reactor operations with significantly reduced staffing or even completely autonomous frameworks to reduce the operations and management costs of the plants. Many SMR and microreactor designs feature extended fuel cycles which limit inspection intervals, reduced access to critical components, and load-following capabilities that expose the reactor unit to different transients. Safe and reliable semi- or fully autonomous operations under these challenging operational regimes must be enabled through an on-line monitoring (OLM) system that effectively detects and diagnoses malfunctions in the reactor plant. This work presents the development of the Fault Diagnosis Module of the previously proposed data-driven OLM system for reactor operations: the Fault Detection and Diagnosis Monitoring System (FDDMS). The Fault Diagnosis Module monitors various sensor signatures from multiple systems and components at a nuclear power plant and accurately diagnoses the type and location of a malfunction. When integrated into the complete FDDMS methodology, the Fault Diagnosis Module can provide power transient dependent fault characterization by using separate convolutional neural network (CNN) models for steady state, ramping up in power, and ramping down in power operations, making the FDDMS especially applicable to load-following operational strategies. Two separate diagnosis approaches were explored in this paper for the Fault Diagnosis Module architecture: Hierarchical and End-to-End. The Hierarchical approach is a two-stage architecture in which the first stage uses a single CNN to classify the plant subsystem where the malfunction initiated. Subsequently in the second stage, a separate CNN is used for each subsystem to describe the specific fault type. The End-to-End approach uses a single CNN to directly classify the fault type from the overall list. To efficiently utilize computational resources, the hyperband intelligent hyperparameter optimization method to generate optimal CNN architectures. The diagnosis approaches were compared in terms of precision rate, recall rate, F1-score, and total accuracy for the possible fault types. Both diagnosis approaches produced good and satisfactory performance by generating total diagnosis accuracies above 99% on 17 different malfunction scenarios for all three power transient datasets. Additionally, robustness against noisy sensor data was tested, with models maintaining 99–100% accuracy at various levels of noise, and an illustrative real-time application of the methodology is provided.

Implementation of Buck DC-DC Converter as Built-In Chaos Generator for Secure IoT

Resource-constrained but widely deployed IoT devices require a new approach to ensure secure and reliable communications. That is why, in recent years, the paramount effort has been applied in lightweight cryptography. Because of its unpredictable nature, chaos is regarded as a potential candidate in cryptographic applications. Chaos mode of operation is observed not only in deliberately designed oscillators but also in switching DC-DC converters, which are part of almost every embedded design. The use of a built-in chaos source may improve performance, energy consumption, PCB area, and cost of IoT devices. In this research, the regions of robust chaos were identified using numerical analysis, and the performance of a real buck DC-DC converter under peak-current-mode control was studied experimentally. It was shown that a compensating ramp acts as a switch between different operating regimes. Despite minor performance degradation, chaos mode can be used for secure communications in IoT networks.

Radiatsionnye poteri deytronov, tritonov i al'fa-chastits na ionakh vol'frama v plazme tokamakov-reaktorov ITER i EU–DEMO

Integral radiative losses of deuterons, tritons, and alpha particles on impurity tungsten ions have been calculated for the first time within the statistical theory of the atom for the designed operational regimes of the ITER and EU-DEMO tokamak reactors. It was previously shown within the statistical theory of the atom that specific radiative losses of this new ion channel are comparable with specific electron radiative losses, which also include losses due to bremsstrahlung, radiative and dielectron recombination. Integral radiative losses have been calculated within the numerical model of fusion power isolines, which was previously proposed to study the operational space and design regimes of tokamak reactors. Spatial distributions of the tungsten density with various degrees of peaking in the center of a plasma column have been considered to study the influence of the accumulation of the impurity on integral radiative losses. It has been found that the studied new channel adds about 20 and 30% to the total integral radiative losses on tungsten in the ITER and E-U‑DEMO tokamak reactors, respectively. Consequently, this channel of radiative losses should be taken into account to examine in more detail the working scenarios of these devices.

Dual-wavelength Nd:CALGO laser based on differential loss of birefringent filter

Continuous-wave dual-wavelength (DW) operation of an a-cut Nd:CALGO (Nd:CaGdAlO4) laser around ∼1.08 μm was demonstrated using a single plate quartz birefringent filter (BRF) with an on-surface optical axis. A wide range of wavelength separations between the two laser lines ranging from sub-nm up to 10 nm was observed with controllable intensity ratios. A new regime of operation of DW laser was also identified where one of the oscillating spectral lines was in the rejection band of the filter. This is in sharp contrast with typical operation of DW lasers with BRF where wavelength separation was limited either to the free spectral range or to the linewidth of a single transmission peak of the used filter. This was enabled by differential loss introduced by a single transmission peak of the BRF. Using this mechanism, generation of a large number of laser wavelength pairs became possible.

Neural network identification of the weakly coherent mode in I-mode discharge on EAST

The improved energy confinement mode (I-mode) is widely considered as an important operation regime for ITER. I-mode implementation depends on the specified basic plasma parameters and certain operation conditions, which are discovered by statistical plasma characteristics from a large number of I-mode discharges on a tokamak. The extraction process of I-mode plasma characteristics is complicated, time-consuming, and limited to the sampling rate of the measured signals. Experimental observation of the I-mode is accompanied by the appearance of a weakly coherent mode (WCM). However, it takes much time to accurately scan and quantify WCM characteristics when analyzing many I-mode discharges. Recently, a neural network identification method was developed as an I-mode detector to traverse a whole database as a replacement for manual identification. Two fully connected neural network models were trained with the spectrum of propagation velocity of density perturbation from Doppler backward scattering and the electron density measured by a polarimeter-interferometer system with the experimental advanced superconducting tokamak I-mode database. An accuracy of 98.30% in identifying WCMs in I-mode discharges is achieved with the WCM classification model. In addition, the regime classification model was also utilized to successfully distinguish between the low confinement mode (L-mode), I-mode, and high confinement mode (H-mode) with 96.03% accuracy. Finally, ablation experiments were performed on the regime classifiers, showing that there is potential for further performance improvement with future use of RNN model.

Comparing continuous and pulsed nitrogen-vacancy DC magnetometry in the optical-power-limited regime

Ensembles of nitrogen-vacancy (NV) center spins in diamond offer a robust, precise, and accurate magnetic sensor. As their applications move beyond the laboratory, practical considerations including size, complexity, and power consumption become important. Here, we compare two commonly employed NV magnetometry techniques—continuous-wave (CW) versus pulsed magnetic resonance—in a scenario limited by the total available optical power. We develop a consistent theoretical model for the magnetic sensitivity of each protocol that incorporates NV photophysics—in particular, including the incomplete spin polarization associated with limited optical power; after comparing the models’ behavior to experiments, we use them to predict the relative DC sensitivity of CW versus pulsed operation for an optical-power-limited, shot-noise-limited NV ensemble magnetometer. We find a ∼2−3× gain in sensitivity for pulsed operation, which is significantly smaller than seen in power-unlimited, single-NV experiments [Phys. Rev. B 84, 195204 (2011)PRBMDO0163-182910.1103/PhysRevB.84.195204]. Our results provide a resource for practical sensor development, informing protocol choice and identifying optimal operation regimes when optical power is constrained.

Mode transition mechanisms in semi-passive flapping-wing propulsion or energy extraction

To facilitate the smooth transition of operational modes in self-sustaining micro-thrusters, this study focuses on a device employing semi-passive flapping wings. Transient numerical methods are used to analyze the variation of flap energy acquisition and propulsion characteristics with pitching frequency, and the relationship between the dominant vortex structure and the force characteristics is analyzed by using the integral momentum theorem and the dynamic mode decomposition (DMD) method. The results indicate that, under the investigated operational conditions, with an increase in the pitching frequency, distinct wake evolution characteristics were observed. In the energy harvesting operational regime, the wake patterns manifest as 2P + mS, 2S + mS, and mS types. During the transitional phase from energy harvesting to propulsion, the wake patterns shift from 2S + mS to 2S transitional types, eventually leading to the manifestation of a reverse Karman vortex street (2S RBVK). In the propulsion operational regime, the wake patterns consist of a reverse Karman vortex street and asymmetric reverse Karman vortex street phenomena. Simultaneously, it was observed that the transition of flapping-wing performance from energy harvesting to propulsion conditions delays behind the transformation of vortex street structures. This delay is attributed to the necessity for the flapping-wing device to overcome its own resistance before generating a net effective propulsive force. The contributions of unsteady wake to thrust primarily encompass vortex thrust, thrust due to localized fluid acceleration, induced momentum force, and induced pressure force. As the pitching frequency increases, the influence of wake vortices on propulsion also intensifies. The contribution of wake vortices to flapping-wing propulsion is determined by the spatial distribution of Lamb vectors and localized fluid accelerations. The conclusions drawn from the dynamic modal analysis and reconstructed flow field analysis of wake vortices align with the findings of the investigation of wake vortices based on the integral momentum theorem.

Sensitivity Analysis of Operational Parameters of a High Temperature-Proton Exchange Membrane Fuel Cell

The lack of widespread commercialization of High-Temperature Proton Exchange Membrane Fuel Cells (HT-PEMFC) is primarily due to their poor performance and durability. Various factors impact the performance of fuel cells, one such crucial factor being the operational parameters. Suitable operating conditions not only enhance the output cell performance but also extend a fuel cell’s life. Current research on the impact of operational factors on HT-PEMFC performance is largely qualitative in nature, with no quantitative indication of affecting the sensitivity of these parameters. In the present work, a three-dimensional, non-isothermal HT-PEMFC model developed earlier is used to investigate the influential sensitivities of five crucial operating parameters, each with four different levels, and is analyzed quantitatively using six evaluation indexes. The orthogonal/Taguchi method L16(45) is implemented to investigate the impact of operating parameters quantitatively. Further, the effect of each operating parameter on evaluation indexes under different operational current density regimes is investigated. The findings show that, of the parameters chosen, the working temperature and cathode pressure are the most sensitive to cell voltage and cathode overpotential distribution under all operating current density regimes. The findings would provide more precise recommendations for experimental research targeted at improving cell performance by optimizing operational parameters.