Measurements Of Local Density Research Articles

Investigation of current density and temperature distribution characteristics under transient conditions based on a 108 cm2 segmented proton exchange membrane fuel cell

Visualizing the electrochemical and temperature distribution characteristics inside proton exchange membrane fuel cell (PEMFC) should greatly contribute to the product development and performance optimization. In the study, a customized 27-segment 108 cm2 fuel cell was fabricated based on the printed circuit board methodology to achieve the local current density and local voltage measurement. In addition, 27 thermocouples were embedded in the segmented cathode graphite gas flow plate for local temperature measurement. Detailed information of fuel cell core components, multi-channel data acquisition system, external temperature control system, and uncertainty analysis was presented. According to the test results of 4000 s current rising conditions and 2400 s current decreasing conditions, the measurement deviation of total current between data acquisition system and TOYO test station is 2.4%–3.2%. Meanwhile, the deviation of output voltage ranges from 0.1% to 2.6%. To quantify the degree of distribution non-uniformity, the range and standard deviation of local parameter values as well as contour map are demonstrated. The non-uniformity of local current density and local temperature becomes more significant under higher operating current conditions. Furthermore, the degree of parameter non-uniformity is more noticeable under current rising conditions compared with current decreasing conditions. The transient increase of operating current leads to the sudden overshoot phenomena of local current range, and the change of local current density among all segments is instantaneously finished. However, the range of current demonstrates relatively smooth transition trends when reactant flow rate rises. Higher temperature area appears in the middle of membrane electrode assembly, especially in the position with higher local current density. The parameter distribution and transition characteristics could provide helpful guidance for fuel cell optimization and diagnosis.

Fundamental role of nonlocal orders in 1D extended Bose-Hubbard model.

Nonlocal order parameters capture the presence of correlated fluctuations between specific degrees of freedom, in otherwise disordered quantum matter. Here, we provide a further example of their fundamental role, deriving the ground state phase diagram of the filling one extended Bose-Hubbard model, exclusively in terms of their ordering. By means of a density matrix renormalization group numerical analysis, we show that in addition to the (even) parity order characteristic of the Mott insulating phase and the string order nonvanishing in the Haldane insulator, the recently proposed odd parity order completes the picture, becoming nonvanishing at the transition from the normal superfluid to the paired superfluid phase. The above three nonlocal parameters capture all the distinct phases, including the density wave phase, in which the local order is seen as the simultaneous presence of correlated fluctuations in different channels. They provide a unique tool for the experimental observation of the full phase diagram of strongly correlated quantum matter, by means of local density measurements.

Machine-learning models for diagnosis of rotator cuff tears in osteoporosis patients based on anteroposterior X-rays of the shoulder joint

ObjectiveThis study aims to diagnose Rotator Cuff Tears (RCT) and classify the severity of RCT in patients with Osteoporosis (OP) through the analysis of shoulder joint anteroposterior (AP) X-ray-based localized proximal humeral bone mineral density (BMD) measurements and clinical information based on machine learning (ML) models. MethodsA retrospective cohort of 89 patients was analyzed, including 63 with both OP and RCT (OPRCT) and 26 with OP only. The study analyzed a series of shoulder radiographs from April 2021 to April 2023. Grayscale values were measured after plotting ROIs based on AP X-rays of shoulder joint. Five kinds of ML models were developed and compared based on their performance in predicting the occurrence and severity of RCT from ROIs' greyscale values and clinical information (age, gender, advantage side, lumbar BMD, and acromion morphology (AM)). Further analysis using SHAP values illustrated the significant impact of selected features on model predictions. ResultsR1-6 had a positive correlation with BMD respectively. The nine variables, including greyscale R1-6, age, BMD, and AM, were used in the prediction models. The RF model was determined to be superior in effectively diagnosing RCT in OP patients, with high AUC scores of 0.998, 0.889, and 0.95 in the training, validation, and testing sets, respectively. SHAP values revealed that the most influential factors on the diagnostic outcomes were the grayscale values of all cancellous bones in ROIs. A column-line graph prediction model based on nine variables was constructed, and DCA curves indicated that RCT prediction in OP patients was favored based on this model. Furthermore, the RF model was also the most superior in predicting the types of RCT within the OPRCT group, with an accuracy of 86.364% and 73.684% in the training and test sets, respectively. SHAP values indicated that the most significant factor affecting the predictive outcomes was the AM, followed by the grayscale values of the greater tubercle, among others. ConclusionsML models, particularly the RF algorithm, show significant promise in diagnosing RCT occurrence and severity in OP patients using conventional shoulder X-rays based on the nine variables. This method presents a cost-effective, accessible, and non-invasive diagnostic strategy that has the potential to substantially enhance the early detection and management of RCT in OP patient population.

Advancement of Langmuir probe-based laser photo-detachment technique for negative ion density measurement in a high-power helicon plasma source.

In the pursuit of precise diagnostics for measuring negative ion density in a helicon plasma source (HPS), a new approach utilizing a radio frequency (RF) broadband transformer-based Langmuir probe is developed specifically for laser photo-detachment (LPD) analysis. This inductively coupled LPD technique is useful for high power RF systems in which capacitive RF noise is in the same scale as the pulsed photo-detachment signal. The signal acquired by this transformer-based probe is compared against the conventional Langmuir probe-based LPD technique, revealing a remarkable enhancement in signal fidelity through an improved signal-to-noise ratio (SNR) achieved by the RF broadband transformer methodology. In addition, the localized hydrogen negative ion density measurements obtained through this probe are harmoniously aligned with the line-averaged negative ion density derived from the cavity ringdown spectroscopy (CRDS) technique. These concurrence measurements highlight the RF broadband transformer-based approach's accuracy in capturing localized negative ion density during helicon mode operation in an HPS setup. Furthermore, the correlation of negative ion density values with RF input exhibits a consistent trend in tandem with background plasma density. Notably, both CRDS and LPD measurements ascertain negative ion densities ranging from ∼5 to 6×1016m-3 under an RF power of 500-700W and a pressure of 8 × 10-3mbar, all under the influence of a 55G axial magnetic field. These specific parameters represent the optimal operational configuration for effective negative ion production with the present experimental HPS setup. Due to its better SNR, the RF broadband transformer-based Langmuir probe emerges as a useful tool for LPD diagnostics, particularly in the presence of pervasive RF noise.

Перенос аврорального километрового радиоизлучения посредством каналов с пониженной плотностью на границе плазмосферы

We present the results of Auroral Kilometric Radiation (AKR) measurements near the plasmapause on the ERG (Arase) satellite. The apogee of the satellite's orbit is located near the ecliptic plane, at latitudes ±30°. According to the generally accepted point of view, AKR observation is impossible in this region since it is shielded by the plasmasphere. Simultaneous measurements of AKR and local plasma density made it possible to determine that AKR in near-equatorial regions occur in plasma channels — density inhomogeneities elongated along magnetic field lines. AKR from sources located in the auroral magnetosphere is transferred by these channels to the equatorial region. This work analyzes the conditions for the capture and propagation of AKR in low plasma density channels. In the geometrical optics approximation, we have simulated the conditions for the radiation capture and propagation. The calculation results show that the proposed scheme for AKR capture into plasma channels can explain the measurement results — the radiation transfer from the auroral region to the near-equatorial region.

Transfer of auroral kilometric radiation through low-density channels at the boundary of plasmasphere

We present the results of Auroral Kilometric Radiation (AKR) measurements near the plasmapause on the ERG (Arase) satellite. The apogee of the satellite's orbit is located near the ecliptic plane, at latitudes ±30°. According to the generally accepted point of view, AKR observation is impossible in this region since it is shielded by the plasmasphere. Simultaneous measurements of AKR and local plasma density made it possible to determine that AKR in near-equatorial regions occur in plasma channels — density inhomogeneities elongated along magnetic field lines. AKR from sources located in the auroral magnetosphere is transferred by these channels to the equatorial region. This work analyzes the conditions for the capture and propagation of AKR in low plasma density channels. In the geometrical optics approximation, we have simulated the conditions for the radiation capture and propagation. The calculation results show that the proposed scheme for AKR capture into plasma channels can explain the measurement results — the radiation transfer from the auroral region to the near-equatorial region.

On discriminating tokamak sawtooth crash models via localized density and temperature measurements

The core electron temperature drops rapidly during the sawtooth crash in tokamak plasmas, which causes heat loss and may lead to fast particle losses or even a disruption. Several models have been proposed for the periodic crash, including the Kadomtsev model with magnetic reconnection and the quasi-interchange model with the growth of higher-mode-number pressure-driven instabilities. 3D MHD simulations were performed for these two models with a goal to develop intuition and to predict qualitatively how different types of sawtooth will appear in various diagnostics. The structures of electron density ne and electron temperature Te show a dominant (1, 1) mode for the Kadomtsev case and a dominant (4, 4) mode for the quasi-interchange case. The oscillations of ne and Te have a positive correlation near the inversion layer for both cases, while their frequencies and amplitudes are different depending on the dominant modes. Particularly, for the Kadomtsev case, we find a relation between the amount of flux reconnected during a sawtooth event and ne or Te oscillations. Therefore, we connect recently developed measurement capabilities for ne and Te to the internal sawtooth behavior. We propose that this method of analysis can help in identifying the type of sawtooth in future experiments augmented by simulations.

Contribution of Oxygen Reduction to Mg Corrosion: Experimental Evidence By Electrochemical Microprobes

Unravelling the mechanisms of magnesium corrosion is vital for establishing reliable research methodologies, developing new alloys and predicting magnesium degradation behaviour. Hydrogen evolution reaction is widely regarded as by far the main cathodic process during corrosion of magnesium. Hence, tracing the amount of released hydrogen was thought to be a reliable measure of magnesium degradation rate. Recently, experimental evidences obtained by different methods have been presented by several groups that oxygen reduction (ORR) is important secondary cathodic reaction during Mg corrosion [1-8]. For model galvanic couple Al-Cu-Mg, oxygen consumption on the surface of Mg along with that on Cu was observed by using oxygen sensing microoptode [1]. A simultaneous measurement of local current density by scanning vibrating electrode technique (SVET) and local oxygen concentration by oxygen sensing microoptode found a strong oxygen consumption at the active corrosion sites on the surface of commercially pure Mg in NaCl electrolyte [2]. Then, the evidence for the varying contributions of ORR to the total cathodic process on Mg alloys during atmospheric and aqueous corrosion was presented based on newly developed respirometric methods [3-5]. While around 10% of the total cathodic current was ascribed to ORR during aqueous corrosion, up to 60% of the total corrosion process was shown to be due to the ORR contribution during simulated atmospheric corrosion with wet-dry cycles. Nanoparticle-based O2 imaging was used to map decreased O2 concentration at the interface of several Mg alloys exposed to simulated body fluids [6].High ORR rate on a slowly corroding ultra-high-purity Mg (UHP-Mg) in NaCl electrolyte was shown in our recent work [7]. Comparing that with lower ORR rate for faster corroding commercial purity Mg (CP-Mg), the rate of ORR was found to depend on the growth rate of Mg(OH)2 , which is the main corrosion product of Mg in the simple saline solution. The formation of Mg(OH)2 impeded the diffusion of oxygen from bulk electrolyte to metal interface, preventing metallic Mg substrate from the interaction with oxygen. The distribution of local concentration of dissolved gaseous H2 and O2 assessed by amperometric Clark-type micorprobes at the interface of UHP-Mg and CP-Mg demonstrated the inverse relationship between HER and ORR, and supports the finding that diffusion-controlled ORR highly depends on the barrier property of corrosion products on the surface [8]. The contribution of ORR current to total cathodic current reached 29.1% for UHP-Mg, while only 0.9% for CP-Mg after 1 hour of immersion in NaCl solution. The contribution of ORR decreases with immersion time, due to the impeded access of dissolved O2 to Mg interface caused by thickening of Mg(OH)2 layer. A numerical model was developed considering the mixed potential diagram and measured local oxygen concentration. REFERENCES: [1] D. Snihirova, M. Taryba, S.V. Lamaka, M.F. Montemor, Corrosion inhibition synergies on a model Al-Cu-Mg sample studied by localized scanning electrochemical techniques, Corrosion Science, 112 (2016) 408-417.[2] E.L. Silva, S.V. Lamaka, D. Mei, M.L. Zheludkevich, The Reduction of Dissolved Oxygen During Magnesium Corrosion, ChemistryOpen, 7 (2018) 664-668.[3] M. Strebl, S. Virtanen, Real-Time Monitoring of Atmospheric Magnesium Alloy Corrosion, Journal of The Electrochemical Society, 166 (2019) C3001-C3009.[4] M. Strebl, M. Bruns, S. Virtanen, Editors’ Choice—Respirometric in Situ Methods for Real-Time Monitoring of Corrosion Rates: Part I. Atmospheric Corrosion, Journal of The Electrochemical Society, 167 (2020) 021510.[5] M. Strebl, M.P. Bruns, G. Schulze, S. Virtanen, Respirometric In Situ Methods for Real-Time Monitoring of Corrosion Rates: Part II. Immersion, Journal of the Electrochemical Society, (2021).[6] B. Zeller-Plumhoff, A.R. Akkineni, H. Helmholz, D. Orlov, M. Mosshammer, M. Kühl, R. Willumeit-Römer, M. Gelinsky, Oxygen-sensitive nanoparticles reveal the spatiotemporal dynamics of oxygen reduction during magnesium implant biodegradation, NPJ Materials Degradation, 6 (2022) 95.[7] C. Wang, D. Mei, G. Wiese, L.Q. Wang, M. Deng, S.V. Lamaka, M.L. Zheludkevich, High rate oxygen reduction reaction during corrosion of ultra-high-purity magnesium, NPJ Materials Degradation, 4 (2020) 42.[8] C. Wang, W. Xu, D. Höche, M.L. Zheludkevich, S.V. Lamaka, Exploring the contribution of oxygen reduction reaction to Mg corrosion by modeling assisted local analysis, Journal of Magnesium and Alloys, 11 (2023) 100-109. ACKNOWLEDGEMENTS: C. Wang, Wen Xu, thank China Scholarship Council for the funding, grants no. 201806310128 and 201908510177

Quantized valley Hall response from local bulk density variations

The application of a mechanical strain to a 2D material can create pseudo-magnetic fields and lead to a quantized valley Hall effect. However, measuring valley-resolved effects remains a challenging task due to their inherent fragility and dependence on the sample’s proper design. Additionally, non-local transport probes based on multiterminal devices have often proven to be inadequate in yielding conclusive evidence of the valley Hall signal. Here, we introduce an alternative way of detecting the quantized valley Hall effect, which entirely relies on local density measurements, performed deep in the bulk of the sample. The resulting quantized signal is a genuine Fermi sea response, independent of the edge physics, and reflects the underlying valley Hall effect through the Widom-Středa formula. Specifically, our approach is based on measuring the variation of the particle density, locally in the bulk, upon varying the strength of the applied strain. This approach to the quantized valley Hall effect is particularly well suited for experiments based on synthetic lattices, where the particle density (or integrated density of states) can be spatially resolved.

Plating and Stripping of Lithium Metal Stabilized by a Block Copolymer Electrolyte: Local Current Density Measurement and Modeling

Plating and stripping of lithium protrusions in lithium metal symmetric cells containing a solid block copolymer electrolyte was studied as a function of time in 3D using time-resolved X-ray tomography. These measurements enabled determination of the spatial variation in current densities at the plating and stripping electrodes. The initial interelectrode distance was 27 μm. Correlation functions were calculated to reveal the relationships between current densities at the two electrodes and local electrolyte thickness. Current densities at opposing electrode locations during protrusion growth is uncorrelated until the local interelectrode distance decreases to less than 6 μm, just before the cell shorts. Mass balance was used to determine the area from which lithium ions that form a protrusion were stripped. Computational modeling of the plating and stripping process reveals the interplay between electrochemical and mechanical driving forces and their effect on nonuniform current distribution. Model predictions were compared with experiments without resorting to any adjustable parameters. The computed correlation functions were in qualitative agreement with experiments. Finally, the model was used to calculate contour plots of electrochemical potential within the electrolyte, shedding light on how geometry, salt concentration, interelectrode distance, and mechanical stress influence local rates of electrochemical reaction.

Three-way decision-based co-detection for outliers

Outlier detection is an important research topic in data mining and machine learning. However, existing unsupervised outlier detection methods suffer from irrelevant and redundant attributes in high-dimensional data, and their performance is also limited by their outlier detection models that rely on only one view. In this study, we propose a three-way decision-based co-detection model for unsupervised outlier detection. Specifically, we first improve the local outlier factor (LOF) method by introducing the Gaussian kernel function to make the measure of local reachability density more accurate. Then, we introduce fuzzy rough sets to perform attribute reduction, which further reduces the negative effect of irrelevant and redundant attributes on the measure of sample similarity. Finally, we develop a co-detection model that is trained on the original view and the transformed view generated by principal component analysis and uses the strategy of the three-way decision to collaboratively detect outliers. The results of comparative experiments on the selected UCI datasets show that the proposed model outperforms state-of-the-art methods in terms of AUC-ROC index.

An improved density peaks clustering algorithm based on k nearest neighbors and turning point for evaluating the severity of railway accidents

The timely and scientific assessment of railway accident severity can provide effective support for making a suitable rescue plan. This paper proposes an improved density peaks clustering algorithm based on scenario construction for dynamically tackling the severity ranking problem of railway accidents. Firstly, the scenario is introduced into the selection of grading indicators of railway accidents, and a five-dimensional railway accident scenario expression model based on knowledge element is proposed to dynamically select and express the grading indicators. Secondly, an improved density peaks clustering algorithm based on k nearest neighbors and turning point (IDPC-KNN-TP) as the grading model of railway accidents is established, which optimizes the local density measurement, the selection of cluster center points, and the assignment strategy of density peaks clustering (DPC). Finally, the railway accidents from 2010 to 2021 in the UK as a case study are analyzed. The results show that the performance of IDPC-KNN-TP is better than others, and the grading algorithm in this paper has good practical performance. The dynamic grading strategy and the emergency disposal suggestions are put forward to provide a reference for the hierarchical response to railway accidents.

Mapping port wine stain in vivo by optical coherence tomography angiography and multi-metric characterization.

Port wine stain (PWS) is a congenital cutaneous capillary malformation composed of ecstatic vessels, while the microstructure of these vessels remains largely unknown. Optical coherence tomography angiography (OCTA) serves as a non-invasive, label-free and high-resolution tool to visualize the 3D tissue microvasculature. However, even as the 3D vessel images of PWS become readily accessible, quantitative analysis algorithms for their organization have mainly remained limited to analysis of 2D images. Especially, 3D orientations of vasculature in PWS have not yet been resolved at a voxel-wise basis. In this study, we employed the inverse signal-to-noise ratio (iSNR)-decorrelation (D) OCTA (ID-OCTA) to acquire 3D blood vessel images in vivo from PWS patients, and used the mean-subtraction method for de-shadowing to correct the tail artifacts. We developed algorithms which mapped blood vessels in spatial-angular hyperspace in a 3D context, and obtained orientation-derived metrics including directional variance and waviness for the characterization of vessel alignment and crimping level, respectively. Combining with thickness and local density measures, our method served as a multi-parametric analysis platform which covered a variety of morphological and organizational characteristics at a voxel-wise basis. We found that blood vessels were thicker, denser and less aligned in lesion skin in contrast to normal skin (symmetrical parts of skin lesions on the cheek), and complementary insights from these metrics led to a classification accuracy of ∼90% in identifying PWS. An improvement in sensitivity of 3D analysis was validated over 2D analysis. Our imaging and analysis system provides a clear picture of the microstructure of blood vessels within PWS tissues, which leads to a better understanding of this capillary malformation disease and facilitates improvements in diagnosis and treatment of PWS.

Relaxed blue ellipticals: accretion-driven stellar growth is a key evolutionary channel for low mass elliptical galaxies

ABSTRACT How elliptical galaxies form is a key question in observational cosmology. While the formation of massive ellipticals is strongly linked to mergers, the low mass (M⋆/M⊙ < 109.5) regime remains less well explored. In particular, studying elliptical populations when they are blue, and therefore rapidly building stellar mass, offers strong constraints on their formation. Here, we study 108 blue low-mass ellipticals (which have a median stellar mass of 108.7 M⊙) at z < 0.3 in the COSMOS field. Visual inspection of extremely deep optical HSC images indicates that less than 3 per cent of these systems have visible tidal features, a factor of 2 less than the incidence of tidal features in a control sample of galaxies with the same distribution of stellar mass and redshift. This suggests that the star formation activity in these objects is not driven by mergers or interactions but by secular gas accretion. We combine accurate physical parameters from the COSMOS2020 catalogue, with measurements of local density and the locations of galaxies in the cosmic web, to show that our blue ellipticals reside in low-density environments, further away from nodes and large-scale filaments than other galaxies. At similar stellar masses and environments, blue ellipticals outnumber their normal (red) counterparts by a factor of 2. Thus, these systems are likely progenitors of not only normal ellipticals at similar stellar mass but, given their high star formation rates, also of ellipticals at higher stellar masses. Secular gas accretion therefore likely plays a significant (and possibly dominant) role in the stellar assembly of elliptical galaxies in the low-mass regime.

Probabilistic Map Matching for Robust Inertial Navigation Aiding

<h3>Abstract</h3> Robust aiding of inertial navigation systems in GNSS-denied environments is critical for the removal of accumulated navigation error caused by the drift and bias inherent in inertial sensors. One way to perform such an aiding uses matching of geophysical measurements, such as gravimetry, gravity gradiometry or magnetometry, with a known geo-referenced map. Although simple in concept, this map-matching procedure is challenging: The measurements themselves are noisy, their associated spatial location is uncertain, and the measurements may match multiple points within the map (i.e., non-unique solution). In this paper, we propose a probabilistic multiple-hypotheses tracker to solve the map-matching problem and allow robust inertial navigation aiding. Our approach addresses the problem both locally, via probabilistic data association, and temporally by incorporating the underlying platform kinematic constraints into the tracker. The estimated platform position from the output of map matching is then integrated into the navigation state using an unscented Kalman filter. Additionally, we present a statistical measure of local map information density — the map feature variability — and use it to weight the output covariance of the proposed algorithm. The effectiveness and robustness of the proposed algorithm are demonstrated using a navigation scenario involving gravitational map matching.

Изучение взаимосвязи состояния костной системы по данным двойной энергетической рентгеновской абсорбциометрии и локальной плотности челюстей у пациентов с адентией при планировании дентальной имплантации

Background. Timely an accurate diagnostics before the implant placement allows to get a correct anatomical rehabilitation and a satisfactory functional result. The success of dental implants in patients with osteoporosis depends primarily on the quality of the jaw bones. Aims. To study the relationship between the state of the skeletal system according to double energy X-ray absorptiometry and local density of the jaws in patients with adentia when planning dental implantation. Materials and methods. By using a densitometric method 690 patients aged between 18 to 84 years were examined prior the dental implantation. The 547 of 690 patients were women (79.3%) and 143 men (20.7%). Measurements of bone mineral density were carried out on a bone densitometer "QDR-4500A" ("Hologic"), which allows to evaluate the following parameters: elasticity, density and stiffness of the bone tissue. The study of the local density of the jaw bones was carried out by the method of cone-beam computed tomography(CBCT). Local bone density measurements were recorded in Hounsfield units (HU). Results. There is a directly proportional relationship between the results of densitometry of the axial skeleton and the density of the bone tissue of the jaws – the lower the mineral density of the bone tissue of the axial skeleton, the lower the absorption coefficient of the jaw – the Hounsfield index. As an effective sign, indicators of the state of the bone of the alveolar ridge of the lower jaw were used. The correlation between the mineral density of the skeletal system from the alveolar process of the jaws was r=0.88, which indicates a high level of feedback of these indicators. Conclusions. Diagnosis of the normal bone density, osteopenia, osteoporosis by using bone densitometry allows to determine the indications for implantation with great accuracy. There is a directly proportional relationship between the results of densitometry of the axial skeleton and the local density of the bone tissue of the jaws. Keywords: osteoporosis, densitometry (dual energy x-ray absorptiometry), dental implantation, cone beam computed tomography

Elastic Valley Spin Controlled Chiral Coupling in Topological Valley Phononic Crystals.

Distinct from the phononic valley pseudospin, the real physical spin of elastic waves adds a novel tool kit capable of envisaging the valley-spin physics of topological valley phononic crystals from a local viewpoint. Here, we report the observation of local elastic valley spin as well as the hidden elastic spin-valley locking mechanism overlooked before. We demonstrate that the selective one-way routing of valley phonon states along the topological interface can be reversed by imposing the elastic spin metasource at different interface locations with opposite valley-spin correspondence. We unveil the physical mechanism of selective directionality as the elastic spin controlled chiral coupling of valley phonon states, through both analytical theory and experimental measurement of the opposite local elastic spin density at different interface locations for different transport directions. The elastic spin of valley topological edge phonons can be extended to other topological states and offers new tool to explore topological metamaterials.

A Robust and Quantified Analysis of Mass Transport and Its Application in Designing Next Generation Architecture for Polymer Electrolyte Water Electrolysis Cells

Investigations to better understand the nature of mass transport and two-phase flow within a polymer electrolyte water electrolyzer (PEWE) have gained popularity as researchers strive to improve system performance and efficiency. Along with traditional polarization experiments, the use of in-situ spatial and temporal current distribution measurement techniques has proven to be very attractive. Different methods for spatial current distribution measurements include the use of resistor networks, potential probes, and printed circuit boards (PCB) [1–3]. Using such techniques, Mench and co-workers have previously demonstrated [4–7] that, under mass transport limited conditions for any combination of flow-field and diffusion media, the current density distributions consistently exhibit a gradient – with high current towards the inlet and low towards the outlet. These contour plots showed certain dissimilarities; however, they serve as a qualitative picture to gauge cell performance and characterize mass transport. Therefore, in this work a robust analysis was developed that provides a quantitative understanding and better characterization of the mass transport limitation within the electrolyzer. A mass transport number (MTN) was defined and used to further characterize the influence of mass transport limitation experienced within an electrolyzer.Applying this new analysis to our the investigations revealed that the PEWE system performance using high-performance micro-patterned Ti-foil liquid-gas-diffusion-layer (LGDL) [8,9] was highly sensitive to the cell architecture and exhibited poor mass transport behavior using traditional channel based flow-fields. Compared with the conventional porous transport layer (PTL) morphology, the lack of in-plane permeability of the LGDLs caused faster onset of mass transport limitations at lower flowrates, local increase in HFR, and poor area utilization. Therefore, a unitized single flow-field-LDGL component that mitigates these problems has been designed. Through this work it will be shown that the flow-field is designed to have pins that allow for greater in-plane transport. The staggered pattern reduces pressure drop and promotes exchange in-between channels that assist in efficient bubble removal. Additionally, the cross-section of the pin, the pitch, and aspect-ratios are adjustable to maximize porosity for different LGDLs. Finally, making this into a single unitized component having a permanently attached LGDL will decrease interfacial contact resistances and improve cell performance (as shown in Figure 1).[1] T. V. Reshetenko, G. Bender, K. Bethune, R. Rocheleau, A segmented cell approach for studying the effects of serpentine flow field parameters on PEMFC current distribution, Electrochim. Acta. 88 (2013) 571–579. https://doi.org/10.1016/j.electacta.2012.10.103.[2] A. Phillips, M. Ulsh, J. Porter, G. Bender, Utilizing a Segmented Fuel Cell to Study the Effects of Electrode Coating Irregularities on PEM Fuel Cell Initial Performance, Fuel Cells. 17 (2017) 288–298. https://doi.org/10.1002/fuce.201600214.[3] C. Immerz, B. Bensmann, P. Trinke, M. Suermann, R. Hanke-Rauschenbach, Local Current Density and Electrochemical Impedance Measurements within 50 cm Single-Channel PEM Electrolysis Cell, J. Electrochem. Soc. 165 (2018) F1292–F1299. https://doi.org/10.1149/2.0411816jes.[4] F.H. Roenning, A. Roy, D. Aaron, M.M. Mench, Spatially-Resolved Current Distribution Measurements in Polymer Electrolyte Water Electrolyzers, ECS Meet. Abstr. MA2020-02 (2020) 2457–2457. https://doi.org/10.1149/MA2020-02382457mtgabs.[5] A. Roy, F. Roenning, D. Aaron, M.M. Mench, Quantifying Lateral Current Spread While Measuring Performance Using a Segmented Polymer Electrolyte Water Electrolysis Cell, ECS Meet. Abstr. MA2020-02 (2020) 2458–2458. https://doi.org/10.1149/MA2020-02382458mtgabs.[6] A. Roy, F. Roenning, D. Aaron, M.M. Mench, Local Two-Phase Flow and Performance in Polymer Electrolyte Water Electrolysis Cells, ECS Meet. Abstr. MA2021-01 (2021) 1190–1190. https://doi.org/10.1149/MA2021-01381190mtgabs.[7] A.Z. Weber, R.L. Borup, R.M. Darling, P.K. Das, T.J. Dursch, W. Gu, D. Harvey, A. Kusoglu, S. Litster, M.M. Mench, R. Mukundan, J.P. Owejan, J.G. Pharoah, M. Secanell, I. V. Zenyuk, A Critical Review of Modeling Transport Phenomena in Polymer-Electrolyte Fuel Cells, J. Electrochem. Soc. 161 (2014) F1254–F1299. https://doi.org/10.1149/2.0751412jes.[8] J. Mo, Z. Kang, S.T. Retterer, D.A. Cullen, T.J. Toops, J.B. Green, M.M. Mench, F.-Y. Zhang, Discovery of true electrochemical reactions for ultrahigh catalyst mass activity in water splitting, Sci. Adv. 2 (2016) e1600690. https://doi.org/10.1126/sciadv.1600690.[9] Y. Li, Z. Kang, X. Deng, G. Yang, S. Yu, J. Mo, D.A. Talley, G.K. Jennings, F.-Y. Zhang, Wettability effects of thin titanium liquid/gas diffusion layers in proton exchange membrane electrolyzer cells, Electrochim. Acta. 298 (2019) 704–708. https://doi.org/10.1016/j.electacta.2018.12.162. Figure 1

Development and experimental validation of a fast and accurate field calculation tool for axial flux permanent magnet machines

A fast calculation method of magnetic flux density in axial flux permanent magnet (AFPM) machine is presented. This method is based on an original combination of magnetic charges concept, image theory, and relative permeance functions. Using this combined approach, significant 3D effects, which are present in axial flux machines such as curvature and edge effects as well as slotting effects due to stator slots, are considered. The main electromagnetic specifications of the AFPM machine such as cogging torque, Back Electromotive Force (EMF), and local air-gap flux density are calculated accurately in very short times. To validate this approach, an original prototype of double stator ironless rotor AFPM machine with adjustable air-gap is used. Experimental protocol including measurements of global characteristics (EMF, Torque) and measurements of local field density is presented. The obtained results are in good agreement with the experimental measurements which allows validating the proposed computation method.

Independent changes in bone mineralized and marrow soft tissues following acute knee injury require dual-energy or high-resolution computed tomography for accurate assessment of bone mineral density and stiffness

Musculoskeletal injuries often induce local accumulation of blood and/or fluid within the bone marrow, which is detected on medical imaging as edema-like marrow signal intensities (EMSI). In addition to its biological effects on post-injury recovery, the displacement of low-attenuating, largely adipocytic marrow by EMSI may introduce errors into quantitative computed tomography (QCT) measurements of bone mineral density (vBMD) and resulting bone stiffness estimates from image-based finite element (FE) analysis. We aimed to investigate the impact of post-injury changes in marrow soft tissue composition on CT-based bone measurements by applying CT imaging at multiple spatial resolutions. To do so, dual energy QCT (DECT) material decomposition was used to detect EMSI in the tibiae of nineteen participants with a recent anterior cruciate ligament tear. We then measured bone density and FE-based apparent modulus within the EMSI region and in a matched volume in the uninjured contralateral knee. Three measurement methods were applied: 1.) standard, QCT density calibration and density-based FEM; 2.) a DECT density calibration that provides density measurements adjusted for marrow soft tissues; and 3.) high-resolution peripheral QCT (HR-pQCT) density and microFE analyses. When measured using standard, single-energy QCT, vBMD and apparent modulus were elevated in the EMSI compared to the contralateral. After adjusting for marrow soft tissue composition using DECT, these measurements were no longer different between the two regions. By allowing for high-resolution, localized density analysis, HR-pQCT indicated that trabecular tissue mineral density was 9 mgHA/cm3 lower, while density of marrow soft tissues was 18 mgHA/cm3 higher, in the EMSI than the contralateral region, suggesting that EMSI have opposite effects on the measured density of trabecular bone and the underlying soft marrow. Thus, after an acute injury, altered composition of marrow soft tissues may artificially inflate overall measurements of bone density and apparent modulus obtained using standard QCT. This can be corrected by accounting for marrow soft tissue attenuation, either by using DECT-based density calibration or HR-pQCT microFE and measurements of local density of trabeculae.