Staircase Response Research Articles

Influence of the loading regime on the uniaxial compressive behaviour of density graded Citrus Maxima peel

To conceive more efficient protective structures, it is possible to draw inspiration from natural structures. However, the origin of the mechanical absorption properties of natural structures is not always clear. Among the multitude of existing natural structures, the density graded peel of the Citrus Maxima was studied in this work to characterize its mechanical behaviour under uniaxial compression, from the quasi-static regime to the dynamic regime. The resulting behaviour is very different from a classical foam behaviour as no linear part is observed for small strains. Furthermore, the mechanical behaviour is deeply influenced by the loading regime: a stair-case response appears under dynamic loading.

Observation and Analysis of Staircase Response of Single Palladium Nanoparticle Collision on Gold Ultramicroelectrodes.

Collision (or impact) of single palladium nanoparticles (Pd NPs) on gold (Au), copper (Cu), nickel (Ni), and platinum (Pt) ultramicroelectrodes (UMEs) were investigated via electrocatalytic amplification method. Unlike the blip responses of previous Pd NP collision studies, the staircase current response was obtained with the Au UME. The current response, including collision frequency and peak magnitude, was analyzed depending on the material of the UME and the applied potential. Adsorption factors implying the interaction between the Pd NP and the UMEs are suggested based on the experimental results.

Electrochemical Detection and Analysis of Various Current Responses of a Single Ag Nanoparticle Collision in an Alkaline Electrolyte Solution.

A single silver (Ag) nanoparticle (NP) collision was observed and analyzed in an alkaline solution using the electrocatalytic amplification (EA) method. Previously, the observation of a single Ag NP collision was only possible through limited methods based on a self-oxidation of Ag NPs or a blocking strategy. However, it is difficult to characterize the electrocatalytic activity of Ag NPs at a single NP level using a method based on the self-oxidation of Ag NPs. When using a blocking strategy, size analysis is difficult owing to the edge effect in the current signal. The fast oxidative dissolution of Ag NPs has been a problem for observing the staircase response of a single Ag NP collision signal using the EA method. In alkaline electrolyte conditions, Ag oxides are stable, and the oxidative dissolution of Ag NPs is sluggish. Therefore, in this study, the enhanced magnitude and frequency of the current response for single Ag NP collisions were obtained using the EA method in an alkaline electrolyte solution. The peak height and frequency of single Ag NP collisions were analyzed and compared with the theoretical estimation.

Numerical methods to predict human induced vibrations on low frequency stairs. Part 1: Literature review, modelling

Recent trends towards slender construction with prominent and exigent architectural requirements often result in low frequency staircases that are significantly flexible and susceptible to unacceptable vibrations, which may promote safety concerns for their users. For structural engineers, however, there is still a lack of understanding, available information and specific design guides for predicting the dynamic behaviour of staircases due to human induced vibrations.To address this problem, this work reviews and applies the main existing numerical methods for predicting vibrations, to evaluate their precision and provide practical guidance when designing flexible staircases.The work developed is presented in a two-part paper. In Part 1, the actual paper, several numerical methods are introduced and a detailed description is given of how these can be employed in a design stage. The distinction between low and high frequency staircases is explained, since it directly influences the structure’s behaviour and, subsequently, the selected method. A description is given of how to simulate walking dynamic loads, which forms the basis of all methods. The group effect is also discussed because it tends to considerably amplify the staircase response. Finally, the different numerical procedures are applied to a practical case and compared.It was observed that, although the four numerical methods were employed with the same staircase, their results were different. The reasons for the higher results of Fourier series walking models are explained. In Part 2, the follow-up paper, the numerical methods are employed on a real staircase, comparing the estimated and experimental results.

Detecting longitudinal changes in activities of daily living (ADL) dependence: Optimizing ADL staircase response choices

IntroductionUsing a sum score based on a three-graded response scale for the activities of daily living staircase has previously been found to increase the statistical power compared to dichotomize...

Phase-Slip Lines in Wide Superconducting Strips: Charge and Spin Relaxation Lengths

Penetration of spin-polarized charges from a nearby ferromagnetic metallic layer into 100-μm-wide superconducting films of Pb and Mo–Re alloy with similar critical parameters but quite different spin-orbit coupling strengths is studied. It is shown that the diffusion of magnetic properties into a nearby superconductor can be employed as an electrically tunable source of phase-slip events manifesting itself by a staircase response in current-voltage characteristics of the superconductor with discrete metastable resistivity states. Unlike for normal metals, the spin injection into an adjoining quasi-two-dimensional superconducting strip creates not only spin but also charge imbalance in the quasiparticle population which are not necessarily relaxing over the same time scale. Interplay of the two intrinsic length scales sets the width of a phase-slip line in superconducting strips under the injection which may change from nano- to micro-scales. Its experimental determination can be used for estimating the longest relaxation length in a superconductor. Our observations show that spin-orbit coupling in superconductors may lead to novel non-trivial effects linking spin and charge degrees of freedom.

Challenges in semiconductor single-entity photoelectrochemistry

Abstract It is challenging to study the single semiconductor nanocrystal electrochemistry and photoelectrochemistry. The photocatalytic processes, such as the oxidation of methanol and iodide, that result from the electron–hole pair formed within a nanoparticle (NP) allow the detection of discrete current transient events assigned to single entities. Photocatalytic current amplification allows detection of collisions between the semiconductor NPs and the ultramicroelectrode that produce current transient. Staircase responses and blips in the i vs. t response indicate that irreversible and reversible NP/electrode interactions result depending on the experimental conditions. Dye sensitization increases the photocurrent magnitude of ZnO and TiO2 with respect to bare TiO2 NPs. The microelectrodes used are Pt, TiO2/Pt, TiO2/Au, and F-doped SnO2.

Chronoamperometric Observation and Analysis of Electrocatalytic Ability of Single Pd Nanoparticle for Hydrogen Peroxide Reduction Reaction.

The current generated by the collision of a single nanoparticle (NP) of palladium (Pd) on a gold (Au) ultramicroelectrode (UME) surface was observed using an electrocatalytic amplification method. The hydrogen peroxide reduction reaction was used for the electrocatalytic reaction because the hydrogen peroxide reduction reaction has no gas-phase product, which would induce rapid signal decay. The electrocatalytic current resulting from a single Pd nanoparticle on the Au UME shows a staircase response with accompanying slow current decay. The applying potential and concentration of hydrogen peroxide were optimized for clear distinction of signal. The height of the current step and signal frequency were analyzed and compared with the theoretical expectation. The analysis of the electrocatalytic activity of single Pd NPs provides insight toward their future application.

Staircase in magnetization and entanglement entropy of spinor condensates

Staircases in response functions are associated with physically observable quantities that respond discretely to continuous tuning of a control parameter. A well-known example is the quantization of the Hall conductivity in two dimensional electron gases at high magnetic fields. Here, we show that such a staircase response also appears in the magnetization of spin-1 atomic ensembles evolving under several spin-squeezing Hamiltonians.We discuss three examples, two mesoscopic and one macroscopic, where the system's magnetization vector responds discretely to continuous tuning of the applied magnetic field or the atom density, thus producing a magnetization staircase. The examples that we consider are directly related to Hamiltonians that have been implemented experimentally in the context of spin and spin-nematic squeezing. Thus, our results can be readily put to experimental test in spin-1 ferromagnetic $^{87}$Rb and anti-ferromagnetic $^{23}$Na condensates.

Electrochemical Dynamics of a Single Platinum Nanoparticle Collision Event for the Hydrogen Evolution Reaction

AbstractChronoamperometry was used to study the dynamics of Pt nanoparticle (NP) collision with an inert ultramicroelectrode via electrocatalytic amplification (ECA) in the hydrogen evolution reaction. ECA and dynamic light scattering (DLS) results reveal that the NP colloid remains stable only at low proton concentrations (1.0 mm) under a helium (He) atmosphere, ensuring that the collision events occur at genuinely single NP level. Amperometry of single NP collisions under a He atmosphere shows that each discrete current profile of the collision event evolves from spike to staircase at more negative potentials, while a staircase response is observed at all of the applied potentials under hydrogen‐containing atmospheres. The particle size distribution estimated from the diffusion‐controlled current in He agrees well with electron microscopy and DLS observations. These results shed light on the interfacial dynamics of the single nanoparticle collision electrochemistry.

Electrochemical Dynamics of a Single Platinum Nanoparticle Collision Event for the Hydrogen Evolution Reaction.

Chronoamperometry was used to study the dynamics of Pt nanoparticle (NP) collision with an inert ultramicroelectrode via electrocatalytic amplification (ECA) in the hydrogen evolution reaction. ECA and dynamic light scattering (DLS) results reveal that the NP colloid remains stable only at low proton concentrations (1.0 mm) under a helium (He) atmosphere, ensuring that the collision events occur at genuinely single NP level. Amperometry of single NP collisions under a He atmosphere shows that each discrete current profile of the collision event evolves from spike to staircase at more negative potentials, while a staircase response is observed at all of the applied potentials under hydrogen-containing atmospheres. The particle size distribution estimated from the diffusion-controlled current in He agrees well with electron microscopy and DLS observations. These results shed light on the interfacial dynamics of the single nanoparticle collision electrochemistry.

An Electrochemical Ammonia Sensor on Paper Substrate

In this article, a room temperature ammonia sensor on a paper substrate is reported. The electrochemical sensor is constructed using platinum electrodes and ionic liquid electrolyte. The amperometric staircase response shows discernible signal differentiation between each concentration of NH3 (5-25ppm). The rise time and fall time for the NH­3 sensor were found to be 8 s and 7s respectively. The authors believe such a fast responding NH3 sensor on a paper substrate has never been reported. The detection limit was deduced to be 1 ppm based on the sensitivity versus concentration plot. A 17% decrease in sensor response was observed over 30 days of testing. Implementing an antenna on the paper substrate co-located with the sensor for wireless operation is envisioned in future.

An Electrochemical Ammonia Sensor on Paper Substrate

In this article, a room temperature ammonia sensor on a paper substrate is reported. The electrochemical sensor is constructed using platinum electrodes and ionic liquid electrolyte. The amperometric staircase response shows discernible signal differentiation between each concentration of NH3 (5–25 ppm). The rise time and fall time for the NH3 sensor were found to be 8 s and 7 s respectively. The authors believe such a fast responding NH3 sensor on a paper substrate has never been reported. The detection limit was deduced to be 1 ppm based on the sensitivity versus concentration plot. A 17% decrease in sensor response was observed over 30 days of testing. Implementing an antenna on the paper substrate co-located with the sensor for wireless operation is envisioned in future.

Response Characteristics of Stable Mixed-Potential NH3 Sensors in Diesel Engine Exhaust

A mixed-potential, electrochemical sensor platform is extended to NH3 sensing by the introduction of a new gold alloy working electrode. A planar, pre-commercial NH3 sensor utilized LANL’s controlled interface approach, and a Pd-Au alloy working electrode was tested in exhaust of a GM 1.9 L diesel engine downstream of a diesel oxidation catalyst through a slipstream arrangement. A fraction of the exhaust was pulled across the sensor with a pump at 20 L/min. In order to simulate NH3 slip inside of a full SCR emissions control system, NH3 was injected immediately upstream of the sensor using a calibrated mass flow controller. The sensor response quantitatively tracked the NH3 as measured via Fourier transform infrared (FTIR) analyzer. A calibration curve was obtained in the exhaust from an ammonia staircase response with the engine running at steady-state engine conditions resulting in low background concentrations of NOx and HC (<20 ppm) during calibration. Exhaust gas recirculation (EGR) switching and sweeps were used to evaluate the NH3 sensor response under different amounts of total background NOx. The calibration curve was used to directly compare the [NH3] calculated from sensor response to the gas phase composition measured via FTIR. In general, there was excellent quantitative agreement between the sensor response and the actual NH3 in the exhaust gas, and fast response time such that transients (<5 ppm) could be easily discerned from baseline. A LANL pre-commercial NOx sensor was tested simultaneously with the NH3 sensor and the extent of cross-sensitivity between the two sensors will be discussed.

How to determine cardiac ion channels targeted by drugs using the isolated rabbit ventricular wedge model

IntroductionThe rabbit left ventricular wedge (RLVW) has been demonstrated as a highly sensitive and specific preclinical model in assessing drug-induced QT prolongation and proarrhythmias. However, there is a need to determine drugs' cardiac ion channel profiles beyond QT measurement. In this study, we present an approach to determine cardiac ion channels targeted by drugs with analyzing a few key ECG parameters plus a contractility parameter obtained from the RLVW. MethodsThe RLVW assay was used for testing 18 drugs with well-known ion channel profiles. A transmural ECG and isometric contractility were recorded. Five parameters including QRS, QT, Tp-e/QT ratio, QT-BCL slope and the positive staircase response of contractility were analyzed. ResultsThere were distinguished drug-induced ECG and contractility changes from which targeted cardiac ion channels by drugs could be determined. Inhibition of sodium channel resulted in rate-dependent QRS widening, QT and Tp-e shortening and a reduced QT-BCL slope. Although both IKr and IKs blockers prolonged QT interval, IKr blockers but not IKs increased Tp-e/QT ratio. Both potassium channel openers and calcium channel blockers markedly shortened QT and Tp-e intervals, but only calcium channel blockers could reverse the positive staircase response of contractility. DiscussionThe results in the present study are correlated closely to the drugs' well-known clinical profiles. This indicates that the RLVW assay with an adequate experimental protocol plus analysis of 5 key parameters is highly valuable in preclinical assessment of drug candidates for their detailed ion channel activities, proarrhythmic risks and other adverse effects. The limitations of the RLVW assay are also addressed.

Development and Testing of an Electrochemical Methane Sensor

In this paper, the development of an electrochemical methane sensor is presented. The mixed potential based sensor is based on tin doped indium oxide (ITO) and platinum electrodes and yttria-stabilized zirconia (YSZ) electrolyte. The sensor was fabricated using the inexpensive tape-cast method. The sensor responded to methane with a response time of 15 s. The staircase response to methane indicated a 44 mV sensor response to 100 ppm of methane. The sensor response indicated a log-linear relationship with the methane concentration. Upon 500 hrs of sensor testing, a 5% reduction in methane sensitivity was observed. The cross-sensitivity study on the sensor indicated minimal interference to NO, NO2, and CO2. To improve the sensitivity to methane, a signal conditioning method referred to as the pulsed discharge technique (PDT) was applied. A fourfold increase in methane sensitivity was observed when the sensor was subjected to PDT. Future studies include the miniaturization of the sensor with integrated heater design.

Response Characteristics of a Pre-Commercial Mixed Potential Ammonia Sensor in Diesel Engine Exhaust

Advancements in both combustion system design and emission control technologies have allowed more efficient diesel engines to meet stringent exhaust emissions standards. With very stringent emission regulations currently in place, combustion system design and combustion management are used in conjunction with available exhaust after treatment technologies for optimal reduction of emissions to meet regulatory targets. Current diesel vehicles in the US are equipped with a diesel oxidation catalyst (DOC) to control CO and HC emissions, a diesel particulate filter (DPF) to control particulate matter (PM) and selective catalyst reduction (SCR) or lean-NOx trap (LNT) to control NOX emissions. In SCR, NOx is reduced to H2O and N2over a catalyst through the injection of an ammonia source provided by the onboard storage of diesel exhaust fluid (DEF), typically a mixture of urea and de-ionized water. These emission control technologies add significant complexity and cost to a vehicle and some result in additional fuel penalty needed for their operation. Meeting the EPA Tier 3 emissions reduction requirements while simultaneously increasing fuel economy to meet new CAFE standards will require optimization of advanced combustion strategies and emissions control technologies as well as their state of operation under transient vehicle operation. NH3 sensors are needed to monitor DEF injection and prevent NH3 slip—a condition under which unreacted ammonia from the SCR is emitted in the tailpipe exhaust. Ideally, both NH3 and NOxsensors would be incorporated into a closed-loop system to maintain ammonia close to stoichiometry in the SCR system, and could also serve to monitor engine out and tailpipe out emissions in order to ensure regulatory compliance. Mixed-potential sensors are electrochemical devices that develop a non-Nernstian potential due to differences in the redox kinetics of various gas species at each electrode/electrolyte gas interface1,2. The difference in the steady-state redox reaction rates between the “fast” and “slow” electrodes gives rise to the measured mixed potential response. A patented LANL sensor design incorporates dense electrodes and a porous electrolyte and reproducible and stable sensors are prepared using a high temperature ceramic co-fire approach3. The use of dense electrodes minimizes deleterious heterogeneous catalysis, and the increased morphological stability of dense electrodes yields a robust electrochemical interface, increasing lifetime durability4. The use of a dense gold-alloy working electrode (e.g. the slow electrode), imparts preferential selectivity to NH3, and avoids the stability problems one finds when using thin film, porous Au electrodes5. Previously, we reported on the response of an experimental, tape-cast version of a mixed potential ammonia sensor to simulated diesel exhaust in a high-flow bench reactor at the Oak Ridge National Laboratory (ORNL) National Transportation Research Center (NTRC)7. In this work, we present recent results from evaluating the performance of a pre-commercial form of a mixed potential-based NH3 sensor in engine exhaust conditions at the NTRC using a GM 1.9L CIDI diesel engine. A planar NH3 sensor with a protective porous overcoat was tested in diesel engine exhaust gas (20 L/min) sampled downstream of the engine’s DOC. In order to simulate NH3 slip from a full SCR emissions control system, NH3 was injected immediately upstream of the sensor using a calibrated mass flow controller. The sensor response quantitatively tracked levels of injected NH3 and transients measured via Fourier transform infrared (FTIR) analyzer, using a calibration curve derived from an ammonia staircase response measured in the engine exhaust at low NOx and HC concentrations (<20 ppm) and steady-state engine conditions. Exhaust gas recirculation (EGR) switching and EGR sweeps were used to evaluate the NH3 sensor response under different amounts of total NOx. This calibration curve was used to directly compare the [NH3] calculated from sensor response to the gas phase composition measured via FTIR. References J. W. Fergus, Journal of Solid State Electrochemistry 15 (5), 971-984 (2010).F. H. Garzon, R. Mukundan and E. L. Brosha, Solid State Ionics 136-137, 633-638 (2000).P.K.Sekhar et. al., Sensors and Actuators B: Chemical 144, 112 (2010).R. Mukundan, E. L. Brosha and F. H. Garzon, Journal of The Electrochemical Society 150 (12), H279 (2003).J. Tsitron et. al., Sensors and Actuators B 192 (2014) 283-293.E. L. Brosha et al., “Response Characteristics of a Stable Mixed Potential NH3 Sensor in Simulated Diesel Exhaust,” 228th Meeting of the ECS, Phoenix, AZ, October 2015. Acknowledgments The authors would like to thank Roland Gravel and the DOE Vehicle Technology Office for providing funding for this work. Engine-based studies were conducted at the National Transportation Research Center User Facility at Oak Ridge National Laboratory. Figure 1

Combined Blip and Staircase Response of Ascorbic Acid-Stabilized Copper Single Nanoparticle Collision by Electrocatalytic Glucose Oxidation.

The current response of the collision of ascorbic acid-stabilized copper (Cu) single nanoparticles (NPs) on a gold (Au) ultramicroelectrode (UME) surface was observed by using an electrocatalytic amplification method. Here, the glucose oxidation electrocatalyzed by oxidized Cu NPs was used as the indicating reaction. In this system, the NP collision signals were obtained simultaneously by both direct particle electrolysis and electrocatalytic amplification. For example, when the applied potential was high enough for Cu NP oxidation, a blip response combined with a staircase response was observed as a current signal. The blip part in the single Cu NP collision signal indicates the self-oxidation of a Cu NP, and the staircase part indicates the steady-state electrocatalytic reaction by oxidized Cu NP.

Observation of Blip Response in a Single Pt Nanoparticle Collision on a Cu Ultramicroelectrode

The collision of a single Pt nanoparticle (NP) was observed by an electrocatalytic amplification method. A Au ultramicroelectrode (UME) is usually used for the detection of Pt single NP collisions. The transient current response of the colliding Pt NP with the Au UME was observed as a staircase response. However, the response of the transient current by NP collision is affected by various factors including the material of the UME. In this study, a Cu UME was employed for the detection of a single Pt NP collision to investigate the effect of the UME material on the current response. A different current response, namely a blip response, was obtained by using Cu UME unlike the other UMEs. The peak height and collision frequency were analyzed and compared with the previous results using Au, Hg, or Ni UME for a better understanding of the UME material's effect on single Pt NP collision.

Development and testing of an electrochemical methane sensor

In this article, the development of an electrochemical methane sensor is presented. The mixed potential based sensor is based on tin doped indium oxide (ITO) and platinum electrodes and yttria-stabilized zirconia (YSZ) electrolyte. The sensor was fabricated using the inexpensive tape-cast method. The sensor responded to methane with a response time of 15s. The staircase response to methane indicated a 44mV sensor response to 100ppm of methane. The sensor response indicated a log-linear relationship with the methane concentration. Upon 500h of sensor testing, a 5% reduction in methane sensitivity was observed. The cross-sensitivity study on the sensor indicated minimal interference to NO, NO2, and CO2. To improve the sensitivity to methane, a signal conditioning method referred to as the pulsed discharge technique (PDT) was applied. A fourfold increase in methane sensitivity was observed when the sensor was subjected to PDT. Future studies include the miniaturization of the sensor with integrated heater design.