Pulsed Mode Operation Research Articles

Influence of Detonation Spraying Parameters on the Microstructure and Mechanical Properties of Hydroxyapatite Coatings

The process of osteointegration depends significantly on the surface roughness, structure, chemical composition, and mechanical characteristics of the coating. In this regard, an important direction in the development of medical materials is the development of new techniques of surface modification and the creation of bioactive ceramic coatings. Calcium-phosphate materials based on hydroxyapatite have been proposed as bioactive ceramic coatings on titanium implants for the effective acceleration of bone tissue healing. To obtain bioactive ceramic coatings, pulse power sources are best suited, namely detonation spraying, in which the energy of the explosion of gas mixtures is used as a source of pulse action. The pulse mode of operation in the detonation spraying method is preferable for the formation of bioactive ceramic coatings. It provides a high velocity of hydroxyapatite particles, which promotes their effective fixation on the titanium substrate, while minimizing the heating of the material. This approach preserves the substrate structure and improves the coating adhesion. Four different types of coatings with varying O2/C2H2 molar ratios, ranging from 2.6 to 3.7, were obtained using detonation spraying. Powders and obtained coatings of hydroxyapatite were studied by Raman spectroscopy and XRD structural analysis. The results of XRD phase analysis showed the partial conversion of the hydroxyapatite phase to the α-tricalcium phosphate (α-TCP) phase during the detonation spraying process. The results obtained by Raman spectroscopy indicate that hydroxyapatite is the main phase in coatings. All hydroxyapatite-based coatings exhibited hydrophobic properties, which was confirmed by contact-angle values above 90° in wettability tests, characteristic of hydrophobic surfaces. The adhesive strength of the coatings was measured by the scratch test method. Tribological tests were conducted using the ball-on-disk method under both dry conditions and in Ringer’s solution. This approach enabled the evaluation of wear resistance and friction coefficient of the coatings in different environments, simulating both lubrication-free conditions and those resembling physiological environments.

Sintering of Copper Nanoparticles using Intense Pulsed Light for screen-printed films on flexible substrate

Abstract Rapid growth in applications involving large area flexible electronics has led to wide adoption of the technique of sintering printed films using intense pulsed light (IPL) due to its pulse mode operation and ability to reach high sintering temperatures without affecting the underlying substrate significantly. We study sintering mechanisms of screen-printed thin films of copper nanoparticles on polyethylene terephthalate (PET) plastic substrate by varying irradiance energy over a wide range to monitor conductivity and associated microstructure changes. We obtain optimized parameters which indicate existence of a sharp threshold irradiance energy to kickstart sintering, and two distinct regimes beyond that. The low temperature regime has a high energy barrier while the high temperature regime has a substantially reduced energy barrier with change of phase due to local melting.

Circulation process of methyl ester production from pretreated sludge palm oil using CaO/ABS catalytic static mixer coupled with an ultrasonic clamp

This study investigates the potential of fused deposition modeling (FDM) three-dimensional (3D) printing techniques for manufacturing catalytic static mixers during biodiesel synthesis. The printed catalytic mixing elements comprises acrylonitrile butadiene styrene (ABS) plastic with 15 wt% calcium oxide (CaO) as a solid catalyst. When the reactants flowed through the CaO/ABS mixing device, the blending and acceleration processes were both significantly impacted. Moreover, their characteristics, performance in biodiesel production, reusability, and economy were analyzed. The effects of methanol to oil (M:O) molar ratio, circulation time, and sonication time on methyl ester (ME) purity were also examined. The results showed that CaO crystals were distributed on the CaO/ABS mixer’s surface, which is crucial for catalytic purposes. During circulation process of ME from pretreated sludge palm oil (PSPO), catalytic static mixer (CSM) and CSM coupled with ultrasound (CSM/US) reactors were employed. The full ultrasonic power of CSM/US reactor of 16 × 400 W (total 6400 W) was operated at 20 kHz frequency. Moreover, the continuous and pulse ultrasonic modes of CSM/US reactor were compared to determine the ME purity and electricity consumption for ME production. For the CSM reactor, 12:1 M:O molar ratio and 8.5 h circulation time were recommended to realize 94.2 wt% ME purity. For the CSM/US reactor, 12:1 M:O molar ratio and 2.25 h circulation time were recommended to achieve 96.5 wt% ME purity. Under the pulsed mode operation, ME purity of 95.09 wt% was achieved, with a reduction in electricity consumption by approximately 37.6 % compared to continuous mode operation. Furthermore, the CaO/ABS catalytic static mixer was determined to be reusable for up to three cycles in both CSM and CSM/US reactors. Thus, CaO/ABS catalytic static mixers assure high purity ME production through FDM 3D printing technology with a CaO solid catalyst.

A Decoupled Feedback and Fast Norm Optimal Control approach for Normal and Superconducting RF Cavity disturbances compensation

Iterative learning controller (ILC)s of different types have been used in various engineering applications for system control in presence of repetitive disturbance, often encountered in batch control systems. A particle accelerator usually comprising of Radiofrequnecy (RF) cavities, when operated in pulsed mode processes particle beam similar to that in batch systems. However, an injected particle beam disturbs electric field inside RF cavity. In additions to beam loading disturbance encountered in all types of RF cavities, a superconducting cavity also encounters disturbance due to Lorentz force detuning. Under presence of such persisting disturbance/s, a Fast Norm Optimal ILC (FNOILC), helps achieve specified amplitude and phase stability of electric field, which results in beam of specified quality. A sophisticated control system helps achieve this objective. In this paper, FNOILC technique is explored for this purpose. Though, it has been reported for few accelerator facilities, in this work, a decoupling strategy is used in a feedback control loop, resulting into overall enhancement of control performance. Behavioral model of RF cavity is represented as dual input dual output system exhibiting two loops, found interacting due to nonzero cavity detuning. A decoupler is designed based on well known technique/s used in process control applications. Relative gain array element values are used to quantify interaction. In presence of beam loading disturbance, a FNOILC demonstrates an excellent control performance. A standard performance index has been used to assess control performance. It is found that use of decoupler in main feedback loop of RF cavity, enhances the resulting performance index. Besides, an ILC performance needs assessment with practical issues like model uncertainty, sensing delays, high detuning and observation noise. In this paper, most of conclusions are drawn based on large number of modeling and simulation studies carried out for lab prototype 650MHz cavity. Interesting studies like effects of low controller sampling frequency, feedback controller gain tuning, severe detuning, etc. are presented using a novel state plane representation. A zero phase filtering is simulated and proposed as an effective strategy when measurements have noise. This paper forms a case study which can be applied to any general system encountering repetitive disturbance. Additionally, paper also elaborates on FNOILC algorithm application for Lorentz force detuning compensation often encountered in superconducting cavity during pulse mode of operation.

CTC and CT5TEA: An advanced multi-channel digitizer and trigger ASIC for imaging atmospheric Cherenkov telescopes

We have developed a new set of Application-Specific Integrated Circuits (ASICs) of the TARGET family (CTC and CT5TEA), designed for the readout of signals from photosensors in cameras of Imaging Atmospheric Cherenkov Telescopes (IACTs) for ground-based gamma-ray astronomy. We present the performance and design details. Both ASICs feature 16 channels, with CTC being a Switched-Capacitor Array (SCA) sampler at 0.5 to 1GSa/s with a 16,384 sample deep storage buffer, including the functionality to digitize full waveforms at arbitrary times. CT5TEA is its companion trigger ASIC (though may be used on its own), which provides trigger information for the analog sum of four (and 16) adjacent channels. Since sampling and triggering takes place in two separate ASICs, the noise due to interference from the SCA is suppressed, and allows a minimal trigger threshold of ≤ 2.5 mV (0.74photo electrons (p.e.)) with a trigger noise of ≤ 0.5 mV (0.15p.e.). For CTC, a maximal input voltage range from −0.5V up to 1.7V is achieved with an effective bit range of > 11.6bits and a baseline noise of 0.7 mV. The cross-talk improved to ≤ 1% over the whole −3 dB bandwidth of 220MHz and even down to 0.2% for 1.5V pulses of 10 ns width. Not only is the performance presented, but a temperature-stable calibration routine for pulse mode operation is introduced and validated. The resolution is found to be ∼ 2.5% at 33.7 mV (10p.e.) and ≤ 0.3% at 337 mV (100p.e.) with an integrated non-linearity of < 1.6mV. Developed for the Small-Sized Telescope (SST) and Schwarzschild-Couder Telescope (SCT) cameras of the Cherenkov Telescope Array Observatory (CTAO), CTC and CT5TEA are deployed for both prototypes and shall be integrated into the final versions.

Innovative Integration of Dual Quantum Cascade Lasers on Silicon Photonics Platform.

For the first time, we demonstrate the hybrid integration of dual distributed feedback (DFB) quantum cascade lasers (QCLs) on a silicon photonics platform using an innovative 3D self-aligned flip-chip assembly process. The QCL waveguide geometry was predesigned with alignment fiducials, enabling a sub-micron accuracy during assembly. Laser oscillation was observed at the designed wavelength of 7.2 μm, with a threshold current of 170 mA at room temperature under pulsed mode operation. The optical output power after an on-chip beam combiner reached sub-milliwatt levels under stable continuous wave operation at 15 °C. The specific packaging design miniaturized the entire light source by a factor of 100 compared with traditional free-space dual lasers module. Divergence values of 2.88 mrad along the horizontal axis and 1.84 mrad along the vertical axis were measured after packaging. Promisingly, adhering to i-line lithography and reducing the reliance on high-end flip-chip tools significantly lowers the cost per chip. This approach opens new avenues for QCL integration on silicon photonic chips, with significant implications for portable mid-infrared spectroscopy devices.

Void closure in a pulsed complex plasma in microgravity

A new experimental method for creating void-free complex (dusty) plasmas under microgravity conditions is presented. The method is based on a pulsed operation mode of a four-channel radio frequency generator for plasma sustainment. A dust cloud of micrometer-sized particles can be immersed in the bulk of a low temperature plasma under microgravity conditions. It typically contains a central volume depleted of particles—the void—that prevents the generation of large, continuous clouds. Experiments performed at different neutral gas pressures and discharge volumes during the microgravity phase of a parabolic flight show that the central void is closed completely once the pulsed operation mode is applied. The particle cloud shape and the density distribution within the cloud are practically independent of the pulse period within the investigated parameter range and mainly depend on the overall discharge parameters neutral gas pressure and discharge volume. This indicates that the pulsed operation of the plasma source does not introduce new physical effects on the particles aside from the void closure. The proposed method has great potential for future application in experimental facilities dedicated to fundamental studies of large three-dimensional, homogeneous complex plasma systems in microgravity.

Pulse operation mode of inertial electrostatic plasma confinement devices

The paper discusses the operation features of the inertial electrostatic plasma confinement (IEC) devices in the pulsed high voltage mode. The pulse operation mode offers significant advantages in IEC devices, which are associated with high discharge currents that are inaccessible for continuous operating modes. However, the implementation of such operating modes is associated with a number of physical limitations and technical difficulties.A stand with an IEC chamber powered by a high-voltage pulse transformer and a unit for gas preliminary ionization in the IEC chamber has been developed. In the chamber, ions are accelerated from a background glow discharge. A study of the burning background discharge in the IEC chamber, background discharge current Ipre influence on the duration of current and voltage pulses of the main discharge and the delay between them was carried out. The results of the neutron yield measuring in an IEC chamber operating in pulsed mode are presented at a charging voltage up to 105 kV, a discharge current amplitude of several tens of amperes, a preionization current of 8 mA, and a pulse repetition rate from single to 300 Hz. A stable neutron flux with an energy of 2.5 MeV at a level of 106 neutrons/s was experimentally obtained.

Lactic Acid Production by Enterococcus durans Is Improved by Cell Recycling and pH Control

Lactic acid bacteria are widely used because they produce lactic acid naturally, are resistant to acidic pH and a wide temperature range, and frequently produce lactic acid as a primary metabolite. In this study, Enterococcus durans isolated from buffalo milk was employed in lactic acid fermentation with the primary goal of obtaining fermentation parameters for an effective process enabling the use of lactose as an alternative carbon source. Fermentative parameters such as initial concentration of carbon source, dissolved oxygen concentration, cell recycling, and batch with pulse operation mode were studied to find the best conditions for L-(+)-lactic acid production. The association of 20 g·L−1 of lactose with 10 g·L−1 of glucose enabled the best bioconversion to lactic acid. Anaerobiosis did not contribute to increasing lactic acid production. Batch fermentation with cell recycling was the strategy that enhanced lactic acid production and lactose consumption, reaching 26.07 g·L−1, 0.36 g·L−1·h−1 of productivity and yielding about 0.86 g·g−1. It is fundamental to evaluate the parameters of lactic acid fermentation and provide efficient and sustainable production methods.

Generation of superposed orbital angular momentum beams using a free-electron laser oscillator.

With wavelength tunability, free-electron lasers (FELs) are well-suited for generating orbital angular momentum (OAM) beams in a wide photon energy range. We report here the first experimental demonstration of OAM beam generation using an oscillator FEL with the tens of picosecond pulse duration. Lasing around 458 nm, we have produced the four lowest orders of superposed Laguerre-Gaussian beams using a very long FEL resonator of 53.73 m. The produced beams have good beam quality, excellent stability, and substantial average power. We have also developed a pulsed operation mode for these beams with a highly reproducible temporal structure for a range of repetition rate of 1-30 Hz. This development can be extended to short wavelengths, for example to x-rays using a future x-ray FEL oscillator. The OAM operation of such a storage-ring FEL also paves the way for the generation of OAM gamma-ray beams via inverse Compton scattering.

An Efficient Electrothermal Model of a Thermoelectric Converter for a Thermal Energy Harvesting Process Simulation and Electronic Circuits Powering

This paper deals with an electrothermal model of a thermoelectric converter dedicated to performing simulations of coupled thermal and electrical phenomena taking place in harvesting processes. The proposed model is used to estimate the electrical energy gain from waste heat that would be sufficient to supply electronic circuits, in particular autonomous battery-less nodes of wireless sensor networks (WSN) and Internet of Things (IoT) devices. The developed model is not limited to low-power electronic solutions such as WSN or IoT; it can also be scaled up and applied to simulations of considerably higher thermal power conversion. In this paper, a few practical case studies are presented that show the feasibility and suitability of the proposed model for complex simultaneous simulation processes in both the electrical and thermal domains. The first example deals with a combined simulation of the electrothermal model of a thermoelectric generator (TEG) and an electronic harvester circuit based on Analog Devices’ power management integrated circuit LTC3108. The second example relates to the thermalization effect in heat sink-less harvesting applications that could be mitigated by a pulse mode operation. The unique contribution and advancement of the model is the hierarchical structure for scaling up and down, incorporating the complexity of the Seebeck effect, the Joule effect, heat conduction, as well as the temperature dependence of the used materials and the thermoelectric pellet geometries. The simulations can be performed in steady as well as transient states under changing electrical loads and temperatures.

Pulsed Dielectric Barrier Discharges for Gas-Phase Composition Control: A Simulation Model

We present results obtained from the numerical simulation of the gas-phase chemical kinetics in atmospheric pressure air non-equilibrium plasmas. In particular, we addressed the effect of the pulsed operation mode of a planar dielectric barrier discharge. As conjectured, the large difference in the time scales involved in the fast dissociation of molecules in plasmas and their subsequent reactions to produce stable chemical species makes the presence of a continuously repeated plasma production stage unnecessary and a waste of electrical power and efficiency. The results on NOx remediation, ozone production, water vapor and ammonia dissociation are discussed. A few comparisons with experimental findings in a dielectric barrier discharge reactor already used for applications are also briefly addressed. Our results clearly indicate a pattern for the optimization of the discharge using a carefully designed repetition rate and duty cycle.

A wearable and flexible lactic-acid/O2 biofuel cell with an enhanced air-breathing biocathode

The performance of biocathode in an enzymatic biofuel cell (EBFC) in the real application is somehow overlooked. Herein, a wearable and flexible lactic-acid/O2 EBFC enhanced with an air-breathing biocathode is designed to solve the limitation of biocathode that arises from the low solubility and slow mass transfer of the dissolved oxygen. To improve the oxygen supply efficiency for the air-breathing biocathode, a superhydrophobic base electrode creating an efficient air-solid-liquid triphase interface is developed. The designed EBFC with an ‘island-bridge’ configuration is integrated by assembling the current collectors of air-breathing biocathode and bioanode on a commercial laminating film (LF) screen-printed with a noninterfering circuit. It is found that the biocathode/bioanode area ratio should exceed 9:1 so that the designed EBFC (1A//9C) can achieve the optimal performance. This EBFC delivers an open circuit voltage of ca. 0.75 V and outputs a maximum power density of ca. 1.78 mW cm−2. In addition, a scaled-up EBFC (total bioanode area: 1.5 cm2) successfully powers a self-developed low-power device of heartrate in the pulse operation mode when applied on a volunteer's arm.

Dosimetry for radiobiological in vivo experiments at laser plasma-based proton accelerators

Objective. Laser plasma-based accelerators (LPAs) of protons can contribute to research of ultra-high dose rate radiobiology as they provide pulse dose rates unprecedented at medical proton sources. Yet, LPAs pose challenges regarding precise and accurate dosimetry due to the high pulse dose rates, but also due to the sources’ lower spectral stability and pulsed operation mode. For in vivo models, further challenges arise from the necessary small field dosimetry for volumetric dose distributions. For these novel source parameters and intended applications, a dosimetric standard needs to be established. Approach. In this work, we present a dosimetry and beam monitoring framework for in vivo irradiations of small target volumes with LPA protons, solving aforementioned challenges. The volumetric dose distribution in a sample (mean dose value and lateral/depth dose inhomogeneity) is provided by combining two independent dose measurements using radiochromic films (dose rate-independent) and ionization chambers (dose rate-dependent), respectively. The unique feature of the dosimetric setup is beam monitoring with a transmission time-of-flight spectrometer to quantify spectral fluctuations of the irradiating proton pulses. The resulting changes in the depth dose profile during irradiation of an in vivo sample are hence accessible and enable pulse-resolved depth dose correction for each dose measurement. Main results. A first successful small animal pilot study using an LPA proton source serves as a testcase for the presented dosimetry approach and proves its performance in a realistic setting. Significance. With several facilities worldwide either setting up or already using LPA infrastructure for radiobiological studies with protons, the importance of LPA-adapted dosimetric frameworks as presented in this work is clearly underlined.

Recent developments in terahertz quantum cascade lasers for practical applications

Abstract Terahertz (THz) quantum cascade laser (QCL) is an electrically pumped unipolar photonic device in which light emission takes place due to electronic transitions between subbands formed by multiple strongly coupled quantum wells. THz QCL is arguably the most promising solid-state source to realize various THz applications, such as high-resolution spectroscopy, real-time imaging, chemical and biological sensing, and high-speed wireless communication. To date, THz QCLs have covered emitting frequency from 1.2 to 5.4 THz when operating without the assistance of an external magnetic field. The highest output power is in hundreds milliwatt and watt levels continuous-mode and pulsed-mode operations, respectively. THz QCL-based local oscillators have been implemented in astronomy for the identification of atoms and ions. However, there are also limitations, including under room-temperature operation, large divergent beam, narrow single-mode frequency tuning range, incomplete polarization control, and narrow-range frequency comb operation that hinder the widespread applications of THz QCLs. Continuous efforts have been made to improve those THz QCL properties in order to satisfy the requirements of different THz applications. This report will review the key output characteristic developments of THz QCLs in the past few years, which aim to speed up THz QCLs toward practical applications.

Development of minimalistic propulsion system for university nanosatellite

The paper presents the results of development of a neutralizer-free high-frequency ion thruster for university nanosatellite propulsion systems which allow it to perform orbit correction tasks. The application of high-frequency ion thruster technologies allows the self-neutralization mode and is relevant for the development of engines for CubeSat format small satellites where the size and weight of the propulsion system must be as minimal as possible. A pair of shapes of neutralizer-free high-frequency ion thrusters with different accelerating region geometries are proposed. The analysis of plasma flow and the charged particles acceleration was carried out. The trajectory and acceleration of a quasi-neutral plasma flow was calculated for crossed electric and magnetic fields. The cyclotron resonance model was applied for the quasi-neutral plasma flow acceleration in an ambipolar field. The coaxial structure of the ion thruster model is discussed. Preliminary estimate of the performance of the propulsion system prototype was carried out for a pulsed operation mode. Additionally, the energy budget of a high-frequency ion thruster prototype was calculated.

Gliding Arc Reactor under AC Pulsed Mode Operation: Spatial Performance Profile for NOx Synthesis.

A two-dimensional gliding arc reactor for NOx synthesis was investigated in this study using AC pulsed mode operation. Tests with a duty cycle of 40 or 60% achieved the lowest energy consumption of 6.95 MJ/mol, which is an improvement of 15% from the case of continuous operation. Based on the results achieved, a new method for analyzing the spatial profile of the reactor was presented. The reactor was divided into five zones along the arc propagation, and results indicated that the first zone and last zone of the gliding arc reactor had higher energy consumption (9.59 and 8.63 MJ/mol, respectively), while lower consumption was observed in the middle parts of the reactor with a minimum of 5.00 MJ/mol. Spatial-resolved optical emission spectra, the deduced electron density, and temperature indicated the nonuniformity in plasma properties, which corresponds to the NOx production performance across the reactor. This research provides information and discussion that can be used for understanding and optimization of gliding arc reactors toward efficient nitrogen fixation.

Cavity Quantum Optomechanical Nonlinearities and Position Measurement beyond the Breakdown of the Linearized Approximation.

Several optomechanics experiments are now entering the highly sought nonlinear regime where optomechanical interactions are large even for low light levels. Within this regime, new quantum phenomena and improved performance may be achieved; however, a corresponding theoretical formalism of cavity quantum optomechanics that captures the nonlinearities of both the radiation-pressure interaction and the cavity response is needed to unlock these capabilities. Here, we develop such a nonlinear cavity quantum optomechanical framework, which we then utilize to propose how position measurement can be performed beyond the breakdown of the linearized approximation. Our proposal utilizes optical general-dyne detection, ranging from single to dual homodyne, to obtain mechanical position information imprinted onto both the optical amplitude and phase quadratures and enables both pulsed and continuous modes of operation. These cavity optomechanical nonlinearities are now being confronted in a growing number of experiments, and our framework will allow a range of advances to be made in, e.g., quantum metrology, explorations of the standard quantum limit, and quantum measurement and control.

Динамическая теплоэлектрическая модель гетеропереходного биполярного транзистора с учетом падения напряжения на эмиттерных дорожках металлизации

A dynamic 3D thermoelectric model has been developed to calculate the temperature field and emitter current density in the comb structure of a heterojunction bipolar transistor (HBT) with the length of the emitter metallization paths comparable to the size of the crystal, taking into account the inhomogeneous distribution of current density under the emitter paths caused by a voltage drop on the resistance of the current-carrying metallization. The model is based on an iterative solution in the COMSOL Multiphysics software environment of a non-stationary heat equation together with a system of equations for the distribution of electric potential along the emitter path and the current density under the path. It is shown that during the action of the heating power pulse in the HBT, the distribution of temperature and current density along the emitter tracks change character, respectively, from homogeneous and monotonically decreasing to non-monotonically changing. At the same time, the maximum temperature and current density reach stationary values with a rate significantly exceeding the rate of overheating increase with homogeneous heating of the structure, and the maxima of temperature and current density in the process of self-heating shift from the beginning to the center of the tracks. The proposed model can be used to evaluate the thermomechanical stresses in the structure of the HBT and the limiting electrical parameters in the pulsed modes of operation of the HBT.

Самодвойственные функциональные элементы для синтеза контролепригодных цифровых систем

All self-dual analogs of elementary functional gates have been considered, the use of which allows for the synthesis of self-dual circuit implementations of arbitrary Boolean functions. In this case, two synthesis methods can be used, each one based on the property of any Boolean function to be transformed into a self-dual function using one additional variable. The first method involves replacing all non-self-dual functional gates in the device structure with self-dual analogs. The second one involves obtaining a self-dual function from the original formula. The study conducted modeling of self-dual functional gates in pulse mode of operation. It has been shown that all self-dual functional gates, except for those implementing equivalence and nonequivalence functions (modulo-2 addition), are fully self-checkable with respect to stuck-at faults when checking computations based on the belonging of the generated functions to the class of self-dual Boolean functions. However, the gates that implement the mentioned functions require additional monitoring. For them, error masking occurs due to the simultaneous distortion of signals on both combinations in a pair. This feature of these self-dual functional gates should be taken into account when developing controllable self-checking digital computing devices and systems. The article provides an example of using methods for constructing self-dual circuit implementations. The obtained results can be used in the synthesis of controllable self-dual computing devices and systems.