Pulse Experiments Research Articles

Nuclear hyperpolarization of (1-13C)-pyruvate in aqueous solution by proton-relayed side-arm hydrogenation.

We employ Parahydrogen Induced Polarization with Side-Arm Hydrogenation (PHIP-SAH) to polarize (1-13C)-pyruvate. We introduce a new method called proton-relayed side-arm hydrogenation (PR-SAH) in which an intermediate proton is used to transfer polarization from the side-arm to the 13C-labelled site of the pyruvate before hydrolysis. This significantly reduces the cost and effort needed to prepare the precursor for radio-frequency transfer experiments while still maintaining acceptable polarization transfer efficiency. Experimentally we have attained on average 4.33% 13C polarization in an aqueous solution of (1-13C)-pyruvate after about 10 seconds of cleavage and extraction. PR-SAH is a promising pulsed NMR method for hyperpolarizing 13C-labelled metabolites in solution, conducted entirely in high magnetic field.

Experimental Study on Pressure Wave Characteristics of High-Voltage Discharge in Water With Hemispherical Electrodes

High-voltage pulse discharge in water is a promising technology to enhance the permeability of coal seam and rock mass by generating fractures within them. With the aim of improving the stability and efficiency of this technology, a high voltage electric pulse experiment system was constructed. The discharge electrodes in the experiment was hemispherical. The positive and negative electrodes were arranged on the same axis with adjustable spacing. Five sets of experiments were undertaken with the electrode spacing of 1mm, 2mm, 3mm, 4mm, and 5mm, respectively. In the experiments, an oscilloscope was used to analyze the voltage, current, and pressure wave signals. The experimental results of two typical voltage-current curves indicate that the peak pressure of plasma shock wave follows a parabolic trend with the electrode spacing, and there is an optimal electrode spacing for a given discharge voltage. The peak pressure of plasma shock wave tends to increase linearly with the increase of discharge voltage. The greater the electrode spacing, the greater the sensitivity of shock wave peak pressure to the discharge voltage. The shock wave peak pressure sensitivity of 5 mm discharge spacing is 4.7 times that of 1 mm discharge spacing. The experimental results for the voltages of 9 kV, 12 kV, and 24 kV with the optimal electrode spacing show that a power function is the best fit for the attenuation of the peak pressure of shock wave with its propagation distance.

Heat transfer under powerful heat release in supercritical-pressure liquids

The aim of the present article is to summarize the results of pulse experiments performed under conditions of powerful heat release in supercritical-pressure liquids. The parameters of the discussion are the values of the speed of crossing the vicinity of the critical temperature and pressure reduced to the critical one. These results obtained for “heater-probe / supercritical fluid” system and based solely on comparison of the primary data indicate a threshold decrease in the intensity of heat transfer near the critical temperature. The purpose of this summary is to suggest a relatively simple approach to reconciling the pulse heating results with the peaks of thermophysical properties derived from experiments in stationary conditions. It is assumed that the action of gradient in temperature and the presence of heat-transfer surface can serve as factors that suppress large-scale fluctuations in pulse heated system, leading to a “smoothing” the critical enhancement of the properties.

Robot-Aided Training of Propulsion During Walking: Effects of Torque Pulses Applied to the Hip and Knee Joints During Stance.

We sought to evaluate the effects of the application of torque pulses to the hip and knee joint via a robotic exoskeleton in the context of training propulsion during walking. Based on our previous study, we formulated a set of conditions of torque pulses applied to the hip and knee joint associated with changes in push-off posture, a component of propulsion. In this work, we quantified the effects of hip/knee torque pulses on metrics of propulsion, specifically hip extension (HE) and normalized propulsive impulse (NPI), in two experiments. In the first experiment, we exposed 16 participants to sixteen conditions of torque pulses during single strides to observe the immediate effects of pulse application. In the second experiment, we exposed 16 participants to a subset of those conditions for 200 strides to quantify short-term adaptation effects. During pulse application, NPI aligned with the expected modulation of push-off posture, while HE was modulated in the opposite direction. The timing of the applied pulses, early or late stance, was crucial, as the effects were often in the opposite direction when changing timing condition. Extension torque applied at late stance increased HE in both experiments - range of change in HE: (2.9 ± 0.4 deg, 7.7 ± 1.0 deg), . The same conditions resulted in a negative change in NPI only in the single pulse experiment - change in NPI for knee torque: -3.0 ± 0.4 ms, - and no significant change for hip torque. Also, knee extension and flexion torque during early and late stance, respectively, increased NPI during single pulse application - range of change in NPI: (3.8, 4.6) ± 0.8 ms, . During repeated pulse application, NPI increased for late stance flexion torque - range of change in NPI: (4.5 ± 0.7 ms, 4.8 ± 0.8 ms), , but not late stance extension torque. After exposure, we observed positive after-effects in HE in three conditions - range of change in HE: (2.0 ± 0.3 deg, 3.7 ± 0.7 deg) - and significant positive after-effects in NPI for early stance flexion torques - change in NPI: (2.7 ± 0.6 ms, ). These results indicate that positive propulsive after-effects can be achieved through repeated exposure to torque pulses.

(Keynote) Tuning the Selectivity of CO2 Electroreduction through Dynamic Catalyst Transformations Under Reaction Conditions

The utilization of fossil fuels as the main energy source gives rise to serious environmental issues, including global warming caused by the continuously increasing level of atmospheric CO2. Recently, the electrochemical conversion of CO2 (CO2RR) to chemicals and fuels driven by electricity derived from renewable energy has been recognized as a promising strategy towards sustainable energy.In my talk I will provide examples of recent advances in the development of highly active size- and shape-controlled nanoparticle (NP) electrocatalysts (Cu, Cu-Zn, Cu-Ag) and how their structure (crystal orientation, atomic arrangement, size, shape, defects), oxidation state and composition influence their selectivity in CO2RR. I will also discuss how important morphological motives and chemical sites can be created and regenerated in pulsed electrochemistry experiments. Additionally, the determining role of the electrolyte in the surface restructuring, reaction activity and selectivity will be illustrated. Finally, the importance of in situ and operando characterization methods (e.g. EC-AFM, Liquid-TEM, XAS, XPS, XRD, LEEM/XPEEM) to gain in depth understanding on the structure- and electrolyte-sensitivity of real CO2RR catalysts under working conditions will be demonstrated. Our results are expected to open up new routes for the reutilization of CO2 through its direct selective conversion into higher value products such as ethylene and ethanol.

Pulse Measurements on LiNi0.6Co0.2Mn0.2O2 Cathodes with Various Electrode Parameters Affecting the Charge-Discharge Rate Performance

Li-ion batteries (LIBs) are used globally as power sources for various applications, such as portable electronics, electric vehicles, and large-format stationary energy storage systems, driving a wireless, fossil fuel-free sustainable society [1,2]. Together with the increasing demands for higher energy and longer lifespan, faster charging capability and higher (discharging) power characteristic are of significant interests. In this study, we investigated the rate capability of LiNi0.6Co0.2Mn0.2O2 (NCM) cathodes, as one of Ni-rich, layered oxide cathodes, for LIBs. We examined the rate performance and the limiting factors for both charging and discharging at current rates of 0.2-10C using electrochemical impedance spectroscopy (EIS) and pulse polarization measurements. The electrodes were prepared by varying the electrode density from 1.9 g cm-3 to 3.6 g cm-3 at a fixed electrode thickness of ~63 μm and the mass loading from 3 mg cm-2 to 23 mg cm-2 at a fixed electrode density of 2.7g cm-3.With increasing C-rate, both the discharge and charge capacities are decreased for all the electrode densities (see Fig. a and b). A low C-rates, no prominent difference in the charge and discharge capacities is found with respect to the electrode density. The moderate electrode density of 2.7 g cm-3 shows the best rate capability owing to a balance between electron conduction and ion transport in the electrode. The 1.9 g cm-3 electrode displays lower discharge capacities at C-rates of 0.2C-2C, as compared to the 3.6 g cm-3 electrode. However, capacity reversal is found at high C-rates (>2C). On the other hand, the 3.6 g cm-3 electrode shows better rate properties than the 1.9 g cm-3 electrode for charging. In order to probe the electrochemical kinetics behind the different rate properties of the NCM electrode with respect to the electrode density, we carried out EIS measurements; however, the resulting Nyquist plots could not differentiate the limiting factors affecting the kinetics for charge and discharge, in terms of the relationship between the electrode density and charge (electron and Li-ion) transports (not shown).We performed pulse experiments to generate pulse polarization profiles for charge and discharge of the electrodes with different electrode densities. Pulse polarization measurements are techniques used to measure voltage differences during time-limited charging or discharging of a cell at a CC and given state-of-charge [3,4]. Fig. c depicts a schematic of the pulse measurements for discharge and charge. When a certain amount of current is applied to the cell upon charging or discharging, a voltage difference can occur due to various polarization factors according to DC-IR = Eocv + EIR-drop + ∆Et, where EIR-drop is an initial voltage change upon charging/discharging (IR drop) and ∆Et is a voltage change for the pulse region at a CC and time. The DC-IR, EIR-drop, and ∆Et at a pulse time (∆tp) of 100 s with respect to the current density for pulse discharge and charge are plotted in Fig. 2b and 2c, respectively. For pulse discharging (Fig. d), the 3.6 g cm-3 electrode exhibits a relatively large ∆Et with increasing current density, compared to those of the 1.9 g cm-3 electrode, which is contrast to the variation of DC-IR. These pulse polarization data suggest the limiting factors affecting the charge and discharge rate capabilities of the electrodes with different electrode parameters. The pulse measurements with respect to the mass loading (electrode thickness) will be also discussed.This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIT) (2020R1C1C1013253).[1] Nat. Energy 3, 290-300 (2018).[2] ACS Energy Lett. 5, 807-816 (2020).[3] J. Electrochem. Soc. 164, E3539-E3546 (2017).[4] J. Power Sources 196, 412-427 (2011).Figure. Rate capability of the NCM622 cathodes with electrode densities of 1.9-3.6 g cm-3 upon (a) discharging and (b) charging; (c) Schematic of the pulse measurements of the NCM622 cathodes with electrode densities of 1.9-3.6 g cm- 3 for charge and discharge and the resulting parameters including (d) discharge DC-IR, EIR-drop, and ∆Et (∆tp=100 s) and (e) charge DC-IR, EIR-drop, and ∆Et (∆tp=100s) versus the current density. Figure 1

A sensitivity leap for X-band EPR using a probehead with a cryogenic preamplifier

Inspired by the considerable success of cryogenically cooled NMR cryoprobes, we present an upgraded X-band EPR probehead, equipped with a cryogenic low-noise preamplifier. Our setup suppresses source noise, can handle the high microwave powers typical in X-band pulsed EPR, and is compatible with the convenient resonator coupling and sample access found on commercially available spectrometers. Our approach allows standard pulsed and continuous-wave EPR experiments to be performed at X-band frequency with significantly increased sensitivity compared to the unmodified setup. The probehead demonstrates a voltage signal-to-noise ratio (SNR) enhancement by a factor close to 8× at a temperature of 6 K, and remains close to 2× at room temperature. By further suppressing room-temperature noise at the expense of reduced microwave power (and thus minimum π-pulse length), the factor of SNR improvement approaches 15 at 6 K, corresponding to an impressive 200-fold reduction in EPR measurement time. We reveal the full potential of this probehead by demonstrating such SNR improvements using a suite of typical hyperfine and dipolar spectroscopy experiments on exemplary samples.

Dynamic Nuclear Polarization with Vanadium(IV) Metal Centers

Summary Dynamic nuclear polarization (DNP) harnesses the large polarization of electron spins to dramatically increase nuclear magnetic resonance (NMR) sensitivity. This study expands the scope of DNP beyond its traditional focus on hyperpolarizing the solvent network using exogenous polarizing agents (PAs). We introduce 1H DNP with endogenous V4+ centers positioned in a set of vanadyl complexes with tunable V4+-1H distances. We traced the polarization transfer from V4+ to 1H spins, specifically differentiating between direct V4+-1Hs polarization transfer and the 1H spin-diffusion-mediated bulk solvent 1H polarization buildup and illuminated the effect of the V4+-1H distance on these processes. These results deepen our understanding of polarization pathways and expand the catalog of PAs to broad-line transition metals. This study establishes crucial first steps toward employing strategically positioned endogenous paramagnetic metal centers for DNP and the conceptual framework of hyperfine DNP spectroscopy that merges both spatial and chemical diagnosis of target nuclear spins.

Solute trapping in rapid solidification

Abstract

Comparative study of structure-catalytic activity relationship for Ni–Cr–Al–O and Cu–Ni–Cr–Al–O spinel oxide solid solutions

A spinel solid solution expressed by a composition formula of CuxNi1−xAl1.8Cr0.2O4 (0 ≤ x ≤ 0.2) was studied focusing on the role of Cu species in the catalytic activity toward NO reduction under a simulated three-way catalysis condition. X-ray Rietveld analysis revealed that Cu and Cr prefer to occupy the tetrahedral site and the octahedral site, respectively, whereas Ni and Al are distributed across both sites. Although NiAl1.8Cr0.2O4 (x = 0) showed negligible catalytic activity for NO reduction, the partial replacement of Ni by Cu significantly enhanced the activity, achieving the highest activity at x = 0.05 not only for NO reduction but also for CO and C3H6 oxidation. Based on the infrared spectra and pulsed reaction experiments, it was concluded that the monovalent Cu site in the tetrahedral site plays a key role in CO chemisorption, oxygen vacancy formation, and subsequent NO reduction via the Mars–van Krevelen mechanism.

Microbial upgrading of acetate into 2,3-butanediol and acetoin by E. coli W

BackgroundAcetate is an abundant carbon source and its use as an alternative feedstock has great potential for the production of fuel and platform chemicals. Acetoin and 2,3-butanediol represent two of these potential platform chemicals.ResultsThe aim of this study was to produce 2,3-butanediol and acetoin from acetate in Escherichia coli W. The key strategies to achieve this goal were: strain engineering, in detail the deletion of mixed-acid fermentation pathways E. coli W ΔldhA ΔadhE Δpta ΔfrdA 445_Ediss and the development of a new defined medium containing five amino acids and seven vitamins. Stepwise reduction of the media additives further revealed that diol production from acetate is mediated by the availability of aspartate. Other amino acids or TCA cycle intermediates did not enable growth on acetate. Cultivation under controlled conditions in batch and pulsed fed-batch experiments showed that aspartate was consumed before acetate, indicating that co-utilization is not a prerequisite for diol production. The addition of aspartate gave cultures a start-kick and was not required for feeding. Pulsed fed-batches resulted in the production of 1.43 g l−1 from aspartate and acetate and 1.16 g l−1 diols (2,3-butanediol and acetoin) from acetate alone. The yield reached 0.09 g diols per g acetate, which accounts for 26% of the theoretical maximum.ConclusionThis study for the first time showed acetoin and 2,3-butanediol production from acetate as well as the use of chemically defined medium for product formation from acetate in E. coli. Hereby, we provide a solid base for process intensification and the investigation of other potential products.

Photo-thermionic emission and photocurrent dynamics in low crystallinity carbon nanotubes

Within this work, it is studied the photo-thermionic and photocurrent behavior of two kinds of carbon nanotube arrays, grown by chemical vapor deposition. One kind is fabricated by using a co-catalyst bilayer approach and other by a catalyst-free route by using a porous alumina membrane as a template. The carbon nanotubes fabricated by both approaches exhibit low crystallinity. To compute the thermal properties of the nanomaterials, a photothermal experiment was measured at 1064 nm wavelength, and numerical simulations were conducted to analyze the photo-thermionic emission dynamics. The high absorbance of the carbon nanotubes leads to reach temperatures above 1500 K, with time response in the millisecond order and emission currents in the nanoampere range. On the other hand, the photodetector behavior was confirmed by a single pulse experiment that induces fast photocurrent recognition associated to a photodiode. Our results highlighted the coexistence of stable states related to high-power and high-speed electronic conversion energy dependent on the growth mechanism of carbon nanotubes.

Direct Photon-by-Photon Analysis of Time-Resolved Pulsed Excitation Data using Bayesian Nonparametrics

SUMMARYLifetimes of chemical species are typically estimated by either fitting time-correlated single-photon counting (TCSPC) histograms or phasor analysis from time-resolved photon arrivals. While both methods yield lifetimes in a computationally efficient manner, their performance is limited by choices made on the number of distinct chemical species contributing photons. However, the number of species is encoded in the photon arrival times collected for each illuminated spot and need not be set by hand a priori. Here, we propose a direct photon-by-photon analysis of data drawn from pulsed excitation experiments to infer, simultaneously and self-consistently, the number of species and their associated lifetimes from a few thousand photons. We do so by leveraging new mathematical tools within the Bayesian nonparametric. We benchmark our method for both simulated and experimental data for 1–4 species.

Microwave-induced thermacoustic signal characteristics during pulsed microwave ablation

Microwave ablation (MWA) is a minimally invasive thermal therapy in which an interstitial antenna delivers microwave power locally to diseased tissue to cause cell death. Thermoacoustic (TA) signals can be generated with internally pulsed microwave energy that simultaneously ablates tissue. When pulsed microwave energy is absorbed by tissue, the tissue undergoes an incremental temperature rise which leads to thermoelastic expansion and the generation of an acoustic wave that can be detected by ultrasound transducers. The characteristics of the TA signals are linked to features of the local ablation environment from which they are generated, and thus can be exploited for ablation monitoring. In this experimental and computational study, we examine the fundamental characteristics of TA signals generated from within the ablation zone and observe how the TA signal changes as the ablation zone evolves. We performed pulsed microwave heating experiments in non-coagulating and coagulating liquids and measured the resulting TA signals. We also performed multiphysics simulations of the MWA process that encompass the electromagnetic, thermal, and acoustics physics. This study provides insights into TA signal generation and propagation during MWA and establishes the feasibility of using the TA signals for ablation monitoring.

Study on Laminated Bus Bar for High-pulse Power Converter Module

Aiming at the problems of high switching overvoltage of power semiconductor devices and unbalanced current of parallel power devices in high-pulse power converters, this paper proposes a laminated bus bar of symmetrical path on the basis of the theoretical analysis and key points of laminated bus bar. The finite element simulation software was used to analyze the stray inductance of laminated bus bars. The actual stray inductance and overvoltage of the converter commutation circuit were measured by single pulse experiment. The results show that the laminated bus bar of symmetrical path can effectively reduce stray inductance, suppress switching impulse overvoltage and improve the current balance of the parallel power devices. It is of great significance to analyze the performance of laminated bus bar of symmetrical path, and it can be used for high-pulse power conversion technologies.

Correction of residence time distribution measurements for short holding times in pasteurization processes

Abstract When in-line cells are used for obtaining residence time distribution (RTD) data from systems with short residence time, the signal distortion caused by the cell can compromise the results. A procedure to correct such distortion using convolution of signals in the time domain is proposed. First, the RTD of the cell is characterized, and then the E-curve of an RTD model is convoluted with the cell curve. The convoluted E-curve is fitted to the experimental data by adjusting the mean time and the model parameter. The procedure is demonstrated using a pilot scale pasteurization unit with two heaters, one cooler and six options of holding tube. Pulse experiments were performed, E-curves were obtained for each process step and five RTD models were tested. The convolution procedure was successful in removing the distortion caused by the detection cell, which was very significant for the holding tubes.

Passive internalization and active extrusion determines PLGA-nanoparticle concentration in cancer cell lines.

Background: Poly(lactic-co-glycolic) acid nanoparticle (PLGA-NP) trafficking across cell membranes was investigated to confirm preliminary results that contradicted existing studies. Materials & methods: Uptake and retention of PLGA-NPs at 37and 4°C in the presence and absence of metabolic inhibitors in various cell lines was estimated. Results: Pulse experiments with metabolic inhibitors and culturing at 4°C demonstrated the predominantly passive nature of PLGA-NP uptake. Chase experiments with metabolic inhibitors indicated the role of active exocytosis in the extrusion of these NPs. PLGA-NPs with ionic or nonionic hydrophilic coats with highly positive or negative ζ-potential also showed similar results. Conclusion: Our study opens up the possibility of modulation of active exocytosis to increase intracellular retention of NPs for an extended period of drug delivery.

Detailed simulations of the DLR auto-igniting pulsed jet experiment

Numerical simulations of an auto-igniting pulsed jet in a vitiated co-flow experiment by DLR (German Aerospace Center) are conducted by highly-resolved large-eddy simulations using direct chemistry with an augmented reduced mechanism. The experiments consist of two operation modes: continuous injection used for code-verification and pulsed injection utilized for fundamental investigation of auto-ignition dynamics. Initially, reference one-dimensional self-igniting counter-flow flames are investigated. Then, a grid convergence study has been performed. It is shown that even a coarser grid would be sufficient to describe the ignition chemistry since the ignition kernel appears at low velocities and fuel-lean conditions in zones of low scalar dissipation rates. For the statistically steady jet, numerical predictions are in a very good agreement with the experiments, giving confidence in the applied models. For the pulsed jet, all of the predicted ignition delay times and locations are in the range of the experimental observations. Time-resolved statistics reveal that thermochemical properties of the gas in a pulsed jet achieve states that are impossible to reproduce in laminar conditions. For further analysis, hydroxyl and formaldehyde are chosen as a marker for the established flame and for the ignition, respectively. In laminar conditions, these two species are perfectly correlated. However, the unsteady dynamics of the pulsed jet invalidates the correlation between the minor species chemistry prior to ignition. This yields the discrepancy in the auto-ignition delay time and the location of the ignition kernel between different pulses, as the thermochemical state needed for the ignition occurs in a random manner.

Backwards extrapolation activation diagnostics and their dynamic range for pulsed neutron source measurements

Activation materials implanted within radiation detectors can be used to measure pulsed neutron fields. This work develops an instrument concept with the aim to maximise sensitivity to pulsed fusion neutron fields and, using a data-rejection algorithm combined with backwards extrapolation, enable neutron fluence estimates to be made over a large dynamic range. Through high-fidelity modelling of residual temporal emissions, and a parameterised approach, we study the sensitivity to neutrons of a plastic scintillator–Ag foil layer detector concept. For an optimal design we apply paralysable and non-paralysable deadtime models to the predicted response to D–D fusion neutron fields at various neutron field intensities. In high neutron fluence irradiation scenarios, where deadtime effects are strongly evident, we use our approach to make estimates of the fluence from instrument response data. We discuss the practical applications of such diagnostics used for plasma focus (PF) fusion experiments, such as at the PF-1000U facility in IPPLM, Poland, inertial confinement fusion and pulsed tokamak experiments, for example at MAST-U, where such diagnostics could complement fission counter-based neutron diagnostics in the future. Finally, we show that the calibration of such detection systems may be achieved using relatively low emission rate, steady state neutron sources, with calibration factors that are straightforward to apply to pulsed neutron field measurements.

Benchmarking the Performance of Electropolymerized Poly(3,4-ethylenedioxythiophene) Electrodes for Neural Interfacing.

The development of electronics adept at interfacing with the nervous system is an ever-growing effort, leading to discoveries in fundamental neuroscience applied in clinical setting. Highly capacitive and electrochemically stable electronic materials are paramount for these advances. A systematic study is presented where copolymers based on 3,4-ethylenedioxythiophene (EDOT) and its hydroxyl-terminated counterpart (EDOTOH) are electropolymerized in an aqueous solution in the presence of various counter anions and additives. Amongst the conducting materials developed, the copolymer p(EDOT-ran-EDOTOH) doped with perchlorate in the presence of ethylene glycol shows high specific capacitance (105 F g-1 ), and capacitance retention (85%) over 1000 galvanostatic charge-discharge cycles. A microelectrode array-based on this material is fabricated and primary cortical neurons are cultured therein for several days. The microelectrodes electrically stimulate targeted neuronal networks and record their activity with high signal-to-noise ratio. The stability of charge injection capacity of the material is validated via long-term pulsing experiments. While providing insights on the effect of additives and dopants on the electrochemical performance and operational stability of electropolymerized conducting polymers, this study highlights the importance of high capacitance accompanied with stability to achieve high performance electrodes for biological interfacing.