Current Step Research Articles

An 80 × 60 Flash LiDAR Sensor With In-Pixel Delta-Intensity Quaternary Search Histogramming TDC

This article presents a flash light detection and ranging (LiDAR) sensor featuring an in-pixel histogramming time-to-digital converter (hTDC) based on a delta-intensity quaternary search (DIQS) technique. The proposed 12-b DIQS hTDC is a two-step converter consisting of a 6-b coarse hTDC and a 7-b fine hTDC with 1-b redundancy. The DIQS hTDC synthesizes depth maps with three subframes from the coarse mode and a single subframe from the fine mode, achieving 100-ps resolution without a clock frequency of a few gigahertz. The DIQS repeats dividing the time range of a current step into four periods and finding the location where a target object is placed by comparing the number of events in each period, which is similar to the binary search method but doubles its operating speed. Two time-of-flight (ToF) bits are consecutively determined in every coarse step, and seven ToF bits are estimated by the indirect ToF technique with photon counts. An up–down counter is employed to reduce the memory size by half and enable the delta-intensity technique that can extend the dynamic range by suppressing the uniform background light. The prototype LiDAR with an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$80\times60$ </tex-math></inline-formula> pixel array was fabricated in a 110-nm CMOS image sensor (CIS) process and fully characterized. The maximum detectable range is measured to 45 m with a success rate of 100% at night and 60% under 70-klux background light. The depth accuracy and precision are 2.5 and 1.5 cm from 3 to 4.5 m indoor, respectively, and the precision is maintained to 1.8 cm for the target located at a 1.5-m distance under 60-klux background light. Inherent time-gating and differential signaling of the DIQS hTDC effectively suppress common-mode noise, accomplishing real-time acquisition of depth images with 30 frames/s in a 9-m range at 30-klux background light.

An Improved Calculational Model for Inductance of CRDM Based on Equivalent Magnetic Circuit

In the magnetic lifting control rod drive mechanism (CRDM), it is essential to obtain the dynamic inductance of each coil for research of a mathematical model and state monitoring. It is demonstrated from the working principle and circuit model of the CRDM that the coil inductance has a significant effect on the current step response time. This article proposes an improved equivalent magnetic circuit (IEMC) model that takes into account flux leakage and coupling. The model focuses on calculating the dynamic inductance of the CRDM. First, the magnetic reluctance expression of each unit in the IEMC model is deduced. A flux area correction coefficient is introduced to consider the edge effect of working air gaps. Then, the dynamic inductance of the CRDM is analyzed and calculated based on the proposed model. Finally, the performance of the proposed method is compared with finite element analysis (FEA) and a simplified equivalent magnetic circuit (SEMC) method. Results show that the proposed method can approach the results of FEA better than the SEMC method.

PT controlled PCCM buck converter with adaptive pulse train generator and NMOS current sensor

A pulse train controlled buck converter operating in pseudo continuous conduction mode (PCCM) is implemented in the 0.18-μm CMOS process in this paper. An adaptive pulse train generator, which adjusts duty cycle based on the output power, is proposed to improve the output voltage range and transient response. To operate in PCCM, an NMOS current sensor using a double common-gate amplifier with a high slew rate is utilized to detect the falling inductor current. Simulation results demonstrate that the converter obtains a well regulated variable output voltage from 1 V to 4 V, providing a maximum load current of 1000 mA at the switching frequency of 1 MHz. The transient spike is smaller than 35 mV and recovery time is less than 6.3μs for a 300 mA load current step. The peak efficiency is 94.4% at 300-mA load current.

The influence of magnetic vortices motion on the inverse ac Josephson effect in asymmetric arrays

We report on the influence a preferential magnetic vortices motion has on the magnitude of the inverse ac Josephson effect (the appearance of dc current Shapiro steps) and the coherent operation of asymmetrical parallel arrays of YBa2Cu3O7−δ Josephson junctions (JJ) irradiated with microwave (MW) radiation in the presence of an applied magnetic field B. The preferential direction of motion of the Josephson vortices is due to the asymmetry-induced ratchet effect and has a dramatic impact: for a particular positive dc bias current I when the flux-flow is robust multiple pronounced Shapiro-steps are observed consistent with a coherent operation of the array. This suggests an efficient emission/detection of MW in related applications. In contrast, when we reverse the direction of I, the flux-flow is reduced and the Shapiro steps are strongly suppressed due to a highly incoherent operation that suggests an inefficient emission/detection of MW. Remarkably, by changing B slightly, the situation is reversed: Shapiro steps are now suppressed for a positive I while well pronounced for a reverse current −I. Our results suggest that a preferential vortex-flow has a very significant impact on the coherent MW operation of superconducting devices consisting of either multiple JJs or an asymmetrically biased single long JJ. This is particularly relevant in the case of flux-flow oscillators for sub-terahertz integrated-receivers, flux-driven Josephson (travelling-wave) parametric amplifiers, or on-chip superconducting MW generators, which usually operate at bias currents in the Shapiro step region.

(Digital Presentation) Electrochemical Single Impact Method for Electroactive Bacterial Detection Onto Carbon Ultramicroelectrode

This work aims to design a high sensitivity and selectivity biosensor based on the electrochemistry of single impacts onto ultramicroelectrode (UME) to detect and identify various bacterial strains. The main objective is to establish a unique electrochemical signature for each bacterial cell through the individual impact event signal on the surface of the UME [1, 2]. First, we focus on the detection of well-known electroactive Gram-negative bacteria such as Shewanella oneidensis in order to be able to selectively detect these different single cells. In this case, the strategy currently used is to record a chronoamperometric curve in an aqueous potassium phosphate buffer (pH = 7.4) solution containing a redox probe at an UME polarized at the oxidation or reduction potential of the electrochemical active aqueous species and to observe a “current step” when one bacterium impacts the UME, corresponding to a “blocking effect” [3] (Figure A). The response signal expected from single bacterium collision may also be a “current spike” corresponding to either the own electrochemical activity of the bacterium toward the redox probe and the UME applied potential or a “bouncing effect” of the bacterium which does not stick onto UME surface (Figure B).In order to be able to identify the type of bacterial cell striking the UME surface, an adapted functionalization (covalent grafting via reduction of diazonium aryl salts) with appropriate affinity (bio)chemical species such as antibodies or aptamers could be performed. This strategy could confer to the UME surface a selectivity of the signal generated during single impacts. For example, the electro-grafting of diazo-pyridinium cations for microbial fuel cell electrodes showed to promote and improve the development of bacterial electroactive films [4].[1] E. Lebègue, N. L. Costa, R. O. Louro, F. Barrière, J. Electrochem. Soc. 16 (2020) 105501[2] A. T. Ronspees, S. N.Thorgaard, Electrochimica Acta. 278 (2018) 412-420[3] G. Guanyue, W. Dengchao, B. Ricardo, Z. Jinfang, M. Michael V. Anal. Chem. 90 (2018) 12123−12130[4] H. Smida, E. Lebègue, J-F. Bergamini, F. Barrière, C. Lagrost, Bioelectrochemistry. 120 (2018) 157-165 Figure 1

Multifunctional double active layers formed with electrochemically controlled nanoparticle dispersion for resistive switching memory arrays

Expanding resistive random-access memory (RRAM) from a single device to an array requires a selector to suppress the sneak path and an external device to control the compliance current. Thus, a unique crossbar array that can be independently driven through the novel design of a multilayer RRAM structure with intelligently controlled Cu2O consisting of nanoparticles embedded in the amorphous matrix (ANPs) is proposed. The ANPs–Cu2O active layers are prepared by electrodeposition, and the negative shift of the deposition potential induces a higher density and smaller size of the nanoparticles. The ANPs–Cu2O films show different set voltages and extremely uniform reset voltages, and thus a functional double active layer (DAL) structure consisting of two ANPs–Cu2O layers with different set voltages is proposed. The electrochemically fabricated VCu-controlled DALs effectively protected the reverse current from the self-rectifying characteristics of a large forward/reverse current ratio, thus realizing selector-less RRAMs. In addition, the soft-breakdown showing filament formation in the upper layer reveals the saturation current step acting as a self-compliance current without the assistance of transistors. Finally, a 4 × 4 crossbar DAL RRAM array with transistor-less self-rectification is demonstrated, which shows excellent memory performance and endurance without interfering with adjacent cells.

Sparrow search algorithm applied to temperature control in PEM fuel cell systems

Working temperature is a critical parameter that influences the performance of proton exchange membrane fuel cells (PEMFCs). Appropriate thermal management can improve the efficiency of PEMFCs and prevent irreversible internal damage such as membrane degradation. To solve the slow response and poor dynamic performance of traditional temperature control strategies, the dynamic temperature mode of PEMFCs is established and a temperature control strategy based on the sparrow search algorithm-proportional integral differential (SSA-PID) is proposed in this study. The performance of the SSA-PID temperature control is verified by the simulations of current step change, vehicle dynamic load, and working parameter variation. The results show that the proposed method has the advantages of fast convergence, better dynamic performance, and anti-disturbance ability. The maximum power density of the SSA-PID temperature controller is 6.58% and 12.94% higher than GA (genetic algorithm)-PID and traditional PID controllers, respectively. Moreover, the proposed method can ensure temperature fluctuations within 0.5 K under dynamic disturbance.

Extremum-Seeking-Based Adaptive Model-Free Control and Its Application to Automated Vehicle Path Tracking

Traditional automated vehicle path-tracking algorithms require plant models to derive the respective control laws. However, the accurate vehicle model is difficult to obtain due to the complex tire-road interaction, time-varying parameters, and unknown disturbances. Consequently, data-driven controllers, which do not rely on a predefined plant model, have become increasingly popular. Notably, the model-free control (MFC), which expresses the derivatives of a controlled output as the sums of an amplified control input and an offset term, provides a straightforward solution to ground vehicle path tracking. Despite its ease of use, the control gain tuning of MFC remains largely a trial-and-error process, which could be both painstaking and poorly performing. Existing adaptive gain-tuning methods either rely on the command at the last step to iteratively update the control gain at the current step, or try to simultaneously identify the control gain and the offset term. However, they could yield chattering or unbounded control gains. To provide a new perspective for the MFC control gain tuning while improving MFC's control performance, we integrate MFC with the extremum-seeking control (ESC). ESC updates the control gain of MFC in real time to progressively enhance the control performance of MFC. Simulink–CarSim simulations and scaled car field tests demonstrate the effectiveness of the proposed extremum-seeking-based adaptive model-free controller.

Multi-label fault recognition framework using deep reinforcement learning and curriculum learning mechanism

In the actual working site, the equipment often works in different working conditions while the manufacturing system is rather complicated. However, traditional multi-label learning methods need to use the pre-defined label sequence or synchronously predict all labels of the input sample in the fault diagnosis domain. Deep reinforcement learning (DRL) combines the perception ability of deep learning and the decision-making ability of reinforcement learning. Moreover, the curriculum learning mechanism follows the learning approach of humans from easy to complex. Consequently, an improved proximal policy optimization (PPO) method, which is a typical algorithm in DRL, is proposed as a novel method on multi-label classification in this paper. The improved PPO method could build a relationship between several predicted labels of input sample because of designing an action history vector, which encodes all history actions selected by the agent at current time step. In two rolling bearing experiments, the diagnostic results demonstrate that the proposed method provides a higher accuracy than traditional multi-label methods on fault recognition under complicated working conditions. Besides, the proposed method could distinguish the multiple labels of input samples following the curriculum mechanism from easy to complex, compared with the same network using the pre-defined label sequence.

Discretization-Free Particle-Based Taxi Dispatch Methods With Network Flow Decomposition

The increasing popularity of on-demand ride-hailing services has introduced research problems, including those related to fleet management. Many existing fleet management approaches discretize a spatiotemporal distribution to reduce the problem complexity. Although spatial discretization greatly simplifies the problems, this approximation results in a suboptimal solution. To address this limitation, we present a novel spatial discretization-free, particle-based formulation of fleet management. Our model requires only temporal discretization. The nodes in our spatiotemporal network model represent the positions of the fleet and ride requests over the time horizon. Under this representation, a taxi dispatch problem can be solved by the minimum-cost maximum-flow (MCMF) algorithm. We show some structural properties that disclose a type of monotonicity by applying the MCMF algorithm to our problem. The obtained dispatch solution maximizes the number of served requests from these structural properties at least at the most current time step, regardless of the demand prediction quality. Moreover, these properties enable the decomposition of the MCMF algorithm without sacrificing optimality, and the decomposed multistage maximum-flow algorithm is significantly faster than the MCMF algorithm. Furthermore, we propose an efficient method that alleviates the dearth of input data for service providers who lack sufficient computing power to calculate substantial travel time information. We demonstrate the performance of our method by using data collected in New York City, USA. Our simulation studies indicate that a service provider can fulfill 74–85% of the ride requests within 2 minutes.

Convergence of the Fourth Order Variable Step Size Super Class of Block Backward Differentiation Formula for Solving Stiff Initial Value Problems

In many fields of study such as science and engineering, various real life problems are created as mathematical models before they are solved. These models often lead to special class of ordinary differential equations known as stiff ODEs. A system is regarded as ‘stiff’; if the existing explicit numerical methods fail to efficiently integrate it, or when the step size is determined by the requirements of its stability, rather than the accurateness. The solution of stiff ODEs contains a component with both slowly and rapidly decaying rates due to a large difference in the time scale exhibited by the system. The stiffness property prevents the conventional explicit method from handling the problem efficiently. This nature of stiff ODEs has led to considerable research efforts in developing many implicit mathematical methods. This paper discussed the convergence and order of the current variable step size super-class of block backward differentiation formula (BBDF) for solving stiff initial value problems. The necessary conditions for the convergence of the fourth order variable step size super class of BBDF for solving stiff initial value problems, has been established in this work. It has been shown that the new method is both zero-stable and consistent, which are the requirements for the convergence of any numerical method. The order of the method is also derived to be four. It is therefore concluded that the method is convergent and has significance in solving more complex stiff initial value problems, and could be robustly applied in many fields of study.

Joint state-of-health and remaining-useful-life prediction based on multi-level long short-term memory model prognostic framework considering cell voltage inconsistency reflected health indicators

Battery-health prognostics for the state-of-health (SOH) and remaining-useful-life (RUL) are necessary to ensure the safety and reliability of system operation. However, the aging of an actual battery pack is related to internal electrochemical reactions in the constituent cells and the inter-cell inconsistency effect, which cannot be measured directly. Thus, reasonable feature selection and an effective prognostic framework are indispensable for achieving feasible and accurate results in actual systems. This paper proposes a prognostic framework for the joint prediction of the SOH and RUL of a battery pack. The proposed method utilizes indirect health indicators (HIs) during the charging stage. Moreover, Pearson correlation analysis and incremental capacity analysis are used to recognize the inconsistency effect and optimize the sampling interval of the HIs that can be adapted to the battery pack. A multi-level long short-term memory (LSTM) model is designed to jointly predict the SOH and RUL for a battery pack. The first-level LSTM model is applied to short-term SOH estimation using the optimized HIs. For the RUL prediction, the second-level LSTM is established iteratively to extend the degradation pattern from the current step to end of life using the SOH estimation result and previous output. The robustness of the extracted features and predictive capability of the multi-level LSTM model are demonstrated by accelerated aging tests for series battery packs. The experimental results confirm that the proposed prognostic framework can provide robust, reliable, and accurate SOH and RUL predictions.

Predicting task performance for intelligent human-machine interactions.

Human-machine teams are deployed in a diverse range of task environments and paradigms that may have high failure costs (e.g., nuclear power plants). It is critical that the machine team member can interact with the human effectively without reducing task performance. These interactions may be used to manage the human's workload state intelligently, as the overall workload is related to task performance. Intelligent human-machine teaming systems rely on a facet of the human's state to determine how interaction occurs, but typically only consider the human's state at the current time step. Future task performance predictions may be leveraged to determine if adaptations need to occur in order to prevent future performance degradation. An individualized task performance prediction algorithm that relies on a multi-faceted human workload estimate is shown to predict a supervisor's task performance accurately. The analysis varies the prediction time frame (from 0 to 300 s) and compares results to a generalized algorithm.

Low-frequency development approximations to the transmissive Warburg diffusion impedance

A study of the behaviour of the low-frequency development approximations to the transmissive Warburg diffusion impedance in both the frequency and time domains is presented. Simple low-frequency electric circuits have been derived from the Weierstrass products expansion and the equivalent ladder networks based on Foster, Maxwell and Cauer series. An original comparative study of the different low-frequency approximated impedances, including the characteristic frequencies, and those of the transmissive Warburg element is reported. The galvanostatic small-signal dynamic responses involving current steps and ramps have been compared by using exact numerical solutions and the approximated solutions at low frequencies derived from the different electric circuits. This study allows the dynamic response of electrochemical energy devices, such as fuel cells or rechargeable batteries, to be physically interpreted on the basis of an only relaxation time by means of the charging/discharging process of a capacitor through one or two resistors.

Three-Mediator Enhanced Collisions on an Ultramicroelectrode for Selective Identification of Single Saccharomyces cerevisiae.

Selective detection of colliding entities, especially cells and microbes, is of great challenge in single-entity electrochemistry. Herein, based on the different cellular electron transport pathways between microbes and mediators, we report a three-mediator system [K3Fe(CN)6, K4Fe(CN)6, and menadione] to achieve redox activity analysis and selective identification of single Saccharomyces cerevisiae without the usage of antibodies. K4Fe(CN)6 in the three-mediator system will oxidize near the electrode surface and increase the local concentration of K3Fe(CN)6, which will promote the redox reaction of S. cerevisiae. The hydrophobic mediator─menadione─can selectively penetrate through the S. cerevisiae membrane and get access to its intracellular redox center and can further react with K3Fe(CN)6 in the bulk solution. In contrast, the mediator can only get access to the bacterial membranes of Escherichia coli and Staphylococcus aureus, which results in different electrochemical collision signals between the above microbes. In the three-mediator system, upward step-like collision signals were observed in S. cerevisiae suspension, which are related to their microbial redox activity. In comparison, E. coli or S. aureus only generated downward current steps because the blockage effect of mediator diffusion suppresses their redox activities. When S. cerevisiae co-existed with E. coli or S. aureus, transients generated by both blockage and redox activity were observed. The approach enables us to trace the collision behaviors of different microbes and distinguish their simultaneous collisions, which is the foundation for further application of electrochemical collision technique in the specific identification of single biological entities.

Prayer Flags.

Ad LibitumSeptember 2022Prayer FlagsSylvia S. Villarreal, MEd, MPHSylvia S. Villarreal, MEd, MPHMcGovern Center for Humanities and Ethics Houston, TexasSearch for more papers by this authorAuthor, Article, and Disclosure Informationhttps://doi.org/10.7326/M21-4657 Audio Reading - “Prayer Flags” Audio. Michael A. Lacombe, MD, Annals Associate Editor, reads “Prayer Flags” by Sylvia S. Villarreal, MEd, MPH Your browser does not support the audio element. Audio player progress bar Step backward in current audio track Play current audio trackPause current audio track Step forward in current audio track Mute current audio trackUnmute current audio track 00:00/ SectionsAboutFull TextPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinkedInRedditEmail Strung abovemy concrete patiothey fill the airwith wind tossedmantras snappingsilent blessingson this fall morning.Pausing for breathin the momentary lullthen cracking the blueof sky in renewed assault.One set from youmy warrior girl, the othercarried from Tibetby your restless brother,seeker of the authentic.Tied like me to this place,my claim on you both isnow long past, frayedabout the edges likethis fine cloth.Your lives spreadout over new terrainunfurling in waysthat dazzle and disturb. Author, Article, and Disclosure InformationAffiliations: McGovern Center for Humanities and Ethics Houston, TexasCorresponding Author: Sylvia S. Villarreal, MEd, MPH, 6431 Fannin Street, Suite JJL 410, Houston, TX 77030; e-mail, Sylvia.S.[email protected]tmc.edu. PreviousarticleNextarticle Advertisement Audio Reading - “Prayer Flags” Audio. Michael A. Lacombe, MD, Annals Associate Editor, reads “Prayer Flags” by Sylvia S. Villarreal, MEd, MPH Your browser does not support the audio element. Audio player progress bar Step backward in current audio track Play current audio trackPause current audio track Step forward in current audio track Mute current audio trackUnmute current audio track 00:00/ FiguresReferencesRelatedDetails Metrics September 2022Volume 175, Issue 9Page: 1343 ePublished: 20 September 2022 Issue Published: September 2022 Copyright & PermissionsCopyright © 2022 by American College of Physicians. All Rights Reserved.PDF downloadLoading ...

On the effect of electrode material in electrical conductivity relaxation - An alternative interpretation of the two-fold relaxation behavior in La5.4WO11.1-δ

Oxygen and proton transport properties of La5.4WO11.1-δ are investigated using electrical conductivity relaxation. Chemical diffusion coefficients and surface exchange coefficients of both hydrogen and oxygen presumed to govern conductivity relaxation are extracted from fitting the two-fold conductivity relaxation observed after hydration/dehydration steps at fixed oxygen partial pressure to the model equations. Surprisingly, the kinetic parameters obtained from fitting are found to depend on the magnitude of the current used in the measurements. A two-fold relaxation behavior with characteristics depending on the magnitude of the current is also observed after oxidation/reduction steps under dry conditions. Furthermore, at fixed temperature, oxygen and water partial pressures, the conductivity is found to exhibit relaxation behavior after a current step, while the apparent steady-state conductivity is found to depend on the applied current. The observations are attributed to the use of gold electrodes in the experiments and associated interfacial capacitances. It is obvious from this study that the use of partially ion-blocking electrodes in conductivity and conductivity relaxation measurements on mixed ionic-electronic conducting oxides with prevailing ionic conduction may lead to erroneous results and interpretations.

Stigma.

Ad LibitumSeptember 2022StigmaSylvia S. Villarreal, MEd, MPHSylvia S. Villarreal, MEd, MPHMcGovern Center for Humanities and Ethics Houston, TexasSearch for more papers by this authorAuthor, Article, and Disclosure Informationhttps://doi.org/10.7326/M21-3972 Audio Reading - “Stigma” Audio. Michael A. Lacombe, MD, Annals Associate Editor, reads “Stigma” by Sylvia S. Villarreal, MEd, MPH Your browser does not support the audio element. Audio player progress bar Step backward in current audio track Play current audio trackPause current audio track Step forward in current audio track Mute current audio trackUnmute current audio track 00:00/ SectionsAboutFull TextPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinkedInRedditEmail feels likea red welt imprinted on vulnerable fleshthe glare of harsh light trained on intimate corners of our livesa bone deep aching—only relieved by connection to anothersounds likefine crystal being pulverized by a hammerpounding footsteps of predator and prey, muffled criesof pain when outdated, cruel beliefs separate and shame ussmells likethe stench of rotting piles of stereotypesthe mildew of fear compounded by ignorancemixed with a whiff of arrogance toward the unfortunate “other”a cold lump of sorrow that we swallow today ... Author, Article, and Disclosure InformationAffiliations: McGovern Center for Humanities and Ethics Houston, TexasCorresponding Author: Sylvia S. Villarreal, MEd, MPH, 6431 Fannin Street, Suite JJL 410, Houston, TX 77030; e-mail, Sylvia.S.[email protected]tmc.edu. PreviousarticleNextarticle Advertisement Audio Reading - “Stigma” Audio. Michael A. Lacombe, MD, Annals Associate Editor, reads “Stigma” by Sylvia S. Villarreal, MEd, MPH Your browser does not support the audio element. Audio player progress bar Step backward in current audio track Play current audio trackPause current audio track Step forward in current audio track Mute current audio trackUnmute current audio track 00:00/ FiguresReferencesRelatedDetails Metrics September 2022Volume 175, Issue 9Page: 1344 ePublished: 20 September 2022 Issue Published: September 2022 Copyright & PermissionsCopyright © 2022 by American College of Physicians. All Rights Reserved.PDF downloadLoading ...

CURRENT CLIMATE POLICY OF GERMANY

The article is deals with the German policy aimed at reducing greenhouse gases emission. The author analyses the way current measures correspond with «Klimaschutzprogramm 2030» adopted in 2019. The paper pays special attention to theoretical provisions as well as practical decisions. The author also examines the contribution of the European Emissions Trading System to the German climate actions, as well as the adoption of the national system. In addition, the article concentrates on the amendments to the Renewable Energy Law (EEG) as well as the establishment of new construction standards and the experiment in paying for public transport. The study revealed that current German political steps redistribute the financial burden on the consumers, with the support measures for green energy being changed. The conclusions are important for understanding the further development of the German climate policy influencing the economy and foreign trade of the nation.

In-situ characterization of gas distribution in proton exchange membrane fuel cell stacks

Uniform gas distribution contributes greatly to output performance, operating reliability, and durability of fuel cell stacks, which still lacks detection means and remains a great challenge. In this study, a non-invasive and in-situ characterization method of gas distribution is originally presented, based on the dual-chamber model that describes the mathematical relationship among gas flow, hydrogen crossover, and hydrogen transfer in the cathode side during electrochemical testing (N2/H2). By means of micro-current excitation, the hydrogen crossover of every cell in a stack is synchronously identified and then the gas distribution can be decoupled. In a specially designed step-current test that aims for direct evidence, the voltage response characteristics to artificially induced air starvation coincide perfectly with the identified gas distribution. Typically, as the current density steps up to 175 mA·cm−2, the voltages of under-supplied cells, classified by the identified stoichiometric ratios of nearly-one and within 1.13–1.15, decline rapidly to around zero and abnormally to around only 0.5 V, respectively, while the sufficiently supplied cells remain normal. Based on the in-situ method, the artificially channel-choked fuel cell is precisely recognized, and different choke degrees can be distinguished. As identified at the corresponding current densities of 50, 100, and 500 mA·cm−2 and the average stoichiometric ratio of two, the gas flow rate of a certain cell only reduces by 22.8 %, 20.2 %, and 13.7 %, respectively, even with all the cathodic channels choked. The significant role of convection in the mass transfer is experimentally confirmed in fuel cells, and correspondingly, the mass transfer indicators are available by this electrochemical means.