Operating Regimes Research Articles

Predicting xylose yield from prehydrolysis of hardwoods: A machine learning approach

Hemicelluloses are amorphous polymers of sugar molecules that make up a major fraction of lignocellulosic biomasses. They have applications in the bioenergy, textile, mining, cosmetic, and pharmaceutical industries. Industrial use of hemicellulose often requires that the polymer be hydrolyzed into constituent oligomers and monomers. Traditional models of hemicellulose degradation are kinetic, and usually only appropriate for limited operating regimes and specific species. The study of hemicellulose hydrolysis has yielded substantial data in the literature, enabling a diverse data set to be collected for general and widely applicable machine learning models. In this paper, a dataset containing 1955 experimental data points on batch hemicellulose hydrolysis of hardwood was collected from 71 published papers dated from 1985 to 2019. Three machine learning models (ridge regression, support vector regression and artificial neural networks) are assessed on their ability to predict xylose yield and compared to a kinetic model. Although the performance of ridge regression was unsatisfactory, both support vector regression and artificial neural networks outperformed the simple kinetic model. The artificial neural network outperformed support vector regression, reducing the mean absolute error in predicting soluble xylose yield of test data to 6.18%. The results suggest that machine learning models trained on historical data may be used to supplement experimental data, reducing the number of experiments needed.

Noise Spectroscopy of Transport and Ion‐Related Phenomena in Silicon Nanowire Field‐Effect Transistor Biosensors

AbstractHigh‐quality, liquid‐gated two‐layer (TL) nanowire (NW) field‐effect transistor (FET) structures are fabricated and studied in different operation regimes and with different concentrations of MgCl2 solutions. The space‐charge‐limited current (SCLC) effect is sensitive to surface phenomena and is registered at the drain‐source voltage (VDS) above 0.14 V, and analyzed using several methods including noise spectroscopy. Noise spectra reflect the clear transformation from 1/f to 1/ (f in power 1.5) behavior, confirming the SCLC effect, which is sensitive to ion processes at the NW FET surface. Moreover, the dimensionless Hooge parameters, measured at a level of 10−3, reflect the high quality of the fabricated devices and demonstrate the suppression of noise with VDS increasing up to 0.48 V. Such behavior additionally confirms the SCLC effect in the NW channel. The effect of suppression is stronger for small concentrations of MgCl2 solutions. The results should be taken into account for the detection of very small signals in biochemical solutions.

Quasicontinuous Exhaust Scenario for a Fusion Reactor: The Renaissance of Small Edge Localized Modes.

Tokamak operational regimes with small edge localized modes (ELMs) could be a solution to the problem of large transient heat loads in fusion reactors. A ballooning mode near the last closed flux surface governed by the pressure gradient and the magnetic shear there has been proposed for small ELMs. In this Letter, we experimentally investigate several stabilizing effects near the last closed flux surface and present linear ideal simulations that indeed develop ballooninglike fluctuations there and connect them with nonlinear resistive simulations. The dimensionless parameters of the small ELM regime in the region of interest are very similar to those in a reactor, making this regime the ideal exhaust scenario for a future device.

Statistical analysis of hard X-ray radiation at the PAL-XFEL facility performed by Hanbury Brown and Twiss interferometry.

A Hanbury Brown and Twiss interferometry experiment based on second-order correlations was performed at the PAL-XFEL facility. The statistical properties of the X-ray radiation were studied within this experiment. Measurements were performed at the NCI beamline at 10 keV photon energy under various operation conditions: self-amplified spontaneous emission (SASE), SASE with a monochromator, and self-seeding regimes at 120 pC, 180 pC and 200 pC electron bunch charge. Statistical analysis showed short average pulse duration from 6 fs to 9 fs depending on the operational conditions. A high spatial degree of coherence of about 70-80% was determined in the spatial domain for the SASE beams with the monochromator and self-seeding regime of operation. The obtained values describe the statistical properties of the beams generated at the PAL-XFEL facility.

Time-dependent transport in graphene Mach-Zender interferometers

Graphene nanoribbons provide an ideal platform for electronic interferometry in the Integer Quantum Hall regime. Here, we solve the time-dependent four-component Schroedinger equation for single carriers in graphene and expose several dynamical effects of the carrier localization on their transport characteristics in pn junctions. We simulate two kinds of Mach-Zender Interferometers (MZI). The first is based on Quantum Point Contacts and is similar to traditional GaAs/AlGaAs interferometers. As expected, we observe Aharonov-Bohm oscillations and phase averaging. The second is based on Valley Beam Splitters, where we observe unexpected phenomena due to the intersection of the Edge Channels that constitute the MZI. Our results provide further insights into the behavior of graphene interferometers. Additionally, they highlight the operative regime of such nanodevices for feasible single-particle implementations.

Operating regimes of a constricted arc discharge in a forevacuum-pressure, plasma-cathode electron source of pulsed large-radius electron beams

We have investigated the operating regimes of a pulsed constricted arc discharge in a forevacuum plasma-cathode electron source of large-radius electron beams. The configuration of the intermediate electrode (IE) with a constricting channel (CC) determines the maximum parameters (current and pulse duration) and operating regimes of the constricted arc. An IE with ceramic (aluminum nitride) CC and an IE with sectional tantalum CC, formed by several electrically insulated tantalum disks with co-axial holes, lead to an increase in the maximum parameters compared to an IE with metal CC. In particular, an IE with sectional tantalum CC provides the highest maximum parameters. The ceramic and sectional tantalum constricting channels also provide lower minimum pressure for which the constricted arc operates stably. When the pressure reaches a certain threshold value, which depends on arc current, a discharge system with IE with sectional tantalum CC provides stable operation for pulse duration up to 10 ms. An increase in pressure provides higher discharge current in the millisecond regime of the discharge operation. When the arc current reaches threshold values from 84 to 92 A (depending on gas pressure), a self-compressed (pinched) mode of operation of the constricted arc occurs. The pinched arc regime is characterized by the highest current and the longest pulse duration. The forevacuum electron source based on the constricted arc discharge with IE with sectional tantalum CC offers generation of low-energy (up to 8 keV) electron beam with current up to tens of amperes and pulse duration up to 10 ms.

The study of the spark ignition engine performance at fueling with n-butanol-gasoline mixture

The actual challenges regarding renewable energy sources, pollution and climate changes have pushed industries sectors (including the automotive sector) to find sustainable solutions for long-term. Numerous studies have been conducted for to find the alternative fuels sources to solve the energetic and pollution problems. A special attention was given to alcohols use (ethanol, butanol, methanol) in mixture with the conventional fuels like gasoline or diesel. Butanol has a great advantage comparative with other alcohols due its better miscibility properties, allowing a butanol higher percentages use in mixture with gasoline or diesel fuel. Butanol is also less corrosive VS ethanol or methanol, which makes it ideal for the spark-ignition engines. An automotive gasoline engine with a 1.5L displacement was fueled with butanol in mixture with gasoline in deferent percentages, deferent dosages and deferent engine operation regimes. In the paper the effects are presented of the engine fueling with B15 fuel (15%-vol. n-butanol in mixture with 85%-vol. gasoline) on the combustion, on the engine energetic performances and pollutants. The experimental investigations (engine load 55% and 2500 rpm engine speed) showed the brake specific energetic consumption and the level of the pollutants emissions decrease at the butanol and the lean mixtures use, at the same engine power, comparative to engine gasoline. Another advantage of n-butanol is the stable engine operation at lean mixtures use.

The study of the influence of speed regimes on smoke emissions for a diesel injection car

Because the air pollution is a serious environmental problem, this study aims to identify the smoke emissions level of different driving regimes for diesel-powered vehicles that run on roads in urban and extra-urban areas. For the experimental determinations we used a car within the Euro 3 pollution norm, because according to the statistics of the National Institute of Statistics, in 2020 the number of Euro 3 and Euro 4 cars in Romania represents 54% of the total of 7,3 million registered cars and only 1,7 million Euro 5 and Euro 6 are registered. The study has been performed in laboratory conditions and simulates various driving modes. To simulate the load regimes on horizontal roads, chassis dynamometer V-Tech Dyno VT-2/B1 was used, equipment that is in the Thermal Systems and Automotives Department. This work investigates the effects of vehicle speed and fuel consumption on smoke emissions and at the same time makes recommendations concerning the optimal operating regimes of diesel cars to reduce the level of smoke pollution.

Experimental study on combustion of an automotive diesel engine fuelled with CNG

Presenting the influence of compressed natural gas (CNG) used as alternative fuel on the combustion of an automotive diesel engine represents the main objective of this paper. The paper studies brake specific energetic consumption, in-cylinder pressure and pressure rise rate, carbon dioxide, nitrogen oxides, smoke and hydrocarbons emissions at 2000 rev/min and at 40%, 55% and 70% load. Low carbon content of the alternative fuel will determine lower CO2 at all loads; NOx and smoke emissions are influenced by both energetic substitution and engine operating regime. HC emission will reach higher levels in diesel-gas mode than in conventional mode as the homogeneous percentage of the charge per cycle grows with the quantity of CNG admitted into the cylinder. In all cases in-cylinder pressure and pressure rise rate are higher in dual-fuel mode than those in conventional operating mode due to higher quantity of premixed charge developed during the ignition delay phase. The higher LHV (lower heating value) and the gaseous state of CNG will determine at all loads lower brake specific energetic consumption. Smoke emission will be negatively influenced in low to medium loads but in high loads it will drop by more than 30 percent.

On the relationship between turbine thrust and near-wake velocity and vorticity

Vortical impulse theory is used to investigate the relationship between turbine thrust and the near-wake velocity and vorticity fields. Three different hypotheses regarding the near-wake structure allow the derivation of novel expressions for the thrust on a steadily rotating wind turbine, and these are tested using stereoscopic particle-image velocimetry (PIV) data acquired just behind a rotor in a water channel. When one assumes that vortex lines and streamlines are aligned in a rotor-fixed frame of reference, one obtains a PIV-based thrust estimate that fails even to capture the trend of the directly measured thrust, and this failure is attributed to an implicit assumption that most of the generated thrust does useful work. When one neglects the axial gradients of radial velocity, the PIV-based thrust estimate captures the measured thrust trend, but underpredicts its magnitude by approximately $33\,\%$ . The third and most promising physical proposition treats the trailing vortices as purely ‘rolling’ structures that exhibit zero-strain rate in their cores, with the corresponding thrust estimates in close agreement with direct thrust measurements. This best-performing expression appears as a correction to the classical thrust expression from momentum theory, possessing additional squared-velocity terms that can account for the high-thrust regime of turbine operation that is typically addressed empirically.

Four-channel parity-time symmetry

In this letter, we propose a general scheme for four-channel parity-time symmetry. We theoretically demonstrate how to achieve novel features via exploiting the parity-time symmetry for four-channel coupled-mode equations and study the spontaneous symmetry breaking manifold, separating the parity-time symmetric and parity-time broken regimes, for various parameter configurations. We also propose a possible candidate (an optoelectronic oscillator) which can demonstrate the theoretically derived features, which include broadband tunability, eigenfrequency selection and flipping, and single/dual frequency operation regimes.

Efficiency comparison for frequency comb formations in a silicon nitride microring within anomalous dispersion regime

The energy efficiency of silicon nitride (SiN) microresonator-based frequency combs is investigated using numerical simulations. The formation of stable frequency comb solutions is numerically studied for a resonator with properly engineered dispersion. The required conditions for the pump power and frequency detuning are analyzed to obtain modulation instability (MI-comb), single soliton, multi-soliton, and soliton-crystal. The performance of the micro combs in terms of the power conversion efficiency, the number of generated comb lines, and line spacing required for different applications of the frequency combs are investigated. Our numerical simulations, based on the parameters of the studied microring, show a configurable multi-wavelength source with up to 23% power conversion efficiency, 200 comb-lines with more than -10dBm power, and switchable line spacing from 100 GHz to 3THz is feasible for different regimes of the proposed frequency comb. The efficiency sensitivity to the input pump power is also studied to find the most energy-efficient operation regime for the multi-wavelength source.

Определениe рациональных режимных параметров виброударного грохота

The paper deals with the problem of vibroimpact screen operating regimes selection for the regime of anti-phase oscillations of its elements. The criteria of effective screen operation accepted are impact impulse transferred to sieve from vibroimpact lattice and sieve double amplitude, which provide effective regimes of sieve cleaning from clogging particles and maintenance of preset sieve oscillations regime for support of technological parameters of material screening. Using the developed mathematical model and program the computational experiment was conducted for operating oscillation frequency range from 105 rad/s to 160 rad/s and adjustment gap between vibroimpact lattice and sieve for operating range from 0 to 5,5 mm. Influences of oscillation frequency and adjustment gap on impact impulse transferred to sieve and sieve double amplitude are obtained in the form of regression equations. On its base the recommendations for determining effective operating regimes of vibroimpact screen are offered. Obtained regularities explain nonlinear behavior of two-mass vibroimpulse oscillating system according to its operating parameters changing and show principal opportunities of system control. Also obtained results could find an application in screen operating regimes adjustment during commissioning and start-up operation and screen operation period, and could decrease labor costs and fasten the procedure of rational screen operating parameters searching.

Simulation of lithium flow, redeposition, and vapor shielding in liquid lithium divertor of T-15MD tokamak with SOLPS 4.3 code

The erosion module of the SOLPS 4.3 code package for the liquid Li divertor target is developed to include the thermal sputtering, evaporation, and prompt redeposition effects. Eroded Li atoms are treated within a fully kinetic approach. Simulations for the T-15MD tokamak with liquid Li divertor targets are performed for various operational regimes. The main parameters characterizing the divertor operation are identified. The Li shielding effect is found significant at the input power P SOL > 15 MW. The target conditions remain reasonable in terms of both the erosion rate and target temperature but core plasma dilution with Li remains a problem. The Li flow patterns in the scrape-of-layer (SOL) are analyzed in detail. About 80% of eroded Li is redeposited back on the target. The energy dissipated per an eroded Li particle, E sh, is calculated and its values are in the range of 100–200 eV. These values are 2–4 times lower than those obtained from a simple 0D estimation of E sh. Therefore, relying on simple 0D models for the analysis of Li divertor performance may cause an overestimation of the shielding efficiency.

Simultaneous distance and vibration mapping of FMCW-LiDAR with akinetic external cavity diode laser

In this study, the simultaneous distance and vibration mapping of frequency-modulated continuous-wave light detection and ranging (FMCW-LiDAR) is performed using an electro-optical external cavity diode laser (ECDL). Owing to the akinetic operation regime of the ECDL, a uniform (R2 = 1.0000) interference signal can be generated over a bandwidth of 1 GHz at an optical frequency sweep rate of 10 kHz without any postprocessing or system for linearization. Furthermore, the proposed ECDL exhibits a high optical frequency sweep rate of 200 kHz with a considerable linearity of R2 = 0.99975. Based on a point sensing experiment using the FMCW-LiDAR system, three measurands, namely, distance, vibration frequency, and vibration velocity change, are demonstrated with a highly linear relationship between the beat frequency and amplitude of each individual parameter. Furthermore, temporal variations in multiple targets with rapidly frequency-varying vibrations, such as those occurring in music or voice sounds, can be successfully acquired by tracking the temporal change in the beat frequency of each target. Moreover, three-dimensional (3D) mapping of distance, vibration frequency, and vibration velocity change is simultaneously implemented in the same 3D space. The results show that the proposed FMCW-LiDAR system can be used for the 3D visualized display of various measurands within the same space frame.

THERMALLY INDUCED BIREFRINGENCE AND MODE SELECTION IN CAVITY OF PASSIVELY Q-SWITCHED DIODE PUMPED Nd:YAG LASER

Operating regimes of an optical system consisted of compact pulsed master diode-pumped Q-switched Nd:YAG laser and triple-crystal (KTP) ring cell of the optical parametric oscillator have been investigated. It has been experimentally shown that frequency-selective properties of a passive Q-switched unit in the “natural mode selection” are enhanced by creating a polarization interference filter Lyot with the phase plate in the form of a laser active element with the thermally induced birefringence and a polarizer. Such filter Lyot appears in the Nd:YAG laser cavity during operation at relatively high energy and repetition rate of radiation pulses (60–100 mJ, 20 Hz). The combined action of the “natural mode selection” process and the Lyot filter ensures the stable operation of a passive Q-switched Nd:YAG laser in the single frequency lasing mode (the lasing bandwidth is less than 57 MHz). The master single frequency pulsed Nd:YAG laser (λ = 1.06 μm) allows reducing the energy of pulses applied to the input of the optical parametric oscillator by more than 1.5 times while maintaining the specified energy level of the output pulses (30 mJ, λ = 1.57 μm). An additional increase in the efficiency of the optical parametric oscillator conversion is achieved by introducing
 a two-lens 1.3x telescope into the master laser cavity.

30 W-average-power femtosecond NIR laser operating in a flexible GHz-burst-regime

Laser sources which produce GHz bursts of ultrashort pulses attract a lot of attention by demonstrating superior performance in material processing. Flexibility of the laser source in a selection of parameters for custom application is highly preferable. In this work, we demonstrate a very versatile method for burst formation using the active fiber loop (AFL). It allows forming GHz bursts containing from 2 up to approximately 2200 pulses in a burst (1000 ns burst width) with identical pulse separation and any predefined intra-burst pulse repetition rate (PRR). The burst pre-shaping by the amplification conditions in the AFL and by the modulation of transmission of the acousto-optic modulator was demonstrated. Industrial-grade ultrafast laser system was able to operate in the single-pulse and GHz-burst regimes. The laser system delivered high-quality 368 fs duration (FWHM) pulses of 15.3 µJ pulse energy and 30.6 W average output power at 2 MHz PRR in the single-pulse regime. In the GHz-burst operation regime, bursts of 2.2 GHz intra-burst repetition rate were formed and amplified to more than 30 W average output power with a burst energy up to 135 µJ at a burst repetition rate of 200 kHz. The sub-picosecond duration of pulses was obtained in the GHz-burst regime at different burst widths.

The development of a new method of definition of formation parameters via the processing of non-stationary recovery of bottomhole pressure in the wells

To regulate the operation of oil and gas formations, it is necessary to survey separate wells. The most informative methods amongst well known well survey techniques are the ways of well surveys while unknown operation regime. One of them is the method of curves of pressure recovery, which allows obtaining important parameters of formation.

Design of a NARX-ANN-Based SP Controller for Control of an Irrigation Main Canal Pool

The management of irrigation main canals are studied in this research. One way of improving this is designing an efficient automatic control system of the water that flows through the canal pools, which is usually carried out by PI controllers. However, since canal pools are systems with large time delays and nonlinear hydrodynamics, these PIs are tuned in a very conservative way so that the closed-loop instability that may appear depending on the chosen operation regime is avoided. These controllers are inefficient because they have slow time responses. In order to obtain faster responses that remain stable independently of the operation regime, a control system that combines a Smith predictor, which is appropriate to control linear systems with large time delays, with a NARX artificial neural network (ANN), that models the nonlinear dynamics of the pools, is proposed. By applying system identification procedures, two nonlinear NARX-ANN-based models and a linear mathematical model of a real canal pool were obtained. These models were applied to implement a modified NARX-ANN-based SP controller and a conventional linear SP controller. Experimental results on our real canal pool showed that our modified NARX-ANN-based SP controller overcomes conventional linear SP controllers in both setpoint tracking and load disturbance rejection.

ANALYSIS OF ALTERNATIVE FUEL PROCESSING TECHNOLOGIES

The article presents the results of a comparative analysis and experimental testing of the efficiency of technological processes for the processing of some types of alternative energy sources into fuel for transport engines.
 The accumulated research experience in the development of on-board conversion systems (reactors) of traditional motor fuels shows that the level of their technical and technological complexity is incomparable with the ecological and economic effect of their use in an RTS power plant. The high temperature level of the processing of these fuels necessitates the need for additional energy expenditure for the organization of the conversion process (for example, burning part of the fuel to support the necessary thermal regime of operation in thermochemical reactors), and the presence of sulfur compounds in motor fuel excludes the possibility of using highly efficient catalysts. In addition, the large relative content of inert (non-combustible) components in the composition of the target conversion products create additional difficulties when they are burned in the engine. In general, the choice of an acceptable alternative energy carrier as a raw product for the production of motor fuel is a compromise that takes into account its energy value, temperature conditions of conversion, the spectrum of gases formed during conversion, cost, availability of raw materials, the possibility of adaptation to the conditions of the RTS, etc. From the set of factors considered above, it can be concluded that today methanol is one of the most energetically beneficial sources of cheap and efficient hydrogen-containing fuel for RTS engines. It should be noted that in the future, in the world of technology development and the corresponding raw material bases, it may be economically justified to use other compounds, which, according to their characteristics, will be able to meet the energetically favorable conditions in the technological structure of the on-board conversion implementation. This will allow creating a stable fuel and energy base , which practically does not depend on the imported hydrocarbon fuel.