Measurement Of Density Distribution Research Articles

Diagnosing current distributions in batteries with magnetic resonance imaging.

Batteries and their defects are notoriously difficult to analyze non-destructively, and consequently, many defects and failures remain little noticed and characterized until they cause grave damage. The measurement of the current density distributions inside a battery could reveal information about deviations from ideal cell behavior, and could thus provide early signs of deterioration or failures. Here, we describe methodology for fast nondestructive assessment and visualization of the effects of current distributions inside Li-ion pouch cells. The technique, based on magnetic resonance imaging (MRI), allows measuring magnetic field maps during charging/discharging. Marked changes in the distributions are observed as a function of the state of charge, and also upon sustaining damage. In particular, it is shown that nonlinearities and asymmetries of current distributions could be mapped at different charge states. Furthermore, hotspots of current flow are also shown to correlate with hotspots in charge storage. This technique could potentially be of great utility in diagnosing the health of cells and their behavior under different charging or environmental conditions.

Effects of the grid geometry on the performances of a triode-type corona electrode system

The triode-type electrode system is frequently employed for accurately controlling the corona charging of insulating materials. The primarily aim of this paper is to characterize the effects of grid geometry of the triode-type corona electrode system by current-voltage and current density distribution measurements. The ionizing element of the electrode system is a thin Tungsten wire (diameter: 200 μm) attached to a cylinder (diameter: 26 mm) and distanced at 34 mm from its axis. The wire-cylinder assembly is a “dual” electrode, facing a grid electrode, connected to a well-defined potential, and a grounded plate electrode. The geometry of the grid has a very significant influence on the current-voltage characteristics of the triode system, on the corona onset voltage value and on the repartition of the current density. The experimental results obtained for different geometries of the grid electrode system are interpreted in order to make some recommendations regarding its design.

Measurement of charge density in nanoscale materials using off-axis electron holography

Three approaches for the measurement of charge density distributions in nanoscale materials from electron optical phase images recorded using off-axis electron holography are illustrated through the study of an electrically biased needle-shaped sample. We highlight the advantages of using a model-based iterative algorithm, which allows a priori information, such as the shape of the object and the influence of charges that are located outside the field of view, to be taken into account. The recovered charge density can be used to infer the electric field and electrostatic potential.

Operando and Ex-Situ Investigation of PEMFC Degradation

Longevity is one of key requirements of PEMFC for automotive applications. Hence, understanding degradation phenomena and durability limitations is fundamental to increase PEMFC life time and to make this technology competitive In this contribution a selection of our recent work on these topics is presented. In particular, attention in dedicated to study effect of performance limitations at low Pt loadings and to investigate impact of operation conditions on local degradation phenomena such as drying, contaminations or heterogeneities during dynamic operation. Moreover, specific operando accelerated stress tests are being developed and the relative impact on various stressors on individual MEA components is studied. Eventually, we present results related to on-line fault monitoring using current density distribution measurements linked with impedance spectroscopy.

Investigation of the effect of cathode stoichiometry of proton exchange membrane fuel cell using localized electrochemical impedance spectroscopy based on print circuit board

Proton Exchange Membrane Fuel Cell can have a large active area, and the working condition in different areas can be entirely different. Localized electrochemical impedance spectroscopy can directly observe the proton exchange membrane fuel cell internal reaction conditions. In this work, localized electrochemical impedance spectroscopy test system based on print circuit board is implemented in a 50 cm2 multi-channel serpentine flow fields. The localized electrochemical impedance spectroscopy performances of different segments with different cathode stoichiometry (1.8, 2.3 and 2.8) at different current density (100 mA cm−2, 500 mA cm−2 and 900 mA cm−2) are studied. The result demonstrates that the fuel cell may suffer from local drying and flooding at the same time. To make full use of the potential of a fuel cell, a suitable cathode stoichiometry should be identified to control the drying of the inlet and the flooding of the outlet at the same time. It is shown that a cathode stoichiometry of 2.3 is close to the optimum cathode stoichiometry to keep the fuel cell in good consistency without gas waste. Besides, a current density distribution measurement is performed to verify the conclusions of this work.

Quantitative measurement of nanoscale electrostatic potentials and charges using off-axis electron holography: Developments and opportunities

Off-axis electron holography has evolved into a powerful electron-microscopy-based technique for characterizing electromagnetic fields with nanometer-scale resolution. In this paper, we present a review of the application of off-axis electron holography to the quantitative measurement of electrostatic potentials and charge density distributions. We begin with a short overview of the theoretical and experimental basis of the technique. Practical aspects of phase imaging, sample preparation and microscope operation are outlined briefly. Applications of off-axis electron holography to a wide range of materials are then described in more detail. Finally, challenges and future opportunities for electron holography investigations of electrostatic fields and charge density distributions are presented.

Effect of non-linear amplification of phase and amplitude modulations on laser-induced damage of thick fused silica optics with large beams at 351 nm

Nonlinear propagation of high power, large aperture laser beams leads to the amplification of the spatial pre-existing small scale modulations, and therefore locally increases the laser energy density as the beam propagates through the optical component. The measurement of the energy density distribution on the exit face of the tested component is therefore more challenging, as the impact of the propagation must be taken into account. It is for this reason that the damage densities of thick fused silica components have never been precisely measured. To this end, a dedicated imaging setup has been developed to accurately measure the energy density distribution on the exit face of 34-mm thick fused silica optical components during laser damage experiments with a centimeter-scale laser beam. The impact of nonlinear propagation on the beam spatial profile has been studied experimentally and confronted to numerical simulations that solve the nonlinear Schrödinger equation for the experimental spatial and phase profiles. The results clearly indicate that the imaging setup can accurately measure the amplification of the beam spatial modulations. The beam energy density on the exit face is therefore correctly measured and, for the first time, the damage density of thick optics can be accurately determined.

Simulation of the multi-component process gas flow for the explanation of oxidation during laser cladding

Usually the process gas flow rates and the process gas types are not regarded as the primary process parameters of the laser cladding process. Herein it is shown, how the melt pool surface oxidation can be significantly reduced by the change of the carrier gas type, by a reduced carrier gas flow rate and by minor changes in the powder nozzle design. However, the absorptivity may decrease concurrently by up to 15%. A simulation model for the gas flow and the powder particle flow between the powder nozzle and the melt pool surface has been developed, which reveals the volume percentage of different gas types and so the quality of the shield gas atmosphere. Additionally, the powder particle distribution and the attenuation of the laser beam by the powder particles can be simulated. The simulation results are confirmed by experimental measurements of the powder particle density distribution in the working plane, by measurements of the oxygen volume percentage at the workpiece surface, by high-speed camera images of the melt pool surface and by absorptivity measurements, which show the effect of oxidation on the process.

Late stages of mineralization and their signature on the bone mineral density distribution

ABSTRACTPurpose: Experimental measurements of bone mineral density distributions (BMDDs) enable a determination of secondary mineralization kinetics in bone, but the maximum degree of mineralization and how this maximum is approached remain uncertain. We thus test computationally different hypotheses on late stages of bone mineralization by simulating BMDDs in low-turnover conditions. Materials and methods: An established computational model of the BMDD that accounts for mineralization and remodeling processes was extended to limit mineralization to various maximum calcium capacities of bone. Simulated BMDDs obtained by reducing turnover rate from the reference trabecular BMDD under different assumptions on late stage mineralization kinetics were compared with experimental BMDDs of low-turnover bone. Results: Simulations show that an abrupt stopping of mineralization near a maximum calcium capacity induces a pile-up of minerals in the BMDD statistics that is not observed experimentally. With a smooth decrease of mineralization rate, imposing low maximum calcium capacities helps to match peak location and width of simulated low-turnover BMDDs with peak location and width of experimental BMDDs, but results in a distinctive asymmetric peak shape. No tuning of turnover rate and maximum calcium capacity was able to explain the differences found in experimental BMDDs between trabecular bone (high turnover) and femoral cortical bone (low turnover). Conclusions: Secondary mineralization in human bone does not stop abruptly, but continues slowly up to a calcium content greater than 30 wt% Ca. The similar mineral heterogeneity seen in trabecular and femoral cortical bones at different peak locations was unexplained by the turnover differences tested.

Scaling Analysis of Multipulsed Turbidity Current Evolution With Application to Turbidite Interpretation

AbstractDeposits of submarine turbidity currents, turbidites, commonly exhibit upward‐fining grain size profiles reflecting deposition under waning flow conditions. However, more complex grading patterns such as multiple cycles of inverse‐to‐normal grading are also seen and interpreted as recording deposition under cycles of waxing and waning flow. Such flows are termed multipulsed turbidity currents, and their deposits pulsed or multipulsed turbidites. Pulsing may arise at flow initiation, or following downstream flow combination. Prior work has shown that individual pulses within multipulsed flows are advected forward and merge, such that complex longitudinal velocity profiles eventually become monotonically varying, although transition length scales in natural settings could not be predicted. Here we detail the first high frequency spatial (vertical, streamwise) and temporal measurements of flow velocity and density distribution in multipulsed gravity current experiments. The data support both a process explanation of pulse merging and a phase‐space analysis of transition length scales; in prototype systems, the point of merging corresponds to the transition in any deposit from multipulsed to normally graded turbidites. The scaling analysis is limited to quasi‐horizontal natural settings in which multipulsed flows are generated by sequences of relatively short sediment failures (<10 km long) that develop progressively up‐dip and predicts pulse merging after only a few tens of kilometers. The model cannot provide quantitative estimation of merging in down‐slope flows generated by axially extensive (>10 km) sequences of breaches or where pulsing arises from combination at confluences of single‐pulsed flows, such flows may be responsible for the pulsing signatures seen in some distal turbidites, >100 km from source.

Mono and di-substituted BODIPY with electron donating carbazole, thiophene, and 3,4-ethylenedioxythiophene units

In an effort to extend the conjugation system of boron-dipyrrin (BODIPY), the dye was coupled with polymerisable units of carbazole, alkylthiophene, and 3,4-ethylenedioxythiophene (EDOT). Due to electron donating character of the units connected to the strong electron accepting segment of tri-coordinated boron, the optical and electrochemical properties of the dye changed, and followed the strength of the electron donating substituent. All studied compounds exhibited electroactivity in both anodic and cathodic potential ranges, however, electropolymerisation was only observed for BODIPY modified with EDOT, leading to trimeric and tetrameric substituents. Potential controlled optical changes (spectroelectrochemistry) and in situ spin density distribution measurements, supported by quantum chemical calculations using density functional theory, were undertaken in order to understand the reversibility of the electrochemical processes. Hyperfine split ESR spectra of the radical anion species were successfully modelled revealing intriguing, hyperconjugation type unpaired spin delocalisation patterns.

Analytical solutions and dimensional analysis of pseudo 2D current density distribution model in PEM fuel cells

Abstract In this paper, a new dimensionless pseudo 2D steady state current density distribution model along the channel of a polymer electrolyte membrane (PEM) fuel cell is presented. This model includes four fundamental phenomena observed in PEM fuel cell cathode such as the air concentration depletion along the channel, the mass transport through the gas diffusion layer (GDL), the charge transport through the membrane and the electrochemical transfer in the catalyst layer (CL). A dimensional analysis is performed, and three dimensionless parameters are found to govern the current density distribution along the channel: a Peclet number at the channel/GDL interface, a Damkholer number at the GDL/CL interface, and a Wagner number at the CL/PEM interface. Four regimes of operation are defined based on the values of these dimensionless numbers, and for each of them new analytical solutions are developed. A good agreement with the experimental measurements of current density distribution reported in literature is found, concluding that the macroscopic PEM fuel cell physic is well described by our model. The specific operating regime described with relatively simple equations of current density distributions paves the way for a better control of fuel cell operation and performance, and in situ characterisation of fuel cell material properties.

Acoustic Profiling of Bottom Sediments in Large Oil Storage Tanks

Characteristic features of acoustic profiling of bottom sediments in large oil storage tanks are considered. Basic acoustic parameters of crude oil and bottom sediments are presented. It is shown that, because of the presence of both transition layers in crude oil and strong reverberation effects in oil tanks, the volume of bottom sediments that is calculated from an acoustic surface image is generally overestimated. To reduce the error, additional post-processing of acoustic profilometry data is proposed in combination with additional measurements of viscosity and tank density distributions in vertical at several points of the tank.

Measurement of magnetic flux density distribution generated by magnetic circuit for driving implantable hearing aid and evaluation of vibration property of bone conduction transducer

Measurement of magnetic flux density distribution generated by magnetic circuit for driving implantable hearing aid and evaluation of vibration property of bone conduction transducer

Beam hardening correction in polychromatic x-ray grating interferometry.

The beam hardening is one of the two causes of the fringe shift distortion in polychromatic X-ray grating interferometry. Based on the assumption of the uniform energy dependence, we developed a novel analytic approach to accurately retrieve the monochromatic attenuation function and fringe phase shift from the polychromatic measurement. This approach provides a useful tool for precise measurement of sample electron density distribution in X-ray grating interferometry.

Ionomer equivalent weight structuring in the cathode catalyst layer of automotive fuel cells: Effect on performance, current density distribution and electrochemical impedance spectra

To improve the performance of proton exchange membrane fuel cells, membrane electrode assemblies (MEAs) with segmented cathode electrodes have been manufactured. Electrodes with a higher and lower ionomer equivalent weight (EW) were used and analyzed using current density and temperature distribution, polarization curve, temperature sweep and electrochemical impedance spectroscopy measurements. These were performed using automotive metallic bipolar plates and operating conditions. Measurement data were used to manufacture an optimized segmented cathode electrode. We were able to show that our results are transferable from a small scale hardware to automotive application and that an ionomer EW segmentation of the cathode leads to performance improvement in a broad spectrum of operating conditions. Furthermore, we confirmed our results by using in-situ electrochemical impedance spectroscopy.

Observing Power-Law Dynamics of Position-Velocity Correlation in Anomalous Diffusion.

In this Letter, we present a measurement of the phase-space density distribution (PSDD) of ultracold ^{87}Rb atoms performing 1D anomalous diffusion. The PSDD is imaged using a direct tomographic method based on Raman velocity selection. It reveals that the position-velocity correlation function C_{xv}(t) builds up on a time scale related to the initial conditions of the ensemble and then decays asymptotically as a power law. We show that the decay follows a simple scaling theory involving the power-law asymptotic dynamics of position and velocity. The generality of this scaling theory is confirmed using MonteCarlo simulations of two distinct models of anomalous diffusion.

Alpha Decay Width of212Po from a quartetting wave function approach

An effective α particle equation is derived for cases where an α particle is bound to a doubly magic nucleus. As an example, we consider212Po with the α on top of the208Pb core. The fully quantal solution of the problem is inspired by the THSR (Tohsaki-Horiuchi-Schuck-Röpke) wave function concept that has been successfully applied to light nuclei. Shell model calculations are improved by including four-particle (α-like) correlations that are of relevance when the matter density becomes low. In the region where the α-like cluster penetrates the core nucleus, the intrinsic bound state wave function transforms at a critical density into an unbound four-nucleon shell model state. We present a microscopic calculation of both α-cluster preformation probability and decay width in typical α-emitter212Po. Using actually measured density distribution of the208 Pb core, the calculated alpha decay width of212Po agrees fairly well with the measured one. Applications to other nuclei (20Ne) are discussed.

In-plane structuring of proton exchange membrane fuel cell cathodes: Effect of ionomer equivalent weight structuring on performance and current density distribution

Abstract Within the active area of a fuel cell inhomogeneous operating conditions occur, however, state of the art electrodes are homogenous over the complete active area. This study uses current density distribution measurements to analyze which ionomer equivalent weight (EW) shows locally the highest current densities. With this information a segmented cathode electrode is manufactured by decal transfer. The segmented electrode shows better performance especially at high current densities compared to homogenous electrodes. Furthermore this segmented catalyst coated membrane (CCM) performs optimal in wet as well as dry conditions, both operating conditions arise in automotive fuel cell applications. Thus, cathode electrodes with an optimized ionomer EW distribution might have a significant impact on future automotive fuel cell development.

Experiment and finite element analysis of compaction densification mechanism of Ag-Cu-Sn-In mixed metal powder

Experiments and finite element analysis were performed to investigate the compaction densification mechanism of Ag57.6-Cu22.4-Sn10-In10 mixed metal powder. Firstly, the friction coefficient for lubricated and unlubricated die between the powder and die wall were determined experimentally. It is observed that the friction coefficient varies with the top punch pressure, and μ increases with the top punch pressure at low pressure regime (≤100MPa), while maintain constants at high pressure regime (>100MPa). The difference between the friction coefficients of lubricated/unlubricated die indicates that the lubrication (zinc stearate alcohol solution) could reduce the die wall friction greatly. Furthermore, the relative density distribution in the compacts for lubricated and unlubricated die compaction were characterized and mapped experimentally using the Vickers hardness method. Globally, the agreement between simulation calculation and experimental measurement of relative density distribution is reasonably good, indicating that the model parameters give an adequate description of the compaction behavior for the mixed metal powder. Moreover, a nonlinear compaction equation containing the die wall friction effect was proposed and established as: ln1−D1−D0=kP1−k1μ+b1−k2μP, k1 and k2 are correction coefficients related to the powder property. It is shown that the established nonlinear compaction equation could represent the relative density-compaction pressure relationship for the mixed metal powder under different die wall friction. At last, the influence mechanisms of die wall friction on the compaction behavior of mixed metal powder were detailedly analyzed in simulations using the modified Drucker-Prager Cap model. The results show that the friction induced inhomogeneous stress distribution and powder flows in compact during compaction, which caused density gradient and the occurrence of cracks and capping during ejection.